Direct Flip-Chip Bonding of SiC ICs on Alumina Substrate Using Gold Stud Bumps for up to 600 °C High-Temperature Applications

This article studies the feasibility of direct flip-chip bonding of silicon carbide (SiC) chips onto alumina substrate for high-temperature applications up to 600 degrees C. SiC dummy chips were prepared with sputtered thin-film Ti/TaSi2/Pt metal conductive pads, while alumina substrates were made with screen-printed thick-film gold conductive pads with a film thickness of about 12 mu m. Thermocompression flip-chip bonding was implemented with gold stud bumps made using a wire bonder. Two strategies were used in the flip-chip bonding and compared: bump-on-substrate (BoS), where gold stud bumps were made on the conductive pads of the alumina substrate, and bump-on-chip (BoC), where gold stud bumps were made on the thin-film conductive pads of the SiC chip. The SiC flip-chip packages showed a trend of decreasing daisy chain electric resistance after thermal aging and stabilization. Die shear tests and daisy chain electrical resistance measurements were carried out for the BoS and BoC packages before and after up to 16 days of thermal aging in lab air at 600 degrees C. Die shear tests showed that the bonding strength of the packages increased from about 15 g force per bump (gf/bump) before thermal aging to about 40 gf/bump after thermal aging because of the effects of thermal annealing.