Effect of leveler on performance and reliability of copper pillar bumps in wafer electroplating under large current density

Abstract

This work investigated the effects of levelers on the electroplating performance and reliability of copper pillar bumps (CPBs) on wafer. Under large current density, the usage of Janus green B (JGB) or a commercial leveler (L1) could obtain a satisfied performance in flatness, co-planarity and growth rate. It was found that this qualified leveler possessed a remarkable electrochemical characteristic, i.e., strong convection dependent adsorption (CDA). The void growth at the plated CPBs/Sn-Ag soldering interface during thermal aging was greatly accelerated when the leveler was applied during electroplating. The mass spectrum analysis showed that the level of impurities in the plated CPBs using JGB was much higher than that plated without JGB. The usage of leveler could produce a high level of impurities in the plated CPBs, which accounted for the boosting of voids at the soldering interface during thermal aging.