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

The morphology and orientation evolution of Cu₆Sn₅ grains formed on (001)Cu and (011)Cu single crystal substrates under temperature gradient (TG) were investigated. The initial orientated prism-type Cu₆Sn₅ grains transformed to non-orientated scallop-type after isothermal reflow. However, the Cu₆Sn₅ grains with strong texture were revealed on cold end single crystal Cu substrates by imposing TG. The Cu₆Sn₅ 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 Cu₆Sn₅ grains showing about 30° angle with the substrate. The merging between neighboring Cu₆Sn₅ 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 Cu₆Sn₅ 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 Cu₆Sn₅ grains is really benefitial to solve the reliability problems caused by anisotropy in 3D packaging.