Regulating Sn Grain Orientations in Soldered Joints through CoSn₃

The grain orientation of Sn in lead-free solder joints significantly impacts their reliability. This study demonstrates that the preferential growth of CoSn3 and its lattice matching with Sn crystals can partially control the grain orientation in soldered joints. CoSn3 exhibits preferential growth along the (002) plane, which can be further enhanced through ion milling. Sn grains solidified on the ion-milled IMCs surface also displayed distinct orientation characteristics, with most grains having a [001] axis forming an angle of approximately 30° with the substrate. Such Sn grain orientations are expected to improve the electromigration resistance of soldered joints.