A double-layered flexible printed circuit board and a processing method thereof

Abstract

This invention discloses a double-layer bend-resistant flexible circuit board and its processing method, comprising: a core layer, wherein circuit layers are laid on both the upper and lower surfaces of the core layer. This invention has the following beneficial effects: functional layering and electromagnetic shielding are achieved through conductive patterns on the two circuit layers. The conductive patterns on the top circuit layer are arranged in a ring, serving as a complete grounding / shielding layer. Together with the four rings of conductive patterns at the bottom, they form an upper shielding and lower signal architecture, providing a stable reference plane and Faraday cage shielding for internal high-speed signals. This greatly suppresses signal crosstalk and external electromagnetic interference. Furthermore, through stress holes and protrusions, the openings form a controllable low-stiffness zone on the bending axis, actively guiding the uniform release of bending stress at this point. This protects fragile vias and delicate conductive pattern traces from fatigue fracture. Moreover, the protrusions wrapping around the conductive patterns can generate additional deformation space and buffer, dispersing the stress acting on the conductive patterns.

Description

Technical Field

[0001] This invention relates to the field of flexible circuit boards, and more particularly to a double-layer bend-resistant flexible circuit board and its processing method. Background Technology

[0002] With the continuous advancement of technology, electronic products such as mobile phones and laptops are gradually moving towards bent screens and rollable screens. As a key component in electronic products that carries signal transmission and current transmission, flexible circuit boards face increasingly stringent requirements for their functionality, stability, and bending lifespan. How to shield the power lines from the noise generated by the signal lines while meeting the requirements of dynamic bending has become a challenge. Therefore, a double-layer bend-resistant flexible circuit board and its processing method are needed to solve the above problems. Summary of the Invention

[0003] The purpose of this invention is to provide a double-layer bend-resistant flexible circuit board and its processing method, which solves the problem that flexible circuit boards are prone to fatigue and damage when bent.

[0004] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a double-layer bend-resistant flexible circuit board, comprising: The core layer has circuit layers laid on both its upper and lower surfaces, and a protective layer laid on the circuit layers. Multiple conductive patterns are arranged on the circuit layers, and the outer surfaces of the conductive patterns are attached to the protective layer. The protective layer has protrusions at the positions of the conductive patterns, and a portion of the conductive patterns is located within the protrusions. Multiple stress holes are formed on the core layer.

[0005] Furthermore, the circuit layer above the core layer is configured as a first circuit layer, the circuit layer below the core layer is configured as a second circuit layer, the protective layer laid on the first circuit layer is configured as a first protective layer, and the protective layer laid on the second circuit layer is configured as a second protective layer.

[0006] Furthermore, the conductive pattern on the first circuit layer is set as a first conductive pattern, and the number of the first conductive patterns is set to multiple, with the multiple first conductive patterns arranged in parallel and the spacing between the multiple first conductive patterns being equal.

[0007] Furthermore, the first conductive pattern is configured as a single conductive loop.

[0008] Furthermore, the conductive pattern on the second circuit layer is configured as a second conductive pattern, and the number of the second conductive patterns is configured as multiple, with the multiple second conductive patterns arranged in parallel and the spacing between the multiple second conductive patterns being equal.

[0009] Furthermore, the second conductive pattern is configured as a whole as four conductive loops, with the four conductive loops being concentrically nested in sequence.

[0010] Furthermore, the protrusion on the first protective layer is configured as a first protrusion, and the protrusion on the second protective layer is configured as a second protrusion. Both the first protrusion and the second protrusion have a semi-groove inside, and the semi-groove of the first protrusion and the second protrusion are respectively adapted to the first conductive pattern and the second conductive pattern.

[0011] Furthermore, vias and connection holes are vertically formed on the first protective layer, the first circuit layer, the core layer, the second circuit layer, and the second protective layer. The multiple vias are interconnected, and the first conductive pattern and the second conductive pattern are electrically connected through the vias. The multiple connection holes are interconnected.

[0012] Furthermore, the size of the plurality of stress holes is set to two types, one of which has a diameter of 0.30 mm and the other has a diameter of 0.50 mm. The four sides of the stress holes are set to an inner arc structure with themselves as the center, and the four corners of the stress holes are set to an outer arc structure with themselves as the center.

[0013] Secondly, the present invention also proposes a method for processing a double-layer bend-resistant flexible circuit board, used to process a double-layer bend-resistant flexible circuit board as described in any of the above-mentioned schemes, comprising the following steps: S1. The core layer is provided with a flexible insulating material, and copper foil is laminated on its upper and lower surfaces to form the initial circuit layer structure; S2. Pattern etching is performed on the copper foil on both the top and bottom surfaces to form the circuit layer and the plurality of conductive patterns thereon; S3. Prepare two protective layer materials, one upper and one lower, and pre-form the protrusion on each protective layer corresponding to the area of ​​the conductive pattern to be protected. Then, align and press the two protective layers onto the upper and lower surfaces of the core layer, so that the conductive pattern is covered by the corresponding protective layer and part of its structure is embedded in the protrusion. S4. At a predetermined location in the core layer, the stress hole is formed through the core layer.

[0014] Furthermore, it also includes the step: S5. When it is necessary to realize the electrical connection between the upper and lower circuit layers, through holes are processed at the designated locations and the holes are metallized.

[0015] Compared with the prior art, the present invention has the following beneficial effects: Functional layering and electromagnetic shielding are achieved through conductive patterns on two circuit layers. The conductive patterns on the top circuit layer are arranged in a ring, serving as a complete grounding / shielding layer. Together with the four rings of conductive patterns at the bottom, they form an architecture of upper shielding and lower signal, providing a stable reference plane and Faraday cage shielding for internal high-speed signals. This greatly suppresses signal crosstalk and external electromagnetic interference. Furthermore, through stress holes and protrusions, the openings form a controllable low-stiffness zone on the bending axis, actively guiding the uniform release of bending stress at this point. This protects fragile vias and delicate conductive pattern traces from fatigue fracture. The protrusions wrapping around the conductive patterns provide additional deformation space and buffering, dispersing the stress acting on the conductive patterns and preventing fatigue fracture due to repeated bending. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] The structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0018] Figure 1 This is a schematic diagram of the first partial structure of the flexible circuit board. Figure 2 This is a schematic diagram of the second partial structure of the flexible circuit board; Figure 3 This is a schematic diagram of the third partial structure of the flexible circuit board; Figure 4 This is a schematic cross-sectional view of the overall structure of the flexible circuit board. Figure 5 This is a schematic diagram of the flexible circuit board manufacturing process.

[0019] Illustration: 1. First protective layer; 11. First protrusion; 2. First circuit layer; 21. First conductive pattern; 3. Core layer; 31. Stress hole; 4. Second circuit layer; 41. Second conductive pattern; 5. Second protective layer; 51. Second protrusion; 6. Through hole; 7. Connecting hole. Detailed Implementation

[0020] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In the description of this invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component positioned centrally in the connection.

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0023] This invention provides a double-layer bend-resistant flexible circuit board. Please refer to [link / reference]. Figures 1-4 It includes: a core layer 3, with circuit layers laid on both the top and bottom surfaces of the core layer 3, and a protective layer laid on the circuit layers. Multiple conductive patterns are arranged on the circuit layers, with the outer surface of the conductive patterns attached to the protective layer. The protective layer has protrusions at the positions of the conductive patterns, and part of the conductive patterns are located inside the protrusions. Multiple stress holes 31 are opened on the core layer 3.

[0024] like Figures 1-4 As shown, the core layer 3 is the flexible substrate of the circuit board, usually made of materials such as polyimide. Its function is to serve as the mechanical support and electrical insulation body of the overall structure. It provides the physical basis for the circuit to be repeatedly bent, and its material properties directly determine the most basic temperature resistance and bending life of the circuit board.

[0025] With circuit layers laid on both the top and bottom, this structure frees the circuit board from the limitation of single-sided wiring, allowing for higher wiring density and more complex circuit functions in a compact space. Its beneficial effect is that it creates the necessary conditions for the subsequent realization of functional partitioning with "one layer responsible for electrical shielding and one layer responsible for signal transmission", which is a physical prerequisite for improving circuit integration and electrical performance.

[0026] The protective layer is usually a covering film, and its basic function is to provide environmental protection such as insulation, moisture protection, and pollution protection. Its presence ensures the long-term working stability of conductive patterns and avoids short circuits or corrosion caused by environmental factors. It is the "basic protective clothing" for the reliable operation of the entire circuit.

[0027] The protrusions form a locally thickened area, providing direct physical protection for the delicate and fragile conductive patterns, resisting external scratches and pressure damage. When bending occurs, the three-dimensional structure of the protrusions can undergo elastic deformation, providing additional deformation space for the conductive patterns embedded within, thereby absorbing and dispersing the stress concentrated on the metal wires. This fundamentally changes the stress action mode, transforming the concentrated stress that easily leads to metal fatigue into dispersed stress that can be buffered by polymer materials, thus significantly extending the service life of the circuit under dynamic bending.

[0028] Stress holes 31 create regular weak points in the non-electrical functional area of ​​the core layer 3 of the circuit board. The lines connecting these points form a preset, low-stiffness "bending guide line". When the circuit board bends, the deformation will preferentially and concentratedly occur on this preset axis. This allows the destructive bending stress to be actively "attracted" and confined to a safe, non-circuitous area for release. This precisely protects the critical electrical structures around the stress holes 31 (such as wires, pads and vias 6) from fatigue stress damage, thus achieving a shift from passively "enduring" bending to actively "resisting" bending fracture.

[0029] Specific process: When the double-layer flexible circuit board is subjected to external bending force, the array of stress holes 31 on the core layer 3 takes effect first. Due to the presence of these holes, the stiffness of the board is lowest at this axis. Therefore, the bending deformation is precisely guided and limited within this "safe bending zone". Most of the energy is consumed here through the deformation of the material. The micro-stress and strain that cannot be completely eliminated and are transmitted to the circuit area are effectively borne by the protrusions on the protective layer. The protrusions provide a buffer zone for the conductive pattern inside through their own compression or stretching elastic deformation, converting the direct metal deformation into the deformation of the polymer material, thereby avoiding the plastic deformation or breakage of the conductive pattern.

[0030] Please see Figure 4 The circuit layer above the core layer 3 is designated as the first circuit layer 2, the circuit layer below the core layer 3 is designated as the second circuit layer 4, the protective layer laid on the first circuit layer 2 is designated as the first protective layer 1, and the protective layer laid on the second circuit layer 4 is designated as the second protective layer 5.

[0031] like Figure 4As shown, the first circuit layer 2 is located above the core layer 3 and is one of the important parts of the circuit board to realize specific functions. It carries specific circuit designs and can be used to transmit specific electrical signals, such as as a signal input layer or a specific functional circuit layer. It works together with the second circuit layer 4 below to complete complex circuit functions. The second circuit layer 4 is located below the core layer 3 and works in conjunction with the first circuit layer 2. It can be used as a signal output layer, a power supply layer, or a circuit layer that complements the function of the first circuit layer 2 to realize the transmission and processing of different signals and jointly build a complete circuit system.

[0032] The first protective layer 1 directly covers the first circuit layer 2, mainly serving to protect the first circuit layer 2 and its conductive patterns. It can prevent the first circuit layer 2 from being corroded by the external environment, such as oxidation, moisture, and chemical corrosion, and can also resist a certain degree of mechanical damage, such as scratches and collisions. Similar to the first protective layer 1, the second protective layer 5 covers the second circuit layer 4, providing a protective barrier for the formation of the second circuit layer 4 and its conductive patterns, preventing the second circuit layer 4 from being adversely affected by the external environment, and ensuring the normal operation of the second circuit layer 4.

[0033] Please see Figures 1-4 The conductive pattern on the first circuit layer 2 is set as a first conductive pattern 21. The number of first conductive patterns 21 is set to multiple. The multiple first conductive patterns 21 are arranged in parallel and the spacing between the multiple first conductive patterns 21 is equal. The first conductive pattern 21 as a whole is set as a conductive loop. The conductive pattern on the second circuit layer 4 is set as a second conductive pattern 41. The number of second conductive patterns 41 is set to multiple. The multiple second conductive patterns 41 are arranged in parallel and the spacing between the multiple second conductive patterns 41 is equal. The second conductive pattern 41 as a whole is set as four conductive loops. The four conductive loops are concentrically nested.

[0034] like Figures 1-4 As shown, multiple first conductive patterns 21 are arranged in a flush configuration with equal spacing, which helps to achieve uniform signal transmission or distribution. In the circuit, different first conductive patterns 21 can serve different signal paths or functional modules. The flush configuration and equal spacing ensure that the signal has relatively consistent electrical characteristics during transmission, reducing signal interference and attenuation caused by uneven layout. The first conductive pattern 21 is set as a conductive loop, which mainly serves the functions of electromagnetic shielding and grounding. In electronic circuits, electromagnetic interference is a common problem. A conductive loop can form a Faraday cage effect, effectively shielding the external electromagnetic field from interfering with the internal circuit. At the same time, it can also limit the electromagnetic radiation generated by the internal circuit to the inside of the loop, reducing interference to external devices. In addition, as a grounding layer, it can provide a stable reference potential for the circuit, ensuring the normal operation of the circuit.

[0035] Similar to the first circuit layer 2, multiple second conductive patterns 41 are arranged side-by-side with equal spacing to achieve uniform signal transmission and rational layout of functional modules on the second circuit layer 4. Different second conductive patterns 41 can undertake different signal processing or transmission tasks. The design of four concentric conductive loops further enhances the electromagnetic shielding effect. Different loops can shield electromagnetic interference in different frequency ranges, forming a multi-layered electromagnetic protection system. At the same time, this structure can also realize more complex signal processing and transmission functions, such as enabling layered transmission and isolation of different signals, reducing crosstalk between signals. The concentric multi-loop layout allows for parallel transmission of multiple signals in a compact space, and the equal spacing between each loop can optimize and maintain the consistency of the characteristic impedance of each channel, reducing signal crosstalk between adjacent channels.

[0036] To achieve functional layering and electromagnetic shielding, the "one-ring" pattern typically serves as a complete grounding / shielding layer, forming an "upper shield, lower signal" architecture with the bottom "four-ring" signal layer. This provides a stable reference plane and Faraday cage shielding for internal high-speed signals, greatly suppressing signal crosstalk and external electromagnetic interference.

[0037] Please continue reading. Figures 1-4 The protrusion on the first protective layer 1 is configured as a first protrusion 11, and the protrusion on the second protective layer 5 is configured as a second protrusion 51. Both the first protrusion 11 and the second protrusion 51 have a semi-groove inside. The semi-grooves of the first protrusion 11 and the second protrusion 51 are respectively adapted to the first conductive pattern 21 and the second conductive pattern 41.

[0038] like Figures 1-4 As shown, since the first conductive pattern 21 (one-loop circuit) and the second conductive pattern 41 (four-loop concentric circuit) have different shapes, functions and vulnerabilities, the protection strategies required for them should also be different. This naming allows the first protrusion 11 and the second protrusion 51 to be designed independently in terms of size, shape and layout to achieve the best protection effect. The first protrusion 11 may be designed as a continuous strip to fit the ring circuit, while the second protrusion 51 may be designed as an array of four independent protrusions to fit the four-loop circuit.

[0039] The presence of the semi-groove allows the groove wall to undergo elastic deformation when the protrusion is subjected to compression perpendicular to the circuit board direction or tension parallel to the circuit board direction. This provides valuable displacement margin for the embedded conductive pattern, which is like a miniature "shock absorber". It transforms the concentrated stress acting on the conductive pattern into dispersed deformation of the protective layer, thereby absorbing and dissipating energy.

[0040] Furthermore, the outer surface of the conductive pattern and the inner surface of the semi-groove achieve a large-area, tight fit. This allows stress to be evenly and smoothly transferred from the conductive pattern to the entire protruding structure when the circuit board is bent, enabling the latter to fully exert its buffering capacity and avoiding local stress concentration points caused by shape mismatch. The matching groove forms a three-dimensional wrapping and constraint on the conductive pattern, which not only provides buffering but also restricts the conductive pattern from micro-movement, misalignment, or warping within the groove, further enhancing mechanical stability.

[0041] Please see Figures 1-3 Through holes 6 and connecting holes 7 are vertically formed on the first protective layer 1, the first circuit layer 2, the core layer 3, the second circuit layer 4, and the second protective layer 5. Multiple through holes 6 are interconnected. The first conductive pattern 21 and the second conductive pattern 41 are electrically connected through the through holes 6, and multiple connecting holes 7 are interconnected.

[0042] like Figures 1-3 As shown, via 6 is a key structure used to realize electrical connections between different circuit layers. In a double-layer flexible circuit board, the first circuit layer 2 and the second circuit layer 4 are located on the upper and lower sides of the core layer 3, respectively. Through the vertically opened via 6, current or signals can be smoothly transmitted between different layers, thereby realizing complex circuit functions.

[0043] Connection hole 7 provides a physical interface for connecting the circuit board to other external components or modules. Through connection hole 7, the circuit board can be reliably connected to other devices using solder, pins, etc., which facilitates the assembly and integration of the circuit board and improves the scalability and maintainability of the entire electronic system.

[0044] Multiple vias 6 are interconnected to form an electrical path network, which can increase the selection of current or signal transmission paths and improve the reliability and stability of the circuit. The first conductive pattern 21 and the second conductive pattern 41 are located on different circuit layers, each undertaking different circuit functions. Electrical connection through vias 6 can integrate and coordinate the functions on the two circuit layers. For example, the first conductive pattern 21 can serve as a ground or shielding layer, and the second conductive pattern 41 can serve as a signal transmission layer. After being connected through vias 6, a stable reference plane and effective shielding protection can be provided for the signal. In addition, vias 6 make the shielding layers of the "one-ring" conductive patterns on the upper and lower surfaces equipotential, eliminate resonance points, form a complete shielding cavity, and provide the shortest, low-impedance return path for the signal of the "four-ring" conductive pattern, reducing the signal loop area and radiation.

[0045] Multiple interconnected connection holes 7 can form a unified connection interface area. When connecting with other external components, this design can provide more connection points and more flexible connection methods, making it convenient to wire and connect according to actual needs.

[0046] Please see Figure 3 The size of the multiple stress holes 31 is set to two types. One type of stress hole 31 has a diameter of 0.30 mm, and the other type of stress hole 31 has a diameter of 0.50 mm. The four sides of the two types of stress holes 31 are set to an inner arc structure with themselves as the center, and the four corners of the stress holes 31 are set to an outer arc structure with themselves as the center.

[0047] like Figure 3 As shown, the stress concentration at different locations on the bending axis may vary. By setting two apertures, a region with a gradient change in stiffness along the bending axis can be formed on the core layer 3. The harder and softer regions can be alternated or arranged as needed, which can guide the stress distribution more precisely and prevent the stress from being excessively concentrated in a region with a single aperture.

[0048] Small-diameter (0.30mm) holes can serve as secondary stress guides or support points, while large-diameter (0.50mm) holes serve as primary, deformation-concentrated "hinges." This combination can more smoothly transmit and dissipate bending energy, avoid discontinuities or "folding" phenomena in macroscopic deformation, and make bending smoother and more controllable.

[0049] The two aperture designs provide flexibility to accommodate different bending radii or application scenarios. In areas where a smaller bending radius is required, more 0.50mm large holes can be arranged; in areas where a certain level of support strength is required, 0.30mm small holes are the main type.

[0050] The four corners of the stress hole 31 are free of sharp right angles to prevent stress concentration and tearing. Any sharp right angle is a natural source of stress concentration and is very likely to cause microcracks to propagate under cyclic loading. By designing the four sides as inner arcs, these dangerous sharp right angles are completely eliminated. When bending stress is transmitted to the edge of the hole, the arc edge can distribute and transmit stress more smoothly, which greatly reduces the risk of initial tearing at the edge of the hole. In addition, the inner arc edge is longer than the straight line, which provides a small, extra space for the material to stretch when bent, allowing the hole shape to change more gently and further absorb energy.

[0051] This invention provides a double-layer bend-resistant flexible circuit board for fabricating such a board. (See also: [link to relevant documentation]). Figures 1-4 This includes the following steps: S1. A core layer 3 made of flexible insulating material is provided, and copper foil is laminated on its upper and lower surfaces to form an initial circuit layer structure; S2. Pattern etching is performed on the copper foil on both the top and bottom sides to form a circuit layer and multiple conductive patterns on it; S3. Prepare two protective layer materials, and pre-form protrusions on each protective layer corresponding to the area of ​​the conductive pattern to be protected. Then align and press the two protective layers onto the upper and lower surfaces of the core layer 3, so that the conductive pattern is covered by the corresponding protective layer and part of its structure is embedded in the protrusion. S4. At a predetermined position in the core layer 3, a through stress hole 31 is formed; S5. When electrical connections between upper and lower circuit layers are required, through holes are machined at designated locations and the holes are metallized.

[0052] like Figures 1-4 As shown, in step S3, the protrusion is pre-formed on the protective layer by means of hot pressing with a mold, curing after photoresist molding, or precision printing.

[0053] In step S4, the process for processing the stress hole 31 is laser cutting, mechanical drilling or precision die punching, and the shape of the stress hole 31 is one or more combinations of circular, elliptical or elongated shapes.

[0054] In step S3, before pressing the protective layer, an adhesive is applied to the surface of the protective layer or circuit layer.

[0055] Between steps S2 and S3, there is also a step of performing anti-oxidation or surface roughening treatment on the etched conductive pattern surface.

[0056] In step S5, the hole metallization process includes chemical copper plating and electroplating.

[0057] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A double-layer, bend-resistant flexible circuit board, characterized in that, include: The core layer (3) has circuit layers laid on both the top and bottom surfaces, and a protective layer laid on the circuit layers. Multiple conductive patterns are arranged on the circuit layers. The outer surface of the conductive patterns is attached to the protective layer. The protective layer has protrusions at the positions of the conductive patterns. Part of the conductive patterns are located inside the protrusions. Multiple stress holes (31) are opened on the core layer (3).

2. The double-layer bend-resistant flexible circuit board according to claim 1, characterized in that, The circuit layer above the core layer (3) is configured as the first circuit layer (2), the circuit layer below the core layer (3) is configured as the second circuit layer (4), the protective layer laid on the first circuit layer (2) is configured as the first protective layer (1), and the protective layer laid on the second circuit layer (4) is configured as the second protective layer (5).

3. The double-layer bend-resistant flexible circuit board according to claim 2, characterized in that, The conductive pattern on the first circuit layer (2) is set as a first conductive pattern (21), and the number of the first conductive patterns (21) is set to multiple, the multiple first conductive patterns (21) are arranged in a parallel manner, and the spacing between the multiple first conductive patterns (21) is equal.

4. The double-layer bend-resistant flexible circuit board according to claim 3, characterized in that, The first conductive pattern (21) is configured as a conductive loop.

5. A double-layer bend-resistant flexible circuit board according to claim 2, characterized in that, The conductive pattern on the second circuit layer (4) is set as a second conductive pattern (41), and the number of the second conductive patterns (41) is set to multiple, the multiple second conductive patterns (41) are arranged in a parallel manner, and the spacing between the multiple second conductive patterns (41) is equal.

6. A double-layer bend-resistant flexible circuit board according to claim 5, characterized in that, The second conductive pattern (41) is configured as a four-circle conductive loop, with the four conductive loops being arranged concentrically in sequence.

7. A double-layer bend-resistant flexible circuit board according to any one of claims 1-6, characterized in that, The protrusion on the first protective layer (1) is configured as a first protrusion (11), and the protrusion on the second protective layer (5) is configured as a second protrusion (51). Both the first protrusion (11) and the second protrusion (51) have a semi-groove inside. The semi-grooves of the first protrusion (11) and the second protrusion (51) are respectively adapted to the first conductive pattern (21) and the second conductive pattern (41).

8. A double-layer bend-resistant flexible circuit board according to any one of claims 1-6, characterized in that, The first protective layer (1), the first circuit layer (2), the core layer (3), the second circuit layer (4) and the second protective layer (5) are all vertically provided with vias (6) and connecting holes (7). The multiple vias (6) are interconnected. The first conductive pattern (21) and the second conductive pattern (41) are electrically connected through the vias (6). The multiple connecting holes (7) are interconnected.

9. A double-layer bend-resistant flexible circuit board according to claim 1, characterized in that, The size of the multiple stress holes (31) is set to two types, one of which has a diameter of 0.30 mm and the other has a diameter of 0.50 mm. The four sides of the two types of stress holes (31) are set to an inner arc structure with themselves as the center, and the four corners of the stress holes (31) are set to an outer arc structure with themselves as the center.

10. A method for processing a double-layer bend-resistant flexible circuit board, characterized in that, A method for processing a double-layer bend-resistant flexible circuit board as described in any one of claims 1-9, comprising the following steps: S1. The core layer (3) is provided with a flexible insulating material, and copper foil is respectively coated on its upper and lower surfaces to form the initial circuit layer structure; S2. The copper foil on both the top and bottom surfaces is patterned and etched to form the circuit layer and the plurality of conductive patterns thereon; S3. Prepare two protective layer materials, and pre-form the protrusion on each protective layer corresponding to the area of ​​the conductive pattern to be protected. Then align and press the two protective layers onto the upper and lower surfaces of the core layer (3) so that the conductive pattern is covered by the corresponding protective layer and part of its structure is embedded in the protrusion. S4. At a predetermined position in the core layer (3), a through stress hole (31) is formed.

11. A method for processing a double-layer bend-resistant flexible circuit board according to claim 10, characterized in that, It also includes the step: S5. When it is necessary to realize the electrical connection between the upper and lower circuit layers, process through holes at the specified locations and perform hole metallization treatment.

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