Plating Q&A: Stressed-Out Nickel Deposits

Q. We receive parts requiring a “low stress” nickel deposit. Are there numerical ranges for high and low stress nickel deposits?

A. I am not aware of any standard that specifies numeric values for high and low stress deposits, but this is a good opportunity to briefly discuss stress in nickel deposits.

The plating bath composition affects residual stress in nickel deposits. The table below shows some stress values for different nickel plating baths:
 

SOLUTION ANION	RESIDUAL STRESS (PSI)
Sulfamate	8,600
Sulfate	23,100
Chloride	33,000

Typically when a low stress deposit is specified, sulfamate nickel is required. The conventional Watts nickel bath, which contains sulfate and chloride, gives a deposit with a high residual stress. Adding stress-reducing agents to the plating bath, which can be obtained from your chemical vendor, can lessen this stress. In some cases this is satisfactory, but if an additive-free deposit is required you will have to consider the sulfamate plating bath.

Other factors like the temperature of the plating bath and the actual substrate itself, may influence the residual stress of the deposit. 

Originally published in the November 2015 issue.