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Author Topic: Aluminium etching  (Read 728 times)

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conner

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Aluminium etching
« on: July 04, 2017, 12:40:29 AM »

Hi, I'm trying to etch a very fine pitch (0.5mm) 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.

Q1: I believe the saline sulfate etch can be used without adding electricity to it, but would it make sense to add electricity to a saline sulfate etch to speed up the process or should this only be done with a saltwater solution?

Q2: If I'm using the electro procedure the aluminium plate that should be etch is used as the anode, but what metal makes sense to use as cathode?

Q3: I like to know what chemical reactions that are going on, in order to be aware of any reaction that could led to hazardous/toxic compounds/substances.

So what is added to the solution is:

Al (alumnium anode) +
X (some metal cathode, not sure what to use) +
NaCl + H20 + CuSO4 (electrolyte solution)
(seen suggestions to also add NaHSO4, any reasons why this should help?)

All these are probably split into ions:
Al^(+3)  +  Na^(+)  +  Cl^(-)  +  Cu^(2+)  +  SO4^(2-)  +  2H^(+)  +  O^(-2)

Know how can I tell which reactions that are going to take place? From googling+guessing i think i might end up with some of the following:
AlCl3  +  Cu  +  Na(SO)4  +  H20 + Al(OH)3 + NaOH + Cl

The reaction most likely to take place has something to do with number of electrons in the outer most shell? It has been 15 years since i have had chemistry in high school, so i cant remember much of this stuff any more. Hope you can help

Best regards
conner
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conner

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Re: Aluminium etching
« Reply #1 on: July 04, 2017, 08:38:25 AM »

After more reading i think i'm getting a bit of what is going on:

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

Al (s) + Cu(SO)4 (aq) = Cu (s) + Al(SO)4 (aq)

NaCl is not dissolved and a part of the reaction but merely a catalyst to speed up the reaction.

However i'm still not exactly sure what will happen if add electric current to it 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 cause a electrolytic decomposition of NaCl as well and merge with H2O. So i assume there will be produced chloride and hydrogen gas and NaOH (sodium hydroxide) in the process.

NaCl (s) + 2H2O (aq) = 2NaOH (s) + H2 (g) + Cl2 (g)

The gas will probably bubble out, so i would be needing a fume hood i guess.
Also i guess the CuSO4 and NaOH will react into copper hydroxide and sodium sulfate:

CuSO4 (aq) + 2NaOH (s) = Cu(OH)2 (s) + Na2SO4 (s)

Can anyone confirm if this is what will happen?
Do i need to add something to the solution to neutralize it before i dispose it at a recycling facility?
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