Effect of a Cationic Polymer, Polyethyleneimine, on Ni/SiC Co-Deposition

Abstract

Co-deposition of ceramic particles to enhance properties of electroplated films is difficult to control due to problems involved in dispersing the particles. In this study, co-deposition of 1 μm SiC particles with nickel from a Watts bath in the presence of a cationic polymer, polyethyleneimine (PEI) as dispersant was investigated. All plating experiments were performed on a rotating disk electrode, under direct current. It is seen that the addition of PEI at a concentration of 200 ppm increases the SiC incorporation without affecting the current efficiency. The SiC fraction in the deposit as a function of SiC bath concentration, current density, rotation speed and molecular weight of PEI are also discussed. PEI of 1200 molecular weight increases electrode polarization and lowers the current efficiency more than PEI of 60000 molecular weight; however the increase in SiC vol% as a result of the addition of lower MW polymer is more pronounced. A pre-coating procedure for the SiC particles is described. With this method, highly dispersed plating solutions that result in SiC loadings as high as 14 vol% with current efficiencies higher than 90% can be obtained. Optimization of conditions for best dispersion and efficient deposition is the key for successful processing.