The Study of Complexed Copper(II) Ion and Its Application for Electroless Copper Deposition

Abstract

Nowadays, sidewall metallization of microvias and through holes of a printed circuit board (PCB) after drilling and desmearing processes mainly utilizes palladium as a catalyst for electroless copper plating process. Although the palladium catalyst has been commonly used in PCB metallization, the palladium catalyst is expensive. In this work, we use complexed copper(II) ion to replace the palladium catalyst in order to greatly reduce the process cost and maintain the same metallization performance and reliability as that of palladium. The synthesis process of the complexed copper ion is simple and its cost is inexpensive compared to palladium. Particularly, they have no oxidation issue because they are not metallic copper nanoparticles but copper(II) ions. In this study, we utilized a PCB with through holes as a substrate. A conditioner with a quaternary ammonium group was employed to graft the complexed copper(II) ions onto the sidewalls of these through holes. Before electroless copper plating, the grafted copper(II) ions were chemically reduced to copper atoms, so that they can catalyze electroless copper deposition. The deposition performance of the electroless copper plating on the sidewall of a through hole catalyzed by the grafted copper catalyst were examined by backlight degree analysis using an optical microscope (OM) and surface morphology analysis using a scanning electron microscope (SEM). The thermal reliability of the electroless copper deposition catalyzed by the grafted copper catalyst was examined after copper electroplating using thermal shock in a tin bath at 288℃ for ten seconds and repeated it for 5 times. Results show that it can pass the thermal shock test.