Bismuth in many languages1
Bismuth (Bi) is being used more and more as a replacement for lead in solder alloys because it is non-toxic. Although the melting temperature of pure bismuth is 271°C, the addition of bismuth will lower the melting temperature of most metals it is alloyed with. Bismuth compounds are also widely used in medical and cosmetic applications.
- The most popular lead-free bismuth solder alloys are Indalloy® #281 (58Bi 42Sn) which melts at 138°C and Indalloy® #282 (57Bi42Sn1Ag) which melts at 140°C. The addition of the 1% Ag makes the alloy more malleable. Both alloys can be used for step soldering applications. After the initial joints are made with a standard SAC alloy (220°C) subsequent soldering operations can be done using the bismuth alloys.
- Indalloy #281 and #282 have joint properties similar to those of tin-lead solders, with superior fatigue and copper dissolution characteristics.
- Bismuth is the most diamagnetic and the least thermally conductive of all metals
- In addition to being non-toxic it does not oxidize as readily as lead does.
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Some alloys that melt below 300° Celsius are used for applications other than joining two surfaces.
Low temperature alloys have a number of applications, including step soldering and interconnection of molded components. Additionally, its thermal and electrical conductivity make it attractive for bonding and heat transfer.
Expansion during cooling is a property of low-temperature alloys that can be very useful.
From One Engineer to Another®
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