Microstructural analysis of the Ag/graphene-coated-Cu composite sinter paste in high-temperature reliability

This study was carried out to understand the effects of graphene coating the high-temperature stability of Ag Cu hybrid sintered joints. The microstructure and mechanical properties of the graphene coated Cu and Ag (Ag-Cu-Gr) hybrid sintered joint were investigated during high-temperature aging test for up to 1000 h at 250 °C. As the storage time increased, the average die bonding strength of the Ag-Cu-Gr sintered joint reached a peak of 65.51 MPa at 500 h and decreased thereafter. In contrast, the die bonding strength of Ag Cu sintered joint reached a peak of 56.23 MPa at 200 h, but subsequently decreased to 40.28 MPa at 500 h. In addition, the porosity decreased with increasing high-temperature aging time due to the densification of the Ag and the formation of Cu oxides. The Ag-Cu-Gr sintered joint exhibited a uniform microstructure without phase separation between Ag and Cu during aging test, which was attributed to diffusion barrier effect of graphene. In addition, we confirmed the effectiveness of the graphene coating in preventing the copper oxidation through XRD and EPMA analysis. As a result, the hybrid paste can potentially provide for power module die attach materials with high-temperature stability. • Graphene coated Cu hybrid paste exhibits high thermal reliability up to 500 h. • The addition of graphene to the sintered joints achieved the highest shear strength of 65.51 MPa at 500 h. • Graphene coating on Cu powder suppressed the formation of Cu oxide during aging test.