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 degrees 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. (C) 2021 Published by Elsevier Ltd on behalf of Chinese Society for Metals.