Influence of under-bump metallurgy and solder alloys on the crack in the wafer level chip scale packaging
The finite element method (FEM) is employed to investigate the solder crack mechanism in wafer level chip scale packaging (WLCSP). The location of the initial crack is calculated and is compared to the experimental one. Moreover, the impact of the following three aspects, e.g. under-bump metallurgy (UBM) materials, solder alloy, and the thickness of the UBM layers on the initial crack growth in solder is investigated by calculating J-integral, respectively, which reflects the possibility of crack growth. It is concluded that the J-integral values in 96.5Sn3.5Ag solder and the Au-Ni-Cu-Ti UBM material are smaller than other cases.