Flexible circuit board, display module and display device

Abstract

The flexible circuit board comprises a first covering film, the first covering film is made of photosensitive ink, the photosensitive ink is provided with a grounding opening, an electromagnetic film shielding layer and a conductive adhesive layer, the shielding layer is arranged on one side, far away from the first covering film, of the conductive adhesive layer, and the conductive adhesive layer penetrates through the grounding opening and is connected with a grounding wire. The shielding layer serves as a reference plane, continuity of the reference plane can be kept, the upper layer and the lower layer of the differential impedance line are the reference planes, insertion loss of differential signals can be reduced, stability of the differential signals is ensured, and blurred screens during display are reduced or avoided. The invention further provides a display module comprising the flexible circuit board and a display device comprising the display module.

Description

Technical Field

[0001] The present disclosure relates to the field of display technology, and in particular to a flexible circuit board, a display module and a display device. Background Art

[0002] Silicon-based OLEDs are widely used in the fields of augmented reality (AR) and virtual reality (VR). VR display devices require two screens for the left and right eyes. The differential signals of the two screens use two interfaces, and the differential signals of the two interfaces are required to be designed as symmetrically as possible to meet the impedance matching requirements.

[0003] The routing area of ​​the differential impedance line is compressed, and multiple layers of differential impedance lines need to be set. In an area where a reference ground is not set on a conductive layer of the flexible circuit board, the differential signal will be divided on the reference plane, causing fluctuations in the differential signal and resulting in a distorted screen when displayed.

[0004] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0005] The purpose of the present disclosure is to overcome the problem that the differential signal is divided on the reference plane, causing the differential signal to fluctuate, resulting in a distorted screen during display, and to provide a flexible circuit board, a display module and a display device.

[0006] According to one aspect of the present disclosure, a flexible circuit board is provided, which includes a circuit board body, a first covering film and an electromagnetic film, the circuit board body includes at least two conductive layers, an insulating layer is provided between two adjacent conductive layers, the conductive layer includes a first external conductive layer closest to the side of the circuit board body, and the first external conductive layer is provided with a grounding wire; the first covering film is provided on one side of the first external conductive layer, the material of the first covering film is photosensitive ink, and the first covering film is provided with a grounding opening; the electromagnetic film includes a shielding layer and a conductive adhesive layer, the conductive adhesive layer is provided on a side of the first covering film away from the first external conductive layer, the shielding layer is provided on a side of the conductive adhesive layer away from the first covering film, and the conductive adhesive layer passes through the grounding opening to be connected to the grounding wire.

[0007] In one embodiment of the present disclosure, the thickness of the shielding layer is 0.3-0.6 times the thickness of the conductive layer.

[0008] In one embodiment of the present disclosure, the conductive layer also includes an internal conductive layer and a second external conductive layer, the second external conductive layer is arranged on the other side of the circuit board body, the internal conductive layer is arranged between the first external conductive layer and the second external conductive layer, a first high-frequency hot-melt polyimide layer is arranged between the first external conductive layer and the internal conductive layer, and a second high-frequency hot-melt polyimide layer is arranged between the second external conductive layer and the internal conductive layer.

[0009] In one embodiment of the present disclosure, the width of the ground opening is less than or equal to the width of the ground line, and the orthographic projection of the ground opening on the circuit board body is located within the ground line.

[0010] In one embodiment of the present disclosure, the grounding wires have different widths, and the number of grounding openings corresponding to the grounding wires with larger widths is less than the number of grounding openings corresponding to the grounding wires with smaller widths.

[0011] In one embodiment of the present disclosure, the circuit board body has a first area and a second area, the orthographic projections of the second external conductive layer and the internal conductive layer on the circuit board body are located in the first area, the orthographic projections of the first external conductive layer on the circuit board are located in the first area and the second area, and the second area is located in the bending area of ​​the flexible circuit board.

[0012] In one embodiment of the present disclosure, the grounding line includes a first grounding segment and a second grounding segment, the first grounding segment is at least partially arranged in a first area, the second grounding segment is arranged in a second area, the width of the second grounding segment is smaller than the width of the first grounding segment, and the number of grounding openings corresponding to the second grounding segment is greater than the number of grounding openings corresponding to the first grounding segment.

[0013] In one embodiment of the present disclosure, the outer conductive layer is further provided with a plurality of groups of differential impedance lines, and a group of differential impedance lines is provided between two adjacent ground lines.

[0014] In one embodiment of the present disclosure, a group of differential impedance lines includes at least two differential impedance lines, and a line distance between two adjacent differential impedance lines is 3 times the line width of the differential impedance line.

[0015] In one embodiment of the present disclosure, the differential impedance line includes a first differential impedance line and a second differential impedance line, the first differential impedance line is a curve, the second differential impedance line is a straight line, and the number of ground openings corresponding to the ground line adjacent to the first differential impedance line is greater than the number of ground openings corresponding to the ground line adjacent to the second differential impedance line.

[0016] In one embodiment of the present disclosure, the differential impedance line includes a first impedance segment and a second impedance segment, the first impedance segment is at least partially disposed in the first region, the second impedance segment is disposed in the second region, and the width of the second impedance segment is smaller than that of the first impedance segment.

[0017] In one embodiment of the present disclosure, the electromagnetic film further includes a metal film layer, and the metal film layer is disposed on a side of the shielding layer away from the conductive adhesive layer.

[0018] In one embodiment of the present disclosure, the flexible circuit board further includes a reinforcing film, and the reinforcing film is disposed on a side of the metal film layer away from the conductive adhesive layer.

[0019] In one embodiment of the present disclosure, the flexible circuit board further includes a second covering film, which is disposed on a side of the second outer conductive layer away from the first outer conductive layer, and is made of photosensitive ink.

[0020] According to another aspect of the present disclosure, a display module is provided, including the flexible circuit board provided in one aspect of the present disclosure.

[0021] According to another aspect of the present disclosure, a display device is provided, including the display module provided by one aspect of the present disclosure.

[0022] The flexible circuit board disclosed in the present invention includes a first covering film, the material of the first covering film is photosensitive ink, a ground opening is provided on the photosensitive ink, an electromagnetic film shielding layer and a conductive adhesive layer, the shielding layer is provided on a side of the conductive adhesive layer away from the first covering film, and the conductive adhesive layer passes through the ground opening and is connected to the ground wire. The shielding layer serves as a reference plane, which can maintain the continuity of the reference plane, and the upper and lower layers of the differential impedance line are both reference planes, which can reduce the insertion loss of the differential signal, ensure the stability of the differential signal, and reduce or avoid the occurrence of screen defects during display.

[0023] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0025] Figure 1 It is a cross-sectional schematic diagram of the flexible circuit board involved in the embodiment of the present disclosure when the flexible circuit board includes a first adhesive layer, a second adhesive layer, a first covering adhesive layer and a second covering adhesive layer.

[0026] Figure 2 A partial cross-sectional schematic diagram of the flexible circuit board involved in an embodiment of the present disclosure is a schematic diagram of a differential impedance line that forms a complete reference plane only near the first internal conductive layer but does not form a complete reference plane on the side near the first cover film.

[0027] Figure 3 A schematic plan view of a first covering film according to an embodiment of the present disclosure is shown when a grounding opening is punched out on the first covering film using a film tool.

[0028] Figure 4 A schematic cross-sectional view of the flexible circuit board involved in the embodiment of the present disclosure when the material of the first covering film and the second covering film is photosensitive ink.

[0029] Figure 5 Another cross-sectional schematic diagram of the flexible circuit board involved in the embodiment of the present disclosure when the material of the first covering film and the second covering film is photosensitive ink.

[0030] Figure 6 The first covering film is made of photosensitive ink and a ground opening is formed on the first covering film by exposure and development. This is a schematic diagram of the positional relationship between the ground line, the differential impedance line and the ground opening involved in the embodiment of the present disclosure.

[0031] Figure 7 A schematic diagram of the three-dimensional structure of the electromagnetic film involved in an embodiment of the present disclosure is when the electromagnetic film includes a shielding layer and a conductive adhesive layer.

[0032] Figure 8 A partial cross-sectional schematic diagram of the flexible circuit board involved in an embodiment of the present disclosure when the upper and lower layers of the differential impedance line are both reference planes.

[0033] Fig. 9 A schematic diagram of the positional relationship among the grounding wires, differential impedance wires and grounding openings involved in an embodiment of the present disclosure when the number of grounding openings corresponding to the grounding wires with larger widths is less than the number of grounding openings corresponding to the grounding wires with smaller widths.

[0034] Fig.10 It is a schematic diagram of the positional relationship among the ground line, the differential impedance line and the ground opening involved in the embodiment of the present disclosure when the first differential impedance line is a curve and the second differential impedance line is a straight line.

[0035] Fig.11 Schematic diagram of the positional relationship among the ground line, the differential impedance line and the ground opening involved in the embodiment of the present disclosure when the width of the second impedance segment is smaller than the width of the first impedance segment.

[0036] Fig.12 Schematic diagram of the positional relationship among the grounding line, the differential impedance line and the grounding opening involved in the embodiment of the present disclosure when the width of the second grounding segment is smaller than the width of the first grounding segment.

[0037] In the figure: 1-circuit board body, 11-first surface layer, 111-first external conductive layer, 1111-ground line, 1112-differential impedance line, 1113-first differential impedance line, 1114-second differential impedance line, 1115-first impedance section, 1116-second impedance section, 1117-first grounding section, 1118-second grounding section, 112-first high-frequency hot-melt polyimide layer, 113-first external insulating layer, 12-second surface layer, 121-second external conductive layer, 122-second high-frequency hot-melt polyimide layer, 123-second external insulating layer, 13-core board, 131-first internal conductive layer, 132-second internal conductive layer, 133-internal insulating layer, 14-first adhesive layer, 15-second adhesive layer, 101-first area, 102-second area, 2-first covering film, 21-grounding opening, 22-first covering insulating layer, 23-first covering rubber layer, 3-electromagnetic film, 31-shielding layer, 32-conductive rubber layer, 33-shielding rubber layer, 34-metal film layer, 321-conductive particles, 4-second covering film, 41-second covering insulating layer, 42-second covering rubber layer, 5-reinforcement film. DETAILED DESCRIPTION

[0038] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in a variety of forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the present disclosure will be comprehensive and complete and fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar structures, and thus their detailed description will be omitted. In addition, the drawings are only schematic illustrations of the present disclosure and are not necessarily drawn to scale.

[0039] Although relative terms such as "upper" and "lower" are used in this specification to describe the relative relationship of one component of the illustration to another component, these terms are used in this specification only for convenience, such as according to the orientation of the examples described in the drawings. It is understood that if the device of the illustration is turned upside down, the component described as "upper" will become the component "lower". When a structure is "on" other structures, it may mean that the structure is formed integrally on the other structure, or that the structure is "directly" disposed on the other structure, or that the structure is "indirectly" disposed on the other structure through another structure.

[0040] The terms "a", "an", "the", "said" and "at least one" are used to indicate the presence of one or more elements / components / etc.; the terms "including" and "having" are used to express an open-ended inclusive meaning and mean that additional elements / components / etc. may exist in addition to the listed elements / components / etc.; the terms "first", "second" and "third" etc. are used merely as labels and are not intended to limit the quantity of their objects.

[0041] Silicon-based OLEDs are small in size and high in resolution, and are widely used in the fields of augmented reality (AR) and virtual reality (VR). Taking a 1.35-inch silicon-based display device as an example, it has an ultra-high resolution of 3840*3552 and a refresh rate of 90Hz. The bandwidth requirement can only be met when the corresponding differential signal (MIPI) rate is set to 1.3Ghz according to the minimum leading and trailing edges (porch value) of each frame of the image.

[0042] VR display devices require two screens for the left and right eyes, and the design must meet the requirements of consistent latency. At present, the differential signals of the left and right eye screens use two interfaces, and the differential signals of the two interfaces are required to be designed as symmetrically as possible to meet the impedance matching requirements. If the impedance does not match, half of the screen is prone to flowery screens. In the display device, the power signal, function selection signal, etc. divide the differential signal channel, and multiple layers of differential impedance lines 1112 need to be set. In the area where the reference ground is not set in a certain layer of the stack of flexible circuit boards, the differential signal reference plane will be divided, which will cause the differential signal loaded by the differential signal line to fluctuate.

[0043] According to the current simulation calculation of the stacked structure of the flexible circuit board, the corresponding eye diagram can pass 2Ghz (differential signal rate). On the VR display device, the differential signal is transmitted to the driver chip through the mainboard, the transfer flexible circuit board, the screen flexible circuit board, and the binding end. The differential signal line is long, the process fluctuation is too large, and other factors cause excessive insertion loss. The measured eye diagram shows abnormal display at 1.3GHz. Therefore, it is necessary to improve the stability of the differential signal and reduce the insertion loss of the differential signal.

[0044] like Figure 1As shown, the flexible circuit board includes a circuit board body 1, the circuit board body 1 includes a core board 13 and a first surface layer 11 and a second surface layer 12 arranged on both sides of the core board 13, the core board 13 includes an internal conductive layer and an internal insulating layer 133, the internal conductive layer includes a first internal conductive layer 131 and a second internal conductive layer 132, the internal insulating layer 133 is arranged between the first internal conductive layer 131 and the second internal conductive layer 132, the first surface layer 11 includes a first external conductive layer 111 and a first external insulating layer 113, the first external insulating layer 113 includes a first conductive layer 111 and a first external conductive layer 113, and the first conductive layer 111 includes a first conductive layer 111 and a first external conductive layer 113. The insulating layer 113 is arranged on a side of the first internal conductive layer 131 away from the internal insulating layer 133, the first external conductive layer 111 is arranged on a side of the first external insulating layer 113 away from the first internal conductive layer 131 away from the internal insulating layer 133, the second surface layer 12 includes a second external conductive layer 121 and a second external insulating layer 123, the second external insulating layer 123 is arranged on a side of the second internal conductive layer 132, and the second external conductive layer 121 is arranged on a side of the second external insulating layer 123 away from the second internal conductive layer 132. A first adhesive layer 14 is arranged between the first external insulating layer 113 and the first internal conductive layer 131, and a second adhesive layer 15 is arranged between the second external insulating layer 123 and the second internal conductive layer 132.

[0045] The flexible circuit board further includes a first covering film 2 and a second covering film 4. The first covering film 2 includes a first covering insulating layer 22 and a first covering rubber layer 23. The first covering rubber layer 23 is arranged on a side of the first external conductive layer 111 away from the first external insulating layer 113. The first covering rubber layer 23 is arranged on a side of the first external conductive layer 111 away from the first external insulating layer 113. The first covering rubber layer 22 is arranged on a side of the first covering rubber layer 23 away from the first external conductive layer 111. The second covering film 4 includes a second covering insulating layer 41 and a second covering rubber layer 42. The second covering rubber layer 42 is arranged on a side of the second external conductive layer 121 away from the second external insulating layer 123. The second covering rubber layer 42 is arranged on a side of the second external conductive layer 121 away from the second external insulating layer 123. The second covering rubber layer 41 is arranged on a side of the second covering rubber layer 42 away from the second external conductive layer 121.

[0046] In order to ensure the shielding effect of the flexible circuit board, the flexible circuit board also includes an electromagnetic film 3, which includes a shielding layer 31 and a shielding adhesive layer 33. The shielding adhesive layer 33 is arranged on the side of the first covering insulating layer 22 away from the first covering adhesive layer 23, and the shielding layer 31 is arranged on the side of the shielding adhesive layer 33 away from the first covering insulating layer 22. The electromagnetic film 3 also includes a metal film layer 34, which is arranged on the side of the shielding layer 31 away from the conductive adhesive layer 32. The material of the shielding layer 31 is usually copper, and the material of the metal film layer 34 is usually gold, nickel or a gold-nickel composite layer. The flexible circuit board also includes a reinforcing film 5, which is arranged on the side of the metal film layer 34 away from the conductive adhesive layer 32. It plays a protective role on the electromagnetic film 3 to prevent the electromagnetic film 3 from being broken during the bending process of the flexible circuit board.

[0047] The thickness of the shielding layer 31 of the electromagnetic film 3 is only 0.3um, and the shielding performance is 60db-70db. The thickness of the shielding layer 31 is too thin to be used as a reference plane for differential signals. Figure 2 As shown, the differential impedance line 1112 forms a complete reference plane only near the first internal conductive layer 131, but does not form a complete reference plane on the side near the first covering film 2. In this case, the differential signal reference plane will be divided in the area where the complete reference plane is not formed, causing differential impedance fluctuations in the differential impedance line 1112.

[0048] like Figure 3 As shown, a ground opening 21 can be provided in the first covering film 2, the first external conductive layer 111 can include a differential impedance line and a grounding line, the shielding layer 31 is connected to the grounding line through the ground opening 21, the first covering film 2 includes a first covering insulating layer 22 and a first covering adhesive layer 23, and a film tool is used to punch and cut the ground opening 21 on the first covering film 2, the width d1 of the ground opening 21 is 0.5mm, the minimum specification of the ground opening 21 is 0.5mm*0.5mm, and the punching tolerance of the film tool is generally ±150um. The width of the grounding line is usually only between 100-200um, and it is obvious that the grounding opening 21 formed by punching is too large to meet the alignment requirements of the grounding line.

[0049] It can be considered that the thickness of the shielding layer 31 of the electromagnetic film 3 is increased as the reference plane of the differential signal, and a ground opening 21 is formed on the first cover film 2 by drilling. The minimum width of the ground opening 21 formed in this way can be 100um, the hole ring of the ground opening 21 can be 75um, and the minimum spacing from the ground opening 21 to the differential impedance line 1112 can be 75um. For example, the shielding layer 31 is connected to the ground line 1111 by the above method. At least 400um of routing space is required. This method will greatly affect the wiring density of the differential impedance line 1112 and the ground line 1111.

[0050] In addition, in the flexible circuit board of this structure, the first surface layer 11 includes a first external conductive layer 111 and a first external insulating layer 113. The material of the first external conductive layer 111 is copper, and the material of the first external insulating layer 113 is polyimide (PI). The dielectric constant of the first surface layer 11 is 4.0-4.2, and the loss factor is 0.018-0.020. The dielectric constant of the first adhesive layer 14 is 3.0-3.25, and the loss factor is 0.029-0.031. The second surface layer 12 includes a second external conductive layer 121 and a second external insulating layer 123. The material of the second external conductive layer 121 is copper, the material of the second external insulating layer 123 is polyimide (PI), the dielectric constant of the second surface layer 12 is 4.0-4.2, the loss factor is 0.018-0.020, the dielectric constant of the second adhesive layer 15 is 3.0-3.25, and the loss factor is 0.029-0.031. The shielding layer 31 of the electromagnetic film is made of gold or silver, the dielectric constant of the electromagnetic film 3 is 3.6-3.8, and the loss factor is 0.02-0.022. It can be understood that the dielectric constant and loss factor of the flexible circuit board are relatively large.

[0051] Based on this, the present disclosure provides a flexible circuit board. Figures 4 to 12 As shown, the flexible circuit board includes a circuit board body 1, a first covering film 2 and an electromagnetic film 3. The circuit board body 1 includes at least two conductive layers, an insulating layer is provided between two adjacent conductive layers, the conductive layer includes a first external conductive layer 111 closest to the side of the circuit board body 1, and the first external conductive layer 111 is provided with a grounding wire 1111; the first covering film 2 is provided on one side of the first external conductive layer 111, the material of the first covering film 2 is photosensitive ink, and a grounding opening 21 is provided on the photosensitive ink; the electromagnetic film 3 includes a shielding layer 31 and a conductive adhesive layer 32, the conductive adhesive layer 32 is provided on the side of the first covering film 2 away from the first external conductive layer 111, the shielding layer 31 is provided on the side of the conductive adhesive layer 32 away from the first covering film 2, and the conductive adhesive layer 32 passes through the grounding opening 21 to connect with the grounding wire 1111.

[0052] The material of the first covering film 2 is photosensitive ink, and a grounding opening 21 is provided on the photosensitive ink; the electromagnetic film 3 has a shielding layer 31 and a conductive adhesive layer 32, wherein the shielding layer 31 is provided on the side of the conductive adhesive layer 32 away from the first covering film 2, and the conductive adhesive layer 32 passes through the grounding opening 21 and is connected to the grounding line 1111. The shielding layer 31 serves as a reference plane, and the continuity of the reference plane can be maintained. The upper and lower layers of the differential impedance line 1112 are both reference planes, and the impedance of the differential impedance line 1112 will not fluctuate, which can ensure the stability of the differential signal, so that the impedances of the two interfaces match each other, and reduce or avoid the occurrence of screen defects during display.

[0053] The flexible circuit board involved in the embodiment of the present disclosure is described in detail below with reference to specific examples.

[0054] like Figure 4 and Figure 5 As shown, the material of the first surface layer 11 and the second surface layer 12 is a high-frequency hot-melt copper clad plate, the first surface layer 11 includes a first external conductive layer 111 and a first high-frequency hot-melt polyimide layer 112, and the second surface layer 12 includes a second external conductive layer 121 and a second high-frequency hot-melt polyimide layer 122. The first high-frequency hot-melt polyimide layer 112 is sandwiched between the first internal conductive layer 131 and the first external conductive layer 111, and the second high-frequency hot-melt polyimide layer 122 is sandwiched between the second internal conductive layer 132 and the second external conductive layer 121. The material of the first covering film 2 and the second covering film 4 is photosensitive ink. The thickness of the first outer conductive layer 111, the second outer conductive layer 121, the first inner conductive layer 131 and the second inner conductive layer 132 are all 10-15 μm, the thickness of the first high-frequency hot-melt polyimide layer 112 and the second high-frequency hot-melt polyimide layer 122 are 35-40 μm, and the thickness of the photosensitive ink is 25-35 μm.

[0055] The dielectric constant of the first high-frequency hot-melt polyimide layer 112 and the second high-frequency hot-melt polyimide layer 122 is 2.6-2.8, and the loss factor is 0.012-014. The dielectric constant of the first high-frequency hot-melt polyimide layer 112 and the first external conductive layer 111 is reduced compared with the first surface layer 11 and the first adhesive layer 14. The loss factor of the first high-frequency hot-melt polyimide layer 112 and the first external conductive layer 111 is reduced compared with the first surface layer 11 and the first adhesive layer 14. The material of the first covering film 2 and the second covering film 4 is photosensitive ink, and the dielectric constant of the photosensitive ink is 2.9-3.16, and the loss factor is 0.016-0.018. Compared with the first covering film 2 and the second covering film 4 which are composite layers of covering insulation layer and covering adhesive layer, the dielectric constant of the first covering film 2 and the second covering film 4 is reduced and the loss factor is reduced, thereby reducing the insertion loss of the differential impedance line 1112. In addition, the flexible circuit board can omit the first adhesive layer 14, the second adhesive layer 15, the first cover adhesive layer 23 and the second cover adhesive layer 42, which can simplify the manufacturing process of the flexible circuit board.

[0056] like Figure 6As shown, the material of the first covering film 2 is photosensitive ink, and a grounding opening 21 is provided on the photosensitive ink. The electromagnetic film 3 includes a shielding layer 31 and a conductive adhesive layer 32. The conductive adhesive layer 32 is provided on the side of the first covering film 2 away from the first external conductive layer 111. The first external conductive layer 111 includes a grounding line 1111 and a differential impedance line 1112. The first external conductive layer 111 includes a plurality of grounding lines 1111 and a plurality of groups of differential impedance lines 1112. A group of differential impedance lines 1112 is provided between two adjacent grounding lines 1111. A group of differential impedance lines 1112 includes at least two differential impedance lines 1112. The line spacing between two adjacent differential impedance lines 1112 is 3 times the line width of the differential impedance line 1112.

[0057] The material of the first covering film 2 is photosensitive ink, and a grounding opening 21 can be formed on the first covering film 2 by exposure and development. When the process accuracy of the exposure and development method is ±25um, the width d2 of the grounding opening 21 is 100-120um. This method can meet the grounding opening 21 with a specification of 100-120um*100-120um. The above-mentioned grounding opening 21 can be formed on the grounding line 1111 with a line width greater than 100um. The width of the grounding opening 21 is less than or equal to the width of the grounding line 1111, and the orthographic projection of the grounding opening 21 on the circuit board body 1 is located within the grounding line 1111.

[0058] The thickness of the shielding layer 31 is 0.3-0.6 times the thickness of the conductive layer. Specifically, the thickness of the shielding layer 31 can be greater than or equal to 6μm. The shielding performance of the shielding layer 31 is 80db-100db. Under the premise of meeting the high shielding performance, it can also be used as a reference plane. The dielectric constant of the electromagnetic film 3 of the flexible circuit board of this structure is 2.8-3.04, and the loss factor is 0.013-0.015. The dielectric constant of the electromagnetic film 3 is compared with Figure 3 Reduced loss factor compared to Figure 3 It should be noted that the conductive layer includes a first outer conductive layer 111, a second outer conductive layer 121, a first inner conductive layer 131 and a second inner conductive layer 132, and the conductive layer is one of the first outer conductive layer 111, the second outer conductive layer 121, the first inner conductive layer 131 and the second inner conductive layer 132.

[0059] When the size of the ground opening 21 is reduced, the wiring space for connecting the shielding layer 31 and the grounding line 1111 can be reduced. This method can ensure the wiring density of the differential impedance line 1112 and the grounding line 1111. Figure 7As shown, the conductive adhesive layer 32 in the electromagnetic film 3 connects the conductive particles 321 in the conductive adhesive layer 32 to the grounding wire 1111 exposing the grounding opening 21 by heat pressing, and a grounding opening 21 can be set every 3 mm in the length direction of the grounding wire 1111.

[0060] like Figure 8 As shown, the shielding layer 31 is arranged on the side of the conductive adhesive layer 32 away from the first cover film 2, and the conductive adhesive layer 32 passes through the grounding opening 21 and is connected to the grounding line 1111. The shielding layer 31 can be used as a reference plane to maintain the continuity of the reference plane. The upper and lower layers of the differential impedance line 1112 are both reference planes, which can reduce the insertion loss of the differential signal, ensure the stability of the differential signal, and reduce or avoid the occurrence of screen defects during display.

[0061] like Fig. 9 As shown, if there is enough space, the width of some grounding wires 1111 can be set larger, and the grounding wires 1111 with large width can reduce the insertion loss of differential signals. The number of connecting parts between grounding wires 1111 with different widths and the shielding layer 31 can be set differently, and the number of grounding openings 21 corresponding to grounding wires 1111 with large width is less than the number of grounding openings 21 corresponding to grounding wires 1111 with small width. Setting more grounding openings 21 for grounding wires 1111 with small width can further enhance the grounding continuity of the area, and even if setting fewer grounding openings 21 for grounding wires 1111 with large width, the grounding continuity of the area can be guaranteed. The grounding continuity of different areas can be balanced, so that the energy loss is balanced, thereby reducing the insertion loss of differential signals.

[0062] like Fig.10 As shown, the differential impedance line 1112 includes a first differential impedance line 1113 and a second differential impedance line 1114, the first differential impedance line 1113 is a curve, and the second differential impedance line 1114 is a straight line. The number of ground openings 21 corresponding to the ground line 1111 adjacent to the first differential impedance line 1113 is greater than the number of ground openings 21 corresponding to the ground line 1111 adjacent to the second differential impedance line 1114. For the first differential impedance line 1113 in the form of a curve, since the line spacing at different parts thereof may be different and the length of its energy reflection path is different, more ground openings 21 can eliminate the difference in energy reflection path, and can reduce the insertion loss of the differential signal.

[0063] like Fig.11 and Fig.12As shown, the circuit board body 1 has a first area 101 and a second area 102, the orthographic projection of the first internal conductive layer 131 on the circuit board body 1 is located in the first area 101, and the orthographic projection of the first external conductive layer 111 on the circuit board is located in the first area 101 and the second area 102, and the second area 102 is the bending area of ​​the flexible circuit board. Only the first external conductive layer 111 is retained in the bending area of ​​the flexible circuit board, which can reduce the bending stress of the flexible circuit board in the bending area.

[0064] like Fig.11 As shown, since the first region 101 is provided with the first internal conductive layer 131, and the second region 102 is not provided with the first internal conductive layer 131, the differential signal reference plane may be split in the second region 102 not covered with the first internal conductive layer 131, thereby causing differential impedance fluctuations in the differential impedance line 1112, and therefore the width of the differential impedance line 1112 in the first region 101 is set to be greater than the width of the differential impedance line 1112 in the second region 102. That is, the differential impedance line 1112 includes a first impedance segment 1115 and a second impedance segment 1116, the first impedance segment 1115 is at least partially provided in the first region 101, the second impedance segment 1116 is provided in the second region 102, and the width of the second impedance segment 1116 is less than the width of the first impedance segment 1115.

[0065] The first impedance segment 1115 forms a loop with the first outer conductive layer 111 which is closer in the first region 101, and the signal transmission time is short. A smaller impedance value can be set to meet the shorter signal transmission time, so the width of the first impedance segment 1115 is wider. The differential impedance line 1112 is emitted to the air or a reference ground farther in the first region 101, and a longer signal transmission time is required. A larger impedance value needs to be set to meet the longer signal transmission time, so the width of the second impedance segment 1116 is smaller.

[0066] like Fig.12 As shown, in order to further reduce the bending stress of the flexible circuit in the bending area, the width of the ground line 1111 in the second area 102 is set to be smaller than the width of the ground line 1111 in the first area 101, and the ground line 1111 includes a first ground segment 1117 and a second ground segment 1118. The first ground segment 1117 is at least partially arranged in the first area 101, and the second ground segment 1118 is arranged in the second area 102. The width of the second ground segment 1118 is smaller than the width of the first ground segment 1117, and the number of ground openings 21 corresponding to the second ground segment 1118 is greater than the number of ground openings 21 corresponding to the first ground segment 1117. The energy loss on the same ground line 1111 tends to be balanced, thereby further reducing the insertion loss of the differential signal on each differential impedance line 1112.

[0067] The embodiment of the present disclosure also provides a display module, and the display device may include the flexible circuit board mentioned in the embodiment of the present disclosure. The specific structure and beneficial effects of the display module can refer to the flexible circuit board, and the specific structure and beneficial effects of the flexible circuit board have been described in detail above, so they will not be repeated here.

[0068] The embodiment of the present disclosure also provides a display device, which may include the display module mentioned above in the embodiment of the present disclosure. The specific structure and beneficial effects of the display module have been described in detail above, so they will not be repeated here.

[0069] It should be noted that, in addition to the display panel, the display device also includes other necessary components and components, such as a housing, a circuit board, a power cord, etc. Those skilled in the art may make corresponding supplements according to the specific use requirements of the display device, which will not be repeated here.

[0070] The display device can be a traditional electronic device, such as a mobile phone, a computer, a television, and a camcorder, or it can be an emerging wearable device, such as a virtual reality device and an augmented reality device, which are not listed here one by one.

[0071] It should be noted that the above embodiments are interoperable and can be combined with each other to form other schemes, and the scheme of the present disclosure is not limited to the schemes described in the above embodiments. After considering the specification and practicing the invention disclosed herein, those skilled in the art will easily think of other embodiments of the present disclosure. This application is intended to cover any modification, use or adaptive change of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary technical means in the technical field that are not disclosed in the present disclosure. The description and embodiments are to be regarded as exemplary only, and the true scope and spirit of the present disclosure are indicated by the appended claims.

Claims

1. A flexible circuit board, characterized in that: include: The circuit board body comprises at least two conductive layers, an insulating layer is provided between two adjacent conductive layers, the conductive layers comprise a first outer conductive layer closest to the side of the circuit board body, and the first outer conductive layer is provided with a grounding wire; A first covering film is provided on one side of the first external conductive layer, the first covering film is made of photosensitive ink, and a grounding opening is provided on the first covering film; The electromagnetic film includes a shielding layer and a conductive adhesive layer. The conductive adhesive layer is arranged on the side of the first covering film away from the first external conductive layer, and the shielding layer is arranged on the side of the conductive adhesive layer away from the first covering film. The conductive adhesive layer passes through the grounding opening and is connected to the grounding wire.

2. The flexible circuit board according to claim 1, characterized in that: The thickness of the shielding layer is 0.3-0.6 times the thickness of the conductive layer.

3. The flexible circuit board according to claim 1, characterized in that: The conductive layer also includes an internal conductive layer and a second external conductive layer, the second external conductive layer is arranged on the other side of the circuit board body, the internal conductive layer is arranged between the first external conductive layer and the second external conductive layer, a first high-frequency hot-melt polyimide layer is arranged between the first external conductive layer and the internal conductive layer, and a second high-frequency hot-melt polyimide layer is arranged between the second external conductive layer and the internal conductive layer.

4. The flexible circuit board according to claim 1, characterized in that: The width of the grounding opening is smaller than or equal to the width of the grounding line, and the orthographic projection of the grounding opening on the circuit board body is located within the grounding line.

5. The flexible circuit board according to claim 1, characterized in that: The grounding wires have different widths, and the number of grounding openings corresponding to the grounding wires with larger widths is less than the number of grounding openings corresponding to the grounding wires with smaller widths.

6. The flexible circuit board according to claim 3, characterized in that: The circuit board body has a first area and a second area, the orthographic projections of the second external conductive layer and the internal conductive layer on the circuit board body are located in the first area, the orthographic projections of the first external conductive layer on the circuit board are located in the first area and the second area, and the second area is located in the bending area of ​​the flexible circuit board.

7. The flexible circuit board according to claim 6, characterized in that: The grounding line includes a first grounding segment and a second grounding segment, the first grounding segment is at least partially arranged in the first area, the second grounding segment is arranged in the second area, the width of the second grounding segment is smaller than the width of the first grounding segment, and the number of grounding openings corresponding to the second grounding segment is greater than the number of grounding openings corresponding to the first grounding segment.

8. The flexible circuit board according to claim 6, characterized in that: The outer conductive layer is also provided with a plurality of groups of differential impedance lines, and a group of the differential impedance lines is provided between two adjacent grounding lines.

9. The flexible circuit board according to claim 8, characterized in that: A group of the differential impedance lines includes at least two differential impedance lines, and a line distance between two adjacent differential impedance lines is three times the line width of the differential impedance line.

10. The flexible circuit board according to claim 8, characterized in that: The differential impedance line includes a first differential impedance line and a second differential impedance line, the first differential impedance line is a curve, the second differential impedance line is a straight line, and the number of ground openings corresponding to the ground line adjacent to the first differential impedance line is greater than the number of ground openings corresponding to the ground line adjacent to the second differential impedance line.

11. The flexible circuit board according to claim 8, characterized in that: The differential impedance line includes a first impedance segment and a second impedance segment, the first impedance segment is at least partially disposed in the first region, the second impedance segment is disposed in the second region, and a width of the second impedance segment is smaller than a width of the first impedance segment.

12. The flexible circuit board according to claim 1, characterized in that: The electromagnetic film further comprises a metal film layer, and the metal film layer is arranged on a side of the shielding layer away from the conductive adhesive layer.

13. The flexible circuit board according to claim 12, characterized in that: The flexible circuit board further comprises a reinforcing film, and the reinforcing film is arranged on a side of the metal film layer away from the conductive adhesive layer.

14. The flexible circuit board according to claim 3, characterized in that: The flexible circuit board further includes a second covering film, which is arranged on a side of the second external conductive layer away from the first external conductive layer, and is made of photosensitive ink.

15. A display module, characterized in that: A flexible circuit board comprising any one of claims 1 to 14.

16. A display device, characterized in that: Includes the display module described in claim 15.

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