SiC Power Device Packaging Technologies for 300 to 350°C Applications
The challenges of packaging SiC power devices for high temperatures include high operating temperature, wide thermal cycle range, high currents and high voltages. This paper describes ongoing research to develop suitable materials and processes for packaging SiC power devices. Ohmic and Schottky contacts must be protected from oxidation at elevated temperatures. TaSi2:N2 is an effective oxidation barrier, protecting the contacts when exposed to 350 oC in air. For package substrates, silicon nitride ceramics with a thick brazed copper foil are used. A nickel/thick gold or nickel/thick silver surface finish is plated onto the copper foil; depending on the die attach brazing process. With the nickel/thick gold finish, gold-tin eutectic has demonstrated no degradation in die shear strength after 2000 hours at 350 oC or after 500 hours at 400 oC. Work is currently underway with nickel/thick silver and gold-silicon eutectic die attach. No degradation in shear strength has been observed with this system after 100 hours at 400 oC. Gold wire (250 µm) bonding has been demonstrated on both substrate and SiC metallizations. An initial decrease in strength is observed due to annealing of the gold wire, but shear and pull strengths remain high. Polyimide has been used to increase the dc breakdown strength of a test pattern by a factor of ~3x at 300 oC compared to no passivation. The breakdown strength increased with storage in air at 300 oC through 1000 hours.
Dr. Roberta Nipoti, Antonella Poggi and Andrea Scorzoni
R.W. Johnson and J. R. Williams, "SiC Power Device Packaging Technologies for 300 to 350°C Applications", Materials Science Forum, Vols. 483-485, pp. 785-790, 2005