Growth behavior of intermetallic compounds on Sn-10Bi-0.7Cu-0.15Co/Co interface under multiple reflows

The interface reaction between the Sn-0.7Cu-10Bi-0.15Co and Co substrate during multiple reflow cycles and the growth and evolution rhythm of intermetallic compounds (IMCs) were investigated. The results showed that as the reflow cycles increased in number, different growth morphologies and evolution rules of the IMCs layer including its primary growth, dissolution and secondary growth appeared. In the primary stage of multiple reflows, Co could be continuously diffused from the Co substrate to the IMCs/solder interface to provide enough Co for the growth of IMCs layer. As the IMCs layer became thick, the diffusion of Co to the interface was inhibited, and the dynamic equilibrium of IMCs growth was broken. When the growth rate was higher than the dissolution rate, the IMCs layer grew as a whole and whereas the IMCs were dissolved. And under the action of adsorption force, the dissolved IMCs particles re-aggregated and grew.