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Extreme Thermal Transient Stress Analysis with Pre-Stress in a Metal Matrix Composite Power Package
Keywords: power, extreme temperature, MMC
This paper describes the culminating results of a six-year development of an aluminum-based metal matrix composite power package that used cast aluminum interconnects on a cast-in AlN ceramic substrate. The harsh environment package houses a SiC semiconductor used as a solid-state circuit breaker for aerospace applications. The package was targeted for -65 ˚C to +105 ˚C ambient operation with the semiconductor generating a transient +245 ˚C increase in <1 microsecond when interrupting fault currents in excess of ten-times normal operation. Previously reported design results used a 4.1mm X 4.1 mm SiC semiconductor chips. Final test results are reported for 48A/chip clearing current from a 300 Vdc bus with a di/dt of 2.1 kA/us (in 390 ns). The chip absorbed ~4.6 J inducing a transient junction temperature increase of ~245 °C from a +25 °C and +105 °C ambient. The junction temperature conservatively exceeded +350 °C during a 5 ms fault-current conducting pulse at the 105˚C ambient. The electrical testing demonstrated acceptable performance for over 750 cycles, most from 105 ˚C ambient. Earlier publications reported on electro-thermal performance. The final work added here, used extensive FEA modeling to show substantially increased electrical power performance for 7mm X 8mm SiC chips replacing the small chips described above. Thermal profiles are provided for transient performance for 96A/chip clearing current during a 3 ms fault-current conducting pulse at 105 ˚C ambient. The majority of the analysis is focused on thermally induced stresses in the package as the larger chips undergo simulated operation down to -65 ˚C ambient. Coupled with the analysis is an FEA of embedded pre-stress from the casting process while the composite package was fabricated. The analysis shows the composite structure needs reformulation to reach -65 ˚C.
Douglas C. Hopkins, Professor
North Carolina State University
Raleigh, NC

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