The microstructure of eta'-Cu6Sn5 during the early stage of growth was Studied. Sn was electroplated onto thin Cu foil at room temperature and the specimen was annealed at 150 degrees C for 30 s. The Cu and Sn on the eta'-Cu6Sn5 surfaces were removed electrolytically and the specimens were analyzed by scanning and transmission electron microscopy. The eta'-Cu6Sn5 grains on the Cu side were as small as 5 run but grew rapidly to 0.3 to 0.5 mu m on the Sn side. The orientation relationships between eta'-Cu6Sn5 and Cu were studied by a thin-film technique. Cu was evaporated onto the NaCl (001) and (111) Surfaces to form epitaxial Cu thin films and Sn was then evaporated onto the Cu films to form eta'-Cu6Sn5. Two types of orientation relationships were found, i.e., (1) [204](eta')//[001](Cu), (zone axis), (40 (2) over bar)(eta')//(110)(Cu), and (020)(eta')//(1 (1) over bar0)(Cu) (2) [204](eta')//[111](Cu) (zone axis), (40 (2) over bar)(eta')//(1 (1) over bar0)(Cu), and (020)(eta')//((1) over bar(1) over bar2)(Cu). The interfaces were analyzed (C) 2009 Elsevier B.V. All rights reserved.