Thermal Stability of Al2O3-Filled Silicone-Based Elastomers for Power Electronic Encapsulation
Silicones are widely used for encapsulating power electronic modules due to their high dielectric strength and thermal stability. However, silicones are found to be insufficiently stable at 250°C, which is the maximum junction temperature of commercial SiC devices. In this study, the thermal stability of pure silicone and its Al2O3 fiber-filled composites were investigated by thermogravimetric analysis (TGA) and isothermal (250°C) soak tests. Both tests revealed that Al2O3 fiber improved the thermal stability of silicone (Fig. 1). TGA results indicate that the temperature of degradation onset increased from 330°C to 379°C with a fiber loading of 30 wt%. In the isothermal soak test, pure and 30 wt%-filled silicones lost 10% of polymer weight in 700 and 1,800 hours, respectively. Improved thermal stability was explained by a restrained chain mobility caused by hydrogen bonds formed between the Al2O3 surface and the polymer matrix. Removal of hydrogen bonds impaired thermal stability, increasing the initial weight-loss rate from 0.025 to 0.036 wt%/hour.