The effect of rare earth elements on the shear behavior of BGA solder joints under board-level

In this paper, four kinds of solder-SAC305, SAC0307, SAC0307-0.07La and SAC0307-0.07La-0.05Ce were prepared by experiment. The BGA solder joints (whose diameter is 900μm) of board-level structure was obtained by twice reflow soldering. We analyzed the shear strength, the fracture mode, and the fracture mechanism by applying shear load. At the same time, the effect of the thickness and morphology of the IMC on shear mechanical properties of four kinds solder joints were studied. The results show that the shear strength of the high silver solder joints (SAC305) is much larger than that of the low silver solder joints (SAC0307), the shear strength of low silver solder with rare earth elements is greatly improved and can basically reached the level of high silver solder joints shear strength. It can be concluded from the fracture analysis that the high silver solder joints are fractured at the interface between the bulk solder and the IMC, and the fracture surface presented a mixed-mode of ductile and brittle fracture while the low silver solder joints were broken on the bulk solder which shows the typical characteristics of ductile fracture. The second phase particle appeared in the solder joints with rare earth elements improved the mechanical properties of the solder joints. In addition, the analysis on thickness and morphology of IMC showed that the rare earth elements has affinity with Sn tendency, the activity of Sn in the solder and the driving force for IMC growth is lowered.