BiInSn

BiInSn is a ternary alloy system composed of bismuth (Bi), indium (In), and tin (Sn). The best-known composition is Bi32.5In51Sn16.5, commonly referred to as Field’s metal, which melts at a temperature around 62°C. Other Bi–In–Sn compositions exist that exhibit similarly low melting behavior, making the family of alloys useful as low-temperature solders and heat-transfer materials.

The primary use of BiInSn alloys is in low-temperature soldering and rework, where a molten phase can be achieved with modest heating. They are also employed as thermal fuses or heat-transfer media in educational demonstrations of phase transitions and alloy solidification. Because the melting point is well below many common solder alloys, BiInSn can be advantageous in temperature-sensitive assemblies or rapid heating scenarios.

In terms of properties, BiInSn alloys are more dense than many lead-free solders and exhibit good fluidity in the molten state, which supports filling small joints. They are generally considered to be less toxic than traditional lead-containing solders, though safety practices apply as with any molten metal. Mechanical properties in the solid state tend to reflect the brittle-to-ductile characteristics typical of bismuth-containing alloys, and oxidation during handling can affect surface quality. The alloys are not suitable for high-temperature service and may form intermetallics with certain substrates if misused, so fluxing and surface preparation are important for reliable joints.

BiInSn alloys are not a single compound but a family of low-melting compositions, with the Bi–In–Sn system offering tunable melting points around room to low-temperature ranges. They are most often discussed in the context of Field’s metal and related low-melting solder applications.