Properties and microstructure evolution of Sn–Cu–Ni/Cu joints bearing carbon nanotubes and graphene nanosheets for solar cell

In this paper, 0.5 wt% carbon nanotubes (CNTs) and 0.05 wt% graphene nanosheets (GNSs) were selected as additives to modify the properties of Sn–Cu–Ni solder joints for solar cell. The mechanical properties of Sn–Cu–Ni solder joints can be improved by 20–25%. The interface growth behavior of Cu–Sn intermetallic compounds at Sn–Cu–Ni/Cu and Sn–Cu–Ni–0.5CNTs–0.05GNSs/Cu couples after 250 °C and 260 °C soldering with 10 min and 20 min. The experimental results indicate that the growth rate of Cu₆Sn₅ IMC of Sn–Cu–Ni/Cu solder joints is higher than that of Sn–Cu–Ni–0.5CNTs–0.05GNSs/Cu solder joints. That is, adding 0.5 wt% CNTs and 0.05 wt% GNSs can reduce the growth rate of the Cu₆Sn₅ IMC layer, which can be attributed to the reduction of the element diffusion coefficient. In addition, the stress–strain of the two solder joints were calculated using finite element method, it is found that the Sn–Cu–Ni–0.5CNTs–0.05GNSs/Cu solder joints have significantly less stress–strain than Sn–Cu–Ni/Cu solder joints, due to the reduction of Cu₆Sn₅ layer thickness, fatigue life of solder joints can be enhanced by three times.