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

Area of Science:

• Materials Science
• Solid-State Chemistry
• Metallurgy

Background:

• Indium (In) is a promising low-temperature solder due to its low melting point and good mechanical properties.
• The solid-state microstructure evolution of In with various substrates is not well understood, primarily due to In's softness.
• Investigating Cu/In interfaces is crucial for understanding solder joint reliability and material interactions.

Purpose of the Study:

• To investigate the phase identification and microstructure evolution at the Cu/In interface after prolonged thermal aging.
• To determine the stability of phases formed in the Cu-In binary system.
• To elucidate the mechanism governing the growth rate of intermetallic compounds at the Cu/In interface.

Main Methods:

• Cryogenic broad Ar+ beam ion polishing was employed to prepare artifact-free Cu/In interfaces for microstructural analysis.
• Long-term thermal aging was performed on Cu/In samples.
• Phase identification and microstructure investigation techniques were utilized to analyze the aged interfaces.

Main Results:

• The intermetallic compound CuIn2 was identified as a stable phase forming at the Cu/In interface.
• The peritectoid temperature for the reaction Cu11In9 + In → CuIn2 was determined to be between 100 and 120 °C.
• The growth rate of CuIn2 was found to be influenced by the curvature of the Cu11In9/In phase and the temperature differential relative to the peritectoid temperature.

Conclusions:

• CuIn2 is a stable phase in the Cu-In binary system, forming at the Cu/In interface during thermal aging.
• The growth kinetics of CuIn2 are dependent on interfacial geometry and thermal conditions relative to the peritectoid temperature.
• A comprehensive mechanism for the solid-state interfacial reaction in Cu/In systems was proposed based on the experimental findings.