Ion milling-enhanced preferential growth of CoSn3 for crystallographic orientation control of Sn on polycrystalline Co substrates

• Ion milling enhances the overall texture of the α-CoSn 3 layer. • A modified edge-to-edge model effectively predict the ORs between β-Sn and α-CoSn 3 . • Sn grains nucleated on ion-milled CoSn₃ show c-axes mostly within 30° of the substrate. Controlling the grain orientation of Sn is vital for enhancing the electromigration reliability of solder joints, particularly in fine-pitch applications where joints may consist of a single grain. In this study, we investigate the use of preferentially grown α-CoSn 3 to influence Sn orientation. Firstly, α-CoSn 3 formed at the Sn/Co interface during reflow at 267 °C exhibited orientation-dependent growth. Its texture was improved via ion milling, which selectively removed smaller, misoriented grains and preserved well-anchored, favorably oriented ones. This treatment significantly improved the overall crystallographic alignment, with the (600) planes of α-CoSn 3 oriented nearly perpendicular to the substrate and the (002) planes parallel to the substrate. Subsequently, Sn powders were melted and solidified on the textured α-CoSn 3 surface to induce a preferential orientation, guided by lattice matching. A modified edge-to-edge lattice matching model, predicted the (1 0 1) β-Sn/(600) α-CoSn 3 with [0 1 0] β-Sn/[0 1 0] α-CoSn 3 as the favorable pairs. EBSD analysis confirmed this prediction, indicating that the [0 0 1] axes of the Sn grains nucleated on ion-milled α-CoSn 3 were oriented mostly within 30° of the substrate plane. These results demonstrate that the ion-milled α-CoSn 3 surface enables effective Sn orientation control, offering a practical route for improving solder joint reliability.