etching pyralux circuitboards with a Phaser wax printer

i designed the circuit in KiCAD, the Free and Open-Source Software package for laying out circuits. It's much better than Eagle, and you won't go to hell for using non-free software.
For the future, remember that 0.013\" gaps are too small (like on the bottom right) and if your circuits should be a certain size, fill in the cutout parts with copper so you know where to run your scissors - otherwise you're stuck eyeballing it.
also it's nice to reduce the amount of copper that dissolves in your etchant by covering it with ink.

after you print your circuit on a piece of paper, measure with a ruler to see if the scale is correct! I had KiCAD plot the circuit to .SVG format, which I think is most likely to keep scale all the way to the paper. I actually printed from a web browser.
Cut out the amount of pyralux for your circuits, leaving EXTRA which will be covered by tape! You need to put a piece of tape across the leading edge (where it feeds into the printer) and then feed the same piece of paper through, in the original orientation.
I always use manual feed for the paper. Write a little arrow on the paper before you feed it in, so you can remember to put it in the same way the second time around (after you tape on the pyralux). Otherwise you'll end up upside down or backwards or something.

after running it through the printer, your circuits will be in wax on the copper. I didn't pre-heat the pyralux as it was about to go into the printer, but doing that with a hair dryer might help the wax to stick better than it did.

i knew there was trouble when these perfectly-shaped pieces of wax started popping up.
this is the Ferric Chloride etchant. you can see the pieces of wax that came off of the first piece of pyralux that i etched. This does not happen if you put the piece in the oven first, to melt the wax in, which is the next step. Alternately, it might help to somehow heat up the pyralux just as it's going into the printer, but the oven seems much easier.

this is the first batch i etched. Most of the wax ink flaked off of the copper before it was finished etching, thus the visible corrosion. five of these worked fine, three more looked fine but I didn't try them. The corrosion came off with sandpaper and they were fine.

i used this infrared oven to heat up the second piece of printed pyralux circuits, to cause the wax to melt in, so it wouldn't come loose like it did in the first piece i etched. I turned it off when it reached 150 degrees C, but I will stop at 120 degrees next time since 150 was too much (the wax spread out a tiny bit)
you could probably achieve the same effect with a toaster oven.
MAKE SURE YOUR PYRALUX IS FLAT TO MINIMIZE WAX MOVEMENT

these were the unusable ones, as the ink melted in the oven and caused bridges in the copper. I didn't etch them because they obviously would not come out right. Of course you can easily scratch off the wax and then etch it, but i didn't do that.
but i still might, or maybe i'll remove this wax and print something else on this material.

don't be like me, don't do this until after you bake the wax in.
pour some etchant into a tray (not a metal one!) and drop your waxed pyralux in there so it etches.
if you don't heat up your etchant somehow before you start, it will take a lot longer to etch. I recommend heating up a pot of water and resting the bottle of FeCl in it to warm up, after loosening the cap on the bottle so it doesn't pop from heat expansion. You could also heat up the FeCl with a hair dryer but that sounds like a PITA.
When i finished etching (after plucking out the wax floaters) i put the used FeCl back in the bottle. It's still good.

the floaters are still there from the first batch, i picked them out with a piece of paper while waiting for etching to happen. This piece of pyralux was in the oven and turned out well.
yes the pigment in the wax ink migrated to the center, but there was plenty of wax in the right places to cause a perfect etch.

these were etched after baking the ink on there to 150 degrees in the infrared oven. You can see that even though the pigment bunched up in the oven, the wax still did its job.

the pyralux is thin enough that light shines through. You can see that on the top right of some of them, the 0.013\" gap is not enough to prevent bridging.
you can prevent this by setting and observing \"design rule check\" in KiCAD and not having gaps less than 0.015\" or whatever you can get away with.

program all the chips before you solder them onto the boards. I wrote a bash script that attempts to program a chip, and makes a happy or sad sound depending on whether it worked or not. Then it waits 5 seconds, makes a beep, waits another second, and starts over.
This way, you have both hands free to fit the chips in the programming clip, and you can get into a rhythm.

this was the ugliest one, the first one i made. it worked though, barely. You can see that a trace at the fold was no good and i jumped it with a strand of wire, but it's a delicate repair, especially since this is a USB stick and needs to be durable. But I started with a badly etched piece to save the good ones for later.
I made a mistake in the CAD and used a narrow SOIC footprint for the chip, it's actually SOIJ and 2mm wider. Fortunately I was able to snip off 3 legs and move the capacitor and everything worked out.
The black crusty stuff is burned flux from the solder paste i was using, and the iron. who cares.

etching your own circuits this way is much easier than the toner-transfer method, and yields FLEXIBLE circuits that you can stack for multi-layer boards!
yes they all worked. The chip is an ATTINY85-20SU and it's loaded with micronucleus firmware so you can upload to it from USB and make it do anything.

NOTE: i am not the first person to do this with pyralux and a wax printer, i first heard about it from Meredith Scheff-King, whose instructable does not say anything about what kind of printer works (A LASER PRINTER WILL NOT WORK FOR THIS)
here's a link to her instructable

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