Mechanical behavior of Au–In intermetallics for low temperature solder diffusion bonding

In this study, gold (Au)–indium (In) intermetallic compounds (IMCs) formation for low temperature solder bonding was investigated by imbedding a gold wire into the annealing indium solder. According to available research on liquid–solid reaction of gold and indium, experiments were only conducted at an annealing temperature in the range of 200–300 °C. To investigate the feasibility of forming the Au–In IMCs at lower temperature, a low annealing temperature of 160 °C was applied in this study, which is just above the melting point of indium of 156 °C. AuIn2 precipitates were confirmed to be predominately formed in the IMCs by X-ray diffraction. Different annealing times of 10, 40, and 120 min were applied to study the stabilization time of IMC AuIn2. With thermal considerations, AuIn2 was confirmed to form with a low annealing temperature of 160 °C, and a short annealing time of 10 min. In addition, the microstructure of the cross-sections in the interfacial region of the gold wire and indium solder was investigated by scanning electron microscopy. The mechanical behavior of gold, indium, and their IMCs with different annealing times were studied by nanoindentation. Mechanical properties including reduced modulus and hardness were extracted after taking into account of the pile-up effect. Increased reduced modulus and hardness were observed with increasing annealing times, due to the strengthening of the atomic bonding in the compounds. The reduced modulus and hardness measured from nanoindentation indicate a significant strengthening of the indium solder by the AuIn2 nanoparticles.