We have a sporadic problem with parts tarnishing after electroless nickel plating. How do we prevent this? P.N.
Tarnishing of electroless nickel (EN) is not the most common phenomenon, but it does happen. The place to start looking when troubleshooting this problem is the rinse water and particularly the final rinse. Nickel concentration in the final rinse should be less than 20 ppm and the pH must be around seven. EN is also susceptible to tarnishing in a sulfur-containing environment.
To minimize the latter problem you may have to passivate the EN surface. Dipping of the parts into a dilute solution of chromic acid 0.20–0.30 oz/gal will help minimize this problem. You can also obtain additional help by contacting vendors listed in the 2002 PRODUCTS FINISHING DIRECTORY AND TECHNOLOGY GUIDE or at PF Online under Tarnish-Preventive Treatments.