If you want to piss off an electrical engineer, tell them that future electronics might be built using a room-temperature metallic glue instead of conventional soldering techniques. Despite the tedium, burns, bad joins, and dangerous lead fumes, soldering is a prized and hard-fought skill. It's also unavoidable: a technique central to absolutely everything to do with building and repairing electronics at all levels.
Materials scientists at Northeastern University in Boston are daring to suggest, however, that its days may be numbered. This is thanks to a recent creation dubbed MesoGlue: a "revolutionary joining solution that lets you attach items together with a metal bond, at room temperature." Soldering without the heat, in other words. The new material is described in this month's Advanced Materials and Processes.
The origins of soldering are usually put at around 5,000 BC. Metalworking had already been around then for 7,000 years or so, but the idea of using molten metal to join stuff together came later with the discovery of naturally occurring alloys featuring lower melting points. Earlier solders were made of gold and tin, with the tin-lead combination employed in contemporary electronics appearing some time during the Roman empire. In other words, soldering is old as hell.
MesoGlue is by contrast a relatively high-tech material, with its adhesive properties made possible thanks to engineered nanorods that act to "lock" together two surfaces in a similar way to two combs meshing together, but a lot more permanent. "When the mating surfaces are brought together, the large spacing of the nanorods allows them to slide between those on the opposing surface and to interpenetrate," the current paper explains.
The nanorods are encased by a shell that liquefies as it they interlock with the nanorods of the other surface to be bonded. The result is a liquid alloy that squishes around the interlocked nanorods, soon solidifying into a strong bond featuring the crucial ability to withstand high temperatures (as might be found in electronic componentry).
"When indium and galium touch each other, they form a liquid," explains Northeastern's Hanchen Huang in a Q&A. "The metal core of the rods acts to turn that liquid into a solid. The resulting glue provides the strength and thermal/?electrical conductance of a metal bond."
As the paper explains, the need for extreme temperatures in the conventional soldering process is more than just a danger to the fingers of a wayward Arduino hacker—it's a danger to the electronics themselves. While good connections are necessary to dissipate heat from CPU, the process of soldering the connections carries its own thermal dangers.
"As component size decreases, soldering or wire bonding becomes more challenging and voids can lead to joint failure," the Northeastern group writes. "A metallic glue bond eliminates the possibility of heat damage during attachment and simplifies the soldering process to merely pressing parts together to attach."
What's more, the researchers found that their metallic glue dissipated heat even more efficiently than the thermal grease usually used to pack the spaces between electronic components and nearby heat sinks, with simulations showing CPU temperatures of around 8 degrees Celsius lower on average.
Naturally, the scientists have already patented MesoGlue. But good old lead remains as cheap as ever.