Bubble-free injection of liquid metal for the direct microfabrication of leaf-inspired 3D-topological conduit-networks and a flexible serpentine circuit with superior electrical resistance to aging

Flexible circuit boards are widely used in smart consumer electronic devices. In this paper, a novel methodology, which is different from the traditional etching and screen printing methods that generally rely on screen printed conductive ink as a conductor to form the required circuit in a dielectric film, has been reported. Liquid metal was directly injected into biocompatible polymer microchips, based on the air-diffusion mechanism, in order to prevent the circuit board from being directly exposed to the outside environment. The liquid metal circuit board that was produced had good thermal conductivity because the thermal conductivity of gallium is about 60 times that of water and 1000 times higher than that of air. In addition, the liquid metal circuit board has good ductility and repeatability, which is required to meet the extreme deformation that is experienced in most electrical applications. The proposed method has the ability to fabricate irregular circuit boards and complex patterns with channel-lengths as high as 4 m or channel-widths as small as 30 μm. This method can not only solve the problem of the traditional circuit boards being difficult to modify and repair, but it can also effectively protect the circuit and realize high fidelity of the circuit.