Bismuth/Indium/Tin alloy (Bi57/In26/Sn17) is a low-melting-point, lead-free solder alloy designed for precision electronic and thermal management applications. Known for its superior wettability, ductility, and minimal thermal fatigue, this ternary alloy offers an environmentally safe and mechanically stable alternative to traditional tin–lead solders.
Material Overview
Composed of approximately 57 wt% bismuth, 26 wt% indium, and 17 wt% tin, this eutectic alloy exhibits a melting temperature near 80 °C, significantly lower than that of conventional Sn–Pb solders. The microstructure typically consists of a bismuth-rich phase, β-Sn matrix, and fine BiIn2 intermetallic compounds that enhance both mechanical strength and ductility. Studies by Chen et al. (2017) showed that the Bi–In–Sn alloy forms Cu6(In,Sn)5 intermetallic layers when bonded to copper substrates, providing robust metallurgical adhesion. Furthermore, Jin et al. (2018) demonstrated that indium improves the elastic deformation capacity of Bi-based solders, enhancing fatigue resistance during thermal cycling. Electrical conductivity and creep resistance also remain high compared with other low-temperature solders, making Bi57/In26/Sn17 particularly effective for sensitive microelectronic assemblies.
Applications and Advantages
The Bi57/In26/Sn17 alloy is widely applied in microelectronic packaging, flexible electronics, and optical module assembly. Its low process temperature protects heat-sensitive components such as sensors, LEDs, and polymer-based substrates. According to Liu and Tu (2020), Sn–Bi–In alloys exhibit strong potential for next-generation semiconductor packaging, offering high wettability and reduced brittleness compared to Sn–Bi or Sn–In systems alone. In addition, the alloy’s excellent wetting behavior on copper and gold finishes enables precise bonding in fine-pitch circuits. The balance of thermal and mechanical performance allows it to maintain joint reliability under repeated heating and cooling cycles, which is critical in wearable electronics and aerospace instrumentation. Its lead-free composition also meets RoHS and REACH environmental compliance standards.
Goodfellow Availability
Goodfellow supplies Bismuth/Indium/Tin (Bi57/In26/Sn17) alloy in high-purity, research-grade form suitable for soldering, joining, and materials testing. Custom dimensions and configurations are available to support thermal interface design, electronic prototyping, and low-temperature bonding experiments.
Explore Bismuth/Indium/Tin Bi57/In26/Sn17 – Material Information and other advanced materials in Goodfellow’s online catalogue: Goodfellow product finder.
References
- Chen, C. H., Chakroborty, S., Lee, B. H., Chen, H. C., Wang, C. M., & Wu, A. T. (2017). Assessment of microstructure and shear strength for low-melting-point tin-free alloys on Cu. Materials Science and Engineering A, 696, 341–349. https://doi.org/10.1016/j.msea.2017.09.129
- Jin, S., Kim, M. S., Kanayama, S., & Nishikawa, H. (2018). Microstructure and mechanical properties of indium–bismuth alloys for low melting-temperature solder. Journal of Materials Science: Materials in Electronics, 29(14), 12124–12133. https://doi.org/10.1007/s10854-018-9738-0
- Li, Q., Ma, N., Lei, Y., Lin, J., Fu, H., & Gu, J. (2016). Characterization of low-melting-point Sn–Bi–In lead-free solders. Journal of Electronic Materials, 45(2), 1174–1185. https://doi.org/10.1007/s11664-016-4366-z
- Liu, Y., & Tu, K. N. (2020). Low melting point solders based on Sn, Bi, and In elements. Materials Today Advances, 8, 100115. https://doi.org/10.1016/j.mtadv.2020.100115