JP2000196205A - Flexible printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress springing back by making the metal conductor loading quantity per unit area in a bent region larger, as compared with that at a non-bent region near the bent region. SOLUTION: A metal conductor wiring pattern 31, formed on a base film layer 1 via an adhesive layer 2 is bent along a bending center line to form a bent metal conductor wiring pattern 311 is made thicker at bent parts than at non-bent parts. The bent region of a flexible printed board 100 with this constitution is made, by reinforcing the metal loading quantity against the spring back force due to the elastic deformation of a high-elasticity plastic film which is bent such as polyimide, etc., used for the base film layer 1 and a cover lay film 4. This increases the deformation holding force after plastic deformation of the metal conductor pattern 31 when it is bent, and as a result, the springing back of the flexible printed board 100 can be suppressed as a whole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed circuit board used for connecting board terminals built in, for example, electronic equipment and electric equipment.

In recent years, in order to electrically connect a plurality of rigid printed circuit boards constituting the function of the device by using a limited narrow space in accordance with a demand for miniaturization of the device. In many cases, flexible printed boards are used.

[0003]

2. Description of the Related Art A conventional flexible printed circuit board is formed by etching a copper foil formed on a base film having a heat resistance and flexibility, for example, a plastic film such as a polyimide film into a predetermined pattern. And a coverlay film made of the same material as the base film for protecting the conductor pattern. The thickness of the flexible printed circuit board configured as described above is usually 1 mm or less, and the flexible printed circuit board has high flexibility. For this reason, flexible printed circuit boards are used to mount circuits in narrow spaces that are difficult with ordinary rigid printed circuit boards, and to mount high-density equipment by repeatedly bending, including bending, such as circuit connections between printed circuit boards. Widely used for applications.

Usually, the thickness of the coverlay film and the base film is usually about 20 μm. For example, in the case of a flexible printed circuit board having a structure in which a conductor pattern is formed on only one side of the base film, the entire board is About 80% of the thickness is the resin layer,
It consists of a resin layer and an adhesive layer for bonding between copper foils, and it is flexible and easy to bend.On the other hand, elasticity is relatively strong,
When this is bent, springback occurs and it is difficult to secure a predetermined bending angle. In order to arrange a flexible printed circuit board in a narrow space, it is often difficult to realize this bending at a predetermined bending angle and a predetermined bending radius from the above circumstances, and a solution is required. .

Conventionally, as a method of solving the above-mentioned problem of the flexible printed circuit board and improving the flexibility, a method of forming various slits in a bent portion as shown in FIGS. 4 and 5, for example, has been used. I have.

FIG. 4 is a view for explaining a method of forming a slit except for a coverlay film layer at a bent portion. (A) is a long flexible printed circuit board 400.
Shows a plan view of the flexible printed circuit board 400,
A plurality of circuit-connecting metal conductor patterns 34 in the form of parallel lines are formed in the left-right longitudinal direction of the figure, and the substrate has a constant width in the vertical direction of the figure. FIG. 2 is a cross-sectional view of an A-A portion including the above.

In the drawing, 1 is a base film layer made of, for example, a polyimide film or the like, which constitutes a flexible printed board, 2 is an adhesive layer, 34 is a metal conductor wiring pattern made of, for example, copper foil, 5 is, for example, a base film layer A coverlay film layer 341 made of the same material as above is a slit formed with a certain width on the center line of the bend by removing the coverlay film and the bonding adhesive layer. The bend is bent in a convex shape on the near side along the refraction center line in the plan view (a). The feature of this method is that the bent portion can be clearly identified.

FIG. 5 is an explanatory view of a method of providing a slit in a bent portion in a part of a row of through holes 351 in a flexible printed circuit board 500 having the same wiring pattern as FIG. ) Shows a plan view thereof, and (b) shows a cross-sectional view of an AA portion including a through-hole portion in the plan view.

In the drawing, the same reference numerals are the same as those in FIG. 1, and reference numeral 351 is a through hole formed on the bending center line so as to avoid the metal conductor pattern portion. I do.

[0010]

However, in the case of the method shown in FIG. 4, the thickness of the substrate at the bent portion is thinner than at other portions, and the bending stress at the time of bending causes an excessive external stress particularly at that portion. And it is easily broken when subjected to an electrical load or the like. In the method of FIG. 5, it is necessary to form a slit avoiding the metal conductor pattern portion, and an effective effect cannot be obtained when the formable portion has a small area. Further, basically, the mechanical strength of the bent portion is deteriorated, and is weak against external stress.

Accordingly, the present invention relates to bending of a flexible printed circuit board, and suppresses springback without impairing the resistance of a bent portion to external stress and reliability, and sets a predetermined bending angle within a limited space. It is an object of the present invention to provide a flexible printed circuit board having good bending workability such as bending at a bending radius.

[0012]

DISCLOSURE OF THE INVENTION The present invention has been proposed to achieve the above-mentioned object, and in a flexible printed circuit board to be bent and used, a unit area per unit area in a bent area of the flexible printed circuit board is provided. Is characterized in that the metal conductor mounting amount is larger than the metal conductor mounting amount per unit area in the non-bent region near the refraction region.

[0013] The present invention is characterized in that the metal conductor layer thickness of the metal conductor wiring pattern in the bent region is larger than the metal conductor layer thickness of the metal conductor wiring pattern in the non-bent region.

Further, the present invention is characterized in that the width of the metal conductor wiring pattern in the bent region is larger than the width of the metal conductor wiring pattern in the non-bent region.

Further, the present invention is characterized in that a dummy metal conductor pattern is formed between the metal conductor wiring patterns in the bent region.

Further, the present invention is characterized in that the thickness of the metal conductor layer of the dummy metal conductor pattern is made larger than the thickness of the metal conductor layer of the metal conductor wiring pattern in the non-bent region.

The flexible region of the flexible printed circuit board constructed as described above is designed to oppose a springback force caused by elastic deformation of the plastic film portion having high elasticity, such as polyimide used for the base film and the overlay film, at the time of bending. By reinforcing the mounting amount of the metal conductor, the deformation maintaining force after plastic deformation of the metal conductor layer at the time of bending is increased, and as a result, it is possible to suppress springback of the entire flexible printed circuit board. As a result, it is possible to realize a good bending property of realizing bending at a predetermined bending angle and a predetermined bending radius, and to prevent a decrease in the reliability of the bent portion, which is likely to occur in a slit processing substrate. .

[0018]

FIG. 1 is a block diagram of an embodiment of the present invention.
1 shows a flexible printed circuit board. (A) in the figure, a flexible printed circuit board 10 elongated in the left-right direction.
0 is a plan view, and (b) is a cross-sectional view of an AA portion including the bent metal conductor wiring pattern portion 311.

In the figure, the metal conductor wiring pattern 31 formed on one base film layer via the adhesive layer 2 has a film thickness of the metal conductor wiring pattern at the bent portion along the center line of the bending, compared with that of the non-bent portion. (The bent portion metal conductor wiring pattern portion 311). The formation of the metal conductor wiring pattern having the step of the film thickness can be easily realized by a photolithography technique to which the film thickness control by etching is applied. Although the thickness of each layer constituting the flexible printed circuit board varies depending on the application, the thickness of each constituent layer in the figure is 2
In the case of an example of about 0 to 25 μm, in order to enhance the flexibility, it is desirable that the thickness of the metal conductor wiring pattern at the bent part is about twice or more, for example, about 50 μm or more than that of the non-bent part. For this reason, in order to increase the accuracy of the bending angle, it is effective to use a jig such as a punch and a die as necessary.

FIG. 2 is a structural view of another embodiment of the present invention, showing a flexible printed circuit board 200 which is also long and has different wiring patterns. (A) is a plan view, (b) is a bent portion metal conductor wiring pattern 321
FIG. 2 is a cross-sectional view of an A-A portion including the above.

In the figure, a metal conductor wiring pattern 32 formed on one base film layer via an adhesive layer 2 has a bent metal conductor wiring pattern width along a bending center line which is larger than that of a non-bent portion. Widely formed (bent metal conductor wiring pattern portion 321). For example, in the case where the pattern width of the pattern 32 is 100 μm and the pitch of the parallel pattern is 300 μm, for example, the pattern width of the pattern portion 321 is increased to 50 μm symmetrically at the center to 200 μm. This example can be easily realized by an effect different from that shown in FIG. 1, that is, a pattern formation method of a simple metal conductor without photo control by photolithography.

FIG. 3 is a structural view of another embodiment of the present invention, showing a flexible printed circuit board 400 which is also long and has different wiring patterns. (A) is a plan view, and (b) is a cross-sectional view of the AA portion including the metal conductor dummy pattern 331.

In the figure, a metal conductor dummy pattern 331 is formed in a bent region of a gap on a plane of a metal conductor wiring pattern 33 formed on one base film layer via an adhesive layer 2. In this example, when the wiring pattern and the dummy pattern have the same metal conductor film thickness, it can be realized by a pattern formation technique using photolithography once. For example, similar to the example shown in FIG.
Is formed, a dummy pattern having a width of, for example, 50 μm, that is, a width of 100 μm is formed symmetrically with respect to the center line between the parallel patterns as the dummy pattern width. In the case where the dummy pattern is formed to have a larger film thickness, it can be realized by using a thick conductor foil and using a technique of controlling the film thickness by etching and forming a pattern by photolithography. For example, lamination is performed using a conductor foil having a thickness of 50 μm, the dummy pattern portion uses the same conductor thickness, and the other pattern portions are etched to have a thickness of 20 to 25 μm to form a required pattern shape. This method is more recommended in terms of flexibility.

In the above embodiments, all the examples in which the metal conductor layer is formed on one side of the base film are described. However, the present invention is not limited to this, and the metal conductor layers are formed on both sides of the base film. It goes without saying that the same operation can be performed even in the case where the

[0025]

As is clear from the above description, according to the flexible printed circuit board of the present invention, more metal conductors are mounted on the bent portion than the neighboring metal conductors are mounted. By increasing the width of the metal conductor pattern, or forming a dummy pattern between the metal conductor patterns, or increasing the thickness of the dummy pattern, a predetermined bending angle in a narrow space is determined. With this bending radius, the spring pack can be restrained and bent, and the effect of improving the resistance to external stress at the bent portion and the reliability as compared with the conventional slitting method can be achieved.

[Brief description of the drawings]

FIG. 1 is a plan view and a cross-sectional view of a flexible printed circuit board according to an embodiment of the present invention.

FIG. 2 is a plan view and a sectional view of a flexible printed circuit board according to another embodiment of the present invention.

FIG. 3 is a plan view and a sectional view of a flexible printed circuit board according to another embodiment of the present invention.

FIG. 4 is a plan view and a cross-sectional view of an example of a conventional flexible printed circuit board.

FIG. 5 is a plan view and a sectional view of another example of a conventional flexible printed circuit board.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 base film 2 adhesive layer 31, 32, 33, 34, 35 metal conductor wiring pattern 4 coverlay film 100, 200, 300, 400, 500 flexible printed board 311 metal conductor pattern 321 in which the thickness of the bent region is increased 321 bent region 331 Metal conductor dummy pattern in bent region 341 Slit portion in bent region 351 Through hole in bent region

Claims (5)

[Claims] 1. A flexible printed circuit board to be bent and used, wherein the amount of metal conductor mounted per unit area in a bent region of the flexible printed circuit board is equal to the amount of metal conductor mounted per unit area in a non-bent region near the refraction region. Flexible printed circuit board characterized by more than that. 2. The method according to claim 1, wherein the thickness of the metal conductor layer of the metal conductor wiring pattern in the bent region of the flexible printed board is greater than the thickness of the metal conductor layer of the metal conductor wiring pattern in the non-bent region. Item 7. The flexible printed circuit board according to Item 1. 3. The flexible printed board according to claim 1, wherein the width of the metal conductor wiring pattern in the bent region of the flexible printed board is larger than the width of the metal conductor wiring pattern in the non-bent region. 4. The flexible printed circuit board according to claim 1, wherein a dummy metal conductive pattern is formed between the metal conductive wiring patterns in the bent area of the flexible printed circuit board. 5. The method according to claim 4, wherein the thickness of the metal conductor layer of the dummy metal conductor pattern formed in the bent region is larger than the thickness of the metal conductor wiring pattern of the metal conductor wiring pattern in the non-bent region. The flexible printed circuit board according to claim 1.