Strengthening mechanism of Ni-modified graphene nanosheets reinforced SnAgCuRE composite solder/Cu joints

Based on the unique structure, excellent physical and mechanical properties of graphene nanosheets (GNSs), thermal decomposition method was used to modify the GNSs for preparing Ni-modified GNSs (Ni-GNSs) in this paper. Varying amounts of Ni-GNSs were added to SnAgCuRE solder alloy to synthesize composite solders. The soldering behaviors of the composite solders were studied, and the strengthening mechanism of Ni-GNSs on the SnAgCuRE lead-free solder/Cu joints was discussed. Compared with Sn2.5Ag0.7Cu0.1RE0.05Ni solder alloy joint, the interfacial IMC morphology of Ni-GNSs/SnAgCuRE composite solder joints changed from cobblestone to cobblestone and short bar, the interfacial IMC layer thickness was smaller, the IMC grains and microstructure of solder joints were refined. The addition of GNSs changed the structure of the composite solder/Cu joints, and formed a subinterface area enriched with Ni-GNSs between the interfacial IMC and the soldering seam, which helped enhance the reliability of the composite solder joints through the dispersion strengthening of solder by GNSs. Meanwhile, the fracture location of the solder joint was in the soldering seam, so strengthening the solder alloy was also beneficial to improving the strength of the solder joints. After modified by Ni, GNSs was combined with β-Sn matrix to produce a good semi-coherent interface by the bridging action of Ni, revealing a new mechanism of interface strengthening between Ni-GNSs and β-Sn matrix in Ni-GNSs/SnAgCuRE composite solder, which contributed to the improvement of shear strength of composite solder joints.