The growth behavior of IMC on the Sn/Cu interface during solidification of multiple reflows

The appearance of IMCs on the Sn/Cu interface plays an important role in the joint reliability. Their growth behavior during solidification of multiple reflows was investigated. Compressed air was employed to blow away the residual liquid solder immediately after heating preservation so that the morphology corresponding to heating preservation would remain unaltered; and then by compared they with samples experienced air cooling, the growth of interfacial Cu
₆
Sn
₅
grains could be investigated separately. The morphology of Cu
₆
Sn
₅
grains remained a scallop-type during heating preservations of multiple reflows and they always converted to prism-type after air cooling. The dissolution and precipitation of Cu in liquid Sn with the temperature fluctuations should be responsible to the transformation. Moreover, scalloped Cu
₆
Sn
₅
grains appeared at heating preservation became larger with the increasing number of reflows due to the ripening reaction. Their growth in dimension induced a change in appearance of those prismatic Cu
₆
Sn
₅
grains formed on them. Shorter but larger main facets formed on those prismatic Cu
₆
Sn
₅
grains with the increasing number of reflows.