Chris Lohr Demonstrates and Tests PolyLMN "Liquid Metal" Stretchy Circuit Boards

Developed by the Air Force, PolyLMN — polymerized liquid metal — has some really interesting properties for circuit design.

Electrical engineer Charles Lohr has published a video on polymerized liquid metal (PolyLMN), a novel nanomaterial currently under investigation by researchers for flexible, stretchy circuit boards.

"It's got some crazy properties," Lohr explains of the material, "like it can be stretched, and it's conductive, and it doesn't follow Pouillet's Law — which means that when it is stretched it doesn't really change resistance much at all. The thing that I was most interested was to find out if this material could be used to make stretchy transparent circuit boards."

PolyLMN has proven a great material for making flexible, stretchable circuits. (📹: Charles Lohr)

Figuring the best approach is a practical one, Lohr set about designing a board for testing the material. "We started about two weeks beforehand: I designed the STM32F042 board here, and it has USB. I designed an ESP32 board with Wi-Fi, this pass-through board, and a backstop board. The idea is that we would clamp the PolyLMN on its substrate between the backstop board and whatever board we wanted to test with.

"We made the pass-through board to test the interface because that was what I was most worried about, but in the end it really wasn't that bad. The interfacing became even less of a problem after we started experimenting with different types of interfaces. We started with this gold finish, then we moved to HASL which is just a lead finish, and then we tried solder bumps."

The full video, which includes a showcase of the manufacturing process for PolyLMN circuits, can be found on Lohr's YouTube channel.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire:
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