Introduction: SLA 3D Printer Acid Etched Circuit Boards
Remix..remix.. Well, I need a development board for my ATtiny chips. I don't have a CNC to cut a PCB I don't know Kicad, and I don't want to order boards. But I have a resin printer... and acid and I know SketchUp. And like to make things. What happens when you mix SLA Resin printing with homebrew PCB etching? Lets find out! Inspired by Chris Garrett's laser etching project.
I had an idea. I was wondering if cured SLA resin could be used as etch resist for making my own PCBs at home. And you know what? Turns out it can be! And uncured resin is washed off by Ferric Chloride (win win!) So I made a design in SketchUp 2017 for an ATtiny development board idea I had and dove head first into the rabbit hole of making things do what they should not do. If you want to see all the wrong ways to do this check out my YouTube channel. The video of this will be up soon here
But let's not dwell on my mistakes. This is how you can do it yourself.
You will need the following.
Blank copper board, Ferric Chloride, Acetone, A green scouring pad, Electrical tape, Scissors, Standard 405nm Photopolymer Resin, A resin printer, A 0.8mm drill bit and a way to hold it, Jar with an airtight lid, A sturdy acid proof container big enough to hold your PCB (Pyrex is best), A bit of bent wire, A well ventilated work area, Nitrile gloves, Goggles, Paper towels an STL file of the pattern you want etched. And the willingness to jab bits of wire into the end stops of your nice new SLA printer.
Step 1: Clean Your Board and Add the Tape
The tape should keep the copper off the vat but if your board has any sharp edges knock them off with some sandpaper before prepping. Add two strips of electrical tape on each side of the board right on top of each other (After I changed my FEP I was able to make it one layer of electrical tape and increase the resolution). Don't pull the tape when you put it on cause that will make it thinner and mess things up. You can trim the extra tape with your scissors. This will provide the proper gap between the copper and the membrane in your vat. Now scrub the copper side to side with the scouring pad in nice straight lines. No circles or changing directions. Clean it with the Acetone and let it dry. Now don't touch it.
Step 2: Abuse Your 3D Resin Printer
Now you have to trick your printer into thinking it is in the right position to print. Manually raise your platform with the touchscreen so it is up about 2/3rds of the way. Now hit your Z home. As the platform is moving down trigger the sensor at the bottom of the Z axis with the bit of wire (or a long allen key). Your platform will move up a bit and start coming down again. Trigger the sensor again and it will stop. Now remove your platform.
Put a blob of resin on the membrane where the image will show up. Do not shake your resin. Air bubbles will really mess things up. Lay the board copper side down on the resin. Kinda put one edge down and tip it till it is flat. You don't want to plop it straight down and catch a bubble.
Take your platform and put it on top of the copper board. It'll want to slide around especially if your machine isn't level but after a few seconds the weight of the platform will press out all the extra resin and you can put everything centered.
Now grab your bent wire, find your sliced file and hit print. Your platform will try to move again but just trigger the sensor at the bottom of the Z axis again. Let the first layer expose and then shut off the machine. Don't just hit stop because your platform will try to raise up and it will crash the upper limit. There is no upper Z limit switch to stop it.
Step 3: Etch
Remove the platform from on top of the PCB, Slide your vat out of the SLA printer and gently push up on the underside of the membrane till you can get the PCB out. Dab the board clean with paper towels and throw it in the etchant. Do not UV cure it. Don't expose it to sunlight or bright fluorescents. Do not rub with a brush or anything in the acid. Just tip the Ferric Chloride bath gently back and forth till the uncovered copper is gone. If you stop rocking your bath the board will float up and the etching will stop. Shown in the etch bath is a failed twenty layer attempt. Your board will not look like this it will only have a single layer.
Step 4: Drill and Peel
Wash your new PCB, remove the tape, drill the holes and use the tip of a blade to peel off the resin that drilling didn't break. Tiny holes won't etch but a little dimple will appear in the resin showing you where to drill. Use a cleaner knife than I do... I think I'd die if that thing cut me. Time to swap that one out. Gross.
Step 5: Assemble!
A couple swipes of the scouring pad and your board is ready to solder! Put your new toxic goo in a properly labeled jar and keep it somewhere dark so it doesn't do....whatever the heck it is capable of doing now? I have used mine about ten times so far and it seems to be working just fine.
What the board does. The board breaks all the (easily) useable pins from the atTiny out to a point next to a positive rail and the ground plane. I program my chip on another board that attaches to an Arduino Uno. You can attach sensors, displays, buttons, potentiometers or whatever to the free pins. In this example I have attached LEDs to the legs and then jumped over to ground with a resistor on all the available legs. The reset leg goes to a switch. I have Red,Yellow,Green arranged in a stoplight pattern on one side and blue and white on the other. The little half moon on the board indicates the top of the chip where pin one's dot is. This little board would be nice for controlling a stop light in a scale model or maybe flipping dollhouse lights on and off like someone is moving room to room. Feel free to modify the file as you see fit. It is posted at the bottom of this instructable.
I am very happy that this new method works so well. If you would like to use this method for your own entertainment or projects it is GPL licensed as open source in the same way as the RepRap project. So if you want to patent this method you can't. It's out here for the makers. Not for the patent trolls.
If you would like to chip in on another bottle of resin you can PayPal me at email@example.com
If you want to play with the file I have included the SketchUp 2017 file and an STL. You will have to slice the STL file for your own SLA printer. Mine is an Elegoo Mars at the default settings.
I hope you found this useful. Please vote for my ATtiny development board in the remix contest.
Step 6: Calibration
After I changed my FEP I was able to use just one layer of electrical tape for a spacer and get higher resolution. Anything over half a millimeter turned out really well! so half millimeter traces, 1 millimeter diameter holes and half millimeter gaps all turned out perfect. I could probably use .2 millimeter traces with .5 millimeter gaps if I wanted to really push it but this is just fine for anything I would want to do at home. The board is for using an Arduino UNO to program an atTiny. It just needs a 10u cap, an LED, appropriate resistor, headers and a dip socket. *** The programmer has a few things backwards so I took the file down. I'll add it again after I fix it. And for those who were curious yes resin makes a great solder mask. I put a tiny bit on each trace just before the solder pads with the tip of an exacto knife then cured it with a UV light. It kept the solder from leaving the pads and turned out very neat!
Step 7: Solder Masking
I made a small sprung PLA frame for putting the board back in the same place. This is for exposing a solder mask after etching. If you do this don't drill the holes until after you expose the mask.
Participated in the