The Real Elliot

How are you agitating the solution? What temperature is it? How did you clean and/or prepare the board's surface beforehand? 20 min for a fresh acid/peroxide mix is _way_ long if you're constantly swirling stuff around, unless it's very cold. Look at the board as it etches. If you swirl a bit and you see a thin cloud of darker stuff coming off the board -- dissolved copper -- then you're not agitating enough. Swirl more / continuously.

Do what you want, and what you feel comfortable with. But...The reaction of acid with copper is not exothermic, and will not "get away from you". That's HCl and aluminum. (Which is a whole different ballpark of danger/fun.)"Muriatic acid is nothing to play with" is correct, but we're not "playing" here, we're using it. And before it gets diluted down to the final etchant, 10M muriatic _is_ a strong acid and you don't want to spill it all over, for instance. But it's un-dangerous enough that you can pick it up in the hardware store without any hassle. People tune their pool pH with the stuff all the time without a chemistry degree. Add acid to water.Vinegar as an acid: OK if you're afraid of the strong acid, or have storage issues. It's not cheaper or...

Do what you want, and what you feel comfortable with. But...The reaction of acid with copper is not exothermic, and will not "get away from you". That's HCl and aluminum. (Which is a whole different ballpark of danger/fun.)"Muriatic acid is nothing to play with" is correct, but we're not "playing" here, we're using it. And before it gets diluted down to the final etchant, 10M muriatic _is_ a strong acid and you don't want to spill it all over, for instance. But it's un-dangerous enough that you can pick it up in the hardware store without any hassle. People tune their pool pH with the stuff all the time without a chemistry degree. Add acid to water.Vinegar as an acid: OK if you're afraid of the strong acid, or have storage issues. It's not cheaper or purer, just more diluted. But _do not_ put used etchant down the drain when you're done with it. It's the copper salts that are the problem, and they're present whether you use this etchant, ferric chloride, vinegar, or dragon's tears. No matter what, I wouldn't be doing any of this with my bare hands. The limited copper exposure is _probably_ benign. But I'm not really down with "probably" when it's avoidable. Use gloves or tongs.

For aluminum, the HCl that we're using here will work just fine just by itself. Look up "aluminum foil hydrochloric acid" on the web -- it's a well-known way of producing hydrogen gas, but the aluminum gets eaten up in the process.The downside of the reaction is that it creates heat, and speeds up (creating more heat) as it gets hotter. If you're reacting a lot of material, you're going to need to cool it or else you'll end up with runaway boiling hydrochloric acid in large quantites, which is about as fun as it sounds.I would call etching aluminum with HCl a strictly-outdoors activity, with lots of cool water in buckets on hand if things go wrong. Because of the hydrogen gas it produces, you want to make sure there are no open flames anywhere nearby. I'd experiment with dilu...

For aluminum, the HCl that we're using here will work just fine just by itself. Look up "aluminum foil hydrochloric acid" on the web -- it's a well-known way of producing hydrogen gas, but the aluminum gets eaten up in the process.The downside of the reaction is that it creates heat, and speeds up (creating more heat) as it gets hotter. If you're reacting a lot of material, you're going to need to cool it or else you'll end up with runaway boiling hydrochloric acid in large quantites, which is about as fun as it sounds.I would call etching aluminum with HCl a strictly-outdoors activity, with lots of cool water in buckets on hand if things go wrong. Because of the hydrogen gas it produces, you want to make sure there are no open flames anywhere nearby. I'd experiment with diluted acid solutions first.OTOH, it's a great way to fill party balloons with hydrogen. :)

There are a million ways to skin a cat. (Gross!)I do 10 mil traces with toner transfer all the time now. I've run a couple boards at 6 mil, which is the design limit for a bunch of the cheaper overseas PCB factories. The etching is not the limiting factor -- it's getting the etch resist uniformly and reliably on such small features.I agitate the boards constantly in the tank -- meaning swishing the etchant around, not rubbing on them. I've never had problems with damaged traces. OTOH, if the electrical idea ends up a good replacement for swirling, I'm all for it. Tipping a tupperware back and forth is boring.So yeah. Try it out -- you might hit on an improvement. Let us know.