A Robust Palladium-Free Activation Process for Electroless Copper Plating

Abstract

A new activation process for electroless copper plating has been developed, which does not require the use of a palladium-based activation bath as typically employed in the plating industry. The activation bath of the new process described herein is entirely free of palladium and is based on colloidal metallic copper particles, which are nanoscopic in size. This bath can also be readily analysed and controlled. The new copper-based activation bath can be operated in such a way that colloid agglomeration and colloid oxidation are efficiently and effectively suppressed, while electroless copper plating quality and electroless copper bath stability is maintained. In addition, the new activation bath can be operated for several weeks without any detectable deterioration in electroless copper plating performance. Furthermore, acrylonitrile butadiene styrene (ABS) and FR4 coupons treated with the new copper-based colloidal activation bath can be vigorously rinsed with water for several minutes prior to immersion in the electroless copper bath without loss of plating quality. The new activation process performs comparably to an established palladium-based process operated at typical vertical equipment immersion times. Even though the electroless copper plating initiation is somewhat delayed for the new copper-based activation process, the final electroless copper deposit thicknesses are the same for both the new process and the palladium-based reference process. The adhesion of the electroless copper deposit obtained with the copper-based activation process is also similar to that obtained with the palladium-based reference activation system. Moreover, the electroless copper coverage performance of the new copper-based activation process, as determined by the backlight test, is comparable to that of the palladium-based reference process.