Research on applying direct plating to additive process for printed circuit board

Abstract

The feasibility of applying direct-metallization as an additive process for printed circuit board was explored. Pd/Sn catalyst was used in the activation step and the content of Pd adsorption was found to be the controlling factor. The Pd content was affected by the conditions of various steps including condition, activation, acceleration, and promotion. The sequence of applying photoresist and activation with Pd/Sn catalyst plus promotion with Na2S solution was also studied. It was found that a well-defined pattern could be obtained by applying the Pd/Sn catalyst layer before applying the photo-resist film. If the photoresist was applied before the activation step, copper deposition tended to develop beyond the desired pattern region on the surface. We also found that the lateral growth rate of copper deposition was inversely affected by the concentration of copper sulfate. This can be explained by a deposition model in which the lateral growth of copper deposition is caused by the charge transfer of the sulfur atom as a bridging ligand.