The orientation relationships of the Cu3Sn/Cu interfaces and a discussion of the formation sequence of Cu3Sn and Cu6Sn5

Experimentally Cu3Sn forms after Cu6Sn5 in the reaction of Cu and Sn-containing solder. Analysis showed that the interfacial energies of the Cu6Sn5/Cu interfaces should be lower than those of the Cu3Sn/Cu interfaces due to better interfacial coherency. That is the main reason that Cu6Sn5 nucleates before Cu3Sn, even though Cu3Sn has a larger energy of formation.