A bend-resistant multilayer FPC board
By using a symmetrical stacked architecture and gradient adhesive layer design, combined with serpentine traces, buffer zones, and reinforcing ribs, the problem of interlayer delamination and substrate breakage during bending of FPC boards is solved, achieving stable signal transmission and heat dissipation, making it suitable for flexible electronic devices.
Patent Information
- Application Number
- CN202522075861.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-25
- Publication Date
- 2026-08-25
- Estimated Expiration
- 2035-09-25
AI Technical Summary
Existing FPC boards are prone to problems such as interlayer delamination, substrate breakage, and film detachment when bent, making it difficult to meet the requirements of thinness, flexibility, and multi-functionality.
It adopts a symmetrical layered architecture with the signal transmission layer at the center. The thermal expansion coefficient between layers is balanced by a gradient bonding layer. The bending area uses serpentine routing, buffer space and reinforcing ribs to resist bending. The composite shielding and heat dissipation layer takes into account both electromagnetic shielding and heat dissipation.
It achieves a balance between stable signal transmission, bending resistance, and heat dissipation in high-frequency flexible application scenarios, avoiding interlayer delamination and substrate cracking, and is compatible with narrow bezel designs.
Smart Images
Figure CN224684427U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of FPC board technology, and in particular to a bend-resistant multilayer FPC board. Background Technology
[0002] With the popularization of flexible electronic devices such as foldable screen phones and wearable devices, flexible printed circuit boards, as core signal transmission components, have increasingly stringent requirements for bending resistance, electromagnetic compatibility, and heat dissipation.
[0003] However, existing FPCs have shortcomings. Their stacked architectures are mostly asymmetrical, and the conductors in the bending area are mostly arranged in straight lines. When folded, the stress is concentrated in the conductors. Electromagnetic shielding and heat dissipation functions are mostly implemented independently. Setting up a separate metal shielding layer will increase the thickness and reduce flexibility. Attaching a heat dissipation film alone will easily fall off when bending. It is difficult to meet the requirements of thinness, flexibility and multi-functionality. Although some FPCs have added buffer structures, they are not designed in conjunction with the copper foil layer and the substrate layer. Problems such as substrate cracking and conductor wrinkling still exist. They cannot be adapted to high-frequency flexible application scenarios. Therefore, a multi-layer FPC board that is resistant to bending is needed. Utility Model Content
[0004] The purpose of this invention is to provide a bend-resistant multilayer FPC board that solves the problems of interlayer peeling, easy breakage of the substrate, and easy detachment of the film when bent in the prior art.
[0005] To achieve the above objectives, this utility model provides the following technical solution: a bend-resistant multilayer FPC board, comprising an FPC substrate body, wherein the FPC substrate body is divided into a bending area and a non-bending area, characterized in that: the FPC substrate body adopts a symmetrical stacked structure, consisting of, from the inside out, a signal transmission layer, a first gradient adhesive layer, a first substrate layer, a first copper foil layer, and a composite shielding and heat dissipation layer; the side of the signal transmission layer away from the first gradient adhesive layer is connected to the second substrate layer through a second gradient adhesive layer, and the side of the second substrate layer away from the signal transmission layer is connected to the second copper foil layer, and the first copper foil layer and the second copper foil layer are symmetrically distributed about the signal transmission layer; both the first copper foil layer and the second copper foil layer in the bending area are provided with The serpentine trace has buffer zones on both sides. Each buffer zone is a hollow structure that connects the corresponding first and second copper foil layers with the adjacent first and second substrate layers. Reinforcing ribs are provided at the edges of the buffer zones. These reinforcing ribs are integrally formed with the corresponding first and second substrate layers and extend along the stacking direction of the FPC substrate body. The composite shielding and heat dissipation layer covers the side of the first copper foil layer away from the first substrate layer. Flexible folds are provided on the surface of the bending area of the composite shielding and heat dissipation layer, and the direction of these flexible folds matches the direction of the serpentine trace. The composite shielding and heat dissipation layer includes a conductive shielding sublayer and a heat dissipation sublayer that are sequentially bonded together and fixedly connected along the stacking direction.
[0006] Preferably, both the first gradient adhesive layer and the second gradient adhesive layer are disposed along the stacking direction of the FPC substrate body, and the two ends of the first gradient adhesive layer are fixedly connected to the signal transmission layer and the first substrate layer, respectively, and the two ends of the second gradient adhesive layer are fixedly connected to the signal transmission layer and the second substrate layer, respectively.
[0007] Preferably, the first substrate layer and the second substrate layer are symmetrically distributed about the signal transmission layer, and the side of the first substrate layer away from the first gradient adhesive layer is fixedly connected to the first copper foil layer, and the side of the second substrate layer away from the second gradient adhesive layer is fixedly connected to the second copper foil layer.
[0008] Preferably, the extension direction of the serpentine trace forms a preset angle with the bending direction of the FPC substrate body, and the serpentine trace is continuously distributed along the length direction of the first copper foil layer and the second copper foil layer.
[0009] Preferably, the buffer zone is a dumbbell-shaped hollow structure, and both ends of the buffer zone extend to the transition position between the bending zone and the non-bending zone.
[0010] Preferably, the number of reinforcing ribs is at least two, and the two reinforcing ribs are symmetrically distributed on both sides of the long axis of the buffer void area, and the end of the reinforcing rib away from the first substrate layer and the second substrate layer is fixedly connected to the corresponding first copper foil layer and the second copper foil layer.
[0011] Preferably, a third gradient adhesive layer is provided between the conductive shielding sublayer and the heat dissipation sublayer. The two ends of the third gradient adhesive layer are fixedly connected to the conductive shielding sublayer and the heat dissipation sublayer, respectively, and the extension direction of the third gradient adhesive layer is consistent with the extension direction of the first gradient adhesive layer.
[0012] Preferably, the flexible folds are spaced apart along the width direction of the composite shielding heat dissipation layer, and the depth of the flexible folds gradually decreases from the center of the bending area to both sides.
[0013] Compared with the prior art, the beneficial effects of this utility model are:
[0014] This FPC board adopts a symmetrical stacked architecture centered on the signal transmission layer. The gradient adhesive layer balances the thermal expansion coefficient between layers, avoiding delamination at high and low temperatures and ensuring structural stability. The bending area uses serpentine traces, buffer spaces, and reinforcing ribs to work together to resist bending. The serpentine traces disperse folding stress, the buffer spaces provide space for substrate deformation, and the reinforcing ribs strengthen the connection between the foil layer and the substrate. The composite shielding and heat dissipation layer only covers the first copper foil layer. The inner conductive shielding sublayer isolates electromagnetic interference, and the outer heat dissipation sublayer conducts heat away. The flexible folds in the bending area absorb tensile deformation, taking into account signal transmission, bending resistance, and heat dissipation. Attached Figure Description
[0015] Figure 1 This is a schematic diagram of the copper foil layer structure of the product of this utility model;
[0016] Figure 2 This is a schematic diagram of the overall frontal arrangement structure of the product of this utility model;
[0017] Figure 3 This is a schematic diagram of the flexible pleated structure of the product of this utility model;
[0018] Figure 4 This is a schematic diagram of the composite shielding and heat dissipation layer structure of the product of this utility model.
[0019] In the figure: 1. FPC substrate body; 2. Bending area; 3. Non-bending area; 4. Signal transmission layer; 5. First gradient adhesive layer; 6. First substrate layer; 7. First copper foil layer; 8. Composite shielding and heat dissipation layer; 9. Second gradient adhesive layer; 10. Second substrate layer; 11. Second copper foil layer; 12. Serpentine trace; 13. Buffer area; 14. Reinforcing rib; 15. Flexible pleat; 16. Conductive shielding sublayer; 17. Heat dissipation sublayer; 18. Third gradient adhesive layer. Detailed Implementation
[0020] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.
[0021] This utility model relates to a bend-resistant multilayer FPC board, such as... Figure 1-4 As shown, the FPC substrate body 1 is a long, flexible sheet with a narrow, elongated rectangle shape. Along its length, the FPC substrate body 1 is clearly divided into a bending area 2 and a non-bending area 3, with no physical dividing line between them. The bending area 2 is located in the middle of the FPC's length direction, which corresponds exactly to the opening and closing movement area of the phone's hinge. It is the core deformation section during folding. All special structures for resisting bending, such as the serpentine traces 12, buffer spaces 13, reinforcing ribs 14, and flexible folds 15, are concentrated in this area. The non-bending area 3 is divided into two sections, located at the two ends of the bending area 2. The first non-bending area is located at the motherboard connection end of the FPC. Its surface has no special structure and is only a flat, multilayered substrate, used for soldering to the display driver interface of the motherboard through reflow soldering. The second non-bending area is located at the screen connection end of the FPC. It is also a flat, multilayered substrate, used for soldering to the screen's driver chip.
[0022] Furthermore, the signal transmission layer 4 is located at the very center of the FPC stack-up architecture and is the core of signal transmission for the entire FPC. Its upper and lower surfaces are directly bonded to the first gradient adhesive layer 5 and the second gradient adhesive layer 9, respectively, without any other interlayer structures. All display drive signals (red, green, blue, and synchronization signals) are transmitted through this layer. The first gradient adhesive layer 5 directly covers the upper surface of the signal transmission layer 4, and its two ends are fixedly connected to the signal transmission layer 4 and the first substrate layer 6 by thermoforming. Its function is to balance the thermal expansion difference between the signal transmission layer 4 and the first substrate layer 6 by using a compositional gradient with a higher epoxy content near the signal transmission layer 4 and a higher polyurethane content near the substrate layer, thus preventing interlayer delamination during high and low temperature cycling. The substrate layer 6 is directly bonded to the upper surface of the first gradient adhesive layer 5. The side away from the first gradient adhesive layer 5 is tightly bonded to the first copper foil layer 7, serving as a flexible support substrate. Its function is to provide structural support for the first copper foil layer while ensuring the overall flexibility of the FPC. The first copper foil layer 7 directly covers the upper surface of the first substrate layer 6. The side away from the first substrate layer 6 has only its upper surface covered by a composite shielding and heat dissipation layer 8. This layer serves as an auxiliary conductive layer, working in conjunction with the signal transmission layer 4 to transmit signals, and also provides a bonding substrate for the composite shielding and heat dissipation layer 8. The composite shielding and heat dissipation layer 8 only covers the first copper foil layer. The upper surface of layer 7 is away from the first substrate layer 6 and does not extend to the second copper foil layer of the lower FPC structure. However, flexible pleats 15 are only provided on the surface of the bending area 2. Their function is to simultaneously achieve electromagnetic shielding and heat dissipation without increasing the thickness of the lower FPC layer, thus adapting to the narrow bezel design of mobile phones. The second gradient adhesive layer 9 directly covers the lower surface of the signal transmission layer 4. Its thickness, material, and width are completely consistent with the first gradient adhesive layer 5. Both ends are fixedly connected to the signal transmission layer 4 and the second substrate layer 10, respectively. Its function is the same as that of the first gradient adhesive layer 5. The symmetrical design further balances the interlayer stress. The second substrate layer 10 is directly attached to the lower surface of the second gradient adhesive layer 9. Its thickness, material, and width are completely consistent with those of the first substrate layer 6. The side away from the second gradient adhesive layer 9 is closely attached to the second copper foil layer 11, and its function is symmetrical with that of the first substrate layer, providing support for the second copper foil layer 11. The second copper foil layer 11 directly covers the lower surface of the second substrate layer 10. Its thickness, material, and width are completely consistent with those of the first copper foil layer 7. The surface is not covered by the composite shielding heat dissipation layer 8, and its function is symmetrical with that of the first copper foil layer 7, serving as an auxiliary conductive layer, while avoiding the lower layer structure being too thick and affecting the internal space of the mobile phone.
[0023] Furthermore, the serpentine trace 12 is formed only on the upper surface of the first copper foil layer 7 and the lower surface of the second copper foil layer 11 in the bending area 2. There is no serpentine trace in the non-bending area 3. Each serpentine trace is continuously distributed in the bending area 2 along the length direction of the FPC, located in the middle of the width direction of the copper foil layer, and does not exceed the range of the copper foil layer. The extension direction of the serpentine trace 12 forms a preset angle of 45° with the bending direction of the FPC. The bending direction of the FPC is vertically perpendicular to the width direction when folded up and down. The serpentine trace 12 forms a continuous S-shaped meandering structure at a 45° angle. When the FPC is folded, the conductor on the outside of the bending area 2 is subjected to tensile force and the inside is subjected to compressive force. Traditional straight conductors are prone to breakage at stress concentration points. However, the S-shaped structure of the serpentine trace 12 can disperse the concentrated stress to each segment of the bent conductor, ensuring signal conduction.
[0024] Furthermore, the buffer zone 13 is a hollow structure that penetrates the corresponding copper foil layer and the adjacent substrate layer. It exists only in the bending zone 2. The upper layer penetrates the first copper foil layer 7 and the first substrate layer 6 from the upper surface of the first copper foil layer 7 to the lower surface of the first substrate layer 6, forming an upper layer hollow. The lower layer penetrates the second copper foil layer 11 and the second substrate layer 10 from the lower surface of the second copper foil layer 11 to the upper surface of the second substrate layer 10, forming a lower layer hollow. There are a total of 2 buffer zones, located on both sides of the serpentine trace 12. The long axis of each buffer zone extends along the length of the FPC, and both ends extend to the bending zone 2. The transition position between the non-bending area 3 and the buffer zone is such that one end is within the bending area 2 and the other end is within the non-bending area 3, ensuring that the deformation stress can be extended to the non-bending area 3 for release. When the FPC is folded, the first substrate layer 6 and the second substrate layer 10 will undergo bending deformation. If there is no deformation space, the substrate is prone to cracking due to compression. The hollow structure of the buffer zone 13 can provide sufficient space for the substrate deformation, avoiding the accumulation and wrinkling of the copper foil layer. The copper foil layer is closely attached to the substrate layer. When folded, the copper foil layer is prone to accumulation due to the deformation of the substrate. The buffer zone 13 can reduce the compression contact area of the copper foil layer and avoid signal interruption caused by copper foil wrinkling.
[0025] Furthermore, the reinforcing ribs 14 are integrally formed with the substrate layer and are only distributed at the edge of the buffer void 13 in the bending area 2. The upper reinforcing ribs 14 are integrally formed with the first substrate layer 6 and are symmetrically distributed on both sides of the long axis of the buffer void 13, with two reinforcing ribs 14 in each buffer void 13. One end of the reinforcing rib 14 is integrally connected with the first substrate layer 6, and the other end extends upward perpendicular to the surface direction along the FPC's lamination direction, directly and fixedly connected to the lower surface of the first copper foil layer 7 without an additional adhesive layer. They are bonded by a hot-pressing process, and the lower reinforcing rib 14 is integrally formed with the first substrate layer 6. The reinforcing rib 14 is integrally formed with the second substrate layer 10 and is completely symmetrical with the upper reinforcing rib 14. It is distributed along the edge of the buffer void 13 of the second substrate layer 10. One end is integral with the second substrate layer 10, and the other end extends downward along the lamination direction and is fixedly connected to the upper surface of the second copper foil layer 11. The length of the reinforcing rib 14 is consistent with the bending area 2 of the buffer void 13. When the FPC is repeatedly folded, the copper foil layer and the substrate layer are prone to peeling due to stress. The reinforcing rib 14 enhances the bonding force between the two through mechanical interlocking and hot pressing.
[0026] Furthermore, the composite shielding and heat dissipation layer 8 is the top outer layer structure of the FPC, covering only the upper surface of the first copper foil layer 7 away from the first substrate layer 6, and does not extend to the second copper foil layer 11. Its interior is divided into three layers along the stacking direction: "conductive shielding sub-layer 16, third gradient adhesive layer 18, and heat dissipation sub-layer 17". The inner layer is the conductive shielding sub-layer 16, which is directly and tightly attached to the upper surface of the first copper foil layer 7, and its length covers the entire FPC. The middle layer is the third gradient adhesive layer 18, which is directly attached to the upper surface of the conductive shielding sub-layer 16, and its extension direction is consistent with the first gradient adhesive layer 5. Its two ends are fixedly connected to the conductive shielding sub-layer 16 and the heat dissipation sub-layer 17, respectively. The outer layer is the heat dissipation sub-layer 17, which is directly attached to the upper surface of the third gradient adhesive layer 18. Flexible folds 15 are only provided on the surface of the bending area 2, and the surface of the non-bending area 3 is flat.
[0027] Furthermore, the conductive shielding sublayer 16, located at the innermost layer of the composite shielding and heat dissipation layer, directly contacts the first copper foil layer 7 and is the core layer of electromagnetic shielding. It uses nickel-plated copper foil with a passivated surface and has no adhesive layer on its bonding surface with the first copper foil layer 7; it is directly fixed by hot pressing. The copper substrate can absorb low-frequency interference, preventing screen flicker caused by radio frequency interference. The third gradient adhesive layer 18 uses epoxy-siloxane gradient adhesive, with its composition gradually changing along the stacking direction. Located between the conductive shielding sublayer 16 and the heat dissipation sublayer 17, it only serves a connecting function and has no other function, thus solving the problem of mismatch between the metal material of the conductive shielding sublayer 16 and the composite material of the heat dissipation sublayer 17. To prevent the two layers from separating due to rigidity differences during bending, and to maintain the overall flexibility of the composite shielding heat dissipation layer, the heat dissipation sub-layer 17 is made of graphene polyimide composite film. It is located on the outermost layer of the composite shielding heat dissipation layer and is in direct contact with the air. It is the core layer for heat dissipation and can quickly dissipate the heat conducted by the conductive shielding sub-layer 16 into the air. The flexible folds 15 are only distributed on the bending area 2 surface of the heat dissipation sub-layer 17 and correspond to the bending area of the first copper foil layer. They are spaced apart along the width direction of the FPC. When the FPC is folded, the outer side of the heat dissipation sub-layer 17 will be stretched. The flexible folds 15 can absorb the stretching amount through the unfolding of the folds, preventing the heat dissipation layer from breaking due to excessive stretching.
[0028] In practical use: The FPC board adopts a symmetrical stacked architecture with the signal transmission layer 4 as the center. The gradient adhesive layer balances the thermal expansion coefficient between layers to avoid delamination between layers at high and low temperatures and ensure structural stability. The bending area 2 is resisted by serpentine traces 12, buffer space 13 and reinforcing ribs 14 working together to resist bending. The serpentine traces 12 disperse the folding stress, the buffer space 13 leaves space for the deformation of the substrate layer, and the reinforcing ribs 14 strengthen the connection between the foil layer and the substrate. The composite shielding and heat dissipation layer 8 only covers the first copper foil layer 7. The inner conductive shielding sub-layer 16 isolates electromagnetic interference, and the outer heat dissipation sub-layer 17 conducts heat away. The flexible folds 15 of the bending area 2 absorb tensile deformation, taking into account signal transmission, bending resistance and heat dissipation.
[0029] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0030] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A bend-resistant multilayer FPC board, comprising an FPC substrate body (1), wherein the FPC substrate body (1) is divided into a bending region (2) and a non-bending region (3), characterized in that: The FPC substrate body (1) adopts a symmetrical stacked structure, consisting of a signal transmission layer (4), a first gradient adhesive layer (5), a first substrate layer (6), a first copper foil layer (7), and a composite shielding and heat dissipation layer (8) from the inside out. The side of the signal transmission layer (4) away from the first gradient adhesive layer (5) is connected to the second substrate layer (10) through a second gradient adhesive layer (9), and the side of the second substrate layer (10) away from the signal transmission layer (4) is connected to the second copper foil layer (11). The first copper foil layer (7) and the second copper foil layer (11) are symmetrically distributed about the signal transmission layer (4). The first copper foil layer (7) and the second copper foil layer (11) in the bending area (2) are provided with serpentine traces (12), and buffer spaces (13) are provided on both sides of the serpentine traces (12). The buffer spaces (13) are connected to the corresponding first copper foil. The layer (7) and the second copper foil layer (11) have a hollow structure with the adjacent first substrate layer (6) and second substrate layer (10), and the edge of the buffer area (13) is provided with reinforcing ribs (14). The reinforcing ribs (14) are integrally formed with the corresponding first substrate layer (6) and second substrate layer (10) and extend along the stacking direction of the FPC substrate body (1). The composite shielding heat dissipation layer (8) covers the side of the first copper foil layer (7) away from the first substrate layer (6), and the composite shielding heat dissipation layer (8) is provided with flexible folds (15) on the surface of the bending area (2). The direction of the flexible folds (15) is adapted to the direction of the serpentine trace (12). The composite shielding heat dissipation layer (8) includes a conductive shielding sublayer (16) and a heat dissipation sublayer (17) that are bonded together in sequence. The conductive shielding sublayer (16) and the heat dissipation sublayer (17) are fixedly connected along the stacking direction.
2. The bend-resistant multilayer FPC board according to claim 1, characterized in that: Both the first gradient adhesive layer (5) and the second gradient adhesive layer (9) are arranged along the stacking direction of the FPC substrate body (1), and the two ends of the first gradient adhesive layer (5) are fixedly connected to the signal transmission layer (4) and the first substrate layer (6) respectively, and the two ends of the second gradient adhesive layer (9) are fixedly connected to the signal transmission layer (4) and the second substrate layer (10) respectively.
3. The bend-resistant multilayer FPC board according to claim 1, characterized in that: The first substrate layer (6) and the second substrate layer (10) are symmetrically distributed about the signal transmission layer (4), and the side of the first substrate layer (6) away from the first gradient adhesive layer (5) is fixedly connected to the first copper foil layer (7), and the side of the second substrate layer (10) away from the second gradient adhesive layer (9) is fixedly connected to the second copper foil layer (11).
4. The bend-resistant multilayer FPC board according to claim 1, characterized in that: The extension direction of the serpentine trace (12) is at a preset angle to the bending direction of the FPC substrate body (1), and the serpentine trace (12) is continuously distributed along the length direction of the first copper foil layer (7) and the second copper foil layer (11).
5. The bend-resistant multilayer FPC board according to claim 1, characterized in that: The buffer zone (13) is a dumbbell-shaped hollow structure, and the two ends of the buffer zone (13) extend to the transition position between the bending zone (2) and the non-bending zone (3).
6. The bend-resistant multilayer FPC board according to claim 1, characterized in that: The number of the reinforcing ribs (14) is at least two, and the two reinforcing ribs (14) are symmetrically distributed on both sides of the long axis of the buffer zone (13). The end of the reinforcing rib (14) away from the first substrate layer (6) and the second substrate layer (10) is fixedly connected to the corresponding first copper foil layer (7) and second copper foil layer (11).
7. The bend-resistant multilayer FPC board according to claim 1, characterized in that: A third gradient adhesive layer (18) is provided between the conductive shielding sublayer (16) and the heat dissipation sublayer (17). The two ends of the third gradient adhesive layer (18) are fixedly connected to the conductive shielding sublayer (16) and the heat dissipation sublayer (17) respectively, and the extension direction of the third gradient adhesive layer (18) is consistent with the extension direction of the first gradient adhesive layer (5).
8. The bend-resistant multilayer FPC board according to claim 1, characterized in that: The flexible folds (15) are distributed at intervals along the width direction of the composite shielding heat dissipation layer (8), and the depth of the flexible folds (15) gradually decreases from the center of the bending area (2) to both sides.