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. CuIn2 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 Cu11In9 + In -> CuIn2 reaction was confirmed to be between 100 and 120 degrees C. In addition, the growth rate of CuIn2 was discovered to be dominated by the curvature of the reactant Cu11In9/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.

Automated summary

In this study, cryogenic broad Ar+ beam ion polishing was used to prepare artifact-free Cu/In interfaces for investigation of the solid-state microstructure evolution of In with different substrates. CuIn2 growth and stability were observed, and the peritectoid temperature of the Cu11In9 + In -> CuIn2 reaction was determined.