Pits in Electroless Nickel

Q. We are plating electroless nickel (EN) on leaded brass, but find pits in the EN layer. What is the best way to prepare the leaded brass substrate so that we do not get a pitted finish? M.K.

A. The root cause of your problem is the lead present in the brass alloy. Classically, small amounts of lead have been added to certain alloys and steels to improve the machinability of the metal. Unfortunately, this can cause problems when attempting to plate these parts. The lead tends to smear on the surface during the machining steps and must be removed prior to plating. A standard cleanup process used for other materials does not do a good job of removing the lead from the surface.

The problem can be solved by using a fluoride or citrate acid step prior to plating. I recommend the citrate-based process, since it is easier to work with than fluoride-containing materials. The actual process steps are as follows and are taken from an excellent article by Brad Durkin that appeared in Products Finishing in March 1999. You can read this article, “Basic Substrate Strategies and Approaches for Electroless Nickel,” at pfonline.com/articles/basic-substrate-strategies-and-approaches-for-electroless-nickel. The abbreviated basic steps are as follows:

1. Soak clean
2. Rinse
3. Electroclean
4. Rinse
5. Rinse
6. Fluorboric or citric acid soak
7. Rinse
8. Rinse
9. Sulfamate or a Wood’s nickel strike
10. Rinse
11. Rinse
12. Electroless nickel plate

Be the sure to read the original article to get the complete details for this process.