Flexible circuit board, manufacturing method of flexible circuit board and communication equipment

Abstract

The invention relates to the technical field of circuit boards, and provides a flexible circuit board which comprises a first outer metal layer, a second outer metal layer and at least one inner metal layer arranged between the first outer metal layer and the second outer metal layer. The inner metal layer comprises a plurality of groups of signal lines and ground lines arranged on the two sides of the signal lines, and the first outer metal layer and the second outer metal layer serve as reference layers of the signal lines and are used for providing a backflow path. The flexible circuit board provided by the embodiment of the invention can replace a high-speed cable, and space is saved. The embodiment of the invention further provides a manufacturing method of the flexible circuit board and communication equipment.

Description

Technical Field

[0001] The present application relates to the technical field of circuit boards, and in particular to a flexible circuit board, a method for manufacturing a flexible circuit board, and a communication device. Background Art

[0002] Communication equipment such as servers and switches usually use high-speed cables to connect different functional modules. With the development of technology, the speed of each functional module is gradually increasing, and the number of high-speed cables required to be installed in the chassis of communication equipment is increasing, resulting in insufficient space in the chassis. Summary of the invention

[0003] The purpose of the present application is to provide a flexible circuit board, a method for manufacturing a flexible circuit board, and a communication device. The flexible circuit board can replace high-speed cables and save space.

[0004] An embodiment of the first aspect of the present application provides a flexible circuit board, which includes a first outer metal layer, a second outer metal layer, and at least one inner metal layer arranged between the first outer metal layer and the second outer metal layer; the inner metal layer includes multiple groups of signal lines, and ground lines arranged on both sides of the signal lines, and the first outer metal layer and the second outer metal layer serve as reference layers for the signal lines, and are used to provide a return path.

[0005] The flexible circuit board provided in the embodiment of the present application includes multiple metal layers, and multiple groups of signal lines are arranged in the inner metal layer, each group of signal lines can transmit signals, so that the flexible circuit board can replace at least one traditional high-speed cable to achieve electrical performance; ground wires are arranged on both sides of the signal line, and the ground wires can play an isolation and shielding effect on the signal line in the direction parallel to the flexible circuit board; the top and bottom layers of the flexible circuit board are reference layers for the signal line, and the reference layers play an isolation and shielding effect in the direction perpendicular to the flexible circuit board. Therefore, the above-mentioned flexible circuit board can replace at least one high-speed cable, save installation space, and help reduce the size of communication equipment; and the flexible circuit board has good shielding effect and small signal loss, and can achieve high-speed, low-latency, and high-reliability data transmission.

[0006] In some embodiments, the flexible circuit board also includes an adhesive layer, which is arranged on at least one side of the signal line along the thickness direction of the flexible circuit board; a partial area of ​​the adhesive layer is hollowed out to form a window portion, and the area of ​​the adhesive layer that is not hollowed out is a non-window portion, and the projection of the window portion on the inner metal layer covers multiple groups of the signal lines.

[0007] In some embodiments, a ground hole penetrating the ground wire and the non-window portion is provided in the flexible circuit board, and the ground hole conducts the first outer metal layer, the ground wire and the second outer metal layer.

[0008] In some embodiments, at least a portion of the signal line extends along a first direction, and the first direction is perpendicular to a thickness direction of the flexible circuit board;

[0009] Along the first direction, the adhesive layer includes a plurality of the window portions and a plurality of the non-window portions that are alternately arranged.

[0010] In some embodiments, the window portion penetrates the flexible circuit board along a second direction, and the second direction intersects with the first direction and is perpendicular to a thickness direction of the flexible circuit board.

[0011] In some embodiments, along the first direction, the distance between the two ground holes located on both sides of the window portion and closest to the window portion is D1, and the wavelength of the operating frequency of the signal line adjacent to the ground holes is λ, where D1<1 / 4λ.

[0012] In some embodiments, the width of the ground line is greater than or equal to three times the diameter of the ground hole.

[0013] In some embodiments, at least one group of the signal lines is a differential signal line, and the differential signal line includes a first differential trace and a second differential trace;

[0014] The distance between the differential signal line and the ground line adjacent thereto is D2, and the center distance between the first differential line and the second differential line is D3, wherein D2>D3.

[0015] In some embodiments, the head end and the tail end of each of the signal lines are respectively provided with a first connection portion, and a plurality of the first connection portions are arranged in sequence;

[0016] A plurality of second connection parts are disposed on the first outer metal layer, and the plurality of second connection parts are electrically connected to the plurality of first connection parts in a one-to-one manner.

[0017] In some embodiments, the second connection portion is a gold finger, and a reinforcing piece is attached to the second outer metal layer. In the thickness direction of the flexible circuit board, the reinforcing piece is arranged opposite to the gold finger.

[0018] In some embodiments, a whole piece of copper foil is respectively disposed in the first outer metal layer and the second outer metal layer, and the whole piece of copper foil covers a plurality of groups of the signal wires and a plurality of the ground wires.

[0019] The embodiment of the second aspect of the present application provides a method for manufacturing a flexible circuit board, comprising: providing a first sub-board, manufacturing an inner layer circuit on the first sub-board, wherein the inner layer circuit comprises a plurality of groups of signal lines and a plurality of ground lines, and the ground lines are provided on both sides of each group of the signal lines;

[0020] Stacking and pressing the first sub-board and at least one second sub-board to form a flexible circuit board;

[0021] In which, the flexible circuit board is provided with a first outer metal layer and a second outer metal layer on opposite sides along its thickness direction, respectively, the inner layer circuit is located between the first outer metal layer and the second outer metal layer, and the first outer metal layer and the second outer metal layer serve as reference layers for the signal line to provide a return path.

[0022] The flexible circuit board manufactured by the above-mentioned method for manufacturing a flexible circuit board can replace at least one high-speed cable, thus saving installation space and being helpful in reducing the size of communication equipment.

[0023] In some embodiments, stacking and pressing the first sub-board and at least one second sub-board comprises:

[0024] Providing at least one adhesive layer, making a window portion in the adhesive layer, and forming the rest of the adhesive layer as a non-window portion;

[0025] The first sub-board, at least one second sub-board and at least one layer of the adhesive layer are stacked and pressed together, the adhesive layer is arranged on a side of the signal line close to the first outer metal layer, and / or the adhesive layer is arranged on a side of the signal line close to the second outer metal layer;

[0026] Wherein, the projection of the window portion on the inner metal layer covers a plurality of groups of signal lines.

[0027] An embodiment of the third aspect of the present application proposes a communication device, comprising a first device, a second device and a flexible circuit board, wherein the first device and the second device are connected through the flexible circuit board, and the flexible circuit board is a flexible circuit board as provided in the first aspect, or a flexible circuit board manufactured by the flexible circuit board manufacturing method provided in the second aspect.

[0028] The communication device provided in the embodiment of the present application can use a flexible circuit board to connect a first device and a second device. The flexible circuit board replaces the high-speed cable, saves the installation space in the box, and is conducive to the miniaturization of the communication equipment. The flexible circuit board has good shielding effect and low signal loss, and can achieve high-speed, low-latency, and high-reliability data transmission.

[0029] In some embodiments, the first component and the second component are electrically connected to a second connection portion on the flexible circuit board.

[0030] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 One of the structural schematic diagrams of the flexible circuit board provided in one embodiment of the present application;

[0033] Figure 2 A second structural schematic diagram of a flexible circuit board provided in an embodiment of the present application;

[0034] Figure 3 A schematic diagram of the structure of an inner layer circuit in a flexible circuit board provided in an embodiment of the present application;

[0035] Figure 4 A partial schematic diagram of an inner circuit and an adhesive layer provided in an embodiment of the present application;

[0036] Figure 5 A partial schematic diagram of a first connection portion and a second connection portion in a flexible circuit board provided in an embodiment of the present application;

[0037] Figure 6 A flowchart of a method for manufacturing a flexible circuit board provided in one embodiment of the present application;

[0038] Figure 7 A schematic diagram of a module of a communication device provided in one embodiment of the present application.

[0039] Description of main component symbols:

[0040] 10. Flexible circuit board; 101. Ground hole; 102. Conductive hole; 11. First outer metal layer; 111. Second connection part; 12. Second outer metal layer; 13. Inner metal layer; 131. Inner line; 1311. Signal line; 13111. First connection part; 1311a. First differential line; 1311b. Second differential line; 1312. Ground line; 14. Glue layer; 141. Window part; 142. Non-window part; 15. Insulation layer; 16. Cover film; 17. Reinforcement member; 100. Communication equipment; 20. First device; 30. Second device. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0042] It should be noted that when a component is referred to as being "fixed on" or "disposed on" another component, it may be directly or indirectly on the other component. When a component is referred to as being "connected to" another component, it may be directly or indirectly connected to the other component. The orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", etc. is based on the orientation or positional relationship shown in the accompanying drawings and is only for the convenience of description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation on the patent. The terms "first" and "second" are only used for the convenience of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0043] References to "one embodiment", "some embodiments" or "an embodiment" described in the specification of this application mean that a particular feature, structure or characteristic described in conjunction with the embodiment is included in one or more embodiments of the present application. Thus, the phrases "in one embodiment", "in some other embodiments", "in some other embodiments", etc., which appear at different places in this specification, do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. In addition, in one or more embodiments, particular features, structures or characteristics may be combined in any suitable manner.

[0044] Communications equipment such as servers and switches usually use cables to connect different functional modules. High-speed cables are used for high-speed data transmission. They are usually made of silver-plated conductors and foamed insulated core wires, and are constructed with line pair shielding and overall shielding. With the development of technology, the speed of each functional module has gradually increased, and the number of high-speed cables that need to be installed in the chassis of communications equipment has increased, resulting in insufficient space in the chassis.

[0045] In view of this, an embodiment of the present application provides a flexible circuit board that can replace high-speed cables and save space. The flexible circuit board includes a first outer metal layer, a second outer metal layer, and at least one inner metal layer disposed between the first outer metal layer and the second outer metal layer; the inner metal layer includes multiple groups of signal lines and ground wires disposed on both sides of the signal lines, and the first outer metal layer and the second outer metal layer serve as reference layers for the signal lines. The above-mentioned flexible circuit board has multiple groups of signal lines arranged in the inner metal layer, and the flexible circuit board can replace at least one traditional high-speed cable to achieve electrical performance; ground wires are arranged on both sides of the signal line, and the ground wires can isolate and shield external interference to the signal line in a direction parallel to the flexible circuit board; the top and bottom layers of the flexible circuit board are reference layers for the signal line, and the reference layers can isolate and shield external interference to the signal line in a direction perpendicular to the flexible circuit board. Therefore, the above-mentioned flexible circuit board can replace at least one high-speed cable, save installation space, and help reduce the size of communication equipment.

[0046] The embodiment of the first aspect of the present application provides a flexible circuit board 10. Figures 1 to 4 The flexible circuit board 10 includes a first outer metal layer 11, a second outer metal layer 12, and at least one inner metal layer 13 arranged between the first outer metal layer 11 and the second outer metal layer 12; the inner metal layer 13 includes a plurality of signal lines 1311, and ground lines 1312 arranged on both sides of the signal lines 1311. The first outer metal layer 11 and the second outer metal layer 12 serve as reference layers of the signal lines 1311 for providing a return path.

[0047] The flexible printed circuit board 10 provided in the embodiment of the present application may be a high-frequency multi-layer flexible printed circuit board (Flexible Printed Circuit, FPC). The flexible printed circuit board 10 includes at least three metal layers, and the plurality of metal layers are arranged along the thickness direction ( Figure 1 The metal layers are stacked in the Z direction, and an insulating layer 15 is provided between adjacent metal layers. Figure 1 For example, the flexible circuit board 10 is provided with an inner metal layer 13. It can be understood that the number of inner metal layers 13 can also be two or more. When the number of inner metal layers 13 is two or more, one or more inner metal layers 13 are provided with a signal line 1311.

[0048] The inner metal layer 13 includes an inner circuit 131, and the inner circuit 131 includes multiple groups of signal lines (signal line) 1311 and multiple ground lines (GND line) 1312. The signal line 1311 can be a high-speed signal line or a low-speed signal line; it can be understood that during design, multiple pairs of high-speed cables with similar plug-in ports or connection ports can be replaced with signal lines 1311 designed on a flexible circuit board 10, that is, the flexible circuit board 10 is used to replace multiple high-speed cables. Optionally, the number of signal lines 1311 is greater than 2 groups.

[0049] The ground wire 1312 and the signal wire 1311 are preferably arranged in the same layer, that is, the ground wire 1312 and the signal wire 1311 are located on the same inner metal layer 13, and ground wires 1312 are arranged on both sides of each group of signal wires 1311. The ground wires 1312 on both sides of the signal wires 1311 can play an isolation and shielding effect in the direction parallel to the board surface of the flexible circuit board 10, that is, to isolate and shield the electromagnetic interference of other factors on the signal wires 1311. Specifically, a ground wire 1312 is arranged between two adjacent groups of signal wires 1311, and a ground wire 1312 is arranged on both sides of multiple groups of signal wires 1311, so as to achieve good shielding and isolation effects.

[0050] The signal line 1311 is used to realize signal transmission from the signal transmitting end to the signal receiving end. In order to realize the signal loop, a reference layer is required for signal return. The first outer metal layer 11 and the second outer metal layer 12 are reference layers of the signal line 1311, providing a signal return path for the signal line 1311.

[0051] The first outer metal layer 11 and the second outer metal layer 12 are the outermost metal layers located on both sides of the flexible circuit board 10, that is, the top metal layer and the bottom metal layer of the flexible circuit board 10. In this way, the first outer metal layer 11 and the second outer metal layer 12 can have an isolation and shielding effect on the signal line 1311 in a direction perpendicular to the flexible circuit board 10.

[0052] When the flexible circuit board 10 is applied to communication equipment such as a server and a switch, two ends of the signal line 1311 are electrically connected to two functional modules in the communication equipment respectively.

[0053] The flexible circuit board 10 provided in the embodiment of the present application has multiple groups of signal lines 1311 arranged in the inner metal layer 13, each group of signal lines 1311 can transmit signals, and the flexible circuit board 10 can replace at least one traditional high-speed cable to achieve electrical performance; ground lines 1312 are arranged on both sides of the signal line 1311, and the ground lines 1312 can play an isolation and shielding effect on the signal line 1311 in a direction parallel to the flexible circuit board 10; the first outer metal layer 11 and the second outer metal layer 12 are used as reference layers for the signal line 1311, and can play an isolation and shielding effect in a direction perpendicular to the flexible circuit board 10. Therefore, the above-mentioned flexible circuit board 10 integrates multiple groups of signal lines 1311 and can provide isolation and shielding effects for the signal line 1311 in the horizontal and vertical directions, and the flexible circuit board 10 can replace at least one high-speed cable to achieve signal transmission. Compared with multiple high-speed cables, the flexible circuit board 10 has a smaller volume, saves installation space, and is conducive to reducing the size of communication equipment; and the flexible circuit board 10 has a good shielding effect and a small signal loss, and can achieve high-speed, low-latency, and high-reliability data transmission.

[0054] In some embodiments, the flexible circuit board 10 also includes an adhesive layer 14, which is arranged on at least one side of the signal line 1311 along the thickness direction (Z direction) of the flexible circuit board 10; a partial area of ​​the adhesive layer 14 is hollowed out to form a window portion 141, and the area of ​​the adhesive layer 14 that is not hollowed out is a non-window portion 142, and the projection of the window portion 141 on the inner metal layer 13 covers multiple groups of signal lines 1311.

[0055] Figure 1 , Figure 2 It is shown that a layer of adhesive 14 is provided on both sides of the signal line 1311 in the Z direction, and both layers of adhesive 14 have window portions 141. In other embodiments, an adhesive layer 14 including a window portion 141 may also be provided on one side of the signal line 1311 in the Z direction.

[0056] The flexible circuit board 10 is a multi-layer circuit board. The flexible circuit board 10 includes a plurality of stacked sub-boards. The sub-boards may be flexible copper clad laminates (FCCL), copper foil, etc. The flexible copper clad laminate refers to a copper clad laminate formed by bonding copper foil to one or both sides of a flexible insulating material such as a polyester film or a polyimide film through a certain process. The insulating material layer in the flexible copper clad laminate is used to make the insulating layer 15 in the flexible circuit board 10, and the copper foil in the flexible copper clad laminate is used to make the metal layer in the flexible circuit board 10. It can be understood that the insulating layer 15 in the flexible circuit board 10 can not only be the insulating material layer in the flexible copper clad laminate, but one or more insulating layers can also be other insulating medium layers.

[0057] In the flexible circuit board 10, adjacent sub-boards can be bonded by the adhesive layer 14 to improve the insulation strength and mechanical properties. The adhesive layer 14 can be a pure adhesive layer, and its material includes epoxy resin, and the adhesive layer 14 can also be other adhesive layers. The adhesive layer 14 is located between the reference layer and the signal line 1311, and the adhesive layer 14 can be provided on one side or both sides of the signal line 1311.

[0058] The flexible circuit board 10 forms an air layer at the position of the window portion 141. Figure 2 As shown, in some embodiments, air layers are provided between the signal line 1311 and the first outer metal layer 11 , and between the signal line 1311 and the second outer metal layer 12 . In other embodiments, an air layer may be provided only on one side of the signal line 1311 .

[0059] The window portion 141 is a hollow area that penetrates the adhesive layer 14, and the window portion 141 can be made by drilling, photolithography, etc. The flexible circuit board 10 forms an air layer at the position of the window portion 141, that is, the flexible circuit board 10 forms a suspended layered structure at the window portion of the adhesive layer 14. The dielectric loss (Dissipation Factor, DF) value of air is the lowest, which is approximately equal to 0; the DF value of the existing insulating dielectric layer in the FPC industry is usually between 0.006 and 0.001. Therefore, by adding an air layer in the dielectric layer between the signal line 1311 and the reference layer, the DF value of the entire dielectric layer can be lowered. The smaller the DF value, the smaller the signal loss.

[0060] In the embodiment of the present application, a window portion 141 is provided in the adhesive layer 14, so that an air layer can be formed at the position of the window portion 141, which effectively reduces the signal loss of the signal line 1311 and improves the signal transmission quality of the flexible circuit board 10. At the same time, the signal loss affects the transmission rate. In the case where the length of the signal line 1311 is long, if the signal loss of the signal line 1311 is large, the transmission rate of the signal line 1311 may not meet the use requirements; in the embodiment of the present application, since the window portion 141 in the adhesive layer 14 reduces the signal loss of the signal line 1311, the flexible circuit board 10 provided in the embodiment of the present application solves the problem that the transmission rate cannot meet the use requirements due to the excessive length of the signal line, and improves the substitutability of the flexible circuit board 10.

[0061] Please refer to Figure 1 In some embodiments, a ground hole 101 penetrating the ground line 1312 and the non-window portion 142 is provided in the flexible circuit board 10 , and the ground hole 101 conducts the first outer metal layer 11 and the second outer metal layer 12 .

[0062] The ground hole 101 is provided on the ground line 1312, and the ground hole 101 passes through the non-windowed portion 142 of the adhesive layer 14, and the windowed portion 141 is not provided with the ground hole 101. The ground hole 101 conducts the first outer metal layer 11 and the second outer metal layer 12, that is, the ground hole 101 is used to conduct the reference layer on both sides of the signal line 1311. The ground hole 101 is drilled on the ground line 1312 in the non-windowed area, and at least one ground hole 101 is designed according to the length of the non-windowed portion 142 and the line width of the corresponding ground line 1312. It can be understood that in order to improve the isolation effect in the direction perpendicular to the flexible circuit board 10 (Z direction), multiple ground holes 101 can be provided.

[0063] In some embodiments, the ground hole 101 is a metallized through hole that passes through the first outer metal layer 11 and the second outer metal layer 12. It can be understood that the ground hole 101 may also include one or more blind holes as long as it can conduct the first outer metal layer 11 and the second outer metal layer 12.

[0064] By setting the ground hole 101 in the flexible circuit board 10 , the shielding and isolation crosstalk effect of the signal line 1311 in the direction perpendicular to the flexible circuit board 10 can be improved; a non-opening portion 142 is reserved in the adhesive layer 14 to facilitate the manufacture of the ground hole 101 .

[0065] Please refer to Figure 3 and Figure 4 In some embodiments, at least a portion of the signal line 1311 extends along a first direction, which is perpendicular to the thickness direction of the flexible circuit board 10; along the first direction, the adhesive layer 14 includes a plurality of window portions 141 and a plurality of non-window portions 142 that are alternately arranged.

[0066] Specifically, one or more ground holes 101 are provided on the non-windowed portion 142 , and the signal line 1311 spans across a plurality of windowed portions 141 and a plurality of non-windowed portions 142 .

[0067] The first direction may be the length direction of the flexible circuit board 10 , and in this embodiment, the first direction is the X direction. The signal line 1311 may partially or completely extend along the first direction, and a plurality of groups of signal lines 1311 are arranged in parallel.

[0068] Along the first direction, the adhesive layer 14 includes a plurality of window portions 141 and a plurality of non-window portions 142 that are alternately arranged, and the window design adopts a "string-in-string" type (i.e., segmented windowing); one or more non-window portions 142 are provided with ground holes 101, and the number of ground holes 101 on each non-window portion 142 may be one or more.

[0069] By adopting the above technical scheme, the adhesive layer 14 is provided with a plurality of window portions 141 in the extension direction of the signal line 1311, so as to form an air layer on one side of the signal line 1311, thereby effectively reducing the signal loss of the signal line 1311 and improving the transmission rate of the signal line 1311; at the same time, the non-window portion 142 can be provided with a ground hole 101, through which the first outer metal layer 11 and the second outer metal layer 12 are connected, thereby maintaining a good shielding and isolation crosstalk effect.

[0070] In some embodiments, the window portion 141 extends to two opposite ends of the flexible circuit board 10 along a second direction, and the second direction intersects the first direction.

[0071] like Figure 3 , Figure 4 As shown, the second direction is the Y direction in the figure, and the second direction may be the width direction of the flexible circuit board 10. The window portion 141 extends to opposite ends of the flexible circuit board 10 along the second direction Y, that is, the window portion 141 penetrates the flexible circuit board 10 along the second direction Y, forming an air layer connected to the outside, the inner metal layer 13 where the signal line 1311 is located is separated from the reference layer at the position of the window portion 141, and there is an air layer between the signal line 1311 and the reference layer, and the inner metal layer 13 where the signal line 1311 is located is bonded and connected to the reference layer at the position of the non-window portion 142 through the non-window portion 142.

[0072] By adopting the above technical solution, the window portion 141 of the adhesive layer 14 forms an air layer in the flexible circuit board 10 that runs through the opposite ends of the flexible circuit board 10, so that the flexible circuit board 10 forms a suspended stacked structure in the area corresponding to the window portion 141, further reducing signal loss and improving the transmission rate of the signal line 1311.

[0073] In some embodiments, the second direction Y is perpendicular to the first direction X.

[0074] The first direction X may be the length direction of the flexible circuit board 10, and the second direction Y may be the width direction of the flexible circuit board 10. It can be understood that in other embodiments, the second direction may also be oblique to the first direction.

[0075] In some embodiments, the minimum length of the window portion 141 depends on the window opening capability of the flexible circuit board 10, and the length of the window portion 141 is less than 1 / 4 of the wavelength of the operating frequency of the signal line 1311. Optionally, the wavelengths of the operating frequencies of different signal lines 1311 may be different, and the length of the window portion 141 is uniformly calculated according to the signal line 1311 with the highest transmission rate and / or application frequency domain. In this way, no obvious resonance will be formed at the window portion 141. The application frequency domain of the signal line 1311 refers to the frequency range that the signal line 1311 can cover in actual applications; the operating frequency of the signal line 1311 is the upper limit of its application frequency domain. If the application frequency domain is the highest, then the operating frequency of the signal line 1311 is also the highest.

[0076] like Figure 4 As shown, in some embodiments, the distance between two ground holes 101 located on both sides of the window portion 141 and closest to the window portion 141 is D1, and the wavelength of the operating frequency of the signal line 1311 adjacent to the ground hole 101 is λ, where D1<1 / 4λ.

[0077] The distance D1 between the two ground holes 101 on both sides of the window portion 141 and closest to the window portion 141 is the distance along the extension direction (first direction X) of the signal line 1311. In some cases, D1 is equal to the length of the window portion 141. It is understood that D1 may also be greater than the length of the window portion 141.

[0078] The window portion 141 is the part where the adhesive layer 14 is cut, and the metalized ground holes 101 cannot be set in this part. The ground holes 101 are all set on the non-window portion 142; along the first direction X, if there is no ground hole 101 for a long distance around the high-speed signal line, the high-speed signal line will be affected by crosstalk and resonance will occur. This distance is 1 / 4 of the wavelength of the working frequency of the group of signal lines 1311. By setting the distance D1 between the two ground holes 101 on both sides of the window portion 141 to be less than 1 / 4λ, it is possible to prevent obvious resonance from forming at the window portion 141, thereby reducing signal crosstalk.

[0079] In some embodiments, there is a group of signal lines 1311 adjacent to the ground line 1312 on both sides of the ground line 1312. If the operating frequencies of the two groups of signal lines 1311 are different, the distance D1 between the two ground holes 101 on both sides of the window portion 141 can be set according to the signal line 1311 with the highest transmission rate and / or application frequency domain. In other words, there is a group of signal lines 1311 adjacent to the ground line 1312 on both sides of the ground line 1312, one of which has a higher transmission rate and / or application frequency domain and the operating frequency wavelength of the group of signal lines 1311 is λ, then D1<1 / 4λ.

[0080] Please refer to Figure 3 and Figure 4In some embodiments, the width of the ground line 1312 is greater than or equal to three times the diameter of the ground hole 101 .

[0081] The ground line 1312 located between two groups of adjacent signal lines 1311 can isolate and shield the two groups of signal lines 1311 . The ground line 1312 is provided with a ground hole 101 in a region corresponding to the non-window portion 142 .

[0082] Optionally, the width of the ground line 1312 is greater than or equal to the sum of three times the diameter of the ground hole 101 and the offset tolerance when drilling the ground hole 101.

[0083] By setting the width of the ground line 1312 , the isolation and shielding effect of two groups of adjacent signal lines 1311 is improved.

[0084] In some embodiments, at least one group of signal lines 1311 are differential signal lines, and the differential signal lines include a first differential trace 1311a and a second differential trace 1311b; the distance from the differential signal line to the adjacent ground line 1312 is D2, and the center distance between the first differential trace 1311a and the second differential trace 1311b is D3, where D2>D3.

[0085] Differential transmission is a signal transmission technology. Different from the traditional method of one signal line and one ground line, differential transmission transmits signals on both lines. The two signals have the same amplitude and opposite phase. The signal transmitted on these two lines is a differential signal. Differential traces are two lines of equal length, equal width, close proximity, and on the same layer. The signal line 1311 in the flexible circuit board 10 uses a differential signal line 1311, which has the advantages of strong anti-interference ability and effective consistent electromagnetic interference. The flexible circuit board 10 can replace traditional high-speed cables.

[0086] A ground line 1312 is provided on both sides of a group of differential signal lines, that is, the first differential line 1311a is adjacent to a ground line 1312, and the distance between the first differential line 1311a and the ground line 1312 is D2; the second differential line 1311b is adjacent to another ground line 1312, and the distance between the second differential line 1311b and the ground line 1312 is also D2; the distance between the center lines of the first differential line 1311a and the second differential line 1311b is the center distance D3, where D2 is greater than D3.

[0087] By adopting the above technical solution, the isolation effect between the signal line 1311 and the ground line 1312 can be enhanced.

[0088] Optionally, the signal line 1311 may also be of other types, for example, the signal line 1311 may also be a single-ended signal line.

[0089] Please refer to Figure 1 , Figure 3and Figure 5 In some embodiments, a first connection portion 13111 is respectively provided at the head end and the tail end of each signal line 1311, and a plurality of first connection portions 13111 are arranged in sequence; a plurality of second connection portions 111 are provided on the first outer metal layer 11, and the plurality of second connection portions 111 are electrically connected one-to-one with the plurality of first connection portions 13111.

[0090] The head end and tail end of the signal line 1311 refer to the two opposite ends of the signal line 1311 along its extension direction. Figure 3 As shown, the first connection parts 13111 at the head ends of the plurality of signal lines 1311 are sequentially arranged on one side of the first direction X, and the first connection parts 13111 at the tail ends of the plurality of signal lines 1311 are sequentially arranged on the other side of the first direction X. In this way, the first connection parts 13111 at the head ends and the tail ends of the plurality of signal lines 1311 are sequentially arranged, respectively, and the flexible circuit board 10 can replace a plurality of high-speed cables adjacent to the sockets or ports.

[0091] In some embodiments, a plurality of second connection portions 111 are disposed on the first outer metal layer 11 , each second connection portion 111 is respectively connected to a corresponding first connection portion 13111 , and the second connection portion 111 is used to connect components outside the flexible circuit board 10 .

[0092] Optionally, a second connecting portion 111 connected to the first connecting portion 13111 may also be provided on the second outer metal layer 12 .

[0093] Since the signal line 1311 is located in the inner layer of the flexible circuit board 10, by providing a second connection portion 111 corresponding to the signal line 1311 on the first outer metal layer 11, the signal line 1311 can be conveniently electrically connected to external components through the second connection portion 111, thereby using the signal line 1311 to transmit signals.

[0094] In some embodiments, the second connection portion 111 is a gold finger.

[0095] The gold finger is a contact piece arranged in a finger shape. Optionally, the gold finger is a contact piece that has been surface treated, wherein the surface treatment uses nickel-palladium gold or hard gold to enhance the wear resistance and plug-in resistance of the gold finger. The first connecting portion 13111 and the second connecting portion 111 are electrically connected through the conductive hole 102, and the conductive hole 102 is a metallized hole.

[0096] By adopting the above technical solution, the flexible circuit board 10 can be connected to external components using gold fingers arranged in sequence. The gold fingers can replace the high-speed connector of the traditional high-speed cable, reducing the signal loss indirectly caused by welding between the connector and the flexible circuit board 10; the gold fingers have a simple structure, occupy a small space and have a low production cost.

[0097] In some embodiments, the first outer metal layer 11 further includes a GND line (not shown), which is disposed between gold fingers corresponding to adjacent signal lines 1311 . The GND line can shield and isolate gold fingers corresponding to adjacent signal lines 1311 to avoid crosstalk.

[0098] Optionally, a reinforcing piece 17 is attached to the second outer metal layer 12 , and in the thickness direction of the flexible circuit board 10 , the reinforcing piece 17 is arranged opposite to the gold finger.

[0099] The thickness of the reinforcing piece 17 can be greater than 0.1 mm. By pasting the reinforcing piece 17 on the back of the second outer metal layer 12, the reinforcing piece 17 can be used to provide support for other components of the flexible circuit board 10, so that the end of the flexible circuit board 10 can be directly plugged in and used, with better reliability.

[0100] In other embodiments, the second connection portion 111 may also be a pad or other connection components.

[0101] In some embodiments, the flexible circuit board 10 further includes a plurality of insulating layers 15 , and the dielectric loss (DF) of the insulating layers 15 is less than 0.001.

[0102] The flexible circuit board 10 may include a plurality of stacked flexible copper-clad laminates, and the insulating dielectric layer in the flexible copper-clad laminates is formed as the insulating layer 15 in the flexible circuit board 10. It can be understood that the insulating layer 15 may also be other insulating materials. Optionally, the dielectric loss of each insulating layer 15 is less than 0.001, or the dielectric loss of at least one insulating layer 15 is less than 0.001.

[0103] DF is an indicator of the energy loss of dielectric materials. The lower the DF, the better the integrity of the signal transmitted in the medium. By adopting the above technical solution, a low-loss material is selected as the insulating layer 15 when selecting materials, which can reduce the transmission loss of the signal line 1311 and help improve the transmission rate of the flexible circuit board 10.

[0104] In some embodiments, a whole piece of copper foil is provided in the first outer metal layer 11 and the second outer metal layer 12 respectively, and the whole piece of copper foil covers the multiple groups of signal lines 1311 and the multiple ground lines 1312 .

[0105] Furthermore, in some embodiments, the first outer metal layer 11 further includes a GND line, the GND line is provided between the gold fingers corresponding to the adjacent signal lines 1311 , and the GND line is connected to the copper foil.

[0106] In this way, the flexible circuit board 10 is covered with full copper on the upper and lower sides of the top and bottom layers corresponding to the signal lines 1311 for shielding and isolation, which can enhance the shielding and isolation effect.

[0107] It can be understood that in other embodiments, the first outer metal layer 11 and the second outer metal layer 12 include an outer layer circuit, and the outer layer circuit includes a plurality of reference ground lines, each of which is arranged corresponding to the signal line 1311 to play a shielding role.

[0108] Please refer to Figures 1 to 5 Some embodiments of the present application provide a flexible circuit board 10, comprising a plurality of metal layers and a plurality of insulating layers 15 stacked and alternately arranged, wherein the plurality of metal layers include a first outer metal layer 11, a second outer metal layer 12, and at least one inner metal layer 13 disposed between the first outer metal layer 11 and the second outer metal layer 12; the inner metal layer 13 includes a plurality of signal lines 1311 and ground lines 1312 disposed on both sides of the signal lines 1311, and the first outer metal layer 11 and the second outer metal layer 12 serve as reference layers for the signal lines 1311. A glue layer 14 is disposed on at least one side of the signal line 1311, and a window portion 141 and a non-window portion 142 are disposed in the glue layer 14, and the window portion 141 and the non-window portion 142 are distributed along the extension direction of the signal line 1311, and the flexible circuit board 10 forms an air layer at the position of the window portion 141. A ground hole 101 is provided in the flexible circuit board 10 . The ground hole 101 penetrates the ground line 1312 and the non-window portion 142 . The ground hole 101 conducts the first outer metal layer 11 and the second outer metal layer 12 .

[0109] The flexible circuit board 10 may further include a multi-layer covering film 16 , which covers the inner metal layer 13 , the first outer metal layer 11 and the second outer metal layer 12 respectively, for protecting the circuits.

[0110] The flexible circuit board 10 provided in the embodiment of the present application includes a plurality of groups of signal lines 1311 . The flexible circuit board 10 can replace at least one high-speed cable. The flexible circuit board 10 can provide good isolation and shielding effects for the signal lines 1311 , thereby improving the transmission quality of the signal lines 1311 .

[0111] Please refer to Figures 1 to 6 The embodiment of the second aspect of the present application provides a method for manufacturing a flexible circuit board 10, which is used to manufacture the flexible circuit board 10 provided in the first aspect. The method for manufacturing the flexible circuit board 10 includes:

[0112] Step S1 : providing a first sub-board, and manufacturing an inner layer circuit 131 on the first sub-board, wherein the inner layer circuit 131 includes a plurality of signal lines 1311 and ground lines 1312 arranged on both sides of the signal lines 1311 .

[0113] In order to improve the isolation and shielding effect, ground lines 1312 are disposed on both sides of each group of signal lines 1311 .

[0114] like Figure 1As shown, the flexible circuit board 10 includes three metal layers. For example, step S1 specifically includes: cutting, drilling, shading, copper plating, inner layer circuit production, and laminating the inner layer cover film 16.

[0115] Cutting is to provide a first sub-board, which includes a dielectric layer and a copper layer provided on at least one side of the dielectric layer. The dielectric layer is used to form an insulating layer 15 in the flexible circuit board 10, and the copper layer is used to form a metal layer in the flexible circuit board 10. The first sub-board can be a single-sided copper-clad board or a double-sided copper-clad board. If it is a double-sided copper-clad board, the dielectric layer is an insulating material layer, and the copper layers on both sides of the dielectric layer can be used as inner metal layers, or the copper layer on one side is used as the inner metal layer and the copper layer on the other side is used as the outer metal layer. Drilling refers to processing the inner layer via holes / tool ​​holes, etc. by mechanical drilling, laser method, etc.; black shadow is pre-treatment of hole metallization; copper plating is metallization of the holes; laminating the inner layer covering film 16 is to use the covering film 16 to protect the signal line 1311 and the ground line 1312.

[0116] Step S2: stacking and pressing the first sub-board and at least one second sub-board to form a flexible circuit board 10.

[0117] The flexible circuit board 10 is provided with a first outer metal layer 11 and a second outer metal layer 12 on opposite sides along its thickness direction, and the inner layer circuit 131 is located between the first outer metal layer 11 and the second outer metal layer 12. The first outer metal layer 11 and the second outer metal layer 12 serve as reference layers of the signal line 1311 for providing a signal return path.

[0118] Specifically, in step S2, one or more second sub-boards are provided, and the first sub-board and the second sub-board are stacked and pressed to form a laminated structure of the flexible circuit board 10. It can be understood that the first sub-board and the second sub-board can be structures such as flexible copper-clad boards, copper foils, etc., and the number of first sub-boards and second sub-boards can be set according to needs. The metal layer located at both ends of the flexible circuit board 10 and arranged on the outermost sub-boards serves as the first outer metal layer 11 and the second outer metal layer 12. For example, the first sub-board is a single-sided copper-clad board, the metal layer on the first sub-board is an inner metal layer, the two second sub-boards are single-sided copper-clad boards or double-sided copper-clad boards, and the two second sub-boards are stacked on opposite sides of the first sub-board, respectively. Then, the copper layers on the outer sides of the two second sub-boards serve as the first outer metal layer 11 and the second outer metal layer 12, respectively.

[0119] For example, step S2 specifically includes: laminating an outer layer sub-board (such as FCCL layer), outer layer drilling, plasma cleaning, black shadow, outer layer copper plating, outer layer circuit production, and laminating an outer layer cover film 16. The outer layer drilling is to use mechanical drilling, laser processing holes, etc. to make interlayer conductive holes 102; plasma cleaning refers to cleaning impurities in the hole.

[0120] The above-mentioned manufacturing method can manufacture a flexible circuit board 10, and a plurality of groups of signal lines 1311 are arranged in the inner metal layer 13 of the flexible circuit board 10. The flexible circuit board 10 can replace a plurality of traditional high-speed cables to achieve electrical performance; ground lines 1312 are arranged on both sides of the signal line 1311, and the ground lines 1312 can play an isolation and shielding effect in a direction parallel to the flexible circuit board 10; the top and bottom layers of the flexible circuit board 10 are reference layers for the signal line 1311, and the reference layers not only provide a signal return path, but also play an isolation and shielding effect in a vertical direction of the flexible circuit board 10, thereby reducing the interference of external factors on the signal line 1311. Therefore, the flexible circuit board 10 manufactured by the above-mentioned manufacturing method of the flexible circuit board 10 can replace at least one high-speed cable, save installation space, and help reduce the size of the communication device 100.

[0121] In some embodiments, step S2 stacks and presses the first sub-board and at least one second sub-board, including: providing an adhesive layer 14, making a window portion 141 in the adhesive layer 14, and forming the rest of the adhesive layer 14 as a non-window portion 142; stacking and pressing the first sub-board, at least one second sub-board and at least one layer of adhesive layer 14, the adhesive layer 14 is arranged on the side of the signal line 1311 close to the first outer metal layer 11, and / or the adhesive layer 14 is arranged on the side of the signal line 1311 close to the second outer metal layer 12; wherein the projection of the window portion 141 on the inner layer circuit 131 covers multiple groups of signal lines 1311.

[0122] The adhesive layer 14 is used to bond adjacent sub-boards. The adhesive layer 14 may be a pure adhesive sheet, but is not limited thereto. Specifically, after the adhesive layer 14 is provided, a plurality of window portions 141 are made on the adhesive layer 14 by drilling or the like, and the rest of the adhesive layer 14 is formed as a non-window portion 142.

[0123] When laminating the boards, the adhesive layer 14 is placed between adjacent sub-boards, and the adhesive layer 14 can be placed on one side or two opposite sides of the signal line 1311. After lamination, the multi-layer sub-boards and the adhesive layer 14 form a flexible circuit board 10. The window portion 141 and the non-window portion 142 are distributed along the extension direction of the signal line 1311, and the flexible circuit board 10 forms an air layer at the position of the window portion 141.

[0124] In some embodiments, at least a portion of the signal line 1311 extends along the first direction X; along the first direction X, a plurality of window portions 141 and a plurality of non-window portions 142 are alternately provided in the adhesive layer 14 , and the signal line 1311 spans across the plurality of window portions 141 and the plurality of non-window portions 142 .

[0125] By adopting the above technical solution, a window portion 141 is pre-set in the adhesive layer 14. After stacking and pressing, an air layer can be formed at the position of the flexible circuit board 10 corresponding to the window portion 141, which effectively reduces the signal loss of the signal line 1311 and improves the signal transmission rate and signal transmission quality.

[0126] In some embodiments, in the step of forming the window portion 141 in the adhesive layer 14, the width of the window portion 141 is at least 1 mm greater than the preset width of the flexible circuit board 10. After the lamination step, the manufacturing method further includes: cutting the flexible circuit board 10 according to the preset width.

[0127] The preset outer width of the flexible circuit board 10 refers to the finished width of the flexible circuit board 10 after cutting or punching. In this way, after the flexible circuit board 10 is cut, the window portion 141 can pass through the opposite ends of the flexible circuit board 10, and an air layer is formed at the position of the window portion 141. The DF value of the air layer is small, which can reduce the transmission loss of the signal line 1311.

[0128] In some embodiments, after step S2 , the manufacturing method further includes: manufacturing a ground hole 101 penetrating the ground line 1312 and the non-window portion 142 in the flexible circuit board 10 , wherein the ground hole 101 connects the first outer metal layer 11 and the second outer metal layer 12 .

[0129] Specifically, after lamination and pressing, the ground hole 101 and other interlayer conductive holes are made by mechanical drilling, laser processing, etc. In some embodiments, the ground hole 101 is a metallized through hole that penetrates the first outer metal layer 11 and the second outer metal layer 12, and is used to conduct the first outer metal layer 11 and the second outer metal layer 12.

[0130] By providing the ground hole 101 in the flexible circuit board 10 , the shielding and crosstalk isolation effect of the signal line 1311 in the vertical direction can be improved.

[0131] In some embodiments, the inner layer circuit 131 is manufactured on the first sub-board, and further includes: setting a first connection part 13111 at the beginning and the end of the signal line 1311 respectively, so that a plurality of first connection parts 1311 are arranged in sequence; after the first sub-board and at least one second sub-board are stacked and pressed together, the manufacturing method further includes: setting a plurality of second connection parts 111 on the first outer metal layer 11, and electrically connecting the plurality of second connection parts 111 with the plurality of first connection parts 13111 one by one; and performing surface treatment on the second connection parts 111.

[0132] The steps of making the outer layer circuit include setting a plurality of second connection parts 111, that is, making a plurality of second connection parts 111 at the end of the first outer metal layer 11, and electrically connecting the plurality of second connection parts 111 with the first connection parts 13111 at the beginning or end of a plurality of signal lines 1311 one by one; and then performing surface treatment on the second connection parts 111.

[0133] The first connection parts 13111 at the head ends of the plurality of signal lines 1311 are sequentially arranged on one side of the first direction X, and the first connection parts 13111 at the tail ends of the plurality of signal lines 1311 are sequentially arranged on the other side of the first direction X. In this way, the first connection parts 13111 at the head ends of the plurality of signal lines 1311 are sequentially arranged, and the flexible circuit board 10 can design a plurality of high-speed cables with adjacent sockets onto the same flexible circuit board 10. A plurality of second connection parts 111 are arranged on the first outer metal layer 11, so that each second connection part 111 is respectively connected to the corresponding first connection part 13111, so that the second connection part 111 can be connected to components outside the flexible circuit board 10, thereby electrically connecting the signal line 1311 to the external components.

[0134] Optionally, the second connection portion 111 is a gold finger. The second connection portion 111 is surface treated, and the gold finger can be treated with nickel-palladium gold or hard gold to enhance the wear resistance and plug-in resistance of the gold finger. In other embodiments, the second connection portion 111 can also be a pad or other connection component.

[0135] By adopting the above technical solution, since the signal line 1311 is located in the inner layer of the flexible circuit board 10, by making the second connecting portion 111 corresponding to the signal line 1311 on the first outer metal layer 11, the signal line 1311 can be conveniently electrically connected to external components through the second connecting portion 111, so that the signal line 1311 can be used to transmit signals; the flexible circuit board 10 can be connected to external components using the second connecting portions 111 arranged in sequence, thereby reducing the signal loss indirectly caused by welding between the connector and the flexible circuit board 10.

[0136] In some embodiments, the second connection portion 111 is a gold finger. After the second connection portion 111 is subjected to surface treatment, the manufacturing method further includes: pasting a reinforcing member 17 on the back side of the second outer metal layer 12 facing the gold finger.

[0137] In this way, the gold finger can be directly connected to the external device by plugging and unplugging, and the reinforcing member 17 provides support for the flexible circuit board 10, so that the end of the flexible circuit board 10 can be directly plugged in and used, with better reliability and less signal loss.

[0138] Please refer to Figures 1 to 6 , the following Figure 1 The flexible circuit board 10 shown is taken as an example to illustrate the design and manufacturing process of the flexible circuit board 10.

[0139] During the design phase, the schematic diagram of the cable is evaluated with the aim of designing a high-frequency multi-layer flexible circuit board to replace multiple high-speed cables, converting the electrical performance of the high-speed cables into signal lines 1311 on the flexible circuit board, and under certain wiring space conditions, converting multiple pairs of high-speed cables with similar ports into signal lines and designing them onto a flexible circuit board 10.

[0140] The flexible circuit board 10 is designed as a multi-layer circuit board with 3 layers or more, with high-speed signal lines running on the inner layer, and the top and bottom layers being reference layers for shielding and isolation; the routing details are designed, including ground line width design, window width design, window distance design, ground hole design, etc.; low-loss materials are selected as the materials for the insulation layer.

[0141] During the production stage, the flexible circuit board 10 is produced according to the design process and circuit data, including: cutting, drilling, shading, copper plating, inner layer circuit production, inner layer covering film 16, cleaning, outer layer FCCL board lamination, outer layer drilling, plasma cleaning, shading, outer layer copper plating, outer layer circuit production, outer layer covering film 16 lamination, outer layer pad / gold finger surface treatment, shape punching or cutting (FPC molding cutting), and post-processing; then, check whether the delamination area is completely delaminated, function test and signal line test, the tested signal meets the quality requirements, and mass production is carried out.

[0142] Before laminating the outer FCCL board, the adhesive layer 14 is pre-opened with windows, and the outer reference stratum is laminated in this process; after punching or cutting the outer shape, the position where the window portion 141 is located can form a suspended layered stacking structure.

[0143] After the shape is punched, check whether the delamination area is completely delaminated, and perform functional tests and signal line tests. If the test signal reduction meets the quality requirements, batch production can be carried out.

[0144] For example, Figure 1 The flexible circuit board 10 shown includes three metal layers, and the manufacturing method of the flexible circuit board includes: providing a single-sided copper-clad FCCL board (i.e., inner layer FCCL board), making an inner layer circuit 131 on the FCCL board, and laminating a covering film 16 on the inner layer circuit 131; then, stacking and laminating the outer layer FCCL board, the adhesive layer 14, the inner layer FCCL board, the adhesive layer 14, and the outer layer FCCL board in sequence; then, performing processes such as outer layer drilling, outer layer circuit manufacturing, and laminating the outer layer covering film 16.

[0145] Please refer to Figures 1 to 7The embodiment of the third aspect of the present application provides a communication device 100, including the flexible circuit board 10 provided in the first aspect or the flexible circuit board 10 manufactured by the manufacturing method provided in the second aspect. The communication device 100 also includes a first device 20 and a second device 30, and the first device 20 and the second device 30 are connected through the flexible circuit board 10.

[0146] The flexible circuit board 10 can replace the high-speed cable connected between the first device 20 and the second device 30. The communication device 100 can be a high-speed server (such as an AI server), a data center, a high-speed computing platform, a network communication device, etc.; the first device 20 and the second device 30 can be a server, a switch, an optical communication device, a router, etc., but are not limited thereto. For example, the communication device 100 is a data center, and the first device 20 and the second device 30 are different servers in the data center.

[0147] The communication device provided in the embodiment of the present application can use a flexible circuit board 10 to connect a first device 20 and a second device 30. The flexible circuit board 10 replaces a high-speed cable, saves installation space, and is conducive to the miniaturization of the communication device 100. The flexible circuit board 10 has a good shielding effect and low signal loss, and can achieve high-speed, low-latency, and high-reliability data transmission.

[0148] The flexible circuit board 10 provided in the embodiment of the present application improves the transmission quality through the stacking design and the circuit design, and can meet the transmission requirements of the signals in the communication device 100.

[0149] In some embodiments, the first device 20 and the second device 30 are electrically connected to the second connection portion 111 on the flexible circuit board 10 .

[0150] The first device 20 and the second device 30 both include circuit boards. Both ends of the flexible circuit board 10 are connected to the circuit board in the first device 20 and the circuit board in the second device 30 through the second connecting portion 111, respectively, so that the flexible circuit board 10 can directly connect the two circuit boards without setting up a traditional connector, saving the installation space in the box and reducing the signal loss caused by welding the connector and the flexible circuit board 10.

[0151] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A flexible circuit board, Features: The flexible circuit board comprises a first outer metal layer, a second outer metal layer and at least one inner metal layer disposed between the first outer metal layer and the second outer metal layer; The inner metal layer includes a plurality of signal lines and ground lines arranged on both sides of the signal lines. The first outer metal layer and the second outer metal layer serve as reference layers for the signal lines and are used to provide a return path.

2. The flexible circuit board according to claim 1, Features: The flexible circuit board further comprises a glue layer, and along the thickness direction of the flexible circuit board, the glue layer is arranged on at least one side of the signal line; Part of the adhesive layer is hollowed out to form a window portion, and the area of ​​the adhesive layer that is not hollowed out is a non-window portion. The projection of the window portion on the inner metal layer covers multiple groups of signal lines.

3. The flexible circuit board as claimed in claim 2, Features: The flexible circuit board is provided with a ground hole penetrating the ground wire and the non-windowed portion, and the ground hole conducts the first outer metal layer, the ground wire and the second outer metal layer.

4. The flexible circuit board as claimed in claim 3, Features: At least a portion of the signal line extends along a first direction, and the first direction is perpendicular to a thickness direction of the flexible circuit board; Along the first direction, the adhesive layer includes a plurality of the window portions and a plurality of the non-window portions that are alternately arranged.

5. The flexible circuit board as claimed in claim 4, Features: The window portion penetrates the flexible circuit board along a second direction, and the second direction intersects with the first direction and is perpendicular to a thickness direction of the flexible circuit board.

6. The flexible circuit board as claimed in claim 4, Features: Along the first direction, the distance between the two ground holes respectively located on both sides of the window portion and closest to the window portion is D1, and the wavelength of the operating frequency of the signal line adjacent to the ground holes is λ, wherein D1<1 / 4λ.

7. The flexible circuit board as claimed in claim 3, Features: The width of the ground line is greater than or equal to three times the diameter of the ground hole.

8. The flexible circuit board according to any one of claims 1 to 7, Features: At least one group of the signal lines is a differential signal line, and the differential signal line includes a first differential routing line and a second differential routing line; The distance between the differential signal line and the ground line adjacent thereto is D2, and the center distance between the first differential line and the second differential line is D3, wherein D2>D3.

9. The flexible circuit board according to any one of claims 1 to 7, Features: The head end and the tail end of each of the signal lines are respectively provided with a first connection portion, and a plurality of the first connection portions are arranged in sequence; A plurality of second connection parts are disposed on the first outer metal layer, and the plurality of second connection parts are electrically connected to the plurality of first connection parts in a one-to-one manner.

10. The flexible circuit board according to claim 9, Features: The second connection portion is a gold finger, and a reinforcing piece is attached to the second outer metal layer. In the thickness direction of the flexible circuit board, the reinforcing piece is arranged opposite to the gold finger.

11. The flexible circuit board according to any one of claims 1 to 7, Features: A whole piece of copper sheet is respectively provided in the first outer metal layer and the second outer metal layer, and the whole piece of copper sheet covers a plurality of groups of the signal lines and a plurality of the ground lines.

12. A method for manufacturing a flexible circuit board, It is characterized in that include: Providing a first sub-board, and manufacturing inner-layer circuits on the first sub-board, wherein the inner-layer circuits include a plurality of groups of signal lines and a plurality of ground lines, and the ground lines are arranged on both sides of each group of signal lines; Stacking and pressing the first sub-board and at least one second sub-board to form a flexible circuit board; In which, the flexible circuit board is provided with a first outer metal layer and a second outer metal layer on opposite sides along its thickness direction, respectively, the inner layer circuit is located between the first outer metal layer and the second outer metal layer, and the first outer metal layer and the second outer metal layer serve as reference layers for the signal line to provide a return path.

13. The method according to claim 12, Features: The step of stacking and pressing the first sub-board and at least one second sub-board comprises: Providing at least one adhesive layer, making a window portion in the adhesive layer, and forming the rest of the adhesive layer as a non-window portion; The first sub-board, at least one second sub-board and at least one layer of the adhesive layer are stacked and pressed together, the adhesive layer is arranged on a side of the signal line close to the first outer metal layer, and / or the adhesive layer is arranged on a side of the signal line close to the second outer metal layer; The projection of the window portion on the inner layer circuit covers a plurality of groups of signal lines.

14. A communication device, It is characterized in that It comprises a first device, a second device and a flexible circuit board, wherein the first device and the second device are connected via the flexible circuit board, and the flexible circuit board is a flexible circuit board as described in any one of claims 1 to 11, or a flexible circuit board manufactured by the method for manufacturing a flexible circuit board as described in any one of claims 12 to 13.

15. The communication device according to claim 14, Features :The first device and the second device are electrically connected to the second connecting portion on the flexible circuit board.

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