Altering Electromigration Response in Aluminum Wire Bonds through Heat Treatment

In this study, a control group of aluminum wire bonds attached to direct bond copper pads are subjected to electromigration conditions of 57,000 [A/cm²] at an ambient homologous temperature of 0.5 [K/K] (194 [°C]). Treatment groups in this study subjected wire bonded cards to heat treatment prior to electromigration stressing. The four treatments consisted of one- or 24-hour durations at homologous ambient temperatures of 0.45 or 0.55 [K/K]. The results show a negative relationship between electromigration lifetime and wire length in both the control and treatment groups. Heat treatment groups show increased electrical resistivity, indicating increased sensitivity to wire length with respect to electromigration lifetime. Standard deviation of heat treatment groups is also notably larger than that of the control group, indicating that extended periods of time at homologous temperatures in the 0.45 to 0.55 range reduce the quality of high-purity aluminum wire bonded regions but do not necessarily indicate a reduced lifetime. Additional examination of the effects of wire length on thermal-electric failure modes is examined and discussed in relation to the aforementioned observations.