JP2013157497A - Flexible printed wiring board and connection structure of printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible printed wiring board for forming a connection structure of a printed wiring board capable of visually revealing exfoliation in an invisible state generated between a wiring circuit and a conductive adhesive, and to provide a connection structure of the printed wiring board.SOLUTION: A flexible printed wiring board 10 includes a plurality of wiring circuits 12a and also includes a connection region S1 in which the wiring circuits 12a are exposed. The connection region S1 is connected to the connection region of another printed wiring board via a conductive adhesive 30. A stress concentration part M is provided in a non-connection region N adjacent to the connection region S1.

Description

  The present invention relates to a flexible printed wiring board provided with a stress concentration portion, and a printed wiring board in which a connection area of the flexible printed wiring board and a connection area of another printed wiring board are connected via a conductive adhesive. Concerning connection structure.

Various flexible printed wiring boards are arranged in an electronic device such as a mobile phone or a hard disk device according to the application.
In such a printed wiring board, a connection area formed by exposing a wiring circuit is provided, and the connection area is electrically connected to a connection area such as another printed wiring board via a conductive adhesive. There are some which constitute the connection structure of the printed wiring board.
As a prior art showing such a flexible printed wiring board and a connection structure of the printed wiring board, for example, there is Patent Document 1 below.

JP 2004-170824 A

In the printed wiring board connection structure as shown in Patent Document 1, in particular, in the printed wiring board connection structure in which a plurality of printed wiring boards are electrically and mechanically connected via a conductive adhesive, a plurality of printed wiring board connection structures are provided. In general, a printed wiring board is transported as a product in a state where it is connected via a conductive adhesive, or is incorporated into a housing or the like.
Therefore, in such a printed wiring board connection structure, when stress is applied to the printed wiring board during transportation or installation in a housing, the adhesion between the wiring circuit and the conductive adhesive is visually visible. By peeling in a state that cannot be performed (hereinafter referred to as an invisible state), there is a possibility that the electrical connection is broken in the invisible state.
In other words, although there is no defect as a product in appearance, there is a possibility that a product with an electrical defect is actually shipped.
Therefore, in the printed wiring board that forms the connection structure of the printed wiring board, it is an important development issue how to visually reveal the invisible peeling that may occur between the wiring circuit and the conductive adhesive It has become.

  Therefore, the present invention solves the above-described conventional problems and visually reveals invisible peeling between the wiring circuit and the conductive adhesive in the flexible printed wiring board forming the connection structure of the printed wiring board. It is an object of the present invention to provide a flexible printed wiring board and a printed wiring board connection structure that can be realized.

  The flexible printed wiring board of the present invention includes a plurality of wiring circuits, and includes a connection region in which the wiring circuit is exposed, and the connection region is connected to a connection region of another printed wiring board via a conductive adhesive. A flexible printed wiring board to be connected is characterized in that a stress concentration portion is provided in a non-connection region adjacent to the connection region.

According to the first aspect of the present invention, the flexible printed wiring board includes a plurality of wiring circuits, and includes a connection region in which the wiring circuit is exposed, and the connection region is interposed via a conductive adhesive. A flexible printed wiring board that is connected to a connection area of another printed wiring board, and a stress concentration portion is provided in a non-connection area adjacent to the connection area. When stress is applied to the flexible printed wiring board in a state where it is connected to the board via the conductive adhesive, the applied stress can be distributed to the stress concentration portion. Therefore, it is possible to effectively prevent peeling in an invisible state between the plurality of wiring circuits and the conductive adhesive.
If the flexible printed wiring board is subjected to a certain level of stress (stress that causes peeling in an invisible state between the wiring circuit and the conductive adhesive), the flexible printed wiring board starts from the stress concentration part. Can be broken. Therefore, peeling in an invisible state that occurs between the plurality of wiring circuits and the conductive adhesive can be made visible (visualized).

  Further, in the flexible printed wiring board of the present invention, in addition to the first feature of the present invention, the stress concentration portion is a cut formed by cutting at least one side surface of the flexible printed wiring board, and the cutting direction thereof is The second feature is that the direction intersects the wiring circuit.

According to the second feature of the present invention, in addition to the function and effect of the first feature of the present invention, the stress concentration portion is a cut formed by cutting at least one side surface of the flexible printed wiring board. Since the cutting direction is a direction crossing the wiring circuit, stress is applied in a direction crossing the wiring circuit in a state where the flexible printed wiring board is connected to another printed wiring board via a conductive adhesive. Can be distributed to the stress concentration part. Therefore, it is possible to effectively prevent peeling in an invisible state between the wiring circuit and the conductive adhesive.
In addition, when stress exceeding a certain level (stress that causes peeling in the invisible state between the wiring circuit and the conductive adhesive) is applied in the direction intersecting the wiring circuit, the stress concentration part (cutting) is the starting point. As described above, the flexible printed wiring board can be broken. Therefore, peeling in an invisible state that occurs between the wiring circuit and the conductive adhesive can be made obvious.

  In addition to the second feature of the present invention described above, the flexible printed wiring board of the present invention has a third feature that the cut is formed by cutting from the side surface to at least the outermost wiring circuit of the plurality of wiring circuits. It is a feature.

According to the third aspect of the present invention, in addition to the function and effect of the second aspect of the present invention, the cut is formed by cutting from the side surface to at least the outermost wiring circuit of the plurality of wiring circuits. Therefore, in the state where the flexible printed wiring board is connected to another printed wiring board via a conductive adhesive, when stress is applied in a direction intersecting the wiring circuit, at least the outermost of the plurality of wiring circuits The stress applied to the wiring circuit and the conductive adhesive can be effectively reduced. Therefore, it is possible to more effectively prevent peeling in an invisible state between at least the outermost wiring circuit of the plurality of wiring circuits and the conductive adhesive.
In addition, when a stress above a certain level (stress that causes peeling in the invisible state between the wiring circuit and the conductive adhesive) is applied in the direction intersecting the wiring circuit, the flexible printed wiring board starts from the stress concentration part. Can be more easily broken. Therefore, peeling in an invisible state that occurs between the wiring circuit and the conductive adhesive can be more easily manifested.

  Further, in the flexible printed wiring board of the present invention, in addition to the first feature of the present invention, the stress concentration portion is formed by projecting at least one side surface of the flexible printed wiring board into a convex shape. A fourth feature is that the outgoing direction is a direction intersecting the wiring circuit constituting the connection region.

According to the fourth feature of the present invention, in addition to the function and effect of the first feature of the present invention, the stress concentration portion bulges at least one side surface of the flexible printed wiring board into a convex shape. In addition, since the bulging direction is a direction intersecting the wiring circuit constituting the connection region, in a state where the flexible printed wiring board is connected to another printed wiring board via a conductive adhesive, When stress is applied in a direction crossing the wiring circuit, the applied stress can be distributed to the stress concentration portion. Therefore, it is possible to effectively prevent peeling in an invisible state between the wiring circuit and the conductive adhesive.
In addition, when a stress exceeding a certain level (stress that causes peeling in the invisible state between the wiring circuit and the conductive adhesive) is applied in the direction intersecting the wiring circuit, the flexible print starts from the stress concentration part. The wiring board can be broken. Therefore, peeling in an invisible state that occurs between the wiring circuit and the conductive adhesive can be made obvious.

  Further, in the flexible printed wiring board of the present invention, in addition to any one of the first to fourth features of the present invention, the stress concentration portion is provided at an opposing position on both side surfaces of the flexible printed wiring board. This is the fifth feature.

According to the fifth aspect of the present invention, in addition to the function and effect of any one of the first to fourth aspects of the present invention, the stress concentration portion is formed on the side surfaces on both sides of the flexible printed wiring board. Since the flexible printed wiring board is connected to another printed wiring board via a conductive adhesive because the flexible printed wiring board is connected to the other printed wiring board, stress is applied to the flexible printed wiring board. Can be further dispersed in the stress concentration part. Therefore, it is possible to more effectively prevent peeling in an invisible state between the wiring circuit and the conductive adhesive.
In addition, when a stress above a certain level is applied to the flexible printed wiring board (stress that causes peeling in an invisible state between the wiring circuit and the conductive adhesive), the flexible printed wiring board is further separated from the stress concentration portion. It can be easily broken. Therefore, peeling in an invisible state that occurs between the wiring circuit and the conductive adhesive can be more easily manifested.

  Moreover, the connection structure of the printed wiring board of this invention is a connection area | region of the flexible printed wiring board of any one of Claims 1-5, and the connection area | region of another printed wiring board through a conductive adhesive. The sixth feature is that they are connected together.

According to the sixth aspect of the present invention, the connection structure of the printed wiring board includes a connection region of the flexible printed wiring board according to any one of claims 1 to 5 and a connection region of another printed wiring board. Are connected via a conductive adhesive, when stress is applied to the flexible printed wiring board having the stress concentration portion, the applied stress can be distributed to the stress concentration portion. Therefore, it is possible to effectively prevent peeling in an invisible state between the wiring circuit and the conductive adhesive.
In addition, when a certain level of stress (stress that causes peeling in the invisible state between the wiring circuit and the conductive adhesive) is applied to the flexible printed wiring board having the stress concentration portion, the flexible printed wiring board is flexible starting from the stress concentration portion. The printed wiring board can be broken.
Therefore, peeling in an invisible state that occurs between the wiring circuit and the conductive adhesive can be made obvious.
Therefore, it is possible to effectively prevent the connection structure of the electrically defective printed wiring board from being shipped as a product.
Therefore, it is possible to provide a printed wiring board connection structure capable of realizing efficient quality control.

  In addition to the sixth feature of the present invention, the printed wiring board connection structure of the present invention has a seventh feature that the conductive adhesive is an anisotropic conductive adhesive.

  According to the seventh aspect of the present invention, in addition to the function and effect of the sixth aspect of the present invention, the conductive adhesive is an anisotropic conductive adhesive, so that it is good in the vertical direction. In addition, it is possible to achieve a high conductivity and maintain a good insulating property in the horizontal direction.

According to the flexible printed wiring board of the present invention, it is possible to effectively prevent peeling in an invisible state between the wiring circuit and the conductive adhesive.
Further, the invisible peeling that occurs between the wiring circuit and the conductive adhesive can be visually revealed (visualized).
Moreover, according to the connection structure of the printed wiring board of this invention, it can prevent effectively that peeling in an invisible state arises between a wiring circuit and a conductive adhesive. In addition, the invisible peeling that occurs between the wiring circuit and the conductive adhesive can be revealed, effectively preventing the connection structure of electrically defective printed wiring boards from being shipped as a product. can do.
Therefore, it is possible to provide a printed wiring board connection structure capable of realizing efficient quality control.
In addition, good conductivity can be realized in the vertical direction, and good insulation can be maintained in the horizontal direction.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the connection structure of the flexible printed wiring board which concerns on embodiment of this invention, and a printed wiring board, (a) is a perspective view which shows the connection structure of a printed wiring board, (b) is a perspective view which shows a flexible printed wiring board. It is. It is a top view which shows the principal part of the flexible printed wiring board which concerns on embodiment of this invention. It is a figure which shows the connection structure of the flexible printed wiring board which concerns on embodiment of this invention, and a printed wiring board, (a) is a top view which shows the opening part in a flexible printed wiring board, (b) is the connection structure of a printed wiring board. It is sectional drawing which shows a connection area | region. It is a figure which shows the connection structure of the printed wiring board which concerns on embodiment of this invention, (a) is a perspective view which shows the state before stress is applied to the connection structure of a printed wiring board, (b) is a printed wiring board. It is a perspective view which shows the state which the fracture | rupture produced in the connection structure of the printed wiring board from the stress concentration part as a starting point by stress being applied to the connection structure. It is a figure which shows the modification of the stress concentration part of the flexible printed wiring board which concerns on embodiment of this invention, (a) is a perspective view which shows the connection structure of a printed wiring board, (b) is a perspective view which shows a flexible printed wiring board. It is. It is a top view of the principal part which shows the modification of the stress concentration part of the flexible printed wiring board which concerns on embodiment of this invention. It is a figure which shows the modification of the stress concentration part of the printed wiring board which concerns on embodiment of this invention, (a) is a perspective view which shows the state before stress is applied to the connection structure of a printed wiring board, (b) is It is a perspective view which shows the state which the fracture | rupture had arisen in the connection structure of the printed wiring board from the stress concentration part as the stress was loaded to the connection structure of the printed wiring board. It is a perspective view which shows the connection structure of the conventional printed wiring board.

  With reference to the following drawings, a flexible printed wiring board 10 and a printed wiring board connection structure 1 according to an embodiment of the present invention will be described to provide an understanding of the present invention. However, the following description is an embodiment of the present invention, and does not limit the contents described in the claims.

First, referring to FIG. 1, a printed wiring board connection structure 1 according to an embodiment of the present invention will be described.
As shown in FIG. 1, a printed wiring board connection structure 1 according to an embodiment of the present invention is a printed wiring board in which two printed wiring boards are electrically and mechanically connected to each other by a conductive adhesive. It is a connection structure and is disposed inside an electronic device (not shown).
As shown in FIG. 1B, the printed wiring board connection structure 1 includes flexible printed wiring boards 10 and 20 and an anisotropic conductive adhesive 30 that is a conductive adhesive.

The flexible printed wiring board 10 is a so-called single-sided flexible printed wiring board provided with a wiring circuit 12a on one side of the base material layer 11, as shown in FIGS. 1 (b) and 3 (b).
As shown in FIGS. 1B and 3B, the flexible printed wiring board 10 includes a base material layer 11, a conductive layer 12 laminated on the base material layer 11, and the base material layer 11 and the conductive layer. And an insulating layer 13 covering 12.

The base material layer 11 serves as a base of the flexible printed wiring board 10 and is formed of a resin film.
As a resin film, what consists of a resin material excellent in the softness | flexibility is used. For example, any resin film may be used as long as it is normally used as a resin film for forming a flexible printed wiring board such as a polyimide film or a polyester film.
In particular, those having high heat resistance in addition to flexibility are desirable. For example, polyamide resin films, polyimide resin films such as polyimide and polyamideimide, and polyethylene naphthalate can be preferably used.
The heat-resistant resin may be any resin as long as it is normally used as a heat-resistant resin for forming a flexible printed wiring board, such as a polyimide resin or an epoxy resin.
The thickness of the base material layer 11 is desirably about 5 μm to 50 μm, more preferably about 10 μm to 25 μm. If the thickness is less than 5 μm, the insulation is not sufficient, and if it exceeds 50 μm, the flexibility of the flexible printed wiring board 10 is impaired.

The conductive layer 12 is a layer made of a conductive metal, and is a layer that forms the wiring circuit 12 a of the flexible printed wiring board 10.
The wiring circuit 12a can be formed using a known forming method such as coating the surface of the base material layer 11 with a conductive metal such as copper by plating and etching.
In the present embodiment, as shown in FIGS. 1B and 2, a plurality (five) of wiring circuits 12 a are arranged in parallel in a connection region S <b> 1 described later.
A plurality of wiring circuits 12a arranged in parallel in a non-connecting region N to be described later are arranged narrower on the inner side than the stress concentration portion M at a position of a stress concentration portion M to be described later. More specifically, in the stress concentration portion M (cut portion K) formed by cutting the side surfaces A on both sides of the flexible printed wiring board 10 to be described later, from the connection region S1 except for the wiring circuit 12a disposed in the center. The extended wiring circuit 12a is bent so as to follow the shape of the notch forming the stress concentration portion M, and the wiring circuit 12a is arranged to converge at the center of the flexible printed wiring board 10.
Note that the thickness of the wiring circuit 12a is desirably about 5 μm to 50 μm, more preferably about 9 μm to 35 μm. If it is less than 5 μm, the wiring circuit 12 a is likely to be disconnected, and if it exceeds 50 μm, the flexibility of the flexible printed wiring board 10 is impaired.
The width B of the wiring circuit 12a shown in FIG. 2 is desirably about 50 μm to 300 μm, more preferably about 150 μm to 200 μm. This is because if the thickness is less than 50 μm, the connection reliability is deteriorated, and if it exceeds 300 μm, the connection region S1 becomes large and cannot be made compact.
The length C between the adjacent wiring circuits 12a in the connection region S1 is desirably about 50 μm to 300 μm, more preferably about 150 μm to 200 μm. This is because if it is less than 50 μm, the insulation between the wiring circuits 12a is not sufficient, and if it exceeds 300 μm, the connection region S1 becomes large and cannot be made compact.

The insulating layer 13 constitutes an insulating layer of the flexible printed wiring board 10 by covering the base material layer 11 and the wiring circuit 12a.
In this embodiment, as shown in FIGS. 1B and 2, the opening 13 a is formed in a part of the insulating layer 13, and the wiring circuit 12 a is exposed from the opening 13 a, thereby opening the opening 13 a. Is the connection region S1. As shown in FIG. 1, the wiring circuit 12a disposed in the connection region S1 is electrically connected to the wiring circuit 22a disposed in the connection region S2 of the flexible printed wiring board 20 via an anisotropic conductive adhesive 30. Connected mechanically and mechanically.
As the insulating layer 13, those usually used for forming an insulating layer of a flexible printed wiring board, such as a polyimide film with an adhesive, a photosensitive resist, and a liquid resist, can be used.
The thickness of the insulating layer 13 is desirably about 5 μm to 50 μm, more preferably about 10 μm to 25 μm. This is because if the thickness is less than 5 μm, the insulation is insufficient, and if it exceeds 50 μm, the flexibility of the flexible printed wiring board 10 is impaired.
Further, the length D in the longitudinal direction of the opening 13a shown in FIG. 2 is preferably about 3 mm to 500 mm, more preferably about 20 mm to 50 mm, and the length E in the short direction is about 1 mm to 20 mm, more preferably. It is desirable to be about 3 mm to 5 mm.

Further, in the present embodiment, as shown in FIG. 2, the stress concentration portion M is provided in the non-connection region N adjacent to the connection region S1 in the flexible printed wiring board 10 having the above-described configuration. More specifically, by providing a cut formed by cutting the side surface A of the flexible printed wiring board 10 in the non-connection region N adjacent to the connection region S1, the stress concentration portion M (the cut portion K) having the stress concentration point M1 is provided. ) Is provided. Further, the cutting direction of the cut portion K is a direction intersecting with the wiring circuit 12a (more specifically, the wiring circuit 12a arranged in the connection region S1).
Here, the “non-connection region N” means a region that is not connected to the flexible printed wiring board 20 via the anisotropic conductive adhesive 30 in the flexible printed wiring board 10.
In addition, the “stress concentration part M” means that when a stress such as a bending stress is applied to the flexible printed wiring board 10, the stress can be applied more concentratedly than the other parts of the flexible printed wiring board 10. It means the part.
Further, as shown in FIG. 2, the cut portion K is formed by cutting the side surface A of the flexible printed wiring board 10 to the inner side of the outermost wiring circuit 12a among the wiring circuits 12a arranged in parallel in the connection region S1. In addition, the flexible printed wiring board 10 is provided at opposing positions on the side surface A on both sides.
The cut portion K can be formed by punching the flexible printed wiring board 10 using a mold, for example.
2 is about 1 mm to 10 mm, and more preferably about 3 mm to 5 mm. This is because if the thickness is less than 1 mm, the insulation is not sufficient, and if it exceeds 10 mm, the effect of dispersing stress is not sufficient.

The flexible printed wiring board 20 is electrically and mechanically connected to the flexible printed wiring board 10 via an anisotropic conductive adhesive 30 to form a flexible printed wiring board constituting the printed wiring board connection structure 1. It is.
In the present embodiment, the flexible printed wiring board 20 is provided with a point that no cut portion is provided and a wiring circuit 22a is linearly arranged as shown in FIGS. Except for the flexible printed wiring board 10 having the same configuration and the same size as those already described, the same member and the same function as the flexible printed wiring board 10 have the same last digit number and alphabet. The same thing is attached | subjected and the following detailed description shall be abbreviate | omitted.

The anisotropic conductive adhesive 30 electrically and mechanically connects the flexible printed wiring board 10 and the flexible printed wiring board 20.
More specifically, a conductive component is contained in a binder (binder), and has conductivity in the vertical direction (thickness direction) by heating and pressurization during thermal bonding, and in the horizontal direction ( It has an insulating property in the (surface direction) and further has an adhesive property for bonding members together.
The binder may be any one as long as it is normally used as a binder for forming the anisotropic conductive adhesive 30, such as a thermoplastic resin or a thermosetting resin.
The conductive component may be any material as long as it is normally used as a conductive component for forming the anisotropic conductive adhesive 30 such as nickel.
Further, the size of the anisotropic conductive adhesive 30 before being applied with heat and pressure is such that the length G in the longitudinal direction (lateral direction) is arranged in the connection region S1, as shown by a one-dot chain line in FIG. The length between the wiring circuits 12a at both ends provided is slightly longer, and the length H in the short direction (longitudinal direction) is slightly shorter than the length J of the wiring circuit 12a constituting the connection region S1. It is desirable that the size of the region surrounded by the substantially quadrangle be covered.
In this embodiment, a film-like anisotropic conductive adhesive is used as the anisotropic conductive adhesive 30.
Of course, the present invention is not limited to such a configuration, and a paste-like anisotropic conductive adhesive may be used as the anisotropic conductive adhesive 30.

The flexible printed wiring board 10 and the printed wiring board connection structure 1 according to the embodiment of the present invention having such a configuration have the following effects.
The connection region S1 of the flexible printed wiring board 10 and the connection region S2 of the flexible printed wiring board 20 are electrically and mechanically connected via the anisotropic conductive adhesive 30 (printed wiring board connection structure 1 In a direction intersecting the wiring circuits 12a and 22a with respect to the flexible printed wiring board 10 and / or the flexible printed wiring board 20 (more specifically, wiring arranged in the connection regions S1 and S2). When a stress such as a bending stress is applied in a direction intersecting the circuits 12a and 22a), the stress is concentrated on the stress concentration portion M (stress concentration point M1) more than other portions of the flexible printed wiring board 10. Can be loaded. Therefore, the stress originally applied to the other parts excluding the stress concentration part M can be effectively distributed to the stress concentration part M.
Therefore, in particular, the stress applied to the connection regions S1 and S2 can be effectively distributed to the cut portions K that are the stress concentration portions M, and the wiring circuit 12a and / or the wiring circuit 22a and the anisotropic conductive adhesive 30 can be dispersed. It is possible to effectively prevent peeling in an invisible state.
Further, in the flexible printed wiring boards 10 and 20 constituting the printed wiring board connection structure 1, the direction intersecting the wiring circuits 12 a and 22 a (more specifically, the wiring circuits 12 a and 22 a arranged in the connection areas S 1 and S 2). When a stress of a certain level or more is applied in the direction intersecting with the flexible printed wiring board 10, the flexible printed wiring board 10 can be broken starting from the cut portion K (stress concentration point M1). Therefore, peeling in an invisible state that occurs between the wiring circuit 12a and / or the wiring circuit 22a and the anisotropic conductive adhesive 30 can be made visible (visualized).
Therefore, it is possible to effectively prevent the connection structure of the electrically defective printed wiring board from being shipped as a product.
Therefore, when the printed wiring board connection structure 1 is formed, the flexible printed wiring board 10 capable of realizing efficient quality control can be obtained. Further, it is possible to provide a printed wiring board connection structure 1 capable of realizing quality control efficiency.
Here, “when stress of a certain level or more is applied” means that stress that causes peeling in an invisible state between the wiring circuit 12 a and / or the wiring circuit 22 a and the anisotropic conductive adhesive 30 is applied. Means that This stress can be defined by peel strength (90 degree peel strength).
In addition, here, “break” means that the printed wiring board connection structure 1 (flexible printed wiring board 10) is separated from the stress concentration portion M as shown in FIG. It is a concept that includes both the case where the board connection structure 1 (flexible printed wiring board 10) is not separated from the stress concentration portion M as a starting point, and only a part is torn.

That is, the printed wiring board connection structure 1 includes an anisotropic conductive adhesive 30 between the connection area S1 of the flexible printed wiring board 10 and the connection area S2 of the flexible printed wiring board 20, as shown in FIG. It is formed by applying heat and pressure in the state of interposing.
Therefore, as shown in a simplified manner in FIG. 3A, the anisotropic conductive adhesive 30 to which heat and pressure are applied gradually spreads in four directions from the size indicated by the broken line to the direction indicated by the white arrow (melted). Finally, the printed wiring board connection structure 1 is formed in a size indicated by a one-dot chain line.
3B, in a state in which the printed wiring board connection structure 1 is formed, the anisotropic conductive adhesive 30 is applied to the base material layer 11 of the flexible printed wiring board 10 and the flexible printed circuit board. The substrate layer 21 of the wiring board 20 is mechanically connected, and the wiring circuit 12a of the flexible printed wiring board 10 and the wiring circuit 22a of the flexible printed wiring board 20 are electrically and mechanically connected.
In such a printed wiring board connection structure 1, when considering the mechanical connection strength in the connection region S constituted by the connection region S 1 and the connection region S 2, first, as shown in FIG. Adhesion between the material layer 11 and the anisotropic conductive adhesive 30 is resin-resin adhesion. On the other hand, the adhesion between the wiring circuit 12a and the anisotropic conductive adhesive 30 is an adhesion between the resin and the conductive metal.
Therefore, the connection strength between the wiring circuit 12 a and the anisotropic conductive adhesive 30 is weaker than the connection strength between the base material layer 11 and the anisotropic conductive adhesive 30. Although not shown, the same applies to the flexible printed wiring board 20.
Further, as shown in FIG. 3A, the bonding length between the wiring circuit 12a and the anisotropic conductive adhesive 30 is the wiring circuit 12a in a direction crossing the wiring circuit 12a, for example, in a direction orthogonal to the wiring circuit 12a. It becomes the adhesion length of width B. On the other hand, in a direction not intersecting with the wiring circuit 12a (laying direction of the wiring circuit 12a), an adhesive length of a length L that is substantially the same as the length of the wiring circuit 12a constituting the connection region S1 shown in FIG. Become.
Therefore, the connection strength between the wiring circuit 12a and the anisotropic conductive adhesive 30 is weaker than the connection strength in the direction not intersecting with the wiring circuit 12a. Although not shown, the same applies to the flexible printed wiring board 20.

As described above, in the printed wiring board connection structure 1, when considering the mechanical connection strength (adhesion strength) in the connection region S, the wiring between the wiring circuits 12 a and 22 a and the anisotropic conductive adhesive 30 and the wiring The connection strength in the direction intersecting the circuits 12a and 22a is the weakest connection strength (the connection strength at which peeling is most likely to occur).
Therefore, in the printed wiring board connection structure 1, the flexible printed wiring board 10 and / or the flexible printed wiring board 20 are arranged in the direction intersecting the wiring circuits 12 a and 22 a (more specifically, in the connection areas S 1 and S 2. When stress such as bending stress is applied in the direction intersecting the wiring circuits 12a and 22a), peeling in the invisible state between the wiring circuit 12a and / or the wiring circuit 22a and the anisotropic conductive adhesive 30 is the most. However, the occurrence of peeling in such an invisible state can be effectively prevented by using the configuration of the embodiment of the present invention.
That is, by providing the notch portion K as the stress concentration portion M, the flexible printed wiring board 10 and / or the flexible printed wiring board 20 is crossed with the wiring circuits 12a and 22a (more specifically, the connection regions S1 and S2). When a stress such as a bending stress is applied to the wiring circuits 12a and 22a arranged in the wiring area 12a, the stress applied to the connection regions S1 and S2 is effectively applied to the stress concentration point M1 provided in the cut portion K. Can be distributed and concentrated. Therefore, it is possible to effectively prevent peeling in the invisible state between the wiring circuit 12a and / or the wiring circuit 22a and the anisotropic conductive adhesive 30.
Further, a direction intersecting the flexible printed wiring board 10 and / or the flexible printed wiring board 20 with the wiring circuits 12a and 22a (more specifically, a direction intersecting with the wiring circuits 12a and 22a arranged in the connection regions S1 and S2). 4), when a stress such as a bending stress of a certain level or more is applied, the printed wiring board connection structure 1 (printed wiring) starts from the notch K (stress concentration point M1) as shown in FIG. 4B. The board 10) can be broken, and the invisible peeling that occurs between the wiring circuit 12a and / or the wiring circuit 22a and the anisotropic conductive adhesive 30 can be made visible (visualization).

Further, among the wiring circuits 12a arranged in parallel in the connection region S1, the side surface A of the flexible printed wiring board 10 is cut into the inner side of the outermost wiring circuit 12a to form the cut portion K, whereby the printed wiring In the state in which the board connection structure 1 is formed, the flexible printed wiring board 10 and / or the flexible printed wiring board 20 intersects the wiring circuits 12a and 22a (more specifically, the connection regions S1 and S2). When a stress such as a bending stress is applied to the wiring circuits 12a and 22a that constitute the wire), the stress applied to the connection regions S1 and S2 is further distributed to the cut portion K (stress concentration point M1). be able to.
More specifically, the flexible printed wiring board 10 and / or the flexible printed wiring board 20 are crossed with the wiring circuits 12a and 22a (more specifically, the wiring circuits 12a and 12a disposed in the connection regions S1 and S2). When a stress such as a bending stress is applied in the direction intersecting 22a), a stress larger than that of the other wiring circuits 12a and 22a is applied by being disposed on the side surface side of the flexible printed wiring boards 10 and 20. It is possible to more effectively prevent peeling in an invisible state between the outermost wiring circuit 12a and / or the outermost wiring circuit 22a and the anisotropic conductive adhesive 30.
Further, in the flexible printed wiring boards 10 and 20 constituting the printed wiring board connection structure 1, the direction intersecting the wiring circuits 12 a and 22 a (more specifically, the wiring circuits 12 a and 22 a arranged in the connection areas S 1 and S 2). When a stress of a certain level or more is applied in the direction intersecting with the flexible printed wiring board 10, the flexible printed wiring board 10 can be more easily broken starting from the cut portion K (stress concentration point M1). Therefore, peeling in an invisible state that occurs between the wiring circuit 12a and / or the wiring circuit 22a and the anisotropic conductive adhesive 30 can be more easily revealed (visualized).
Further, by providing the notch K which is the stress concentration part M at the opposing position on the side surface A on both sides of the flexible printed wiring board 10, the flexible printed wiring in a state where the printed wiring board connection structure 1 is formed. In a direction crossing the wiring circuits 12a and 22a with respect to the board 10 and / or the flexible printed wiring board 20 (more specifically, a direction crossing the wiring circuits 12a and 22a arranged in the connection regions S1 and S2). When stress such as bending stress is applied, the stress applied to the connection regions S1 and S2 of the flexible printed wiring boards 10 and 20 can be more efficiently distributed to the cut portion K (stress concentration point M1). . Therefore, it is possible to more effectively prevent peeling in the invisible state between the wiring circuit 12a and / or the wiring circuit 22a and the anisotropic conductive adhesive 30.
Further, in the flexible printed wiring boards 10 and 20 constituting the printed wiring board connection structure 1, the direction intersecting the wiring circuits 12 a and 22 a (more specifically, the wiring circuits 12 a and 22 a arranged in the connection areas S 1 and S 2). When a stress of a certain level or more is applied in the direction intersecting with the flexible printed wiring board 10, the flexible printed wiring board 10 can be more easily broken starting from the cut portion K (stress concentration point M1). Therefore, peeling in an invisible state that occurs between the wiring circuit 12a and / or the wiring circuit 22a and the anisotropic conductive adhesive 30 can be more easily manifested.

In addition, the notch K which is the stress concentration portion M is formed in the non-connection region N adjacent to the connection region S1, more specifically, in the non-connection region N having a length of about 3 mm to 5 mm from the connection region S1. Thus, in the state in which the printed wiring board connection structure 1 is formed, the flexible printed wiring board 10 and / or the flexible printed wiring board 20 intersects the wiring circuits 12a and 22a (more specifically, When stress such as bending stress is applied to the wiring regions 12a and 22a arranged in the connection regions S1 and S2), the stress applied to the connection region S is cut into the cut portion K (stress concentration point M1). Can be dispersed more efficiently. Therefore, it is possible to more efficiently prevent peeling in the invisible state between the wiring circuit 12a and / or the wiring circuit 22a and the anisotropic conductive adhesive 30.
Further, in the flexible printed wiring boards 10 and 20 constituting the printed wiring board connection structure 1, the direction intersecting the wiring circuits 12 a and 22 a (more specifically, the wiring circuits 12 a and 22 a arranged in the connection areas S 1 and S 2). When a stress of a certain level or more is applied in the direction that intersects with the flexible printed wiring board 10, the flexible printed wiring board 10 can be more efficiently broken starting from the notch K (stress concentration point M1). Therefore, peeling in the invisible state that occurs between the wiring circuit 12a and / or the wiring circuit 22a and the anisotropic conductive adhesive 30 can be more effectively manifested.
In addition, a configuration in which a plurality of wiring circuits 12a arranged in parallel in the non-connection region N are arranged narrower to the inside than the stress concentration portion M at the position of the stress concentration portion M, more specifically, the flexible printed wiring board 10 At the position of the stress concentration portion M (cut portion K) formed by cutting the side surfaces A on both sides of the wiring circuit 12a, the wiring circuit 12a extended from the connection region S1 is removed from the stress concentration portion except for the wiring circuit 12a disposed in the center. As shown in FIG. 2, a connection region is formed by bending so as to conform to the shape of the cut forming M and arranging the wiring circuit 12 a to converge at the center of the flexible printed wiring board 10. The length D in the longitudinal direction of the opening 13a forming S1 can be made longer than the length between the pair of stress concentration points M1. Therefore, even if it is the structure which provides the cut | notch part K, in connection area | region S1, a space can be effectively provided between the adjacent wiring circuits 12a. Therefore, as described above, it is possible to effectively secure a bonding area between the base material layer 11 and the anisotropic conductive adhesive 30 which is a resin-resin bonding, and a connection with a good mechanical connection strength. Region S1 can be formed. Moreover, the space for forming the cut | notch part K in the side surface A of the both sides of the flexible printed wiring board 10 can be ensured efficiently.
Further, by using the anisotropic conductive adhesive 30 as the conductive adhesive, good conductivity can be realized in the vertical direction (thickness direction) and good insulation in the horizontal direction (plane direction). The printed wiring board connection structure 1 can maintain the performance.

On the other hand, as shown in FIG. 8, the conventional printed wiring board connection structure 2 connects the substantially rectangular flexible printed wiring board 3 and the substantially rectangular flexible printed wiring board 4 with a conductive adhesive (not shown). In general, it has a configuration in which it is electrically and mechanically connected.
Therefore, in such a configuration, the flexible printed wiring board 3 and / or the flexible printed wiring board 4 crosses the wiring circuits 3a and 4a (more specifically, the wiring circuits 3a and 4a arranged in the connection region). When a stress such as a bending stress of a certain level or more is applied in the direction intersecting with the wiring circuit 3a and / or the wiring circuit 4a and the conductive adhesive, there is a problem that peeling in an invisible state is likely to occur. It was.
Further, when such invisible peeling occurs, there is a problem that a product having an electrical defect is actually shipped although there is no defect as a product in appearance.

Therefore, by using the configuration of the flexible printed wiring board 10 according to the embodiment of the present invention, when the printed wiring board connection structure 1 is formed, between the wiring circuits 12 a and 22 a and the anisotropic conductive adhesive 30. It can be set as the flexible printed wiring board 10 which can prevent effectively that peeling in an invisible state arises. Moreover, it can be set as the flexible printed wiring board 10 which can reveal (visualize) peeling in the invisible state which arises between the wiring circuits 12a and 22a and the anisotropic conductive adhesive 30. FIG.
In addition, with the configuration of the printed wiring board connection structure 1 according to the embodiment of the present invention, it is effective that peeling in an invisible state occurs between the wiring circuits 12a and 22a and the anisotropic conductive adhesive 30. Can be prevented.
Further, the invisible peeling between the wiring circuits 12a and 22a and the anisotropic conductive adhesive 30 can be made visible (visualized). Therefore, it is possible to provide a printed wiring board connection structure 1 that can effectively prevent the electrically defective printed wiring board connection structure from being shipped as a product.
Therefore, it is possible to provide a printed wiring board connection structure capable of realizing efficient quality control.

Next, with reference to FIGS. 5-7, the modification of the stress concentration part of the flexible printed wiring board which concerns on embodiment of this invention is demonstrated.
In this modification, the configuration (shape, etc.) of the stress concentration portion M and the configuration (arrangement direction) of the wiring circuit 12a are changed with respect to the flexible printed wiring board 10 according to the embodiment of the present invention described above. It is. Other configurations are the same as those of the flexible printed wiring board 10 according to the embodiment of the present invention described above.
Therefore, the same members and the same functions as those of the flexible printed wiring board 10 are denoted by the same numbers and the same alphabets, and the detailed description below is omitted.

With reference to FIGS. 5 and 6, in this modification, the side surface A of the flexible printed wiring board 10 is bulged in a non-connecting area N adjacent to the connecting area S <b> 1 of the flexible printed wiring board 10. The stress concentration part M is provided by forming the convex part T.
The bulging direction of the convex portion T is a direction intersecting with the wiring circuit 12a (more specifically, the wiring circuit 12a arranged in the connection region S1).
Furthermore, the convex part T is provided in the position which opposes in the side surface A of the both sides of the flexible printed wiring board 10. FIG.
Further, in the present modification, as shown in FIG. 6, a plurality of wiring circuits 12a extending from the connection region S1 are arranged in parallel without being bent.
The vertical length P of the convex portion T shown in FIG. 6 is preferably 1 mm or more, more preferably 3 mm or more. This is because if the thickness is less than 1 mm, the stress cannot be effectively distributed to the stress concentration portion M.
Further, it is desirable that the lateral length Q of the convex portion T shown in FIG. 6 is 1 mm or more, more preferably 3 mm or more. This is because if the thickness is less than 1 mm, the stress cannot be effectively distributed to the stress concentration portion M.
The convex portion T can be formed by punching the flexible printed wiring board 10 using a mold, for example.

By providing the stress concentration portion M having such a configuration, the flexible printed wiring board 10 and / or the flexible printed wiring board 20 is crossed in a direction intersecting the wiring circuits 12a and 22a (not shown) (more specifically, connection). When stress such as bending stress is applied to the areas S1 and S2 (in the direction intersecting the wiring circuits 12a and 22a) (not shown), particularly stress applied to the connection areas S1 and S2 is applied to the stress concentration portion. It is possible to effectively disperse and concentrate to the stress concentration point M1 provided for the convex portion T which is M.
Therefore, it is possible to effectively prevent peeling in the invisible state between the wiring circuit 12a and / or the wiring circuit 22a (not shown) and the anisotropic conductive adhesive 30.
Further, wirings arranged on the flexible printed wiring board 10 and / or the flexible printed wiring board 20 in a direction intersecting the wiring circuits 12a and 22a (not shown) (more specifically, connection regions S1 and S2 (not shown)). When a stress such as a bending stress of a certain level or more is applied in the direction intersecting the circuits 12a and 22a), as shown in FIG. 7B, the printed wiring starts from the convex portion T (stress concentration point M1). The board connection structure 1 (printed wiring board 10) can be broken, and the invisible peeling between the wiring circuit 12a and / or the wiring circuit 22a and the anisotropic conductive adhesive 30 becomes obvious (visualization). ).
7B shows a state in which the flexible printed wiring board 10 is broken starting from the stress concentration point M1 on the lower side (the side far from the connection region S1) among the four stress concentration points M1 shown in FIG. Shall be shown.
Further, by forming the stress concentration portion M as the convex portion T, the stress concentration point M1 can be effectively increased. Therefore, the wiring arranged on the flexible printed wiring board 10 and / or the flexible printed wiring board 20 in the direction intersecting the wiring circuits 12a and 22a (not shown) (more specifically, the connection areas S1 and S2 (not shown)). When a stress such as a bending stress is applied in a direction intersecting the circuits 12a and 22a), particularly the stress applied to the connection regions S1 and S2 is more effectively applied to the stress concentration point M1 provided in the stress concentration portion M. Can be dispersed.

In the embodiment of the present invention, the configuration of the flexible printed wiring boards 10 and 20 is a so-called single-sided flexible printed wiring board. However, the configuration is not necessarily limited to such a configuration and is not necessarily limited to both sides of the base material layer. It is good also as a structure set as what is called a double-sided flexible printed wiring board provided with a conductive layer. By adopting such a configuration, it is possible to obtain a printed wiring board connection structure 1 capable of achieving higher density wiring.
Further, the printed wiring board connected to the flexible printed wiring board 10 having the stress concentration portion M via the conductive adhesive is not necessarily limited to the flexible printed wiring board, but other printed wiring such as a rigid flexible printed wiring board. It is good also as a structure using a board.
Further, the configuration of the stress concentration portion M is not limited to the configuration (shape, size, etc.) of the present embodiment and this modification, and in the printed wiring board connection structure 1, the wiring circuit 12 a that forms the connection regions S 1 and S 2. When the stress is applied in the direction intersecting with 22a, any configuration (shape, size, etc.) can be applied so that the stress can be applied more intensively than other portions of the flexible printed wiring board 10. It is good also as a structure.
For example, in this embodiment, among the wiring circuits 12a arranged in parallel in the connection region S1, the side surface A of the flexible printed wiring board 10 is cut to the inner side of the outermost wiring circuit 12a, so that the stress concentration portion M is cut. Although the configuration in which the portion K is provided, the configuration (shape, size, etc.) of the cut portion K is not necessarily limited to such a configuration, and can be changed as appropriate. However, when the stress concentration portion M is provided as the cut portion K, the side surface A is provided to at least the outermost wiring circuit 12a of the plurality of wiring circuits 12a (more specifically, the wiring circuits 12a arranged in parallel in the connection region S1). It is desirable that the cut portion K be provided by cutting.
In the present embodiment, the stress concentration portions M are provided at the opposing positions on the side surfaces A on both sides of the flexible printed wiring board 10. However, the present invention is not limited to such a configuration. It is good also as a structure which provides the stress concentration part M in the different position in the side surface A of both sides, and it is good also as a structure which provides the stress concentration part M only in the one side A of the flexible printed wiring board 10. FIG.
In the present embodiment, the stress concentration portion M is provided only on the flexible printed wiring board 10. However, the configuration is not necessarily limited to such a configuration, and the stress concentration portion M is provided only on the flexible printed wiring board 20. Alternatively, the stress concentration portion M may be provided on both the flexible printed wiring boards 10 and 20. Further, the number of stress concentration portions M is not limited to that of the present embodiment, and can be changed as appropriate.
In this embodiment, the anisotropic conductive adhesive is used as the conductive adhesive. However, the configuration is not necessarily limited to such a configuration, and another conductive adhesive may be used. However, it is desirable to use an anisotropic conductive adhesive.
Further, the number of wiring circuits 12a and 22a is not limited to that of the present embodiment, and can be changed as appropriate.

  According to the present invention, in the flexible printed wiring board forming the connection structure of the printed wiring board, it is possible to visually reveal (visualize) peeling in an invisible state that occurs between the wiring circuit and the conductive adhesive. Therefore, industrial applicability in the field of flexible printed wiring boards that form a printed wiring board connection structure is high.

DESCRIPTION OF SYMBOLS 1 Connection structure of printed wiring board 2 Connection structure of printed wiring board 3 Flexible printed wiring board 3a Wiring circuit 4 Flexible printed wiring board 4a Wiring circuit 10 Flexible printed wiring board 11 Base material layer 12 Conductive layer 12a Wiring circuit 13 Insulating layer 13a Opening Part 20 Flexible printed wiring board 21 Base layer 22 Conductive layer 22a Wiring circuit 23 Insulating layer 23a Opening 30 Anisotropic conductive adhesive A Side B Width C Length D Length E Length F Length G Length H Length Length J Length K Cut portion L Length M Stress concentration portion M1 Stress concentration point N Non-connection region P Length Q Length S Connection region S1 Connection region S2 Connection region T Convex

Claims (7)

  A flexible printed wiring board that includes a plurality of wiring circuits, includes a connection region that exposes the wiring circuit, and is connected to a connection region of another printed wiring board via a conductive adhesive. A flexible printed wiring board, wherein a stress concentration portion is provided in a non-connection region adjacent to the connection region.   2. The flexible according to claim 1, wherein the stress concentration portion is a cut formed by cutting at least one side surface of the flexible printed wiring board, and the cutting direction is a direction intersecting the wiring circuit. Printed wiring board.   The flexible printed wiring board according to claim 2, wherein the cut is formed by cutting from the side surface to at least an outermost wiring circuit of the plurality of wiring circuits.   The stress concentration portion is formed by projecting at least one side surface of the flexible printed wiring board in a convex shape, and the bulging direction is a direction intersecting with a wiring circuit constituting the connection region. The flexible printed wiring board according to claim 1.   The flexible printed wiring board according to any one of claims 1 to 4, wherein the stress concentration portion is provided at opposing positions on both side surfaces of the flexible printed wiring board.   The connection structure of the printed wiring board in which the connection area | region of the flexible printed wiring board of any one of Claims 1-5 and the connection area | region of another printed wiring board are connected through a conductive adhesive.   The printed wiring board connection structure according to claim 6, wherein the conductive adhesive is an anisotropic conductive adhesive.

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