Enhancing thermal reliability of ceramic substrates using lotus-type porous copper

초록

A novel design employing lotus-type porous copper was proposed and evaluated to improve the thermal reliability of alumina (Al2O3)-based direct bonded copper (DBC) substrates. Finite element method (FEM) simulations were conducted to analyze the thermal stress and plastic strain induced during thermal shock cycling, and the results were validated through thermal shock cycling experiments (-50/150 degrees C). Compared with conventional sheet-type DBC substrates, the lotus-type design reduced thermal stress by 16-34 % and plastic strain by 37-56 %. In thermal shock cycling tests, the sheet-type specimens exhibited steady crack growth up to 5 mm at 12,000 cycles (failure), whereas the lotus-type specimens showed negligible crack propagation (<0.7 mm). Fatigue life estimation based on the Smith-Watson-Topper model indicated approximately 10,800 cycles for the sheet-type substrate and about 166,000 cycles for the lotus-type substrate, and crack growth analysis using the Paris law showed that the lotus-type substrate exhibited a crack growth rate approximately four times slower, consistent with the experimentally observed enhancement in crack resistance of more than eightfold. The improved reliability of the lotus-type DBC was attributed to stress redistribution and plastic strain accommodation around the internal pores, which effectively suppressed continuous crack propagation. These results demonstrate that the introduction of porous copper into DBC substrates can significantly extend thermal fatigue life and enhance structural reliability for power semiconductor applications.

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