Circuit boards are usually hard, but U.S. and Chinese researchers have worked together to develop a light, soft FPC circuit board that is conceptually validated as a "smart bandage" that can be attached to the skin to monitor a variety of physiological signals. The "smart bandage" consists of four layers of interconnected, thin, flexible FPC stacked together, the overall size and thickness of a dollar coin, according to a cover article published in the British magazine Nature Electronics on the 13th.

Researchers say the circuit board uses an island-bridge structure based on silicon elastomers, in which the island is a small rigid electronic device, such as sensors, antennas, Bluetooth chips, and so on; and the bridge is a stretchable copper wire used to connect the island so that the FPC circuit board can be stretched and bent without affecting its function. Communication author Xu Sheng, a professor of nanoengineering at the University of California, San Diego, said the design difficulty was not stacked circuit boards, but current connections between FPC circuit boards.

The Xu Sheng team has found that traditional lithography and etching techniques are not suitable for flexible elastomers. So they mix silicone elastomers with black organic dyes, make circuits, stack them, weld them with lasers, and fill them with conductive materials. The circuit board thus obtained has both normal function and flexibility of traditional circuit boards. The researchers say the "smart bandage" made from the flexible circuit board is widely used and can be attached to different parts of the body to record electrocardiograms, electroencephalograms, eye movements and muscle behavior.

In addition, it can communicate with a smartphone or notebook computer within 10 meters, and can be used for remote control of robotic arms. The researchers said that after 6 months of continuous use, the performance and scalability of the FPC circuit did not decrease. Researchers from the University of Electronic Science and technology of China and the US Air Force Research Laboratory participated in the research.