Stressed Nickel Deposits

Question:

What causes high stress levels in a nickel sulfamate bath? B.N.

Answer:

Normally, a well maintained nickel sulfamate bath will give a nickel deposit with low tensile stress. If this is not the case, there are a number of things that can cause higher stress levels in the nickel deposit.

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Lower current densities usually in the range of 20–40 asf should be used, particularly if the plating bath is being used for electroforming.

Another culprit may be plating bath temperature. The bath should not be run at a temperature higher than 145F. At higher temperatures the sulfamate ions will break down and cause stress problems.

Last, but not least, determine whether there are metallic impurities in the bath. Heavy metals such as iron and copper can cause problems with stress.

A book, Electrodeposition—The Material Science of Coatings and Substrates, by Jack W. Dini has an excellent chapter on the issues involved with stress in electroplated layers. The book is available from Metal Finishing Publications, 212-633-3100, www.metalfinishing.com.