Long-Term Aging Study on the Solid State Interfacial Reactions of In on Cu Substrate

Indium is considered a candidate low-temperature solder because of its low melting temperature and excellent mechanical properties. However, the solid-state microstructure evolution of In with different substrates has rarely been studied due to the softness of In. To overcome this difficulty, cryogenic broad Ar(+) beam ion polishing was used to produce an artifact-free Cu/In interface for observation. In this study, we accomplished phase identification and microstructure investigation at the Cu/In interface after long-term thermal aging. CuIn(2) was observed to grow at the Cu/In interface and proved to be a stable phase in the Cu–In binary system. The peritectoid temperature of the Cu(11)In(9) + In → CuIn(2) reaction was confirmed to be between 100 and 120 °C. In addition, the growth rate of CuIn(2) was discovered to be dominated by the curvature of the reactant Cu(11)In(9)/In phase and the temperature difference with the peritectoid temperature. Finally, a comprehensive microstructural evolution mechanism of the Cu/In solid-state interfacial reaction was proposed.