Evaluation on Wedge Bond Performance of Different Cu Wire Types during Thermal Cycling Test (IMPACT 2020)

It is widely believed that wedge crack is resulted from thermal stress occurring at wire bonding area due to coefficient of thermal expansion(CTE) mismatches among epoxy molding compound (EMC), bonding wire and Leadframe(LF). Wedge bond heel area has the higher risk due to stress concentration. With the increasingly higher requirements in reliability qualification, thin Cu wire wedge crack can still be a high risk in thermal cycling test (TCT). In this study, a delamination condition was created, thin Cu wire wedge bond robustness during TCT was evaluated in a DFN package with different wire types, including bare Cu wires with different purity, Cu alloy wires and Pd-coated Cu wire. The results showed that Cu wire wedge bond performance in TCT depends on a robust wedge bond profile, CTE mismatch between wire and EMC, wire surface condition, delamination at wedge bond critical area etc. Through suitable material selection and process optimization, thin Cu wire can achieve higher reliability qualification requirements. Furthermore, wedge bond fatigue behaviors were discussed to illustrate the wedge bond robustness of different Cu wires during TCT.