Advanced Projects Lab - User contributions [en]

SRS Photon Counter

2021-11-11T20:36:13Z

Aplstudent: Created page with " The SR400 gated photon counter is a Stanford Research Systems instrument that can receive, and then count, electronic pulses from a single-photon detector. This page will des..."

The SR400 gated photon counter is a Stanford Research Systems instrument that can receive, and then count, electronic pulses from a single-photon detector. This page will describe the basic operations of the SR400 and give some examples of how to use the unit with signals sent from a function generator. Additional details about the instrument, and more complicated examples, can be found in the manual for the instrument.

The SR400 is equipped with three counters, labeled A, B, and T, which can count rates up to 200 MHz. The input to counter A can be either the 10 MHz internal timebase or the signal at INPUT 1. The input to counter B can be either the signal at INPUT 1 or INPUT 2. The input to counter T can be the 10 MHz internal timebase, INPUT 2, or an external TRIGGER source. Each of these inputs can be selected using the MODE menu on the front panel. To move between different settings, use the up, down, left, and right arrows. Once on a setting, the knob on the front panel can be used to change the settings.

In order to count any signals, the COUNT PERIOD needs to be set. The simplest way to set the COUNT PERIOD is to select the source to counter T as the 10 MHz timebase. This allows the user to select a fixed interval, ranging from 100 ns to 25 hours, over which to count. This interval may be selected by changing the TSET parameter, which is on the same setting page as the one used to select the source to input T. More than one COUNT PERIOD can be implemented by changing N PERIODS to a number other than 1. If multiple count periods are being used, then there will be a DWELL TIME between COUNT PERIODS. The DWELL TIME can be changed under the DWELL setting in the MODE menu. On the same setting page there is an option to set N=STOP or N=START. If N=STOP is selected, then once the last COUNT PERIOD is reached all counting is paused. If N=START is selected, then once the last COUNT PERIOD is reach, all counting is repeated. This setting is used for continuous data acquisition. To count during the entire COUNT PERIOD, the GATE settings on A GATE and B GATE should be set to CW. Gate settings can be adjusted using the GATE menus. Lastly, the discriminator level should be set under the LEVEL menu. The discriminator level determines what threshold is used to count signals. The DISC level may be FIXED or in a SCAN mode (in which case a SCAN step size must be chosen). The FIXED or starting SCAN level can be adjusted under DISC LVL.
Once the COUNT PERIOD, DWELL TIME, and GATE menus are set, one can connect signals to INPUT 1 and INPUT 2. Both inputs are internally terminated into 50 ohms and can accept signals up to ±300 mV (but are protected to ±5 Vdc). Pulses as small as 10 mV can be detected. To display the counts for A and B select A,B FOR T PRESET on the MODE menu. Before moving onto the example experiments, it is worth noting that SR400 has more features that can be taken advantage of. For example, one can scan a gate across the COUNT PERIOD, or use and external TRIGGER to start the COUNT PERIOD, instead of the internal timebase.

'''Example 1: Counting the Timebase'''

This example is taken from page 59 of the manual and involves no external inputs to the counters. Before turning on the SR400 press down the STOP key on the front panel and hold it down. Then push in the power button. This resets all settings to their defaults and will display a message RECALL DEFAULT. In the MODE menu select the A input to be the 10 MHz timebase, and then press the START key once to start a count period. The A counter should display A=10000000, as the default count period is 1 second. Press STOP to reset the counter. Now set the N PERIODS to N PERIODS=10 and press START again. The counter should cycle through 10 COUNT PERIODS with a DWELL TIME of 1 second.

'''Example 2: Counting from an External Source'''

Reset the settings to their defaults by pressing down the STOP key while powering on the SR400. This resets all settings to their defaults and will display a message RECALL DEFAULT. Connect a BNC splitter to a function generator to allow the signal from the function generator to be viewed on an oscilloscope and sent to the SR400. Use the function generator to send a 1 kHz square wave with a trough to peak amplitude of 100 mV. Verify this is the output on an oscilloscope. Now connect the function generator to the SR400, with a 50 Ohm termination, and press START. The count on A should read 1000, because the COUNT PERIOD is 1 second by default.
One can extend this example by scanning the discriminator threshold. To do this set the A DISK LVL to -15 mV and A DISC SCAN to -10 mV. Next set N PERIODS to 5. Now press START. There are five count periods, but the counter should only make it to 1000 counts during the first three count periods as the signal will be less than the discriminator threshold level for the last two count periods. The discriminator threshold level can be viewed on the DISC LVL settings page. To add another signal, one can use INPUT 2 with another function generator.

Spontaneous Parametric Downconversion

2021-11-08T22:23:51Z

Aplstudent:

= Quantum Optics and Spontaneous Parametric Downconversion =

The goal of this project is to use a series of table-top laser-based optics experiments to investigate various quantum mechanical phenomena. These include, but are not limited to: quantization of the electric field (proof of the existence of photons), single-photon interference, violation of Bell inequalities, and quantum information measurements.

= Physics Background =

== Overview ==

Spontaneous parametric downconversion (SPDC) is a non-linear optical process that takes place with the assistance of specially-engineered optical crystals. These optical crystals are designed with specific index of refraction properties along given crystalline axis. When light of a specific frequency is incident upon the lattice, it will undergo a parametric downconversion process. This will result in an overall "splitting" of one incident light beam into two beams, a "signal" and an "idler" beam, at some well-defined angle with respect to the optical input axis (serving as the zero). The quanta of light will experience a downconversion but within this the momentum and energy of the beam is conserved in the signal and idler beams. See figure 1 for an illustration, below for a simplified explanation, and the WikiPedia article for maximum detail.[http://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion].

[[File:SPDC.png|x500px|thumb|center|'''Left:''' SPDC semi-classical overview '''Right:''' Solving the wave equations for resultant wave vectors via conservation of energy and momentum]]

== Downconversion ==

If we reduce the incident beam to a series of single photons, whose existence is a central postulate of quantum theory, the above description need only be slightly altered. A single photon incident on the crystalline lattice has a certain probability of being downconverted via the interaction with the lattice (roughly 1 in 10^12)[http://www.qolah.org/papers/CLEO-SanJose.pdf]. When this conversion takes place, the single photon, with its inherent polarization properties, is converted into a ''pair of polarization entangled photons at half the energy and wavelength.'' The output pair has the same polarization, but is polarized orthogonal to the input beam. Type II follows the same characteristic downconversion (DC) as the Type I but with one very crucial difference. In Type II downconversion the polarizations of the output beams are now orthogonal to one another (with some overlap in their respective electric fields so that there is a possibility for photon interaction, and unlike that of Type I where there is no possibility for interaction after the downconversion crystal). The way one sets their experiment for Type I or Type II downconversion is by choosing the correct the crystal lattice cut (i.e. purchasing the correct crystal). The lattice will be cut in such a way that the axis with varying indices of refraction will favor one DC type over the other.

[[File:TYPEI&II.png|x750px|thumb|center|'''Type I SPDC''': output beams are polarized orthogonal to the input beam '''Type II SPDC''': overlapping output fields with orthogonal polarizations]]

== Single Photon Fields and g2 ==

NOTE: This section ''heavily'' references from Mark Beck's text ''Quantum Mechanics: Theory and Experiment'' which is mentioned in the references and available in the lab.

In any optics experiment the experimenters usually convert light to electric current via some photodetector and diode scheme. If one wishes to measure single photons, the question must then arise - how could you distinguish the "granularity" of a single photon incident on your detector from that of the single electrons flowing in your electrical detection scheme? Fortunately there exists a way to quantize the electric field incident on the detector that circumvents this issue entirely. The quantization of the electric field will not be presented in detail here, nor will the derivation of the g2 values. These details can be found in section 16 of Beck.

For ease of presentation, it should suffice to say that the g2 factor (degree of second-order coherence) is a numerical value describing the ratio of intensities between two electric fields. This ratio can be cleverly mainpulated, after the coherent electric field from a laser source has been properly quantized, to yield detection probabilities in different regions of space. These probabilities can then be averaged over time to yield estimates for the number of photons one would expect to be incident upon a detector placed in the region of the field. Below are the most basic depictions of these values. For more detail, see the WikiPedia page [http://en.wikipedia.org/wiki/Degree_of_coherence#Degree_of_second-order_coherence] .

[[File:G2info.png|x350px|thumb|center|Left: Summary of g2 values as a ratio of electric field intensities in a two-detector scheme. (See Beck for relevant details). Right: Summary of g2 values relevant for this experiment]]

 Because the downconverted photons are produced at (approximately) the same time, and the distance along the path of each photon is equal, the photons generated in the SPDC process will reach the detector at the same time. Therefor, it is useful to count the number of coincidences at the detectors to tell when down conversion happens. The detectors have a 'temporal resolution' of a few nanoseconds. If the photons arrive at detectors A & B within this window, the FPGA designates this event as a coincidence and shows up in labview as an AB count. The speed of light is ~1 foot per nanosecond, so if a coincidence is counted then the arriving photons were spatially separated by less than a few feet. 

 The single photon state can be determined by adding a beam splitting cube in the path of the signal beam and a third detector placed perpendicular. In the classical view of electromagnetic fields described by Maxwell, the excitations of the field propagate like waves. If this were the case, the excitation along the signal beam would split into two at the PBS and arrive at detectors B AND B' at the same time. 

 A more accurate view of nature describes the excitations with wavelike and particle like properties. When considering a photon traveling down path B', the photon will choose one discrete direction at the beam splitting cube and arrive at detector B OR B'. 

 The second order temporal coherence parameter measures the amount of bunching of the photons. Bunching describes photons that arrive grouped together. If we consider a photon that arrives at B, if the photons are bunched the probability of a photon arriving at B' within a very short time window increases. (i.e. they arrive in bunches, so if one arrives then another is probably going to arrive right after that.) If we ignore what is happening at detector A, we see these photons are bunched and the parameter that measures this, G2 is greater than 1 

 If we consider the relationship between the coincidences AB & AB', the photons arrive antibunched. We are now detecting the SPDC photon pairs, so the photon in the signal path that corresponds to the photon in the idler path goes to EITHER B OR B'. (The process of using detector A to signal events in the other path is known as heralding, because it is like the photon at detector A is saying, “hear ye, hear ye. A SPDC process occurred and my fellow is in one of the other detectors) Therefor, if an detection happens at AB, it is more likely that the next arrival at AB' will be separated in time. The parameter that measures bunching (G2), is less than one, indicating an antibunched single photon state. 

Measurement of photon counts over time at an array of photodetectors can be analyzed for their degree of correlation. Positive, zero, and anti-correlations at the detectors all play a very important role in claiming the nature of the electric field present in the chosen experiment. The constraints on g2 being 0 < g2 ≤ 1 for a quantum mechanical field and g2 ≥ 1 for a classical electric field are determined by analyzing the ratios for the 2-detector and 3-detector schemes for our chosen experiments. To understand this in the context of the experiment, please see the results section.

== Single Photon Interference and the Polarization Interferometer ==
How to align to polarization interferometer:

 The B collection lens was displaced 4 mm to the right, coupled to the alignment laser and aligned through two irises set to the level of the BBO crystal. (mainly for the vertical alignment, the irises were placed on the center of the track about 1 & 2 feet from the BBO, so the beam was slightly displaced to the right on the irises.) The tilt of the the BBO was kept constant for the rest of the polarization interferometer. The B lens was then moved to the center of the track and an iris was placed such that the beam passed through the center. 
 The Beam Displacement Prism (BDP) closer to the collection lens was added to the center of the track. This is the BDP with the picomotor on the horizontal tilt. The BDP transmits one polarization and displaces the other about 4 mm to the right (not to the left like the illustration on the BDP suggests), so the position of the BDP was moved so the beam entered the left half of the calcite. The horizontal and vertical tilt were adjusted to set the surface of the BDP orthogonal to the beam by aligning the back-scattered radiation from the BDP through the center of the iris. The process of adjusting the position of the BDP and aligning the back-scattered radiation was iterated until the beams passed the through the calcite without hitting the mount on the front or back of the BDP. A mount was constructed to keep the red part of the picomotor fixed in place. 
 The displaced beam (the one on the right) was pointed towards the center of the BBO crystal by adjusting the position of the collection lens orthogonal to the optical axis to pass through the center of two irises placed one and two feet from the BBO. The BDP was checked to make sure the beam passed through without clipping the edges. 
 A Polarizing Beam Splitting cube (PBS) was placed perpendicular between collection lens B and the third iris. The green sticker was oriented toward detector B. One of the beams emerging from the BDP appeared much lighter due to the PBS decreasing the intensity of one of the beams. A half wave plate set to 22.5° was added between the iris and the BDP to rotate the polarization 45°. The half wave plate was placed perpendicular to the alignment beam. 
 A half wave plate rotated 45° was placed perpendicular to the beams behind the BDP to change the polarization of each beam by 90°. This was done so the path length difference would be approximately equal when the beams converge in the second BDP. 
 A BDP placed in a kinematic mount was added behind the second half wave plate to make the beams converge. The beams passed through the BDP with minimal clipping on both sides and aligned parallel to the other BDP by making the back-scattered radiation pass through the center of the iris closest to the collection lens. A third half wave plate was added after the BDP and set to 22.5° to rotate the polarization another 45°, so the beam entering and exiting the polarizer would shifted a total of 180°. 
 An interference pattern was observed with the alignment laser by placing a horizontal polarizer and screen between the BBO & half wave plate. The horizontal tilt of the BDP closest to the collection lens was adjusted with a picomotor to observe interference on the screen. The size of the fringes were comparable to the spot size of the beam, so it was difficult to observe the interference unless the tilt was varied. The picomotor was used to make a darker spot on the screen and the contrast was maximized by slightly changing the angle (on the order of a few degrees) of each half wave plate such that the intensity on the dark fringe was minimized. 
 The alignment laser was disconnected from B and connected to B'. The B' detector was translated parallel to the signal beam to make the alignment laser go through the iris between the PBS and polarizing interferometer. The horizontal and vertical tilt of the collection lens were adjusted to make the alignment laser go through the interferometer. This process was iterated until the beam passed through the center of all three irises. 
 With the lights out, FPGA, violet laser, SPCM, and labview running, the horizontal tilt of the BDP closer to the collection lenses was slowly adjusted with a picomotor. Interference was not observed, so the angle of the 45 degree half wave plate (with respect to the signal beam) was adjusted to make sure it was perpendicular to the signal beam, and the orientation angle of the BDP closer to the BBO was varied by a degree at a time, scanning over the horizontal range each time. When interference was observed, the BDP closer to the collection lens was rotated to 355°, while the BDP closer to the BBO was near 2°. 

== Double Slit and the Quantum Eraser ==

= Experimental Setup =

== Basic Setup ==

In our experiment we start with a 405nm blue diode pump laser. We then put the laser through an iris and a linear polarizer to ensure horizontal polarization. Once through the polarizer the laser was then pushed through a half wave plate in order to change the polarization of the beam to vertical. After being reflected off of two mirrors the light is incident on the downconversion crystal, producing two 810nm horizontally polarized output beams (signal and idler). A beam blocker was placed down the beam path to block any stray 405nm light. The two output beams travel at an angle of roughly 3 degrees off axis with respect to the input beam. The signal and idler beams travel down their respective legs and reach a photodetector to record both their individual and coincidence counts. Coincidence at the B and B' detectors is determined via a polarizing beam-splitting cube (PBSC) designed for 810nm light. The photodetectors are multi-mode fiber-coupled to a FPGA board and the outputs are sent to a custom LabView counting program (Coincidence.vi or Angle Scan.vi) on a desktop computer setup right on the optics table.

[[File:Diagram.png|x350px|thumb|center|'''Left:''' block diagram of SPDC experiment (some optics not included in all experiments). '''Right:''' Optics table overview. Purple beam = 405nm input, Red beams = 810 DC outputs.]]

== Quantum Eraser Setup ==
We continued to use the basic setup described above, ensuring that we used a double layered BBO that produces entangled photons. Note that a single layered BBO does not produce entanglement, which is required for the quantum eraser experiment. Down the signal leg, between the downconversion crystal and the PBSC, we installed our interferometer, which included in order, a half-wave plate set to 22.5 degrees, a beam displacement prism (BDP), a half-wave plate set to 45 degrees, another BDP, oriented oppositely in order to recombine the light beams, and finally another half-wave plate set to either 22.5 or zero degrees, depending on the stage of the experiment. 
We followed the procedure described in Beck's book to install and align the interferometer. One important note is to calibrate and set all of the wave plates independently of this installation. The fast axes are not always truly aligned how they are marked, and their alignment must be empirically and accurately determined before their use in the interferometer. 
After the interferometer was properly aligned, we verified that it produced interference by setting the third waveplate to our empirically found 22.5 degrees and scanning the path lengths with the picomotor, plotting coincidence counts as a function of time. Proper interference was observed when we saw coincidence counts between AB and AB' oscilate in opposition of each other. 
We were not able to complete the rest of the quantum eraser experiment for various reasons, but our suggested procedure is as follows: Set the third waveplate to zero degrees instead of 22.5. This should provide "which-path" information and interrupt the interference pattern. Then insert a quarter-wave plate into the idler leg. Entanglement should ensure that the "which-path" information is erased, and the interference pattern should reappear.

= Results =

== Group 3: Kevin Masson and Alex Schachtner ==

=== Maximizing Photon Counts ===

In order to have the best possible experimental results, we sought to maximize the photon counts on each optical leg of the experiment. To do this, we varied the angle of each optical leg from 2.5 degrees to 4 degrees by increments of one-tenth of a degree from the central axis. Recorded values of photon counts are shown below. We found that the maximum counts occurred at approximately 3.2 degrees. This matches the theoretical maximum angle for photon counts of 3 degrees.

[[File:anglemax1.png|x350px|thumb|center|Maximum photon counts as a function of topical leg angle. NOTE: counts were later centralized between legs to remove the offset present on this plot. This will be plotted again in the future.]]

[[File:Coincidence.png|x350px|thumb|center|Maximized coincidence counts as a function of optical leg angle]]

=== Proving the Existence of Individual Photons ===

Measurement of individual photons is done in this experiment via determining the g2 value referenced in the background section. Two measurements were devised for comparison of their resultant values - a two-detector measurement for illustrating the classical electric field value of g2, and a three-detector measurement for verifying the quantized electromagnetic field.

For a two-detector scheme, coincidence counts are seen as a result of positively-correlated or non-correlated measurements of a single input electric field being split by the polarizing beam-splitting cube (PBSC). If one pictures the electric field incidence on a refractive crystal, they expect the outputs at subsequent faces to be phase-shifted copies of the input field. This is purely a classical electrodynamic effect - polarized EM plane waves incident on the PBSC become phase-shifted polarized plane waves when re-emitted. g2 measurements at the B and B' detector show these results by expecting g2 ≥ 1 in the mathematical scheme outlined above. Our results indeed show g2 approximately 3.9 for this measurement:
[[File:g2_2det.png|x350px|thumb|center|2-detector measurement of g2 with appropriate error. Note that each data point is an average value of 100 points. Average value of g2 3.981 ± 0.252 with maximum error ±0.154]]

For a three-detector scheme, coincidence counts are a result of anti-correlated measurements on a single-photon field across detectors A, B, and B'. Single photons incident on the PBSC have a 50% probability of reflection or transmission at the PBSC refraction face. When analyzing the AB and AB' coincidence counts, one would expect at least one of these values to be ''exactly zero'' when considering a ''perfect'' single photon source - the photon will only be incident on ''either'' the B or B' detector, not both. Since this is not achievable in the lab, the value can approach zero but will never reach it. However, it should ''never'' breach 1 for a quantum mechanical effect to be claim. Our scheme then yields a measurable value of 0 < g2 ≤ 1 by virtue of the ratios outlined above. Our results show an average value of g2 approximately 0.235:
[[File:g2_3det.png|x350px|thumb|center|3-detector measurement of g2 with appropriate error. Note that each data point is an average value of 100 points. Average value of g2 0.235 ± 0.081 with maximum error ±0.052]]

For the next part of our experiment we added the third detector (B') and the polarizing beam splitting cube as described above. In this part we did a coincidence count between sensor A from the signal beam and sensor B from the idler beam from here we then were able record the g2 number for the two detector case. In this case we got a number greater than one which then solidifies the fact of light having a classical characteristic about it. We then proceeded to take a 3-detector coincidence count in order to look at the g2 number. From here we then took recordings from the B' sensor on the idler beam. This then allowed us to get an ABB' coincidence count. Here we got a value much less than one, which in our case as described above gives us that light has quantum characteristics to it. This then tells us that light is composed of particles and these particles are called photons. This experiment gives us a certainty to the existence of photons but not only that, it expressly shows that of which Thomas Young found in his famous nineteenth century experiment commonly called Young's experiment, which is that light has characteristics of both waves and particles.

== Group 3.1: Alex Schachtner, Kevin Masson, Tyler Anderton ==

=== Quantum Eraser ===
Here is where we actually set up the experiment to determine certain characteristics of light, namely the concept of entanglement. We started by placing the interferometer into the signal leg of the system that we had already had in place. We followed the procedure lined up in the Beck book but we still found it to be an incredibly difficult task to align the interferometer correctly. We broke the whole procedure down and found that both the B and B' sensors should be placed on translation stages for easier access. It takes a very large amount of patient in order to setup and odds are since this is on such a small scale that you will have to repeat the procedure many times in order to see any sort of intrference pattern by altering one of the Beam Displacing Prisms (BDPs) and watching the spot get brighter and dimmer as the angle changes. Once properly aligned the alignment laser can be taken out of the setup and then the actual laser diode can be turned on (after lights out procedure) and then you can view the interference pattern that was visually seen now by the photon counts. they should gradually fluctuate such as what is shown below. If properly aligned the B and B' counts should be symmetrical but some issues arose and the interferometer was not competely aligned.

[[File:Bcounts.jpg|x350px|thumb|center|alt=B detector counts.|]]

[[File:B'counts.jpg|x350px|thumb|center|alt=B' detector counts.|]]

Sadly were not able to get past this part since we had too many complications and so we are now just going to talk theory rather than what we have done experimentally. Here is where we would have placed a polarized into the idler leg and if the system would work properly we would be able to see the photon counts on the B and B'sensors to fluctuate and then this wold show that at certain polarizations of the A sensor the B and B' sensors would be minimum showing the fact that even when the photons are not in contact they are still able to communicate and thus they are constantly entangled, expressly showing the theory of quantum entanglement.

[[SRS Photon Counter]]

= External Resources =

[http://hank.uoregon.edu/experiments/spdc/spdc-home.html SPDC Web Page]

[http://people.whitman.edu/~beckmk/QM/ Mark Beck's Page, Whitman College]

= References =

1.) Beck, M. Quantum Mechanics: Theory and Experiment. 2011. Wiley & Sons. [http://people.whitman.edu/~beckmk/QM/]

2.) S. P. Walborn, M. O. Terra Cunha, S. Padua, A Double-Slit Quantum Eraser Physical Review A, (65, 033818, 2002).

Original Authors of this page are Alex Schachtner and Kevin Masson. First devised March, 2015.

Operating Fusion Splicers and Preparing the Fiber

2021-10-15T22:56:52Z

Aplstudent: /* Step 1: Preparing the Fiber */

== Fusion Splicing - The Basics ==
When connecting bare fiber, Fusion Splicing is the most commonly used approach. Fusion Splicing has the least loss and reflectance and also provides the strongest joint of the different connectorizing methods. A Fusion Splicer connects two ends of a Fiber by virtue of welding, using an electrical arc.
Each Fusion Splicer works slightly different, this page provides an overview on the different Splicers available and the steps which they have in common.
=== The S185 Series FUSION SPLICER ===
==== Step 1: Preparing the Fiber ====
This step is similar to other connectorizing methods and involves cleaning, stripping and cleaving (these steps are explained [[Fiber_Optics|here]]. It is important to notice that a precision cleaving device is needed to get a good Splice. Once the two bare fiber ends are cleaned, stripped and cleaved, put a shrinking sleeve on one of the ends and push it beyond the bare part.
[[File:Shrinking.JPEG|thumb|right|Shrinking sleeve on Fiber end]]

Operating Fusion Splicers and Preparing the Fiber

2021-10-15T22:55:03Z

Aplstudent: /* Step 1: Preparing the Fiber */

== Fusion Splicing - The Basics ==
When connecting bare fiber, Fusion Splicing is the most commonly used approach. Fusion Splicing has the least loss and reflectance and also provides the strongest joint of the different connectorizing methods. A Fusion Splicer connects two ends of a Fiber by virtue of welding, using an electrical arc.
Each Fusion Splicer works slightly different, this page provides an overview on the different Splicers available and the steps which they have in common.
=== The S185 Series FUSION SPLICER ===
==== Step 1: Preparing the Fiber ====
This step is similar to other connectorizing methods and involves cleaning, stripping and cleaving (these steps are explained [[Fiber_Optics|here]]. It is important to notice that a precision cleaving device is needed to get a good Splice. Once the two bare fiber ends are cleaned, stripped and cleaved, put a shrinking sleeve on one of the ends and push it beyond the bare part.
[[File:IMG 1448.JPEG|thumb|right|Shrinking sleeve on Fiber end]]

Operating Fusion Splicers and Preparing the Fiber

2021-10-15T22:53:48Z

Aplstudent: /* Step 1: Preparing the Fiber */

== Fusion Splicing - The Basics ==
When connecting bare fiber, Fusion Splicing is the most commonly used approach. Fusion Splicing has the least loss and reflectance and also provides the strongest joint of the different connectorizing methods. A Fusion Splicer connects two ends of a Fiber by virtue of welding, using an electrical arc.
Each Fusion Splicer works slightly different, this page provides an overview on the different Splicers available and the steps which they have in common.
=== The S185 Series FUSION SPLICER ===
==== Step 1: Preparing the Fiber ====
This step is similar to other connectorizing methods and involves cleaning, stripping and cleaving (these steps are explained [[Fiber_Optics|here]]. It is important to notice that a precision cleaving device is needed to get a good Splice. Once the two bare fiber ends are cleaned, stripped and cleaved, put a shrinking sleeve on one of the ends and push it beyond the bare part.
[[File:IMG_4448.JPEG|300px|thumb|right|Fluke 179 Multimeter and accessories ]]

Operating Fusion Splicers and Preparing the Fiber

2021-10-15T22:51:27Z

Aplstudent: /* Step 1: Preparing the Fiber */

Operating Fusion Splicers and Preparing the Fiber

2021-10-15T22:40:24Z

Aplstudent: /* Step 1: Preparing the Fiber */

Operating Fusion Splicers and Preparing the Fiber

2021-10-15T22:19:16Z

Aplstudent: /* Step 1: Preparing the Fiber */

Operating Fusion Splicers and Preparing the Fiber

2021-10-15T22:17:21Z

Aplstudent: /* Step 1: Preparing the Fiber */

Operating Fusion Splicers and Preparing the Fiber

2021-10-15T22:08:09Z

Aplstudent: Created page with "== Fusion Splicing - The Basics == When connecting bare fiber, Fusion Splicing is the most commonly used approach. Fusion Splicing has the least loss and reflectance and also..."

Advanced Projects Lab:Community portal

2021-10-15T21:42:44Z

Aplstudent:

Welcome to the University of Oregon, Department of Physics, Advanced Projects Lab's Wiki.

To see our main website visit [http://hank.uoregon.edu Advanced Projects Lab].

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[[File:APL.jpg|450px|right]]
[[Advanced Projects]]

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- ''[[Operating Fusion Splicers and Preparing the Fiber]]''

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[http://en.wikipedia.org/wiki/Wikipedia:Extended_image_syntax Wikipedia:Extended image syntax]

[http://www.mediawiki.org/wiki/Help:Tables Help: Tables]

=== CDF (Computable Document Format) Help: ===
''(Note - The Wolfram CDF player for Linux currently doesn't support the browser plugin)''

[http://www.wolfram.com/cdf-player/ Get the Wolfram CDF Player]

[http://en.wikipedia.org/wiki/Computable_Document_Format CDF - Wikipedia]

[http://www.mediawiki.org/wiki/Extension:WolframCDF#Usage How to include CDF files on wiki pages]

APL HPC Cluster

2020-03-18T05:58:22Z

Aplstudent: /* Hardware */

== Cluster Specifications ==
Server Rack: Rosewill 9U/12U/15U Portable
=== Compute Nodes (Includes Master Node) ===
==== Hardware ====

'''Chassis:''' Dell PowerEdge R710 Server

'''Power Supply:''' Dell 870W PSU

'''Central Processing:''' Intel Xeon CPU X5670 (2 processors, each with 6 dual-threaded cores, @ 2.93GHz base frequency)

'''Memory:''' 128GiB

'''RAID Controller:''' Dell PERC H700

'''Networking (InfiniBand) Adapter:''' Mellanox Technologies MT25408A0-FCC-QI ConnectX, Dual Port 40Gb/s 10GigE Adapter IC with PCIe 2.0 x8 5.0GT/s Interface

==== Operating System ====

'''Linux Version:''' CentOS 7.7.1908 (Core)

'''Kernel:''' Linus 3.10.0-1062.12.1.el7.x86_64

'''Architecture:''' x86-64

=== Storage Server ===
==== Hardware ====
==== Operating System ====

=== Networking (InfiniBand) Switch ===

'''Model:''' IS5031

'''Firmware version:''' 2.9.1000

'''Driver version:''' MLNX_OFED_LINUX-4.7-3.2.9.0

APL HPC Cluster

2020-03-18T05:58:00Z

Aplstudent:

== Cluster Specifications ==
Server Rack: Rosewill 9U/12U/15U Portable
=== Compute Nodes (Includes Master Node) ===
==== Hardware ====

'''Chassis:''' Dell PowerEdge R710 Server

'''Power Supply:''' Dell 870W PSU ... 1240.00

'''Central Processing:''' Intel Xeon CPU X5670 (2 processors, each with 6 dual-threaded cores, @ 2.93GHz base frequency) ... 1443.00*2

'''Memory:''' 128GiB

'''RAID Controller:''' Dell PERC H700

'''Networking (InfiniBand) Adapter:''' Mellanox Technologies MT25408A0-FCC-QI ConnectX, Dual Port 40Gb/s 10GigE Adapter IC with PCIe 2.0 x8 5.0GT/s Interface

==== Operating System ====

'''Linux Version:''' CentOS 7.7.1908 (Core)

'''Kernel:''' Linus 3.10.0-1062.12.1.el7.x86_64

'''Architecture:''' x86-64

=== Storage Server ===
==== Hardware ====
==== Operating System ====

=== Networking (InfiniBand) Switch ===

'''Model:''' IS5031

'''Firmware version:''' 2.9.1000

'''Driver version:''' MLNX_OFED_LINUX-4.7-3.2.9.0

APL HPC Cluster

2020-03-18T05:12:12Z

Aplstudent: Created page with "===== Hardware ===== Rosewill 9U/12U/15U Portable Server Rack"

===== Hardware =====

Rosewill 9U/12U/15U Portable Server Rack

Scientific Python Primer

2020-03-11T17:38:43Z

Aplstudent:

This Python Primer utilizes an IPython notebook kernel running on a computer in the APL and a browser-based IPython notebook front end located on your computer. That is, you don't need any special software just a computer with a web-browser and a SSH client.

You will start your IPython session by establishing a SSH tunnel.

'''Step 1'''
''SSH into the remote machine'' and run the IPython web-based environment and direct it to a specific port. The command for this should look something like (you replace the xx with numbers):

jupyter notebook --no-browser --port=70xx

'''Step 2'''
''On the local machine'' you can access this remote port using an SSH tunnel with port forwarding. The command for that will look like:

ssh -N -f -L localhost:70xx:localhost:70xx username@remotemachine

'''Step 3'''
Now to use the session all you have to do is (from the local machine) run your preferred web browser with the URL:

http://localhost:70xx

==SSH Tunnel on Chromebook==
Step 1: Open two secure shells. Right click the secure shell icon and open it in window mode. Enter ctrl+shift+n to create a second shell.

Step 2: From secure shell enter username as the user name and host as the host name. Open an ipython notebook with the command
jupyter notebook --no-browser --port=70xx

Step3: In the second shell use the same user name and host name
in SSH arguments enter
-L 70xx:localhost:70xx

Step4: Go to http//:localhost:70xx and the ipython notebook should be running.

note: if multiple instances of ipython are running the notebook might not execute commands

note: occasionally the kernel cannot be killed in the shell and must be killed in the system monitor on mother

== Textbook for the module ==

A Primer on Scientific Programming with Python by Hans Petter Langtangen (3rd Edition). Available online through the UO Library. To access it, follow this link: http://link.springer.com/book/10.1007%2F978-3-642-30293-0

== Activities ==

Intro to Python, Definitions - Chapter 1

Loops, logic, and lists - Chapter 2

Functions - Chapter 3 and NumPy

Input data and error handling - Chapter 4 and PANDAS

Functions on arrays and curve fitting - Chapter 5

String handling, files, and dictionaries - Chapter 6 and PANDAS

== Useful Links ==
PANDAS - http://pandas.pydata.org/

NumPy - http://www.numpy.org

codecademy - https://www.codecademy.com/

Python Flow Visualization - http://pythontutor.com/

==Chapter 1==
Section 1.1: If this is your first time programming anything, begin with 1.1.1. Otherwise, it will suffice to read 1.1.1 for a statement of the problem and skip to 1.1.11. This introduces the syntax for commenting and basic arithmetic operations.

Section 1.2: This will give you relevant vocabulary for talking about Python and programs more generally. If this is not your first time programming, this section should just be skimmed.

Section 1.3: Introduction to potential calculation difficulties, primarily floating point versus integer data.

Section 1.4: Importing mathematical functions from a library.

Section 1.5: Interactive computing. This section will teach you how to have the user input various parameters. IPython is introduced as well.

Section 1.6: Complex numbers in Python.

Section 1.7: Summary

Section 1.8: Suggested exercises: While all are useful (after 1.6), the following will help immensely in debugging.
1.6 - Introduction to basic functions
1.9 - Error Correction
1.17 - Error Finding in a program that uses the quadratic formula

Start-Up Procedure

2020-02-26T23:59:43Z

Aplstudent: Created page with "'''Start-up Procedure:''' 1. Make sure lab door is closed, and don appropriate eye protection. 2. Turn on power strip. (This should only turn on the UC-2000 controller,..."

'''Start-up Procedure:''' 

1. Make sure lab door is closed, and don appropriate eye protection.

2. Turn on power strip. (This should only turn on the UC-2000 controller, everything else should still be off).

3. On UC-2000 Controller:
* Hold the 'SELECT' and 'ENTER' buttons down to enter 'Setup Mode'.
* Set Frequency to 5 kHz, Gate Pull to 'Up', Maximum PWM to 95%, Lase On Pwr-Up to 'N', Checksum to (On). Use the 'SELECT' 
: button to switch between options and the 'ENTER' button to change the setting selected. Once finished, select 'SAVE AND EXIT' 
: and hit the 'ENTER' button on the controller.
* Set mode to manual by hitting the 'SELECT' button on the main screen until 'MANUAL' option comes up, and hit 'ENTER'. 
: (Make sure not to select 'MANUAL CLOSED', as this may not operate in output intended if not in the recommended range.)
* Turn adjustment knob until PWM is set to 0.0%.

4. Turn on power supply unit for cooling fans. Turn coarse voltage to ~12V, and current to ~0.5A. (The maximum power rating of each
:is 24V @ 0.46A each, and can be increased as needed if laser begins to heat during operation.)

5. Turn on power supply for Laser. Set voltage to 30V and turn knob for current all the way to the right. The current will not appear
:to rise at this point, but when the laser is turned on it will draw as much current as necessary for the set PWM %.

6. Remove aperture dust cover.

7. Set PWM to 1.0% and toggle 'LASE' to 'ON'. You can confirm the laser is in operation by the red LED being lit on the rear of the
:laser. Using an IR Detector card, ensure beam is aligned with an appropriate beam block or power meter, ensuring the beam does
:not go past the table.

8. Once beam is safely aligned, this is now ready to use.

Synrad Firestar V30 CO2 laser

2020-02-26T23:59:29Z

Aplstudent: /* Synrad Firestar V30 CO2 laser */

Synrad Firestar V30 CO2 laser

2020-02-26T23:19:06Z

Aplstudent: /* Synrad Firestar V30 CO2 laser */

==== Synrad Firestar V30 CO2 laser ====

'''Specifications:''' 
Wavelength: 10.2-10.8 μm 
Output power: 30 W 
Power Stability: +- 5% (cold start), +-3% (after two minutes) 
Continuous Wave (CW) 
Polarization: Linear, horizontal 
Beam Diameter: 2.5 +- 0.5 mm (<math>1/e^2</math>) 
Full Divergence Angle: < 7mrads (Beam diverges 7mm / m) 
Rise Time < 100 μs 

'''Start-up Procedure:''' 

1. Make sure lab door is closed, and don appropriate eye protection.

2. Turn on power strip. (This should only turn on the UC-2000 controller, everything else should still be off).

3. On UC-2000 Controller:
* Hold the 'SELECT' and 'ENTER' buttons down to enter 'Setup Mode'.
* Set Frequency to 5 kHz, Gate Pull to 'Up', Maximum PWM to 95%, Lase On Pwr-Up to 'N', Checksum to (On). Use the 'SELECT' 
: button to switch between options and the 'ENTER' button to change the setting selected. Once finished, select 'SAVE AND EXIT' 
: and hit the 'ENTER' button on the controller.
* Set mode to manual by hitting the 'SELECT' button on the main screen until 'MANUAL' option comes up, and hit 'ENTER'. 
: (Make sure not to select 'MANUAL CLOSED', as this may not operate in output intended if not in the recommended range.)
* Turn adjustment knob until PWM is set to 0.0%.

4. Turn on power supply unit for cooling fans. Turn coarse voltage to ~12V, and current to ~0.5A. (The maximum power rating of each
:is 24V @ 0.46A each, and can be increased as needed if laser begins to heat during operation.)

5. Turn on power supply for Laser. Set voltage to 30V and turn knob for current all the way to the right. The current will not appear
:to rise at this point, but when the laser is turned on it will draw as much current as necessary for the set PWM %.

6. Remove aperture dust cover.

7. Set PWM to 1.0% and toggle 'LASE' to 'ON'. You can confirm the laser is in operation by the red LED being lit on the rear of the
:laser. Using an IR Detector card, ensure beam is aligned with an appropriate beam block or power meter, ensuring the beam does
:not go past the table.

8. Once beam is safely aligned, this is now ready to use.

Useful Links: 
[[Media:Operators_Manual_v30.pdf| Firestar V30 Users Manual]] 
[[Media:Operators_Manual_UC2000.pdf| UC2000 Controller Users Manual]]

Clark-MXR CPA-Series Ti:Sapphire laser

2020-02-26T23:18:13Z

Aplstudent: /* Clark-MXR CPA 2110 Ti:Sapphire laser */

==== Clark-MXR CPA 2110 Ti:Sapphire laser ====

[[File:ClarkMXRTiSapph.jpg|450px|frame|right|Clark MXR CPA 2110]]

Wavelength: 775nm 
Output Average Power: 1 W 
Pulse Energy: 1mJ 
Peak Power: 6.7 GW 
Peak Intensity: 33.5 GW/cm^2 
Rep Rate: 1kHz (up to 2 kHz) 
Pulse Width: <150fs 
Polarization: linear horizontal 
Beam Diameter: 4-6 mm FWHM 
Beam Area: ~ 0.2 cm^2

Useful Info: 
[[Media:CPA-Series-N-201801-01.pdf | Clark-MXR CPA 2110 Specs]] 
[[Media:Topas-C.pdf | Topas-C OPA Specs]]

Coherent Avia 355-23-250

2020-02-26T23:14:56Z

Aplstudent: /* Avia 355-23-250 */

==== Avia 355-23-250 ====

Wavelength: 354.7nm 
Output power: 8.4W @ 250 kHz 
Peak Power: ~ 450W (at 250kHz)
Rep Rate: Single shot to 400 kHz 
Pulse Width: <75 ns up to 250 kHz 
Polarization: >100:1 horizontal 
Beam Diameter: 3.6mm (<math>1/e^2</math>) 

Useful Info: 
[[Media:Avia-355-X-Solid-State-Q-Switched-UV-Laser-.pdf| Avia 355-23-250 Specs]]

NLight Element e03 laser

2020-02-26T23:13:23Z

Aplstudent: /* nLight Element e03 laser */

==== nLight Element e03 laser ====

Wavelength: 915 nm 
Output power: 30 W 
Continuous Wave (CW) 
Spectral Width (FWHM): 4.5 nm 
Coupled into a 105/125 μm MM Fiber 
Fiber: 0.22 NA/Step Index 
Threshold Current: ~ 0.4 A 
Max Operating Current (at max optical power): ~ 12.0 A 
Max Operating Voltage (at max optical power): ~ 5.3 V 

Useful Links: 
[[Media:Datasheet for e03.0300915105.pdf| e03 Datasheet]] 
[[Media: NLight-element_protection_circuitry.jpg| Diode Protection Circuitry]] 
[[Media: NLight-elementLD-Spectra.xlsx| e03 Spectra]] 
[[Media: NLight-elementLD-Data.xlsx| e03 Data]]

File:NLight-elementLD-Data.xlsx

2020-02-26T23:12:31Z

Aplstudent:

File:NLight-elementLD-Spectra.xlsx

2020-02-26T23:10:55Z

Aplstudent:

File:NLight-element protection circuitry.jpg

2020-02-26T23:09:06Z

Aplstudent:

File:Datasheet for e03.0300915105.pdf

2020-02-26T23:06:43Z

Aplstudent:

Synrad Firestar V30 CO2 laser

2020-02-25T20:39:19Z

Aplstudent: /* Synrad Firestar V30 CO2 laser */

Synrad Firestar V30 CO2 laser

2020-02-25T20:38:11Z

Aplstudent:

==== Synrad Firestar V30 CO2 laser ====

Wavelength: 10.2-10.8 μm 
Output power: 30 W 
Power Stability: +- 5% (cold start), +-3% (after two minutes) 
Continuous Wave (CW) 
Polarization: Linear, horizontal 
Beam Diameter: 2.5 +- 0.5 mm (<math>1/e^2</math>) 
Rise Time < 100 μs 

Useful Links: 
[[Media:Operators_Manual_v30.pdf| Firestar V30 Users Manual]] 
[[Media:Operators_Manual_UC2000.pdf| UC2000 Controller Users Manual]]

File:Operators Manual UC2000.pdf

2020-02-25T20:36:56Z

Aplstudent:

Printing the Paper Copy

2019-04-22T20:25:44Z

Aplstudent: /* Creating Files to Print */

==Negative or Positive, Mirrored or Not Mirrored==

We need to determine if the paper copy should be the negative (color inverted) or positive (color not inverted) of the layer's digital image. The PCB process leaves copper in the unexposed areas (i.e. the black ink areas on the film = copper areas on the PCB) so we ultimately want the film to be the positive of our digital layer. Although, the film takes the negative image of the paper during the transition from paper to film. Thus, we want to print a negative image on paper so the film will show the positive.

We also want to make sure that when we expose the top and bottom layers everything lines up. This means we need to print the the top layer as a regular image and the bottom layer as a mirrored image.

==Creating Files to Print==

To create a SVG (Scalable Vector Graphic) of a schematic in KiCad open [[Pcbnew]] and select File -> Export SVG. Next, select the front copper layer (F.Cu) or back copper layer (B.Cu). If you are converting the front copper layer do not mirror the image, but if you are printing the back copper layer, select "Print mirrored". Once you've chosen a location to save the files (the "Output Directory") select plot for each layer with the appropriate settings (mirrored or not mirrored).

Now, with your SVG files saved somewhere accessible we'll want to create negatives of the images. Unfortunately, printing a PNG or SVG of a negative can be surprisingly troublesome. The main issue is that a PNG or SVG contains black, white, and transparent regions and the transparent areas, which print as white, will not turn black when creating a negative image. The fix is to print the PNG or SVG on top of a black rectangle the size of your PCB. To do this we'll use a program like photoshop, GIMP, or Inkscape to create two digital layers, one top layer with the PCB schematic and one bottom layer with a black rectangle.

(Both GIMP and Inkscape can be found on the "Hank" computer in the APL or downloaded for free, in this tutorial we'll use Inkscape)

Open Inkscape and select File -> Open..., find your SVG images and select "Open". Once you're schematic is loaded we'll want to add the SVG images to a layer. First create a blank layer by selecting Layer -> Add Layer.. then click Add. Now, use the mouse tool to click and drag a selection box around you're schematic. Once you have everything in your schematic selected right click somewhere in the selection box and click "Move to layer ...". Select the layer you just created and click "Move". This will enable you to create a second layer below your schematic layer and draw a black background. Now, create a new layer the same way we created the first layer but in the popup menu select "Position: Below current". Open the Layers... meun by pressing Shift+Ctrl+L and select your first layer (the one with your schematic). Next click Extensions -> Color -> Negative to create a negative image. You'll notice that most of the detail in your schematic disappears. To get this detail back, select your second layer and use the "Create rectangles and squares" tool (make sure black is selected from the row of colors at the bottom of the screen) to draw a large black rectangle around you circuit. To avoid wasting ink don't fill the entire page with the black rectangle, just fill the area of the page that contains the PCB schematic. When you're finished if everything went correctly the areas of the board we want to be copper should be white and everything else should be black.

Before you're ready to print you'll want to make sure the page size matches the printer paper. This can be done in inkscape by holding Ctrl+Shift+D to open the document properties. Now select the "Page Size", this will most likely be 8.5 x 11 inches. Now make sure everything fits on the page. '''Do not''' rescale any of the PCB elements, only move them. The scale of the PCB must match the original scale of your schematic.

Finally, you'll want to create a PDF or PNG copy of your SVG negatives. This can be done in Inkscape by changing the settings in File -> Save As... section. This PDF or PNG can be emailed to the UO [https://uoprint.uoregon.edu/about-campus-copy "Campus Copy"] to be printed with a high resolution printer on #28 photo paper. Alternatively, if you have access to one, a 1200 dpi printer will be sufficient.

Printing the Paper Copy

2019-04-22T20:01:12Z

Aplstudent: /* Creating Files to Print */

==Negative or Positive, Mirrored or Not Mirrored==

We need to determine if the paper copy should be the negative (color inverted) or positive (color not inverted) of the layer's digital image. The PCB process leaves copper in the unexposed areas (i.e. the black ink areas on the film = copper areas on the PCB) so we ultimately want the film to be the positive of our digital layer. Although, the film takes the negative image of the paper during the transition from paper to film. Thus, we want to print a negative image on paper so the film will show the positive.

We also want to make sure that when we expose the top and bottom layers everything lines up. This means we need to print the the top layer as a regular image and the bottom layer as a mirrored image.

==Creating Files to Print==

To create a SVG (Scalable Vector Graphic) of a schematic in KiCad open [[Pcbnew]] and select File -> Export SVG. Next, select the front copper layer (F.Cu) or back copper layer (B.Cu). If you are converting the front copper layer do not mirror the image, but if you are printing the back copper layer, select "Print mirrored". Once you've chosen a location to save the files (the "Output Directory") select plot for each layer with the appropriate settings (mirrored or not mirrored).

Now, with your SVG files saved somewhere accessible we'll want to create negatives of the images. Unfortunately, printing a PNG or SVG of a negative can be surprisingly troublesome. The main issue is that a PNG or SVG contains black, white, and transparent regions and the transparent areas, which print as white, will not turn black when creating a negative image. The fix is to print the PNG or SVG on top of a black rectangle the size of your PCB. To do this we'll use a program like photoshop, GIMP, or Inkscape to create two digital layers, one top layer with the PCB schematic and one bottom layer with a black rectangle.

(Both GIMP and Inkscape can be found on the "Hank" computer in the APL or downloaded for free, in this tutorial we'll use Inkscape)

Open Inkscape and select File -> Open..., find your SVG images and select "Open". Once you're schematic is loaded we'll want to add the SVG images to a layer. First create a blank layer by selecting Layer -> Add Layer.. then click Add. Now, use the mouse tool to click and drag a selection box around you're schematic. Once you have everything in your schematic selected right click somewhere in the selection box and click "Move to layer ...". Select the layer you just created and click "Move". This will enable you to create a second layer below your schematic layer and draw a black background. Now, create a new layer the same way we created the first layer but in the popup menu select "Position: Below current". Open the Layers... meun by pressing Shift+Ctrl+L and select your first layer (the one with your schematic). Next click Extensions -> Color -> Negative to create a negative image. You'll notice that most of the detail in your schematic disappears. To get this detail back, select your second layer and use the "Create rectangles and squares" tool (make sure black is selected from the row of colors at the bottom of the screen) to draw a large black rectangle around you circuit. To avoid wasting ink don't fill the entire page with the black rectangle, just fill the area of the page that contains the PCB schematic. When you're finished if everything went correctly the areas of the board we want to be copper should be white and everything else should be black.

Before you're ready to print you'll want to make sure the page size matches the printer paper. This can be done in inkscape by holding Ctrl+Shift+D to open the document properties. Now select the "Page Size", this will most likely be 8.5 x 11 inches. Now make sure everything fits on the page. '''Do not''' rescale any of the PCB elements, only move them. The scale of the PCB must match the original scale of your schematic.

Finally, you'll want to create a PDF or PNG copy of your SVG negatives. This can be done in Inkscape by changing the settings in File -> Save As... section. This PDF or PNG can be emailed to the UO [https://uoprint.uoregon.edu/about-campus-copy "Campus Copy"] to be printed with a high resolution printer on fine photo paper. Alternatively, if you have access to one, a 1200 dpi printer will be sufficient.

Etching the PCB

2019-04-16T23:39:33Z

Aplstudent: /* Etching with the Aggregation Tank */

The APL has a container of etchant, copper chloride (CuCl2) mixed with hydrochloric acid (HCl), that should be used for etching the PCB. These chemicals are dangerous and should be handled with care.

Hydrochloric acid (HCl) is very acidic and should not touch your skin and copper chloride is extremely harmful to water treatment plants, so DO NOT pout this solution down the drain (see the warning in the [[Etching the PCB#After Etching|After Etching]] section). Fortunately, there should be no need to dispose of any etchant because the etchant is reusable after the etching process (see how in the [[Etching the PCB#Technical Information| Technical Information]] section).

Also note that the fumes from the etchant are dangerous, thus the etchant should only be opened and used under a fume hood (Dr.Boggs has access to one in CAMCOR).

==Testing the CuCl2==

Before using the CuCl2 you want to make sure that the etchant has the correct pH balance and the correct specific gravity.

The ideal pH of the solution is < 1 and the ideal specific gravity is between 1.2393 and 1.3303.

===Testing the pH===

To test the pH you'll want to use a pH meter. In the APL we have one called a pH spear. This can be calibrated and then used to test the pH of the etchant. Calibration should be done once a week.

To calibrate the pH meter you will need 3 clear, liquid solutions called pH buffers. Each pH buffer has a precisely determined pH that can be used to calibrate the pH meter. First, put on eye protection and gloves. Then, set up the three buffer solutions in three labeled trays like the picture below (make sure to write on the bottom side of the trays to avoid changing the pH of the solution in the tray) and place the three small trays in a large tray to contain spillage or dripping. Also, make sure the solutions are about room temperature and then proceed to calibration.

[[File:PH Meter.png]]

When you are ready to calibrate the pH meter, turn on the meter by pressing the ON/OFF button. Next, carefully remove the storage cap and solution from the tip of the pH meter. Make sure the storage solution does not spill and place the cap in a secure location for later. Rinse the tip of the pH spear with deionized water to remove the storage solution from the tip. Be sure to rinse the pH spear with deionized water between every submergence in a different liquid to wash away the previous liquid. Next, press the CAL button to begin calibration. Submerge the tip of the pH spear 2cm - 3cm below the surface of the 4 pH buffer solution for 2 minutes (this allows the electrode in the tip to stabilize). The screen will display two numbers, the top number is the reading for the current pH and the bottom number is the pH the meter is being calibrated to. Ideally, for the pH 4 buffer solution the top number will gradually drop or rise to 4.01 while the bottom number remains at 4.01 (the bottom number will only ever display 4.01, 7.00, or 10.01 which correspond to the different buffer solutions).

After 2 minutes in the solution, without removing the tip from the solution, press the HOLD/ENT button, this will save the current calibration. Rinse the tip with deionized water and submerge the tip in the pH 7 buffer solution. Once again press enter after 2 minutes and rinse the tip. Finally repeat this process for the pH 10 solution and rinse the tip with deionized water.

Now that the pH meter is calibrated, dip the pH meter 2cm - 3cm into the etchant and record the pH. At the time of writing this the pH of the solution is 0.07, which is well below 1 and thus adequate. When you remove the pH Spear from the etchant the tip will have a small amount of bright green etchant on it, because the etchant is caustic and should not go down the drain (see warnings below) you do not want to immediately rinse the tip with deionized water. First, while wearing gloves, gently dry the green liquid from the tip with kimtech wipes. This will absorb the excess liquid and you can then rinse the tip with deionized water.

If you are finished with pH meter return the pH spear into the storage cap with the storage solution and appropriately dispose of your excess chemicals (do not just pour them down the drain). Also, after adjusting the pH, record the date and pH on the side of the container.

If any of these instructions were unclear please refer to the pH Spear manual, which should be with the pH Spear.

====Decreasing the pH====

If the pH is above 1, you can decrease the pH by adding more HCl to the etchant. Handling pure HCl is dangerous and should be done with extreme caution. Ask professor Boggs for help with this.

===Testing the Specific Gravity===

To test the specific gravity you will need a hydrometer, again the ideal range is between 1.24 and 1.33. This will determine the relative density of the etchant. Using the hydrometer just requires you to place the weighted end down in the liquid, the hydrometer will then float (make sure there is enough liquid in your container to ensure the hydrometer will not touch the bottom of your container). The level at which the hydrometer floats in the liquid indicates the specific gravity, thus after a few seconds the hydrometer will stabilize and you can read the specific gravity from where the markings on the inside of the tube match with the top surface of the liquid.

If the specific gravity is too high you need add water. The specific gravity should not be too low because the etching process increases the specific gravity, although if too much water is added and brings the specific gravity down below 1.24 you can still perform suboptimal etching that will increase the specific gravity in the process.

Lastly, after adjusting the specific gravity, date and record your measurement on table tapped to the side of the container.

==Using the CuCl2==

Before interacting with the chemicals, make sure you have latex gloves, safety glasses, and a lab coat on.

===Etching with the Aggregation Tank===

Before you start the etching process you will want to set up the thermometer in the aggregation tank (this thermometer can fall into the tank and is difficult to remove so use the attached wire to prevent this), turn on the heating pillar by plugging it in, start the bubbler by plugging it in, and set up a tray of water/sodium bicarbonate mix (this mix should contain very roughly 1 tablespoon of sodium bicarbonate and 500 mL of water). The sodium bicarbonate will be used to neutralize the HCl in the CuCl2 and halt the etching process after you are finished. While increasing the temperature increases etching speed, it also boils off more HCl (which has a very low boiling point). I recommend bringing the CuCl2 solution up to 32 degrees Celsius and then unplugging the heater. The solution should roughly maintain this temperature for the duration of the etching process without being plugged back in.

The aggregator with the CuCl2 should look like this when set up, but make sure this is done under a fume hood (the HCl fumes are toxic and cause rust). Also make sure you have your sodium bircarbonate solution set up near by.

[[File:PCB Bubbler.png]]

Once you're all set up and the etchant is up to temperature you can attach you're PCB to a clip and submerge it in the liquid. You're goal is to remove all the copper from the areas without the green photoresist. You'll need to continue the etching process as long as it takes to do this, although my PCB took about 13.5 minutes so you can use this as a rough estimate. This time will not be the same for you and you must check the board at least every 3-5 minutes, if the board is left unattended for too long even the copper under the photoresist will be removed and you will just be left with a piece of fibreglass. As the copper is removed you will begin to see the fibreglass board. You're etching process is complete when all that is left on the board is the green photoresist (which protects the copper layer below it) and fibreglass. There should be no visible copper.

===Etching without the Aggregation Tank===

Before you start etching make sure you set up a tray of sodium bicarbonate and water to neutralize the acids after etching. The action is slow at our room temp (22C) and may require as long as 30 minutes of agitation. Agitation *must* be continuous (and currently, by hand as we lack a bubbler). The etching process occurs at the surface and not in the volume, thus it is a diffusion limited process - agitation is *essential* or the metal simply forms a depletion zone adjacent to itself devoid of etching ions. Etching is complete once close inspections shows NO remaining exposed copper.

Note that the board cannot be left to etch unattended even with automatic agitation - the acid etches across as it cuts down (at a fairly small angle), but if left indefinitely it will eat *all* the copper off the board.

===After Etching===

Once etching is complete, remove the board from the etchant with a gloved hand. Try to shake as much etchant as possible back off into the tank before putting the board into a prepared small tray of sodium bicarbonate solution. This will immediately halt the etch action, and remove all remaining copper ions from the etchant solution that remained to the board. You will see light blue particles form in the sodium bicarbonate solution when it contacts the etchant.Gentle brushing will take any copper bicarbonate (the light blue particles) off the board.

Once the board is clean, we want to remove the remaining photoresist from the copper traces. Pour a very small amount of acetone over the board and you should see the green layer disappear to reveal your copper traces. This step is necessary so you will be able to solder components to the copper of the board.

Once the acetone washes away the green photoresist, the board should look like this, with copper traces exposed on the layer of substrate:

[[File:Etched_PCB.png]]

====Etchant Warning====
Make sure none of the etchant goes down the drain because putting copper ions down the drain is very illegal:

https://nature.nps.gov/water/ecencyclopedia/assets/contaminant-pdfs/copper.pdf

'''Copper ion concentrations measured in single-digit parts per million are dangerous to aquatic life, and the required dilutions for copper ion contaminated water to go down the drain are concomitant: Our tank of etchant would contaminate several olympic swimming pools of water beyond legal release limits.

Under no circumstances allow any amount of green etchant solution to go down the drain! If any does, dump the sodium bicarbonate in immediately, chase it with a torrent of water, and pour additional bicarbonate in the sink straight from the box to 'kill it' before it enters the wastewater stream. If substantial spillage (more than a thimble full) occurs, get Dr. Boggs and call EHS immediately. A large release of copper ions down the drain threatens the entire city's wastewater treatment plant.'''

===Technical Information===

The Acopper chloride etchant functions via the following reactions. The obvious attraction of this process is that it produces no waste stream: The result of etching copper is more etchant! Be very careful with the etchant as HCL is extremely acidic, also see the warnings below about the proper way to dispose of the etchant (do not pour it down the drain).

Cu(s) + CuCl2 -> 2CuCl

CuCl + chlorinating oxidation -> CuCl2

The tank contains a not insignificant amount of hydrochloric acid (the unmistakeable smell of which is detectable when it is open). However, the HCl is not free: It is almost entirely bound up in complexes with the copper chloride. Transition metal salts are known for being extremely colorful, and copper is no exception.

Dilute solutions of copper chloride in water are a serene blue (the copper ion coordinates with 6 waters). Intermediate concentrations are yellowish, and the addition of hydrochloric acid to a concentrated solution results in the copper ions forming a complex with two waters and four chloride ions (CuCl_4^{-2} \cdot 2H_2O), and it is this complex which gives our etchant its beautiful and almost hypnotically intense green hue.

The second reaction above is a summary of what is actually a rather complicated series of ion-complex reactions. The first reaction proceeds rapidly, while the second is the rate limiting factor (the insertion of a powerful oxidizer, like hydrogen peroxide, to the solution can speed this up).

This can be observed if the board is withdrawn entirely from the etchant solution to examine: Immediately, brownish liquid can be seen draining off of all exposed copper areas - these drops are etchant in which all available acid has been used up and copper (II) has saturated the solution with brown copper (I) ions.

This underscores why turbulent action is essential to the etching process: Like photographic development, etching is a surface reaction whose components come from a bulk fluid, and the bulk must be turbulently washed over the surface to continuously bring "new" etchant, unladen with copper I ions, within diffusion range of the surface.

If the CuCl2 becomes over saturated during the etching process the addition of hydrogen peroxide will restore the copper chloride to its original state.

The Darkroom

2019-04-16T20:53:35Z

Aplstudent: /* An aside: */

==Print to Film==

The photo center requires that you either know how to use a chemical darkroom already or that you take an introduction course.

Access to their chemicals is $10 per quarter or $2 for a day. They don't take index numbers but you can be reimbursed.

Before you go to the darkroom you will need lithographic film, latex gloves, lithographic developer parts A and B (these each come in a separate bottle), and your paper negative print of your PCB. Everything else you need can be found in the craft center.

The lithographic film is kept in an envelop and a black film jacket; this film will become useless if it is exposed to light (except red/yellowish lights in the dark room) so never open the film container outside the darkroom. Continue reading for how to properly handle the film in the dark room.

The lithographic film developer comes in two bottles, part A concentrate and part B concentrate and the two parts will be mixed at the time of development. Part A is a dark purple color and part B is clear.

[[File:Labeled developer.png]]

In the darkroom, keep the lights low and let your eyes adapt.

===Prep and setup===

- Lay out chemical trays: developer, stop bath (water), fixer, hypowash.

There free-to-use containers of fixer and hypowash (hypoclear) in the cabinets labelled "Open Use Chemicals". These cabinets are located on the right side of the small hallway as you walk in through the door of the dark room (the hall between the door and the curtains). In this cabinet you will also see containers of "Stop", don't use this chemical for the stop bath, just use water.

The developer comes in two parts (A and B). Per the instructions on the bottles, mix 100ml of Part A concentrate to 300ml of water. Then separately Mix 100ml of Part B to 300ml of water. Disregard the nonsense about 68*F -as long as the temperature of the AB mix is in the vicinity of 80*F before development you are okay. It was found that just diluting the concentrates of A and B with hot water straight from the darkroom's hot tap worked quite well with the still fridge-cold concentrate. Pour the water mixed with A into the tray, then the mix of B and water into the same tray. Then wash the beaker thoroughly (water/agitate/dump 3x). Once mixed, the developer apparently has a frighteningly short useful lifetime - order of a few hours - which is why it comes in separated bottles.

The developer tray should be floated in a second tray containing hot water as thermal ballast. If the tray of developer is left on the cold metal table the developing liquid will quickly cool below working temperature. The target temp is around 80*F... 75*F is too cold, 85*F or more will be too hot. As an added layer of thermal protection you can flip over an empty tub on the metal table, place your hot water bath on the flipped over tub, and place your A/B mix tray in the hot water bath. This way the table will not cool the bath.

Next you will want to set up a stop bath, the fixer, and the hypowash. Fill one tray with water (this will be your stop bath), then fill one tray with Fixer (this will be in a labeled container in the dark room), and fill one tray with hypowash (this is a container labeled Iypoclear). The photo below shows 3 of the 4 contianers (the water stop bath is not shown).

[[File:Lith film dev chemicals.png]]

===Contact Printing===

- Next, prepare the contact print setup. You need two 8x10 glass sheets from two normal contract printing beds, to make a glass-film-paper-glass sandwich. Glass is very flat and must be used to ensure the maximum retention of detail. There should be flat sheets of glass in the dark room but it may require some searching to find them.

- Prepare film to approximately the size of your art. We have 8x10 inch film sheets, so that it is natural to cut each down to four 4x5 inch pieces if this can accommodate your art. There is a paper cutter in the corner of the dark room behind a curtain. When cutting, don't be afraid to have some spare border so the film can easily be handled after without getting fingerprints on the art itself. You will also need test strips of Lithographic film to confirm the correct exposure. Check the film jacket for existing cut-down pieces before getting out another 8x10 sheet.

All film that is not this very second being cut, exposed or developed must be stored in the black film jacket and returned there promptly between cutting and exposure. Never take more than one sheet out at a time. The orange safelight will not expose it quickly, but the safelight and stray light from the enlarger will expose it eventually and this mal-exposure (known as fogging) is undetectable until the film is developed. Wear gloves while handling the film to avoid getting filthy dirty meatpaw marks all over it (a glove will be needed during development anyway). To the greatest extent possible, handle the film by its edges.

The film has a back and an emulsion side. The emulsion side is allegedly pinkish, which is spectacularly useless to know given that it can only be viewed in a darkroom under red light. The best way to tell the difference is by "tasting" the edge of the film with your lips. The emulsion side feels unsmooth/tacky while the anti-halation backing of the far side feels smooth. Always make sure that the emulsion side is up when exposing!

Thus, the layers for the exposure process should be a sheet of glass, the film (emulsion side up), the paper print (ink side down), and another sheet of glass.

The light source for your exposure will be the enlarger. An enlarger is commonly used to enlarge 35mm negatives, but you already have a paper negative so the enlarger will just act as a timed flashlight. A picture of the enlarge can be found below. You will place your glass-film-paper-glass sandwich under the enlarger and use the timer to vary the exposure time. The light will turn on for that amount of time and then turn off automatically. The enlarger has multiple color capabilities and is adjustable. Set the enlarger to white by flipping the "W" switch up, which ensures the light is white. Next, adjust the lens distance (essentially the focus) until the enlarger produces a uniform area of light that will cover your print. If the light is not uniform over the whole area of the print the film will not develop evenly.

[[File:Enlarger.png]]

===Make Test Strips===

Test strips are used to determine the ideal exposure time for your film and are made by contact printing a strip of film with different exposure times. To test the different times you will set up a contact print with your paper negative and test strip, then cover 4/5 with a light blocking material (thick cardboard or plastic) and expose 1/5 of the strip for 5 seconds. Next you will move the light blocking material to reveal 2/5 of your strip and expose the strip for another 5 seconds. You will repeat this process by covering less and less of your strip until the whole strip is exposed. This results in a strip having 5 different exposer times (the first 1/5 having 25 seconds of exposure while the last 1/5 only having 5 seconds of exposure). This [https://brucetannerphotographer.files.wordpress.com/2014/04/hast-lin.jpg image] demonstrates how the variations of exposure times will affect an image and how the test strip should look with regards to 5 different exposure areas.

To make your strip cut a small strip of film paper (an inch wide and about 5 inches long) and place this under the enlarger. Exposure time depends somewhat on enlarger head height and strongly on developer temperature (development is a thermodynamic process and is exponential in temperature). With an empty 35mm film holder in the enlarger, all color filters set to neutral, the lens aperture fully open, and the enlarger head moved down so that the image is about 11 inches wide, begin exposing the film for 5 second increments.

Follow the steps below to develop this test strip and determine which exposure time yields the best results. The ideal exposure time will result in completely clear regions where the paper negative was black and completely black regions where the paper negative was white. The black is black enough if you can hold the developed test strip up to a bright light and not see any light through the black regions.

===Chemical Development Process===

1. Developer (2-5 minutes)

2. Stop Bath (30 seconds)

3. Fixer (5 minutes)

4. Hypowash (5 minutes)

5. Rinse

6. Clean Up (developer and hypowash can be poured down the drain with water, fixer should be poured into the a container labelled "Spent Fixer" which can be found in the dark room). Also be sure to rinse out all containers used.

====Technical Information====

----

Normal photographic development is designed to convert a continuous range of light exposures into a continuous range of densities on the film or paper. This process generally has a roughly linear dynamic range of between 100 and 1000 to 1 separating "black" and "clear" (papers being nearer to 100 and films to 1000). At extremes of over- or under-exposure, the transfer function graphing optical density vs exposure saturates, resembling a graph of arctan(x). The steepness of the linear region defines the contrast level of the film, and is affected by both the film itself and the development process used.

In the normal, modern, black & white photographic development process, photons have reduced tiny amounts of silver halide in the film surface to silver metal. Within each grain, the developer converts silver metal to black silver oxide such that the darkness of a grain is proportional to how much light it received.

In the lithographic process, this normal process is augmented with positive feedback: Both silver AND silver oxide contribute to the development process. Obviously this results in exponential runaway, as a grain that develops at all will quickly turn completely black.

Photographic artists manipulate the lithographic process to produce exotic image tones (generally by gross overexposure, followed by great underdevelopment, such that the exponential runaway proceeds only to the point of producing an intriguingly nonlinear response curve), but we are interested in its "intended" property: The production of incredibly high contrast (10000:1) images with incredibly high resolutions (resolvable features on the micron scale).

For any given amount of exposure E, a given development process will result in an output film optical density D(E). For the halftone process, done correctly,

<math>D(E) ~= 4 * heaviside(E - E_{crit})</math>.

The contrast ratio of the printed image on paper is remarkably low when backlit - maybe 10, as opposed to over 100 viewed in diffuse reflective light - and suffers considerable fluctuations due to the random fiber packing of paper causing the transmission of "clear" areas to fluctuate considerably.

Thus the range of acceptable exposures, meaning those for which all black areas get E < E_crit and all clear areas get E > E_crit, is not nearly so wide as might be imagined.

Furthermore, the brightness of the light rectangle supplied by the enlarger experiences a nontrivial (~20%) decrease towards its corners, further eroding exposure margin.

This will demonstrate itself on test strips: If an exposure of 12 seconds works, most likely 6 seconds will result in a very weak image and 18 will blacken everything.

----

Development time should be roughly 2-5 minutes. Put the film into the developer emulsion up, as it was exposed. With a glove or tongs, agitate continuously for 30 seconds, then 5 seconds every 30. The film should quickly turn whiteish, and the shadow of an image should begin to darken within about 30 seconds. If it does not, either exposure was insufficient or the developer is cold.

Note that photographic development is a diffusion-limited process: The developer exists in the bulk fluid, but image formation occurs at a semi-infinite plane surface. This means that fluid agitation is *ESSENTIAL* to the process.

Overexposure with underdevelopment (Less than 2 minutes in developer) will be associated with clear areas exhibiting a continuous-tone brown muddiness, which is not OK for us (but is typical of what artistic lith printers are after). Underexposure with overdevelopment (over 4-ish minutes in developer) will be associated with waiting for the exposed areas to finish turning fully black when suddenly black dots begin to appear in clear areas.

If the developer is not legit warm through the glove, it is too cold. Floating the developer tray in a second tray filled with a thermal ballast of hot water will maintain its temperature for longer.

After developing, grab the film (either with tongs or glove) and wash it for 30 seconds in the stop bath (water) with continous swishing. This halts the development process, but the film is still photosensitive.

After placing the film in the fixer and agitating, almost immediate clearing of the substrate from white to transparent should occur. The fixing process takes about 5 minutes with intermittent agitation. As its name implies, the fixer "fixes" the image: It disintegrates and dissolves the remaining silver halide, leaving only the black silver oxide created by the developer.

After fixing, the film needs to be washed in hypowash to assure long-term stability of the photographic substrate. Around 5 minutes is sufficient, but more is not harmful. Agitate occasionally. Hypowash lets the fixer molecules diffuse out of the film, and also neutralizes any remaining acids that would slowly damage the substrate.

After hypowash, the film can be left in a final bath of plain water until all images are done.

Once fixed and washed, dry the film immediately by GENTLY enfolding both sides with a paper towel and pressing (not rubbing) to absorb most of the water. This directly removes the water and avoids the need to use a wetting agent and spend a long drying interval (don't let photographers see you wipe it with the paper towel, they may have heart attacks). The film's surface will still be "wet" like skin after washing dishes, and like wrinkled fingers the absorbed water will need time to evaporate out.

Now the film can be taken to normal room lights and inspected. Key points to check include optical density (it should be nearly impossible to see even direct fluorescent tubes through the black regions), and speckling (development of individual black grains in nominally unexposed regions, indicating overexposure/overdevelopment). It also goes without saying, the image should be unimpeachably finer than the unaided eye can resolve.

If the image is acceptable, clean the darkroom up, make certain the film bag is completely closed and put away, put the developed image in a negative sheet and you're done.

The following image demonstrates the transformation from digital image, to printed image, to photographic film:

[[File:Print examples.png]]

This is from a resolution test art. Six denotes that the array of vertical traces are 6 mils wide, while 12 and 15 denote that their centers are spaced by 15 and 12 mils. In terms of what might be sent to a commercial fabricator, 6 mil traces on 12 mil centers is middle of the road.

The right image is the "perfect" digital original, vector art rasterized at 600dpi. The middle panel is a photomicrograph of the paper output: As part of the resolution limit process, the toner demonstrates a clear preference to smear from black into areas that should be clear.

The left image is a reflection photomicrograph of the lithographic film, which exhibits contrast vastly inferior to a transmission image. Testing in the UV exposure chamber using a power meter found that when clear areas transmitted a measured power of 200uW, bulk opaque areas transmitted approximately 20nW: The clear/black contrast ratio exceeds 10000:1.

The Darkroom

2019-04-15T23:56:40Z

Aplstudent: /* Chemical Development Process */

==Print to Film==

The photo center requires that you either know how to use a chemical darkroom already or that you take an introduction course.

Access to their chemicals is $10 per quarter or $2 for a day. They don't take index numbers but you can be reimbursed.

Before you go to the darkroom you will need lithographic film, latex gloves, lithographic developer parts A and B (these each come in a separate bottle), and your paper negative print of your PCB. Everything else you need can be found in the craft center.

The lithographic film is kept in an envelop and a black film jacket; this film will become useless if it is exposed to light (except red/yellowish lights in the dark room) so never open the film container outside the darkroom. Continue reading for how to properly handle the film in the dark room.

The lithographic film developer comes in two bottles, part A concentrate and part B concentrate and the two parts will be mixed at the time of development. Part A is a dark purple color and part B is clear.

[[File:Labeled developer.png]]

In the darkroom, keep the lights low and let your eyes adapt.

===Prep and setup===

- Lay out chemical trays: developer, stop bath (water), fixer, hypowash.

There free-to-use containers of fixer and hypowash (hypoclear) in the cabinets labelled "Open Use Chemicals". These cabinets are located on the right side of the small hallway as you walk in through the door of the dark room (the hall between the door and the curtains). In this cabinet you will also see containers of "Stop", don't use this chemical for the stop bath, just use water.

The developer comes in two parts (A and B). Per the instructions on the bottles, mix 100ml of Part A concentrate to 300ml of water. Then separately Mix 100ml of Part B to 300ml of water. Disregard the nonsense about 68*F -as long as the temperature of the AB mix is in the vicinity of 80*F before development you are okay. It was found that just diluting the concentrates of A and B with hot water straight from the darkroom's hot tap worked quite well with the still fridge-cold concentrate. Pour the water mixed with A into the tray, then the mix of B and water into the same tray. Then wash the beaker thoroughly (water/agitate/dump 3x). Once mixed, the developer apparently has a frighteningly short useful lifetime - order of a few hours - which is why it comes in separated bottles.

The developer tray should be floated in a second tray containing hot water as thermal ballast. If the tray of developer is left on the cold metal table the developing liquid will quickly cool below working temperature. The target temp is around 80*F... 75*F is too cold, 85*F or more will be too hot. As an added layer of thermal protection you can flip over an empty tub on the metal table, place your hot water bath on the flipped over tub, and place your A/B mix tray in the hot water bath. This way the table will not cool the bath.

Next you will want to set up a stop bath, the fixer, and the hypowash. Fill one tray with water (this will be your stop bath), then fill one tray with Fixer (this will be in a labeled container in the dark room), and fill one tray with hypowash (this is a container labeled Iypoclear). The photo below shows 3 of the 4 contianers (the water stop bath is not shown).

[[File:Lith film dev chemicals.png]]

===Contact Printing===

- Next, prepare the contact print setup. You need two 8x10 glass sheets from two normal contract printing beds, to make a glass-film-paper-glass sandwich. Glass is very flat and must be used to ensure the maximum retention of detail. There should be flat sheets of glass in the dark room but it may require some searching to find them.

- Prepare film to approximately the size of your art. We have 8x10 inch film sheets, so that it is natural to cut each down to four 4x5 inch pieces if this can accommodate your art. There is a paper cutter in the corner of the dark room behind a curtain. When cutting, don't be afraid to have some spare border so the film can easily be handled after without getting fingerprints on the art itself. You will also need test strips of Lithographic film to confirm the correct exposure. Check the film jacket for existing cut-down pieces before getting out another 8x10 sheet.

All film that is not this very second being cut, exposed or developed must be stored in the black film jacket and returned there promptly between cutting and exposure. Never take more than one sheet out at a time. The orange safelight will not expose it quickly, but the safelight and stray light from the enlarger will expose it eventually and this mal-exposure (known as fogging) is undetectable until the film is developed. Wear gloves while handling the film to avoid getting filthy dirty meatpaw marks all over it (a glove will be needed during development anyway). To the greatest extent possible, handle the film by its edges.

The film has a back and an emulsion side. The emulsion side is allegedly pinkish, which is spectacularly useless to know given that it can only be viewed in a darkroom under red light. The best way to tell the difference is by "tasting" the edge of the film with your lips. The emulsion side feels unsmooth/tacky while the anti-halation backing of the far side feels smooth. Always make sure that the emulsion side is up when exposing!

Thus, the layers for the exposure process should be a sheet of glass, the film (emulsion side up), the paper print (ink side down), and another sheet of glass.

The light source for your exposure will be the enlarger. An enlarger is commonly used to enlarge 35mm negatives, but you already have a paper negative so the enlarger will just act as a timed flashlight. A picture of the enlarge can be found below. You will place your glass-film-paper-glass sandwich under the enlarger and use the timer to vary the exposure time. The light will turn on for that amount of time and then turn off automatically. The enlarger has multiple color capabilities and is adjustable. Set the enlarger to white by flipping the "W" switch up, which ensures the light is white. Next, adjust the lens distance (essentially the focus) until the enlarger produces a uniform area of light that will cover your print. If the light is not uniform over the whole area of the print the film will not develop evenly.

[[File:Enlarger.png]]

===Make Test Strips===

Test strips are used to determine the ideal exposure time for your film and are made by contact printing a strip of film with different exposure times. To test the different times you will set up a contact print with your paper negative and test strip, then cover 4/5 with a light blocking material (thick cardboard or plastic) and expose 1/5 of the strip for 5 seconds. Next you will move the light blocking material to reveal 2/5 of your strip and expose the strip for another 5 seconds. You will repeat this process by covering less and less of your strip until the whole strip is exposed. This results in a strip having 5 different exposer times (the first 1/5 having 25 seconds of exposure while the last 1/5 only having 5 seconds of exposure). This [https://brucetannerphotographer.files.wordpress.com/2014/04/hast-lin.jpg image] demonstrates how the variations of exposure times will affect an image and how the test strip should look with regards to 5 different exposure areas.

To make your strip cut a small strip of film paper (an inch wide and about 5 inches long) and place this under the enlarger. Exposure time depends somewhat on enlarger head height and strongly on developer temperature (development is a thermodynamic process and is exponential in temperature). With an empty 35mm film holder in the enlarger, all color filters set to neutral, the lens aperture fully open, and the enlarger head moved down so that the image is about 11 inches wide, begin exposing the film for 5 second increments.

Follow the steps below to develop this test strip and determine which exposure time yields the best results. The ideal exposure time will result in completely clear regions where the paper negative was black and completely black regions where the paper negative was white. The black is black enough if you can hold the developed test strip up to a bright light and not see any light through the black regions.

===Chemical Development Process===

1. Developer (2-5 minutes)

2. Stop Bath (30 seconds)

3. Fixer (5 minutes)

4. Hypowash (5 minutes)

5. Rinse

6. Clean Up (developer and hypowash can be poured down the drain with water, fixer should be poured into the a container labelled "Spent Fixer" which can be found in the dark room). Also be sure to rinse out all containers used.

====An aside:====

----

Normal photographic development is designed to convert a continuous range of light exposures into a continuous range of densities on the film or paper. This process generally has a roughly linear dynamic range of between 100 and 1000 to 1 separating "black" and "clear" (papers being nearer to 100 and films to 1000). At extremes of over- or under-exposure, the transfer function graphing optical density vs exposure saturates, resembling a graph of arctan(x). The steepness of the linear region defines the contrast level of the film, and is affected by both the film itself and the development process used.

In the normal, modern, black & white photographic development process, photons have reduced tiny amounts of silver halide in the film surface to silver metal. Within each grain, the developer converts silver metal to black silver oxide such that the darkness of a grain is proportional to how much light it received.

In the lithographic process, this normal process is augmented with positive feedback: Both silver AND silver oxide contribute to the development process. Obviously this results in exponential runaway, as a grain that develops at all will quickly turn completely black.

Photographic artists manipulate the lithographic process to produce exotic image tones (generally by gross overexposure, followed by great underdevelopment, such that the exponential runaway proceeds only to the point of producing an intriguingly nonlinear response curve), but we are interested in its "intended" property: The production of incredibly high contrast (10000:1) images with incredibly high resolutions (resolvable features on the micron scale).

For any given amount of exposure E, a given development process will result in an output film optical density D(E). For the halftone process, done correctly,

<math>D(E) ~= 4 * heaviside(E - E_{crit})</math>.

The contrast ratio of the printed image on paper is remarkably low when backlit - maybe 10, as opposed to over 100 viewed in diffuse reflective light - and suffers considerable fluctuations due to the random fiber packing of paper causing the transmission of "clear" areas to fluctuate considerably.

Thus the range of acceptable exposures, meaning those for which all black areas get E < E_crit and all clear areas get E > E_crit, is not nearly so wide as might be imagined.

Furthermore, the brightness of the light rectangle supplied by the enlarger experiences a nontrivial (~20%) decrease towards its corners, further eroding exposure margin.

This will demonstrate itself on test strips: If an exposure of 12 seconds works, most likely 6 seconds will result in a very weak image and 18 will blacken everything.

----

Development time should be roughly 2-5 minutes. Put the film into the developer emulsion up, as it was exposed. With a glove or tongs, agitate continuously for 30 seconds, then 5 seconds every 30. The film should quickly turn whiteish, and the shadow of an image should begin to darken within about 30 seconds. If it does not, either exposure was insufficient or the developer is cold.

Note that photographic development is a diffusion-limited process: The developer exists in the bulk fluid, but image formation occurs at a semi-infinite plane surface. This means that fluid agitation is *ESSENTIAL* to the process.

Overexposure with underdevelopment (Less than 2 minutes in developer) will be associated with clear areas exhibiting a continuous-tone brown muddiness, which is not OK for us (but is typical of what artistic lith printers are after). Underexposure with overdevelopment (over 4-ish minutes in developer) will be associated with waiting for the exposed areas to finish turning fully black when suddenly black dots begin to appear in clear areas.

If the developer is not legit warm through the glove, it is too cold. Floating the developer tray in a second tray filled with a thermal ballast of hot water will maintain its temperature for longer.

After developing, grab the film (either with tongs or glove) and wash it for 30 seconds in the stop bath (water) with continous swishing. This halts the development process, but the film is still photosensitive.

After placing the film in the fixer and agitating, almost immediate clearing of the substrate from white to transparent should occur. The fixing process takes about 5 minutes with intermittent agitation. As its name implies, the fixer "fixes" the image: It disintegrates and dissolves the remaining silver halide, leaving only the black silver oxide created by the developer.

After fixing, the film needs to be washed in hypowash to assure long-term stability of the photographic substrate. Around 5 minutes is sufficient, but more is not harmful. Agitate occasionally. Hypowash lets the fixer molecules diffuse out of the film, and also neutralizes any remaining acids that would slowly damage the substrate.

After hypowash, the film can be left in a final bath of plain water until all images are done.

Once fixed and washed, dry the film immediately by GENTLY enfolding both sides with a paper towel and pressing (not rubbing) to absorb most of the water. This directly removes the water and avoids the need to use a wetting agent and spend a long drying interval (don't let photographers see you wipe it with the paper towel, they may have heart attacks). The film's surface will still be "wet" like skin after washing dishes, and like wrinkled fingers the absorbed water will need time to evaporate out.

Now the film can be taken to normal room lights and inspected. Key points to check include optical density (it should be nearly impossible to see even direct fluorescent tubes through the black regions), and speckling (development of individual black grains in nominally unexposed regions, indicating overexposure/overdevelopment). It also goes without saying, the image should be unimpeachably finer than the unaided eye can resolve.

If the image is acceptable, clean the darkroom up, make certain the film bag is completely closed and put away, put the developed image in a negative sheet and you're done.

The following image demonstrates the transformation from digital image, to printed image, to photographic film:

[[File:Print examples.png]]

This is from a resolution test art. Six denotes that the array of vertical traces are 6 mils wide, while 12 and 15 denote that their centers are spaced by 15 and 12 mils. In terms of what might be sent to a commercial fabricator, 6 mil traces on 12 mil centers is middle of the road.

The right image is the "perfect" digital original, vector art rasterized at 600dpi. The middle panel is a photomicrograph of the paper output: As part of the resolution limit process, the toner demonstrates a clear preference to smear from black into areas that should be clear.

The left image is a reflection photomicrograph of the lithographic film, which exhibits contrast vastly inferior to a transmission image. Testing in the UV exposure chamber using a power meter found that when clear areas transmitted a measured power of 200uW, bulk opaque areas transmitted approximately 20nW: The clear/black contrast ratio exceeds 10000:1.

The Darkroom

2019-04-15T23:51:30Z

Aplstudent: /* Contact Printing */

==Print to Film==

The photo center requires that you either know how to use a chemical darkroom already or that you take an introduction course.

Access to their chemicals is $10 per quarter or $2 for a day. They don't take index numbers but you can be reimbursed.

Before you go to the darkroom you will need lithographic film, latex gloves, lithographic developer parts A and B (these each come in a separate bottle), and your paper negative print of your PCB. Everything else you need can be found in the craft center.

The lithographic film is kept in an envelop and a black film jacket; this film will become useless if it is exposed to light (except red/yellowish lights in the dark room) so never open the film container outside the darkroom. Continue reading for how to properly handle the film in the dark room.

The lithographic film developer comes in two bottles, part A concentrate and part B concentrate and the two parts will be mixed at the time of development. Part A is a dark purple color and part B is clear.

[[File:Labeled developer.png]]

In the darkroom, keep the lights low and let your eyes adapt.

===Prep and setup===

- Lay out chemical trays: developer, stop bath (water), fixer, hypowash.

There free-to-use containers of fixer and hypowash (hypoclear) in the cabinets labelled "Open Use Chemicals". These cabinets are located on the right side of the small hallway as you walk in through the door of the dark room (the hall between the door and the curtains). In this cabinet you will also see containers of "Stop", don't use this chemical for the stop bath, just use water.

The developer comes in two parts (A and B). Per the instructions on the bottles, mix 100ml of Part A concentrate to 300ml of water. Then separately Mix 100ml of Part B to 300ml of water. Disregard the nonsense about 68*F -as long as the temperature of the AB mix is in the vicinity of 80*F before development you are okay. It was found that just diluting the concentrates of A and B with hot water straight from the darkroom's hot tap worked quite well with the still fridge-cold concentrate. Pour the water mixed with A into the tray, then the mix of B and water into the same tray. Then wash the beaker thoroughly (water/agitate/dump 3x). Once mixed, the developer apparently has a frighteningly short useful lifetime - order of a few hours - which is why it comes in separated bottles.

The developer tray should be floated in a second tray containing hot water as thermal ballast. If the tray of developer is left on the cold metal table the developing liquid will quickly cool below working temperature. The target temp is around 80*F... 75*F is too cold, 85*F or more will be too hot. As an added layer of thermal protection you can flip over an empty tub on the metal table, place your hot water bath on the flipped over tub, and place your A/B mix tray in the hot water bath. This way the table will not cool the bath.

Next you will want to set up a stop bath, the fixer, and the hypowash. Fill one tray with water (this will be your stop bath), then fill one tray with Fixer (this will be in a labeled container in the dark room), and fill one tray with hypowash (this is a container labeled Iypoclear). The photo below shows 3 of the 4 contianers (the water stop bath is not shown).

[[File:Lith film dev chemicals.png]]

===Contact Printing===

- Next, prepare the contact print setup. You need two 8x10 glass sheets from two normal contract printing beds, to make a glass-film-paper-glass sandwich. Glass is very flat and must be used to ensure the maximum retention of detail. There should be flat sheets of glass in the dark room but it may require some searching to find them.

- Prepare film to approximately the size of your art. We have 8x10 inch film sheets, so that it is natural to cut each down to four 4x5 inch pieces if this can accommodate your art. There is a paper cutter in the corner of the dark room behind a curtain. When cutting, don't be afraid to have some spare border so the film can easily be handled after without getting fingerprints on the art itself. You will also need test strips of Lithographic film to confirm the correct exposure. Check the film jacket for existing cut-down pieces before getting out another 8x10 sheet.

All film that is not this very second being cut, exposed or developed must be stored in the black film jacket and returned there promptly between cutting and exposure. Never take more than one sheet out at a time. The orange safelight will not expose it quickly, but the safelight and stray light from the enlarger will expose it eventually and this mal-exposure (known as fogging) is undetectable until the film is developed. Wear gloves while handling the film to avoid getting filthy dirty meatpaw marks all over it (a glove will be needed during development anyway). To the greatest extent possible, handle the film by its edges.

The film has a back and an emulsion side. The emulsion side is allegedly pinkish, which is spectacularly useless to know given that it can only be viewed in a darkroom under red light. The best way to tell the difference is by "tasting" the edge of the film with your lips. The emulsion side feels unsmooth/tacky while the anti-halation backing of the far side feels smooth. Always make sure that the emulsion side is up when exposing!

Thus, the layers for the exposure process should be a sheet of glass, the film (emulsion side up), the paper print (ink side down), and another sheet of glass.

The light source for your exposure will be the enlarger. An enlarger is commonly used to enlarge 35mm negatives, but you already have a paper negative so the enlarger will just act as a timed flashlight. A picture of the enlarge can be found below. You will place your glass-film-paper-glass sandwich under the enlarger and use the timer to vary the exposure time. The light will turn on for that amount of time and then turn off automatically. The enlarger has multiple color capabilities and is adjustable. Set the enlarger to white by flipping the "W" switch up, which ensures the light is white. Next, adjust the lens distance (essentially the focus) until the enlarger produces a uniform area of light that will cover your print. If the light is not uniform over the whole area of the print the film will not develop evenly.

[[File:Enlarger.png]]

===Make Test Strips===

Test strips are used to determine the ideal exposure time for your film and are made by contact printing a strip of film with different exposure times. To test the different times you will set up a contact print with your paper negative and test strip, then cover 4/5 with a light blocking material (thick cardboard or plastic) and expose 1/5 of the strip for 5 seconds. Next you will move the light blocking material to reveal 2/5 of your strip and expose the strip for another 5 seconds. You will repeat this process by covering less and less of your strip until the whole strip is exposed. This results in a strip having 5 different exposer times (the first 1/5 having 25 seconds of exposure while the last 1/5 only having 5 seconds of exposure). This [https://brucetannerphotographer.files.wordpress.com/2014/04/hast-lin.jpg image] demonstrates how the variations of exposure times will affect an image and how the test strip should look with regards to 5 different exposure areas.

To make your strip cut a small strip of film paper (an inch wide and about 5 inches long) and place this under the enlarger. Exposure time depends somewhat on enlarger head height and strongly on developer temperature (development is a thermodynamic process and is exponential in temperature). With an empty 35mm film holder in the enlarger, all color filters set to neutral, the lens aperture fully open, and the enlarger head moved down so that the image is about 11 inches wide, begin exposing the film for 5 second increments.

Follow the steps below to develop this test strip and determine which exposure time yields the best results. The ideal exposure time will result in completely clear regions where the paper negative was black and completely black regions where the paper negative was white. The black is black enough if you can hold the developed test strip up to a bright light and not see any light through the black regions.

===Chemical Development Process===

1. Developer (2-5 minutes)

2. Stop Bath (30 seconds)

3. Fixer (5 minutes)

4. Hypowash (5 minutes)

5. Rinse

====An aside:====

----

Normal photographic development is designed to convert a continuous range of light exposures into a continuous range of densities on the film or paper. This process generally has a roughly linear dynamic range of between 100 and 1000 to 1 separating "black" and "clear" (papers being nearer to 100 and films to 1000). At extremes of over- or under-exposure, the transfer function graphing optical density vs exposure saturates, resembling a graph of arctan(x). The steepness of the linear region defines the contrast level of the film, and is affected by both the film itself and the development process used.

In the normal, modern, black & white photographic development process, photons have reduced tiny amounts of silver halide in the film surface to silver metal. Within each grain, the developer converts silver metal to black silver oxide such that the darkness of a grain is proportional to how much light it received.

In the lithographic process, this normal process is augmented with positive feedback: Both silver AND silver oxide contribute to the development process. Obviously this results in exponential runaway, as a grain that develops at all will quickly turn completely black.

Photographic artists manipulate the lithographic process to produce exotic image tones (generally by gross overexposure, followed by great underdevelopment, such that the exponential runaway proceeds only to the point of producing an intriguingly nonlinear response curve), but we are interested in its "intended" property: The production of incredibly high contrast (10000:1) images with incredibly high resolutions (resolvable features on the micron scale).

For any given amount of exposure E, a given development process will result in an output film optical density D(E). For the halftone process, done correctly,

<math>D(E) ~= 4 * heaviside(E - E_{crit})</math>.

The contrast ratio of the printed image on paper is remarkably low when backlit - maybe 10, as opposed to over 100 viewed in diffuse reflective light - and suffers considerable fluctuations due to the random fiber packing of paper causing the transmission of "clear" areas to fluctuate considerably.

Thus the range of acceptable exposures, meaning those for which all black areas get E < E_crit and all clear areas get E > E_crit, is not nearly so wide as might be imagined.

Furthermore, the brightness of the light rectangle supplied by the enlarger experiences a nontrivial (~20%) decrease towards its corners, further eroding exposure margin.

This will demonstrate itself on test strips: If an exposure of 12 seconds works, most likely 6 seconds will result in a very weak image and 18 will blacken everything.

----

Development time should be roughly 2-5 minutes. Put the film into the developer emulsion up, as it was exposed. With a glove or tongs, agitate continuously for 30 seconds, then 5 seconds every 30. The film should quickly turn whiteish, and the shadow of an image should begin to darken within about 30 seconds. If it does not, either exposure was insufficient or the developer is cold.

Note that photographic development is a diffusion-limited process: The developer exists in the bulk fluid, but image formation occurs at a semi-infinite plane surface. This means that fluid agitation is *ESSENTIAL* to the process.

Overexposure with underdevelopment (Less than 2 minutes in developer) will be associated with clear areas exhibiting a continuous-tone brown muddiness, which is not OK for us (but is typical of what artistic lith printers are after). Underexposure with overdevelopment (over 4-ish minutes in developer) will be associated with waiting for the exposed areas to finish turning fully black when suddenly black dots begin to appear in clear areas.

If the developer is not legit warm through the glove, it is too cold. Floating the developer tray in a second tray filled with a thermal ballast of hot water will maintain its temperature for longer.

After developing, grab the film (either with tongs or glove) and wash it for 30 seconds in the stop bath (water) with continous swishing. This halts the development process, but the film is still photosensitive.

After placing the film in the fixer and agitating, almost immediate clearing of the substrate from white to transparent should occur. The fixing process takes about 5 minutes with intermittent agitation. As its name implies, the fixer "fixes" the image: It disintegrates and dissolves the remaining silver halide, leaving only the black silver oxide created by the developer.

After fixing, the film needs to be washed in hypowash to assure long-term stability of the photographic substrate. Around 5 minutes is sufficient, but more is not harmful. Agitate occasionally. Hypowash lets the fixer molecules diffuse out of the film, and also neutralizes any remaining acids that would slowly damage the substrate.

After hypowash, the film can be left in a final bath of plain water until all images are done.

Once fixed and washed, dry the film immediately by GENTLY enfolding both sides with a paper towel and pressing (not rubbing) to absorb most of the water. This directly removes the water and avoids the need to use a wetting agent and spend a long drying interval (don't let photographers see you wipe it with the paper towel, they may have heart attacks). The film's surface will still be "wet" like skin after washing dishes, and like wrinkled fingers the absorbed water will need time to evaporate out.

Now the film can be taken to normal room lights and inspected. Key points to check include optical density (it should be nearly impossible to see even direct fluorescent tubes through the black regions), and speckling (development of individual black grains in nominally unexposed regions, indicating overexposure/overdevelopment). It also goes without saying, the image should be unimpeachably finer than the unaided eye can resolve.

If the image is acceptable, clean the darkroom up, make certain the film bag is completely closed and put away, put the developed image in a negative sheet and you're done.

The following image demonstrates the transformation from digital image, to printed image, to photographic film:

[[File:Print examples.png]]

This is from a resolution test art. Six denotes that the array of vertical traces are 6 mils wide, while 12 and 15 denote that their centers are spaced by 15 and 12 mils. In terms of what might be sent to a commercial fabricator, 6 mil traces on 12 mil centers is middle of the road.

The right image is the "perfect" digital original, vector art rasterized at 600dpi. The middle panel is a photomicrograph of the paper output: As part of the resolution limit process, the toner demonstrates a clear preference to smear from black into areas that should be clear.

The left image is a reflection photomicrograph of the lithographic film, which exhibits contrast vastly inferior to a transmission image. Testing in the UV exposure chamber using a power meter found that when clear areas transmitted a measured power of 200uW, bulk opaque areas transmitted approximately 20nW: The clear/black contrast ratio exceeds 10000:1.

The Darkroom

2019-04-15T23:45:58Z

Aplstudent: /* Contact Printing */

==Print to Film==

The photo center requires that you either know how to use a chemical darkroom already or that you take an introduction course.

Access to their chemicals is $10 per quarter or $2 for a day. They don't take index numbers but you can be reimbursed.

Before you go to the darkroom you will need lithographic film, latex gloves, lithographic developer parts A and B (these each come in a separate bottle), and your paper negative print of your PCB. Everything else you need can be found in the craft center.

The lithographic film is kept in an envelop and a black film jacket; this film will become useless if it is exposed to light (except red/yellowish lights in the dark room) so never open the film container outside the darkroom. Continue reading for how to properly handle the film in the dark room.

The lithographic film developer comes in two bottles, part A concentrate and part B concentrate and the two parts will be mixed at the time of development. Part A is a dark purple color and part B is clear.

[[File:Labeled developer.png]]

In the darkroom, keep the lights low and let your eyes adapt.

===Prep and setup===

- Lay out chemical trays: developer, stop bath (water), fixer, hypowash.

There free-to-use containers of fixer and hypowash (hypoclear) in the cabinets labelled "Open Use Chemicals". These cabinets are located on the right side of the small hallway as you walk in through the door of the dark room (the hall between the door and the curtains). In this cabinet you will also see containers of "Stop", don't use this chemical for the stop bath, just use water.

The developer comes in two parts (A and B). Per the instructions on the bottles, mix 100ml of Part A concentrate to 300ml of water. Then separately Mix 100ml of Part B to 300ml of water. Disregard the nonsense about 68*F -as long as the temperature of the AB mix is in the vicinity of 80*F before development you are okay. It was found that just diluting the concentrates of A and B with hot water straight from the darkroom's hot tap worked quite well with the still fridge-cold concentrate. Pour the water mixed with A into the tray, then the mix of B and water into the same tray. Then wash the beaker thoroughly (water/agitate/dump 3x). Once mixed, the developer apparently has a frighteningly short useful lifetime - order of a few hours - which is why it comes in separated bottles.

The developer tray should be floated in a second tray containing hot water as thermal ballast. If the tray of developer is left on the cold metal table the developing liquid will quickly cool below working temperature. The target temp is around 80*F... 75*F is too cold, 85*F or more will be too hot. As an added layer of thermal protection you can flip over an empty tub on the metal table, place your hot water bath on the flipped over tub, and place your A/B mix tray in the hot water bath. This way the table will not cool the bath.

Next you will want to set up a stop bath, the fixer, and the hypowash. Fill one tray with water (this will be your stop bath), then fill one tray with Fixer (this will be in a labeled container in the dark room), and fill one tray with hypowash (this is a container labeled Iypoclear). The photo below shows 3 of the 4 contianers (the water stop bath is not shown).

[[File:Lith film dev chemicals.png]]

===Contact Printing===

- Next, prepare the contact print setup. You need two 8x10 glass sheets from two normal contract printing beds, to make a glass-film-paper-glass sandwich. Glass is very flat and must be used to ensure the maximum retention of detail. There should be flat sheets of glass in the dark room but it may require some searching to find them.

- Prepare film to approximately the size of your art. We have 8x10 inch film sheets, so that it is natural to cut each down to four 4x5 inch pieces if this can accommodate your art. There is a paper cutter in the corner of the dark room behind a curtain. When cutting, don't be afraid to have some spare border so the film can easily be handled after without getting fingerprints on the art itself. You will also need test strips of Lithographic film to confirm the correct exposure. Check the film jacket for existing cut-down pieces before getting out another 8x10 sheet.

All film that is not this very second being cut, exposed or developed must be stored in the black film jacket and returned there promptly between cutting and exposure. Never take more than one sheet out at a time. The orange safelight will not expose it quickly, but the safelight and stray light from the enlarger will expose it eventually and this mal-exposure (known as fogging) is undetectable until the film is developed. Wear gloves while handling the film to avoid getting filthy dirty meatpaw marks all over it (a glove will be needed during development anyway). To the greatest extent possible, handle the film by its edges.

The film has a back and an emulsion side. The emulsion side is allegedly pinkish, which is spectacularly useless to know given that it can only be viewed in a darkroom under red light. The best way to tell the difference is by "tasting" the edge of the film with your lips. The emulsion side feels unsmooth/tacky while the anti-halation backing of the far side feels smooth. Always make sure that the emulsion side is up when exposing!

Thus, the layers for the exposure process should be a sheet of glass, the film (emulsion side up), the paper print (ink side down), and another sheet of glass.

The light source for your exposure will be the enlarger. An enlarger is commonly used to enlarge 35mm negatives, but you already have a paper negative so the enlarger will just act as a timed flashlight. A picture of the enlarge can be found below. You will place your glass-film-paper-glass sandwich under the enlarger and use the timer to vary the exposure time. The light will turn on for that amount of time and then turn off automatically.

[[File:Enlarger.png]]

===Make Test Strips===

Test strips are used to determine the ideal exposure time for your film and are made by contact printing a strip of film with different exposure times. To test the different times you will set up a contact print with your paper negative and test strip, then cover 4/5 with a light blocking material (thick cardboard or plastic) and expose 1/5 of the strip for 5 seconds. Next you will move the light blocking material to reveal 2/5 of your strip and expose the strip for another 5 seconds. You will repeat this process by covering less and less of your strip until the whole strip is exposed. This results in a strip having 5 different exposer times (the first 1/5 having 25 seconds of exposure while the last 1/5 only having 5 seconds of exposure). This [https://brucetannerphotographer.files.wordpress.com/2014/04/hast-lin.jpg image] demonstrates how the variations of exposure times will affect an image and how the test strip should look with regards to 5 different exposure areas.

To make your strip cut a small strip of film paper (an inch wide and about 5 inches long) and place this under the enlarger. Exposure time depends somewhat on enlarger head height and strongly on developer temperature (development is a thermodynamic process and is exponential in temperature). With an empty 35mm film holder in the enlarger, all color filters set to neutral, the lens aperture fully open, and the enlarger head moved down so that the image is about 11 inches wide, begin exposing the film for 5 second increments.

Follow the steps below to develop this test strip and determine which exposure time yields the best results. The ideal exposure time will result in completely clear regions where the paper negative was black and completely black regions where the paper negative was white. The black is black enough if you can hold the developed test strip up to a bright light and not see any light through the black regions.

===Chemical Development Process===

1. Developer (2-5 minutes)

2. Stop Bath (30 seconds)

3. Fixer (5 minutes)

4. Hypowash (5 minutes)

5. Rinse

====An aside:====

----

Normal photographic development is designed to convert a continuous range of light exposures into a continuous range of densities on the film or paper. This process generally has a roughly linear dynamic range of between 100 and 1000 to 1 separating "black" and "clear" (papers being nearer to 100 and films to 1000). At extremes of over- or under-exposure, the transfer function graphing optical density vs exposure saturates, resembling a graph of arctan(x). The steepness of the linear region defines the contrast level of the film, and is affected by both the film itself and the development process used.

In the normal, modern, black & white photographic development process, photons have reduced tiny amounts of silver halide in the film surface to silver metal. Within each grain, the developer converts silver metal to black silver oxide such that the darkness of a grain is proportional to how much light it received.

In the lithographic process, this normal process is augmented with positive feedback: Both silver AND silver oxide contribute to the development process. Obviously this results in exponential runaway, as a grain that develops at all will quickly turn completely black.

Photographic artists manipulate the lithographic process to produce exotic image tones (generally by gross overexposure, followed by great underdevelopment, such that the exponential runaway proceeds only to the point of producing an intriguingly nonlinear response curve), but we are interested in its "intended" property: The production of incredibly high contrast (10000:1) images with incredibly high resolutions (resolvable features on the micron scale).

For any given amount of exposure E, a given development process will result in an output film optical density D(E). For the halftone process, done correctly,

<math>D(E) ~= 4 * heaviside(E - E_{crit})</math>.

The contrast ratio of the printed image on paper is remarkably low when backlit - maybe 10, as opposed to over 100 viewed in diffuse reflective light - and suffers considerable fluctuations due to the random fiber packing of paper causing the transmission of "clear" areas to fluctuate considerably.

Thus the range of acceptable exposures, meaning those for which all black areas get E < E_crit and all clear areas get E > E_crit, is not nearly so wide as might be imagined.

Furthermore, the brightness of the light rectangle supplied by the enlarger experiences a nontrivial (~20%) decrease towards its corners, further eroding exposure margin.

This will demonstrate itself on test strips: If an exposure of 12 seconds works, most likely 6 seconds will result in a very weak image and 18 will blacken everything.

----

Development time should be roughly 2-5 minutes. Put the film into the developer emulsion up, as it was exposed. With a glove or tongs, agitate continuously for 30 seconds, then 5 seconds every 30. The film should quickly turn whiteish, and the shadow of an image should begin to darken within about 30 seconds. If it does not, either exposure was insufficient or the developer is cold.

Note that photographic development is a diffusion-limited process: The developer exists in the bulk fluid, but image formation occurs at a semi-infinite plane surface. This means that fluid agitation is *ESSENTIAL* to the process.

Overexposure with underdevelopment (Less than 2 minutes in developer) will be associated with clear areas exhibiting a continuous-tone brown muddiness, which is not OK for us (but is typical of what artistic lith printers are after). Underexposure with overdevelopment (over 4-ish minutes in developer) will be associated with waiting for the exposed areas to finish turning fully black when suddenly black dots begin to appear in clear areas.

If the developer is not legit warm through the glove, it is too cold. Floating the developer tray in a second tray filled with a thermal ballast of hot water will maintain its temperature for longer.

After developing, grab the film (either with tongs or glove) and wash it for 30 seconds in the stop bath (water) with continous swishing. This halts the development process, but the film is still photosensitive.

After placing the film in the fixer and agitating, almost immediate clearing of the substrate from white to transparent should occur. The fixing process takes about 5 minutes with intermittent agitation. As its name implies, the fixer "fixes" the image: It disintegrates and dissolves the remaining silver halide, leaving only the black silver oxide created by the developer.

After fixing, the film needs to be washed in hypowash to assure long-term stability of the photographic substrate. Around 5 minutes is sufficient, but more is not harmful. Agitate occasionally. Hypowash lets the fixer molecules diffuse out of the film, and also neutralizes any remaining acids that would slowly damage the substrate.

After hypowash, the film can be left in a final bath of plain water until all images are done.

Once fixed and washed, dry the film immediately by GENTLY enfolding both sides with a paper towel and pressing (not rubbing) to absorb most of the water. This directly removes the water and avoids the need to use a wetting agent and spend a long drying interval (don't let photographers see you wipe it with the paper towel, they may have heart attacks). The film's surface will still be "wet" like skin after washing dishes, and like wrinkled fingers the absorbed water will need time to evaporate out.

Now the film can be taken to normal room lights and inspected. Key points to check include optical density (it should be nearly impossible to see even direct fluorescent tubes through the black regions), and speckling (development of individual black grains in nominally unexposed regions, indicating overexposure/overdevelopment). It also goes without saying, the image should be unimpeachably finer than the unaided eye can resolve.

If the image is acceptable, clean the darkroom up, make certain the film bag is completely closed and put away, put the developed image in a negative sheet and you're done.

The following image demonstrates the transformation from digital image, to printed image, to photographic film:

[[File:Print examples.png]]

This is from a resolution test art. Six denotes that the array of vertical traces are 6 mils wide, while 12 and 15 denote that their centers are spaced by 15 and 12 mils. In terms of what might be sent to a commercial fabricator, 6 mil traces on 12 mil centers is middle of the road.

The right image is the "perfect" digital original, vector art rasterized at 600dpi. The middle panel is a photomicrograph of the paper output: As part of the resolution limit process, the toner demonstrates a clear preference to smear from black into areas that should be clear.

The left image is a reflection photomicrograph of the lithographic film, which exhibits contrast vastly inferior to a transmission image. Testing in the UV exposure chamber using a power meter found that when clear areas transmitted a measured power of 200uW, bulk opaque areas transmitted approximately 20nW: The clear/black contrast ratio exceeds 10000:1.

The Darkroom

2019-04-15T23:42:08Z

Aplstudent: /* Prep and setup */

==Print to Film==

The photo center requires that you either know how to use a chemical darkroom already or that you take an introduction course.

Access to their chemicals is $10 per quarter or $2 for a day. They don't take index numbers but you can be reimbursed.

Before you go to the darkroom you will need lithographic film, latex gloves, lithographic developer parts A and B (these each come in a separate bottle), and your paper negative print of your PCB. Everything else you need can be found in the craft center.

The lithographic film is kept in an envelop and a black film jacket; this film will become useless if it is exposed to light (except red/yellowish lights in the dark room) so never open the film container outside the darkroom. Continue reading for how to properly handle the film in the dark room.

The lithographic film developer comes in two bottles, part A concentrate and part B concentrate and the two parts will be mixed at the time of development. Part A is a dark purple color and part B is clear.

[[File:Labeled developer.png]]

In the darkroom, keep the lights low and let your eyes adapt.

===Prep and setup===

- Lay out chemical trays: developer, stop bath (water), fixer, hypowash.

There free-to-use containers of fixer and hypowash (hypoclear) in the cabinets labelled "Open Use Chemicals". These cabinets are located on the right side of the small hallway as you walk in through the door of the dark room (the hall between the door and the curtains). In this cabinet you will also see containers of "Stop", don't use this chemical for the stop bath, just use water.

The developer comes in two parts (A and B). Per the instructions on the bottles, mix 100ml of Part A concentrate to 300ml of water. Then separately Mix 100ml of Part B to 300ml of water. Disregard the nonsense about 68*F -as long as the temperature of the AB mix is in the vicinity of 80*F before development you are okay. It was found that just diluting the concentrates of A and B with hot water straight from the darkroom's hot tap worked quite well with the still fridge-cold concentrate. Pour the water mixed with A into the tray, then the mix of B and water into the same tray. Then wash the beaker thoroughly (water/agitate/dump 3x). Once mixed, the developer apparently has a frighteningly short useful lifetime - order of a few hours - which is why it comes in separated bottles.

The developer tray should be floated in a second tray containing hot water as thermal ballast. If the tray of developer is left on the cold metal table the developing liquid will quickly cool below working temperature. The target temp is around 80*F... 75*F is too cold, 85*F or more will be too hot. As an added layer of thermal protection you can flip over an empty tub on the metal table, place your hot water bath on the flipped over tub, and place your A/B mix tray in the hot water bath. This way the table will not cool the bath.

Next you will want to set up a stop bath, the fixer, and the hypowash. Fill one tray with water (this will be your stop bath), then fill one tray with Fixer (this will be in a labeled container in the dark room), and fill one tray with hypowash (this is a container labeled Iypoclear). The photo below shows 3 of the 4 contianers (the water stop bath is not shown).

[[File:Lith film dev chemicals.png]]

===Contact Printing===

- Next, prepare the contact print setup. You need two 8x10 glass sheets from two normal contract printing beds, to make a glass-film-paper-glass sandwich. Glass is very flat and must be used to ensure the maximum retention of detail.

- Prepare film to approximately the size of your art. We have 8x10 inch film sheets, so that it is natural to cut each down to four 4x5 inch pieces if this can accommodate your art. Don't be afraid to have some spare border so the film can easily be handled after without getting fingerprints on the art itself. You will also need test strips of Lithographic film to confirm the correct exposure. Check the film jacket for existing cut-down pieces before getting out another 8x10 sheet.

All film that is not this very second being cut, exposed or developed must be stored in the black film jacket and returned there promptly between cutting and exposure. Never take more than one sheet out at a time. The orange safelight will not expose it quickly, but the safelight and stray light from the enlarger will expose it eventually and this mal-exposure (known as fogging) is undetectable until the film is developed. Wear gloves while handling the film to avoid getting filthy dirty meatpaw marks all over it (a glove will be needed during development anyway). To the greatest extent possible, handle the film by its edges.

The film has a back and an emulsion side. The emulsion side is allegedly pinkish, which is spectacularly useless to know given that it can only be viewed in a darkroom under red light. The best way to tell the difference is by "tasting" the edge of the film with your lips. The emulsion side feels unsmooth/tacky while the anti-halation backing of the far side feels smooth. Always make sure that the emulsion side is up when exposing!

Thus, the layers for the exposure process should be a sheet of glass, the film (emulsion side up), the paper print (ink side down), and another sheet of glass.

The light source for your exposure will be the enlarger. An enlarger is commonly used to enlarge 35mm negatives, but you already have a paper negative so the enlarger will just act as a timed flashlight. A picture of the enlarge can be found below. You will place your glass-film-paper-glass sandwich under the enlarger and use the timer to vary the exposure time. The light will turn on for that amount of time and then turn off automatically.

[[File:Enlarger.png]]

===Make Test Strips===

Test strips are used to determine the ideal exposure time for your film and are made by contact printing a strip of film with different exposure times. To test the different times you will set up a contact print with your paper negative and test strip, then cover 4/5 with a light blocking material (thick cardboard or plastic) and expose 1/5 of the strip for 5 seconds. Next you will move the light blocking material to reveal 2/5 of your strip and expose the strip for another 5 seconds. You will repeat this process by covering less and less of your strip until the whole strip is exposed. This results in a strip having 5 different exposer times (the first 1/5 having 25 seconds of exposure while the last 1/5 only having 5 seconds of exposure). This [https://brucetannerphotographer.files.wordpress.com/2014/04/hast-lin.jpg image] demonstrates how the variations of exposure times will affect an image and how the test strip should look with regards to 5 different exposure areas.

To make your strip cut a small strip of film paper (an inch wide and about 5 inches long) and place this under the enlarger. Exposure time depends somewhat on enlarger head height and strongly on developer temperature (development is a thermodynamic process and is exponential in temperature). With an empty 35mm film holder in the enlarger, all color filters set to neutral, the lens aperture fully open, and the enlarger head moved down so that the image is about 11 inches wide, begin exposing the film for 5 second increments.

Follow the steps below to develop this test strip and determine which exposure time yields the best results. The ideal exposure time will result in completely clear regions where the paper negative was black and completely black regions where the paper negative was white. The black is black enough if you can hold the developed test strip up to a bright light and not see any light through the black regions.

===Chemical Development Process===

1. Developer (2-5 minutes)

2. Stop Bath (30 seconds)

3. Fixer (5 minutes)

4. Hypowash (5 minutes)

5. Rinse

====An aside:====

----

Normal photographic development is designed to convert a continuous range of light exposures into a continuous range of densities on the film or paper. This process generally has a roughly linear dynamic range of between 100 and 1000 to 1 separating "black" and "clear" (papers being nearer to 100 and films to 1000). At extremes of over- or under-exposure, the transfer function graphing optical density vs exposure saturates, resembling a graph of arctan(x). The steepness of the linear region defines the contrast level of the film, and is affected by both the film itself and the development process used.

In the normal, modern, black & white photographic development process, photons have reduced tiny amounts of silver halide in the film surface to silver metal. Within each grain, the developer converts silver metal to black silver oxide such that the darkness of a grain is proportional to how much light it received.

In the lithographic process, this normal process is augmented with positive feedback: Both silver AND silver oxide contribute to the development process. Obviously this results in exponential runaway, as a grain that develops at all will quickly turn completely black.

Photographic artists manipulate the lithographic process to produce exotic image tones (generally by gross overexposure, followed by great underdevelopment, such that the exponential runaway proceeds only to the point of producing an intriguingly nonlinear response curve), but we are interested in its "intended" property: The production of incredibly high contrast (10000:1) images with incredibly high resolutions (resolvable features on the micron scale).

For any given amount of exposure E, a given development process will result in an output film optical density D(E). For the halftone process, done correctly,

<math>D(E) ~= 4 * heaviside(E - E_{crit})</math>.

The contrast ratio of the printed image on paper is remarkably low when backlit - maybe 10, as opposed to over 100 viewed in diffuse reflective light - and suffers considerable fluctuations due to the random fiber packing of paper causing the transmission of "clear" areas to fluctuate considerably.

Thus the range of acceptable exposures, meaning those for which all black areas get E < E_crit and all clear areas get E > E_crit, is not nearly so wide as might be imagined.

Furthermore, the brightness of the light rectangle supplied by the enlarger experiences a nontrivial (~20%) decrease towards its corners, further eroding exposure margin.

This will demonstrate itself on test strips: If an exposure of 12 seconds works, most likely 6 seconds will result in a very weak image and 18 will blacken everything.

----

Development time should be roughly 2-5 minutes. Put the film into the developer emulsion up, as it was exposed. With a glove or tongs, agitate continuously for 30 seconds, then 5 seconds every 30. The film should quickly turn whiteish, and the shadow of an image should begin to darken within about 30 seconds. If it does not, either exposure was insufficient or the developer is cold.

Note that photographic development is a diffusion-limited process: The developer exists in the bulk fluid, but image formation occurs at a semi-infinite plane surface. This means that fluid agitation is *ESSENTIAL* to the process.

Overexposure with underdevelopment (Less than 2 minutes in developer) will be associated with clear areas exhibiting a continuous-tone brown muddiness, which is not OK for us (but is typical of what artistic lith printers are after). Underexposure with overdevelopment (over 4-ish minutes in developer) will be associated with waiting for the exposed areas to finish turning fully black when suddenly black dots begin to appear in clear areas.

If the developer is not legit warm through the glove, it is too cold. Floating the developer tray in a second tray filled with a thermal ballast of hot water will maintain its temperature for longer.

After developing, grab the film (either with tongs or glove) and wash it for 30 seconds in the stop bath (water) with continous swishing. This halts the development process, but the film is still photosensitive.

After placing the film in the fixer and agitating, almost immediate clearing of the substrate from white to transparent should occur. The fixing process takes about 5 minutes with intermittent agitation. As its name implies, the fixer "fixes" the image: It disintegrates and dissolves the remaining silver halide, leaving only the black silver oxide created by the developer.

After fixing, the film needs to be washed in hypowash to assure long-term stability of the photographic substrate. Around 5 minutes is sufficient, but more is not harmful. Agitate occasionally. Hypowash lets the fixer molecules diffuse out of the film, and also neutralizes any remaining acids that would slowly damage the substrate.

After hypowash, the film can be left in a final bath of plain water until all images are done.

Once fixed and washed, dry the film immediately by GENTLY enfolding both sides with a paper towel and pressing (not rubbing) to absorb most of the water. This directly removes the water and avoids the need to use a wetting agent and spend a long drying interval (don't let photographers see you wipe it with the paper towel, they may have heart attacks). The film's surface will still be "wet" like skin after washing dishes, and like wrinkled fingers the absorbed water will need time to evaporate out.

Now the film can be taken to normal room lights and inspected. Key points to check include optical density (it should be nearly impossible to see even direct fluorescent tubes through the black regions), and speckling (development of individual black grains in nominally unexposed regions, indicating overexposure/overdevelopment). It also goes without saying, the image should be unimpeachably finer than the unaided eye can resolve.

If the image is acceptable, clean the darkroom up, make certain the film bag is completely closed and put away, put the developed image in a negative sheet and you're done.

The following image demonstrates the transformation from digital image, to printed image, to photographic film:

[[File:Print examples.png]]

This is from a resolution test art. Six denotes that the array of vertical traces are 6 mils wide, while 12 and 15 denote that their centers are spaced by 15 and 12 mils. In terms of what might be sent to a commercial fabricator, 6 mil traces on 12 mil centers is middle of the road.

The right image is the "perfect" digital original, vector art rasterized at 600dpi. The middle panel is a photomicrograph of the paper output: As part of the resolution limit process, the toner demonstrates a clear preference to smear from black into areas that should be clear.

The left image is a reflection photomicrograph of the lithographic film, which exhibits contrast vastly inferior to a transmission image. Testing in the UV exposure chamber using a power meter found that when clear areas transmitted a measured power of 200uW, bulk opaque areas transmitted approximately 20nW: The clear/black contrast ratio exceeds 10000:1.

How to Make a Printed Circuit Board (PCB)

2019-04-11T20:32:48Z

Aplstudent: /* Making the Board */

=='''''Using KiCAD'''''==

===[[ Youtube Tutorial]]===

For those who want a detailed, visual, walk-through of the KiCad program, this series of 10 youtube videos demonstrates a KiCad project form start to finish.

===[[Installing and Opening KiCad]]===

The first steps in using KiCad.

=== [[Eeschema]]===

Eeschema is the first program you'll use, where you'll create a digital copy of your circuit diagram and assign footprints to the different components. This will allow you to generate a [[Eeschema#Generating a Netlist| netlist]], which will be read into [[Pcbnew]].

===[[Footprint Editor]]===

The Footprint Editor program may or may not be necessary but it allows you to draw new footprints or edit preexisting footprints. Footprints are necessary for every different component of your circuit, so the footprint editor becomes necessary if the footprint for your component is not already in one of the KiCad footprint libraries.

===[[Pcbnew]]===

Pcbnew is the program used after Eeschema. Pcbnew allows you to design the physical layout of your PCB and draw the copper connections between the your different components. All the information about the different connections and components is saved in the [[Eeschema#Generating a Netlist| netlist]] so be sure to complete and upload your [[Eeschema#Generating a Netlist| netlist]] before you begin.

===[[Gerbview]]===

Gerbview is a program where you can upload and view Gerber and Drill files. These files make up the different layers of the PCB and making checking for mistakes easier. Ultimately, you'll use these files to print the different layer transparencies when you make your PCB.

=='''''Creating the PCB Artwork (with Film)'''''==

While it is possible to use a printer to print transparencies for the different layers of your board, printing the layers on film will yield the best results. Using a printer to print transparencies results in poor resolution, bad contrast, and poor optical density. These three issues are resolvable by developing your artwork on a specific type of film, called ''lithographic'' film, or ''lith'' film.

===[[Printing the Paper Copy]]===

To make a film copy, you want to start with a high resolution paper copy. This paper copy will be used later to transfer the paper image onto the lithographic film in a process called "contact printing". The film from the contact print will then be developed.

===[[The Darkroom]]===

To create the film print and develop it you'll need to use the darkroom in the Craft Center (found on the ground floor of the EMU). Developing in the darkroom is an involved process with many steps; be sure to read through the whole process before you go and if possible go with someone experienced.

=='''''Making the Board'''''==

===[[Cutting the Board]] ===

How to cut the PCB properly.

===[[UV testing and Cutting Glass (Optional)]]===
How to properly test and cut glass. This step is necessary if you do not have a sheet of glass to place on top of your PCB during the UV curing Process.

===[[Preparing the UV Chamber and Board]] ===

How to set up the UV chamber for PCB development.

=== [[Developing the Board]] ===

How to remove the layer of resist from the PCB.

===[[Etching the PCB]]===

How to etch the copper from the PCB.

===[[Populating the PCB]]===

How to drill holes in the PCB and solder the components. If you have surface mount devices (SMDs) this will also instruct you on how to apply solder paste and use the reflow oven.

== Using gEDA ==

===[[Introduction To gEDA]]===

This tutorial is not as robust as the [[How to Make a Printed Circuit Board (PCB)#Using KiCAD|KiCAD tutorial]], but it has some useful resources if you want to use gEDA.

How to Make a Printed Circuit Board (PCB)

2019-04-11T20:32:36Z

Aplstudent: /* Creating the PCB Artwork (with Film) */

=='''''Using KiCAD'''''==

===[[ Youtube Tutorial]]===

For those who want a detailed, visual, walk-through of the KiCad program, this series of 10 youtube videos demonstrates a KiCad project form start to finish.

===[[Installing and Opening KiCad]]===

The first steps in using KiCad.

=== [[Eeschema]]===

Eeschema is the first program you'll use, where you'll create a digital copy of your circuit diagram and assign footprints to the different components. This will allow you to generate a [[Eeschema#Generating a Netlist| netlist]], which will be read into [[Pcbnew]].

===[[Footprint Editor]]===

The Footprint Editor program may or may not be necessary but it allows you to draw new footprints or edit preexisting footprints. Footprints are necessary for every different component of your circuit, so the footprint editor becomes necessary if the footprint for your component is not already in one of the KiCad footprint libraries.

===[[Pcbnew]]===

Pcbnew is the program used after Eeschema. Pcbnew allows you to design the physical layout of your PCB and draw the copper connections between the your different components. All the information about the different connections and components is saved in the [[Eeschema#Generating a Netlist| netlist]] so be sure to complete and upload your [[Eeschema#Generating a Netlist| netlist]] before you begin.

===[[Gerbview]]===

Gerbview is a program where you can upload and view Gerber and Drill files. These files make up the different layers of the PCB and making checking for mistakes easier. Ultimately, you'll use these files to print the different layer transparencies when you make your PCB.

=='''''Creating the PCB Artwork (with Film)'''''==

While it is possible to use a printer to print transparencies for the different layers of your board, printing the layers on film will yield the best results. Using a printer to print transparencies results in poor resolution, bad contrast, and poor optical density. These three issues are resolvable by developing your artwork on a specific type of film, called ''lithographic'' film, or ''lith'' film.

===[[Printing the Paper Copy]]===

To make a film copy, you want to start with a high resolution paper copy. This paper copy will be used later to transfer the paper image onto the lithographic film in a process called "contact printing". The film from the contact print will then be developed.

===[[The Darkroom]]===

To create the film print and develop it you'll need to use the darkroom in the Craft Center (found on the ground floor of the EMU). Developing in the darkroom is an involved process with many steps; be sure to read through the whole process before you go and if possible go with someone experienced.

=='''Making the Board'''==

===[[Cutting the Board]] ===

How to cut the PCB properly.

===[[UV testing and Cutting Glass (Optional)]]===
How to properly test and cut glass. This step is necessary if you do not have a sheet of glass to place on top of your PCB during the UV curing Process.

===[[Preparing the UV Chamber and Board]] ===

How to set up the UV chamber for PCB development.

=== [[Developing the Board]] ===

How to remove the layer of resist from the PCB.

===[[Etching the PCB]]===

How to etch the copper from the PCB.

===[[Populating the PCB]]===

How to drill holes in the PCB and solder the components. If you have surface mount devices (SMDs) this will also instruct you on how to apply solder paste and use the reflow oven.

== Using gEDA ==

===[[Introduction To gEDA]]===

This tutorial is not as robust as the [[How to Make a Printed Circuit Board (PCB)#Using KiCAD|KiCAD tutorial]], but it has some useful resources if you want to use gEDA.

How to Make a Printed Circuit Board (PCB)

2019-04-11T20:32:22Z

Aplstudent: /* Using KiCAD */

=='''''Using KiCAD'''''==

===[[ Youtube Tutorial]]===

For those who want a detailed, visual, walk-through of the KiCad program, this series of 10 youtube videos demonstrates a KiCad project form start to finish.

===[[Installing and Opening KiCad]]===

The first steps in using KiCad.

=== [[Eeschema]]===

Eeschema is the first program you'll use, where you'll create a digital copy of your circuit diagram and assign footprints to the different components. This will allow you to generate a [[Eeschema#Generating a Netlist| netlist]], which will be read into [[Pcbnew]].

===[[Footprint Editor]]===

The Footprint Editor program may or may not be necessary but it allows you to draw new footprints or edit preexisting footprints. Footprints are necessary for every different component of your circuit, so the footprint editor becomes necessary if the footprint for your component is not already in one of the KiCad footprint libraries.

===[[Pcbnew]]===

Pcbnew is the program used after Eeschema. Pcbnew allows you to design the physical layout of your PCB and draw the copper connections between the your different components. All the information about the different connections and components is saved in the [[Eeschema#Generating a Netlist| netlist]] so be sure to complete and upload your [[Eeschema#Generating a Netlist| netlist]] before you begin.

===[[Gerbview]]===

Gerbview is a program where you can upload and view Gerber and Drill files. These files make up the different layers of the PCB and making checking for mistakes easier. Ultimately, you'll use these files to print the different layer transparencies when you make your PCB.

=='''Creating the PCB Artwork (with Film)'''==

While it is possible to use a printer to print transparencies for the different layers of your board, printing the layers on film will yield the best results. Using a printer to print transparencies results in poor resolution, bad contrast, and poor optical density. These three issues are resolvable by developing your artwork on a specific type of film, called ''lithographic'' film, or ''lith'' film.

===[[Printing the Paper Copy]]===

To make a film copy, you want to start with a high resolution paper copy. This paper copy will be used later to transfer the paper image onto the lithographic film in a process called "contact printing". The film from the contact print will then be developed.

===[[The Darkroom]]===

To create the film print and develop it you'll need to use the darkroom in the Craft Center (found on the ground floor of the EMU). Developing in the darkroom is an involved process with many steps; be sure to read through the whole process before you go and if possible go with someone experienced.

=='''Making the Board'''==

===[[Cutting the Board]] ===

How to cut the PCB properly.

===[[UV testing and Cutting Glass (Optional)]]===
How to properly test and cut glass. This step is necessary if you do not have a sheet of glass to place on top of your PCB during the UV curing Process.

===[[Preparing the UV Chamber and Board]] ===

How to set up the UV chamber for PCB development.

=== [[Developing the Board]] ===

How to remove the layer of resist from the PCB.

===[[Etching the PCB]]===

How to etch the copper from the PCB.

===[[Populating the PCB]]===

How to drill holes in the PCB and solder the components. If you have surface mount devices (SMDs) this will also instruct you on how to apply solder paste and use the reflow oven.

== Using gEDA ==

===[[Introduction To gEDA]]===

This tutorial is not as robust as the [[How to Make a Printed Circuit Board (PCB)#Using KiCAD|KiCAD tutorial]], but it has some useful resources if you want to use gEDA.

How to Make a Printed Circuit Board (PCB)

2019-04-11T20:29:58Z

Aplstudent: /* Using KiCAD */

=='''Using KiCAD'''==

===[[ Youtube Tutorial]]===

For those who want a detailed, visual, walk-through of the KiCad program, this series of 10 youtube videos demonstrates a KiCad project form start to finish.

===[[Installing and Opening KiCad]]===

The first steps in using KiCad.

=== [[Eeschema]]===

Eeschema is the first program you'll use, where you'll create a digital copy of your circuit diagram and assign footprints to the different components. This will allow you to generate a [[Eeschema#Generating a Netlist| netlist]], which will be read into [[Pcbnew]].

===[[Footprint Editor]]===

The Footprint Editor program may or may not be necessary but it allows you to draw new footprints or edit preexisting footprints. Footprints are necessary for every different component of your circuit, so the footprint editor becomes necessary if the footprint for your component is not already in one of the KiCad footprint libraries.

===[[Pcbnew]]===

Pcbnew is the program used after Eeschema. Pcbnew allows you to design the physical layout of your PCB and draw the copper connections between the your different components. All the information about the different connections and components is saved in the [[Eeschema#Generating a Netlist| netlist]] so be sure to complete and upload your [[Eeschema#Generating a Netlist| netlist]] before you begin.

===[[Gerbview]]===

Gerbview is a program where you can upload and view Gerber and Drill files. These files make up the different layers of the PCB and making checking for mistakes easier. Ultimately, you'll use these files to print the different layer transparencies when you make your PCB.

=='''Creating the PCB Artwork (with Film)'''==

While it is possible to use a printer to print transparencies for the different layers of your board, printing the layers on film will yield the best results. Using a printer to print transparencies results in poor resolution, bad contrast, and poor optical density. These three issues are resolvable by developing your artwork on a specific type of film, called ''lithographic'' film, or ''lith'' film.

===[[Printing the Paper Copy]]===

To make a film copy, you want to start with a high resolution paper copy. This paper copy will be used later to transfer the paper image onto the lithographic film in a process called "contact printing". The film from the contact print will then be developed.

===[[The Darkroom]]===

To create the film print and develop it you'll need to use the darkroom in the Craft Center (found on the ground floor of the EMU). Developing in the darkroom is an involved process with many steps; be sure to read through the whole process before you go and if possible go with someone experienced.

=='''Making the Board'''==

===[[Cutting the Board]] ===

How to cut the PCB properly.

===[[UV testing and Cutting Glass (Optional)]]===
How to properly test and cut glass. This step is necessary if you do not have a sheet of glass to place on top of your PCB during the UV curing Process.

===[[Preparing the UV Chamber and Board]] ===

How to set up the UV chamber for PCB development.

=== [[Developing the Board]] ===

How to remove the layer of resist from the PCB.

===[[Etching the PCB]]===

How to etch the copper from the PCB.

===[[Populating the PCB]]===

How to drill holes in the PCB and solder the components. If you have surface mount devices (SMDs) this will also instruct you on how to apply solder paste and use the reflow oven.

== Using gEDA ==

===[[Introduction To gEDA]]===

This tutorial is not as robust as the [[How to Make a Printed Circuit Board (PCB)#Using KiCAD|KiCAD tutorial]], but it has some useful resources if you want to use gEDA.

How to Make a Printed Circuit Board (PCB)

2019-04-11T20:29:44Z

Aplstudent: /* Creating the PCB Artwork (with Film) */

==Using KiCAD ==

===[[ Youtube Tutorial]]===

For those who want a detailed, visual, walk-through of the KiCad program, this series of 10 youtube videos demonstrates a KiCad project form start to finish.

===[[Installing and Opening KiCad]]===

The first steps in using KiCad.

=== [[Eeschema]]===

Eeschema is the first program you'll use, where you'll create a digital copy of your circuit diagram and assign footprints to the different components. This will allow you to generate a [[Eeschema#Generating a Netlist| netlist]], which will be read into [[Pcbnew]].

===[[Footprint Editor]]===

The Footprint Editor program may or may not be necessary but it allows you to draw new footprints or edit preexisting footprints. Footprints are necessary for every different component of your circuit, so the footprint editor becomes necessary if the footprint for your component is not already in one of the KiCad footprint libraries.

===[[Pcbnew]]===

Pcbnew is the program used after Eeschema. Pcbnew allows you to design the physical layout of your PCB and draw the copper connections between the your different components. All the information about the different connections and components is saved in the [[Eeschema#Generating a Netlist| netlist]] so be sure to complete and upload your [[Eeschema#Generating a Netlist| netlist]] before you begin.

===[[Gerbview]]===

Gerbview is a program where you can upload and view Gerber and Drill files. These files make up the different layers of the PCB and making checking for mistakes easier. Ultimately, you'll use these files to print the different layer transparencies when you make your PCB.

=='''Creating the PCB Artwork (with Film)'''==

While it is possible to use a printer to print transparencies for the different layers of your board, printing the layers on film will yield the best results. Using a printer to print transparencies results in poor resolution, bad contrast, and poor optical density. These three issues are resolvable by developing your artwork on a specific type of film, called ''lithographic'' film, or ''lith'' film.

===[[Printing the Paper Copy]]===

To make a film copy, you want to start with a high resolution paper copy. This paper copy will be used later to transfer the paper image onto the lithographic film in a process called "contact printing". The film from the contact print will then be developed.

===[[The Darkroom]]===

To create the film print and develop it you'll need to use the darkroom in the Craft Center (found on the ground floor of the EMU). Developing in the darkroom is an involved process with many steps; be sure to read through the whole process before you go and if possible go with someone experienced.

=='''Making the Board'''==

===[[Cutting the Board]] ===

How to cut the PCB properly.

===[[UV testing and Cutting Glass (Optional)]]===
How to properly test and cut glass. This step is necessary if you do not have a sheet of glass to place on top of your PCB during the UV curing Process.

===[[Preparing the UV Chamber and Board]] ===

How to set up the UV chamber for PCB development.

=== [[Developing the Board]] ===

How to remove the layer of resist from the PCB.

===[[Etching the PCB]]===

How to etch the copper from the PCB.

===[[Populating the PCB]]===

How to drill holes in the PCB and solder the components. If you have surface mount devices (SMDs) this will also instruct you on how to apply solder paste and use the reflow oven.

== Using gEDA ==

===[[Introduction To gEDA]]===

This tutorial is not as robust as the [[How to Make a Printed Circuit Board (PCB)#Using KiCAD|KiCAD tutorial]], but it has some useful resources if you want to use gEDA.

How to Make a Printed Circuit Board (PCB)

2019-04-11T20:29:32Z

Aplstudent: /* Making the Board */

==Using KiCAD ==

===[[ Youtube Tutorial]]===

For those who want a detailed, visual, walk-through of the KiCad program, this series of 10 youtube videos demonstrates a KiCad project form start to finish.

===[[Installing and Opening KiCad]]===

The first steps in using KiCad.

=== [[Eeschema]]===

Eeschema is the first program you'll use, where you'll create a digital copy of your circuit diagram and assign footprints to the different components. This will allow you to generate a [[Eeschema#Generating a Netlist| netlist]], which will be read into [[Pcbnew]].

===[[Footprint Editor]]===

The Footprint Editor program may or may not be necessary but it allows you to draw new footprints or edit preexisting footprints. Footprints are necessary for every different component of your circuit, so the footprint editor becomes necessary if the footprint for your component is not already in one of the KiCad footprint libraries.

===[[Pcbnew]]===

Pcbnew is the program used after Eeschema. Pcbnew allows you to design the physical layout of your PCB and draw the copper connections between the your different components. All the information about the different connections and components is saved in the [[Eeschema#Generating a Netlist| netlist]] so be sure to complete and upload your [[Eeschema#Generating a Netlist| netlist]] before you begin.

===[[Gerbview]]===

Gerbview is a program where you can upload and view Gerber and Drill files. These files make up the different layers of the PCB and making checking for mistakes easier. Ultimately, you'll use these files to print the different layer transparencies when you make your PCB.

==Creating the PCB Artwork (with Film)==

While it is possible to use a printer to print transparencies for the different layers of your board, printing the layers on film will yield the best results. Using a printer to print transparencies results in poor resolution, bad contrast, and poor optical density. These three issues are resolvable by developing your artwork on a specific type of film, called ''lithographic'' film, or ''lith'' film.

===[[Printing the Paper Copy]]===

To make a film copy, you want to start with a high resolution paper copy. This paper copy will be used later to transfer the paper image onto the lithographic film in a process called "contact printing". The film from the contact print will then be developed.

===[[The Darkroom]]===

To create the film print and develop it you'll need to use the darkroom in the Craft Center (found on the ground floor of the EMU). Developing in the darkroom is an involved process with many steps; be sure to read through the whole process before you go and if possible go with someone experienced.

=='''Making the Board'''==

===[[Cutting the Board]] ===

How to cut the PCB properly.

===[[UV testing and Cutting Glass (Optional)]]===
How to properly test and cut glass. This step is necessary if you do not have a sheet of glass to place on top of your PCB during the UV curing Process.

===[[Preparing the UV Chamber and Board]] ===

How to set up the UV chamber for PCB development.

=== [[Developing the Board]] ===

How to remove the layer of resist from the PCB.

===[[Etching the PCB]]===

How to etch the copper from the PCB.

===[[Populating the PCB]]===

How to drill holes in the PCB and solder the components. If you have surface mount devices (SMDs) this will also instruct you on how to apply solder paste and use the reflow oven.

== Using gEDA ==

===[[Introduction To gEDA]]===

This tutorial is not as robust as the [[How to Make a Printed Circuit Board (PCB)#Using KiCAD|KiCAD tutorial]], but it has some useful resources if you want to use gEDA.

Preparing the UV Chamber and Board

2019-04-11T20:27:59Z

Aplstudent: /* Exposure in the UV Chamber */

Before getting any boards out, the UV chamber must be prepared. Get a VIS optical power meter (this detects light in the visible wavelength spectrum) out and lay the detector face down on the middle glass plate. Set the wavelength to 400nm (the actual wavelength is centered on 365; This introduces a roughly 40-50% shortage in measured power, if one is interested in absolute terms).

Plug the lid power connections in, turn the power level all the way off, close the lid and zero the OPM, and turn the chamber on. Dial the potentiometer until the power level reads about 200uW. Kill the power, remove the lid and put the OPM away.

==Single Side Board==

Exposure of a single side board is simple: Lay down bottom glass plate, peel the white protective coating off the circuit board and lay it sensitive side up (for a top-copper-only, presumably for an all-surface-mount circuit) or down (bottom-copper-only, typical of an all-through-hole circuit). Lay the film with emulsion in contact with the green photoresist, then lay the upper glass plate on top to acheive close contact. Small bits of aluminum scrap make good weights.

==Double Side Board==

At this point you should have both sides of your artwork printed on lithographic film. Before you expose the PCB, it is essential that the two pieces of film are aligned on either side of the board as precisely as possible. To achieve maximum precision, it is recommended to use the L-shaped aluminum jig is in the UV curing chamber.

The first step is to cut one corner of your film artwork. Before you cut, line up both pieces of film as if you were to expose your board (that is, all the through holes match up) and tape the pieces of film together so that the drill holes stay aligned. Then, using a paper cutter to ensure straight cuts, make at least two cuts such that the edge of your artwork has a 90 degree corner. The edge of your PCB artwork should have edge cuts indicated which makes for an ideal way to align your corner cuts. Note: it is important that you cut both pieces of film simultaneously so that the the artwork stays aligned when the tape is removed. After the corner cut, make sure that the excess lithographic film is cut off.

The objective is to produce a corner in the artwork that fits into the jig while the artwork is aligned:

[[File:Artwork Alignment Cuts.png]]

Now, remove the tape from the film and use the L shaped jig in the UV curing chamber to line up your bottom layer artwork, the PCB, and your top layer artwork. Lastly, place a sheet of glass on top of the artwork/PCB/artwork layer. The glass will keep all the different components lying flatly against each other.

It can be very difficult to lay the PCB on top of the bottom piece of lithographic film without moving the film, and also difficult to lay the top sheet of glass on top of the top piece of lithographic film without moving it. If you are having trouble with alignment you can see the alternative approach below or drill a few holes in the PCB to help you align the through holes or vias on the lithographic film.

===An Alternative Alignment Approach:===

Making a double sided board introduces a new technical hurdle: The requirement that the near and far sides be aligned within a few thousands of an inch, with a completely opaque and finitely thick layer between them!

[[File:PCB film alignment.png]]

The finite thickness is very problematic as demonstrated above, because the parallactic shifts it can introduce (if the vertical placement of the two film joints is neglected) can easily be on the order of 50 mils, which is much, much larger than the top-bottom alignment tolerance (consider 5 mils an upper bound on acceptability).

A successful approach has been developed for lining up two-layer boards:

A 1/32" thick piece of steel is used. WIth two small bits double sided tape (DST), tack the bottom layer down to the steel, emulsion up. Lay a longer strip of DST across the top of this film, above where the plate is.

Now hold the light close and line the top film layer up on top of the bottom one. Through-hole pins provide convenient concentric circles to align on. Check for basic sanity - do the through-hole sets of pins associated with integrated circuits line up?

Making sure the films are still aligned - it is very difficult to not let them slip a few thousands of an inch - slowly bring the top layer film down and tape it to the bottom one. Now, *provided that the layers are not separated*, the images are vertically lined up.

Gently pluck the combined image off the plate and remove the DST used to hold it: The two pieces of film are now a unit.

When exposing, the double-side board goes between the films and the plate goes underneath the taped edge of the films. By doing this, the middle scenario in the posited alignment cartoon is (approximately) brought about because the plate, 1/32" thick, is half as thick as our prototype boards (1/16" thick). The thickness of the film (2.5 mil) and the tape (4mil) are uncompensated, but so it goes.

Once the film, plate and board are positioned, lay the upper thin glass plate down. Use some small aluminum blocks to provide a small amount of weigh-down; Upon very close inspection, it should be clear that there is no (or next to no) air gap between the emulsion and photoresist via lack of any shadow.

==Exposure in the UV Chamber==

Before you begin exposing your board, read the next section ([[Developing the Board]]) and make sure that you have a prepared tray of mixed NaOH and water nearby. The NaOH solution removes photoresist and you risk unintentional overexposure from over-head lighting if you leave your exposed board out while preparing the NaOH solution. To avoid UV exposure from the florescent lights preform the UV exposure step in the quantum optics room with only the green overhead lights.

With the board assembly on the middle glass plate, put the upper diffuser plate in place if appropriate, close the lid, and turn the chamber on. The eerie violet glow should immediately appear.

Minimum exposure time, with an Optical Power Meter (OPM) reading of 200uW, is roughly 1m30s. Because the lithographic film has an enormous contrast ratio, there is a substantial margin for overexposure.

The margin is NOT a thousand times one minute: Edge effects (light diffracting around borders, and arriving at an angle, etc) mean that excessive overexposure will cause sufficient exposure to strip the mask to gradually bleed outwards from intentionally-exposed areas.

Inadvertently, a board was exposed for 7 minutes; This was sufficient to cause isolated thin copper rings to shrink very appreciably.

Preparing the UV Chamber and Board

2019-04-11T20:27:46Z

Aplstudent: /* Exposure in the UV Chamber */

Before getting any boards out, the UV chamber must be prepared. Get a VIS optical power meter (this detects light in the visible wavelength spectrum) out and lay the detector face down on the middle glass plate. Set the wavelength to 400nm (the actual wavelength is centered on 365; This introduces a roughly 40-50% shortage in measured power, if one is interested in absolute terms).

Plug the lid power connections in, turn the power level all the way off, close the lid and zero the OPM, and turn the chamber on. Dial the potentiometer until the power level reads about 200uW. Kill the power, remove the lid and put the OPM away.

==Single Side Board==

Exposure of a single side board is simple: Lay down bottom glass plate, peel the white protective coating off the circuit board and lay it sensitive side up (for a top-copper-only, presumably for an all-surface-mount circuit) or down (bottom-copper-only, typical of an all-through-hole circuit). Lay the film with emulsion in contact with the green photoresist, then lay the upper glass plate on top to acheive close contact. Small bits of aluminum scrap make good weights.

==Double Side Board==

At this point you should have both sides of your artwork printed on lithographic film. Before you expose the PCB, it is essential that the two pieces of film are aligned on either side of the board as precisely as possible. To achieve maximum precision, it is recommended to use the L-shaped aluminum jig is in the UV curing chamber.

The first step is to cut one corner of your film artwork. Before you cut, line up both pieces of film as if you were to expose your board (that is, all the through holes match up) and tape the pieces of film together so that the drill holes stay aligned. Then, using a paper cutter to ensure straight cuts, make at least two cuts such that the edge of your artwork has a 90 degree corner. The edge of your PCB artwork should have edge cuts indicated which makes for an ideal way to align your corner cuts. Note: it is important that you cut both pieces of film simultaneously so that the the artwork stays aligned when the tape is removed. After the corner cut, make sure that the excess lithographic film is cut off.

The objective is to produce a corner in the artwork that fits into the jig while the artwork is aligned:

[[File:Artwork Alignment Cuts.png]]

Now, remove the tape from the film and use the L shaped jig in the UV curing chamber to line up your bottom layer artwork, the PCB, and your top layer artwork. Lastly, place a sheet of glass on top of the artwork/PCB/artwork layer. The glass will keep all the different components lying flatly against each other.

It can be very difficult to lay the PCB on top of the bottom piece of lithographic film without moving the film, and also difficult to lay the top sheet of glass on top of the top piece of lithographic film without moving it. If you are having trouble with alignment you can see the alternative approach below or drill a few holes in the PCB to help you align the through holes or vias on the lithographic film.

===An Alternative Alignment Approach:===

Making a double sided board introduces a new technical hurdle: The requirement that the near and far sides be aligned within a few thousands of an inch, with a completely opaque and finitely thick layer between them!

[[File:PCB film alignment.png]]

The finite thickness is very problematic as demonstrated above, because the parallactic shifts it can introduce (if the vertical placement of the two film joints is neglected) can easily be on the order of 50 mils, which is much, much larger than the top-bottom alignment tolerance (consider 5 mils an upper bound on acceptability).

A successful approach has been developed for lining up two-layer boards:

A 1/32" thick piece of steel is used. WIth two small bits double sided tape (DST), tack the bottom layer down to the steel, emulsion up. Lay a longer strip of DST across the top of this film, above where the plate is.

Now hold the light close and line the top film layer up on top of the bottom one. Through-hole pins provide convenient concentric circles to align on. Check for basic sanity - do the through-hole sets of pins associated with integrated circuits line up?

Making sure the films are still aligned - it is very difficult to not let them slip a few thousands of an inch - slowly bring the top layer film down and tape it to the bottom one. Now, *provided that the layers are not separated*, the images are vertically lined up.

Gently pluck the combined image off the plate and remove the DST used to hold it: The two pieces of film are now a unit.

When exposing, the double-side board goes between the films and the plate goes underneath the taped edge of the films. By doing this, the middle scenario in the posited alignment cartoon is (approximately) brought about because the plate, 1/32" thick, is half as thick as our prototype boards (1/16" thick). The thickness of the film (2.5 mil) and the tape (4mil) are uncompensated, but so it goes.

Once the film, plate and board are positioned, lay the upper thin glass plate down. Use some small aluminum blocks to provide a small amount of weigh-down; Upon very close inspection, it should be clear that there is no (or next to no) air gap between the emulsion and photoresist via lack of any shadow.

==Exposure in the UV Chamber==

Before you begin exposing your board, read the next section ([Developing the Board]) and make sure that you have a prepared tray of mixed NaOH and water nearby. The NaOH solution removes photoresist and you risk unintentional overexposure from over-head lighting if you leave your exposed board out while preparing the NaOH solution. To avoid UV exposure from the florescent lights preform the UV exposure step in the quantum optics room with only the green overhead lights.

With the board assembly on the middle glass plate, put the upper diffuser plate in place if appropriate, close the lid, and turn the chamber on. The eerie violet glow should immediately appear.

Minimum exposure time, with an Optical Power Meter (OPM) reading of 200uW, is roughly 1m30s. Because the lithographic film has an enormous contrast ratio, there is a substantial margin for overexposure.

The margin is NOT a thousand times one minute: Edge effects (light diffracting around borders, and arriving at an angle, etc) mean that excessive overexposure will cause sufficient exposure to strip the mask to gradually bleed outwards from intentionally-exposed areas.

Inadvertently, a board was exposed for 7 minutes; This was sufficient to cause isolated thin copper rings to shrink very appreciably.

Preparing the UV Chamber and Board

2019-04-11T20:24:04Z

Aplstudent: /* Exposure in the UV Chamber */

Before getting any boards out, the UV chamber must be prepared. Get a VIS optical power meter (this detects light in the visible wavelength spectrum) out and lay the detector face down on the middle glass plate. Set the wavelength to 400nm (the actual wavelength is centered on 365; This introduces a roughly 40-50% shortage in measured power, if one is interested in absolute terms).

Plug the lid power connections in, turn the power level all the way off, close the lid and zero the OPM, and turn the chamber on. Dial the potentiometer until the power level reads about 200uW. Kill the power, remove the lid and put the OPM away.

==Single Side Board==

Exposure of a single side board is simple: Lay down bottom glass plate, peel the white protective coating off the circuit board and lay it sensitive side up (for a top-copper-only, presumably for an all-surface-mount circuit) or down (bottom-copper-only, typical of an all-through-hole circuit). Lay the film with emulsion in contact with the green photoresist, then lay the upper glass plate on top to acheive close contact. Small bits of aluminum scrap make good weights.

==Double Side Board==

At this point you should have both sides of your artwork printed on lithographic film. Before you expose the PCB, it is essential that the two pieces of film are aligned on either side of the board as precisely as possible. To achieve maximum precision, it is recommended to use the L-shaped aluminum jig is in the UV curing chamber.

The first step is to cut one corner of your film artwork. Before you cut, line up both pieces of film as if you were to expose your board (that is, all the through holes match up) and tape the pieces of film together so that the drill holes stay aligned. Then, using a paper cutter to ensure straight cuts, make at least two cuts such that the edge of your artwork has a 90 degree corner. The edge of your PCB artwork should have edge cuts indicated which makes for an ideal way to align your corner cuts. Note: it is important that you cut both pieces of film simultaneously so that the the artwork stays aligned when the tape is removed. After the corner cut, make sure that the excess lithographic film is cut off.

The objective is to produce a corner in the artwork that fits into the jig while the artwork is aligned:

[[File:Artwork Alignment Cuts.png]]

Now, remove the tape from the film and use the L shaped jig in the UV curing chamber to line up your bottom layer artwork, the PCB, and your top layer artwork. Lastly, place a sheet of glass on top of the artwork/PCB/artwork layer. The glass will keep all the different components lying flatly against each other.

It can be very difficult to lay the PCB on top of the bottom piece of lithographic film without moving the film, and also difficult to lay the top sheet of glass on top of the top piece of lithographic film without moving it. If you are having trouble with alignment you can see the alternative approach below or drill a few holes in the PCB to help you align the through holes or vias on the lithographic film.

===An Alternative Alignment Approach:===

Making a double sided board introduces a new technical hurdle: The requirement that the near and far sides be aligned within a few thousands of an inch, with a completely opaque and finitely thick layer between them!

[[File:PCB film alignment.png]]

The finite thickness is very problematic as demonstrated above, because the parallactic shifts it can introduce (if the vertical placement of the two film joints is neglected) can easily be on the order of 50 mils, which is much, much larger than the top-bottom alignment tolerance (consider 5 mils an upper bound on acceptability).

A successful approach has been developed for lining up two-layer boards:

A 1/32" thick piece of steel is used. WIth two small bits double sided tape (DST), tack the bottom layer down to the steel, emulsion up. Lay a longer strip of DST across the top of this film, above where the plate is.

Now hold the light close and line the top film layer up on top of the bottom one. Through-hole pins provide convenient concentric circles to align on. Check for basic sanity - do the through-hole sets of pins associated with integrated circuits line up?

Making sure the films are still aligned - it is very difficult to not let them slip a few thousands of an inch - slowly bring the top layer film down and tape it to the bottom one. Now, *provided that the layers are not separated*, the images are vertically lined up.

Gently pluck the combined image off the plate and remove the DST used to hold it: The two pieces of film are now a unit.

When exposing, the double-side board goes between the films and the plate goes underneath the taped edge of the films. By doing this, the middle scenario in the posited alignment cartoon is (approximately) brought about because the plate, 1/32" thick, is half as thick as our prototype boards (1/16" thick). The thickness of the film (2.5 mil) and the tape (4mil) are uncompensated, but so it goes.

Once the film, plate and board are positioned, lay the upper thin glass plate down. Use some small aluminum blocks to provide a small amount of weigh-down; Upon very close inspection, it should be clear that there is no (or next to no) air gap between the emulsion and photoresist via lack of any shadow.

==Exposure in the UV Chamber==

Before you begin exposing your board, read the next section ([]) and make sure that you have a prepared tray of mixed NaOH and water nearby. The NaOH solution removes photoresist and you risk unintentional overexposure from over-head lighting if you leave your exposed board out while preparing the NaOH solution. Preforming the exposure step in the quantum optics room with only the green overhead lights on protects your board from the stray UV light of the florescent overhead lights.

With the board assembly on the middle glass plate, put the upper diffuser plate in place if appropriate, close the lid, and turn the chamber on. The eerie violet glow should immediately appear.

Minimum exposure time, with an Optical Power Meter (OPM) reading of 200uW, is roughly 1m30s. Because the lithographic film has an enormous contrast ratio, there is a substantial margin for overexposure.

The margin is NOT a thousand times one minute: Edge effects (light diffracting around borders, and arriving at an angle, etc) mean that excessive overexposure will cause sufficient exposure to strip the mask to gradually bleed outwards from intentionally-exposed areas.

Inadvertently, a board was exposed for 7 minutes; This was sufficient to cause isolated thin copper rings to shrink very appreciably.

The Darkroom

2019-04-10T18:14:22Z

Aplstudent: /* Chemical Development Process */

==Print to Film==

The photo center requires that you either know how to use a chemical darkroom already or that you take an introduction course.

Access to their chemicals is $10 per quarter or $2 for a day. They don't take index numbers but you can be reimbursed.

Before you go to the darkroom you will need lithographic film, latex gloves, lithographic developer parts A and B (these each come in a separate bottle), and your paper negative print of your PCB. Everything else you need can be found in the craft center.

The lithographic film is kept in an envelop and a black film jacket; this film will become useless if it is exposed to light (except red/yellowish lights in the dark room) so never open the film container outside the darkroom. Continue reading for how to properly handle the film in the dark room.

The lithographic film developer comes in two bottles, part A concentrate and part B concentrate and the two parts will be mixed at the time of development. Part A is a dark purple color and part B is clear.

[[File:Labeled developer.png]]

In the darkroom, keep the lights low and let your eyes adapt.

===Prep and setup===

- Lay out chemical trays: developer, stop bath (water), fixer, hypowash.

The developer comes in two parts (A and B). Per the instructions on the bottles, mix 100ml of Part A concentrate to 300ml of water. Then separately Mix 100ml of Part B to 300ml of water. Disregard the nonsense about 68*F -as long as the temperature of the AB mix is in the vicinity of 80*F before development you are okay. It was found that just diluting the concentrates of A and B with hot water straight from the darkroom's hot tap worked quite well with the still fridge-cold concentrate. Pour the water mixed with A into the tray, then the mix of B and water into the same tray. Then wash the beaker thoroughly (water/agitate/dump 3x). Once mixed, the developer apparently has a frighteningly short useful lifetime - order of a few hours - which is why it comes in separated bottles.

The developer tray should be floated in a second tray containing hot water as thermal ballast. If the tray of developer is left on the cold metal table the developing liquid will quickly cool below working temperature. The target temp is around 80*F... 75*F is too cold, 85*F or more will be too hot. As an added layer of thermal protection you can flip over an empty tub on the metal table, place your hot water bath on the flipped over tub, and place your A/B mix tray in the hot water bath. This way the table will not cool the bath.

Next you will want to set up a stop bath, the fixer, and the hypowash. Fill one tray with water (this will be your stop bath), then fill one tray with Fixer (this will be in a labeled container in the dark room), and fill one tray with hypowash (this is a container labeled Iypoclear). The photo below shows 3 of the 4 contianers (the water stop bath is not shown).

[[File:Lith film dev chemicals.png]]

===Contact Printing===

- Next, prepare the contact print setup. You need two 8x10 glass sheets from two normal contract printing beds, to make a glass-film-paper-glass sandwich. Glass is very flat and must be used to ensure the maximum retention of detail.

- Prepare film to approximately the size of your art. We have 8x10 inch film sheets, so that it is natural to cut each down to four 4x5 inch pieces if this can accommodate your art. Don't be afraid to have some spare border so the film can easily be handled after without getting fingerprints on the art itself. You will also need test strips of Lithographic film to confirm the correct exposure. Check the film jacket for existing cut-down pieces before getting out another 8x10 sheet.

All film that is not this very second being cut, exposed or developed must be stored in the black film jacket and returned there promptly between cutting and exposure. Never take more than one sheet out at a time. The orange safelight will not expose it quickly, but the safelight and stray light from the enlarger will expose it eventually and this mal-exposure (known as fogging) is undetectable until the film is developed. Wear gloves while handling the film to avoid getting filthy dirty meatpaw marks all over it (a glove will be needed during development anyway). To the greatest extent possible, handle the film by its edges.

The film has a back and an emulsion side. The emulsion side is allegedly pinkish, which is spectacularly useless to know given that it can only be viewed in a darkroom under red light. The best way to tell the difference is by "tasting" the edge of the film with your lips. The emulsion side feels unsmooth/tacky while the anti-halation backing of the far side feels smooth. Always make sure that the emulsion side is up when exposing!

Thus, the layers for the exposure process should be a sheet of glass, the film (emulsion side up), the paper print (ink side down), and another sheet of glass.

The light source for your exposure will be the enlarger. An enlarger is commonly used to enlarge 35mm negatives, but you already have a paper negative so the enlarger will just act as a timed flashlight. A picture of the enlarge can be found below. You will place your glass-film-paper-glass sandwich under the enlarger and use the timer to vary the exposure time. The light will turn on for that amount of time and then turn off automatically.

[[File:Enlarger.png]]

===Make Test Strips===

Test strips are used to determine the ideal exposure time for your film and are made by contact printing a strip of film with different exposure times. To test the different times you will set up a contact print with your paper negative and test strip, then cover 4/5 with a light blocking material (thick cardboard or plastic) and expose 1/5 of the strip for 5 seconds. Next you will move the light blocking material to reveal 2/5 of your strip and expose the strip for another 5 seconds. You will repeat this process by covering less and less of your strip until the whole strip is exposed. This results in a strip having 5 different exposer times (the first 1/5 having 25 seconds of exposure while the last 1/5 only having 5 seconds of exposure). This [https://brucetannerphotographer.files.wordpress.com/2014/04/hast-lin.jpg image] demonstrates how the variations of exposure times will affect an image and how the test strip should look with regards to 5 different exposure areas.

To make your strip cut a small strip of film paper (an inch wide and about 5 inches long) and place this under the enlarger. Exposure time depends somewhat on enlarger head height and strongly on developer temperature (development is a thermodynamic process and is exponential in temperature). With an empty 35mm film holder in the enlarger, all color filters set to neutral, the lens aperture fully open, and the enlarger head moved down so that the image is about 11 inches wide, begin exposing the film for 5 second increments.

Follow the steps below to develop this test strip and determine which exposure time yields the best results. The ideal exposure time will result in completely clear regions where the paper negative was black and completely black regions where the paper negative was white. The black is black enough if you can hold the developed test strip up to a bright light and not see any light through the black regions.

===Chemical Development Process===

1. Developer (2-5 minutes)

2. Stop Bath (30 seconds)

3. Fixer (5 minutes)

4. Hypowash (5 minutes)

5. Rinse

====An aside:====

----

Normal photographic development is designed to convert a continuous range of light exposures into a continuous range of densities on the film or paper. This process generally has a roughly linear dynamic range of between 100 and 1000 to 1 separating "black" and "clear" (papers being nearer to 100 and films to 1000). At extremes of over- or under-exposure, the transfer function graphing optical density vs exposure saturates, resembling a graph of arctan(x). The steepness of the linear region defines the contrast level of the film, and is affected by both the film itself and the development process used.

In the normal, modern, black & white photographic development process, photons have reduced tiny amounts of silver halide in the film surface to silver metal. Within each grain, the developer converts silver metal to black silver oxide such that the darkness of a grain is proportional to how much light it received.

In the lithographic process, this normal process is augmented with positive feedback: Both silver AND silver oxide contribute to the development process. Obviously this results in exponential runaway, as a grain that develops at all will quickly turn completely black.

Photographic artists manipulate the lithographic process to produce exotic image tones (generally by gross overexposure, followed by great underdevelopment, such that the exponential runaway proceeds only to the point of producing an intriguingly nonlinear response curve), but we are interested in its "intended" property: The production of incredibly high contrast (10000:1) images with incredibly high resolutions (resolvable features on the micron scale).

For any given amount of exposure E, a given development process will result in an output film optical density D(E). For the halftone process, done correctly,

<math>D(E) ~= 4 * heaviside(E - E_{crit})</math>.

The contrast ratio of the printed image on paper is remarkably low when backlit - maybe 10, as opposed to over 100 viewed in diffuse reflective light - and suffers considerable fluctuations due to the random fiber packing of paper causing the transmission of "clear" areas to fluctuate considerably.

Thus the range of acceptable exposures, meaning those for which all black areas get E < E_crit and all clear areas get E > E_crit, is not nearly so wide as might be imagined.

Furthermore, the brightness of the light rectangle supplied by the enlarger experiences a nontrivial (~20%) decrease towards its corners, further eroding exposure margin.

This will demonstrate itself on test strips: If an exposure of 12 seconds works, most likely 6 seconds will result in a very weak image and 18 will blacken everything.

----

Development time should be roughly 2-5 minutes. Put the film into the developer emulsion up, as it was exposed. With a glove or tongs, agitate continuously for 30 seconds, then 5 seconds every 30. The film should quickly turn whiteish, and the shadow of an image should begin to darken within about 30 seconds. If it does not, either exposure was insufficient or the developer is cold.

Note that photographic development is a diffusion-limited process: The developer exists in the bulk fluid, but image formation occurs at a semi-infinite plane surface. This means that fluid agitation is *ESSENTIAL* to the process.

Overexposure with underdevelopment (Less than 2 minutes in developer) will be associated with clear areas exhibiting a continuous-tone brown muddiness, which is not OK for us (but is typical of what artistic lith printers are after). Underexposure with overdevelopment (over 4-ish minutes in developer) will be associated with waiting for the exposed areas to finish turning fully black when suddenly black dots begin to appear in clear areas.

If the developer is not legit warm through the glove, it is too cold. Floating the developer tray in a second tray filled with a thermal ballast of hot water will maintain its temperature for longer.

After developing, grab the film (either with tongs or glove) and wash it for 30 seconds in the stop bath (water) with continous swishing. This halts the development process, but the film is still photosensitive.

After placing the film in the fixer and agitating, almost immediate clearing of the substrate from white to transparent should occur. The fixing process takes about 5 minutes with intermittent agitation. As its name implies, the fixer "fixes" the image: It disintegrates and dissolves the remaining silver halide, leaving only the black silver oxide created by the developer.

After fixing, the film needs to be washed in hypowash to assure long-term stability of the photographic substrate. Around 5 minutes is sufficient, but more is not harmful. Agitate occasionally. Hypowash lets the fixer molecules diffuse out of the film, and also neutralizes any remaining acids that would slowly damage the substrate.

After hypowash, the film can be left in a final bath of plain water until all images are done.

Once fixed and washed, dry the film immediately by GENTLY enfolding both sides with a paper towel and pressing (not rubbing) to absorb most of the water. This directly removes the water and avoids the need to use a wetting agent and spend a long drying interval (don't let photographers see you wipe it with the paper towel, they may have heart attacks). The film's surface will still be "wet" like skin after washing dishes, and like wrinkled fingers the absorbed water will need time to evaporate out.

Now the film can be taken to normal room lights and inspected. Key points to check include optical density (it should be nearly impossible to see even direct fluorescent tubes through the black regions), and speckling (development of individual black grains in nominally unexposed regions, indicating overexposure/overdevelopment). It also goes without saying, the image should be unimpeachably finer than the unaided eye can resolve.

If the image is acceptable, clean the darkroom up, make certain the film bag is completely closed and put away, put the developed image in a negative sheet and you're done.

The following image demonstrates the transformation from digital image, to printed image, to photographic film:

[[File:Print examples.png]]

This is from a resolution test art. Six denotes that the array of vertical traces are 6 mils wide, while 12 and 15 denote that their centers are spaced by 15 and 12 mils. In terms of what might be sent to a commercial fabricator, 6 mil traces on 12 mil centers is middle of the road.

The right image is the "perfect" digital original, vector art rasterized at 600dpi. The middle panel is a photomicrograph of the paper output: As part of the resolution limit process, the toner demonstrates a clear preference to smear from black into areas that should be clear.

The left image is a reflection photomicrograph of the lithographic film, which exhibits contrast vastly inferior to a transmission image. Testing in the UV exposure chamber using a power meter found that when clear areas transmitted a measured power of 200uW, bulk opaque areas transmitted approximately 20nW: The clear/black contrast ratio exceeds 10000:1.

The Darkroom

2019-04-10T18:10:50Z

Aplstudent: /* Chemical Development Process */

==Print to Film==

The photo center requires that you either know how to use a chemical darkroom already or that you take an introduction course.

Access to their chemicals is $10 per quarter or $2 for a day. They don't take index numbers but you can be reimbursed.

Before you go to the darkroom you will need lithographic film, latex gloves, lithographic developer parts A and B (these each come in a separate bottle), and your paper negative print of your PCB. Everything else you need can be found in the craft center.

The lithographic film is kept in an envelop and a black film jacket; this film will become useless if it is exposed to light (except red/yellowish lights in the dark room) so never open the film container outside the darkroom. Continue reading for how to properly handle the film in the dark room.

The lithographic film developer comes in two bottles, part A concentrate and part B concentrate and the two parts will be mixed at the time of development. Part A is a dark purple color and part B is clear.

[[File:Labeled developer.png]]

In the darkroom, keep the lights low and let your eyes adapt.

===Prep and setup===

- Lay out chemical trays: developer, stop bath (water), fixer, hypowash.

The developer comes in two parts (A and B). Per the instructions on the bottles, mix 100ml of Part A concentrate to 300ml of water. Then separately Mix 100ml of Part B to 300ml of water. Disregard the nonsense about 68*F -as long as the temperature of the AB mix is in the vicinity of 80*F before development you are okay. It was found that just diluting the concentrates of A and B with hot water straight from the darkroom's hot tap worked quite well with the still fridge-cold concentrate. Pour the water mixed with A into the tray, then the mix of B and water into the same tray. Then wash the beaker thoroughly (water/agitate/dump 3x). Once mixed, the developer apparently has a frighteningly short useful lifetime - order of a few hours - which is why it comes in separated bottles.

The developer tray should be floated in a second tray containing hot water as thermal ballast. If the tray of developer is left on the cold metal table the developing liquid will quickly cool below working temperature. The target temp is around 80*F... 75*F is too cold, 85*F or more will be too hot. As an added layer of thermal protection you can flip over an empty tub on the metal table, place your hot water bath on the flipped over tub, and place your A/B mix tray in the hot water bath. This way the table will not cool the bath.

Next you will want to set up a stop bath, the fixer, and the hypowash. Fill one tray with water (this will be your stop bath), then fill one tray with Fixer (this will be in a labeled container in the dark room), and fill one tray with hypowash (this is a container labeled Iypoclear). The photo below shows 3 of the 4 contianers (the water stop bath is not shown).

[[File:Lith film dev chemicals.png]]

===Contact Printing===

- Next, prepare the contact print setup. You need two 8x10 glass sheets from two normal contract printing beds, to make a glass-film-paper-glass sandwich. Glass is very flat and must be used to ensure the maximum retention of detail.

- Prepare film to approximately the size of your art. We have 8x10 inch film sheets, so that it is natural to cut each down to four 4x5 inch pieces if this can accommodate your art. Don't be afraid to have some spare border so the film can easily be handled after without getting fingerprints on the art itself. You will also need test strips of Lithographic film to confirm the correct exposure. Check the film jacket for existing cut-down pieces before getting out another 8x10 sheet.

All film that is not this very second being cut, exposed or developed must be stored in the black film jacket and returned there promptly between cutting and exposure. Never take more than one sheet out at a time. The orange safelight will not expose it quickly, but the safelight and stray light from the enlarger will expose it eventually and this mal-exposure (known as fogging) is undetectable until the film is developed. Wear gloves while handling the film to avoid getting filthy dirty meatpaw marks all over it (a glove will be needed during development anyway). To the greatest extent possible, handle the film by its edges.

The film has a back and an emulsion side. The emulsion side is allegedly pinkish, which is spectacularly useless to know given that it can only be viewed in a darkroom under red light. The best way to tell the difference is by "tasting" the edge of the film with your lips. The emulsion side feels unsmooth/tacky while the anti-halation backing of the far side feels smooth. Always make sure that the emulsion side is up when exposing!

Thus, the layers for the exposure process should be a sheet of glass, the film (emulsion side up), the paper print (ink side down), and another sheet of glass.

The light source for your exposure will be the enlarger. An enlarger is commonly used to enlarge 35mm negatives, but you already have a paper negative so the enlarger will just act as a timed flashlight. A picture of the enlarge can be found below. You will place your glass-film-paper-glass sandwich under the enlarger and use the timer to vary the exposure time. The light will turn on for that amount of time and then turn off automatically.

[[File:Enlarger.png]]

===Make Test Strips===

Test strips are used to determine the ideal exposure time for your film and are made by contact printing a strip of film with different exposure times. To test the different times you will set up a contact print with your paper negative and test strip, then cover 4/5 with a light blocking material (thick cardboard or plastic) and expose 1/5 of the strip for 5 seconds. Next you will move the light blocking material to reveal 2/5 of your strip and expose the strip for another 5 seconds. You will repeat this process by covering less and less of your strip until the whole strip is exposed. This results in a strip having 5 different exposer times (the first 1/5 having 25 seconds of exposure while the last 1/5 only having 5 seconds of exposure). This [https://brucetannerphotographer.files.wordpress.com/2014/04/hast-lin.jpg image] demonstrates how the variations of exposure times will affect an image and how the test strip should look with regards to 5 different exposure areas.

To make your strip cut a small strip of film paper (an inch wide and about 5 inches long) and place this under the enlarger. Exposure time depends somewhat on enlarger head height and strongly on developer temperature (development is a thermodynamic process and is exponential in temperature). With an empty 35mm film holder in the enlarger, all color filters set to neutral, the lens aperture fully open, and the enlarger head moved down so that the image is about 11 inches wide, begin exposing the film for 5 second increments.

Follow the steps below to develop this test strip and determine which exposure time yields the best results. The ideal exposure time will result in completely clear regions where the paper negative was black and completely black regions where the paper negative was white. The black is black enough if you can hold the developed test strip up to a bright light and not see any light through the black regions.

===Chemical Development Process===

1. Developer

2. Stop Bath

3. Fixer

4. Hypowash

====An aside:====

----

Normal photographic development is designed to convert a continuous range of light exposures into a continuous range of densities on the film or paper. This process generally has a roughly linear dynamic range of between 100 and 1000 to 1 separating "black" and "clear" (papers being nearer to 100 and films to 1000). At extremes of over- or under-exposure, the transfer function graphing optical density vs exposure saturates, resembling a graph of arctan(x). The steepness of the linear region defines the contrast level of the film, and is affected by both the film itself and the development process used.

In the normal, modern, black & white photographic development process, photons have reduced tiny amounts of silver halide in the film surface to silver metal. Within each grain, the developer converts silver metal to black silver oxide such that the darkness of a grain is proportional to how much light it received.

In the lithographic process, this normal process is augmented with positive feedback: Both silver AND silver oxide contribute to the development process. Obviously this results in exponential runaway, as a grain that develops at all will quickly turn completely black.

Photographic artists manipulate the lithographic process to produce exotic image tones (generally by gross overexposure, followed by great underdevelopment, such that the exponential runaway proceeds only to the point of producing an intriguingly nonlinear response curve), but we are interested in its "intended" property: The production of incredibly high contrast (10000:1) images with incredibly high resolutions (resolvable features on the micron scale).

For any given amount of exposure E, a given development process will result in an output film optical density D(E). For the halftone process, done correctly,

<math>D(E) ~= 4 * heaviside(E - E_{crit})</math>.

The contrast ratio of the printed image on paper is remarkably low when backlit - maybe 10, as opposed to over 100 viewed in diffuse reflective light - and suffers considerable fluctuations due to the random fiber packing of paper causing the transmission of "clear" areas to fluctuate considerably.

Thus the range of acceptable exposures, meaning those for which all black areas get E < E_crit and all clear areas get E > E_crit, is not nearly so wide as might be imagined.

Furthermore, the brightness of the light rectangle supplied by the enlarger experiences a nontrivial (~20%) decrease towards its corners, further eroding exposure margin.

This will demonstrate itself on test strips: If an exposure of 12 seconds works, most likely 6 seconds will result in a very weak image and 18 will blacken everything.

----

Development time should be roughly 2-5 minutes. Put the film into the developer emulsion up, as it was exposed. With a glove or tongs, agitate continuously for 30 seconds, then 5 seconds every 30. The film should quickly turn whiteish, and the shadow of an image should begin to darken within about 30 seconds. If it does not, either exposure was insufficient or the developer is cold.

Note that photographic development is a diffusion-limited process: The developer exists in the bulk fluid, but image formation occurs at a semi-infinite plane surface. This means that fluid agitation is *ESSENTIAL* to the process.

Overexposure with underdevelopment (Less than 2 minutes in developer) will be associated with clear areas exhibiting a continuous-tone brown muddiness, which is not OK for us (but is typical of what artistic lith printers are after). Underexposure with overdevelopment (over 4-ish minutes in developer) will be associated with waiting for the exposed areas to finish turning fully black when suddenly black dots begin to appear in clear areas.

If the developer is not legit warm through the glove, it is too cold. Floating the developer tray in a second tray filled with a thermal ballast of hot water will maintain its temperature for longer.

After developing, grab the film (either with tongs or glove) and wash it for 30 seconds in the stop bath (water) with continous swishing. This halts the development process, but the film is still photosensitive.

After placing the film in the fixer and agitating, almost immediate clearing of the substrate from white to transparent should occur. The fixing process takes about 5 minutes with intermittent agitation. As its name implies, the fixer "fixes" the image: It disintegrates and dissolves the remaining silver halide, leaving only the black silver oxide created by the developer.

After fixing, the film needs to be washed in hypowash to assure long-term stability of the photographic substrate. Around 5 minutes is sufficient, but more is not harmful. Agitate occasionally. Hypowash lets the fixer molecules diffuse out of the film, and also neutralizes any remaining acids that would slowly damage the substrate.

After hypowash, the film can be left in a final bath of plain water until all images are done.

Once fixed and washed, dry the film immediately by GENTLY enfolding both sides with a paper towel and pressing (not rubbing) to absorb most of the water. This directly removes the water and avoids the need to use a wetting agent and spend a long drying interval (don't let photographers see you wipe it with the paper towel, they may have heart attacks). The film's surface will still be "wet" like skin after washing dishes, and like wrinkled fingers the absorbed water will need time to evaporate out.

Now the film can be taken to normal room lights and inspected. Key points to check include optical density (it should be nearly impossible to see even direct fluorescent tubes through the black regions), and speckling (development of individual black grains in nominally unexposed regions, indicating overexposure/overdevelopment). It also goes without saying, the image should be unimpeachably finer than the unaided eye can resolve.

If the image is acceptable, clean the darkroom up, make certain the film bag is completely closed and put away, put the developed image in a negative sheet and you're done.

The following image demonstrates the transformation from digital image, to printed image, to photographic film:

[[File:Print examples.png]]

This is from a resolution test art. Six denotes that the array of vertical traces are 6 mils wide, while 12 and 15 denote that their centers are spaced by 15 and 12 mils. In terms of what might be sent to a commercial fabricator, 6 mil traces on 12 mil centers is middle of the road.

The right image is the "perfect" digital original, vector art rasterized at 600dpi. The middle panel is a photomicrograph of the paper output: As part of the resolution limit process, the toner demonstrates a clear preference to smear from black into areas that should be clear.

The left image is a reflection photomicrograph of the lithographic film, which exhibits contrast vastly inferior to a transmission image. Testing in the UV exposure chamber using a power meter found that when clear areas transmitted a measured power of 200uW, bulk opaque areas transmitted approximately 20nW: The clear/black contrast ratio exceeds 10000:1.

The Darkroom

2019-04-10T18:10:35Z

Aplstudent: /* Chemical Development Process */

==Print to Film==

The photo center requires that you either know how to use a chemical darkroom already or that you take an introduction course.

Access to their chemicals is $10 per quarter or $2 for a day. They don't take index numbers but you can be reimbursed.

Before you go to the darkroom you will need lithographic film, latex gloves, lithographic developer parts A and B (these each come in a separate bottle), and your paper negative print of your PCB. Everything else you need can be found in the craft center.

The lithographic film is kept in an envelop and a black film jacket; this film will become useless if it is exposed to light (except red/yellowish lights in the dark room) so never open the film container outside the darkroom. Continue reading for how to properly handle the film in the dark room.

The lithographic film developer comes in two bottles, part A concentrate and part B concentrate and the two parts will be mixed at the time of development. Part A is a dark purple color and part B is clear.

[[File:Labeled developer.png]]

In the darkroom, keep the lights low and let your eyes adapt.

===Prep and setup===

- Lay out chemical trays: developer, stop bath (water), fixer, hypowash.

The developer comes in two parts (A and B). Per the instructions on the bottles, mix 100ml of Part A concentrate to 300ml of water. Then separately Mix 100ml of Part B to 300ml of water. Disregard the nonsense about 68*F -as long as the temperature of the AB mix is in the vicinity of 80*F before development you are okay. It was found that just diluting the concentrates of A and B with hot water straight from the darkroom's hot tap worked quite well with the still fridge-cold concentrate. Pour the water mixed with A into the tray, then the mix of B and water into the same tray. Then wash the beaker thoroughly (water/agitate/dump 3x). Once mixed, the developer apparently has a frighteningly short useful lifetime - order of a few hours - which is why it comes in separated bottles.

The developer tray should be floated in a second tray containing hot water as thermal ballast. If the tray of developer is left on the cold metal table the developing liquid will quickly cool below working temperature. The target temp is around 80*F... 75*F is too cold, 85*F or more will be too hot. As an added layer of thermal protection you can flip over an empty tub on the metal table, place your hot water bath on the flipped over tub, and place your A/B mix tray in the hot water bath. This way the table will not cool the bath.

Next you will want to set up a stop bath, the fixer, and the hypowash. Fill one tray with water (this will be your stop bath), then fill one tray with Fixer (this will be in a labeled container in the dark room), and fill one tray with hypowash (this is a container labeled Iypoclear). The photo below shows 3 of the 4 contianers (the water stop bath is not shown).

[[File:Lith film dev chemicals.png]]

===Contact Printing===

- Next, prepare the contact print setup. You need two 8x10 glass sheets from two normal contract printing beds, to make a glass-film-paper-glass sandwich. Glass is very flat and must be used to ensure the maximum retention of detail.

- Prepare film to approximately the size of your art. We have 8x10 inch film sheets, so that it is natural to cut each down to four 4x5 inch pieces if this can accommodate your art. Don't be afraid to have some spare border so the film can easily be handled after without getting fingerprints on the art itself. You will also need test strips of Lithographic film to confirm the correct exposure. Check the film jacket for existing cut-down pieces before getting out another 8x10 sheet.

All film that is not this very second being cut, exposed or developed must be stored in the black film jacket and returned there promptly between cutting and exposure. Never take more than one sheet out at a time. The orange safelight will not expose it quickly, but the safelight and stray light from the enlarger will expose it eventually and this mal-exposure (known as fogging) is undetectable until the film is developed. Wear gloves while handling the film to avoid getting filthy dirty meatpaw marks all over it (a glove will be needed during development anyway). To the greatest extent possible, handle the film by its edges.

The film has a back and an emulsion side. The emulsion side is allegedly pinkish, which is spectacularly useless to know given that it can only be viewed in a darkroom under red light. The best way to tell the difference is by "tasting" the edge of the film with your lips. The emulsion side feels unsmooth/tacky while the anti-halation backing of the far side feels smooth. Always make sure that the emulsion side is up when exposing!

Thus, the layers for the exposure process should be a sheet of glass, the film (emulsion side up), the paper print (ink side down), and another sheet of glass.

The light source for your exposure will be the enlarger. An enlarger is commonly used to enlarge 35mm negatives, but you already have a paper negative so the enlarger will just act as a timed flashlight. A picture of the enlarge can be found below. You will place your glass-film-paper-glass sandwich under the enlarger and use the timer to vary the exposure time. The light will turn on for that amount of time and then turn off automatically.

[[File:Enlarger.png]]

===Make Test Strips===

Test strips are used to determine the ideal exposure time for your film and are made by contact printing a strip of film with different exposure times. To test the different times you will set up a contact print with your paper negative and test strip, then cover 4/5 with a light blocking material (thick cardboard or plastic) and expose 1/5 of the strip for 5 seconds. Next you will move the light blocking material to reveal 2/5 of your strip and expose the strip for another 5 seconds. You will repeat this process by covering less and less of your strip until the whole strip is exposed. This results in a strip having 5 different exposer times (the first 1/5 having 25 seconds of exposure while the last 1/5 only having 5 seconds of exposure). This [https://brucetannerphotographer.files.wordpress.com/2014/04/hast-lin.jpg image] demonstrates how the variations of exposure times will affect an image and how the test strip should look with regards to 5 different exposure areas.

To make your strip cut a small strip of film paper (an inch wide and about 5 inches long) and place this under the enlarger. Exposure time depends somewhat on enlarger head height and strongly on developer temperature (development is a thermodynamic process and is exponential in temperature). With an empty 35mm film holder in the enlarger, all color filters set to neutral, the lens aperture fully open, and the enlarger head moved down so that the image is about 11 inches wide, begin exposing the film for 5 second increments.

Follow the steps below to develop this test strip and determine which exposure time yields the best results. The ideal exposure time will result in completely clear regions where the paper negative was black and completely black regions where the paper negative was white. The black is black enough if you can hold the developed test strip up to a bright light and not see any light through the black regions.

===Chemical Development Process===

1. Developer
2. Stop Bath
3. Fixer
4. Hypowash

====An aside:====

----

Normal photographic development is designed to convert a continuous range of light exposures into a continuous range of densities on the film or paper. This process generally has a roughly linear dynamic range of between 100 and 1000 to 1 separating "black" and "clear" (papers being nearer to 100 and films to 1000). At extremes of over- or under-exposure, the transfer function graphing optical density vs exposure saturates, resembling a graph of arctan(x). The steepness of the linear region defines the contrast level of the film, and is affected by both the film itself and the development process used.

In the normal, modern, black & white photographic development process, photons have reduced tiny amounts of silver halide in the film surface to silver metal. Within each grain, the developer converts silver metal to black silver oxide such that the darkness of a grain is proportional to how much light it received.

In the lithographic process, this normal process is augmented with positive feedback: Both silver AND silver oxide contribute to the development process. Obviously this results in exponential runaway, as a grain that develops at all will quickly turn completely black.

Photographic artists manipulate the lithographic process to produce exotic image tones (generally by gross overexposure, followed by great underdevelopment, such that the exponential runaway proceeds only to the point of producing an intriguingly nonlinear response curve), but we are interested in its "intended" property: The production of incredibly high contrast (10000:1) images with incredibly high resolutions (resolvable features on the micron scale).

For any given amount of exposure E, a given development process will result in an output film optical density D(E). For the halftone process, done correctly,

<math>D(E) ~= 4 * heaviside(E - E_{crit})</math>.

The contrast ratio of the printed image on paper is remarkably low when backlit - maybe 10, as opposed to over 100 viewed in diffuse reflective light - and suffers considerable fluctuations due to the random fiber packing of paper causing the transmission of "clear" areas to fluctuate considerably.

Thus the range of acceptable exposures, meaning those for which all black areas get E < E_crit and all clear areas get E > E_crit, is not nearly so wide as might be imagined.

Furthermore, the brightness of the light rectangle supplied by the enlarger experiences a nontrivial (~20%) decrease towards its corners, further eroding exposure margin.

This will demonstrate itself on test strips: If an exposure of 12 seconds works, most likely 6 seconds will result in a very weak image and 18 will blacken everything.

----

Development time should be roughly 2-5 minutes. Put the film into the developer emulsion up, as it was exposed. With a glove or tongs, agitate continuously for 30 seconds, then 5 seconds every 30. The film should quickly turn whiteish, and the shadow of an image should begin to darken within about 30 seconds. If it does not, either exposure was insufficient or the developer is cold.

Note that photographic development is a diffusion-limited process: The developer exists in the bulk fluid, but image formation occurs at a semi-infinite plane surface. This means that fluid agitation is *ESSENTIAL* to the process.

Overexposure with underdevelopment (Less than 2 minutes in developer) will be associated with clear areas exhibiting a continuous-tone brown muddiness, which is not OK for us (but is typical of what artistic lith printers are after). Underexposure with overdevelopment (over 4-ish minutes in developer) will be associated with waiting for the exposed areas to finish turning fully black when suddenly black dots begin to appear in clear areas.

If the developer is not legit warm through the glove, it is too cold. Floating the developer tray in a second tray filled with a thermal ballast of hot water will maintain its temperature for longer.

After developing, grab the film (either with tongs or glove) and wash it for 30 seconds in the stop bath (water) with continous swishing. This halts the development process, but the film is still photosensitive.

After placing the film in the fixer and agitating, almost immediate clearing of the substrate from white to transparent should occur. The fixing process takes about 5 minutes with intermittent agitation. As its name implies, the fixer "fixes" the image: It disintegrates and dissolves the remaining silver halide, leaving only the black silver oxide created by the developer.

After fixing, the film needs to be washed in hypowash to assure long-term stability of the photographic substrate. Around 5 minutes is sufficient, but more is not harmful. Agitate occasionally. Hypowash lets the fixer molecules diffuse out of the film, and also neutralizes any remaining acids that would slowly damage the substrate.

After hypowash, the film can be left in a final bath of plain water until all images are done.

Once fixed and washed, dry the film immediately by GENTLY enfolding both sides with a paper towel and pressing (not rubbing) to absorb most of the water. This directly removes the water and avoids the need to use a wetting agent and spend a long drying interval (don't let photographers see you wipe it with the paper towel, they may have heart attacks). The film's surface will still be "wet" like skin after washing dishes, and like wrinkled fingers the absorbed water will need time to evaporate out.

Now the film can be taken to normal room lights and inspected. Key points to check include optical density (it should be nearly impossible to see even direct fluorescent tubes through the black regions), and speckling (development of individual black grains in nominally unexposed regions, indicating overexposure/overdevelopment). It also goes without saying, the image should be unimpeachably finer than the unaided eye can resolve.

If the image is acceptable, clean the darkroom up, make certain the film bag is completely closed and put away, put the developed image in a negative sheet and you're done.

The following image demonstrates the transformation from digital image, to printed image, to photographic film:

[[File:Print examples.png]]

This is from a resolution test art. Six denotes that the array of vertical traces are 6 mils wide, while 12 and 15 denote that their centers are spaced by 15 and 12 mils. In terms of what might be sent to a commercial fabricator, 6 mil traces on 12 mil centers is middle of the road.

The right image is the "perfect" digital original, vector art rasterized at 600dpi. The middle panel is a photomicrograph of the paper output: As part of the resolution limit process, the toner demonstrates a clear preference to smear from black into areas that should be clear.

The left image is a reflection photomicrograph of the lithographic film, which exhibits contrast vastly inferior to a transmission image. Testing in the UV exposure chamber using a power meter found that when clear areas transmitted a measured power of 200uW, bulk opaque areas transmitted approximately 20nW: The clear/black contrast ratio exceeds 10000:1.

Printing the Paper Copy

2019-04-10T17:53:18Z

Aplstudent: /* Negative or Positive, Mirrored or Not Mirrored */

==Negative or Positive, Mirrored or Not Mirrored==

We need to determine if the paper copy should be the negative (color inverted) or positive (color not inverted) of the layer's digital image. The PCB process leaves copper in the unexposed areas (i.e. the black ink areas on the film = copper areas on the PCB) so we ultimately want the film to be the positive of our digital layer. Although, the film takes the negative image of the paper during the transition from paper to film. Thus, we want to print a negative image on paper so the film will show the positive.

We also want to make sure that when we expose the top and bottom layers everything lines up. This means we need to print the the top layer as a regular image and the bottom layer as a mirrored image.

==Creating Files to Print==

To create a SVG (Scalable Vector Graphic) of a schematic in KiCad open [[Pcbnew]] and select File -> Export SVG. Next, select the front copper layer (F.Cu) or back copper layer (B.Cu). If you are converting the front copper layer do not mirror the image, but if you are printing the back copper layer, select "Print mirrored". Once you've chosen a location to save the files (the "Output Directory") select plot for each layer with the appropriate settings.

Now, with your SVG files saved somewhere accessible we'll want to create negatives of the images. Unfortunately, printing a PNG or SVG of a negative can be surprisingly troublesome. The main issue is that a PNG or SVG contains black, white, and transparent regions and the transparent areas, which print as white, will not turn black when creating a negative image. The fix is to print the PNG or SVG on top of a black rectangle the size of your PCB. To do this we'll use a program like photoshop, GIMP, or Inkscape to create two digital layers, one top layer with the PCB schematic and one bottom layer with a black rectangle.

(Both GIMP and Inkscape can be found on the "Hank" computer in the APL or downloaded for free, in this tutorial we'll use Inkscape)

Open Inkscape and select File -> Open..., find your SVG images and select "Open". Once you're schematic is loaded we'll want to add the SVG images to a layer. First create a blank layer by selecting Layer -> Add Layer.. then click Add. Now, use the mouse tool to click and drag a selection box around you're schematic. Once you have everything in your schematic selected right click somewhere in the selection box and click "Move to layer ...". Select the layer you just created and click "Move". This will enable you to create a second layer below your schematic layer and draw a black background. Now, create a new layer the same way we created the first layer but in the popup menu select "Position: Below current". Open the Layers... meun by pressing Shift+Ctrl+L and select your first layer (the one with your schematic). Next click Extensions -> Color -> Negative to create a negative image. You'll notice that most of the detail in your schematic disappears. To get this detail back, select your second layer and use the "Create rectangles and squares" tool (make sure black is selected from the row of colors at the bottom of the screen) to draw a large black rectangle around you circuit. To avoid wasting ink don't fill the entire page with the black rectangle, just fill the area of the page that contains the PCB schematic. When you're finished if everything went correctly the areas of the board we want to be copper should be white and everything else should be black.

Before you're ready to print you'll want to make sure the page size matches the printer paper. This can be done in inkscape by holding Ctrl+Shift+D to open the document properties. Now select the "Page Size", this will most likely be 8.5 x 11 inches. Now make sure everything fits on the page. '''Do not''' rescale any of the PCB elements, only move them. The scale of the PCB must match the original scale of your schematic.

Finally, you'll want to create a PDF or PNG copy of your SVG negatives. This can be done in Inkscape by changing the settings in File -> Save As... section. This PDF or PNG can be emailed to the UO [https://uoprint.uoregon.edu/about-campus-copy "Campus Copy"] to be printed with a high resolution printer on fine photo paper. Alternatively, if you have access to one, a 1200 dpi printer will be sufficient.

Populating the PCB

2019-04-03T23:50:21Z

Aplstudent: /* Optional: Surface Mount Devices (SMDs) */

If your board only contains through-hole components (components with wires or leads that will mounted through the board) you can ignore the section on Surface Mount Devices below. If your board has surface mount devices then you will want to read the section about surface mount devices before you attach any components.

Once the new clean board has had the acetone washed off, any through-holes need to be drilled.

Use the drill press at maximum speed with the miniature carbide drill bits. WEAR GOGGLES, these bits are notable for shattering. Push the bits through the board slowly - they are going at 1/30 of their intended speed in our press! Typical drill holes are .028 for wire pins, .035 and .042 for normal device pins. Be sure that your drill bit matches your component pin size, if the holes are too small the component will not fit and if the holes are too large you run the risk of drilling through the copper that will allow you to solder the pin to the board.

The board obviously will not have plated through holes the way professionally manufactured boards do. Any connections must be soldered on both sides of a through-hole device, and any vias must have wires run through and soldered.

If you have not soldered before, you can read this [https://www.makerspaces.com/how-to-solder/ article], and/or ask someone for help. Soldering isn't wildly difficult but the process has a few nuances that are important to understand to be successful, namely how to ensure that the soldering joint is properly contacting both the wire and the PCB.

==Optional: Surface Mount Devices (SMDs)==

WARNING: SMDs require the use of solder paste, which may contain lead in an easily indigestible form. You should take take extreme care when using solder paste. Wear gloves and clean any surface that the solder paste comes in contact with. Try to avoid any contact between the solder paste an your skin.

Surface mount devices are components that are soldered directly to the surface of your PCB. To attach these, you must use solder paste and a reflow oven, in our case we will be using the "Puhui infrared IC heater", to melt the solder paste.

The heating process requires placing the whole PCB in the reflow oven. Since the melting point of the solder is around 183 degrees Celsius, you want to be sure that you either attach the SMDs before any other components or know that the components already attached to the board can withstand the 183 degree temperature without being damaged. To be safe, it is always better to attach SMDs before attaching any through-hole components.

===Applying Solder Paste===

The first step in attaching SMDs is applying soldering paste. Applying the solder paste is most commonly done in two ways, with a stencil or by gently dabbing solder paste on the PCB. Using a stencil can become necessary when you have many SMDs or if you have surface mount integrated circuit that requires multiple pins to be attached. For larger or fewer SMDs you can apply the solder paste directly to the board without a stencil by dabbing the paste on SMD's board location. When applying solder paste without a stencil it is better to err on the side of less solder paste, rather than more.

====Applying Solder Paste with a Stencil====

If your project requires a stencil that does not exist in the lab already you should talk to Professor Boggs about how to obtain one. The fabrication of a stencil is beyond the scope of this tutorial but as a reference you can look at Seeedstudio's stencil fabrication, or talk to people in the maker's space or machine shop.

Assuming you have the stencil, your goal is to evenly spread solder paste over all the surface mount locations on the PCB at once. First you want to secure your PCB to a flat surface and make sure your stencil is securely and flatly attached to your board. You want to prevent any lateral movement of the the PCB or the stencil as you smear soldering paste across the stencil. Once your PCB and stencil are secured to each other and flat against each other, apply a large amount of solder paste to the area above the holes of the stencil (see the picture below). Next, in one motion you want to drag a blade (or other flat object) across the stencil to smear solder paste over the holes. Proper execution of this motion results in an even distribution of solder paste across every hole in the stencil. Unsuccessful solder application can be rectified by washing away the solder paste and trying again.

===Attaching SMDs===

After applying solder paste, you can begin attaching SMDs to your board. Due to the small nature of SMDs and the precision necessary to attach SMDs to the PCB, use finely tipped tweezers to place your components on your PCB. After placing all your components on the PCB carefully bring your PCB to the reflow oven.

===Using the Reflow Oven===

Read the brief manual taped to the top of the reflow oven before you use it. The manual will tell you which program you need based on the kind of solder paste you are using (the solder paste currently in the lab is 63Sn/37Pb). As mentioned before, double check that the reflow oven's heat will not damage any components that may be attached to your PCB.