Nickel Plating Blisters

Q. We are barrel plating the enclosed parts. (The reader sent examples of plated terminals.) Lately, the parts have been showing blistering and peeling on the end with the blind hole. The procedure we use consists of a presoak, electroclean, rinse, acid dip (dilute hydrochloric acid), rinse, Watts nickel bath (0.0002-0.0004-inches thick), rinse and dry. Can you help us? –J.M.

A. I have examined the parts and found evidence of blisters on other areas besides the blind hole area, although that area has the greatest amount of blisters and peeling, by far. You indicate that this problem has started recently, implying that something has recently changed in your process.

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There are a number of causes of blistering and peeling in nickel plating. The major ones are: improper cleaning of the substrate, contamination of the plating bath and interrupted current flow through the plating bath. 

The procedure you outlined in your e-mail indicates an adequate cleaning process, so I would look elsewhere. Look at your plating bath and determine if you are operating the bath at the proper pH (4.5-5.0), current density, etc.

Look at your electrical system as well. Are you getting continuous current flow through the system? Have you changed your barrel load size?

Bottom line: a thorough review of your plating process is required.