Preparation method and application of grounding layer based on lig-cu composite material

Abstract

This invention relates to the field of flexible smart wearable device technology, and particularly to a method for preparing a grounding layer based on LIG-Cu composite material and its application. The preparation method includes: fabricating a precursor film using polyimide paper; processing the precursor film with a picosecond ultraviolet laser in a laser processing system to obtain laser-induced graphene; cleaning the laser-induced graphene and a substrate separately, then placing the laser-induced graphene on the substrate for drying; placing the dried laser-induced graphene in a copper sulfate electrolyte for electroplating, removing, cleaning, and drying to obtain the grounding layer based on the LIG-Cu composite material. This grounding layer combines the unique three-dimensional structure of LIG with the excellent conductivity of copper, significantly improving the bending reliability, high-frequency signal integrity, and lightweight nature of the grounding layer. It can be applied to flexible MEMS pressure sensors and flexible smart wristbands, making products lighter and more efficient.

Description

Technical Field

[0001] This invention relates to the field of flexible smart wearable device technology, and in particular to a method for preparing a grounding layer based on LIG-Cu composite material and its application. Background Technology

[0002] In high-frequency, high-density packaging and flexible electronic devices, the ground plane is a critical structure for ensuring signal integrity, power integrity, and electromagnetic compatibility. An ideal ground plane needs to have extremely low resistance to provide a stable reference potential, excellent thermal conductivity to aid heat dissipation, and also needs to be able to accommodate the skin effect caused by high-frequency current transmission, while meeting the mechanical performance requirements of flexible devices for bending and folding.

[0003] Currently, the most widely used grounding layer material in the industry is metallic copper, specifically electrolytic copper foil or rolled copper foil. However, despite copper's high electrical and thermal conductivity, its limitations are increasingly apparent in the development of future electronic devices: First, high-frequency performance bottlenecks. As signal frequencies enter the GHz and even THz range, current concentrates on the conductor surface due to the skin effect. The microscopic roughness of traditional copper foil significantly increases high-frequency resistance, leading to a sharp increase in signal transmission loss. Second, inherent mechanical defects. Copper foil itself is brittle and prone to fatigue cracks under repeated bending, resulting in deterioration of conductivity or even open circuits, making it difficult to meet the long-term reliability requirements of high-performance flexible electronic devices. Furthermore, there are issues with process complexity and substrate adhesion. In flexible printed circuit boards, copper foil needs to be bonded to flexible substrates such as polyimide using adhesives. However, the interface between them is prone to delamination under thermal or mechanical stress, and the additional adhesive layer introduces additional thermal resistance and instability. Finally, there are issues with materials and manufacturing processes. Copper has a high density, which is not conducive to achieving extreme lightweighting of electronic devices. Furthermore, its traditional subtractive manufacturing (etching) process generates a large amount of chemical waste liquid, which is not environmentally friendly.

[0004] Existing technologies include flexible electrodes, such as the graphene-copper composite flexible electrode fabrication process and apparatus disclosed in CN115512899A. This involves coating a polyimide film with copper oxalate powder, followed by laser irradiation to generate a graphene-CuO composite material. After peeling from the PI substrate, a high-temperature reduction treatment is performed. Multiple layers of the graphene-copper composite material are then stacked and pressed together to obtain the graphene-copper flexible electrode. Clearly, the flexibility of the flexible electrode obtained by this multi-layer pressing method is still insufficient to meet the reliability requirements for long-term use of flexible devices, and its lightweighting is also limited.

[0005] In view of this, it is necessary to provide a grounding layer material that combines metallic conductivity, excellent high-frequency characteristics and mechanical flexibility, and can be integrated with flexible electronic processes. Summary of the Invention

[0006] The purpose of this invention is to propose a method for preparing a grounding layer based on LIG-Cu composite material and its application. This grounding layer combines the unique three-dimensional structure of LIG with the excellent conductivity of copper, which significantly improves the bending reliability, high-frequency signal integrity and lightweighting of the grounding layer. It can be applied to flexible MEMS pressure sensors and flexible smart wristbands, making the products lighter and more efficient in operation.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] A method for preparing a grounding layer based on LIG-Cu composite material includes the following steps:

[0009] (1) Fix polyimide paper onto a substrate and coat the polyimide paper with a copper nitrate precursor solution to make a precursor film;

[0010] (2) The substrate carrying the precursor film is placed in a laser processing system, and the precursor film is acted on by a picosecond ultraviolet laser to obtain laser-induced graphene.

[0011] (3) The laser-induced graphene is peeled off from the substrate, the laser-induced graphene and the substrate are cleaned respectively, and then the laser-induced graphene is placed on the substrate for drying.

[0012] (4) The dried laser-induced graphene is placed in copper sulfate electrolyte for electroplating, then taken out, cleaned and dried to obtain the grounding layer based on LIG-Cu composite material.

[0013] Furthermore, in step (1), the method for preparing the copper nitrate precursor solution includes:

[0014] Mix 0.2~0.5g / mL polyvinylpyrrolidone aqueous solution with 5~8mol / L Cu(NO3)2·3H2O at a volume ratio of 1:1 to obtain a homogeneous mixture;

[0015] The copper nitrate precursor solution was obtained by diluting the mixture with deionized water at a ratio of 1: (3~4).

[0016] Furthermore, in step (1), 230~300uL of copper acid precursor solution is coated onto a processing area of ​​50~150um thickness and 15~20cm. 2 On polyimide paper.

[0017] Furthermore, in step (2), the parameters of the picosecond ultraviolet laser are: wavelength of 355nm, pulse width of 8~12ps, laser power of 3~5W, scanning speed of 100~400mm / s, and scanning spacing of 0.01~0.04mm.

[0018] Furthermore, in step (3), the laser-induced graphene and the substrate are first soaked in deionized water, then the laser-induced graphene and the substrate are cleaned by sputtering deionized water, and finally the cleaned laser-induced graphene is placed on the substrate and dried at 60~95°C.

[0019] Furthermore, in step (4), the concentration of the copper sulfate electrolyte is 0.25~0.35mol / L, the constant current is 0.06~0.10mA, the electroplating time is set to 80~120min, and the electroplating temperature is 10~20℃.

[0020] Furthermore, a pure copper plate is used as the anode and laser-induced graphene as the cathode, with the anode and cathode parallel to each other and a distance of 3-8 cm between them.

[0021] A flexible grounding layer is prepared by the above-described method for preparing a grounding layer based on LIG-Cu composite material.

[0022] A flexible MEMS pressure sensor includes a flexible substrate, a MEMS piezoresistive film, and the aforementioned flexible grounding layer, wherein the MEMS piezoresistive film and the flexible grounding layer are respectively connected to the flexible substrate.

[0023] A flexible smart wristband includes a flexible band body, a flexible circuit board, and the aforementioned flexible MEMS pressure sensor. The flexible MEMS pressure sensor is mounted on the flexible circuit board, and the flexible circuit board is embedded in the flexible band body.

[0024] The flexible circuit board is provided with the aforementioned flexible grounding layer;

[0025] The flexible MEMS pressure sensor is used to measure the wearer's blood pressure.

[0026] The technical solution provided by this invention may include the following beneficial effects:

[0027] This method involves in-situ preparation of a flexible host film of copper-doped graphene as a grounding electrode on polyimide paper. After inducing uniform deposition of copper ions on its surface and within its pores, the conductive cross-section is significantly increased, the surface resistivity is reduced, and the surface of the flexible host film is further filled and smoothed, forming a dense, flat copper coating that is firmly bonded to the LIG network. Simultaneously, the material's flexibility is maintained, and a low-roughness surface suitable for high-frequency signal transmission is obtained. Using polyimide paper as a substrate effectively improves component loading and uniformity, which is beneficial for obtaining a loose, continuous, and stable laser-induced graphene layer. It also enhances material stability and facilitates the efficient, repeatable, and large-scale preparation of LIG-Cu composite materials.

[0028] The grounding layer prepared by this method is used in flexible MEMS pressure sensors and flexible smart wristbands, making the products lighter and more efficient in operation. Attached Figure Description

[0029] Figure 1 This is a SEM image of the initial LIG-Cu surface after laser scanning processing in Embodiment 5 of the present invention;

[0030] Figure 2 This is a SEM image of the initial LIG-Cu cross-section after laser scanning processing in Embodiment 5 of the present invention;

[0031] Figure 3 This is a SEM image of the LIG-Cu composite grounding layer surface after electroplating in Embodiment 5 of the present invention;

[0032] Figure 4 This is a SEM image of the cross-section of the LIG-Cu composite material grounding layer after electroplating in Embodiment 5 of the present invention. Detailed Implementation

[0033] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the present invention.

[0034] This invention provides a method for preparing a grounding layer based on LIG-Cu composite material, comprising the following steps:

[0035] (1) Fix polyimide paper onto a substrate and coat the polyimide paper with a copper nitrate precursor solution to make a precursor film;

[0036] (2) The substrate carrying the precursor film is placed in a laser processing system, and the precursor film is acted on by a picosecond ultraviolet laser to obtain laser-induced graphene.

[0037] (3) The laser-induced graphene is peeled off from the substrate, the laser-induced graphene and the substrate are cleaned respectively, and then the laser-induced graphene is placed on the substrate for drying.

[0038] (4) The dried laser-induced graphene is placed in copper sulfate electrolyte for electroplating, then taken out, cleaned and dried to obtain the grounding layer based on LIG-Cu composite material.

[0039] In this method, a flexible substrate film of copper-doped graphene as a grounding electrode is prepared in situ on polyimide paper. After inducing uniform deposition of copper ions on its surface and within its pores, the conductive cross-section is significantly increased, the sheet resistance is reduced, and the surface of the flexible substrate film is further filled and smoothed, forming a dense, flat copper coating that is firmly bonded to the LIG network, while maintaining the flexibility of the material. This invention uses picosecond lasers to prepare copper-doped graphene in situ, eliminating the need for high-temperature reduction to obtain elemental copper, thus avoiding damage to the flexible substrate and fine structure caused by high-temperature treatment. This results in a ready-to-use, high-performance grounding layer film that can be directly integrated into flexible circuits. It should be noted that completing the copper deposition in a copper sulfate electrolyte not only significantly improves conductivity but also maintains the flexibility of the material and obtains a low-roughness surface suitable for high-frequency signal transmission.

[0040] On the other hand, this invention uses polyimide paper as a substrate. PI paper has a porous fibrous structure, a large specific surface area, and stronger wettability and adsorption capacity, allowing the precursor solution to be fully adsorbed and uniformly distributed on the substrate surface and interior, effectively improving component loading and uniformity. During laser processing, the porous structure facilitates the rapid escape of reactive gases, preventing film bubbling and cracking, resulting in a loose, continuous, and stable laser-induced graphene layer. Simultaneously, the fibrous structure can physically anchor the generated LIG-Cu composite material, enhancing the bonding force between the composite material and the substrate and improving material stability. Furthermore, PI paper has lower cost, higher process tolerance, and requires no complex pretreatment, making it more conducive to the efficient, repeatable, and large-scale preparation of LIG-Cu composite materials.

[0041] Specifically, the grounding layer obtained from the LIG-Cu composite material in this solution has the following characteristics:

[0042] 1. Excellent flexibility and bending reliability: The LIG-Cu composite material combines the inherent flexibility of graphene with the reinforcing effect of copper plating. It can maintain stable conductivity even under repeated bending, especially in the dynamic bending parts of flexible equipment or components.

[0043] 2. Excellent high-frequency performance: The graphene-copper composite structure has a smooth surface, which effectively reduces the loss caused by the skin effect at high frequencies, making it suitable for high-bandwidth applications such as flexible displays and high-frequency radio frequency circuits.

[0044] 3. Lightweight and highly integrated: Compared with pure copper grounding layers and multilayer graphene copper electrodes, the composite material density of this solution is significantly reduced, which is conducive to achieving lightweight equipment; and it can be directly prepared on PI (polyimide) substrate without adhesives, improving interface stability and heat dissipation efficiency.

[0045] 4. Environmentally friendly and patternable process: The process combines laser induction and electroplating, which is simple, produces little waste liquid, and allows for flexible design of grounding layer patterns through the laser path, adapting to the layout of various flexible devices.

[0046] During the picosecond ultraviolet laser irradiation process in step (2), two key reactions occur simultaneously: 1) the polyimide substrate is directly carbonized and grapheneized to form a three-dimensional porous LIG; 2) copper nitrate is directly reduced in situ to copper nanoparticles (Cu) in the instantaneous high temperature and reducing atmosphere (from PI decomposition products) generated by the laser, and then embedded into the newly formed LIG network. This process is completed in one step, without the need for subsequent high-temperature reduction, which simplifies the process, reduces energy consumption, and avoids the potential impact of high temperature on the material structure.

[0047] Furthermore, in step (1), the method for preparing the copper nitrate precursor solution includes:

[0048] Mix 0.2~0.5g / mL polyvinylpyrrolidone aqueous solution with 5~8mol / L Cu(NO3)2·3H2O at a volume ratio of 1:1 to obtain a homogeneous mixture;

[0049] The copper nitrate precursor solution was obtained by diluting the mixture with deionized water at a ratio of 1: (3~4).

[0050] This invention uses copper nitrate The solution is mixed with polyvinylpyrrolidone (PVP) to form a precursor film. Adding PVP, a high-molecular-weight surfactant, to the precursor solution effectively improves the wettability of the solution on the PI paper surface, prevents solution aggregation, and ensures film uniformity. The subsequent pre-drying process removes the solvent water, allowing copper nitrate and PVP to adhere to the PI surface in solid film form. The resulting copper-containing salt precursor film provides a metal source and dopant source for the subsequent laser-induced reaction.

[0051] By controlling the concentration of polyvinylpyrrolidone aqueous solution at 0.2–0.5 g / mL, A concentration controlled at 5–8 mol / L, mixed at a 1:1 volume ratio and then diluted with deionized water at a ratio of 1:(3–4), allows for sufficient complexation of copper ions with the polymer carrier, forming a precursor solution with suitable viscosity, uniform dispersion, and excellent film-forming properties. This dosage range effectively avoids problems such as component agglomeration, film cracking, and decreased adhesion caused by excessively high concentrations, while preventing defects such as insufficient copper loading and poor conductivity caused by excessively low concentrations. During laser processing, the synergistic effect of the component ratios facilitates the uniform in-situ reduction of the Cu component and its tight bonding with the graphene-based carbon matrix, ultimately resulting in a structurally complete, highly conductive, and mechanically stable LIG-Cu composite material. As an example, the Fikentscher K value range for polyvinylpyrrolidone (PVP) is 23–27.

[0052] As an example: PVP aqueous solution concentrations are selected from 0.2, 0.3, 0.4, 0.35, and 0.5 g / mL. The concentration of the solution was selected from 5, 6, 6.5, 7, and 8 mol / L, and the deionized water was diluted at ratios of 1:3, 1:35, and 1:4.

[0053] Furthermore, in step (1), 230~300uL of copper acid precursor solution is coated onto a processing area of ​​50~150um thickness and 15~20cm. 2 On polyimide paper.

[0054] The coating amount of the precursor solution directly affects the thickness, porosity, and conductivity of the LIG-Cu composite layer formed after laser induction. Insufficient coating may result in a sparse graphene network, insufficient copper particle loading, and poor conductivity of the composite layer; excessive coating may lead to an overly thick film, affecting laser energy transfer and causing incomplete graphene formation or uneven copper reduction. Experimental optimization showed that coating approximately 250 μL of the aforementioned precursor solution onto a 40 mm × 40 mm target area of ​​90 μm thick polyimide paper can achieve a composite layer with suitable thickness and high conductivity while ensuring film uniformity. The preferred thickness of the polyimide paper is 50-150 μm; too thin a layer may result in insufficient mechanical support, while too thick a layer will affect laser penetration and thermal effects, increasing the complexity of the process.

[0055] Furthermore, in step (2), the parameters of the picosecond ultraviolet laser are: wavelength of 355nm, pulse width of 8~12ps, laser power of 3~5W, scanning speed of 100~400mm / s, and scanning spacing (line spacing) of 0.01~0.04mm.

[0056] The 355nm ultraviolet wavelength in this scheme has high absorption efficiency for polyimide, enabling efficient graphene formation. The 8-12ps picosecond pulse falls within the cold processing range, resulting in a minimal heat-affected zone, effectively avoiding substrate deformation, film cracking, and copper particle agglomeration and sintering problems caused by heat accumulation. Based on the limited amount of copper nitrate precursor solution coating, a scanning speed of 100-400mm / s and a scanning spacing of 0.01-0.04mm are matched to ensure uniform laser irradiation, no missed scans, and no excessive overlap, thus guaranteeing effective graphene formation and metallization.

[0057] Furthermore, in step (3), the laser-induced graphene and the substrate are first immersed in deionized water, then cleaned by sputtering deionized water, and finally the cleaned laser-induced graphene is placed on the substrate and dried at 60~95℃. By cleaning the laser-induced graphene and the substrate, soluble impurities such as unreacted copper salts, PVP residues, nitrate ions, and small molecule byproducts remaining after laser treatment can be removed. In the graphene layer generated by laser induction, there will be a small amount of loose, unbonded carbon fragments or weak bonding layers. These can be gently peeled off by immersion and water sputtering, leaving only the dense and strongly bonded LIG-Cu composite material. The surface is cleaner after cleaning, which can reduce interfacial impedance and improve conductivity. At the same time, it avoids the dissolution of residual impurities or structural detachment during subsequent use, enhances the stability and reliability of the material, and makes it easier to deposit elemental copper during electroplating.

[0058] Furthermore, in step (4), the concentration of the copper sulfate electrolyte is 0.25~0.35 mol / L, the constant current is 0.06~0.10 mA, the electroplating time is set to 80~120 min, and the electroplating temperature is 10~20℃. The electroplating process is completed at a low temperature, avoiding damage to the flexible substrate and fine structure caused by high-temperature treatment, and the final product is a grounding layer that can be directly integrated into flexible circuits.

[0059] Specifically, controlling the copper sulfate electrolyte concentration to 0.25~0.35 mol / L matches the ion transport requirements of LIG-Cu's high specific surface area, avoids concentration polarization, and ensures uniform deposition of copper ions on the porous framework surface. Using a micro-current constant current electroplating of 0.06~0.10 mA adapts to the uneven electric field distribution on the LIG-Cu surface, suppressing excessive copper deposition at tips and edges, achieving uniform adhesion of the copper layer on the graphene framework, and preventing pore blockage and particle agglomeration. Controlling the electroplating time to 80~120 min allows the copper layer to reach a suitable reinforcing thickness, improving the conductivity and structural strength of the composite material while preserving its three-dimensional porous channels, and the prepared grounding electrode possesses sufficient flexibility. Setting the electroplating temperature to a low temperature of 10~20℃ reduces the crystal growth rate, resulting in a fine-grained, dense, and flat copper coating with low internal stress, while avoiding damage to the original structure and interfacial bonding of LIG-Cu caused by high temperatures. Through the synergistic effect of the above parameters, uniform, dense, and firm deposition of copper layers can be achieved without damaging the porous structure of LIG-Cu, ultimately resulting in a composite electrode material with excellent conductivity, large specific surface area, stable structure, high bonding strength, and strong flexibility.

[0060] Furthermore, a pure copper plate is used as the anode and laser-induced graphene as the cathode, with the anode and cathode parallel to each other and a spacing of 3-8 cm between them. The electric field distribution between the two parallel electrodes is uniform, ensuring a uniform copper layer thickness, no edge effects, and no localized over-plating on a large-area LIG-Cu substrate. The 3-8 cm electrode spacing is the optimal range for both electric field uniformity and solution mass transfer, ensuring a uniform electric field distribution while also considering ion diffusion and mass transfer efficiency. This avoids problems such as excessive localized current, rough coating, and structural scorching caused by too small a spacing, or uneven current distribution and low deposition efficiency caused by too large a spacing.

[0061] Accordingly, the present invention also provides a flexible grounding layer, which is prepared by the above-described method for preparing a grounding layer based on LIG-Cu composite material.

[0062] Accordingly, the present invention also provides a flexible MEMS pressure sensor, comprising a flexible substrate, a MEMS piezoresistive film and the aforementioned flexible grounding layer, wherein the MEMS piezoresistive film and the flexible grounding layer are respectively connected to the flexible substrate.

[0063] Accordingly, the present invention also provides a flexible smart wristband, including a flexible band body, a flexible circuit board and the aforementioned flexible MEMS pressure sensor, wherein the flexible MEMS pressure sensor is mounted on the flexible circuit board and the flexible circuit board is embedded in the flexible band body;

[0064] The flexible circuit board is provided with the aforementioned flexible grounding layer;

[0065] The flexible MEMS pressure sensor is used to measure the wearer's blood pressure.

[0066] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to conventional methods and conditions or according to the product instructions. Unless otherwise specified, the reagents are commercially available; and the performance of products from different sources does not have a significant impact.

[0067] Example 1

[0068] The method for preparing the grounding layer based on LIG-Cu composite material in this embodiment includes the following steps (1) to (4):

[0069] Step (1):

[0070] Rinse the glass substrate surface with deionized water and wipe it with a lint-free cloth to remove surface dust and organic impurities. Then dry it with nitrogen or allow it to air dry in a clean environment. Take a 50µm thick sheet with a processing area of ​​15cm... 2Polyimide paper was fixed to a 50mm × 50mm glass substrate with transparent tape. A 0.2g / mL aqueous solution of polyvinylpyrrolidone and a 5mol / L Cu(NO3)2·3H2O solution were mixed at a volume ratio of 1:1 to obtain a homogeneous mixture. The mixture was then diluted with deionized water at a ratio of 1:3 to obtain a copper nitrate precursor solution. 230µL of the copper nitrate precursor solution was vertically dropped onto the polyimide paper, and immediately spread evenly with a doctor blade or spin coater to cover the entire target PI area. The coated sample was placed on a heating stage at a preset temperature of 80℃ until a uniform, dry, blue-green copper-containing precursor film formed on the PI paper surface.

[0071] Step (2): The substrate carrying the precursor film is placed on the laser processing system. By adjusting the focusing system of the three-dimensional platform and the laser head, the laser spot is precisely aligned with the surface of the precursor film and focused. The initial defocusing amount is set to +5 mm. The laser scanning path is planned using computer-aided design software, and key laser process parameters are set. Picosecond ultraviolet laser is applied to the precursor film to obtain laser-induced graphene. The parameters of the picosecond ultraviolet laser are: wavelength of 355 nm, pulse width of 8 ps, laser power of 3 W, scanning speed of 100 mm / s, and scanning spacing of 0.01 mm.

[0072] Step (3): Use tweezers to peel the laser-induced graphene off the substrate. First, soak the laser-induced graphene and the substrate in deionized water for 30 seconds. Then, clean the laser-induced graphene and the substrate by sputtering deionized water. Finally, place the cleaned laser-induced graphene on the substrate and dry it at 60°C.

[0073] Step (4): The dried laser-induced graphene was placed in a copper sulfate electrolyte for electroplating. After removal, the surface was immediately rinsed with plenty of deionized water and then thoroughly dried in an 80℃ oven to obtain a grounding layer based on the LIG-Cu composite material. The concentration of the copper sulfate electrolyte was 0.25 mol / L, the constant current was 0.06 mA, the electroplating time was 80 min, and the electroplating temperature was 10℃. A pure copper plate was used as the anode and the laser-induced graphene as the cathode, with the anode and cathode parallel to each other and a distance of 3 cm between them.

[0074] Example 2

[0075] The preparation method of the grounding layer based on LIG-Cu composite material in this embodiment is basically the same as that in Example 1, except that:

[0076] Step (1):

[0077] A 90µm thick sheet with a processing area of ​​20cm 2Polyimide paper was fixed to a glass substrate with transparent tape. A 0.3 g / mL aqueous solution of polyvinylpyrrolidone and a 6 mol / L Cu(NO3)2·3H2O solution were mixed at a volume ratio of 1:1 to obtain a homogeneous mixture. The mixture was then diluted with deionized water at a ratio of 1:4 to obtain a copper nitrate precursor solution. 270 μL of the copper nitrate precursor solution was vertically dropped onto the polyimide paper to prepare a precursor film.

[0078] Step (2): The parameters of the picosecond ultraviolet laser used to prepare the laser-induced graphene are: wavelength of 355nm, pulse width of 8ps, laser power of 5W, scanning speed of 200mm / s, and scanning spacing of 0.02mm.

[0079] Step (3): Laser-induced graphene at 70°C.

[0080] Step (4): The concentration of copper sulfate electrolyte is 0.25 mol / L, the constant current is 0.08 mA, the electroplating time is set to 100 min, and the electroplating temperature is 15℃. Pure copper plate is used as the anode and laser-induced graphene is used as the cathode. The anode and cathode are parallel to each other, and the distance between the anode and cathode is 7 cm.

[0081] Example 3

[0082] The preparation method of the grounding layer based on LIG-Cu composite material in this embodiment is basically the same as that in Example 1, except that:

[0083] Step (1):

[0084] A 120um thick sheet with a processing area of ​​15cm 2 Polyimide paper was fixed to a glass substrate with transparent tape. A 0.4 g / mL aqueous solution of polyvinylpyrrolidone and a 7 mol / L Cu(NO3)2·3H2O solution were mixed thoroughly at a volume ratio of 1:1. The mixture was then diluted with deionized water at a ratio of 1:3 to obtain a copper nitrate precursor solution. 270 μL of the copper nitrate precursor solution was vertically dropped onto the polyimide paper to prepare a precursor film.

[0085] Step (2): The parameters of the picosecond ultraviolet laser used to prepare the laser-induced graphene are: wavelength of 355nm, pulse width of 10ps, laser power of 4W, scanning speed of 300mm / s, and scanning interval of 0.03mm.

[0086] Step (3): Laser-induced graphene is dried at 80°C.

[0087] Step (4): The concentration of copper sulfate electrolyte is 0.35 mol / L, the constant current is 0.10 mA, the electroplating time is set to 110 min, and the electroplating temperature is 18℃. Pure copper plate is used as the anode and laser-induced graphene is used as the cathode. The anode and cathode are parallel to each other, and the distance between the anode and cathode is 5 cm.

[0088] Example 4

[0089] The preparation method of the grounding layer based on LIG-Cu composite material in this embodiment is basically the same as that in Example 1, except that:

[0090] Step (1):

[0091] A 150µm thick sheet with a processing area of ​​20cm 2 Polyimide paper was fixed to a glass substrate with transparent tape. A 0.5 g / mL aqueous solution of polyvinylpyrrolidone and an 8 mol / L Cu(NO3)2·3H2O solution were mixed thoroughly at a volume ratio of 1:1. The mixture was then diluted with deionized water at a ratio of 1:4 to obtain a copper nitrate precursor solution. 300 μL of the copper nitrate precursor solution was vertically dropped onto the polyimide paper to prepare a precursor film.

[0092] Step (2): The parameters of the picosecond ultraviolet laser used to prepare the laser-induced graphene are: wavelength of 355nm, pulse width of 12ps, laser power of 5W, scanning speed of 400mm / s, and scanning interval of 0.04mm.

[0093] Step (3): Laser-induced graphene is dried at 95°C.

[0094] Step (4): The concentration of copper sulfate electrolyte is 0.3 mol / L, the constant current is 0.08 mA, the electroplating time is set to 120 min, and the electroplating temperature is 20℃. Pure copper plate is used as the anode and laser-induced graphene is used as the cathode. The anode and cathode are parallel to each other, and the distance between the anode and cathode is 8 cm.

[0095] Example 5

[0096] The electron microscope scanning image of the grounding layer obtained in this embodiment is as follows: Figures 1-4 As shown. The preparation method of the grounding layer based on LIG-Cu composite material in this embodiment is basically the same as that in Example 1, except that:

[0097] Step (1):

[0098] A 90µm thick sheet with a processing area of ​​16cm 2Polyimide paper was fixed to a glass substrate with transparent tape. A 0.3 g / mL aqueous solution of polyvinylpyrrolidone and a 6 mol / L Cu(NO3)2·3H2O solution were mixed thoroughly at a volume ratio of 1:1. The mixture was then diluted with deionized water at a ratio of 1:3 to obtain a copper nitrate precursor solution. 250 μL of the copper nitrate precursor solution was vertically dropped onto the polyimide paper to prepare a precursor film.

[0099] Step (2): The parameters of the picosecond ultraviolet laser used to prepare the laser-induced graphene are: wavelength of 355nm, pulse width of 10ps, laser power of 3W, scanning speed of 300mm / s, and scanning interval of 0.02mm.

[0100] Step (3): Laser-induced graphene is dried at 80°C.

[0101] Step (4): The concentration of copper sulfate electrolyte is 0.32 mol / L, the constant current is 0.09 mA, the electroplating time is set to 120 min, and the electroplating temperature is 20℃. Pure copper plate is used as the anode and laser-induced graphene is used as the cathode. The anode and cathode are parallel to each other, and the distance between the anode and cathode is 5 cm.

[0102] Comparative Example 1

[0103] The preparation method of the grounding layer in this comparative example is basically the same as that in Example 5, except that a polyimide film with a thickness of 90 μm is used.

[0104] Comparative Example 2

[0105] The preparation method of the grounding layer in this comparative example is basically the same as that in Example 5, except that the electrolyte in step (4) consists of: 70 g / L copper sulfate pentahydrate, 200 g / L sulfuric acid, 60 mg / L chloride ions, and 15 mg / L additives, the additive being sodium dodecylbenzene sulfonate, a quaternary ammonium salt surfactant.

[0106] The performance of the grounding layers obtained in Examples 1-5 and Comparative Examples 1-2 is shown in the table below.

[0107]

[0108] Other configurations and operations of the method for preparing the grounding layer based on LIG-Cu composite material according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here. When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. The described performance can be achieved within the proportions range of the present invention. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by those skilled in the art to which this invention pertains.

[0109] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a grounding layer based on LIG-Cu composite material, characterized in that, Includes the following steps: (1) Fix polyimide paper onto a substrate and coat the polyimide paper with a copper nitrate precursor solution to make a precursor film; (2) The substrate carrying the precursor film is placed in a laser processing system, and the precursor film is acted on by a picosecond ultraviolet laser to obtain laser-induced graphene. (3) The laser-induced graphene is peeled off from the substrate, the laser-induced graphene and the substrate are cleaned respectively, and then the laser-induced graphene is placed on the substrate for drying. (4) The dried laser-induced graphene is placed in copper sulfate electrolyte for electroplating, then taken out, cleaned and dried to obtain the grounding layer based on LIG-Cu composite material.

2. The preparation method according to claim 1, characterized in that, In step (1), the preparation method of the copper nitrate precursor solution includes: Mix 0.2~0.5g / mL polyvinylpyrrolidone aqueous solution with 5~8mol / L Cu(NO3)2·3H2O at a volume ratio of 1:1 to obtain a homogeneous mixture; The copper nitrate precursor solution was obtained by diluting the mixture with deionized water at a ratio of 1: (3~4).

3. The preparation method according to claim 2, characterized in that, In step (1), 230-300 μL of copper acid precursor solution is coated onto a processing area of ​​50-150 μm thick and 15-20 cm wide. 2 On polyimide paper.

4. The preparation method according to claim 1, characterized in that, In step (2), the parameters of the picosecond ultraviolet laser are: wavelength of 355nm, pulse width of 8~12ps, laser power of 3~5W, scanning speed of 100~400mm / s, and scanning interval of 0.01~0.04mm.

5. The preparation method according to claim 1, characterized in that, In step (3), the laser-induced graphene and the substrate are first soaked in deionized water, then the laser-induced graphene and the substrate are cleaned by sputtering deionized water, and finally the cleaned laser-induced graphene is placed on the substrate and dried at 60~95°C.

6. The preparation method according to claim 1, characterized in that, In step (4), the concentration of the copper sulfate electrolyte is 0.25~0.35mol / L, the constant current is 0.06~0.10mA, the electroplating time is set to 80~120min, and the electroplating temperature is 10~20℃.

7. The preparation method according to claim 6, characterized in that, A pure copper plate is used as the anode and laser-induced graphene as the cathode. The anode and cathode are parallel to each other, and the distance between the anode and cathode is 3~8cm.

8. A flexible grounding layer, characterized in that, It is prepared by the method for preparing a grounding layer based on LIG-Cu composite material as described in any one of claims 1-7.

9. A flexible MEMS pressure sensor, characterized in that, It includes a flexible substrate, a MEMS piezoresistive film, and the flexible grounding layer as described in claim 8, wherein the MEMS piezoresistive film and the flexible grounding layer are respectively connected to the flexible substrate.

10. A flexible smart wristband, characterized in that, It includes a flexible strip, a flexible circuit board, and the flexible MEMS pressure sensor as described in claim 9, wherein the flexible MEMS pressure sensor is mounted on the flexible circuit board, and the flexible circuit board is embedded in the flexible strip; The flexible circuit board is provided with the flexible grounding layer as described in claim 8; The flexible MEMS pressure sensor is used to measure the wearer's blood pressure.

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