This work presents a rapid method to selectively print liquid alloy circuits on soft substrate at ambient environment using a laser-treated stamp, by tuning the liquid alloy wettability on different surfaces. This technology has the advantage of efficient as it only need inking and imprinting in just two steps. It can compatibility with existed industrial line equipment for complex and volume automation production easily.
Room temperature liquid alloy has been widely used in stretchable and flexible electronics because of high adaptability, fluidity and high conductivity. Numerous approaches were developed for pattern, such as injection, masked deposition, directly writing, and so on. However, these processing techniques are lack of compatibility to fit existing production lines directly. A simple way with more excellent portability is still being sought. In this work, a stamp was fabricated by selectively laser treatment on the surface of carbon filled PDMS (cPDMS). The laser processed cPDMS demonstrated an alloy-phobic behavior which could attach and then transfer liquid alloy to target substrate easily, while the left parts show an alloy-philic behavior. The difference of adhesion can be characterized quantitatively by measuring the bias of advancing and receding contact angles and calculating theoretically. After inked on stamp, the liquid alloy was printed on target substrate by gently pressing the stamp on target substrate. The liquid alloy would attach on both stamp and target substrate because of adhesion effective and surface oxide layer, and the liquid alloy would separate during lifting off because of Rayleigh-Taylor instabilities. Therefore, liquid alloy would be theoretically left on both stamp and target substrate. Since the oxide layer of liquid alloy exhibits adhesion on sorts of materials, this technique could be widely used on universal substrates, such as pure PDMS, Ecoflex, vinyl tape, glass, polyethylene glycol terephthalate (PET) and so on. Additionally, the method was proved to print arbitrary liquid alloy patterns with resolution as fine as 30 μm with excellent repeatability.
Further, a 64-LED-matrix with bistratal typography with a developable surface stamp were fabricated and demonstrated by this technique.