Strong coupling effects during Cu/In/Ni interfacial reactions at 280 °C

The substantial heat generated in three-dimensional integrated circuits and high-power electronics has made thermal management a critical challenge for reliability in the electronics industry. Pure indium solder has been used as a thermal interface material to minimize the contact thermal resistance between a chip and its heat sink. Indium and indium-based alloys are potential lead-free solder for low-temperature applications. Heat sinks in the heat dissipation system as well as substrates of electronic joints are usually made of copper, with nickel being the most commonly used diffusion barrier on the chip side. Therefore, the Cu/In/Ni sandwich structure would be encountered in electronic devices. The soldering process for forming the Cu/In/Ni structure crucially determines the reliability of devices. In this study, Cu/In/Ni interfacial reactions at 280 C were investigated. Intermetallic compounds were identified and the microstructural evolution was observed. A strong coupling effect between Cu and Ni was found, which caused several peculiar phenomena: (1) the formation of a Cu In compound (the Cu11In9 phase) at the In/Ni interface; (2) the formation of two sub-layers of the Cu11In9 phase at the Cu/In interface; (3) the formation of faceted rod-like Cu11In9 grains; and (4) the formation of a half-Cu11In9, half-Ni3In7 microstructure after prolonged reactions. The mechanism of phase transformations is elucidated based on the calculated Cu -In-Ni ternary phase diagram using CALPHAD thermodynamic modeling. (C) 2014 Elsevier Ltd. All rights reserved.