Phase stabilities and interfacial reactions of the Cu–In binary systems

The Cu–In binary system is receiving increasing attention due to its application in the low-temperature assembly of heat-sensitive devices. Nevertheless, the fundamental behaviors of this binary system are very difficult to study because of the extreme softness of indium. This difficulty was successfully overcome in this study, and the phase stabilities and chemical reactions were established. Binary Cu–In diffusion couples were prepared by electroplating In onto a Cu substrate. During the plating process, CuIn₂ formed even though this intermetallic is not present in the Cu–In binary phase diagram. It was established in this study that CuIn₂ is indeed a stable phase below 100 °C, but decomposes at a temperature between 100 and 120 °C. In addition, the microstructure evolution during solid-state aging at 100, 120, and 140 °C was investigated. The hardness values and Young's moduli for CuIn₂ and Cu₁₁In₉ were measured by using nanoindentation.