Critical solder joint in insulated gate bipolar transistors (IGBT) power module for improved mechanical reliability

This investigation identifies the critical solder joint in a typical Insulated Gate Bipolar Transistor (IGBT) module and provided new knowledge on how operating thermal loads degrade IGBT-attach, Diode-attach, and Substrate solder joints in the device. SolidWorks software is used to create three realistic 3-D Finite Element (FE) models of the typical IGBT module used in this investigation. In-service operating power and IEC 60068–2-14 thermal cycles are implemented in ANSYS mechanical package to simulate the response of the three solder joints in the FE models to the load cycles. The solder in the joints is lead-free alloy of 96.5% tin, 3% silver, and 0.5% copper (SAC305) composition. The SAC305 material properties are modelled as time and temperature dependent with Anand's visco-plastic model employed as the constitutive model. Results show that the key degradation mechanism of solder joints in IGBT module are stress, plastic strain, and strain energy magnitudes. Accumulated plastic strain in the joints is found the predominant damage factor. Critical solder joint in the module depends on the load cycle the device experiences. IGBT-attach solder joint is critical in active power load cycle. Substrate solder joint degraded most in passive thermal cum combined passive thermal and active power load cycles.