Cobalt UBM for fine pitch microbump applications in 3DIC KU Leuven
© 2015 IEEE. In this paper we report results and challenges of replacing Cu with Co as UBM (under bump metallization) in microbumps for 3D technology applications. Cobalt has softer and single IMC (intermetallic compounds) and according to calculations using Cobalt as UBM can reduce consumption of UBM material by solder which is attractive for sub 10um pitches of microbumps. However, cobalt oxidizes very fast which results in poor wetting by ...