DIY PCB Etching

Who needs CAD when you’ve got a sharpie and some HCl

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More of a chemistry question, but is ferric chloride essentially rust(iron oxide) dissolved in HCl and then boiled down to get rid of the hydrogen from HCl and the oxygen from rust? Or is it a bit more difficult so something that should just be bought in its usable form?

Oh hmm I don’t know actually, but I do know you can keep reusing the acid many times.

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Did some research, looks like yes! Found this formula:
6 HCl (aq) + Fe2O3 (s) --> 2 FeCl3 (aq) + 3 H2O (l)

But also looks like HCl will oxidize the iron too, the reaction is just not as efficient, would take longer, and produces hydrogen gas instead of steam.
Fe (s) + 2 HCl (aq) ---> FeCl2 (aq) + H2 (g)

Together this makes it pretty easy to make with a combination of both, so honestly, yeah, making your own ferric chloride seems like the way to go!

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Brings back memories … I used to do this for quick prototypes back in the day way before getting fabbed boards from China was affordable. I think I still have a few bare sensitized boards and a bottle of ferric chloride hiding somewhere in my lab. I guess instead of CAD you could consider it HAD (hand aided design).

I used the toner transfer method to create the arudbracelet before the batch fabs started offering flex circuits.

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Would be very interesting if someone made a whole Arduboy out of it (But also quite challenging). Though the video shows a lack of any safety which is concerning, even wearing surgical gloves or anything to keep it from skin contact would be good.

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I might try this out, been experimenting with the chemicals I have on hand to make a similar solution, just got it working reliably yesterday and today. I didn’t have HCl on hand, nor did I have FeCl3, so I had to improvise. Luckily, getting there wasn’t too difficult, just a bit of a game of finding out when to do what reaction. I used only five things, all which are probably around your house:

  • Acetic acid (vinegar)
  • Hot Water
  • Table Salt (NaCl)
  • Hydrogen Peroxide
  • Chunk of iron (more surface area the better, rustier the better, but neither are necessary qualities, they just make the reaction go quicker)

At first I was trying to make HCl in solution by dissolving table salt in acetic acid which I concentrated by fractional freezing. This was honestly a bust, and while it did produce some results, just wasn’t worth the extra effort, and the higher concentration proved to be a detriment, slowing down the reaction and producing something I still haven’t figured out. Even without concentrating, this reaction just wasn’t efficient enough by itself. While it was making HCl, it just wasn’t doing a good job of it.

In comes the solution, peracetic acid. This is pretty easy to make, just mixing hydrogen peroxide into vinegar. I found it works better with a bit more vinegar than hyrdogen peroxide. The paracetic acid solution is already highly corrosive itself, so caution is necessary! Keep baking soda on hand to neutralize acids you’re working with, and always wear glasses or goggles! This stuff isn’t a big deal if it gets on your hands, but you don’t want to put this stuff down your drain either, so it’s a good idea to have a basic solution nearby for washing purposes (though in earnest I just wipe it off, I haven’t had any big spills yet).

Once you have your peracetic acid solution, you can add salt. it should dissolve very easily but a little hot water can help move things along and won’t really change the reaction much. Once it’s dissolve, add your chunk of iron and wait for the solution to turn dark. At this point it’s ready to be used! Still figuring out what this stuff won’t eat, as it ate right through sharpie, but it works great for removing copper from PCB!

Use safety! Googles, gloves, ventilation, masks, rain coats, steel toe shoes, knee-pads and fall arrest equipment at an absolute minimum!

Arduboy does not condone the use of chemicals do so at your own risk!

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Vinegar, hot water and salt make sense, but I have no clue where you’d get pure H2O2 or iron from. Finding them in other things is easy enough, but extracting them or finding them on their own seems a hassle.

I should’ve been more clear, I was using household materials. So 5% acetic acid vinegar and 3% Hydrogen peroxide. Grocery store stuff. The iron doesn’t need to be pure either, it’s enough just to throw in an old nail or two that are not galvanized. So long as they’re relatively clean (rust is fine & good, but not dirt or paint, etc stuck on it) the reaction goes well. If it’s got stuff on it that hasn’t been washed off, it’ll bubble over slowly, creating a thick foam. I used an old screw that had a thin layer of rust over most of it. I let it corrode for maybe 7-8 hours at room temperature, though I suspect that time could be dramatically decreased just using a hot plate. I also did one version with aluminum instead of iron, which was a much slower reaction but if I filter it all out at the end, it may be a nice source for oxidized aluminum.

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Ok, so you’re saying any substance that contains at least 3% hydrogen peroxide?
E.g. toothpaste, hair dye and so forth?

That makes more sense, although I would have thought the other 97% of the solution (e.g. things like phosphoric acid and sodium stnnate) might hamper the reaction.

Most places I can find don’t really give percentages either, so it would probably be pot luck as to how much you’d actually be getting from a product.

If steel worked as well as iron then there wouldn’t be any problem. Otherwise, it would have to be a fairly old screw - most are steel these days.


For the record I’m not actually planning to attempt this, I was just interested in how you’d actually aquire suitable materials, but it’s nice to know I could do it if I wanted to.

Not as such. I used 3% hydrogen peroxide topical solution, common for debriding scrapes, cuts, and burns. The other 97% is purified water.

True. Steel should work, just slower. I don’t think the extra carbon from the steel would be an issue, but there’s no way to know until it’s tried.

Here’s a really nice video demonstrating how you can use a paper printer, a magazine, and some nail polish to transfer the actual traces:

But there’s plenty of videos out there that demonstrate different methods, I personally like this one because it’s more reliable for the traces.

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Very neat!! I’ll have to try that

Oh that’s cool! I laser printed onto transparency paper and then used a laminator to do the heat and pressure but this seems super easy!

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After a lot of digging I finally managed to find something similar.
In the process I’ve learnt why it’s not so easily accessible over here.

Apparently some chemists do stock it, but they ask a lot of questions about why you want it because it’s sometimes used for making things that good law-abiding citizens shouldn’t be making. (The kind of thing that goes ‘boom’, if you get my meaning.) I’m glad I found that out before asking at the local chemist’s, otherwise I’d probably have ended up on a police watchlist.

Thus, with a satisfactory answer, my foray into chemistry comes to an end.

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