JP2015060718A - Flat cable for signal transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat cable for signal transmission which can suppress deterioration of signal transmission characteristics in a high-frequency frequency band.SOLUTION: A flat cable for signal transmission includes signal conductors 1a and 1b, grounding conductors 2a, 2b, and 2c, and an upper electric insulation thin-film layer 4 and a lower electric insulation thin-film layer 5 which cover an electric insulation substrate 3 vertically in the thickness direction of the cable. A protective shield layer 8 consists of a metal layer 6 and an electric insulation plastic layer 7 and surrounds the outer peripheries of the upper and lower electric insulation thin-film layers in such a way that the metal layer is located inside and the electric insulation plastic layer is located outside. The protective shield layer surrounds the outer periphery, with one end edge part 10 and the other end edge part 11 in the longitudinal direction of the cable butted together. The upper and lower electric insulation thin-film layers 4 and 5 and the metal layer 6 are integrated by adhesion.

Description

  The present invention relates to a signal transmission flat cable that is thin and has excellent electrical characteristics, and more particularly, to a signal transmission flat cable suitable for internal wiring of a mobile phone, a notebook computer, or the like.

  Signal transmission flat cables used in high-density wiring electronic devices such as mobile phones and laptop computers are required to be thin and have low transmission loss in the high-frequency band in order to enable wiring in narrow spaces. Is done.

  As such a signal transmission flat cable, a signal conductor made of a metal thin film, a ground conductor made of a metal thin film, disposed on both sides of the signal conductor in the cable width direction, and an electric insulating base body laminated with the signal conductor and the ground conductor And an upper insulating thin film layer and a lower electrically insulating thin film layer covering these signal conductor, ground conductor and electric insulating base from above and below in the cable thickness direction, and an electrically insulating plastic layer is laminated on one surface of the metal layer, There has been proposed a coaxial cable provided with a protective shielding layer provided directly on the outer periphery of an upper electrically insulating thin film layer and an upper electrically insulating thin film layer so that the electrically insulating plastic layer is on the outside (Patent Document 1).

  In the coaxial cable, the protective shielding layer collectively surrounds the upper electrically insulating thin film layer and the lower electrically insulating thin film layer in the cross section of the cable, and overlaps one end edge on the outside of the other end edge in the cable longitudinal direction. It has an overlapping part formed by joining.

  A number of multi-core coaxials with multiple signal conductors have also been proposed. For example, a cable having a rectangular coaxial structure in which a central conductor through which a signal is transmitted is sandwiched between insulating films and the insulating film is further covered with an external conductor. After forming, bundling them in parallel has been attempted to improve high-speed transmission and noise resistance (Patent Document 2).

JP 2011-119198 A JP 2003-323824 A

  In the flat cable for signal transmission described in Patent Document 1, the protective shielding layer collectively surrounds the upper and lower electrical insulating thin film layers in the cable cross section, and one end portion in the longitudinal direction of the cable is It has the overlapping part formed by overlapping on the outer side of the other edge part. The upper electrical insulation thin film layer, the lower electrical insulation thin film layer, and the metal layer are bonded and integrated by melting the upper electrical insulation thin film layer and the lower electrical insulation thin film layer, thereby preventing the cable from being deformed. There are features.

  However, in this signal transmission flat cable, the overlapping portion is formed at the central portion in the cable width direction, and the upper and lower portions of the cable are surrounded by the protective shielding layer so that the upper and lower electric insulating thin film layers are collectively surrounded by the protective shielding layer. When the pressure is applied in the direction, the upper electrically insulating thin film layer and the lower electrically insulating thin film layer are recessed depending on the thickness of the overlapping portion, and the central portion becomes thinner than the other portions. The central part in the cable width direction where the signal conductor is located is the part where the electric field strength is the largest, and if the thickness of the upper and lower electrically insulating thin film layers changes here, the signal transmission characteristics in the high frequency band will decrease. Will do.

  A multi-core coaxial cable having a plurality of signal conductors also has the same problem in preventing the cable from being deformed and preventing the deterioration of signal transmission characteristics in a high frequency band.

  Therefore, an object of the present invention is to provide a flat cable for signal transmission that can prevent the cable from being deformed and can suppress a decrease in signal transmission characteristics in a high frequency band.

The present invention which achieves the above-described problems
A plurality of signal conductors made of metal thin films extending in the cable length direction parallel to each other on a plane;
A plurality of ground conductors made of metal thin films disposed on both sides of the signal conductor in the cable width direction;
An electrically insulating base on which the signal conductors and ground conductors are laminated;
An upper electric insulating thin film layer and a lower electric insulating thin film layer that cover the signal conductors, the ground conductors, and the electric insulating base from above and below in the cable thickness direction;
A protective shielding layer comprising a metal layer and an electrically insulating plastic layer, and surrounding the outer periphery of the upper electrically insulating thin film layer and the lower electrically insulating thin film layer such that the metal layer is located on the inner side and the electrically insulating plastic layer is located on the outer side. Prepared,
The protective shielding layer surrounds the outer periphery by abutting one end and the other end along the longitudinal direction of the cable, and the upper and lower electrically insulating thin film layers and the metal layer are integrated by bonding. It is characterized by that.

  In such a configuration, the protective shielding layer has a cross section of the upper electric insulating thin film layer and the lower electric insulating thin film layer in the cable longitudinal direction by abutting one end of the cable without overlapping the other edge. The upper electrical insulating thin film layer, the lower electrical insulating thin film layer and the metal layer are bonded and integrated, so that the multi-core coaxial cable can be prevented from being deformed, and in the high frequency band. A decrease in signal transmission characteristics can be suppressed.

  In addition, since the butted portion formed by abutting one end and the other end of the protective shielding layer is located on the ground conductor and away from the signal conductor, the signal transmission characteristics in the high frequency band are reduced. Can be deterred.

  The butt portion is preferably located on a region between the end of the protective shielding layer opposite to the signal conductor of the ground conductor and the central portion in the cable width direction of the ground conductor.

It is the perspective view which showed a part of flat cable for signal transmission of the present invention transversely. (A)-(e) is a cross-sectional view explaining the manufacturing method of the flat cable for signal transmission. (A), (b) is a cross-sectional view explaining the process of extracting the air in the space | gap between a signal conductor and a ground conductor.

  Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

  FIG. 1 is a cross-sectional perspective view of a part of a flat cable 100 for signal transmission showing an embodiment of the present invention. The flat cable 100 is configured as a multi-core coaxial cable, and two signal conductors 1a and 1b made of a metal thin film and three ground conductors 2a, 2b and 2c made of a metal thin film are formed on one surface of the electrically insulating base 3. It is arranged on a plane. The signal conductors 1a and 1b extend in the cable length direction L in parallel with each other. In this embodiment, two signal conductors are provided. The ground conductors 2b and 2a are arranged in parallel on the left and right sides of the signal conductor 1a in the cable width direction, and the ground conductors 2a and 2c are arranged in parallel on the left and right sides of the signal conductor 1b in the cable width direction. The ground conductor 2a is disposed between the signal conductors 1a and 1b, and the lengths of the ground conductors 2a, 2b, and 2c in the cable width direction are substantially equal. In this specification, the cable width direction is a direction indicated by W extending in the left-right direction in FIG. 1 in a direction orthogonal to the cable longitudinal direction indicated by L in FIG. 1 in which the signal transmission flat cable 100 extends long. The cable thickness direction is a direction indicated by D extending vertically in FIG.

  The upper electric insulating thin film layer 4 and the lower electric insulating thin film layer 5 are provided so as to cover the signal conductors 1a, 1b, the ground conductors 2a, 2b, 2c and the electric insulating substrate 3 from above and below in the cable thickness direction. In addition, a protective shielding layer 8 in which an electrically insulating plastic layer 7 is laminated on one surface of a metal layer 6 is provided on the outer periphery of the upper electrically insulating thin film layer 4 and the lower electrically insulating thin film layer 5. It is provided as follows.

  The protective shielding layer 8 is configured so that the upper electric insulating thin film layer 4 and the lower electric insulating thin film layer 5 are crossed in the cable cross section by abutting one end edge 10 without overlapping the other end edge 11 in the cable longitudinal direction. It is formed around the circumference. In other words, the protective shielding layer 8 forms a butt portion 12 in which the end edge portion 10 and the end edge portion 11 are continuously abutted in the cable longitudinal direction in the vicinity of the upper left corner of the cable cross section. The butting portion 12 is located away from the signal conductors 1a and 1b when viewed in the cable width direction, and is located on the left ground conductor 2b. The protective shielding layer 8 is preferably abutted so that the abutting portion 12 is formed as far as possible from the signal conductors 1a and 1b. Further, since the abutting portion 12 approaches the widthwise end of the cable, it becomes difficult to abut, so that the abutting portion 12 has the width X in the cable width direction of the ground conductor 2b as shown in FIG. Formed on a region of X / 2 width between the end of the grounding conductor 2b on the one end edge 10 of the protective shielding layer 8 on the side opposite to the signal conductor 1a and the central portion of the grounding conductor 2b in the cable width direction. Has been. In FIG. 1, the butting portion 12 is positioned on the left ground conductor 2b, but the protective shielding layer 8 may be butted so as to be positioned on the right ground conductor 2c. Thus, by separating the butting portion 12 from the signal conductor 1, the influence on the signal conductor is reduced, and a decrease in signal transmission characteristics in a high frequency band can be suppressed.

  In a state where the protective shielding layer 8 in which the metal layer 6 and the electrically insulating plastic layer 7 are laminated and integrated is formed on the outer periphery of the upper electrically insulating thin film layer 4 and the lower electrically insulating thin film layer 5, the protective shielding layer 8 is viewed from above and below. By applying heat and pressure (hot pressing), the upper electric insulating thin film layer 4 and the lower electric insulating thin film layer 5 are softened and melted and integrated with the metal layer 6, thereby causing the protective shielding layer 8 to be deformed. Can be prevented.

  Further, since the generation of an opening can be prevented simply by abutting the end edge portion 10 and the end edge portion 11 of the protective shielding layer 8 without overlapping each other, the upper electric insulating thin film layer 4 and the lower electric insulating thin film at the time of heating and pressurization can be prevented. The thickness of the layer 5 is constant over the entire cable width, and it is possible to suppress a decrease in signal transmission characteristics in the high frequency band.

  In the present embodiment, the bent portions 9a and 9b are formed by bending the end portions of the ground conductors 2b and 2c and the electrically insulating base 3 laminated to the end portions of the lower electrically insulating thin film layer 5, and the bent portions 9a, 9b, The ground conductors 2b and 2c of 9b are positioned on the metal layer 6 side. Accordingly, the ground conductors 2b and 2c and the metal layer 6 are brought into stable electrical contact, and an increase in signal transmission loss in the high frequency band of the signal transmission flat cable can be suppressed. The bent portion 9 may be formed on the upper electrically insulating thin film layer 4 side.

The signal conductors 1a, 1b and the ground conductors 2a, 2b, 2c are both made of a highly conductive metal, and specifically, copper (conductivity: 5), which is commonly used as a highly conductive metal industrially. .76 × 10 ⁷ Siemens / m) processed into a foil shape is laminated on the electrically insulating thin film layer 4 or the electrically insulating substrate 3, or copper is deposited or plated on the electrically insulating thin film layer 4 or the electrically insulating substrate 3. As the metal other than copper, aluminum (conductivity: 3.96 × 10 ⁷ Siemens / m) can be given.

  In electronic devices that transmit high-frequency signals exceeding 2 GHz, such as mobile phones and laptop computers, current concentrates on the surface layer of several microns due to a phenomenon called the skin effect, so that the conductivity is copper or aluminum. Since a smaller plating layer such as nickel increases transmission loss, it is necessary to prevent such a plating layer from being formed on the surfaces of the signal conductors 1a and 1b and the ground conductors 2a, 2b and 2c.

  The metal layer 6 that forms the protective shielding layer 8 is preferably formed of a highly conductive metal such as copper or aluminum, like the signal conductors 1a and 1b and the ground conductors 2a, 2b, and 2c. In the conventional signal transmission flat cable, a conductive adhesive layer is formed on the surface of the metal layer 6 to bond the upper electrically insulating thin film layer 4 and the lower electrically insulating thin film layer 5 to the metal layer 6. As described above, the conductive adhesive layer increases transmission loss in an electronic device that transmits a high-frequency signal exceeding 2 GHz. Therefore, the upper electrically insulating thin film layer 4, the lower electrically insulating thin film layer 5, the metal layer 6, and the like. It is necessary not to form a conductive adhesive layer between them.

  In this example, the thickness of the upper electrically insulating thin film layer 4 is 0.125 mm, the thickness of the electrically insulating base 3 is 0.025 mm, and the thickness of the lower electrically insulating thin film layer 5 is 0.100 mm. For signal transmission having the same signal transmission characteristics as a round coaxial cable with a characteristic impedance of 50Ω, with the thicknesses of the upper and lower insulators of the signal conductor 1 and the ground conductors 2 and 2 being equal (each 0.125 mm) The multi-core coaxial flat cable 100 can be realized. A copper-clad laminate obtained by laminating a 0.025 mm thick electrically insulating base and a copper foil is commercially available. By using such a commercially available product, the cost of a flat cable for signal transmission can be reduced. .

  The upper electrically insulating thin film layer 4 and the lower electrically insulating thin film layer 5 are made of a thermoplastic resin material having a property of being melt-bonded by heating, and the upper electrically insulating thin film layer 4 and the lower electrically insulating thin film layer 4 are heated by heat applied from the outside of the protective shielding layer 8. By melting and bonding the lower electric insulating thin film layer 5 and the metal layer 6, the upper electric insulating thin film layer 4 and the lower electric insulating thin film layer 5 and the protective shielding layer 8 are hardly peeled off. The upper electric insulating thin film layer 4 and the lower electric insulating thin film layer 5 and the metal layer 6 are directly bonded without an adhesive which causes an increase in transmission loss. Transmission is possible.

  The electrically insulating plastic layer 7 is made of a thermoplastic material having a property of being melt-bonded by heating. For this reason, the protective shielding layer 8 includes the upper electrically insulating thin film layer 4 in the cross section of the cable in a state in which the metal layer 6 is disposed on the inner side and the electrically insulating plastic layer 7 is disposed on the outer side, and the both are directly laminated without inclusions such as adhesive. In addition, the lower electrically insulating thin film layer 5 can be collectively surrounded. That is, the protective shielding layer 8 is formed by laminating the metal layer 6 and the electrically insulating plastic layer 7 without inclusions such as an adhesive, and can be formed as thin as there is no adhesive. A multi-core coaxial flat cable for transmission can be realized.

  Further, the protective shielding layer 8 has a butt portion 12 formed by abutting one end edge portion 10 and the other end edge portion 11 in the cable longitudinal direction. In this case, the metal layer 6 and the electrically insulating plastic layer 7 are bonded and integrated by melting the electrically insulating plastic layer 7 by heating, and an opening is formed at the butted portion 12 between the edge portion 10 and the edge portion 11 and in the vicinity thereof. Is less likely to occur, and the reduction of the shielding effect can be suppressed.

  When hot pressing is performed from above and below the protective shielding layer 8 in a state where the protective shielding layer 8 is coated on the outer periphery of the upper electrically insulating thin film layer 4 and the lower electrically insulating thin film layer 5, the electrically insulating plastic layer is formed by hot pressing. In order to prevent the deformation of 7 or make it difficult to deform, the upper electrically insulating thin film layer 4 and the lower electrically insulating thin film layer 5 and the electrically insulating plastic layer 7 are made of the same material, or the upper electrically insulating film The thin film layer 4 and the lower electrically insulating thin film layer 5 are preferably selected from materials that are thermally softened at a lower temperature than the electrically insulating plastic layer 7.

  The upper electrically insulating thin film layer 4 and the lower electrically insulating thin film layer 5 are preferably materials having a property of being melt-bonded by heating and having a low dielectric constant and dielectric loss tangent in a high frequency band exceeding 2 GHz. Examples of such materials include liquid crystal polymers and polytetrafluoroethylene.

  The liquid crystal polymer is a thermoplastic resin that exhibits optical anisotropy when melted. Specifically, it is a fully aromatic or semi-aromatic polyester, polyesterimide, polyesteramide, or a resin composition containing these. Among them, a liquid crystal polyester resin composition having (A) a liquid crystal polyester as a continuous phase and (B) a copolymer having a functional group having reactivity with the liquid crystal polyester as a dispersed phase is preferable.

  The electrically insulating plastic layer 7 has a property of being melted and bonded by heating, like the upper electrically insulating thin film layer 4 and the lower electrically insulating thin film layer 5, and the upper electrically insulating thin film layer 4 and the lower electrically insulating thin film layer 5 and the metal. The layer 6 must have a property of not being deformed or hardly deformed by heat applied when the layer 6 is bonded by heating. As such a material, when the electrically insulating thin film layer 4 is formed of a liquid crystal polymer, liquid crystal Examples thereof include a plastic composition containing a polymer or a polar organic solvent-soluble polyamideimide resin and a fluorine-based resin.

  The film formed of the polar organic solvent-soluble polyamideimide resin alone has a dielectric constant of 3.5 or more and a dielectric loss tangent of 0.012 or more (both dielectric constant and dielectric loss tangent are measured at a frequency of 1 GHz by cavity resonator perturbation). The film (electrically insulating plastic layer 7) formed of a plastic composition containing a polar organic solvent-soluble polyamideimide resin and a fluororesin has a dielectric constant of 3.20 or less and a dielectric loss tangent of 0.01 or less (dielectric constant). The dielectric loss tangent is measured at a frequency of 1 GHz by perturbation of the cavity resonator), and the electrical characteristics are remarkably improved.

  The fluororesin is one or two selected from polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, and the like. More than seeds are used.

  Next, a method for manufacturing the signal transmission flat cable of this embodiment will be described with reference to FIG. A copper-clad laminate in which a copper foil C having a width wider than that of the electrically insulating substrate 3 is taken into consideration on the upper surface of the electrically insulating substrate 3 in consideration of the bent portions 9a and 9b is prepared (FIG. 2 (a)). The signal conductors 1a and 1b and the ground conductors 2a, 2b and 2c are formed by etching C (FIG. 2B). At this time, the center of the ground conductor 2a coincides with the center 3a of the electrical insulating base 3, and the width between the ground conductors 2a and 2b and the width between the ground conductors 2a and 2c become the same value W1, Etching is performed so that the center of the signal conductor 1a is located at the center between the terminals 2a and 2b and the center of the signal conductor 1b is located at the center between the ground conductors 2a and 2c.

  Next, the upper electrical insulating thin film layer 4 is laminated on the signal conductors 1a, 1b and the ground conductors 2a, 2b, 2c, and the lower electrical insulating thin film layer 5 is provided below the electrical insulating base 3 (FIG. 2 (c). )), Bent portions 9a and 9b are formed by bending both ends of the electrical insulating base 3 in the cable width direction integrally with the ends of the ground conductors 2b and 2c in the cable width direction (FIG. 2D).

  Subsequently, as shown in FIG. 2 (e), a protective shielding layer 8 is formed on the outer periphery of the upper electrical insulating thin film layer 4 and the lower electrical insulating thin film layer 5, and heated and pressurized from above and below the protective shielding layer 8 ( By applying a hot press, the upper electric insulating thin film layer 4 and the lower electric insulating thin film layer 5 are softened and melted and bonded to the metal layer 6 to produce a flat cable 100 for signal transmission as shown in FIG. .

  The flat cable for signal transmission of the present embodiment plays a role of reinforcing the signal conductors 1a and 1b and the ground conductors 2a, 2b and 2c in which the electrically insulating base 3 is a metal thin film. Is significantly improved in the handling of the ground conductors 2b and 2c, and the formation of the bent portions 9a and 9b is facilitated.

  In the embodiment, the bent portions 9a and 9b are formed by bending both ends of the electric insulating base 3 in the cable width direction to the lower electric insulating thin film layer 5 side integrally with the ends of the ground conductors 2b and 2c in the cable width direction. However, the bent portion may be formed by bending toward the upper electrically insulating thin film layer 4 side. In this case, the signal conductors 1a, 1b and the ground conductors 2a, 2b, 2c are provided above the electrically insulating base 3, so that the ground conductors 2b, 2c and the metal layer 6 are brought into contact with each other by bending, and the upper electrical Insulation above and below the signal conductors 1a, 1b and the ground conductors 2a, 2b, 2c so that the thickness of the insulating thin film 4 is equal to the sum of the thickness of the electrical insulating base 3 and the thickness of the lower electrical insulating thin film 5. It is preferable to make the body thickness equal.

  When the signal transmission flat cable is a multi-core coaxial cable as in this embodiment, a large number of air gaps are formed between the signal conductor and the ground conductor, and if air exists there, the dielectric constant increases. Therefore, as shown in FIG. 3A, the position of the electrically insulating substrate 3 corresponding to the gap position between the signal conductor 1a and the ground conductors 2a and 2b and the gap position between the signal conductor 1b and the ground conductors 2a and 2c. Air vent hole 3b is formed. Then, as shown in FIG. 3B, the upper electrically insulating thin film layer 4 is pressed against the signal conductors 1a, 1b and the ground conductors 2a, 2b, 2c by pressing to seal each gap, and then air is vented. . Although not shown in the drawing, the air is removed by using an apparatus in which the air in each gap is extracted from the air vent hole 3b. When the air is released, the lower electrically insulating thin film layer 5 is pressed from the lower part to be brought into close contact with the electrically insulating substrate 3, and the air is released from each gap. Thereafter, the same processes as those shown in FIGS. 2D and 2E are performed, and a multi-core coaxial cable that has been air-bleeded is manufactured.

  In the above-described embodiment, two signal conductors and three ground conductors are provided, but a plurality of signal conductors and ground conductors may be provided. In this case, the number of the ground conductors is provided by the number of signal conductors + 1. In any number, the signal conductors and the ground conductors are arranged so as to be symmetrical with respect to the center line 3a of the electrical insulating base 3, and adjacent ground conductors are provided. The distance between them is the same (W1 in FIG. 2B), and they are arranged so that the center of the signal conductor is located at the center between the ground conductors. In addition, the ground conductors are arranged so as to be located at both ends of the cable in the width direction. When the number of signal conductors is an even number, the ground conductor is located at the position of the center 3a of the electrical insulating base 3, and when the number is odd, the signal conductor is located at the position of the center 3a.

  According to the present invention, the protective shielding layer can be prevented from being deformed due to the occurrence of peeling between the electrically insulating thin film layer and the protective shielding layer, and the upper electrically insulating thin film layer 4 and the lower electrically insulating thin film layer can be prevented. Since the change in thickness in the cable width direction of 5 can be suppressed, it is possible to suppress a decrease in signal transmission characteristics in the high frequency band of the multi-core coaxial cable.

DESCRIPTION OF SYMBOLS 1a, 1b Signal conductor 2a, 2b, 2c Grounding conductor 3 Electrical insulation base | substrate 3a Air vent hole 4 Upper electrical insulation thin film layer 5 Lower electrical insulation thin film layer 6 Metal layer 7 Electrical insulation plastic layer 8 Protective shielding layer 9 Bending part 12 Butting part

The present invention which achieves the above-described problems
A plurality of signal conductors made of metal thin films extending in the cable length direction parallel to each other on a plane;
A plurality of ground conductors made of metal thin films disposed on both sides of the signal conductor in the cable width direction;
An electrically insulating substrate, wherein the signal conductors and each ground conductor are laminated,
Wherein each signal conductor, the upper electrical insulating thin film layer in which the coating each ground conductor and said electrically insulating base from the top and bottom of the cable thickness direction and a lower electrical insulating thin film layer,
A metal layer and the electrically insulating plastic layer, the metal layer on the inside, a protective shield layer, wherein the electrically insulating plastic layer surrounds the outer periphery of the to be located outside the upper electrically insulating thin film layer and the lower electrically insulating thin film layer And comprising
The protective shield layer, as well as abut one edge portion along the cable longitudinal direction and the other edge portion is surrounding the periphery, the upper and lower electrically insulating thin film layer and the metal layer with an adhesive Integrated,
A butted portion formed by abutting one end of the protective shielding layer with the other end of the other is located on a ground conductor that is not sandwiched between the signal conductors .

Claims (6)

A plurality of signal conductors made of metal thin films extending in the cable length direction parallel to each other on a plane;
A plurality of ground conductors made of metal thin films disposed on both sides of the signal conductor in the cable width direction;
An electrically insulating base on which the signal conductors and ground conductors are laminated;
An upper electric insulating thin film layer and a lower electric insulating thin film layer that cover the signal conductors, the ground conductors, and the electric insulating base from above and below in the cable thickness direction;
A protective shielding layer comprising a metal layer and an electrically insulating plastic layer, and surrounding the outer periphery of the upper electrically insulating thin film layer and the lower electrically insulating thin film layer such that the metal layer is located on the inner side and the electrically insulating plastic layer is located on the outer side. Prepared,
The protective shielding layer surrounds the outer periphery by abutting one end and the other end along the longitudinal direction of the cable, and the upper and lower electrically insulating thin film layers and the metal layer are integrated by bonding. Flat cable for signal transmission, characterized in that   The flat cable for signal transmission according to claim 1, wherein a butted portion formed by abutting one end and the other end of the protective shielding layer on each other is located on the ground conductor.   The butted portion is located on a region between an end portion of the protective shielding layer opposite to the signal conductor of the ground conductor on one end edge portion and a central portion in the cable width direction of the ground conductor. The flat cable for signal transmission according to claim 2.   The both ends of the electrical insulation base in the cable width direction and the end of each ground conductor opposite to the signal conductor are bent together so that the ground conductor and the metal layer of the protective shielding layer are in electrical contact. The flat cable for signal transmission according to any one of claims 1 to 3, wherein the flat cable for signal transmission is provided.   Make the thickness of the upper and lower insulators equal to the thickness of the upper and lower insulators of the signal and ground conductors by making the thickness of the upper insulating film equal to the thickness of the insulating base and the lower insulating film. The signal transmission flat cable according to claim 1, wherein the flat cable for signal transmission is provided.   6. An air vent hole for venting air in a gap formed between a ground conductor and a signal conductor is formed at a position of an electrically insulating base corresponding to the gap position. The flat cable for signal transmission according to item 1.

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