The orientation relationships and interfaces between epsilon-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 degrees C to form epsilon-Cu3Sn directly. On the (111) Cu surface the interface is (001)(epsilon) and (100)(epsilon) is parallel to ((1) over bar 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. (C) 2014 Elsevier B.V. All rights reserved.