JP3093709B2 - Double-sided 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 double-sided flexible printed circuit (FPC), and more particularly to an FPC that performs a bending operation.
About.

[0002]

2. Description of the Related Art In recent years, notebook PCs have become smaller, lighter and thinner, and due to the demand for a layout configuration inside the device, a flexible wiring board has been used as a substitute for a connection between key components and a harness cable connection. Came.

FIG. 8 is a perspective view of a notebook personal computer in which an LCD panel 10 is mounted on a personal computer main body 12 provided with a keyboard (not shown) so as to open and close. L
The CD panel 10 is rotatably mounted around a shaft 13 on the personal computer body 12, and the FPC 11 electrically connects the LCD panel 10 and the personal computer body 12. F
The PC 11 has a cylindrical part wound coaxially with the shaft 13, and one part of the cylindrical part that is divided into two parts by an extension of one end is connected to the LCD panel 10, and the other part is connected to the personal computer body 12. The portion near the cylindrical portion of this extension of the FPC 11 is LC
When the D panel 10 is closed, it is entangled in a cylindrical portion, and when the LCD panel 10 is opened, it is unraveled from the cylindrical portion. The FPC 11 is extended particularly close to the cylindrical portion. The portion repeats a bending operation of alternately bending and extending to a plane.

FIG. 6 is a cross-sectional view of a conventional double-sided FPC, in which copper foil layers 22, 24 are provided on both sides of a base film layer 23 having a thickness a.
Are provided, and the outer surfaces of the copper foil layers 22 and 24 are covered with coverlay film layers 21 and 25, respectively. FIG. 7 is a cross-sectional view showing a state in which the double-sided FPC shown in FIG. 6 is bent with the coverlay film layer 25 side inside. Copper foil layer 22
And 24 have the same thickness b and the cover lay film layers 21 and 25 have the same thickness c, so that the neutral surface 29 due to the bending stress of the double-sided FPC is When bent as shown in FIG. 7, the outer copper foil layer 22 is formed.
Tensile stress is generated in the copper foil layer 2
In FIG. 2, disconnection 8 occurs due to metal fatigue.

Conventionally, a double-sided FP has
When C was used, the copper foil layer and the cover lay film layer on both sides were thinned to prevent disconnection, and the flexibility of the double-sided FPC was increased as much as possible.

[0006] Further, since electrolytic plated copper is hard and easily fatigued by metal, the copper foil layer is not subjected to electrolytic plating on the rolled copper foil, and is made of only rolled copper foil which is softer and more elastic than electrolytic plated copper. As for the "flexible double-sided wiring board" described in JP-A-64-45190, an FPC having a single-sided structure in which a copper foil circuit is provided on only one side of a base film is used only for a bent portion.

[0007]

The first problem is that, even if the copper foil layer is made of only rolled copper foil, the flexibility of the double-sided FP is increased.
In the case of C, it is easy to cause metal fatigue disconnection while repeating the bending motion.

The reason is that, as shown in FIG.
In PC, the outer side of the base film layer 3 is the center (the outer side and the inner side of the bending of the FPC are simply referred to as the outer side and the inner side, the same applies hereinafter).
The copper foil layer 22 and the inner copper foil layer 24 have the same thickness b, and the outer coverlay film layer 21 and the inner coverlay film layer 2
5 has a layer structure having the same thickness c.
When the PC is bent, the tensile stress increases toward the outer coverlay film layer 21 around the base film 23 where no tensile stress or compressive stress is applied and the stress is zero. Since the compressive stress is increased, in the case of a signal pattern, the outer copper foil layer 22 is repeatedly affected by the tensile stress as the bending motion is repeated, so that the metal fatigue wire is easily broken.

A second problem is that a double-sided FPC having a single-sided bent portion is susceptible to electrical noise.

[0010] The reason is that the single-sided structure has only the pattern layer, the ground conductor cannot be provided on the entire surface of the layer, the return path of the signal cannot be sufficiently secured, and noise is radiated from the FPC.

A third problem is that electrolytic plating is unavoidable in manufacturing when the double-sided FPC has a single-sided bent portion.

An object of the present invention is to provide a double-sided FPC which can prevent disconnection of a bent portion wiring, has high reliability and is resistant to noise.

[0013]

Means for Solving the Problems A double-sided FPC of the present invention comprises:
The neutral surface (3 in FIG. 1) where no stress is caused by bending is applied to one of the copper foil layers (2 and 4 in FIG. 1) to prevent the disconnection of the copper foil layer (FIG. 1).
Characterized in that is located in 2) of.

The double-sided FPC of the present invention comprises a copper foil layer (2 in FIG. 1) for preventing disconnection on one side of a base film layer (3 in FIG. 1).
A copper foil layer (4 in FIG. 1) is adhered to the other surface, and a coverlay film layer (1, 5 in FIG. 1) is adhered to the outer surface of each of the disconnection preventing copper foil layer and the copper foil layer. In the wiring board, the thickness of the coverlay film layer (1 in FIG. 1) on one side of the base film layer is adjusted to the thickness of the other side of the base film layer, the copper foil layer, and the base film layer. The thickness of the coverlay film layer (5 in FIG. 1) is equal to or larger than the total thickness.

[0015]

[0016]

[0017]

In the above-mentioned double-sided FPC, the base film may be repeatedly bent so that the one side of the base film is on the outside, or the disconnection preventing copper foil layer may be made of a copper foil having a wide width. Is also good.

In the apparatus of the present invention, a lid (10 in FIG. 8) which is pivotally supported on a main body (12 in FIG. 8) and which opens and closes the main body, and the main body are electrically connected by the above-mentioned double-sided FPC (11 in FIG. 8). For example, a display panel (10 in FIG. 8) that is pivotally supported on a main body (12 in FIG. 8) and opens and closes the main body.
And a notebook-type information processing apparatus in which the above-mentioned FPC (11 in FIG. 8) is electrically connected.

According to the present invention, there is provided a use method of repeatedly bending a double-sided flexible wiring board, wherein the double-sided FPC is bent so that the disconnection preventing copper foil layer is on the outside.

[0021]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a double-sided FPC according to the first embodiment of the present invention. In this double-sided FPC, outer and inner copper foil layers 2 and 4 are provided on both sides of a base film layer 3, and outer and inner coverlay film layers 1 and 5 are provided so as to overlap with these.

The thickness of the base film layer 3 is A, the thickness of the outer copper foil layer 2 is B, the thickness of the inner copper foil layer 4 is C, the thickness of the outer cover lay film layer 1 is D, and the inner cover lay is Assuming that the thickness of the film layer 5 is E, the thickness of the layer is A + C + E = D so that a neutral surface where no bending stress is generated comes to the outer copper foil layer 2 when the double-sided FPC is bent. Is ideal, but from the standards of the base film, copper foil, and cover film manufactured and handled by the trader, the thickness of the base film layer 3, the copper foil layers 2, 4, and the cover lay film layers 1, 5 is actually Since the variation, that is, the type is fixed, A
Since it may be difficult to set + C + E = D, A + C + E = D or A + C + E <D. Here, for simplicity, the elastic coefficients of the base film layer 3, the copper foil layers 2, 4 and the cover lay film layers 1, 5 are assumed to be the same.

When the double-sided FPC shown in FIG. 1 is bent as shown in FIG. 2, the outer copper foil layer 2 becomes a neutral layer that does not expand or contract, or a layer that receives only compression and is not pulled, and Even if it is repeated, there is no disconnection due to metal fatigue.

Although the inner copper foil layer 4 generates stress,
Since only compression is received, there is no disconnection.

When the outer coverlay film layer 1 is thicker than the inner coverlay film layer 5 and E <D,
Although it cannot be said that the outer copper foil layer is not necessarily subjected to expansion and contraction or tension, the tensile stress becomes smaller than that of the conventional double-sided FPC shown in FIG. it can.

When the outer copper foil layer 2 is thicker than the inner copper foil layer 4 so that C <B (a copper foil having a normal thickness is used for the inner copper foil layer 4 and Or a copper foil having a normal thickness for the outer copper foil layer 2 and a copper foil thinner than the normal thickness for the inner copper foil layer 4)
Similarly, disconnection of the outer copper foil layer 2 can be reduced.

FIG. 3 is a sectional view of a double-sided FPC according to a second embodiment of the present invention. Double-sided FPC of this embodiment
Has a double-layered coverlay film on the outside.

Referring specifically to FIG. 3, FIG.
The outer coverlay film layer 31 having the same thickness is attached to the outer coverlay film layer 21 of the conventional double-sided FPC. As a result, as shown in FIG. 4, a neutral surface where no tensile and compressive stress is generated is brought closer to the outer copper foil layer 22 that is not desired to be disconnected, and the stress generated in the outer copper foil layer 22 is reduced. It becomes difficult to cause metal fatigue disconnection. In addition, this double-sided FPC can be formed into layers using the same standard cover lay film, copper foil, and base film as those used in the conventional ones. Can be configured.

In the above embodiment, the case where the copper foil layer 2 is subjected to only one side bending with the copper foil layer 2 as the outer side has been described. However, the copper foil layer 4 is a ground layer, a power supply layer, etc. If the copper foil is wide and the copper foil layer 2 is turned outward or the copper foil layer 4 is turned outward if it is not easily broken even if it receives some stress, However, the present invention is applicable. In this case, the copper foil layer 4 receives a tensile stress but does not break because of sufficient strength, and the copper foil layer 2 is a thin signal line and may receive a large tensile stress as described above even if the strength is small. There is no disconnection.

The present invention is not limited to the FPC 11 of the notebook personal computer shown in FIG. 8, but it is needless to say that the present invention can be applied to an FPC for internal connection of a notebook type word processor and other various devices.

[0032]

Next, an example of the first embodiment of the present invention will be described in detail.

Referring to FIG. 1, in this embodiment,
The base film layer 3, the outer coverlay film layer 1 and the inner coverlay film layer 5 are made of polyimide, the thickness A of the base film layer 3 is 12.5 μm, the thickness of the inner copper foil layer 4 is 18 μm, By reducing the thickness E of the inner coverlay film layer 5 to 12.5 μm, increasing the thickness D of the outer coverlay film layer 1 to 50 μm, and increasing the thickness B of the outer copper foil layer 2 to 35 μm, FIG. As described above, in the conventional double-sided FPC, the neutral surface 29 on the base film layer 3 is moved to the neutral surface 9 in the outer copper foil layer 2. Therefore, the outer copper foil layer 2 is a layer with little distortion at and around the neutral plane when the double-sided FPC is bent.

For comparison with the double-sided FPC of this embodiment, FIG.
Using the conventional double-sided FPC shown in FIG. 5 as the FPC 11 of a notebook-type personal computer as shown in FIG. 8, the opening and closing movement test of the LCD panel 10 was performed. As a result, as shown in FIG.
C was broken 5000 times, but the double-sided F
The PC did not break due to metal fatigue even after opening and closing 30,000 times.

Next, an example of the second embodiment of the present invention will be described in detail.

Referring to FIG. 3, in this embodiment,
The thickness a of the base film layer 23 is 25 μm, the thickness b of the outer copper foil layer 22 and the inner copper foil layer 24 is 18 μm, and the thickness c of the outer coverlay film layer 21 and the inner coverlay film layer 25 is 25 μm. Of the same thickness as that of the FPC layer configuration of FIG.
A 5 μm outer coverlay film layer 31 is attached.

[0037]

The first effect is that the double-sided FPC is subjected to bending.
That is, the disconnection of the copper foil layer, which is one of the copper foil layers, can be prevented.

The reason for this is that the stress generated in the disconnection preventing copper foil layer is reduced by positioning or nearing the neutral surface of the double-sided FPC to the bending to the disconnection preventing copper foil layer. Therefore, the other copper foil layer, which is not the disconnection prevention copper foil layer, is made inside the bend so that no tensile stress is generated in the inner copper foil layer, so that the copper foil layers on both sides can be prevented from being disconnected. The life of the FPC can be extended.

The second effect is that it is resistant to noise.

The reason is that a copper foil layer can be provided on both sides even at a bent portion, so that one disconnection preventing copper foil layer is used as a pattern layer for signal wiring, and the other copper foil layer is used as a ground layer. By doing so, the return path of all the signals can be sufficiently ensured, and no noise is radiated.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a double-sided FPC according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the double-sided FPC shown in FIG. 1 when bent.

FIG. 3 is a sectional view of a double-sided FPC according to a second embodiment of the present invention.

4 is a cross-sectional view of the double-sided FPC shown in FIG. 3 when bent.

FIG. 5 shows a double-sided FP according to an example of the first embodiment of the present invention.
FIG. 9 is a diagram showing the results of a life test performed using C in a notebook computer.

FIG. 6 is a cross-sectional view of a conventional double-sided FPC.

7 is a cross-sectional view of the double-sided FPC shown in FIG. 6 when bent.

8 is a perspective view of a notebook personal computer using an FPC 11 for electrical connection between a main body 12 and an LCD panel 10. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cover lay film layer 2 Copper foil layer 3 Base film layer 4 Copper foil layer 5 Cover lay film layer 8 Disconnection 9 Neutral surface 10 LCD panel 11 FPC 12 Main body 21 Cover lay film layer 22 Copper foil layer 23 Base film layer 24 Copper Foil layer 25 Coverlay film layer 31 Coverlay film layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05K 1/02 H05K 3/28 H05K 3/46

Claims (7)

(57) [Claims] 1. A double-sided flexible wiring board, characterized in that a neutral surface where no stress is generated in bending is located on one of the copper foil layers, ie, the disconnection preventing copper foil layer. 2. A copper foil layer is adhered to one surface of a base film layer and a copper foil layer is adhered to the other surface, and a coverlay film layer is formed on an outer surface of each of the copper foil layer and the copper foil layer. In the bonded double-sided flexible wiring board, the thickness of the cover lay film layer on one side of the base film layer is adjusted to the thickness of the base film layer, the copper foil layer, and the cover on the other side of the base film layer. A double-sided flexible wiring board characterized in that the thickness is equal to or greater than the total thickness of the lay film layers. 3. The one side of the base film is outside.
Claims that repeatedly bends to the side
Item 3. Double-sided flexible wiring base according to any one of Items 1-2.
Board. 4. The copper foil layer according to claim 1, wherein said copper foil layer has a wide width.
The method according to any one of claims 1 to 3, wherein
Double-sided flexible wiring board. 5. A lid pivotally supported on the main body to open and close the main body.
And the main body and the double-sided flange according to any one of claims 1 to 4.
It is characterized by being electrically connected by a flexible wiring board.
Device. 6. A table pivotally supported on a main body to open and close the main body.
Display panel with a double-sided frame according to any one of claims 1 to 4.
It is characterized by being electrically connected by a xivable wiring board
Notebook type information processing device. 7. A method used to bend repeatedly double-sided flexible wiring board, bending the double-sided flexible wiring board according to claim 1, 2 or 4 such that the disconnection preventing copper foil layer becomes outside A method for using a double-sided flexible wiring board, comprising: