Flexible circuit boards are now subversive technologies?

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[Frontier] Focus! Flexible circuit boards are now subversive technologies? It can be Fast manufacturing.

Recently, the Department of Biomedical Engineering of Tsinghua University Medical College, in conjunction with the Institute of Physical and Chemical Technology of the Chinese Academy of Sciences, published online the title "Rolling Coating and Transfer Technology Based on Semi-liquid Metal Selective Adhesion Mechanism: Universal Flexible Electronic Rapid Manufacturing Method" (Semi-liquid Metal and Adhesion-selection enable). D Rolling and Transfer (SMART) Printing: A General Method towards Fast Fabrication of Flexible Electronics, 2019. This work is the first report of a universal and flexible ultra-fast electronic manufacturing technology. It can print large area, high precision and complex liquid metal circuits in seconds, which is much faster than all kinds of electronic processing technologies that have been developed so far. The corresponding method is named SMART Printing (Smart Printing) according to its English abbreviation. The first author is Guorui, a third-year doctoral student in the Department of Biomedical Engineering, and the correspondent author is Professor Liu Jing.

As we all know, Printed Circuit Board (PCB) plays a very important role in people's daily life, and it is widely used in the fields of industrial production, national defense and health care. The Traditional Printed Circuit Board (PCB) preparation process is very complex, which needs more than ten processes. The whole process is time-consuming and power-consuming, and has a lot of environmental pollution. In recent years, flexible electronics has been paid more and more attention. Unlike traditional rigid boards, flexible boards can be bent, folded or stretched at will, making them valuable for wearable devices, portable medical devices, skin electronics, and more.

Liu Jing's group, which has more than 10 years'experience in the field of liquid metal flexible electronics, based on previous research on a large number of properties of liquid metal materials, a semi-liquid metal material (Ni-egain) with high viscosity and plasticity can be prepared by mixing liquid gallium-based alloy with solid metal particles (Ni) at room temperature. The adhesion of these materials on different substrate surfaces is very different, and the patterned liquid metal circuit can be printed quickly by using this difference.


The results showed that semi-liquid metal had high adhesion on Pu film, but poor adhesion on carbon powder. To do this, the team first introduced laser printing to deposit toner patterns on paper coated with Pu film, and then a rolling coating method using a semi-liquid metal material with a significant difference in adhesion between the two types of substrates In a very short time (10s) the semi-liquid metal material will be selectively printed to the A4 size paper on the target site, it can be said that the required circuit was made in an instant (figure 1) . The flexible circuit fabricated by this technique has a maximum accuracy of 50 microns and can maintain the stability of the circuit connection during the bending and folding of the substrate. It is further pointed out that the new method is more universal and semi-liquid metal materials have higher adhesion to more substrate materials such as flexible Silica Gel (ECOFLEX) . Based on this phenomenon, semi-liquid metallic ink can also be deposited on the target part of the surface of the flexible Silica Gel by transfer printing.


Figure 1 operation flow of Smart Printing Technology and printed conductive pattern

Using these manufacturing principles, the team developed a series of flexible and stretchable functional circuits (Fig. 2) , such as multilayer circuits, large area circuits (Fig. 3) , and stretchable sensors (Fig. 4)  The experimental results show that the devices have excellent electrical stability, adaptability and recyclability. The implementation of the method does not need complicated equipment, and the flexible circuit can be used in wearable medical equipment, which provides a new way to realize personalized medical electronics.


Fig. 2 Multilayer Circuit fabricated by INTELLIGENT PRINTING TECHNOLOGY


Fig. 3 large area conductive pattern prepared by intelligent printing technology


Figure 4 Stretchable sensor functional electronic circuits and performance prepared and assembled using smart printing technology

It is worth mentioning that, earlier in this work, a joint research group composed of Tsinghua University, the Institute of Science and Technology of the Chinese Academy of Sciences and Beijing Dream Ink Company has made a breakthrough in the exploration of the fast-prepared process of flexible electrons in liquid metals. In a cover story published in the prestigious journal Advanced Materials: Technology, "One-step liquid metal transfer: flexible electronic manufacturing for a wide range of substrates" (One-Step Liquid) Metal Transfer Printing: In a paper on The Space, On Wide Range of Substrates, 2018, the authors developed a paper-based electronic printing Technology can be used to transfer liquid metal materials to the target paper surface using a selective adhesion mechanism on the surface of the PMA glue and paper. In addition, in order to promote the sustained and rapid development of the advanced manufacturing field of liquid metals, the research team also recently published the first domestic and foreign "Liquid Metal Printing Electronics" (Shanghai Science and Technology Press, 2019) (Figure 5), to build this emerging field of theory and technology system, to fill the corresponding academic literature gaps.


Figure 5 Liquid Metal Transfer Methods (left) and The Cover of The Paper Of Liquid Metal Printing Electronics (right) on the cover of the journal cover.

The latest advances in liquid metal printing electronics technology provide new technologies and tools for the rapid manufacture of wearable medical and personalized electronic health products, which are of great scientific significance and application value.