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 Na 2 S 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.

The reaction mechanism between a Pd/Sn catalyst and sulfide ions which were used to promote direct copper plating was studied. The identity of reaction products after activation, acceleration, sulfide promotion, and plating bath dipping were analyzed by infrared absorption spectroscopy and X-ray diffraction. It wa found that the chemically adsorbed sulfides ions do not readily form PdS. The stable PdS appears only after it is dipped in the plating bath. The major agent responsible for this transformation was found to be the sulfate ions.