As is known to all, printed circuit board plays a very important role in People's Daily life, and has been widely used in industrial production, national defense security and medical and health fields. The traditional PCB preparation process is very complicated, which needs to go through more than a dozen processes. In recent years, flexible electronics has become increasingly popular. Unlike traditional rigid circuit boards, flexible circuit boards can be bent, folded or even stretched at will, which makes them of great value in wearable devices, portable medical devices, skin electronics and other fields .

 In the field of liquid metal flexible electronic eppinger s. sourcing by design team has more than 10 years of research experience, based on prior to a large number of studies have found that the characteristic of liquid metal materials at room temperature of liquid gallium alloy mixed with solid metal particles (Ni) can be prepared with high viscosity and plasticity of a liquid metal material (Ni - EGaIn). The adhesion of this kind of material on different substrate surfaces is very different and the patterned liquid metal circuit can be printed quickly. The experimental results show that the semi-liquid metal materials have high adhesion on PU film, but poor adhesion on toner. To this end, the team first used laser printing to deposit the toner pattern on paper coated with PU adhesive film, and then used the significant difference in adhesion between the two substrates of semi-liquid metal materials to roll coating in a very short time (< 10s) the semi-liquid metal material is selectively printed onto the target part of the A4 size paper to produce the required circuit in a matter of seconds (figure 1). The flexible circuit prepared by this technique has a maximum accuracy of 50 microns, and can maintain the stability of the circuit connection in the process of base bending and folding. It was further pointed out that the new method was more general and semi-liquid metal materials had higher adhesion on more substrate materials such as flexible silica gel (Ecoflex). Based on this phenomenon, the semi-liquid metal ink material can also be deposited on the target part of the flexible silica gel surface by transfer printing method, and the stretchable flexible circuit can be quickly prepared .

Using the above manufacturing principles, the research group has produced a series of flexible and stretchable functional circuits, such as multi-layer circuit, large-area circuit and stretchable sensor (figure 4), etc. The tests have shown the excellent electrical stability, adaptability and recyclability advantages of the corresponding devices. The implementation of the proposed method does not require complex equipment, and the flexible circuit can be used in wearable medical devices, which provides a new way for the realization of personalized medical electronics.

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