First-principles calculations to investigate the structural stability, electronic and mechanical properties of CuGa 2 and Cu 9 Ga 4

This paper aims to evaluate the service reliability of intermetallic compounds (IMCs) in Cu-Ga joints. It accomplished this by calculating the thermodynamic and mechanical properties of CuGa 2 and Cu 9 Ga 4 , which are common IMCs in Cu-Ga low temperature interface reaction, based on the first-principles calculation. According to the calculation results of enthalpy of formation and binding energy, both CuGa 2 and Cu 9 Ga 4 are thermodynamically stable, and Cu 9 Ga 4 exhibits superior thermodynamic stability compared to CuGa 2 . The mechanical properties of Cu 9 Ga 4 are better than CuGa 2 , with larger bulk modulus, shear modulus and Young ' s modulus. By comparing the elastic modulus with that of IMCs of Cu-Sn system, Cu 9 Ga 4 shows larger elastic modulus than eta ' -Cu 6 Sn 5 and smaller than Cu 3 Sn. In addition, Cu 9 Ga 4 exhibits excellent toughness. By fitting the thermal expansion coefficients of Cu, CuGa 2 and Cu 9 Ga 4 , the result shows that the thermal expansion coefficients of Cu and Cu 9 Ga 4 are better matched. Additionally, the rapid volume expansion of CuGa 2 weakens the interaction force between its atoms, resulting in a faster decay of its bulk modulus. The prediction of the mechanical properties of Cu-Ga compounds provides a deeper understanding of their properties and is important for the understanding of the feasibility of low-temperature brazing of Cu-Ga soldering systems.