Direct metal printing enables flexible, stretchable circuits

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North Carolina State University researchers say a technique they have developed for directly printing metal circuits could enable the creation of flexible and stretchable electronics. The technique, which can use multiple metals and substrates, is claimed to be compatible with existing manufacturing systems that apply direct printing technologies. The team says it demonstrated the functionality of the technique by creating a touch sensor with a 400 pixel array into an area of 1sq cm.

“Flexible electronics hold promise for use in many fields, but there are significant manufacturing costs involved, which poses a challenge in making them practical for commercial use,” said associate professor Jingyan Dong.

"Our approach should reduce cost and offer an efficient means of producing circuits with high resolution, making them viable for integrating into commercial devices.”

While the technique uses existing electrohydrodynamic printing technology, ink is substituted with molten metal alloys, whose melting points can be as low as 60°C. So far, the team has demonstrated the technique by printing three alloys on four different substrates – glass, paper and stretchable polymers.

“This is direct printing,” said Dong. “There is no mask, no etching and no moulds, making the process much more straightforward.”

Tests of a circuit printed on a polymer substrate found conductivity was unaffected, even after being bent 1000 times. The circuits were also found to be electrically stable when stretched to 70% of the tensile strain limit.

A further benefit was the circuits may be capable of ‘healing’ themselves if broken or stretched too far.

“Because of the low melting point, you can simply heat the affected area up to around 70°C and the metal flows back together, repairing the relevant damage,” Dong claimed.