Q. We have adhesion problems when plating nickel over electroless nickel. The bath analysis for both solutions is within the required tolerances. We are not using a nickel strike prior to the electrolytic nickel plating step. Do you have any suggestions? R.U.V.
A. I’m glad to read that your plating baths are within the required tolerances. That’s a good start! However, as you probably know there is more to electroplating than just having your bath chemistry within the required or recommended values. In this particular case, the base material, electroless nickel, is hard and difficult to over coat. Electroless nickel quite often is used as a substitute for classic chromium plating.
What is required here is preparing the surface so that it has “some bite,” i.e., a surface that can grip other materials. The first thing I would suggest is using a nickel strike over the electroless nickel to prepare the surface. Nickel strike that I would go with is the Wood’s nickel strike. This is a strike bath consists of nickel chloride and hydrochloric acid and is used quite often to prepare stainless steel surfaces prior to plating. I have in the past given formulations for a Woods nickel strike. Here is a formulation you should try:
|Nickel (added as nickel chloride)||45 g/L (6 oz/gal)|
|Hydrochloric acid (22 degree Baumé)||10% by volume|
|Temperature||70 – 80 °F|
|Current density||10 – 40 ASF|
|Time||30 sec – 2 min|