Bend fatigue reliability test and analysis for Pb-free solder joint

In this study, VQFN (very thin quad flat no lead) assembly with Sn-Ag-Cu lead-free solder and Ni/Au board finish was tested under three-point and four-point cyclic bend at room temperature (25degC) and high temperature (125degC). Correlation between three-point and four-point bend was performed. It was found that the cycle to failure increases significantly with displacement ranges decreasing for both bend tests at 25degC and at 125degC. The acceleration factor of cycle to failure due to high temperature effect is higher than that due to room temperature effect. FEA modeling and simulation were performed for different testing conditions to investigate solder joint stress strain behavior. Accumulated energy density for bend at 125degC is more than that at 25degC significantly, which indicates that higher temperature accelerates bending fatigue