I've been experimenting with various setups for PCB etching, and thought I'd share one of the more useful things I'd found, as I don't see much information about the subject anywhere else.

I've been etching using a mixture of HCl and HOOH (see http://www.instructables.com/id/Stop-using-Ferric-Chloride-etchant!--A-better-etc/ for more details) and have no access to a laser printer, which rendered the traditional method of resist application impractical. While thinking of other easily-applied materials, I ended up testing white-out (very poor; dissolves in the acid, porous, not easily removed by acetone), scotch tape (very good, but very hard to apply correctly) and petroleum jelly.

  • There was one particular red marker that used to be popular for homemade boards "Staedtler Permanent Lumocolor". A lot of those type of products have been reformulated to make it safer in case an infant gnaws on it or whatever, so it may not be as good as it used to be. – Spehro Pefhany Feb 10 '16 at 4:25
  • If petroleum jelly gives the resolution you need then try coating the whole board with a thin layer of paraffin (wax), then cut and scrap off wax lines where you want the etching. After etching just heat the whole board to melt away the remaining wax. – Nedd Feb 10 '16 at 6:00
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    @SpehroPefhany Staedtler is still my go-to-brand for touch ups of scratched resist. Although we may have a different formulation here in Europe. They still smell the same as 15 years ago as well. – Asmyldof Feb 10 '16 at 8:21
  • @Nedd That's actually a really good idea. I can think of a couple potential problems - such as wax not adhering well to the copper, letting acid seep between it and the board - do you have experience with doing this yourself? If not, I may have another experiment to do... – P... Feb 10 '16 at 22:20

After cleaning it with Acetone, I spread two different thicknesses of petroleum jelly on my copper-clad board (about 1 mm and 3 mm thick), and scraped away jelly with a toothpick along where I wanted to etch. As an additional experiment, in an otherwise empty section of the board, I wiped off most of the jelly with my finger, leaving just a very thin layer.

After a few minutes the etching was finished. The etch was pretty good; everywhere the jelly covered was protected, and although some of the thinner lines had some copper left they were well-defined enough to be easy to clean up with an exacto-knife (I would recommend using something slightly broader than a toothpick to do the scraping, and to spread the jelly thinner so that there is less chance of residue flowing into other lines). The jelly acted as an equally good resist at all thicknesses, including where I'd wiped most of it off.

  • Interesting, but it doesn't sound at all amenable to any sort of computer-driven process. I mean, people have put Sharpie pens in X-Y plotters and produced PCBs from their CAD systems, but how would you apply/remove something as messy as petroleum jelly in an automated way? – Dave Tweed Feb 10 '16 at 4:51
  • Quite experimental but good idea. Could you post pictures of the board before and after etching? @DaveTweed: Could a dispenser be used to lay traces of petroleum jelly? Or even a modified 3D-printer head? That could also advance the whole fab-community in respect to integrate electronics on surfaces. – Stefan Feb 10 '16 at 7:35
  • One small note: Acetone is a nasty variant of the three-carbon-alcohols, Iso Propanol (IPA) is less hazardous to your skin (and at least short-term brain function) but performs as well to clean smooth(ish) PCBs with finger prints and other fatty/oily marks. – Asmyldof Feb 10 '16 at 8:24
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    @Asmyldof Acetone is absolutely not an alcohol (it is a ketone), and actually twice less toxic than IPA. – ilkhd Feb 10 '16 at 10:08
  • @ilkhd You're right, I was wrong about the comparison of internal toxicity, I apologise for my confusion. Although Acetone does dry out/damage skin at a higher rate. I wish I could remember which chemist once implied on my current memory the faulty knowledge I just shared, so I can ask what he'd said exactly. – Asmyldof Feb 10 '16 at 10:20

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