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Copper Contamination in Gold Plating

February 8, 2009

Ted
I have a gold bath for gold plating using Neutronex309. But some copper is corroded into the bath and now it has a large contamination of copper. I want to electroplate the copper (selectively)in the lowest possible voltage to reduce the copper contamination. Can you tell me if it is possible to have more copper plating than gold plating? and in which voltage it can be done?
Is there any other method to get rid of copper from gold in a solution?

Many Thanks

Reza Kamali
Student - Huntsville, Alabama

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Reza,
Because gold is more noble than copper, there is no way of plating out the copper selectively. I am not familiar with the gold bath that you are using, but it sounds like a soft, pure, neutral pH bath. In other words there are no alloying agents to obtain hardness or cosmetics. The bath may contain a grain refiner however. There was a chemical we used years ago that would tie up the copper in the bath so it would not co-deposit, but today it is taboo. The only thing I can suggest is to lower the pH so you are plating out a little more copper in the co-deposition process. Keep in mind this will be rather expensive. Try it and run copper concentration analysis before and after the process to see how you are progressing. It would be a good idea to contact your gold supplier and see what they think as well. That's why they charge the big bucks!

Mark Baker
fellow plater - Syracuse, N.Y.
February 11, 2009