Properties of CuGa₂ Formed Between Liquid Ga and Cu Substrates at Room Temperature

Ga and Ga-based alloys have received significant attention due to their potential application in the liquid state for low-temperature bonding in microelectronics. This study investigated the interfacial reactions between liquid Ga and pure Cu substrates at room temperature. The directional thermal expansion behaviour of the resulting CuGa₂ was analysed by synchrotron x-ray powder diffraction with supporting observations of single crystal foils in high-voltage transmission electron microscopy. The mechanical properties of CuGa₂ were evaluated by nano-indentation. CuGa₂ was found to have advantages over other intermetallics that are present in assemblies made with current generation lead-free solders, including Ag₃Sn, Cu₆Sn₅ and Cu₃Sn. In addition to enabling lower process temperatures, solder alloys that form CuGa₂ at the interface with Cu offer the possibility of providing more reliable connections in the very small joints that play an increasingly important role as the trend to miniaturisation of electronics continues.