Inhibition of roof-type Cu6Sn5 grains on migration of Cu atoms under temperature gradient

The thermomigration (TM) caused by nonuniform joule heat in micro-solder joints seriously threaten the reliability of electronic device. In this study, the both representative solder joints prepared by different processes with close θ angles were selected to study the effects of the morphology and orientation of Cu6Sn5 grains on TM behavior of Cu atoms. During TM, the IMC layer at the hot end of the both solder joints forms serrated morphology with a large number of diffusion grooves between Cu6Sn5 grains and the IMC layer at the cold end grows excessively. The IMC growth rate at the cold end for reflow solder joints is 1.18 × 10–2 μm/h, 2.7 times that of transient current bonding (TCB) joints, which is only 4.33 × 10–3 μm/h. The Cu6Sn5 geometric model based on microstructure reveals that the roof-type Cu6Sn5 grains with the c-axis parallel to the substrate obtained by TCB process can reduce the diffusion area and increase the migration path, thus effectively weakening the grain boundary diffusion of Cu atoms at the hot end and limiting the source of the TM flux in the solder. Furthermore, TM behavior of Cu atoms is inhibited and reliability of the solder joint is improved.