Circuit board manufacturing method, circuit board and keyboard suitable for multi-angle magnetic attraction keyboard

Abstract

The application relates to the technical field of rigid-flex composite printed circuit boards, and discloses a circuit board manufacturing method suitable for a multi-angle magnetic attraction keyboard, a circuit board, a keyboard and a keyboard comprising the soft circuit board. The manufacturing method comprises the following steps: providing a calendered copper foil substrate, sequentially attaching a photoresist layer on the copper foil layer and performing multiple etchings to form first, second and third sunken parts, filling an elastic buffer layer in the first sunken part, and forming a protective layer on the copper foil layer to obtain a soft circuit board; wherein the line thickness of the soft circuit board gradually increases along the bending center to both ends, a stepped bending part is formed, and the line of the stepped bending part can be in a broken line, a wave shape or an S-shaped line along the bending direction. The soft circuit board can be used in a multi-angle magnetic attraction keyboard, realizes the electrical connection between a keyboard key module and a power supply module, and simultaneously has stress release and bending adaptability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rigid-flex composite printed circuit board, and particularly relates to a circuit board manufacturing method suitable for a multi-angle magnetic attraction keyboard, a circuit board and a keyboard. BACKGROUND

[0002] With the wide application of notebook computers, tablet keyboards and multi-functional magnetic attraction keyboards, users have higher and higher requirements for the thinness, foldability, multi-angle use and durability of the keyboard. The traditional soft circuit board is usually formed by combining a copper foil layer and a substrate layer, and is used to connect the keyboard key module and the power module. However, such a circuit board has many disadvantages in practical application.

[0003] Firstly, the traditional soft circuit board has uniform line thickness when being bent at multiple angles, which can easily cause stress concentration in the center of the bending area, and the copper foil can easily break or fall off after long-term use, thereby reducing the reliability and service life of the keyboard. Secondly, the existing circuit board lacks effective structural design in the bending area and cannot realize graded buffering or stepped thickness, and usually needs additional support or fixing structure, which leads to complex manufacturing process and increased cost. At the same time, in the repeated folding or bending process, the line and the substrate are prone to fatigue deformation, especially in the magnetic attraction keyboard scenario with high frequency use, which is more prone to function damage, and it is difficult to meet the comprehensive needs of thinness, multi-angle and durability.

[0004] In addition, the existing soft circuit board lacks integrated function and structure in the design of terminals, protective layers and bending areas, and it is difficult to balance the reliability of electrical connection, durability and folding adaptability, which restricts the development of the overall thinness and modular design of the keyboard. Therefore, there is an urgent need for a soft circuit board with stepped line thickness in the bending area and elastic buffer and protective layer and a manufacturing method thereof to effectively alleviate the folding stress concentration problem and improve the reliability and service life of the multi-angle magnetic attraction keyboard. SUMMARY

[0005] The present application discloses a soft circuit board suitable for a multi-angle magnetic attraction keyboard and a manufacturing method thereof, which aims to solve the problems of line stress concentration, fatigue fracture and insufficient durability of the existing soft circuit board when being bent at multiple angles. By adopting a three-time etching process to form multiple sinking parts (i.e. a first sinking part, a second sinking part and a third sinking part) on the copper foil layer and filling an elastic buffer layer in the deepest sinking part, the soft circuit board has a stepped thickness increasing structure along the bending center, effectively disperses the folding stress and improves the mechanical reliability and durability of the line.

[0006] Specifically, the manufacturing method of the present application comprises: providing a rolled copper foil substrate, sequentially performing three times of photoresist attaching and etching on the copper foil layer to form a first sunken part, a second sunken part and a third sunken part, wherein the height of the first sunken part is not less than the height sum of the second sunken part and the third sunken part, so as to form a stepped bending part with gradually changing thickness at the bending center. An elastic buffer layer is filled in the deepest first sunken part, and the thickness of the elastic buffer layer is not less than the height of the first sunken part, so as to further absorb the stress in the bending process. Finally, a protective layer is formed on the surface of the rolled copper foil layer to cover the sunken parts to protect the circuit, and a terminal part is reserved to realize reliable electrical connection.

[0007] The present application also provides a corresponding flexible circuit board structure, the copper foil layer has multiple sunken parts, the first sunken part, the second sunken part and the third sunken part constitute a stepped bending area, the elastic buffer layer is filled in the first sunken part, and the protective layer covers the entire bending area, while the thickness of the circuit gradually increases along the bending center to both ends. This structure can effectively relieve the stress concentration in the bending area, and improve the reliability and service life of the flexible circuit board in the multi-angle magnetic attraction keyboard.

[0008] In addition, the present application further provides a multi-angle magnetic attraction keyboard, which comprises a key module, a power supply module and a flexible circuit board suitable for a multi-angle magnetic attraction keyboard as described above, and the flexible circuit board suitable for a multi-angle magnetic attraction keyboard is used to electrically connect the key module and the power supply module. Through the stepped bending part and the elastic buffer layer design of the flexible circuit board, the keyboard can maintain good circuit connectivity and structural stability at different bending angles, ensuring reliable electrical connection between each key module and the power supply module during magnetic attraction folding operation. This design not only enhances the durability of the keyboard, but also supports multi-angle use in complex folding modes, meeting the reliability requirements of modern portable magnetic attraction keyboards during use.

[0009] Through the above technical solutions, the present application realizes the combination of stepped thickness and elastic buffer in the bending area of the flexible circuit board while ensuring the multi-angle bending performance, significantly improves the bending durability and circuit stability, and meets the requirements of durability and reliability of the magnetic attraction keyboard under multi-angle use. BRIEF DESCRIPTION OF DRAWINGS

[0010] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creating any creative labor.

[0011] Among them:

[0012] Figure 1This is a flowchart of the flexible circuit board manufacturing method provided in this embodiment of the technical solution;

[0013] Figure 2 This is a cross-sectional view of the rolled copper foil substrate provided in this embodiment of the technical solution;

[0014] Figure 3 Is Figure 2 A cross-sectional view of the first photoresist layer formed on the rolled copper foil layer;

[0015] Figure 4 Yes Figure 3 A cross-sectional view after the rolled copper foil layer is etched to form the first recessed section;

[0016] Figure 5 Is Figure 4 A cross-sectional view of a second photoresist layer formed on a rolled copper foil layer;

[0017] Figure 6 Yes Figure 5 A cross-sectional view after etching the rolled copper foil layer to form the second recessed section;

[0018] Figure 7 Is Figure 6 A cross-sectional view of a third photoresist layer formed on a rolled copper foil layer;

[0019] Figure 8 Yes Figure 7 A cross-sectional view after etching the rolled copper foil layer to form the third recessed section;

[0020] Figure 9 Is Figure 8 A top view of the rolled copper foil layer after it has formed a stepped bend.

[0021] Figure 10 yes Figure 8 A magnified cross-sectional view of the rolled copper foil layer after the stepped bend is formed;

[0022] Figure 11 Is Figure 8 A cross-sectional view of the elastic buffer layer filling the first recessed section;

[0023] Figure 12 yes Figure 11 A magnified cross-sectional view of the honeycomb structure formed by the elastic buffer layer;

[0024] Figure 13 This is a top view of a variation where an elastic buffer layer is filled in the first recessed section;

[0025] Figure 14 Is Figure 11 A cross-sectional view of the protective layer formed by the rolled copper foil layer;

[0026] Figure 15is in Figure 14 A cross-sectional view of a terminal portion plated surface treatment layer.

[0027] Main component symbol explanation

[0028] DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0030] Please refer to Figure 1 It is a flow chart of the soft circuit board manufacturing method provided by the technical solution embodiment, mainly including the following steps:

[0031] First step S1, please refer to Figure 2, a rolled copper foil substrate 110 is provided, which includes a rolled copper foil layer 111 and a substrate layer 112 formed on one side of the rolled copper foil layer 111. In this embodiment, rolled & annealed copper (RA) is mainly used instead of electro deposit copper (ED), the main reason is that the rolled copper foil has more excellent mechanical properties, especially the durability under bending stress is significantly better than that of the electro deposit copper. Specifically, the rolled copper foil is processed by multiple rolling, the grain arrangement is more uniform, has higher ductility and fatigue resistance, so it can withstand the repeated stress generated by the flexible circuit board under multi-angle bending without easy breaking or peeling. The selection of the substrate layer 112 also plays a supporting role, the substrate layer 112 made of polyimide (PI) or polyethylene terephthalate (PET) not only provides flexible support, but also can maintain stable mechanical properties in high and low temperature environment, so as to realize reliable multi-angle bending with the rolled copper foil layer 111. In addition, the thickness of the rolled copper foil layer 111 can be 0.5-1 oz, and the thickness of the substrate layer 112 is 0.5-1 mil. Specifically, the thickness of the rolled copper foil layer 111 is 17.5-35 microns (μm), and the thickness of the substrate layer 112 is 12.7-25.4 microns (μm). Compared with the general flexible circuit board 100, the thicker copper foil is selected in this embodiment, on the one hand, it can bear larger current, on the other hand, it can have enough copper thickness for subsequent multiple etching, and ensure good bending characteristics. In addition, the substrate layer 112 with the above thickness is selected to effectively cooperate with the rolled copper foil layer 111 and provide basic support. Therefore, the rolled copper foil substrate 110 can maintain good mechanical stability and circuit integrity, and provide a solid foundation for the final prepared flexible circuit board.

[0032] In the second step S2, referring to Figure 3A first photoresist layer 200 is attached to the rolled copper foil layer 111, and the first photoresist layer 200 has a first opening 210 exposing a portion of the rolled copper foil layer 111. In the manufacturing process of the flexible printed circuit board, the first photoresist layer 200 can be in the form of a dry film, and a positive photoresist or a negative photoresist material can be selected, such as an epoxy-based photoresist, an acrylic-based photoresist, or a polyimide-based photoresist. Such photoresist materials have good adhesion, corrosion resistance, and resolution, and can accurately cover the non-etching area of the rolled copper foil, while protecting the covered area from the subsequent etching process. In actual operation, the first photoresist layer 200 can be uniformly attached to the surface of the rolled copper foil layer 111 by lamination, usually completed by a laminator to improve the adhesion of the first photoresist layer 200. Then, the first opening 210 is formed by exposure and development processing, so that a portion of the rolled copper foil layer 111 can be accurately exposed in the first opening 210, and the shape and size of the etching area can be accurately controlled, thereby ensuring that the etching depth and profile meet the design requirements.

[0033] In the third step S3, referring to FIG. 3, Figure 4 A first etching process is performed on the portion of the rolled copper foil layer 111 exposed in the first opening 210 to form a first sunken portion 111a. Preferably, the etching step can use wet chemical etching or dry plasma etching. In wet etching, ferric chloride (FeCl3), copper sulfate / hydrogen peroxide mixture, or copper chloride solution can be used as the etchant; in dry etching, chlorine gas (Cl2), carbon tetrachloride (CCl4), or a mixture of gases can be used to selectively remove the copper layer in a plasma environment. In this embodiment, wet chemical etching is mainly selected. Before performing the first etching, as shown in FIG. 2, Figure 3 During the etching process, the exposed portion of the rolled copper foil layer 111 is removed by the etchant to form the first sunken portion 111a, and the first etching depth can be controlled between 5 microns (μm) and 8 microns (μm) to facilitate subsequent multiple etching steps. The height and edge profile of the first sunken portion 111a are determined by the accuracy of the first opening 210 defined by photolithography, so high-resolution dry film materials can ensure that the etching area is neat, the edges are sharp, and the size is stable. After completing the first etching, the first photoresist layer 200 is removed, cleaned to remove etching residues, and dried to prepare for the second etching.

[0034] In the fourth step S4, referring to FIG. 4, Figure 5In the step of forming the first recessed portion 111a, a second photoresist layer 300 is attached to the copper foil layer 111, the second photoresist layer 300 having a second opening 310 exposing a portion of the copper foil layer 111 and the first recessed portion 111a. The second photoresist layer 300 can be made of the same or different material as the first photoresist layer 200, such as a positive photoresist or a negative photoresist. In detail, the attaching step includes the following operations: (1) surface pretreatment: the surface of the copper foil layer 111 and the first recessed portion 111a is cleaned by plasma or solvent to remove oil and particles, and to improve the adhesion of the photoresist; (2) pressing or coating photoresist: the second photoresist layer 300 is uniformly formed on the surface of the copper foil layer 111 by pressing, spin-coating, doctor blade coating or spraying; (3) exposure and development: the second photoresist layer 300 is exposed to define the opening area of the second opening 310; then the photoresist layer in the opening area is removed by a developing solution, so that the second opening 310 exposes a portion of the copper foil layer 111 and the first recessed portion 111a, providing accurate protection and exposure area for the second etching. Through the above steps, the second photoresist layer 300 can accurately cover the non-etching area while keeping the first recessed portion 111a exposed, ensuring that the second etching is performed on the specified area, and can also reduce the height of the first recessed portion 111a, achieving accurate control of the multi-level stepped structure.

[0035] In the fifth step S5, referring to Figure 6A second etching process is performed on the exposed copper foil layer 111 and the first recessed portion 111a of the second opening 310 to form a second recessed portion 111b and reduce the height of the first recessed portion 111a. The second etching process can be wet etching or dry etching. For example, wet etching uses etching solution such as ferric chloride (FeCl3), copper chloride (CuCl2), or a mixture of sulfuric acid and hydrogen peroxide (H2SO4 / H2O2) to selectively remove the exposed copper foil under controlled temperature, concentration, and time. Dry etching uses plasma etching or reactive ion etching (RIE) to precisely remove the exposed copper foil layer by controlling the type of gas, pressure, power, and etching time. During the etching process, the area covered by the second photoresist layer 300 remains unetched, thereby protecting the non-exposed area of the copper foil layer 111. The second etching depth can be controlled between 3 micrometers (pm) and 5 micrometers (pm) so that after etching, the copper foil layer 111 of the second opening 310 area forms a second recessed portion 111b with a height less than that of the first recessed portion 111a, and the height of the first recessed portion 111a is slightly reduced, so that a stepped structure is formed between the first recessed portion 111a and the second recessed portion 111b. In this embodiment, the etching step is mainly performed using a chemical solution, and the chemical solution etching process usually exhibits isotropic characteristics. Therefore, during the etching process of the second recessed portion 111b, the first recessed portion 111a is also etched, resulting in further deepening of the first recessed portion 111a from the original etching depth. Similarly, after the second etching process is completed, the second photoresist layer 300 is removed, and surface cleaning and drying processes are performed to facilitate subsequent processes.

[0036] In the sixth step S6, please refer to Figure 7A third photoresist layer 400 is attached to the rolled copper foil layer 111 on which the second recessed portion 111b has been formed. The third photoresist layer 400 has a third opening 410, which exposes a portion of the rolled copper foil layer 111, the second recessed portion 111b, and the first recessed portion 111a. The third photoresist layer 400 provides a mask for the third etching. In one embodiment, the third photoresist layer 400 may be made of the same or different type of dry film material as the first two photoresist layers (i.e., the first photoresist layer 200 and the second photoresist layer 300), including positive or negative photoresist, such as epoxy resin-based photoresist (EPON), acrylic photoresist, or polyimide-based photoresist. The selected photoresist material should have good adhesion, corrosion resistance, and resolution to ensure coverage of the non-etched areas and protect the covered rolled copper foil layer 111 and the recessed portion from subsequent etching. In this embodiment, since the third photoresist layer 400 not only protects the non-etched areas but also defines the final circuit pattern of the flexible circuit board, a high-resolution dry film material can be selected to ensure precise control of the etching contour and depth during the third etching process. Specifically, the resolution of the third photoresist layer 400 should be better than or equal to the resolution of the first photoresist layer 200 and the second photoresist layer 300, for example, a pattern resolution of 25 micrometers (μm) or finer, to meet the precise forming requirements of the high-density lines, micro-pitch, and stepped bends 140 of the flexible circuit board. In other words, the third photoresist layer 400 plays a core control role in the entire three-etching process; its high resolution not only determines the distribution accuracy of the stepped structure but also directly affects the overall electrical performance and reliability of the flexible circuit board. By rationally selecting the dry film material and optimizing the exposure and development parameters, it can be ensured that the flexible circuit board still has excellent conductivity and structural strength under multi-angle bending conditions, while accurately forming the final circuit pattern. Similarly, the specific implementation steps are: (1) surface pretreatment, (2) photoresist attachment, and (3) exposure and development, so that the rolled copper foil layer 111, the first recessed portion 111a and the second recessed portion 111b are exposed in the third opening 410, providing precise control for the third etching.

[0037] Step 7, S7, please refer to Figure 8 A third etching process is performed on the rolled copper foil layer 111 exposed in the third opening 410, the second recessed portion 111b, and the first recessed portion 111a to form the third recessed portion 111c and simultaneously reduce the height of the second recessed portion 111b and the first recessed portion 111a. During the etching process, such as Figure 7As shown, the area covered by the third photoresist layer 400 can remain unetched to protect the non-exposed area of the rolled copper foil layer 111, while exposing the first and second recesses 111a, 111b, where the non-exposed area is the area covered by the third photoresist layer 400. After the third etching, the third photoresist layer 400 is removed. The third etching depth can be controlled between 3 micrometers (pm) and 5 micrometers (pm), i.e. the third etching depth is the same as the second etching depth. Since the first and second recesses 111a, 111b are etched simultaneously, the height of the first and second recesses 111a, 111b is also reduced simultaneously, so that the height of the first recess 111a is not less than the height of the second and third recesses 111b, 111c, and thus the local thickness of the rolled copper foil layer 111 gradually increases from the bending center to both ends, to form a one-piece connected stepped bending portion 140. Specifically, as shown Figure 9 The stepped bending portion 140 includes the first recess 111a in the central area, the second recess 111b extending from the first recess 111a to both sides, and the third recess 111c continuing to extend from the second recess 111b to both sides, where the first, second, and third recesses 111a, 111b, 111c are defined by individual areas of the rolled copper foil layer 111, and are actually a one-piece integrated structure. Further, as shown Figure 10As shown, there is a height difference H1 between the first recessed portion 111a and the second recessed portion 111b, a height difference H2 between the second recessed portion 111b and the third recessed portion 111c, and a height difference H3 between the third recessed portion 111c and the upper surface of the rolled copper foil layer 111, so that the first recessed portion 111a, the second recessed portion 111b and the third recessed portion 111c form a stepped overall structure, and no additional dielectric layer or adhesive layer is formed between any recessed portion, so as to ensure that no delamination occurs between any recessed portion to affect the reliability. In an embodiment, the rolled copper foil layer 111 is selected to be a rolled copper foil with a thickness of 35 microns (μm) (i.e., 1 oz), and the stepped bending portion 140 is formed by three selective etching processes with the same etching depth to form three recessed portions (i.e., the first recessed portion 111a, the second recessed portion 111b and the third recessed portion 111c): the height difference H3 of the third recessed portion 111c relative to the upper surface of the rolled copper foil layer 111 is 4 microns (μm); the height difference H2 of the second recessed portion 111b relative to the third recessed portion 111c is 8 microns (μm); and the height difference H1 of the first recessed portion 111a relative to the second recessed portion 111b is 12 microns (μm). Therefore, the stepped height of the three recessed portions of the stepped bending portion 140 decreases step by step from the center to the outside, forming a stress gradient to improve the bending durability. Through the above three etching processes, the integrated stepped bending portion 140 required by the flexible circuit board can be accurately formed, so that the stress distribution of each recessed portion is uniform during the bending process, and the mechanical reliability and conductive performance of the overall structure are improved. In addition, by reasonably selecting the dry film material, high-resolution exposure equipment and optimizing the developing conditions, the line width, pitch and stepped height of the final circuit pattern can meet the design requirements, and the flexible circuit board still has stable electrical performance and structural strength under multi-angle bending and long-term use. That is, the stepped structure of the stepped bending portion 140 can be adjusted according to the line requirements of different applications, according to the selection of copper foils with different thicknesses, and the etching process with different parameters, so as to adjust the height of the recessed portion to control the total thickness of the overall structure.

[0038] It can be understood that in the present application, the specific structure is represented by height, and the process is represented by depth, such as etching depth.

[0039] In the eighth step S8, please refer to Figure 11In the first recess 111a, the elastic buffer layer 120 is filled, so that the thickness of the elastic buffer layer 120 is not less than the height of the first recess 111a. In this embodiment, the elastic buffer layer 120 is filled in the first recess 111a to improve the mechanical buffering performance of the flexible circuit board 100 under bending or stress conditions, and to protect the stepped bending part 140. To ensure the buffering effect, the thickness of the elastic buffer layer 120 should be not less than the height of the first recess 111a, that is, at least covering the first recess 111a to provide continuous and uniform elastic buffering effect, thereby effectively absorbing external force and reducing stress concentration. In a variant, the elastic buffer layer 120 can be further filled in the second recess 111b according to the bending requirements of different use scenarios, while covering the first recess 111a. In this embodiment, the elastic buffer layer 120 can be made of materials with good flexibility, resilience and durability, such as silicone rubber, polyurethane (PU), thermoplastic elastomer (TPE) or polyimide elastomer. The selected material should meet the following requirements: (1) excellent elasticity and resilience: under the action of repeated bending or external force, it can quickly recover to the original shape, ensuring that the stepped bending part 140 is not affected by permanent deformation; (2) good adhesion with copper foil and recess: the filling material should form a tight bond on the surface of the first recess 111a, avoiding separation, bubbles or voids in long-term use; (3) high temperature resistance and chemical stability: adapting to the subsequent processing and use environment of the flexible circuit board, including high temperature reflow soldering, humidity change and other conditions; (4) processability: easy to fill into the first recess 111a by pouring, coating, screen printing or lamination process, and form an elastic buffer layer 120 with uniform thickness.Preferably, the material of the elastic buffer layer 120 should have excellent flexibility, resilience and durability, and meet the following typical performance parameters: (1) the elastic modulus is 0.5 MPa~50 MPa, among which the silicone is preferably 0.5~10 MPa, and the polyurethane or TPE is preferably 5~50 MPa, to ensure both flexibility and support; (2) the Shore A hardness is 20A~90A, preferably in the range of 30A~60A to ensure soft touch, or 70A~90A to enhance support performance; (3) the tensile strength is 2 MPa~20 MPa, to ensure that the buffer layer is not easily broken under repeated bending and external force; (4) the elongation at break is 100%~500%, preferably more than 200%, to provide sufficient ductility and resilience; (5) the compression permanent set is less than 20% (tested at 70℃, 22 hours, 25% compression thickness), to ensure shape and thickness stability after long-term use; (6) the temperature resistance range is -40℃~150℃, preferably -20℃~125℃, which can adapt to the use environment of the flexible circuit board in high and low temperature cycles and reflow soldering process. Therefore, the elastic buffer layer 120 can quickly recover its shape under external force, avoid permanent deformation of the stepped bending part 140 due to stress concentration, and maintain close contact with the copper foil and the surface of the sunken part during long-term use, without separation, bubbles or voids, thereby significantly improving the reliability and durability of the flexible circuit board 100. In the implementation process, the surface of the first sunken part 111a can be pretreated first, such as plasma cleaning or solvent degreasing, to enhance the adhesion of the material; then the elastic buffer material is filled and covered to the first sunken part 111a by injection molding or coating, to ensure thickness coverage and close fit with the stepped bending part 140; finally, solidification or heat treatment (such as silicone or polyurethane curing) is performed to form a stable and continuous elastic structure for the elastic buffer layer 120, to provide mechanical support and buffer protection. Further, as. Figure 12As shown, a honeycomb structure 121 can be formed on the surface of the elastic buffer layer 120 to further enhance the stress dispersion capability and elastic resilience performance of the bending area. In detail, the honeycomb structure 121 can be formed by pressing a mold with a micro honeycomb concave-convex structure before curing the elastic buffer layer 120, or by laser ablation to form a micro-pore array, or by 3D printing or micro-molding technology to embed a honeycomb pattern in the elastic buffer layer 120. That is, the above-mentioned process can be used to locally form the honeycomb structure 121 in the elastic buffer layer 120 without increasing the overall thickness of the structure. By filling the elastic buffer layer 120 in the first sunken part 111a, the local stress concentration of the flexible circuit board under bending, knocking or pressure can be significantly reduced, effectively releasing the stress, and improving the service life and electrical performance stability of the flexible circuit board, providing reliable flexibility support for the entire keyboard or electronic device. Through the design of the honeycomb structure 121, local deformation can be generated when folding or compressing, further dispersing stress concentration. In a variant, as shown in Figure 13 As shown, the rolled copper foil layer 111 has been formed into a predetermined circuit pattern (as shown in the dashed box in the figure), that is, the rolled copper foil layer 111 has been defined as a plurality of circuit regions, each of which is an electrically independent transmission channel. In the step of filling the elastic buffer layer 120, the filling area of the elastic buffer layer 120 is not less than the total area of the first sunken part 111a of each circuit region, to ensure that the elastic buffer layer 120 can completely cover the first sunken part 111a of each circuit region. Finally, according to the predetermined circuit pattern, the rolled copper foil layer 111 and the substrate layer 112 are separated, and the excess part of the elastic buffer layer 120 can be directly cut off.

[0040] Step 9 S9, please refer to Figure 14A protective layer 130 is formed on the copper foil layer 111, covering the first, second and third recesses 111a, 111b and 111c, to obtain the flexible circuit board 100. Specifically, the protective layer 130 covers the stepped bending portion 140, including the first, second and third recesses 111a, 111b and 111c, to provide mechanical protection, insulation and environmental protection, while ensuring the electrical performance stability of the stepped structure during use. In addition, during the coating process of the protective layer 130, the pores formed by the honeycomb structure 121 will be filled, and after the protective layer 130 is solidified, the adhesion between the protective layer 130 and the elastic buffer layer 120 can be further strengthened, avoiding delamination during subsequent bending. Specifically, the stepped bending portion 140 also serves as part of the conductive circuit of the flexible circuit board 100, providing better rigid support and electrical transmission function. The protective layer 130 can be made of epoxy resin, polyimide, acrylic resin or other high-temperature-resistant and flexible polymer materials, and can be formed by spin-coating, doctor blade coating, spray coating or lamination to form a continuous and uniform protective layer 130. In this embodiment, the protective layer 130 is mainly made of polyimide and formed by lamination, so that the thickness of the protective layer 130 can be adjusted according to the design requirements of the flexible circuit board 100, generally between 20 microns (μm) and 50 microns (μm), to ensure that the stepped bending portion 140 is covered while maintaining flexibility. In addition, during the formation of the protective layer 130, the terminal portion 150 is reserved, which is used for electrical connection with external electronic devices, electrical connectors or keyboard key modules. Therefore, the terminal portion 150 is not covered during the formation of the protective layer 130 and remains exposed. Through the above steps, the finally obtained flexible circuit board 100 not only has a stepped bending portion 140 and a high-density circuit, but also has excellent mechanical flexibility, electrical performance stability and environmental protection ability through the combination of the elastic buffer layer 120 and the protective layer 130, and ensures that the terminal portion 150 can reliably dock the keyboard or other electronic components, providing a reliable flexible connection basis for the entire key module or electronic device.

[0041] In this embodiment, the stepped copper foil structure of the flexible circuit board 100 forms multiple levels of sinking portions (a first sinking portion 111a, a second sinking portion 111b, and a third sinking portion 111c) in the bending area, thereby constituting a so-called "stepped bending portion 140". This stepped design can significantly improve the stress distribution of the flexible circuit board 100 during bending, and the main principle is explained as follows:

[0042] (1) Stress dispersion and gradient transition

[0043] In the traditional flat copper foil bending structure, when the flexible circuit board is bent, tensile stress or compressive stress will concentrate on the surface of the copper foil and the substrate, which can easily cause the copper foil to crack, peel off, or the circuit to break. By using a stepped structure, the overall bending area is divided into multiple sinking portions with different heights, and the height difference of each step forms a gradual transition, so that the stress caused by bending is dispersed along the steps, rather than concentrated on a single plane. In this way, the local stress of the copper foil is buffered, reducing the risk of fatigue failure.

[0044] (2) Effectively reducing the local bending radius

[0045] The presence of the stepped bending portion 140 increases the actual bending radius of the copper foil in the bending area, and each level of sinking portion bears part of the bending displacement, thereby reducing the bending amplitude of the copper foil. According to the principle of material mechanics, the larger the bending radius, the lower the tensile stress on the copper foil. Therefore, the stepped structure can significantly reduce the stress concentration of the copper foil during bending while maintaining overall flexibility.

[0046] (3) Buffer layer and stepped structure improve durability

[0047] After filling the elastic buffer layer 120 inside the stepped copper foil structure, the stress generated during bending is further absorbed and dispersed by the elastic material, reducing the mechanical load on the copper foil and the sinking portion. The elastic buffer layer 120 can form an elastic buffer effect between different steps, and the honeycomb structure 121 can provide better compression space, so that the elastic buffer layer 120 can quickly recover to its original state after multiple folding, and the stepped bending portion 140 can still maintain structural integrity and stable electrical performance under repeated folding, bending, or local stress.

[0048] (4) Coordination of steps and line precision

[0049] The height and layout of each sinking portion are precisely designed to ensure that the lines do not stretch or compress excessively in the bending area, and to match the micro-line patterns defined by the high-resolution third photoresist layer 400. In this way, even in the area of the stepped bending portion 140, the micro-line can still reliably transmit current, preventing the occurrence of broken lines or short circuits.

[0050] In summary, the stepped bending portion 140 effectively solves the problem of copper foil fatigue, cracking or disconnection in the bending area of the traditional flexible circuit board by means of "stress dispersion, buffer absorption, and bending radius optimization", thereby improving the mechanical durability, foldability and service life of the flexible circuit board.

[0051] Referring to Figure 14 The present application also provides a flexible circuit board 100, mainly comprising: a rolled copper foil substrate 110, a stepped bending portion 140, an elastic buffer layer 120, and a protective layer 130. The rolled copper foil substrate 110 is composed of a rolled copper foil layer 111 and a flexible substrate layer 112 formed on one side thereof, wherein the thickness of the rolled copper foil layer 111 can be controlled between 17.5 microns (μm) and 35 microns (μm), and the substrate layer 112 can be made of flexible polymer materials such as polyimide (PI) and polyester (PET), with a thickness of about 12.7 microns (μm) to 25.4 microns (μm) to ensure overall flexibility and multi-angle bending reliability. In detail, the rolled copper foil layer 111 forms a multi-level sinking structure along the bending area, including a first sinking portion 111a, a second sinking portion 111b and a third sinking portion 111c, which constitute an integrated stepped bending portion 140, wherein the height of the first sinking portion 111a is not less than the sum of the heights of the second sinking portion 111b and the third sinking portion 111c. The stepped bending portion 140 is formed by multiple photoetching and etching: the first photoresist layer 200 and the first etching form the first sinking portion 111a, the second photoresist layer 300 and the second etching form the second sinking portion 111b, the third photoresist layer 400 and the third etching form the third sinking portion 111c, and at the same time define the final circuit pattern of the flexible circuit board 100. The third photoresist layer 400 uses high-resolution dry film material, which can achieve a resolution of 25 microns (μm) or finer, to ensure accurate profile of the stepped structure, controllable etching depth, and meet the requirements of high-density circuits and micro-pitch.

[0052] To absorb local stress during bending, the first sinking portion 111a is filled with the elastic buffer layer 120, which has a thickness not less than the height of the first sinking portion 111a, and the material can be selected from silicone, polyurethane (PU), thermoplastic elastomer (TPE) or polyimide elastic film (PIE) to improve the reliability of repeated bending and multi-angle use. The combination of the stepped bending portion 140 and the elastic buffer layer 120 can effectively disperse the stress in the bending area, avoid copper foil cracking or circuit disconnection, and keep the flexible circuit board 100 stable in long-term electrical performance during repeated bending, pressing and magnetic folding. In addition, a honeycomb structure 121 can be formed on the surface of the elastic buffer layer 120 to further enhance the stress dispersion ability and elastic rebound performance of the bending area.

[0053] The protective layer 130 covering the stepped bending portion 140 is used to protect the copper foil and the sinking portion from mechanical wear, chemical corrosion or optical leakage. The material can be selected from wear-resistant, high-chemical corrosion-resistant or light-tight polymer materials, such as polyimide, polycarbonate or epoxy resin. The thickness of the protective layer 130 is controlled according to the bending requirements, taking into account the flexibility and protection performance, while ensuring the integrity of the circuit. The protective layer 130 is filled in the pores formed by the honeycomb structure 121, further strengthening the bonding relationship between the protective layer 130 and the elastic buffer layer 120, and reducing the delamination or peeling phenomenon of different materials at the joint during future use. In this embodiment, the flexible circuit board 100 is provided with a terminal portion 150 for electrical connection with the keyboard driving circuit or external interface. The terminal portion 150 is not covered by the protective layer 130 to ensure reliable electrical contact. Further, as shown in Figure 15 The terminal surface can be plated with a surface treatment layer 160, which mainly includes improving the conductivity, enhancing the wear resistance, oxidation resistance and improving the welding reliability. Specifically, the surface treatment layer 160 can be one or more of the following: (1) gold plating layer (Au): suitable for high reliability and high frequency signal transmission scenarios; (2) tin plating layer (Sn) or tin / lead alloy layer (Sn / Pb): suitable for mass production of keyboards and electronic component assembly; (3) nickel / gold composite plating layer (Ni / Au): first plating nickel layer, then gold layer on the nickel layer, which can realize wear resistance, corrosion resistance and good conductivity at the same time, while reducing the cost of gold layer; (4) electroless nickel (EN) or electroless nickel / palladium / gold (EN / Pd / Au): formed by chemical deposition, suitable for complex shapes; (5) organic protective film (Organic Solderability Preservative, OSP): an organic protective film is formed on the surface, which can prevent oxidation, and at the same time, it can be easily removed by solder during subsequent welding process, suitable for short-term storage and welding processing. In practical applications, the thickness of the surface treatment layer 160 can be controlled between 0.05 microns (μm) and 5 microns (μm), depending on the selected material, board thickness and application requirements. By setting the surface treatment layer 160, the terminal portion 150 can still maintain low contact resistance and reliable connection during long-term folding, magnetic attraction operation and high frequency signal transmission, while cooperating with the protective layer 130 and the stepped bending portion 140, further improving the overall reliability and service life of the flexible circuit board 100.

[0054] In the folded state, the stepped bending portion 140 of the flexible circuit board 100 allows multi-angle bending along the bending center without excessive stress on the circuit formed by the rolled copper foil layer 111. Specifically, the stepped bending portion 140 formed by the first sunken portion 111a, the second sunken portion 111b, and the third sunken portion 111c gradually disperses stress from the inside to the outside when folded:

[0055] (1) The first sunken portion 111a is located at the innermost side of the bending center and usually bears higher bending stress. When folded, it is assisted by the filled elastic buffer layer 120 to bear the main bending stress, absorbs the stress generated by folding through elastic deformation, ensures that the first sunken portion 111a and the circuit part formed thereby do not crack or even directly break due to large deformation.

[0056] (2) The second sunken portion 111b is slightly higher than the first sunken portion 111a in stepped distribution (thicker circuit), and is located outside the first sunken portion 111a. Due to the design of the stepped height difference, the circuit formed by the first sunken portion 111a and the second sunken portion 111b does not directly press to form local stress concentration when folded, thereby maintaining the integrity of the circuit structure.

[0057] (3) The third sunken portion 111c is located at the outermost side of the bending center (thicker circuit) and usually bears lower bending stress. It has the smallest height difference relative to the second sunken portion 111b, further buffering the bending stress. That is, each stepped structure between the sunken portions further shares the bending stress when folded.

[0058] (4) The protective layer 130 covers the upper surfaces of the first sunken portion 111a, the second sunken portion 111b, and the third sunken portion 111c. It protects the internal circuit during folding and maintains the overall shape of the flexible circuit board 100, avoiding local excessive stretching or wrinkling.

[0059] (5) The design of the local thickness of the rolled copper foil layer 111 gradually increasing from the bending center to both ends makes the circuit in the folding center area relatively thin, reduces the bending stiffness, thereby achieving a gentle distribution of stress gradient during folding, effectively reducing the risk of open circuit.

[0060] (6) In the folded state, the terminal portion 150 serves as a port for electrically connecting different components or devices of the flexible circuit board 100. The surface treatment layer 160 can provide additional wear resistance and corrosion resistance protection while ensuring reliable contact in the folded state.

[0061] In summary, the stepped bending part 140 combines the elastic buffer layer 120 and the protective layer 130 to form a structure with step-by-step layering from inside to outside, uniform stress distribution and reliable conduction in the folded state, thereby realizing high reliability of the flexible circuit board 100 under conditions of multi-angle bending, magnetic attraction disassembly and long-term use.

[0062] In a variant, in the line design of the stepped bending part 140, the line can be designed as a broken line, a wavy line or an S-shaped line along the bending direction, and the line thickness gradually increases from the center to both ends to improve the tensile strength of the bending center and disperse stress. Through the above structure and process, the embodiment can realize thinning, multi-angle bending, stepped stress dispersion and high-density line layout, and balance the folding flexibility and long-term reliability of the keyboard, thereby providing a reliable flexible circuit board 100 solution for the magnetic attraction keyboard and other flexible electronic devices.

[0063] In an embodiment, the application also provides a multi-angle magnetic keyboard, which comprises the flexible circuit board 100 suitable for the multi-angle magnetic keyboard, and the flexible circuit board 100 is used to electrically connect the key module and the power supply module of the keyboard to realize the transmission of the key operation signal and the power supply. In particular, considering the long endurance requirement of the magnetic keyboard, the power supply module of the conventional magnetic keyboard is usually arranged inside the keyboard body or directly shares the battery power supply of the tablet device. Regardless of the way, the available capacity of the battery is limited, so it is difficult to further prolong the endurance time. In view of this problem, the application selects a thicker calendered copper foil layer 111 and a stepped bending part 140 structure in the design of the flexible circuit board 100, so that the flexible circuit board 100 not only has excellent flexibility and bending resistance, but also can further make full use of the shell structure of the magnetic keyboard, so that the flexible circuit board 100 forms an electrical path and is electrically connected with the power supply module arranged in the shell part. That is to say, the power supply module of the multi-angle magnetic keyboard of the application is not only arranged in the keyboard body, but also includes the power supply module arranged in the shell part (which can be expanded), and the flexible circuit board 100 is used to electrically connect all the power supply modules. Specifically, since the thick copper line can carry more current, the external or modular power supply can be directly connected with the keyboard key module and the power supply module through the flexible circuit board 100, thereby realizing effective power distribution and long endurance support. At the same time, the stepped bending part 140 combined with the filled elastic buffer layer 120 ensures that the multi-angle magnetic keyboard with the flexible circuit board 100 does not have a conductive circuit break or structural damage during multi-angle folding, magnetic attraction and disassembly. Through the above design, the multi-angle magnetic keyboard of the application can maintain the characteristics of lightness, thinness and portability while considering the high reliability of electrical connection and the endurance requirement of long-term use, and provides users with stable and lasting use experience. In addition, the cooperative design of the flexible circuit board 100, the magnetic keyboard shell and the expanded power supply module can be flexibly arranged according to different application requirements. For example: by adjusting the width of the thick copper line, the height of the stepped bending part and the terminal arrangement, the customized power supply expansion for keyboard shells of different sizes or shapes can be realized, and a more efficient energy management scheme is provided for the magnetic keyboard in the scene of sharing power supply with tablets or other electronic devices.

[0064] At present, there are mainly two designs of magnetic keyboard: (1) the keyboard itself has a battery, (2) shares the battery with a tablet or an external device, and the shell of the magnetic keyboard is only used to fix the tablet and establish support by bending between the shell and the keyboard part (while the angle can be changed). The application mainly uses the shell as a setting area for expanding the battery capacity, so the flexible circuit board is needed to connect the keyboard body and the shell, and the flexible circuit board needs to provide electrical connection and solve the bending problem during long-term use.

[0065] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit them; although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method for manufacturing a circuit board suitable for multi-angle magnetic keyboards, characterized in that, include: A rolled copper foil substrate is provided, the rolled copper foil substrate including a rolled copper foil layer and a substrate layer formed on one side of the rolled copper foil layer; A first photoresist layer is attached to the rolled copper foil layer, the first photoresist layer having a first opening, the first opening exposing a portion of the rolled copper foil layer; A first etching is performed on the rolled copper foil layer exposed in the first opening to form a first recess, and the first photoresist layer is removed; A second photoresist layer is attached to the rolled copper foil layer on which the first sinking portion has been formed. The second photoresist layer has a second opening, and the second opening exposes a portion of the rolled copper foil layer and the first sinking portion. A second etching is performed on the rolled copper foil layer exposed in the second opening and the first recessed portion to form the second recessed portion and reduce the height of the first recessed portion, and the second photoresist layer is removed. A third photoresist layer is attached to the rolled copper foil layer on which the second sinking portion has been formed. The third photoresist layer has a third opening, and the third opening exposes a portion of the rolled copper foil layer, the second sinking portion and the first sinking portion. A third etching is performed on the rolled copper foil layer exposed in the third opening, the second recessed portion and the first recessed portion to form the third recessed portion and simultaneously reduce the height of the second recessed portion and the first recessed portion, and the third photoresist layer is removed. An elastic buffer layer is filled within the first sunken portion, such that the thickness of the elastic buffer layer is not less than the height of the first sunken portion; and... A protective layer is formed on the rolled copper foil layer, the protective layer covering the first recessed portion, the second recessed portion and the third recessed portion, to obtain a flexible circuit board; The height of the first sinking portion is not less than the sum of the heights of the second sinking portion and the third sinking portion, so that the local thickness of the rolled copper foil layer gradually increases from the bending center to both ends, thereby forming an integrally connected stepped bending portion.

2. The circuit board manufacturing method for a multi-angle magnetic keyboard as described in claim 1, characterized in that, The thickness of the rolled copper foil layer is 0.5 to 1 ounce; and / or, The substrate layer is made of polyimide film or polyethylene terephthalate film, and the thickness of the substrate layer is 0.5~1 mil.

3. The method for manufacturing a circuit board suitable for a multi-angle magnetic keyboard as described in claim 1, characterized in that, The elastic buffer layer is made of silicone, polyurethane, thermoplastic elastomer, or polyimide elastic film; and / or, Prior to the step of forming the protective layer, a honeycomb structure is formed on the surface of the elastic buffer layer.

4. The circuit board manufacturing method for a multi-angle magnetic keyboard as described in claim 1, characterized in that, In the step of forming the protective layer, the terminal portion of the flexible circuit board is exposed while the protective layer is being formed, so that the terminal portion is not covered by the protective layer.

5. A flexible circuit board suitable for multi-angle magnetic keyboards, characterized in that, The flexible circuit board is manufactured using the circuit board manufacturing method for multi-angle magnetic keyboards as described in any one of claims 1-4, comprising: A rolled copper foil substrate, the rolled copper foil substrate comprising a rolled copper foil layer and a substrate layer formed on one side of the rolled copper foil layer; The rolled copper foil layer has a first sunken portion, a second sunken portion and a third sunken portion. The height of the first sunken portion is not less than the sum of the heights of the second sunken portion and the third sunken portion. The first sunken portion, the second sunken portion and the third sunken portion constitute an integrally connected stepped bending portion. An elastic buffer layer, wherein the elastic buffer layer is filled within the first recessed portion, and the thickness of the elastic buffer layer is not less than the height of the first recessed portion; and, A protective layer covering the first sunken portion, the second sunken portion, and the third sunken portion; The local thickness of the rolled copper foil layer gradually increases from the bending center to both ends.

6. The flexible circuit board for a multi-angle magnetic keyboard as described in claim 5, characterized in that, The flexible circuit board also includes a terminal portion that is not covered by the protective layer.

7. The flexible circuit board for a multi-angle magnetic keyboard as described in claim 6, characterized in that, A surface treatment layer is plated onto the surface of the terminal portion.

8. The flexible circuit board for a multi-angle magnetic keyboard as described in claim 5, characterized in that, The wiring of the stepped bend section is wavy or S-shaped along the bend direction.

9. The flexible circuit board for a multi-angle magnetic keyboard as described in claim 5, characterized in that, The surface of the elastic buffer layer has a honeycomb structure.

10. A multi-angle magnetic keyboard, characterized in that, It includes a key module, a power module, and a flexible circuit board for a multi-angle magnetic keyboard as described in any one of claims 5-9, wherein the flexible circuit board for the multi-angle magnetic keyboard is used to electrically connect the key module and the power module.

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