Flexible printed circuit, manufacturing method for flexible printed circuit, and communication device

Abstract

The present application relates to the technical field of circuit boards. Provided in the embodiments of the present application are a flexible printed circuit (10). The flexible printed circuit (10) comprises 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), wherein the inner metal layer (13) comprises a plurality of groups of signal lines (1311) and ground lines (1312) arranged on two 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) and are used for providing a return path. The flexible printed circuit (10) provided in the embodiments of the present application can replace a high-speed cable, thereby saving on space. Further provided in the embodiments of the present application are a manufacturing method for the flexible printed circuit (10), and a communication device (100).

Description

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

[0001] The present application claims priority from the Chinese patent application No. 202411297373.X filed on September 14, 2024 in the China Patent Office and entitled "Flexible circuit board, manufacturing method of flexible circuit board and communication device", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of circuit board, in particular to a flexible circuit board, a manufacturing method of the flexible circuit board and a communication device. BACKGROUND

[0003] The statements herein are provided only to enhance understanding of the present application and are not necessarily intended to constitute the prior art.

[0004] Communication devices 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 gradually increases, and the number of high-speed cables that need to be arranged in the cabinet of the communication device increases, causing insufficient space in the cabinet. TECHNICAL PROBLEM

[0005] One of the purposes of the embodiments of the present application is to provide a flexible circuit board, a manufacturing method of the flexible circuit board and a communication device, which can replace high-speed cables and save space. TECHNICAL SOLUTION

[0006] The technical solution adopted by the embodiments of the present application is:

[0007] In a first aspect, the present application 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 both 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 to provide a reflow path.

[0008] In some embodiments, the flexible circuit board further comprises an adhesive layer arranged on at least one side of the signal lines in the thickness direction of the flexible circuit board; a part of the adhesive layer is hollowed out to form a windowed portion, and a region of the adhesive layer which is not hollowed out is a non-windowed portion; a projection of the windowed portion on the inner metal layer covers a plurality of groups of the signal lines.

[0009] In some embodiments, the flexible circuit board is provided with a ground hole penetrating through the ground lines and the non-windowed portion, and the ground hole conducts the first outer metal layer, the ground lines and the second outer metal layer.

[0010] In some embodiments, at least part of the signal lines extend along a first direction, which is perpendicular to the thickness direction of the flexible circuit board.

[0011] Along the first direction, the adhesive layer comprises a plurality of the windowed portions and a plurality of the non-windowed portions arranged alternately.

[0012] In some embodiments, the windowed portions extend through the flexible circuit board along a second direction, which intersects the first direction and is perpendicular to the thickness direction of the flexible circuit board.

[0013] In some embodiments, along the first direction, the distance between the two ground holes respectively located on both sides of the windowed portion and closest to the windowed portion is D1, and the wavelength of the operating frequency of the signal line adjacent to the ground hole is λ, wherein D1 < 1 / 4λ.

[0014] In some embodiments, the width of the ground line is greater than or equal to three times the diameter of the ground hole.

[0015] In some embodiments, at least one group of the signal lines is a differential signal line, which comprises a first differential trace and a second differential trace.

[0016] The distance between the differential signal line and the ground line adjacent thereto is D2, and the center distance between the first differential trace and the second differential trace is D3, wherein D2 > D3.

[0017] In some embodiments, the head end and the tail end of each signal line are respectively provided with a first connecting portion, and a plurality of the first connecting portions are arranged in sequence.

[0018] A plurality of second connecting portions are provided on the first outer metal layer, and the plurality of second connecting portions are electrically connected to the plurality of first connecting portions one by one.

[0019] In some embodiments, the second connecting portion is a gold finger, and a reinforcing member is attached to the second outer metal layer, and the reinforcing member and the gold finger are arranged opposite to each other in the thickness direction of the flexible circuit board.

[0020] In some embodiments, the first outer metal layer and the second outer metal layer are respectively provided with a whole copper sheet, and the whole copper sheet covers a plurality of groups of the signal lines and a plurality of the ground lines.

[0021] In a second aspect, the application provides a manufacturing method of a flexible circuit board, comprising: providing a first sub-board, manufacturing an inner layer circuit on the first sub-board, the inner layer circuit comprising a plurality of groups of signal lines and a plurality of ground lines, and the two sides of each group of the signal lines being provided with the ground lines.

[0022] stacking and pressing the first sub-board and the at least one second sub-board to form a flexible circuit board;

[0023] The flexible circuit board is provided with a first outer metal layer and a second outer metal layer on opposite sides along the thickness direction of the flexible circuit board, and 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 of the signal lines to provide a reflux path.

[0024] In some embodiments, the stacking and pressing of the first sub-board and the at least one second sub-board comprises:

[0025] At least one adhesive layer is provided, and a windowed portion is formed in the adhesive layer, and the remaining part of the adhesive layer is formed as a non-windowed portion;

[0026] The first sub-board and the at least one second sub-board are stacked and pressed with the at least one adhesive layer, and the adhesive layer is arranged on a side of the signal line close to the first outer metal layer and / or on a side of the signal line close to the second outer metal layer;

[0027] The projection of the windowed portion on the inner layer metal layer covers a plurality of groups of the signal lines.

[0028] In a third aspect, the present application provides 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 the flexible circuit board provided in the first aspect or is the flexible circuit board manufactured by the manufacturing method of the flexible circuit board provided in the second aspect.

[0029] In some embodiments, the first device and the second device are electrically connected with the second connection portion on the flexible circuit board. Advantages

[0030] The flexible circuit board provided by the embodiments of the present application has the following advantages: the flexible circuit board comprises a plurality of metal layers, a plurality of groups of signal lines are arranged in the inner layer metal layer, each group of signal lines can transmit signals, so that the flexible circuit board can replace at least one conventional high-speed cable to realize electrical performance; the two sides of the signal lines are provided with ground lines, the ground lines can play an isolation and shielding effect on the signal lines in a direction parallel to the flexible circuit board; the top layer and the bottom layer of the flexible circuit board are reference layers of the signal lines, and the reference layers play an isolation and shielding effect 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 be conducive to reducing the size of the communication device; and the shielding effect of the flexible circuit board is good, and the signal loss is small, so that high-speed, low-delay and high-reliability data transmission can be realized.

[0031] The method for manufacturing the flexible circuit board provided by the embodiments of the present application has the beneficial effect that the manufactured flexible circuit board can replace at least one high-speed cable, saves installation space, and is conducive to reducing the size of the communication device.

[0032] The communication device provided by the embodiments of the present application has the beneficial effect that the flexible circuit board is used to connect the first device and the second device, the flexible circuit board replaces the high-speed cable, saves the installation space in the box, and is conducive to miniaturization of the communication device; the flexible circuit board has good shielding effect and small signal loss, and can realize high-speed, low-delay, and high-reliability data transmission. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or exemplary technical descriptions will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0034] FIG. 1 is a structural schematic diagram of a flexible circuit board provided by an embodiment of the present application;

[0035] FIG. 2 is a structural schematic diagram of a flexible circuit board provided by an embodiment of the present application;

[0036] FIG. 3 is a structural schematic diagram of an inner layer circuit in a flexible circuit board provided by an embodiment of the present application;

[0037] FIG. 4 is a partial schematic diagram of an inner layer circuit and a glue layer provided by an embodiment of the present application;

[0038] FIG. 5 is a partial schematic diagram of a first connecting part and a second connecting part in a flexible circuit board provided by an embodiment of the present application;

[0039] FIG. 6 is a flowchart of a method for manufacturing a flexible circuit board provided by an embodiment of the present application;

[0040] FIG. 7 is a module schematic diagram of a communication device provided by an embodiment of the present application. Embodiments of the present application

[0041] In order to make the purposes, technical solutions and advantages of the present application more clear, the present application will be further described in detail below with reference to the 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 is to be noted that when a component is referred to as being "fixed" or "set" on another component, it can be directly on the other component or indirectly on the other component. When a component is referred to as being "connected" to another component, it can be directly or indirectly connected to the other component. The terms "upper", "lower", "left", "right", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. For those skilled in the art, the specific meanings of the above terms can be understood according to the specific circumstances. The terms "first", "second" are only for the convenience of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features.

[0043] In order to illustrate the technical solutions provided in the present application, the following will be described in detail in combination with specific drawings and examples.

[0044] Communication devices such as servers, switches, etc. usually use cables to connect different functional modules. High-speed cables are cables used for high-speed data transmission, usually high-speed transmission cables made of silver-plated conductors and foamed insulation core wires, adopting line pair shielding and total shielding. With the development of technology, the speed of each functional module gradually increases, and the number of high-speed cables that need to be arranged in the chassis of the communication device increases, causing insufficient space in the chassis.

[0045] Therefore, the embodiments of the present application provide a flexible circuit board which can replace high-speed cables and save space. The flexible circuit board 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 both 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. The above flexible circuit board is provided with a plurality of groups of signal lines in the inner metal layer, and the flexible circuit board can replace at least one conventional high-speed cable to achieve electrical performance; ground lines are arranged on both sides of the signal lines, and the ground lines can isolate and shield external interference on the signal lines in the direction parallel to the flexible circuit board; the top layer and the bottom layer of the flexible circuit board serve as reference layers of the signal lines, and the reference layers can isolate and shield external interference on the signal lines in the direction perpendicular to the flexible circuit board. Therefore, the above flexible circuit board can replace at least one high-speed cable, save installation space, and be conducive to reducing the size of the communication device.

[0046] The embodiment of the first aspect of the application provides a flexible circuit board 10. Referring to FIGS. 1-4, the flexible circuit board 10 comprises 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 comprises a plurality of groups 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 serving as reference layers of the signal lines 1311 to provide a reflow path.

[0047] The flexible circuit board 10 provided by the embodiment of the application can be a high-frequency multilayer flexible printed circuit (FPC). The flexible circuit board 10 comprises at least three metal layers, the plurality of metal layers are arranged in a stacking manner along the thickness direction (Z direction in FIG. 1) of the flexible circuit board 10, and an insulating layer 15 is arranged between adjacent metal layers. For example, as shown in FIG. 1, the flexible circuit board 10 comprises one inner metal layer 13. It can be understood that the number of the inner metal layer 13 can also be two or more. When the number of the inner metal layer 13 is two or more, one or more inner metal layers 13 are provided with signal lines 1311.

[0048] The inner metal layer 13 comprises an inner layer circuit 131, the inner layer circuit 131 comprises a plurality of groups of signal lines 1311 and a plurality of ground lines 1312, and the signal lines 1311 can be high-speed signal lines or low-speed signal lines. It can be understood that, in the design, a plurality of pairs of high-speed cables with similar plug-in ports or connection ports can be replaced by the signal lines 1311 designed on one flexible circuit board 10, that is, the flexible circuit board 10 is used instead of a plurality of high-speed cables. Optionally, the number of the signal lines 1311 is greater than two groups.

[0049] The ground lines 1312 and the signal lines 1311 are preferably arranged on the same layer, that is, the ground lines 1312 and the signal lines 1311 are located on the same inner metal layer 13. The ground lines 1312 are arranged on both sides of each group of signal lines 1311, and the ground lines 1312 on both sides of the signal lines 1311 can play a shielding effect in a direction parallel to the surface of the flexible circuit board 10, that is, the ground lines 1312 can shield and isolate other factors from interfering with the signal lines 1311. Specifically, one ground line 1312 is arranged between two adjacent groups of signal lines 1311, and one ground line 1312 is arranged on both sides of a plurality of groups of signal lines 1311 to achieve a good shielding and isolation effect.

[0050] The signal line 1311 is used for signal transmission from the signal sending end to the signal receiving end. In order to realize the signal loop, the signal return flow needs to use the reference layer. The first outer metal layer 11 and the second outer metal layer 12 are the reference layers of the signal line 1311, and provide the signal return flow 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 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 isolate and shield the signal line 1311 in the direction perpendicular to the flexible circuit board 10.

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

[0053] The flexible circuit board 10 provided by the embodiment of the present application has a plurality of groups of signal lines 1311 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 conventional high-speed cable to realize electrical performance. The signal line 1311 is provided with a ground line 1312 on both sides, and the ground line 1312 can isolate and shield the signal line 1311 in the direction parallel to the flexible circuit board 10. The first outer metal layer 11 and the second outer metal layer 12 serve as the reference layers of the signal line 1311, and can isolate and shield the signal line 1311 in the direction perpendicular to the flexible circuit board 10. Therefore, the above flexible circuit board 10 integrates a plurality of groups of signal lines 1311 and can provide horizontal and vertical isolation and shielding effects for the signal line 1311. The flexible circuit board 10 can replace at least one high-speed cable to realize signal transmission. Compared with a plurality of high-speed cables, the flexible circuit board 10 has a smaller size, saves installation space, and is conducive to reducing the size of the communication device. In addition, the flexible circuit board 10 has good shielding effect and small signal loss, and can realize high-speed, low-delay, and high-reliability data transmission.

[0054] In some embodiments, the flexible circuit board 10 further includes a glue layer 14. The glue layer 14 is arranged on at least one side of the signal line 1311 in the thickness direction (Z direction) of the flexible circuit board 10. Part of the area of the glue layer 14 is hollowed out to form a windowed portion 141. The area of the glue layer 14 which is not hollowed out is a non-windowed portion 142. The projection of the windowed portion 141 on the inner metal layer 13 covers a plurality of groups of signal lines 1311.

[0055] Fig. 1 and Fig. 2 show that the signal line 1311 is provided with a layer of adhesive 14 on both sides in the Z direction, and the two layers of adhesive 14 are provided with windowed portions 141. In other embodiments, the signal line 1311 can be provided with a layer of adhesive 14 including a windowed portion 141 on one side in the Z direction.

[0056] The flexible circuit board 10 is a multi-layer circuit board, and the flexible circuit board 10 includes a plurality of sub-boards stacked together. The sub-boards can be flexible copper clad laminates (FCCL), copper foils, etc. The flexible copper clad laminate refers to a copper clad laminate formed by bonding a copper foil to a single side 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 of the 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 insulating strength and mechanical properties. The adhesive layer 14 can be a pure adhesive layer, and the material thereof includes epoxy resin. 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 windowed portion 141. As shown in Fig. 2, in some embodiments, the signal line 1311 and the first outer metal layer 11, and the signal line 1311 and the second outer metal layer 12 are both provided with air layers. In other embodiments, the air layer can be provided on only one side of the signal line 1311.

[0059] The windowed portion 141 is a hollowed-out area penetrating through the adhesive layer 14, and the windowed portion 141 can be made by drilling, photolithography, etc. The flexible circuit board 10 forms an air layer at the position of the windowed portion 141, i.e., the flexible circuit board 10 forms a suspended layered structure at the windowed portion of the adhesive layer 14. The dielectric loss (Dissipation Factor, Df) value of air is the lowest, slightly equal to 0; the Df value of the existing insulating medium layer in the FPC industry is usually between 0.006 and 0.001, and therefore, by adding an air layer in the medium layer between the signal line 1311 and the reference layer, the Df value of the entire medium layer can be reduced, and the smaller the Df value is, the smaller the signal loss is.

[0060] The embodiment of the present application sets the windowing part 141 in the glue layer 14, can form an air layer at the position of the windowing part 141, 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 that the length of the signal line 1311 is relatively long, if the signal loss of the signal line 1311 is relatively large, it may cause that the transmission rate of the signal line 1311 cannot meet the use requirement. In the embodiment of the present application, the windowing part 141 in the glue layer 14 reduces the signal loss of the signal line 1311, and the flexible circuit board 10 provided by the embodiment of the present application solves the problem that the transmission rate cannot meet the use requirement caused by the too long signal line, and improves the replaceability of the flexible circuit board 10.

[0061] Please refer to FIG. 1. In some embodiments, the flexible circuit board 10 is provided with a ground hole 101 penetrating the ground line 1312 and the non-windowing part 142. The ground hole 101 connects the first outer metal layer 11 and the second outer metal layer 12.

[0062] The ground hole 101 is arranged on the ground line 1312 and penetrates the non-windowing part 142 of the glue layer 14. The windowing part 141 is not provided with the ground hole 101. The ground hole 101 connects the first outer metal layer 11 and the second outer metal layer 12, that is, the ground hole 101 is used to connect the reference layers on both sides of the signal line 1311. The ground hole 101 is arranged on the ground line 1312 in the non-windowing area. According to the length of the non-windowing part 142 and the line width of the corresponding ground line 1312, at least one ground hole 101 is designed. It can be understood that, in order to improve the isolation effect in the vertical direction (Z direction) of the flexible circuit board 10, the ground hole 101 can be provided with multiple ground holes.

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

[0064] By arranging 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. The non-windowing part 142 is reserved in the glue layer 14 to facilitate the manufacture of the ground hole 101.

[0065] Please refer to FIG. 3 and FIG. 4. In some embodiments, at least part of the signal line 1311 extends along a first direction, and the first direction is perpendicular to the thickness direction of the flexible circuit board 10. Along the first direction, the glue layer 14 includes a plurality of windowing parts 141 and a plurality of non-windowing parts 142 arranged alternately.

[0066] Specifically, the non-windowing part 142 is provided with one or more ground holes 101, and the signal line 1311 crosses the plurality of windowing parts 141 and the plurality of non-windowing parts 142.

[0067] The first direction can be a length direction of the flexible circuit board 10, and in this embodiment, the first direction is the X direction. The signal lines 1311 can extend partially or entirely along the first direction, and multiple groups of the signal lines 1311 are arranged side by side.

[0068] Along the first direction, the adhesive layer 14 includes multiple windowed portions 141 and multiple non-windowed portions 142 arranged alternately, the windowed portions are designed in a "string-string" manner (i.e., sectional windowing); one or more non-windowed portions 142 are provided with ground holes 101, and the number of the ground holes 101 on each non-windowed portion 142 can be one or more.

[0069] By adopting the above technical solution, the adhesive layer 14 is provided with multiple windowed portions 141 in the extension direction of the signal lines 1311, so as to form an air layer on one side of the signal lines 1311, effectively reducing the signal loss of the signal lines 1311 and improving the transmission rate of the signal lines 1311; at the same time, the non-windowed portions 142 can be provided with the ground holes 101, the first outer metal layer 11 and the second outer metal layer 12 are conducted through the ground holes 101, and a good shielding and isolation crosstalk effect is maintained.

[0070] In some embodiments, the windowed portions 141 extend to opposite ends of the flexible circuit board 10 along a second direction, and the second direction intersects the first direction.

[0071] As shown in FIGS. 3 and 4, the second direction is the Y direction in the figure, and the second direction can be a width direction of the flexible circuit board 10. The windowed portions 141 extend to opposite ends of the flexible circuit board 10 along the second direction Y, that is, the windowed portions 141 penetrate through the flexible circuit board 10 along the second direction Y, forming an air layer in communication with the outside, the inner metal layer 13 where the signal lines 1311 are located is arranged separately from the reference layer at the position of the windowed portions 141, and there is an air layer between the signal lines 1311 and the reference layer, and the inner metal layer 13 where the signal lines 1311 are located is adhesively connected to the reference layer at the position of the non-windowed portions 142 through the non-windowed portions 142.

[0072] By adopting the above technical solution, the windowed portions 141 of the adhesive layer 14 form an air layer penetrating through opposite ends of the flexible circuit board 10, so that the flexible circuit board 10 forms a suspended laminated structure in the region corresponding to the windowed portions 141, further reducing the signal loss and improving the transmission rate of the signal lines 1311.

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

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

[0075] In some embodiments, the minimum length of the windowed portion 141 depends on the windowing capability of the flexible circuit board 10, and the length of the windowed portion 141 is less than 1 / 4 of the wavelength of the operating frequency of the signal line 1311. Alternatively, the wavelengths of the operating frequencies of different signal lines 1311 can be different, and the length of the windowed portion 141 is calculated according to the signal line 1311 with the highest transmission rate and / or the highest application frequency domain. In this way, no obvious resonance is formed at the windowed 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 application; the operating frequency of the signal line 1311 is the upper limit of the application frequency domain of the signal line 1311. The highest application frequency domain means the highest operating frequency of the signal line 1311.

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

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

[0078] The windowed portion 141 is the part of the adhesive layer 14 that is cut, and no metallized ground hole 101 can be provided at this part. If there is no ground hole 101 around the high-speed signal line for a long distance in the first direction X, the high-speed signal line will be affected by crosstalk and resonance. This distance is 1 / 4 of the wavelength of the operating frequency of the signal line 1311. By setting the distance D1 between the two ground holes 101 on both sides of the windowed portion 141 to be less than 1 / 4 λ, no obvious resonance is formed at the windowed portion 141, and signal crosstalk is reduced.

[0079] In some embodiments, there are two groups 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 windowed portion 141 can be set according to the signal line 1311 with the highest transmission rate and / or the highest application frequency domain. That is, there are two groups of signal lines 1311 adjacent to the ground line 1312 on both sides of the ground line 1312, one group of signal lines 1311 has a higher transmission rate and / or a higher application frequency domain, and the wavelength of the operating frequency of this group of signal lines 1311 is λ, and D1 < 1 / 4 λ.

[0080] Referring to FIGS. 3 and 4, in 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 between the two groups of adjacent signal lines 1311 can isolate and shield the two groups of signal lines 1311, and the ground line 1312 is provided with a ground hole 101 in the area corresponding to the non-windowed part 142.

[0082] Optionally, the width of the ground line 1312 is greater than or equal to the sum of 3 times the diameter of the ground hole 101 and the offset tolerance when the ground hole 101 is drilled.

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

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

[0085] Differential transmission is a signal transmission technology that differs from the traditional method of one signal line and one ground line. Differential transmission transmits signals on both lines, and the amplitudes of the two signals are the same and the phases are opposite. The transmitted signals on the two lines are differential signals. Differential traces are two lines that are equal in length, width, closely adjacent, and on the same plane. The signal lines 1311 in the flexible circuit board 10 use differential signal lines 1311, which have the advantages of strong anti-interference ability and effective consistent electromagnetic interference, and the flexible circuit board 10 can replace traditional high-speed cables.

[0086] One group of differential signal lines is provided with one ground line 1312 on each side, i.e., the first differential trace 1311a is adjacent to one ground line 1312, and the distance between the first differential trace 1311a and the ground line 1312 is D2; the second differential trace 1311b is adjacent to another ground line 1312, and the distance between the second differential trace 1311b and the ground line 1312 is also D2; the center distance between the center lines of the first differential trace 1311a and the second differential trace 1311b is D3, wherein D2>D3.

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

[0088] Optionally, the signal lines 1311 can also be other types, for example, the signal lines 1311 can also be single-ended signal lines.

[0089] Referring to FIG. 1, FIG. 3 and FIG. 5, in some embodiments, the first end and the tail end of each signal line 1311 are respectively provided with a first connecting part 13111, and the plurality of first connecting parts 13111 are sequentially arranged; the first outer metal layer 11 is provided with a plurality of second connecting parts 111, and the plurality of second connecting parts 111 are electrically connected to the plurality of first connecting parts 13111 one by one.

[0090] The first end and the tail end of the signal line 1311 refer to the opposite ends of the signal line 1311 along the extension direction thereof. As shown in FIG. 3, the first connecting parts 13111 of the first ends of the plurality of groups of signal lines 1311 are sequentially arranged on one side of the first direction X, and the first connecting parts 13111 of the tail ends of the plurality of groups of signal lines 1311 are sequentially arranged on the other side of the first direction X. In this way, the first connecting parts 13111 of the plurality of groups of signal lines 1311 are sequentially arranged at the first ends and the tail ends respectively, and the flexible circuit board 10 can replace a plurality of high-speed cables adjacent to a socket or a port.

[0091] In some embodiments, the first outer metal layer 11 is provided with a plurality of second connecting parts 111, each second connecting part 111 is connected to a corresponding first connecting part 13111, and the second connecting part 111 is used to connect a component or device outside the flexible circuit board 10.

[0092] Optionally, the second outer metal layer 12 can also be provided with a second connecting part 111 connected to the first connecting part 13111.

[0093] Since the signal line 1311 is located in the inner layer of the flexible circuit board 10, by arranging the second connecting part 111 corresponding to the signal line 1311 on the first outer metal layer 11, the signal line 1311 can be conveniently electrically connected to the component or device outside through the second connecting part 111, so as to transmit signals by using the signal line 1311.

[0094] In some embodiments, the second connecting part 111 is a gold finger.

[0095] The gold finger is a contact sheet arranged in the shape of a finger. Optionally, the gold finger is a contact sheet subjected to surface treatment, and the surface treatment uses a treatment method of nickel-palladium-gold or hard gold to enhance the wear resistance and plug resistance of the gold finger. The first connecting part 13111 and the second connecting part 111 are electrically connected through a via hole 102, and the via hole 102 is a metalized hole.

[0096] By using the above technical solution, the flexible circuit board 10 can be plugged into the component or device outside by using the sequentially arranged gold fingers, the gold finger can replace the high-speed connector of the traditional high-speed cable, and the signal loss caused by the welding between the connector and the flexible circuit board 10 is reduced; the structure of the gold finger is simple, occupies small space and has low manufacturing cost.

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

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

[0099] The thickness of the reinforcing member 17 can be greater than 0.1 mm. By attaching the reinforcing member 17 to the back of the second outer metal layer 12, the reinforcing member 17 can provide support to other components of the flexible circuit board 10, so that the end of the flexible circuit board 10 can be directly plugged in for use, and the reliability is good.

[0100] In other embodiments, the second connecting part 111 can also be a solder pad or other connecting component.

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

[0102] The flexible circuit board 10 can comprise a plurality of laminated flexible copper-clad plates, and the insulating medium layer in the flexible copper-clad plate is formed into the insulating layer 15 in the flexible circuit board 10. It can be understood that the insulating layer 15 can 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 index for measuring the energy loss of dielectric materials. The lower the Df, the better the integrity of the signal transmission in the medium. By using the above technical solutions, low-loss materials are selected as the insulating layer 15 when selecting materials, which can reduce the transmission loss of the signal lines 1311 and is beneficial to improve the transmission rate of the flexible circuit board 10.

[0104] In some embodiments, the first outer metal layer 11 and the second outer metal layer 12 respectively comprise a whole copper sheet, which covers a plurality of groups of signal lines 1311 and a plurality of ground lines 1312.

[0105] Further, in some embodiments, the first outer metal layer 11 further comprises a GND line, which is arranged between the gold fingers corresponding to the adjacent signal lines 1311, and is connected to the copper sheet.

[0106] In this way, the flexible circuit board 10 uses full copper to shield and isolate the signal lines 1311 on the top and bottom sides of the corresponding signal lines 1311, 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 outer layer lines, and the outer layer lines include a plurality of reference ground lines, each of which is arranged corresponding to the signal line 1311 to play a shielding role.

[0108] Referring to FIGS. 1-5, some embodiments of the present application provide a flexible circuit board 10, which includes a plurality of metal layers and a plurality of insulating layers 15 stacked and arranged alternately, the plurality of metal layers including 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 groups of signal lines 1311 and ground lines 1312 arranged 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 of the signal lines 1311. At least one side of the signal line 1311 is provided with a glue layer 14, and the glue layer 14 is provided with a windowed portion 141 and a non-windowed portion 142, the windowed portion 141 and the non-windowed portion 142 being 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 windowed portion 141. The flexible circuit board 10 is provided with a ground hole 101, the ground hole 101 penetrating the ground line 1312 and the non-windowed portion 142, and the ground hole 101 connecting the first outer metal layer 11 and the second outer metal layer 12.

[0109] The flexible circuit board 10 can further include a plurality of cover films 16, the cover films 16 covering the inner metal layer 13, the first outer metal layer 11, and the second outer metal layer 12 respectively, for protecting the lines.

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

[0111] Referring to FIGS. 1-6, the embodiments of the second aspect of the present application provide a manufacturing method of a flexible circuit board 10, for manufacturing the flexible circuit board 10 provided by the first aspect, and the manufacturing method of the flexible circuit board 10 includes:

[0112] Step S1: providing a first sub-board, and manufacturing inner layer lines 131 on the first sub-board, the inner layer lines 131 including a plurality of groups 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, the ground lines 1312 are arranged on both sides of each group of signal lines 1311.

[0114] As shown in FIG. 1, taking the example of a flexible circuit board 10 including three layers of metal layers for illustration. Specifically, step S1 includes cutting, drilling, black shadow, copper plating, inner layer circuit manufacturing, and pasting the inner layer covering film 16.

[0115] The cutting refers to providing a first sub-board, the first sub-board including a dielectric layer and a copper layer disposed on at least one side of the dielectric layer, the dielectric layer being used to form an insulating layer 15 in the flexible circuit board 10, and the copper layer being 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 the first sub-board 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 layer metal layers, or the copper layer on one side can be used as an inner layer metal layer, and the copper layer on the other side can be used as an outer layer metal layer. The drilling refers to processing inner layer vias / tooling holes and the like by mechanical drilling, laser processing, or the like. The black shadow refers to pre-treatment of hole metallization. The copper plating refers to hole metallization. The pasting of the inner layer covering film 16 refers to the use of the covering film 16 to protect the signal lines 1311 and the ground lines 1312.

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

[0117] The flexible circuit board 10 is provided with a first outer layer metal layer 11 and a second outer layer metal layer 12 on opposite sides thereof along the thickness direction, and the inner layer circuit 131 is located between the first outer layer metal layer 11 and the second outer layer metal layer 12. The first outer layer metal layer 11 and the second outer layer metal layer 12 serve as reference layers of the signal lines 1311 and are used to provide a signal reflow path.

[0118] Specifically, in step S2, one or more second sub-boards are provided, and the first sub-board and the second sub-boards 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 flexible copper-clad boards, copper foils, or the like, and the number of the first sub-board and the second sub-board can be set according to requirements. The metal layers on the sub-boards located at the two ends of the flexible circuit board 10 and on the outermost sides thereof serve as the first outer layer metal layer 11 and the second outer layer metal layer 12. Specifically, the first sub-board is a single-sided copper-clad board, the metal layer on the first sub-board is an inner layer metal layer, and the two second sub-boards are single-sided copper-clad boards or double-sided copper-clad boards. The two second sub-boards are respectively stacked on opposite sides of the first sub-board, and the outer copper layers on the two second sub-boards respectively serve as the first outer layer metal layer 11 and the second outer layer metal layer 12.

[0119] Specifically, step S2 includes pasting outer layer sub-boards (e.g., FCCL layers), outer layer drilling, plasma cleaning, black shadow, outer layer copper plating, outer layer circuit manufacturing, and pasting outer layer covering films 16. The outer layer drilling refers to manufacturing interlayer vias 102 by mechanical drilling, laser processing holes, or the like. The plasma cleaning refers to cleaning impurities in the holes.

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

[0121] In some embodiments, the step S2 of stacking and pressing the first sub-board and the at least one second sub-board comprises: providing the adhesive layer 14, manufacturing the windowed portions 141 in the adhesive layer 14, and forming the remaining portions of the adhesive layer 14 into non-windowed portions 142; and stacking and pressing the first sub-board and the at least one second sub-board with the at least one adhesive layer 14, the adhesive layer 14 being arranged on one side of the signal lines 1311 close to the first outer layer metal layer 11 and / or on one side of the signal lines 1311 close to the second outer layer metal layer 12; and wherein the projection of the windowed portions 141 on the inner layer lines 131 covers the plurality of groups of signal lines 1311.

[0122] The adhesive layer 14 is used to bond adjacent sub-boards. The adhesive layer 14 can be a pure adhesive sheet, but is not limited thereto. Specifically, after the adhesive layer 14 is provided, a plurality of windowed portions 141 are manufactured on the adhesive layer 14 by drilling or the like, and the remaining portions of the adhesive layer 14 are formed into non-windowed portions 142.

[0123] When stacking the sub-boards, the adhesive layer 14 is arranged between adjacent sub-boards, and the adhesive layer 14 can be arranged on one side or opposite sides of the signal lines 1311. After pressing, the plurality of sub-boards and the adhesive layer 14 form the flexible circuit board 10. The windowed portions 141 and the non-windowed portions 142 are distributed along the extension direction of the signal lines 1311, and the flexible circuit board 10 forms an air layer at the positions of the windowed portions 141.

[0124] In some embodiments, at least part of the signal lines 1311 extends along the first direction X; along the first direction X, the adhesive layer 14 alternately has a plurality of windowed portions 141 and a plurality of non-windowed portions 142, and the signal lines 1311 cross the plurality of windowed portions 141 and the plurality of non-windowed portions 142.

[0125] By adopting the above technical scheme, the window part 141 is arranged in the adhesive layer 14, and after the laminating and pressing, the air layer is formed in the flexible circuit board 10 corresponding to the position of the window part 141, the signal loss of the signal line 1311 is effectively reduced, and the signal transmission rate and signal transmission quality are improved.

[0126] In some embodiments, in the step of making the window part 141 in the adhesive layer 14, the width of the window part 141 is at least 1 mm larger than the preset outline width of the flexible circuit board 10. After the pressing step, the manufacturing method further comprises: performing outline cutting on the flexible circuit board 10 according to the preset outline width.

[0127] The preset outline width of the flexible circuit board 10 refers to the finished product width of the flexible circuit board 10 after cutting or outline punching. In this way, after the outline cutting of the flexible circuit board 10, the window part 141 can penetrate through the opposite ends of the flexible circuit board 10, the position of the window part 141 forms an air layer, the Df value of the air layer is small, and the transmission loss of the signal line 1311 can be reduced.

[0128] In some embodiments, after step S2, the manufacturing method further comprises: making a through ground wire 1312 and a ground hole 101 in the flexible circuit board 10, the ground hole 101 being conductive to the first outer metal layer 11 and the second outer metal layer 12.

[0129] Specifically, after laminating and pressing, the ground hole 101 and other interlayer through holes are made by mechanical drilling, laser processing holes and the like. In some embodiments, the ground hole 101 is a metallized through hole penetrating through 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 arranging the ground hole 101 in the flexible circuit board 10, the shielding and isolation crosstalk effect of the signal line 1311 in the vertical direction can be improved.

[0131] In some embodiments, the step of making the inner layer circuit 131 on the first sub-board further comprises: arranging a first connecting part 13111 at the head end and tail end of the signal line 1311 respectively, and sequentially arranging a plurality of first connecting parts 1311; after laminating and pressing the first sub-board and at least one second sub-board, the manufacturing method further comprises: arranging a plurality of second connecting parts 111 on the first outer metal layer 11, and electrically connecting the plurality of second connecting parts 111 with the plurality of first connecting parts 13111 one by one; and performing surface treatment on the second connecting part 111.

[0132] The step of manufacturing the outer layer circuit includes: arranging a plurality of second connecting parts 111, i.e. manufacturing a plurality of second connecting parts 111 at the end of the first outer layer metal layer 11, and electrically connecting the plurality of second connecting parts 111 with the first connecting parts 13111 of the plurality of signal lines 1311 in one-to-one correspondence; and then performing surface treatment on the second connecting parts 111.

[0133] In the above technical solution, the first connecting parts 13111 of the plurality of groups of signal lines 1311 are sequentially arranged on one side of the first direction X, and the first connecting parts 13111 of the plurality of groups of signal lines 1311 are sequentially arranged on the other side of the first direction X. In this way, the first connecting parts 13111 of the plurality of groups of signal lines 1311 are sequentially arranged, and the flexible circuit board 10 can design a plurality of high-speed cables adjacent to the socket on the same flexible circuit board 10. The plurality of second connecting parts 111 are arranged on the first outer layer metal layer 11, and each second connecting part 111 is connected to a corresponding first connecting part 13111, so that the second connecting part 111 can be connected to a component outside the flexible circuit board 10, and the signal line 1311 is electrically connected to the component outside the flexible circuit board 10.

[0134] Optionally, the second connecting part 111 is a gold finger. The surface treatment of the second connecting part 111 can be nickel-palladium-gold or hard gold treatment, which can enhance the wear resistance and plug-in resistance of the gold finger. In other embodiments, the second connecting part 111 can also be a solder pad or other connecting part.

[0135] By using the above technical solution, since the signal line 1311 is located in the inner layer of the flexible circuit board 10, the second connecting part 111 corresponding to the signal line 1311 is manufactured on the first outer layer metal layer 11, so that the signal line 1311 can be electrically connected to the component outside the flexible circuit board 10 through the second connecting part 111, and the signal line 1311 can be used to transmit signals. The flexible circuit board 10 can be connected to the component outside the flexible circuit board 10 by using the sequentially arranged second connecting part 111, and the signal loss caused by the welding between the connector and the flexible circuit board 10 is reduced.

[0136] In some embodiments, the second connecting part 111 is a gold finger, and after the surface treatment of the second connecting part 111, the manufacturing method further includes: attaching a reinforcing part 17 to the part of the back surface of the second outer layer metal layer 12 opposite to the gold finger.

[0137] In this way, the gold finger can be directly connected to the external device for plugging and connecting, the reinforcing part 17 provides support for the flexible circuit board 10, so that the end of the flexible circuit board 10 can be directly plugged and used, the reliability is good, and the signal loss is small.

[0138] Please refer to FIGS. 1-6, and the following will take the flexible circuit board 10 shown in FIG. 1 as an example to explain the design and manufacturing process of the flexible circuit board 10.

[0139] In the design stage, the schematic diagram of the cable is evaluated, aiming to design a high-frequency multi-layer flexible circuit board to replace multiple high-speed cables, convert the electrical performance of the high-speed cable into a signal line 131 on the flexible circuit board, and under certain wiring space conditions, convert multiple pairs of high-speed cables with similar ports into signal lines and design them into one flexible circuit board 10.

[0140] The flexible circuit board 10 is designed as a 3-layer or more multi-layer circuit board, the high-speed signal line runs in the inner layer, and the top layer and the bottom layer are reference layers for shielding and isolation; the wiring 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 material of the insulating layer.

[0141] In the manufacturing stage, the flexible circuit board 10 is manufactured according to the design process and circuit data, including: cutting, drilling, black shadow, copper plating, inner layer circuit manufacturing, attaching and pressing the inner layer cover film 16, cleaning, attaching and pressing the outer layer FCCL board, outer layer drilling, plasma cleaning, black shadow, outer layer copper plating, outer layer circuit manufacturing, attaching and pressing the outer layer cover film 16, surface treatment of the outer layer pad / gold finger, shape punching or cutting (FPC forming cutting), post-process; then, check that the delamination area is completely delaminated, perform functional testing and signal line testing, and if the tested signal meets the quality requirements, proceed with mass production.

[0142] Before attaching and pressing the outer layer FCCL board, the adhesive layer 14 is pre-windowed, and the outer layer reference ground layer is attached and pressed together in this process; after shape punching or cutting, the position of the windowed part 141 can form a suspended delamination structure.

[0143] After shape punching, check that the delamination area is completely delaminated, perform functional testing and signal line testing, and if the tested signal meets the quality requirements, proceed with mass production.

[0144] As an example, the flexible circuit board 10 shown in FIG. 1 includes three metal layers, and the manufacturing method of the flexible circuit board includes: providing a single-sided copper-clad FCCL board (i.e., an inner layer FCCL board), manufacturing an inner layer circuit 131 on the FCCL board, and attaching and pressing a cover film 16 on the inner layer circuit 131; then, sequentially stacking and pressing the outer layer FCCL board, the adhesive layer 14, the inner layer FCCL board, the adhesive layer 14, and the outer layer FCCL board; then, perform outer layer drilling, outer layer circuit manufacturing, and attaching and pressing the outer layer cover film 16.

[0145] Please refer to FIGS. 1-7, the embodiment of the third aspect of the application provides a communication device 100, which includes the flexible circuit board 10 provided by the first aspect or the flexible circuit board 10 manufactured by the manufacturing method provided by the second aspect. The communication device 100 further includes a first device 20 and a second device 30, and the first device 20 and the second device 30 are connected by 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 by the embodiments of the present application can connect the first device 20 and the second device 30 by using the flexible circuit board 10. The flexible circuit board 10 replaces the high-speed cable, saves the installation space, and is conducive to miniaturization of the communication device 100. The flexible circuit board 10 has good shielding effect and small signal loss, and can realize high-speed, low-delay, and high-reliability data transmission.

[0148] The flexible circuit board 10 provided by the embodiments of the present application improves the transmission quality through the superposition design and the circuit design, and can adapt to the transmission requirements of signals in the communication device 100.

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

[0150] The first device 20 and the second device 30 each include a circuit board. The two 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 part 111, so that the flexible circuit board 10 can directly connect the two circuit boards, without the need to set a traditional connector, thereby saving the installation space in the box and reducing the signal loss caused by welding of the connector and the flexible circuit board 10.

[0151] The above is only an optional embodiment of the present application and is not used to limit the present application. The present application can have various changes and modifications for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of claims of the present application.

Claims

1. A flexible circuit board, characterized in that: the flexible circuit board 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 both sides of the signal lines, the first outer metal layer and the second outer metal layer serving as reference layers of the signal lines to provide a reflow path.

2. The flexible circuit board of claim 1, wherein: the flexible circuit board further comprises an adhesive layer arranged on at least one side of the signal lines along the thickness direction of the flexible circuit board; a part of the adhesive layer is hollowed out to form a windowed portion, and a region of the adhesive layer not hollowed out is a non-windowed portion, and a projection of the windowed portion on the inner metal layer covers a plurality of groups of the signal lines.

3. The flexible circuit board of claim 2, wherein: the flexible circuit board is provided with a ground hole penetrating through the ground lines and the non-windowed portion, and the ground hole electrically connects the first outer metal layer, the ground lines, and the second outer metal layer.

4. The flexible circuit board of claim 3, wherein: at least part of the signal lines extends along a first direction perpendicular to the thickness direction of the flexible circuit board; along the first direction, the adhesive layer comprises a plurality of windowed portions and a plurality of non-windowed portions arranged alternately.

5. The flexible circuit board of claim 4, wherein: the windowed portion penetrates through the flexible circuit board along a second direction intersecting the first direction and perpendicular to the thickness direction of the flexible circuit board.

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

7. The flexible circuit board of claim 3, wherein: 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 of any one of claims 1-7, wherein: at least one group of the signal lines is a differential signal line, and the differential signal line comprises a first differential trace and a second differential trace; the distance between the differential signal line and the ground line adjacent to the differential signal line is D2, and the center distance between the first differential trace and the second differential trace is D3, wherein D2 > D3. 9.The flexible circuit board of any one of claims 1-7, characterized in that: a first connection portion is arranged at the head end and the tail end of each signal line, and a plurality of first connection portions are arranged in sequence; a plurality of second connection portions are arranged on the first outer metal layer, and each of the plurality of second connection portions is electrically connected to one of the plurality of first connection portions one by one.

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

11. The flexible circuit board of any one of claims 1-7, wherein: a whole copper sheet is arranged in the first outer metal layer and the second outer metal layer, and the whole copper sheet covers a plurality of groups of the signal lines and a plurality of ground lines.

12. A method of manufacturing a flexible circuit board, characterized by, including: providing a first sub-board, and manufacturing an inner layer circuit on the first sub-board, the inner layer circuit comprising a plurality of groups of signal lines and a plurality of ground lines, and the ground lines being arranged on both sides of each group of the signal lines; stacking and pressing the first sub-board and at least one second sub-board to form a flexible circuit board. The flexible circuit board is provided with a first outer metal layer and a second outer metal layer on opposite sides along the thickness direction of the flexible circuit board, and 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 of the signal lines and provide a backflow path.

13. The method of claim 12, wherein: The stacking and pressing of the first sub-board and the at least one second sub-board comprises: At least one adhesive layer is provided, and a window part is formed in the adhesive layer, and the remaining part of the adhesive layer is formed as a non-window part; The first sub-board and the at least one second sub-board are stacked and pressed with the at least one adhesive layer, and the adhesive layer is arranged on the side of the signal line close to the first outer metal layer and / or the adhesive layer is arranged on the side of the signal line close to the second outer metal layer; The projection of the window part on the inner layer circuit covers a plurality of groups of the signal lines.

14. A communication device, characterized by The application further provides a device comprising a first device, a second device and a flexible circuit board, wherein the first device and the second device are connected by the flexible circuit board, and the flexible circuit board is the flexible circuit board according to any one of claims 1-11 or is the flexible circuit board manufactured by the manufacturing method of the flexible circuit board according to any one of claims 12-13.

15. The communication device of claim 14, wherein The first device and the second device are electrically connected with the second connection part on the flexible circuit board.

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