Dependency of the porosity and the layer thickness on the reliability of Ag sintered joints during active power cycling

In order to analyze the reliability of Ag sintered joints in dependency of their porosity and their layer thickness, Si IGBTs were mounted on DCB substrates via Ag sintering by applying a certain pressure as well as conducting pressure-less sintering. The assemblies were subjected to active power cycling tests at which the electric current was controled such that the die attach was exposed to temperatures from +30 °C up to +180 °C. The results show that depending on the applied pressure and the initial layer thickness Ag sintered joints exhibit a 10 to 100 times higher lifetime than standard SnAg3.5 solder joints. Furthermore, the analyses of cross sections show that the occurring failures of the thermomechanically treated Ag sintered joints are deviating from those of soldered joints which fail due to creep fatigue solely. It is also shown that the occurring failures can be detected non-destructively by combining X-ray and ultrasonic-microscopy.