Flexible circuit board resistant to bending and method for manufacturing the same

Abstract

The application provides a flexible circuit board resistant to bending and a preparation method thereof. The application replaces the original copper circuit layer with a conductive layer formed by graphene in the bending area. The conductive layer formed by graphene has higher ductility and malleability, and higher tensile strength, so that the conductive layer can withstand more bending times than the copper circuit layer. In addition, the conductivity of graphene is also higher. Therefore, the flexible circuit board of the application improves the bending performance of the bending area while ensuring the inherent electrical properties of the bending area.

Description

Technical Field

[0001] This application relates to the field of circuit board technology, and in particular to a flexible circuit board that is resistant to bending and a method for preparing the same. Background Technology

[0002] With the rapid development of technology, electronic products (such as foldable screen phones) have increasingly higher requirements for flexible printed circuit boards (FPCs). These FPCs typically need to withstand hundreds of thousands or even more repeated bending cycles to meet the demands of frequent screen folding in daily use. Existing FPCs are usually made by bonding two single-sided copper foils together with a layer of adhesive (AD) in between. Before bonding, the bending area of ​​this AD layer is punched out, creating an adhesive-free area after bonding—a structure commonly referred to in the industry as an airgap. However, there is still room for improvement in the bending performance of FPCs with this airgap structure. Summary of the Invention

[0003] In view of this, this application proposes a flexible circuit board with bend resistance and a method for manufacturing the same, so as to improve the bending performance of the circuit board.

[0004] One embodiment of this application provides a bend-resistant flexible circuit board. Along the extension direction of the flexible circuit board, the flexible circuit board includes a connected non-bending region and a bending region. Along the thickness direction of the flexible circuit board, the non-bending region includes a first dielectric layer and a circuit layer located on the surface of the first dielectric layer. Along the thickness direction of the flexible circuit board, the bending region includes a second dielectric layer and a conductive layer located on the surface of the second dielectric layer. The second dielectric layer is connected to the first dielectric layer, and the conductive layer is connected to the circuit layer; the conductive layer includes graphene.

[0005] In one embodiment, the conductive layer further covers a portion of the surface of the circuit layer that faces away from the first dielectric layer.

[0006] In one embodiment, the thickness of the conductive layer is 5 nm to 50 nm along the thickness direction of the flexible circuit board.

[0007] In one embodiment, along the thickness direction of the flexible circuit board, the surface of the second dielectric layer near the conductive layer is not coplanar with the surface of the first dielectric layer near the circuit layer, and the thickness of the second dielectric layer is less than the thickness of the first dielectric layer.

[0008] In one embodiment, the flexible circuit board further includes a protective film layer that covers the bending area and the non-bending area.

[0009] In one embodiment, the linewidth of the conductive layer is 40 μm or more, and the line spacing of the conductive layer is 40 μm or more.

[0010] One embodiment of this application provides a method for fabricating a bend-resistant flexible circuit board, comprising the following steps: providing a copper-clad laminate; wherein, along the extension direction of the copper-clad laminate, the copper-clad laminate includes a connected bending region and a non-bending region, and along the thickness direction of the copper-clad laminate, the copper-clad laminate includes a dielectric layer and a copper foil layer located on the surface of the dielectric layer; removing the copper foil layer in the bending region and forming a circuit layer from the copper foil layer in the non-bending region; thinning the thickness of the dielectric layer in the bending region; and providing a conductive layer in the bending region, the conductive layer connecting to the circuit layer, the conductive layer comprising graphene.

[0011] In one embodiment, the step of "setting a conductive layer in the bending area" further includes: degreasing the bending area with a cleaning agent at a temperature of 30°C to 50°C for a treatment time of 30s to 90s; washing the degreased bending area with water; immersing the washed bending area in a chemical solution to form the conductive layer; wherein the solid content of graphene in the chemical solution is 0.01% to 0.5%; and drying at a temperature of 90°C to 100°C for a time of 10s to 60s.

[0012] In one embodiment, the preparation method further includes: providing a protective film layer on the surface of the bending area and the non-bending area.

[0013] In one embodiment, after the step of "thinning the dielectric layer of the bending region", the preparation method further includes cleaning with plasma.

[0014] This application replaces the original copper circuit layer with a conductive layer formed of graphene in the bending region. The conductive layer formed of graphene has high ductility and extensibility, and high tensile strength (1 MPa to 100 MPa), which allows the conductive layer described in this application to withstand more bends than the copper circuit layer. In addition, graphene has high electrical conductivity. Therefore, the flexible circuit board of this application improves the bending performance of the bending region while ensuring the inherent electrical performance of the bending region. Attached Figure Description

[0015] Figure 1 This is a cross-sectional view of a flexible circuit board in the prior art.

[0016] Figure 2 This is a cross-sectional view of a flexible circuit board according to one embodiment of this application.

[0017] Figures 3A to 3D For preparation Figure 2 The cross-sectional view of the flexible circuit board shown.

[0018] Explanation of main component symbols

[0019] Flexible circuit board 1,100

[0020] Adhesive layer 2

[0021] Dielectric layer 3, 10

[0022] Line layer 4

[0023] Protective film layer 5, 40

[0024] No glue area 6

[0025] Non-bending area 101

[0026] Bending area 102

[0027] First dielectric layer 11

[0028] Second dielectric layer 12

[0029] Line layer 20

[0030] Copper foil layer 20a

[0031] Conductive layer 30

[0032] Copper Clad Laminate 50

[0033] Thickness H

[0034] The following detailed description, in conjunction with the accompanying drawings, further illustrates the embodiments of this application. Detailed Implementation

[0035] 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 the embodiments of this application pertain. The terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the embodiments of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0036] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0037] It will be understood that when a layer is referred to as "on" another layer, it can be directly on that other layer or there may be an intermediate layer in between. Conversely, when a layer is referred to as "directly on" another layer, there is no intermediate layer. When a component is referred to as "attached to," "mounted to," "set on," or "connected to" another component, it can be directly on that other component or there may be an intervening component. The term "and / or" as used herein includes all and any combination of one or more of the associated listed items.

[0038] Embodiments of this application are described herein with reference to cross-sectional views, which are schematic diagrams of idealized embodiments (and intermediate configurations) of this application. Therefore, variations in the shapes illustrated due to manufacturing processes and / or tolerances are foreseeable. Consequently, embodiments of this application should not be construed as limited to the specific shapes of the areas illustrated herein, but should include, for example, deviations in shape due to manufacturing processes. The areas shown in the figures are merely illustrative, and their shapes are not intended to represent the actual shapes of the illustrated devices, nor are they intended to limit the scope of this application.

[0039] like Figure 1 As shown, taking a double-sided flexible circuit board (with two circuit layers) as an example, the existing flexible circuit board 1 generally includes an adhesive layer 2 and a dielectric layer 3, a circuit layer 4, and a protective film layer 5 located on opposite surfaces of the adhesive layer 2. The adhesive layer 2 can be formed from pure adhesive (AD), the dielectric layer 3 can be a conventional or unconventional flexible material in the art, the circuit layer 4 can be formed from copper, and the protective film layer 5 can be, but is not limited to, a cover film layer (CVL). The adhesive layer 2 has an adhesive-free area 6 (i.e., an airgap) to reduce bending stress and improve bending performance during bending. However, the bending performance of this type of flexible circuit board 1 is limited, and it fails after a certain number of bends. Further analysis of the flexible circuit board 1 that failed due to bending revealed that many failures of the flexible circuit board 1 were caused by microcracks or fractures in the circuit layer 4 (copper layer). Based on this, the inventors of this application have improved the existing flexible circuit board 1 and filed this application.

[0040] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0041] Please see Figure 2 The first aspect of this application provides a flexible circuit board 100 that is resistant to bending. Along the extending direction of the flexible circuit board 100 (i.e.... Figure 2 The horizontal direction (which can be either the length or width direction of the flexible circuit board 100) is defined in the text. The flexible circuit board 100 includes a connected non-bending region 101 and a bending region 102. Along the thickness direction of the flexible circuit board 100 (i.e.,...) Figure 2In the vertical direction of the flexible circuit board 100, the non-bending region 101 includes a first dielectric layer 11 and a circuit layer 20 located on the surface of the first dielectric layer 11. Along the thickness direction of the flexible circuit board 100, the bending region 102 includes a second dielectric layer 12 and a conductive layer 30 located on the surface of the second dielectric layer 12. The second dielectric layer 12 is connected to the first dielectric layer 11, and the conductive layer 30 is connected to the circuit layer 20. The conductive layer 30 includes graphene.

[0042] During dynamic bending, the bending angle is typically 0° to 180°. The structure within the bending region 102 (especially the conductive layer) is subjected to both tensile and compressive stresses. Therefore, the ductility and malleability of the conductive layer within the bending region 102 are crucial in determining the bending performance of the flexible circuit board 100. Ductility refers to the property of a metal to extend into a filament without breaking under tensile stress. Malleability refers to the property of a metal to be rolled into a thin sheet without cracking under compressive stress. If the conductive layer within the bending region 102 is made of copper, although copper has good ductility, its malleability is insufficient. Therefore, copper-based circuit layers are prone to cracking or breaking during bending, leading to the failure of the flexible circuit board. In this application, the conductive layer 30 within the bending region 102 is made of graphene. Graphene is a pure two-dimensional planar crystal with both high ductility and malleability, as well as high tensile strength (1 MPa to 100 MPa). Therefore, it can withstand more bends than copper, improving the bending performance of the bending region 102. In addition, graphene has high electrical conductivity (10⁻⁶). 4 S / m~10 6 Setting it as the conductive layer 30 of the bending region 102 (S / m) will not affect the electrical connection with the line layer 20 of the non-bending region 101, thus ensuring the inherent functions of the bending region 102 and the non-bending region 101.

[0043] like Figure 2 As shown, in some embodiments, the flexible circuit board 100 includes two non-bending regions 101 and one bending region 102, with the bending region 102 located between the two non-bending regions 101. In other embodiments, the flexible circuit board 100 may include more than two bending regions 102, with each bending region 102 located between two adjacent non-bending regions 101.

[0044] like Figure 2As shown, in some embodiments, the flexible circuit board 100 includes two circuit layers 20 and two conductive layers 30, with the two conductive layers 30 located on opposite surfaces of the second dielectric layer 12. In other embodiments, the flexible circuit board 100 may include one circuit layer 20 or three or more circuit layers 20, with the number of conductive layers 30 being the same as the number of circuit layers 20. When there are three or more circuit layers 20, the first dielectric layer 11 and the second dielectric layer 12 are both two or more layers, with each first dielectric layer 11 disposed between two adjacent circuit layers 20, and each second dielectric layer 12 disposed between two adjacent conductive layers 30, and each first dielectric layer 11 is connected to a second dielectric layer 12.

[0045] like Figure 2 As shown, in some embodiments, the conductive layer 30 also covers a portion of the surface of the circuit layer 20 facing away from the first dielectric layer 10. That is, the conductive layer 30 can extend from the bending region 102 to the non-bending region 101 (extending only a short distance to the non-bending region 101). In this way, the circuit layer 20 in the non-bending region 101 can be better electrically connected to the conductive layer 30.

[0046] Furthermore, along the thickness direction of the flexible circuit board 100, the thickness H of the conductive layer 30 is 5nm to 50nm. This ensures that the conductive layer 30 has sufficient tensile strength for good bending performance, guarantees electrical connection with the circuit layer 20, and also controls costs.

[0047] In some embodiments, the linewidth of the conductive layer 30 may be 40 μm or more (≥40 μm), and the line spacing of the conductive layer 30 may be 40 μm or more (≥40 μm). When the linewidth and line spacing of the conductive layer 30 are within the above range, the electrical performance of the conductive layer 30 will not be affected when the bending region 102 is bent, and the conductive layer 30 can normally complete the transmission and distribution of current.

[0048] like Figure 2 As shown, in some embodiments, along the thickness direction of the flexible circuit board 100, the surface of the second dielectric layer 12 near the conductive layer 30 is not coplanar with the surface of the first dielectric layer 11 near the circuit layer 20, and the thickness of the second dielectric layer 12 is less than the thickness of the first dielectric layer 11. Overall, the second dielectric layer 12 can be considered as a portion of the first dielectric layer 11 thinned along its thickness direction, and this thinned portion forms a groove. This groove is used to accommodate the conductive layer 30, which can reduce the bending stress of the conductive layer 30 and further improve its bending performance.

[0049] like Figure 2As shown, in some embodiments, the flexible circuit board 100 further includes a protective film layer 40, which covers the non-bending area 101 and the bending area 102. It is understood that when the circuit layer 20 and the conductive layer 30 have multiple layers, the protective film layer 40 covers the outermost circuit layer 20 and conductive layer 30.

[0050] Furthermore, the protective film layer 40 can be, but is not limited to, CVL.

[0051] In some embodiments, the first dielectric layer 11 and the second dielectric layer 12 may each be independently selected from one or more flexible materials such as polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate dimethyl acid glycol ester (PEN), polydimethylsiloxane (PDMS), and liquid crystal polymer (LCP). The materials of the first dielectric layer 11 and the second dielectric layer 12 may be the same or different, and this application does not impose any limitations. In this embodiment, both the first dielectric layer 11 and the second dielectric layer 12 are PI.

[0052] like Figure 1 As shown, taking an existing flexible circuit board 1 with two circuit layers 4 as an example, the thickness of its adhesive layer 2 is approximately 15 μm, the thickness of each dielectric layer 3 is approximately 12.5 μm, the thickness of each circuit layer 4 is approximately 12 μm, and the thickness of each protective film layer 5 is approximately 27.5 μm (the protective film layer 5 includes an AD adhesive layer and a PI layer; the thickness of the AD adhesive layer is 15 μm, and the thickness of the PI layer is 12.5 μm). Therefore, Figure 1 The flexible circuit board 1 shown has a thickness of 119 μm. However, in this application, as... Figure 2 The flexible circuit board 100 shown has an overall thickness equal to the sum of the thicknesses of the first dielectric layer 11, the two circuit layers 20, and the two protective film layers 40. The thickness of the first dielectric layer 11 is... Figure 1 The thickness of dielectric layer 3 is constant, i.e., 12.5 μm. The thickness of each circuit layer 20 is the same as... Figure 1 Each circuit layer 4 has the same thickness, i.e., 12μm. The thickness of each protective film layer 40 is... Figure 1 Each protective film layer 5 has the same thickness, i.e., 27.5 μm. Therefore, this application... Figure 2 The flexible circuit board 100 shown has a thickness of 91.5 μm, compared to Figure 1The thickness of the flexible circuit board 1 is reduced by 23%. Therefore, the flexible circuit board 100 described in this embodiment not only has improved bending performance but also a thinner thickness.

[0053] Please see Figures 3A to 3D as well as Figure 2 The second aspect of this application provides a method for preparing a flexible circuit board 100, which includes steps S10 to S60.

[0054] Please see Figure 3A Step S10: Provide copper-clad laminate 50.

[0055] like Figure 3A As shown, along the extension direction of the copper-clad laminate 50 (i.e. Figure 3A The copper-clad laminate 50 includes a connected non-bending region 101 and a bending region 102 along the thickness direction of the copper-clad laminate 50 (i.e., along the thickness direction). Figure 3A In the vertical direction, the copper-clad laminate 50 includes a dielectric layer 10 and a copper foil layer 20a located on the surface of the dielectric layer 10. In this embodiment, the copper foil layer 20a is located on two opposite surfaces of the dielectric layer 10 in the thickness direction. In other embodiments, the copper foil layer 20a may be located on only one surface of the dielectric layer 10.

[0056] In some embodiments, the dielectric layer 10 may be made of, but is not limited to, PI, PET, PEN, PDMS, LCP, etc.

[0057] Please see Figure 3B In step S20, the copper foil layer 20a of the bending area 102 is removed, and the copper foil layer 20a of the non-bending area 101 is used to form the circuit layer 20.

[0058] In some embodiments, the copper foil layer 20a of the bending region 102 can be removed by steps such as pressing dry film, exposure, development, etching, and stripping. After removal, the dielectric layer 10 of the bending region 102 is exposed. For clarity, the dielectric layer 10 of the non-bending region 101 is represented by the first dielectric layer 11, and the dielectric layer 10 of the bending region 102 is represented by the second dielectric layer 12.

[0059] In some embodiments, the circuit layer 20 can be formed by steps such as pressing dry film, exposure, development, etching, and stripping. The above steps are conventional techniques in the art and will not be described in detail here.

[0060] Please see Figure 3C In step S30, the thickness of the dielectric layer 10 (i.e. the second dielectric layer 12) in the bending region 102 is reduced.

[0061] In some embodiments, the second dielectric layer 12 can be thinned by, but is not limited to, laser ablation. It is understood that the thickness of the thinned second dielectric layer 12 is less than the thickness of the first dielectric layer 11. Of the two surfaces of the thinned second dielectric layer 12 that are opposite each other along the thickness direction, at least one surface is not coplanar with the surface of the first dielectric layer 11. The thinned portion forms a groove and communicates with the blank area left after removing the copper foil layer 20a; the two together can form the receiving space for the conductive layer 30 prepared in subsequent steps.

[0062] Step S40: Use plasma to clean the circuit layer 20 to ensure that the circuit layer 20 is not contaminated.

[0063] Please see Figure 3D In step S50, a conductive layer 30 is provided in the bending area 102. The conductive layer 30 is connected to the circuit layer 20. The conductive layer 30 includes graphene.

[0064] In some embodiments, the conductive layer 30 may be formed by the following steps.

[0065] First, the bending area 102 can be degreased using a cleaning agent. The cleaning temperature of the cleaning agent is 30℃~50℃, and the treatment time is 30s~90s. The solvent and cationic surfactant in the cleaning agent can clean the second dielectric layer 12 and the circuit layer 20 and adjust their polarity charge, which is beneficial for the subsequent adsorption of negatively charged graphene microsheets.

[0066] Then, the degreased bending area 102 can be washed with water to remove excess cleaning agent.

[0067] Next, the washed bending region 102 can be immersed in a chemical solution to form a conductive layer 30. The chemical solution includes graphene (microsheets) and may also include auxiliary materials such as anhydrous ethanol, polyvinylpyrrolidone (PVP), and 1-methyl-2-pyrrolidone (NMP). The solid content of graphene can be 0.01% to 0.5%. Graphene is a two-dimensional material with high specific surface area, high surface energy, and easy adsorption properties, allowing it to be oriented to form a film at the interface between two phases. Furthermore, through electrostatic and hydrogen bonding interactions, as well as van der Waals forces (molecular forces) formed at the microscopic level of the graphene microsheets (less than 10 nm thick) and the substrate (second dielectric layer 12, circuit layer 20), a sheet-like, stretchable film layer is formed in the bending region 102. The thickness of this film layer can be 5 nm to 50 nm.

[0068] Finally, the film is dried to solidify it, making it more dense, thereby giving the resulting conductive layer 30 excellent conductivity and a certain degree of hardness. The drying temperature can be 90℃~100℃, and the drying time can be 10s~60s.

[0069] like Figure 3D As shown, in some embodiments, the conductive layer 30 may extend a short distance from the bending region 102 to the non-bending region 101 to cover a portion of the surface of the circuit layer 20 facing away from the first dielectric layer 10. This allows for better electrical connection between the circuit layer 20 in the non-bending region 101 and the conductive layer 30.

[0070] Please see Figure 2 In step S60, a protective film layer 40 is formed on the surface of the bending area 102 and the non-bending area 101 to obtain the flexible circuit board 100. It is understood that when the circuit layer 20 and the conductive layer 30 have multiple layers, the protective film layer 40 covers the outermost circuit layer 20 and conductive layer 30. The protective film layer 40 can be, but is not limited to, CVL.

[0071] The flexible circuit board 100 and its preparation method in this application embodiment replace the original copper circuit layer 20 with a conductive layer 30 formed of graphene in the bending region 102. The conductive layer 30 formed of graphene has high ductility and extensibility, and high tensile strength (1 MPa to 100 MPa), so that the conductive layer 30 can withstand more bends than the copper circuit layer. In addition, graphene has high electrical conductivity. Therefore, the flexible circuit board 100 in this application embodiment improves the bending performance of the bending region 102 while ensuring the inherent electrical performance of the bending region 102.

[0072] The above description describes some specific embodiments of this application, but in actual applications, the application should not be limited to these embodiments. For those skilled in the art, other modifications and alterations made based on the technical concept of this application should fall within the protection scope of this application.

Claims

1. A flexible circuit board resistant to bending, characterized in that, Along the extension direction of the flexible circuit board, the flexible circuit board includes a connected non-bending area and a bending area; Along the thickness direction of the flexible circuit board, the non-bending region includes a first dielectric layer and a circuit layer located on the surface of the first dielectric layer; Along the thickness direction of the flexible circuit board, the bending region includes a second dielectric layer and a conductive layer located on the surface of the second dielectric layer. The second dielectric layer is connected to the first dielectric layer, and the conductive layer is connected to the circuit layer. The conductive layer includes graphene.

2. The flexible circuit board as described in claim 1, characterized in that, The conductive layer also covers a portion of the surface of the circuit layer that is away from the first dielectric layer.

3. The flexible circuit board as described in claim 1, characterized in that, Along the thickness direction of the flexible circuit board, the thickness of the conductive layer is 5nm to 50nm.

4. The flexible circuit board as described in claim 1, characterized in that, Along the thickness direction of the flexible circuit board, the surface of the second dielectric layer near the conductive layer is not coplanar with the surface of the first dielectric layer near the circuit layer, and the thickness of the second dielectric layer is less than the thickness of the first dielectric layer.

5. The flexible circuit board as described in claim 1, characterized in that, The flexible circuit board also includes a protective film layer that covers the bending area and the non-bending area.

6. The flexible circuit board as described in claim 1, characterized in that, The linewidth of the conductive layer is 40 μm or more, and the line spacing of the conductive layer is 40 μm or more.

7. A method for preparing a bend-resistant flexible circuit board, characterized in that, Includes the following steps: A copper-clad laminate is provided; wherein, along the extension direction of the copper-clad laminate, the copper-clad laminate includes connected bent and non-bent regions; along the thickness direction of the copper-clad laminate, the copper-clad laminate includes a dielectric layer and a copper foil layer located on the surface of the dielectric layer; Remove the copper foil layer in the bending area and form a circuit layer from the copper foil layer in the non-bending area; The thickness of the dielectric layer in the bending region is reduced; A conductive layer is provided in the bending region, the conductive layer is connected to the circuit layer, and the conductive layer includes graphene.

8. The preparation method according to claim 7, characterized in that, The step of "providing a conductive layer in the bending area" further includes: The bending area is degreased using a cleaning agent at a temperature of 30°C to 50°C for 30 to 90 seconds. The bending area after washing and degreasing; The bent area after washing is immersed in a chemical solution to form the conductive layer; wherein the solid content of graphene in the chemical solution is 0.01% to 0.5%; Drying is performed at a temperature of 90℃~100℃ for 10s~60s.

9. The preparation method according to claim 7, characterized in that, The preparation method further includes: setting a protective film layer on the surface of the bending area and the non-bending area.

10. The preparation method according to claim 7, characterized in that, After the step of "reducing the thickness of the dielectric layer in the bending region", the preparation method further includes cleaning with plasma.

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