FPC with built-in bending guide skeleton and preparation method thereof

Abstract

The application discloses an FPC with a built-in bending guide framework and a preparation method thereof. The FPC with the built-in bending guide framework comprises, from bottom to top, an upper cover film, an upper PI insulating layer, a copper foil circuit layer, a bending guide framework, a lower PI insulating layer and a lower cover film, which are sequentially and orderly stacked. The upper cover film, the upper PI insulating layer, the copper foil circuit layer, the bending guide framework, the lower PI insulating layer and the lower cover film are integrally formed through a high-temperature-resistant pressing process. The bending guide framework is arranged only in a bending area, and no bending guide framework is arranged in a non-bending area. The FPC can solve the problems of unconstrained bending track, poor assembly consistency and easy dead folding of the existing FPC, realize precise and controllable FPC bending track, ensure uniform bending shape of assembly by different workers, improve assembly qualification rate, solve the problems of stress concentration and easy fatigue fracture of the existing FPC during repeated bending, greatly improve the repeated bending life of the FPC by dispersing bending stress, and adapt to the requirements of high-end equipment such as folding screens.

Description

Technical Field

[0001] This invention relates to the field of flexible printed circuit board technology, and more specifically, to an FPC with a built-in bending guide skeleton and its preparation method. Background Technology

[0002] Flexible printed circuit boards (FPCs) have become core connecting components for electronic devices such as foldable screen phones, flip devices, and laptops due to their advantages of being thin, flexible, and adaptable to compact spaces. Their main function is to realize the transmission of electrical signals between different modules inside the device. Especially in parts that need to be bent for assembly or repeated bending, the reliability of FPCs directly determines the service life and stability of the device.

[0003] Currently, existing FPCs in the industry face three major technical challenges: First, the bending trajectory is unrestrained, resulting in poor assembly consistency. Existing FPCs are extremely flexible and lack an active guidance structure. During assembly, workers must manually bend them to the preset shape. Due to differences in workers' operating techniques and force, bending angle deviations, bending trajectory offsets, and even "dead bends" (sharp-corner bends) are prone to occur. This damages the copper foil circuitry inside the FPC, leading to unstable signal transmission or even complete breakage, causing malfunctions such as screen not lighting up or touch malfunction. The assembly qualification rate is only about 85%.

[0004] Second, repeated bending can easily lead to fatigue and breakage. For devices such as foldable screen phones that require repeated bending, the bending stress of the FPC is concentrated at a single contact point. After long-term repeated bending, the copper foil circuit in this part is prone to fatigue aging and breakage, leading to equipment failure. The current FPC's repeated bending life is generally less than 100,000 times, which cannot meet the service life requirements of high-end foldable screen devices (which need to reach more than 500,000 times).

[0005] Third, existing reinforcement methods have defects. Some manufacturers use "bending area reinforcement plates" to improve bending performance by pasting them on the FPC surface. However, this method can only enhance the rigidity of the bending area and cannot control the bending trajectory. Moreover, the reinforcement plates are externally pasted, which can easily fall off or lift up, potentially scratching the FPC circuitry or affecting assembly space. At the same time, it increases assembly processes and production costs.

[0006] As electronic devices become thinner, lighter, foldable, and more compact, higher requirements are placed on the bending reliability, assembly consistency, and service life of FPCs. Existing FPCs can no longer meet industry needs, and there is an urgent need for a new type of FPC structure that can achieve controllable bending trajectory, stress dispersion, and controllable production costs without increasing assembly processes. Summary of the Invention

[0007] The technical problem to be solved by this invention is how to constrain the bending trajectory of FPC, improve assembly consistency, increase repeated bending life, and eliminate the need for external reinforcing plates.

[0008] The technical problem to be solved by the present invention is achieved through the following technical solution: To address the aforementioned technical problems, this invention provides an FPC with a built-in bending guide frame, comprising an upper cover film, an upper PI insulating layer, a copper foil circuit layer, a bending guide frame, a lower PI insulating layer, and a lower cover film stacked sequentially from bottom to top. The upper cover film, upper PI insulating layer, copper foil circuit layer, bending guide frame, lower PI insulating layer, and lower cover film are integrally formed by a high-temperature resistant pressing process. The bending guide frame is only provided in the bending area, and no bending guide frame is provided in the non-bending area.

[0009] As a preferred embodiment of the FPC with built-in bending guide skeleton provided by the present invention, the bending guide skeleton is made of 304 stainless steel sheet or reinforced polyimide sheet, the thickness of the bending guide skeleton is 0.08mm-0.12mm, the width of the bending guide skeleton is the same as the width of the bending area, and the length of the bending guide skeleton is 1.2 times-1.5 times the length of the bending area.

[0010] In a preferred embodiment of the FPC with built-in bending guide skeleton provided by the present invention, the edge of the bending guide skeleton is provided with a transition fillet, the radius of which is greater than or equal to 0.1 mm.

[0011] As a preferred embodiment of the FPC with built-in bending guide skeleton provided by the present invention, the bending guide skeleton adopts a pre-formed arc surface structure, the arc surface structure includes a single arc type, a straight arc combination type, and an S-shaped arc surface type, the arc radius of the arc area of ​​the bending guide skeleton is 1.2mm-3.0mm, and the preset bending angle is 30°-180°.

[0012] In a preferred embodiment of the FPC with built-in bending guide skeleton provided by the present invention, the bending guide skeleton is a shape memory material.

[0013] As a preferred embodiment of the FPC with built-in bending guide skeleton provided by the present invention, the bending guide skeleton adopts a segmented arc surface structure, each segment having a length of 2mm-3mm, and the segments are connected by a flexible transition; a 0.02mm thick flexible PI buffer layer is provided between the bending guide skeleton and the copper foil circuit layer, with a stress dispersion efficiency of greater than or equal to 80% and a repeated bending life of greater than or equal to 500,000 cycles.

[0014] As a preferred embodiment of the FPC with built-in bending guide skeleton provided by the present invention, the bending guide skeleton is bonded to the upper PI insulation layer and the lower PI insulation layer by a high-temperature resistant epoxy resin adhesive, the pressing temperature is 180℃-200℃, the pressing pressure is 0.3MPa-0.5MPa, and the bonding strength is greater than or equal to 15MPa.

[0015] In a preferred embodiment of the FPC with built-in bending guide skeleton provided by the present invention, the radius R of the bending guide skeleton and the bending angle θ satisfy the following relationship: ,in, The radius (mm) of the arc of the bending guide frame. The length of the FPC bending area (mm). Preset bending angle (°).

[0016] In a preferred embodiment of the FPC with built-in bending guide skeleton provided by the present invention, the stability of the shape self-holding is determined by the thickness t, elastic modulus E, and bending angle θ of the bending guide skeleton, which satisfy the following relationship: ,in, The internal stress (MPa) of the bending guide frame. The elastic modulus of the material for the bending guide frame. The thickness (mm) of the bending guide frame. The bending angle is (°). The radius (mm) of the arc of the bending guide frame.

[0017] This invention provides a method for fabricating an FPC with a built-in bending guide skeleton, which includes the following steps: S1: Prepare a pre-formed bending guide skeleton, determine the skeleton shape and size according to the preset bending requirements, and perform rounded corner treatment and pre-aging treatment; S2: Prepare the upper PI insulating layer, copper foil circuit layer and lower PI insulating layer according to conventional process, and lay a buffer layer between the copper foil circuit layer and the lower PI insulating layer; S3: Precisely position and embed the pre-formed bending guide frame between the upper PI insulation layer and the lower PI insulation layer, and apply high-temperature resistant epoxy resin adhesive. S4: After stacking the upper and lower cover films in sequence, place them into the pressing equipment, control the temperature at 180℃-200℃ and the pressure at 0.3MPa-0.5MPa, and then press them together to form the shape; S5: After cutting and testing the compressed product, the finished FPC is obtained.

[0018] The present invention has the following beneficial effects: The upper cover film, upper PI insulation layer, copper foil circuit layer, bending guide frame, lower PI insulation layer, and lower cover film are integrally formed through a high-temperature resistant pressing process, ensuring structural stability and eliminating the risk of delamination. Furthermore, since the bending guide frame is only embedded in the pre-set bending area of ​​the FPC and not in non-bending areas, the flexibility of the rest of the FPC is not affected, allowing it to be freely bent and conform to the internal space of the equipment.

[0019] Based on the "rigid constraint-flexible adaptation" collaborative mechanism, the bending guide frame has a certain degree of rigidity, which can accurately constrain the bending direction and trajectory of the FPC, avoiding random bending and sharp-corner bending of the FPC due to its own high flexibility; at the same time, the bending guide frame is made of flexible rigid composite material, which has a certain degree of elasticity and can produce slight deformation during bending, adapting to the preset bending angle of the equipment, and will not cause the FPC to break due to excessive rigidity.

[0020] It can solve the problems of unrestrained bending trajectory, poor assembly consistency, and easy occurrence of dead bends in existing FPCs, achieving precise and controllable bending trajectory, ensuring uniform bending shape for assembly by different workers, and improving assembly qualification rate; it solves the problem of stress concentration and easy fatigue fracture when repeatedly bending existing FPCs, significantly improving the life of repeated bending of FPCs by dispersing bending stress, and adapting to the needs of high-end equipment such as foldable screens; it eliminates the defects of existing externally pasted reinforcing plates, adopting an integrated design of built-in frame and FPC, avoiding the problems of reinforcing plates falling off and warping, while not adding extra assembly steps, thus controlling production costs; it ensures that the new FPC is compatible with existing production processes, and can be directly mass-produced using existing FPC production lines without the need for new production equipment, reducing the difficulty of promotion. Attached Figure Description

[0021] To more clearly illustrate the solutions in this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of an FPC with a built-in bending guide frame provided by the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of Example 2.

[0024] Explanation of icon numbers: 1. Upper cover film; 2. Upper PI insulation layer; 3. Copper foil circuit layer; 4. Bending guide frame; 5. Lower PI insulation layer; 6. Lower cover film; 7. Buffer layer. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0026] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0027] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0028] This invention provides an FPC with a built-in bending guide frame, which includes an upper cover film, an upper PI insulating layer, a copper foil circuit layer, a bending guide frame, a lower PI insulating layer, and a lower cover film stacked sequentially from bottom to top. The upper cover film, upper PI insulating layer, copper foil circuit layer, bending guide frame, lower PI insulating layer, and lower cover film are integrally formed by a high-temperature resistant pressing process. The bending guide frame is only provided in the bending area, and there is no bending guide frame in the non-bending area.

[0029] The upper cover film, upper PI insulation layer, copper foil circuit layer, bending guide frame, lower PI insulation layer, and lower cover film are integrally formed through a high-temperature resistant pressing process, ensuring structural stability and eliminating the risk of delamination. Furthermore, since the bending guide frame is only embedded in the pre-set bending area of ​​the FPC and not in non-bending areas, the flexibility of the rest of the FPC is not affected, allowing it to be freely bent and conform to the internal space of the equipment.

[0030] Based on the "rigid constraint-flexible adaptation" collaborative mechanism, the bending guide frame has a certain degree of rigidity, which can accurately constrain the bending direction and trajectory of the FPC, avoiding random bending and sharp-corner bending of the FPC due to its own high flexibility; at the same time, the bending guide frame is made of flexible rigid composite material, which has a certain degree of elasticity and can produce slight deformation during bending, adapting to the preset bending angle of the equipment, and will not cause the FPC to break due to excessive rigidity.

[0031] It can solve the problems of unrestrained bending trajectory, poor assembly consistency, and easy occurrence of dead bends in existing FPCs, achieving precise and controllable bending trajectory, ensuring uniform bending shape for assembly by different workers, and improving assembly qualification rate; it solves the problem of stress concentration and easy fatigue fracture when repeatedly bending existing FPCs, significantly improving the life of repeated bending of FPCs by dispersing bending stress, and adapting to the needs of high-end equipment such as foldable screens; it eliminates the defects of existing externally pasted reinforcing plates, adopting an integrated design of built-in frame and FPC, avoiding the problems of reinforcing plates falling off and warping, while not adding extra assembly steps, thus controlling production costs; it ensures that the new FPC is compatible with existing production processes, and can be directly mass-produced using existing FPC production lines without the need for new production equipment, reducing the difficulty of promotion.

[0032] The core innovation lies in breaking through the technical bottlenecks of existing FPCs, such as unrestrained bending, poor assembly consistency, and easy fatigue fracture. By integrating the bending guide frame with the FPC body into an integrated design, multiple functions such as controllable bending trajectory, self-maintaining shape, and stress dispersion are achieved. No additional auxiliary parts are required, making it suitable for various electronic devices that require bending assembly or repeated bending. The practicality and reliability are greatly improved, and it is compatible with existing FPC production processes, allowing for direct mass production.

[0033] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. The present invention will be described in detail below with reference to the accompanying drawings and embodiments, examples of which are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0034] Example 1, please refer to Figure 1 The present invention provides an FPC with a built-in bending guide frame, which includes an upper cover film 1, an upper PI insulating layer 2, a copper foil circuit layer 3, a bending guide frame 4, a lower PI insulating layer 5, and a lower cover film 6 stacked sequentially from bottom to top. The upper cover film 1, the upper PI insulating layer 2, the copper foil circuit layer 3, the bending guide frame 4, the lower PI insulating layer 5, and the lower cover film 6 are integrally formed by a high-temperature resistant pressing process. The bending guide frame 4 is only provided in the bending area, and there is no bending guide frame 4 in the non-bending area.

[0035] The upper cover film 1, upper PI insulation layer 2, copper foil circuit layer 3, bending guide frame 4, lower PI insulation layer 5, and lower cover film 6 are integrally formed through a high-temperature resistant pressing process to ensure structural stability and eliminate the risk of delamination. Furthermore, since the bending guide frame is only embedded in the pre-set bending area of ​​the FPC and not in non-bending areas, the flexibility of the remaining parts of the FPC remains unaffected, allowing it to be freely bent and conform to the internal space of the equipment.

[0036] Based on the "rigid constraint-flexible adaptation" collaborative mechanism, the bending guide frame has a certain rigidity, which can accurately constrain the bending direction and trajectory of the FPC, avoiding random bending and sharp corner bending of the FPC due to its own high flexibility; at the same time, the bending guide frame 4 is made of flexible rigid composite material, which has a certain elasticity and can produce slight deformation during bending, adapting to the preset bending angle of the equipment, and will not cause the FPC to break due to excessive rigidity.

[0037] It can solve the problems of unrestrained bending trajectory, poor assembly consistency, and easy occurrence of dead bends in existing FPCs, achieving precise and controllable bending trajectory, ensuring uniform bending shape for assembly by different workers, and improving assembly qualification rate; it solves the problem of stress concentration and easy fatigue fracture when repeatedly bending existing FPCs, significantly improving the life of repeated bending of FPCs by dispersing bending stress, and adapting to the needs of high-end equipment such as foldable screens; it eliminates the defects of existing externally pasted reinforcing plates, adopting an integrated design of built-in frame and FPC, avoiding the problems of reinforcing plates falling off and warping, while not adding extra assembly steps, thus controlling production costs; it ensures that the new FPC is compatible with existing production processes, and can be directly mass-produced using existing FPC production lines without the need for new production equipment, reducing the difficulty of promotion.

[0038] Furthermore, the material of the bending guide frame 4 is a 304 stainless steel sheet or a reinforced polyimide sheet. The thickness of the bending guide frame 4 is 0.08mm-0.12mm. The width of the bending guide frame 4 is consistent with the width of the bending area. The length of the bending guide frame 4 is 1.2-1.5 times the length of the bending area to ensure stress dispersion effect.

[0039] Integrated molding and compatibility principles: The bending guide frame 4 is embedded between the upper PI insulation layer 2 and the lower PI insulation layer 5 of the FPC, and is integrally molded using a high-temperature pressing process. The adhesive used is an epoxy resin adhesive compatible with the PI insulation layer, with a bonding strength ≥15MPa, ensuring that there is no risk of delamination or detachment between the frame and the FPC body. Simultaneously, the frame thickness is controlled between 0.08mm and 0.12mm, matching the overall thickness of the FPC (0.15mm-0.3mm), without increasing the overall thickness of the FPC, allowing direct adaptation to the assembly space of existing equipment. Its precise thickness match to the overall thickness of the FPC ensures that the FPC is neither too thick to fit in a compact assembly space nor too thin to lose its guiding and restraining function.

[0040] During the production process, only the skeleton positioning and embedding steps need to be added to the existing FPC pressing process. No new production equipment is required. It is fully compatible with the existing FPC production process, has high mass production feasibility, and the production cost is only 5%-8% higher than that of traditional FPC, which is far lower than the cost of externally pasted reinforcing plates (15%-20% higher).

[0041] Furthermore, the edges of the bending guide frame 4 are provided with transition fillets, the radius of which is greater than or equal to 0.1 mm.

[0042] Furthermore, existing FPCs lack shape retention capability after bending. They require external fasteners (such as clips or adhesive) to maintain their shape after bending. During assembly, workers must hold the FPC in place with one hand and operate the fasteners with the other, making the process cumbersome, inefficient, and prone to loosening, causing the FPC's bent shape to shift and affecting electrical signal transmission. In this embodiment, the shape of the bending guide frame 4 is customized according to the equipment's bending requirements. The bending guide frame adopts a pre-formed arc surface structure, including single arc, straight arc combination, and S-shaped arc. The radius of the arc area of ​​the bending guide frame is 1.2mm-3.0mm to avoid sharp corners and prevent scratching of the copper foil circuitry. The preset bending angle is 30°-180°.

[0043] The bending guide frame is made of shape memory material, giving it shape memory properties and allowing it to automatically maintain a preset shape after bending. By pre-aging the bending guide frame 4, it acquires shape memory properties, and the pre-formed arc shape is the preset bending shape of the FPC. During assembly, a slight external force of 5-10N is applied, and the FPC naturally bends along the arc trajectory of the bending guide frame 4. The bending angle can be preset from 30° to 180° according to equipment requirements. After bending, the bending guide frame 4 maintains its shape through its own elasticity, requiring no additional fasteners. It can maintain its bent state for a long time after assembly. This solves the problem of existing FPCs lacking shape self-holding ability after bending and requiring additional fasteners, achieving automatic shape retention after bending, simplifying the assembly process, and improving assembly efficiency.

[0044] The shape of the bending guide frame 4 is customized according to the bending requirements of specific devices, adopting a "pre-formed arc surface structure". Common types include single arc type (suitable for C-shaped bends), straight arc combination type (suitable for L-shaped bends), and S-shaped arc surface type (suitable for bidirectional bends). The edges of the bending guide frame 4 are rounded to avoid scratching the copper foil circuits inside the FPC. This frame has "shape memory characteristics". It is given a preset bending trajectory through a pre-forming process. During assembly, only a slight external force is applied, and the FPC can bend naturally along the preset trajectory of the frame. After bending, it maintains the preset shape by relying on the elasticity of the frame itself, without the need for additional fasteners. For scenarios such as foldable screen phones that require repeated bending, the frame adopts a segmented arc surface design, which evenly distributes the bending stress throughout the bending area, avoiding circuit breakage caused by stress concentration, and can increase the repeated bending life of the FPC by more than 80%.

[0045] This FPC does not require changes to the existing assembly process. Workers can assemble it directly in the conventional way without additional training. Moreover, the bending guide frame 4 is integrally molded with the FPC. During production, the bending guide frame 4 only needs to be embedded in the PI insulation layer lamination stage, without adding any extra production steps. Production costs are controllable, and it can be widely adapted to various products that require bending FPC, such as foldable screen mobile phones, flip devices, laptop hinges, and compact electronic devices.

[0046] Example 2, please refer to Figure 1 As a further optimization of Embodiment 1, in this embodiment, for scenarios requiring repeated bending, the bending guide frame adopts a segmented arc surface structure, with each segment having a length of 2mm-3mm. Flexible transition connections are used between segments to evenly distribute bending stress throughout the bending area, avoiding stress concentration. A 0.02mm thick flexible PI buffer layer 7 is provided between the bending guide frame 4 and the copper foil circuit layer 3, with a stress dispersion efficiency greater than or equal to 80% and a repeated bending life greater than or equal to 500,000 cycles, further buffering bending stress and improving repeated bending life.

[0047] Furthermore, during the PI insulation layer lamination stage of FPC production, the pre-formed bending guide skeleton 4 is precisely positioned and embedded between the upper PI insulation layer 2 and the lower PI insulation layer 5. The bending guide skeleton is bonded to the upper PI insulation layer 2 and the lower PI insulation layer 5 with a high-temperature resistant epoxy resin adhesive. The lamination temperature is 180℃-200℃, the lamination pressure is 0.3MPa-0.5MPa, and the bonding strength is greater than or equal to 15MPa, ensuring that the skeleton is integrated with the FPC body, with no risk of loosening or falling off, and without affecting the electrical signal transmission of the copper foil circuit.

[0048] Principle of controllable bending trajectory: Based on the "rigid constraint-flexible adaptation" collaborative mechanism, the built-in guide frame has a certain degree of rigidity, which can accurately constrain the bending direction and trajectory of the FPC, avoiding random bending and sharp corner bending of the FPC due to its own high flexibility; at the same time, the frame is made of flexible rigid composite material, which has a certain degree of elasticity and can produce slight deformation during bending, adapting to the preset bending angle of the device, and will not cause the FPC to break due to excessive rigidity.

[0049] The radius R of the arc of the bending guide frame 4 and the bending angle θ satisfy the following relationship: , in, The radius (mm) of the arc of the bending guide frame 4. The length of the FPC bending area (mm). The pre-formed dimensions of the bending guide frame 4 can be accurately calculated using this formula to preset the bending angle (°), ensuring that the FPC bending trajectory is fully matched with the equipment requirements, achieving controllable bending trajectory, and improving assembly consistency to over 99%.

[0050] Shape self-holding principle: After pre-aging treatment, the bending guide frame 4 forms a stable stress structure inside. When the FPC is bent to the preset shape, the internal stress of the bending guide frame 4 reaches a state of equilibrium and maintains the shape by its own elastic stress. No external fasteners are required. The stability of the shape self-maintaining is determined by the thickness t, elastic modulus E, and bending angle θ of the bending guide frame 4, which satisfy the following relationship: , in, The internal stress (MPa) of the bending guide frame 4. The elastic modulus of the material for the bending guide skeleton 4 is (E=200GPa for stainless steel sheet and E=30GPa for reinforced polyimide sheet). The thickness (mm) of the bending guide frame 4. The bending angle is (°). For the radius (mm) of the arc of the bending guide frame 4, when Within the elastic limit range of the bending guide skeleton 4 material (elastic limit of stainless steel sheet ≥200MPa, elastic limit of polyimide ≥50MPa), the bending guide skeleton 4 can maintain its bent shape for a long time without springback or deformation.

[0051] Stress dispersion principle: When a traditional FPC is bent, stress concentrates at a single bending point, resulting in a large stress value. Repeated bending over a long period can easily lead to circuit breakage. This invention, through the segmented design and dimensional optimization of the bending guide frame 4, disperses the bending stress throughout the entire bending area. The formula for calculating the stress dispersion efficiency η is as follows: in, Stress dispersion efficiency (%) This represents the maximum stress (MPa) experienced when a traditional FPC is bent. This represents the maximum stress (MPa) experienced during bending of the FPC according to this invention. By optimizing the length and number of segments of the bending guide frame 4, the stress dispersion efficiency η can be increased to ≥80%, significantly reducing the stress on the copper foil circuitry and increasing the FPC's repeated bending life from 100,000 cycles to over 500,000 cycles.

[0052] Principle of preventing line damage: The edges of the bending guide frame 4 are rounded (rounded radius ≥ 0.1mm) to avoid sharp edges scratching the copper foil circuit. At the same time, a buffer layer 7 is added between the bending guide frame 4 and the copper foil circuit layer 3. The buffer layer 7 is made of flexible PI material, which can absorb the small deformation generated during the bending process, avoid direct contact between the bending guide frame 4 and the copper foil circuit to prevent friction and squeezing, further protect the copper foil circuit and reduce the risk of circuit damage.

[0053] This invention provides a method for fabricating an FPC with a built-in bending guide skeleton, which includes the following steps: S1: Prepare a pre-formed bending guide skeleton, determine the skeleton shape and size according to the preset bending requirements, and perform rounded corner treatment and pre-aging treatment; S2: Prepare the upper PI insulating layer, copper foil circuit layer and lower PI insulating layer according to conventional process, and lay a buffer layer between the copper foil circuit layer and the lower PI insulating layer; S3: Precisely position and embed the pre-formed bending guide frame between the upper PI insulation layer and the lower PI insulation layer, and apply high-temperature resistant epoxy resin adhesive. S4: After stacking the upper and lower cover films in sequence, place them into the pressing equipment, control the temperature at 180℃-200℃ and the pressure at 0.3MPa-0.5MPa, and then press them together to form the shape; S5: After cutting and testing the compressed product, the finished FPC is obtained.

[0054] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0055] Obviously, the embodiments described above are only some embodiments of this application, not all embodiments. The accompanying drawings show preferred embodiments of this application, but do not limit the patent scope of this application. This application can be implemented in many different forms; rather, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this application's specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the scope of patent protection of this application.

Claims

1. An FPC with a built-in bending guide frame, characterized in that, It includes an upper cover film, an upper PI insulating layer, a copper foil circuit layer, a bending guide frame, a lower PI insulating layer, and a lower cover film, which are stacked sequentially from bottom to top. The upper cover film, upper PI insulating layer, copper foil circuit layer, bending guide frame, lower PI insulating layer, and lower cover film are integrally formed by a high-temperature resistant pressing process. The bending guide frame is only provided in the bending area, and there is no bending guide frame in the non-bending area.

2. The FPC with built-in bending guide frame according to claim 1, characterized in that, The bending guide frame is made of 304 stainless steel sheet or reinforced polyimide sheet. The thickness of the bending guide frame is 0.08mm-0.12mm. The width of the bending guide frame is the same as the width of the bending area. The length of the bending guide frame is 1.2-1.5 times the length of the bending area.

3. The FPC with built-in bending guide frame according to claim 1, characterized in that, The edges of the bending guide frame are provided with transition fillets, and the radius of the transition fillets is greater than or equal to 0.1 mm.

4. The FPC with built-in bending guide frame according to claim 1, characterized in that, The bending guide frame adopts a pre-formed arc surface structure, which includes single arc type, straight arc combination type, and S-shaped arc surface type. The arc radius of the arc area of ​​the bending guide frame is 1.2mm-3.0mm, and the preset bending angle is 30°-180°.

5. The FPC with built-in bending guide frame according to claim 1, characterized in that, The bending guide frame is made of shape memory material.

6. The FPC with built-in bending guide frame according to claim 1, characterized in that, The bending guide frame adopts a segmented arc surface structure, with each segment having a length of 2mm-3mm, and the segments are connected by a flexible transition. A 0.02mm thick flexible PI buffer layer is provided between the bending guide frame and the copper foil circuit layer, with a stress dispersion efficiency of greater than or equal to 80% and a repeated bending life of greater than or equal to 500,000 cycles.

7. The FPC with built-in bending guide skeleton according to claim 1, characterized in that, The bending guide skeleton is bonded to the upper and lower PI insulation layers with high-temperature resistant epoxy resin adhesive. The pressing temperature is 180℃-200℃, the pressing pressure is 0.3MPa-0.5MPa, and the bonding strength is greater than or equal to 15MPa.

8. The FPC with built-in bending guide frame according to claim 1, characterized in that, The radius R of the arc of the bending guide frame and the bending angle θ satisfy the following relationship: ,in, The radius (mm) of the arc of the bending guide frame. The length of the FPC bending area (mm). Preset bending angle (°).

9. The FPC with built-in bending guide frame according to claim 1, characterized in that, The shape-maintaining stability is determined by the thickness t of the bending guide skeleton, the elastic modulus E, and the bending angle θ, and satisfies the following relationship: ,in, The internal stress (MPa) of the bending guide frame. The elastic modulus of the material for the bending guide frame. The thickness (mm) of the bending guide frame. The bending angle is (°). The radius (mm) of the arc of the bending guide frame.

10. A method for fabricating an FPC with a built-in bending guide skeleton, characterized in that, It includes the following steps: S1: Prepare a pre-formed bending guide skeleton, determine the skeleton shape and size according to the preset bending requirements, and perform rounded corner treatment and pre-aging treatment; S2: Prepare the upper PI insulating layer, copper foil circuit layer and lower PI insulating layer according to conventional process, and lay a buffer layer between the copper foil circuit layer and the lower PI insulating layer; S3: Precisely position and embed the pre-formed bending guide frame between the upper PI insulation layer and the lower PI insulation layer, and apply high-temperature resistant epoxy resin adhesive. S4: After stacking the upper and lower cover films in sequence, place them into the pressing equipment, control the temperature at 180℃-200℃ and the pressure at 0.3MPa-0.5MPa, and then press them together to form the shape; S5: After cutting and testing the compressed product, the finished FPC is obtained.

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