JP2788701B2 - Multi-layer flexible wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer flexible printed wiring board (hereinafter, referred to as a multilayer FPC wiring board) used for a video camera, a cellular phone, a wireless device, and the like.

[0002]

2. Description of the Related Art A conventional technique will be described with reference to FIG. FIG. 2 is a schematic diagram showing a connection state of a conventional multilayer printed wiring board.

As shown in FIG. 2, a plurality of multilayer printed wiring boards according to a conventional example are connected by providing a connector 11 on each multilayer wiring board 10 and connecting the connectors 11 with an FPC cable (or a flat cable, hereinafter referred to as an FPC cable). 12).

However, according to this structure, the connector 1
1. Since the FPC cable 12 is used, there is a problem in that processing costs are high due to the number of components and the number of working steps due to connector mounting and FPC cable connection.

Further, since the connection between the multilayer wiring boards is performed by the connector 11 and the FPC cable 12, there is a problem that the connection reliability is lacking.

[0006] In recent years, as video cameras, mobile phones, wireless devices, electronic organizers and the like have been required to be miniaturized,
It is desirable that the connection structure between the multilayer wiring boards is also reduced in size.

In order to solve the above problem, FIG.
A multilayer FPC wiring board having the structure shown in FIG.

In the multilayer FPC wiring board shown in FIG. 3, the FPC cable 14 is laminated as a part of the multilayer wiring board 13. FIG. 4 is an enlarged sectional view of the multilayer FPC wiring board.

The multilayer wiring board 13 shown in FIG.
A film cover lay 17 for pattern protection is laminated on the FPC material 16 on which 5 is formed, and both sides thereof are further laminated with a base substrate 19 via an adhesive sheet 18. As a material of the base material 19, a phenol resin or a glass epoxy resin is used.

Reference numeral 20 denotes a copper foil portion on the base substrate 19, and reference numeral 21 denotes a through hole.

The FPC cable 14 has a copper foil pattern 15
Coverlay 1 on FPC material 16 on which is formed
7 are laminated.

The multilayer FPC wiring board having the above structure is
It has the following features. (1) Thinner and lighter than conventional multilayer printed wiring boards and composite multilayer wiring boards can be realized. In addition, the wiring board can be bent at the designated position without using the cable FPC with the connector, and the wiring board can be three-dimensionally and compactly incorporated into the device 17, so that the size, weight and thickness of the device can be reduced.

(2) Since no connector is required, the number of parts and the number of processing steps can be reduced, and the cost of equipment can be reduced.

(3) Since the connector mounting area can be reduced, the size of the wiring board can be made small and high-density can be designed, and the connection reliability can be improved.

[0015]

However, the multilayer FPC wiring board shown in FIG. 4 still has the following problems. That is, (1) When an epoxy resin containing glass cloth is used as the base material 19 of the multilayer wiring board 13, interlayer displacement occurs due to a dimensional change due to the glass cloth.

(2) In the multilayer wiring board 13, since the base material and the adhesive layer are made of different materials (for example, the base material is an epoxy resin and the adhesive layer is a polyimide resin), a difference in dimensional change causes The displacement between the layers occurs.

(3) When performing throughhole drilling on the multilayer wiring board 13, smear is generated, so that desmear processing is separately required, which increases the number of steps and leads to an increase in cost.

(4) In order to protect the circuit portion of the FPC cable 14, a protective material such as a film coverlay is required, which leads to an increase in cost.

In view of the above problems, it is an object of the present invention to provide a highly reliable multilayer FPC wiring board which has no interlayer displacement and can reduce the cost.

[0020]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a multilayer wiring board comprising a plurality of base substrate films on which conductive patterns are formed, which are laminated via an adhesive sheet; A flexible cable obtained by extracting a part of a laminate from a board, and using a polyimide resin as a material of the base substrate film and the adhesive sheet, and both sides of the flexible cable are formed of the plurality of bases. It is characterized by comprising a base substrate film having no conductor pattern formed on the outside of the substrate film.

[0021]

[Function] Since a polyimide resin is used as the material of the base substrate film, the material does not include glass cloth,
There is no gap between layers due to dimensional change due to glass cloth, which is a conventional problem.

Further, since the adhesive sheet is made of a polyimide resin, the same material is used for the base substrate film and the adhesive sheet, and the dimensional behavior of each layer due to the temperature change is substantially the same. Warpage and twist can be minimized.

Furthermore, since a polyimide resin is used as a constituent material, the multilayer FPC wiring board of the present invention has excellent heat resistance, and no smear is generated in the through hole even during drilling when forming the through hole, which has been conventionally indispensable. In addition, the desmear process can be omitted, and the man-hour can be reduced.

In addition, since the base substrate films provided on both sides of the FPC cable are used as a protective layer for the conductor pattern formed inside the film, there is no need for a film coverlay for protecting the conductor pattern as in the prior art, and the cost is reduced. Can be down.

Further, since the multilayer wiring board is formed of the same base substrate film as the FPC cable, the size and weight can be reduced as compared with the case where a PWB substrate is used as a constituent material of the multilayer wiring board.

[0026]

An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a sectional view of a multilayer FPC wiring board according to the present embodiment.

As shown in FIG. 1, the multilayer FPC of this embodiment
The wiring board is composed of a multilayer wiring board 1 and an FPC cable 2, of which the multilayer wiring board 1 has six layers of conductor patterns 3 and F
The PC cable 2 has two layers of conductor patterns 3 laminated.

The multilayer wiring board 1 has five layers of a base substrate film 4 laminated with an adhesive sheet 5 interposed therebetween. The conductor pattern 3 is not formed on both surfaces of the base base film 4 in the center of the five base base films 4.
The conductor patterns 3 are formed on both sides of the base substrate film 4 on both sides. Outermost base substrate film 4
Has a conductor pattern 3 formed only on the outside. 6 is a through hole.

Here, as a material of the base substrate film 4, a polyimide resin containing no glass cloth is used. In addition, a polyimide adhesive sheet is used as a material of the adhesive sheet 5.

The FPC cable 2 has a structure in which three layers of the base substrate film 4 at the center of the multilayer wiring board 1 are drawn out, and the outermost portion has a structure in which the base substrate film 4 is exposed as it is. Has become.

In the multilayer FPC wiring board having the above structure,
Since a polyimide resin containing no glass cloth is used as the material of the base substrate film 4, there is no gap between layers due to a dimensional change due to the glass cloth, which is a conventional problem.

Further, since the adhesive sheet 5 is also made of polyimide, the constituent material of the multilayer FPC wiring board 1 is the same material except for the conductor pattern 3, that is, only the polyimide resin. And the dimensional behavior associated therewith is substantially the same, and the displacement between layers, warpage and twisting of the wiring board can be minimized.

When a polyimide resin containing no glass cloth is used as the material of the base substrate film 4,
The strength of the base film is slightly reduced due to the absence of the glass cloth. On the other hand, if the area of the conductor pattern 3 is increased, the reduced amount can be sufficiently reinforced.

As described above, the multi-layer FPC of this embodiment
Since the material of the wiring board is polyimide except for the conductor pattern 3, it is excellent in heat resistance. Even during drilling when forming the through hole 6, smear does not occur in the through hole 6, so that the desmear step which is conventionally indispensable can be omitted, and the number of steps can be reduced.

Further, since all of the base substrate films 4 constituting the multilayer FPC wiring board are the same as the base substrate film 4 of the FPC cable 2, the base substrate 19 is smaller than the conventional example shown in FIG. As a result of replacing the base substrate film 4, the thickness and weight can be reduced.

Table 1 shows a weight comparison between the multilayer FPC circuit board according to the present embodiment and the conventional circuit board.

[0037]

[Table 1]

As is clear from Table 1, according to the present embodiment, the thickness and weight can be reduced as compared with the prior art.

Further, in the FPC cable portion of the conventional multilayer FPC wiring board, a protective material such as a film cover lay was necessary to protect the circuit portion. Is provided with a base substrate film 4 on the outside of which no conductor pattern is formed, and this base substrate film 4 is used as it is as a protective material for the conductor pattern 3 inside the film. Therefore, a conventional film coverlay as a protective layer is unnecessary, and the cost can be reduced.

Further, in the structure of this embodiment, since the conductor pattern 3 is not formed on both sides of the central layer of the five-layer base substrate film 4, this central layer is It functions as an insulating layer of the base substrate film 4 on both sides. For this reason, even if the FPC cable 2 is bent, the conductor patterns 3 do not come into contact with each other, and high insulation reliability can be guaranteed.

As described above, according to this embodiment, since the polyimide resin is used as the material of the multilayer wiring board and the flexible cable, the displacement between the layers can be reduced, and the desmear process is not required, and the number of manufacturing processes is reduced. , And can be made thinner and lighter.

In this embodiment, the connection between the layers is made only by the through holes. However, a structure in which the layers are electrically connected by the inner via holes may be used if necessary.

[0043]

As described above, the multilayer FPC of the present invention is
According to the wiring board, the displacement between the layers can be suppressed small, and the number of manufacturing steps can be reduced, the thickness and the weight can be reduced, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a multilayer FPC wiring board according to one embodiment of the present invention.

FIG. 2 is a schematic perspective view of a conventional multilayer FPC wiring board.

FIG. 3 is a schematic perspective view of a multilayer FPC wiring board according to another conventional example.

FIG. 4 is a sectional view of the multilayer FPC wiring board of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Multilayer wiring board 2 Flexible cable 3 Conductor pattern 4 Base substrate film 5 Adhesive sheet

Claims (1)

(57) [Claims] 1. A multilayer wiring board in which a plurality of base substrate films on which a conductor pattern is formed are laminated via an adhesive sheet, and a flexible cable formed by extracting a part of the laminate from the multilayer wiring board. A polyimide resin is used as a material of the base substrate film and the adhesive sheet, and a conductive pattern is not formed on both sides of the flexible cable on the outside of the plurality of base substrate films. A multilayer flexible wiring board comprising a base substrate film.