Foldable display device

Abstract

The present application relates to the technical field of electronic products. Provided is a foldable display device, which is used for mitigating the problem of abnormal noise generated during the opening and closing of a foldable display device. The foldable display device comprises: a first door panel, a second door panel, a third door panel, a hinge structure and a flexible printed circuit, wherein the first door panel and the third door panel are located on two opposite sides of the second door panel; the hinge structure is located on one side of the second door panel, and the first door panel and the third door panel are both rotatably connected to the hinge structure; and the flexible printed circuit comprises a fixed portion and a bendable portion. The foldable display device further comprises a limiting structure, which is located between the flexible printed circuit and the second door panel and covers at least part of the bendable portion. Using the limiting structure can improve the mechanical performance of the flexible printed circuit, and can also limit the abrupt shape change of the flexible printed circuit, thereby effectively solving the problem of abrupt shape change during the opening and closing of the foldable display device, and further solving the problem of abnormal noise generated during the opening and closing of the foldable display device.

Description

A foldable display device

[0001] This application claims priority to Chinese Patent Application No. 202422652226.1, filed with the State Intellectual Property Office of China on October 30, 2024, entitled "A Foldable Display Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electronic product technology, and more particularly to a foldable display device. Background Technology

[0003] Because foldable screens can provide a larger screen space while maintaining portability, they offer users a richer visual experience. With continuous breakthroughs and innovations in foldable screen technology, foldable display devices are increasingly appearing on the market.

[0004] Foldable display devices connect adjacent components via a hinge, and a complete foldable flexible screen covers the hinge and the surfaces of the adjacent components. Various signals are transmitted between the components on both sides of the hinge using a flexible printed circuit board (FPC) that passes through the hinge. However, during the large-angle opening and closing of a foldable display device, the space through the hinge gradually decreases from its maximum size, which may compress the FPC and cause it to creak. How to solve the creaking noise generated during the opening and closing of foldable display devices is a pressing problem that needs to be addressed.

[0005] Utility Model Content

[0006] This application provides a foldable display device that can effectively suppress the problem of abrupt changes in the shape of the flexible circuit board during the opening and closing of the foldable display device, thereby reducing the abnormal noise generated during the opening and closing of the foldable display device.

[0007] To achieve the above objectives, the embodiments of this application adopt the following technical solutions:

[0008] In a first aspect, embodiments of this application provide a foldable display device, comprising: a first door panel, a second door panel, a third door panel, a hinge structure, a flexible circuit board, and a limiting structure. The first door panel and the third door panel are located on opposite sides of the second door panel. The hinge structure is located on one side of the second door panel, and both the first and third door panels are rotatably connected to the hinge structure. Along the direction from the second door panel to the first door panel, the flexible circuit board includes a first fixing portion and a bendable portion connected to the first fixing portion. The first fixing portion is fixed to the side of the second door panel facing the hinge structure. The limiting structure is located on the side of the flexible circuit board facing the second door panel, and the limiting structure covers at least a portion of the bendable portion.

[0009] During the opening and closing process of foldable display devices, the limiting structure can improve the mechanical properties of flexible circuit boards and limit abrupt changes in the shape of flexible circuit boards, effectively suppressing the problem of abrupt changes in shape during the opening and closing process of foldable display devices, and further reducing the problem of abnormal noise generated during the opening and closing process of foldable display devices.

[0010] In one possible implementation, the hinge structure includes a first end near the first door panel. A bendable portion is located above the first end. A portion of the limiting structure is fixed between the second door panel and the flexible circuit board, while another portion extends toward the first door panel and beyond the first end.

[0011] During the opening and closing process of the foldable display device, the flexible circuit board is subjected to an extrusion force pointing towards the second door panel and an elastic force to maintain its shape, which easily causes deformation towards the second door panel. By having another part of the limiting structure extend towards the first door panel and beyond the first end, the limiting structure is more effective in restricting the deformation of the flexible circuit board towards the second door panel.

[0012] In one possible implementation, the foldable display device further includes a mid-frame. The mid-frame includes a first portion and a second portion, located on opposite sides of a hinge structure. The flexible circuit board also includes a second fixing portion and a third fixing portion, the second fixing portion being fixed to the first portion and the third fixing portion being fixed to the second portion. The portion of the flexible circuit board located between the first and second fixing portions has a segmented groove, and the bendable portions located on opposite sides of the segmented groove include a first bendable portion and a second bendable portion. A limiting structure covers at least a portion of the first bendable portion and at least a portion of the second bendable portion.

[0013] This is because a flexible circuit board containing segmented slots is also called a segmented flexible circuit board. For segmented flexible circuit boards, the bendable portion of each segment may experience abrupt changes in shape. The limiting structure covers at least a portion of the first bendable portion and at least a portion of the second bendable portion, which can specifically limit the abrupt changes in shape of the bendable portion of each segment of the flexible circuit board.

[0014] In one possible implementation, the limiting structure includes a first limiting structure and a second limiting structure. The first limiting structure covers at least a portion of the first bendable portion, and the second limiting structure covers at least a portion of the second bendable portion. The first and second limiting structures are integrated as a single unit. This is because, for segmented flexible circuit boards, the widths of the two flexible circuit boards on either side of the segmented groove may differ, and the morphological changes of different segments will also differ during the opening and closing of the foldable display device. Therefore, the first and second limiting structures can respectively limit the morphological changes of the first and second bendable portions. The integral design of the first and second limiting structures as a single unit facilitates the processing and installation of the limiting structure.

[0015] In one possible implementation, the first bendable part has a dimension of S1 in the first direction, and the second bendable part has a dimension of S2 in the first direction, where S1 and S2 are not equal. The first limiting structure has a dimension of h1 in the second direction, and the second limiting structure has a dimension of h2 in the second direction, where h1 and h2 are not equal. The first direction is parallel to the length direction of the hinge structure, and the second direction is parallel to the arrangement direction of the first door panel, the second door panel, and the third door panel.

[0016] The dimension in the first direction is defined as the width, and the dimension in the second direction is defined as the length. When the widths of the two flexible circuit boards on either side of the segmented slot are different, the shape changes of the two flexible circuit boards during the opening and closing process of the foldable display device will also be different. Moreover, the narrower the flexible circuit board, the greater the elastic force or extrusion force generated during the opening and closing process of the foldable display device, and the longer the limiting structure required.

[0017] In one possible implementation, S1 is less than S2, and h1 is greater than h2. Since the dimension S1 of the first bendable part in the first direction is less than the dimension S2 of the second bendable part in the first direction, during the opening and closing process of the foldable display device, the elastic force or extrusion force generated by the first bendable part is greater than that generated by the second bendable part, resulting in different degrees of deformation of the first and second bendable parts towards the second door panel. The dimension h1 of the first limiting structure in the second direction is greater than the dimension h2 of the second limiting structure in the second direction, which can correspondingly counteract the deformation generated by the first and second bendable parts towards the second door panel.

[0018] In one possible implementation, the side of the limiting structure facing the flexible circuit board has an insulating layer, or the surface of the flexible circuit board facing the limiting structure is covered with a film. This prevents electrical connection between the circuit board and the limiting structure, avoids short circuits between different signal lines or electrical components, and ensures normal circuit operation.

[0019] In one possible implementation, the limiting structure includes at least one of a polyester film sheet or a polyimide sheet. Both polyester film sheets and polyimide sheets possess excellent high-temperature resistance, corrosion resistance, and chemical resistance. Using polyester film sheets and polyimide sheets as materials for the limiting structure helps improve the durability and stability of the circuit board, thereby extending the product's lifespan.

[0020] In one possible implementation, the stiffness of the bendable portion is less than that of the first fixed portion. During the opening and closing of the foldable display device, the reduced stiffness of the bendable portion improves the limiting structure's effect on the abrupt changes in the shape of the flexible circuit board, effectively suppressing the problem of abrupt shape changes during the opening and closing of the foldable display device, and further mitigating the problem of abnormal noise generated during the opening and closing of the foldable display device.

[0021] In one possible implementation, the volume fraction of the metal traces in the bendable portion is less than the volume fraction of the metal traces in the first fixed portion. This allows the stiffness of the bendable portion to be lower than that of the first fixed portion, resulting in a better restraining effect of the limiting structure on abrupt changes in the shape of the flexible circuit board.

[0022] In one possible implementation, the flexible circuit board includes a first layer of metal traces and a second layer of metal traces stacked together, with the first layer of metal traces closer to the second door panel than the second layer of metal traces. The volume fraction of the first layer of metal traces in the bendable portion is less than the volume fraction of the first layer of metal traces in the first fixing portion. In this way, when the flexible circuit board is a multi-layer flexible circuit board, the layer closer to the second door panel is designated as the "first layer," and the other layer is designated as the "second layer." The stiffness of the first layer of the bendable portion is less than that of the second layer of the bendable portion, which can better accommodate the different bending radii of each layer and better cooperate with the limiting structure to restrict the abrupt changes in the shape of the flexible circuit board.

[0023] In one possible implementation, the first layer of metal traces is the surface layer metal traces. In this case, it is easier to process pre-fabricated multilayer flexible circuit boards with the first layer of metal traces being the surface layer metal traces.

[0024] In one possible implementation, the elastic modulus of the bendable portion is less than that of the first fixed portion. This reduces the elastic modulus and stiffness of the bendable portion, decreasing the probability of abrupt changes in the flexible circuit board's shape and allowing for better control of such changes in conjunction with the limiting structure.

[0025] In one possible implementation, the flexible circuit board includes a first flexible substrate and a second flexible substrate stacked together, with the first flexible substrate positioned closer to the second panel than the second flexible substrate. The elastic modulus of the first flexible substrate in the bendable portion is less than that of the second flexible substrate. This results in the inner layer having less stiffness than the outer layer, better adapting to the different bending radii of each layer and better coordinating with the limiting structure to restrict abrupt changes in the shape of the flexible circuit board.

[0026] In one possible implementation, the flexible circuit board further includes a third flexible substrate, with the second flexible substrate located between the first and third flexible substrates. The elastic modulus of the second flexible substrate in the bendable portion is less than or equal to the elastic modulus of the third flexible substrate. In this way, the stiffness of the inner layer is less than that of the middle and outer layers, the stiffness of the middle layer is less than that of the outer layer, and the stiffness of the different layers of the flexible circuit board adopts a gradient distribution, which can better cooperate with the limiting structure to restrict the abrupt changes in the shape of the flexible circuit board.

[0027] Secondly, embodiments of this application provide a foldable display device, including: a first door panel, a second door panel, a third door panel, a hinge structure, and a flexible circuit board. The first door panel and the third door panel are located on opposite sides of the second door panel. Both the first door panel and the third door panel are rotatably connected to the hinge structure. Along the direction from the second door panel to the first door panel, the flexible circuit board includes a first fixing part and a bendable part connected to the first fixing part. The first fixing part is fixed to the side of the second door panel facing the hinge structure. The stiffness of the bendable part is less than the stiffness of the first fixing part.

[0028] Stress concentration often occurs at locations where the structural shape changes abruptly. This phenomenon can cause deformation in structures made of flexible materials and static load fracture in structures made of brittle materials. One way to reduce stress concentration is to reduce the stiffness of the stress concentration point. Stiffness is a physical quantity used to describe the ability of a structure or material to resist deformation. The bendable portion is a stress concentration point in a flexible circuit board. If the stiffness of the bendable portion is less than that of the first fixed portion, the stress can be distributed more evenly on the flexible circuit board when subjected to external forces, reducing the probability of stress concentration and thus reducing the probability of abrupt changes in the flexible circuit board's shape. Ultimately, this can reduce the abnormal noise caused by abrupt changes in the shape of the flexible circuit board during the opening and closing of foldable display devices.

[0029] In one possible implementation, the volume fraction of the metal traces in the bendable portion is less than the volume fraction of the metal traces in the first fixed portion. Within the elastic limits of the structure or material, the stiffness of the structure or material can be measured by the elastic modulus. Reducing the volume fraction of the metal traces can weaken the local elastic modulus. In this way, the elastic modulus of the bendable portion is weakened and the stiffness is reduced, which can effectively reduce the elastic force at the stress concentration points of the flexible circuit board and reduce the abnormal noise caused by the sudden shape change of the flexible circuit board during the opening and closing of the foldable display device.

[0030] In one possible implementation, the flexible circuit board includes a first layer of metal traces and a second layer of metal traces stacked together, with the first layer of metal traces being closer to the second door panel than the second layer of metal traces.

[0031] When a flexible circuit board is a multilayer flexible circuit board, each layer can have metal traces. Due to the different bending radii of each layer, the flexible circuit board layer closer to the second panel has more redundancy and a higher probability of morphological abrupt changes. Among them, the flexible circuit board layer closest to the second panel is the top layer, the layer furthest from the flexible circuit board is the bottom layer, and any other layers are collectively referred to as intermediate layers.

[0032] In one possible implementation, the volume fraction of the first layer of metal traces in the bendable portion is less than the volume fraction of the first layer of metal traces in the first fixed portion. In this case, when the flexible circuit board is a multilayer flexible circuit board, the layer closer to the second panel is designated as the "first layer," and the other layer is designated as the "second layer." The stiffness of the first layer of the bendable portion is less than that of the second layer, which better accommodates the different bending radii of each layer and better coordinates with the limiting structure to restrict abrupt changes in the shape of the flexible circuit board.

[0033] In one possible implementation, the first layer of metal traces is the surface layer metal traces. This makes it easier to process pre-fabricated multilayer flexible circuit boards when modifying the manufacturing process.

[0034] In one possible implementation, the elastic modulus of the bendable portion is less than that of the first fixed portion. This reduces the elastic modulus of the bendable portion and its stiffness, thereby decreasing the probability of abrupt changes in the flexible circuit board's shape.

[0035] In one possible implementation, the flexible circuit board includes a first flexible substrate and a second flexible substrate stacked together, with the first flexible substrate positioned closer to the second door panel than the second flexible substrate. The elastic modulus of the first flexible substrate in the bendable portion is less than that of the second flexible substrate. This reduces the stiffness of the inner layer compared to the outer layer, decreasing the probability of abrupt changes in the inner layer's shape, thereby reducing the probability of abrupt changes in the flexible circuit board's shape and the likelihood of abnormal noises during the opening and closing of the foldable display device.

[0036] In one possible implementation, the flexible circuit board further includes a third flexible substrate, with the second flexible substrate located between the first and third flexible substrates. The elastic modulus of the second flexible substrate in the bendable portion is less than or equal to the elastic modulus of the third flexible substrate. In this way, the stiffness of the inner layer is less than that of the middle and outer layers, the stiffness of the middle layer is less than that of the outer layer, and the stiffness of different layers of the flexible circuit board adopts a gradient distribution. This can reduce the probability of abrupt changes in the shape of the inner layer, thereby reducing the probability of abrupt changes in the shape of the flexible circuit board and the probability of abnormal noises during the opening and closing of the foldable display device.

[0037] During the unfolding or closing of a foldable display device, the stiffness of the bendable portion of the flexible circuit board decreases, making it more prone to deformation under external force and absorbing more energy during deformation. This reduces the abnormal noise caused by the sudden change in shape of the flexible circuit board during the opening and closing of the foldable display device. Attached Figure Description

[0038] Figure 1 is a structural schematic diagram of the first type of foldable display device provided in an embodiment of this application;

[0039] Figure 2 is a structural schematic diagram of a second type of foldable display device provided in an embodiment of this application;

[0040] Figure 3 is a structural schematic diagram of a foldable display device in a closed state according to an embodiment of this application;

[0041] Figure 4 is a structural schematic diagram of the intermediate state of the foldable display device in Figure 3;

[0042] Figure 5 is a structural schematic diagram of the unfolded state of the foldable display device in Figure 3;

[0043] Figure 6 is a two-dimensional structural diagram of the foldable display device in Figure 5;

[0044] Figure 7A is a two-dimensional structural diagram of the unfolded state of the foldable display device in Figure 6. The extrusion force is greater than the elastic force, and the bendable part is arched.

[0045] Figure 7B is a two-dimensional structural diagram of the foldable display device in the intermediate state shown in Figure 6. The extrusion force is greater than the elastic force, and the bendable part is arched.

[0046] Figure 7C is a two-dimensional structural schematic diagram of the foldable display device in the intermediate state shown in Figure 6. The extrusion force is less than the elastic force, and the arch of the bendable part disappears.

[0047] Figure 8 is a two-dimensional structural diagram of a foldable display device with an added limiting structure in the unfolded state according to an embodiment of this application;

[0048] Figure 9 is a two-dimensional structural diagram of a foldable display device in an unfolded state according to an embodiment of this application. The flexible circuit board of the foldable display device includes segmented slots.

[0049] Figure 10A is a two-dimensional structural schematic diagram of the folding display device in Figure 9 from another angle, with the width of the reinforcing plate being a constant.

[0050] Figure 10B is a two-dimensional structural schematic diagram of the foldable display device in Figure 9 from another angle. The width of the reinforcing plate varies with the width of each segment of the flexible circuit board.

[0051] Figure 10C is a schematic diagram of the flexible circuit board in the foldable display device shown in Figures 10A and 10B;

[0052] Figure 11 is a two-dimensional structural diagram of a foldable display device with an added limiting structure in the unfolded state according to an embodiment of this application. The flexible circuit board of the foldable display device includes segmented slots.

[0053] Figure 12A is a two-dimensional structural diagram of the folding display device in Figure 11 from another angle. The three limiting structures can be set separately.

[0054] Figure 12B shows another implementation of the limiting structure in Figure 12A, which can be a two-section structure.

[0055] Figure 13A is a two-dimensional structural diagram of the folding display device in Figure 11 from another angle. The three limiting structures can be connected into one unit.

[0056] Figure 13B shows another implementation of the limiting structure in Figure 13A, which can be a two-stage structure;

[0057] Figure 14A is a two-dimensional structural diagram of the folding display device in Figure 11 from another angle. The sizes of the three limiting structures can be different.

[0058] Figure 14B shows another implementation of the limiting structure in Figure 14A, which can be a two-stage structure.

[0059] Figure 15 shows a folding display device with an optimized flexible circuit board structure provided in an embodiment of this application, which adopts a design to reduce copper distribution by reducing stress concentration points;

[0060] Figure 16 shows a folding display device with an optimized flexible circuit board structure provided in an embodiment of this application, which adopts a stress concentration point removal of surface copper design;

[0061] Figure 17 shows a folding display device with an optimized flexible circuit board structure provided in an embodiment of this application, which adopts a stress concentration point striped copper design.

[0062] Figure 18 shows a folding display device with an optimized flexible circuit board structure provided in an embodiment of this application, which adopts a stress concentration point grid copper design. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of this application clearer, the application will now be described in further detail with reference to the accompanying drawings.

[0064] In the following description, the terms "first," "second," etc., 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. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0065] Furthermore, in this application, directional terms such as "upper" and "lower" are defined relative to the orientation of the components shown in the accompanying drawings. It should be understood that these directional terms are relative concepts, used for relative description and clarification, and can change accordingly depending on the orientation of the components in the accompanying drawings.

[0066] This application provides a foldable display device that can be applied to various communication systems or protocols, such as Bluetooth (BT) communication technology, Global Positioning System (GPS) communication technology, Global System for Mobile Communication (GSM) communication technology, Wireless Fidelity (WiFi) communication technology, Wideband Code Division Multiple Access (WCDMA) communication technology, Long Term Evolution (LTE), 5G communication technology, and other future communication technologies.

[0067] The foldable display device in this application embodiment can be a mobile phone, tablet, laptop, smart home device, smart wearable device (e.g., smartwatch, smart bracelet, smart glasses, smart helmet), virtual reality (VR) display terminal, augmented reality (AR) display terminal, etc. The display terminal can also be a handheld device with wireless communication capabilities, a computing device or other processing device connected to a wireless modem, an in-vehicle device, a display terminal in a 5G network, or a display terminal in a future evolved public land mobile network (PLMN), etc., and this application embodiment is not limited to these categories.

[0068] This application provides a foldable display device. The foldable display device may include various electronic devices having a flexible screen and capable of changing the unfolded or folded form of the flexible screen and itself. Under different usage requirements, the foldable display device can be unfolded to a flattened state, folded to a closed state, or in an intermediate state between the flattened and closed states. That is, the foldable display device has at least two states: a flattened state and a closed state. In some cases, a third state may be further included, namely, an intermediate state between the flattened and closed states. It is understood that the intermediate state is not a unique state, but can be any one or more states between the flattened and closed states of the foldable display device.

[0069] In the embodiments of this application, the foldable display device is illustrated by taking a foldable mobile phone as an example.

[0070] In some embodiments, as shown in FIG1, a structural diagram of a foldable display device is provided. This example foldable display device is a dual-screen foldable phone. The dual-screen foldable phone includes a first housing 100a, a second housing 100b, a first printed circuit board 101a, a second printed circuit board 101b, a flexible circuit board 102, a display module 11, and a hinge structure. The display module 11 can continuously cover the first housing 100a and the second housing 100b. The first housing 100a and the second housing 100b are disposed on both sides of the hinge structure and are respectively connected to the hinge structure. Under the action of the hinge structure, the display module 11 can be flattened and closed. The first printed circuit board 101a is connected to the second printed circuit board 101b through the flexible circuit board 102, enabling signal transmission on both sides of the hinge structure.

[0071] In one possible implementation, the portion of the display module 11 on the first housing 100a is the left half of the screen of the foldable display device, and the portion of the display module 11 on the second housing 100b is the right half of the screen of the foldable display device; that is, the foldable display device is a horizontally folding phone. Compared to foldable display devices with non-foldable screens, the foldable display device provided in this embodiment has a larger screen area within the same volume, making it more suitable for different user scenarios.

[0072] In another possible implementation, the portion of the display module 11 on the first housing 100a is the upper half of the foldable display device's screen, and the portion of the display module 11 on the second housing 100b is the lower half of the foldable display device's screen; that is, the foldable display device is a vertically folding phone. Compared to foldable display devices with non-foldable screens, the foldable display device provided in this embodiment is smaller in size for the same screen area, making it more convenient for users to carry.

[0073] In another possible implementation, with the display module 11 closed, it is positioned between the first housing 100a and the second housing 100b, meaning the foldable display device is an inward-folding phone. Compared to foldable display devices with non-foldable screens, the foldable display device provided in this embodiment has its screen protected when folded, reducing the risk of damage from direct screen exposure. This design is not only safer but also reduces the possibility of accidental touches, giving users greater peace of mind during use.

[0074] In another possible implementation, with the display module 11 closed, the first housing 100a and the second housing 100b are inside the display module 11, meaning the foldable display device is an outward-folding phone. Compared to display devices with non-foldable screens, the foldable display device provided in this embodiment is relatively lighter and more suitable for users who prioritize portability. Compared to inward-folding phones, the foldable display device provided in this embodiment has a less noticeable screen crease, making it more suitable for users who prioritize visual experience.

[0075] In some embodiments, as shown in FIG2, is a structural diagram of another foldable display device, which is a three-screen foldable phone. This three-screen foldable phone may include a first housing 100a, a second housing 100b, a third housing 100c, a first hinge structure, a second hinge structure, a first printed circuit board 101a, a second printed circuit board 101b, a third printed circuit board 101c, a flexible circuit board 102, and a display module 11. The display module 11 may continuously cover the first housing 100a, the second housing 100b, and the third housing 100c. The first housing 100a and the second housing 100b are disposed on both sides of the first hinge structure and are respectively connected to the first hinge structure. The first hinge structure is movable to fold or unfold the first housing 100a and the second housing 100b relative to each other, thereby flattening and closing the display module 11 disposed on the first housing 100a and the second housing 100b. The second housing 100b and the third housing 100c are disposed on both sides of the second rotating shaft structure and are respectively connected to the second rotating shaft structure. The second rotating shaft structure is movable, so that the second housing 100b and the third housing 100c are folded or unfolded relative to each other, realizing the flattening and closing of the display module 11 disposed on the second housing 100b and the third housing 100c. The first printed circuit board 101a is connected to the second printed circuit board 101b through the flexible circuit board 102, and the second printed circuit board 101b is connected to the third printed circuit board 101c through the flexible circuit board 102, realizing signal transmission on both sides of the first rotating shaft structure and the second rotating shaft structure respectively.

[0076] This application does not limit the number of hinge structures in the foldable display device. For ease of explanation, the following description assumes there is only one hinge structure. The hinge structure includes: a first door panel, a second door panel, a third door panel, and a hinge structure. When the foldable display device is a mobile phone and there is only one hinge structure, the dual-screen foldable phone shown in Figure 1 can be used as an example. A coordinate system is established with the direction perpendicular to the display module 11 in the flattened state as the z-direction, the direction parallel to the long side of the hinge structure as the y-direction, and the direction perpendicular to the long side of the hinge structure as the x-direction. The coordinate system directions in Figures 3 to 18 are the same.

[0077] In some embodiments, as shown in Figures 3, 4, and 5, the process of a foldable display device unfolding from closed to open is illustrated sequentially. The foldable display device includes a hinge structure and a mid-frame 204. The hinge structure includes a first door panel 201, a second door panel 202, a third door panel 203, a hinge structure 205, a reinforcing plate 206, and a flexible circuit board 102. The first door panel 201 and the third door panel 203 are located on opposite sides of the second door panel 202. The hinge structure 205 is located on one side of the second door panel 202. Both the first door panel 201 and the third door panel 203 are rotatably connected to the hinge structure 205. The first door panel 201 and the third door panel 203 can move towards or away from each other, allowing the foldable display device to switch between a flattened state and a closed state.

[0078] It should be noted that the hinge structure is usually contained inside the pivot back cover, so in this embodiment, the hinge structure contained inside the pivot back cover is shown. Figure 6 is a view of Figure 5 in the opposite direction along the x-axis. The middle frame 204 includes a first part 2041, a second part 2042, a third part 2043, and a fourth part 2044. The reinforcing plate 206 includes a first reinforcing plate 2061, a second reinforcing plate 2062, and a third reinforcing plate 2063. The flexible circuit board 102 includes a first fixing part B1, a second fixing part B2, and a third fixing part B3. The first reinforcing plate 2061 is fixed to the first fixing part B1, which is fixed to the side of the second door panel 202 facing the hinge structure 205. The second reinforcing plate 2062 is fixed to the second fixing part B2, which is fixed to the first part 2041. The third reinforcing plate 2063 is fixed to the third fixing part B3, and the third fixing part B3 is fixed to the second part 2042.

[0079] Along the direction from the second door panel 202 to the first door panel 201 (in the opposite direction of the x direction as shown in Figure 6), the flexible circuit board 102 also includes a first bendable portion A1 connected to the first fixed portion B1.

[0080] Along the direction from the second door panel 202 to the third door panel 203 (as shown in the x direction of Figure 6), the flexible circuit board 102 also includes a second bendable portion A2 connected to the first fixed portion B1.

[0081] It is understandable that the structures on both sides of a hinge structure are symmetrical. When one side has a certain design, the other side can have the same design and achieve the same technical effect. For ease of explanation, the following descriptions of symmetrical structural designs will use the left side of the hinge structure as an example.

[0082] This application does not limit the method of fixing the flexible circuit board 102 and the second door panel 202. For example, the flexible circuit board 102 and the second door panel 202 can be fixed by adhesive.

[0083] This application does not limit the materials that can be selected for the reinforcing plate 206. The reinforcing plate 206 can be sheet material, such as steel plate; or, it can be glass fiber epoxy resin copper clad laminate, which can be called FR-4 material; or, other materials can be used.

[0084] This application does not limit the method of fixing the reinforcing plate 206 and the flexible circuit board 102. For example, an adhesive layer can be used to fix the flexible circuit board to the reinforcing plate. For instance, pressure-sensitive adhesive (PSD) can be used to fix the reinforcing plate and the flexible circuit board. Since PSD is an adhesive that is sensitive to pressure, it can enhance the flexibility of the flexible circuit board to adapt to increased length when it is bent.

[0085] Analyze the closing process of the rotating shaft structure using Figures 7A to 7C.

[0086] As shown in Figure 7A, the rotating shaft structure is in a flattened state. The first bendable portion A1 of the flexible circuit board is subjected to an extrusion force F1 pointing towards the center of rotation and an elastic force F2 that restores its shape. Since the extrusion force F1 is greater than the elastic force F2, the first bendable portion A1 of the flexible circuit board is arched.

[0087] As shown in Figure 7B, the rotating shaft structure is in an intermediate state, and the space through the shaft is smaller than the flattened state in Figure 7A. The first bendable portion A1 of the flexible circuit board is subjected to an extrusion force F1 pointing towards the center of rotation and an elastic force F2 that restores its shape. When the extrusion force F1 is greater than the elastic force F2, the first bendable portion A1 of the flexible circuit board still maintains its arched shape.

[0088] As shown in Figure 7C, the rotating shaft structure is in an intermediate state, and the space through the shaft is further reduced compared to the intermediate state in Figure 7B. The first bendable part A1 of the flexible circuit board is subjected to an extrusion force F1 pointing towards the center of rotation and an elastic force F2 that restores its own shape. When the extrusion force F1 is less than the elastic force F2, the arch of the first bendable part A1 of the flexible circuit board disappears, the shape changes abruptly, and thus an abnormal noise is generated.

[0089] It is understandable that the flattening process of the rotating shaft structure is a process from the intermediate state in Figure 7C through the intermediate state in Figure 7B to the flattened state in Figure 7A. During this process, the extrusion force F1 gradually exceeds the elastic force F2, and the first bendable part A1 of the flexible circuit board will still undergo abrupt shape changes, which in turn leads to abnormal noise.

[0090] It should be noted that there is no clear boundary between the first fixed portion B1 and the first bendable portion A1 and the second bendable portion A2 of the flexible circuit board 102. The first fixed portion B1, the first bendable portion A1 and the second bendable portion A2 are defined to more conveniently describe the abrupt changes in the shape of the flexible circuit board 102 during the opening and closing of the foldable display device.

[0091] To address the issue of abnormal noise caused by the sudden change in the shape of the flexible circuit board during the large-angle opening and closing of foldable display devices, embodiments of this application provide other foldable display devices, as detailed in the following structural description.

[0092] To solve the problem of abnormal noise generated by the bendable part of the flexible circuit board during the large-angle opening and closing of foldable display devices, the first step is to address the issue of abrupt changes in the shape of the bendable part. Abrupt changes in the structure's shape can be limited by introducing new structural elements.

[0093] Figure 8 illustrates a folding display device according to an embodiment of this application, including: a first door panel 201, a second door panel 202, a third door panel 203, a hinge structure 205, a flexible circuit board 102, and a limiting structure 300. The first door panel 201 and the third door panel 203 are located on opposite sides of the second door panel 202. The hinge structure is located on one side of the second door panel 202. Both the first door panel 201 and the third door panel 203 are rotatably connected to the hinge structure 205. Along the direction from the second door panel 202 to the first door panel 201, the flexible circuit board 102 includes a first fixing part B1 and a first bendable part A1 connected to the first fixing part. The first fixing part B1 is fixed to the side of the second door panel facing the hinge structure 205. The limiting structure 300 is disposed on the side of the flexible circuit board 102 facing the second door panel 202, and the limiting structure 300 covers at least a portion of the first bendable part A1.

[0094] In one possible implementation, the limiting structure 300 is connected to the second door panel 202 and the flexible circuit board 102. This application does not limit the fixing process of the limiting structure 300 to the second door panel 202 and the flexible circuit board 102. For example, the limiting structure 300 can be directly connected to the second door panel 202 and the flexible circuit board 102 via an adhesive layer. A hot-pressing process can be used, which can be understood as converting the adhesive layer into a semi-solid state with adhesive properties at a certain temperature, thereby bonding the limiting structure 300 to the flexible circuit board 102.

[0095] It is understood that the first fixing part B1 in this embodiment is the part connecting the flexible circuit board 102 and the second door panel 202. Due to the physical properties of the flexible circuit board 102, each segment of the flexible circuit board 102 has the characteristic of being bendable. The bendable part in this embodiment specifically refers to the part that will undergo a sudden change in shape during the opening and closing of the foldable display device. Structurally, the bendable part is usually located in the part of the flexible circuit board 102 that is connected to the first fixing part B1. For example, as shown in FIG8, the bendable part includes a first bendable part A1 and a second bendable part A2.

[0096] During the large-angle opening and closing process of the foldable display device, the bendable part is subjected to an extrusion force pointing towards the rotation center and an elastic force to restore its own shape. The limiting structure 300 exerts a force on the flexible circuit board 102, which can balance the elastic force and extrusion force of the first bendable part A1 of the flexible circuit board 102, limit the deformation of the flexible circuit board 102, effectively suppress the problem of abrupt shape change during the opening and closing of the foldable display device, thereby reducing the problem of abnormal noise generated during the large-angle opening and closing of the foldable display device.

[0097] In some embodiments, the flexible circuit board is a multilayer flexible circuit board. A multilayer flexible circuit board is formed by laminating two or more flexible circuit boards together, and forming conductive paths between different layers through metal vias.

[0098] Because each layer has a different bending radius, the flexible circuit board layer closer to the second door panel has more redundancy and a higher probability of morphological abrupt changes. This application does not limit the number of layers in the multilayer flexible circuit board. The layer closest to the second door panel is the surface layer (also called the "inner layer"), and the layer furthest from the door panel is the bottom layer (also called the "outer layer"). Any remaining layers are collectively referred to as intermediate layers. The surface layer has the most bending redundancy and a higher probability of morphological abrupt changes.

[0099] Understandably, the limiting structure is positioned between the surface layer of the flexible circuit board and the second door panel. During the large-angle opening and closing process of the foldable display device, the limiting structure exerts a force on the multi-layer flexible circuit board, which can balance the elastic force and extrusion force of the bendable part of the multi-layer flexible circuit board, limit the deformation of the multi-layer flexible circuit board, and thus reduce the problem of abnormal noise generated during the large-angle opening and closing of the foldable display device.

[0100] In one possible implementation, continuing as shown in FIG8, the hinge structure 205 includes a first end 205A near the first door panel 201. A portion of the bendable first part A1 is located above the first end 205A. A portion of the limiting structure 300 is fixed between the second door panel 202 and the flexible circuit board 102, and another portion extends toward the first door panel 201 and beyond the first end 205A. By having the other portion of the limiting structure 300 extend toward the first door panel 201 and beyond the first end 205A, the limiting structure 300 provides better restriction on the deformation of the flexible circuit board 102.

[0101] Understandably, the hinge structure 205 also includes a second end 205B near the third door panel 203. A portion of the second bendable portion A2 is located above the second end 205B. A portion of the limiting structure 300 is fixed between the second door panel 202 and the flexible circuit board 102, and another portion extends toward the third door panel 203 and beyond the second end 205B.

[0102] In one possible implementation, as shown in Figures 9, 10A, and 10C, the foldable display device further includes a mid-frame 204 and a reinforcing plate 206. The mid-frame 204 includes a first portion 2041 and a second portion 2042. The first portion 2041 and the second portion 2042 are located on opposite sides of the hinge structure. The reinforcing plate 206 includes a first reinforcing plate 2061, a second reinforcing plate 2062, and a third reinforcing plate 2063. The flexible circuit board 102 also includes a second fixing portion B2 and a third fixing portion B3. The second fixing portion B2 is fixed to the first portion 2041, and the third fixing portion B3 is fixed to the second portion 2042. The first reinforcing plate 2061 is fixed to the first fixing portion B1. The second reinforcing plate 2062 is fixed to the second fixing portion B2. The third reinforcing plate 2063 is fixed to the third fixing portion B3.

[0103] In one possible implementation, the portion of the flexible circuit board 102 and the limiting structure 300 fixed on the second door panel 202 is projected as region X1 (not shown in the figure), and the portion of the flexible circuit board 102 and the first reinforcing plate 2061 fixed on the second door panel 202 is projected as region X2 (not shown in the figure). Regions X1 and X2 are equal in size and overlap.

[0104] In one possible implementation, the portion of the flexible circuit board 102 and the portion of the limiting structure 300 fixed on the second door panel 202 is projected as region X1 (not shown in the figure), and the portion of the flexible circuit board 102 and the portion of the first reinforcing plate 2061 fixed on the second door panel 202 is projected as region X2 (not shown in the figure). Region X1 is located inside region X2.

[0105] In some embodiments, as shown in FIG10C, which is a view of the flexible circuit board in FIG10A along the z-direction, the flexible circuit board 102 may further include segmented slots 400. The segmented slots 400 penetrate the flexible circuit board 102 along its thickness direction (i.e., the z-direction), dividing the flexible circuit board 102 into multiple segments to establish connections between different circuit portions of different segments. The design of the segmented slots 400 helps to distribute stress and improve the durability and reliability of the circuit board. The flexible circuit board 102 containing segmented slots 400 is also called a segmented flexible circuit board. This application embodiment does not limit the number of segmented slots 400 on the flexible circuit board 102; for ease of explanation, the following description uses two segmented slots 400 (i.e., the first segmented slot 401 and the second segmented slot 402).

[0106] Continuing as shown in Figures 9 and 10A, the portion of the flexible circuit board 102 located between the first fixing portion B1 and the second fixing portion B2 has a first segmentation groove 401 and a second segmentation groove 402. The first segmentation groove 401 and the second segmentation groove 402 divide the flexible circuit board into three segments: a first segment 102a, a second segment 102b, and a third segment 102c.

[0107] This application does not limit the width of the multi-segment flexible circuit board. In some embodiments, the first segment 102a, the second segment 102b, and the third segment 102c have the same width. This design simplifies the manufacturing process and facilitates production. In other embodiments, the widths of the first segment 102a, the second segment 102b, and the third segment 102c may be different. Through the non-uniform distribution design of the multi-segment flexible circuit board, the flexible circuit board can better adapt to various space constraints and special shape requirements. In this case, since the widths of the two flexible circuit boards on both sides of the segmented slot may be different, the shape changes of different segments will also differ during the opening and closing of the folding display device.

[0108] In some embodiments, the width of the reinforcing plate 206 can be a fixed value. As shown in FIG10A, the lengths (dimensions along the x direction in FIG10A) of the first reinforcing plate 2061, the second reinforcing plate 2062, and the third reinforcing plate 2063 do not change with the widths (dimensions along the y direction in FIG10A) of the first segment 102a, the second segment 102b, and the third segment 102c.

[0109] In other embodiments, the width of the reinforcing plate 206 can vary according to the width of different segments of the flexible circuit board. As shown in Figure 10B, the widths (dimensions along the y-direction in Figure 10B) of the first segment 102a, the second segment 102b, and the third segment 102c are S1, S2, and S3, respectively. The length of the fixed portion of the first reinforcing plate 2061 and the first segment 102a (dimensions along the x-direction in Figure 10B) is L11, the length of the fixed portion of the first reinforcing plate 2061 and the second segment 102b is L12, and the length of the fixed portion of the first reinforcing plate 2061 and the third segment 102c is L13. When S1, S2, and S3 satisfy S1 < S2 < S3, then L11 < L12 < L13. It is understood that the widths of the second reinforcing plate 2062 and the third reinforcing plate 2063 also vary according to the width of different segments of the flexible circuit board, which will not be elaborated here.

[0110] This application embodiment does not limit the form of the reinforcing plate 206 for the multi-segment flexible circuit board. For ease of explanation, this application embodiment uses a fixed width for the reinforcing plate 206 as an example. To accommodate the difference in deformation of the flexible circuit boards on both sides of the segmented groove, this application embodiment further improves the folding display device shown in FIG8.

[0111] In one possible implementation, as shown in Figures 11 and 12A, the first segment 102a includes a first bendable portion, a first segment A11; the second segment 102b includes a first bendable portion, a second segment A12; and the third segment 102c includes a first bendable portion, a third segment A13. The limiting structure 300 includes a first limiting structure 301 covering at least a portion of the first bendable portion, a second limiting structure 302 covering at least a portion of the first bendable portion, a second limiting structure 302 covering at least a portion of the first bendable portion, a third limiting structure 303 covering at least a portion of the first bendable portion, a third segment A13. In this way, the first limiting structure 301, the second limiting structure 302, and the third limiting structure 303 can respectively limit the morphological changes of the first bendable portion, the first bendable portion, the second bendable portion, the first bendable portion, and the first bendable portion, the third segment A13. At this point, region X1 (not shown in Figures 11 and 12A) and region X2 (not shown in Figures 11 and 12A) are of equal size and overlap.

[0112] It is understandable that the portion of the flexible circuit board 102 shown in Figure 10C located between the first fixing portion B1 and the third fixing portion B3, if it has a segmented groove, can also adopt the same design.

[0113] The embodiments of this application do not limit the number of limiting structures. It is understood that the number of limiting structures is adapted to the number of segments into which the flexible circuit board is divided by the segmented slots.

[0114] In one possible implementation, as shown in Figure 12B, the first limiting structure 301 may include a first block 3011 and a second block 3012, the second limiting structure 302 may include a third block 3021 and a fourth block 3022, and the third limiting structure 303 may include a fifth block 3031 and a sixth block 3032. In this case, region X1 (not shown in Figure 12B) is located inside region X2 (not shown in Figure 12B). This saves material in the limiting structures, making the rotating shaft structure lighter.

[0115] In one possible implementation, as shown in Figure 13A, the first limiting structure 301, the second limiting structure 302, and the third limiting structure 303 are connected as a single unit. This makes it easier to manufacture and install the limiting structure 300. In this case, the X1 region (not shown in Figure 13A) and the X2 region (not shown in Figure 13A) are of equal size and overlap.

[0116] In one possible implementation, as shown in Figure 13B, the first limiting structure 301 may include a first block 3011 and a second block 3012, the second limiting structure 302 may include a third block 3021 and a fourth block 3022, and the third limiting structure 303 may include a fifth block 3031 and a sixth block 3032. In this case, region X1 (not shown in Figure 13B) is located inside region X2 (not shown in Figure 13B). This saves some material in the limiting structures, making the rotating shaft structure lighter.

[0117] In one possible implementation, as shown in Figure 14A, the first bendable portion has a dimension of S1 in the first direction (y-direction as shown in Figure 14A), and the second bendable portion has a dimension of S2 in the first direction, where S1 and S2 are not equal. The first limiting structure 301 has a dimension of h1 in the second direction (x-direction as shown in Figure 14A), and the second limiting structure 302 has a dimension of h2 in the second direction, where h1 and h2 are not equal. The first direction is parallel to the length direction of the hinge structure, and the second direction is parallel to the arrangement direction of the first door panel, the second door panel, and the third door panel.

[0118] The dimension in the first direction is defined as the width, and the dimension in the second direction is defined as the length. When the widths of the two flexible circuit boards on either side of the segmented slot are different, the shape changes of the two flexible circuit boards during the opening and closing process of the foldable display device will also be different. Moreover, the narrower the flexible circuit board, the greater the elastic force or extrusion force generated during the opening and closing process of the foldable display device, and the longer the limiting structure required.

[0119] In one possible implementation, as shown in Figure 14A, S1 is less than S2, and h1 is greater than h2. Since the dimension S1 of the first bendable part in the first direction is less than the dimension S2 of the second bendable part in the first direction, during the opening and closing of the folding display device, the elastic force or extrusion force generated by the first bendable part is greater than that generated by the second bendable part, resulting in different degrees of deformation of the first and second bendable parts towards the second door panel. The dimension h1 of the first limiting structure 301 in the second direction is greater than the dimension h2 of the second limiting structure 302 in the second direction, which can correspondingly offset the deformation generated by the first and second bendable parts during the large-angle opening and closing of the folding display device.

[0120] For example, as shown in Figures 11 and 14A, the first segment 102a includes a first bendable portion A11, the second segment 102b includes a first bendable portion A12, and the third segment 102c includes a first bendable portion A13. The limiting structure 300 includes a first limiting structure 301 covering at least a portion of the first bendable portion A11, a second limiting structure 302 covering at least a portion of the first bendable portion A12, and a third limiting structure 303 covering at least a portion of the first bendable portion A13. The first bendable portion has a dimension of S1 in a first direction (y-direction as shown in Figure 14A), the second bendable portion has a dimension of S2 in the first direction, and the third bendable portion has a dimension of S3 in the first direction. The first limiting structure 301 has a dimension of h1 in a second direction (x-direction as shown in Figure 14A), the second reinforcing structure 302 has a dimension of h2 in the second direction, and the third limiting structure 303 has a dimension of h3 in the second direction. Since S1 < S2 < S3, then h1 > h2 > h3.

[0121] In one possible implementation, continuing as shown in Figure 14A, the ratio of S1 to S2 is equal to the ratio of h1 to h2. This allows for further quantification of the relationship between the width of the flexible circuit board and the length of the limiting structure.

[0122] For example, the first segment of the first bendable part has a dimension of S1 in the first direction (y-direction as shown in Figure 14A), the second segment of the first bendable part has a dimension of S2 in the first direction, and the third segment of the first bendable part has a dimension of S3 in the first direction. The first limiting structure 301 has a dimension of h1 in the second direction (x-direction as shown in Figure 14A), the second reinforcing structure 302 has a dimension of h2 in the second direction, and the third limiting structure 303 has a dimension of h3 in the second direction. When S1:S2:S3 = 1:1:1, then h1:h2:h3 = 1:1:1.

[0123] For example, the first segment of the first bendable part has a dimension of S1 in the first direction (y-direction as shown in FIG. 14A), the second segment of the first bendable part has a dimension of S2 in the first direction, and the third segment of the first bendable part has a dimension of S3 in the first direction. The first limiting structure 301 has a dimension of h1 in the second direction (x-direction as shown in FIG. 14A), the second reinforcing structure 302 has a dimension of h2 in the second direction, and the third limiting structure 303 has a dimension of h3 in the second direction. When S1:S2:S3 = 1:2:2, then h1:h2:h3 = 1:2:2.

[0124] In one possible implementation, referring to Figures 11 and 14B, the first segment 102a includes a first bendable portion, a first segment A11; the second segment 102b includes a first bendable portion, a second segment A12; and the third segment 102c includes a first bendable portion, a third segment A13. The limiting structure 300 includes a first limiting structure 301, a second limiting structure 302, and a third limiting structure 303. The first limiting structure 301 includes a first block 3011 and a second block 3012; the second limiting structure 302 includes a third block 3021 and a fourth block 3022; and the third limiting structure 303 includes a fifth block 3031 and a sixth block 3032. The first block 3011 covers at least a portion of the first bendable portion, the third block 3021 covers at least a portion of the first bendable portion, the second segment A12; and the fifth block 3031 covers at least a portion of the first bendable portion, the third segment A13. The first segment of the first bendable part has a dimension of S1 in the first direction (y-direction as shown in Figure 14A), the second segment of the first bendable part has a dimension of S2 in the first direction, and the third segment of the first bendable part has a dimension of S3 in the first direction. The first block 3011 has a dimension of h11 in the second direction (x-direction as shown in Figure 14A), the second block 3012 has a dimension of h21 in the second direction, and the third block 3021 has a dimension of h31 in the second direction. Because S1 < S2 < S3, therefore h11 > h21 > h31.

[0125] In one possible implementation, the flexible circuit board includes a flexible substrate and metal traces. The flexible substrate provides support for the metal traces, ensuring that the flexible circuit board can be bent without damage. When the flexible circuit board is a multilayer flexible circuit board, each layer includes a flexible substrate and metal traces.

[0126] In one possible implementation, as shown in Figure 8, a limiting structure 300 is disposed between the second door panel 202 and the flexible circuit board 102. The surface of the flexible circuit board 102 near the limiting structure 300 has metal wires. The limiting structure 300 includes a first side and a second side. The first side is near the flexible circuit board 102, and the second side is near the second door panel 202. The first side of the limiting structure 300 has an insulating layer. This prevents electrical connection between the flexible circuit board 102 and the limiting structure 300, avoids short circuits between different signal lines or electrical components, and ensures normal circuit operation.

[0127] In another possible implementation, the flexible circuit board 102 has metal lines on its surface near the limiting structure 300, and the metal lines are covered with a coating. This also prevents the flexible circuit board 102 and the limiting structure 300 from being electrically connected.

[0128] In one possible implementation, the limiting structure includes at least one of a polyester film (PET) sheet or a polyimide (PI) sheet. Both PET and PI sheets have good high-temperature resistance, corrosion resistance, and chemical resistance, which helps to improve the durability and stability of the circuit board, thereby extending the product's lifespan.

[0129] In addition to using limiting structures to restrict the abrupt changes in the shape of the bendable portion of the flexible circuit board, the stiffness of the bendable portion of the flexible circuit board can be reduced by further optimizing the structure of the flexible circuit board, thereby reducing the probability of abrupt changes in the shape of the bendable portion when the foldable display device is opened and closed at a large angle.

[0130] This application provides a foldable display device, as shown in FIG6, including: a first door panel 201, a second door panel 202, a third door panel 203, a hinge structure 205, and a flexible circuit board 102. The first door panel 201 and the third door panel 203 are located on opposite sides of the second door panel 202. Both the first door panel 201 and the third door panel 203 are rotatably connected to the hinge structure 205. Along the direction from the second door panel 202 to the first door panel 201, the flexible circuit board includes a first fixing part B1 and a bendable part connected to the first fixing part. The bendable part includes a first portion A1 and a second portion A2. Along the direction from the second door panel 202 to the third door panel 203, the flexible circuit board 102 includes the first fixing part B1 and the second portion A2 of the bendable part connected to the first fixing part B1. The first fixing part B1 is fixed to the side of the second door panel 202 facing the hinge structure 205.

[0131] To limit the deformation of the bendable portion, this application also provides some possible methods. For example, the stiffness of the first part A1 and the second part A2 of the bendable portion can be reduced by some technical means, so that the stiffness of the bendable portion is less than the stiffness of the first fixed part B1. The following are the methods for reducing the stiffness of the bendable portion.

[0132] It is understandable that a flexible circuit board consists of a flexible substrate and a metal trace layer. To reduce the stiffness of the first part A1 of the bendable section, either the metal trace layer or the flexible substrate can be modified. The implementation methods are given below from these two perspectives.

[0133] The first bendable portion A1 and the second bendable portion A2 are stress concentration points of the flexible circuit board 102. Reducing the elastic force at these stress concentration points can decrease the abnormal noise caused by sudden changes in shape during the opening and closing of the foldable display device. During the unfolding or closing of the foldable display device, the through-axis space of the hinge structure gradually decreases from its maximum size. This decrease in the stiffness of the first bendable portion A1 and the second bendable portion A2 of the flexible circuit board 102 reduces the elastic force and extrusion force, thus lowering the probability of the flexible circuit board deforming towards the second door panel. Reducing the stiffness of the bendable portion of the flexible circuit board can also effectively solve the problem of sudden changes in shape and abnormal noise during the opening and closing of the foldable display device.

[0134] This application does not limit the implementation method of reducing the stiffness of the bendable part, and provides the following solutions for reducing the stiffness of the bendable part. For ease of explanation, the following description uses a flexible circuit board without segmented slots as an example. It can be understood that when the flexible circuit board has segmented slots, all technical solutions can be applied to any segment or any number of segments of the flexible circuit board.

[0135] In some embodiments, reducing the stiffness of the bendable portion can be achieved by reducing the volume fraction of the metal traces in the bendable portion.

[0136] In one possible implementation, the volume fraction of the metal traces in the bendable portion is less than the volume fraction of the metal traces in the first fixed portion. Reducing the volume fraction of the metal traces can decrease the local modulus.

[0137] In this way, the modulus and stiffness of the bendable portion are reduced, which can effectively reduce the elastic force at the stress concentration point (i.e., the bendable portion) of the flexible circuit board and reduce the abnormal noise caused by the sudden change in shape of the flexible circuit board during the opening and closing of the foldable display device. This application does not limit the metal material of the metal traces in the bendable portion; for ease of explanation, copper wire is used as an example below.

[0138] For example, as shown in Figure 15, the stiffness of the bendable portion can be reduced by decreasing the copper distribution design at stress concentration points (i.e., the "bendable portion"). As shown in Figure 15, the first portion of the bendable portion has a first copper removal area 501. It can be understood that the second portion of the bendable portion has a second copper removal area 502, which has the same design as the first copper removal area 501.

[0139] For example, as shown in Figure 16, the volume fraction of the metal traces in the bendable section can be reduced by using a copper removal design at stress concentration points, thereby reducing the stiffness of the bendable section. As shown in Figure 16, the first part of the bendable section has a first copper removal area 501, with two copper wires connecting its two sides. It can be understood that the second part of the bendable section has a second copper removal area 502, which has the same design as the first copper removal area 501.

[0140] For example, as shown in Figure 17, the volume fraction of the metal traces in the bendable portion can be reduced by using a striped copper design at stress concentration points, thereby reducing the stiffness of the bendable portion. As shown in Figure 17, the first portion of the bendable portion has a first copper stripping area 501, which features a striped copper design. It is understood that the second portion of the bendable portion has a second copper stripping area 502, which has the same design as the first copper stripping area 501.

[0141] For example, as shown in Figure 18, the volume fraction of the metal traces in the bendable portion can be reduced by using a grid-like copper design at stress concentration points, thereby reducing the stiffness of the bendable portion. As shown in Figure 18, the first portion of the bendable portion has a first copper removal area 501, which features a grid-like copper design. It is understood that the second portion of the bendable portion has a second copper removal area 502, which has the same design as the first copper removal area 501.

[0142] It is understandable that when the flexible circuit board is a multilayer flexible circuit board, the reduction of copper distribution at stress concentration points, the copper removal design at stress concentration points, the grid copper design, and the striped copper design can all be applied to a single layer in the multilayer flexible circuit board, or to several layers of the flexible circuit board at the same time.

[0143] In one possible implementation, the flexible circuit board includes a first layer of metal traces and a second layer of metal traces stacked together, with the first layer of metal traces closer to the second door panel than the second layer. The volume fraction of the first layer of metal traces in the bendable portion is less than the volume fraction of the first layer of metal traces in the first fixing portion. In this case, the flexible circuit board is a multilayer flexible circuit board. When the flexible circuit board is a multilayer flexible circuit board, each layer can have metal traces. Of the two layers in the multilayer flexible circuit board, the one closer to the second door panel is the "first layer," and the other layer is the "second layer." The stiffness of the first layer of the bendable portion is less than the stiffness of the second layer of the bendable portion, which can better adapt to the different bending radii of each layer and better cooperate with the limiting structure to restrict the abrupt changes in the shape of the flexible circuit board.

[0144] In one possible implementation, the flexible circuit board is a multilayer flexible circuit board, with the layer closest to the second panel being the surface layer. In the above embodiment, the first layer of metal traces is the surface layer metal trace. In this way, it is easier to process the already fabricated multilayer flexible circuit board by having the first layer of metal traces as the surface layer metal trace.

[0145] In one possible implementation, the volume fraction of the metal traces in the bendable portion of the multilayer flexible circuit board is greater in each layer from the layer closest to the second panel to the layer furthest from the second panel than in the layer above. This better accommodates the different bending radii of each layer and better coordinates with the limiting structure to restrict abrupt changes in the shape of the flexible circuit board.

[0146] In some embodiments, the stiffness of the bendable portion can be reduced by using a method that differentiates the elastic modulus of different layers of a multilayer flexible circuit board.

[0147] In one possible implementation, the elastic modulus of the bendable portion is less than that of the first fixed portion. This reduces the stiffness of the bendable portion, thereby decreasing the probability of abrupt changes in the shape of the flexible circuit board.

[0148] In one possible implementation, when the flexible circuit board is a multilayer flexible circuit board, each layer of the flexible circuit board has a flexible substrate. For example, the multilayer flexible circuit board includes two layers stacked together. The inner layer is a first layer, including a first flexible substrate. The outer layer is a second layer, including a second flexible substrate. Ignoring other layers within the flexible circuit board, the first and second flexible substrates are stacked, and in position, the first flexible substrate is closer to the second panel than the second flexible substrate.

[0149] In other examples, the elastic modulus of the first flexible substrate of the bendable portion is equal to the elastic modulus of the second flexible substrate.

[0150] In other examples, the elastic modulus of the first flexible substrate of the bendable portion is less than that of the second flexible substrate.

[0151] In other words, the inner layer uses a first flexible substrate with a lower elastic modulus, while the other layers use a second flexible substrate with a higher elastic modulus. For example, the elastic modulus of the first flexible substrate is less than 4 GPa, and the elastic modulus of the second flexible substrate is greater than 6 GPa. This means the stiffness of the inner layer is lower than that of the other layers, which reduces the probability of abrupt changes in the shape of the inner layer, thereby reducing the probability of abrupt changes in the shape of the flexible circuit board and the probability of abnormal noises during the opening and closing of the foldable display device.

[0152] For example, the multilayer flexible circuit board includes three layers: an inner layer, a middle layer, and an outer layer. The inner layer uses a first flexible substrate with an elastic modulus of 3 GPa. The middle and outer layers use a second flexible substrate with an elastic modulus of 6.5 GPa.

[0153] In one possible implementation, the flexible circuit board further includes a third flexible substrate, with the second flexible substrate located between the first and third flexible substrates. The elastic modulus of the second flexible substrate in the bendable portion is less than or equal to the elastic modulus of the third flexible substrate.

[0154] In other words, the inner layer uses a first flexible substrate with a low elastic modulus, the middle layer uses a second flexible substrate with a high elastic modulus, and the outer layer uses a third flexible substrate. For example, the elastic modulus of the first flexible substrate is less than 4 GPa, the elastic modulus of the second flexible substrate is greater than 4 GPa and less than 6 GPa, and the elastic modulus of the third flexible substrate is greater than 6 GPa.

[0155] In this way, the stiffness of the inner layer is less than that of the middle and outer layers, and the stiffness of the middle layer is less than that of the outer layer. The stiffness of different layers of the flexible circuit board adopts a gradient distribution. This can reduce the probability of abrupt changes in the shape of the inner layer, thereby reducing the probability of abrupt changes in the shape of the flexible circuit board and the probability of abnormal noises during the opening and closing of the foldable display device.

[0156] For example, a multilayer flexible circuit board has three layers: an inner layer, a middle layer, and an outer layer. The inner layer uses a first flexible substrate with an elastic modulus of 3 GPa. The middle layer uses a second flexible substrate with an elastic modulus of 5 GPa. The outer layer uses a third flexible substrate with an elastic modulus of 6.5 GPa.

[0157] For example, a multilayer flexible circuit board has four layers: an inner layer, a first middle layer, a second middle layer, and an outer layer. The inner layer uses a first flexible substrate with an elastic modulus of 3 GPa. The first and second middle layers both use a second flexible substrate with an elastic modulus of 5 GPa. The outer layer uses a third flexible substrate with an elastic modulus of 6.5 GPa.

[0158] It is understandable that the technical solution of adding a limiting structure proposed in Figure 8 and the optimized flexible circuit board shown in Figure 15 can be combined in the same foldable display device.

[0159] For example, a foldable display device includes: a first door panel, a second door panel, a third door panel, a hinge structure, a flexible circuit board, and a limiting structure. The first door panel and the third door panel are located on opposite sides of the second door panel. Both the first door panel and the third door panel are rotatably connected to the hinge structure. Along the direction from the second door panel to the first door panel, the flexible circuit board includes a first fixing part and a bendable part connected to the first fixing part. The first fixing part is fixed to the side of the second door panel facing the hinge structure. The limiting structure is located on the side of the flexible circuit board facing the second door panel and covers at least a portion of the bendable part. The stiffness of the bendable part is less than the stiffness of the first fixing part.

[0160] This can be understood as follows: in foldable display devices, not only are limiting structures set up, but the stiffness of the bendable part is also designed to be less than that of the first fixed part. In this way, the limiting structure is more effective in restricting abrupt changes in the shape of the flexible circuit board.

[0161] In the aforementioned device integrating reinforcement and rigidity, the volume fraction of the metal traces in the bendable portion can be less than the volume fraction of the metal traces in the first fixed portion. This allows the rigidity of the bendable portion to be less than the rigidity of the first fixed portion.

[0162] Alternatively, in some embodiments, the flexible circuit board is a multilayer flexible circuit board, which may employ a first flexible substrate and a second flexible substrate stacked together, with the first flexible substrate being closer to the second door panel than the second flexible substrate. The elastic modulus of the first flexible substrate in the bendable portion is less than that of the second flexible substrate. In this way, the stiffness of the inner layer is less than that of the outer layer, which can better adapt to the different bending radii of each layer and better cooperate with the limiting structure to restrict the abrupt changes in the shape of the flexible circuit board.

[0163] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0164] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A foldable display device, characterized in that, include: A first door panel, a second door panel, and a third door panel, wherein the first door panel and the third door panel are located on opposite sides of the second door panel; A hinge structure is located on one side of the second door panel, and both the first door panel and the third door panel are rotatably connected to the hinge structure. A flexible circuit board, along the direction from the second door panel to the first door panel, the flexible circuit board includes a first fixing part and a bendable part connected to the first fixing part, the first fixing part being fixed to the side of the second door panel facing the hinge structure; A limiting structure is located on the side of the flexible circuit board facing the second door panel, and the limiting structure covers at least a portion of the bendable portion.

2. The foldable display device according to claim 1, characterized in that, The hinge structure includes a first end near the first door panel; The portion of the bendable part is located above the first end; A portion of the limiting structure is fixed between the second door panel and the flexible circuit board, while another portion extends toward the first door panel and beyond the first end.

3. The foldable display device according to claim 1 or 2, characterized in that, The foldable display device further includes a mid-frame; the mid-frame includes a first part and a second part; the first part and the second part are located on opposite sides of the hinge structure; The flexible circuit board further includes a second fixing part and a third fixing part, wherein the second fixing part is fixed to the first part and the third fixing part is fixed to the second part; The portion of the flexible circuit board located between the first fixing portion and the second fixing portion has a segmented groove, and the bendable portion located on opposite sides of the segmented groove includes a first bendable portion and a second bendable portion. The limiting structure covers at least a portion of the first bendable portion and at least a portion of the second bendable portion.

4. The foldable display device according to claim 3, characterized in that, The limiting structure includes a first limiting structure and a second limiting structure; the first limiting structure covers at least a portion of the first bendable portion, and the second limiting structure covers at least a portion of the second bendable portion; the first limiting structure and the second limiting structure are connected as one unit.

5. The foldable display device according to claim 3 or 4, characterized in that, The first bendable part has a dimension of S1 in the first direction, and the second bendable part has a dimension of S2 in the first direction. S1 and S2 are not equal. The first limiting structure has a dimension of h1 in the second direction, and the second limiting structure has a dimension of h2 in the second direction. h1 and h2 are not equal. The first direction is parallel to the length direction of the hinge structure, and the second direction is parallel to the arrangement direction of the third door panel of the first door panel, the second door panel, and the third door panel.

6. The foldable display device according to claim 5, characterized in that, S1 is less than S2, and h1 is greater than h2.

7. The foldable display device according to any one of claims 1-6, characterized in that, The limiting structure has an insulating layer on the side facing the flexible circuit board, or the flexible circuit board has a coating on the surface facing the limiting structure.

8. The foldable display device according to any one of claims 1-7, characterized in that, The limiting structure includes at least one of a polyester film plate or a polyimide plate.

9. The foldable display device according to any one of claims 1-8, characterized in that, The stiffness of the bendable part is less than that of the first fixed part.

10. The foldable display device according to claim 9, characterized in that, The volume fraction of the metal traces in the bendable portion is less than the volume fraction of the metal traces in the first fixed portion.

11. The foldable display device according to claim 10, characterized in that, The flexible circuit board includes a first layer of metal traces and a second layer of metal traces stacked together. The first layer of metal traces is closer to the second door panel than the second layer of metal traces. The volume fraction of the first layer of metal traces in the bendable portion is less than the volume fraction of the first layer of metal traces in the first fixed portion.

12. The foldable display device according to claim 11, characterized in that, The first layer of metal traces is the surface metal trace.

13. The foldable display device according to any one of claims 9-12, characterized in that, The elastic modulus of the bendable part is less than that of the first fixed part.

14. The foldable display device according to claim 13, characterized in that, The flexible circuit board includes a first flexible substrate and a second flexible substrate stacked together, wherein the first flexible substrate is closer to the second door panel than the second flexible substrate. The elastic modulus of the first flexible substrate of the bendable portion is less than that of the second flexible substrate.

15. The foldable display device according to claim 14, characterized in that, The flexible circuit board further includes a third flexible substrate, and the second flexible substrate is located between the first flexible substrate and the third flexible substrate; The elastic modulus of the second flexible substrate of the bendable portion is less than or equal to the elastic modulus of the third flexible substrate.

16. A foldable display device, characterized in that, include: A first door panel, a second door panel, and a third door panel, wherein the first door panel and the third door panel are located on opposite sides of the second door panel; A hinge structure, wherein both the first door panel and the third door panel are rotatably connected to the hinge structure; A flexible circuit board, along the direction from the second door panel to the first door panel, the flexible circuit board includes a first fixing part and a bendable part connected to the first fixing part, the first fixing part being fixed to the side of the second door panel facing the hinge structure; The stiffness of the bendable part is less than that of the first fixed part.

17. The foldable display device according to claim 16, characterized in that, The volume fraction of the metal traces in the bendable portion is less than the volume fraction of the metal traces in the first fixed portion.

18. The foldable display device according to claim 17, characterized in that, The flexible circuit board includes a first layer of metal traces and a second layer of metal traces stacked together, wherein the first layer of metal traces is closer to the second door panel than the second layer of metal traces. The volume fraction of the first layer of metal traces in the bendable portion is less than the volume fraction of the first layer of metal traces in the first fixed portion.

19. The foldable display device according to claim 18, characterized in that, The first layer of metal traces is the surface metal trace.

20. The foldable display device according to any one of claims 16-19, characterized in that, The elastic modulus of the bendable part is less than that of the first fixed part.

21. The foldable display device according to claim 20, characterized in that, The flexible circuit board includes a first flexible substrate and a second flexible substrate stacked together, wherein the first flexible substrate is closer to the second door panel than the second flexible substrate. The elastic modulus of the first flexible substrate in the bendable portion is less than that of the second flexible substrate.

22. The foldable display device according to claim 21, characterized in that, The flexible circuit board further includes a third flexible substrate, and the second flexible substrate is located between the first flexible substrate and the third flexible substrate; The elastic modulus of the second flexible substrate in the bendable portion is less than or equal to the elastic modulus of the third flexible substrate.

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