Effects of Sn grain orientation and microbump geometry on thermomigration failure in microbump joints

Purpose The purpose of this study is to investigate the failure mechanisms of thermal migration in microbump joints with limited Sn grains under temperature gradients and to assess the effectiveness of hourglass structures in suppressing intermetallic compound (IMC) growth and improving thermal reliability. Design/methodology/approach A thermal migration test platform was used to expose barrel- and hourglass-shaped Cu/Ni/Sn-3.5Ag microbump joints to a temperature gradient of 16,029°C/cm. Through the integration of FE-SEM, electron backscatter diffraction and finite element simulations, the correlation between IMC growth behavior and Sn grain orientation was systematically analyzed. Findings When subjected to temperature gradients, IMC grows asymmetrically along high-misorientation-angle boundaries (ß > 15°) and medium-to-low a-angle (< 55°) Sn grains, with the IMC/Sn interface at the hot end being particularly susceptible to cracking. While hourglass structures increase diffusion distance, they are unable to regulate grain orientation and, thus, demonstrate limited effectiveness in suppressing thermal migration. Originality/value This study identifies three distinct mechanisms by which Sn grain orientation and grain boundaries govern preferential IMC growth. It clarifies the limitations of hourglass structures in suppressing thermal migration, offering new insights for microbump reliability design.