I am making my own PCBs at home with printing on laser printer. Creating copper layer and non-soldering pads is easy, but I would like add documentation layer too and now I am stuck. How do you solve this problem?
Is there an easy way to doo that? Thanks for all suggestions :)
I fount this https://www.aliexpress.com/item/Super-PCB-UV-photosensitive-inks-white-PCB-UV-curable-solder-resist-ink-solder-mask-UV-ink/32684337516.html and first test came out good:
First of all - I am really happy and satisfied.
The ink came good packed, wrapped in a lot of plastic bubles and the container itself was packed in extra layer if thin plastic. Anyway a part of the ink was split over the can, not much, as the inner plastic keep it tight as you can see. The can screw is not very tight and in consideration, how long it traveled (free delivery), the result is not bad at all.
I used part of those splits (not nearly all) for fast test - treated it as other UV curable solder resist - I run it thru cold laminator in plastic bag, placed laser-printed clear scheat over it, weighted it with glas and exposed for 20 minutes (maybe 10 would be better as some small point was hollowed, but did not cler fully after), then gently rub it with spirit (alcohol, C2H5OH).
You see result on the last foto - even small pads for SMD parts (atmega328) went well. There is a big hole in lower part, where the ink stuck with the bag instead of PCB - I blame myself to not clean the PBC at all and it will went better next time, as I get better with this ink and adjust my process for it.
The result was basically really really good. But the smalest letters was not fully readable as its insides went all away, while some other little holes (the spotted line on top) end hollowed, but not fully cleaned thru. As I want it for Silk Screen mainly (those names printed all over PCB) it is not problem, I just would use 2. smallest fot and use it in bold variant. I tried some markers to write over, but none stick well. So dirt would probably also not stick. The painting is not as hard as green UV solder mask, can be mechanically scratched off easily (as in winning ticket - cratch this area and if you find 3 stars, you won). So for soldering it is OK, but not for long time protection/duration under mechanical influence. I will engrave core info to the copper anyway, this I would use for more visual hints.
Maybe more UV after-curing would little hardened it too.
The color is nice glassy white after curing.
As you can see, it is negative (what is exposed to light will remain, what is hidden goes away )
Edit: 2017-06-16: I tried to make full documentation and hit some problems:
- as the white covers the PCB, nothing under it can be seen, so it is extremly hard to right align the printed mask (I should made some marks away from covered area just for this reason)
- it does not stick well to the green non-soldering paste - cleaning unexposed white many times take small parts of exposed white away too (even if it was hardened and separated well from cover, leaving empty space on it)
- also if there is any miss-alignment and the white cover some sordering pad, even if I cut the white before removing, usually also some other parts went off. Finally from like 30 marks was left only like 10 and half of it was moved from original point.
So the white ink performed even worse on the non-soldering paste then on uncleaned PCB. I will try combining layers of grean/red/yellow/blue pastes next time as the masks can be preciselly aligned and smaller details can be used to form symbols. I will report then here too.
I will use the white ink only on small parts of PCB next time - like logo, version or date aligned with decorative copper parts of PCB only.