Indium Blog

Making Bismuth Solder Less Brittle

  • Bismuth
  • Flux
  • Indalloy
  • Indium Corporation
  • Solder
  • Solder Alloys
  • Solder Flux
  • Soldering
  • Solder Wire
  • Solderability
  • Tin Silver

  • The binary eutectic alloy of bismuth and tin (Bi/Sn) is well suited for many low temperature applications due to its melting point of 138°C, but the alloy is known for being rather brittle for a solder alloy.

    All hope is not lost though - there is a similar alloy, known as Indalloy 282, which drastically reduces the brittle nature of the Bi/Sn alloy with the addition of just 1% Silver (Ag).  This 57%Bi/42%Sn/1%Ag alloy has a 1°C higher melting point.  Although you won’t be able to notice this reflow change, you will immediately notice the physical difference if you compare solder wire made from each alloy.  The Bi/Sn wire is likely to break upon bending, unlike the Bi/Sn/Ag alloy.
    The easiest (and most economical) way to experiment with these alloys is with a solder wire kit . With a wire kit you can obtain both wires in the same diameter, and you get 5 fluxes to help with soldering.  You can also get up to 10 different alloys if you want to experiment-your-heart-out and compare Bi/Sn and Bi/Sn/Ag to other alloys like Sn/Pb or Sn/Ag/Cu.