Electroplated Cu Bump with Ultra-Large Grain without Thermal Annealing and Kirkendall Void at the Interface of Cu/Sn Joint

Sn-containing solder is still comprehensively used for chip packaging. Not only copper pillar but also copper bump will contact the Sn-containing solder. However, after the soldering process, not only IMC but also Kirkendall voids will be formed, which leads to poor reliability. In this work, copper bump was formed by electroplating at 25~35°C. After the copper electroplating, the copper bump has a grain size of 15~20 μm. Moreover, it has a preferred orientation of (111). Since the grain size is so big, it does not need to be annealed after electroplating. Also, it has no Kirkendall voids after soldering process at 200°C for 1000 hr.