Flexible circuit board, middle frame assembly and electronic equipment

Abstract

The embodiment of the invention provides an FPC, a middle frame assembly and electronic equipment, and relates to the technical field of electronics. The FPC comprises three conductor layers and a shielding layer located on the surface, air gaps exist between the first conductor layer and the second conductor layer, air gaps exist between the second conductor layer and the third conductor layer, and no air gap exists between the first conductor layer and the shielding layer. And a signal line in the FPC extends in the second conductor layer, extends to the gap region, is transferred to the first conductor layer through the via hole, extends, crosses the gap region and then is transferred back to the second conductor layer. Therefore, the distance from the signal line in the gap area to the shielding layer does not change along with the bending of the flexible circuit board, and only the distance from the signal line to the second conductor layer and the distance from the signal line to the third conductor layer change along with the bending of the FPC. Signal line characteristic impedance fluctuation caused by layering at the gap can be reduced only by distance change on one side, so that the signal quality is improved, and the signal quality improvement effect on high-speed signals is more obvious.

Description

Technical Field

[0001] The present application relates to the field of electronic technology, and in particular to a flexible circuit board, a middle frame assembly, and an electronic device. Background Art

[0002] With the continuous development of display technology, foldable electronic devices are gradually becoming a development trend of future mobile electronic products. When unfolded, foldable electronic devices can obtain a larger display area to improve the viewing effect. When folded, foldable electronic devices can obtain a smaller volume, which is convenient for users to carry.

[0003] Folding electronic devices usually include multiple circuit boards and flexible printed circuits (FPCs) that are set through a rotating shaft. Signal transmission between multiple circuit boards is usually completed by FPCs. Therefore, the signal transmission quality of FPCs is linked to the performance of electronic devices, and the stability of the characteristic impedance of the signal line in FPCs has a direct impact on the signal transmission quality. Summary of the invention

[0004] The embodiments of the present application provide a flexible circuit board, a middle frame assembly, and an electronic device, which are used to improve the stability of the characteristic impedance of a signal line, thereby improving the signal transmission quality of the flexible circuit board.

[0005] In order to achieve the above objectives, this application adopts the following technical solutions:

[0006] In a first aspect of an embodiment of the present application, a flexible circuit board is provided, which can be used as a through-axis flexible circuit board in a folding electronic device, for example. The flexible circuit board includes a first conductor layer, a second conductor layer and a third conductor layer, and the second conductor layer is located between the first conductor layer and the third conductor layer. The flexible circuit board also includes a first connecting layer and a first shielding layer, and the first connecting layer is located between the first conductor layer and the second conductor layer, and the first connecting layer has a first gap. The first shielding layer is located on the side of the first conductor layer away from the second conductor layer and is coupled to the first conductor layer. The flexible circuit board also includes at least one signal line, and the signal line includes a first sub-signal line, two second sub-signal lines and two first connecting portions. The first sub-signal line is located in the first conductor layer and is opposite to the first gap. For example, along the thickness direction, the first sub-signal line is located above the first gap. The two second sub-signal lines are located in the second conductor layer, and along the extension direction of the signal line, the two second sub-signal lines are respectively located on both sides of the first gap; the first connecting portion penetrates the first connecting layer along the thickness direction of the first connecting layer; the two ends of the first sub-signal line are respectively coupled with the two second sub-signal lines through the two first connecting portions, that is, the first end of the first sub-signal line is coupled with a second sub-signal line through a first connecting portion, and the second end of the first sub-signal line is coupled with another second sub-signal line through another first connecting portion.

[0007] In the flexible circuit board provided by the embodiment of the present application, the first sub-signal line of the signal line is located in the first conductor layer, and the first sub-signal line forms a stripline structure with the first shielding layer and the second conductor layer. Since there is no gap structure between the first shielding layer and the first conductor layer, there will be no delamination between the first shielding layer and the first conductor layer during the bending process of the flexible circuit board. The third distance from the first shielding layer to the first sub-signal line remains unchanged during dynamic bending, and only the fourth distance from the first sub-signal line to the second conductor layer undergoes a delamination mutation. During the bending process of the flexible circuit board, compared with the change in the distance from the signal line to the ground on both sides, the change in the distance on only one side can significantly reduce the characteristic impedance fluctuation caused by delamination at the first gap (for example, the impedance fluctuation can be reduced by about 50%), thereby reducing signal reflection and improving signal quality. In addition, the second sub-signal line is located in the second conductor layer, and the signal is transmitted in a standard stripline structure formed by the second sub-signal line and the first conductor layer, and the first shielding layer is no longer required to participate in the signal return. The loss and far-end crosstalk caused by the first shielding layer to the high-speed signal can be reduced, providing a better shielding effect. That is, the flexible circuit board provided in the present application can achieve high-quality signal transmission through a specific routing structure while meeting the bending performance of the flexible circuit board for foldable electronic devices through the axis, and can also take into account the loss problem.

[0008] In a possible implementation, the flexible circuit board further includes at least one ground line, which is arranged side by side with the signal line; the ground line includes a first sub-ground line, two second sub-ground lines, and two second connecting parts; the first sub-ground line is located in the first conductor layer and is opposite to the first gap, for example, along the thickness direction, the first sub-ground line is located above the first gap. The two second sub-ground lines are located in the second conductor layer, and along the extension direction of the signal line, the two second sub-ground lines are respectively located on both sides of the first gap; the second connecting part penetrates the first connecting layer along the thickness direction of the first connecting layer; and the two ends of the first sub-ground line are coupled to the two second sub-ground lines through the two second connecting parts.

[0009] In the flexible circuit board provided in the embodiment of the present application, the first sub-signal line forms a coplanar waveguide structure with ground with two second sub-ground lines, a first shielding layer, and a second conductor layer. The characteristic impedance of the first sub-signal line is affected by four parts: the fifth distance from the first sub-signal line to the second sub-ground line on the left, the sixth distance from the first sub-signal line to the second sub-ground line on the right, the third distance from the first sub-signal line to the first shielding layer, and the fourth distance from the first sub-signal line to the second conductor layer. During the bending process of the flexible circuit board, the third distance, the fifth distance, and the sixth distance do not change, and only the fourth distance changes suddenly due to delamination. Therefore, the influence of the sudden change of the fourth distance on the characteristic impedance of the first sub-signal line can be significantly reduced, and the stability of the characteristic impedance of the first sub-signal line can be further improved.

[0010] In a possible implementation, the first sub-signal line includes a first section, a second section, and a third section that are connected in sequence; the second section is directly opposite to the first gap, for example, the projection of the second section on the first connection layer is located within the first gap. The first section and the third section are respectively located on both sides of the first gap, for example, the projections of the first section and the third section on the first connection layer are located on both sides of the first gap. The first section and the third section are respectively coupled to the first connection portion. The first section and the third section in the first sub-signal line are equivalent to transition portions, so that the first connection portion does not need to pass through the first gap, but passes through the first connection layer from a non-first gap, thereby reducing the process difficulty and process accuracy requirements of the first connection portion.

[0011] In a possible implementation, the first sub-ground line includes a fourth section, a fifth section, and a sixth section connected in sequence; the fifth section is directly opposite to the first gap, for example, the projection of the fifth section on the first connection layer is located within the first gap. The fourth section and the sixth section are respectively located on both sides of the first gap, for example, the projections of the fourth section and the sixth section on the first connection layer are located on both sides of the first gap, and the fourth section and the sixth section are respectively coupled to the second connection portion. The fourth section and the sixth section in the first sub-ground line are equivalent to transition parts, so that the second connection portion does not need to pass through the first gap, but passes through the first connection layer from a non-first gap, thereby reducing the process difficulty and process accuracy requirements of the second connection portion.

[0012] In one possible implementation, the spacing between the second section and the fifth section is smaller than the spacing between the first section and the fourth section. At the position corresponding to the first gap, the second section and the fifth section are close to each other (that is, the signal line and the ground line are close to each other), which can change the electromagnetic field distribution of the second section, and make full use of the field distribution characteristics of the coplanar waveguide structure with ground to reduce the impedance fluctuations generated during the bending process. At the positions on both sides of the first gap, the flexible circuit board does not delaminate during the bending process, and the thickness is reduced compared to the first gap. Therefore, the thickness from the first section to the adjacent layer is smaller, while the thickness from the second section to the adjacent layer is larger, which is equivalent to the characteristic impedance of the first section being lower than the characteristic impedance of the second section. By making the first section relatively far away from the fourth section, the characteristic impedance of the first section can be improved so that the characteristic impedance of the first section and the characteristic impedance of the second section remain stable and balanced.

[0013] In a possible implementation, the distance between the first segment and the fourth segment is 60 um to 200 um. By setting the distance between the first segment and the fourth segment to 60 um to 200 um, the characteristic impedance of the first segment can be optimized.

[0014] In a possible implementation, the distance between the second segment and the fifth segment is 50 um to 100 um. By setting the distance between the second segment and the fifth segment to 50 um to 100 um, the second segment can have better anti-interference ability, lower common mode and smaller RE.

[0015] In a possible implementation, the spacing between the second sub-signal line and the second sub-ground line is smaller than the spacing between the first section and the fourth section. By reducing the spacing between the second sub-signal line and the second sub-ground line, space can be left for increasing the width of the second sub-signal line. Increasing the width of the second sub-signal line increases the volume of the effective conductor used to propagate electromagnetic waves, thereby reducing the loss of the second sub-signal line.

[0016] In a possible implementation, the spacing between the second sub-signal line and the second sub-ground line is 60um to 200um. By limiting the spacing between the second sub-signal line and the second sub-ground line to 60um to 200um, the width of the second sub-signal line can be increased while reducing process difficulty and ensuring process yield.

[0017] In one possible implementation, the width of the second section is greater than the width of the first section. At the positions on both sides of the first gap, the flexible circuit board does not delaminate during the bending process, and the thickness is reduced compared to the first gap. Therefore, the thickness from the first section to the adjacent layer is smaller, while the thickness from the second section to the adjacent layer is larger, which is equivalent to the characteristic impedance of the first section being lower than the characteristic impedance of the second section. By increasing the width of the second section, the characteristic impedance of the second section can be reduced, so that the characteristic impedance of the first section and the second section remain stable and balanced.

[0018] In a possible implementation, the width of the first section is 30 um to 60 um. By setting the width of the first section to 30 um to 60 um, multiple factors such as conductor loss, preparation process, and characteristic impedance can be optimized.

[0019] In a possible implementation, the width of the second segment is 40 um to 70 um. By setting the width of the second segment to 40 um to 70 um, multiple factors such as conductor loss, preparation process, and characteristic impedance can be optimized.

[0020] In a possible implementation, the width of the first segment is smaller than the width of the second sub-signal line. By increasing the width of the second sub-signal line, the volume of the effective conductor used to propagate electromagnetic waves can be increased, thereby reducing the loss of the second sub-signal line.

[0021] In a possible implementation, the width of the second sub-signal line is 45 um to 80 um. By setting the width of the second sub-signal line to 45 um to 80 um, multiple factors such as conductor loss, preparation process, and characteristic impedance can be optimized.

[0022] In a possible implementation, the width of the fifth segment is greater than the width of the fourth segment. By increasing the width of the fifth segment, the fifth segment can be brought closer to the second segment of the signal line to change the electromagnetic field distribution of the second segment, and make full use of the field distribution characteristics of the coplanar waveguide structure with ground to reduce the impedance fluctuation generated during the bending process.

[0023] In a possible implementation, the width of the fourth segment is equal to the width of the second sub-ground line. This can simplify the preparation process and layout of the ground line.

[0024] In a possible implementation, at least one signal line includes two adjacent signal lines; the differential characteristic impedance of the two signal lines is 80 ohm to 100 ohm. By setting the differential characteristic impedance of the two signal lines to 80 ohm to 100 ohm, the flexible circuit board can be adapted to signal transmission of a variety of chips.

[0025] In a possible implementation, the spacing between the first segments of the two signal lines is greater than the spacing between the second segments. By bringing the second segments of the differential pair signal lines closer together, the differential line coupling is tighter, the radiation is smaller, and the crosstalk with the outside is smaller. By moving the first segments of the differential pair signal lines away from each other, the characteristic impedance of the differential pair signal lines can be improved.

[0026] In a possible implementation, the spacing between the first segments of the two signal lines is 60um to 150um. By setting the spacing between the first segments of the differential pair signal lines to 60um to 150um, the characteristic impedance jump of the first sub-signal line in the signal line can be reduced.

[0027] In a possible implementation, the spacing between the second segments of the two signal lines is 50um to 100um. By setting the spacing between the second segments of the differential pair signal lines to 50um to 100um, various performances of the differential pair signal lines can be balanced and the impact of delamination on characteristic impedance can be reduced.

[0028] In a possible implementation, the spacing between the first segments of the two signal lines is greater than the spacing between the second sub-signal lines. By reducing the spacing between the second sub-signal lines in the differential pair signal lines, space can be left for increasing the width of the second sub-signal lines, thereby increasing the width of the second sub-signal lines and reducing the loss of the second sub-signal lines.

[0029] In a possible implementation, the spacing between the second sub-signal lines in the two signal lines is 60um to 150um. By setting the spacing between the second sub-signal lines in the differential pair signal lines to 60um to 150um, the width of the second sub-signal line can be increased while reducing the process difficulty and ensuring the process yield.

[0030] In a possible implementation, the fifth segment includes a first end close to the fourth segment and a second end close to the sixth segment, and the width of the first end decreases along the direction from the middle to the first end; the width of the second end decreases along the direction from the middle to the second end. The width of the fifth segment gradually decreases to be equal to the width of the fourth segment and the sixth segment, so that a smooth transition of the line width of the first sub-ground line can be achieved, reducing the risk of bending and breaking of the first sub-signal line.

[0031] In a possible implementation, the second conductor layer further includes a hollow area, and the first sub-signal line is opposite to the hollow area, for example, the projection of the first sub-signal line on the second conductor layer is located in the hollow area. The projection area of ​​the first sub-signal line is hollowed out on the second conductor layer, and there is no ground signal in the projection area, and no magnetic field is generated, which will not affect the characteristic impedance of the first sub-signal line, and can further reduce the influence of the distance change between the first conductor layer and the second conductor layer on the characteristic impedance of the first sub-signal line of the signal line.

[0032] In a possible implementation, the distance from the first connection portion to the first gap is 0.5 mm to 2 mm. Setting the distance from the first connection portion to the first gap to 0.5 mm to 2 mm can improve process yield, reduce process difficulty, and optimize the characteristic impedance of the first sub-signal line.

[0033] In a possible implementation, the rate of the signal transmitted by the signal line is greater than or equal to 10 Gbps. In the scenario of transmitting high-speed signals, the flexible circuit board provided by the present application has a more significant effect on improving the signal transmission quality.

[0034] In a possible implementation, the signal line is used to transmit a radio frequency signal. The flexible circuit board provided in the present application can also be used to transmit a radio frequency signal.

[0035] In a possible implementation, the flexible circuit board also includes a second connecting layer, a multi-layer insulating layer and a second shielding layer; the second connecting layer is located between the second conductor layer and the third conductor layer, the second connecting layer has a second gap, and the projection of the second gap on the first connecting layer overlaps with the first gap; the two opposite surfaces of the first conductor layer, the second conductor layer and the third conductor layer are respectively covered with insulating layers; the second shielding layer is located on the side of the third conductor layer away from the second conductor layer.

[0036] In a possible implementation, the dielectric constant of the material of the first connection layer or the insulating layer is 2.8 to 3.5. By adjusting the dielectric constants of the materials of the first connection layer and the insulating layer, the characteristic impedance of the signal line can be further optimized.

[0037] In a possible implementation manner, the flexible circuit board further includes a second shielding layer, and the second shielding layer is located on a side of the third conductor layer away from the second conductor layer.

[0038] In a possible implementation, the thickness of the first shielding layer is 6 um to 14 um, which can further solve the problem of sudden change in characteristic impedance of the signal line.

[0039] In a possible implementation, the thickness of the first conductor layer, the second conductor layer or the third conductor layer is 6 um to 15 um, which can further solve the problem of sudden change in characteristic impedance of the signal line.

[0040] In a possible implementation, the thickness of the first connection layer or the second connection layer is 10 um to 20 um, which can further solve the problem of sudden change in characteristic impedance of the signal line.

[0041] In a possible implementation, the distance from the first conductor layer to the first shielding layer is 30 um to 55 um, which can further improve the problem of sudden change in characteristic impedance of the signal line.

[0042] In a possible implementation, the distance from the first conductor layer to the first connection layer is 6 um to 18 um, which can further solve the problem of sudden change in characteristic impedance of the signal line.

[0043] In a possible implementation, the distance from the first connection layer to the second conductor layer is 15 um to 30 um, which can further solve the problem of sudden change in characteristic impedance of the signal line.

[0044] In a possible implementation, the distance from the second connection layer to the second conductor layer or the distance from the third conductor layer is 6 um to 18 um. This can further improve the problem of sudden change in characteristic impedance of the signal line.

[0045] According to a second aspect of an embodiment of the present application, a middle frame assembly is provided, which includes a first frame body, a second frame body, a hinge mechanism and a flexible circuit board. The first frame body and the second frame body are connected by the hinge mechanism. The flexible circuit board extends from the side where the first frame body is located to the side where the second frame body is located through the hinge mechanism. The flexible circuit board includes the flexible circuit board of any one of the first aspects.

[0046] According to a third aspect of the embodiments of the present application, an electronic device includes a middle frame assembly and a display screen, wherein the display screen is arranged on the middle frame assembly, and the middle frame assembly includes the middle frame assembly of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1A A schematic diagram of an electronic device in an unfolded state provided in an embodiment of the present application;

[0048] Figure 1BA schematic diagram of a folded state of an electronic device provided in an embodiment of the present application;

[0049] Figure 2A A schematic diagram of the layout of an electronic device provided in an embodiment of the present application;

[0050] Figure 2B A schematic diagram of the structure of a middle frame assembly provided in an embodiment of the present application;

[0051] Figure 3A A method provided in the embodiment of the present application Figure 2B A1-A2 sectional view;

[0052] Figure 3B A schematic diagram of an FPC at a first gap position in a flattened state provided in an embodiment of the present application;

[0053] Figure 3C A schematic diagram of an FPC in a bent state at a first gap position provided in an embodiment of the present application;

[0054] Figure 3D A schematic diagram of a stripline electromagnetic field distribution provided in an embodiment of the present application;

[0055] Figure 4A A method provided in the embodiment of the present application Figure 2B A1-A2 sectional view;

[0056] Figure 4B A stripline electromagnetic field distribution diagram provided in an embodiment of the present application;

[0057] Figure 5A A method provided in the embodiment of the present application Figure 2B A1-A2 sectional view;

[0058] Figure 5B A conductive magnetic field distribution diagram of a coplanar waveguide with ground provided in an embodiment of the present application;

[0059] Figure 6 A schematic diagram of the layout of the wiring in an FPC provided in an embodiment of the present application;

[0060] Fig. 7A A schematic diagram of the layout of the wiring in an FPC provided in an embodiment of the present application;

[0061] Figure 7B A conductive magnetic field distribution diagram of a coplanar waveguide with ground provided in an embodiment of the present application;

[0062] Figure 7C A conductive magnetic field distribution diagram of a coplanar waveguide with ground provided in an embodiment of the present application;

[0063] Fig. 8A A schematic diagram of the structure of a signal line and a ground line of an FPC provided in an embodiment of the present application;

[0064] Figure 8B A schematic diagram of the structure of a signal line and a ground line of an FPC provided in an embodiment of the present application. DETAILED DESCRIPTION

[0065] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0066] In the following, the terms "second", "first", etc. are used only for convenience of description and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "second", "first", etc. may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0067] In addition, in the embodiments of the present application, directional terms such as "up", "down", "left" and "right" may be defined including but not limited to the orientation relative to the schematic placement of the components in the drawings. It should be understood that these directional terms may be relative concepts, which are used for relative description and clarification, and may change accordingly according to changes in the orientation of the components in the drawings.

[0068] In the embodiments of the present application, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. In addition, the term "coupled" can be a direct electrical connection or an indirect electrical connection through an intermediate medium. The term "contact" can be a direct contact or an indirect contact through an intermediate medium.

[0069] In the embodiments of the present application, "and / or" describes the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B may represent: A exists alone, A and B exist at the same time, and B exists alone, where A and B may be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0070] The embodiment of the present application provides an electronic device, which may be, for example, a folding electronic device. The electronic device may be, for example, a consumer electronic product, a home electronic product, a vehicle-mounted electronic product, or a financial electronic product. Among them, consumer electronic products may be, for example, mobile phones, tablet computers (pads), laptop computers, e-readers, personal computers (PCs), personal digital assistants (PDAs), desktop displays, smart wearable products (e.g., smart watches, smart bracelets), virtual reality (VR) electronic devices, augmented reality (AR) electronic devices, drones, etc. Home electronic products may be, for example, smart door locks, televisions, refrigerators, rechargeable small household appliances (e.g., soybean milk machines, sweeping robots), etc. Vehicle-mounted electronic products may be, for example, vehicle-mounted navigation systems, vehicle-mounted DVDs, etc. Financial electronic products may be, for example, ATM machines, electronic devices for self-service transactions, etc.

[0071] Figure 1A A schematic diagram of an electronic device in an unfolded state provided in an embodiment of the present application, Figure 1B A schematic diagram of a folded state of an electronic device provided in an embodiment of the present application.

[0072] In order to facilitate understanding of the electronic device provided in the embodiment of the present application, Figure 1A , an existing electronic device is introduced as follows:

[0073] like Figure 1A As shown, the electronic device 1 includes a screen protection layer 10, a display screen 20, a middle frame 30, and a back cover (or back shell, battery cover, etc.) 40. The screen protection layer 10 is arranged on the display screen 20 and is located on the light emitting side of the display screen 20. The display screen 20 is arranged on the middle frame 30, and the middle frame 30 is used to carry the display screen 20. The back cover 40 is covered on the middle frame 30, and forms a receiving space with the side of the middle frame 30 away from the display screen 20.

[0074] For example, the electronic device 1 is a foldable electronic device, and the display screen 20 is a flexible display screen. The display screen 20 is a self-luminous display screen, and there is no need to set a backlight module (BLM). The display screen 20 is a self-luminous display screen such as an organic light emitting diode (OLED) display screen, an active-matrix organic light-emitting diode (AMOLED) display screen, a mini organic light-emitting diode (Mini-OLED) display screen, a micro light-emitting diode (Micro-LED) display screen, a micro organic light-emitting diode (Micro-OLED) display screen, a quantum dot light emitting diode (QLED) display screen, etc.

[0075] The middle frame 30 includes a first frame body 301, a second frame body 302 and a hinge mechanism 303. The first frame body 301 and the second frame body 302 are arranged on both sides of the hinge mechanism 303, and the hinge mechanism 303 is connected to the first frame body 301 and the second frame body 302 respectively. The first frame body 301 and the second frame body 302 can be used to carry the flexible display screen 20, so that the flexible display screen 20 is kept as flat as possible during use, and the non-display surface of the flexible display screen 20 is protected. For example, a part of the flexible display screen 20 is fixed to the first frame body 301 by a glue layer, and a part is fixed to the second frame body 302 by a glue layer. The glue layer can be a thin film layer formed after coating glue, and the specific form of the glue layer is not limited in the embodiment of the present application.

[0076] In some embodiments, the display screen 20 may include a first display area 201 corresponding to the first frame 301, a second display area 202 corresponding to the second frame 302, and a bendable display area 203 corresponding to the hinge mechanism 303, and the bendable display area 203 may be connected between the first display area 201 and the second display area 202. The first display area 201 may be connected to the first frame 301, and the second display area 202 may be connected to the second frame 302.

[0077] In addition, other electronic components may be provided on the side of the first frame 301 and the second frame 302 away from the display screen 20, for example, a printed circuit board (PCB), a battery, a receiver, a speaker, a camera, etc. may be provided. The PCB may integrate electronic components such as the main controller, storage unit, antenna module, power management module, etc. of the electronic device, and the battery may power the electronic components such as the display screen 20, the circuit board, the receiver, the speaker, and the camera. Of course, the electronic components provided on the first frame 301 and the second frame 302 are not limited in the embodiment of the present application.

[0078] The back cover 40 includes a first shell 401 and a second shell 402 . The first shell 401 is buckled with the first frame body 301 , and the second shell 402 is buckled with the second frame body 302 .

[0079] Under the action of the hinge mechanism 303, the first frame 301 and the second frame 302 can move closer to or farther from each other. Accordingly, the first display area 201 and the second display area 202 of the display screen 20 can move closer to or farther from each other, so that the display screen 20 can be folded or unfolded.

[0080] In the unfolded state, the angle between the first frame body 301 and the second frame body 302 may be approximately 180°, and the display screen 20 is in the unfolded state.

[0081] In the folded state, the angle between the first frame 301 and the second frame 302 can be rotated from 180° to the first frame 301 and the second frame 302 being parallel to each other and arranged opposite to each other, and the interval between the first frame 301 and the second frame 302 is the smallest. At this time, the first display area 201 and the second display area 202 can be regarded as being arranged on different planes. Figure 1B As shown, when the electronic device 1 is folded, the display screen 20 faces inward, the first display area 201 and the second display area 202 face each other (folded inward). Similarly, the electronic device 1 can also be folded with the display screen 20 facing outward, the first shell 401 and the second shell 402 facing each other (folded outward).

[0082] Of course, the electronic device 1 is not limited to being a two-fold electronic device 1 , and the electronic device 1 may also be a multi-fold electronic device 1 , which is not limited in the embodiment of the present application.

[0083] Figure 2A A schematic diagram of the layout of an electronic device provided in an embodiment of the present application. Figure 2B A schematic diagram of the structure of a middle frame assembly provided in an embodiment of the present application.

[0084] In some embodiments, Figure 2AAs shown, a foldable electronic device usually includes multiple circuit boards, and signal transmission between the multiple circuit boards is completed by a flexible printed circuit (FPC) arranged by relying on a rotating shaft mechanism 303.

[0085] In some electronic devices, a centralized layout is usually adopted, placing the system on chip (SOC) and the radio frequency integrated circuit (RFIC) on the same circuit board to reduce the communication loss between them.

[0086] In other electronic devices, such as Figure 2A As shown, the SOC and part of the RFIC are placed on different circuit boards to obtain a larger available antenna area and separate the RF system heating components to obtain better heat dissipation performance of the whole machine. Under this type of layout, the data communication between the first circuit board where the SOC is located and the second circuit board where the RFIC is located needs to be completed by a set of high-speed signals (for example, a rate of >10Gbps). This set of high-speed signals is transmitted from the first circuit board to the second circuit board. For example, Figure 2B As shown, the signal transmission from the first circuit board to the second circuit board can be realized by the FPC arranged through the shaft. The FPC extends from the side where the first frame 301 is located through the rotating shaft mechanism 303 to the side where the second frame 302 is located, and pads are arranged at both ends of the FPC, and the FPC is coupled to the first circuit board and the second circuit board through the pads.

[0087] Figure 3A A method provided in the embodiment of the present application Figure 2B Cross-sectional view along A1-A2.

[0088] In some embodiments, Figure 3A As shown, the FPC includes a first shielding layer 51, a first insulating covering film 61, a first conductor layer 71, a first insulating substrate 62, a first connecting layer 81, a first insulating film 63, a second conductor layer 72, a second insulating film 64, a second connecting layer 82, a second insulating substrate 65, a third conductor layer 73, a second insulating covering film 66 and a second shielding layer 52 in sequence.

[0089] The first conductor layer 71 is a ground layer, the second conductor layer 72 is a signal line layer, the second conductor layer 72 includes, for example, a signal line 721 and ground lines 722 arranged on both sides of the signal line 721 , and the third conductor layer 73 is a ground layer.

[0090] In some embodiments, Figure 3AAs shown, the first connection layer 81 has a first air gap 811, and the second connection layer 82 has a second air gap 821. When the FPC is applied to the electronic device 1, the positions of the first air gap 811 and the second air gap 821 correspond to the position of the hinge mechanism 303, and the first air gap 811 and the second air gap 821 are located below the bendable display area 203 in the display screen 20.

[0091] By setting a first gap 811 on the first connecting layer 81 and a second gap 821 on the second connecting layer 82, the structure in which the three conductor layers are originally pressed and bonded together can be locally layered into three independent structures to release bending stress, so that the FPC can meet the requirements of multiple dynamic bending reliability in the application scenarios of folding electronic devices.

[0092] Figure 3B A schematic diagram of an FPC at a first gap position in a flattened state provided in an embodiment of the present application, Figure 3C A schematic diagram of an FPC in a bent state at a first gap position provided in an embodiment of the present application.

[0093] However, for the FPC at the first gap 811, Figure 3B As shown in FIG. 1 , when the electronic device is in a flattened state, the three conductor layers in the FPC are in a pressed and bonded state. Figure 3C As shown, when the FPC bends with the electronic device during the bending process, the three conductor layers will produce irregular stratification at local positions as the FPC bends at different angles. The stratification causes the distance from the second conductor layer 72 to the first conductor layer 71 and the third conductor layer 73 (the lower two ground layers) in the stripline structure to change dramatically and irregularly. And because of the air layer of uncertain thickness mixed in the middle, the equivalent dielectric constant of the medium between the second conductor layer 72 and the first conductor layer 71 and between the second conductor layer 72 and the third conductor layer 73 will be reduced.

[0094] Figure 3D A schematic diagram of a stripline electromagnetic field distribution provided in an embodiment of the present application.

[0095] like Figure 3D As shown in the figure, the FPC including three conductor layers is equivalent to constructing a stripline transmission structure. The stripline structure refers to a transmission line structure composed of a signal conductor on a dielectric substrate and grounded metal plates on opposite sides thereof. One side of the conductor line is bonded to the substrate, and the other side is exposed to air or other dielectric materials.

[0096] The stripline transmission solution has the characteristics of simple production, easy installation, low cost, low loss, low radiation, and low far-end crosstalk, making the FPC structure a high-speed signal transmission solution with good electrical performance.

[0097] In actual products, considering that the signal line 721 needs to be thickened (to reduce loss and improve bending resistance) and simplify the manufacturing process, the ground wires 722 on both sides of the signal line 721 are usually designed to be farther away from the signal line 721. Therefore, the influence of the ground wire 722 on the magnetic field of the signal line 721 is usually not considered. Figure 3D It can be seen that the first distance H1 from the signal line 721 to the first conductor layer 71 and the second distance H2 from the signal line 721 to the second conductor layer 72 have a direct impact on the magnetic field, thereby affecting the characteristic impedance of the signal line 721 .

[0098] Generally, the first distance H1 from the signal line 721 to the first conductor layer 71 and the second distance H2 from the signal line 721 to the third conductor layer 73 are proportional to the characteristic impedance of the signal line 721. Therefore, the greater the separation of the second conductor layer 72 from the first conductor layer 71 and the third conductor layer 73, the higher the characteristic impedance of the signal line 721. The existence of separation results in a sudden difference in the characteristic impedance of the high-speed signal running in the second conductor layer 72 at the first gap 811 and the second gap 821, and at other positions, thereby causing signal reflection and affecting signal quality.

[0099] Characteristic impedance (or simply impedance): refers to the characteristic impedance of the transmission line. During signal transmission, the signal will generate an instantaneous electric field between the signal line conductor and the reference plane due to the level flip. This electric field will generate a corresponding instantaneous current. When the transmission line is isotropic (uniform), there will always be a stable current I as long as the signal is transmitted. If the output level of the signal is V, during the signal transmission process, the transmission line will be equivalent to a resistance of V / I. This equivalent resistance is called the characteristic impedance of the transmission line.

[0100] Based on this, an embodiment of the present application provides an FPC for reducing impedance fluctuations of signal lines and improving signal quality.

[0101] Figure 4A A method provided in the embodiment of the present application Figure 2B A1-A2 cross-sectional view, Figure 4B A stripline electromagnetic field distribution diagram provided in an embodiment of the present application.

[0102] like Figure 4A As shown, the FPC includes a first conductor layer 71, a second conductor layer 72 and a third conductor layer 73, and the second conductor layer 72 is located between the first conductor layer 71 and the third conductor layer 73. The embodiment of the present application is not limited to the FPC including three conductor layers. The FPC may also include more conductor layers. The embodiment of the present application is only illustrated by taking three conductor layers as an example.

[0103] In some embodiments, both sides of each conductor layer in the first conductor layer 71, the second conductor layer 72 and the third conductor layer 73 are covered with an insulating layer. Figure 4A As shown, along Figure 4A From a viewing angle, the first conductor layer 71 is covered with a first insulating cover film 61 above, and the first conductor layer 71 is covered with a first insulating substrate 62 below. The second conductor layer 72 is covered with a first insulating film 63 above, and the second conductor layer 72 is covered with a second insulating film 64 below. The third conductor layer 73 is covered with a second insulating substrate 65 above, and the third conductor layer 73 is covered with a second insulating cover film 66 below.

[0104] In some embodiments, the dielectric constant of the material of the insulating layer included in the FPC is 2.8 to 3.5. For example, the dielectric constant of the material of the insulating layer is 2.8, 2.9, 3.0, 3.12, 3.2, 3.3, 3.4, 3.5. For example, when the frequency of the transmitted signal is 5 GHz, the dielectric constant of the material of the insulating layer is 3. By adjusting the dielectric constant of the material of the insulating layer, the characteristic impedance of the signal line 721 can be further optimized.

[0105] Dielectric constant: It is the main parameter that reflects the dielectric properties or polarization properties of piezoelectric material dielectrics under the action of electrostatic fields. It is usually expressed by ε. Piezoelectric elements for different purposes have different requirements for the dielectric constant of piezoelectric materials.

[0106] like Figure 4A As shown, the FPC further includes a first connection layer 81, and the first connection layer 81 is located between the first conductor layer 71 and the second conductor layer 72. For example, the first connection layer 81 is located between the first insulating substrate 62 and the first insulating film 63. The first connection layer 81 serves as an interlayer connection layer between the first conductor layer 71 and the second conductor layer 72, and for example, the first connection layer 81 may be a bonding sheet.

[0107] For example, the first connection layer 81 has a first gap 811. When the FPC is applied to the electronic device 1, the first gap 811 is located below the bendable display area 203. Figure 4A In the viewing direction (the extending direction of the signal line 721), the first gap 811 may, for example, penetrate the first connection layer 81. The first gap 811 may, for example, be an air gap or a vacuum gap.

[0108] The FPC may further include a second connection layer 82, and the second connection layer 82 is located between the second conductor layer 72 and the third conductor layer 73. For example, the second connection layer 82 is located between the second insulating film 64 and the second insulating substrate 65. The second connection layer 82 serves as an interlayer connection layer between the second conductor layer 72 and the third conductor layer 73, and for example, the second connection layer 82 may be an adhesive sheet.

[0109] For example, the second connection layer 82 has a second gap 821. When the FPC is applied to the electronic device 1, the second gap 821 is located below the bendable display area 203. Figure 4A In the direction of the viewing angle (the extension direction of the signal line 721), the second gap 821 may, for example, penetrate the second connection layer 82. The second gap 821 may, for example, be an air gap, or a vacuum gap, etc. When the FPC is in a flattened state, the projection of the first gap 811 on the second connection layer 82 may overlap (for example, coincide with) the second gap 821.

[0110] By providing the first gap 811 on the first connection layer 81 and the second gap 821 on the second connection layer 82 , the bending performance of the FPC can be improved.

[0111] In some embodiments, the dielectric constant of the material of the first connection layer 81 and / or the second connection layer 82 is 2.8 to 3.5. For example, the dielectric constant of the material of the first connection layer 81 and / or the second connection layer 82 is 2.8, 2.9, 3.0, 3.12, 3.2, 3.3, 3.4, 3.5. For example, when the frequency of the transmitted signal is 5 GHz, the dielectric constant of the material of the first connection layer 81 and / or the second connection layer 82 is 3. The materials of the first connection layer 81 and the second connection layer 82 may be the same or different, and the embodiments of the present application are not limited thereto.

[0112] By adjusting the dielectric constant of the material of the first connection layer 81 and / or the second connection layer 82 , the characteristic impedance of the signal line 721 can be further optimized.

[0113] In some embodiments, the FPC further includes a first shielding layer 51, and the first shielding layer 51 is located on the surface of the FPC. The first shielding layer 51 is located on the side of the first conductor layer 71 away from the second conductor layer 72 and is coupled to the first conductor layer 71. For example, the first shielding layer 51 covers the insulating layer located on the surface of the first conductor layer 71, and is coupled to the first conductor layer 71 through the insulating layer. For example, the first shielding layer 51 covers the first insulating cover film 61, and is coupled to the first conductor layer 71 through the first insulating cover film 61.

[0114] The FPC attaches the first shielding layer 51 above the surface of the first conductor layer 71, which can shield the electromagnetic interference (EMI) generated by the high-speed signal, reduce the interference to the radio frequency system in the electronic device, and reduce the interference of the radio frequency system to the high-speed signal. In addition, after the first shielding layer 51 is set on the surface of the FPC, when the signal line 721 moves with the rotating shaft mechanism 303, it will not be close to the metal layer in the rotating shaft mechanism 303, so the signal line 721 will not form a strip line structure with the rotating shaft mechanism 303, avoiding the influence of the strip line structure on the characteristic impedance of the signal line 721, and improving the transmission performance.

[0115] The first shielding layer 51 is coupled to the first conductor layer 71 through the first insulating cover film 61 , and provides a return current for the signal of the first conductor layer 71 .

[0116] In some embodiments, the third conductor layer 73 is a planar structure, and the third conductor layer 73 itself can serve as a shielding layer. There is no need to provide a shielding layer on the side of the third conductor layer 73 away from the second conductor layer 72 .

[0117] In other embodiments, the third conductor layer 73 is a linear structure, and the FPC further includes a second shielding layer 52, the second shielding layer 52 is located on the other surface of the FPC, and the second shielding layer 52 is located on the side of the third conductor layer 73 away from the second conductor layer 72. For example, the second shielding layer 52 covers the insulating layer located on the surface of the third conductor layer 73. For example, the second shielding layer 52 covers the second insulating covering film 66.

[0118] In some embodiments, Figure 4A As shown, the FPC includes a signal line 721 , and the signal line 721 includes a first sub-signal line 7211 , two second sub-signal lines 7212 and two first connection portions 7213 .

[0119] The first sub-signal line 7211 is located in the first conductor layer 71, and the first sub-signal line 7211 is opposite to the first gap 811. The two second sub-signal lines 7212 are located in the second conductor layer 72, and the two second sub-signal lines 7212 are respectively located on both sides of the first gap 811. The first connecting portion 7213 penetrates the first connecting layer 81 along the thickness direction of the first connecting layer 81, and the two ends of the first sub-signal line 7211 are coupled to the two second sub-signal lines 7212 through the two first connecting portions 7213.

[0120] from Figure 4AFrom a viewing angle, the first sub-signal line 7211 is located above the first gap 811, and the projection of the first sub-signal line 7211 on the first connection layer 81 overlaps the first gap 811. For example, along the extension direction of the first sub-signal line 7211, the size of the first sub-signal line 7211 is greater than or equal to the size of the first gap 811. The two second sub-signal lines 7212 are located on the left and right sides of the first gap 811, the second sub-signal line 7212 on the left is coupled to the left end of the first sub-signal line 7211 through one or more first connection parts 7213, and the second sub-signal line 7212 on the right is coupled to the right end of the first sub-signal line 7211 through one or more first connection parts 7213.

[0121] Of course, considering the process and yield issues, the embodiment of the present application does not limit the end of the first sub-signal line 7211 to be coupled to the first connecting portion 7213, and a certain amount of redundancy can be set to reduce the process difficulty and improve the coupling yield. Similarly, a certain amount of redundancy can also be set at the end of the second sub-signal line 7212.

[0122] In the embodiment of the present application, the signal line 721 first extends in the second conductor layer 72, jumps to the first conductor layer 71 at the position of the first gap 811, and then jumps back to the second conductor layer 72 after crossing the first gap 811. The signal line 721 no longer always extends in the second conductor layer 72.

[0123] In the FPC provided in the embodiment of the present application, Figure 4B As shown, the first sub-signal line 7211 of the signal line 721 is located in the first conductor layer 71, and the first sub-signal line 7211 forms a stripline structure with the first shielding layer 51 and the second conductor layer 72. Since there will be no delamination between the first shielding layer 51 and the first conductor layer 71 during the bending process of the FPC, the third distance H3 from the first shielding layer 51 to the first sub-signal line 7211 remains unchanged during the dynamic bending, and only the fourth distance H4 from the first sub-signal line 7211 to the second conductor layer 72 undergoes a delamination mutation. Compared with the above-mentioned mutations in both the first distance H1 and the second distance H2, the change in distance on only one side can reduce the characteristic impedance fluctuation of the first sub-signal line 7211 caused by delamination at the first gap 811 (for example, the impedance fluctuation can be reduced by about 50%), thereby reducing signal reflection and improving signal quality. In addition, the second sub-signal line 7212 is located in the second conductor layer 72, and the signal is transmitted in the standard stripline structure formed by the second sub-signal line 7212 and the first conductor layer 71, and the first shielding layer 51 is no longer required to participate in the signal return. The loss and far-end crosstalk caused by the first shielding layer 51 to the high-speed signal can be reduced, providing a better shielding effect. That is, the FPC provided in the present application can achieve high-quality signal transmission through a specific routing structure while meeting the bending performance of the FPC through the axis of the foldable electronic device, and can also take into account the loss problem.

[0124] Among them, if the first shielding layer 51 is to meet the requirements of bending performance, the thickness of the first shielding layer 51 usually needs to be less than 1um. At this time, if the first shielding layer 51 is to play a shielding role, the shielding metal layer that mainly plays a shielding role in the first shielding layer 51 needs to overlap with the ground signal of the FPC, and the actual signal return path will be transmitted in the shielding metal layer. In order to maintain the flexibility and bending resistance of the first shielding layer 51, the thickness of the shielding metal layer generally does not exceed 0.5um. This thickness is less than the skin depth of the electrical signal transmitted by the FPC in the metal. When the conductor thickness is less than the signal skin depth, the conductor loss of the signal transmission will increase significantly. Therefore, in this application, when the first shielding layer 51 is no longer required to participate in the signal return, the loss and far-end crosstalk caused by the first shielding layer 51 to the high-speed signal can be reduced, providing a better shielding effect.

[0125] Skin depth means: when there is alternating current or alternating electromagnetic field in the conductor, the current distribution inside the conductor is uneven, and the current is concentrated in the "skin" part of the conductor, that is, the current is concentrated in the thin layer on the surface of the conductor. The closer to the surface of the conductor, the greater the current density, and the actual current inside the conductor is smaller. As a result, the resistance of the conductor increases, and its power loss also increases. This phenomenon is called the skin effect. The thickness from the surface to the current density drops to 0.368 (i.e. 1 / e) of the surface current density is defined as the skin depth.

[0126] Figure 5A A method provided in the embodiment of the present application Figure 2B A1-A2 cross-sectional view, Figure 5B A conductive magnetic field distribution diagram of a coplanar waveguide with ground provided in an embodiment of the present application.

[0127] In some embodiments, Figure 5A As shown, the FPC further includes at least one ground line (or referred to as companion ground line) 722 , and the ground line 722 is arranged side by side with the signal line 721 , and the ground line 722 and the signal line 721 extend in the same direction. Figure 5A In the figure, an example is taken in which the FPC includes two ground lines 722 and the ground lines 722 are respectively arranged on both sides of the signal line 721.

[0128] By adding an accompanying ground line 722 on at least one side of the signal line 721 , while providing better isolation between signals, a more flexible impedance control solution can be provided by adjusting the distance between the ground line 722 and the signal line 721 .

[0129] The ground line 722 includes a first sub-ground line 7221, two second sub-ground lines 7222, and two second connecting portions 7223. The first sub-ground line 7221 is located in the first conductor layer 71 and is opposite to the first gap 811. The two second sub-ground lines 7222 are located in the second conductor layer 72, and the two second sub-ground lines 7221 are respectively located on both sides of the first gap 811. The second connecting portions 7223 penetrate the first connecting layer 81 along the thickness direction of the first connecting layer 81, and the two ends of the first sub-ground line 7221 are correspondingly coupled to the two second sub-ground lines 7222 through the second connecting portions 7223.

[0130] That is, the ground wires 722 on both sides of the signal wire 721 jump from the second conductor layer 72 to the first conductor layer 71 at the first gap 811, just like the signal wire 721. The structure of the ground wire 722 is not described here any more, and the above description of the signal wire 721 may be referred to.

[0131] like Figure 5B As shown, the signal line 721, the ground line 722, the first shielding layer 51 and the second conductor layer 72 constitute a coplanar waveguide ground (CPWG) structure.

[0132] Among them, a central conductor strip ( Figure 5B The first sub-signal line 7211 in the center conductor strip is formed by making conductor planes ( Figure 5B On the basis of the coplanar waveguide, a complete conductor plane ( Figure 5B The first shielding layer 51 and the second conductor layer 72 in the stripline are connected to the conductor surfaces on both sides (the second sub-ground wire 7221) through vertical holes to form a return ground for the center conductor. This structure is called a coplanar waveguide structure with ground. Or it can be understood that the coplanar waveguide with ground is based on the stripline, with two conductors added on both sides of the signal conductor, close to the signal conductor. And the two newly added conductors are connected to the ground plane below through metal holes to achieve a more complete grounding effect. The difference between the coplanar waveguide structure with ground and the stripline structure is that there are more conductors on both sides as additional return surfaces. In addition to the influence of materials, such as Figure 4B As shown in Figure 1, the characteristic impedance of the stripline structure is mainly determined only by the ground plane distance (H3, H4). Figure 5B As shown, the characteristic impedance of the coplanar waveguide structure with ground is jointly determined by the distance between the ground wires on both sides (H5, H6) and the distance between the ground planes (H3, H4). Moreover, compared with the stripline structure, the electromagnetic field of the coplanar waveguide structure with ground is more distributed near the conductors on both sides (two second sub-ground wires 7221), and the coplanar waveguide with ground has a more solid grounding structure, so it has the characteristics of smaller surface wave leakage and radiation loss.

[0133] In the FPC provided in the embodiment of the present application, Figure 5B As shown, the first sub-signal line 7211 forms a coplanar waveguide structure with ground with two second sub-ground lines 7221, the first shielding layer 51, and the second conductor layer 72. The characteristic impedance of the first sub-signal line 7211 is affected by four parts: the fifth distance H5 from the first sub-signal line 7211 to the second sub-ground line 7221 on the left, the sixth distance H6 from the first sub-signal line 7211 to the second sub-ground line 7221 on the right, the third distance H3 from the first sub-signal line 7211 to the first shielding layer 51, and the fourth distance H4 from the first sub-signal line 7211 to the second conductor layer 72. During the bending process of the FPC, the third distance H3, the fifth distance H5, and the sixth distance H6 do not change, and only the fourth distance H4 changes suddenly due to delamination. Therefore, the influence of the sudden change of the fourth distance H4 on the characteristic impedance of the first sub-signal line 7211 can be significantly reduced, and the stability of the characteristic impedance of the first sub-signal line 7211 can be further improved.

[0134] Figure 6 A schematic diagram of the layout of routing in an FPC provided in an embodiment of the present application.

[0135] In some embodiments, Figure 6 As shown, the signal line 721 is a single-ended signal line. For example, the signal line 721 is a radio frequency signal line. The distance from the first sub-signal line 7211 to the second sub-ground line 7221 on one side is Figure 5B The fifth distance H5 in the figure is that the distance from the first sub-signal line 7211 to the second sub-ground line 7221 on the other side is Figure 5B The sixth distance H6 in .

[0136] Fig. 7A A schematic diagram of the layout of the wiring in an FPC provided in an embodiment of the present application, Figure 7B and Figure 7C A conductive magnetic field distribution diagram of a coplanar waveguide with ground provided in an embodiment of the present application.

[0137] In other embodiments, Fig. 7A As shown, the FPC includes two signal lines 721 arranged adjacent to each other, and the two signal lines 721 constitute a pair of differential signal lines.

[0138] For example, the differential characteristic impedance of the two signal lines 721 is 80 ohm to 100 ohm. For example, the differential characteristic impedance of the two signal lines 721 is 80 ohm, 83 ohm, 85 ohm, 87 ohm, 90 ohm, 93 ohm, 95 ohm, 97 ohm, and 100 ohm. The characteristic impedance fluctuation within the process error (±10%) is within the protection scope of the embodiment of the present application.

[0139] By setting the differential characteristic impedance of the two signal lines 721 to 80 ohm to 100 ohm, the FPC can be adapted to signal transmission of various chips.

[0140] In the embodiment of the present application, the line width of the multiple signal lines 721, the spacing between the signal lines 721, and the spacing between the signal lines 721 and the ground line 722 can be controlled so that the characteristic impedance of the signal line 721 can always be maintained near the calibrated value.

[0141] In some embodiments, the signal line 721 is used to transmit high-speed signals. For example, the rate of the signal transmitted by the signal line 721 is greater than or equal to 10 Gbps. For example, the speed of the signal transmitted by the signal line 721 is 10 Gbps, 16 Gbps, 20 Gbps, 23.4 Gbps, 32 Gbps, etc.

[0142] In the scenario of transmitting high-speed signals, the FPC provided in the present application has a more significant effect on improving the signal transmission quality.

[0143] In some embodiments, Fig. 7A As shown, the first sub-signal line 7211 of the signal line 721 includes a first segment 701, a second segment 702 and a third segment 703 which are connected in sequence.

[0144] The second section 702 is directly opposite to the first gap 811, and the projection of the second section 702 on the first connection layer 81 is located in the first gap 811. For example, the length of the second section 702 is the same as the size of the first gap 811, and the end of the second section 702 is located on the boundary of the first gap 811. The first section 701 and the third section 703 are respectively located on both sides of the second section 702, and the first section 701 and the third section 703 are respectively located on both sides of the first gap 811. For example, the projections of the first section 701 and the third section 703 on the first connection layer 81 are located on both sides of the first gap 811, and the first section 701 and the third section 703 are respectively coupled to the first connection portion 7213 to achieve coupling between the first sub-signal line 7211 and the first connection portion 7213.

[0145] “Directly facing” may be understood as, for example, that along the extension direction of the signal line 721 , the boundary line between the second section 702 and the first section 701 and the boundary line between the second section 702 and the third section 703 coincide with the boundary line position of the first gap 811 .

[0146] The first section 701 and the third section 703 can be symmetrically arranged on both sides of the second section 702 to improve the symmetry of the FPC bending force. The first section 701 and the third section 703 can also be asymmetrically arranged on both sides of the second section 702 to improve the flexibility of the FPC layout.

[0147] The first section 701 and the third section 703 in the first sub-signal line 7211 are equivalent to transition parts, so that the first connection part 7213 does not need to pass through the first gap 811, but passes through the first connection layer 81 from the non-first gap 811, thereby reducing the process difficulty and process accuracy requirements of the first connection part 7213.

[0148] For example, the distance from the first connection portion 7213 to the first gap 811 is 0.5 mm to 2 mm. The distance from the first connection portion 7213 to the first gap 811 refers to the distance from the side of the first connection portion 7213 away from the first gap 811 to the boundary of the first gap 811 close to the first connection portion 7213. Alternatively, it can be understood that the lengths of the first section 701 and the third section 703 are 0.5 mm to 2 mm. The length of the first section 701 refers to the dimension from the end of the first section 701 to the boundary between the first section 701 and the second section 702.

[0149] For example, the distance from the first connection portion 7213 to the first gap 811 is 0.5 mm, 0.75 mm, 1.0 mm, 1.25 mm, 1.5 mm, 1.75 mm, or 2 mm.

[0150] Setting the distance from the first connection portion 7213 to the first gap 811 to 0.5 mm to 2 mm can improve process yield, reduce process difficulty, and optimize the characteristic impedance of the first sub-signal line 7211 .

[0151] In some embodiments, Fig. 7A As shown, the first sub-ground line 7221 of the ground line 722 includes a fourth segment 704, a fifth segment 705 and a sixth segment 706 which are connected in sequence.

[0152] The fifth segment 705 is directly opposite to the first gap 811, and the projection of the fifth segment 705 on the first connection layer 81 is located within the first gap 811. For example, the end of the fifth segment 705 is located on the boundary of the first gap 811. The fourth segment 704 and the sixth segment 706 are respectively located on both sides of the fifth segment 705, and the fourth segment 704 and the sixth segment 706 are respectively located on both sides of the first gap 811. For example, the projections of the fourth segment 704 and the sixth segment 706 on the first connection layer 81 are located on both sides of the first gap 811. The fourth segment 704 and the sixth segment 706 are respectively coupled to the second connection portion 7223 to achieve coupling of the first sub-ground line 7221 with the second connection portion 7223.

[0153] “Directly facing” may be understood as, for example, that along the extension direction of the signal line 721 , the boundary line between the fifth segment 705 and the fourth segment 704 , and the boundary line between the fifth segment 705 and the sixth segment 706 coincide with the boundary position of the first gap 811 .

[0154] The fourth section 704 and the sixth section 706 can be symmetrically arranged on both sides of the fifth section 705 to improve the symmetry of the FPC bending force. The fourth section 704 and the sixth section 706 can also be asymmetrically arranged on both sides of the fifth section 705 to improve the flexibility of the FPC layout.

[0155] The fourth section 704 and the sixth section 706 in the first sub-ground line 7221 are equivalent to transition parts, so that the second connection part 7223 does not need to pass through the first gap 811, but passes through the first connection layer 81 from the non-first gap 811, thereby reducing the process difficulty and process accuracy requirements of the second connection part 7223.

[0156] For the sake of convenience, only the structures of the first section 701 and the fourth section 704 are described below. The structures of the third section 703 and the sixth section 706 can refer to the relevant descriptions of the first section 701 and the fourth section 704.

[0157] In some embodiments, Fig. 7A As shown, the distance h1 between the second segment 702 and the fifth segment 705 is smaller than the distance h2 between the first segment 701 and the fourth segment 704 .

[0158] At the position corresponding to the first gap 811, the second section 702 and the fifth section 705 are close to each other (reducing the spacing h1, that is, the signal line 721 and the ground line 722 are close to each other), which can change the electromagnetic field distribution of the second section 702 and make full use of the field distribution characteristics of the coplanar waveguide structure with ground to reduce the impedance fluctuation generated during the bending process. At the position of the first gap 811, the FPC will be delaminated during the bending process. At the positions on both sides of the first gap 811, the FPC will not be delaminated during the bending process. Figure 7B As shown, during the bending process of the FPC, the fourth distance H4 between the second section 702 and the second conductor layer 72 will change (increase). Figure 7C As shown in FIG. 1 , during the bending process of the FPC, the fourth distance H4 between the first section 701 and the second conductor layer 72 does not change. Therefore, the fourth distance H4 from the first section 701 to the second conductor layer 72 is smaller, while the fourth distance H4 from the second section 702 to the second conductor layer 72 is larger, which is equivalent to the characteristic impedance of the first section 701 being lower than the characteristic impedance of the second section 702. Figure 7C The fifth distance H5 and the sixth distance H6 (spacing h2) between the first segment 701 and the adjacent fourth segment 704 are greater than, Figure 7B The fifth distance H5 and the sixth distance H6 (spacing h1) between the second section 702 and the adjacent fifth section 705 can improve the characteristic impedance of the first section 701 so that the characteristic impedances of the first section 701 and the second section 702 remain stable and balanced.

[0159] For example, the distance h1 between the second segment 702 and the fifth segment 705 is 50 um to 100 um. For example, the distance h1 between the second segment 702 and the fifth segment 705 is 50 um, 60 um, 70 um, 80 um, 90 um, or 100 um.

[0160] By setting the interval h1 between the second section 702 and the fifth section 705 to 50 um to 100 um, the second section 702 can have better anti-interference capability, lower common mode and smaller electromagnetic radiation.

[0161] For example, the spacing h2 between the first section 701 and the fourth section 704 is 60um to 200um. For example, the spacing h2 between the first section 701 and the fourth section 704 is 60um, 70um, 80um, 90um, 100um, 110um, 120um, 130um, 140um, 150um, 160um, 170um, 180um, 190um, 200um.

[0162] By setting the interval h2 between the first segment 701 and the fourth segment 704 to 60 um to 200 um, the characteristic impedance of the first segment 701 can be optimized.

[0163] In some embodiments, Fig. 7A As shown, the distance h3 between the second sub-signal line 7212 and the second sub-ground line 7222 is smaller than the distance h2 between the first section 701 and the fourth section 704 .

[0164] By reducing the interval h3 between the second sub-signal line 7212 and the second sub-ground line 7222, space can be reserved for increasing the width of the second sub-signal line 7212. Increasing the width of the second sub-signal line 7212 increases the volume of the effective conductor for propagating electromagnetic waves, thereby reducing the loss of the second sub-signal line 7212.

[0165] For example, the spacing h3 between the second sub-signal line 7212 and the second sub-ground line 7222 is 60um to 200um. For example, the spacing h3 between the second sub-signal line 7212 and the second sub-ground line 7222 is 60um, 70um, 80um, 90um, 100um, 110um, 120um, 130um, 140um, 150um, 160um, 170um, 180um, 190um, 200um.

[0166] By limiting the interval h3 between the second sub-signal line 7212 and the second sub-ground line 7222 to 60 um to 200 um, it is possible to increase the width of the second sub-signal line 7212 while reducing the process difficulty and ensuring the process yield.

[0167] In some embodiments, Fig. 7A As shown, the width w1 of the second segment 702 is greater than the width w2 of the first segment 701 .

[0168] For example, the width w1 of the second section 702 is 40 um to 70 um. For example, the width w1 of the second section 702 is 40 um, 50 um, 60 um, or 70 um.

[0169] For example, the width w2 of the first section 701 is 30 um to 60 um. For example, the width w2 of the first section 701 is 30 um, 40 um, 50 um, or 60 um.

[0170] At the positions on both sides of the first gap 811, the FPC does not delaminate during the bending process, and the thickness is reduced compared to the first gap 811. Therefore, the thickness from the first section 701 to the adjacent layer is smaller, while the thickness from the second section 702 to the adjacent layer is larger, which is equivalent to the characteristic impedance of the first section 701 being lower than the characteristic impedance of the second section 702. By increasing the width w1 of the second section 702, the characteristic impedance of the second section 702 can be reduced, so that the characteristic impedances of the first section 701 and the second section 702 remain stable and balanced.

[0171] In some other embodiments, the width w1 of the second segment 702 is equal to the width w2 of the first segment 701 .

[0172] This can simplify the preparation process of the first sub-signal line 7211 and reduce the risk of the first sub-signal line 7211 breaking at the junction of the first section 701 and the second section 702 .

[0173] In some other embodiments, the width w1 of the second segment 702 is smaller than the width w2 of the first segment 701. This can reserve space for thickness variation of the film layer below the first segment 701 and the film layer below the second segment 702. The characteristic impedance of the first segment 701 and the second segment 702 is adjusted by matching the line width and spacing.

[0174] In some embodiments, Fig. 7A As shown, the width w2 of the first segment 701 is smaller than the width w3 of the second sub-signal line 7212 .

[0175] By increasing the width w3 of the second sub-signal line 7212, the volume of the effective conductor used to propagate electromagnetic waves can be increased, thereby reducing the loss of the second sub-signal line 7212. In addition, by reducing the width of the first section 701 and the second section 702, the characteristic impedance fluctuation caused by the change in the distance to the ground after the first sub-signal line 7211 jumps to the first conductor layer 71 can be compensated.

[0176] For example, the width w3 of the second signal sub-line 7212 is 45 um to 80 um. For example, the width w3 of the second signal sub-line 7212 is 45 um, 50 um, 60 um, 70 um, or 80 um.

[0177] By setting the width w3 of the second sub-signal line 7212 to 45 um to 80 um, multiple factors such as conductor loss, manufacturing process, and characteristic impedance can be optimized.

[0178] In some embodiments, Fig. 7A As shown, the width w4 of the fifth segment 705 is greater than the width w5 of the fourth segment 704 .

[0179] By increasing the width w4 of the fifth section 705, the fifth section 705 can be brought closer to the second section 702 of the signal line 721 to change the electromagnetic field distribution of the second section 702 and make full use of the field distribution characteristics of the ground coplanar waveguide structure to reduce the impedance fluctuation generated during the bending process.

[0180] For example, the width of the fifth section 705 is wide in the middle and narrow at both ends. For example, the fifth section 705 includes a first end close to the fourth section 704 and a second end close to the sixth section 706, and the width of the first end decreases along the direction from the middle to the first end. The width of the second end decreases along the direction from the middle to the second end (for example, decreases in a conical shape), so that the line width of the first sub-ground line 7221 transitions smoothly, reducing the risk of bending and breaking of the first sub-signal line 7211.

[0181] In some embodiments, Fig. 7A As shown, the width w5 of the fourth segment 704 is equal to the width w6 of the second sub-ground line 7222. This can simplify the preparation process and layout of the ground line 722.

[0182] In some embodiments, Fig. 7A As shown, in the two signal lines 721 , the spacing h4 between the first segments 701 is greater than the spacing h5 between the second segments 702 .

[0183] By bringing the second sections 702 of the differential pair signal lines 721 closer together, the differential line coupling is tighter, the radiation is smaller, and the crosstalk with the outside is smaller. By moving the first sections 701 of the differential pair signal lines 721 farther apart, the characteristic impedance of the differential pair signal lines 721 can be increased.

[0184] For example, in two signal lines 721, the spacing h4 between the first segments 701 is 60um to 150um. For example, in two signal lines 721, the spacing h4 between the first segments 701 is 60um, 70um, 80um, 90um, 100um, 110um, 120um, 130um, 140um, 150um.

[0185] By setting the interval h4 between the first segments 701 of the differential pair signal lines 721 to 60 um to 150 um, the characteristic impedance jump of the first sub-signal line 7211 in the signal line 721 can be reduced.

[0186] For example, in two signal lines 721, the spacing h5 between the second segments 702 is 50 um to 100 um. For example, in two signal lines 721, the spacing h5 between the second segments 702 is 50 um, 60 um, 70 um, 80 um, 90 um, or 100 um.

[0187] By setting the spacing h5 between the second sections 702 of the differential pair signal lines 721 to 50 um to 100 um, various performances of the differential pair signal lines 721 can be balanced and the influence of delamination on characteristic impedance can be reduced.

[0188] In some embodiments, Fig. 7A As shown, in the two signal lines 721 , the spacing h4 between the first segments 701 is greater than the spacing h6 between the second sub-signal lines 7212 .

[0189] By reducing the interval h6 between the second sub-signal lines 7212 in the differential pair signal lines 721 , space can be reserved for increasing the width of the second sub-signal lines 7212 , thereby increasing the width of the second sub-signal lines 7212 and reducing the loss of the second sub-signal lines 7212 .

[0190] For example, in two signal lines 721, the spacing h6 between the second sub-signal lines 7212 is 60um to 150um. For example, in two signal lines 721, the spacing h6 between the second sub-signal lines 7212 is 60um, 70um, 80um, 90um, 100um, 110um, 120um, 130um, 140um, 150um.

[0191] By setting the spacing h6 between the second sub-signal lines 7212 in the differential pair signal lines 721 to 60 um to 150 um, it is possible to increase the width of the second sub-signal line 7212 while reducing the process difficulty and ensuring the process yield.

[0192] In some embodiments, the thickness of the first shielding layer 51 is 6 um to 14 um. For example, the thickness of the first shielding layer 51 is 6 um, 7 um, 8 um, 9 um, 10 um, 11 um, 12 um, 13 um, or 14 um.

[0193] In some embodiments, the thickness of the first conductor layer 71, the second conductor layer 72 or the third conductor layer 73 is 6um to 15um. Taking the first conductor layer 71 as an example, the thickness of the first conductor layer 71 is 6um, 7um, 8um, 9um, 10um, 11um, 12um, 13um, 14um, 15um.

[0194] In some embodiments, the thickness of the first connection layer 81 or the second connection layer 81 is 10um to 20um. Taking the first connection layer 81 as an example, the thickness of the first connection layer 81 is 10um, 11um, 12um, 13um, 14um, 15um, 16um, 17um, 18um, 19um, or 20um.

[0195] In some embodiments, the distance from the first conductor layer 71 to the first shielding layer 51 is 30um to 55um. For example, the thickness of the first insulating cover film 61 is 30um to 55um. For example, the distance from the first conductor layer 71 to the first shielding layer 51 is 30um, 35um, 40um, 45um, 50um, or 55um.

[0196] In some embodiments, the distance from the first conductor layer 71 to the first connection layer 81 is 6um to 18um. For example, the thickness of the first insulating substrate 62 is 6um to 18um. For example, the distance from the first conductor layer 71 to the first connection layer 81 is 6um, 7um, 8um, 9um, 10um, 11um, 12um, 13um, 14um, 15um, 16um, 17um, 18um.

[0197] In some embodiments, the distance from the first connection layer 81 to the second conductor layer 72 is 15um to 30um. For example, the thickness of the first insulating film 63 is 15um to 30um. For example, the distance from the first connection layer 81 to the second conductor layer 72 is 15um, 16um, 17um, 18um, 19um, 20um, 21um, 22um, 23um, 24um, 25um, 26um, 27um, 28um, 29um, 30um.

[0198] In some embodiments, the distance from the second connection layer 82 to the second conductor layer 72 is 6um to 18um. For example, the thickness of the second insulating film 64 is 6um to 18um. For example, the distance from the second connection layer 82 to the second conductor layer 72 is 6um, 7um, 8um, 9um, 10um, 11um, 12um, 13um, 14um, 15um, 16um, 17um, 18um.

[0199] In some embodiments, the distance from the second connection layer 82 to the third conductor layer 73 is 6um to 18um. For example, the thickness of the second insulating substrate 65 is 6um to 18um. For example, the distance from the second connection layer 82 to the third conductor layer 73 is 6um, 7um, 8um, 9um, 10um, 11um, 12um, 13um, 14um, 15um, 16um, 17um, 18um.

[0200] The embodiment of the present application does not limit the thickness of the second shielding layer 52 and the second insulating covering film 66 , and can be reasonably set according to the application scenario of the FPC.

[0201] By adjusting the thickness of each film layer in the FPC, the characteristic impedance of the signal line 721 can be further optimized, and the impact of delamination on the signal transmission quality can be reduced.

[0202] Fig. 8A and Figure 8B A schematic diagram of the structure of a signal line and a ground line of an FPC provided in an embodiment of the present application.

[0203] In some embodiments, Fig. 8A and Figure 8B As shown, the second conductor layer 72 further includes a hollow area 723, and the first sub-signal line 7211 is opposite to the hollow area 723. For example, the projection of the first sub-signal line 7211 of the signal line 721 on the second conductor layer 72 overlaps with the hollow area 723. For example, the projection of the first sub-signal line 7211 on the second conductor layer 72 is located in the hollow area 723.

[0204] The embodiment of the present application does not limit the contour shape of the hollow area 723. The contour of the hollow area 723 may coincide with the projection contour of the first sub-signal line 7211, or the contour of the hollow area 723 may be a concentric pattern with the projection contour of the first sub-signal line 7211, or the contour of the hollow area 723 may be different from the projection contour shape of the first sub-signal line 7211.

[0205] The projection area of ​​the first sub-signal line 7211 is hollowed out on the second conductor layer 72. There is no ground signal in the projection area and no magnetic field is generated. This will not affect the characteristic impedance of the first sub-signal line 7211, and can further reduce the effect of the change in the distance between the first conductor layer 71 and the second conductor layer 72 on the characteristic impedance of the first sub-signal line 7211 of the signal line 721.

[0206] In some embodiments, the third conductor layer 73 further includes a hollow region, and the projection of the first sub-signal line 7211 of the signal line 721 on the third conductor layer 73 overlaps with the hollow region. For example, the projection of the first sub-signal line 7211 on the third conductor layer 73 is located in the hollow region.

[0207] The present application also provides a middle frame assembly, such as Figure 2B As shown, the middle frame assembly includes a first frame body 301, a second frame body 302, a hinge mechanism 303 and an FPC, and the first frame body 301 and the second frame body 302 are located on both sides of the hinge mechanism 303 and are connected by the hinge mechanism 303. The FPC passes through the hinge mechanism 303 from the side where the first frame body 301 is located and extends to the side where the second frame body 302 is located. The middle frame assembly provided in the embodiment of the present application can be applied to the electronic device provided in the embodiment of the present application, in which case the side where the first conductor layer 71 of the FPC is located faces the display screen 20, and the side where the third conductor layer 73 is located faces away from the display screen 20.

[0208] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A flexible circuit board, characterized in that: include: a first conductor layer, a second conductor layer and a third conductor layer, wherein the second conductor layer is located between the first conductor layer and the third conductor layer; A first connection layer is located between the first conductor layer and the second conductor layer; the first connection layer has a first gap; A first shielding layer, located at a side of the first conductor layer away from the second conductor layer and coupled to the first conductor layer; at least one signal line, the signal line comprising a first sub-signal line, two second sub-signal lines and two first connecting portions; The first sub-signal line is located in the first conductor layer and is opposite to the first gap; the two second sub-signal lines are located in the second conductor layer and are respectively located on both sides of the first gap; the first connecting portion penetrates the first connecting layer along the thickness direction of the first connecting layer; the two ends of the first sub-signal line are respectively coupled to the two second sub-signal lines through the two first connecting portions.

2. The flexible circuit board according to claim 1, characterized in that: The flexible circuit board further comprises at least one ground line, and the ground line is arranged side by side with the signal line; The ground wire includes a first sub-ground wire, two second sub-ground wires and two second connecting parts; the first sub-ground wire is located in the first conductor layer and is opposite to the first gap; the two second sub-ground wires are located in the second conductor layer and are respectively located on both sides of the first gap; the second connecting part penetrates the first connecting layer along the thickness direction of the first connecting layer; the two ends of the first sub-ground wire are coupled to the two second sub-ground wires through the two second connecting parts.

3. The flexible circuit board according to claim 1 or 2, characterized in that: The first sub-signal line includes a first section, a second section and a third section connected in sequence; the second section is opposite to the first gap, the first section and the third section are respectively located on both sides of the first gap, and the first section and the third section are respectively coupled to the first connecting portion.

4. The flexible circuit board according to claim 2 or 3, characterized in that: The first sub-ground line includes a fourth section, a fifth section and a sixth section connected in sequence; the fifth section is directly opposite to the first gap, the fourth section and the sixth section are respectively located on both sides of the first gap, and the fourth section and the sixth section are respectively coupled to the second connecting portion.

5. The flexible circuit board according to claim 4, characterized in that: The distance between the second segment and the fifth segment is smaller than the distance between the first segment and the fourth segment; and / or, A distance between the second sub-signal line and the second sub-ground line is smaller than a distance between the first segment and the fourth segment.

6. The flexible circuit board according to claim 5, characterized in that: The distance between the first section and the fourth section is 60um to 200um; and / or, The distance between the second section and the fifth section is 50um to 100um; and / or, The distance between the second sub-signal line and the second sub-ground line is 60 um to 200 um.

7. The flexible circuit board according to any one of claims 4 to 6, characterized in that: The width of the second segment is greater than the width of the first segment; and / or, The width of the first segment is smaller than the width of the second sub-signal line.

8. The flexible circuit board according to claim 7, characterized in that: The width of the first section is 30um to 60um; and / or, The width of the second section is 40um to 70um; and / or, The width of the second sub-signal line is 45um-80um.

9. The flexible circuit board according to any one of claims 4 to 8, characterized in that: The width of the fifth segment is greater than the width of the fourth segment; and / or, The width of the fourth segment is equal to the width of the second sub-ground line.

10. The flexible circuit board according to any one of claims 4 to 9, characterized in that: The at least one signal line includes two adjacently arranged signal lines; the differential characteristic impedance of the two signal lines is 80 ohm to 100 ohm.

11. The flexible circuit board according to claim 10, characterized in that: In the two signal lines, the spacing between the first segments is greater than the spacing between the second segments; and / or, In the two signal lines, the spacing between the first segments is greater than the spacing between the second sub-signal lines.

12. The flexible circuit board according to claim 11, characterized in that: In the two signal lines, the spacing between the first sections is 60um to 150um; and / or, In the two signal lines, the spacing between the second sections is 50um to 100um; and / or, In the two signal lines, the interval between the second sub-signal lines is 60um to 150um.

13. The flexible circuit board according to any one of claims 4 to 12, characterized in that: Along the direction from the middle to the end, the width of the end of the fifth section tends to decrease.

14. The flexible circuit board according to any one of claims 1 to 13, characterized in that: The second conductor layer further includes a hollow area, and the first sub-signal line is opposite to the hollow area.

15. The flexible circuit board according to any one of claims 1 to 14, characterized in that: The distance from the first connecting portion to the first gap is 0.5 mm to 2 mm.

16. The flexible circuit board according to any one of claims 1 to 15, characterized in that: The rate of the signal transmitted by the signal line is greater than or equal to 10 Gbps; or, The signal line is used to transmit radio frequency signals.

17. The flexible circuit board according to any one of claims 1 to 16, characterized in that: The flexible circuit board also includes a second connecting layer, a multi-layer insulating layer and a second shielding layer; The second connecting layer is located between the second conductor layer and the third conductor layer, the second connecting layer has a second gap, and a projection of the second gap on the first connecting layer overlaps with the first gap; The two opposite surfaces of the first conductor layer, the second conductor layer and the third conductor layer are respectively covered with the insulating layer; The second shielding layer is located on a side of the third conductor layer away from the second conductor layer.

18. A middle frame assembly, characterized in that: The invention comprises a first frame, a second frame, a hinge mechanism and a flexible circuit board, wherein the first frame and the second frame are connected via the hinge mechanism, and the flexible circuit board extends from the side where the first frame is located through the hinge mechanism to the side where the second frame is located, and the flexible circuit board comprises the flexible circuit board according to any one of claims 1 to 17.

19. An electronic device, characterized in that: It comprises a middle frame assembly and a display screen, wherein the display screen is arranged on the middle frame assembly, and the middle frame assembly comprises the middle frame assembly according to claim 18.

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