Electrical and Microstructural Reliability of Pressureless Silver-Sintered Joints on Silicon Carbide Power Modules Under Thermal Cycling and High-Temperature Storage

Abstract

Low-temperature and pressureless silver (Ag) sintering was applied to a 1200 V/200 A silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) power module with a Ag-finished silicon nitride active metal-brazed substrate, and the results were evaluated for applicability in electric and hybrid electric vehicles. The sintering was performed at 220–240°C, 90 min in vacuum under nitrogen gas conditions; the bonding strength, bonding layer thickness (BLT), void content, and densification of the as-sintered Ag joints were 39 MPa, 71.4 µm, 2%, and 90.5%, respectively. The shear strength, BLT, densification, and microstructure of the Ag-sintered joints were compared before and after the thermal cycling test (− 50–150°C, 1100 cycles, TCT) and high temperature storage test (200°C, 1000 h, HTST). To simultaneously compare the electrical properties of the SiC power module with lead (Pb)-free solder joints, the same SiC MOSFET power module was manufactured using a Sn-3.0Ag-0.5Cu (SAC305) Pb-free solder. The shear strength and densification after TCT and HTST were 35.5 MPa and 39.7 MPa, as well as 92.8% and 94.8%, respectively. The on-resistance and total switching efficiency of the SiC power module with the Ag-sintered joint were also compared to those of the SAC305 solder joint module, which evinced maximum values of 7.3 mΩ and 10.7 mJ that were superior to those of 8.5 mΩ and 11.3 mJ for the SAC305 solder joint, respectively. Under the same measurement conditions, the maximum generated current and voltage values are lower than those of the solder joint module, so it is envisaged that stable power module operation is realizable for long-term use. The Ag-sintered joint surpassed the SAC305 solder interconnects in terms of the electrical and mechanical reliability of the power module. When a SiC wide band gap device was used, it was discovered that Ag sintering was superior to Pb-free solder interconnects to increase the power conversion efficiency of the power module.