We have greatly expanded our electroless nickel plating (EN) in the last two years. This has helped our bottom line tremendously, but the downside is that we must pay much more attention to the monitoring and maintenance of the plating tanks. We need help in doing this. Do you have any suggestions? N J.
As with any plating process, the first place to start is to make a real commitment to reviewing the details of the process as performed in your shop. This means that not only must the day-to-day chemistry be monitored but also the equipment used in the process. Some of the things to consider are:
- Plating Tank Construction and Plumbing
- Water Quality
- Temperature Control
- Chemical/Solution Maintenance
Before embarking on this review, make sure you have your chemical supplier in the “loop.” Your vendor should be able to supply you data sheets and maintenance information for the EN baths.
Tanks used for EN are usually made from polypropylene or stainless steel. Polypropylene is the preferred material because it tends to minimize plate-out of EN on the tank itself. Stainless steel tanks will last longer than polypropylene tanks, but the tanks must be passivated by making the tank anodic. The plumbing used should be made of stainless steel or chlorinated polyvinyl chloride, CPVC.
EN solutions are very sensitive to “tramp” metal ions. Hence, good rinsing prior to the parts entering the plating tank is essential.
Continuous filtering of the EN tank is required. The filtration rate should be at least 4–5 turnovers per hour using a filter with a porosity of five microns or less.
The best quality water must be used in the EN tank. Water containing even small amounts of metal ions, particulates, chloride ions or organic materials will cause problems.
Temperature control is important with most people recommending control within 1–2 F. Higher temperatures give higher plating speeds but also more rapid decomposition of the bath. Lower temperatures usually allow more metal turnovers but also give lower plating speeds.
Solution maintenance is performed by either continuous testing or by manual testing. Continuous testing allows for automatic replenishment of chemicals as needed. The cost of implemented and maintaining such a system can be high. Manual testing requires frequent testing, usually once an hour. The operator usually performs the testing and makes additions based on these results.
There are two excellent papers that discuss this topic in much greater detail: Frank Altmayer, Plating & Surface Finishing, 87, 40-43 (October 2000) and 29-31 (November 2000).
One last comment, EN solutions are very complex. Various components are added to the plating solution to balance a number of different chemical reactions that take place. If one of these components is not just right, you are in trouble!