Q. We are having trouble plating electroless nickel/boron nitride. Our basic procedure is as follows: alkaline degrease at 190°F for 10 min, hot rinse, cold rinse, activate in a pickle, double rinse, and plate at 185°F for 45 min. The base materi-al is carbon steel. Seventy-five to 80 percent of the parts plate satisfactorily, but the rest of the parts do not plate at all. Can you offer any suggestions on how to solve this problem? W.W.
A. The first question I would ask: are you absolutely sure all of the pieces are made of the same material? For example, you may have a leaded steel alloy that is difficult to plate and may require a nickel or copper strike prior to the EN plating step. If you are certain that all of the parts are made from the same mate-rial, then there are some other areas you should investigate:
Stabilizer concentration. Too much stabilizer can cause bare spots and the lack of plating. You may be adding large amounts of replenishers infrequently when a better method would be to add smaller amounts on a more frequent basis. This avoids large changes in concentration.
Agitation rate. Are you agitating your bath in a consistent manner? Over-agitation or under-agitation can be a real problem for this type of bath. Poor agitation can cause great variation in plating bath concentration and the resulting non-plated parts.
pH control. If you have a larger plating tank you may find that the pH is not consistent throughout the tank. This usually can be resolved by improving your agitation. You should also routinely take a pH measurement at two different locations within the tank.
Base material not autocatalytic. Certain base materials require a strike prior to being plated. Again, this goes back to verifying that all of your parts are of the same base material.
Metallic contamination. Certain types of tramp metals can play havoc with your EN bath. Some of these metals can be removed from the plating bath using electrolytic dummying.
You can find more information on the care and maintenance of electroless nickel plating baths in the book “Electroless Nickel Plating” by Wolfgang Riedel.