4
\$\begingroup\$

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?

I can do PCBs like this This is what I can do, but I would like to add the while texts on them too like here enter image description here

Is there an easy way to doo that? Thanks for all suggestions :)

EDIT

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.

the can some waste

The can is half full, see content and so much - I show, how much full was. It will last me for years, I think.

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.

Test of the same mask

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.

\$\endgroup\$
4
  • \$\begingroup\$ Nice PCB you make at home! I’m curious: how do you make the solder mask? As for the documentation, I think it should be possible to print it mirrored with a laser printer and then transfer the toner on your PCB (perhaps before the solder mask). You may find a lot of information about toner transfer, for example: instructables.com/id/… \$\endgroup\$
    – user2233709
    Apr 8, 2017 at 9:23
  • \$\begingroup\$ I print it (mirrored) on laser printer to the projector sheet (transparent one, made for laser printers), for basic copper I use positive photosensitive way (black lines does remain there) UV LEDs to make exposition, NaOh to remove exposed film, then FeCl3 to remove copper. Then I expose it UV again (without mask) and remove the rest of mask with NaOH. For solder mask I use negative way (black points came out) and dx.com/p/soldering-green-oil-for-pcb-fbc-board-10ml-145565 UV green paste. Clean out unexposed parts (pads) with C2H5OH (spiritus). Tin-lead the pads manually. \$\endgroup\$
    – gilhad
    Apr 8, 2017 at 18:43
  • \$\begingroup\$ Thanks for your information, I didn’t think it was this easy to make a solder mask. \$\endgroup\$
    – user2233709
    Apr 9, 2017 at 21:00
  • \$\begingroup\$ Basicaly it is. There are some details, as how to make the paste thin and equally plain (I use clear pockets for A4 papers), the paste have unlimited potential do make everything dirty, you need UV source (like home made, or the one for nails or anything like that) and do some experiment, how long to expose and how concentrated chemical use, and align the mask eith the pads unde it good ... but basically it is really so simple and easy (IMHO easier and more reliable than toner transfer, but I had seen toner transfer only on youtube) \$\endgroup\$
    – gilhad
    Apr 10, 2017 at 8:06

2 Answers 2

Reset to default
3
\$\begingroup\$

Note: We call it Silkscreen (SS) layer not documentation layer.

print screen uses white epoxy ink and SS screen then baked. Can you make these this or know someone who can? If not then try Laser reverse print using color or black Toner and transfer like this .

I use Irfanview to easily reverse images Vertical and horizontal.

http://youtube.com/watch?v=MQsKOczo1gU

Then use acetone and alcohal as shown.

\$\endgroup\$
2
  • \$\begingroup\$ You are right, it is SS layer,my bad. I use GIMP for image manipulation, but anything works for such simple tasks as mirroring (and small improvements of traces/pads/separation lines). As I replyed elsewhere here, I would like to use photo sensitive path, as like for other parts of the process (etching mask, solder mask). I had problems with toner transfer some time ago, as I was not able to get consistent and sharp results so I need a lot of manual fixing. Photo way let me use the same masks for more PCBs and get identical results. I usually do 2-4 PCBs of kind at least, to share with friend \$\endgroup\$
    – gilhad
    Apr 9, 2017 at 10:41
  • \$\begingroup\$ Also got to some interesting sites from your link, which aswered some of my other questions even before asked them actually :) \$\endgroup\$
    – gilhad
    Apr 9, 2017 at 10:42
1
\$\begingroup\$

You can transfer toner to the PCB same as using it for etch resist, but there are two disadvantages:

  1. There is not usually white toner available. Black may work for you, or you could try a colour laser toner- cyan, magenta or yellow.

  2. The toner comes off rather easily with solvents used to clean the board after soldering.

The normal way is to silk-screen print the designators. Once you have the silk screen made all you need is white epoxy ink or UV cured ink. Since there is not much ink compared to the PCB area, it's not as messy as printing solder mask.

For very fine printing there are also liquid photo image (LPI) methods, but that's a bit much even for some commercial PCB houses. The same method may be used for high-resolution solder masks.

\$\endgroup\$
5
  • \$\begingroup\$ oops edited wrong one then undo \$\endgroup\$
    – Tony Stewart EE75
    Apr 8, 2017 at 11:31
  • \$\begingroup\$ Thanks, I think also about the LPI (or something like that). I did more research and found on aliexpress this ink - I hope it could be used the same way as solder mask - aliexpress.com/item/… - I see the problem, that my laser "cheats" on large black areas by "saving" toner, so it looks black from far, but is more like grey dalmatin on close inspection, so the cover is not perfect. But it is mainly problem on etching, hope it would not hit here much. \$\endgroup\$
    – gilhad
    Apr 9, 2017 at 10:29
  • \$\begingroup\$ Also found this aliexpress.com/item/… yellow paste, so I may try do the solder mask yellow and then overlay green mask with yellow letters left empty. Not sure, how resistors and leds would react to double layers solder mask - if it would not be too deep for good soldering. I hope pin-legged pieces would fall inside the holes and have no problems after all. (also I would probably need to increase the pads on the outer layer to avoid alignment issues) \$\endgroup\$
    – gilhad
    Apr 9, 2017 at 10:33
  • \$\begingroup\$ @gilhad Nice find. Please update when it arrives and you get a chance to try it out. Paste through mail is a bit iffy legality-wise but chances are it will get through. \$\endgroup\$
    – Spehro Pefhany
    Apr 9, 2017 at 16:35
  • \$\begingroup\$ I bought the green paste last year there and it works well. (Also bought a lot of small electronic pieces the same way - some arduinos-like, transistors, resistors in book, sensors...-nearly everything worked as expected and none was blatlant theft like stone instead item), so it payed off a lot. I do not know, why the paste should be of bad legality - apart of being cheap unlicenced copy, but I do not target for a brand name, but for working tool - if it is not sold here at shop, I will buy elsewhere. (And if it happens to be first item not working, the other buys still made it for the loss.) \$\endgroup\$
    – gilhad
    Apr 9, 2017 at 21:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.