JP2003258389A - Flexible printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible printed circuit board (FPC) capable of reinforcing mechanical weak points of the FPC and inhibiting disconnection of a conductor and rupture of the FPC itself. <P>SOLUTION: This is a flexible printed circuit board 1 having a bent part with a conductor 10 arranged in a resin film 11. A distance between an edge of the resin film and the edge of the conductor at this bent part is 0.5 to 1.0 mm. Thus, having the distance between the edge of the resin film 11 and the edge of the conductor 10 of 0.5 to 1.0 mm can reinforce the FPC, and inhibit the disconnection of the conductor 10 and the rupture of the FPC itself. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed wiring board (FPC). In particular, it relates to an FPC that can reduce the probability of conductor breakage when it is placed at a location where repeated bending is applied.

[0002]

2. Description of the Related Art In recent years, the development of mobile phones has been remarkable. In particular, recently, in consideration of the large screen of the display unit, compactness, fashionability, and protection of operation buttons, the folding (shell-type) mobile phone has become the mainstream, and this trend will continue in the future. Expected to continue.

A shell type mobile phone has a structure in which a display unit such as a liquid crystal screen is foldably connected to a key switch unit in which operation buttons are arranged. The key switch section and the display section are electrically connected via the FPC.

As shown in FIG. 5 (A), the FPC used here has an offset type shape in which straight portions 50 at both ends are connected by S-shaped bent portions 51, as shown in FIG. 5 (B). S as shown
The mold bending part 51 is wound once in the hinge to obtain folding resistance when the key switch part and the display part are repeatedly bent.

[0005]

However, the offset type FPC has mechanical weak points depending on its shape.
In particular, the location inside the bend in the S-shaped bend,
Bending and wrinkling are likely to occur, strain stress concentrates, and in the worst case, it may lead to breakage of the conductor or breakage of the FPC itself.

[0006] Therefore, a main object of the present invention is to provide an FPC capable of improving mechanical weaknesses of the FPC and suppressing disconnection of the conductor and breakage of the FPC itself.

[0007]

The present invention achieves the above object by specifying the distance between the side edge of the resin film and the side edge of the conductor in the FPC.

That is, the flexible printed wiring board of the present invention is a flexible printed wiring board in which a conductor is arranged in a resin film and has a bent portion, and the distance between the side edge of the resin film and the conductor side edge at the bent portion. Is 0.5
It is characterized by being ~ 1.0 mm.

Conventionally, the distance between the side edge of the FPC resin film and the side edge of the conductor has generally been about 0.3 mm. As a result of various studies on the layout of the conductor circuit as a measure for alleviating the strain concentration due to bending of the FPC, the present inventors set the distance between the side edge of the resin film and the conductor side edge to 0.5 to 1.0 mm, thereby
It has been found that it is possible to reinforce, and to suppress disconnection of the conductor and breakage of the FPC itself.

Here, the distance between the side edge of the resin film of the FPC and the side edge of the conductor is the distance in the width direction of the FPC. FPC
By concentrating the conductor in the central part of the and widening the resin film width on both sides of the conductor, the concentration of stress due to the bending of the bent portion is relieved. This is because if the distance is less than 0.5 mm, the effect of alleviating the concentration of stress is small, and if it exceeds 1.0 mm, the side edge portion of the resin film unnecessarily becomes wide.

The range for specifying the distance between the side edge of the resin film and the side edge of the conductor is applied to at least the bent portion of the FPC. Of course, similar specification of the distance may be applied to a portion other than the bent portion.

Further, it is preferable to integrate a reinforcing material in the bent portion. Specific examples of the reinforcing material include plastic film strips, thin metal wires, and metal nets. A flexible material such as polyimide is suitable for the plastic film strip. Further, as a method of integrating the plastic film strips, it is preferable to bond the plastic film strips to the FPC. For fine metal wires and metal nets, copper, aluminum, silver,
A metal having excellent flexibility such as gold is preferable. In addition, as a method of integrating the metal thin wires and the metal net, there is a method of incorporating the metal thin wires in the resin film portion of the FPC or covering the entire bent portion of the FPC with the metal net. Especially when a metal net is used,
The effect of shielding the electric field can also be expected.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. (Example 1) As shown in FIG. 5 (A), the FPC of the present invention also has an appearance of an offset type in which straight portions at both ends are connected by S-shaped bent portions. In general, such an FPC has connection electrode portions (not shown) for connection with a mating substrate, which are not shown. The conductors other than the connecting electrodes are sandwiched between resin films such as polyimide to form an FPC. In this example, a conductor is formed of a copper foil having a thickness of 18 μm, and each conductor is sandwiched between a polyimide upper surface resin film and a polyimide lower surface resin film having a thickness of 12.5 μm.

A schematic plan view of the S-shaped bent portion is shown in FIG. FPC1 of the present invention, the conductor 10 is brought close to the central portion of the FPC width direction,
The side edge portion made of only the resin film 11 is wide.
Here, the distance k from the side edge of the resin film 11 to the side edge of the conductor 10 in the S-shaped bent portion was set to 0.5 mm, 0.7 mm, and 1.0 mm.

Using the FPC thus constructed, repeated bending tests were conducted. For comparison, the same bending test was performed on FPCs in which the distance from the side edge of the resin film to the side edge of the conductor was 0.3 mm. The test conditions are as follows.
The FPC is mounted on the actual shell type mobile phone, and the opening and closing operations of the key switch section and the display section are repeated. Here, "fully open"
The above-mentioned opening / closing operation was repeated in a 2-second cycle between and "closed". The inner diameter of FPC is about 5 mmφ.

As a result, in the FPC in which the distance from the side edge of the resin film to the side edge of the conductor is 0.5 mm, 0.7 mm, and 1.0 mm, the conductor breaks or the FPC breaks after being repeatedly bent 100,000 times. Was not seen. On the other hand, the same distance is 0.3mm
In the FPC, the conductor was broken after repeated bending of 80,000 times.

(Example 2) Further, an example using a reinforcing material will be described. FIG. 2 is a schematic explanatory view of the FPC of the present invention using a plastic film strip as a reinforcing material.

This FPC 2 can be obtained by adhering the plastic film strip 20 to the FPC of the first embodiment.
Here, the thickness at both edges along the bend in FPC2
A 50 μm polyimide strip was attached. Although the strip is shown only on one side of the FPC in the figure, the strips are similarly attached to the other side. The strips may be attached to one side or both sides of the FPC.

In this structure, the plastic film strip is integrated with the bent portion, whereby the mechanical strength against repeated bending of the bent portion can be further improved.

(Embodiment 3) An embodiment of the present invention using a reinforcing material for a fine metal wire will be described with reference to FIG. This embodiment uses a thin metal wire 30 instead of the plastic film strip of the second embodiment. The thin metal wire 30 may be sandwiched between the resin films forming the FPC 3. Here, the diameter is 0.1m
A copper wire of m was used as a reinforcing material.

Also with this structure, the mechanical strength against repeated bending of the bent portion can be further improved.

(Embodiment 4) An embodiment of the present invention using a reinforcing material for a metal net will be described with reference to FIG. In this embodiment, the entire bent portion of the FPC 4 is covered with the metal net 40. Here, a copper foil having a thickness of 70 μm shaped into a net was used as a reinforcing material.

Also with this structure, the mechanical strength against repeated bending of the bent portion can be further improved.

[0024]

As described above, according to the present invention,
By specifying the distance between the side edge of the resin film and the side edge of the conductor in the bent portion of the FPC, it is possible to reduce the probability of conductor breakage and FPC breakage with respect to repeated bending.

Further, by further integrating the reinforcing material in the bent portion, it is possible to further improve the mechanical strength.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a bent portion of an FPC of the present invention.

FIG. 2 is a schematic explanatory view of an FPC of the present invention using a plastic film strip as a reinforcing material.

FIG. 3 is a schematic explanatory view of an FPC of the present invention in which a thin metal wire is used as a reinforcing material.

FIG. 4 is a schematic explanatory view of an FPC of the present invention in which a metal net is used as a reinforcing material.

FIG. 5 (A) is a schematic diagram showing the overall configuration of an FPC, and FIG. 5 (B) is an explanatory diagram showing a bent state when the FPC is used in a mobile phone.

[Explanation of symbols]

10 Conductor 11 Resin film 20 Plastic film strip 30 Metal fine wire 40 Metal net 50 Straight part 51 Bent part

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshihide Kimura             30 Hinokigaoka, Mizuguchi-cho, Koga-gun, Shiga Prefecture             Inside Todenko Print Circuit F term (reference) 5E338 AA05 AA12 BB72 CD40 EE27                       EE28

Claims (5)

[Claims] 1. A flexible printed wiring board in which a conductor is arranged in a resin film and has a bent portion, wherein a distance between a side edge of the resin film and a conductor side edge in the bent portion is 0.5 to 1.0 mm. Flexible printed wiring board characterized by. 2. The flexible printed wiring board according to claim 1, further comprising a reinforcing material integrated with the bent portion. 3. The flexible printed wiring board according to claim 2, wherein the reinforcing material is a plastic film strip. 4. The flexible printed wiring board according to claim 2, wherein the reinforcing material is a fine metal wire. 5. The flexible printed wiring board according to claim 2, wherein the reinforcing material is a metal net.