Manufacturing method of flexible circuit board, flexible circuit board and terminal device

Abstract

A manufacturing method of a flexible circuit board comprises the steps that two opposite surfaces of an adhesive layer are bonded to a substrate, the substrate comprises a dielectric layer, a first graphene layer and a copper layer which are sequentially stacked, a through hole is formed in the adhesive layer, and the surface of the dielectric layer is exposed out of the through hole; forming a second graphene layer on the surface, deviating from the first graphene layer, of the copper layer, wherein the projection of the second graphene layer covers the through hole; and circuit manufacturing is carried out on the first graphene layer, the copper layer and the second graphene layer to form a circuit layer, so that the flexible circuit board can be obtained, and the flexible circuit board can be bent in the area where the first graphene layer and the second graphene layer are arranged. The invention also provides a flexible circuit board and a terminal device.

Description

Technical Field

[0001] This application relates to the field of circuit board manufacturing technology, and in particular to a method for manufacturing a flexible circuit board, a flexible circuit board, and a terminal device. Background Technology

[0002] Foldable devices (such as foldable phones) offer a combination of large screen display, slim design, and portability, making them increasingly popular. The flexible circuit boards within these devices change state (switching between folded and unfolded). As devices become thinner and lighter, the thickness and bending radius of the flexible circuit boards decrease, reducing the number of bends they can withstand and impacting the device's lifespan. Summary of the Invention

[0003] In view of this, it is necessary to provide a manufacturing method that can increase the number of bends of a flexible circuit board, and it is also necessary to provide a flexible circuit board and a terminal device to solve the above problems.

[0004] A method for manufacturing a flexible circuit board includes: bonding a substrate to two opposing surfaces of an adhesive layer, the substrate comprising a dielectric layer, a first graphene layer, and a copper layer stacked sequentially, wherein a through-hole is formed in the adhesive layer, and the surface of the dielectric layer is exposed to the through-hole; forming a second graphene layer on the surface of the copper layer opposite to the first graphene layer, the projection of the second graphene layer covering the through-hole; and fabricating circuitry on the first graphene layer, the copper layer, and the second graphene layer to form a circuit layer, thereby obtaining a flexible circuit board, the flexible circuit board being bendable in the area where the first graphene layer and the second graphene layer are disposed.

[0005] In one possible embodiment of this application, the step of forming a substrate includes: covering the surface of a dielectric layer with a protective layer; forming a first graphene layer on the surface of the dielectric layer opposite to the protective layer; removing the protective layer; and forming a copper layer on the surface of the dielectric layer opposite to the first graphene layer, thereby obtaining a substrate.

[0006] In one possible embodiment of this application, the step of forming a first graphene layer on the surface of the dielectric layer away from the protective layer includes: immersing the dielectric layer with the protective layer in a solution containing graphene and then removing it, whereby the graphene is adsorbed onto the surface of the dielectric layer; and drying the dielectric layer to form the first graphene layer.

[0007] In one possible embodiment of this application, before the step of forming the circuit layer, the manufacturing method further includes: forming a groove that penetrates the substrate and the adhesive layer, and forming a copper plating layer in the groove, wherein the copper plating layer is used to conduct copper layers located on both sides of the adhesive layer.

[0008] In one possible embodiment of this application, prior to the step of forming the circuit layer, the fabrication method further includes: covering the surface of the copper layer with a first dry film, the first dry film having a first opening, the projection of the first opening covering the via; forming a second graphene layer on the surface of the copper layer exposed to the first opening; and removing the first dry film to expose the surface of the copper layer.

[0009] In one possible embodiment of this application, the step of forming a circuit layer includes: covering the surfaces of a copper layer and a second graphene layer with a second dry film, forming a second opening in the second dry film, with a portion of the surface of the second graphene layer and a portion of the surface of the copper layer exposed to the second opening; removing the second graphene layer exposed to the second opening; removing the copper layer exposed to the second opening; removing the first graphene layer exposed to the second opening, so that the remaining first graphene layer, copper layer and second graphene layer together form a circuit layer; and removing the second dry film.

[0010] In one possible embodiment of this application, the step of removing the second graphene layer includes: irradiating the second graphene layer exposed to the second opening with ultraviolet light in an atmosphere containing an inert gas to remove the second graphene layer.

[0011] A flexible circuit board includes an adhesive layer, a dielectric layer, and a circuit layer. The adhesive layer has through-holes; the dielectric layer is located on two opposite surfaces of the adhesive layer; the circuit layer is located on the surface of the dielectric layer facing away from the adhesive layer, and the circuit layer includes a first graphene layer, a copper layer, and a second graphene layer stacked together. The first graphene layer is connected to the surface of the dielectric layer, and the second graphene layer is located on the surface of the copper layer facing away from the dielectric layer. The flexible circuit board can be bent in the areas where the through-holes, the first graphene layer, and the second graphene layer are provided.

[0012] In one possible embodiment of this application, the flexible circuit board further includes a copper plating layer that penetrates the adhesive layer, the dielectric layer, the first graphene layer, and the copper layer, and the copper plating layer is used to conduct circuit layers located on both sides of the adhesive layer.

[0013] A terminal device, the terminal device including a flexible circuit board.

[0014] The flexible circuit board manufacturing method provided in this application produces a circuit board by setting a first graphene layer and a second graphene layer containing graphene on opposite surfaces of a copper layer. Graphene has a negative Poisson's ratio. When the flexible circuit board is bent, the bent area is equivalent to being stretched. Graphene with a negative Poisson's ratio expands in the portion perpendicular to the stretching direction during stretching. During bending, the copper layer near the first graphene layer experiences compressive stress, while the side near the second graphene layer experiences tensile stress. The increased cross-sectional area of ​​the graphene due to expansion reduces both compressive and tensile stresses on the entire copper layer, thus providing the copper layer with fracture resistance. Therefore, the circuit layer in the flexible circuit board utilizes the negative Poisson's ratio property of graphene to enhance the circuit layer's resistance to tensile and compressive stresses during bending, thereby increasing the effective bending cycles of the flexible circuit board and ultimately extending the lifespan of the terminal device. Attached Figure Description

[0015] Figure 1 This is a cross-sectional schematic diagram of the dielectric layer provided in an embodiment of this application.

[0016] Figure 2 In order to be in Figure 1 The diagram shows a cross-sectional view of the dielectric layer with a protective layer and a first graphene layer on opposite surfaces.

[0017] Figure 3 To remove Figure 2 The diagram shows a cross-sectional view of the protective layer.

[0018] Figure 4 In order to be in Figure 3 The diagram shows a cross-sectional view of the substrate obtained after a copper layer is deposited on the surface of the first graphene layer away from the dielectric layer.

[0019] Figure 5 To bond the adhesive layer to the two opposite surfaces respectively Figure 4 A schematic cross-sectional view of the substrate is shown.

[0020] Figure 6 To form a through Figure 5 The diagram shows a cross-sectional view of the substrate and adhesive layer with grooves, and the copper plating layer formed in the grooves.

[0021] Figure 7 In order to be in Figure 6 The diagram shows a cross-sectional view of the copper layer surface covered with a first dry film, forming a first opening.

[0022] Figure 8 In order to be in Figure 7 A schematic diagram of a cross-section showing the formation of a second graphene layer in the first opening.

[0023] Figure 9 To remove Figure 8 The diagram shows a cross-sectional view of the first dry film.

[0024] Figure 10 In order to be in Figure 9 The diagram shows a cross-sectional view of the copper layer and the second graphene layer covering the surface of the second dry film and forming a second opening.

[0025] Figure 11 To remove Figure 10 A schematic cross-section of the second graphene layer exposed by the second opening.

[0026] Figure 12 To remove Figure 11 A schematic cross-section of the copper layer exposed to the second opening.

[0027] Figure 13 To remove Figure 12 A schematic cross-sectional view of the first graphene layer exposed to the second opening is obtained.

[0028] Figure 14 To remove Figure 13 A schematic diagram of the cross-section of the second dry film.

[0029] Figure 15 In order to be in Figure 14 A schematic cross-sectional view of the flexible circuit board obtained after covering the surface of the circuit layer and dielectric layer with a cover layer.

[0030] Figure 16 This is a schematic diagram of the structure of a terminal device including a flexible circuit board, provided in an embodiment of this application.

[0031] Explanation of main component symbols

[0032] Flexible circuit board 100 Dielectric layer 10 First surface 11 Second surface 12 protective layer 13 Line layer 20 First graphene layer 21 copper layer 22 Second graphene layer 23 substrate 25 adhesive layer 30 Through hole 31 Grooving 40 Copper plating 41 First dry film 50 First opening 51 Second dry film 60 Second opening 61 Cover layer 70 terminal device 200 First shell 210 Second shell 220 Display screen 230 District 1 231 Second District 232 Detailed Implementation

[0033] To better understand the above-mentioned objectives, features, and advantages of this application, the application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. Many specific details are set forth in the following description to provide a thorough understanding of this application; the described embodiments are merely some, not all, of the embodiments described in this application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The term "and / or" as used herein includes all and any combination of one or more of the associated listed items.

[0035] In the various embodiments of this application, for ease of description and not limitation, the term "connection" used in the patent application specification and claims is not limited to physical or mechanical connections, whether direct or indirect. Terms such as "upper," "lower," "above," "below," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship also changes accordingly.

[0036] Please see Figure 1 This application provides a method for manufacturing a flexible circuit board 100, which may include the following steps:

[0037] Step S1: Please refer to Figure 1 A dielectric layer 10 is provided, the dielectric layer 10 including a first surface 11 and a second surface 12 disposed opposite to each other.

[0038] The dielectric layer 10 is made of a flexible material, including but not limited to one of polyimide (PI), liquid crystal polymer (LCP), and modified polyimide (MPI), so that the flexible circuit board 100 subsequently manufactured can be bent.

[0039] Step S2: Please refer to Figure 2 A protective layer 13 is covered on the first surface 11 of the dielectric layer 10, and a first graphene layer 21 is formed on the second surface 12 of the dielectric layer 10.

[0040] The protective layer 13 is used to protect the first surface 11 in the subsequent step of forming the first graphene on the second surface 12.

[0041] The step of forming the first graphene layer 21 on the second surface 12 of the dielectric layer 10 may include:

[0042] Step S21: Clean the second surface 12 of the medium layer 10.

[0043] The dielectric layer 10, with the protective layer 13, can be immersed in a degreasing solution at a temperature of 30℃-50℃ for 30s-90s to remove oil stains from the second surface 12. Then, it is rinsed with clean water to remove the degreasing solution from the surface of the dielectric layer 10. In addition to the cleaning agent used for cleaning, the degreasing solution may also include a cationic surfactant. The cationic surfactant is used to further clean the second surface 12 of the dielectric layer 10 and can also adjust the charge of the second surface 12 to facilitate the subsequent adsorption of negatively charged graphene.

[0044] Step S22: Place the cleaned medium layer 10 into a solution containing graphene to adhere graphene to the second surface 12 of the medium layer 10.

[0045] The dielectric layer 10 with the protective layer 13 can be immersed in a graphene-containing solution at a temperature of 20℃-30℃ for 10s-60s, allowing the graphene in the solution to adsorb onto the second surface 12 of the dielectric layer 10. In some embodiments, the solid content of graphene in the solution can range from 0.01% to 0.5%. Graphene is a two-dimensional material with a high specific surface area and high surface free energy, exhibiting easy adsorption properties, thus forming a film at the interface between two phases. Graphene can also form a stacked first graphene layer 21 on the second surface 12 of the dielectric layer 10 through electrostatic, electrostatic, and van der Waals forces, with the thickness of the first graphene layer 21 ranging from a few nanometers to tens of nanometers.

[0046] Step S23: The medium layer 10, after being soaked in a solution containing graphene, is dried to form a first graphene layer 21 on the second surface 12 of the medium layer 10.

[0047] After drying, graphene can form a dense first graphene layer 21 with excellent conductivity and hardness.

[0048] Step S3: Please refer to Figure 3 Remove the protective layer 13 to expose the first surface 11 of the dielectric layer 10.

[0049] The protective layer 13 can be removed by peeling.

[0050] Step S4: Please refer to Figure 4 A copper layer 22 is formed on the surface of the first graphene layer 21 away from the dielectric layer 10 to obtain the substrate 25.

[0051] The first copper foil can be pressed onto the surface of the graphene using a high-temperature roll forming or high-temperature pressing machine. The formed substrate 25 includes a dielectric layer 10, a first graphene layer 21, and a copper layer 22 stacked sequentially, with the first graphene layer 21 located between the dielectric layer 10 and the copper layer 22. The first graphene layer 21 is disposed on the second surface 12 of the dielectric layer 10, and the first surface 11 of the dielectric layer 10 is exposed.

[0052] Step S5: Please refer to Figure 5 Substrate 25 is bonded to the two opposite surfaces of adhesive layer 30, dielectric layer 10 is bonded to adhesive layer 30, adhesive layer 30 has through hole 31, and the surface of dielectric layer 10 is exposed to through hole 31.

[0053] After the adhesive layer 30 bonds the substrate 25, the copper layer 22 is located on the outermost layer. The adhesive layer 30 bonds the first surface 11 of the dielectric layer 10, and part of the first surface 11 is exposed to the through hole 31. The substrate 25 is bonded to both sides of the adhesive layer 30, so both sides of the through hole 31 are covered by the dielectric layer 10. The area with the through hole 31 is the adhesive-free area, which is beneficial for the bending of the flexible circuit board 100 formed later.

[0054] Step S6: Please refer to Figure 6 A groove 40 is formed that penetrates the substrate 25 and the adhesive layer 30, and a copper plating layer 41 is formed in the groove 40.

[0055] The groove 40 penetrates the entire length of both substrates 25 and the adhesive layer 30 located between the two substrates 25. Specifically, the groove 40 penetrates the copper layer 22, the first graphene layer 21, the dielectric layer 10, the adhesive layer 30, another dielectric layer 10, another first graphene layer 21, and another copper layer 22, but does not penetrate the second graphene layer 23. A copper plating layer 41 is located on the inner wall of the groove 40 and is also formed on a portion of the surface of the copper layer 22. The copper plating layer 41 serves to conduct the copper layers 22 located on both sides of the adhesive layer 30.

[0056] Step S7: Please refer to Figure 7 A first dry film 50 is covered on the surface of the copper layer 22. A first opening 51 is formed on the first dry film 50, and the projection of the first opening 51 covers the through hole 31.

[0057] The first dry film 50 covers two copper layers 22, and also covers a copper plating layer 41 on the surface of the copper layers 22. The first opening 51 can be formed on the first dry film 50 by exposure and development.

[0058] A portion of the surface of the copper layer 22 is exposed to the first opening 51. Along the direction in which the substrate 25 and the adhesive layer 30 are stacked, the projection of the first opening 51 covers the through hole 31.

[0059] Step S8: Please refer to Figure 8 A second graphene layer 23 is formed on the surface of the copper layer 22 exposed to the first opening 51.

[0060] The steps for forming the second graphene layer 23 can be referred to the steps for forming the first graphene layer 21 described above. In this step, the first dry film 50 can protect the surface of the copper layer 22.

[0061] Since the second graphene is formed in the first opening 51, the projection of the second graphene layer 23 covers the through hole 31 along the direction in which the substrate 25 and the adhesive layer 30 are stacked.

[0062] Step S9: Please refer to Figure 9 Remove the first dry film 50 to expose the surface of the copper layer 22.

[0063] Step S10: Please refer to Figure 10 A second dry film 60 is covered on the surfaces of the copper layer 22 and the second graphene layer 23, and a second opening 61 is formed on the second dry film 60, exposing a portion of the surface of the second graphene layer 23 and a portion of the surface of the copper layer 22 to the second opening 61.

[0064] After the second dry film 60 is covered, the second opening 61 can be formed by exposure and development. The opening is formed in the area that needs to be removed. In this embodiment, part of the surface of the second graphene layer 23 and part of the surface of the copper layer 22 are exposed to the second opening 61.

[0065] Step S11: Please refer to Figure 11 Remove the second graphene layer 23 exposed to the second opening 61.

[0066] The removal of the second graphene layer 23 can be achieved by ultraviolet light irradiation in an atmosphere containing an inert gas. In one specific embodiment, the removal step may include: placing an ultraviolet lamp capable of emitting a wavelength of 150 nm in an atmospheric environment, introducing nitrogen gas around the ultraviolet lamp to achieve a nitrogen content of 90%-97% in the environment, and then irradiating the second graphene layer 23 with the ultraviolet lamp for 30 seconds. The carbon-carbon bonds in the second graphene layer 23 absorb the ultraviolet light and are broken, forming free carbon. This free carbon reacts with the reactive gas formed by ultraviolet irradiation in the environment, generating gaseous products that escape, thereby removing the second graphene layer 23 exposed to the second opening 61. After the second graphene layer 23 exposed to the second opening 61 is removed, the surface of the copper layer 22 covered by the removed second graphene layer 23 is exposed. In other embodiments, the inert gas may also be argon, used to isolate the second graphene layer 23 from oxygen in the environment.

[0067] Step S12: Please refer to Figure 12 Remove the copper layer 22 exposed to the second opening 61.

[0068] The copper layer 22 exposed to the second opening 61 can be removed using etching solutions such as copper chloride or ferric chloride. After the copper layer 22 exposed to the second opening 61 is removed, the surface of the first graphene layer 21 covered by the removed copper layer 22 is exposed.

[0069] Step S13: Please refer to Figure 13 The first graphene layer 21 exposed to the second opening 61 is removed so that the remaining first graphene layer 21, copper layer 22 and second graphene layer 23 together form the circuit layer 20.

[0070] The first graphene layer 21 can be removed in the same way as the second graphene layer 23. After removing the first graphene layer 21 exposed to the second opening 61, the circuit layer 20 is formed, i.e., steps S10-S13 are the circuit fabrication steps.

[0071] Step S14: Please refer to Figure 14 After forming the circuit layer 20, the second dry film 60 is removed.

[0072] Step S15: Please refer to Figure 15 A cover layer 70 is formed on the surface of the circuit layer 20 to obtain a flexible circuit board 100.

[0073] The cover layer 70 covers the surface of the circuit layer 20, and also covers the surfaces of the dielectric layer 10 and the copper plating layer 41 exposed to the circuit layer 20, and fills the slot 40.

[0074] In other embodiments, the number of circuit layers 20 is not limited to the two layers in this embodiment, but can be one or more layers. When the number of circuit layers 20 is multiple, the fabrication method may also include a layer-addition step before the step of forming the cover layer 70. The specific steps can be referred to the steps of forming the first graphene layer 21 and / or the second graphene layer 23 described above.

[0075] The flexible circuit board 100 includes an adhesive layer 30, a dielectric layer 10, a circuit layer 20, and a cover layer 70. The dielectric layer 10 is located on two opposite surfaces of the adhesive layer 30, the circuit layer 20 is located on the surface of the dielectric layer 10 away from the adhesive layer 30, and the cover layer 70 covers the circuit layer 20 and the surface of the dielectric layer 10 exposed to the circuit layer 20.

[0076] A through-hole 31 is provided on the adhesive layer 30, and the surfaces of the dielectric layer 10 located on opposite surfaces of the adhesive layer 30 are exposed through the through-hole 31. The dielectric layer 10 is made of a flexible material.

[0077] The circuit layer 20 may include a first graphene layer 21, a copper layer 22, and a second graphene layer 23 stacked together. The first graphene layer 21 and the second graphene layer 23 are located on opposite surfaces of the copper layer 22. The first graphene layer 21 is connected to the surface of the dielectric layer 10, and the second graphene layer 23 is located on the surface of the copper layer 22 away from the dielectric layer 10.

[0078] The flexible circuit board 100 also includes a copper plating layer 41 that penetrates the substrate 25 and the adhesive layer 30. The copper plating layer 41 is used to conduct the circuit layers 20 located on both sides of the adhesive layer 30. The cover layer 70 covers the surface of the circuit layers 20, and also covers the surfaces of the dielectric layer 10 and the copper plating layer 41 exposed to the circuit layers 20, and fills the slot 40.

[0079] The flexible circuit board 100 can be bent in the area where the through-hole 31, the first graphene layer 21, and the second graphene layer 23 are provided. The graphene in the first graphene layer 21 and the second graphene layer 23 not only has excellent thermal and electrical conductivity but also a negative Poisson's ratio, with a Poisson's ratio of -0.55 to -0.25. When the flexible circuit board 100 is bent, the bent area is essentially stretched. The graphene with the negative Poisson's ratio expands in the portion perpendicular to the stretching direction during stretching. The copper layer 22 has the first graphene layer 21 and the second graphene layer 23 respectively disposed on its two opposite surfaces. During bending, the side of the copper layer 22 closer to the first graphene layer 21 experiences compressive stress, while the side closer to the second graphene layer 23 experiences tensile stress. The expansion of the graphene increases its cross-sectional area, thus reducing both the compressive and tensile stresses on the entire copper layer 22, thereby providing the copper layer 22 with fracture resistance. Therefore, with the same copper layer 22 thickness, the copper layer 22 with graphene has better bending resistance than the copper layer without graphene. Thus, the circuit layer 20 in the flexible circuit board 100 utilizes the negative Poisson's ratio property of graphene to enhance the tensile and compressive stress resistance of the circuit layer 20 during bending, thereby increasing the effective bending cycles of the flexible circuit board 100.

[0080] Please see Figure 16 This application also provides a terminal device 200 including a flexible circuit board 100, which can be bent during use. The terminal device 200 can be a foldable electronic product, including but not limited to foldable screen phones, watches, etc. In this embodiment, the terminal device 200 is a foldable screen phone.

[0081] The terminal device 200 includes a flexible circuit board 100, a display screen 230, a first housing 210, and a second housing 220. The display screen 230 includes a first area 231 and a second area 232. The first area 231 is disposed on the surface of the first housing 210, and the second area 232 is disposed on the surface of the second housing 220. The flexible circuit board 100 is disposed in the corresponding areas of the first area 231 and the second area 232. The first housing 210 and the second housing 220 can be folded together or unfolded relative to each other. Therefore, the first area 231 and the second area 232 of the display screen 230, as well as the flexible circuit board 100 disposed on the display screen 230, fold together or unfold relative to each other synchronously with the first housing 210 and the second housing 220. When the terminal device 200 is another electronic product, the specific structure and name of the terminal device 200 may change accordingly.

[0082] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A method for manufacturing a flexible circuit board, characterized in that, include: A substrate is bonded to the two opposite surfaces of an adhesive layer. The substrate includes a dielectric layer, a first graphene layer, and a copper layer stacked sequentially. A through-hole is formed in the adhesive layer, and the surface of the dielectric layer is exposed to the through-hole. A second graphene layer is formed on the surface of the copper layer opposite to the first graphene layer, and the projection of the second graphene layer covers the through hole. The first graphene layer, the copper layer, and the second graphene layer are fabricated to form a circuit layer, thereby obtaining the flexible circuit board, which can be bent in the area where the first graphene layer and the second graphene layer are disposed.

2. The method for manufacturing a flexible circuit board according to claim 1, characterized in that, The steps for forming the substrate include: A protective layer is applied to the surface of the dielectric layer; The first graphene layer is formed on the surface of the dielectric layer opposite to the protective layer; Remove the protective layer; The copper layer is formed on the surface of the dielectric layer opposite to the first graphene layer, thereby obtaining the substrate.

3. The method for manufacturing a flexible circuit board according to claim 2, characterized in that, The step of forming the first graphene layer on the surface of the dielectric layer opposite to the protective layer includes: The medium layer with the protective layer is immersed in a solution containing graphene and then removed; the graphene is adsorbed onto the surface of the medium layer. The graphene is dried to form the first graphene layer.

4. The method for manufacturing a flexible circuit board according to claim 1, characterized in that, Prior to the step of forming the circuit layer, the fabrication method further includes: A groove is formed that penetrates the substrate and the adhesive layer, and a copper plating layer is formed in the groove. The copper plating layer is used to conduct the copper layers located on both sides of the adhesive layer.

5. The method for manufacturing a flexible circuit board according to any one of claims 1 to 4, characterized in that, Prior to the step of forming the circuit layer, the fabrication method further includes: A first dry film is covered on the surface of the copper layer, and a first opening is formed on the first dry film, the projection of the first opening covering the through hole; A second graphene layer is formed on the surface of the copper layer exposed to the first opening; and Remove the first dry film to expose the surface of the copper layer.

6. The method for manufacturing a flexible circuit board according to any one of claims 1 to 4, characterized in that, The steps for forming the circuit layer include: A second dry film is covered on the surfaces of the copper layer and the second graphene layer, and a second opening is formed on the second dry film, with a portion of the surface of the second graphene layer and a portion of the surface of the copper layer exposed to the second opening; Remove the second graphene layer exposed to the second opening; Remove the copper layer exposed in the second opening; Remove the first graphene layer exposed to the second opening, so that the remaining first graphene layer, the copper layer, and the second graphene layer together form the circuit layer; and Remove the second dry film.

7. The method for manufacturing a flexible circuit board according to claim 6, characterized in that, The steps for removing the second graphene layer include: In an atmosphere containing an inert gas, the second graphene layer exposed to the second opening is irradiated with ultraviolet light to remove the second graphene layer.

8. A flexible circuit board, characterized in that, include: The adhesive layer has through holes; A dielectric layer is located on the opposite surfaces of the adhesive layer; as well as A circuit layer is located on the surface of the dielectric layer opposite to the adhesive layer. The circuit layer includes a first graphene layer, a copper layer, and a second graphene layer stacked together. The first graphene layer is connected to the surface of the dielectric layer, and the second graphene layer is located on the surface of the copper layer opposite to the dielectric layer. The flexible circuit board can be bent in the area where the through-hole, the first graphene layer, and the second graphene layer are provided.

9. The flexible circuit board according to claim 8, characterized in that, The flexible circuit board further includes a copper plating layer that penetrates the adhesive layer, the dielectric layer, the first graphene layer, and the copper layer. The copper plating layer is used to conduct the circuit layers located on both sides of the adhesive layer.

10. A terminal device, characterized in that, The terminal device includes the flexible circuit board as described in any one of claims 8-9.

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