Interfacial reaction, wettability, and shear strength of ultrasonic-assisted lead-free solder joints prepared using Cu-GNSs-doped flux

This paper aims to investigate the influence of composite flux on the interfacial reaction, wettability, and shear strength evolution of Sn-3.0Ag-0.5Cu (SAC305) solder joint; the ultrasonic vibration (USV) was performed to the solder joint during reflowing. Cu-modified graphene nanosheets (Cu-GNSs)-doped flux were prepared by chemical modification. It was found that the wettability of the solder was enhanced after the addition of Cu-GNSs, and the wetting angle was reduced up to 14.43%. While, the presence of Cu-GNSs could reduce the thickness of the intermetallic compound (IMC) layer and the size of IMC grain within the solder joint by 4.15% and 3.19%, respectively. Interestingly, the solder joint was prepared with 0.1 wt% Cu-GNSs-doped flux which had the optimal effect on enhancing the wettability of the solder and inhibiting the growth of the IMC layer. The application of USV during reflow could enhance the wettability of the solder and decrease the thickness and grain size of IMC within the solder joint. Shear test results stated that the employment of Cu-GNSs and USV made the shear strength of Cu/SAC305/Cu solder joint enhanced by up to 9.34% and 9.76%, respectively. Furthermore, as the content of Cu-GNSs doped in the flux increased, the fracture type of solder joints without USV treatment gradually changed from the ductile-brittle mixed type to the ductile type, whereas, the fracture type of all the solder joints-relayed USV treatment was the ductile type.

Automated summary

The addition of Cu-GNSs in the flux improved the wettability of the solder, reduced the thickness and grain size of the IMC layer within the solder joint. The application of USV during reflow further enhanced the wettability of the solder and decreased the thickness and grain size of IMC. The employment of Cu-GNSs and USV significantly increased the shear strength of Cu/SAC305/Cu solder joint.