Anti-foaming agent for HCl + copper chloride solution

Question

I am trying to etch my own circuit boards at home, and have whipped up some DIY cupric chloride etchant (just CuCl with a bunch of free HCl)

The problem I have found is that when I try to bubble air through it to regenerate it, the solution foams aggressively enough to come up over the top of my etching tank.

I'm more of an engineer than a chemist, so i'm unaware of what anti-foaming agents will work well in the strongly acidic solution.

I'm hoping for something I can buy in small quantites or create relatively cheaply.

Answer 1

The circuit etch solution is made from CuCl$_2$ rather than CuCl. https://www.instructables.com/PCB-Etching-Solution-Cupric-Chloride/

After etching/dissolving some copper, you would get CuCl, and regeneration involves reoxidizing the Cu$^+$ to Cu$^{2+}$. When you use air, not all the O$_2$ is captured, and none of the N$_2$, so you have lots of gas bubbles forming and rising. One way to reduce the foaming would be to reduce the rate of aeration. A possible cause of foam is the presence of surfactant or a film-former from reaction with the circuit board.

One way to defeat the foam is to treat it with a low surface tension agent. Isopropanol (rubbing alcohol (70%) or 91%) sprayed onto the surface - just a little bit - can break the foam and let it settle down. Most of the isopropanol will evaporate easily so the treatment will have to be repeated. I have done this on a large scale.

Another additive would be a silicone lubricant. Spray cans of this type of product are used for nuts and bolts type of mechanics. A little goes a long way, and could interfere with your etch, but has potential.

Consider using hydrogen peroxide to reoxidize your Cu$^+$, as in the link above. This would significantly reduce the bubbling and might give you more control over the regeneration, although it does dilute the product.

Answer 2

Instead of oxygen bubbling, add some hydrogen peroxide $\ce{H2O2}$. It is not expensive. And it works perfectly well. Here is a formula that does your job in less than 1 minute, without any foam.

Dissolve $\ce{20 g CuCl2·6 H2O}$ in $\pu{100 mL}$ water. Add $\ce{100 mL HCl}$ $35$% and $\ce{100 mL H2O2}$ $30$%. Here you are. Dip your circuit board in this solution. In less than one minute, the copper metal from the board is attacked and dissolved. The total equation is :

$$\ce{Cu + 4HCl + H2O2 -> [CuCl4]^{2-} + 2H2O + 2 H+}$$

To be true, this equation is the sum of a couple of equations taking place simultaneously, which are : $$\ce{Cu + CuCl2 -> 2 CuCl}$$ $$\ce{CuCl + HCl -> HCuCl2}$$ $$\ce{2 HCuCl2 + H2O2 + 4 HCl -> 2 [CuCl4]^{2-} + 4 H+ + 2H2O}$$

And this reaction does not produce any foam !-