Morphology and orientation evolution of Cu6Sn5 grains on (001)Cu and (011)Cu single crystal substrates under temperature gradient

Abstract

• Cu 6 Sn 5 grains on (001)Cu grew with < 11 2 ¯ 0 >//RD and finally merged into one grain to form a fully IMC joint. • Cu 6 Sn 5 grains on (011)Cu showed strong texture and merged into several grains have about 30° angle with the substrate. • Merging of perpendicular Cu 6 Sn 5 grain pairs on (001)Cu was driven by sufficient Cu flux and grain boundary migration. • Innate gaps and small grain boundary area prevented perpendicular Cu 6 Sn 5 grain pairs on (011)Cu from merging into one grain. • Morphology transformation of Cu 6 Sn 5 grains during isothermal reflow was attributed to insufficient flux and destruction of atomic matching relationship. The morphology and orientation evolution of Cu 6 Sn 5 grains formed on (001)Cu and (011)Cu single crystal substrates under temperature gradient (TG) were investigated. The initial orientated prism-type Cu 6 Sn 5 grains transformed to non-orientated scallop-type after isothermal reflow. However, the Cu 6 Sn 5 grains with strong texture were revealed on cold end single crystal Cu substrates by imposing TG. The Cu 6 Sn 5 grains on (001)Cu grew along their c -axis parallel to the substrate and finally merged into one grain to form a fully IMC joint, while those on (011)Cu presented a strong texture and merged into a few dominant Cu 6 Sn 5 grains showing about 30° angle with the substrate. The merging between neighboring Cu 6 Sn 5 grain pair was attributed to the rapid grain growth and grain boundary migration. Accordingly, a model was put forward to describe the merging process. The different morphology and orientation evolutions of the Cu 6 Sn 5 grains on single crystal and polycrystal Cu substrates were revealed based on crystallographic relationship and Cu flux. The method for controlling the morphology and orientation of Cu 6 Sn 5 grains is really benefitial to solve the reliability problems caused by anisotropy in 3D packaging.