Effect of Operating Ambient Temperatures on Degradation of Solder Joints in IGBT Power Module

Insulated gate bipolar transistor (IGBT) power modules experience power and thermal cycles in field operation which significantly degrade their solder joints, leading to reduced designed life. This investigation evaluates mechanical reliability of an IGBT power module in four key applications to provide new knowledge on the impact of ambient temperatures on the degradation of its solder joints and fatigue life. SolidWorks software is used to create eight 3-D computer-aided design (CAD) models of a typical IGBT module. Power load, induced by field operation, and IEC 60068-2-14 accelerated thermal cycle (ATC) specific to aeronautics, automotive passenger compartment, automotive under-the-hood and railway applications are used as loads. The loads and Anand’s visco-plastic model are implemented in the static structural solver within the Ansys mechanical package to simulate the degradation of 96.5% tin, 3.0% silver, and 0.5% copper (SAC305) solder joints in the modules. Aeronautic ambient temperature degrades solder joints in an IGBT power module the most, while railway ambient temperature degrades it the least. Consequently, the module has the shortest average fatigue life of 7.5 years and longest average life of 16.2 years in operations in aeronautic and railway ambient temperatures, respectively. In comparison with operation in the aeronautic condition, the module operates 36.0% and 85.3% longer life in auto under-the-hood and auto passenger ambient temperatures, respectively. Implementation of obtained laboratory test cycles in predicting the field fatigue lives of the modules in years is presented. Stress damage is found to concentrate at the periphery of solder joints which is the area to strengthen to improve device reliability. This study provides new knowledge on the deployment of an IGBT power module in four critical applications.