Thermal interface material evaluation for IGBT modules under realistic power cycling conditions

The long-term reliability of the thermal interface material (TIM) between an IGBT and heat sink is a critical aspect of motor drive design and customer satisfaction. Studies in the literature have focused on TIM characterization using idealized flat surfaces that are not representative of the wavy mounting surface found on IGBT base plates. In the authors´ experience, there is limited correlation between TIM data sheet specifications obtained using idealized flat surfaces and the actual thermal and long-term reliability performance observed in the field. This paper describes the test process and test fixture designed to evaluate TIMs under real world power cycling conditions using actual IGBT modules and heat sink surfaces. Commercially available non-silicone oil thermal greases from three suppliers were tested with the TIM thermal resistance and junction temperatures measured approximately every 5000 cycles. A thermal grease was found to be most stable over 15,000 power cycles. Furthermore, chemical analyses indicated that the best-performing TIM has the smallest particle size of the three manufacturers.