This invention is related to an electroless copper plating process.
Electroless copper plating is a significant step in the fabrication of printed circuit boards. One of the problems with the electroless plating process is a significant build-up of contaminants such as formate and carbonate ions which are detrimental to copper plating quality and bath stability. One approach to this problem is simply to replace the bath with a new one after several plating cycles (each typically 24 hours). Not only is such an approach expensive, it creates serious waste disposal problems. In present and future factory processes, it is far more desirable, if not mandatory to meet EPA regulations, to replenish the existing baths and eliminate the need to discard any material which could be harmful to the environment.
In order to replenish electroless copper baths, it has been suggested to use electrodialysis apparatus to remove a variety of contaminants therefrom. (See, e.g., U.S. Pat. No. 4,805,553 issued to Krulik, and U.S. Pat. No. 5,091,070 issued to Bauer et al.) In practice, it has been extremely difficult to apply electrodialysis such that the resultant wash is not compromised by the addition of contaminants which cannot be easily disposed of, or the subsequent use of the plating solution does not adversely affect the final product.