Homebrew_PCBs

When you mix the salt (sodium chloride, NaCl) with vinegar (5% acetic acid, HAc),  the result is  weak homemade hydrochloric acid (HCl) and some leftovers.  It's slower because it's weaker, and needs replenishment as the Cl ions are used up in the etching reaction (more salt = more Cl ions). Might as well start with the pool muriatic acid (HCl), admittedly stronger than the vinegar/salt, since that's what you wind up with anyway, just weaker.  Beauty shop suppliers will have higher concentration peroxide in quart bottles for reasonable prices. Their concentration is measured by 'volume'  -  typically,  40 volume = ~12%, IIRC, so use 1/4 as much as the 3%.  The overall solution will be stronger, since there is less water than using the 3%. You just use less of the higher concentration peroxide.   Both the pool acid and higher concentration peroxide are quite caustic/corrosive, and need to be treated with real care and respect.  Rubber/plastic apron and gloves, safety glasses!  Ventilation!  And don't use it (or ferric chloride, for that matter) around your tools - the vapors from an exposed etch tank will leave a nice rust patina on the iron surfaces!

If you can find it, Sechelle had written an excellent article on CuCl etching, explaining the chemical process.  It seem to have disappeared from it's old internet sites.

Norm

 

I’m trying to wrap my head around how this works, to better mix it.  I actually like working with this method – the resulting etchant is way less unpleasant than ferric or the HCl/peroxide stuff.  It is way slower, although I’ve found adding peroxide/salt seems to speed things up a bit.

 

The only negative I’ve found is that peroxide typically is only available in small 300-500ml bottles, which depending on which store you raid cost anywhere from $1.99 to $3.99 CDN each.  And you kinda get weird ‘is this guy a terrorist?’ looks when you check out six or eight of em at a time.  I’ve looked around for ‘bulk’ peroxide but have only found industrial stuff that is at 32% (vs 3%).. wondering how that would change things in the reaction?

 

I’m also wondering why it seems like I can keep the reaction going indefinitely if I constantly intervene to stir, add a bit of salt, add peroxide, etc.. but once I let it go it cannot be restarted again.  Also curious why sometimes I get a blue coloured etchant at the end, whereas other times I get this foamy, nasty green.

 

I’d love to figure this out more and refine it.  The real obstacle is the cost and small quantities available of peroxide.  I’d love to find a way to buy that that doesn’t leave me feeling like a weirdo.  J

 

Brad

 

Virus-free. www.avg.com

I'm not a chemist - (College Chem101 in 1958).  That's why I referenced the article - I'll see if I can find it again - might even be in the files in this group. 

As I understand it, the etching is a conversion of metallic copper to copper chloride, which is soluble.  Therefore, the free chlorine ion is required.  I don't think the chlorine in the HCl is free to combine.  The formation of the copper chloride is what turns the solution blue-green (also why ferrous chloride turns greenish as it is used).

Anyway, the HCl + H2O2 works for me, it's cheap, and just about inexhaustible (Bubble air through it  - converts the CuCL to CuO (or some such) and releases the Cl ions for re-use.  Adding the small amounts of H2O2 would also add the needed oxygen to regenerate the solution without the bubbles.

Again, not a chemist, but this is what I've read/experienced.

Norm

 

Thanks Norm.

 

Yeah, I’m just reluctant about using actual HCl for the reasons you mentioned.  I’m generally pretty careful but I’m also a bit accident prone and I don’t want to wreck something, or myself, messing around with that kind of acid.  I’ve accidentally splashed this vinegar/salt/peroxide solution on me and not even slight irritation.  I’m sure that wouldn’t be the case with HCl.

 

What I’m curious about though is that supposedly the reaction will still work *without* salt.. just takes longer?

 

Virus-free. www.avg.com