Metallic glue could replace soldering & welding

The “way” of attaching them is, aston­ish­ingly, a glue made out of metal that sets at room tem­per­a­ture and requires very little pres­sure to seal. “It’s like welding or sol­dering but without the heat,” says Huang, Pro­fessor and Chair, Depart­ment of Mechan­ical and Indus­trial Engineering.

In a paper, pub­lished in the Jan­uary issue of Advanced Mate­rials & Processes, Huang and col­leagues, including North­eastern doc­toral stu­dent Paul Elliott, describe their latest advances in the glue’s devel­op­ment. The curiosity was piqued: Sol­dering with no heat? The university asked Huang to elaborate.

“Both ‘metal’ and ‘glue’ are familiar terms to most people, but their com­bi­na­tion is new and made pos­sible by unique prop­er­ties of metallic nanorods—infinitesimally small rods with metal cores that we have coated with the ele­ment indium on one side and galium on the other. These coated rods are arranged along a sub­strate like angled teeth on a comb: There is a bottom ‘comb’ and a top ‘comb.’ We then inter­lace the ‘teeth.’ When indium and galium touch each other, they form a liquid. 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. We recently received a new pro­vi­sional patent for this devel­op­ment through North­eastern University.”

a) Coated rods are arranged along a sub­strate, like angled teeth on a comb. b) The teeth are then inter­laced. c) When indium and galium come into con­tact, they form a liquid. d) The metal core of the rods turns that liquid into a solid. The resulting glue pro­vides the strength and thermal/​electrical con­duc­tance of a metal bond. From “Advanced Mate­rials & Processes,” Jan­uary 2016

“The stan­dard polymer glue does not func­tion at high tem­per­a­tures or high pres­sures, but the metallic glue does. The stan­dard glue is not a great con­ductor of heat and/​or elec­tricity, but the metallic glue is. Fur­ther­more, the stan­dard glue is not very resis­tant to air or gas leaks, but the metallic glue is.

“‘Hot’ processes like sol­dering and welding can result in metallic con­nec­tions that are sim­ilar to those pro­duced with the metallic glue, but they cost much more. In addi­tion, the high tem­per­a­ture nec­es­sary for these processes has dele­te­rious effects on neigh­boring com­po­nents, such as junc­tions in semi­con­ductor devices. Such effects can speed up failure and not only increase cost but also prove dan­gerous to users.”

“The metallic glue has mul­tiple appli­ca­tions, many of them in the elec­tronics industry. As a heat con­ductor, it may replace the thermal grease cur­rently being used, and as an elec­trical con­ductor, it may replace today’s sol­ders. Par­tic­ular prod­ucts include solar cells, pipe fit­tings and com­po­nents for com­puters and mobile devices.”

Image description: A schematic illus­trating appli­ca­tions of metallic glue: a) A CPU on a printed cir­cuit board con­nected to a heat sink. b) A sur­face mount device being attached to a printed cir­cuit board. c) A press-​​fit pipe fit­ting for envi­ron­ments where welding is dan­gerous or impos­sible. d) A glass plate being attached to metal with a dif­ferent thermal-​​expansion coef­fi­cient to cover a cavity with a her­metic seal. From “Advanced Mate­rials & Processes,” Jan­uary 2016