Flexible wiring board and electronic device

Abstract

The application discloses a flexible circuit board and an electronic device, and relates to the technical field of flexible circuit boards. The flexible circuit board comprises a flexible insulating substrate layer, a conductive circuit, a cover film layer and a stress buffer layer. The conductive circuit is arranged on the upper surface of the flexible insulating substrate layer and located in the bending area of the flexible circuit board. The conductive circuit is parallel to the bending axis of the bending area of the flexible circuit board and extends in a periodic wave shape. The cover film layer is arranged above the conductive circuit and located in the bending area of the flexible circuit board. The shape of the upper surface of the cover film layer and the shape of the lower surface of the cover film layer are both conformal to the wave shape of the conductive circuit. The stress buffer layer is arranged between the flexible insulating substrate layer and the conductive circuit. The elastic modulus of the stress buffer layer is lower than the elastic modulus of the flexible insulating substrate layer. In the premise of not increasing the thickness of the flexible circuit board, not changing the number of layers and not improving the material cost, the in-plane stress is effectively released, and the dynamic bending life of the flexible circuit board is improved by 5-10 times.

Description

Technical Field

[0001] This invention relates to the field of circuit board technology, and more specifically, to a flexible circuit board and electronic device. Background Technology

[0002] Flexible circuit boards, with their thinness, bendability, and rollability, have become core connection components for electronic devices such as foldable screen phones, wearable devices, robot joints, and flexible sensors. Their core function is to transmit electrical signals in the moving connection parts of the device (such as the hinge of a foldable screen or a flip phone), and they need to withstand repeated bending, dynamic bending, or small-radius bending over a long period of time.

[0003] Currently, fatigue fracture of copper foil in the bending zone is a common pain point in the industry for existing flexible printed circuit boards, leading to signal interruption and frequent malfunctions. Existing technical solutions all have obvious defects and have not fundamentally solved the stress concentration problem. The specific shortcomings are as follows: 1. Traditional straight-line traces suffer from severe stress concentration: In existing flexible circuit boards, the copper foil traces in the bending area are mostly arranged in straight parallel lines. When bending, the copper foil is located on the outside of the bending neutral layer and bears tensile stress, while the inside bears compressive stress. The stress is concentrated at the edge of the copper foil, and the elongation at break of the copper foil is usually less than 10%. After multiple bends, micro-cracks will appear at the edge, which will gradually expand to complete breakage. The bending life is generally only about 50,000 times, which cannot meet the usage requirements of foldable screen mobile phones and other devices throughout their entire life cycle (at least 300,000 times).

[0004] 2. Existing stress dispersion solutions are not practical: Some technologies disperse stress by increasing the thickness of copper foil, adding reinforcing plates, or using multi-layer staggered traces, but this will significantly increase the thickness and rigidity of flexible circuit boards, which goes against the development trend of ultra-thin and lightweight electronic devices. At the same time, it reduces the bending flexibility of flexible circuit boards and cannot be adapted to small radius bending scenarios (such as the bending radius of folding screen hinge ≤1mm).

[0005] 3. The constraint effect of the cover film exacerbates the fracture: The traditional cover film (polyimide material) has a planar structure and is tightly attached to the copper foil. When bent, the cover film restricts the free deformation of the copper foil, causing the actual strain of the copper foil to be greater than the theoretical strain, which exacerbates the fatigue of the copper foil and further shortens the bending life. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to enable flexible circuit boards to effectively release in-plane stress without increasing thickness, changing the number of layers, or increasing costs.

[0007] The technical problem to be solved by the present invention is achieved through the following technical solution: To address the aforementioned technical problems, the present invention provides a flexible circuit board, comprising a flexible insulating substrate layer, conductive lines, a cover film layer, and a stress buffer layer. The conductive lines are at least one in number, disposed on the upper surface of the flexible insulating substrate layer and located within the bending region of the flexible circuit board. The conductive lines are parallel to the bending axis of the bending region of the flexible circuit board and extend in a periodic wavy shape. The cover film layer covers the conductive lines and is located within the bending region of the flexible circuit board. The shapes of the upper and lower surfaces of the cover film layer are conformal to the wavy contour of the conductive lines. The stress buffer layer is disposed between the flexible insulating substrate layer and the conductive lines, and the elastic modulus of the stress buffer layer is lower than that of the flexible insulating substrate layer.

[0008] In a preferred embodiment of the flexible circuit board provided by the present invention, the wave shape of the conductive line is a sine wave, a triangular wave, or a trapezoidal wave; the amplitude A of the wave shape is 1 to 3 times the width of the conductive line, the period length L of the wave shape is 2 to 5 times the amplitude, and the amplitude A of the wave shape and the period length L of the wave shape satisfy L / A=S, where S is 2-5.

[0009] In a preferred embodiment of the flexible circuit board provided by the present invention, the total length of the conductive lines in the bending area is 10%-30% longer than the straight length of the bending area along the bending axis.

[0010] In a preferred embodiment of the flexible circuit board provided by the present invention, the thickness of the cover film is consistent at the crests and troughs of the wave, and the thickness of the cover film at the inclined portion between the crests and troughs of the wave is 10%-30% thinner than the thickness at the crests.

[0011] In a preferred embodiment of the flexible circuit board provided by the present invention, the stress buffer layer is made of silicone rubber, polyurethane elastomer or acrylic pressure-sensitive adhesive, the elastic modulus of the stress buffer layer is 10MPa-100MPa, and the thickness of the stress buffer layer is 0.5 times to 2 times the thickness of the conductive circuit.

[0012] As a preferred embodiment of the flexible circuit board provided by the present invention, the flexible circuit board has a multi-layer structure, comprising at least two layers of conductive lines, wherein each layer has a wavy structure in the bending area, and the wavy phases of the conductive lines in adjacent layers are opposite.

[0013] In a preferred embodiment of the flexible circuit board provided by the present invention, a wavy insulating dielectric layer is provided between the multilayer conductive lines, and the wavy parameters of each layer of conductive lines are the same.

[0014] In a preferred embodiment of the flexible circuit board provided by the present invention, at least one wavy virtual stress relief line parallel to the conductive line is provided in the bending area, and the virtual stress relief line is not connected to any circuit.

[0015] In a preferred embodiment of the flexible circuit board provided by the present invention, a transition zone is provided at the junction of the bending zone and the non-bending zone of the conductive line. The amplitude of the wave-like oscillation on the conductive line in the transition zone gradually decreases from the maximum value in the bending zone to zero in the non-bending zone. The length of the transition zone is at least two wave-like cycles.

[0016] The present invention provides an electronic device comprising a first body, a second body, and a hinge structure connecting the two, and further comprising a flexible circuit board as described in any of the preceding claims, wherein the bending area of ​​the flexible circuit board is located at the hinge structure.

[0017] The present invention has the following beneficial effects: By converting the tensile or compressive stress generated by bending into the local bending strain of the wave structure, the constraint stress of the cover film on the conductive lines is eliminated, and the in-plane stress is effectively dispersed and absorbed. Without increasing the thickness of the flexible circuit board, changing the number of layers, or increasing the material cost, the in-plane stress is effectively released, and the dynamic bending life of the flexible circuit board is increased by 5-10 times. At the same time, it is compatible with existing flexible circuit board production lines, realizes mass production, and meets the usage needs of high-frequency bending scenarios such as foldable screen mobile phones and wearable devices. Attached Figure Description

[0018] 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.

[0019] Figure 1 This is a schematic diagram of a flexible circuit board provided by the present invention.

[0020] Explanation of icon numbers: 1. Flexible insulating substrate; 2. Conductive circuit; 3. Covering film; 4. Stress buffer layer. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] Please see Figure 1The present invention provides a flexible circuit board comprising a flexible insulating substrate layer 1, conductive lines 2, a cover film layer 3, and a stress buffer layer 4. The conductive lines 2 are at least one in number and are disposed on the upper surface of the flexible insulating substrate layer 1 within the bending region of the flexible circuit board. The conductive lines 2 are parallel to the bending axis of the bending region of the flexible circuit board and extend in a periodic wavy shape. The cover film layer 3 covers the conductive lines 2 and is located within the bending region of the flexible circuit board. The shapes of the upper and lower surfaces of the cover film layer 3 are conformal to the wavy contour of the conductive lines 2. The stress buffer layer 4 is disposed between the flexible insulating substrate layer 1 and the conductive lines 2, and the elastic modulus of the stress buffer layer 4 is lower than that of the flexible insulating substrate layer 1.

[0026] The conductive line 2 can be made of conventional electrolytic copper foil (without the need for high-ductility rolled copper foil), with a thickness of 0.01mm-0.03mm. The non-bending area of ​​the flexible circuit board is a traditional straight line, while the conductive line 2 extends in a periodic wave shape within the bending area of ​​the flexible circuit board, with the wave propagation direction parallel to the bending axis of the flexible circuit board.

[0027] The tensile or compressive stress generated by bending is transformed into local bending strain of the wave structure, eliminating the constraint stress of the cover film on the conductive line 2, and realizing the effective dispersion and absorption of in-plane stress. Without increasing the thickness of the flexible circuit board, changing the number of layers, or increasing the material cost, it effectively releases in-plane stress and increases the dynamic bending life of the flexible circuit board by 5-10 times. At the same time, it is compatible with existing flexible circuit board production lines, realizes mass production, and meets the usage needs of high-frequency bending scenarios such as foldable screen mobile phones and wearable devices.

[0028] Furthermore, the wave shape of the conductive line 2 is a sine wave, a triangular wave, or a trapezoidal wave; the amplitude A of the wave shape is 1 to 3 times the width of the conductive line 2, and the period length L of the wave shape is 2 to 5 times the amplitude, and the amplitude A and the period length L of the wave shape satisfy L / A=S, where S is 2-5. When bending, the wave-shaped structure absorbs and disperses the tensile or compressive stress generated by bending through local deformation of the crest flattening and the trough contraction.

[0029] Furthermore, the total length of the conductive line 2 within the bending zone is 10%-30% longer than the straight length of the bending zone along the bending axis, ensuring sufficient deformation allowance.

[0030] Furthermore, the thickness of the covering film 3 is consistent at the crests and troughs of the wave, and the thickness of the sloping portion (i.e., the sidewall) of the covering film 3 between the crests and troughs of the wave is 10%-30% thinner than the thickness at the crest, so as to reduce the constraint of the covering film on the bending of the conductive line 2 and improve the deformation freedom of the conductive line 2.

[0031] Furthermore, the stress buffer layer 4 is made of silicone rubber, polyurethane elastomer, or acrylic pressure-sensitive adhesive. The elastic modulus of the stress buffer layer 4 is 10 MPa-100 MPa, and its thickness is 0.5-2 times the thickness of the conductive line 2. The stress buffer layer 4 is disposed between the flexible insulating substrate layer 1 and the conductive line 2, or fills the troughs of the corrugated conductive line 2. During the formation of the corrugated structure, it fills the gaps, supporting the corrugated structure, preventing trough collapse, converting point stress into surface stress, and redistributing stress. Furthermore, the flexible circuit board has a multi-layer structure, comprising at least two layers of conductive lines 2, wherein each layer has a wavy structure in the bending area, and the wavy phases of the conductive lines 2 in adjacent layers are opposite, in order to balance the shear stress between the layers during bending, avoid impedance abrupt changes, and ensure signal transmission stability.

[0032] Furthermore, a wavy insulating dielectric layer is provided between the multilayer conductive lines 2, and the wavy parameters of each layer of conductive lines 2 are the same, so as to balance the shear stress between the layers when bending, avoid impedance abrupt change, and ensure signal transmission stability.

[0033] Furthermore, at least one wavy virtual stress relief line parallel to the conductive line 2 is provided in the bending area. The virtual stress relief line is not connected to any circuit and is only used to absorb the lateral stress generated by bending, further disperse the in-plane stress, and prevent the conductive line 2 from bearing all the stress alone.

[0034] Furthermore, the conductive line 2 has a transition zone at the junction of the bending zone and the non-bending zone. The amplitude of the wave-shaped oscillation on the conductive line 2 in the transition zone gradually decreases from the maximum value in the bending zone to zero in the non-bending zone. The length of the transition zone is at least two wave-shaped cycles to avoid stress concentration caused by abrupt shape changes at the junction of the lines and to ensure a smooth transition in signal transmission.

[0035] The present invention provides an electronic device comprising a first body, a second body, and a hinge structure connecting the two, and further comprising a flexible circuit board as described in any of the preceding claims, wherein the bending area of ​​the flexible circuit board is located at the hinge structure.

[0036] 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.

[0037] 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. A flexible circuit board, characterized in that, It includes: Flexible insulating substrate; At least one conductive line is disposed on the upper surface of the flexible insulating substrate and located within the bending area of ​​the flexible circuit board. The conductive line is parallel to the bending axis of the bending area of ​​the flexible circuit board and extends in a periodic wavy shape. A cover film layer is placed over the conductive lines and located within the bending area of ​​the flexible circuit board. The shape of the upper surface and the shape of the lower surface of the cover film layer are conformal to the wavy contour of the conductive lines. A stress buffer layer is disposed between the flexible insulating substrate and the conductive line, wherein the elastic modulus of the stress buffer layer is lower than that of the flexible insulating substrate.

2. The flexible circuit board according to claim 1, characterized in that, The wave shape of the conductive line is a sine wave, a triangular wave, or a trapezoidal wave; the amplitude A of the wave shape is 1 to 3 times the width of the conductive line, the period length L of the wave shape is 2 to 5 times the amplitude, and the amplitude A and the period length L of the wave shape satisfy L / A=S, where S is 2-5.

3. The flexible circuit board according to claim 1, characterized in that, The total length of the conductive line within the bending zone is 10%-30% longer than the straight length of the bending zone along the bending axis.

4. The flexible circuit board according to claim 1, characterized in that, The thickness of the covering film is consistent at the crests and troughs of the wave, and the thickness of the covering film at the sloping portion between the crests and troughs of the wave is 10%-30% thinner than the thickness at the crests.

5. The flexible circuit board according to claim 1, characterized in that, The stress buffer layer is made of silicone rubber, polyurethane elastomer, or acrylic pressure-sensitive adhesive. The elastic modulus of the stress buffer layer is 10MPa-100MPa, and the thickness of the stress buffer layer is 0.5-2 times the thickness of the conductive circuit.

6. The flexible circuit board according to claim 1, characterized in that, The flexible circuit board has a multi-layer structure, including at least two layers of conductive lines, wherein each layer has a wavy structure in the bending area, and the wavy phases of the conductive lines in adjacent layers are opposite.

7. The flexible circuit board according to claim 6, characterized in that, A wavy insulating dielectric layer is provided between the multi-layer conductive lines, and the wavy parameters of each conductive line are the same.

8. The flexible circuit board according to claim 1, characterized in that, At least one wavy virtual stress relief line parallel to the conductive line is provided in the bending area, and the virtual stress relief line is not connected to any circuit.

9. The flexible circuit board according to claim 1, characterized in that, The conductive line has a transition zone at the junction of the bending zone and the non-bending zone. The amplitude of the wave-like oscillation on the conductive line in the transition zone gradually decreases from the maximum value in the bending zone to zero in the non-bending zone. The length of the transition zone is at least two wave-like cycles.

10. An electronic device comprising a first body, a second body, and a hinge structure connecting the two, characterized in that, It also includes a flexible circuit board as described in any one of claims 1 to 9, wherein the bending area of ​​the flexible circuit board is located at the hinge structure.

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