Glass for Encapsulating High-Temperature Power Modules

Conventional polymeric or organic encapsulants cannot survive long-term operation at high temperatures (>250 °C) due to their thermal degradation. In this work, we evaluated an inorganic material, i.e., a low-melting-point (T _melt < 500 °C) lead glass, as a potential high-temperature encapsulant for SiC power modules. Processing of the glass on an Al ₂ O ₃ direct-bond-copper (DBC) substrate was studied, and a stress-relief solution was devised to solve the thermal-stress-induced glass cracking. The electrical insulation capability of the glass was characterized by measuring partial discharge inception voltage (PDIV). The average PDIV of the glass-encapsulated test coupons across a 1-mm gap was >3 kV at temperatures up to 250 °C. The glass-encapsulated 1-kV, 36-A SiC MOSFETs showed normal static and dynamic characteristics, suggesting that the glass did not cause damages to the SiC devices during processing. As for reliability, the glass encapsulant survived a much longer time than several high-temperature polymeric encapsulants (rated temperature > 300 °C) soaked at 250 °C.