JP2014093354A - Flexible printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible printed circuit board of less disconnection in a first conductive film caused by folding.SOLUTION: A flexible printed circuit board comprises: a first conductive film 14 including a folding position P, which is formed on a surface 13a of a base film 13 to electrically connecting both sides of the folding position P; a second conductive film 21 formed on a rear face 13b of the base film 13 except the folding position P; a resist layer 15 which includes at least the folding position P and covers at least a part of the first conductive film 14; a coating layer 16 which includes an anisotropic conductive adhesive layer 45 bonded to the resist layer 15 and includes at least the folding position P and covers at least a part of the resist layer 15; a cover layer 22 which covers at least a part of the second conductive film 21 across both sides of the folding position P; and an adhesive layer 23 which bonds the cover layer 22 except the folding position P with the second conductive film 21.

Description

  Embodiments described herein relate generally to a flexible printed circuit board that is bent at a predetermined bending position.

  A flexible printed circuit (FPC) is flexible and can be deformed greatly, and thus is suitably used for various portable terminals, for example.

  In recent years, with the miniaturization and high density of portable terminals, there are increasing opportunities to bend and use flexible printed circuit boards so that they can be accommodated in limited areas and spaces. In such a case, it is necessary to prevent disconnection of the flexible printed circuit board.

JP 2010-251587 A

  As described above, there is a demand for a flexible printed board that is less likely to be broken by bending.

  The problem to be solved by the present invention is to provide a flexible printed circuit board in which disconnection is unlikely to occur in the first conductive film due to bending.

  The flexible printed circuit board of the embodiment is a flexible printed circuit board that is bent at a predetermined bending position. The flexible printed board includes a base film, a first conductive film, a second conductive film, a first protective layer, a covering layer, a second protective layer, and an adhesive layer. The base film has a first surface and a second surface facing each other. The first conductive film is formed on the first surface of the base film so as to include a folding position, and conducts between both sides of the folding position. The second conductive film is formed on the second surface of the base film except for the bending position. The first protective layer covers at least a part of the first conductive film including at least the bent position. The covering layer includes a covering adhesive layer bonded to the first protective layer, and covers at least a part of the first protective layer including at least a folding position. The second protective layer covers at least a part of the second conductive film across both sides of the bending position. The adhesive layer adheres the second protective layer to the second conductive film except for the bending position.

It is sectional drawing which shows the flexible printed circuit board of 1st Embodiment. It is sectional drawing which shows the flexible printed circuit board of 2nd Embodiment. It is sectional drawing which shows the flexible printed circuit board of 3rd Embodiment.

  The configuration of the first embodiment will be described below with reference to FIG.

  In FIG. 1, 11 indicates a flexible printed circuit (FPC), and this flexible printed circuit 11 is used for a portable terminal such as a cellular phone (not shown). The flexible printed circuit board 11 includes a base film 13, a first conductive film 14 that covers a surface 13 a that is a first surface of the base film 13, and a first film that partially covers the first conductive film 14. A resist layer 15 as a protective layer, a covering layer 16 which covers and covers a part of the resist layer 15, and a second conductive layer which covers a back surface 13b which is a second surface facing the front surface 13a of the base film 13. Double-sided wiring comprising a film 21, a cover layer 22 as a second protective layer covering the second conductive film 21, and an adhesive layer 23 for adhering the cover layer 22 to the second conductive film 21 FPC. In the flexible printed board 11, a wiring region 25 where at least one of the conductive films 14 and 21 is located is formed in the center, and an ILB (Inner Lead Bonding) portion 26 is formed on one side of the wiring region 25. Then, an OLB (Outer Lead Bonding) terminal portion 27 is formed on the other side of the wiring region 25, and a predetermined position in the wiring region 25, for example, a position near the ILB portion 26 is defined as a bending position P. The base film 13 is configured to be folded in, for example, 180 ° so as to be stored in the portable terminal so that the front surface 13a side is a mountain and the back surface 13b side is a valley.

  The base film 13 is a film of about 25 μm, for example, formed of a synthetic resin such as polyimide.

  The first conductive film 14 is, for example, a copper foil (Cu) 31 that is a (first) conductor of about 12 μm, and a (second) conductor formed on the copper foil 31 in an overlapping manner. A (first) through-hole plating layer 32 of about 8 μm made of copper or the like is integrally laminated to form a film. Further, the first conductive film 14 is formed on the surface 13 a of the base film 13 so as to include the bending position P. Accordingly, the first conductive film 14 is electrically connected and electrically connected to both sides of the bending position P, that is, the ILB portion 26 and the OLB terminal portion 27 sandwiching the bending position P.

  The resist layer 15 is formed so as to cover substantially the entire first conductive film 14 (through-hole plating layer 32) with a synthetic resin such as a photosensitive resist (Photo Sensitive Resist, PSR). The resist layer 15 is formed in a predetermined pattern by performing predetermined film formation and etching processes, and the covering layer 16 and the first conductive film 14 (through-hole plating layer 32) are electrically connected. A plurality of contact holes 34 for connection to each other and a contact hole 36 in which various terminals 35 are formed are formed. The resist layer 15 is formed at a position including the bending position P. In other words, the resist layer 15 is formed to be bent in a mountain shape at the bending position P.

  Further, the terminal 35 covers a nickel (Ni) plating layer 41 of about 1 to 6 μm, for example, which is electrically connected to the first conductive film 14 (through-hole plating layer 32), and covers the nickel plating layer 41, for example. A gold (Au) plating layer 42 having a thickness of about 0.03 to 0.19 μm is integrally laminated to form a film. Furthermore, various components 43 are mounted on the wiring region 25 or the terminal 35 located in the ILB portion 26, respectively.

  The covering layer 16 is a so-called EMI (Electro Magnetic Interference) layer for preventing electromagnetic noise, and is an anisotropic conductive adhesive layer which is a thermosetting adhesive layer as a covering adhesive layer of about 3 μm, for example. The agent layer 45, an electromagnetic shield layer 46 of about 0.1 μm, for example, and an insulating layer 47 of about 5 μm, for example, are integrally laminated. Here, the anisotropic conductive adhesive layer 45 is formed in a hard state by curing the anisotropic conductive adhesive. Further, the coating layer 16 is disposed by thermocompression bonding with an anisotropic conductive adhesive layer 45 at a position including the contact hole 34 of the resist layer 15, and the contact hole 34 and the anisotropic conductive adhesive layer 45 are disposed. The electromagnetic shield layer 46 is electrically connected to the first conductive film 14 (through-hole plating layer 32) via the via. The covering layer 16 is formed so as to cover the resist layer 15 in the wiring region 25 and at a position including the bending position P. In other words, the coating layer 16 is formed so as to be bent in a mountain shape at the folding position P.

  On the other hand, the second conductive film 21 is, for example, a copper foil (Cu) 51 which is a (third) conductor of about 12 μm, and a (fourth) conductor formed to overlap the copper foil 51. A through-hole plating layer 52 of about 8 μm made of copper or the like is integrally laminated to form a film. The second conductive film 21 has an opening 54 at a position including the bending position P. That is, the first conductive film 14, the resist layer 15, and the coating layer 16 are located on the surface 13 a side of the base film 13 corresponding to the position of the opening 54. In other words, the second conductive film 21 is formed on the back surface 13b of the base film 13 except for the bending position P. Therefore, there is no thermosetting adhesive including the adhesive layer 23 at least on the inner side (back side) of the flexible printed circuit board 11 at the position including the bending position P. The second conductive film 21 is not electrically connected between both sides of the opening 54. That is, the opening 54 is an insulating space that insulates (separates) one side (ILB part 26 side) and the other side (OLB terminal part 27 side) of the second conductive film 21. Therefore, at the position of the opening 54, the flexible printed circuit board 11 is wired only by the first conductive film 14 on the front surface 13a side of the base film 13, and is not wired by the back surface 13b side. That is, in the wiring region 25, the position of the opening 54 is a single-sided wiring region 55, and the wiring region 25 excluding this single-sided wiring region 55 is a double-sided wiring region.

  The cover layer 22 is a film of, for example, about 12.5 μm formed of a synthetic resin such as polyimide. This cover layer 22 is formed continuously over the wiring region 25 and the ILB portion 26. That is, the cover layer 22 is continuously formed across the both sides of the folding position P (opening 54) including the folding position P. In other words, the cover layer 22 is continuous across the opening 54 (single-plane wiring region 55). That is, the cover layer 22 is formed so as to cover the opening 54.

  Further, the adhesive layer 23 is formed to have a thickness of about 15 μm by, for example, a thermosetting adhesive, and adheres the cover layer 22 to the second conductive film 21 except for the bending position P (position of the opening 54). doing. In other words, the adhesive layer 23 is not located in the vicinity of the folding position P including the folding position P, and is separated from each other on one side and the other side by the opening 54. Accordingly, the cover layer 22 formed across the bending position P (covering the opening 54) is separated from the base film 13 through the space at the position of the opening 54.

  The ILB portion 26 has an increased strength because, for example, a cured layer 57 of about 275 μm formed of, for example, polyimide on the cover layer 22 is adhered by a cured adhesive layer 58 of about 50 μm, for example. Yes.

  The OLB terminal portion 27 is a portion for electrically connecting a component 43 located in the ILB portion 26 and the like to an external circuit, and the terminal 35 is located exposed on the front side.

  Then, when the flexible printed circuit board 11 is stored in, for example, the interior of a portable terminal, the adhesive layer 23 is not positioned at the folding position P when the flexible printed circuit board 11 is folded at the folding position P with the opening 54 side inside. Since the vicinity of the bending position P (the portion corresponding to the opening 54) does not become harder than necessary, the bending radius (inner diameter) when bent is set appropriately. Further, since the inner diameter side of the bending radius can be secured by the thickness of the cover layer 22, it is not sharp. Therefore, disconnection hardly occurs in the first conductive film 14.

  That is, in order to make the flexible printed board 11 easy to bend, the position of the single-sided wiring region 55 is set as a bent position P. When the flexible printed board 11 is bent from the bent position P with the opening 54 inside, If nothing is applied to the opening 54, the inner diameter of the fold is reduced, sharply bent, and the anisotropic conductive adhesive layer 45, which is a hard part of the covering layer 16, is cracked and bent. As a result, the first conductive film 14 is disconnected and a conduction failure occurs. Therefore, in the present embodiment, a cover layer 22 that covers a part of the second conductive film 21 is provided between both sides of the bending position P, and the cover layer 22 is disposed at the position excluding the bending position P. By bonding to the second conductive film 21 by 23, that is, by minimizing the area of the adhesive layer 23, the bending radius (inner diameter) of the flexible printed circuit board 11 is relatively increased. The disconnection hardly occurs at the bending position P in one conductive film 14.

  Also, since the bending radius (inner diameter) of the flexible printed circuit board 11 is secured by using the cover layer 22 for protecting the second conductive film 21, for example, an insulating tape having a thickness of about 15 μm is formed on the inner edge of the opening 54. Compared to the case where the inner diameter of the fold is made larger (to avoid bending sharply) by attaching (consisting of an insulating layer and adhesive tape), additional steps such as attaching an insulating tape are not required. Thus, the cost can be reduced.

  In addition, since the relatively hard thermosetting adhesive layer 23 does not exist in the opening 54, the cover layer 22 is formed by the adhesive layer 23 at the position of the opening 54 (including the folding position P). Compared to the case of bonding to the second conductive film 21, the bending does not become unnecessarily hard, and the bending with an appropriate bending radius becomes possible.

  Next, a second embodiment will be described with reference to FIG. In addition, about the structure and effect | action similar to the said 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  In the second embodiment, the cover layer 22 of the first embodiment is separated at one side and the other side of the folding position P (opening 54) and includes the folding position P, that is, the opening. An adhesive layer opening 61 is formed in the anisotropic conductive adhesive layer 45 of the covering layer 16 at a position corresponding to the portion 54.

  The adhesive layer opening 61 is formed with a width dimension substantially the same as the width dimension of the opening 54. Therefore, the anisotropic conductive adhesive layer 45 is bonded to the resist layer 15 except for the bending position P. In other words, the anisotropic conductive adhesive layer 45 is deleted at a position including the bending position P.

  When the flexible printed circuit board 11 is folded, for example, in the interior of a portable terminal or the like at the folding position P with the opening 54 side inside, the adhesive layer 23 and the anisotropic conductive material are placed at the folding position P. Since the adhesive layer 45 is not positioned and the vicinity of the bending position P (the portion corresponding to the opening 54) does not become harder than necessary, the flexible printed circuit board 11 can be bent more easily, and the bending radius when bent Even if it becomes sharp, since the breakage of the relatively hard anisotropic conductive adhesive layer 45 that becomes the starting point of the disconnection of the first conductive film 14 does not occur, the disconnection occurs in the first conductive film 14. Hard to do.

  Next, a third embodiment will be described with reference to FIG. In addition, about the structure and effect | action similar to said each embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  The third embodiment is a combination of the first embodiment and the second embodiment.

  That is, in this embodiment, the cover layer 22 is continuous between one side and the other side of the folding position P (opening 54), and the adhesive layer 23 is not located at the folding position P. An adhesive layer opening 61 is formed in the anisotropic conductive adhesive layer 45 of the covering layer 16 corresponding to the bending position P.

  When the flexible printed circuit board 11 is folded, for example, in the interior of a portable terminal or the like at the folding position P with the opening 54 side inside, the adhesive layer 23 and the anisotropic conductive material are placed at the folding position P. Since the adhesive layer 45 is not positioned and the vicinity of the bending position P (the portion corresponding to the opening 54) does not become harder than necessary, the bending radius when being bent is appropriately set. Further, since the inner diameter side of the bending radius can be secured by the thickness of the cover layer 22, it is not sharp. Therefore, disconnection hardly occurs in the first conductive film 14.

  That is, a cover layer 22 covering a part of the second conductive film 21 is provided between both sides of the bending position P, and the cover layer 22 is formed by the adhesive layer 23 at a position excluding the bending position P. By bonding to the conductive film 21, the bending radius (inner diameter) of the flexible printed circuit board 11 is made relatively large, and the coating layer 16 is resisted by the anisotropic conductive adhesive layer 45 at a position other than the bending position P. The flexible printed circuit board 11 can be easily folded by being bonded to the layer 15 and preventing the anisotropic conductive adhesive layer 45 from breaking the first conductive film 14 when bent. However, disconnection of the first conductive film 14 can be more reliably suppressed.

  According to at least one embodiment described above, the covering layer 16 includes the electromagnetic shield layer 46, so that noise can be prevented more reliably.

  In each of the above embodiments, the adhesive layer 23 and the covering adhesive layer are not limited to those formed of a thermosetting adhesive, and may be any adhesive that cures at the time of bonding, such as an ultraviolet curable adhesive. Can be formed.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

11 Flexible printed circuit boards
13 Base film
13a First surface
13b 2nd side, back side
14 First conductive film
15 Resist layer as first protective layer
16 Coating layer
21 Second conductive film
22 Cover layer as second protective layer
23 Adhesive layer
45 Anisotropic conductive adhesive layer as covering adhesive layer
46 Electromagnetic shield layer P Bending position

Claims (4)

A flexible printed circuit board that can be bent at a predetermined bending position,
A base film having a first surface and a second surface facing each other;
A first conductive film formed on the first surface of the base film so as to include the bent position, and conducting between both sides of the bent position;
A second conductive film formed on the second surface of the base film except for the bending position;
A first protective layer covering at least a part of the first conductive film including at least the bent position;
A coating layer comprising a covering adhesive layer bonded to the first protective layer, and covering at least a part of the first protective layer including at least the folding position;
A second protective layer covering at least part of the second conductive film across both sides of the bending position;
A flexible printed circuit board comprising: an adhesive layer that adheres the second protective layer to the second conductive film except for the bending position. A flexible printed circuit board that can be bent at a predetermined bending position,
A base film having a first surface and a second surface facing each other;
A first conductive film formed on the first surface of the base film so as to include the bent position, and conducting between both sides of the bent position;
A second conductive film formed on the second surface of the base film except for the bending position;
A first protective layer covering at least a part of the first conductive film including at least the bent position;
A second protective layer covering at least a part of the second conductive film except for the bending position;
An adhesive layer for adhering the second protective layer to the second conductive film except for the bending position;
A coating adhesive layer that is bonded to the first protective layer except for the folding position, and includes a coating layer that includes at least the folding position and covers at least a part of the first protective layer. A flexible printed circuit board characterized by that. A flexible printed circuit board that can be bent at a predetermined bending position,
A base film having a first surface and a second surface facing each other;
A first conductive film formed on the first surface of the base film so as to include the bent position, and conducting between both sides of the bent position;
A second conductive film formed on the second surface of the base film except for the bending position;
A first protective layer covering at least a part of the first conductive film including at least the bent position;
A covering adhesive layer that is bonded to the first protective layer except for the folding position; a covering layer that includes at least the folding position and covers at least a part of the first protective layer;
A second protective layer covering at least part of the second conductive film across both sides of the bending position;
A flexible printed circuit board comprising: an adhesive layer that adheres the second protective layer to the second conductive film except for the bending position. The flexible printed circuit board according to any one of claims 1 to 3, wherein the coating layer includes an electromagnetic shield layer.

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