Flexible circuit board

Abstract

The utility model discloses a flexible circuit board, which comprises a first substrate, a first differential wiring layer, a first reference ground layer, a first cover film and a second cover film, and is characterized in that the first differential wiring layer is attached to one side of the first substrate; the first reference ground layer is attached to the side, away from the first differential wiring layer, of the first substrate, and a defected ground structure used for suppressing common-mode noise is formed on the first reference ground layer; the first covering film is attached to the first differential wiring layer and the first substrate; the second covering film is attached to the side, away from the first substrate, of the first reference ground layer. By means of the arrangement, suppression of common-mode noise can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of circuit board, in particular to a flexible circuit board. BACKGROUND

[0002] In the circuit board, the existing common mode noise suppression methods include: adding a common mode inductor near the PCB (Printed Circuit Board) port connected with the flexible circuit board to suppress the common mode noise on the differential signal; or adding a defect ground structure on the reference ground plane of the PCB differential signal to suppress the common mode noise.

[0003] However, the above common mode noise suppression methods need to add additional components, which have high cost and occupy the layout space on the PCB; and for the filter frequency band below 2GHz, since the lower the frequency, the longer the wavelength, the required transverse size of the defect ground structure will be large, which will affect the layout wiring of the corresponding area on the PCB, i.e. the layout space without the defect ground structure on the PCB.

[0004] Therefore, how to realize common mode suppression under the condition that the PCB does not have layout space with common mode suppression structure is a technical problem urgently to be solved in the field. CONTENT OF THE INVENTION

[0005] In order to solve the problems of the prior art, the purpose of the present application is to provide a flexible circuit board which can suppress common mode noise.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A flexible circuit board, comprising a first substrate, a first differential trace layer, a first reference ground layer, a first cover film and a second cover film, the first differential trace layer being attached to one side of the first substrate; the first reference ground layer being attached to the side of the first substrate away from the first differential trace layer, the first reference ground layer being formed with a defect ground structure for suppressing common mode noise; the first cover film being attached to the first differential trace layer and the first substrate; and the second cover film being attached to the side of the first reference ground layer away from the first substrate.

[0008] Further, the first differential trace layer comprises a first differential trace and a second differential trace, the first differential trace and the second differential trace are parallel to a preset straight line, and the first differential trace and the second differential trace are symmetrically arranged about the preset straight line, and the defect ground structure is symmetrically arranged about the preset straight line.

[0009] Further, the defect ground structure comprises a first defect ground mechanism, the first defect ground mechanism comprises a first transverse portion perpendicular to the preset straight line, a first longitudinal portion and a second longitudinal portion extending along the preset straight line, the first transverse portion is located between the first longitudinal portion and the second longitudinal portion, and two ends of the first transverse portion are connected to the middle of the first longitudinal portion and the middle of the second longitudinal portion respectively.

[0010] Further, the defect ground structure comprises a second defect ground mechanism, the second defect ground mechanism comprises a second transverse portion perpendicular to the preset straight line, a third longitudinal portion and a fourth longitudinal portion extending along the preset straight line, the second transverse portion is located between the third longitudinal portion and the fourth longitudinal portion, and two ends of the second transverse portion are connected to one end of the third longitudinal portion and one end of the fourth longitudinal portion respectively.

[0011] Further, the defect ground structure comprises a first defect ground mechanism and two second defect ground mechanisms; the first defect ground mechanism comprises a first transverse portion perpendicular to the preset straight line, a first longitudinal portion and a second longitudinal portion extending along the preset straight line, the first transverse portion is located between the first longitudinal portion and the second longitudinal portion, and two ends of the first transverse portion are connected to the middle of the first longitudinal portion and the middle of the second longitudinal portion respectively; the two second defect ground mechanisms are located between the first longitudinal portion and the second longitudinal portion, the first transverse portion is located between the two second defect ground mechanisms, and the two second defect ground mechanisms are symmetrically arranged about the first transverse portion; the two second defect ground mechanisms do not contact the first defect ground mechanism.

[0012] Further, the second defect ground mechanism comprises a second transverse portion perpendicular to the preset straight line, a third longitudinal portion and a fourth longitudinal portion extending along the preset straight line, the second transverse portion is located between the third longitudinal portion and the fourth longitudinal portion, and two ends of the second transverse portion are connected to one end of the third longitudinal portion and one end of the fourth longitudinal portion respectively; the third longitudinal portion is closer to the first longitudinal portion than the fourth longitudinal portion, the fourth longitudinal portion is closer to the second longitudinal portion than the third longitudinal portion, the second transverse portion is connected to one end of the third longitudinal portion away from the first transverse portion, and the second transverse portion is also connected to one end of the fourth longitudinal portion away from the first transverse portion.

[0013] Further, the maximum distance between the two second defect ground mechanisms along the direction of the preset straight line is equal to the maximum length of the first defect ground mechanism along the direction of the preset straight line.

[0014] Further, the defect ground structure comprises a plurality of first defect ground mechanisms distributed along the preset straight line direction, each first defect ground mechanism comprises a first transverse part perpendicular to the preset straight line, a first longitudinal part and a second longitudinal part extending along the preset straight line, the first transverse part is located between the first longitudinal part and the second longitudinal part, and the two ends of the first transverse part are connected to the middle part of the first longitudinal part and the middle part of the second longitudinal part respectively; or, the defect ground structure comprises a plurality of second defect ground mechanisms distributed along the preset straight line direction, each second defect ground mechanism comprises a second transverse part perpendicular to the preset straight line, a third longitudinal part and a fourth longitudinal part extending along the preset straight line, the second transverse part is located between the third longitudinal part and the fourth longitudinal part, and the two ends of the second transverse part are connected to one end of the third longitudinal part and one end of the fourth longitudinal part respectively; or, the defect ground structure comprises a plurality of third defect ground mechanisms distributed along the preset straight line direction, each third defect ground mechanism comprises a first defect ground mechanism and two second defect ground mechanisms, the two second defect ground mechanisms are located between the first longitudinal part and the second longitudinal part of the first defect ground mechanism, the first transverse part of the first defect ground mechanism is located between the two second defect ground mechanisms, and the two second defect ground mechanisms are symmetrically arranged about the first transverse part of the first defect ground mechanism; neither of the two second defect ground mechanisms contacts the first defect ground mechanism.

[0015] Further, the lengths of the at least two first defect ground mechanisms in the preset straight line direction are inconsistent; the lengths of the at least two second defect ground mechanisms in the preset straight line direction are inconsistent; and the lengths of the at least two third defect ground mechanisms in the preset straight line direction are inconsistent.

[0016] Further, a plurality of defect ground structures are provided, the plurality of defect ground structures are distributed along the preset straight line direction, the defect ground structure is one of the first defect ground mechanism, the second defect ground mechanism and the third defect ground mechanism, and the structures of at least two defect ground structures are different; and the lengths of the at least two defect ground structures in the preset straight line direction are inconsistent.

[0017] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0018] A flexible circuit board, comprising a first substrate, a first differential trace layer, a first reference ground layer, a second substrate, a second reference ground layer, a first cover film and a second cover film, the first differential trace layer is attached to one side of the first substrate; the first reference ground layer is attached to the side of the first substrate away from the first differential trace layer, and the first reference ground layer is formed with a defect ground structure for suppressing common mode noise; the second substrate is attached to the side of the first reference ground layer away from the first substrate; the second reference ground layer is attached to the side of the second substrate away from the first reference ground layer; the first cover film is attached to the first differential trace layer and the first substrate; and the second cover film is attached to the side of the second reference ground layer away from the second substrate.

[0019] or, the flexible circuit board comprises a first substrate, a first differential trace layer, a first reference ground layer, a second substrate, a second reference ground layer, a first cover film, and a second cover film, the first differential trace layer is attached to one side of the first substrate; the first reference ground layer is attached to the side of the first substrate away from the first differential trace layer; the second substrate is attached to the side of the first differential trace layer away from the first substrate; the second reference ground layer is attached to the side of the second substrate away from the first differential trace layer; the first cover film is attached to the side of the second reference ground layer away from the second substrate; and the second cover film is attached to the side of the first reference ground layer away from the first substrate; the first reference ground layer or the second reference ground layer is formed with a defective ground structure for suppressing common mode noise;

[0020] or, the flexible circuit board comprises a first substrate, a first differential trace layer, a first reference ground layer, a third substrate, a second differential trace layer, a second substrate, a second reference ground layer, a first cover film, and a second cover film, the first differential trace layer is attached to one side of the first substrate; the first reference ground layer is attached to the side of the first substrate away from the first differential trace layer, and the first reference ground layer is formed with a defective ground structure for suppressing common mode noise; the third substrate is attached to the side of the first reference ground layer away from the first substrate; the second differential trace layer is attached to the side of the third substrate away from the first reference ground layer; the second substrate is attached to the side of the second differential trace layer away from the third substrate; the second reference ground layer is attached to the side of the second substrate away from the second differential trace layer, and the second reference ground layer is formed with a defective ground structure for suppressing common mode noise; the first cover film is attached to the first differential trace layer and the first substrate; and the second cover film is attached to the side of the second reference ground layer away from the second substrate;

[0021] or, the flexible circuit board comprises a first substrate, a first differential trace layer, a first reference ground layer, a third substrate, a second differential trace layer, a second substrate, a second reference ground layer, a first cover film, and a second cover film, the first differential trace layer is attached to one side of the first substrate; the first reference ground layer is attached to the side of the first substrate away from the first differential trace layer, and the first reference ground layer is formed with a defective ground structure for suppressing common mode noise; the second substrate is attached to the side of the first reference ground layer away from the first substrate; the second reference ground layer is attached to the side of the second substrate away from the first reference ground layer, and the second reference ground layer is formed with a defective ground structure for suppressing common mode noise; the third substrate is attached to the side of the second reference ground layer away from the second substrate; the second differential trace layer is attached to the side of the third substrate away from the second reference ground layer; the first cover film is attached to the first differential trace layer and the first substrate; and the second cover film is attached to the second differential trace layer and the third substrate;

[0022] Or, the flexible circuit board comprises a first substrate, a first differential trace layer, a first reference ground layer, a third substrate, a second differential trace layer, a second substrate, a second reference ground layer, a first cover film and a second cover film, the first differential trace layer is attached to one side of the first substrate; the first reference ground layer is attached to the side of the first substrate away from the first differential trace layer, and the first reference ground layer is formed with a defective ground structure for suppressing common mode noise; the third substrate is attached to the side of the first differential trace layer away from the first substrate; the second differential trace layer is attached to the side of the third substrate away from the first differential trace layer; the second substrate is attached to the side of the second differential trace layer away from the third substrate; the second reference ground layer is attached to the side of the second substrate away from the second differential trace layer, and the second reference ground layer is formed with a defective ground structure for suppressing common mode noise; the first cover film is attached to the side of the first reference ground layer away from the first substrate; and the second cover film is attached to the side of the second reference ground layer away from the third substrate.

[0023] The flexible circuit board can form a defective ground structure into a planar resonator, so that when the common mode noise passes through the first reference ground layer, the defective ground structure can be excited to suppress the common mode noise; for a filter frequency band below 2GHz, the length of the flexible circuit board can be adjusted according to the transverse size of the defective ground structure, so that a defective ground structure with a larger transverse size can be etched on the flexible circuit board; and in the case that the device using the flexible circuit board does not have a layout space for the defective ground structure, the defective ground structure can be arranged by the flexible circuit board to achieve suppression of the common mode noise. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 An exploded view of the flexible circuit board provided by the embodiment of the present application.

[0025] Figure 2 A structural schematic view of the first differential trace layer and the first reference ground layer of the flexible circuit board provided by the embodiment of the present application.

[0026] Figure 3 A schematic view of the first defective ground structure of the flexible circuit board provided by the embodiment of the present application.

[0027] Figure 4 A schematic view of the second defective ground structure of the flexible circuit board provided by the embodiment of the present application.

[0028] Figure 5 A schematic view of the third defective ground structure of the flexible circuit board provided by the embodiment of the present application.

[0029] Figure 6 A simulation structural view of the third defective ground structure of the flexible circuit board provided by the embodiment of the present application.

[0030] Figure 7A schematic view of a plurality of third defect-free mechanisms in cascade of a flexible circuit board provided by an embodiment of the present application.

[0031] Figure 8 A simulation structure view of a plurality of third defect-free mechanisms in cascade of a flexible circuit board provided by an embodiment of the present application.

[0032] Figure 9 An exploded view of a second flexible circuit board provided by an embodiment of the present application.

[0033] Figure 10 An exploded view of a third flexible circuit board provided by an embodiment of the present application.

[0034] Figure 11 An exploded view of a fourth flexible circuit board provided by an embodiment of the present application.

[0035] Figure 12 An exploded view of a fifth flexible circuit board provided by an embodiment of the present application.

[0036] Figure 13 An exploded view of a sixth flexible circuit board provided by an embodiment of the present application. DETAILED DESCRIPTION

[0037] In order to make the personnel in the art better understand the scheme of the present application, the technical scheme in the specific embodiments of the present application will be described clearly and completely below by combining the drawings in the embodiments of the present application.

[0038] It should be noted that the "first", "second" and similar words used in the specification and claims of the present application do not represent any order, quantity or importance, but are only used to distinguish different components. Similarly, "one" or "a" and similar words do not represent a quantity limit, but represent the existence of at least one. "Multiple" or "several" represents at least two. Unless otherwise indicated, "before", "after", "left", "right", "lower" and / or "upper" and similar words are only for the convenience of description, and are not limited to a position or a spatial orientation. "Include" or "contain" and similar words mean that the elements or objects appearing before "include" or "contain" cover the elements or objects listed after "include" or "contain" and their equivalents, and do not exclude other elements or objects. "Connected" or "connected" and similar words are not limited to physical or mechanical connection, but can include electrical connection, whether direct or indirect.

[0039] As used in the specification and the appended claims, the singular forms "a," "an" and "the" are intended to include plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0040] As shown in the drawings, Figure 1 The present application provides a flexible circuit board 100, which comprises a first substrate 11, a first differential trace layer 12, a first reference ground layer 13, a first cover film 14 and a second cover film 15. Wherein, the first cover film 14, the first differential trace layer 12, the first substrate 11, the first reference ground layer 13 and the second cover film 15 are stacked in order to constitute the flexible circuit board 100.

[0041] In order to clearly illustrate the technical solutions of the present application, the front, back, left, right, up and down as shown in Figure 1

[0042] Specifically, the first cover film 14, the first differential trace layer 12, the first substrate 11, the first reference ground layer 13 and the second cover film 15 are stacked in order from top to bottom.

[0043] More specifically, the first differential trace layer 12 is attached to one side of the first substrate 11, the first reference ground layer 13 is attached to the side of the first substrate 11 away from the first differential trace layer 12, the first cover film 14 is attached to the first differential trace layer 12 and the first substrate 11, and the second cover film 15 is attached to the side of the first reference ground layer 13 away from the first substrate 11. Wherein, the first cover film 14 is above the first differential trace layer 12, the first differential trace layer 12 is above the first substrate 11, the first reference ground layer 13 is below the first substrate 11, and the second cover film 15 is below the first reference ground layer 13.

[0044] In the present embodiment, the first reference ground layer 13 is formed with a defective ground structure 131 for suppressing common mode noise. Wherein, the defective ground structure 131 is formed by using etching process on the first reference ground layer 13. Through the above arrangement, the defective ground structure 131 can form a planar resonator, so that when the common mode noise passes through the first reference ground layer 13, the defective ground structure 131 can be excited, and the defective ground structure 131 can suppress the common mode noise. In addition, by setting the defective ground structure 131 on the first reference ground layer 13, additional resonators and other components can not be needed, thereby reducing the cost of the device using the flexible circuit board 100, and reducing the space occupancy of the device using the flexible circuit board 100, thereby improving the structural compactness of the device using the flexible circuit board 100.

[0045] ​Furthermore, for filtering frequency bands below 2 GHz, the lower the frequency, the longer the wavelength, resulting in a larger lateral dimension of the defective ground structure 131. However, the length of the flexible circuit board 100 can be adjusted based on the lateral dimension of the defective ground structure 131, allowing for the etching of a larger lateral defective ground structure 131 on the flexible circuit board 100. Furthermore, if the device using the flexible circuit board 100 lacks space for the defective ground structure 131, common-mode noise can be suppressed by arranging the defective ground structure 131 on the flexible circuit board 100. The lateral dimension of the defective ground structure 131 refers to its dimension along the front-to-back direction of the flexible circuit board 100.

[0046] It should be noted that, since the flexible circuit board 100 itself is relatively thin, a higher precision defective ground structure 131 (eg, a fine size below 3 mil) can be processed on the flexible circuit board 100 , thereby improving the precision of the defective ground structure 131 .

[0047] It should be noted that, compared to a PCB, the defective ground structure 131 on the flexible circuit board 100 can achieve the same filtering effect as a PCB using a smaller area. Specifically, etching the defective ground structure 131 on the flexible circuit board 100 can reduce the space occupied by the defective ground structure 131, thereby improving the structural compactness of the defective ground structure 131. Specifically, compared to a PCB, the area of ​​the defective ground structure 131 on the flexible circuit board 100 can be reduced by 25%.

[0048] like Figure 2 As shown, as an implementation, the first differential routing layer 12 includes a first differential routing 121 and a second differential routing 122. Both the first differential routing 121 and the second differential routing 122 are parallel to a predetermined straight line 101, and the first differential routing 121 and the second differential routing 122 are symmetrically arranged about the predetermined straight line 101. In this application, the predetermined straight line 101 is parallel to the front-to-back direction of the flexible circuit board 100. In this embodiment, the defective ground structure 131 is symmetrically arranged about the predetermined straight line 101, thereby enabling the defective ground structure 131 to suppress common-mode noise.

[0049] Specifically, the working principle of the defective ground structure 131 is as follows;

[0050] The differential signal on the first differential trace layer 12 is transmitted through the defective ground structure 131. The symmetry plane between the first differential trace 121 and the second differential trace 122 is an ideal electrical wall. When the first differential trace 121 and the second differential trace 122 are tightly coupled, less current flows through the ground plane. Conversely, the common-mode signal is transmitted in even mode. In this case, the symmetry plane between the first differential trace 121 and the second differential trace 122 is an ideal magnetic wall. The common-mode signal is completely returned to the reference ground plane, thereby exciting the resonance of the defective ground structure 131 and suppressing common-mode noise.

[0051] like Figures 3 to 5 As shown, in this application, the defective ground structure 131 includes a first defective ground mechanism 1311, a second defective ground mechanism 1312, or a third defective ground mechanism 1313. That is, the defective ground structure 131 is one of the first defective ground mechanism 1311, the second defective ground mechanism 1312, and the third defective ground mechanism 1313. It should be noted that the defective ground structure 131 includes but is not limited to the above three structures. That is, the defective ground structure 131 may also be other structures, and this application does not limit this.

[0052] like Figure 3 As shown, as an implementation method, the first defective ground mechanism 1311 includes a first transverse portion 1311a, a first longitudinal portion 1311b, and a second longitudinal portion 1311c. The first transverse portion 1311a is perpendicular to the preset straight line 101, and the first longitudinal portion 1311b and the second longitudinal portion 1311c both extend along the preset straight line 101. The first transverse portion 1311a is located between the first longitudinal portion 1311b and the second longitudinal portion 1311c, and the two ends of the first transverse portion 1311a respectively connect the middle portion of the first longitudinal portion 1311b and the middle portion of the second longitudinal portion 1311c. That is, the first defective ground mechanism 1311 basically has an "I"-shaped structure. The ratio of the length of the first defective ground mechanism 1311 along the preset straight line 101 to the wavelength corresponding to the resonant frequency of the first defective ground mechanism 1311 is in the range of 0.3 to 0.35.

[0053] Specifically, the first transverse portion 1311 a extends in the left-right direction of the flexible circuit board 100 , and the first longitudinal portion 1311 b and the second longitudinal portion 1311 c extend in the front-rear direction of the flexible circuit board 100 .

[0054] like Figure 4As shown, as another implementation, the second defective ground mechanism 1312 includes a second transverse portion 1312a, a third longitudinal portion 1312b, and a fourth longitudinal portion 1312c. The second transverse portion 1312a is perpendicular to the preset straight line 101, and the third longitudinal portion 1312b and the fourth longitudinal portion 1312c both extend along the preset straight line 101. The second transverse portion 1312a is located between the third longitudinal portion 1312b and the fourth longitudinal portion 1312c, and the two ends of the second transverse portion 1312a are respectively connected to one end of the third longitudinal portion 1312b and one end of the fourth longitudinal portion 1312c. That is, the second defective ground mechanism 1312 is basically a "C"-shaped structure. The ratio of the length of the second defective ground mechanism 1312 along the preset straight line 101 to the wavelength corresponding to the resonant frequency of the second defective ground mechanism 1312 is in the range of 0.13 to 0.18.

[0055] Specifically, the second transverse portion 1312a extends in the left-right direction of the flexible circuit board 100, and the third longitudinal portion 1312b and the fourth longitudinal portion 1312c extend in the front-to-back direction of the flexible circuit board 100. The second transverse portion 1312a is connected to the front end of the third longitudinal portion 1312b and the front end of the fourth longitudinal portion 1312c; alternatively, the second transverse portion 1312a is connected to the rear end of the third longitudinal portion 1312b and the rear end of the fourth longitudinal portion 1312c, thereby forming the second defective ground structure 1312 in a substantially C-shaped structure.

[0056] It should be noted that, since the defective ground structure 131 is symmetrically arranged about the preset straight line 101 , when viewed from a direction perpendicular to the preset straight line 101 , the third longitudinal portion 1312 b and the fourth longitudinal portion 1312 c overlap.

[0057] like Figure 5 As shown, as another implementation, the third defective ground mechanism 1313 includes a first defective ground mechanism 1311 and two second defective ground mechanisms 1312. The two second defective ground mechanisms 1312 are located between the first longitudinal portion 1311b and the second longitudinal portion 1311c. The first transverse portion 1311a is located between the two second defective ground mechanisms 1312, and the two second defective ground mechanisms 1312 are symmetrically arranged about the first transverse portion 1311a. Neither of the two second defective ground mechanisms 1312 contacts the first defective ground mechanism 1311. The ratio of the length of the third defective ground mechanism 1313 along the predetermined straight line 101 to the wavelength corresponding to the resonant frequency of the third defective ground mechanism 1313 is in the range of 0.11 to 0.15.

[0058] Specifically, the two second defect ground mechanisms 1312 are distributed along the front-rear direction of the flexible circuit board 100, and the first transverse portion 1311a is located between the two second defect ground mechanisms 1312 along the front-rear direction of the flexible circuit board 100.

[0059] In the present embodiment, the third longitudinal portion 1312b is closer to the first longitudinal portion 1311b than the fourth longitudinal portion 1312c, the fourth longitudinal portion 1312c is closer to the second longitudinal portion 1311c than the third longitudinal portion 1312b, and the second transverse portion 1312a is connected to one end of the third longitudinal portion 1312b away from the first transverse portion 1311a and is also connected to one end of the fourth longitudinal portion 1312c away from the first transverse portion 1311a.

[0060] More specifically, the two second defect ground mechanisms 1312 are defined as a first mechanism 1312d and a second mechanism 1312e, both of which are substantially in the shape of a "C", and the openings of the first mechanism 1312d and the second mechanism 1312e are both directed towards the first transverse portion 1311a, i.e. the opening of the first mechanism 1312d is arranged towards the opening of the second mechanism 1312e.

[0061] It should be noted that the two second defect ground mechanisms 1312 not contacting the first defect ground mechanism 1311 means that:

[0062] There is a gap between the third longitudinal portion 1312b and the first longitudinal portion 1311b, a gap between the fourth longitudinal portion 1312c and the second longitudinal portion 1311c, a gap between the third longitudinal portion 1312b and the first transverse portion 1311a, a gap between the fourth longitudinal portion 1312c and the first transverse portion 1311a, a gap between the first longitudinal portion 1311b and the second transverse portion 1312a, and a gap between the second longitudinal portion 1311c and the second transverse portion 1312a.

[0063] As an alternative implementation, the maximum distance between the two second defect ground mechanisms 1312 along the predetermined straight line 101 is equal to the maximum length of the first defect ground mechanism 1311 along the predetermined straight line 101. The first mechanism 1312d is defined as being located in front of the second mechanism 1312e, the frontmost end of the first mechanism 1312d is flush with the frontmost end of the first defect ground mechanism 1311, and the rearmost end of the second mechanism 1312e is flush with the rearmost end of the first defect ground mechanism 1311, thereby improving the space utilization of the first defect ground mechanism 1311 and the two second defect ground mechanisms 1312 on the first reference ground layer 13, and further making the structure of the first reference ground layer 13 more compact and the structure of the flexible circuit board 100 more compact. In addition, the above arrangement can also expand the filter bandwidth of the defect ground structure 131.

[0064] As Figure 5As shown, the third defective ground mechanism 1313 is taken as an example for description, the length of the third defective ground mechanism 1313 along the preset straight line 101 direction is defined as L1, that is, the length of the first longitudinal part 1311b and the second longitudinal part 1311c along the preset straight line 101 direction is L1; the width of the third defective ground mechanism 1313 along the direction perpendicular to the preset straight line 101 is defined as H1, that is, the width of the third defective ground mechanism 1313 along the left-right direction of the flexible circuit board 100 is H1; the distance between the first longitudinal part 1311b and the second longitudinal part 1311c along the direction perpendicular to the preset straight line 101 is defined as H2, that is, the distance between the first longitudinal part 1311b and the second longitudinal part 1311c along the left-right direction of the flexible circuit board 100 is H2; the width of the second defective ground mechanism 1312 along the direction perpendicular to the preset straight line 101 is defined as H3, that is, the width of the second defective ground mechanism 1312 along the left-right direction of the flexible circuit board 100 is H3; the distance between the third longitudinal part 1312b and the fourth longitudinal part 1312c along the direction perpendicular to the preset straight line 101 is defined as H4, that is, the distance between the third longitudinal part 1312b and the fourth longitudinal part 1312c along the left-right direction of the flexible circuit board 100 is H4; the length of the second transverse part 1312a along the preset straight line 101 is defined as L2; the minimum distance between the third longitudinal part 1312b and the first transverse part 1311a along the preset straight line 101 is defined as L3, or the minimum distance between the fourth longitudinal part 1312c and the first transverse part 1311a along the preset straight line 101 is defined as L3; the thickness of the first transverse part 1311a along the preset straight line 101 is defined as G.

[0065] Wherein, the maximum distance between two second defective ground mechanisms 1312 along the preset straight line 101 direction and the maximum length of the first defective ground mechanism 1311 along the preset straight line 101 are both L1.

[0066] It should be noted that L1 is 0.11 to 0.15 of the wavelength corresponding to the resonant frequency of the third defective ground mechanism 1313.

[0067] Specifically, taking the resonant frequency of the third defective ground mechanism 1313 as 900MHz, L1 as 1800mil, L2 as 2mil, L3 as 2mil, H1 as 37mil, H2 as 27mil, H3 as 23mil, H4 as 15mil, and G as 4mil as an example for simulation, a simulation structure diagram as shown in Figure 6 is obtained.

[0068] The differential signal passes through the third defect ground mechanism 1313, and the attenuation of the differential signal in the range of 2 GHz is not more than 2 dB, so the third defect ground mechanism 1313 does not affect the differential signal itself. The common mode signal can achieve a maximum attenuation of 53 dB at 900 MHz, and the attenuation bandwidth greater than or equal to 15 dB reaches 1.11 GHz, so that the wide-band common mode signal attenuation can be achieved, and the common mode noise can be suppressed through the third defect ground mechanism 1313.

[0069] It should be noted that, in the present application, the length of the defect ground structure 131 along the direction of the preset straight line 101 can be adjusted, that is, the resonance frequency point of the defect ground structure 131 can be adjusted, so that different frequency common mode noise can be filtered out. Figure 6 In the present application, the differential signal attenuation curve is shown as a blue curve, and the common mode signal attenuation curve is shown as an orange curve.

[0070] It should be noted that, in the present application, the length of the defect ground structure 131 along the direction of the preset straight line 101 can be adjusted, that is, the resonance frequency point of the defect ground structure 131 can be adjusted, so that different frequency common mode noise can be filtered out.

[0071] As an implementation manner, in the present application, if it is necessary to achieve the suppression of common mode noise of a wider frequency, defect ground structures 131 of different lengths can be cascaded to achieve. Different lengths of the defect ground structure 131 refer to different lengths of the defect ground structure 131 along the direction of the preset straight line 101.

[0072] For example, the defect ground structure 131 includes a plurality of first defect ground mechanisms 1311 distributed along the direction of the preset straight line 101. Each first defect ground mechanism 1311 includes a first transverse portion 1311a perpendicular to the preset straight line 101, a first longitudinal portion 1311b and a second longitudinal portion 1311c extending along the preset straight line 101. The first transverse portion 1311a is located between the first longitudinal portion 1311b and the second longitudinal portion 1311c, and the two ends of the first transverse portion 1311a are connected to the middle portions of the first longitudinal portion 1311b and the second longitudinal portion 1311c respectively.

[0073] For example, the defect ground structure 131 includes a plurality of second defect ground mechanisms 1312 distributed along the direction of the preset straight line 101. Each second defect ground mechanism 1312 includes a second transverse portion 1312a perpendicular to the preset straight line 101, a third longitudinal portion 1312b and a fourth longitudinal portion 1312c extending along the preset straight line 101. The second transverse portion 1312a is located between the third longitudinal portion 1312b and the fourth longitudinal portion 1312c, and the two ends of the second transverse portion 1312a are connected to one end of the third longitudinal portion 1312b and one end of the fourth longitudinal portion 1312c respectively.

[0074] As shown in FIG. 1, the defect ground structure 131 includes a plurality of first defect ground mechanisms 1311 distributed along the direction of the preset straight line 101. Figure 7As shown, exemplarily, the defective ground structure 131 includes a plurality of third defective ground mechanisms 1313 distributed along the preset straight line 101, each third defective ground mechanism 1313 includes a first defective ground mechanism 1311 and two second defective ground mechanisms 1312, the two second defective ground mechanisms 1312 are both located between the first longitudinal portion 1311b and the second longitudinal portion 1311c of the first defective ground mechanism 1311, the first transverse portion 1311a of the first defective ground mechanism 1311 is located between the two second defective ground mechanisms 1312, and the two second defective ground mechanisms 1312 are symmetrically arranged about the first transverse portion 1311a of the first defective ground mechanism 1311; the two second defective ground mechanisms 1312 are not in contact with the first defective ground mechanism 1311.

[0075] As an optional implementation, the lengths of at least two first defective structures 1311 along the preset straight line 101 are inconsistent.

[0076] As an optional implementation, the lengths of at least two second defective structures 1312 along the preset straight line 101 are inconsistent.

[0077] As an optional implementation, the lengths of at least two third defect structures 1313 along the preset straight line 101 are inconsistent.

[0078] Through the above-mentioned setting, it is possible to achieve suppression of common-mode noise of a wider frequency, that is, the bandwidths of the two third defective ground structures 1313 of inconsistent lengths can be combined, thereby increasing the bandwidth of the defective ground structure 131 for suppressing common-mode noise, thereby enabling the defective ground structure 131 to achieve common-mode signal attenuation in a wide frequency band.

[0079] like Figure 7 As shown, the defective ground structure 131 includes two third defective ground mechanisms 1313 distributed along the preset straight line 101. The resonance frequency of one third defective ground mechanism 1313 is 190 MHz, and the resonance frequency of the other third defective ground mechanism 1313 is 500 MHz. That is, only L1 of the two third defective ground mechanisms 1313 is changed, and the other parameters remain unchanged. The simulation is performed as follows. Figure 8 Specifically, the L1 of the third defective ground structure 1313 corresponding to the resonant frequency of 190 MHz is 8600 mil, and the L1 of the third defective ground structure 1313 corresponding to the resonant frequency of 500 MHz is 3500 mil.

[0080] When the differential signal is transmitted in an even mode, the differential signal is attenuated by no more than 4 dB in a 2 GHz range after passing through the two third defect ground mechanisms 1313, and thus the two third defect ground mechanisms 1313 do not affect the differential signal itself; the common mode signal can be attenuated by 53 dB at 190 MHz, by 58 dB at 500 MHz, and can be attenuated by no less than 15 dB in a range from 180 MHz to 1 GHz, so that the cascaded third defect ground mechanisms 1313 can realize wide-band common mode signal attenuation, and thus can suppress common mode noise in a wider frequency band through the cascaded third defect ground mechanisms 1313.

[0081] It should be noted that, in the present application, Figure 8 , the differential signal attenuation curve is shown as a blue curve, and the common mode signal attenuation curve is shown as an orange curve.

[0082] It should be noted that, in the present application, the length of the two third defect ground mechanisms 131 in the direction of the preset straight line 101 can be adjusted to adjust the resonance frequency point of the common mode noise suppression, so that common mode noise of different frequencies can be filtered out.

[0083] As an implementation manner, the defect ground mechanism 131 is provided in a plurality of manners, the plurality of defect ground mechanisms 131 are distributed in the direction of the preset straight line 101, the defect ground mechanism 131 is one of the first defect ground mechanism 1311, the second defect ground mechanism 1312 and the third defect ground mechanism 1313, and the structures of at least two defect ground mechanisms 131 are different. That is, the defect ground mechanism can be a combination of the first defect ground mechanism 1311 and the second defect ground mechanism 1312, the defect ground mechanism 131 can be a combination of the second defect ground mechanism 1312 and the third defect ground mechanism 1313, the defect ground mechanism 131 can be a combination of the first defect ground mechanism 1311 and the third defect ground mechanism 1313, and the defect ground mechanism 131 can also be a combination of the first defect ground mechanism 1311, the second defect ground mechanism 1312 and the third defect ground mechanism 1313.

[0084] As an optional implementation manner, the lengths of the at least two defect ground mechanisms 131 in the direction of the preset straight line 101 are inconsistent. Through the above setting, wider frequency common mode noise suppression can be realized, that is, the bandwidths of the two defect ground mechanisms 131 with inconsistent lengths can be combined, so that the bandwidth of the defect ground mechanism 131 for suppressing common mode noise is improved, and thus the defect ground mechanism 131 can realize wide-band common mode signal attenuation.

[0085] It can be understood that the lengths of the at least two defective ground structures 131 in the direction of the preset straight line 101 can also be consistent, so that the common mode noise of the same frequency band is suppressed by the plurality of defective ground structures 131, and the filtering effect of the common mode noise is improved, so as to improve the suppression effect of the defective ground structure 131 on the common mode noise of the same frequency band.

[0086] It should be noted that for the cascade of the plurality of defective ground structures 131, the length of the single defective ground structure 131 in the direction of the preset straight line 101 can be obtained according to the wavelength corresponding to the resonant frequency of the single defective ground structure 131. Specifically, if the resonant frequencies of the plurality of defective ground structures 131 are inconsistent, the lengths of the plurality of defective ground structures 131 in the direction of the preset straight line 101 are inconsistent. Wherein, the distance D (refer to Figure 7 ) between any two defective ground structures 131 can be adjusted according to actual needs.

[0087] As shown in Figure 9 and Figure 10 , the present application also provides another flexible circuit board 100, which comprises a first substrate 11, a first differential trace layer 12, a first reference ground layer 13, a second substrate 16, a second reference ground layer 17, a first cover film 14 and a second cover film 15.

[0088] As shown in Figure 9 , for example, the first differential trace layer 12 is attached to one side of the first substrate 11, the first reference ground layer 13 is attached to the side of the first substrate 11 away from the first differential trace layer 12, and the second substrate 16 is attached to the side of the first reference ground layer 13 away from the first substrate 11; the second reference ground layer 17 is attached to the side of the second substrate 16 away from the first reference ground layer 13, the first cover film 14 is attached to the first differential trace layer 12 and the first substrate 11, and the second cover film 15 is attached to the side of the second reference ground layer 17 away from the second substrate 16. Wherein, the first reference ground layer 13 is formed with a defective ground structure 131 for suppressing common mode noise. That is, in this embodiment, only for the first differential trace layer 12, the first reference ground layer 13 and the second reference ground layer 17, the first reference ground layer 13 is located between the first differential trace layer 12 and the second reference ground layer 17. At this time, the defective ground structure 131 is located on the first reference ground layer 13 close to the first differential trace layer 12, so that the defective ground structure 131 can suppress the common mode noise generated by the common mode signal of the first differential trace layer 12.

[0089] As shown in Figure 10As shown, the first differential trace layer 12 is attached to one side of the first substrate 11; the first reference ground layer 13 is attached to the side of the first substrate 11 away from the first differential trace layer 12, the second substrate 16 is attached to the side of the first differential trace layer 12 away from the first substrate 11, the second reference ground layer 17 is attached to the side of the second substrate 16 away from the first differential trace layer 12; the first cover film 14 is attached to the side of the second reference ground layer 17 away from the second substrate 16, and the second cover film 15 is attached to the side of the first reference ground layer 13 away from the first substrate 11. The first reference ground layer 13 or the second reference ground layer 17 is formed with a defective ground structure 131 for suppressing common mode noise. That is, in this embodiment, only for the first differential trace layer 12, the first reference ground layer 13 and the second reference ground layer 17, the first differential trace layer 12 is located between the first reference ground layer 13 and the second reference ground layer 17. At this time, the defective ground structure 131 can be located on any one of the first reference ground layer 13 and the second reference ground layer 17.

[0090] It should be noted that, Figure 10 In this embodiment, the defective ground structure 131 is located on the first reference ground layer 13.

[0091] As Figures 11 to 13 As shown, the present application also provides another flexible circuit board 100, which comprises a first substrate 11, a first differential trace layer 12, a first reference ground layer 13, a third substrate 18, a second differential trace layer 19, a second substrate 16, a second reference ground layer 17, a first cover film 14 and a second cover film 15.

[0092] As Figure 11As shown, the first differential trace layer 12 is attached to one side of the first substrate 11, the first reference ground layer 13 is attached to the side of the first substrate 11 away from the first differential trace layer 12, the third substrate 18 is attached to the side of the first reference ground layer 13 away from the first substrate 11, the second differential trace layer 19 is attached to the side of the third substrate 18 away from the first reference ground layer 13, the second substrate 16 is attached to the side of the second differential trace layer 19 away from the third substrate 18, the second reference ground layer 17 is attached to the side of the second substrate 16 away from the second differential trace layer 19, the first cover film 14 is attached to the first differential trace layer 12 and the first substrate 11, and the second cover film 15 is attached to the side of the second reference ground layer 17 away from the second substrate 16. The first reference ground layer 13 is formed with a defective ground structure 131 for suppressing common mode noise, and the second reference ground layer 17 is formed with a defective ground structure 131 for suppressing common mode noise. That is, in this embodiment, only for the first differential trace layer 12, the second differential trace layer 19, the first reference ground layer 13, and the second reference ground layer 17, the first reference ground layer 13 is located between the first differential trace layer 12 and the second differential trace layer 19, and the second differential trace layer 19 is located between the first reference ground layer 13 and the second reference ground layer 17. The defective ground structure 131 on the first reference ground layer 13 can suppress common mode noise generated by the common mode signal of the first differential trace layer 12, and the defective ground structure 131 on the second reference ground layer 17 can suppress common mode noise generated by the common mode signal of the second differential trace layer 19.

[0093] As Figure 12As shown, the first differential trace layer 12 is attached to one side of the first substrate 11, the first reference ground layer 13 is attached to the side of the first substrate 11 away from the first differential trace layer 12, the second substrate 16 is attached to the side of the first reference ground layer 13 away from the first substrate 11, the second reference ground layer 17 is attached to the side of the second substrate 16 away from the first reference ground layer 13, the third substrate 18 is attached to the side of the second reference ground layer 17 away from the second substrate 16, the second differential trace layer 19 is attached to the side of the third substrate 18 away from the second reference ground layer 17, the first cover film 14 is attached to the first differential trace layer 12 and the first substrate 11, and the second cover film 15 is attached to the second differential trace layer 19 and the third substrate 18. The first reference ground layer 13 is formed with a defective ground structure 131 for suppressing common mode noise, and the second reference ground layer 17 is formed with a defective ground structure 131 for suppressing common mode noise. That is, in this embodiment, only for the first differential trace layer 12, the second differential trace layer 19, the first reference ground layer 13 and the second reference ground layer 17, the first reference ground layer 13 is located between the first differential trace layer 12 and the second reference ground layer 17, and the second reference ground layer 17 is located between the first reference ground layer 13 and the second differential trace layer 19. At this time, the defective ground structure 131 on the first reference ground layer 13 can suppress the common mode noise generated by the common mode signal of the first differential trace layer 12, and the defective ground structure 131 on the second reference ground layer 17 can suppress the common mode noise generated by the common mode signal of the second differential trace layer 19.

[0094] As Figure 13As shown, the first differential trace layer 12 is attached to one side of the first substrate 11, the first reference ground layer 13 is attached to the side of the first substrate 11 away from the first differential trace layer 12, the third substrate 18 is attached to the side of the first differential trace layer 12 away from the first substrate 11, the second differential trace layer 19 is attached to the side of the third substrate 18 away from the first differential trace layer 12, the second substrate 16 is attached to the side of the second differential trace layer 19 away from the third substrate 18, the second reference ground layer 17 is attached to the side of the second substrate 16 away from the second differential trace layer 19, the first cover film 14 is attached to the side of the first reference ground layer 13 away from the first substrate 11, and the second cover film 15 is attached to the side of the second reference ground layer 17 away from the third substrate 18. The first reference ground layer 13 is formed with a defective ground structure 131 for suppressing common mode noise, and the second reference ground layer 17 is formed with a defective ground structure 131 for suppressing common mode noise. That is, in the present embodiment, only for the first differential trace layer 12, the second differential trace layer 19, the first reference ground layer 13, and the second reference ground layer 17, the first differential trace layer 12 is located between the first reference ground layer 13 and the second differential trace layer 19, and the second differential trace layer 19 is located between the first differential trace layer 12 and the second reference ground layer 17. The defective ground structure 131 on the first reference ground layer 13 can suppress common mode noise generated by the common mode signal of the first differential trace layer 12, and the defective ground structure 131 on the second reference ground layer 17 can suppress common mode noise generated by the common mode signal of the second differential trace layer 19.

[0095] It should be understood that, for those skilled in the art, improvements or changes can be made according to the above description, and all these improvements and changes shall belong to the protection scope of the claims attached to the present application.

Claims

1. A flexible circuit board, characterized by, The flexible circuit board comprises: a first substrate; a first differential trace layer attached to one side of the first substrate; a first reference ground layer attached to the side of the first reference ground layer away from the first substrate, the first reference ground layer being formed with a defective ground structure for suppressing common mode noise; a first cover film attached to the first differential trace layer and the first substrate; a second cover film attached to the side of the first reference ground layer away from the first substrate.

2. The flexible circuit board according to claim 1, wherein the first differential trace layer comprises a first differential trace and a second differential trace, the first differential trace and the second differential trace are parallel to a preset straight line, and the first differential trace and the second differential trace are symmetrically arranged about the preset straight line, and the defective ground structure is symmetrically arranged about the preset straight line.

3. The flexible circuit board according to claim 2, wherein the defective ground structure comprises a first defective ground mechanism, the first defective ground mechanism comprises a first transverse portion perpendicular to the preset straight line, a first longitudinal portion and a second longitudinal portion extending along the preset straight line, the first transverse portion is located between the first longitudinal portion and the second longitudinal portion, and two ends of the first transverse portion are connected to the middle of the first longitudinal portion and the middle of the second longitudinal portion, respectively.

4. The flexible circuit board according to claim 2, wherein the defective ground structure comprises a second defective ground mechanism, the second defective ground mechanism comprises a second transverse portion perpendicular to the preset straight line, a third longitudinal portion and a fourth longitudinal portion extending along the preset straight line, the second transverse portion is located between the third longitudinal portion and the fourth longitudinal portion, and two ends of the second transverse portion are connected to one end of the third longitudinal portion and one end of the fourth longitudinal portion, respectively.

5. The flexible circuit board according to claim 2, wherein the defective ground structure comprises a first defective ground mechanism and two second defective ground mechanisms; the first defective ground mechanism comprises a first transverse portion perpendicular to the preset straight line, a first longitudinal portion and a second longitudinal portion extending along the preset straight line, the first transverse portion is located between the first longitudinal portion and the second longitudinal portion, and two ends of the first transverse portion are connected to the middle of the first longitudinal portion and the middle of the second longitudinal portion, respectively; the two second defective ground mechanisms are located between the first longitudinal portion and the second longitudinal portion, the first transverse portion is located between the two second defective ground mechanisms, and the two second defective ground mechanisms are symmetrically arranged about the first transverse portion; the two second defective ground mechanisms are not in contact with the first defective ground mechanism.

6. The flexible circuit board according to claim 5, wherein The second defect ground mechanism comprises a second transverse portion perpendicular to the preset straight line, a third longitudinal portion and a fourth longitudinal portion extending along the preset straight line, the second transverse portion is located between the third longitudinal portion and the fourth longitudinal portion, and two ends of the second transverse portion are connected to one end of the third longitudinal portion and one end of the fourth longitudinal portion respectively; The third longitudinal portion is closer to the first longitudinal portion than the fourth longitudinal portion, the fourth longitudinal portion is closer to the second longitudinal portion than the third longitudinal portion, the second transverse portion is connected to one end of the third longitudinal portion away from the first transverse portion, and the second transverse portion is also connected to one end of the fourth longitudinal portion away from the first transverse portion.

7. The flexible circuit board according to claim 6, wherein, The maximum distance between two of the second defect ground mechanisms in the direction of the preset straight line is equal to the maximum length of the first defect ground mechanism in the direction of the preset straight line.

8. The flexible circuit board according to claim 2, wherein, The defect ground structure comprises a plurality of first defect ground mechanisms distributed in the direction of the preset straight line, each of the first defect ground mechanisms comprises a first transverse portion perpendicular to the preset straight line, a first longitudinal portion and a second longitudinal portion extending along the preset straight line, the first transverse portion is located between the first longitudinal portion and the second longitudinal portion, and two ends of the first transverse portion are connected to the middle of the first longitudinal portion and the middle of the second longitudinal portion respectively; Or, The defect ground structure comprises a plurality of second defect ground mechanisms distributed in the direction of the preset straight line, each of the second defect ground mechanisms comprises a second transverse portion perpendicular to the preset straight line, a third longitudinal portion and a fourth longitudinal portion extending along the preset straight line, the second transverse portion is located between the third longitudinal portion and the fourth longitudinal portion, and two ends of the second transverse portion are connected to one end of the third longitudinal portion and one end of the fourth longitudinal portion respectively; Or, The defect ground structure comprises a plurality of third defect ground mechanisms distributed in the direction of the preset straight line, each of the third defect ground mechanisms comprises the first defect ground mechanism and two second defect ground mechanisms, the two second defect ground mechanisms are both located between the first longitudinal portion and the second longitudinal portion of the first defect ground mechanism, the first transverse portion of the first defect ground mechanism is located between the two second defect ground mechanisms, and the two second defect ground mechanisms are symmetrically arranged about the first transverse portion of the first defect ground mechanism; neither of the two second defect ground mechanisms is in contact with the first defect ground mechanism.

9. The flexible circuit board according to claim 8, wherein, The lengths of at least two of the first defect ground mechanisms in the direction of the preset straight line are inconsistent; The lengths of at least two of the second defect ground mechanisms in the direction of the preset straight line are inconsistent; The lengths of at least two of the third defect ground mechanisms in the direction of the preset straight line are inconsistent.

10. The flexible circuit board according to claim 2, wherein, The defect-free structures are provided in plurality, the plurality of defect-free structures are distributed along the preset straight line direction, the defect-free structures are one of a first defect-free structure, a second defect-free structure and a third defect-free structure, and structures of at least two defect-free structures are different; Lengths of the at least two defect-free structures along the preset straight line direction are inconsistent.

11. A flexible circuit board, characterized in that, The flexible circuit board comprises: a first substrate; a first differential trace layer attached to one side of the first substrate; a first reference ground layer attached to a side of the first substrate away from the first differential trace layer, the first reference ground layer being formed with a defect-free structure for suppressing common mode noise; a second substrate attached to a side of the first reference ground layer away from the first substrate; a second reference ground layer attached to a side of the second substrate away from the first reference ground layer; a first cover film attached to the first differential trace layer and the first substrate; a second cover film attached to a side of the second reference ground layer away from the second substrate; or, The flexible circuit board comprises: a first substrate; a first differential trace layer attached to one side of the first substrate; a first reference ground layer attached to a side of the first substrate away from the first differential trace layer; a second substrate attached to a side of the first differential trace layer away from the first substrate; a second reference ground layer attached to a side of the second substrate away from the first differential trace layer; a first cover film attached to a side of the second reference ground layer away from the second substrate; a second cover film attached to a side of the first reference ground layer away from the first substrate; the first reference ground layer or the second reference ground layer is formed with a defect-free structure for suppressing common mode noise; or, The flexible circuit board comprises: a first substrate; a first differential trace layer attached to one side of the first substrate; a first reference ground layer attached to a side of the first substrate away from the first differential trace layer, the first reference ground layer being formed with a defect-free structure for suppressing common mode noise; a third substrate attached to a side of the first reference ground layer away from the first substrate; a second differential trace layer attached to a side of the third substrate away from the first reference ground layer; a second substrate attached to a side of the second differential trace layer away from the third substrate; a second reference ground layer attached to a side of the second substrate away from the second differential trace layer, the second reference ground layer being formed with a defect-free structure for suppressing common mode noise; a first cover film attached to the first differential trace layer and the first substrate; a second cover film attached to a side of the second reference ground layer facing away from the second substrate; or, the flexible circuit board comprises: a first substrate; a first differential trace layer attached to a side of the first substrate; a first reference ground layer attached to a side of the first substrate facing away from the first differential trace layer, the first reference ground layer formed with a defective ground structure for suppressing common mode noise; a second substrate attached to a side of the first reference ground layer facing away from the first substrate; a second reference ground layer attached to a side of the second substrate facing away from the first reference ground layer, the second reference ground layer formed with a defective ground structure for suppressing common mode noise; a third substrate attached to a side of the second reference ground layer facing away from the second substrate; a second differential trace layer attached to a side of the third substrate facing away from the second reference ground layer; a first cover film attached to the first differential trace layer and the first substrate; a second cover film attached to the second differential trace layer and the third substrate; or, the flexible circuit board comprises: a first substrate; a first differential trace layer attached to a side of the first substrate; a first reference ground layer attached to a side of the first substrate facing away from the first differential trace layer, the first reference ground layer formed with a defective ground structure for suppressing common mode noise; a third substrate attached to a side of the first differential trace layer facing away from the first substrate; a second differential trace layer attached to a side of the third substrate facing away from the first differential trace layer; a second substrate attached to a side of the second differential trace layer facing away from the third substrate; a second reference ground layer attached to a side of the second substrate facing away from the second differential trace layer, the second reference ground layer formed with a defective ground structure for suppressing common mode noise; a first cover film attached to a side of the first reference ground layer facing away from the first substrate; a second cover film attached to a side of the second reference ground layer facing away from the third substrate.

Images