Abstract
We investigated a recycling process for electroless nickel plating bath using nickel hypophosphite. Phosphite ion accumulated in aged bath were separated as calcium phosphite precipitated by addition of calcium hydroxide, then pH of the phosphite ion separated mother liquor was adjusted to plating condition by way of electrodialysis (method I), which was compared with sulfuric acid addition (method II).
The deposition rate kept constant till 30 MTO in method I, but decreased slightly in method II. The internal stress of deposit tended to be almost 0 constantly in method I, but shifted strongly to the tensile side in method II. In addition, concentration of ingredients in the bath remained almost constant in method I, but sulfuric ion concentration increased by accumulation of sulfuric acid added to adjust pH in method II. We found that method I was superior on the pH adjustment to method II from standpoint of keeping bath life long. Corrosion-resistance of film plated by recycled bath remained good (larger than 9 of rating score in a salt spray test) and the surface of the films stayed clean till 30 MTO.
We found that there was little variation of the recycling bath composition by the treatment in this condition and constant aging state of the bath was maintained and good plating film was obtained.
