The microstructure of η′-Cu6Sn5 and its orientation relationships with Cu in the early stage of growth

The microstructure of η′-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 °C for 30 s. The Cu and Sn on the η′-Cu6Sn5 surfaces were removed electrolytically and the specimens were analyzed by scanning and transmission electron microscopy. The η′-Cu6Sn5 grains on the Cu side were as small as 5 nm but grew rapidly to 0.3 to 0.5 μm on the Sn side.The orientation relationships between η′-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 η′-Cu6Sn5. Two types of orientation relationships were found, i.e., (1) [204]η′//[001]Cu (zone axis), (402̄)η′//(110)Cu, and (020)η′//(11̄0)Cu, and (2) [204]η′//[111]Cu (zone axis), (402̄)η′//(11̄0)Cu, and (020)η′//(1̄1̄2)Cu. The interfaces were analyzed.