Thermal Reliability Evaluation of Cu-Sintered Joints in Encapsulated SiC Power Modules

In this study, the thermal reliability of bimodal Cu-sintered joints for encapsulated SiC power modules was evaluated. A bimodal Cu paste consisting of 1 μm and 0.3 μm Cu particles mixed at a ratio of 25:75 wt.% was used as the die-attach material. ENIG-finished SiC MOSFET chips were bonded to AlN AMB substrates by Cu sintering at 250 ℃ under 10 MPa for 10 min. The fabricated modules were subsequently encapsulated with silicone-gel, followed by high-temperature aging at 200 ℃ for up to 2,000 h and power cycling for 20,000 cycles. After high-temperature aging, only a small amount of Cu2O was observed in the Cu-sintered layer, while CuO was not detected, indicating that further oxidation of Cu was suppressed by the encapsulated structure. The shear strength increased from 36.44 MPa to 41.08 MPa after 2,000 h of aging, while the electrical resistance decreased from 0.69 Ω to 0.58 Ω. In addition, no interfacial delamination or through-thickness cracks were observed after 20,000 power cycles, and the thermal resistance changed only slightly from 0.791 K/W to 0.807 K/W, corresponding to approximately 2.0%. These results demonstrate that the encapsulated Cu-sintered joints maintained stable bonding and heat dissipation characteristics under high-temperature aging and repeated power loading conditions. Therefore, Cu-sintered joints are considered promising high-temperature die-attach materials for WBG power modules.