Fatigue crack evolution and effect analysis of Ag sintering die-attachment in SiC power devices under power cycling based on phase-field simulation

Sintering Ag materials is a promising candidate for the die-attachments in SiC power devices due to its high melting point and low thermal resistance. However, CTE mismatch between the SiC chips and the substrates causes cracks to develop in the sintered interconnection structures. Power cycling conditions lead to periodic loadings on the Ag sintering die-attachment. The incremental accumulation of plastic strain energy, combined with periodic fluctuations of elastic strain energy, results in the fatigue crack evolutions of the sintered structures. Further, the crack evolutions considerably degrade the thermal and mechanical properties of the interconnect structure, and critically affects the integrity of the heat transfer network and the mechanical structure of the power devices. In this paper, the fatigue crack evolution of Ag sintering die-attachment in the SiC power devices is simulated based on the phase-field models. Moreover, the thermal performance degradations and stress distributions of die-attachment under power cycling are analysed. A methodology based on finite element modelling and phase-field simulation is proposed, realised by Abaqus and its subroutines. The fatigue crack in the Ag sintering die-attachment initiates from the chip-side corner point, then propagates to the chip-side centre point until the formation of a penetrative crack, which achieves a good match with experimental results. Moreover, along with the crack propagation, the thermal distributions in the chip and the stress distributions of the sintering layer are obtained to analyse the degradations of thermal and mechanical performances of Ag sintering die-attachment in SiC power devices.