Microstructure and mechanical properties of indium–bismuth alloys for low melting-temperature solder

Abstract

Application of a low-temperature soldering process is preferred in developing wearable and flexible electronic devices because of the temperature sensitivity of unconventional polymer-based substrates or other low-heat budget materials. In this context, indium-based alloy has advantages such as low melting point, wettability, and thermal-fatigue resistance. In particular, indium has good ductility for elastic deformation without fatigue. These solders were developed for low-temperature applications with the alloying element: 30 mass% Bi, 33.7 mass% Bi, 40 mass% Bi and 50 mass% Bi. The alloys were designed to have an onset temperature between 72.7 and 91.3 °C. In the present study, the effect of alloy composition on the microstructure, melting properties, and mechanical properties of In–Bi alloys were investigated. The analysis on the measured characteristics was conducted to optimize the design of the In–Bi alloy.