Interfacial oxidation protection and thermal-stable sinter Ag joining on bare Cu substrate by single-layer graphene coating

In the next generation power electronics packaging, sinter Ag joining technology has become popular for use as a die attach and is receiving greater attention. Herein, it is reported that sinter Ag particles joining performed directly on a bare Cu substrate coated by a single-layer graphene can provide satisfactory interfacial oxidation protection and mechanical reliability. The shear strength obtained in our research achieved 25.4 MPa in low temperature, pressure-free sintering in air. The Cu oxide layer appeared solely at the location of Cu grain boundaries during sintering and was much smaller than when performed on substrates without graphene coating. The bonding mechanism was realized by Ag nanoparticles (AgNPs) self-generated from the Ag paste during the sintering process which tightly bonded to the graphene surface upon interacting with the Cu oxide. A subsequent high temperature (250 °C) aging test demonstrated that die shear strength maintains its value as-sintered for 750 h. Furthermore, the thickness of Cu oxide with graphene coating was about one fourth of that without graphene and this difference increased with aging time. This study puts forward an exciting solution for sinter Ag joining directly on Cu-based substrates in high temperature for longer lifetime in power electronic packaging applications.