JP2010129475A - Flexible flat cable excellent in dielectric characteristics and flexibility - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an FFC superior in dielectric characteristics and flexibility. <P>SOLUTION: This FFC is equipped with a plurality numbers of conductors 2 arranged in parallel, a first insulating layer 3 installed by pinching the plurality of numbers of these conductors 2 from both face sides, and a second insulating layer 4 arranged on one side or both sides of thickness direction of this first insulating layer 3, and on a surface of one side or front and rear both sides of thickness direction of the second insulating layer 4, uneven parts 4a, 4b for dielectric constant adjustment arranged alternately along the plurality of numbers of conductors 2 are formed. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a signal cable that mainly transmits an electric signal in an electronic device, and more particularly to a flexible flat cable having a structure in which a plurality of conductors are arranged in parallel and surrounded by an insulating layer.

In general, signal cables used in the field of electronic equipment are often folded and assembled in the casing of electronic equipment, so flexibility is required, and consideration is given to connectivity including connector connection. In many cases, a flattened structure in which a plurality of conductors are arranged in a row is used. Therefore, the signal cable having the above-described characteristics is referred to as a flexible flat cable and is abbreviated as FFC. (Hereinafter, it may be abbreviated as FFC in this specification.)
In recent years, electronic devices have been rapidly reduced in size, weight and functionality. Therefore, in various electronic devices, a large number of IC chips are mounted, the signal transmission capacity is increased, and the signal transmission speed is increased. In particular, since the signal transmission frequency is becoming high, the electric signal noise in the electronic equipment is also increased, so that an electric signal transmission medium is required to have excellent electromagnetic wave shielding (shielding) characteristics. . Further, it is necessary to use a signal cable with controlled impedance as a signal cable in the electronic apparatus.

In general, it is known that in an FFC that transmits an electric signal, impedance and capacitance change depending on the dielectric constant of the insulator, and as a result, the propagation delay time of the electric signal changes. In many cases, a plastic material is used for the insulator, and it is also known that the dielectric constant as the insulator changes depending on the foaming degree of the plastic material. Furthermore, it is also known that the mechanical strength as an insulator changes depending on the foaming degree of the plastic material.
Usually, the dielectric constant decreases when the foaming degree of the plastic material is increased. Increasing the degree of foaming is synonymous with increasing the volume of air remaining in the plastic material, and is a self-evident phenomenon. That is, when the foaming degree of an insulator made of a plastic material applied to FFC is increased, the dielectric constant of the plastic material is decreased, and the propagation delay time of the electric signal flowing through the conductor is reduced, so that the electrical characteristics as FFC are improved. . However, when the foaming degree is increased, the mechanical properties as a plastic material are decreased, so that excessive foaming leads to a decrease in strength of the FFC, and there is a possibility that the FFC is likely to break due to repeated bending or the like. is there.
In general, FFC is manufactured using a commercially available laminating apparatus, and at that time, a plastic material having a predetermined degree of foaming is used. And as a plastic material applied to this type of FFC, a sheet-like material whose degree of foaming is determined by the blending ratio of the foaming agent is used.

By the way, as an example of the structure of a conventional FFC, a parallel multi-core electric wire in which both sides of a plurality of conductors arranged in parallel are sandwiched between plastic films and formed into a thin tape shape, and the plastic film serving as an insulating layer is stretched in one direction. An FFC that is oriented, contains 5 to 35% by volume of cavities inside, and defines the density of the number of layers of cavities in the film is known. (See Patent Document 1)
In addition, as a flat cable with a shield, an insulating plastic film is provided on both upper and lower surfaces of a conductor group in which a signal line and a ground line are arranged in parallel, a shielding material is provided on at least one side of the insulating plastic film, and insulation on the side where the shielding material is arranged A shielded FFC in which the thickness of a plastic film is 120 μm or more is known. (See Patent Document 2)
Further, an FFC having a structure in which a conductor, an insulating layer covering the conductor, a low dielectric layer provided on the outer surface of the insulating layer, and a shield layer are combined with a polyolefin resin sheet as the low dielectric layer is known (patent) Reference 3), comprising a plurality of conductors, an insulating layer covering the conductor, a low dielectric layer and a shield layer provided on the outer surface of the insulating layer, and a polycarbonate resin, a modified polyphenyl ether resin, polyphenylene sulfide as the low dielectric layer FFCs having a structure mainly composed of a resin composition made of a resin, an imide resin, a polyacrylate resin, or the like are known. (See Patent Document 4)
Moreover, it is a structure consisting of at least one conducting wire and a void-containing thermoplastic resin film, defines the number of voids laminated in a thermoplastic resin film containing 3 to 45% by volume of voids, and further comprises a metal thin film layer. FFCs with different structures are known. (See Patent Document 5)
Japanese Patent No. 4120894 JP 2007-299704 A JP 2008-0475505 A JP 2008-198592 A JP 2007-323918 A

  In the techniques described in Patent Documents 1 and 5, an FFC is proposed in which the foaming degree of a plastic material is controlled by a known technique to adjust the dielectric constant. No consideration is given to the aspect. In the structure in which foamed plastic is applied to FFC as in the techniques described in Patent Documents 1 and 5, foamed PET (polyethylene terephthalate) and foamed PP (polypropylene) can be exemplified as representative examples of foamed plastic. Plastic has a tendency to become harder as the thickness increases, and there is a problem that the flexibility becomes inferior. In the FFC provided with these, there is a problem that the high flexibility that the FFC should originally have is remarkably impaired. . That is, in the FFC that has been provided in the past, the dielectric constant can be adjusted, and a structure in consideration of the flexibility inherent in the FFC has not been provided.

Furthermore, the FFC structure described in Patent Documents 3, 4, and 5 surrounds a conductor group in which a plurality of conductors are arranged in parallel with an insulating layer, and shields an additional resin layer that can be referred to as an intervening outside thereof. Although the transmission characteristic is improved by inserting it between the layers, it is not a structure considering the flexibility that the FFC should originally have.
In general, some FFCs are provided with a shield layer for blocking electromagnetic waves. However, when a shield layer is provided, the FFC is excellent in blocking electromagnetic waves generated during transmission of electric signals. In addition, there is a demand for a structure that can adjust the dielectric constant and considers the flexibility inherent in FFC.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an FFC excellent in dielectric characteristics and excellent in flexibility. Another object of the present invention is to provide an FFC having excellent dielectric properties and flexibility even with a structure having a shield layer.

The flexible flat cable of the present invention includes a conductor group composed of a plurality of conductors arranged in parallel, an insulating layer provided to cover the conductor group, and an intermediate layer disposed on the front side or the back side of the insulating layer. An intervening layer is provided, and concave and convex portions for adjusting a dielectric constant that are alternately arranged along the plurality of conductors are formed on the surface or both surfaces of the intermediate intervening layer.
The flexible flat cable of the present invention is characterized in that the concavo-convex portions are uniformly arranged in the length direction and the width direction with respect to each of the plurality of conductors, and the dielectric constant is averaged.

  The flexible flat cable of the present invention is arranged such that a boundary portion of the uneven portion is arranged in the width direction of the insulating layer or in a specific direction having a predetermined angle with the width direction, and bends along the boundary portion of the uneven portion. It is characterized in that flexibility is improved by the concavo-convex portion so as to allow the above.

The flexible flat cable according to the present invention is characterized in that a vertical width and a horizontal width of the concavo-convex portion are in a range of 0.15 mm to 2.0 mm.
The flexible flat cable of the present invention is characterized in that the plurality of conductors arranged in parallel are arranged at a pitch in the range of 0.3 mm to 1.0 mm.
In the present invention, a shield layer may be formed outside the intermediate intermediate layer.

According to the present invention, even when a conductor structure is formed in which a plurality of conductors are arranged in parallel and covered with an insulating layer, the dielectric constant of the plurality of conductors can be equalized, thereby increasing the signal propagation time. The transmission characteristics can be improved by suppressing the change of the signal and reducing the signal deviation. In addition, the above-described effects can be reliably obtained by adjusting the dielectric constant by alternately arranging the uneven portions in the length direction of the plurality of conductors.
By equalizing the concavo-convex portions in both the length direction and the width direction of the conductor, it is possible to suppress a change in signal propagation time, reduce a signal shift, and further improve transmission characteristics.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a plan view of a flexible flat cable (hereinafter sometimes abbreviated as FFC) according to a first embodiment of the present invention, and FIG. 2 is a partially enlarged view of the FFC. The FFC 1 of the first embodiment according to the present invention includes a conductor group 2A composed of a plurality of conductors 2 arranged in parallel at a predetermined pitch, and a sheet-like insulating layer 3 provided surrounding the conductor group 2A. The intermediate layer 4 provided on one side or both sides of the insulating layer 3 is mainly used. In the example shown in FIGS. 1 and 2, no other layer is disposed outside the intermediate intervening layer 4, but a shield layer is usually disposed outside the intermediate intervening layer 4, so that the shield layer will be described later. To do.

In this embodiment, the conductor 2 is made of a conductor made of a metal material having good conductivity such as a flat copper wire, copper foil, tin-plated annealed copper foil, and the like. A conductor group 2A is configured by arranging two conductors 2 in parallel at a predetermined pitch. For example, the width of the conductor 2 applied to the FFC 1 of the present embodiment may be in the range of 0.1 to 1.0 mm, preferably in the range of 0.2 mm to 0.8 mm.
Moreover, the range between 0.3 mm-1.0 mm can be employ | adopted for the pitch between the conductors 2 arrange | positioned in parallel, for example.

In the insulating layer 3 of the present embodiment, the portions excluding both ends of the plurality of conductors 2 arranged in parallel are sandwiched between insulating sheets with an adhesive layer from both sides in the thickness direction, and the adhesive layer between the insulating sheets The two insulating sheets and the conductor 2 are bonded and integrated, and one of the insulating sheets sandwiching the plurality of conductors 2 is formed to a length reaching both ends of the conductor 2, and the other insulating sheet is a conductor. 2 of the two conductors 2 formed in a length so as to leave a predetermined length at both ends of the two conductors 2, only the portion on one side in the thickness direction of the conductor 2 is exposed. The exposed portion of the conductor 2 is a terminal 2a.
Further, PET (polyethylene terephthalate) is used as a constituent material of the insulating layer 3, and polyester, PP (polypropylene), PVC (polyvinyl chloride), or the like is used as an adhesive. In the present invention, the insulating layer 3 and the adhesive are used. The material is not limited to these. The thickness of the insulating layer 3 can be about 0.015 mm, for example, and the thickness of the adhesive layer can be about 35 μm, for example.

In the present embodiment, the intermediate intervening layer 4 is formed by embossing a sheet of plastic film containing fibers and forming uneven portions on the front and back surfaces.
Specific examples of the material constituting the plastic film sheet include PP (polypropylene), PET (polyethylene terephthalate), PE (polyethylene), and PI (polyimide), but are not limited to these resins. An insulating resin can be used as appropriate. The intermediate intervening layer 4 is not limited to a plastic film sheet containing fibers, and may be a general plastic film containing no fibers, a foam sheet, a foam film, or the like. In the case of using a foamed sheet containing fibers, a material having a pore content ratio of 30 to 80% is used. However, in the present invention, the pore content ratio is not limited to the above range.
In the embodiment shown in FIG. 1, as an example in which the concavo-convex portion is formed, the intermediate intervening layer 4 having a configuration in which the concave portions 4 a and the convex portions 4 b having a square shape in plan view are alternately arranged vertically and horizontally in a grid pattern. The recesses 4 a and the protrusions 4 b are alternately and evenly arranged in the length direction of the conductor 2 and are also alternately and evenly arranged in the width direction of the conductor 2.

  As an example of the intermediate intervening layer 4, as shown in FIG. 4, a resin sheet 7 having a structure in which a plurality of fibers 6 are dispersed therein is embossed with a roll having irregularities on the surface, as shown in FIG. The intermediate intervening layer 4 having a structure in which the concave portions 4a and the convex portions 4b are alternately formed adjacent to each other on the front and back surfaces of the sheet can be preferably applied. When embossing is performed on the fiber-containing sheet 7 as shown in FIG. 4, the size (depth) of the recess of the emboss is such that the sheet is pressed to such an extent that the internal fibers are not in close contact with each other. The size is preferably such that the difference in fiber density is minimized by the unevenness.

Furthermore, in the embodiment shown in FIG. 1, the width of the conductor 2 and the width of the concave portion 4a and the convex portion 4b are made substantially the same and are alternately arranged, and the width of the conductor 2 and the arrangement pitch of the conductor 2 are the same value. As shown, the recesses 4a and the projections 4b are alternately and evenly arranged in the length direction of the conductor 2, and the recesses 4a and the projections 4b are alternately and evenly arranged in the portion between the adjacent conductors 2 and 2. Furthermore, the concave portions 4a and the convex portions 4b are alternately and evenly arranged in the arrangement direction of the plurality of conductors 2.
When the intermediate intervening layer 4 is composed of the fiber-containing sheet 7, the fiber density is different between the concave portion 4a and the convex portion 4b as shown in FIG. 4, so the concave portion 4a portion and the convex portion 4b portion. Therefore, the dielectric constant is different and the thickness is also different. If the dielectric constants of the adjacent conductors 2 in the FFC 1 shown in FIG. 1 are different, the signal propagation time changes, skew (signal deviation) increases, and transmission characteristics such as occurrence of common mode may be affected. is there. In order to avoid this problem, it is preferable that uneven portions exist at the pitch interval of the conductor 2 and the dielectric constant is averaged also in the width direction (lateral direction) and the length direction of the conductor 2.

  The pitch of the concavo-convex portions is preferably the same as the pitch of the conductor 2, but even when it is not the same, it is preferable that the standing wave hardly generate when the conductor 2 is energized. For example, as long as the dielectric constant and thickness of the portion covering the conductor 2 are averaged, the size of the uneven portion may be an integral multiple of the conductor pitch. The size limit is preferably other than an integral multiple of 1/4 of the wavelength of the input signal from the standpoint that standing waves are less likely to occur. For example, in the case of a conductor pitch of 0.3 mm, the pitch of the unevenness can be selected from 0.15 mm, 0.3 mm, 0.6 mm, etc. In the case of 0.5 mm, the concavo-convex pitch can be selected from 0.25 mm, 0.5 mm, 1.0 mm, etc. In the case of the conductor pitch of 0.8 mm, the concavo-convex pitch is 0.4 mm, 0.8 mm, 1.6 mm. When the conductor pitch is 1.0 mm, the concavo-convex pitch can be selected from 0.25 mm, 0.5 mm, 1.0 mm, and the like.

Here, the standing wave means that the effective dielectric constant of FFC (dielectric constant calculated from the propagation time of TDR: Time Domain Reflectometry) is about 2.2 (in the case of an example described later), and λ / of 5 GHz. 4 is 5 mm at 10 mm and 10 GHz. If the third, fifth and seventh harmonics are not reflected as well as the fundamental wave of the transmission signal, the signal quality can be maintained to some extent. When transmitting a signal of 5 Gbps, the fifth harmonic is 12.5 GHz and the seventh harmonic is 17.5 GHz (λ / 4 = about 2.9 mm). Assuming that a signal of 10 Gbps will be handled in the future, λ / 4 of the seventh harmonic is about 1.4 mm. Therefore, it is considered that the embossed irregularities have a good size (vertical width and horizontal width) not exceeding about 2.0 mm.
In other words, the depth of the concave portion 4a is, for example, 80 μm to 130 μm from the upper surface of the convex portion 4b to the bottom of the concave portion 4a. And the depth of this recessed part 4a has preferable 50 to 10% of the total thickness of the intermediate | middle intervening layer 4, for example.

  The shield layer provided outside the intermediate intervening layer 4 is generally composed of a metal layer and an adhesive layer, and the metal layer is a metal sheet having a thickness of about 5 to 20 μm (for example, a highly conductive metal such as Cu, Ag, or Al). Rolled metal sheet), and a conductive layer in which conductive particles are dispersed inside the adhesive resin is applied to the adhesive layer. The conductive particles include conductive carbon particles and metal particles such as copper, aluminum, nickel, and silver. Are distributed uniformly. The application form of the adhesive may be a uniform application on one side or a zebra-like (meandering) form. In the present embodiment, the material of the shield layer and the material of the adhesive layer are not particularly specified. Further, the surface resistivity of the shield layer is generally 10Ω or less, but in this embodiment, the surface resistivity of the shield layer is not particularly specified.

  In the FFC 1 including the intermediate intervening layer 4 having the uneven portion having the structure shown in FIGS. 1 and 2, the intermediate intervening layer 4 itself is provided with flexibility by forming the uneven portion in the intermediate intervening layer 4. In addition, the presence of the intermediate intervening layer 4 can achieve a low dielectric constant as the FFC 1. This is because, for example, an intermediate layer made of a foamed resin used in an FFC having a conventional structure, the porosity of the intermediate layer itself is improved when the porosity is increased to reduce the dielectric constant. Although the strength also decreases, in the intermediate intervening layer 4 having the concavo-convex portion, the volume ratio of the air portion is large due to the presence of the plurality of concave portions 4a. It is advantageous for increasing the dielectric constant. Moreover, in FFC1 provided with the intermediate | middle intervening layer 4 provided with the uneven | corrugated | grooved part of the structure shown in FIG. 1, FIG. 2, when bending is considered, the recessed part 4a and the convex part 4b are those width parts of FFC1 in those width directions. Since the boundaries are arranged in a line, the boundary between the concave portion 4a and the convex portion 4b is easily aligned with the folding when viewed as FFC1, and the intermediate intervening layer 4 is deformed so as to follow the folding. Therefore, flexibility is also good.

  In the present invention, the shape of the concavo-convex portion is not limited to a square shape, and may be a polygonal shape such as a triangle, a quadrangle, a hexagon, an octagon, or an arbitrary shape such as a round shape or a star shape. The shape itself is not limited. From the viewpoint of the above-mentioned bendability, not only the quadrangular shape but also a hexagonal shape, an octagonal shape, or the like that is advantageous for bending can be employed. This is because the flexibility such as bending when viewed as FFC1 is improved at the boundary of the concavo-convex portion as described above.

5 and 6 show a second embodiment of the FFC according to the present invention, and the FFC 10 of this embodiment has a structure in which concave and convex portions are alternately arranged in an oblique direction with respect to the length direction of the conductor. ing.
The basic structure as the FFC 10 is equivalent to the FFC 1 of the previous form, and has a conductor group 2A composed of conductors 2 arranged in parallel, and sheet-like insulating layers 3 and 3 are integrated by adhesion from both sides in the thickness direction, The structure in which the intermediate intervening layer 11 is arranged on one side or both sides thereof and the shield layer is arranged outside the intermediate intervening layer 11 as necessary is equivalent.
The intermediate intervening layer 11 of the present embodiment is different from the intermediate intervening layer 4 of the previous embodiment in that the concave portion 11a and the convex portion 11b formed on the front side or the back side of the intermediate intervening layer 11 are each square. However, the arrangement is inclined 45 ° with respect to the length direction of the conductor 2, that is, each side of the square indicated by the contours of the recess 11 a and the protrusion b is 45 with respect to the length direction of the conductor 2. ° The difference is that they are aligned in a regular manner so as to be inclined.
In this embodiment, as shown in FIGS. 5 and 6, the center of the convex portion 11 b is aligned on the central axis of the conductor 2, and the center of the concave portion 11 a is positioned at the center position of the gap between the adjacent conductors 2 and 2. The concave portions 11a and the convex portions 11b are alternately arranged in the length direction and the width direction of the conductor 2 in alignment. The other components such as the constituent material of the intermediate intervening layer 11 are the same as those of the intermediate intervening layer 4 of the previous embodiment.

The pitch of the conductors 2 and the sizes of the recesses 11a to 11b in the embodiment shown in FIGS. 5 and 6 are the same as the structure of the previous embodiment. For example, the arrangement pitch of the conductors 2. In this case, as in the previous embodiment, if the dielectric constant and thickness of the portion covering the conductor (signal line) 2 are averaged, the size of the uneven portion may be an integral multiple of the arrangement pitch of the conductors 2. Can think. Further, in this embodiment, the arrangement angle of the concavo-convex portions is 45 ° as shown in an enlarged view in FIG. 6, but if the dielectric constant and thickness of adjacent conductors 2 are averaged, the arrangement angle is It is not limited to 45 °. In addition, it is possible to select a size and shape equivalent to the uneven portion of the previous embodiment, such as the size limit and the shape of the uneven portion.
The object of the present invention can be achieved even in the FFC 10 shown in FIGS.

FIG. 7 is a view showing an embodiment in which the shield layer 5 is arranged with respect to the FFC 1 shown in FIGS. 1 and 2, and FIG. 8 is a case in which the shield layer 12 is arranged with respect to the FFC 10 shown in FIGS. It is a figure which shows embodiment.
After the intermediate intervening layer 4 or the intermediate intervening layer 11 is disposed as shown in FIG. 7 or FIG. 8, an FFC with a shield layer is obtained by means such as a method of attaching the shield layer 5 or the shield layer 11 or a method of winding. be able to.
The object of the present invention can be achieved even in the FFC 10 shown in FIGS.

FIGS. 9 and 10 show a double-sided shield structure and a single-sided shield structure in an FFC having a shield layer, respectively. In addition, what is shown with the code | symbol 7 in FIG.9 and FIG.10 is a reinforcement board for reinforcing the terminal 2a part from the back side, when making the both ends of the conductor 2 into the exposed structure with the terminal 2a.
The structure in which the shield layers 13 are arranged on both sides of the conductor 2 as shown in FFC 1 and 10 shown in FIG. 9 and the structure in which the shield layer 13 is arranged only on one side of the conductor 2 as shown in FFC 1 and 10 shown in FIG. Even if it exists, this invention is applicable.
The object of the present invention can be achieved even with the FFC 10 shown in FIGS.

11 and 12 show an embodiment provided with a shield layer grounding structure in an FFC having a double-sided shield structure.
The FFC 20 shown in FIG. 11 uses the drain line 15 provided along the conductor 2 separately from the conductor 2, and arranges both ends of the drain line 15 by bending each of the ends of the shield layer 13. The shield layer 13 is arranged and connected on the bent portion 15 a of the drain line 15.
Further, the FFC 21 shown in FIG. 12 has a metal tape 16 disposed below the both end portions of the shield layer 13, the metal tape 16 is connected to the shield layer 13, and a metal tape on the insulating layer 3 near the terminal 2a portion. A portion of 16 is exposed, and this exposed portion is used as a ground connection portion 16a. In addition, although the tin plating copper tape, the copper tape, the aluminum tape, etc. can be used suitably as the metal tape 16, it is not limited to these in this invention, A highly conductive metal tape can be used suitably. In this structure, the metal tape 16 can be connected to the shield via a connector (not shown) to form a ground structure. In this structure, the metal tape 16 can be connected to the shield via a connector (not shown) to form a ground structure.
The object of the present invention can be achieved even with the FFCs 20 and 21 shown in FIGS.

FIG. 13 and FIG. 14 show an example of the FFC adopting the shield grounding structure. The FFC 22 of this example has a metal plate 23 arranged below both ends of the shield layer 13 and a shield on the metal plate 23. This is a structure in which both end portions of the layer 13 are laid over.
As the metal plate 23 in this example, one made of a rolled material made of copper, aluminum, tin-plated copper, or the like can be used. In this structure, the metal plate 23 can be connected to the shield via a connector (not shown) to form a ground structure.
The object of the present invention can be achieved even in the FFC 22 shown in FIGS.
FIGS. 15 and 16 show another example of the FFC adopting the shield grounding structure. The FFC 25 of this example has the reinforcing plate 7 disposed on the side opposite to the side where the terminal 2a of the conductor 2 is exposed. In this structure, a metal plate 24 is connected to the shield layer 13 on the reinforcing plate mounting side.
FIG. 17 shows an FFC 26 in which a single-sided shield structure is adopted as a grounding structure in which a drain line is connected to a shield layer. FIG. 18 shows a single-sided shield structure in a grounding structure in which a metal plate and a metal tape are connected to a shield layer. FIG. 19 shows an FFC 28 as an example of a single-sided shield structure that employs a grounding structure using a metal plate or metal tape.
Here, as a material of the metal tape and the metal plate, a tin-plated copper tape, a tin-plated metal plate, a copper tape, a copper metal plate, an aluminum tape, an aluminum metal plate, and the like can be used as appropriate, but the present invention is limited to these. Instead, a highly conductive metal tape or metal plate can be used as appropriate.
In any of the structures shown in these drawings, the shield layer 13 can be a ground structure, and the object of the present invention can be achieved.

<Example>
Examples of the present invention will be described below, but it is obvious that the present invention is not limited to the following examples.
30 conductors of tin-plated flat annealed copper wires with a width of 0.3 mm, a thickness of 0.5 mm, and a length of 100 mm are arranged in parallel at a pitch of 0.5 mm as a conductor, and an insulating sheet made of PET (polyethylene terephthalate) with a thickness of 0.025 mm It was sandwiched and bonded and integrated with a thermoplastic adhesive having a thickness of 0.030 mm. As an intermediate intervening layer, an embossed portion using an embossing roll having an uneven portion formed on the surface is used to form uneven portions on the front and back surfaces of a non-woven fabric (made of PET) having a total thickness of 0.253 mm. Then, this was bonded to the periphery of the insulating sheet, and a shield material was further bonded to the upper part thereof to produce the FFC of the example. One end of the insulating sheet was removed by a length of 4 mm to expose the conductor end as a terminal to obtain an FFC.
The dimensions of the nonwoven fabric containing fibers embossed on the front and back surfaces are 1 mm for the pitch between the protrusions, 0.58 mm for the width of the protrusions, 0.130 mm for the height of the protrusions, and the width of the recesses formed between the protrusions. 0.45 mm, the partial thickness of the non-woven fabric, which is located on the bottom side of the embossed concave portion and reduced in thickness, is 0.085 mm, and its outline is shown in FIG.

<Comparative example>
An FFC having the same structure as that of the above example was manufactured except that the intermediate intervening layer was formed of a fiber-containing resin sheet having a thickness of 0.3 mm without embossing.
<Test Example 1>
Using the FFC having the intermediate intervening layer obtained in the examples and the comparative example as a sample, the dielectric constant was measured using a dielectric measurement system (model number: 1199696W) manufactured by Toyo Technica. The measurement frequency was 1 MHz, normal temperature (20 ° C.), and the number of samples was N = 100.
<Test Example 2>
About the sample (FFC) of an Example and a comparative example, it measured by the TDR (Time Domain Reflectometry) method using the oscilloscope (Nippon Tektronix company make: model number TDS8000), and calculated the differential impedance. The measurement temperature was room temperature (20 ° C.), and the number of samples was N = 100.
<Test Example 3>
About the sample (FFC) of the example and the comparative example, the flexibility test is performed by the flexibility test method shown in FIGS. 20 (A) and 20 (B) (load is applied to the center portion of the fulcrum and the change amount of the flexure portion is measured). Carried out. In this test method, after a sample 32 is placed on the fulcrums 30 and 31 as shown in FIG. 20A, a load W is applied to the central portions of the fulcrums 30 and 31 as shown in FIG. The test conditions were set to a distance between FFC fulcrums of 100 mm, a load of 0 to 50 g, and the number of samples N = 50. In the evaluation method, the degree of flexibility was defined by the slope of a curve drawn on a graph with the amount of deflection on the vertical axis and the load on the horizontal axis. Therefore, it can be evaluated that the greater the numerical value of flexibility, the more flexible.
The above test results are listed in Table 1 below. In the test results of Table 1, the unit of dielectric constant is cgs unit system, no dimension, the unit of thickness is mm, the unit of differential impedance is Ω, and the unit of flexibility is no unit.

From the results shown in Table 1, it is clear from the results of Test Example 1 that the dielectric constant of the example sample is lower than the dielectric constant of the comparative sample. Further, it can be seen from the results of Test Example 1 that the impedance of the example sample can be matched by reducing the variation in impedance while making the thickness thinner than that of the comparative example sample. Moreover, from the result of Test Example 2, the average value of the impedance of the example sample and the impedance of the comparative example sample is substantially equal. From the result of Test Example 3, the flexibility of the example sample is more than the flexibility of the comparative example sample. Is also clearly superior.
From the above test results, it was revealed that the sample to which the present invention was applied (FFC) was excellent in the average value of dielectric constant, low in impedance, and excellent in flexibility.

FIG. 1 is a configuration diagram showing an FFC according to a first embodiment of the present invention. FIG. 2 is a partially enlarged view of the FFC shown in FIG. FIG. 3 is a view showing an example of a resin sheet applied to the FFC shown in FIG. FIG. 4 is a view showing a state in which an uneven portion is formed on the sheet shown in FIG. FIG. 5 is a block diagram showing the FFC of the second embodiment according to the present invention. 6 is a partially enlarged view of the FFC shown in FIG. 7 is a view showing a state in which a shield layer is provided on the FFC shown in FIG. 8 is a diagram showing a state in which a shield layer is provided on the FFC shown in FIG. FIG. 9 is a diagram showing an example of an FFC having a double-sided shield structure. FIG. 10 is a diagram illustrating an example of an FFC having a single-sided shield structure. FIG. 11 is a diagram showing an example of a double-sided shield structure using an FFC having a ground structure in which a drain line is connected to a shield layer. FIG. 12 is a diagram showing an example of a double-sided shield structure with an FFC having a ground structure in which a metal tape is connected to a shield layer. FIG. 13 is a diagram showing an example of a double-sided shield structure using an FFC that employs a grounding structure using a metal plate. 14 is a block diagram of the FFC shown in FIG. FIG. 15 is a view showing another example of the FFC adopting a grounding structure using a metal plate. 16 is a block diagram of the FFC shown in FIG. FIG. 17 is a diagram showing an example of a single-sided shield structure using a grounded FFC in which a drain line is connected to a shield layer. FIG. 18 is a diagram showing an example of a single-sided shield structure with an FFC having a ground structure in which a metal tape is connected to a shield layer. FIG. 19 is a diagram illustrating an example of a single-sided shield structure using an FFC that employs a grounding structure using a metal plate. 20A and 20B are explanatory diagrams of the flexibility test, in which FIG. 20A shows a state in which an FFC is disposed between fulcrums, and FIG. 20B shows a state in which a weight is attached to the center between the fulcrums. FIG. 21 is an explanatory view showing an example dimension of the intermediate intervening layer used in the example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 10, 20, 21, 22, 25 ... FFC (flexible flat cable), 2 ... conductor, 2A ... conductor group, 2a ... terminal, 3 ... insulating layer, 4 ... intermediate interposition layer, 4a ... concave, 4b ... convex Part, 5, 12, 13 ... shield layer, 6 ... fiber, 7 ... sheet.

Claims (6)

  A conductor group composed of a plurality of conductors arranged in parallel, an insulating layer provided to cover the conductor group, and an intermediate intervening layer arranged on the front side or the back side of the insulating layer are provided. In addition, the surface of the intermediate intervening layer or both front and back surfaces are formed with irregularities for adjusting the dielectric constant that are alternately arranged along the plurality of conductors. Flat cable.   2. The flexible flat cable according to claim 1, wherein the concavo-convex portions are evenly arranged in the length direction and the width direction with respect to each of the plurality of conductors, and the dielectric constant is averaged.   The concavo-convex portion is arranged such that the boundary portion of the concavo-convex portion is arranged in the width direction of the insulating layer or in a specific direction having a predetermined angle with the width direction, and allows bending along the boundary portion of the concavo-convex portion. The flexible flat cable according to claim 1 or 2, wherein the flexibility is improved by the above.   The flexible flat cable according to any one of claims 1 to 3, wherein a vertical width and a horizontal width of the uneven portion are in a range of 0.15 mm to 2.0 mm.   The flexible flat cable according to any one of claims 1 to 4, wherein the plurality of conductors arranged in parallel are arranged at a pitch in a range of 0.3 mm to 1.0 mm.   The flexible flat cable according to any one of claims 1 to 5, wherein a shield layer is formed outside the intermediate intermediate layer.

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