Effect of Residual TiN on Reliability of Au Wire Bonds during High Temperature Storage

It is well-known that residual TiN on Al bond pads is detrimental to wire bond reliability. However, the exact reliability impact has not been reported. In this work, we characterize the effect of residual TiN on Au wire bond reliability during high temperature storage at 210 degrees C (i.e., a high temperature stress required for automotive qualification). We observe no degradation in wire bond pull and shear strength for bond pads with residual TiN prior to high temperature storage. In addition, after high temperature storage, there is no difference in the measured wire bond resistance for bond pads with vs without residual TiN. However, the pull strength is clearly reduced for bond pads with residual TiN. These results show that the effect of residual TiN on wire bond reliability may not be evident at time zero testing, but is only evident after a reliability stress.