Comparison of a Cu-UBM Versus Co-UBM for Sn Flip Chip Bumps

摘要

In this paper, pure Sn bumps are considered as Pb-free solder alternative. The thermal-cycling reliability of Sn is investigated for two different UBM materials: Cu and Co. A lifetime improvement of 40% is found for the Co-system. This can be explained by a change in failure mechanism: while Cu-Sn samples show a mixed failure mechanism of ductile shear through solder and brittle fracture at the intermetallic interface, the Co-Sn samples are characterized by dominant solder fatigue.