Effect of Ni-coated carbon nanotubes addition on the wettability, microhardness, and shear strength of Sn-3.0Ag-0.5Cu/Cu lead-free solder joints

Sn-3.0Ag-0.5Cu lead-free solder reinforced with different mass fractions (0, 0.05, 0.1, 0.2, 0.5 wt%) of Ni-coated carbon nanotubes (Ni-CNTs) was fabricated by ball-milling method to improve the properties of Sn-3.0Ag-0.5Cu ternary solder alloys. The effect of Ni-CNTs on the wettability, microhardness, and shear strength of Sn-3.0Ag-0.5Cu- x (Ni-CNTs) composite solder joints was investigated. The results show that the wettability of the composite solder undergoes a first enhancement and then a reduction where the spinodal occurs when the amount of Ni-CNTs reaches 0.05 wt%. The mechanical properties verify that Ni-CNTs addition could effectively improve the microhardness and shear strength of the composite solder. Meanwhile, the fracture morphologies of composite solder exhibit ductile dimple morphology. From the fracture morphology, it is revealed that the strengthening mode of Ni-CNTs could probably be in two ways: acting as an obstacle to impede the propagation of cracks and acting as a bridge to transfer stress. In addition, it is concluded that the optimum addition of Ni-CNTs into Sn-3.0Ag-0.5Cu solder is 0.05 wt% in the range of 0 wt% to 0.5 wt%.