Investigation of Pb-free solder interconnect under drop impact by ball pull and shear tests

The reliability of Pb-free solder interconnect under drop impact was investigated. In this paper, solder ball pull and shear tests were introduced to assess the interconnect reliability since high speed pull and shear tests exhibit high strain rate deformation followed by brittle fracture of actual drop scenario. The design, material, and process parameters considered in this study are SR condition, Cu pad surface finish, and strain rate, respectively. The adhesion strength was measured and the failure mode was categorized in each test condition. Next, the maximum applied force in ball pull test was used for loading condition in finite element analysis to calculate the interfacial fracture toughness at the corresponding fracture location. The effect of parameters on interfacial reliability was shown by interfacial fracture toughness, and it was compared with the drop life of board-level reliability test to investigate the correlation. Finally, the applicability and limitation of ball pull/shear tests for replacing BLR test were discussed.