Thermal stability improvement of sintered Ag die-attach materials by addition of transition metal compound particles

Sintered silver (Ag) die-attach has attracted much attention in assembling power modules for high power density and high temperature operation. We have investigated a method to improve the thermal stability of a sintered Ag die-attach structure at high temperature storage (HTS). One of the issues of die-attach with sintered Ag is the growth of a microporous structure after HTS, since the microporous growth of the sintered Ag layer may have severe influence on bonding strength and reliability. It was verified that the addition of transition metal compound particles such as WO3, Nb2O5, MoO3, and RuO2 to sintered Ag paste successfully prevents microporous structure growth beyond 200 °C. From the results of cross-sectional scanning electron microscope observation, the inhibiting effect of microporous growth has a correlation with the difference between the total-circumference-length measured before and after HTS, among which WO3 and Nb2O5 additives were more effective. We propose this amazing die-attach mater...