JP3032320B2 - Flat cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat cable in which a plurality of wiring conductors are arranged on an insulating substrate so as to be insulated from each other.

[0002]

2. Description of the Related Art Conventionally, a flat cable in which a plurality of vinyl-coated cables are arranged and fixed on a plastic flat plate, for example, has been used.
There is a disadvantage that it has a small degree of freedom in bending and it is difficult to route in a narrow space.

[0003] In order to solve such disadvantages, flat cables using flexible wiring boards have begun to be used. In a conventional flat cable of this kind, a plurality of wiring conductors formed on a wiring board are insulated and separated from each other by an epoxy resin. That is, the insulating film is bonded to the wiring board on which the plurality of wiring conductors are formed using an epoxy resin adhesive.

[0004]

In the above-mentioned flat cable using the conventional flexible wiring board,
As described above, since the epoxy resin adhesive is used, the wirings are insulated and separated from each other by the epoxy resin. However, since this epoxy resin has a relatively large dielectric constant ε of 4.0 to 6.0, the wiring between the wiring conductors is relatively small. As the distance becomes shorter, the problem of crosstalk occurs, and therefore, there is a disadvantage that the wiring density cannot be increased.

Further, the conventional flat cable has a drawback that noise is mixed into a signal flowing through a wiring conductor since no measures against external noise are taken. In particular, when the device is used in an environment where the influence of external noise is extremely large, it becomes a serious problem.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional flat cable, and to reduce the distance between the wiring conductors so that the problem of crosstalk does not occur. An object of the present invention is to provide a flat cable configured so as not to be affected by noise.

[0007]

According to the flat cable of the present invention, each of a plurality of wiring conductors formed on a polyimide resin sheet is completely covered with a polyimide resin, and both upper and lower surfaces are sandwiched between electromagnetic shielding films. The electromagnetic shield film is covered with a polyimide resin sheet outside.

[0008]

In the flat cable according to the present invention, each of the plurality of wiring conductors formed on the flexible wiring board is completely covered with the polyimide resin, and the dielectric constant ε of the polyimide resin is 2.8 to 3.5. Since the height is low, the occurrence of crosstalk between the wiring conductors can be effectively prevented, so that the wiring conductors can be arranged closer to each other, and the wiring density can be improved. Also,
Since the electromagnetic shield layers are provided on the upper and lower surfaces, external noise can be shielded, and the signal flowing through the wiring conductor is not affected by the noise.

[0009]

1 to 6 are perspective views showing a structure of a flat cable according to an embodiment of the present invention in a sequential manufacturing process. In this example, a flat cable having two layers of wiring is used.

First, as shown in FIG. 1, a wiring board 4 is prepared in which conductive films, in this example, copper foils 2 and 3 are applied to both surfaces of a flexible polyimide resin sheet 1. next,
Copper foils 2 and 3 are selectively removed by etching according to a predetermined pattern to form a plurality of wiring conductors 5 and 6 as shown in FIG. The etching of the copper foils 2 and 3 can be performed by a known method. At both ends of each of the wiring conductors 5 and 6, a connection portion having a large width is formed in order to connect a wiring to another device.

[0011] Wiring connection to other equipment can be made by soldering, a connector, an anisotropic conductive layer, and the like. Therefore, the connection portions at both ends of the wiring conductors 5 and 6 may be made of copper, or may be gold-plated. , Nickel plating, solder plating,
It may be one subjected to a solder leveler treatment or the like.

Next, as shown in FIG. 3, a polyimide resin sheet 7 having a conductive film, for example, a copper foil 8 on one surface thereof is prepared. Then, the copper foil 8 is etched according to a predetermined pattern to form a shield sheet having an electromagnetic shield film 9 as shown in FIG.

Further, as shown in FIG. 5, a shielding sheet shown in FIG. 4 is provided on both upper and lower surfaces of a wiring board 4 on which predetermined wiring conductors 5 and 6 are formed as shown in FIG. Overlay 12 and 13. At predetermined positions of the polyimide resin films 10 and 11, a through-hole is formed, and a conductive paste 1 is formed in the through-hole.
Fill 4 and 15. The dimensions of the polyimide resin films 10 and 11 and the shield sheets 12 and 13 cover the wiring conductors 5 and 6 formed on the wiring board 4 by these, but do not cover the connection portions formed at both ends of the wiring conductor 4. It is assumed that

After the polyimide resin films 12 and 13 and the shield sheets 10 and 11 are overlaid on the wiring board 4 on which the wiring conductors 5 and 6 are formed as described above, they are heated under pressure and thermally pressed. 6. As shown in FIG. In this thermocompression bonding step, the polyimide resin films 12 and 13 flow and sequentially flow into the gaps between the wiring conductors 5 and 6, so that the wiring conductors are completely covered and fixed at predetermined positions of the shield film 9. Will be done.

During the thermocompression bonding process, the conductive paste 14 filled in the through holes formed in the polyimide resin film 12 is connected to the ground conductor in the wiring conductor 5 and the shield film 9 of the shield sheet 10 and to the polyimide resin. The conductive paste 15 filled in the through holes formed in the film 13 is connected to the ground conductor in the wiring conductor 5 and the shield film 9 of the shield sheet 11.

Finally, as shown in FIG. 6, a portion where the wiring conductors 5 and 6 are not formed is cut and the outer shape is processed to complete a flat cable.

FIG. 7 is a sectional view taken along the line AA of FIG. In the flat cable according to the present embodiment, the polyimide resin sheet 1 and the polyimide resin films 12 and 13 are thermocompression-bonded with the wiring conductors 5 and 6 interposed therebetween. The polyimide resin is present between them, and each wiring conductor is completely covered with the polyimide resin. Since the dielectric constant ε of the polyimide resins 12 and 13 covering the wiring conductors 5 and 6 is 2.8 to 3.5, which is lower than the dielectric constant of the conventional epoxy resin, it is necessary to effectively prevent crosstalk between the wiring conductors. Can be. Therefore, the interval between the wiring conductors 4 can be narrower than before, and the wiring density can be increased.

Further, since the wiring conductors 5 and 6 are sandwiched between the shield films 9 of the shield sheets 10 and 11 stacked one above the other, it is possible to effectively prevent external noise from entering and mixing into signals flowing through the wiring conductor. Can be blocked.

The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in the above-described example, after the wiring conductors 5 and 6 are formed, the polyimide resin films 12 and 13 are overlapped and thermocompression bonded. However, after the wiring conductors are formed, a polyimide varnish is applied on the wiring board and dried. You can also. Even in this case, since the respective wiring conductors 5 and 6 are completely covered with the polyimide resin, crosstalk can be eliminated.

Further, in the above-described embodiment, two-layer wiring is provided. However, a single-layer wiring or a flat cable having three or more-layer wiring can be obtained by repeating the above-described steps alone or in combination. You can also.

The ground wiring conductor and the shield film 9
In addition to the method of using the conductive paste as described above, a method using an eyelet, a method using an eyelet, or cutting or opening a predetermined portion of the intermediate polyimide resin films 12 and 13 is also used. Method, a method of connecting the shield film 9 with a connector, a method of connecting with a solder,
Various connection methods such as a method of connection by wire bonding can be adopted.

Further, in the above-described embodiment, the shield film 9 is made of a uniform copper foil. However, any shape may be used as long as it does not impair the electromagnetic shielding effect, such as a mesh pattern.

[0023]

As described above, in the flat cable according to the present invention, since each of the wiring conductors is completely covered with the polyimide resin having a low dielectric constant, the crosstalk between the wirings can be effectively removed. Therefore, the interval between the wiring conductors can be reduced, and the wiring density can be improved. In this case, if the adjacent wiring conductors are alternately used as a signal line and a ground line, crosstalk can be more effectively removed.

Further, since the wiring conductor is sandwiched between the shielding films having an electromagnetic shielding effect, external noise does not enter and mix into a signal flowing through the wiring conductor.
Therefore, it can be used effectively even in an environment where the influence of noise is large.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first step in manufacturing an embodiment of a flat cable according to the present invention.

FIG. 2 is a perspective view showing a second step in manufacturing one embodiment of the flat cable according to the present invention.

FIG. 3 is a perspective view showing a third step in manufacturing one embodiment of the flat cable according to the present invention.

FIG. 4 is a perspective view showing a fourth step in manufacturing an embodiment of the flat cable according to the present invention.

FIG. 5 is a perspective view showing a fifth step in manufacturing an embodiment of the flat cable according to the present invention.

FIG. 6 is a perspective view showing a sixth step in manufacturing one embodiment of the flat cable according to the present invention.

7 is a cross-sectional view showing a configuration of an embodiment of the flat cable according to the present invention, taken along line AA of FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polyimide resin sheet 2 Copper foil 3 Copper foil 4 Wiring board 5 Wiring conductor 6 Wiring conductor 7 Polyimide resin sheet 8 Copper foil 9 Shield film 10 Shield sheet 11 Shield sheet 12 Polyimide film 13 Polyimide film

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-140312 (JP, A) JP-A-62-154504 (JP, A) JP-A-61-131306 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01B 7/08

Claims (1)

(57) [Claims] 1. A plurality of wiring conductors formed on a polyimide resin sheet are each completely covered with a polyimide resin, and both upper and lower surfaces are sandwiched between electromagnetic shield films, and the outside of these electromagnetic shield films is further covered with a polyimide resin sheet. Flat cable characterized by the following.