Flexible circuit board with parallel signal lines

Abstract

The utility model discloses a flexible circuit board with parallel signal lines, comprising a first base material copper provided with a plurality of first grounding holes; the second base material copper is stacked on the first side of the first base material copper and provided with a first signal line, a plurality of second grounding holes and first signal line via holes formed in the two ends of the first signal line respectively; the third base material copper is stacked on the first side of the second base material copper and is provided with a second signal line, a plurality of third grounding holes and second signal line via holes formed in the two ends of the second signal line respectively; the first signal line and the second signal line are same in routing and corresponding in position, the signal line via holes in the two ends of the two signal lines are same in number and corresponding in position, and electric connection is formed through the corresponding signal line via holes in the two ends; the grounding holes in each layer are the same in number and correspond in position. According to the utility model, a parallel wiring mode is adopted, the purpose of improving the insertion loss of the signal line can be achieved under the condition of the same line width, and the signal transmission quality of the flexible circuit board is effectively improved.

Description

Technical Field

[0001] The utility model relates to the technical field of flexible printed circuit board manufacturing, and particularly relates to a flexible printed circuit board with parallel signal lines. Background Art

[0002] With the development of 5G mobile communication, the number of antennas in mobile terminal devices (such as mobile phones) is increasing. As a device connecting the main board and each sub-board, the traditional radio frequency coaxial cable (abbreviated as RFCable or RF cable) is increasingly difficult to meet the design requirements of multiple antennas. Since the flexible printed circuit board (FPC) can make the antenna feeding position more flexible compared with the RF cable, and can make more full and reasonable use of the metal side frame of the mobile terminal device as the antenna radiator, the mobile terminal device is gradually starting to use the FPC to replace the RF cable.

[0003] For good shielding effectiveness, the signal transmission lines of the FPC generally adopt the form of stripline or microstrip line. However, the insertion loss of the traditional stripline or microstrip line has no advantage compared with the RF cable. To reduce the insertion loss of the stripline or microstrip line, copper foils with low loss and low roughness are usually used, and at the same time, the insertion loss is improved and the signal transmission quality is enhanced by increasing the copper foil thickness and the signal line width.

[0004] However, the signal layer routing of the common stripline or microstrip line is only on one layer of the FPC stack. Under the condition that the shape of the FPC is determined, it is generally very difficult to improve the insertion loss performance by adjusting the copper foil thickness and the signal line width. Summary of the Utility Model

[0005] In view of this, embodiments of the utility model provide a flexible printed circuit board with parallel signal lines to solve the problems of high insertion loss and poor signal transmission quality of the existing flexible printed circuit board with a single-layer stripline or microstrip line.

[0006] The utility model provides a flexible printed circuit board with parallel signal lines, and the flexible printed circuit board includes:

[0007] A first base copper, provided with a plurality of first grounding holes;

[0008] A second base copper, stacked on the first side of the first base copper, provided with a first signal line, a plurality of second grounding holes, and first signal line vias respectively arranged at both ends of the first signal line;

[0009] A third base copper, stacked on the first side of the second base copper, provided with a second signal line, a plurality of third grounding holes, and second signal line vias respectively arranged at both ends of the second signal line;

[0010] Wherein, the routing of the first signal line and the second signal line is the same and their positions correspond to each other. The number of the first signal line vias at both ends of the first signal line and the number of the second signal line vias at both ends of the second signal line are both at least one; the number of the first signal line vias at both ends of the first signal line is the same as the number of the second signal line vias at the first end of the second signal line and their positions correspond one by one, and the number of the first signal line vias at the second end of the first signal line is the same as the number of the second signal line vias at the second end of the second signal line and their positions correspond one by one; the first end of the first signal line is electrically connected to the first end of the second signal line through the corresponding first signal line vias and the corresponding second signal line vias in sequence, and the second end of the first signal line is electrically connected to the second end of the second signal line through the corresponding first signal line vias and the corresponding second signal line vias in sequence;

[0011] On the second copper substrate, all the second grounding holes are distributed on both sides of the first signal line; on the third copper substrate, all the third grounding holes are distributed on both sides of the second signal line; the number of the first grounding holes, the number of the second grounding holes, and the number of the third grounding holes are the same, and the positions of all the first grounding holes correspond to the positions of all the second grounding holes one by one, and the positions of all the second grounding holes correspond to the positions of all the third grounding holes one by one.

[0012] Optionally, the flexible printed circuit board further includes:

[0013] A first protective film, disposed on the second side of the first copper substrate and covering the first copper substrate.

[0014] Optionally, the flexible printed circuit board further includes:

[0015] A first insulating layer, disposed between the first copper substrate and the second copper substrate, and all the first grounding holes on the first copper substrate, all the second grounding holes on the second copper substrate, and all the first signal line vias penetrate through the first insulating layer.

[0016] Optionally, the first insulating layer includes a first PI dielectric layer and a first adhesive layer stacked on the first side of the first copper substrate in sequence;

[0017] All the first grounding holes on the first copper substrate, all the second grounding holes on the second copper substrate, and all the first signal line vias penetrate through the first PI dielectric layer and the first adhesive layer.

[0018] Optionally, the flexible printed circuit board further includes:

[0019] The second PI dielectric layer is disposed between the second base copper and the third base copper, and all the second ground vias, all the first signal line vias on the second base copper, and all the third ground vias and all the second signal line vias on the third base copper penetrate through the second PI dielectric layer.

[0020] Optionally, the flexible printed circuit board further includes:

[0021] A second protective film is stacked on the first side of the third base copper and covers the third base copper.

[0022] Optionally, both the first signal line and the second signal line are striplines or microstrip lines.

[0023] Optionally, when both the first signal line and the second signal line are striplines, the flexible printed circuit board further includes:

[0024] A fourth base copper is stacked on the first side of the third base copper, and is provided with a plurality of fourth ground vias and pads respectively disposed at both ends of the fourth base copper;

[0025] Third signal line vias are further respectively provided on the pads at both ends of the fourth base copper; the number of the third signal line vias of the pads is at least one; the number of the third signal line vias on the pad at the first end of the fourth base copper is the same as and the positions are in one-to-one correspondence with the number of the second signal line vias at the first end of the second signal line, and the number of the third signal line vias on the pad at the second end of the fourth base copper is the same as and the positions are in one-to-one correspondence with the number of the second signal line vias at the second end of the second signal line;

[0026] The number of the fourth ground vias is the same as the number of the third ground vias, and the positions of all the fourth ground vias are in one-to-one correspondence with the positions of all the third ground vias.

[0027] Optionally, when both the first signal line and the second signal line are striplines, the flexible printed circuit board further includes:

[0028] A second insulating layer is disposed between the third base copper and the fourth base copper, and all the third ground vias, all the second signal line vias on the third base copper, and all the fourth ground vias and all the third signal line vias on the fourth base copper penetrate through the second insulating layer.

[0029] Optionally, the second insulating layer includes a second adhesive layer and a third PI dielectric layer sequentially stacked on the first side of the third base copper;

[0030] All of the third ground vias and all of the second signal vias on the third base copper, and all of the fourth ground vias and all of the third signal vias on the fourth base copper penetrate through the second adhesive layer and the third PI dielectric layer.

[0031] Optionally, the flexible printed circuit board further includes:

[0032] At least one fifth base copper, stacked in sequence on the first side of the third base copper, and the structure of each fifth base copper is the same as that of the third base copper.

[0033] The beneficial effects of the present utility model: The second base copper and the third base copper are provided with signal lines (i.e., the first signal line and the second signal line) with corresponding positions, and their wiring is the same, forming a structure of double-layer parallel signal lines; then, first signal vias are provided at both ends of the first signal line, and second signal vias are provided at both ends of the second signal line. The first end of the first signal line and the first end of the second signal line form an electrical connection through the corresponding first signal via and second signal via, and the second end of the first signal line and the second end of the second signal line also form an electrical connection through the first signal via and the second signal via, so the two signal lines are connected; corresponding ground vias (i.e., the first ground via, the second ground via, and the third ground via) are provided between the three-layer base copper (i.e., the first base copper, the second base copper, and the third base copper), and the number of ground vias in each layer is the same and the positions correspond, which can realize the grounding function of the signal line;

[0034] The flexible printed circuit board with parallel signal lines of the present utility model adopts the form of double-layer signal line parallel wiring to replace the common single-layer signal line wiring form. Under the condition of the same line width, it has the advantages of reducing signal interference, optimizing the signal path, and improving the signal quality, thereby achieving the purpose of improving the insertion loss of the signal line and effectively improving the signal transmission quality of the flexible printed circuit board. Description of the Drawings

[0035] The features and advantages of the present utility model will be more clearly understood by referring to the accompanying drawings. The drawings are schematic and should not be construed as any limitation to the present utility model. In the drawings:

[0036] Figure 1 Shows the flat layout diagram of each layer of a flexible printed circuit board with parallel microstrip lines in an embodiment of the present utility model;

[0037] Figure 2 Shows the stacked diagram of area A of the flexible printed circuit board with parallel microstrip lines in an embodiment of the present utility model;

[0038] Figure 3 Shows the stacked diagram of area B of the flexible printed circuit board with parallel microstrip lines in an embodiment of the present utility model;

[0039] Figure 4 Shows the flattened structure diagram of each layer of a flexible printed circuit board with parallel strip lines in an embodiment of the present utility model;

[0040] Figure 5 Shows the stacked structure diagram of area A of the flexible printed circuit board with parallel strip lines in an embodiment of the present utility model;

[0041] Figure 6 Shows the stacked structure diagram of area B of the flexible printed circuit board with parallel strip lines in an embodiment of the present utility model.

[0042] The descriptions of each reference numeral are as follows:

[0043] 1. First base copper, 2. Second base copper, 3. Third base copper, 4. First protective film, 5. First insulating layer, 6. Third PI dielectric layer, 7. Second protective film, 8. Fourth base copper, 9. Second insulating layer, 11. First grounding hole, 21. Second grounding hole, 22. First signal line, 23. First signal line via hole, 31. Third grounding hole, 32. Second signal line, 33. Second signal line via hole, 41. First protective film PI layer, 42. Second protective film adhesive layer, 51. First PI dielectric layer, 52. First adhesive layer, 71. Second protective film PI layer, 72. Second protective film adhesive layer, 81. Fourth grounding hole, 82. Pad, 83. Third signal line via hole, 91. Third PI dielectric layer, 92. Second adhesive layer. Detailed implementation manners

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present utility model clearer, the technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. Apparently, the described embodiments are some but not all of the embodiments of the present utility model. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.

[0045] Embodiment

[0046] This embodiment provides a flexible printed circuit board with parallel signal lines, as Figures 1 to 3 shown, the flexible printed circuit board includes:

[0047] First base copper 1, provided with a plurality of first grounding holes 11;

[0048] Second base copper 2, stacked on the first side of the first base copper 1, provided with a first signal line 22, a plurality of second grounding holes 21, and first signal line via holes 23 respectively arranged at both ends of the first signal line;

[0049] The third copper substrate 3 is stacked on the first side of the second copper substrate 2, and is provided with a second signal line 32, a plurality of third grounding holes 31, and second signal line vias 33 respectively disposed at both ends of the second signal line;

[0050] Wherein, the routing of the first signal line 22 and the second signal line 32 is the same and the positions correspond to each other. The number of the first signal line vias 23 at both ends of the first signal line 22 and the number of the second signal line vias 33 at both ends of the second signal line 32 are both at least one; the number of the first signal line vias 23 at both ends of the first signal line 22 is the same as the number of the second signal line vias 33 at the first end of the second signal line 32 and their positions correspond one by one, and the number of the first signal line vias 23 at the second end of the first signal line 22 is the same as the number of the second signal line vias 33 at the second end of the second signal line 32 and their positions correspond one by one; the first end of the first signal line 22 is electrically connected to the first end of the second signal line 32 through the corresponding first signal line via 23 and the corresponding second signal line via 33 in sequence, and the second end of the first signal line 22 is electrically connected to the second end of the second signal line 32 through the corresponding first signal line via 23 and the corresponding second signal line via 33 in sequence;

[0051] On the second copper substrate 2, all the second grounding holes 21 are distributed on both sides of the first signal line 22; on the third copper substrate 3, all the third grounding holes 31 are distributed on both sides of the second signal line 32; the number of the first grounding holes 11, the number of the second grounding holes 21, and the number of the third grounding holes 31 are the same, and the positions of all the first grounding holes 11 correspond to the positions of all the second grounding holes 21 one by one, and the positions of all the second grounding holes 21 correspond to the positions of all the third grounding holes 31 one by one.

[0052] In this embodiment, signal lines with corresponding positions (i.e., the first signal line and the second signal line) are provided on the second copper substrate and the third copper substrate. Their routings are the same, forming a structure of double-layer parallel signal lines; then, first signal line vias are provided at both ends of the first signal line, and second signal line vias are provided at both ends of the second signal line. The first end of the first signal line and the first end of the second signal line are electrically connected through the corresponding first signal line via and second signal line via, and the second end of the first signal line and the second end of the second signal line are also electrically connected through the first signal line via and second signal line via, so the two signal lines are connected; corresponding grounding holes (i.e., the first grounding hole, the second grounding hole, and the third grounding hole) are provided between the three copper substrates (i.e., the first copper substrate, the second copper substrate, and the third copper substrate). The number of the grounding holes in each layer is the same and the positions correspond to each other, enabling the grounding function of the signal lines.

[0053] The flexible printed circuit board with parallel signal lines in this embodiment adopts the form of double - layer signal lines running in parallel instead of the common single - layer signal line routing form. Under the condition of the same line width, it has the advantages of reducing signal interference, optimizing the signal path, and improving signal quality, thereby achieving the purpose of improving the insertion loss of the signal line and effectively improving the signal transmission quality of the flexible printed circuit board.

[0054] Among them, insertion loss refers to the loss of signal power caused by signal lines or a certain component, device, or branch circuit (such as filters, impedance matchers, etc.) inserted in the signal transmission system.

[0055] Compared with the common single - layer signal line routing form, the flexible printed circuit board with parallel signal lines in this embodiment can improve the insertion loss by about 15% under the condition of the same line width. The comparison results of the insertion loss in the two cases are shown in Table 1.

[0056] Table 1 Comparison of Insertion Loss between Flexible Boards with Parallel Signal Lines and Flexible Boards with Single - Layer Signal Lines

[0057]

[0058]

[0059] In this embodiment, Figure 1 is the flattened view of each layer of the flexible printed circuit board (specifically, the flexible printed circuit board with parallel microstrip lines), Figure 2 is the stacked view of area A of the flexible printed circuit board (specifically, the flexible printed circuit board with parallel microstrip lines), Figure 3 is the stacked view of area B of the flexible printed circuit board (specifically, the flexible printed circuit board with parallel microstrip lines); in Figure 1 , the extension direction of the first signal line 22 and the second signal line 32 is the x - direction, and the direction perpendicular to this extension direction is the y - direction; in Figure 2 , the stacking direction of the flexible printed circuit board is the z - direction. The first side of each layer of the flexible printed circuit board refers to the + z direction (i.e., the upper side in Figures 1 to 3 ), and the second side refers to the - z direction (i.e., the lower side in Figures 1 to 3 ).

[0060] In this embodiment, the numbers of the first ground via 11, the second ground via 21, and the third ground via 31 can be determined according to the actual product requirements, and it is only necessary to ensure that the positions of the three types of ground vias correspond in the stacking direction of the flexible printed circuit board (i.e., the z direction). In addition, the two sides of the first signal line 22 refer to the two sides of the first signal line 22 along the y direction; the second ground vias 21 are distributed on the two sides of the first signal line 22 along the y direction. The numbers of the second ground vias 21 on the two sides can be equal or unequal, and the second ground vias 21 on the two sides can be symmetrically arranged or asymmetrically arranged. The spacing between adjacent second ground vias 21 depends on the specific product design. The third ground vias 31 on the two sides of the second signal line 32 are the same in this regard. Then, the number and layout of the first ground vias 11 on the first base copper 1 are the same as those of the second ground vias 21.

[0061] Specifically, in an alternative embodiment, as Figures 1 to 3 shown, the number of the second ground vias 21 on both sides of the first signal line 21 is 6 each (i.e., the total number of the second ground vias 21 is 12), and they are symmetrically arranged; the number and layout of the first ground vias 11 and the third ground vias 31 are the same as those of the second ground vias 21.

[0062] In this embodiment, the two ends of the first signal line 22 refer to the two ends of the first signal line 22 along the x direction. At each end of the first signal line 22, the number of the first signal line vias 23 is at least one. The numbers of the first signal line vias 23 at the two ends can be the same or different, and the first signal line vias 23 at the two ends can be symmetrically arranged or asymmetrically arranged; when the number of the first signal line vias 23 at each end of the first signal line 22 is multiple, the spacing between adjacent first signal line vias 23 depends on the specific product design. The second signal line vias 33 on the second signal line 32 are the same in this regard and will not be elaborated here.

[0063] Specifically, in an alternative embodiment, as Figures 1 to 3 shown, the number of the first signal line vias 23 at both ends of the first signal line 22 is 1 each (i.e., the total number of the first signal line vias 23 is 2), and they are symmetrically arranged. The number and layout of the second signal line vias 33 at both ends of the second signal line 32 are the same as those of the first signal line vias 23.

[0064] In this embodiment, the routing forms of the first signal line 22 and the second signal line 32 are exactly the same. The line width of the first signal line 22 along the y direction can be the same as or different from the line width of the second signal line 32 along the y direction. The first signal line 22 and the second signal line 32 are only connected through the signal line vias at both ends, forming a new type of double-layer signal line parallel line structure.

[0065] In this embodiment, the first copper substrate 1, the second copper substrate 2, and the third copper substrate 3 can all be solid copper or mesh copper, and the thickness can be a common specification of 12 μm or a common specification of 18 μm.

[0066] Preferably, as Figures 2 to 3 shown, the flexible printed circuit board further includes:

[0067] A first protective film 4, disposed on the second side of the first copper substrate 1 and covering the first copper substrate 1.

[0068] Through the first protective film, it can protect one of the outer surfaces of the entire flexible printed circuit board (i.e., the outer surface on the second side of the first copper substrate), and enhance the anti-interference effect.

[0069] The thickness of the first protective film can be determined according to specific circumstances. As Figure 2 and Figure 3 shown, the first protective film 4 includes a first protective film PI layer 41 and a first protective film adhesive layer 42. In this embodiment, the thicknesses of the first protective film PI layer 41 and the first protective film adhesive layer 42 are 12 μm and 15 μm respectively (i.e., the thickness of the entire first protective film 4 is 27 μm).

[0070] Preferably, as Figures 2 to 3 shown, the flexible printed circuit board further includes:

[0071] A first insulating layer 5, disposed between the first copper substrate 1 and the second copper substrate 2, and all the first grounding holes 11 on the first copper substrate 1, all the second grounding holes 21 on the second copper substrate 2, and all the first signal line vias 23 penetrate through the first insulating layer 5.

[0072] Through the above-mentioned first insulating layer, it can not only isolate the two copper substrates (i.e., the first copper substrate and the second copper substrate) to prevent short circuits, but also support the entire flexible printed circuit board, increasing the stability and reliability of the entire flexible printed circuit board. The first grounding holes and the second grounding holes all penetrate through the first insulating layer, which can ensure the normal realization of the grounding function; the first signal line vias all penetrate through the first insulating layer, which can ensure the normal electrical conduction of the first signal lines.

[0073] Specifically, as Figures 2 to 3 shown, the first insulating layer 5 includes a first PI dielectric layer 51 and a first adhesive layer 52 stacked in sequence on the first side of the first copper substrate 1;

[0074] All the first grounding holes 11 on the first copper substrate 1, all the second grounding holes 21 on the second copper substrate 2, and all the first signal line vias 23 penetrate through the first PI dielectric layer 51 and the first adhesive layer 52.

[0075] The first copper substrate and the second copper substrate are combined through the first adhesive layer, facilitating the formation of a flexible printed circuit board with parallel signal lines that meets the design requirements; through the first PI dielectric layer, it can ensure that, on the basis of forming a flexible printed circuit board with parallel signal lines, an isolation effect is achieved between the first copper substrate and the second copper substrate.

[0076] The specific thicknesses of the first PI dielectric layer 51 and the first adhesive layer 52 can be determined according to the specific product design. In this embodiment, the thickness of the first PI dielectric layer 51 is 125 μm, and the thickness of the first adhesive layer 52 is 30 μm (i.e., the total thickness of the first insulating layer 5 is 155 μm).

[0077] Preferably, as Figures 2 to 3 shown, the flexible printed circuit board further includes:

[0078] A second PI dielectric layer 6, disposed between the second copper substrate 2 and the third copper substrate 3, and all the second ground holes 21 and all the first signal line vias 23 on the second copper substrate 2, as well as all the third ground holes 31 and all the second signal line vias 33 on the third copper substrate 3, penetrate through the second PI dielectric layer 6.

[0079] Through the second PI dielectric layer between the second copper substrate and the third copper substrate, on the one hand, it can isolate the two copper substrates (i.e., the second copper substrate and the third copper substrate) to prevent short circuits; and it can also support the entire flexible printed circuit board, increasing the stability and reliability of the entire flexible printed circuit board; on the other hand, it also facilitates the direct provision of a double-sided board (a double-sided board refers to a flexible substrate including a PI layer and copper layers disposed on both sides of the PI layer) as an inner substrate during the manufacture of the entire flexible printed circuit board, contributing to improving the manufacturing efficiency. Similarly to the first ground hole and the second ground hole, the second ground hole and the third ground hole both penetrate through the second PI dielectric layer, which can ensure the normal realization of the grounding function; the first signal line via and the second signal line via both penetrate through the second PI dielectric layer, which can ensure the normal electrical conduction of both the first signal line and the second signal line, realizing the function of parallel signal lines.

[0080] The specific thickness of the second PI dielectric layer 6 also depends on the specific product design. In this embodiment, the thickness of the second PI dielectric layer 6 is 12 μm, and of course, it can also be other specifications such as 25 μm, 50 μm, etc.

[0081] Preferably, as Figures 2 to 3 shown, the flexible printed circuit board further includes:

[0082] A second protective film 7, stacked on the first side of the third copper substrate 3 and covering the third copper substrate 3.

[0083] Similar to the first protective film, the second protective film can protect the other outer surface of the entire flexible printed circuit board (i.e., the outer surface on the first side of the third copper substrate), enhancing the anti-interference effect.

[0084] The thickness of the second protective film also depends on specific circumstances. For example, Figure 2 and Figure 3 As shown, the second protective film 7 includes a second protective film PI layer 71 and a second protective film adhesive layer 72. In this embodiment, the thicknesses of the second protective film PI layer 71 and the second protective film adhesive layer 72 are 12 μm and 15 μm respectively (i.e., the thickness of the entire second protective film 7 is 27 μm).

[0085] In this embodiment, both the first signal line 22 and the second signal line 32 can be either single lines or differential lines; when they are differential lines, the signal lines within a single layer are not connected to each other and do not interfere with each other.

[0086] In this embodiment, both the first signal line 22 and the second signal line 32 can be either a group of radio frequency lines or multiple groups of radio frequency lines; when they are multiple groups of radio frequency lines, the first signal line 22 and the second signal line 32 in each group are spliced together according to the design of this embodiment along the extension direction of the signal lines (i.e., the x direction).

[0087] In this embodiment, both the first signal line 22 and the second signal line 32 are strip lines or microstrip lines.

[0088] The microstrip line is located on the surface of the entire FPC, that is, the top or bottom layer of the circuit board. Its wire shape is strip-shaped, and it can be exposed to the air on one side and attached to the insulating dielectric on the other side; the signal transmission speed of the microstrip line is relatively fast, but it is vulnerable to external radiation interference and may also radiate RF energy to the surrounding. The strip line is located inside the entire FPC and is a wire placed in the dielectric between two conductive planes; the signal transmission speed of the strip line is relatively slow, but it has better anti-interference performance and radiation shielding effect.

[0089] In practical applications, the types of the first signal line and the second signal line can be selected according to the specific product requirements.

[0090] Preferably, when both the first signal line 22 and the second signal line 32 are strip lines, as Figures 4 to 6 shown, the flexible printed circuit board further includes:

[0091] A fourth copper substrate 8, stacked on the first side of the third copper substrate 3, having a plurality of fourth grounding holes 81 and pads 82 respectively provided at both ends of the fourth copper substrate;

[0092] Third signal line vias 83 are further respectively provided on the pads 82 at both ends of the fourth copper substrate 8; the number of the third signal line vias 83 on the pads 82 is at least one; the number of the third signal line vias 83 on the pads 82 at the first end of the fourth copper substrate 8 is the same as that of the second signal line vias 33 at the first end of the second signal line 32 and their positions correspond one by one, and the number of the third signal line vias 83 on the pads 82 at the second end of the fourth copper substrate 8 is the same as that of the second signal line vias 33 at the second end of the second signal line 32 and their positions correspond one by one;

[0093] The number of the fourth ground vias 81 is the same as that of the third ground vias 31, and the positions of all the fourth ground vias 81 correspond to those of all the third ground vias 31 one by one.

[0094] Through the above-mentioned fourth copper substrate, it can be ensured that the parallel strip line is located inside the entire FPC, ensuring its anti-interference performance and radiation shielding effect required by the strip line. Among them, through the pads at both ends of the fourth copper substrate, the electrical connection between external electronic components and the entire FPC can be facilitated; and through the third signal line vias on the pads, the signal transmission of the internal parallel strip line can be facilitated.

[0095] In this embodiment, Figure 4 is the layout diagram of each layer of the flexible printed circuit board with parallel strip lines, Figure 5 is the stacked diagram of area A of the flexible printed circuit board with parallel strip lines, Figure 6 is the stacked diagram of area B of the flexible printed circuit board with parallel strip lines.

[0096] Preferably, when both the first signal line 22 and the second signal line 32 are strip lines, as Figures 5 to 6 shown, the flexible printed circuit board further includes:

[0097] A second insulating layer 9, which is arranged between the third copper substrate 3 and the fourth copper substrate 8, and all the third ground vias 31 and all the second signal line vias 33 on the third copper substrate 3, as well as all the fourth ground vias 81 and all the third signal line vias 83 on the fourth copper substrate 8, penetrate through the second insulating layer 9.

[0098] Similar to the first insulating layer, the second insulating layer disposed between the third copper substrate and the fourth copper substrate can isolate the two copper substrates (i.e., the third copper substrate and the fourth copper substrate) to prevent short circuits, and can also support the entire flexible printed circuit board, enhancing the stability and reliability of the entire flexible printed circuit board. Similar to the first grounding hole and the second grounding hole, the third grounding hole and the fourth grounding hole penetrate the second insulating layer, ensuring the normal realization of the grounding function; the second signal via hole and the third signal via hole penetrate the second insulating layer, ensuring the normal electrical conduction of the internal parallel strip line and realizing its signal transmission function.

[0099] Specifically, as Figures 5 to 6 shown, the second insulating layer 9 includes a second adhesive layer 92 and a third PI dielectric layer 91 stacked in sequence on the first side of the third copper substrate.

[0100] All the third grounding holes 31 and all the second signal via holes 33 on the third copper substrate 3, as well as all the fourth grounding holes 81 and all the third signal via holes 83 on the fourth copper substrate 8, penetrate the second adhesive layer 92 and the third PI dielectric layer 91.

[0101] Similar to the first adhesive layer, the second adhesive layer combines the third copper substrate and the fourth copper substrate, facilitating the formation of a flexible printed circuit board with parallel strip lines that meets the design requirements; through the third PI dielectric layer, it can ensure that, on the basis of forming a flexible printed circuit board with parallel strip lines, it plays an insulating role between the third copper substrate and the fourth copper substrate.

[0102] The specific thicknesses of the second PI dielectric layer 91 and the second adhesive layer 92 can be determined according to the specific product design. In this embodiment, the thickness of the second PI dielectric layer 91 is 125 μm, and the thickness of the second adhesive layer 92 is 30 μm (i.e., the total thickness of the second insulating layer 9 is 155 μm).

[0103] Preferably, the flexible printed circuit board further includes:

[0104] At least one fifth copper substrate, stacked in sequence on the first side of the third copper substrate, and the structure of each fifth copper substrate is the same as that of the third copper substrate.

[0105] By stacking at least one fifth copper substrate on the first side of the third copper substrate, and the structure of the fifth copper substrate is the same as that of the third copper substrate, more layers of parallel signal lines can be realized, and thus the insertion loss performance can be further improved to a certain extent.

[0106] It should be understood that when at least one fifth copper substrate is stacked on the first side of the third copper substrate, an insulating layer needs to be correspondingly arranged between the layer of the fifth copper substrate closest to the third copper substrate and the third copper substrate to play an isolation role between the fifth copper substrate and the third copper substrate; at the same time, an insulating layer also needs to be arranged between adjacent fifth copper substrates to play an isolation role between adjacent fifth copper substrates. Correspondingly, the signal vias and ground vias on the fifth copper substrate and the signal vias and ground vias on the third copper substrate need to penetrate the corresponding insulating layers to ensure the functionality of each signal via and ground via.

[0107] In addition, in actual production, each signal line in this embodiment can be formed by processes such as etching, and each signal via and ground via can be formed by processes such as laser processing, which are all conventional processes, and specific details are not elaborated here.

[0108] It should be understood that each PI dielectric layer in this embodiment can also be a dielectric layer made of materials such as MPI and LPI.

[0109] Among them, PI refers to polyimide, which has good heat resistance, chemical corrosion resistance, mechanical strength and electrical properties; MPI refers to modified polyimide, a material obtained by modifying PI, which has a lower dielectric constant, a smaller dielectric loss angle and lower water absorption, thus improving the reliability and stability of signal transmission; LPI refers to liquid crystal polymer, which has excellent properties such as low hygroscopicity, low thermal expansion coefficient, low dielectric constant and high dimensional stability. The dielectric constant and dielectric loss angle of LCP are both small, and it is suitable for application scenarios such as high-frequency circuits and high-speed digital connectors.

[0110] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A flexible printed circuit board with parallel signal lines, characterized in that, The flexible printed circuit board includes: A first base copper provided with a plurality of first grounding holes; A second base copper stacked on a first side of the first base copper, provided with a first signal line, a plurality of second grounding holes, and first signal line vias respectively disposed at two ends of the first signal line; A third base copper stacked on a first side of the second base copper, provided with a second signal line, a plurality of third grounding holes, and second signal line vias respectively disposed at two ends of the second signal line; Wherein, the routing of the first signal line and the second signal line is the same and the positions correspond to each other. The number of the first signal line vias at two ends of the first signal line and the number of the second signal line vias at two ends of the second signal line are both at least one; the number of the first signal line vias at two ends of the first signal line is the same as the number of the second signal line vias at a first end of the second signal line and the positions correspond to each other one by one, and the number of the first signal line vias at a second end of the first signal line is the same as the number of the second signal line vias at a second end of the second signal line and the positions correspond to each other one by one; a first end of the first signal line is electrically connected to a first end of the second signal line sequentially through the corresponding first signal line via and the corresponding second signal line via, and a second end of the first signal line is electrically connected to a second end of the second signal line sequentially through the corresponding first signal line via and the corresponding second signal line via; On the second base copper, all the second grounding holes are distributed on two sides of the first signal line; on the third base copper, all the third grounding holes are distributed on two sides of the second signal line; the number of the first grounding holes, the number of the second grounding holes, and the number of the third grounding holes are the same, and the positions of all the first grounding holes correspond to the positions of all the second grounding holes one by one, and the positions of all the second grounding holes correspond to the positions of all the third grounding holes one by one.

2. The flexible printed circuit board having parallel signal lines according to claim 1, wherein The flexible printed circuit board further includes: A first protective film disposed on a second side of the first base copper and covering the first base copper.

3. The flexible printed circuit board with parallel signal lines according to claim 1, wherein The flexible printed circuit board further includes: A first insulating layer disposed between the first base copper and the second base copper, and all the first grounding holes on the first base copper, all the second grounding holes on the second base copper, and all the first signal line vias penetrate through the first insulating layer.

4. The flexible printed circuit board with parallel signal lines according to claim 3, wherein The first insulating layer includes a first PI dielectric layer and a first adhesive layer sequentially stacked on a first side of the first base copper; All the first grounding holes on the first base copper, all the second grounding holes on the second base copper, and all the first signal line vias penetrate through the first PI dielectric layer and the first adhesive layer.

5. The flexible printed circuit board with parallel signal lines according to claim 1, characterized in that, The flexible printed circuit board further includes: A second PI dielectric layer disposed between the second base copper and the third base copper, and all the second grounding holes on the second base copper, all the first signal line vias, all the third grounding holes on the third base copper, and all the second signal line vias penetrate through the second PI dielectric layer.

6. The flexible printed circuit board with parallel signal lines according to claim 1, characterized in that, The flexible printed circuit board further includes: The second protective film is stacked on the first side of the third copper substrate and covers the third copper substrate.

7. The flexible printed circuit board with parallel signal lines according to claim 1, wherein, Both the first signal line and the second signal line are strip lines or microstrip lines.

8. The flexible printed circuit board with parallel signal lines according to claim 7, wherein When both the first signal line and the second signal line are strip lines, the flexible printed circuit board further includes: A fourth copper substrate, stacked on the first side of the third copper substrate, having a plurality of fourth grounding holes and pads respectively provided at both ends of the fourth copper substrate; Third signal line vias are further respectively provided on the pads at both ends of the fourth copper substrate; the number of the third signal line vias on the pads is at least one; the number of the third signal line vias on the pad at the first end of the fourth copper substrate is the same as and the positions are in one-to-one correspondence with the number of the second signal line vias at the first end of the second signal line, and the number of the third signal line vias on the pad at the second end of the fourth copper substrate is the same as and the positions are in one-to-one correspondence with the number of the second signal line vias at the second end of the second signal line; The number of the fourth grounding holes is the same as the number of the third grounding holes, and the positions of all the fourth grounding holes are in one-to-one correspondence with the positions of all the third grounding holes.

9. The flexible printed circuit board with parallel signal lines according to claim 8, wherein, When both the first signal line and the second signal line are strip lines, the flexible printed circuit board further includes: A second insulating layer, disposed between the third copper substrate and the fourth copper substrate, and all the third grounding holes and all the second signal line vias on the third copper substrate, as well as all the fourth grounding holes and all the third signal line vias on the fourth copper substrate penetrate through the second insulating layer.

10. The flexible printed circuit board with parallel signal lines according to claim 9, characterized in that, The second insulating layer includes a second adhesive layer and a third PI dielectric layer sequentially stacked on the first side of the third copper substrate; All the third grounding holes and all the second signal line vias on the third copper substrate, as well as all the fourth grounding holes and all the third signal line vias on the fourth copper substrate penetrate through the second adhesive layer and the third PI dielectric layer.

11. The flexible printed circuit board with parallel signal lines according to any one of claims 1 to 10, characterized in that, The flexible printed circuit board further includes: At least one fifth copper substrate, sequentially stacked on the first side of the third copper substrate, and the structure of each fifth copper substrate is the same as the structure of the third copper substrate.

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