Thermal Fatigue Behavior of Silicon-Carbide-Doped Silver Microflake Sinter Joints for Die Attachment in Silicon/Silicon Carbide Power Devices

Abstract

We studied the thermal fatigue behavior of submicron silicon carbide particle (SiC_p)-doped silver (Ag) microflake sinter joints for die attachment in next-generation power devices. Si dummy chips and direct bonded copper substrates with various metallization schemes were bonded using SiC_p-doped Ag microflakes under mild conditions (250°C, 30 min, 0.4 MPa). The SiC_p was distributed homogeneously in the porous Ag network and inhibited morphological evolution during thermal cycling tests. The shear strength of as-sintered pure Ag and SiC_p-added joints was ∼50 MPa and 35 MPa, respectively. Thermal cycling tests from −40°C to 250°C were conducted for up to 1000 cycles (hours) to characterize the thermostability of the bonded joints. After 1000 cycles, joints with and without SiC_p experienced bonding degradation, with shear strength of ∼25 MPa and 20 MPa, respectively. Thus, after 1000 cycles, the shear strength of pure Ag and SiC_p-doped joints decreased by 58% and 42%, respectively, compared with their maximum value. Coarsening of porous Ag occurred in pure Ag joints. SiC_p addition inhibited morphological evolution of SiC_p-doped joints during thermal cycling. However, vertical cracks generated by thermal stress were observed in joints both with and without SiC_p, which may limit long-term reliability.