Interfacial reaction and thermomigration of copper/indium joints

Indium is a promising joining material for low-temperature soldering and thermal interface applications. Copper is a common metal pad used to join indium to form solder joints. Interfacial reactions and thermomigration are two important research subjects for the reliability assessment of solder joints. In this study, the interfacial reactions of copper/indium joints annealed at 210 °C are investigated with a focus on the growth kinetics of intermetallic compounds (IMCs) formed at the joints. Sandwiched copper/indium/copper joints are prepared via thermocompression to study the thermomigration across the joint driven by a temperature gradient of 794 °C cm −1 . The results show that the Cu 11 In 9 phase forms at the copper/indium joints, whereas its growth rate is influenced by the impurity content and grain size of the electroplated copper substrates. The thermomigration effect is significant in copper/indium/copper joints, wherein the Cu 11 In 9 phase at the cold end grows at a much faster rate than does that at the hot end. The average product of the diffusivity and molar heat of transport ( D × Q∗ ) for copper in molten indium is calculated to be (3.09 ± 0.21) × 10 −2 J cm 2 mol −1 s −1 .