Thermomechanical Reliability Investigation of Insulated Gate Bipolar Transistor Module

Though, significant efforts have led to high solder joint quality, thermomechanical fatigue and delamination of the solder joints are still considered as one main failure cause in Insulated Gate Bipolar Transistor (IGBT) power modules. Frequently used test procedures such as accelerated power cycling and thermal cycling allow to rate reliability and to predict lifetime under assumed power load conditions. However, these tests are less capable of detecting the root physical failure cause. In this paper a non-destructive thermal method to observe the successive effect of solder layer fatigue is suggested and discussed. Somewhat similar to power cycling, the method is based on an accelerated temperature cycling process where the power component is self-heated. The resulting change of thermal conductivity of the solder joint due to degradation is detected by contactless temperature measurement. First metallurgical analyses confirm the degraded solder structure as cause of the thermal changes due to aging.