Bond Reliability Improvement at High Temperature by Pd Addition on Au Bonding Wires

To extend the qualification domain to the biggest package size in the automotive environment at high temperature, it is necessary to improve the Au-Al bond reliability. Thus, the improvement provided by addition of palladium as alloying elements to Au bonding wires is evaluated. In this study, the use of Au-1 wt%Pd instead of pure Au is investigated; samples are aged at 175 and 200°C. In the case of the Au-1 wt%Pd wire, a Pd-rich layer was found at Au/Au-Al interface, which prevented Au diffusion and yielded an even slower intermetallic (IMC) growth rate at the Au-Al interface as compared to the case of the pure Au wire. Wire pull test after thermal aging proved that Pd addition enhanced bond reliability and increased the life-time. Cross-sectional SEM and EDX analyses (mapping and linescan extraction) allowed to identify Au-Al IMC phases and to understand the role of Pd rich layer at the Au/IMC interface. Investigations on the failure mechanisms provided an explanation for the improved robustness of the connections in the case of the alloyed wires as compared to in purse gold wires.