Effects of Bi and Ni addition on shear strength of low-Ag lead-free solder joints

The objective of this paper is to investigate the shear fracture mechanism of solder ball. The shear strength of solder joints were measured by Joint Strength Tester. The results indicate that addition of the Ag element has a significant effect on the shear strength of Sn-Ag-Cu solder joints. The shear strength of Sn0.7Ag0.5Cu-BiNi solder joints is higher than that of Sn-0.3Ag-0.7Cu and Sn-3.0Ag-0.5Cu solder joints as -reflowed or after aging. The 3-D morphology of shear fracture shows that lots of typical dimples were distributed in the solder joints after reflow. But fracture dimples in Sn-0.7Ag-0.5Cu-BiNi solder joints were less than the other two solders and they were all composed of tiny compounds. The fractured position was much more close to the IMC. It indicated that the Sn0.7Ag0.5Cu-BiNi solder shows the best toughness. After aged for 196 hours, the scale of IMC in the surface of shear fracture increases, dimples appear and the shear strength of solder joints decrease.