# Aluminium etching

I'm trying to etch a very fine pitch ($\pu{0.5 mm}$) aluminium stencil for use with SMT printed circuit board making. I've done some reading on the topic and found that the safest way probably is to use a saline sulfate etch and/or use saltwater electro etching.

If not using electrolytic reactions it seems like it is a single displacement reaction since $\ce{Al}$ is more active than $\ce{Cu}$.

$$\ce{Al (s) + Cu(SO)4 (aq) = Cu (s) + Al(SO)4 (aq)}$$

$\ce{NaCl}$ is not dissolved and not a part of the reaction but merely a catalyst to speed up the reaction. Still i'm not sure if this is strong enough to actually etch holes in an aluminium plate or just emboss the surface.

I'm considering adding an electric current to speed things up using the aluminium plate as anode(+) and i assume copper can be used as cathode(-) since it is the other metal that the aluminium ions are replaced with.

It will probably (I'm guessing) cause a electrolytic decomposition of $\ce{NaCl}$ as well and merge with $\ce{H2O}$. So I assume there will be produced chloride and hydrogen gas and $\ce{NaOH}$ (sodium hydroxide) in the process.

$$\ce{NaCl (s) + 2H2O (aq) = 2NaOH (s) + H2 (g) + Cl2 (g)}$$

I figure the gas will bubble out, so i would be needing a fume hood. Also i guess the $\ce{CuSO4}$ and $\ce{NaOH}$ will react into copper hydroxide and sodium sulfate:

$$\ce{CuSO4 (aq) + 2NaOH (s) = Cu(OH)2 (s) + Na2SO4 (s)}$$

Can anyone confirm if this is what will happen?
Any toxic/hazardous reaction that i should be aware of?
Do I need to add something to the solution to neutralize it before i dispose it at a recycling facility?

• As soon as the Cu covers the active Al (that without an oxide coat), any etching would stop. – DrMoishe Pippik Jul 4 '17 at 21:21