A sharp-eyed reader pointed out that I gave an incorrect breakdown product when discussing the electroless nickel process. Yes, I did, and here is the question and answer with the correction.
I recently heard of a new electroless nickel process that gives you many more turnovers of metal compared to conventional electroless nickel processes. Is this true and if so where can I find more information on the process? A. B.
Over the years, many different approaches have been investigated in the hopes of finding an electroless nickel process that will have a longer life and will allow for additional metal turnovers. In my experience a standard electroless nickel bath will give you between 5–7 turnovers before it must be dumped and replaced with a new bath.
The chemistry of electroless nickel is fairly complex. As the electroless nickel bath ages, the concentration of by-products, sulfate, sodium and orthophosphite ions, increases. The increase of these by-products causes the bath to lose its functionality. If these impurities can preferentially be removed, you should be able to use the bath for longer periods of time.
A number of different approaches have been attempted to do exactly this. Bleed and feed, selective ion exchange and different chemistries have all been tried for solving this problem. There are drawbacks to all of these processes.
A newer approach and one that looks like it can be very useful is to use electrodialysis to remove these by-products. A paper presented at the 2005 Sur/Fin conference in St. Louis, The EDEN System for Electroless Nickel Bath Life Extension and Consistent Quality, 2005 Sur/Fin Proceedings, Track IV—Electroless Plating, discusses this approach. This methodology appears to be able to give you unlimited bath extension. In one particular case study, more than 2,000 metal turnovers were achieved. The above referenced paper has a complete discussion on this methodology.