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 (SiCp)-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 SiCp-doped Ag microflakes under mild conditions (250°C, 30 min, 0.4 MPa). The SiCp 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 SiCp-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 SiCp experienced bonding degradation, with shear strength of ∼25 MPa and 20 MPa, respectively. Thus, after 1000 cycles, the shear strength of pure Ag and SiCp-doped joints decreased by 58% and 42%, respectively, compared with their maximum value. Coarsening of porous Ag occurred in pure Ag joints. SiCp addition inhibited morphological evolution of SiCp-doped joints during thermal cycling. However, vertical cracks generated by thermal stress were observed in joints both with and without SiCp, which may limit long-term reliability.