Formation mechanism and orientation of Cu3Sn grains in Cu–Sn intermetallic compound joints

• Columnar Cu3Sn grains grew along directions parallel to Cu6Sn5 grain boundaries in Cu–Sn IMC joints.
• Some small equiaxed Cu3Sn grains were found in the Cu–Sn IMC joints.
• Cu3Sn grains had preferred orientation of Cu3Sn (100) crystal plane being parallel to Cu substrate, whatever orientations of the Cu substrates were.

The formation mechanism and orientation of Cu3Sn grains in Cu–Sn intermetallic compound (IMC) joints formed on polycrystalline and (100), (111) single crystal Cu substrates at 300 °C were investigated. The results showed that when IMC joints were composed of Cu3Sn and Cu6Sn5 phases, columnar Cu3Sn grains grew in clusters at the expense of Cu6Sn5 phase. In addition, the Cu3Sn grains growth direction was parallel to the Cu6Sn5 grain boundaries in the middle layer of the IMC joints. When the Cu3Sn grains from the opposite sides contacted each other, grain growth stopped. Some small equiaxed Cu3Sn grains were found both at the Cu/Cu3Sn interfaces and in the Cu3Sn contact areas in the middle of the joints. A preferred orientation of Cu3Sn (100) crystal plane being parallel to the Cu substrate was found, which was unrelated to the orientation of Cu substrates.