Investigation of the reliability of Cu and Co UBM layers in thermal-cycling tests

Despite the approaching ban on Pb in electronics, possibilities for replacing small pitch SnPb bumps are still limited. Electroplating, which is the most important process for small pitch bumping, complicates the alloy formation. In this paper, pure Sn bumps are investigated on their reliability behavior during thermal-cycling tests. Both electroplated Cu and Co are tested as UBM material. A Cu-SnPb sample is used as reference. The system lifetime of this reference sample could not be achieved with pure Sn. However, it is believed that by modifying some process conditions, the CoSn lifetime could be improved.