Flexible circuit board, display module and display apparatus

Abstract

A flexible circuit board, a display module and a display apparatus. The flexible circuit board comprises: a first cover film (2), wherein the first cover film (2) is made of photosensitive ink, and a grounding opening (21) is provided in the photosensitive ink; and an electromagnetic film (3), which comprises a shielding layer (31) and a conductive adhesive layer (32), wherein the shielding layer (31) is arranged on the side of the conductive adhesive layer (32) that is away from the first cover film (2), and the conductive adhesive layer (32) passes through the grounding opening (21) to connect with a grounding wire (1111). The shielding layer (31), serving as a reference plane, can maintain the continuity of the reference plane, and upper and lower layers of a differential impedance line (1112) are both reference planes, such that the impedance of the differential impedance line (1112) does not fluctuate. Therefore, the stability of differential signals can be ensured, and the impedances of two interfaces can match each other, thereby reducing or avoiding the occurrence of blurred screen defects during display.

Description

Flexible circuit boards, display modules and display devices

[0001] Cross-references

[0002] This disclosure claims priority to Chinese Patent Application No. 202411930889.3, filed on December 25, 2024, entitled "Flexible Circuit Board, Display Module and Display Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of display technology, and more specifically, to a flexible circuit board, a display module, and a display device. Background Technology

[0004] Silicon-based OLEDs are widely used in augmented reality (AR) and virtual reality (VR) fields. VR display devices require two screens for the left and right eyes, and the differential signals for the two screens use two interfaces. The differential signals of the two interfaces must be designed as symmetrically as possible to meet impedance matching requirements.

[0005] The routing area of ​​differential impedance lines is compressed, requiring the setting of multiple layers of differential impedance lines. In areas where a reference ground is not set on a certain conductive layer of the flexible circuit board, the differential signal will be segmented on the reference plane, causing fluctuations in the differential signal and resulting in screen distortion during display.

[0006] It should be noted that the information in the background section above is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to overcome the problem that the differential signal is divided in the reference plane, causing fluctuations in the differential signal and resulting in screen distortion during display. This invention provides a flexible circuit board, a display module, and a display device.

[0008] According to one aspect of the present invention, a flexible circuit board is provided, the flexible circuit board including a circuit board body, a first cover film and an electromagnetic film, the circuit board body including at least two conductive layers, an insulating layer between adjacent conductive layers, the conductive layers including a first outer conductive layer closest to the circuit board body, the first outer conductive layer having a grounding wire; the first cover film is disposed on one side of the first outer conductive layer, the first cover film being made of photosensitive ink, the first cover film having a grounding opening; the electromagnetic film including a shielding layer and a conductive adhesive layer, the conductive adhesive layer being disposed on the side of the first cover film away from the first outer conductive layer, the shielding layer being disposed on the side of the conductive adhesive layer away from the first cover film, the conductive adhesive layer passing through the grounding opening and connected to the grounding wire.

[0009] In one embodiment of the present invention, the thickness of the shielding layer is 0.3-0.6 times the thickness of the conductive layer.

[0010] In one embodiment of the present invention, the conductive layer further includes an inner conductive layer and a second outer conductive layer. The second outer conductive layer is disposed on the other side of the circuit board body, and the inner conductive layer is disposed between the first outer conductive layer and the second outer conductive layer. A first high-frequency hot-melt polyimide layer is disposed between the first outer conductive layer and the inner conductive layer, and a second high-frequency hot-melt polyimide layer is disposed between the second outer conductive layer and the inner conductive layer.

[0011] In one embodiment of the present invention, the width of the grounding opening is less than or equal to the width of the grounding wire, and the orthographic projection of the grounding opening on the circuit board body is located inside the grounding wire.

[0012] In one embodiment of the present invention, the grounding wires have different widths, and the number of grounding openings corresponding to the wider grounding wires is less than the number of grounding openings corresponding to the narrower grounding wires.

[0013] In one embodiment of the present invention, the circuit board body has a first region and a second region, the orthographic projection of the second external conductive layer and the internal conductive layer on the circuit board body is located in the first region, the orthographic projection of the first external conductive layer on the circuit board is located in the first region and the second region, and the second region is located in the bending area of ​​the flexible circuit board.

[0014] In one embodiment of the present invention, the grounding wire includes a first grounding segment and a second grounding segment. The first grounding segment is at least partially located in a first region, and the second grounding segment is located in a second region. 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.

[0015] In one embodiment of the present invention, the outer conductive layer is further provided with multiple sets of differential impedance lines, and a set of differential impedance lines is provided between two adjacent grounding lines.

[0016] In one embodiment of the present invention, a set of differential impedance lines includes at least two differential impedance lines, and the line spacing between two adjacent differential impedance lines is three times the line width of the differential impedance lines.

[0017] In one embodiment of the present invention, the differential impedance line includes a first differential impedance line and a second differential impedance line. The first differential impedance line is a curve, and the second differential impedance line is a straight line. The number of grounding openings corresponding to the grounding wire adjacent to the first differential impedance line is greater than the number of grounding openings corresponding to the grounding wire adjacent to the second differential impedance line.

[0018] In one embodiment of the present invention, the differential impedance line includes a first impedance segment and a second impedance segment, the first impedance segment being at least partially disposed in a first region, the second impedance segment being disposed in a second region, and the width of the second impedance segment being smaller than the width of the first impedance segment.

[0019] In one embodiment of the present invention, the electromagnetic film further includes a metal thin film layer disposed on the side of the shielding layer away from the conductive adhesive layer.

[0020] In one embodiment of the present invention, the flexible circuit board further includes a reinforcing film disposed on the side of the metal thin film layer away from the conductive adhesive layer.

[0021] In one embodiment of the present invention, the flexible circuit board further includes a second cover film, which is disposed on the side of the second external conductive layer away from the first external conductive layer, and the material of the second cover film is photosensitive ink.

[0022] According to another aspect of the present invention, a display module is provided, comprising a flexible circuit board provided in one aspect of the present invention.

[0023] According to another aspect of the present invention, a display device is provided, comprising a display panel provided in one aspect of the present invention.

[0024] The flexible circuit board of the present invention includes a first cover film made of photosensitive ink, a grounding opening on the photosensitive ink, an electromagnetic shielding layer, and a conductive adhesive layer. The shielding layer is disposed on the side of the conductive adhesive layer away from the first cover film, and the conductive adhesive layer passes through the grounding opening and is connected to a grounding wire. The shielding layer serves as a reference plane, maintaining the continuity of the reference plane. With both the upper and lower layers of the differential impedance line being reference planes, the insertion loss of the differential signal can be reduced, ensuring the stability of the differential signal and reducing or avoiding screen flickering defects during display.

[0025] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0027] Figure 1 is a cross-sectional schematic diagram of the flexible circuit board according to an embodiment of the present invention, when the flexible circuit board includes a first adhesive layer, a second adhesive layer, a first cover adhesive layer, and a second cover adhesive layer.

[0028] Figure 2 is a partial cross-sectional schematic diagram of the flexible circuit board involved in the embodiment of the present invention when the differential impedance line forms a complete reference plane only near the first internal conductive layer, and does not form a complete reference plane on the side near the first cover film.

[0029] Figure 3 is a plan view of the first covering film according to an embodiment of the present invention when a grounding opening is formed on the first covering film using a film cutting tool.

[0030] Figure 4 is a cross-sectional schematic diagram of a flexible circuit board according to an embodiment of the present invention when the materials of the first cover film and the second cover film are photosensitive ink.

[0031] Figure 5 is another cross-sectional schematic diagram of the flexible circuit board involved in the embodiment of the present invention when the materials of the first cover film and the second cover film are photosensitive ink.

[0032] Figure 6 is a schematic diagram showing the positional relationship between the grounding wire, differential impedance wire, and grounding opening in an embodiment of the present invention when the material of the first cover film is photosensitive ink and a grounding opening is formed on the first cover film by exposure and development.

[0033] Figure 7 is a three-dimensional structural diagram of the electromagnetic membrane involved in the embodiment of the present invention, when the electromagnetic membrane includes a shielding layer and a conductive adhesive layer.

[0034] Figure 8 is a partial cross-sectional schematic diagram of the flexible circuit board involved in the embodiment of the present invention when both the upper and lower layers of the differential impedance line are reference planes.

[0035] Figure 9 is a schematic diagram showing the positional relationship between the grounding wire, differential impedance line, and grounding openings in an embodiment of the present invention when the number of grounding openings corresponding to the wider grounding wire is less than the number of grounding openings corresponding to the narrower grounding wire.

[0036] Figure 10 is a schematic diagram showing the positional relationship between the grounding wire, differential impedance line, and grounding opening in an embodiment of the present invention when the first differential impedance line is a curve and the second differential impedance line is a straight line.

[0037] Figure 11 is a schematic diagram showing the positional relationship between the grounding wire, differential impedance wire, and grounding opening in an embodiment of the present invention when the width of the second impedance segment is smaller than the width of the first impedance segment.

[0038] Figure 12 is a schematic diagram showing the positional relationship between the grounding wire, differential impedance wire, and grounding opening in an embodiment of the present invention when the width of the second grounding segment is less than the width of the first grounding segment.

[0039] In the diagram: 1-Circuit board body, 11-First surface layer, 111-First external conductive layer, 1111-Ground wire, 1112-Differential impedance line, 1113-First differential impedance line, 1114-Second differential impedance line, 1115-First impedance segment, 1116-Second impedance segment, 1117-First ground segment, 1118-Second ground segment, 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 region, 102-Second region, 2-First cover film, 21-Grounding opening, 22-First cover insulating layer, 23-First cover adhesive layer, 3-Electromagnetic film, 31-Shielding layer, 32-Conductive adhesive layer, 33-Shielding adhesive layer, 34-Metal thin film layer, 321-Conductive particles, 4-Second cover film, 41-Second cover insulating layer, 42-Second cover adhesive layer, 5-Reinforcing film. Detailed Implementation

[0040] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that the invention will be thorough and complete, and the concept of the exemplary embodiments will be fully conveyed to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore their detailed description will be omitted. Furthermore, the drawings are merely illustrative of the invention and are not necessarily drawn to scale.

[0041] Although relative terms such as "up" and "down" are used in this specification to describe the relative relationship of one component of an icon to another, these terms are used only for convenience, such as according to the orientation of the examples shown in the accompanying drawings. It is understood that if the device of the icon is flipped upside down, the component described as "up" will become the component described as "down." When a structure is "up" of another structure, it may mean that the structure is integrally formed on the other structure, or that the structure is "directly" mounted on the other structure, or that the structure is "indirectly" mounted on the other structure through another structure.

[0042] The terms “a,” “one,” “the,” “the,” 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 indicate an open-ended inclusion and to mean that there may be other elements / components / etc. in addition to the listed elements / components / etc.; the terms “first,” “second,” and “third,” etc., are used only as markers and are not a limitation on the number of objects.

[0043] Silicon-based OLEDs are characterized by their small size and high resolution, and are widely used in augmented reality (AR) and virtual reality (VR) fields. Taking a 1.35-inch silicon-based display as an example, it boasts an ultra-high resolution of 3840*3552 and a refresh rate of 90Hz. To meet the bandwidth requirements, the corresponding differential signal (MIPI) rate must be set to 1.3GHz based on the minimum leading and trailing edge (porch value) settings for each frame.

[0044] VR display devices require two screens for the left and right eyes, and the design must ensure consistent latency. Currently, the differential signals for the two screens use two interfaces, requiring the differential signals of the two interfaces to be designed as symmetrically as possible to meet impedance matching requirements. If the impedance is mismatched, half-screen distortion can easily occur. In the display device, power signals, function selection signals, etc., divide the differential signal channel, requiring the setting of multiple layers of differential impedance lines 1112. In the stack-up of flexible circuit boards, if a certain layer does not have a reference ground, the differential signal reference plane will be divided, causing fluctuations in the differential signal loaded on the differential signal lines.

[0045] Based on simulation calculations of the current stack-up structure of flexible circuit boards, the corresponding eye diagram can reach 2GHz (the rate of the differential signal). In VR display devices, the differential signal is transmitted to the driver chip through the motherboard, the adapter flexible circuit board, the screen flexible circuit board, and the bonding terminal. The differential signal path is relatively long, and factors such as excessive process fluctuations cause excessive insertion loss. Actual measurements show display anomalies at 1.3GHz. Therefore, it is necessary to improve the stability of the differential signal and reduce its insertion loss.

[0046] As shown in Figure 1, 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 disposed on both sides of the core board 13. The core board 13 includes an inner conductive layer and an inner insulating layer 133. The inner conductive layer includes a first inner conductive layer 131 and a second inner conductive layer 132. The inner insulating layer 133 is disposed between the first inner conductive layer 131 and the second inner conductive layer 132. The first surface layer 11 includes a first outer conductive layer 111 and a first outer insulating layer 113. An insulating layer 113 is disposed on the side of the first inner conductive layer 131 away from the inner insulating layer 133. A first outer conductive layer 111 is disposed on the side of the first outer insulating layer 113 away from the first inner conductive layer 131. The second surface layer 12 includes a second outer conductive layer 121 and a second outer insulating layer 123. The second outer insulating layer 123 is disposed on one side of the second inner conductive layer 132, and the second outer conductive layer 121 is disposed on the side of the second outer insulating layer 123 away from the second inner conductive layer 132. A first adhesive layer 14 is provided between the first outer insulating layer 113 and the first inner conductive layer 131, and a second adhesive layer 15 is provided between the second outer insulating layer 123 and the second inner conductive layer 132.

[0047] The flexible circuit board also includes a first cover film 2 and a second cover film 4. The first cover film 2 includes a first cover insulating layer 22 and a first cover adhesive layer 23. The first cover adhesive layer 23 is disposed on the side of the first external conductive layer 111 away from the first external insulating layer 113, and the first cover insulating layer 22 is disposed on the side of the first cover adhesive layer 23 away from the first external conductive layer 111. The second cover film 4 includes a second cover insulating layer 41 and a second cover adhesive layer 42. The second cover adhesive layer 42 is disposed on the side of the second external conductive layer 121 away from the second external insulating layer 123, and the second cover insulating layer 41 is disposed on the side of the second cover adhesive layer 42 away from the second external conductive layer 121.

[0048] To ensure the shielding effect of the flexible circuit board, it also includes an electromagnetic film 3, which comprises a shielding layer 31 and a shielding adhesive layer 33. The shielding adhesive layer 33 is disposed on the side of the first covering insulating layer 22 away from the first covering adhesive layer 23, and the shielding layer 31 is disposed 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 thin film layer 34, which is disposed on the side of the shielding layer 31 away from the conductive adhesive layer 32. The shielding layer 31 is typically made of copper, and the metal thin film layer 34 is typically made of gold, nickel, or a gold-nickel composite layer. The flexible circuit board also includes a reinforcing film 5, which is disposed on the side of the metal thin film layer 34 away from the conductive adhesive layer 32. The reinforcing film 5 serves to protect the electromagnetic film 3, preventing it from breaking during bending of the flexible circuit board.

[0049] The shielding layer 31 of the electromagnetic film 3 is only 0.3 μm thick, with a shielding performance of 60 dB-70 dB. The thickness of the shielding layer 31 is too thin to serve as a reference plane for differential signals. As shown in Figure 2, a conductive layer on the flexible circuit board is only partially formed. The differential impedance line 1112 forms a complete reference plane only near the first internal conductive layer 131, while a complete reference plane is not formed on the side near the first cover film 2. In this case, the differential signal reference plane will be fragmented in the area where a complete reference plane is not formed, resulting in differential impedance fluctuations in the differential impedance line 1112.

[0050] As shown in Figure 3, a grounding opening 21 can be provided in the first covering film 2. The first external conductive layer 111 may include a differential impedance line and a grounding line. The shielding layer 31 is connected to the grounding line through the grounding opening 21. The first covering film 2 includes a first covering insulating layer 22 and a first covering adhesive layer 23. The grounding opening 21 is formed by punching on the first covering film 2 using a film cutting tool. The width d1 of the grounding opening 21 is 0.5mm, and the minimum specification of the grounding opening 21 is 0.5mm*0.5mm. The punching tolerance of the film cutting tool is generally ±150um. However, the width of the grounding line is usually only between 100-200um. Obviously, the grounding opening 21 formed by punching is too large and cannot meet the alignment requirements of the grounding line.

[0051] One approach is to increase the thickness of the shielding layer 31 of the electromagnetic membrane 3 as a reference plane for the differential signal. A grounding opening 21 can be formed on the first cover film 2 by drilling. The minimum width of this grounding opening 21 can be 100µm, the annular diameter of the grounding opening 21 can be 75µm, and the minimum distance between the grounding opening 21 and the differential impedance line 1112 can be 75µm. Connecting the shielding layer 31 to the grounding line 1111 using this method would require at least 400µm of routing space. This approach would significantly affect the wiring density of the differential impedance line 1112 and the grounding line 1111.

[0052] 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, and 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, and 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, and the dielectric constant of the electromagnetic film 3 is 3.6-3.8, and the loss factor is 0.02-0.022. It is understood that the dielectric constant and loss factor of this flexible circuit board are relatively large.

[0053] Based on this, the present invention provides a flexible circuit board. As shown in Figures 4 to 12, the flexible circuit board includes a circuit board body 1, a first cover film 2, and an electromagnetic film 3. The circuit board body 1 includes at least two conductive layers, with an insulating layer between adjacent conductive layers. The conductive layers include a first external conductive layer 111 closest to the circuit board body 1, and the first external conductive layer 111 has a grounding wire 1111. The first cover film 2 is disposed on one side of the first external conductive layer 111, and the material of the first cover film 2 is photosensitive ink. The photosensitive ink has a grounding opening 21. The electromagnetic film 3 includes a shielding layer 31 and a conductive adhesive layer 32. The conductive adhesive layer 32 is disposed on the side of the first cover film 2 away from the first external conductive layer 111, and the shielding layer 31 is disposed on the side of the conductive adhesive layer 32 away from the first cover film 2. The conductive adhesive layer 32 passes through the grounding opening 21 and is connected to the grounding wire 1111.

[0054] The first cover film 2 is made of photosensitive ink, and a grounding opening 21 is provided on the photosensitive ink. The electromagnetic film 3 consists of a shielding layer 31 and a conductive adhesive layer 32. The shielding layer 31 is located on the side of the conductive adhesive layer 32 away from the first cover film 2. The conductive adhesive layer 32 passes through the grounding opening 21 and is connected to the grounding wire 1111. The shielding layer 31 serves as a reference plane, maintaining the continuity of the reference plane. Since both the upper and lower layers of the differential impedance line 1112 are reference planes, the impedance of the differential impedance line 1112 will not fluctuate, ensuring the stability of the differential signal. This allows the impedances of the two interfaces to match, reducing or avoiding screen flickering issues during display.

[0055] The flexible circuit board involved in the embodiments of the present invention will be described in detail below with reference to specific examples.

[0056] As shown in Figures 4 and 5, the first surface layer 11 and the second surface layer 12 are made of high-frequency hot-melt copper-clad laminate. 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 first cover film 2 and the second cover film 4 are made of photosensitive ink. The thicknesses of the first external conductive layer 111, the second external conductive layer 121, the first internal conductive layer 131, and the second internal conductive layer 132 are all 10-15 μm, the thicknesses 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.

[0057] 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 0.012-0.14. The dielectric constant of the first high-frequency hot-melt polyimide layer 112 and the first external conductive layer 111 is smaller than that of 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 smaller than that of the first surface layer 11 and the first adhesive layer 14. The material of the first cover film 2 and the second cover 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 cover film 2 and the second cover film 4, which are composite layers covering an insulating layer and a cover adhesive layer, the dielectric constant and loss factor of the first cover film 2 and the second cover film 4 are reduced, thereby reducing the insertion loss of the differential impedance line 1112. In addition, the flexible circuit board can eliminate the need for the first adhesive layer 14, the second adhesive layer 15, the first cover adhesive layer 23, and the second cover adhesive layer 42, which simplifies the manufacturing process of the flexible circuit board.

[0058] As shown in Figure 6, the first cover film 2 is made of photosensitive ink, and the photosensitive ink has a grounding opening 21. The electromagnetic film 3 includes a shielding layer 31 and a conductive adhesive layer 32. The conductive adhesive layer 32 is located on the side of the first cover film 2 away from the first external conductive layer 111. The first external conductive layer 111 includes a grounding wire 1111 and a differential impedance wire 1112. The first external conductive layer 111 includes multiple grounding wires 1111 and multiple sets of differential impedance wires 1112. A set of differential impedance wires 1112 is provided between two adjacent grounding wires 1111. A set of differential impedance wires 1112 includes at least two differential impedance wires 1112. The line spacing between two adjacent differential impedance wires 1112 is three times the line width of the differential impedance wire 1112.

[0059] The first cover film 2 is made of photosensitive ink. A grounding opening 21 can be formed on the first cover film 2 by exposure and development. When the process accuracy of exposure and development is ±25um, the width d2 of the grounding opening 21 is 100-120um. This method can meet the requirements of a grounding opening 21 with a specification of 100-120um*100-120um. The above-mentioned grounding opening 21 can be formed on a grounding wire 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 wire 1111. The orthogonal projection of the grounding opening 21 on the circuit board body 1 is located within the grounding wire 1111.

[0060] 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, and it can also serve as a reference plane while meeting the high shielding performance requirements. The dielectric constant of the electromagnetic film 3 of the flexible circuit board with this structure is 2.8-3.04, and the loss factor is 0.013-0.015. The dielectric constant and loss factor of the electromagnetic film 3 are lower than those in Figure 3, which can further reduce the insertion loss of the flexible circuit board. It should be noted that the conductive layer includes a first external conductive layer 111, a second external conductive layer 121, a first internal conductive layer 131, and a second internal conductive layer 132, wherein the conductive layer is one of the first external conductive layer 111, the second external conductive layer 121, the first internal conductive layer 131, and the second internal conductive layer 132.

[0061] With a smaller grounding opening 21, the wiring space between the shielding layer 31 and the grounding wire 1111 can be reduced, which ensures the wiring density of the differential impedance line 1112 and the grounding wire 1111. As shown in Figure 7, 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 exposed in the grounding opening 21 by hot pressing. A grounding opening 21 can be set every 3mm along the length of the grounding wire 1111.

[0062] As shown in Figure 8, the shielding layer 31 is disposed on the side of the conductive adhesive layer 32 away from the first cover film 2. The conductive adhesive layer 32 passes through the grounding opening 21 and is connected to the grounding wire 1111. The shielding layer 31 can serve as a reference plane, maintaining 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 screen flickering defects during display.

[0063] As shown in Figure 9, if space permits, the width of some grounding wires 1111 can be set to be larger. Wider grounding wires 1111 can reduce insertion loss of differential signals. The number of connection points between grounding wires 1111 of different widths and the shielding layer 31 can be differentiated, with wider grounding wires 1111 having fewer grounding openings 21 than narrower grounding wires 1111. The narrower grounding wires 1111 have more grounding openings 21, which further enhances the grounding continuity in that area. Even with fewer grounding openings 21, the wider grounding wires 1111 can still ensure grounding continuity in that area. This balanced grounding continuity across different areas leads to more balanced energy loss, thereby reducing insertion loss of differential signals.

[0064] As shown in Figure 10, 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 curved, and the second differential impedance line 1114 is a straight line. The number of grounding openings 21 corresponding to the grounding wire 1111 adjacent to the first differential impedance line 1113 is greater than the number of grounding openings 21 corresponding to the grounding wire 1111 adjacent to the second differential impedance line 1114. For the curved first differential impedance line 1113, since the line spacing at different parts may be different, the length of its energy reflection path will also be different. More grounding openings 21 can eliminate the difference in energy reflection path and reduce the insertion loss of differential signals.

[0065] As shown in Figures 11 and 12, the circuit board body 1 has a first region 101 and a second region 102. The orthographic projection of the first inner conductive layer 131 on the circuit board body 1 is located in the first region 101, and the orthographic projection of the first outer conductive layer 111 on the circuit board is located in both the first region 101 and the second region 102. The second region 102 is the bending region of the flexible circuit board. By retaining only the first outer conductive layer 111 in the bending region of the flexible circuit board, the bending stress of the flexible circuit board in the bending region can be reduced.

[0066] As shown in Figure 11, since the first region 101 is provided with a first internal conductive layer 131, while the second region 102 is not provided with a first internal conductive layer 131, the differential signal reference plane may be segmented in the second region 102 where the first internal conductive layer 131 is not covered, resulting in differential impedance fluctuations in the differential impedance line 1112. 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, and the second impedance segment 1116 is provided in the second region 102. The width of the second impedance segment 1116 is less than the width of the first impedance segment 1115.

[0067] The first impedance segment 1115 forms a loop with the nearby first external conductive layer 111 in the first region 101. Since the signal transmission time is short, a smaller impedance value is sufficient to meet this short transmission time; therefore, the width of the first impedance segment 1115 is relatively wide. In contrast, the differential impedance line 1112 is emitted to the air or a more distant reference ground in the first region 101, requiring a longer signal transmission time. Therefore, a larger impedance value is needed to meet this longer transmission time; hence, the width of the second impedance segment 1116 is relatively small.

[0068] As shown in Figure 12, to further reduce the bending stress of the flexible circuit in the bending region, the width of the grounding wire 1111 in the second region 102 is set to be smaller than the width of the grounding wire 1111 in the first region 101. The grounding wire 1111 includes a first grounding segment 1117 and a second grounding segment 1118. The first grounding segment 1117 is at least partially located in the first region 101, and the second grounding segment 1118 is located in the second region 102. The width of the second grounding segment 1118 is smaller than the width of the first grounding segment 1117, and the number of grounding openings 21 corresponding to the second grounding segment 1118 is greater than the number of grounding openings 21 corresponding to the first grounding segment 1117. This makes the energy loss on the same grounding wire 1111 tend to be balanced, thereby further reducing the insertion loss of differential signals on each differential impedance line 1112.

[0069] This invention also provides a display module, which may include the flexible circuit board mentioned above in this invention. The specific structure and beneficial effects of this display module can be found in the flexible circuit board, whose specific structure and beneficial effects have been described in detail above and will not be repeated here.

[0070] This invention also provides a display device, which may include the display panel mentioned above in this invention. The specific structure and beneficial effects of the display panel have been described in detail above, and therefore will not be repeated here.

[0071] It should be noted that, in addition to the display panel, the display device also includes other necessary components and parts, such as the casing, circuit board, power cord, etc. Those skilled in the art can make corresponding additions according to the specific usage requirements of the display device, which will not be elaborated here.

[0072] Display devices can be traditional electronic devices, such as mobile phones, computers, televisions, and video recorders, or emerging wearable devices, such as virtual reality devices and augmented reality devices, which will not be listed here.

[0073] It should be noted that the above embodiments are interconnected and can be combined to form other solutions. The solutions of the present invention are not limited to those described in the above embodiments. Those skilled in the art will readily conceive of other embodiments of the invention upon considering the specification and practicing the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the appended claims.

Claims

1. A flexible circuit board, wherein, include: The circuit board body includes at least two conductive layers, with an insulating layer between adjacent conductive layers. Each conductive layer includes a first outer conductive layer closest to the circuit board body, and the first outer conductive layer is provided with a ground wire. A first cover film is disposed on one side of the first external conductive layer. The material of the first cover film is photosensitive ink, and a grounding opening is provided on the first cover film. An electromagnetic membrane includes a shielding layer and a conductive adhesive layer. The conductive adhesive layer is disposed on the side of the first cover film away from the first external conductive layer, and the shielding layer is disposed on the side of the conductive adhesive layer away from the first cover 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, wherein, 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, wherein, The conductive layer further includes an inner conductive layer and a second outer conductive layer. The second outer conductive layer is disposed on the other side of the circuit board body. The inner conductive layer is disposed between the first outer conductive layer and the second outer conductive layer. A first high-frequency hot-melt polyimide layer is disposed between the first outer conductive layer and the inner conductive layer. A second high-frequency hot-melt polyimide layer is disposed between the second outer conductive layer and the inner conductive layer.

4. The flexible circuit board according to claim 1, wherein, The width of the grounding opening is less than or equal to the width of the grounding wire, and the orthographic projection of the grounding opening on the circuit board body is located within the grounding wire.

5. The flexible circuit board according to claim 1, wherein, The grounding wires have different widths, and the grounding wire with a larger width has fewer grounding openings than the grounding wire with a smaller width.

6. The flexible circuit board according to claim 3, wherein, The circuit board body has a first region and a second region. The orthographic projection of the second external conductive layer and the internal conductive layer on the circuit board body is located in the first region. The orthographic projection of the first external conductive layer on the circuit board is located in the first region and the second region. The second region is located in the bending area of ​​the flexible circuit board.

7. The flexible circuit board according to claim 6, wherein, The grounding wire includes a first grounding section and a second grounding section. The first grounding section is at least partially located in the first region, and the second grounding section is located in the second region. The width of the second grounding section is smaller than the width of the first grounding section, and the number of grounding openings corresponding to the second grounding section is greater than the number of grounding openings corresponding to the first grounding section.

8. The flexible circuit board according to claim 6, wherein, The outer conductive layer is also provided with multiple sets of differential impedance lines, and a set of differential impedance lines is provided between two adjacent grounding lines.

9. The flexible circuit board according to claim 8, wherein, A set of differential impedance lines includes at least two differential impedance lines, and the spacing between two adjacent differential impedance lines is three times the line width of the differential impedance lines.

10. The flexible circuit board according to claim 8, wherein, The differential impedance line includes a first differential impedance line and a second differential impedance line. The first differential impedance line is a curve, and the second differential impedance line is a straight line. The number of grounding openings corresponding to the grounding wire adjacent to the first differential impedance line is greater than the number of grounding openings corresponding to the grounding wire adjacent to the second differential impedance line.

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

12. The flexible circuit board according to claim 1, wherein, The electromagnetic membrane further includes a metal thin film layer, which is disposed on the side of the shielding layer away from the conductive adhesive layer.

13. The flexible circuit board according to claim 12, wherein, The flexible circuit board also includes a reinforcing film, which is disposed on the side of the metal thin film layer away from the conductive adhesive layer.

14. The flexible circuit board according to claim 3, wherein, The flexible circuit board further includes a second cover film, which is disposed on the side of the second external conductive layer away from the first external conductive layer, and the material of the second cover film is photosensitive ink.

15. A display module, wherein, Includes the flexible circuit board as described in any one of claims 1 to 14.

16. A display device, wherein, Includes the display module as described in claim 15.

Images