Flexible circuit substrate film material, method of making and use thereof

Abstract

This invention relates to the field of flexible electronics, and more particularly to a flexible circuit substrate film material, its preparation method, and its applications. The invention utilizes a solvent exchange process to solidify a polymer-rich phase, forming a continuous, interconnected three-dimensional porous framework. Liquid metal is then broken into discrete particles of 2-7 μm using ultrasound. Smaller liquid metal particles are encapsulated and confined by the polymer, while larger particles exert mechanical stress on the surrounding polymer confinement layer, causing spontaneous thinning or rupture of the local polymer walls. Based on this metastable structure, low-pressure imprinting can rupture the gallium oxide shell of the liquid metal particles, releasing the flowing and merging metal cores to form a continuous three-dimensional permeation conductive pathway. The preparation process of this invention is simple, suitable for continuous industrial production, and the film material can be recycled through dissolution and separation. It can be integrated with commercial components to construct flexible sensing systems, showing broad application prospects in wearable devices, biomedical monitoring, and other fields.

Description

Technical Field

[0001] This invention relates to the field of flexible electronics, and in particular to a flexible circuit board film material, its preparation method, and its application. Background Technology

[0002] Flexible electronics is a core technology in the fields of next-generation wearable devices, biosignal monitoring, and soft robotics. Existing technologies have reported methods for fabricating flexible circuits by dispersing liquid metal particles in polymers. For example, CN120456442A discloses a method for fabricating high-temperature resistant flexible circuits, in which liquid metal particles are mixed with a high-temperature resistant polymer solution such as polyimide, coated into a film, and then heated to evaporate the solvent to form a dense polymer film. The film is then sintered onto the surface using ultraviolet laser lithography to form conductive pathways. However, this method has the following limitations: First, it uses a method of heating and evaporating the solvent to form the film, causing the polymer molecular chains to gradually approach and accumulate during the slow evaporation of the solvent, ultimately forming a dense structure. The liquid metal particles are firmly encapsulated in the dense polymer matrix, and conductivity requires high-energy laser sintering to break down the oxide layer on the particle surface and allow them to connect. Laser sintering equipment is complex, energy-intensive, and difficult to achieve large-area continuous production. Furthermore, high-energy lasers can easily cause thermal damage to the polymer substrate, affecting the long-term stability of the circuit. Secondly, the high-temperature resistant polymers used in this method, such as polyimide, are mostly thermosetting or high-performance engineering plastics. Once molded, they cannot be dissolved or reshaped, and the substrate material is not recyclable, becoming electronic waste after use, which does not meet the requirements of green environmental protection and sustainable development. Furthermore, laser sintering is a point-by-point scanning process with low production efficiency, making it difficult to meet the needs of large-scale, low-cost manufacturing of flexible electronic devices. Therefore, developing a flexible circuit board material with a novel structure, mild conduction mechanism, and the ability to achieve continuous industrial production and recycling remains a pressing technical problem to be solved in this field. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the problems of complicated preparation, poor stability and non-recyclability in the prior art, thereby providing a material preparation scheme for flexible circuits.

[0004] To address the aforementioned technical problems, this invention provides a method for preparing a flexible circuit board film material, comprising the following steps: S11: Disperse liquid metal in an organic solvent, add polymer, and obtain casting solution; S12: After coating the casting liquid onto the substrate, a solvent is added for solvent exchange, and the mixture is dried to obtain the flexible circuit board film material; the organic solvent and the solvent are different.

[0005] Preferably, the liquid metal particles are gallium, gallium-indium-tin alloy, eutectic gallium-indium alloy, or bismuth-indium-tin alloy. The liquid metal particles are liquid at room temperature and are essentially low-melting-point alloys.

[0006] Furthermore, the liquid metal is a granular solid obtained by ultrasonically breaking down gallium (Ga), gallium indium tin alloy (Galinstan), eutectic gallium indium alloy (EGaIn), and bismuth indium tin alloy (Field's metal). Macroscopically, it is a solid particle, but essentially it consists of micron-sized liquid metal particles covered with an oxide layer.

[0007] Preferably, the organic solvent is at least one selected from N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, toluene, ethanol, isopropanol, acetone, butanone, ethyl acetate, hexafluoroisopropanol, xylene, n-hexane, dichloromethane, chloroform, and methanol. This organic solvent is used to dissolve the polymer and disperse the liquid metal particles.

[0008] Preferably, in step S11, the dispersion method involves ultrasonication at 198-528 W power for 5-60 minutes in an ice-water bath. This efficiently breaks down and uniformly disperses the liquid metal particles, while also controlling temperature to prevent oxidation, protecting the organic solvent, and improving the stability of the dispersion.

[0009] Preferably, the polymer is at least one selected from thermoplastic polyurethane (TPU), polysiloxane (PDMS), styrene elastomers (SBS, SEBS, SIS), polycaprolactone (PCL), polylactic acid-caprolactone copolymer (PLA-co-PCL), polyglycolic acid-caprolactone copolymer (PGA-co-PCL), polyacrylate rubber (ACM), ethylene-vinyl acetate copolymer (EVA), polyether block amide (PEBA), fluororubber (FKM), perfluorinated rubber (FFKM), thermoplastic polyester elastomer (TPEE), gelatin elastomer, chitosan elastomer, polyacrylamide (PAAm), polyethylene oxide (PEO), polysulfide rubber, polyurethane urea (PUU), and polybutadiene rubber (BR).

[0010] Among them, the number average molecular weight of thermoplastic elastomers (TPU, SBS / SEBS / SIS, PEBA, TPEE) is 10,000-300,000 g / mol, polyesters (PCL, PLA-co-PCL, PGA-co-PCL) is 10,000-80,000 g / mol, silicone rubber (PDMS) is 2,000-80,000 g / mol, water-soluble / hydrogel polymers (gelatin elastomers, chitosan elastomers, PAAm, PEO) is 10,000-2,000,000 g / mol, synthetic rubbers and other elastomers (ACM, EVA, FKM, FFKM, polysulfide rubber, BR) is 20,000-200,000 g / mol, and polyurethane urea (PUU) is 20,000-150,000 g / mol. The polymers mentioned above all possess solubility properties suitable for solvent exchange phase conversion molding, and have controllable flexible elastic intrinsic structures. Their corresponding good solvents can also serve as dispersion media for ultrasonic liquid metals, enabling the molding of polymer-liquid metal composite systems.

[0011] Preferably, the mass ratio of polymer, liquid metal particles, and organic solvent in the casting solution is 0.08-5.8:0.11-25:1. Controlling the mass ratio of polymer, liquid metal particles, and organic solvent in the casting solution allows for precise regulation of the system viscosity, dispersion stability, membrane microstructure, and properties, ensuring uniformity and repeatability of film formation.

[0012] Preferably, in step S12, the solvent added during solvent exchange is methanol, ethanol, isopropanol, water, acetone, hexane, diethyl ether, n-hexane, perfluoroalkanes, chlorofluorocarbons, a mixture of sodium hydroxide and ethanol, or ethyl acetate. Solvent exchange is a process in which the polymer in the casting solution undergoes phase separation to form a porous membrane by gradually replacing solvents with different polarity / solubility parameters. Such solvents can control the phase separation rate, pore structure, membrane density, and surface properties, while ensuring uniform, defect-free, and stable film formation.

[0013] Preferably, in step S12, the drying temperature is 25-80°C.

[0014] Preferably, the base layer is glass, metal plate, polyethylene film, polyimide, polyethylene terephthalate film, polyethylene naphthalate film, or polytetrafluoroethylene film.

[0015] The present invention also provides a flexible circuit board film material prepared by the above preparation method.

[0016] Preferably, the flexible circuit board film material comprises a three-dimensional porous polymer framework with a pore size of 1-50 μm and a porosity of 50%-90%. This porosity balances good mechanical flexibility, efficient loading of liquid metal, and ensures substrate structural stability and resistance to collapse.

[0017] The present invention also provides the application of the above-mentioned flexible circuit substrate film material in the preparation of flexible circuits. The application steps include imprinting the flexible circuit substrate film material, wherein the imprinting pressure is 1-60 kPa.

[0018] Compared with the prior art, the above-described technical solution of the present invention has the following advantages: This invention provides an industrially prepared and recyclable flexible circuit board film material, which is produced by coating a casting solution composed of liquid metal particles and a polymer solution with a coating agent, followed by solvent exchange and drying. The resulting film has a porous structure with liquid metal distributed within the pores. Through template imprinting, local pressure causes the porous network to collapse, the liquid metal particles to break and reconstruct into a three-dimensional continuous conductive path, thereby achieving circuit imprinting. Attached Figure Description

[0019] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0020] Figure 1 This is a graph showing the change in resistance of the flexible porous metal film material prepared in Example 1 of the present invention as a function of pressure. Figure 2 The stress-strain curve of the flexible porous metal membrane material prepared in Example 1 of this invention is shown. Figure 3 The images show a photograph of the flexible porous metal film material used as a circuit board in Embodiment 2 of the present invention and a schematic diagram of the integrated sensing system. Figure 4 A scanning electron microscope (SEM) image of the porous structure of a flexible porous metal membrane material before compression (showing liquid metal particles confined within the pores). Figure 5 This is a scanning electron microscope image of the porous structure of a flexible porous metal membrane material after compression, in which the liquid metal is in a connected state. Figure 6 This is a reaction mechanism diagram of the flexible porous metal membrane material of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0022] Example 1: This embodiment provides a method for preparing a flexible circuit board film material, which includes the following steps: (a) Mix 18g of liquid metal (Galinstan) with 8g of N,N-dimethylformamide (DMF); sonicate the resulting coarse dispersion suspension at 390 W for 30 minutes in an ice-water bath; dissolve the sonicated fine dispersion suspension with 2g of thermoplastic polyurethane (TPU, BASF brand L785, 10000-300000 g / mol) by stirring for 6 hours to obtain the casting solution.

[0023] (b) The casting solution obtained in step (a) is cast onto a polyethylene film (Canon W200, 30000-60000 g / mol: 30cm×20m×10μm), and the scraper speed is set to 1 cm / s and the height is 100 μm for scraping.

[0024] (c) Immerse the membrane obtained in step (b) in water for solvent exchange for 30 minutes, allowing DMF to diffuse into the water, causing the polymer to undergo phase separation and solidify, forming a porous structure. After the exchange is complete, remove the membrane and dry it in a 75°C oven to obtain the flexible membrane material.

[0025] The microstructure of the prepared membrane material was characterized: the cross-sectional morphology of the membrane was observed using scanning electron microscopy (SEM), and the results are as follows. Figure 4 As shown, the membrane material exhibits a continuous, interconnected three-dimensional porous structure with pore sizes mainly ranging from 2 to 20 μm. Liquid metal particles are confined within these pores, with particle diameters ranging from 2 to 7 μm. When external mechanical pressure is applied, the porous framework undergoes irreversible collapse. The liquid metal particles within the pores are compressed, causing the gallium oxide (Ga2O3) shell on their surface to rupture. The released liquid metal cores flow, merge, and ultimately fuse into a continuous three-dimensional permeation conductive pathway (e.g., ...). Figure 5 (As shown).

[0026] (d) Patterning and imprinting the flexible film material obtained in step (c). Using a 3D-printed punch template, a pressure of 20 kPa is applied to cause the porous skeleton in the pressure area to collapse, the gallium oxide shell of the liquid metal particles in the pores to rupture, and the released liquid metal to fuse together to form a three-dimensional continuous conductive network, thus obtaining a flexible circuit substrate.

[0027] The electrical performance of the fabricated circuit was tested: the resistance was measured with pressure using a multimeter, and the results are as follows. Figure 1 As shown. Mechanical properties of the prepared membrane material were tested: the stress-strain curves are shown below. Figure 2 As shown.

[0028] Example 2:

[0029] This embodiment provides an application of the industrially fabricable and recyclable flexible circuit substrate film material prepared in Embodiment 1 in the fabrication of flexible circuits. The specific preparation method is as shown in Embodiment 1. Figure 3 A stretchable accelerometer circuit was fabricated using a 3D-printed mold and integrated with commercial components (including an ADXL345 accelerometer, an LM35 temperature sensor, capacitors, and LEDs) to construct a fully functional sensing system. When this system was attached to the back of a human hand and connected to an Arduino microcontroller, it successfully acquired and recorded real-time acceleration data corresponding to different hand movements, verifying its effectiveness in wearable motion monitoring. This application example demonstrates that the material of this invention can be easily integrated with commercial electronic components to construct a functional flexible sensing system, suitable for wearable applications with high requirements for cost and flexibility, verifying its feasibility in practical applications.

[0030] Example 3:

[0031] Take the flexible circuit board film material (5cm × 5cm in size, containing approximately 0.5g of liquid metal) that has been imprinted in step (d) of Example 1, and perform the following operations: (1) Cut the membrane material into small pieces and place it in a 50 mL beaker. Add 20 mL of DMF and stir magnetically at room temperature (25℃) for 2 hours until the TPU is completely dissolved and a turbid liquid is formed.

[0032] (2) Transfer the above turbid liquid to a centrifuge tube and centrifuge at 4500 rpm for 10 minutes. After centrifugation, the upper layer is a clear TPU / DMF solution, and the bottom layer is a precipitate of liquid metal particles. Carefully pour off the upper layer solution and collect the bottom precipitate.

[0033] (3) Add 10 mL of fresh DMF to the precipitate, sonicate for 1 minute and then centrifuge. Repeat the washing twice to remove residual TPU.

[0034] (4) The washed liquid metal particles were placed in a vacuum oven at 60°C and dried for 2 hours to obtain the recovered liquid metal particles. The recovery rate was calculated by weighing.

[0035] The recovered liquid metal particles weighed 0.48 g, with a recovery rate of approximately 96%. SEM observation of the recovered liquid metal particles showed that their morphology was basically consistent with the original particles, and the particle size was still distributed in the range of 2-7 μm, indicating that the dissolution-separation process did not cause significant damage to the liquid metal.

[0036] The recovered liquid metal particles were re-prepared into a casting solution using the same method as in Example 1: 0.48 g of the recovered liquid metal was taken, and an appropriate amount of DMF was added (added at a solid content ratio of 99:4). After ultrasonic crushing, the mixture was mixed with TPU (maintaining a liquid metal:TPU mass ratio of 9:1). After stirring and dissolving, the mixture was coated onto a film, and after water exchange and drying, a regenerated membrane material was obtained. Then, the same pressure (20 kPa) as in Example 1 was used for imprinting to obtain a regenerated circuit.

[0037] Comparative Example 1: The comparative sample was prepared according to the method in Example 1 of CN120456442A, and the steps are as follows: (1) The solvent is evaporated after heating and crosslinking to form a film, forming a dense structure in which liquid metal particles are encapsulated in the polyimide matrix (CN120456442A specification, paragraphs 0042-0044 and figures). (2) Ultraviolet laser sintering is used with a frequency of 20kHz and a pulse width of 30μs. Point-by-point scanning is required (CN120456442A manual, paragraph 0044). (3) The resistance at room temperature is 0.0012Ω and the resistance at 300℃ is 0.0014Ω (see Table 1 in this document); (4) The polyimide used is a thermosetting material that cannot be dissolved and recycled.

[0038] Effect Evaluation 1: Figure 6 This invention demonstrates the core mechanism of preparing three-dimensional porous thermoplastic polyurethane (TPU)-liquid metal composite elastomers using a non-solvent-induced phase separation (solvent exchange) method: TPU is dissolved in a good solvent DMF, and a uniform casting solution is prepared with uniformly dispersed liquid metal particles. After immersion in non-solvent water, liquid-liquid phase separation is initiated by bidirectional diffusion between the good solvent and the non-solvent. The liquid metal is directionally enriched with the solvent-rich phase. After drying, a multi-level structure is formed, consisting of a "TPU elastic skeleton - three-dimensional through-pores (pore size 2-20 μm) - liquid metal confined within the pores". This structure is fundamentally different from the thermosetting polyimide structure in Comparative Example 1 where the liquid metal is densely wrapped. It does not require high-energy laser sintering and can achieve conductivity with only 10 kPa low-pressure mechanical force. It also has the advantages of dynamic reversible conductive response, material recyclability, and precise performance control, making it suitable for diverse applications in flexible electronics.

[0039] Table 1. Differences between the Examples and Comparative Examples

[0040] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a flexible circuit board film material, characterized in that, Includes the following steps: S11: Disperse liquid metal in an organic solvent, add polymer, and obtain casting solution; S12: After coating the casting liquid onto the substrate, a solvent is added for solvent exchange, and the mixture is dried to obtain the flexible circuit board film material; the organic solvent and the solvent are different.

2. The preparation method according to claim 1, characterized in that: The liquid metal is gallium, gallium indium tin alloy, eutectic gallium indium alloy, or bismuth indium tin alloy.

3. The preparation method according to claim 1, characterized in that: The organic solvent is at least one selected from N,N-dimethylformamide, N,N-dimethylacetamide, tetrahydrofuran, toluene, ethanol, isopropanol, acetone, butanone, ethyl acetate, hexafluoroisopropanol, xylene, n-hexane, dichloromethane, chloroform, and methanol.

4. The preparation method according to claim 1, characterized in that: In step S11, the dispersion method is to use ultrasound at a power of 198-528 W for 5-60 minutes in an ice-water bath.

5. The preparation method according to claim 1, characterized in that: The polymer is at least one selected from thermoplastic polyurethane, polysiloxane, styrene elastomer, polycaprolactone, polylactic acid-caprolactone copolymer, polyglycolic acid-caprolactone copolymer, polyacrylate rubber, ethylene-vinyl acetate copolymer, polyether block amide, fluororubber, perfluorinated rubber, thermoplastic polyester elastomer, gelatin elastomer, chitosan elastomer, polyacrylamide, polyethylene oxide, polysulfide rubber, polyurethane urea, and polybutadiene rubber.

6. The preparation method according to claim 1, characterized in that: In the casting solution, the mass ratio of polymer, liquid metal particles and organic solvent is 0.08-5.8:0.11-25:

1.

7. The preparation method according to claim 1, characterized in that: In step S12, the solvent added during solvent exchange is methanol, ethanol, isopropanol, water, acetone, hexane, diethyl ether, n-hexane, perfluoroalkane, chlorofluorocarbon, or ethyl acetate; the ethanol may or may not contain sodium hydroxide.

8. A flexible circuit board film material prepared by the preparation method according to any one of claims 1-7.

9. The flexible circuit board film material according to claim 8, characterized in that: The flexible circuit board film material includes a three-dimensional porous polymer framework with a pore size of 1-50 μm and a porosity of 50%-90%.

10. The application of the flexible circuit substrate film material according to claim 9 in the fabrication of flexible circuits, characterized in that: The application steps include imprinting the flexible circuit board film material with a pressure of 1-60 kPa.

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