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Unsolderable no more: Liquid-process transistor does the trick

Posted: 02 Mar 2015 ?? ?Print Version ?Bookmark and Share

Keywords:University of Chicago? 3D printer? solder? liquid-processed transistor?

A team of researchers from the University of Chicago, together with Argonne National Laboratory and the Illinois Institute of Technology, snatched a new world record through their liquid-processed transistors that were produced at only a few hundred degrees Celsius. Based on a novel inorganic solder that adapts to disparate semiconductors, the "miracle solder" is used by the researchers to connect semiconductors that were previously unsolderable.

According to the researchers, the solder can also be used in an additive manner to create innovative semiconducting materials by joining their powdered forms into a continuous single-crystal-like material, and the stuff can even be used in 3D printers to join materials that were formerly incompatible.

The miracle solder was invented at the University of Chicago, in collaboration with Argonne National Laboratory and the Illinois Institute of Technology.

"Our 'solder' is an inorganic soluble material that can be applied as liquid and turns into an inorganic semiconductor upon mild heating," Dmitri Talapin, professor at the University of Chicago. "The trick was to find a chemical that is soluble, reactive and does not contaminate semiconductor surfaces."

Jaeyoung Jang

Postdoctoral researcher Jaeyoung Jang works new semiconductor solder in an environmentally controlled glove box facility at the University of Chicago's Gordon Centre for Integrative Science. (Source: University of Chicago)

Talapin's research team searched through many inorganic compounds before hitting up a precise mixture of cadmium, lead and bismuth in liquid form. When used to join two materials that were previously impossible to solder, while maintaining electronic conduction, the solder automatically adapts to the differing characteristics that previously prevented successful soldering, then decomposes to form a seamless joint. What's more, since it is a liquid, new materials can be made by mixing their powdered form into the solder then apply mild heating (at a few hundred degrees Celsius) creating an entirely new type of semiconductor that behaves as if it were grown as a single crystal in a high-temperature oven. It can also be used in 3D printers to form these new materials into useful shapes and sizes.

Miracle solder

Disparate semiconductors can be joined with a new solder developed by Talapin's research group at the University of Chicago. (Source: University of Chicago)

"We found that we can take very fine powder, apply solder to connect the grains and make a material with electron mobility comparable to that in single crystal," said Talapin. "Regarding 3D printing, it is under development at this stage. Currently we are primarily focusing on thermoelectric materials."

Dmitri Talapin

Talapin's research group at the University of Chicago has developed a solder that bridges different types of semiconductors that have resulted in disruptions at the joint in the past. (Source: University of Chicago)


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