Application of precision filtration to an electroless copper plating bath

Abstract

Electrolytic and electroless plating are becoming extremely important for forming functional thin films. Printed circuit boards are indispensable as elements of electronic equipment, and the boards are shrinking in size. Accordingly, the full additive process can be attractive as a substitute for the subtractive process. Extraneous deposition occurs easily on the circuits, however, when copper is deposited using the additive process. The sulfate and formate ions accumulated during the plating reaction are the cause of extraneous deposition, or plate-out. Nascent hydrogen is also a possible cause inasmuch as extraneous deposition develops with the evolution of hydrogen gas, as shown in Fig. 1. 1 Extraneous deposition still occurred, however, even when these related factors were eliminated. Fine inorganic particles in the plating bath are also a possible cause of extraneous deposition. 2 Accordingly, elimination of the extraneous deposition by filtration was investigated, as well as the inhibiting effect of the filtering media.