Researchers at the Daegu Gyeongbuk Institute of Science and Technology (DGIST) have discovered a method for making flexible thin-film electronic circuits considerably more durable — by filling them with thousands of tiny holes.
Flexible printed circuit boards are fantastic inventions, particularly in the wearables field: Rather than needing a flat section of a device to hold the electronics, you can curve them — and even actively bend them in use. The latter feature, however, is tempered with the fact that repeated bending introduces weaknesses and tiny cracks into the circuit - eventually causing it to fail.
"We happened to be passing by a construction site when we saw steel plates with holes, often used in construction," says Professor Jae Eun Jang of the inspiration behind his team's solution to the flexible circuit problem. "We knew that these steel plates with holes are used to reduce stress.
"We thought that this method could also be a solution in the micrometer world and, based on this idea, we began conducting experiments. Our devices were able to maintain conductivity up to 300,000 bending cycles, which means that they can be bent over 80 times a day for 10 years."
The solution, directly inspired by those steel plates: Micrometre-size holes drilled through the flexible circuit board in a zig-zag pattern. While it does nothing to prevent the tiny stress cracks from forming in the first place, it ensures that they can only spread between two adjacent holes — in much the same way ripstop nylon prevents rips from spreading the length of the material.
While the researchers haven't discussed a timescale for getting the technology into production, they have indicated that it would be easy for manufacturers to adopt the approach using equipment already used for display manufacturing.
The team's work has been published under closed-access terms in the journal ACS Applied Materials & Interfaces.