JP2007234500A - High-speed transmission fpc and printed circuit board to be connected to the fpc - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high speed transmission FPC excellent in impedance matching. <P>SOLUTION: An FPC 10 comprises a base 11; a plurality of high-speed transmission paths 11a and a first ground patterns 11b; a dielectric sheet 12; and a first and second ground layers 13, 14. A plurality of high-speed transmission paths 11a are arranged on the base 11 having a constant permittivity, and a plurality of the first ground patterns 11b are arranged so as to sandwitch each of the high-speed transmission paths. A dielectric sheet 12 is layered on the base 11 so that the plurality of high-speed transmission paths 11a and the first ground patterns 11b may be exposed at both ends of the base. A first ground layer 13 is layered on the dielectric sheet 12. A second ground layer 14 is layered on the base 11. A plurality of through-holes 1s connect the first ground patterns 11b with the first and second ground layers 13, 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-speed transmission FPC and a printed circuit board connected to the FPC. In particular, the present invention relates to an FPC structure in which a high-speed transmission line such as a differential signal line is formed and a printed circuit board connected to the FPC. In the present specification, flat flexible cables such as FPC (Flexible Printed Circuit) and FFC (Flexible Flat Cable) are collectively referred to as FPC.

  FPC, which is a flat flexible cable, is used to connect electronic component modules and printed circuit boards mounted on portable information devices represented by recent electronic devices such as mobile phones and PDAs (Personal Digital Assistance). Has been. Also, FPC is frequently used for transmission equipment installed in a communication base station.

  The printed wiring board electrically connects electronic components or electronic devices. Printed wiring boards are required to have functions such as improvement of high-speed and high-frequency characteristics and reduction of unnecessary radiation as well as matching of characteristic impedance as the transmission signal speed increases. Therefore, the printed wiring board has a stripline or microstripline configuration, and the increase in the number of signal lines has led to the development of multilayer boards.

  In the multilayer printed wiring board for high-speed transmission constituting the stripline, various countermeasures have been proposed so far for the problem of crosstalk and the influence of electromagnetic waves from the outside. In the following description, the printed wiring board corresponds to a hard board (so-called rigid board), and the FPC corresponds to a flexible board compared to the rigid board.

  For example, as a printed circuit board that reduces crosstalk and signal interference between signal lines, a printed circuit board on which a plurality of constant impedance lines are arranged includes a ground pattern area provided between adjacent lines, and the ground pattern area. A via hole provided to be electrically connected to the ground pattern region and another ground pattern region along each adjacent line, and shield each adjacent line. The invention of the multilayer printed wiring board which did is disclosed (for example, refer patent document 1).

  As a technique similar to Patent Document 1, a printed wiring board for a high-frequency circuit that facilitates high-frequency wiring and reduces unnecessary electromagnetic coupling between transmission lines includes a plurality of signal layers between two ground conductor layers. In a multilayer printed wiring board for a high frequency circuit of a stripline structure transmission line, a signal line and a ground line are alternately wired to the signal layer, and the signal line and the ground line are wired opposite to each other for adjacent signal layers, An invention of a multilayer printed wiring board for a high-frequency circuit that is wider than the width of a signal line opposed to the ground line is disclosed (for example, see Patent Document 2).

The multilayer printed wiring board for high-frequency circuits according to Patent Document 2 can realize high-density wiring while suppressing the influence of crosstalk between signal lines and external electromagnetic noise. In addition, by providing a microstrip line structure portion on the surface layer, a signal line for passing a signal with little crosstalk can be provided. Furthermore, it is also possible to take the form of a stripline structure portion that does not include a ground line in the inner layer, and a signal with little crosstalk can be passed through the signal line of the stripline structure portion in the inner layer.
Japanese Patent Laid-Open No. 8-242178 JP 2003-69239 A

  According to Patent Document 1, the printed wiring board includes a via hole provided so as to conduct to the ground pattern region and another ground pattern region along each adjacent line, and shields each adjacent line. As a result, a three-dimensional shield can be applied to each adjacent line, thereby reducing crosstalk and signal interference between the lines. However, in the printed circuit board on the surface layer, each line is exposed to the outside, and the influence of electromagnetic noise from the outside is not suppressed. Moreover, although the multilayer printed wiring board by patent document 1 can be connected with a motherboard via a connector, it is not disclosed at all about the problem of impedance matching and whether the ground between printed circuit boards is equipotential.

  In Patent Document 2, crosstalk can be prevented by wiring signal lines and ground lines alternately in the signal layer. In particular, the aim is to reduce the influence of crosstalk between layers by making the width of the grounding line closer to a stripline structure. In Patent Document 2, the same point is intended to reduce the influence of crosstalk by alternately arranging signal lines and ground lines in the signal layer.

  However, with a higher-speed signal, as shown in Patent Document 1 and Patent Document 2, the influence of crosstalk cannot be reduced only by arranging a ground line on a plane. If the distance between the signals is increased in order to reduce the influence of the crosstalk, an inefficient structure in which the signal line mounting density is reduced is obtained. These problems caused by the printed circuit board are common to FPCs that connect devices that are separated from each other. There is a need for a new high-speed transmission FPC and a printed circuit board connected to the FPC that can reduce the influence of crosstalk while maintaining the signal line mounting density suitable for the FPC. The above can be said to be the subject of the present invention.

  The present invention has been made in view of such problems, and reduces the effects of crosstalk and external electromagnetic noise, provides good impedance matching, and enables high-speed transmission where the ground between devices is equipotential. An object is to provide an FPC and a printed circuit board connected to the FPC.

  The inventors have a multilayer FPC in which a pair of ground layers are stacked via a dielectric layer on a base that forms a high-speed transmission path, and a ground pattern sandwiching the high-speed transmission path is connected to the pair of ground layers through holes. In addition, the ground layer laminated on the dielectric layer is found to solve these problems by connecting to the ground of the printed circuit board to be connected. Based on this, the following new FPC for high-speed transmission and A printed circuit board connected to the FPC has been completed.

  (1) A base having a constant dielectric constant, a plurality of high-speed transmission lines arranged on one surface of the base, and a plurality of high-speed transmission lines arranged on one side of the base so as to sandwich each high-speed transmission line A high-speed transmission FPC having a first ground pattern, wherein the plurality of high-speed transmission paths and the first ground pattern are laminated on one surface of the base so as to be exposed at both ends of the base, and A first ground layer laminated on the dielectric sheet; and a second ground layer laminated on the other surface of the base, wherein the first ground pattern and the first and second ground layers are formed as a plurality of through holes. FPC for high-speed transmission connected by

  The high-speed transmission FPC according to the invention of (1) includes a base, a plurality of high-speed transmission paths, and a plurality of first ground patterns. Furthermore, a dielectric sheet and first and second ground layers are provided. The base has a constant dielectric constant. A plurality of high-speed transmission lines are arranged on one surface of the base. A plurality of first ground patterns are arranged on one surface of the base substantially in parallel so as to sandwich each high-speed transmission path. The dielectric sheet is laminated on one surface of the base so that the plurality of high-speed transmission lines and the first ground pattern are exposed at both ends of the base. The first ground layer is laminated on the dielectric sheet. The second ground layer is stacked on the other surface of the base. The first ground pattern and the first and second ground layers are connected by a plurality of through holes.

  FPC functions as a multi-core cable that connects each unit of electronic equipment (including printed circuit boards), and is used as the internal wiring of small and lightweight mobile phones and PDAs by taking advantage of thinness, lightness, and bending performance. Yes. In general, in the FPC, a copper foil laminated on an insulating base is etched to form a plurality of conductor patterns. An insulating coverlay is laminated on the conductor pattern forming surface of the base so that both end portions of these conductor patterns become connection end portions. Thus, FPC has a basic structure of a sandwich structure in which a conductor layer as a wiring material and an insulating layer are stacked.

  Here, the base according to the present invention is formed of a flexible sheet having a predetermined thickness and having a plurality of high-speed transmission lines and a first ground pattern on one surface of the thickness. The flexibility of the base means that the base can bend and that it can be bent. The term “formed by a sheet” means that the sheet has the characteristics of a normal sheet, and has one surface and the other surface defined by a dimension larger than the thickness. It can be said that the base substantially defines the outer shape other than the thickness of the FPC for high-speed transmission according to the present invention. The FPC for high-speed transmission according to the present invention is formed in a long shape, for example, a square or rectangular shape. It does not exclude an aspect or an aspect in which the other end is branched with respect to one end.

  For example, by etching a copper foil of a copper clad laminate using a base having a constant dielectric constant as a base material, a plurality of high-speed transmission lines and first ground patterns can be arranged on one surface of the base. . Alternatively, a plurality of high-speed transmission lines and first ground patterns may be formed by depositing a copper foil on the base by plating using an additive method.

  A copper foil laminated on a copper-clad laminate having a dielectric sheet as a base material may be used as the first ground layer, and a copper foil bonded to the dielectric sheet by being heated and pressurized may be used as the first ground layer. Moreover, it is good also considering the copper foil adhere | attached by heat-pressing on the other surface of the base as a 2nd ground layer. 5 layers in which a second ground layer, a base, a plurality of high-speed transmission lines and a conductor layer having a first ground pattern, a dielectric sheet, and a first ground layer are laminated in this order, and the layers are bonded by heating and pressing. FPC for high-speed transmission. A plurality of through-holes connecting the first ground pattern and the first and second ground layers can be formed by punching the five-layer high-speed transmission FPC and then performing plating.

  In the present invention, these through holes are not intended to mount components, but are intended to electrically connect the first ground pattern and the first and second ground layers, and do not affect the characteristic impedance. Thus, it is preferable that a small hole is drilled in a range acceptable in manufacturing and reliability. For the same reason, these through holes do not need to be so-called through vias, and these through holes may be filled with a conductive paste, or as pad-on-holes. Good.

  The FPC for high-speed transmission according to the invention of (1) forms a first ground pattern sandwiching each high-speed transmission on a common shared plane of a base on which a plurality of high-speed transmission paths are arranged, and further includes a plurality of first and second ground layers. Therefore, it can be said that each high-speed transmission line is three-dimensionally shielded, and the effects of crosstalk and electromagnetic waves on the recent high-speed signals transmitted through the high-speed transmission line can be said. Can be reduced.

  The FPC for high-speed transmission according to the invention of (1) may be said to have a stripline structure in which high-speed transmission lines are arranged inside a dielectric layer having ground layers on both sides. It can be said that it has an offset stripline structure in which the distance from the ground layer is different from each other, and a plurality of through holes connect the first ground pattern and the first and second ground layers. Yes. In the FPC for high-speed transmission according to the invention of (1), in order to facilitate impedance matching, the first ground pattern and the first and second ground layers are connected by a plurality of through holes to be equipotential. By contacting these grounds of the FPC for high-speed transmission according to the invention of (1) and the ground of the device to which the end of the first ground layer is connected, all of these grounds become equipotential.

  (2) A first cover lay stacked on the first ground layer so that the first ground layer is exposed at both ends of the base, and a second cover lay stacked on the second ground layer ( 1) FPC for high-speed transmission as described.

  For example, the first and second coverlays may be thin-film insulating sheets made of polyester, polyimide, or the like, and the first coverlay may be such that the first ground layer is exposed at both ends of the base. It is stacked on one ground layer. The second coverlay is stacked on the second ground layer.

  The first cover lay is laminated on the first ground layer means that the first cover lay covers the first ground layer. For example, the first cover lay covers the first ground layer. Glued. Since the exposed part of the first ground layer is in contact with the ground of the device to be connected, nickel / gold plating may be applied. The fact that the second cover lay is laminated on the second ground layer means that the second cover lay covers the second ground layer. For example, the second cover lay covers the first ground layer. Glued. The FPC for high-speed transmission according to the invention of (2) can prevent the first and second ground layers from being short-circuited inside the device.

  (3) The FPC for high-speed transmission according to (1) or (2), wherein the first and second ground layers are made of silver foil.

  Considering the shielding performance and the bending performance and electrical conductivity required for FPC, the first and second ground layers are preferably made of silver foil. Moreover, since the exposed portions at both ends of the first ground layer can serve as connection terminals to the outside, gold plating may be performed.

  (4) The FPC for high-speed transmission according to any one of (1) to (3), wherein the plurality of through holes are arranged at equal intervals in the extending direction of the first ground pattern.

  In the present invention, the through holes correspond to poles having a certain height, and the pair of through holes have a predetermined interval that is equal to or less than ½ wavelength of the specific electromagnetic wave. By arranging a plurality of through holes at equal intervals or less than ½ wavelength of the specific electromagnetic wave, it can be expected to block electromagnetic waves having a wavelength longer than the specific electromagnetic wave.

Here, assuming that the frequency f of a specific electromagnetic wave is 20 GHz, the wavelength λ _{0 of} this electromagnetic wave is “15” mm. At 1/2 wavelength, it is “7.5” mm.
λ ₀ = C / f = (3 × 10 ⁸ ) / (20 × 10 ⁹ ) = 1.5 × 10 ⁻² m = 15 mm
λ ₀ : wavelength, C: speed of light 3 × 10 ⁸ m / s, f: frequency Also, the effective wavelength λ to be resonated is influenced by the dielectric constant of the dielectric and is obtained by the following equation.
λ = λ ₀ / root εγ = 10-12 mm → λ / 2 = 5-6 mm
[lambda]: Effective wavelength, [epsilon] [gamma]: Dielectric constant That is, as described later, an electromagnetic wave having a frequency lower than 20 GHz can be shielded by setting the interval between the plurality of through holes to about 5 mm.

  (5) The FPC for high-speed transmission according to (4), wherein an interval between the plurality of through holes is equal to or less than a resonance wavelength of a predetermined high-frequency electromagnetic wave.

  (6) The FPC for high-speed transmission according to (4), wherein an interval between the plurality of through holes is approximately 5 mm.

  (7) The FPC for high-speed transmission according to any one of (1) to (4), wherein the base and the dielectric sheet are made of polyimide.

  For the base and the dielectric sheet having a constant dielectric constant, it is preferable to use general polyimide as a dielectric. The polyimide may include a multilayer board in which a thin film polyimide board and a thin film modified polyimide board are laminated.

  In order for the high-speed transmission FPC according to the present invention to perform impedance matching, the base and the dielectric sheet need to have a thickness of about 130 μm, for example. When the base and the dielectric sheet are made thin, it is necessary to narrow the line width of the high-speed transmission path, and visual connection becomes difficult. However, in general, since a thin film polyimide plate is commercially available, a thin film polyimide plate and a thin film modified polyimide plate may be alternately laminated to ensure a required plate thickness. The modified polyimide plate has an advantage that it can be laminated on the polyimide plate without requiring an adhesive by heating and pressing.

  (8) The FPC for high-speed transmission according to any one of (1) to (4), wherein the base and the dielectric sheet are made of a fluororesin.

  For the base and the dielectric sheet having a constant dielectric constant, a fluororesin can also be used as the dielectric. Fluororesin has a low dielectric constant, and is characterized in that it has a merit and flexibility that can ensure a certain thickness without reducing the line width of the high-speed transmission path.

  (9) The high-speed transmission FPC according to any one of (1) to (8), wherein the high-speed transmission path includes a pair of differential signal paths.

  For example, a pair of differential signal paths is a wiring pattern used for LVDS (Low Voltage Differential Signaling), and data communication can be performed with a differential signal having an ultra-small amplitude of about 350 mV. it can.

  (10) A printed circuit board connected to the high-speed transmission FPC according to any one of (1) to (9), formed on one surface of an insulating substrate, and connected to an end of the first ground layer A first ground region, a print contact formed near the first ground region and connected to an end of the plurality of high-speed transmission lines, and a plurality of first contacts connected to an end of the plurality of first ground patterns. A printed circuit board that is connected to the FPC for high-speed transmission by pressing an end of the FPC for high-speed transmission against the printed circuit board.

  The printed circuit board according to the invention of (10) includes a first ground region, a printed contact, and a plurality of second ground patterns. The first ground region is formed on one surface of the insulating substrate and is connected to the end of the first ground layer. The print contact is formed in the vicinity of the first ground region and connected to the ends of the plurality of high-speed transmission paths. The plurality of second ground patterns are connected to the ends of the plurality of first ground patterns. Then, the end of the high-speed transmission FPC is pressed against the printed circuit board, so that the printed circuit board is connected to the high-speed transmission FPC.

  For example, the printed circuit board may be a double-sided printed circuit board in which a conductor layer is formed on both sides of an insulating substrate, and a first ground region, a printed contact, and a plurality of second ground patterns are formed on one surface of the conductive layer. Is done. A second ground region to be described later is formed on the other surface of the conductor layer. Here, the first ground region is a specific region of the conductor layer and has an area where the end portion of the first ground layer contacts. The printed contact is also called an edge connector. The print contacts are arranged in the same row as the plurality of high-speed transmission lines. The plurality of second ground patterns are arranged congruently with the plurality of first ground patterns so as to sandwich each print contact. As a matter of fact, the first ground region, the printed contact, and the plurality of second ground patterns are gold-plated and surrounded by a solder resist.

  In the printed circuit board according to the invention of (10), the end portion of the first ground layer and the ground region are brought into surface contact with each other when the end portion of the FPC for high-speed transmission is pressed against the printed circuit board by an appropriate pressing means. Further, the end portions of the plurality of high-speed transmission paths and the printed contacts are in surface contact. Furthermore, the plurality of second ground patterns are connected to the ends of the plurality of first ground patterns. Therefore, the power loss due to reflection is reduced as compared with the case where the FPC for high-speed transmission and the printed board are connected using the connector having contacts.

  (11) The printed circuit board according to (10), further including a second ground region formed on the other surface of the insulating substrate, wherein the first ground region and the second ground region are connected by a plurality of through holes.

  The FPC for high-speed transmission according to the present invention forms a first ground pattern sandwiching each high-speed transmission path on a common shared plane of a base on which a plurality of high-speed transmission paths are arranged, and the first and second ground layers have a plurality of high-speed transmission paths. Since it is covered with a transmission line, each high-speed transmission line is three-dimensionally shielded, and the influence of crosstalk and electromagnetic waves can be reduced on recent high-speed signals transmitted to the high-speed transmission line. Further, the FPC for high-speed transmission according to the present invention is equipotential by connecting the first ground pattern and the first and second ground layers through a plurality of through holes in order to facilitate impedance matching. By bringing these grounds of the FPC for high-speed transmission according to the present invention into contact with the ground of the device to which the end of the first ground layer is connected, all these grounds become equipotential.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a perspective view showing a configuration of an embodiment of a high-speed transmission FPC and a printed circuit board connected to the FPC according to the present invention. FIG. 2 is a perspective exploded view of the FPC for high-speed transmission according to the embodiment. FIG. 3 is a plan view of the FPC for high-speed transmission according to the embodiment, and shows an enlarged connection end. 4 is a longitudinal sectional view of the FPC for high-speed transmission according to the embodiment, and is a view taken along the line XX of FIG. FIG. 5 is a longitudinal sectional view of the FPC for high-speed transmission according to the embodiment, and is a view taken in the direction of arrows YY in FIG. FIG. 6 is a connection state diagram of the FPC for high-speed transmission and the printed circuit board according to the embodiment. FIG. 7 is a plan view of the printed circuit board according to the embodiment, and shows an enlarged connection portion.

  First, the configuration of a high-speed transmission FPC (hereinafter abbreviated as FPC) and a printed circuit board connected to the FPC according to the present invention will be described.

  1 or 2, the FPC 10 includes a base 11, a plurality of high-speed transmission paths 11a, and a plurality of first ground patterns 11b. The FPC 10 includes a dielectric sheet 12 and first and second ground layers 13 and 14. Further, the FPC 10 includes first and second coverlays 15 and 16.

  In FIG. 1 or FIG. 2, the base 11 has a constant dielectric constant. A plurality of high-speed transmission lines 11 a are arranged on one surface of the base 11. A plurality of first ground patterns 11 b are arranged on one surface of the base 11. The first ground patterns 11b are arranged substantially in parallel so as to sandwich each high-speed transmission path 11a. The dielectric sheet 12 is laminated on one surface of the base 11 so that the plurality of high-speed transmission paths 11 a and the first ground pattern 11 b are exposed at both ends of the base 11.

  The first ground layer 13 is laminated on the dielectric sheet 12. The second ground layer 14 is stacked on the other surface of the base 11. The first ground pattern 11b and the first and second ground layers 13 and 14 are connected by a plurality of through holes 1s (see FIG. 5). The first coverlay 15 is laminated on the first ground layer 13 so that the first ground layer 13 is exposed at both ends. The second coverlay 16 is stacked on the second ground layer 14.

  1 or 2, the base 11 has a predetermined thickness, and is formed of a flexible sheet having a plurality of high-speed transmission lines 11a and first ground patterns 11b on one surface in the thickness direction. ing. It can be said that the base 11 substantially defines an outer shape other than the thickness of the FPC 10, and is formed in a long shape. It is possible to arrange a plurality of high-speed transmission lines 11a and first ground patterns 11b on one surface of the base 11 by etching the copper foil of the copper clad laminate using the base 11 having a constant dielectric constant as a base material. it can.

  In FIG. 1 or FIG. 2, the copper foil laminated | stacked on the copper clad laminated board which used the dielectric material sheet 12 as the base material can be used as the 1st ground layer 13. FIG. In addition, a copper foil bonded to the other surface of the base 11 by heating and pressing can be used as the second ground layer 14.

  A second ground layer 14, a base 11, a conductor layer having a plurality of high-speed transmission lines 11a and a first ground pattern 11b, a dielectric sheet 12, and a first ground layer 13 are laminated in this order, and heated and pressurized to each other. It can be a five-layer FPC 10 where the layers are joined (see FIG. 1). A plurality of through-holes 1s connecting the first ground pattern 11b and the first and second ground layers 13 and 14 can be formed by carrying out a plating process after drilling the five-layer FPC 10.

  In FIG. 1 or FIG. 2, the first and second coverlays 15 and 16 are thin-film insulating sheets made of polyester or polyimide. The first coverlay 15 is bonded to the first ground layer 13. The first coverlay 15 covers the first ground layer 13. The second coverlay 16 is bonded to the second ground layer 14. The second coverlay 16 covers the second ground layer 14. The seven-layer FPC 10 in which the first and second coverlays 15 and 16 are laminated can prevent the first and second ground layers 13 and 14 from being short-circuited inside the device.

  In consideration of shielding performance and bending performance and conductivity required for FPC, the first and second ground layers 13 and 14 are preferably made of silver foil, and the exposed portions 13a and 13b at both ends of the first ground layer 13 are: Since it contacts with the ground (not shown) of the device to be connected, nickel / gold plating is applied (see FIG. 1).

  On the other hand, in FIG. 1, the printed circuit board 20 includes a first ground region 21 a formed on one surface of the insulating substrate 21. The printed circuit board 20 includes a printed contact 21b formed in the vicinity of the first ground region 21a. The first ground region 21 a is connected to the exposed portion 13 b of the first ground layer 13. The print contact 21b is connected to the ends of the plurality of high-speed transmission paths 11a. The plurality of second ground patterns 21c are connected to the ends of the plurality of first ground patterns 11b. And the printed circuit board 20 can be connected with FPC10 by the edge part of FPC10 being pressed by the printed circuit board 20 by the press means which is not illustrated (refer FIG. 6).

  The printed circuit board 20 is a double-sided printed circuit board in which a conductor layer is formed on both surfaces of an insulating substrate 21, and a first ground region 21a, a printed contact 21b, and a plurality of second ground patterns 21c are formed on one surface of the conductor layer. Is formed. A second ground region 22a is formed on the other surface of the conductor layer (see FIG. 6). The first ground region 21a is a specific region of the conductor layer and has an area with which the exposed portion 13b of the first ground layer is in contact. The print contacts 21b are arranged in the same row as the plurality of high-speed transmission paths 11a. The plurality of second ground patterns 21c are arranged congruently with the plurality of first ground patterns 11b so as to sandwich each print contact 21b. (See FIGS. 1 and 7). 1 and 6, the first ground region 21a and the printed contact 21b are plated with gold and surrounded by a solder resist.

  In FIG. 6, the printed circuit board 20 includes a second ground region 22 a formed on the other surface of the insulating substrate 21. The plurality of through holes 2s connect the first ground region 21a and the second ground region 22a (see FIG. 7).

  Next, the operation of the FPC according to the present invention and the printed circuit board connected to the FPC will be described.

  In FIG. 1 or FIG. 2, a plurality of first ground patterns 11b sandwiching each high-speed transmission path 11a are formed on a common plane of the base 11 on which the plurality of high-speed transmission paths 11a are arranged. Further, the first and second ground layers 13 and 14 cover the plurality of high-speed transmission lines 11a. Therefore, it can be said that each high-speed transmission path 11a is three-dimensionally shielded, and the influence of crosstalk between high-speed signals and external electromagnetic waves can be reduced with respect to the high-speed signal transmitted to the high-speed transmission path 11a.

  In FIG. 1 or FIG. 2, the first and second ground layers 13 and 14 are made of silver foil to enhance the shielding performance. From the viewpoint of shielding performance, the first and second ground layers 13 and 14 may be copper foils, but in consideration of bending performance and conductivity required for FPC, a silver foil having excellent flexibility and good conductivity is preferable. . In addition, the exposed portions 13a and 13b at both ends of the first ground layer 13 are gold-plated because they can serve as connection terminals to the outside.

  Further, in FIG. 1, the FPC 10 has a plurality of through holes 2s arranged at equal intervals in the extending direction of the first ground pattern 11b. The arrangement interval P between the plurality of through holes 2s is equal to or less than the resonance wavelength of a predetermined high-frequency electromagnetic wave. For example, the arrangement interval P of the plurality of through holes 1s is 5 mm.

  Here, the through-hole 1s corresponds to a pole having a certain height, and the pair of through-holes 1s have a predetermined interval that is equal to or less than ½ wavelength of the specific electromagnetic wave. By arranging the plurality of through holes 1s at equal intervals or less than ½ wavelength of the specific electromagnetic wave, it can be expected to block the electromagnetic wave having a wavelength longer than the specific electromagnetic wave.

  At present, in the communication field using metal wires, it is considered that there is a certain limit to the frequency used. Assuming that the frequency of the specific electromagnetic wave is 20 GHz and calculating the resonance wavelength based on a predetermined calculation formula, the arrangement interval P of the pair of through holes 2s is about 5 mm. That is, electromagnetic waves having a frequency lower than 20 GHz can be shielded by setting the interval between the plurality of through holes 1 s to about 5 mm.

  On the other hand, the FPC 10 may be said to have a stripline structure in which high-speed transmission lines 11a are arranged inside a dielectric layer having first and second ground layers 13 and 14 on both sides. It can also be said that it has an offset stripline structure in which the distances from the first and second ground layers 13 and 14 on both sides are arranged at different positions (see FIGS. 4 and 5). A plurality of through holes 1s connect the first ground pattern 11b to the first and second ground layers 13 and 14 (see FIG. 5). In order to facilitate impedance matching, the FPC 10 is connected to the first ground pattern 11b and the first and second ground layers 13 and 14 through a plurality of through holes 1s to be equipotential. By contacting these grounds of the FPC 10 and the ground of the device to which the end of the first ground layer is connected, all of these grounds become equipotential.

  For example, a general polyimide can be used as the dielectric for the base 11 and the dielectric sheet 12 having a constant dielectric constant. The polyimide may include a multilayer board in which a thin film polyimide board and a thin film modified polyimide board are laminated. The modified polyimide plate has an advantage that it can be laminated on the polyimide plate without requiring an adhesive by heating and pressing.

  Further, for the base 11 and the dielectric sheet 12 having a constant dielectric constant, a fluororesin can be used as a dielectric. A fluororesin having a low dielectric constant has the advantage that a certain plate thickness can be secured without reducing the line width of the high-speed transmission path, and that it has excellent flexibility.

  As the high-speed transmission path 11a, a pair of differential signal paths defined by LVDS can be used. LVDS has the advantages of low power consumption and high-speed data transmission. And by designing the line width of the differential signal path forming the pair, the thickness of the line, the distance to the ground layer, and the dielectric constant of the dielectric appropriately, the impedance of the terminal of the differential signal path forming the pair is determined. Can be set.

  Then, as shown in FIG. 6, the end of the FPC 10 is pressed against the printed circuit board 20 by an appropriate pressing means, so that the end of the first ground layer 13 and the ground region 21 a are in surface contact. Further, the end portions of the plurality of high-speed transmission paths 11a and the printed contacts 21b are in surface contact. Furthermore, the plurality of second ground patterns 21c are connected to the ends of the plurality of first ground patterns 11b. Therefore, the power loss due to reflection is smaller than when the FPC 10 and the printed circuit board 20 are connected using a connector having contacts. Further, since the first ground region 21a and the second ground region 22a are connected by the plurality of through holes 2s, the ground is strengthened.

  In the present invention, since the ground layer of the printed circuit board is in surface contact with the ground layer of the FPC, the ground of the FPC and the ground of the printed circuit board become equipotential, and impedance mismatching can be prevented.

It is a perspective view which shows the structure of one Embodiment of FPC for high-speed transmission by this invention, and the printed circuit board connected to this FPC. It is a perspective exploded view of the FPC for high-speed transmission according to the embodiment. It is a top view of FPC for high-speed transmission by the said embodiment, and has expanded and showed the connection edge part. It is a longitudinal cross-sectional view of FPC for high-speed transmission by the said embodiment, and is a XX arrow line view of FIG. It is a longitudinal cross-sectional view of FPC for high-speed transmission by the said embodiment, and is a YY arrow line view of FIG. It is a connection state figure of FPC for high-speed transmission and a printed circuit board by the embodiment. It is a top view of the printed circuit board by the said embodiment, and has expanded and showed the connection part.

Explanation of symbols

1s through hole 1 FPC (FPC for high-speed transmission)
11 Base 11a High-speed transmission line 11b First ground pattern 12 Dielectric sheet 13 First ground layer 14 Second ground layer

Claims (11)

A base having a constant dielectric constant, a plurality of high-speed transmission lines arranged on one side of the base, and a plurality of first grounds arranged on one side of the base substantially in parallel so as to sandwich each high-speed transmission line An FPC for high-speed transmission with a pattern,
A dielectric sheet that is laminated on one surface of the base such that the plurality of high-speed transmission lines and the first ground pattern are exposed at both ends of the base;
A first ground layer laminated on the dielectric sheet;
A second ground layer laminated on the other surface of the base,
An FPC for high-speed transmission in which the first ground pattern and the first and second ground layers are connected by a plurality of through holes.   The 1st cover lay laminated | stacked on the said 1st ground layer so that the said 1st ground layer may be exposed to the both ends of the said base, The 2nd cover lay laminated | stacked on the said 2nd ground layer is provided. FPC for high speed transmission.   The FPC for high-speed transmission according to claim 1 or 2, wherein the first and second ground layers are made of silver foil.   4. The FPC for high-speed transmission according to claim 1, wherein the plurality of through holes are arranged at equal intervals in an extending direction of the first ground pattern. 5.   The FPC for high-speed transmission according to claim 4, wherein an interval between the plurality of through holes is equal to or less than a resonance wavelength of a predetermined high-frequency electromagnetic wave.   5. The FPC for high-speed transmission according to claim 4, wherein an interval between the plurality of through holes is about 5 mm.   The FPC for high-speed transmission according to any one of claims 1 to 4, wherein the base and the dielectric sheet are made of polyimide.   The FPC for high-speed transmission according to any one of claims 1 to 4, wherein the base and the dielectric sheet are made of a fluororesin.   The high-speed transmission FPC according to claim 1, wherein the high-speed transmission path includes a pair of differential signal paths. A printed circuit board connected to the high-speed transmission FPC according to claim 1,
A first ground region formed on one surface of the insulating substrate and connected to an end of the first ground layer;
Print contacts formed near the first ground region and connected to the ends of the plurality of high-speed transmission paths;
A plurality of second ground patterns connected to ends of the plurality of first ground patterns,
A printed circuit board in which the printed circuit board is connected to the high-speed transmission FPC when an end of the high-speed transmission FPC is pressed against the printed circuit board.   The printed circuit board according to claim 10, further comprising a second ground region formed on the other surface of the insulating substrate, wherein the first ground region and the second ground region are connected by a plurality of through holes.

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