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

Abstract The orientation relationships and interfaces between e-Cu3Sn and Cu have been studied by transmission electron microscopy. Epitaxial Cu thin films were grown on the NaCl (001) and (111) surfaces and then Sn was evaporated onto the Cu films at 200 or 150 °C to form e-Cu3Sn directly. On the (111)Cu surface the interface is (001)e and (100)e is parallel to 1 ¯ 10 Cu with a low misfit in the direction. However, no orientation relationship was found on the (001)Cu surface. 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.