Development of high-reliability thick Al-Mg2Si wire bonds for high-power modules

Durability of IGBT modules mainly depends on reliability of the thick Al wire bonds used in them. We investigated the reliability of thick Al-0.5mass%Mg₂Si wire bonds in comparison with conventional Al-50ppm Ni wire bonds. The shear strength of both Al-0.5mass%Mg₂Si and Al-50ppmNi wire bonds were measured as a function of the number of thermal cycle tests. The strength ratio of Al-50ppmNi wire bonds decreased substantially with the number of cycles and it was 78.8% of the original strength after 10,000 cycles. On the other hand, that of Al-0.5mass%Mg₂Si wire bonds was almost unchanged after 10,000 cycles. Degradation ratios of Al-0.5mass%Mg₂Si and Al-50ppm Ni wire bonds at 10,000 cycles were about 1.6% and 21.2%, respectively; thus reliability of the former was ten times larger than that for the latter.