FPC board, transmission line and electronic equipment

Abstract

The FPC board at least comprises an insulating base material, a first signal layer and a second signal layer, the insulating base material is located between the first signal layer and the second signal layer, the first signal layer is provided with a radio frequency line and a first reference ground plane arranged at a preset gap between the two sides of the radio frequency line, and the second signal layer is provided with a second reference ground plane arranged at a preset gap between the two sides of the radio frequency line. The second signal layer is provided with a second reference ground plane, the first reference ground planes on the two sides are connected with the second reference ground plane through via holes respectively, and at least one hollowed-out area is arranged in the second reference ground plane. The embodiment of the invention also provides a transmission line and electronic equipment.

Description

Technical Field

[0001] The present application relates to a device connection technology, and in particular to an FPC board, a transmission line and an electronic device. Background Art

[0002] Flexible Printed Circuit (FPC), also known as flexible circuit board, soft circuit board, flexible circuit board, soft board, is a special printed circuit board that is light, thin, soft and bendable. It is currently mainly used in mobile phones, laptops, personal digital assistants (PDA), digital cameras, LCD screens and other products.

[0003] The thickness of mobile phone terminals is getting smaller and smaller, and "thinness" is the goal pursued by many mobile phones. In order to achieve this goal, many mobile phones adopt a discrete printed circuit board (PCB) board design, that is, two PCB boards are located at both ends of the mobile phone, which can be a main board and a small board. The main board refers to one of them, which usually has a radio frequency module on it, and the small board refers to the other one, which has some simple connections and matching circuits on it. The antenna is usually contained above the small board. A coaxial line with a very thin diameter connects the small board and the main board to guide the radio frequency signal from the main board to the small board. The smaller the diameter of the coaxial line, the greater the loss per unit length. However, because the spatial integration of mobile phones is getting higher and higher, it is required to use a coaxial line with the smallest possible diameter. However, a small diameter coaxial line is exactly contradictory to reducing losses. How to reduce the space occupied by this section of coaxial line as much as possible without increasing losses is the challenge we face.

[0004] In the related art, modified polyimide (MPI) or polyimide (PI) is used as a substrate and a microstrip line structure is used to achieve a low insertion loss and bendable routing design. However, the routing design still has a large insertion loss. It can be seen that the existing microstrip line structure routing design as a transmission line has a technical problem of large insertion loss when ensuring a certain thickness of the RF line. Summary of the invention

[0005] The embodiments of the present application provide an FPC board, a transmission line and an electronic device, which can reduce the insertion loss of the FPC board wiring while ensuring a certain thickness of the radio frequency line.

[0006] The technical solution of this application is implemented as follows:

[0007] The embodiment of the present application provides a method comprising at least: an insulating substrate, a first signal layer and a second signal layer, wherein the insulating substrate is located between the first signal layer and the second signal layer;

[0008] The first signal layer is provided with a radio frequency line and a first reference ground plane at two sides of the radio frequency line separated by a preset gap;

[0009] The second signal layer is provided with a second reference ground plane;

[0010] The first reference ground planes on both sides are connected to the second reference ground plane through vias respectively, and at least one hollowed-out area is provided in the second reference ground plane.

[0011] An embodiment of the present application provides a transmission line, comprising the FPC board described in one or more embodiments.

[0012] An embodiment of the present application provides an electronic device, including: a first device and a second device of the electronic device adopt the FPC board described in one or more embodiments.

[0013] The embodiment of the present application provides an FPC board, a transmission line and an electronic device, which at least include: an insulating substrate, a first signal layer and a second signal layer, the insulating substrate is located between the first signal layer and the second signal layer, the first signal layer is provided with a radio frequency line and a first reference ground plane at a preset gap on both sides of the radio frequency line, the second signal layer is provided with a second reference ground plane, the first reference ground planes on both sides are respectively connected to the second reference ground plane through vias, and at least one hollowed-out area is provided in the second reference ground plane; that is, in the embodiment of the present application, the radio frequency line and the first reference ground plane at a preset gap from the radio frequency line are provided on the first signal layer on one side of the insulating substrate, and the impedance of the radio frequency line can be adjusted by the line width and the preset gap of the radio frequency line when the thickness of the radio frequency line is constant, and the second reference ground plane including at least one hollowed-out area is provided on the second signal layer on the other side of the insulating substrate, and the first reference ground planes on both sides are respectively connected to the second reference ground plane through vias, so that the routing design of the FPC is formed, wherein the impedance and insertion loss of the radio frequency line can be adjusted and the return loss of the radio frequency line in the FPC board can be reduced through the hollowed-out area, so that the thickness of the FPC is ensured to be constant while reducing the insertion loss of the routing of the FPC board. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of an FPC laminate structure of a microstrip line on an MPI substrate in the related art;

[0015] Figure 2a FPC design for FPC laminated structure of MPI substrate microstrip line in related technology Figure 1 ;

[0016] Figure 2b The second FPC design diagram of the FPC laminate structure of the MPI substrate microstrip line in the related art;

[0017] Figure 2c FPC design for FPC laminated structure of MPI substrate microstrip line in related technology Figure 3 ;

[0018] Figure 3 It is a 3D structural schematic diagram of the FPC laminate structure of the MPI substrate microstrip line in the related art;

[0019] Figure 4 It is a simulation schematic diagram of the insertion loss of the radio frequency line in the FPC laminate structure of the MPI substrate microstrip line in the related art;

[0020] Figure 5 It is a simulation schematic diagram of the insertion loss of the radio frequency line in the FPC laminate structure of the PI substrate microstrip line in the related art;

[0021] Figure 6 A schematic diagram of the structure of an optional FPC board provided in an embodiment of the present application;

[0022] Figure 7 A simulation diagram of an optional radio frequency line in an FPC board provided in an embodiment of the present application Figure 1 ;

[0023] Figure 8 A second simulation schematic diagram of a radio frequency line in an optional FPC board provided in an embodiment of the present application;

[0024] Fig. 9 A simulation diagram of the insertion loss and return loss of a radio frequency line in an optional FPC board provided in an embodiment of the present application Figure 1 ;

[0025] Fig.10 A top view of an optional FPC board provided in an embodiment of the present application Figure 1 ;

[0026] Fig.11 A second top view of an optional FPC board provided in an embodiment of the present application;

[0027] Fig.12 A second simulation diagram of insertion loss and return loss of a radio frequency line in an optional FPC board provided in an embodiment of the present application;

[0028] Fig.13 A schematic diagram of simulation of impedance of a radio frequency line in an optional FPC board provided in an embodiment of the present application;

[0029] Fig.14A schematic diagram of the structure of an optional steel patching area provided in an embodiment of the present application;

[0030] Fig.15 A schematic diagram of the structure of an optional nearby grounding block provided in an embodiment of the present application;

[0031] Fig.16 A simulation diagram of the insertion loss and return loss of a radio frequency line in an optional FPC board provided in an embodiment of the present application Figure 3 ;

[0032] Fig.17 A schematic diagram of the structure of an optional transmission line provided in an embodiment of the present application;

[0033] Fig.18 A schematic diagram of the structure of an optional electronic device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0035] In related technologies, MPI is generally used as the insulating substrate, and a microstrip line structure is used to achieve low insertion loss and bendable routing design. Figure 1 FIG. 1 is a schematic diagram of an FPC laminate structure of a microstrip line on an MPI substrate in the related art. Figure 1 As shown, the FPC laminate structure is divided into three layers. The middle layer is an insulating substrate with MPI as insulation. The RF trace is located in the signal_1 layer, and the reference ground plane is located in the signal_2 layer. The RF trace and the reference ground plane are covered with a cover film (CoverLay, CVL) to protect the flexible board. The outermost layer is a simulated air environment (AIR). Generally, the thickness of the insulating substrate and the RF trace ranges from 10 to 50um.

[0036] Figure 2a FPC design for FPC laminated structure of MPI substrate microstrip line in related technology Figure 1 ,like Figure 2a As shown in the figure, there are RF traces (the area filled with diagonal lines in the middle) and reference ground planes (the areas filled with diagonal lines on both sides). Figure 2b The FPC design diagram 2 is an FPC laminate structure of an MPI substrate microstrip line in the related art, as shown in FIG. Figure 2b As shown, it is a microstrip line reference ground plane. Figure 2c FPC design for FPC laminated structure of MPI substrate microstrip line in related technology Figure 3 ,like Figure 2c As shown, the connection Figure 2a The reference ground plane in Figure 2b Vias (circles) in the reference ground plane.

[0037] Figure 3 3D schematic diagram of the FPC stacking structure of the MPI substrate microstrip line in the related art, such as Figure 3 As shown, it includes: RF routing, reference ground plane and vias.

[0038] Figure 4 FIG. 1 is a schematic diagram of the simulation of the insertion loss of the RF line in the FPC laminate structure of the MPI substrate microstrip line in the related art. Figure 4 As shown, when the thickness of the FPC is 0.15mm, the insertion loss of the RF line with a length of 73.2mm is: at 2.5GHz, the insertion loss is 0.947dB.

[0039] Figure 5 FIG. 1 is a simulation diagram of the insertion loss of the RF line in the FPC laminate structure of the PI substrate microstrip line in the related art, as shown in FIG. Figure 5 As shown, Figure 5 In comparison, if the middle insulating substrate uses low-cost PI, Figure 5 The insertion loss of the RF trace of the same thickness and length is 1.334dB in the 2.5G frequency band. It can be seen that the insertion loss of ordinary PI substrate is larger.

[0040] In related technologies, using thinner coaxial lines for RF transmission will result in excessive thickness and insertion loss, which does not meet the requirements of lightweight and foldable designs of mobile phone products.

[0041] In order to reduce the insertion loss of the radio frequency line while controlling the spatial thickness of the FPC board to a certain extent, the embodiment of the present application provides an FPC board, Figure 6 A schematic diagram of the structure of an optional FPC board provided in an embodiment of the present application is shown in FIG. Figure 6 As shown, the FPC board 600 at least includes: an insulating substrate 61, a first signal layer 62 and a second signal layer 63, wherein the insulating substrate 61 is located between the first signal layer 62 and the second signal layer 63;

[0042] The first signal layer 62 is provided with a radio frequency line 621 and a first reference ground plane 622 at two sides of the radio frequency line 621 with a preset gap therebetween;

[0043] The second signal layer 63 is provided with a second reference ground plane 631;

[0044] The first reference ground planes 622 on both sides are connected to the second reference ground plane 631 through vias 64 , respectively. At least one hollowed-out area 6311 is provided in the second reference ground plane 631 .

[0045] That is to say, in the embodiment of the present application, the FPC board 600 includes a first signal layer 62, an insulating substrate 61 and a second signal layer 63, an RF line 621 is arranged on the first signal layer 62, and a first reference ground plane 622 is arranged at a preset gap on both sides of the RF line 621, wherein the line width of the RF line 621 is represented by W, and the above-mentioned preset gap is represented by S. Here, the thickness of the RF line 621 can be set to a constant value, and then the impedance of the RF line 621 can be adjusted by adjusting the size of W and S.

[0046] Among them, a second reference ground plane 631 is arranged on the upper body of the above-mentioned second signal layer 63, and at least one hollow area 6311 is arranged in the second reference ground plane 131. In addition, the first reference ground planes 622 on both sides are connected to the second reference ground plane 631 through vias 64. Among them, at least one hollow area 6311 arranged in the second reference plane 631 can be used to adjust the impedance of the RF line 621, and can also be used to reduce the return loss of the RF line 621, thereby reducing the insertion loss of the RF line 621.

[0047] The first signal layer 62 and the second signal layer 63 may be covered with a cover film CVL, and the CVL is used to protect the flexible board.

[0048] Among them, the above-mentioned insulating substrate 61 includes any one of the following: MPI, PI; among them, MPI as the insulating substrate 61 generally makes the insertion loss of the RF line 621 larger, compared with MPI, PI as the insulating substrate 61 makes the insertion loss of the RF line 621 smaller.

[0049] In the embodiment of the present application, the impedance of the RF line 621 is adjusted by setting W and S, and the insertion loss of the RF line 621 can be reduced by at least one hollowed-out area 6311. In this way, even if PI is used as the insulating substrate 61, the insertion loss of the RF line 621 can be reduced when the thickness of the RF line 621 is constant.

[0050] It should be noted that the at least one hollow area 6311 may be one hollow area, two hollow areas, or more than two hollow areas, and the embodiment of the present application does not make any specific limitation on this.

[0051] Among them, by setting the position and size of each hollow area in at least one hollow area 6311, not only the return loss of the RF line is reduced, but also the flexibility of the FPC board is further increased.

[0052] That is to say, the impedance of the RF line 621 and the insertion loss of the RF line 621 that meet the requirements can be obtained through the above-mentioned arrangement of the RF line 621, the second reference ground plane 631 and the at least one hollowed-out area 6311, thereby reducing the insertion loss of the RF line 621 when the thickness of the FPC board 600 is constant.

[0053] In order to further reduce the insertion loss of the RF line 621 , in an optional embodiment, the impedance of the RF line 621 is adjusted by adjusting the line width and / or the preset gap of the RF line 621 .

[0054] Without considering the second signal layer, after determining the impedance required by the transmission system in which the RF line 621 is located, when the thickness of the RF line 621 is constant, the impedance of the RF line 621 can be determined by setting the line width and / or a preset gap of the RF line 621, wherein the determined impedance is generally greater than the impedance required by the transmission system in which the RF line 621 is located.

[0055] For example, the impedance required by the transmission system where the radio frequency line 621 is located is 50 ohms, and by setting appropriate values ​​of W and S, the determined impedance is 75 ohms.

[0056] Then, in order to make the determined impedance value meet the impedance value required by the transmission system, in an optional embodiment, the impedance of the RF line 621 is adjusted by adjusting the position of at least one hollow area 6311 and / or the size of at least one hollow area 6311.

[0057] It can be understood that the impedance of the RF line 621 can be obtained not only by setting appropriate W and S, but also by adjusting the position of at least one hollow area 6311 and / or the size of at least one hollow area 6311. Here, taking the determined impedance of 75 ohms as an example, adding at least one hollow area 6311 on the second reference ground plane 631 can reduce the impedance of the RF line 621. For example, a hollow area is set, the width of the hollow area is equal to the sum of W and 2S, and the position is set relative to W and 2S, and the length is the length of the RF line 621. After simulation, the impedance of the RF line 621 can be reduced to 66 ohms.

[0058] In this way, by providing at least one hollowed-out area 6311 , the impedance of the RF line 621 can be further made close to or equal to the impedance value required by the transmission system in which the RF line 621 is located, so as to meet the transmission requirements.

[0059] In addition, when at least one hollow area 6311 is not set on the second reference ground plane 631, the return loss of the RF line 621 is large, which in turn affects the insertion loss of the RF line 621. Here, in order to further reduce the return loss of the RF line 621, in an optional embodiment, the return loss of the RF line 621 is reduced by adjusting the position of at least one hollow area 6311 and / or the size of at least one hollow area 6311.

[0060] It can be understood that setting at least one hollow area 6311 in the second reference ground plane 631 can reduce the return loss of the RF line 621, and the number, position and size of at least one hollow area 6311 will affect the return loss of the RF line 621. Therefore, the return loss of the RF line 621 can be reduced by adjusting the position of at least one hollow area 6311 and / or the size of at least one hollow area 6311.

[0061] In this way, by setting at least one hollow area 6311 in the second reference ground plane 631, when the impedance of the RF line 621 meets the impedance required by the transmission system in which the RF line 621 is located, the return loss of the RF line 621 can be reduced, thereby reducing the insertion loss of the RF line 621.

[0062] For the at least one hollowed-out area 6311, in an optional embodiment, the width of the hollowed-out area is greater than or equal to the first width and less than or equal to the second width;

[0063] The first width is the sum of the two gaps and the line width of the RF line 621 ; the second width is greater than or equal to 5 times the line width of the RF line 621 ; and the second width is less than the width of the second reference ground plane 631 .

[0064] It can be understood that the width of each hollowed-out area in the at least one hollowed-out area 6311 is greater than or equal to the sum of the two gaps and the line width of the RF line 621, and less than or equal to 5 times the line width of the RF line 621, that is, the minimum width of the hollowed-out area is equal to the sum of 2S and W, and the maximum width is 5W, and 5W is smaller than the width of the second reference ground plane 631.

[0065] In this way, each hollow area is set so that at least one hollow area 6311 is set in the second reference ground plane 631, which can not only adjust the impedance of the RF line 621 when the thickness, line width and gap of the RF line 621 are constant, but also reduce the return loss of the RF line 621, thereby reducing the insertion loss of the RF line 621.

[0066] For the case where at least two hollowed-out areas are provided in the second reference ground plane 631, in an optional embodiment, at least two hollowed-out areas are provided on the second reference ground plane 631;

[0067] Among them, the interval length between two adjacent hollowed-out areas in at least two hollowed-out areas is greater than 0.

[0068] It can be understood that when the second reference ground plane 631 is provided with at least two hollowed-out areas, the interval length between two adjacent hollowed-out areas is greater than 0, that is, each hollowed-out area refers to an independent area that is not connected to other hollowed-out areas, and the hollowed-out areas are separated from each other by a grounding block in the second reference ground plane 631, and the grounding block is a part of the second reference ground plane 631 between two adjacent hollowed-out areas.

[0069] The grounding block can not only increase the flexibility of the FPC board 600, but also achieve the function of filtering the far-end frequency.

[0070] Through the independent and unconnected hollowed-out areas, not only can the impedance of the RF line 621 be adjusted when the thickness, line width and gap of the RF line 621 are constant, but also the return loss of the RF line 621 and the filtering effect on the far-end frequency can be reduced, thereby reducing the insertion loss of the RF line 621.

[0071] Further, for the case where at least three hollowed-out areas are provided in the second reference ground plane 631, in an optional embodiment, when the second reference ground plane 631 includes at least three hollowed-out areas, the interval lengths between adjacent hollowed-out areas are equal.

[0072] It can be understood that when at least three hollowed-out areas are provided in the second reference ground plane 631, the interval lengths between adjacent hollowed-out areas can be set to be equal. For example, there are three hollowed-out areas, each with a length of 2 mm, and the interval length between adjacent hollowed-out areas is 1 mm.

[0073] By setting equal interval lengths, not only can the impedance of the RF line 621 be adjusted when the thickness, line width and gap of the RF line 621 are constant, but the return loss of the RF line 621 can also be reduced, thereby reducing the insertion loss of the RF line 621.

[0074] Furthermore, when the FPC board 600 is used for transmission, in an optional embodiment, the impedance of the radio frequency line 621 is equal to the impedance required by the transmission system in which the FPC board is located.

[0075] It can be understood that when the FPC board 600 is used to transmit signals, since each transmission system requires impedance, for example, when the impedance required by the transmission system is 50 ohms, the impedance of the RF line 621 is required to be equal to 50 ohms. Here, it should be noted that in order to make the impedance of the RF line 621 equal to 50 ohms, the impedance of the RF line 621 can be equal to 50 ohms by setting the line width and gap of the RF line 621 when the thickness of the RF line 621 is constant, as well as the position and size of at least one hollow area 6311 in the second reference ground plane 631.

[0076] That is to say, when the thickness of the RF line 621 is constant, by setting the line width of the RF line 621 and the gap between the RF line 621 and the first reference ground plane, and setting the position and size of at least one hollow area 6311 in the second reference ground plane 631, the impedance of the RF line 621 can be adjusted to be equal to the impedance required by the transmission line where the FPC board 600 is located when the thickness, line width and gap of the RF line 621 are all constant.

[0077] When the FPC board 600 is used as a transmission line to connect different electronic devices, the electronic devices are mainly connected through a board-to-board (BTB) connector. In an optional embodiment, the RF line 621 is divided into: a RF line connected to the BTB connector in the steel patch area of ​​the FPC board 600 and a RF line other than the RF line connected to the BTB connector in the steel patch area of ​​the FPC board 600; wherein,

[0078] The line width of the RF line connected to the BTB connector in the steel patch region of the FPC board 600 is smaller than the line width of the RF line other than the RF line connected to the BTB connector in the steel patch region of the FPC board 600 .

[0079] It can be understood that there is a steel patch area on the FPC board 600, which is used to enhance the connectivity between the FPC board 600 and the hard board. If the steel patch area is grounded to achieve a shielding effect, there will be a large RF mismatch in the steel patch area, which will lead to a large insertion loss. In order to reduce the insertion loss of the RF line 621, the line width of the part of the RF line connected to the BTB connector in the steel patch area can be reduced, so that the line width of the RF line connected to the BTB connector in the steel patch area of ​​the FPC board 600 is smaller than the line width of the RF line other than the RF line connected to the BTB connector in the steel patch area of ​​the FPC board 600.

[0080] In this way, the RF mismatch is optimized and the insertion loss is reduced by reducing the line width of the portion of the RF line in the steel patch area that is connected to the BTB connector.

[0081] In addition, there is a large RF mismatch in the steel-patch area of ​​the FPC board 600, which in turn causes a large insertion loss. In order to reduce the insertion loss of the RF line 621, in an optional embodiment, the FPC board 600 includes: the insertion loss of the RF line 621 is reduced by adjusting the length of the grounding block closest to the steel-patch area of ​​the FPC board 600.

[0082] It can be understood that in order to reduce the insertion loss of the RF line 621, the insertion loss of the RF line 621 can be reduced by reducing the length of the grounding block closest to the steel patch area of ​​the FPC board 600, wherein the grounding block is the portion between two adjacent hollowed-out areas in the second reference ground plane 631; the length of the grounding block is the spacing length between the two adjacent hollowed-out areas, that is, by reducing the spacing length between the two adjacent hollowed-out areas in the second reference ground plane 631, the mismatch is optimized, and then the insertion loss is optimized, thereby achieving the purpose of reducing the insertion loss of the RF line 621.

[0083] The FPC board in one or more of the above embodiments is described below by taking an example.

[0084] This example is divided into three steps to design the FPC board, as follows:

[0085] The first step is to design a RF line with an impedance of 75 ohms;

[0086] Figure 7 A simulation diagram of an optional radio frequency line in an FPC board provided in an embodiment of the present application Figure 1 ,like Figure 7 As shown, a 2-layer board with an ordinary PI substrate is used as an example for explanation, wherein the RF line is on the first layer (signal_1), and the three parts of the first layer filled with oblique lines are the RF line and the reference ground plane. The RF line is the middle part, and the left and right sides of the RF line are the reference ground plane, which is also on the first layer. The line width of the RF line is W, and the gap between the RF line and the left and right sides of the reference ground plane is S. Here, simulation software can be used to optimize the line width W and the gap S, so as to design an RF line with an impedance of 75 ohms.

[0087] like Figure 7 The part filled with diagonal lines is the cross section of the RF line and the reference ground plane. The impedance of the RF line is determined by adjusting the line width (Width) and the clearance (Clearance) between the RF line and the reference ground plane on the same layer. For example, Figure 7 As shown, the line width and gap are 0.25 mm and 0.12 mm respectively, so that the impedance of the RF line is Zc=75 ohms, and the corresponding insertion loss of the RF line of 100 mm length is 0.7 dB.

[0088] Figure 8 FIG. 2 is a second simulation diagram of an optional radio frequency line in an FPC board provided in an embodiment of the present application, as shown in FIG. Figure 8 As shown, Figure 7Compared with the structure in the figure, a reference ground plane is set on the second layer (signal_2), that is, there is a complete reference ground plane under the RF line, which constitutes the microstrip line structure in the related art. Compared with the insertion loss of the RF line in the microstrip line structure of the same length, it is 1.7dB, where the line width W = 0.09mm and the gap S = 0.08mm. It can be seen that Figure 7 Compared with the insertion loss of the RF line Figure 8 The insertion loss of the RF line in the amplifier is reduced by 1dB.

[0089] Fig. 9 A simulation diagram of the insertion loss and return loss of a radio frequency line in an optional FPC board provided in an embodiment of the present application Figure 1 ,like Fig. 9 As shown, the solid line is used to represent the return loss, and the dotted line is used to represent the insertion loss. Since the RF line is used in a 50-ohm transmission system, the 3D electromagnetic field simulation shows that the return loss of the 75-ohm RF line is larger, as shown in Figure 1. Fig. 9 As shown in Figure 2, at 2.5GHz, the maximum value is about -8.7dB. The insertion loss caused by return loss is also large, such as Fig. 9 As shown, approximately -0.81dB.

[0090] Fig.10 A top view of an optional FPC board provided in an embodiment of the present application Figure 1 ,like Fig.10 As shown, the reference ground plane of the second layer is used to optimize the return loss of the RF line, thereby reducing the insertion loss of the RF line; specifically, the reference ground plane corresponding to the RF line is hollowed out, such as Fig.10 As shown, due to the hollowing out of the second reference ground plane, the impedance of the RF line is reduced from 75 ohms to 66 ohms, which is closer to 50 ohms, where 50 ohms is the impedance required by the transmission system.

[0091] After the first step, in the second step, the hollowed area is filled with non-uniform ground blocks; specifically, as follows:

[0092] Fig.11 FIG. 2 is a top view of an optional FPC board provided in an embodiment of the present application, as shown in FIG. Fig.11 As shown, in the second step, a non-uniform grounding block is filled in the hollowed-out area, and the grounding block is the part between two adjacent hollowed-out areas. In this way, the impedance of the RF line is further reduced to optimize the impedance mismatch of the RF line, thereby achieving the purpose of minimizing the insertion loss of the RF line.

[0093] Fig.12 FIG. 2 is a second simulation diagram of insertion loss and return loss of a radio frequency line in an optional FPC board provided in an embodiment of the present application, as shown in FIG. Fig.12As shown, the solid line is used to represent the return loss, and the dotted line is used to represent the insertion loss. It can be seen that the insertion loss of the RF line is 0.19dB, and the return loss of the RF line is less than -37.5dB, which is greatly reduced compared with the microstrip line structure in the related technology.

[0094] Fig.13 FIG. 1 is a schematic diagram of a simulation of the impedance of a radio frequency line in an optional FPC board provided in an embodiment of the present application, such as Fig.13 As shown, the impedance of the RF line is between 47-53.

[0095] It can be seen that in this example, the hollowing out and adding of the grounding block in the second step further increase the flexibility of the FPC board compared to the microstrip line structure, and bring about the filtering effect of the remote frequency. Fig.12 At around 14GHz, the 20mm long RF line achieved a filtering suppression effect greater than 12.5dB.

[0096] The third step is to use the previously optimized 20mm length RF line, based on the total length of the RF line, for example 73.2mm, to cascade the ends and perform overall optimization simulation. The FPC board is designed based on the principle of minimizing the insertion loss of the final RF line and the in-band return loss being less than -20dB.

[0097] In addition, there is usually a BTB socket (equivalent to the above-mentioned BTB connector) at one or both ends of the RF line of the FPC board, which is used to connect the electronic device to the FPC board. The BTB socket is connected to the steel patch area of ​​the FPC board to enhance the connectivity between the FPC board and the hard board. However, if the steel patch area is grounded to achieve a shielding effect, there is a large RF mismatch in the steel patch area, which results in a large insertion loss of the RF line.

[0098] In order to reduce the insertion loss of RF lines, Fig.14 A schematic diagram of an optional steel patching area provided in an embodiment of the present application is shown in FIG. Fig.14 As shown, Fig.14 As shown in the circled area, the RF mismatch is optimized by appropriately reducing the line width of the RF line near the steel patch area, that is, reducing the line width of the RF line in the circled area, thereby optimizing the insertion loss of the RF line.

[0099] In addition, in order to reduce the insertion loss of the RF line, Fig.15 A schematic diagram of the structure of an optional nearby grounding block provided in an embodiment of the present application, such as Fig.15 As shown in the figure, the second layer of grounding blocks close to the steel patch area is as follows Fig.15 As shown in the circled box, the size of the second-layer nearest ground block is optimized to optimize the RF mismatch, thereby optimizing the insertion loss of the RF line. Generally, the RF mismatch is optimized by reducing the length of the nearest ground block, thereby optimizing the insertion loss of the RF line.

[0100] After the above three steps of design, Fig.16 A simulation diagram of the insertion loss and return loss of a radio frequency line in an optional FPC board provided in an embodiment of the present application Figure 3 ,like Fig.16 As shown in the figure, the solid line represents return loss and the dotted line represents insertion loss. At 2.5GHz, the insertion loss of the RF line is 0.76dB. Figure 5 The insertion loss of the RF line in the microstrip line structure designed with MPI substrate is 0.947dB, which is about 0.2dB smaller, achieving better performance and better cost.

[0101] It should be noted that the FPC board in this example can be used in the design of ordinary PCB hard boards. The FPC board in this example can be extended to electronic products that need to use multi-layer FPC (not limited to two layers).

[0102] In this example, the RF line refers to the left and right reference ground planes on the same layer. By adjusting W and S, the impedance of the RF line is 75 ohms, instead of the conventional design of 50 ohms. The RF mismatch is optimized by adding a non-uniform grounding block to the hollow area directly below the RF line, and the insertion loss of the RF line is optimized, and the matching is good within the RF broadband. The steel patch area corresponding to the BTB connector appropriately reduces the line width of the RF line connected to the BTB connector and adjusts the size of the nearest grounding block to the steel patch area to optimize the local RF mismatch and reduce the insertion loss of the RF line.

[0103] It can be seen from the above examples that low insertion loss design is achieved under ordinary low-cost PI substrate, and the flexibility of the FPC board is improved by utilizing the hollowed-out area under the RF. The insertion loss is optimized by optimizing the RF mismatch through the hollowed-out area and adding a non-uniform grounding block, and the matching is good within the RF broadband. The effect of a low-pass filter is achieved, and a high-suppression filtering function is achieved at far-end frequencies above 10 GHz.

[0104] An embodiment of the present application provides an FPC board, which at least includes: an insulating substrate, a first signal layer and a second signal layer, the insulating substrate is located between the first signal layer and the second signal layer, the first signal layer is provided with a radio frequency line and a first reference ground plane at a preset gap on both sides of the radio frequency line, the second signal layer is provided with a second reference ground plane, the first reference ground planes on both sides are respectively connected to the second reference ground plane through vias, and at least one hollowed-out area is provided in the second reference ground plane; that is, in an embodiment of the present application, a radio frequency line and a first reference ground plane at a preset gap from the radio frequency line are provided on the first signal layer on one side of the insulating substrate, and the impedance of the radio frequency line can be adjusted by the line width and the preset gap of the radio frequency line when the thickness of the radio frequency line is constant, and a second reference ground plane including at least one hollowed-out area is provided on the second signal layer on the other side of the insulating substrate, and the first reference ground planes on both sides are respectively connected to the second reference ground plane through vias, so that a routing design of the FPC is formed, wherein the impedance and insertion loss of the radio frequency line can be adjusted and the return loss of the radio frequency line in the FPC board can be reduced through the hollowed-out area, so that the thickness of the FPC is ensured to be constant while reducing the insertion loss of the routing of the FPC board.

[0105] Based on the same inventive concept as the above-mentioned embodiment, the embodiment of the present application provides a transmission line, Fig.17 A schematic diagram of an optional transmission line structure provided in an embodiment of the present application is shown in FIG. Fig.17 As shown, the transmission line 1700 includes the FPC board 600 described in one or more of the above embodiments.

[0106] Based on the same inventive concept as the above-mentioned embodiments, an embodiment of the present application provides an electronic device, Fig.18 A schematic diagram of the structure of an optional electronic device provided in an embodiment of the present application, such as Fig.18 As shown, the electronic device 1800 includes:

[0107] The first device 181 and the second device 182 of the electronic device 1800 are connected using the FPC board 600 described in one or more embodiments.

[0108] The first device 181 and the second device 182 may be located on the same circuit board or on different circuit boards, and this is not specifically limited in the embodiment of the present application.

[0109] The first device 181 and the second device 182 may be connected to the FPC board 600 respectively through the BTB connector or through welding, and this is not specifically limited in the embodiment of the present application.

[0110] The above-mentioned electronic device 1800 can be an electronic device with a fixed screen, an electronic device with a foldable screen, or an electronic device with a sliding screen. Here, the embodiment of the present application does not make any specific limitations on this.

[0111] In an optional embodiment, the first device 181 is a radio frequency unit, and the second device 182 is an antenna unit.

[0112] It can be understood that when the first device 181 is a radio frequency unit and the second device 182 is an antenna unit, in order to send a signal through the radio frequency unit and the antenna unit, the radio frequency unit needs to be connected to the antenna unit. Here, the above-mentioned FPC board 600 can be used as a transmission line to transmit the signal, so that the signal can be transmitted from the radio frequency unit to the antenna unit, received or sent.

[0113] In an optional embodiment, the electronic device 1800 includes a first portion including a first display screen and a second portion including a second display screen, and the first display screen and the second display screen are foldable; wherein,

[0114] The first device 181 is disposed in the first portion, and the second device 182 is disposed in the second portion.

[0115] Here, when the electronic device 1800 is a foldable screen, the electronic device 1800 is usually divided into two parts, one is a first part including a first display screen, and the other is a second part including a second display screen. Then, when the first device 181 is located in the first part and the second device 182 is located in the second part, at this time, due to the flexibility of the FPC board 600, it can be bent. The above-mentioned FPC board 600 has the characteristic of small insertion loss. The first device 181 and the second device 182 located in the two foldable parts are connected. While being bendable, the FPC board 600 has a small thickness, which can save the internal space of the electronic device 1800 and has the characteristic of small insertion loss, which is beneficial to the transmission of signals, thereby improving the transmission efficiency of signals.

[0116] Among them, the computer-readable storage medium can be a ferromagnetic random access memory (FRAM), a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a flash memory, a magnetic surface memory, an optical disk, or a compact disc read-only memory (CD-ROM) and other memories.

[0117] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of hardware embodiments, software embodiments, or embodiments in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage and optical storage, etc.) that contain computer-usable program code.

[0118] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0119] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0120] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0121] The above description is only a preferred embodiment of the present application and is not intended to limit the protection scope of the present application.

Claims

1. An FPC board, characterized in that: At least: An insulating substrate, a first signal layer and a second signal layer, wherein the insulating substrate is located between the first signal layer and the second signal layer; wherein The first signal layer is provided with a radio frequency line and a first reference ground plane at two sides of the radio frequency line separated by a preset gap; The second signal layer is provided with a second reference ground plane; The first reference ground planes on both sides are connected to the second reference ground plane through vias respectively, and at least one hollowed-out area is provided in the second reference ground plane.

2. The FPC board according to claim 1, characterized in that: The impedance of the radio frequency line is adjusted by adjusting the line width of the radio frequency line and / or the preset gap.

3. The FPC board according to claim 1, characterized in that: The impedance of the radio frequency line is adjusted by adjusting the position of the at least one hollow area and / or the size of the at least one hollow area.

4. The FPC board according to claim 1, characterized in that: The return loss of the radio frequency line is reduced by adjusting the position of the at least one hollow area and / or the size of the at least one hollow area.

5. The FPC board according to claim 1, characterized in that: The width of the hollowed-out area is greater than or equal to the first width and less than or equal to the second width; The first width is the sum of the two gaps and the line width of the radio frequency line; the second width is greater than or equal to 5 times the line width of the radio frequency line; and the second width is less than the width of the second reference ground plane.

6. The FPC board according to claim 1, characterized in that: At least two hollowed-out areas are arranged on the second reference ground plane; wherein the interval length between two adjacent hollowed-out areas among the at least two hollowed-out areas is greater than 0.

7. The FPC board according to claim 1, characterized in that: When the second reference ground plane includes at least three hollowed-out areas, intervals between adjacent hollowed-out areas are of equal length.

8. The FPC board according to any one of claims 1 to 7, characterized in that: The impedance of the radio frequency line is equal to the impedance required by the transmission system where the FPC board is located.

9. The FPC board according to any one of claims 1 to 7, characterized in that: The RF lines are divided into: RF lines connected to the BTB connector in the steel patch area of ​​the FPC board and RF lines other than the RF lines connected to the BTB connector in the steel patch area of ​​the FPC board; wherein, The line width of the RF line connected to the BTB connector in the steel patch area of ​​the FPC board is smaller than the line width of the RF line other than the RF line connected to the BTB connector in the steel patch area of ​​the FPC board.

10. The FPC board according to any one of claims 1 to 7, characterized in that: include: The insertion loss of the radio frequency line is reduced by adjusting the length of the ground block closest to the steel patch area of ​​the FPC board; The grounding block is a portion between two adjacent hollowed-out areas in the second reference ground plane; and the length of the grounding block is a spacing length between the two adjacent hollowed-out areas.

11. The FPC board according to any one of claims 1 to 7, characterized in that: The insulating substrate includes any one of the following: MPI, PI.

12. A transmission line, characterized in that: The FPC board comprises any one of claims 1 to 11.

13. An electronic device, characterized in that: include: The first device and the second device of the electronic device are connected by using the FPC board according to any one of claims 1 to 11.

14. The electronic device according to claim 13, characterized in that: The first component is a radio frequency unit, and the second component is an antenna unit.

15. The electronic device according to claim 13, characterized in that: The electronic device comprises a first portion including a first display screen and a second portion including a second display screen, wherein the first display screen and the second display screen are foldable; wherein, The first component is disposed in the first portion, and the second component is disposed in the second portion.

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