Fabrication and properties of Ni-modified graphene nanosheets reinforced Sn-Ag-Cu composite solder

Ni-modified graphene nanosheets (GNSs) are prepared by uniformly mixing and heating reduced graphene oxide nanosheets (r-GONSs) and nickel acetate. Ni-modified graphene nanosheets (Ni-GNSs) reinforced Sn-2.5Ag-0.7Cu composite solder is made using mechanical alloying. The change laws of the Ni nanoparticle distribution, phase composition, and crystallinity during the reinforcement preparation are discussed. The morphology and thickness of intermetallic compound (IMC) layers with different Ni-GNSs contents during the liquid-solid reactions of the wetting interface were studied. The results show that the nanocrystalline Ni nanoparticles obtained by the thermal decomposition method have a uniform distribution, pure single phase and higher crystallinity. The morphology of the IMC was scallop-shaped. The IMC layer thickness of the composite solders decreased with the increasing amount of Ni-GNSs. Microstructural studies also revealed that Ni-GNSs were adsorbed onto the surface of the IMC layers, effectively blocking the diffusion of metal atoms. The role of Ni-GNSs in retarding the growth of IMC during the soldering process is presented. When the GNSs content is greater than 0.05 wt%, the reinforcement showed obvious agglomeration, which led to the growth of the IMC layers. The addition of 0.03-0.05 wt% GNSs will be helpful to decrease the surface tension of the liquid composite solder between the flux and copper substrate and increase the effective stress transfer between the edge of the graphene and solder matrix, causing an excellent wetting effect and high ultimate tensile stress. (C) 2018 Elsevier B.V. All rights reserved.