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Looking to electroplate with a nonporous acid/etchant resistant metal

March 22, 2010

I am experimenting with electroforming and etching processes,trying to create unique components. I am currently trying to electroplate copper with a metal that is completely resistant to strong acids or copper etchants, the most obvious one that came to mind was gold, but when I plated half of a piece of copper with gold and put it in a copper etchant (sodium persulphate), the gold peeled away in a few hours. It did not just peel away from the gold/copper boundary but became uniformly loosened from the copper and evidence of etching beneath the gold was obvious. The conclusion I drew from this is that the gold must be porous and that the etchant is diffusing through it.

My question is first, is this description consistent with your knowledge of electroplated metals and second, do you know of an electroplatable metal that would form an impenetrable barrier to acids and etchants. I would like to try rhodium next but would prefer not to needlessly waste my money do to inexperience.

Thanks in advance!

Mike McKown
student - Palm Springs, California, USA

Try with nickel+chrome but remember porosity is a function of thickness up to a certain point among other variables. I would recommend 0.002"-0.003".

Guillermo Marrufo
Monterrey, NL, Mexico
March 22, 2010

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I still think gold would work, but it would depend on what etchants or acids you are using. I think gold would work fine with persulphates. Something like ferric chloride [on eBay or Amazon] might cause problems.

There are probably at least 200 different gold plating formulations in the world and the deposits from most all of these have different characteristics. As a general rule of thumb, gold deposits are porous if the thickness is less than 100 microinches. There are many exceptions to this rule, mainly depending on the type of bath you use, but it's a good place to start.

The common, bright hard golds, alloyed with a little nickel or cobalt, that are used on PCB fingers or pins, are generally stressed and will allow penetration of the etchant even at greater thicknesses. Also, the design of the part is important, since it's difficult to build up the required thickness on sharp points or edges.

All in all, an educated guess would be that the sulfite golds might be the best thing to use. The deposits from these are generally uniform, bright, ductile, and less porous than many other types of baths. Technic carries a good line of these. I would contact them and tell them what you're trying to do. They surely will be able to help you. Also, they might plate some samples for you to evaluate, before you purchase the bath.

Whatever you do, I think it would be futile to try to formulate your own gold bath. The proprietary baths are far advanced to anything you could make and there are so many to choose from - for every possible purpose.

Chris Owen
- Nevada, Missouri, USA
March 23, 2010