# Ferric Chloride or Muriatic Acid + Hydrogen Peroxide for etching?

Currently purchasing the required kit to start etching my own boards and have gotten to the etching solution stage. Ferric Chloride seems to be the standard for etching but I have also read about Muriatic Acid + Hydrogen Peroxide ecthing, which apparently is better all round (both for the environment and my pocket).

Has anyone had any experience with this method of etching?

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I've used the muriatic acid/hydrogen peroxide solution. It works great when it's fresh, but it does NOT keep for me. If I go back and use it a couple of weeks later, it just doesn't work. I haven't pursued proper disposal, yet, so I've accrued a bit of the stuff in mason jars (whose lids are rusting from the acid, by the way). Once I figure out how to get rid of the acid/peroxide mixture, I think I'm going to try FeCl.

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I believe that if you add a bit of H2O2, it works again. Try it! –  Connor Wolf Feb 23 '11 at 23:32
I did, and that just seems to water it down. :-( –  blalor Feb 28 '11 at 20:18
You want to let some of the water evaporate off, so you are not diluting the strength. –  Connor Wolf Mar 17 '11 at 20:01

I've switched from FeCl to acid/hydrogen peroxide exclusively, in my experience it has an extremely short shelf life but considering how cheap it is that hardly matters, the main benefits are etching speed and results, FeCl takes 3 to 4 times longer than a new batch of acid/hydrogen peroxide and with the latter I've done tracks down to 0.2mm with no problems.

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How do you dispose of the used acid/hydrogen peroxide mixture? –  blalor Oct 25 '10 at 18:19
@blalor moved this repeating question here. –  hhh Apr 30 '13 at 22:33

Can't comment on that specific combo but I know that some alternatives have poor shelf life of made-up solution. FeCl solution lasts indefinitely. The biggest downside of FeCl is that it stains.

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I always use Natrium Persulfate for etching. I quite like it because it is results in a clear liquid so you can see the progress of your etching. It turns blue after a while but with a sufficient concentration you can reuse it multiple times. It will stain your clothes if you're not careful but it's doesn't stain your skin, like Ferric Chloride does. The advantage over Muriatic Acid + Hydrogen Peroxide is that it won't hurt you (as much) if it comes in contact with your skin. If you get Natrium Persulfate on your hands you can just rinse it off. Here's some of my etching being performed using Natrium Persulfate. (photo's in reversed order)

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Does the Persulfate turn the board substrate blue, or did your boards have a blue substrate from the beginning? –  ducksauz Dec 26 '10 at 17:16
My boards were blue from the beginning. The Natrium Persulfate solution turns blue after many uses but this does not affect the color if the board. –  bpijls Jan 3 '11 at 9:49

I just started etching, and have chosen cupric chloride (CuCl2 - the resulting chemical of etching copper with muriatic acid + peroxide). About shelf life: The great thing about CuCl2 is that you can REGENERATE the solution by adding a little oxygen (fish tank pump, shake bottle, or add a little H2O2), or acid once in a while. Which means you almost never have to dispose of the hazardous waste. About the previous comment -- the copper in the waste is poisonous even at very small concentrations. "In Australia the EPA regulates maximum copper in sewage discharge to 5 ppm. If you have etchant containing 150g/L of copper, that means a dilution 1:28000 is necessary to meet regulations" -- from http://members.optusnet.com.au/~eseychell/PCB/etching_CuCl/index.html.

That link has tons of information about using CuCl2 to etch copper. Also this link simplifies the process greatly: http://www.instructables.com/id/Stop-using-Ferric-Chloride-etchant!--A-better-etc/

CuCl2 is slower than muriatic + peroxide, but I think it's worth almost never having to buy more etchant.

Though I haven't tried any very small traces yet. As I understand it slower etching means more undercutting (etching sideways under your resist). As noted -- I'm a beginner.

Also anyone who wants to do this should read about muriatic acid storage -- according to what I've read, even a little gas slowly escaping from the bottle can rust nearby metal. I think I read that the gas is heavier than air, so if I see any rusting, I'm thinking about putting some kind of base chemical in the bottom of a 5-gallon bucket, and storing the acid in there. Maybe concrete rubble?

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I've used both, and I think the issue with Muriatic Acid + Hydrogen Peroxide is the 3% hydrogen peroxide you can buy nowadays: it simple isn't concentrated enough. The idea of muriatic acid + hydrogen peroxide is to make Cupric Chloride, which is the etching solution you can regenerate by bubbling air through. The problem is that most of the online recipes are formulated for something like 30% hydrogen peroxide, which is simply unavailable, at least in the US. So what happens is that we mix our puny 3% hydrogen peroxide with muriatic acid, everything works great on one board, and then over the course of two days the O$_2$ bubbles out of the solution, and you are left with rather diluted muriatic acid, because most of what you added to it (97%, to be exact) is water.

The solution I am in the process of trying is to concentrate the hydrogen peroxide via heating/evaporation of water. I haven't etched any boards with it yet, but I am hopeful that this will get me to the CuCl stage such that the solution can be regenerated by bubbling air and an occasional shot of muriatic (hydrochloric) acid.

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In the US, higher concentrations of peroxide are easily available, just not in the pharmacy. Higher concentrations of peroxide are regularly used when coloring hair, and are available at beauty supply stores. At the Sally Beauty locally (and at their website) they have up to 40% peroxide, in 10% increments. Look for "Salon Care 40 Volume Clear Developer". Be sure to get "Clear" not "Creme", and note that it's 40% by volume, not weight, hence the name. –  Thomee May 20 '13 at 15:15
@Thomee: Thanks for the tip. The ingredients list phosphoric acid as well which concerns me. Have you used this stuff? –  angelatlarge May 20 '13 at 17:22
Yes, I've used it with no problem. I believe the phosphoric acid is only a very small amount, as a preservative or stabilizer or something. –  Thomee Jul 1 '13 at 15:31