Modeling board-level four-point bend fatigue and impact drop tests

In this paper, modeling and simulation of board-level four-point bend fatigue and impact tests were investigated for 7 mm times 7 mm VQFN (48 I/O) assembly and 15 mm times 15 mm FBGA (324 I/O) assembly with Sn-Ag-Cu lead-free solder and OSP board surface finish. For cyclic bending fatigue, four-point bend cyclic loading at room temperature (25degC) and at high temperature (125degC) were investigated in order to develop bend fatigue model for Pb-free solder. The acceleration factor of failure at high temperature (125degC) to room temperature (25degC) is presented. Test results show that the cycle to failure increases significantly when bending displacement ranges decrease for both bend tests at 25degC and 125degC. The acceleration factor of cycle to failure due to high temperature (125degC) effect is higher than that due to room temperature effect. The FBGA component has higher bending fatigue resistance compared to VQFN component. Accumulated energy density per cycle at 125degC is more than that at 25degC significantly, which indicates that higher temperature accelerates bending fatigue failure of solder. Energy-based bending fatigue models were developed for Sn-Ag-Cu lead free solder subjected to cyclic bending load at 25degC and 125degC based on FEA result and experimental data. Using the same FEA model the loading was changed to simulate a four-point bend impact test with the same corresponding magnitude of bending curvatures. Comparisons of solder joint deformation response between the slow cyclic bend test and impact drop bend test are presented