A study of cyclic bending reliability of bare-die-type chip-scale packages

Both experimental and numerical studies were carried out in this work to investigate the second-level reliability of a bare-die-type chip-scale package, named ultra-CSP, under cyclic bending conditions. We performed four-point cyclic bending tests with combinations of deflection amplitudes up to 3 mm and excitation frequencies up to 2 Hz. It was observed from the bending experiments that the influence of these low excitation frequencies on the fatigue life of the solder interconnects is inapparent. Through quasi-static finite element analyses, the plastic strain energy density accumulated per bending cycle within the critical solder bump was calculated and together with the experimental results, parameters for the Coffin-Manson fatigue model were calibrated.