Low Temperature Alloy Solders

Low temperature alloys, which typically contain indium or bismuth, melt at temperatures less than 180°C. These low-melting alloys are required for a wide variety of applications, including:

  1. Step soldering involving temperature sensitive components
  2. Soldering to molded interconnect device (MID) plastics
  3. Fusible alloys/fuse applications
  4. Mercury replacement
  5. Thermal and electrical conductivity

Step Soldering Involving Temperature Sensitive Components

Step soldering is the process of attaching components to a substrate in a series of steps where each step in the soldering process uses a lower reflow temperature than the step before it. Standard components are attached first and then temperature sensitive components (like LEDs) are done last. These temperature sensitive components reflow at temperatures less than 180°C.

Soldering To MID Plastics

Molded interconnect device (MID) plastics have been around for many years, but are becoming more popular in product design. MID plastics, which are formed into 3D shapes to increase the functionality and reduce overall weight of each product, are important in automotive and medical applications.

Fusible Alloys/Fuse Applications

Fusible alloys are valued for their relatively low-temperature melting point precision, as well as for their physical properties at room temperature.

Fusible alloys can be used for:

  • Fuses
  • Tube bending
  • Lens blocking
  • Wax pattern dies
  • Potting molds
  • Punch anchoring

Properties

Property Indalloy
117 158 160-190 217-440 255 281
Melting Point or Range Deg/F 117 158 160-190 217-440 255 281
Weight lbs/in3 .32 .339 .341 .343 .380 .315
Tensile Strength lbs/in2 5,400 5,990 5,400 13,000 6,400 8,000
Brinell Hardness No. 12 9.2 9 .19 10.2 22
Maximum Load
30 sec lbs/in2		 — 10,000 9,000 16,000 8,000 15,000
Safe Load Sustained — 300 300 300 300 500
Conductivity (Electrical) Compared with Pure Copper 3.34% 4.17% 4.27% 2.57% 1.75% 5.00%
Cumulative Growth and Shrinkage Time after Casting
2 min. +.0005 +.0025 -.0004 +.0008 -.0008 +.0007
6 min. +.0002 +.0027 -.0007 +.0014 -.0011 +.0007
30 min. .0000 +.0045 -.0009 +.0047 -.0010 +.0006
1 hr. -.0001 +.0051 .0000 +.0048 -.0008 +.0006
2 hr. -.0002 +.0051 +.0016 +.0048 -.0004 +.0006
5 hr. -.0002 +.0051 +.0018 +.0049 .0000 +.0005
500 hr. -.0002 +.0057 +.0025 +.0061 +.0022 +.0005

Mercury Replacement

Indium Corporation manufactures several alloys that have very low-melting points. These liquid-at-room-temperature alloys are finding increased uses in various applications as a replacement for the more toxic mercury. In addition, the vapor pressures of these alloys are substantially lower than mercury.

Thermal and Electrical Conductivity

Alloy systems that are liquid at room temperature have a high degree of thermal conductivity, far superior than ordinary non-metallic liquids. This allows for the use of these materials in specific heat-conducting applications, such as the heat dissipation of sensitive components during operation, machining, and/or manufacturing.

Other advantages of these liquid alloy systems are their inherent high densities and electrical conductivities. Typical applications for these materials include thermostats, switches, barometers, heat transfer systems, and thermal cooling and heating designs.

The table below lists available Indalloy® alloys which are liquid at room temperature.

Indalloy
Number		 Liquidus C Solidus C Composition Density
lb/in3		 Specific
Gravity
gm/cm3		 Thermal
Conductivity
(W/mK)		 Electrical
Resistivity
(10-8Ω-m)
46L 7.6 6.5 61.0Ga / 25.0In / 13.0Sn / 1.0Zn 0.2348 6.50 15* 33*
51E 10.7 10.7 66.5Ga / 20.5In / 13.0Sn 0.2348 6.50 16.51 28.91
51 16.3 10.7 62.5Ga / 21.5In / 16.0Sn 0.2348 6.50 16.51 28.91
60 15.7 15.7 75.5Ga / 24.5In 0.2294 6.35 20* 29.42
77 25.0 15.7 95Ga/5In 0.2220 6.15 25* 20*
14 29.78 29.78 100Ga 0.2131 5.904 28.13 14.854
* Estimated

References:

1 Geratherm Medical AG, Safety Data Sheet, 93/112/EC, 20042 Michael D. Dickey, et al., Eutectic Gallium-Indium (EGaIn): A Liquid Metal Alloy for the Formation of Stable Structures in Microchannels at Room Temperature, Advanced Functional Materials, 2008, 18, 1097–11043 C.Y.Ho, et al., Thermal Conductivity of the Elements, Journal of Physical Chemical Reference Data, Vol. 1. No 2, 1972.4 Charles Kittle, Introduction to Solid State Physics, 7th Ed., Wiley and Sons, 1996. 

Packaging for Liquid Metal Alloys 

Liquid metal alloys are shipped in polyethylene bottles.

Storage/Shelf Life for Liquid Metal Alloys

Unopened bottles have a guaranteed shelf life of one year. It is recommended that the volume be replaced with dry argon as the material is removed from the bottle. This will minimize any possibility of oxidation on the surface of the alloy. If the alloy has been stored below its melting point and has solidified, it should be remelted and thoroughly shaken or mixed before use.

indium-bismuth_low_melting_temp-solder_252bismuth low-temperature melt solder

 

Source: Carol Gowan, Indium Solder Co.

 

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