Degradation Mechanisms of Au–Al Wire Bonds During Qualification Tests at High Temperature for Automotive Applications: Quality Improvement by Process Modification

Several package families used in automotive environment were aged at different high temperatures. The purpose was to better characterize the predominant failure mechanism of ball bonds and to identify the most influential technological parameters on it. The mechanism is related to the Kirkendall effect, which is a consequence of the Au-Al intermetallic phase growth. For identical materials, the package geometry plays a crucial role: experimental results are confirmed by both analytical model and finite-element simulations. To extend the qualification domain to the biggest package size, the wire bonding process must be improved. In particular, the use of Au-1 wt.% Pd instead of pure Au is investigated, showing that this alloy permits to decrease the Au-Al intermetallic growth and, hence, to increase the lifetime.