Ask Hackaday: What’s Your Etchant?

Although the typical cliché for a mad scientist usually involves Bunsen burners, beakers, and retorts, most of us (with some exceptions, of course) aren’t really chemists. However, there are some electronic endeavors that require a bit of knowledge about chemistry or related fields like metallurgy. No place is this more apparent than producing your own PCBs. Unless you use a mill, you are probably using a chemical bath of some sort to strip copper from your boards.

The standard go-to solution is ferric chloride. It isn’t too tricky to use, but it does work better hot and with aeration, although neither are absolutely necessary. However, it does tend to stain just about everything it touches. In liquid form, it is more expensive to ship, although you can get it in dry form. Another common etchant is ammonium or sodium persulphate.

There’s also a variety of homemade etchants using things like muriatic acid and vinegar. Most of these use peroxide as an oxidizer. There’s lots of information about things like this on the Internet. However, like everything on the Internet, you can find good information and bad information.

When [w_k_fay] ran out of PCB etchant, he decided to make his own to replace it. He complained that he found a lot of vague and conflicting information on the Internet.  He read that the vinegar solution was too slow and the cupric acid needs a heated tank, a way to oxygenate the solution, and strict pH controls. However, he did have successful experiments with the hydrochloric acid and peroxide. He also used the same materials (along with some others) to make ferric chloride successfully.

Even then, it is a good example of conflicting information on the Internet. While  [w_k_fay] says his vinegar solution didn’t do much, we’ve seen examples where it seems quite effective. Bad information could be especially dangerous with this sort of thing. In [w_k_fay’s]  case, he is careful to work outdoors and used protective gear, but you don’t always see discussions of that on web sites. The acid and peroxide will fume, and that can corrode metal. [w_k_fay] read somewhere that the solution would break down after a few days, but one of our editors has been using the same batch for the last five years. Go figure.

A common theme in etchants is to use hydrogen peroxide as an oxidant. The problem is, what you get in the drug store isn’t all that strong. In general, the higher the concentration of peroxide the stronger the solution. You can freeze 3% peroxide to increase the concentration or go to a beauty supply store and by peroxide at higher concentrations, but it will cost more. Of course, if you’re diluting the acid with water anyway, the peroxide concentration may be moot.

Speaking of cost, some of these solutions are cheap, but it isn’t like premade etching solution is that expensive either. However, sometimes the commercial chemicals are hard to source locally, so that may be more of an inducement to homebrew.

So the question for all Hackaday readers is a simple one: what do you use to etch your boards? A commercial solution? Something homebrew? A CNC machine? (Well, that doesn’t really count for the purpose of this question, but we’ll take the answer anyway.) We suppose plasma etching doesn’t count, either, but it would be interesting to know if anyone’s doing that. Leave a comment with what you are using and why.

Just to remind you, copper etching isn’t just for electronics. That’ll give you something to do with your etchant when you decide to just start sending your boards out.

Filed under: chemistry hacks, Featured, tool hacks