Effect of Cu addition on the microstructure and mechanical properties of In–Sn-based low-temperature alloy

Abstract

The In–48Sn eutectic alloy has emerged as a favorable solder for flexible electronic devices, owing to its low operating temperature. However, the low strength of In–48Sn eutectic alloy compared with that of other commercial solders affects the product life and limits its use in the device applications. Herein, we studied the effects of xCu addition (x = 1.0, 2.0, and 8.0 wt %) on melting temperature, phase segregation, and mechanical properties of In–Sn alloy. The results revealed that the melting temperatures of the In–Sn–Cu (ISC) alloys were close to that of eutectic In–Sn alloy (115 °C) due to the ternary reaction in the ISC alloys. In addition, the initial solidification temperature of the η-(Cu,In,Sn) compound took place below 400 °C, and partial solid-transformation to ternary τ-Cu2In3Sn occurred in the temperature range 83–78 °C, owing to the diffusion of Cu-atoms and consumption of the β-In3Sn phase in the new ISC alloys. The phase segregation affected the phase fraction in the ISC matrix and the mechanical properties of ISC alloys. Furthermore, the In–Sn-1.0Cu alloy exhibited the highest elongation of 74%, which was more than twice that of In–48Sn alloy. Simultaneously, the In–Sn-8.0Cu alloy presented the highest tensile strength of approximately 17.0 MPa, which was 1.5 times that of the In–48Sn alloy.