Cu wire bond reliability improvement through focused heat treatment after bonding

Currently, there is a great interest in applying copper material to wire bonding of fine pitch assembly packaging, particularly for cost saving purposes. However, the hardness property of copper is harder compared to the conventional gold wire. The hardness factor of copper, coupled with the work hardening effect of the USG power and force during wire bonding, is a major cause for bond pad crack and pad cratering, especially on sensitive pad devices. Known methods to soften the FAB has been evaluated and discussed. Softening the FAB has proved to play a role in decreasing the bond pad cratering. However, it does not resolve the problem completely. The proposed solution is to introduce heat after wire bonding to enhance the intermetallic adhesion strength between the copper to the Al bond pad.