How to Solder Without Heat
Jenn U posted on May 11, 2016 |
New method uses Field’s metal to solder at room temperature.
A vial containing Field's metal particles suspended in ethanol. (Image courtesy of Iowa State University.)
A vial containing Field's metal particles suspended in ethanol. (Image courtesy of Iowa State University.)

From hobbyists building their first circuits to assembly lines in the microelectronics industry, soldering is the most common method of attaching components to a circuit board. 

But what happens when you don’t have power for a hot soldering iron or can’t afford to risk holding that heat near your delicate components?

Thanks to a recent breakthrough, you could soon be soldering at room temperature.

Engineering researchers have developed a method of soldering without an iron by manipulating the natural properties of metal alloys. Instead of typical Tin-Silver-Copper or Tin-Lead solder, the new method uses Field’s metal - an alloy of bismuth, indium, and tin which typically solidifies at 62 degrees Celsius. 

By isolating tiny droplets - less than 5 micrometers in diameter - the metal can be supercooled to room temperature while remaining in liquid form. Each droplet is encased in a thin solid shell. When these droplets are punctured or crushed, the liquid can flow into the desired region before quickly solidifying.  Currently, this is done using a tiny probe under a microscope.

Heatless Soldering


(A) Schematic of the process for mechanically separating the liquid or molten metal into smaller pieces in an acid-containing carrier fluid. (B) SEM micrograph of Field's metal nanoparticles derived from mechanical separation. (C) Close-up of a liquid metal microparticle. (D) Schematic of cross-section of the droplet structure. (Image courtesy of Nature.)

The droplets are created by adding liquid Field’s metal to a solution of acetic acid in diethylene glycol. The resulting alloy is then broken up mechanically into tiny droplets.

A double layer of solid material forms on the outside of the droplets: first, a layer of oxidized Field’s metal and then a layer of solid compound created through reaction with the acetic acid solution. Each layer is on the nanometer scale. Undisturbed, the material inside the droplet remains in supercooled liquid form until used.

The researchers are currently working on commercializing the technology, including creating SAFI-Tech as a distribution company, filing for a patent and employing further testing to prove the technology’s reliability and conductivity. Additional research will also be needed to scale the product up from its current micrometer size.

The goal for this technology is to increase the practicality and reduce the price of soldering technology. For the industrial assembly line, this technology reduces the need for hot soldering irons to come into proximity with delicate electronic components.

Provided the technology can be scaled up, it may allow for students and enthusiasts to cheaply solder boards without the need for an iron. This could expand access to electronic projects to those living with little access to sufficient power sources as well as younger enthusiasts for whom a soldering iron could be dangerous. 

Iowa State University assistant professor Martin Thuo, who led the reserach, hopes that this development could have as great an impact on electronic manufacturing as the development of lead-free solder did in 1996.

Read more about Professor Thuo’s lab here.

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