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 degrees C and 260 degrees 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.