Qwicktrace PCB

A "smart" exposure table for small photosensitive PCB etching using Raspberry Pi 4 and LCD from SLA resin printers

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The quickest way to make a PCB using chemical etching. Upload the Gerber or SVG of your circuit, and the circuit trace mask appears on the LCD screen. Select your desired exposure profile from the touch screen, and the photosensitive copper board is exposed to UV light with traces masked appropriately for the perfect time.

UPDATE: While the stand alone exposure table in this project is still a valid option, I have released a completely revised hardware system that includes a small CNC machine for drilling holes as well as the exposure table. For information, see

How Photo Etching works:

The unit is designed to facilitate "photo etching" of copper boards. "Etching" a PCB is done by protecting the copper that represents the traces with an "etch resistant" coating. The board is then placed in an etchant like Ferric Chloride, where the copper that is not covered with etch resist is chemically disolved away.  What remains are the copper traces.  Qwicktrace works with various "photosensitive copper boards", where the "etch resist" of the traces is made in one of two ways:

  1. Expose the traces to UV light, which strengthens the etch resist, making the copper underneath the exposed area slower to eat away. This allows the non-trace area to be removed first, leaving the traces behind.
  2. Hide the traces from UV light, which weakens the etch resist on the rest of the board. The board is placed in a "developer" chemical that eats away UV exposed etch resist, leaving behind the entire copper clad board, but with traces still covered by the resistant. The board is then placed in the same etchant in step #1, where the non protected copper is eaten away.

How Qwicktrace PCB works:

The Raspberry Pi 4 controls the unit, including the small TFT touchscreen used for the user interface. A simple custom "Hat" PCB fits onto the Pi to help it out with controlling the various components.  The Qwicktrace software understands how to read and render Gerber files and SVG files, so the process of using the unit is as follows:

  1. Upload a Gbr or SVG file to the unit's "pcb-files" directory
  2. Select the file you uploaded on the unit's touch screen. Files are listed in reverse date order (most recent on top).
  3. Select a "profile" used to expose the photosenstive copper board.  The profile determines whether the UV light reaches the traces or the non-traced area, as well as the total exposure time needed.
  4. The Qwicktrace unit renders the circuit traces as either a negative or positive image, turns on the UV LEDs to expose the board, then turns off the board when exposure is complete.

The LEDs run on 24 volts, but their on/off state is controlled by the Pi via a PWM on a GPIO pin that is connected to the lamp's LED controller IC. The Pi and the HDMI interface board both require 5 volts, which is supplied by the small voltage regulator module on the Pi Hat.  The Rev 2 board of the Pi Hat uses a "stackable header pin connector", which has extra long pins, and allows the GPIO pins of the Pi to be exposed and connected to even with the PiHat board in place (for future expansion). 


Schematics for PiHat

application/pdf - 109.00 kB - 03/31/2021 at 20:45


Qwicktrace PCB assembly.mp4

Video that shows component assembly

MPEG-4 Video - 4.85 MB - 03/26/2021 at 17:40



3D printer file for section that holds SLA printer screen

- 176.64 kB - 03/26/2021 at 17:40



3D printer file for lid that fits over circuit board during exposure

- 176.06 kB - 03/26/2021 at 17:40


LED holder.stl

3D printer file for section where Sparkmaker UV lamp

- 217.86 kB - 03/26/2021 at 17:40


View all 8 files

  • 1 × Raspberry Pi 4 Used to control the entire system
  • 1 × Elegoo 5.5 inch 2K LCD Screen with glass A replacement part for the Mars Pro SLA 3D printer
  • 1 × HDMI to MIPI-DSI interface board for Sharp LS055R1SX04 LCD The Sharp LS055R1SX04 LCD is what is used by the Mars Pro printers. This board is used to allow the RasPi to generate images on it.
  • 1 × Sparkmaker UV backlight lamp Used as the UV source to expose the presensitized copper
  • 1 × Mini HDMI to Micro HDMI cable Connects Pi to the HDMI.DSI interface board

View all 29 components

  • Introducing the all new QwickFab PCB

    Joel Kozikowski11/16/2021 at 23:50 0 comments

    The CNC mill I mentioned before, and the software to control it is now ready. I've actually been silently working almost every day since I released the Qwicktrace PCB system to make a new and improved system for homemade PCB fabrication. 

    There has been so much work done that I think it is deserving of an entirely new project.  That project is here:

  • Spectacular smoke. PiHat Rev 2.1 released :)

    Joel Kozikowski05/22/2021 at 19:55 0 comments

    For future reference, the GPIO pins on the Raspberry Pi supports a maximum of about 50 mA of current through the GPIO pins. As I was laying out the rev 2 PiHat board, I mistakenly routed the GND trace of the UV lamp thru a conveniently nearby GND pin on the Raspberry Pi (vs. making a trace directly to the primary ground trace).  Big mistake on my part.  A bad solder joint actually made the UV lamp work in this configuration for a short period, but once I fixed the joint, I managed to damage the Pi, which in turn sent too much current through the LED control pin of the UV lamp chip, which in turn smoked it in a spectacular fashion!  Fortunately I had a spare Pi and a spare Sparkmaker UV lamp (my China shipment finally arrived), which allowed me to test Rev 2.1 of the PiHat.

    Lesson learned: The Rat's Nest lines of your EDA tool may pick the nearest connection point, but it may not be the one you need. :)

    The rev 2.1 board fixes and Gerber files have been uploaded to GitHub.

  • Rev 2 PiHat ready for use

    Joel Kozikowski05/20/2021 at 21:13 0 comments

    I have updated the KiCad design, Gerber files, and build instructions on this page to reflect "Rev 2" of the PiHat board, which makes this build officially use the Sparkmaker  UV lamp.  The Rev 2 board now contains a 5 pin JST header that can be connected directly to the Sparkmaker UV lamp using the cable that comes with it.

    The Rev2 board also adds two "expansion connectors": a single 3 pin JST connector, and an additional 2 pin JST connector for 5v continuous power.  These two expansion connectors  are going to be used in the upcoming CNC mill project that will help speed your DIY PCB fabrication even more!

  • Drilling holes

    Joel Kozikowski04/29/2021 at 23:28 0 comments

    After a short break to work on other things, I am back working on this project.  I've expanded the capability goals and am adding a small CNC mill that integrates with the Pi controller so it will be able to quickly drill PCB holes.  This "QwickDrill" module will be optional, but should add a lot.  Here is a sneak peek at the Fusion 360 design:

  • New UV Lamp - HUGE improvement!!

    Joel Kozikowski04/16/2021 at 22:08 2 comments

    I got my hands on a UV lamp from an inexpensive consumer mSLA printer. This lamp fixture is part of the original Sparkmaker 3D resin printer.  After hacking a wire harness to retrofit the lamp fixture into the already existing Qwicktrace internals and a super quick software change, I got it functioning and was excited to test.

    Sparkmarker UV lamp
    Sparkmaker UV lamp installed

    This particular lamp was taken directly from a used Sparkmaker I purchased off of eBay (I didn't want to wait for my shipment from China).  While disassembling the printer, I noticed that they had put their protective glass UNDER the LCD, putting the LCD mask much closer to their resin vat.  Hackaday community member @crun made some excellent comments on this project regarding defocus problems that can be caused by parallax in glass, so I decided to flip the glass in the Qwicktrace unit over, making the PCB sit directly on top of the LCD and eliminating the two or three millimeters of glass between the mask LCD and the copper board during exposure.  What resulted was incredible results!

    Latest exposure test
    Latest exposure results

    The above was four minutes and 30 second exposure with the new lamp and new LCD glass orientation, then 2 minutes and 45 seconds in the developer solution used previously.  Notice how sharp the individual traces and pads are compared to the previous results done with my other UV lamp.  Ignore the dark boarder to the left and top - this was a scrap piece of exposure board, and the protective film had peeled slightly which pre-exposed that edge of the board.

    Pleased with the results, I decided to go to the next phase and test out a new etching vat I had put together: 

    The "etching vat" consists of a rectangular glass flower vase, an aquarium heater with thermometer, and an aquarium pump with "air stone."  Also in the mix is a 3d printed board hanger.  All is submerged in a 2 to 1 solution of Hydrogen Peroxide and Muriatic Acid (available at your local pharmacy and swimming pool supply store respectively).  I really like this mixture over ferric chloride, as it is less messy, and most important, you can see the board as the etching progresses.

    Here is the final results after only five minutes spent in the etching vat:

    Final test results

    I stopped the etch a little early because I wanted to see how well the 0.25mm trace would come out (it looked like it was about to go).  IT SURVIVED!  The copper on the top and bottom of the board is a result of how the hanger I made holds the board. It is slotted, and it actually inhibits the acid from coming in contact with the copper, so that needs to be reworked. That, combined with the pre-exposed edges made the sides take longer to etch. At about the four minutes and change mark I think the middle of the board was about ready, so I think the 0.25mm could have come out even better.

    These are all things that can be fine tuned, but I'm now confident that this unit is going to be able to produce some really nice boards with minimal effort.

  • LED test fails, but prototype exposures improve

    Joel Kozikowski04/07/2021 at 18:20 0 comments

    I finally got a chance to run some etch tests with the new unit, and sadly it failed.  Exposure time went from about four minutes up to 8+ minutes, and the results were almost unusable. As predicted in the project discussions, there was a lot of defocus problems around the edges.

    I have ordered three different UV sources to try as alternatives: one is a different LED strip with a higher concentration of LEDs and is intended to use for UV curing, and two are the actual UV sub-systems from two different mSLA printer manufacturers.

    To create a baseline (and to prove that this was only a minor setback), I went back to my prototype and made a few minor adjustments based on community feedback: Using the original "UV floodlight" I was using in the prototype, I increased the distance from the LED panel to the LCD by about 3 inches. I also centered the LEDs around the copper board (to remove the "uneven exposure" I had originally dealt with). Doing these changes, I got the best exposure and etch I've had so far, so this is my new benchmark.

    Here is the sample "circuit" I used for testing:

    Notice I am testing for traces between 0.25 mm and 1.5 mm.

    Here is what the board looked like after a 4 minute and 30 second exposure, then 2 minutes and 15 seconds in a "developer" mixture consisting of 10 ounces of water and 3/4 teaspoon of 100% lye drain opener:

    I then put the board in a small container of ferric chloride for 43 minutes, and this was the final result:

    You can see that the 0.25 mm trace was over etched a bit, the 0.5 mm trace is mostly in tact, and the 0.75 mm and beyond traces are perfect. All but one of the 16 pads for the IDC16 connector came out well, and it's fairly easy to see the difference between the square pad of pin #1 and the and round pads of the other pins.

    I'm pretty happy with these results. It is more than useable for prototype boards, which is what this device is intended for.

    During the etching process, I had time think about things and already plan for the future. For sure I am going to ditch the ferric chloride (first time I've tried it) and go back to the muriatic acid and peroxide mix that I've used before.  Ferric chloride is way too messy, but more important: you can't see the board as it's etching to see when it's done.  The 0.25mm trace may very well have survived if I had pulled it out just a little earlier.  It seemed in tact the two to three minutes prior when I did a spot check.

    Another huge idea: I've been thinking about a way to make it quick and easy to apply a solder mask to the board.  Solder masks are applied and cured pretty much the same way that the 3d printing resin was applied on the YouTube hack video that inspired this project. If I can come up with a quick way to evenly and consistently apply liquid resin while eliminating mess, this device should handle resin as a much better etch resist, which would eliminate the "developer" step. Also - the exact same process would apply to solder mask.

  • Instructions with pictures

    Joel Kozikowski03/31/2021 at 20:40 0 comments

    I've added instructions with pictures to the project page. There should now be enough information to assemble the unit, as well as install the software. Now that I have this documented, its back to running more tests to perfect exposure times.

  • Instructions and Schematics released

    Joel Kozikowski03/28/2021 at 21:50 0 comments

    I've put some VERY rudimentary instructions on how to configure a stock Raspberry Pi installation for use with the Qwicktrace hardware in the README on Github.  Also on Github are the schematics of the Hat, along with several different file formats for making the Hat (if you are so inclined).  The README can fairly easily be rolled into a single Setup script (if anyone would like to contribute it :) ).

    See the Hackaday project page for a link to the Github repo.

  • Exposing to the world

    Joel Kozikowski03/26/2021 at 20:53 0 comments

    I've been working on this project offline and now have it working.  Today is the first day I've uploaded source code and STL files needed to build the unit.  I've got assembly and software notes on my machine (or in my brain) that are not really ready for publication, so its going to take me a little time to get everything documented here.  We are talking a day or two, not a week or two. I'll get those notes published, and then will start working on phase 2 of the project, which is perfecting exposure times and chemical recipes.  You can, for example, buy a 32 oz bottle of developer for $20, and another 32 oz bottle of etchant online for another $20.  Or, you can buy a jug of lye crystals, disguised as drain opener, from the local home improvement store for about $12 and you can make swimming pool's worth of your own developer.  Same for the etchant.

View all 9 project logs

  • 1

    There are five phases to this project:

    1. Download the STL files and 3D print the case
    2. Make the "Hat" PCB that sits on top of the Raspberry Pi
    3. Make the custom wires
    4. Assemble the unit
    5. Configure the Raspberry Pi and install the UI control software

    A link to all components as listed on Amazon is available on this project's home page.  The "Make the Hat" PCB is kind of chicken and egg. I am assuming that if you are interested in the project, you already have used at least one method of obtaining your own circuit boards (whether you've fabricated them yourself, or you've ordered them online).  The Gerber files for the Hat is available on this project's GitHub page. Personally, I milled mine with a cheap desktop CNC machine that I have.  An easier approach is to send the Gerber file to a fab house and wait for it to arrive while you are waiting to get all the other components from Amazon.

  • 2
    Tools needed

    In addition to the components listed, I needed the following tools to build and assemble the project:

    1. Dupont and JST pin crimper
    2. IDC ribbon cable crimper
    3. Wire stripper and cutter
    4. M3 thread tap (to make screw hole threads in 3D printed parts).
    5. soldering iron
    6. Hex screwdriver for M3 screws
  • 3
    Make the Pi Hat

    I've placed the KiCad files, along with various versions of the traces on Github in the 'hardware' directory of the project.  It's designed to be a single sided board to make it easier to make DIY style. 

    PiHat PCB
    PiHat PCB

    The one "trick" I'm currently using to facilitate a single sided board is I'm using a 40 pin "stackable female header" (which is a female header with extra long pins).  This allows the female side of the header to be mounted on the same side of the board as the copper layer, yet still be soldered on that side. Just be sure to leave a small gap (don't mount the header flush) which will make it easier to solder from that side. 

    Stackable Header
    Mounting female header copper (bottom) side

    When mounting the 2 pin JST female connectors, be sure to pay attention to the orientation of the connectors.  If board is oriented so the Pi GPIO header is on the right, then the pins at the "top" are all power, and the pins at the "bottom" are all grounds. The component list includes pre-fabricated 2 pin JST header wires. My package came like this (one set placed in a female connector):

    JST power connector orientation

    With that orientation, the connects are mounted on the Hat this way:

    The power module is mounted first by soldering four header pins to the holes in the power module area, and then soldering the power module to the pins.  This power module is used to convert the 24 volt input into 5 VDC, which is used by the Pi, the HDMI board, the fan, and the PiHat itself.  You set the output of this power module either by turning the small screw until the output is how you want it, or you can cut the trace that attaches to the screw pot, and place a solder blob over the 5V connection to set the board's output to a constant 5 volts.  I prefer to use the screw adjustment, as you can dial in a full 5 vDC AFTER the protection diode's small voltage drop.  To do this, simply apply your 24v power to the JST XH 2 pin male component in the upper left hand corner, then measure the voltage on pin #2 of the GPIO connector (pin #2 would be first/top row, second/right column on the 40 pin connector).  Pin #39 (last row, first/left column) is Ground on this board. Dial the screw until 5 volts appears.

    The white and blue wires shown on the picture above are two additional traces (a poor man's double sided board) that add the Pi's I2C interface pins (SDA and SCL) to two currently unused pins on the IDC-16 connector. I'm doing some experiments here that uses I2C, but the current iteration of this build does does not need them. This connection IS in the design and Gerber files in GitHub, but they take this board from a single sided board to a double sided board if you are going to have your board commercially built. There are two small via holes near the IDC connector that the other end of the wires connect to if you are doing DIY but want to use them for your own experimentation.

View all 9 instructions

Enjoy this project?



bombela wrote 03/26/2022 at 22:35 point

I jerryrigged the same LCD + a random 50W UV lamp from amazon together. I was able to expose 0.2mm traces, double sided. I aligned the two side manually on the edge of the LCD itself. I used the same corner of the PCB. I simply aligned the masks on the opposite edges of the LCD to achieve that.  It was really easy to align. A proper case would add some corner bracket for a perfectly repeatable alignment. I found you also need enough weight on the PCB to keep it flat against the LCD. I did use the LCD upside down. To reduce the parallax. I was surprised by the quality of the result. I don't think my UV light is supposed to send the light rays parallel.

There is one thing odd though. If I put a piece of photoresist front of the UV light, it takes 10 seconds to fully expose it. But through the LCD it takes 15 minutes! That seems excessive. Its cooking the hell out of the LCD itself. Is it some sort of UV wavelength mismatch? How are MSLA printers doing it in few seconds?

edit: pictures of a the successful test. The hardest part is applying the photoresist film. I didn't do a good job.

  Are you sure? yes | no

John Loeffler wrote 04/29/2021 at 16:35 point

Love this Project.   If you could combine this with a simple Mill for vias this could be the next Othermill.   I was researching to do something like this and was scared of the complexity but one feature would be premade/presensitized double sided  boards with pre drilled fuducal holes so users can flip it over and do 2 sided without too much trouble.  Then a second (slow) CNC Drill can cut the holes, vias and board outline.  

Also It looks like there is a lot of light creep maybe a polarize lens should be what the PCB comes in contact with the glass on the lcd allows the light to scatter

  Are you sure? yes | no

Joel Kozikowski wrote 04/29/2021 at 16:38 point

Funny you should mention "CNC drill"/mill.  Parts are printing for that on my 3D printer as I type! :)

  Are you sure? yes | no

Joel Kozikowski wrote 04/29/2021 at 16:54 point

Simple double sided boards is my final goal.  I plan on experimenting with various frames/jigs to allow for this. Right now, the Qwicktrace software does have a "mirror" option, and it not only mirrors the image sent to it, but it does so on the opposite side of the screen.  Thus, one side is exposed with the upper left corner and left edge of board "squared" to the corner, and the other side is exposed with that same "corner" squared to the upper right corner of the screen. My hope is that any skew correction that may be required will be handled in software.  Same will go for the mill portion that drills the thru holes.  I'd like to avoid the REQUIREMENT to cut the board after the fact if possible. I have a small desktop table saw that is perfect for taking large pre-sensitized boards and cutting them down to usable sizes (like two 4" x 3" boards out of a 4" x 6" purchase, and further two 2" x 3" out of one of the cut 4" by 3"). I only want to have to mill the board edges for non square shapes.

  Are you sure? yes | no

crun wrote 04/02/2021 at 00:50 point

Way back when I used to make pcbs, I found that using a UV light box with diffuse or multiple sources e.g. flouro tubes, multiple leds etc, results in poor edge definition.  Due to parrallax, any gap between the mask plane (which is up inside the lcd glass in your case, so quite big) and the photo resist plane, means that light can come from multiple directions past the edge of tracks, and end up in different places on the pcb i.e. the edges are blurred. (commercially vacuum printing frames, and putting the emulsion down onto the photoresist somewhat solved this)

I found that having the light source a good distance from the pcb gives much more reliable results, and a point source is best. i.e. have some high power leds with lenses focused on it from some distance away.  As a matter of interest, I just used the sun on a clear day quite often.

It is a simple optical lever so 

Distance / Wsource = Tlcd / Parallax

If you want Parallax<=0.05mm , and the Tlcd glass is 0.3mm thick, and Wsource is 100mm, then 

Distance = 100 * 0.3 / 0.05  = 600mm

WSource is the diameter/diagonal of  the diffuse/multi point source. If you put the whole source through a single lens, it will be the source size, not the lens size that counts as WSource.

If instead you used a single lensed led where the die itself was 2mm square

D = 2*sqrt(2) *0.3/0.05 = 17mm

Well thats too close, but using a single lensed led at 100mm is going to give you ~10um parallax. Using the most powerfull single led is probably going to be best

  Are you sure? yes | no

Joel Kozikowski wrote 04/02/2021 at 19:29 point

Great information!  Thanks.  I do have an "LCD only" with a backlight that I can remove, which would allow me to place the board directly on the mask with no glass in between.  My initial tests had problems with under exposure in certain places, but I was using an entertainment UV light that had the LCDs concentrated in a single area, but it was fairly close to the board.  You've given me some good stuff to contemplate.

  Are you sure? yes | no

crun wrote 04/02/2021 at 22:33 point

The masking part of the LCD is on the inside, i.e. in between two sheets of glass. (above) I assumed 0.3mm for one sheet of glass. In the context of a negative for making pcbs thats _very_ thick. When we made film negatives, you made sure to print them mirrored, so that the emulsion side was against the photoresist, not on the outside of the film. The film was a lot thinner than LCD glass. 

BTW what parallax defocus really affects is your ability to make fine gaps between tracks (with negative photoresist) and to get the track and gap widths correct. 

It might also manifest in exposure and developer time becoming critical. i.e. your tracks and gaps are only OK, if you get exposure just right and the time in the developer right. When you have a high density/contrast mask, and properly collimated light source, neither is critical. i.e. you should be able to overexpose by 2x without tracks/gaps changing size.

  Are you sure? yes | no

Joel Kozikowski wrote 04/03/2021 at 00:07 point

While the LCD part I am using for the mask is a resin printer part, it in turn is actually a hi res screen from a smartphone. It is flexible and incredibly thin. That in turn is mounted to tempered glass to protect the screen.  The LCD by itself is about 0.7 mm thick. When you say “glass”, are you referring to the transparent but flexible material on this part?

In any event - my prototype tests were consistent with what you said re: exposure and/or developer times. I was dealing with highly concentrated UV in the center and not as much toward the edges, leading to uneven exposure for the same amount of time. 

My shipment of photo positive boards just arrived today (I consumed my previous supply with the prototype) so now I can repeat my tests with this new unit

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crun wrote 04/03/2021 at 00:44 point

> The LCD by itself is about 0.7 mm thick. When you say “glass”, are you referring to the transparent but flexible material on this part? 

Yes. There is glass, then polariser plastic stuck to the outside.

The image is formed in the middle of the 0.7mm thickness i.e. 0.3mm above the photoresist.

> actually a hi res screen from a smartphone

So is it just a normal colour lcd then, and not a special monochrome one?

  Are you sure? yes | no

Joel Kozikowski wrote 04/03/2021 at 19:43 point

> So is it just a normal colour lcd then, and not a special monochrome one?

Yes, this one is color.  The monochrome LCDs are more expensive as monochrome MSLA printers are relatively new.  No reason a mono LCD couldn't be used, other than price.  This is intended to be a homebrew machine, so I am trying to see if I can keep costs down using less expensive parts.

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Joel Kozikowski wrote 04/05/2021 at 23:07 point

I've done some additional digging, and have uncovered some interesting facts.  Many of the mSLA printers available are using sub-systems from a company named Chitu Systems.  They have a "parallel UV light" fixture which appears to use lenses to correct for the parallax and makes the UV beans parallel. It is a tad bit pricey at $75 USD, but not out of the ballpark. I've also located some other manufacturers that have UV lights with corrective lenses that are in the $35 USD range, which makes them a little more practical.  I've ordered a pair of both for experimentation.

Once UV is corrected for parallax, the primary difference between the use of color LCDs and monochrome LCDs appears to be exposure time. The monochrome LCDs allow more light through, and thus needs less exposure time. It seems, however, that the monochrome LCDs seem to be special purpose built for the mSLA printer guys, so they also make some adjustments to the polarizers.

I found this blog post from Chitu Systems helpful: helpful:

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demski wrote 03/29/2021 at 12:12 point

What an awesome idea! How do you make sure that the board has full contact to the screen? I assume there must not be any gap between the two, right?

Have you already had time to test what the smallest pitch would be with sharp contours?

  Are you sure? yes | no

Joel Kozikowski wrote 03/29/2021 at 15:22 point

The copper board sits directly on the glass of the LCD screen (the screen is a replacement part for a Mars Pro SLA printer, so the screen is attached to the glass). The "Lid" part then sits on top of the board to hold it in place. I've thought about adding a weight to it, but right now, I don't think it's necessary. The lid really serves more to block external light than holding the board down.

My first prototype used a pre-assembled blacklight used for entertainment purposes, and the exposure was uneven across the board. This build uses UV LED strips, and I can control the intensity of the light, so it should be more even (though I really need to try and find a good diffuser layer).  I have a test pattern to print, and the results were just "OK" with the blacklight - but again, it was uneven intensity at 100% only.

I am going to re-run my experiments with this new build shortly. I am hopeful that a slightly longer exposure time at a less than 100% intensity will be the ticket to a perfect mask. A lower intensity should not leak thru the black masked areas as much I think.

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crun wrote 04/02/2021 at 22:39 point

> A lower intensity should not leak thru the black masked areas as much I think

See my comments above about exposure sensitivity above. If you are using a normal LCD backlight, it is almost certain to be causing major parallax defocus.

But also, if you think about normal LCD's , you would notice that they only really have best contrast at a single viewing angle. Again, getting a collimated / single point light source a reasonable distance from the LCD will probably also increase the actual contrast of the lcd masking significantly as well. (You might also be able to adjust the lcd contrast voltage to improve perhaps)

Further, polarisers are also tuned for visible light not UV/NIR. Making a photodiode sensor so you can actually measure the actual UV light on/off levels vs angle/contrast voltage is probably well worth the trouble.

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Joel Kozikowski wrote 04/03/2021 at 00:29 point

@crun - For clarity: what the consumer resin printer guys do is take a hi res LCD meant for a smartphone, they remove the backlight, then they attach it to tempered glass to protect the LCD from the resin tank that sits on top of it. They then place a UV projection system under that. I am basically doing the same thing with the LCD part, but am using LED strip lights as the UV source in hopes of cost savings. 

Depending on the next round of testing, I could end up repurposing their UV apparatus (the ones I’ve seen use some specialized lenses which I presume helps with evening out the UV light). Of course, if I do that, I will have ended up building 2/3 of a resin printer. 

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crun wrote 04/03/2021 at 20:26 point

> They then place a UV projection system under that. 

Is it LED's or some kind of arc lamp? Do you know what wavelength, and what wavelengths your photoresist is sensitive to?

>they attach it to tempered glass

The thick sheet of tempered glass makes the parallax defocus much worse, so they need a very well collimated light projector. 

>the ones I’ve seen use some specialized lenses 

I would guess that fancy lenses would be a short-throw projector. They want a short box. Short is what makes it difficult. If you bring the distance out to 1x-2x the screen diagonal it is easy.

The key question is can you get a workable exposure time (<5mins) from a single LED at 6" from the screen. Start with a high power lensed LED. You can get leds with 60deg lens moulded on. You can also get 30degree external lenses. 

>which I presume helps with evening out the UV light). 

It is very easy to even it out: Multiply your pcb image x illumination map.

Since it is a visible colour LCD, the different colours will transmit different amounts of UV (and this will depend on the LED wavelength), so the illumination map is different for each colour.

 (This also means you need to do some testing with you photo diode to measure the transmission of 100% R,G and B images. It is also key that you actually do get your UV through the green and red pixels, and not just blue. Otherwise you are relying on defocus and what light goes through the blue pixel, and will never be able to get very sharp pcbs, no matter what you do.)

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demski wrote 04/06/2021 at 04:16 point

Thanks for the response! That answers it.

Be aware that the longer you expose, the more light "creeps" through at the edges which will make lines thinner than designed!

In the offset printing industry, before laser imaging of printing plates became a thing in the 90ies there was the need for a calibration process to ensure the correct dot size when "copying" the printing film to a plate. There were fairly big machines that produced a vacuum inside to ensure perfect contact between film and plate and a meticoulously fine tuned exposure time. The wrong exposure time would have produced wrong colors in CMYK rastered images…

Here some more insight on what I'm talking about:

As these machines are all out of need there must be a used market for plate making machines…

Btw: Why do you go through the pain of constructing the whole UV-light-construction? Is there any other advantage besides saving money?

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Joel Kozikowski wrote 04/06/2021 at 15:18 point

> Btw: Why do you go through the pain of constructing the whole UV-light-construction? Is there any other advantage besides saving money?

My first prototype used a pre-assembled Black light flood light. It "sort of" worked, but the exposure was not even. The use of LED strips is an attempt to even out the exposure.  User @crun pointed out the problems with non-parallel light beams, so I've ordered two different UV assemblies created specifically for 3D resin printers. They range in price from $40 USD to $75 USD, so they do add to the cost of the build. We'll see if the extra money is worth it.

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Dan Maloney wrote 03/26/2021 at 18:24 point

Trying to wrap my head around this: are you basically making a one-layer SLA printer, and printing the mask onto the PCB?

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Joel Kozikowski wrote 03/29/2021 at 15:22 point

I am using pre-sensitized copper boards.  No resin is used. The SLA printer's LCD is re-purposed to mask the UV light directly on to the copper board. Take it off the exposure table, and drop directly into the developer to remove exposed etch resist, then drop that into etchant to remove the copper

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Dan Maloney wrote 04/01/2021 at 17:44 point

Gotcha, thanks. But you know what -- my idea wouldn't actually be that bad. At least if you didn't have pre-sensitized boards for some reason ;-)

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Joel Kozikowski wrote 04/03/2021 at 00:17 point

So, using actual resin for etch resist with an actual resin printer was the inspiration for this project. I saw a guy do that with success on YouTube (after some crazy hacks to his printing process). My thought  was that presensitized boards would be significantly less messy than using resin. That being said, today I was using my resin printer, and I had a few thoughts that may make the process less messy. I may in fact give it a try with this unit with one simple modification. My goal is the best traces for the least amount of effort and time from CAD to soldering. 

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