Where's the Copper Coming From?


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 Q. We use a cyanide copper strike bath in a couple of our plating processes. Over time the copper concentration increases in the bath. Why? M.D.

A. I looked through my earlier columns and realized I answered a similar question many years ago. Here is what I wrote at that time: 
“This type of bath is operated at low cathode efficiency. This allows for better coverage, cleaning and activation of the parts. The cathode efficiency is generally in the range of 50–60%. To achieve this type of efficiency, the bath will contain a lot of free cyanide. The high concentration of free cyanide in the bath allows the copper anodes to remain unpolarized. The anodes will continually dissolve and the copper concentration in the strike bath will increase.”