Liquid metal flexible circuit manufacturing method based on paper-based seal

Abstract

The invention discloses a liquid metal flexible circuit manufacturing method based on a paper-based seal, and belongs to the field of intelligent manufacturing. Firstly, a hollowed-out mask of a circuit pattern is carved on adhesive sticker printing paper, the hollowed-out paper-based mask is pasted to a transparent adhesive film, the paper-based seal of a hollowed-out structure is manufactured, and the adhesive sticker printing paper is composed of an upper layer surface material, a middle adhesive layer and lower layer release paper; secondly, liquid metal is evenly squeezed into a groove formed in the hollowed-out position of the paper-based seal; thirdly, the upper-layer surface material is torn off, the lower-layer release paper of the paper-based seal is attached to the flexible substrate, then the remaining paper-based seal is torn off, and a liquid metal circuit pattern on the flexible substrate is obtained; and finally, uniformly spraying a protective coating on the surface to obtain the liquid metal flexible circuit. The thickness of the manufactured liquid metal flexible circuit is only less than 30 microns, and flow migration caused by the too thick liquid metal layer can be effectively prevented; the manufacturing method is simple, convenient and rapid, and has a wide application prospect in the field of manufacturing of flexible wearable equipment.

Description

Technical Field

[0001] The invention belongs to the field of intelligent manufacturing and relates to a method for manufacturing a liquid metal flexible circuit based on a paper-based stamp. Background Art

[0002] Flexible electronic devices can maintain their good performance when stretched, bent or even twisted, and show great application potential in the fields of biomedicine, health monitoring equipment, brain-computer interface, wearable devices, etc. Flexible circuits are the basis for realizing the functions of flexible electronic devices. How to manufacture high-performance flexible circuits conveniently and at low cost has received widespread attention from academia and industry. Gallium-based liquid metal not only has the excellent properties of both metals and fluids, but also can maintain the conductivity of metals even when highly deformed, and it has good biocompatibility. Therefore, using gallium-based liquid metal to manufacture flexible circuits on flexible substrates such as Ecoflex, PDMS, SEBS and elastic silicone is an important way to achieve flexibility.

[0003] At present, the mainstream methods for manufacturing liquid metal circuits on flexible substrates include direct writing, microfluidic channel method, screen printing method, etc.; the direct writing method is to use liquid metal as ink to directly write or print patterns on the substrate. For example, Chinese patent CN114945249A proposes an electrofluid printing method for a multi-layer functional circuit structure based on electrowetting. This method can be combined with computer-aided design technology, but the oxidation of liquid metal during the printing process will lead to a low yield rate, and the multi-layer structure may cause failure of the internal circuit structure and collapse of the stacked structure during the bending and stretching process. The microfluidic channel method is to make a microchannel in the substrate and use a micro-syringe to inject liquid metal into the channel to form a circuit. This method has high processing accuracy, but due to the need to manufacture microchannels, its process complexity is very high. For example, the Deng Zhongshan team of the Institute of Physical and Chemical Technology of the Chinese Academy of Sciences (Ronghang Wang, et al. Porous membrane-enabled fast liquid metal patterning in thin blind-ended microchannels. Advanced Materials Technologies, 4, 9 (2019): 1900256.) achieved a 12μm wide and 20μm high liquid metal circuit. The screen printing method is to use a laser to create a designed circuit on a screen, and then add the prepared liquid metal ink to the screen plate for printing. This method is suitable for mass production because it matches the current microelectronics manufacturing technology, but its disadvantage is that the precision is low. For example, Chinese patent CN113613395 A proposes a method for making liquid metal patterns using PET film as a screen. This method is simple to make, but the thickness of the PET film used in the process is 0.1mm, and the amount of liquid metal filled in the PET screen is large, which leads to the liquid metal being easily flowed and migrated after the film is removed, thereby making the manufactured circuit invalid.

[0004] As mentioned above, although a variety of liquid metal circuit pattern production methods have been proposed, the above methods have more or less various disadvantages. Therefore, how to ensure a certain processing accuracy while taking into account the cost has become an urgent problem to be solved in the liquid metal flexible circuit manufacturing technology. Summary of the invention

[0005] The purpose of the present invention is to provide a method for manufacturing a liquid metal flexible circuit based on a paper-based stamp, which can ensure a certain processing accuracy while taking into account the cost. It is a method for quickly and efficiently making a liquid metal circuit on a flexible substrate.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for manufacturing a liquid metal flexible circuit based on a paper-based stamp, the method comprising the following steps:

[0008] The first step is to design the required circuit pattern, use a laser engraving machine to engrave a hollow mask of the required circuit pattern on the self-adhesive printing paper, and paste the paper-based mask with the hollow structure on the transparent adhesive film to make a paper-based stamp with a hollow structure. The self-adhesive printing paper is composed of an upper layer material, a middle adhesive layer and a lower layer release paper, wherein the upper layer material and the lower layer release paper can be torn off and separated separately to achieve the layering of the paper-based stamp.

[0009] The second step is to use a patch roller to evenly squeeze the liquid metal into the grooves formed in the hollowed-out area of ​​the paper-based stamp.

[0010] The third step is to peel off the upper layer of the paper-based stamp, adhere the lower layer of release paper of the paper-based stamp to the cut flexible substrate tightly, and then tear off the remaining paper-based stamp to obtain the liquid metal circuit pattern on the flexible substrate.

[0011] The fourth step is to spray a protective coating uniformly on the surface of the liquid metal pattern and to cure it using an ultraviolet UV lamp at room temperature to protect the liquid metal circuit pattern, thereby obtaining a liquid metal flexible circuit.

[0012] Furthermore, in the first step, the transparent adhesive film is a transparent tape, which is used to adhere the liquid metal to the transparent tape to facilitate transfer.

[0013] Furthermore, in the first step, the weight per square meter of the self-adhesive printing paper is 110 g and the thickness is 120 μm, wherein the thickness of the surface material on the upper surface is 20-30 μm, and the thickness of the release paper on the lower surface is 90-100 μm.

[0014] Furthermore, in the first step, the circuit pattern is a customized pattern, and the designed circuit pattern is imported into the laser engraving machine control software. The speed parameters and power parameters of the laser engraving machine are respectively set to 3000-5000 mm / min and 6-10 W, with a step of 0.01 mm. During the specific implementation, adjustments should be made according to the size of the circuit pattern and the layout of the circuit components to determine the optimal parameters.

[0015] Furthermore, in the second step, the liquid metal is a gallium-indium-tin alloy, which contains 67.5% gallium metal, 22.5% indium metal and 10% tin metal by mass fraction, and the melting point of the liquid metal under standard atmospheric pressure is 8-10° C. The liquid metal doped with tin powder has a lower surface tension, which makes it easier to form a stable connection interface when it contacts with a flexible substrate, and the liquid metal has a certain plasticity and can stably adhere to the transparent adhesive film.

[0016] Furthermore, in the third step, the flexible substrate can be one or more of polydimethylsiloxane (also known as PDMS), Ecoflex, and styrene-ethylene-butylene-styrene block copolymer (SEBS). It has good tensile properties and biocompatibility and can directly contact the skin. At the same time, since the flexible substrate and the liquid metal can be fully infiltrated, the liquid metal circuit pattern on the stamp can be adhered to achieve the purpose of transferring the circuit pattern. Furthermore, after peeling off the upper surface material of the paper-based stamp in the third step, the paper-based stamp can be directly attached to the skin to obtain a liquid metal circuit tattoo pattern.

[0017] Furthermore, the thickness of the liquid metal circuit pattern obtained in the third step is 20 to 30 μm, and after tearing off the upper layer of the material, the liquid metal pattern is 20 to 30 μm higher than the release paper plane, and after being transferred to the flexible substrate, a 20 to 30 μm thick liquid metal flexible circuit can be obtained. The thickness of the flexible substrate is 2 mm, and the size of the prepared flexible substrate can be cut according to the liquid metal circuit pattern.

[0018] Furthermore, in the fourth step, the protective coating uses acrylic resin three-proof coating. The three-proof coating uses acrylic resin three-proof coating to provide a protective film with extremely good flexibility. After this protective film dries and solidifies, it can protect the liquid metal circuit from oxidation and provide a certain waterproof performance.

[0019] Furthermore, in the fourth step, an ultraviolet UV lamp is used to irradiate for 30 to 40 seconds at room temperature to cure it. After curing, it can be stretched like a flexible substrate and is often used as a protective coating for printed circuit boards. It can prevent liquid metal from oxidizing and losing conductivity, and enable the circuit pattern structure to still work normally after contacting water. The thickness of the protective coating is 50 to 60 μm.

[0020] Furthermore, the liquid metal flexible circuit produced in the fourth step can withstand a strain of up to 300% without causing deformation of the circuit structure, and its function under tensile strain remains normal.

[0021] The present invention proposes a method for manufacturing a liquid metal flexible circuit based on a paper-based stamp, which is simple, fast and low-cost. The obtained liquid metal pattern product can be applied to the fields of flexible circuits, flexible sensors, electronic skin and wearable devices, and can also be used to make electrodes and heating coils directly attached to the skin.

[0022] The beneficial effects of the present invention are:

[0023] (1) The unique advantage of the present invention is that compared with the existing liquid metal patterning method, the thickness of the liquid metal circuit prepared by the present invention is less than 30 μm, which can effectively prevent the flow migration caused by the excessive thickness of the liquid metal layer. In addition, the addition of a flexible protective coating can also well protect the liquid metal pattern, preventing it from being oxidized, short-circuited, or smeared due to accidental touch.

[0024] (2) The method proposed in the present invention does not require the use of expensive instruments or materials such as photolithography machines, and can ensure a certain processing accuracy while taking into account the cost, that is, the manufacturing method is simple, fast and low-cost. The present invention realizes the rapid and low-cost printing of liquid metal patterns, which is expected to lay a foundation for the formation and manufacturing of flexible circuits and further expand the technical field of manufacturing and application of flexible wearable devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic flow chart of a method for manufacturing a liquid metal flexible circuit based on a paper-based stamp proposed by the present invention.

[0026] Figure 2 It is a schematic diagram of a paper-based seal made by the method proposed in the present invention.

[0027] Figure 3 This is a schematic diagram of the structure of a liquid metal flexible circuit made by the method proposed in the present invention.

[0028] Figure 4 This is a schematic diagram of the stretched state of the liquid metal flexible circuit made by the method proposed in the present invention

[0029] Figure 5 This is an observation diagram of a liquid metal circuit made by the method proposed in the present invention under a microscope.

[0030] Figure 6 This is a cross-sectional view of a liquid metal pattern produced by the method proposed in the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and display effect of the present invention clearer, the present invention is further described in detail below in conjunction with specific examples. Those skilled in the art should know that the examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. In the examples, unless otherwise stated, the technical means used are all conventional technical means in the art.

[0032] An embodiment of a method for manufacturing a liquid metal flexible circuit based on a paper-based stamp of the present invention includes the following specific steps:

[0033] 1. Preparation of raw materials

[0034] 1. Preparation of liquid metal materials (Sn-GaIn alloy)

[0035] Use an analytical balance to weigh 67.5g of gallium metal and 22.5g of indium metal into a clean beaker, place the beaker on a heating table, adjust the temperature to 100°C and stir thoroughly, wait until it cools to room temperature and presents a uniform silver liquid state, then you can get a gallium-indium alloy. Weigh 10g of tin powder particles and add them to the prepared gallium-indium alloy. Use a glass rod to continuously stir the liquid metal mixture in the beaker until the tin particles and gallium-indium liquid metal are fully mixed and present a bright silver color, then you can get the desired liquid metal alloy.

[0036] 2. Preparation of Ecoflex flexible substrate

[0037] After mixing the liquid gel (type A) and curing agent (type B) of Ecoflex at a volume fraction ratio of 1:1, pour it into a rectangular mold with a length of 15 cm, a width of 10 cm, and a depth of 2 mm, put it into a vacuum pump to remove bubbles, and let it stand at room temperature for 3 hours to solidify to obtain the required 2 mm thick stretchable Ecoflex flexible substrate. The flexible substrate can achieve a maximum strain of 300%, which can adhere liquid metal from the paper-based stamp.

[0038] 2. Preparation and packaging of liquid metal patterns

[0039] (1) Use electronic design automation software to design the required circuit or specific pattern, use a laser engraving machine to hollow out the mask of the required pattern on the self-adhesive printing paper, and stick the mask tightly on the transparent film to make a paper-based stamp. There should be no bubbles inside the stamp. In this step, the stepping of the laser engraving machine should be controlled at 0.01mm, and the speed parameters and laser power parameters of the laser engraving machine are set to 3000mm / min and 10W. The specific values ​​can be adjusted according to the actual situation.

[0040] (2) Use a patch roller to squeeze the liquid metal evenly into the hollow groove of the paper-based stamp. During the process, pay attention to whether the liquid metal pattern is damaged, adhered, oxidized, or broken.

[0041] (3) Peel off the upper layer of the seal material, and do not touch the liquid metal pattern when peeling off the upper layer of the seal material. Attach the lower layer of the release paper of the seal to the flexible substrate tightly and then tear off the seal to obtain a liquid metal pattern adhered to the flexible substrate cut to size. In this step, the total thickness of the self-adhesive printing paper is 120μm, which is divided into two parts: the upper layer of the material and the lower layer of the release paper. The thickness of the upper layer of the material is 30μm, and the thickness of the lower layer of the release paper is 90μm. There is a transparent adhesive film cover at the bottom to form a paper-based seal. The thickness of the circuit pattern formed after the liquid metal is evenly squeezed into the hollow groove is consistent with that of the self-adhesive printing paper. After tearing off the upper layer of the self-adhesive printing paper, the liquid metal pattern is still 120μm, which is higher than the remaining release paper plane thickness of 30μm. After the liquid metal is transferred to the flexible substrate, the liquid metal with a thickness of 30μm above the release paper is adhered and adsorbed on the flexible substrate, and the liquid metal with a thickness of 90μm below the release paper is adsorbed and clamped in the hollow groove by the transparent adhesive film at the bottom of the paper-based seal and the rough etched lines on the hollow vertical inner wall of the laser-engraved seal. The liquid metal pattern is divided into two parts of 30μm and 90μm by the applied tension, thus obtaining a 30μm thick liquid metal circuit tightly attached to the flexible substrate.

[0042] (4) Use acrylic resin conformal coating to evenly spray the liquid metal pattern with a coating thickness of 50 μm. After spraying, use ultraviolet UV lamp to cure the conformal coating for 30 seconds to form a stable and stretchable protective coating.

[0043] The above examples are only used to describe the specific implementation methods of the present invention, and are not intended to limit the scope of application of the present invention. For those skilled in the art, improvements or changes can be made based on the above descriptions, but all such improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for manufacturing a liquid metal flexible circuit based on a paper-based stamp, characterized in that: The manufacturing method comprises the following steps: The first step is to carve a hollow mask with a circuit pattern on a self-adhesive printing paper, and to stick the self-adhesive printing paper with the hollow mask on a transparent adhesive film to make a paper-based stamp with a hollow structure; the self-adhesive printing paper is composed of an upper layer material, a middle adhesive layer and a lower layer release paper; The second step is to squeeze the liquid metal evenly into the grooves formed by the hollowing out of the paper-based stamp; The third step is to peel off the upper surface of the paper-based stamp, adhere the lower release paper of the paper-based stamp to the flexible substrate tightly, and then tear off the remaining paper-based stamp to obtain the liquid metal circuit pattern on the flexible substrate; The fourth step is to evenly spray a protective coating on the surface of the liquid metal circuit pattern, and obtain a liquid metal flexible circuit after the protective coating is cured.

2. The method for manufacturing a liquid metal flexible circuit based on a paper-based stamp according to claim 1, characterized in that: In the first step, a laser engraving machine is used to engrave a hollow mask of a desired circuit pattern on the self-adhesive printing paper.

3. The method for manufacturing a liquid metal flexible circuit based on a paper-based stamp according to claim 2, characterized in that: In the first step: The transparent adhesive film is a transparent adhesive tape, which is used to adhere the liquid metal to the transparent adhesive tape; The thickness of the self-adhesive printing paper is 120 μm, wherein the thickness of the surface material on the upper surface is 20-30 μm, and the thickness of the release paper on the lower surface is 90-100 μm; The circuit pattern is a customized pattern, and the designed circuit pattern is imported into the laser engraving machine control software; The speed and power parameters of the laser engraving machine were set to 3000-5000 mm / min and 6-10 W, respectively, with a stepping of 0.01 mm.

4. The method for manufacturing a liquid metal flexible circuit based on a paper-based stamp according to claim 1, characterized in that: In the second step: Use a patch roller to squeeze the liquid metal evenly into the grooves formed by the hollowing out of the paper-based stamp; The liquid metal is a gallium-indium-tin alloy, which contains 67.5% gallium metal, 22.5% indium metal and 10% tin metal in a mass fraction ratio. The melting point of the liquid metal is 8-10° C. under standard atmospheric pressure.

5. The method for manufacturing a liquid metal flexible circuit based on a paper-based stamp according to claim 1, characterized in that: In the third step, the flexible substrate is made of one or more of polydimethylsiloxane (PDMS), Ecoflex degradable plastic, and styrene-ethylene-butylene-styrene block copolymer (SEBS).

6. The method for manufacturing a liquid metal flexible circuit based on a paper-based stamp according to claim 1, characterized in that: The thickness of the liquid metal circuit pattern is 20 to 30 μm. After tearing off the upper layer of material, the liquid metal pattern is 20 to 30 μm higher than the plane of the release paper. After being transferred to a flexible substrate, a 20 to 30 μm thick liquid metal flexible circuit is obtained. The thickness of the flexible substrate is 2 mm, and the size of the prepared flexible substrate can be cut according to the liquid metal circuit pattern.

7. The method for manufacturing a liquid metal flexible circuit based on a paper-based stamp according to claim 1, characterized in that: In the fourth step, after spraying the protective coating, an ultraviolet UV lamp is used to cure it at room temperature to protect the liquid metal circuit pattern; the thickness of the protective coating is 50-60 μm.

8. The method for manufacturing a liquid metal flexible circuit based on a paper-based stamp according to claim 7, characterized in that: In the fourth step, ultraviolet UV lamp is used to irradiate for 30 to 40 seconds at room temperature to cure the coating; the protective coating adopts acrylic resin triple-proof coating.

9. The method for manufacturing a liquid metal flexible circuit based on a paper-based stamp according to claim 1, characterized in that: The liquid metal flexible circuit obtained in the fourth step can withstand a strain of up to 300% without causing deformation of the circuit structure.

10. The method for manufacturing a liquid metal flexible circuit based on a paper-based stamp according to claim 9, characterized in that: The liquid metal flexible circuit can be applied to the fields of flexible circuits, flexible sensors, electronic skin, and wearable devices, or used to make electrodes and heating coils directly attached to the skin.

Images