Stressed Nickel Sulfamate Deposits
Why is a nickel sulfamate plating bath producing deposits with high stress?
Q. Our company plates a lot of parts using nickel sulfamate plating baths. Recently, our plating baths started giving us deposits with greater-than-expected stress. Any ideas on what causes this? –T.J.M.
A. There are a number of possible causes for increased stress in nickel deposits. We normally consider nickel sulfamate baths as those that deliver a low-stressed deposit. While this is true, these baths require maintenance on a regular basis. For starters, organic impurities such as ammonia can accumulate in the bath from the decomposition of the sulfamate ion at higher temperatures. This particular process accelerates at temperatures above 70° C. Heavy metals such as iron—if present in the plating bath at concentrations of 50 to 100 ppm—will also cause stress. Current densities that are too high are also a culprit. Normally you should keep your current density in the range of 10 to 30 asf.
If you wish to get into the subject of stress in more detail, get a copy of Electrodeposition: The Materials Science of Coatings and Substrates (Materials Science and Process Technology) by Jack Dini.