Method for manufacturing a flexible circuit board and flexible circuit board

Abstract

The present application belongs to the technical field of high polymer materials, and relates to a preparation method of a flexible circuit board, wherein a bonding film comprises an adhesive layer and a high-activity film layer; the adhesive is a cross-linked structure polyimide adhesive prepared by using silanol small molecule substances and 3-aminobenzene boronic acid as composite fillers; the covalent connection between the fillers and the matrix is used to optimize the mechanical and thermal properties of the polyimide adhesive; the high-activity film is prepared by dispersing modified graphene oxide into polyimide, and a large number of active groups are used to improve the wettability, expansion coefficient and thermal conductivity of the matrix, so that the prepared bonding film has excellent adhesion with the flexible wiring substrate, thereby ensuring the reliability and reversibility of the bonding, prolonging the stretching frequency, improving the heat dissipation effect, and being suitable for 5G flexible circuit boards.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer materials, and particularly relates to a preparation method of a flexible circuit board, and especially to a preparation method of an adhesive film in the flexible circuit board. BACKGROUND

[0002] Compared with traditional rigid circuit boards, flexible circuit boards have the advantages of being arbitrarily bendable, having high wiring density, good bending resistance, light weight, and thin thickness, and thus are increasingly widely applied in the fields of aerospace, navigation, digital products, mobile communication, etc. A flexible circuit board is composed of a copper foil, an adhesive layer, and a film substrate. At present, most of the film substrates are bright polyimide films, which can achieve the purpose of shielding, but the glossiness of the surface of the polyimide film is still too bright, and thus cannot meet the needs of specific optical applications. Moreover, although traditional permanent adhesive layers have high cohesive strength and can form strong adhesion to the substrate, they are not detachable, difficult to clean, and cannot be well recycled and reused, and also do not allow transient positioning or mispositioning during the adhesion process, thus causing environmental pollution and resource waste.

[0003] A kind of adhesive film for flexible circuit board is disclosed in Chinese patent CN114702908B, which is prepared by introducing a hydroxyacrylamide compound into traditional polyurethane resin, phenoxy resin, epoxy resin, polyester resin, butadiene resin, polyimide resin, polyamide resin and polyolefin resin resin matrix, so that the prepared adhesive film has excellent adhesion to the flexible wiring substrate, thereby ensuring the reliability of adhesion, and even after high temperature and high humidity environmental testing, it can still maintain good adhesion strength, thereby avoiding the problem of poor connection. However, the compatibility problem of the adhesive layer and the substrate and the reversible and repeated use problem have not been solved. Because the surface of inert film materials such as polyimide film lacks polar groups, the reaction activity is weak, and the wettability with adhesive glue solution is poor, so the adhesion strength is not high. Moreover, the interfacial bonding energy between ordinary polyimide adhesive and copper foil is only 28 mJ / m 2 , resulting in a 90° peeling strength of less than 0.8 N / mm. Atomic force microscope observation shows that when the thickness of the copper oxide layer exceeds 5 nm, the adhesion failure probability increases by 80%.

[0004] As a preferred matrix for heat-resistant adhesives, polyimide exhibits significant application value. Its superior performance primarily stems from its rigid polymer chains, high-density π-π interactions between aromatic molecules, and uniform chain crystallization. However, when used as an adhesive, the strong inter-chain interactions of polyimide often lead to excessively high cohesive forces, while weak interfacial interactions cause interfacial failure, resulting in low adhesive strength. Furthermore, the high molecular weight of polyimide gives it excellent mechanical strength, but this leads to problems such as high viscosity, low solubility, and poor wettability in polyimide adhesives, further contributing to low adhesive strength. Introducing flexible segments or asymmetric structures into the polyimide backbone can reduce the rigidity of the molecular chains, inhibit tight chain packing, and reduce inter-chain interactions, but this results in a sharp decline in the thermal and chemical stability of polyimide. Therefore, more effective strategies are still needed to improve the reversibility and adhesiveness of polyimide adhesives without sacrificing their thermal and chemical stability. In particular, the development of high-temperature resistant reversible adhesives with good mechanical and adhesive properties under operating conditions is a pressing issue. Developing a new generation of adhesive systems that combine superior adhesion, extreme environmental stability, and eco-friendliness will drive the advancement of flexible electronics technology towards thinner, more flexible, and smarter designs. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method for preparing a flexible circuit board, thereby resolving one or more technical problems existing in the prior art and at least providing a beneficial option or creating conditions. This application provides a method for preparing a flexible circuit board, wherein the method involves subjecting a prepared flexible copper-clad laminate to subsequent welding, etching, and drilling processes to obtain the flexible circuit board. The flexible copper-clad laminate is a copper-clad laminate material formed by composite pressing of copper foil and an adhesive film. The adhesive film comprises a thin film substrate and an adhesive layer located on the surface of the substrate, wherein the adhesive layer is a layer formed by adhesive.

[0006] Firstly, a method for optimizing the film substrate is provided. This method utilizes the covalent bonding of multiple molecular groups between the filler and the substrate to optimize the mechanical, hydrophobic, and thermal properties of the polyimide composite film, thereby improving the overall performance of the film substrate. Secondly, an adhesive with high adhesion and peel strength is also provided. Furthermore, the prepared adhesive exhibits low volume shrinkage after curing and maintains a high recovery rate after repeated large deformations and recovery, thus belonging to a reversible adhesive category.

[0007] Ordinary polyimide films are inert film materials. Due to the lack of polar groups on their surface, their reactivity is weak, resulting in poor wettability of adhesives and thus low bonding strength. Therefore, surface modification of ordinary polyimide films is performed to introduce polar active groups and increase their surface roughness, thereby improving their performance.

[0008] The polyimide film substrate is modified to obtain a high-activity polyimide film substrate, specifically:

[0009] The graphite is added into a mixed solution of H2SO4 and H3PO4, and stirred at room temperature until fully dissolved. Then KMnO4 is slowly added, and the stirring is continued for 30 minutes. The temperature is raised to 40℃, and the stirring is continued for 60 minutes. The temperature is raised to 90℃, and the stirring is continued for 100 minutes. A mixed solution of deionized water and H2O2 is slowly added dropwise to obtain an oxidized graphite mixture. The oxidized graphite mixture is centrifuged and washed for 2-3 times, and is treated by dialysis with deionized water. Then, the oxidized graphite mixture is vacuum freeze-dried to obtain a sponge-like oxidized graphene;

[0010] N-methyl pyrrolidone is added into the sponge-like oxidized graphene, and stirred at room temperature for 100 minutes until fully dissolved. Then hyperbranched polyamide-amine is added, followed by 1-ethyl-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride. The stirring is continued at 60-80℃ for 20-24 hours to obtain the oxidized graphene grafted with hyperbranched polyamide-amine. The product is centrifuged, washed with water, and dried.

[0011] The mass ratio of graphite to KMnO4 is 1:5. The mass ratio of oxidized graphene, 1-ethyl-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride, and hyperbranched polyamide-amine is 2:2-3:4-5. The mass ratio of hyperbranched polyamide-amine grafted oxidized graphene to polyimide resin is 0.9%-1.1%.

[0012] The polyimide resin and hyperbranched polyamide-amine grafted oxidized graphene are fully dispersed in an aprotic polar solvent to obtain a homogeneous solution. The homogeneous solution is dried by molding to obtain a high-activity polyimide film with low expansion coefficient.

[0013] The polyimide resin is a thermoplastic resin with a number average molecular weight of 50000-80000. The aprotic polar solvent includes one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methyl pyrrolidone.

[0014] The centrifugal washing is performed as follows: a dilute hydrochloric acid solution is prepared with a volume ratio of 1:10, and the oxidized graphite mixture is centrifuged. The centrifugation is continued until the supernatant is detected to be free of white precipitate by a dilute BaCl2 solution. Then, the centrifugation is continued with deionized water until the supernatant is detected to be free of white precipitate by a dilute AgNO3 solution.

[0015] Graphene oxide is a carbon skeleton material with two-dimensional nanostructure, which can not only realize the adsorption of metal ions, but also is a good carrier for loading other substances. Hyperbranched polyamide-amine is a kind of dendrimer with non-toxic and good biocompatibility, and contains a large number of amine groups at the end, which is an ideal modifier. After modification, graphene oxide is uniformly dispersed in the polyimide resin, which can effectively improve the adhesion of the film matrix surface. The rich polar groups in the polymer chain are the key to the high adhesive strength of the adhesive. The hyperbranched polyamide containing many terminal amine groups has rich polar groups (N-H, -NH2 and C=O) in the hyperbranched structure, which can form high-density multiple hydrogen bonds with the substrate to adapt to the adhesion of different substrates, and show good adhesion performance.

[0016] In addition, the addition of graphene as a photo-thermal modification material to the polyimide adhesive can also realize the reversible adhesion effect induced by light, and the N-H, -NH2 and C=O groups can also produce metal complexation with metal ions on the surface of the substrate to further improve the adhesion strength.

[0017] Due to the regular molecular arrangement, small molecule solvents are difficult to enter the polyimide, and in addition, as the molecular weight increases and the aromatic structure has strong intermolecular interaction, the polyimide also has the disadvantages of large rigidity, difficult processing, poor flexibility, low solubility and difficult melting. The cohesive energy of the polyimide adhesive can be reduced to improve its processability and adhesion, and at the same time, it can also be given the characteristics of detachability and recyclability to adapt to the field of reversible adhesion. In order to destroy the regular structure of polyimide, flexible segments (ether bonds, carbonyl sulfone groups, etc.) or aliphatic units (methyl and methylene, etc.), bulky side groups (trifluoromethyl, etc.) or asymmetric structures are often introduced into the main chain.

[0018] Therefore, we introduced siloxane segments and borate bonds to improve the flexibility of polyimide and increase the toughness; at the same time, the wettability, ductility and reversibility of the adhesive are also improved. The adhesive is a cross-linked modified polyimide, which is prepared by gradually polymerizing silanol small molecules through cross-linking of siloxane diamine, 4,4'-oxybenzene dianhydride, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane and 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and the specific preparation process is as follows:

[0019] Dimethyldichlorosilane, phenyltrichlorosilane and methylphenyldichlorosilane are added to toluene, stirred and mixed uniformly, then deionized water is added, the temperature is kept at 20-30℃, and high-speed stirring is carried out for 18-20 hours to obtain a silanol small molecule intermediate;

[0020] The mass ratio of dimethyldichlorosilane, phenyltrichlorosilane and methylphenyldichlorosilane is 1:2:2;

[0021] The siloxane diamine and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane are added to 10 times the mass of solvent N-methylpyrrolidone under the protection of N2 atmosphere, and stirred thoroughly for 30-50 min. After the mixed diamine is completely dissolved, 4,4'-oxybenzene dicarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and finally 3-aminobenzoic acid are added in batches, and constant temperature stirring is performed for 12-15 hours to obtain a prepolymer,

[0022] The graphene oxide grafted with hyperbranched polyamide-amine is ground and crushed, the prepolymer is added, and after stirring and dispersing uniformly, the silanol small molecule substance is added, and stirring is performed at a low constant temperature of 5°C for 8-10 hours to obtain a yellow solution, and a modified polyimide adhesive with a crosslinked structure is obtained.

[0023] The mass ratio of the siloxane diamine and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane is 1:2-3; the mass ratio of the siloxane diamine, 4,4'-oxybenzene dicarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 3-aminobenzoic acid is 1-2:2-3:1-2:0.8-1.2; the mass ratio of the graphene oxide grafted with hyperbranched polyamide-amine, the silanol small molecule substance, and the prepolymer is 1:8-15:40-50;

[0024] 2,2-bis[4-(4-aminophenoxy)phenyl]propane with good flexibility is introduced into the monomer for copolymerization modification to improve the bonding performance of the adhesive. The siloxane is crosslinked to further improve its flexibility, and the silanol small molecule substance also generates a siloxane group in the condensation reaction, further connecting the high molecular substance, and at the same time, the low molecular substance released by the cured polymer polyimide can significantly repair the defect problem at the interface caused by the release of the low molecular substance.

[0025] The siloxane crosslinked structure polyimide adhesive can effectively reduce the glass body temperature of the polymer, because the decomposition temperature of the alkyl part and the Si-CH3 part of the siloxane part is lower compared with the imine ring and the aromatic segment. And the siloxane crosslinking has a phase separation structure, and the siloxane is concentrated on the surface of the polymer, the phase separation structure improves the segment mobility and interface wettability of the polymer, and improves the adhesion behavior, which is manifested as the improvement of the peeling strength.

[0026] Finally, a flexible copper clad plate with three-dimensional bending part is provided, and an adhesive layer and a high-activity film substrate are provided as an adhesive film; a cross-linked structure of a modified polyimide adhesive is coated on the high-activity polyimide film substrate to form an adhesive layer, the film thickness is 20-30 μm, and the adhesive layer is cured at 130-160 °C for 6-8 minutes to obtain a surface-dried and non-sticky adhesive film; the adhesive film is laminated with a copper foil, and is laminated on a hot press at 170-200 °C / 1-3 MPa for 2-4 minutes, and then is placed in an oven at 170-180 °C for 1 hour to obtain the flexible copper clad plate.

[0027] We found that the prepared adhesive has poor adhesion with ordinary polyimide film substrates, and the expansion coefficients of the adhesive film and the copper foil are inconsistent, which can cause adhesion failure. However, the high-activity polyimide film provided in the present application significantly improves the above problems. Since the unmodified polyimide contains a large number of imide rings and benzene rings and other rigid structures, the interaction between the polymer chains is strong, the wettability of the substrate during adhesion is poor, and small molecule substances are released after curing, forming cavities and voids on the contact surface, which results in low adhesion strength and cohesive force dominated interface failure. However, when flexible soft segments are introduced into the rigid main chain of polyimide, the toughness of the polymer is improved, the glass transition temperature of the system is reduced, and the wettability and ductility of the system are also improved. During the heating and adhesion process, the soft segment easily expands to the surface of the substrate, increases the contact area, and better forms a mechanical interlocking structure to enhance the interfacial adhesion. In addition, the Si-O bond network structure formed by the small molecule silanol substance during the curing process can solidify and release small molecules, and the fluffy structure formed after the modification of graphene oxide is cross-linked with the main chain to form a dense and flexible structure, which reduces the expansion coefficient and improves the thermal conductivity, thereby significantly improving the mechanical properties of the adhesive. This is the result of the combined action of macromolecular siloxane chains and small molecular siloxane groups.

[0028] The reversible properties of van der Waals forces, hydrogen bonds, coordination interactions and host-guest interactions are all physical interactions, which can affect the cohesive energy both inside the adhesive structure and between the interface of the adhesive and the bonding substrate. However, since the physical interaction is a relatively weak intermolecular force, the thermal stability and mechanical properties of the adhesive based on these interactions are poor, and although it has excellent reversible effect, it is difficult to be applied to high temperature and high strength adhesion scenarios. And the cross-linked structure of the modified polyimide adhesive prepared in the application is through covalent bond interaction, which is a chemical bond, showing strong interaction between adjacent two or more atoms, and its strength is much greater than that of van der Waals force, hydrogen bond and other physical forces. The covalent cross-linked network increases the cohesive energy of the adhesive film. In addition to providing reversibility, the stable covalent cross-linked network can also improve the adhesion strength, thermal stability and dimensional stability. The cross-linked structure of the modified polyimide adhesive contains various polar bonds such as ether group, hydroxyl group and phenyl group, and multiple molecular interactions are the source of its adhesion. At the same time, we add dynamic borate ester group to the prepolymer and form dynamic covalent connection with Si, and form dynamic exchangeable covalent bond with hydroxyl group on the surface of various fillers and substrates. The dynamic interaction between the matrices enhances the cohesive force of the block copolymer network, and the synergistic effect of flexible ether bond and meta-bond structure significantly improves its tensile strength, toughness and temperature resistance, while maintaining recyclability. The introduction of twisted non-coplanar or asymmetric structure in the polyimide molecular structure can effectively disturb the regularity of the molecular chain and reduce the conjugation effect of the benzene ring and the molecular chain. The molecular chains of the cross-linked structure polymer are not easy to entangle with each other, and there are a large number of active groups at the ends of the molecular chains, among which larger groups can also increase the distance between the molecular chains, so that they have more moving space under tension. Small and short side chain groups not only destroy the regularity of the main chain, but also improve the flexibility of the molecular chain. The synergistic effect of these two factors leads to the increase of the elongation at break of polyimide, thereby expanding its application range.

[0029] Compared with the prior art, the application has the following beneficial effects:

[0030] 1) The present application provides a flexible circuit board with three-dimensional reversible bending resistance, providing an adhesive layer and a high-activity film substrate as an adhesive film; a modified polyimide adhesive with a cross-linked structure is coated on a high-activity polyimide film substrate to form an adhesive layer, and finally cured to obtain an adhesive film. By introducing macromolecular siloxane chains and small molecule Si-O bonds into the polyimide rigid main chain, not only the toughness of the polymer is improved, the glass transition temperature of the system is reduced, but also the wettability and ductility of the system are improved. In the process of heating and bonding, the soft segment is easy to expand to the surface of the substrate, increase the contact area, better form a mechanical interlocking structure, enhance the interfacial adhesion, and the Si-O bond network structure formed by the small molecule silanol substance in the curing process can release the small molecule substance, cooperate with the fluffy structure formed after the modification of graphene oxide, and the main chain after cross-linking, form a dense and flexible structure, reduce the expansion coefficient, improve the thermal conductivity, and significantly improve the mechanical properties of the adhesive film. And the dynamic borate functional group in the cross-linked structure is added to the prepolymer to form a dynamic covalent connection with Si, which significantly improves its tensile strength, toughness and temperature resistance, while maintaining reversibility and remoldability.

[0031] 2) The present application provides a modified polyimide adhesive with a cross-linked structure, which is prepared by polymerizing siloxane diamine, 4,4'-oxybenzene dianhydride, 2,2'-di[4-(4-aminophenoxy)phenyl]propane, 3,3',4,4'-benzophenone tetracarboxylic dianhydride through cross-linking silanol small molecule substance and borate functional group. The modified polyimide adhesive with a cross-linked structure is a high molecular adhesive material with shape memory, reversibility and remoldability, and has self-repairing function. The introduced siloxane segment and borate bond form a dynamic exchangeable covalent bond with the hydroxyl group on the surface of various fillers and substrates, and the covalent cross-linked network increases the cohesive energy of the adhesive film. In addition to providing reversibility, the stable covalent cross-linked network can also improve the bonding strength, thermal stability and dimensional stability, significantly improve its tensile strength, toughness and temperature resistance, and improve the flexibility of polyimide, the wettability, ductility and reversibility of the adhesive.

[0032] 3) The present application also provides a high-activity polyimide film, which is modified by introducing polar active groups on the surface of the polyimide film substrate and increasing the surface roughness, which significantly improves the performance in mechanics, hydrophobicity and thermal properties, and improves the comprehensive performance of the film. The introduction of micro-scale hyperbranched polyamide-amine graphene oxide in the film substrate effectively improves the thermal conductivity. When the system temperature is high, the interlayer spacing of graphene oxide is reduced, and the heat is quickly conducted along the graphene plane, so that the flexible circuit board has good heat dissipation.

[0033] 4) The raw materials for preparing the adhesive film are simple and easy to obtain, and no additional pollution to the environment is caused. The adhesive film prepared has the functions of high-temperature resistance and shape memory, and has good mechanical properties and adhesive properties under use conditions, and is easy to debond and re-bond with high strength after use. The adhesive film has low dielectric constant and dielectric loss, and good flame retardance. The flexible circuit board prepared according to the present application has high peel strength, good flexibility, dielectric properties, processability, heat resistance and chemical corrosion resistance, and also has high flame retardance. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 . Infrared spectrum of the polyimide adhesive;

[0035] Figure 2 . Electron microscope image of the graphene oxide grafted with hyperbranched polyamide-amine. DETAILED DESCRIPTION

[0036] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the present application after reading the content of the present application, and these equivalent forms also fall within the scope defined by the appended claims.

[0037] Example 1

[0038] The preparation of a flexible circuit board first modifies the polyimide film substrate to obtain a high-activity polyimide film substrate, specifically:

[0039] 1 part of graphite is added to 100 parts of a mixed solution of H2SO4 and H3PO4, and stirred at room temperature until fully dissolved. Then 5 parts of KMnO4 is slowly added, and stirring is continued at room temperature for 30 minutes. The temperature is raised to 40°C, and stirring is continued for 60 minutes. The temperature is raised to 90°C, and stirring is continued for 100 minutes. A mixed solution of 100 parts of deionized water and 16 parts of H2O2 is slowly added dropwise to obtain an oxidized graphite mixture. The oxidized graphite mixture is washed with a 1:10 volume ratio of dilute HCl solution by centrifugation for 3 times, and then washed with deionized water by centrifugation. Finally, the sponge-like oxidized graphene is obtained by vacuum freeze-drying.

[0040] 100 parts of N-methyl pyrrolidone is added to 4 parts of the sponge-like oxidized graphene, and stirred at room temperature for 100 minutes until fully dissolved. Then 8 parts of hyperbranched polyamide-amine is added, and 4 parts of 1-ethyl-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride is added. The mixture is stirred at 80°C for 20 hours to obtain the graphene oxide grafted with hyperbranched polyamide-amine. The product is centrifuged, washed with water, and dried.

[0041] 99 parts of thermoplastic polyimide resin, 1 part of hyperbranched polyamide-amine graphene oxide, are fully dispersed in a mixed solvent of N,N-dimethylacetamide and N-methylpyrrolidone to obtain a homogeneous solution, and the homogeneous solution is dried by molding to prepare a high-activity polyimide film matrix.

[0042] Further, the preparation method of the cross-linked structure modified polyimide adhesive is as follows: 4 parts of dimethyl dichlorosilane, 8 parts of phenyl trichlorosilane and 8 parts of methyl phenyl dichlorosilane are added to 40 parts of toluene, stirred and mixed uniformly, then 10 parts of deionized water is added, the temperature is kept at 20℃, and high-speed stirring is carried out for 20 hours to obtain a silanol small molecule substance.

[0043] 5 parts of siloxane diamine and 15 parts of 2,2'-bis[4-(4-aminophenoxy)phenyl]propane are added to 30 parts of solvent N-methylpyrrolidone under the protection of N2 atmosphere, fully stirred for 50 minutes, and after the mixed diamine is completely dissolved, 10 parts of 4,4'-oxybenzene dianhydride is added in three times, 5 parts of 3,3',4,4'-benzophenone tetracarboxylic dianhydride is added in two times, and finally 4 parts of 3-aminobenzoic acid is added, constant temperature stirring is carried out for 15 hours to obtain a prepolymer,

[0044] 2 parts of graphene oxide grafted with hyperbranched polyamide-amine is ground and crushed, 100 parts of the prepolymer is added, stirred and dispersed uniformly, then 12 parts of the silanol small molecule substance is added, constant temperature stirring is carried out at 5℃ for 10 hours to obtain a yellow solution, and a cross-linked structure modified polyimide adhesive is obtained.

[0045] Finally, the flexible copper-clad plate with three-dimensional bending part is prepared. The cross-linked structure modified polyimide adhesive is coated on the high-activity polyimide film matrix to form an adhesive layer, the film thickness is 22μm, the adhesive film is obtained after curing at 150℃ for 8 minutes, the surface is dry and not sticky, the adhesive film is combined with the copper foil, and the hot press is pressed at 170℃ / 1MPa for 2 minutes, then it is put into the oven at 180℃ for 1 hour to obtain the flexible copper-clad plate; finally, the prepared copper-clad plate is subjected to subsequent welding, etching and punching process to obtain a flexible circuit board.

[0046] Example 2

[0047] A flexible circuit board is prepared. First, the polyimide film matrix is modified to obtain a high-activity polyimide film matrix, which is prepared as follows:

[0048] 1 part of graphite is added into 100 parts of a mixture of H2SO4 and H3PO4, and stirred at room temperature until fully mixed; 5 parts of KMnO4 is slowly added, and continues to be stirred at room temperature for 30 minutes; the temperature is increased to 40℃, and fully stirred for 60 minutes; the temperature is increased to 90℃, and stirred for 100 minutes; a mixture of 100 parts of deionized water and 16 parts of H2O2 is slowly added dropwise to obtain an oxidized graphite mixture; the oxidized graphite mixture is washed with a dilute hydrochloric acid solution with a volume ratio of 1:10 by centrifugation for 3 times, and then washed with deionized water by centrifugation, and finally vacuum freeze-dried to obtain a sponge-like oxidized graphene;

[0049] 4 parts of the sponge-like oxidized graphene is added into 100 parts of N-methyl pyrrolidone, and stirred at room temperature for 100 minutes until fully dissolved, then 10 parts of hyperbranched polyamide-amine is added, and then 6 parts of 1-ethyl-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride is added, and stirred at 80℃ for 22 hours to obtain the oxidized graphene grafted with hyperbranched polyamide-amine, which is centrifuged, washed with water, and dried.

[0050] 91 parts of thermoplastic polyimide resin and 1 part of the oxidized graphene grafted with hyperbranched polyamide-amine are fully dispersed in N,N-dimethylacetamide solvent to obtain a homogeneous solution, and the homogeneous solution is dried by molding to prepare a high-activity polyimide film matrix.

[0051] Further, the preparation method of the modified polyimide adhesive with cross-linked structure is as follows: 4 parts of dimethyl dichlorosilane, 8 parts of phenyl trichlorosilane and 8 parts of methyl phenyl dichlorosilane are added into 40 parts of toluene, and stirred and mixed uniformly, then 10 parts of deionized water is added, and the temperature is kept at 30℃, and stirred at high speed for 20 hours to obtain a small molecule silanol substance;

[0052] 5 parts of siloxane diamine and 10 parts of 2,2'-bis[4-(4-aminophenoxy)phenyl]propane are added into 30 parts of solvent N-methyl pyrrolidone under the protection of N2 atmosphere, and fully stirred for 50 minutes until the mixed diamine is completely dissolved, then 5 parts of 4,4'-oxybenzene dianhydride is added in two portions, then 5 parts of 3,3',4,4'-benzophenone tetracarboxylic dianhydride is added in two portions, and finally 6 parts of 3-aminobenzoic acid is added, and constant temperature stirring is carried out for 12-15 hours to obtain a prepolymer.

[0053] 2 parts of the oxidized graphene grafted with hyperbranched polyamide-amine is ground and crushed, and added into 100 parts of the prepolymer, and stirred and dispersed uniformly, then 20 parts of the small molecule silanol substance is added, and constant temperature stirring is carried out at 5℃ for 8-10 hours to obtain a yellow solution, and a modified polyimide adhesive with cross-linked structure is obtained.

[0054] Finally, the flexible copper-clad plate with three-dimensional bending part is prepared by coating the cross-linked modified polyimide adhesive on the high-activity polyimide film substrate to form an adhesive layer, the film thickness is 28 μm, the adhesive layer is cured at 160 ℃ for 6 minutes to obtain a dry and non-sticky adhesive film, the adhesive film is laminated with a copper foil, and then is pressed in a hot press at 200 ℃ / 1 MPa for 2 minutes, and then is placed in an oven at 180 ℃ for 1 hour to obtain the flexible copper-clad plate; finally, the prepared copper-clad plate is subjected to subsequent welding, etching and punching process to obtain a flexible circuit board.

[0055] Example 3

[0056] A flexible circuit board is prepared by first modifying a polyimide film substrate to obtain a high-activity polyimide film substrate, specifically:

[0057] 1 part of graphite is added to 100 parts of a mixed solution of H2SO4 and H3PO4, and stirred at room temperature until fully dissolved; then 5 parts of KMnO4 is slowly added, and the stirring is continued at room temperature for 30 minutes; the temperature is increased to 40 ℃, and the stirring is continued for 60 minutes; the temperature is increased to 90 ℃, and the stirring is continued for 100 minutes; a mixed solution of 100 parts of deionized water and 16 parts of H2O2 is slowly added dropwise to obtain an oxidized graphite mixed solution; the oxidized graphite mixed solution is washed with a dilute hydrochloric acid solution at a volume ratio of 1:10 by centrifugation for 3 times, and then washed with deionized water by centrifugation; finally, the sponge-like oxidized graphene is obtained by vacuum freeze-drying.

[0058] 4 parts of the sponge-like oxidized graphene is added to 100 parts of N-methyl pyrrolidone, and stirred at room temperature for 100 minutes until fully dissolved; then 9 parts of hyperbranched polyamide-amine is added, and 4 parts of 1-ethyl-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride is added, and the stirring is continued at 70 ℃ for 22 hours to obtain the oxidized graphene grafted with hyperbranched polyamide-amine; the product is centrifuged, washed with water, and dried.

[0059] 95 parts of thermoplastic polyimide resin and 1 part of the oxidized graphene grafted with hyperbranched polyamide-amine are fully dispersed in a mixed solvent of N,N-dimethylacetamide and N-methyl pyrrolidone to obtain a homogeneous solution; the homogeneous solution is dried by molding to obtain the active polyimide film substrate.

[0060] Further, the preparation method of the cross-linked modified polyimide adhesive is as follows: 4 parts of dimethyl dichlorosilane, 8 parts of phenyl trichlorosilane and 8 parts of methyl phenyl dichlorosilane are added to 40 parts of toluene, and stirred and mixed uniformly; then 10 parts of deionized water is added, and the temperature is maintained at 25 ℃, and the stirring is continued at a high speed for 19 hours to obtain a small molecule silanol.

[0061] At 2℃, 5 parts of siloxane diamine and 15 parts of 2,2'-bis[4-(4- aminophenoxy)phenyl]propane are added to 30 parts of solvent N-methylpyrrolidone, and stirred for 30-50 minutes under the protection of N2 atmosphere. After the mixed diamine is completely dissolved, 5 parts of 4,4'-oxybenzene dianhydride is added in two portions, 7 parts of 3,3',4,4'-benzophenone tetracarboxylic dianhydride is added in two portions, and finally 5 parts of 3- aminobenzoic acid is added. The reaction is stirred at constant temperature for 12-15 hours to obtain a prepolymer,

[0062] The 2 parts of graphene oxide grafted with hyperbranched polyamide-amine are ground and crushed, and 90 parts of the prepolymer is added. After stirring and uniformly dispersing, 15 parts of a silanol small molecule substance is added. The reaction is stirred at a constant temperature of 5℃ for 10 hours to obtain a yellow solution, and a modified polyimide adhesive with a cross-linked structure is obtained.

[0063] Finally, a flexible copper-clad plate with a three-dimensional bending part is prepared. The modified polyimide adhesive with a cross-linked structure is coated on the high-activity polyimide film substrate to form an adhesive layer, the film thickness is 20μm, and the adhesive film is obtained after curing at 150℃ for 6 minutes. The surface is dry and not sticky. The adhesive film is combined with a copper foil, and is pressed on a hot press at 170℃ / 3MPa for 2 minutes, and then is placed in an oven at 170℃ for 1 hour to obtain a flexible copper-clad plate. Finally, the prepared copper-clad plate is subjected to subsequent welding, etching and punching process to obtain a flexible circuit board.

[0064] Comparative Example 1: The ordinary polyimide film is directly used to replace the high-activity polyimide film as the substrate, and the other steps are the same as those in Example 1.

[0065] Comparative Example 2: The ordinary graphene oxide is directly added to the polyimide resin to prepare a film substrate, and the ordinary graphene oxide is directly added to the prepolymer, and the other steps are the same as those in Example 1.

[0066] Comparative Example 3: The silanol small molecule substance and 3- aminobenzoic acid are not added when preparing the prepolymer, and the other steps are the same as those in Example 1.

[0067] Comparative Example 4: The ordinary polyimide film is directly used to replace the high-activity polyimide film as the substrate, the silanol small molecule substance and 3- aminobenzoic acid are not added when preparing the prepolymer, and the ordinary graphene oxide is not added when preparing the adhesive, and the other steps are the same as those in Example 1.

[0068] Test data and result analysis

[0069] 1. Infrared test diagram of the adhesive

[0070] The structure and functional groups of the sample are characterized by infrared absorption spectrum. Specifically, the infrared test of the semi-cured film of Example 1 is carried out by ATR accessory, and the test scanning range is 4000-400cm -1, room temperature scan, see Figure 1 , room temperature scan, see Figure 1 As can be seen, the adhesive film of Example 1 containing siloxane has a stretching vibration absorption peak at 1020 and 800 cm -1 It can be observed that the stretching vibration absorption peak of Si-O skeleton, while the ordinary polyimide film layer is not this absorption peak, so under the action of silanol small molecule and containing siloxane group diamine material, has successfully crosslinked Si-O skeleton into the grid system.

[0071] 2. TEM image of graphene oxide grafted with hyperbranched polyamide-amine

[0072] Using field emission scanning electron microscope, the acceleration voltage is 20.0 kV, the graphene oxide grafted with hyperbranched polyamide-amine prepared in Example 1 is adhered to the sample stage, the sample is sprayed with gold, and then scanning electron microscope observation is carried out, see Figure 2 , room temperature scan, see Figure 2 As can be seen, the microstructure of grafted graphene oxide is more loose and light, like a thin gauze, and the surface is curved and wrinkled. The surface of the graphene oxide is oxidized, and the newly formed oxygen-containing functional group is a chemical bond formed in sp3 hybridization form, which destroys the original sp2 planar structure of C=C, so that the thin layer of graphene oxide presents a certain wrinkle shape. For the thin layer of graphene oxide, this wrinkle shape can well reduce the surface energy and improve the stability, improve the surface of the polyimide film to have high active groups, and increase the surface roughness, significantly improve the performance in mechanics, hydrophobicity and thermal, improve the comprehensive performance of the film, and significantly improve the bonding performance of the adhesive film.

[0073] 3. Mechanical property test

[0074] The bending performance test is tested by using Z010 type universal material testing machine of Germany Zwick / Roell Company, and the bending pressure head descending rate is 5 mm / min during testing. The results are shown in Table 1,

[0075] Adhesive strength test: lap shear strength data is measured by Z010 tensile testing machine of Germany Zwick / Roell Company, the bonding area is 20 mm x 12.5 mm x 0.2 mm, the sample number is at least 5, and the test results are averaged; test at room temperature and test at high temperature and high humidity, respectively; high temperature and high humidity environment: after placing in 85℃ / 85% environment for 500 hours, the adhesive strength is measured by the same method, and the results are shown in Table 1.

[0076] The flexible copper clad laminate was tested for peel strength using a UT-2080 computerized tensile testing machine from ORIENTEC, according to GB / T 7122-1996, with a sample size of 25 mm x 120 mm, and a 180° peel at a peel rate of 50 mm / min at room temperature. The results are shown in Table 1.

[0077] Table 1. Mechanical property test results

[0078]

[0079]

[0080] As shown in Table 1, the polar group or active group-containing polymer formed in Examples 1-3 was deposited on the surface of the substrate to be modified, so that the surface of the substrate was no longer inert, and the reactive polymer was deposited on the surface of the substrate, acting as a “link” between the substrate and the adhesive film, thereby improving the adhesive strength. In particular, in a high temperature and high humidity environment, the adhesive strength changes little, while Comparative Example 1 and Comparative Example 4 use unmodified film substrates, so that the adhesive strength decreases easily under high temperature and high humidity, and adhesive failure occurs. By using a highly active film substrate, the surface roughness of the substrate increases continuously, and the contact angle of the substrate surface decreases continuously as the grafting and crosslinking structure is formed, indicating that the surface wettability of the substrate is improved, and the combination of the two improves the adhesive strength between the substrate and the adhesive. As a core component of modern electronic devices, the performance of the flexible circuit board is directly affected by the adhesive technology. The adhesive not only withstands high temperature reflow soldering above 200°C, but also meets the demand for dynamic bending more than 100,000 times. Dynamic bending tests show that the adhesive strength of Example 1 decreases by 3.5% after 5000 times of 180° bending, while the adhesive strength of Comparative Example 4 decreases by 38.2% after 5000 times of 180° bending, revealing a brittle fracture problem. By using the crosslinked silanol small molecules and boric acid provided in the present application, the introduced siloxane segment and borate ester bond form a dynamic exchangeable covalent bond with the hydroxyl group on the surface of various fillers and substrates, and the covalent crosslinking network increases the cohesive energy of the adhesive film, so that the peel strength is significantly increased, the peel strength stability is higher, and the reliability of the flexible circuit board is ensured.

[0081] 1) Deformation rate

[0082] The deformation rates of the circuit boards prepared in each example and each comparative example were evaluated and compared, and the evaluation method was as follows:

[0083] (1) The distance L0 between the two ends of the sample was measured, and then the two ends of the sample were fixed on the tensile fatigue tester clamps, keeping the natural shape of the sample circuit board.

[0084] (2) The sample was cycled to stretch 10,000 times, each time to stretch the sample circuit board to 100% of its length, 45 times per minute.

[0085] (3) The sample circuit board after 10,000 times of stretching was unloaded from the tensile fatigue tester, and the distance Ll between the two ends of the sample was measured after the sample was left at room temperature for 30 minutes.

[0086] (4) The deformation rate of the sample circuit board was calculated.

[0087] The formula for calculating the deformation rate is: σ = (Ll - L0) ÷ L0 x 100%, where σ is the deformation rate. The comparative results of the deformation rate obtained through the evaluation are shown in Table 2 below;

[0088] Table 2 Deformation rate

[0089]

[0090]

[0091] As can be seen from Table 2, the deformation rate of Examples 1-3 is very small. Because of the special cross-linking structure of the flexible circuit board prepared in the present application, the dynamic borate ester group functional group in the cross-linking structure forms a dynamic covalent connection with Si-O, and a dynamic exchangeable covalent bond is formed between the hydroxyl groups on the surface of various fillers and substrates, and a covalent cross-linking network, which significantly improves the reversibility of the flexible circuit board, and the deformation rate is much smaller than that of ordinary adhesives.

[0092] 2) Reversibility

[0093] The adhesive film was cut into pieces, soaked in a mixed solvent, and the dynamic B-O bond was broken by acid, and the polyimide in the cross-linking structure was dissolved by a polar solvent to obtain a uniform solution; the solution was again spread on a mold, and most of the solvent and hydrochloric acid were removed by heating to 100°C, and further heating to 200°C to re-form the cross-linked polymer. According to the above recycling process, we used a mixed solvent to perform a 5-time dissolution-reshaping cycle process on the adhesive film in Example 1. After 5 times of dissolution-reshaping cycle process, the adhesive obtained still maintained high mechanical properties, confirming that the adhesive film has good recyclability and reworkability, and the results are shown in Table 3. After 5 cycles, the bending strength of the adhesive film decreased to 183 MPa, which may be related to the breaking of some irreversible chemical bonds during the reshaping process. In addition, we reused the recycled mixture for adhesion again, and the adhesion strength of the reused adhesive film could still be maintained at 20-22 MPa (about 90% of the original adhesion strength), indicating that the adhesive film prepared in the present application has good reusability.

[0094] Table 3 Reversibility test

[0095]

[0096]

[0097] 5. Polarity and wettability

[0098] The water contact angle test method was used for characterization, 2 μL of test liquid was dropped on the surface of the adhesive film of Examples 1-3 and Comparative Examples 1-4 by microsyringe, the contact angle was recorded uniformly, and the final test results were taken from the average of different positions of the sample, see Table 4;

[0099] As can be seen from Table 4, the contact angle of the copper foil is 32.1°, and the liquid has good wettability on its surface. However, the contact angle of the adhesive film of Comparative Example 4 without modification is as high as 82.3°, which is too different from the contact angle of the copper foil, and the adhesive film tends to be more prone to wettability and adhesion to the copper foil. This is mainly due to the fact that the unmodified polyimide contains a large number of imide rings and benzene rings and other rigid structures, the interaction between the polymer chains is strong, the wettability of the substrate during adhesion is poor, and small molecule substances are released after curing, forming cavities and appearing gaps on the contact surface, which shows that the adhesion strength is low, and the failure mode is interface failure dominated by cohesion; and the surface of the unmodified adhesive is smooth and flat, and does not contain polar groups and active groups, making the surface very stable. Thus, when the peel strength test is performed on the flexible circuit board using the film substrate without surface modification, the failure of the flexible circuit board is not the destruction of the cohesion of the adhesive, but the interfacial failure between the adhesive and the film substrate, and the peel strength is small. Examples 1-3, through the action of the active groups of the double layers of the film substrate and the adhesive, significantly reduce the surface contact angle, so that the interaction between the adhesive film and the copper foil surface is better, and the wettability and ductility of the system are improved. During the heating and bonding process, the soft segment easily expands to the surface of the substrate, better forming a mechanical interlocking structure and enhancing the interfacial adhesion.

[0100] Table 4, test results of contact angle

[0101] Item Contact angle Example 1 34.8 Example 2 35.2 Example 3 35.6 Comparative Example 1 71.8 Comparative Example 2 67.4 Comparative Example 3 48.1 Comparative Example 4 82.5 Copper foil 32.1

[0102] 6. Thermal conductivity and expansion coefficient test results

[0103] The thermal conductivity of the adhesive film prepared in each example and comparative example was analyzed by a laser thermal conductivity analyzer. The thermal expansion rate was measured by a thermal expansion rate tester, and the thermal expansion coefficient was calculated, see Table 5,

[0104] Table 5, performance test of adhesive film

[0105]

[0106]

[0107] The thermal expansion absorption of the copper foil is 16.5*10-6 / ℃ or so, from table 4, it can be seen that the adhesive film formed by the adhesive prepared by comparative example 1-4 and copper foil is inconsistent with the expansion coefficient, and adhesion failure will occur, while in the present application examples 1-3, the problem of inconsistent expansion coefficient is significantly improved. This is mainly because the Si-O bond grid structure formed by the small molecule silanol material in the curing process not only can solidify the released small molecule material, but also can occupy the hole position, crosslink into a three-dimensional grid structure, and after the combination of the modified graphene oxide, a fluffy structure is formed, and after crosslinking with the main chain, a dense and flexible structure is formed, reducing the porosity, reducing the expansion coefficient,

[0108] The thermal conductivity is improved, and the graphene oxide grafted with hyperbranched polyamide-amine can well construct the thermal conductivity path of the matrix when the amount of the added thermal conductive filler is small. After grafting, the graphene oxide is better dispersed in the matrix, and the graphene oxide with high thermal conductivity coefficient is distributed in the S-O bond grid structure, and then dispersed through the three-dimensional grid effect, so that the prepared material has more excellent thermal conductivity effect, effectively solves the heat dissipation problem of the circuit board, and the shape memory polymer bonding system triggers shape recovery at high temperature.

[0109] The above description is only used to illustrate the technical solutions of the present application but not limit the present application. Any equal modification and change of the technical solutions of the present application made by those skilled in the art, as long as it does not deviate from the overall concept of the present application, still belongs to the scope of the present application.

Claims

1. A method of manufacturing a flexible wiring board, characterized by: The flexible circuit board comprises a copper-clad plate, which is a copper-clad plate laminated material composed of a copper foil and a bonding film, and the flexible circuit board is obtained after the copper-clad plate is subjected to subsequent welding, etching and punching process treatments; the bonding film comprises a film substrate and a bonding agent layer on the surface of the substrate, and the bonding agent layer is a layer formed by a bonding agent; The film substrate is a high-activity polyimide film substrate prepared by modifying a polyimide film substrate, and the preparation method of the high-activity polyimide film substrate is as follows: The graphite is added into a mixed solution of H2SO4 and H3PO4, and stirred uniformly at room temperature; then KMnO4 is slowly added, and stirring is continued for 30 minutes; the temperature is increased to 40℃, and stirring is continued for 60 minutes; the temperature is increased to 90℃, and stirring is continued for 100 minutes; a mixed solution of deionized water and H2O2 is slowly added dropwise after the reaction to obtain an oxidized graphite mixed solution; after centrifugal washing 2-3 times and deionized water dialysis treatment, the oxidized graphite mixed solution is vacuum freeze-dried to obtain a sponge-like oxidized graphene; N-methyl pyrrolidone is added into the sponge-like oxidized graphene, and stirred at room temperature for 100 minutes to fully dissolve the sponge-like oxidized graphene; hyperbranched polyamide-amine is added; 1-ethyl-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride is added; and stirring is carried out at 60-80℃ for 20-24 hours to obtain oxidized graphene grafted with hyperbranched polyamide-amine; centrifugal, water washing and drying are carried out; The polyimide resin and the oxidized graphene grafted with hyperbranched polyamide-amine are fully dispersed in an aprotic polar solvent to obtain a homogeneous solution; and the homogeneous solution is molded and dried to prepare the active polyimide film substrate. The bonding agent is a modified polyimide with a crosslinked structure, and the preparation method of the modified polyimide with a crosslinked structure is as follows: Dimethyldichlorosilane, phenyltrichlorosilane and methylphenyldichlorosilane are added into toluene, and stirred and mixed uniformly; then deionized water is added, and the temperature is kept at 20-30℃; and high-speed stirring is carried out for 18-20 hours to obtain a silanol small molecule substance; Siloxane diamine and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane are added into a solvent N-methyl pyrrolidone under the protection of N2 atmosphere, and fully stirred for 30-50 minutes; after the mixed diamine is completely dissolved, 4,4'-oxybenzene dicarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 3-aminobenzoic acid are added in batches; and pre-polymer is obtained after constant-temperature stirring reaction for 12-15 hours; the oxidized graphene grafted with hyperbranched polyamide-amine is ground and crushed; the pre-polymer is added and stirred and dispersed uniformly; then the silanol small molecule substance is added; and stirring reaction is carried out at low temperature of 5℃ for 8-10 hours to obtain a yellow solution, thereby obtaining the modified polyimide bonding agent with a crosslinked structure.

2. The method of claim 1, wherein the flexible circuit board is prepared by the steps of: The mass ratio of graphite and KMnO4 is 1:5; the mass ratio of graphene oxide, 1-ethyl-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride and hyperbranched polyamide-amine is 2:2-3:4-5; the volume ratio of H2SO4 and H3PO4 is 2:1; the mass ratio of hyperbranched polyamide-amine, graphene oxide and polyimide resin is 0.9%-1.1%.

3. The method of claim 1, wherein the flexible circuit board is prepared by the steps of: The number average molecular weight of the polyimide resin is 50000-80000; the aprotic polar solvent comprises one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone; the centrifugal washing is as follows: the washing liquid is a dilute hydrochloric acid solution prepared at a volume ratio of 1:10, the graphene oxide mixture is centrifuged until the supernatant is detected to be free of white precipitate by using a dilute BaCl2 solution; then the centrifugal washing is performed by using deionized water until the supernatant is detected to be free of white precipitate by using a dilute AgNO3 solution.

4. The method of claim 1, wherein the flexible circuit board is prepared by the steps of: The mass ratio of dimethyldichlorosilane, phenyltrichlorosilane and methylphenyldichlorosilane is 1:2:

2.

5. The method of claim 1, wherein the flexible circuit board is prepared by the steps of: The mass ratio of siloxane diamine and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane is 1:2-3; the mass ratio of siloxane diamine, 4,4'-oxyphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride and 3-aminobenzoic acid is 1-2:2-3:1-2:0.8-1.2; the mass ratio of hyperbranched polyamide-amine, graphene oxide, silanol small molecule substance and prepolymer is 1:8-15:40-50.

6. The method of claim 1, wherein the flexible circuit board is prepared by the steps of: The copper-clad plate is a flexible copper-clad plate having a three-dimensional bending part, and an adhesive layer and a high-activity film substrate are provided respectively; the specific preparation method is as follows: a modified polyimide adhesive with a crosslinked structure is coated on a high-activity polyimide film substrate to form an adhesive layer, the film thickness is 20-30 μm, curing is performed at 130-160 ℃ for 6-8 minutes, and an adhesive film with a dry surface and no stickiness is obtained; the adhesive film is laminated with a copper foil, and lamination is performed on a hot press at 170-200 ℃ / 1-3 MPa for 2-4 minutes, and then the lamination is placed in an oven at 170-180 ℃ for curing for 1 hour, and a flexible copper-clad plate is obtained.

7. A flexible wiring board, characterized by, The flexible circuit board is prepared according to the preparation method in any one of claims 1-6.

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