JP2007157907A - Flexible printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible printed wiring board which allows a connection electrode to be surely connected electrically to an external electrode of an electronic component, using an anisotropic conductive adhesive, through an additional simple process, even if the connection electrode is covered with a cover lay. <P>SOLUTION: The connection electrode (2) is formed of a bump electrode made by forming metal plating layers (6, 7) on a conductive line, and the surface of the bump electrode is projected to be at least closer to an external electrode (51) than to the vicinity of the surface of the cover lay (5) is. The external electrode (51) is pressurized between the external electrode (51) and the bump electrode and is surely connected electrically to the bump electrode via the anisotropic conductive adhesive (10). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flexible printed wiring board that draws external electrodes exposed around an electronic component to the outside, and more particularly to a flexible printed wiring board that is electrically connected to external electrodes of an electronic component using an anisotropic conductive adhesive.

  In recent years, with the miniaturization of electronic components, external electrodes for connecting to external circuits have also become finer and narrower in pitch, and high-resolution connections are required for the connection, and lead is also used from the viewpoint of protecting the natural environment. A connection in place of solder is required, and a connection method using an anisotropic conductive adhesive such as an anisotropic conductive film (ACF) or an anisotropic conductive adhesive paste (ACP) has attracted attention.

  In this connection method, the external electrode exposed around the electronic component and the counterpart connected electrode are opposed to each other, and an anisotropic conductive adhesive is interposed therebetween, and the connecting electrode and the connected electrode are heated and pressurized. In the pressurization direction, the electrodes are electrically connected via the conductive particles contained in the anisotropic conductive adhesive, and in the arrangement direction of the connection electrodes or connected electrodes orthogonal to the pressurization direction, between adjacent electrodes Thus, the outer diameter of the conductive particles is smaller than the insulation interval, and insulation is maintained even between the electrodes having a narrow pitch.

  On the other hand, the connection using anisotropic conductive adhesive lacks the heat resistance of reflow. Conventionally, the electronic parts connected using anisotropic conductive adhesive are surface-mounted on a printed wiring board through a reflow furnace. In addition to the electronic components, the printed circuit board was connected to the printed wiring board via a flexible printed wiring board (see Patent Document 1).

Japanese Patent Laying-Open No. 2005-252134 (page 7, lines 30 to 48, FIGS. 4 and 5)

  FIG. 7 is a cross-sectional view showing a state in which the flexible printed circuit board and the electronic component are connected. External electrodes 102 and 103 exposed on the upper surface and the lower surface of the electronic component 101 are connected to the conductive lines 105 of the flexible printed circuit board 104, respectively. Connect and pull out.

  The external electrodes 102 and 103 are connected to the internal circuit of the electronic component 101, are arranged along one side of the upper surface and the lower surface of the electronic component 101, and are formed of bump electrodes that slightly protrude from the surrounding surface. Among these, the external electrode 103 exposed on the lower surface is connected to the lead pattern 107a printed on the transparent substrate 107 by using an anisotropic conductive adhesive, and is connected along the end of the transparent substrate 107. Part 108 is drawn out.

  As shown in FIG. 8, the flexible printed wiring board 104 is provided with a plurality of conductive lines 105 corresponding to the number of external electrodes 102 and 103 along the longitudinal direction of the strip-shaped insulating film base 106. A connection electrode portion 105A is formed at the end. The connection electrode portion 105 </ b> A is formed at a portion facing the exposed position of the external electrode 102 and the connection terminal portion 108 to be connected.

  Each connection electrode portion 105A of the flexible printed wiring board 104 is opposed to the external electrode 102 and the connection terminal portion 108, and an anisotropic conductive adhesive 109 is interposed therebetween to heat and pressurize the two. As a result, the binder contained in the anisotropic conductive adhesive 109 is cured, the flexible printed wiring board 104 is fixed to the electronic component 101 and the transparent substrate 107, and the external electrodes 102 and 103 of the electronic component 101 are connected to the corresponding flexible print. Electrical connection is made to the conductive wire 105 of the wiring board 104.

  The other side of the flexible printed wiring board 104 is connected to a printed wiring board on which another electronic component is mounted by a flexible printed wiring board connector 110, whereby the electronic component 101 can be connected to an external circuit.

  In the above-described flexible printed wiring board 104, a plurality of conductive lines 105 wired on the insulating film base 106 are exposed. However, the conventional flexible printed wiring board prevents the conductive lines 105 from being oxidized and is conductive. The connection electrode portion 105A at the end portion is left and the surface thereof is covered with an insulating cover lay so as not to cause a short circuit between the adjacent conductive wires 105 when touched by a foreign object.

  When the connection electrode portion 105A of the flexible printed circuit board 104 is surrounded by a coverlay, a gap is formed between the opposing external electrodes, and even if an anisotropic conductive adhesive is interposed between them and the two are pressurized, they are in contact with each other. There was a risk that electrical connection could not be made. Therefore, the external electrodes 102 and 103 of the electronic component 101 and the connection terminal portion 108 of the transparent substrate 107 are arranged along the respective end portions, and the connection electrode portion 105A is formed at the end portion of the conductive wire 105. The connection is not surrounded by the coverlay.

  However, as shown in FIG. 5, when a single flexible printed wiring board is connected to the electronic component 50 in which the plurality of external electrodes 51 are dispersedly exposed on the bottom surface, it is formed at a corresponding portion of the external electrode 51. Since the conductive wire drawn out from the connected electrode portion may come into contact with the other external electrode 51, the entire surface facing the electronic component 50 other than the connecting electrode portion is covered with an insulating coverlay, thereby connecting The periphery of the electrode part is surrounded by a coverlay.

  Here, the surface of the connection electrode portion is provided with a gold-plated surface plating layer with nickel as a base plating in order to obtain good electrical connection characteristics on the conductive wire. The thickness of the external electrode 51 exposed on the bottom surface of 50 is about 6 to 10 μm, whereas the thickness of the cover lay is usually 20 to 30 μm at the minimum, so that it is interposed between the external electrode 51 and the connection electrode portion. The anisotropic conductive adhesive is not sufficiently pressurized and cannot be electrically connected.

  As a flexible printed wiring board 60 that solves this problem, as shown in FIG. 6, a bump electrode obtained by printing a silver paste 63 thicker than the thickness of the coverlay 62 on the surface plating layer 61 is used as a connection electrode portion 64. However, since the bump electrode is formed by the silver paste 63, the height and shape of the bump electrode are not stabilized due to the state of the silver ink and bleeding at the time of printing. In mass production, there is a problem that connection with the external electrode 51 is not possible under the same conditions.

  Moreover, sufficient hardness cannot be obtained with the silver paste 63, and in the heating and pressurizing step with the anisotropic conductive adhesive interposed, 5 to 6 μm conductive particles contained in the anisotropic conductive adhesive are contained in the silver paste 63. There is a possibility that electrical connection between the silver paste 63 and the external electrode 51 interposing the conductive particles is not possible. This problem is caused by the above-mentioned problem that the height of each connection electrode portion 64 is not stable, and the connection electrode portion 64 that is relatively lower than the other connection electrode portions 64 is likely to cause a connection failure. It was.

  Furthermore, since the silver paste 63 having a thickness exceeding the thickness of the cover lay 62 cannot be printed in a single printing process, a plurality of printing processes are required, resulting in an increase in manufacturing cost.

  The present invention has been made in view of such conventional problems. Even if the connection electrode portion is surrounded by a coverlay, an anisotropic conductive adhesive is used only by adding a simple processing step. An object of the present invention is to provide a flexible printed wiring board that can be reliably electrically connected to an external electrode of an electronic component.

In order to achieve the above object, a flexible printed wiring board according to claim 1 includes a plurality of insulating film bases and a plurality of external electrodes exposed to the periphery of the electronic component, and a plurality of parts formed on the insulating film bases facing each other. A connection electrode portion, a plurality of conductive wires drawn from the connection electrode portions onto the insulating film base (3), and a coverlay that leaves the connection electrode portion and covers the surface of the insulating film base and the conductive wires. A flexible printed wiring board that connects the external electrode and the connecting electrode portion that are arranged opposite to each other using a conductive adhesive,
The connection electrode portion is formed of a bump electrode in which a metal plating layer is provided on a conductive wire, and the surface of the bump electrode protrudes at least from the vicinity of the surface of the coverlay toward the external electrode.

  Since the surface of the bump electrode with the metal plating layer protrudes from the vicinity of the surface of the coverlay to the external electrode side, the anisotropic conductive adhesive is heated and pressurized between the external electrode and the connection electrode part, Make sure electrical connection.

  The flexible printed wiring board according to claim 2 is characterized in that the plurality of connection electrode portions are formed at portions facing the plurality of external electrodes that are dispersedly exposed on the bottom surface of the electronic component.

  Since the connection electrode portions arranged opposite to the external electrodes are also distributed, the periphery is surrounded by a cover lay covering the conductive wires, but the connection electrode portions formed by the bump electrodes are external electrodes from the cover lay. Since it protrudes to the side, it is securely connected to the external electrode.

  The flexible printed wiring board according to claim 3, wherein the bump electrode is formed of a surface plating layer in which gold plating is applied to a nickel base plating, and a thick plating layer provided between the surface plating layer and the conductive wire. The thickness of the plating layer is substantially equal to the thickness of the coverlay.

  A thick plating layer having a bump electrode equal to or greater than the thickness of the cover lay is formed by a continuous plating process before the plating process for performing surface plating.

  The flexible printed wiring board according to claim 4 is characterized in that the thick plating layer is made of the same metal material as the conductive wire.

  A thick plating layer having a bump electrode equal to or larger than the thickness of the cover lay is applied to the surface of the conductive wire of the same metal material.

  According to the first aspect of the present invention, the connection electrode portion can be reliably electrically connected to the connection electrode portion of the electronic component by using the anisotropic conductive adhesive only by adding the processing step for applying the metal plating layer.

  In addition, since the bump electrode is formed of a metal plating layer, it can be formed with high accuracy with little manufacturing error in the shape and thickness of the bump electrode, and the external electrode and the connection electrode portion can be connected in a stable connection state when mass-produced. Can be electrically connected.

  In addition, since the bump electrode made of the metal plating layer faces the external electrode, the hardness of the metal plating layer can be adjusted according to the connection conditions using the anisotropic conductive adhesive, and connection failure does not occur.

  According to the invention of claim 2, even if a plurality of external electrodes are dispersedly exposed on the bottom surface of the electronic component, the anisotropic conductive adhesive can be obtained only by adding a processing step of applying a metal plating layer on the conductive wire. It can be pulled out from one flexible printed wiring board.

  According to the invention of claim 3, the bump electrode can be formed without drastically changing the manufacturing process because the plating process of the thick plating layer is only added before the plating process of surface plating on the conductive wire.

  According to the invention of claim 4, since the thick plating layer is made of the same metal material as the conductive wire, there is no difference in characteristics such as the conductive wire and conductivity, and thick plating can be easily performed.

  A flexible printed circuit board (hereinafter referred to as FPC) 1 according to an embodiment of the present invention will be described below with reference to FIGS. 1 is a longitudinal sectional view of a principal part of the FPC 1, FIG. 2 is a longitudinal sectional view of a principal part showing a state in which the FPC 1 is connected using an anisotropic conductive adhesive 10, and FIG. 3 is a partially omitted plan view of the FPC 1. is there.

  The flexible printed wiring board 1 according to the present embodiment includes a camera module 50 housed in a mobile phone, which is an electronic component shown in FIGS. 4 and 5, and a printed wiring board on which main circuit components of the mobile phone are mounted (not shown). Used to connect to).

  The camera module 50 is a module that incorporates optical circuit components such as a lens for imaging of a mobile phone. In order to connect the internal circuit to an external circuit, a power source, etc., a large number of external electrodes 51 and 52 are exposed to the periphery. ing. The camera module 50 can be connected to a printed wiring board not only by the FPC 1 but also by a module socket (not shown). The external electrode 51 exposed with a rectangular outline on the bottom surface is connected to the connection electrode portion 2 of the FPC 1 on the side surface. The external electrodes 52 exposed from to the periphery of the bottom surface are external electrodes connected to the contacts of the module socket. Accordingly, the external electrodes 51 to be connected to the connection electrode portion 2 of the FPC 1 are insulated from the external electrodes 52 exposed around the bottom surface and are distributed on the bottom surface.

  The FPC 1 includes a strip-shaped insulating film base 3, a plurality of connection electrode portions 2 formed on the surface (surface shown in FIG. 3) side of the insulating film base 3, conductive wires 4 drawn from the connection electrode portions 2, and Except for the connection electrode portion 2, the insulating film base 3 and the coverlay 5 covering the conductive wire 4 are configured.

  The insulating film base 3 is a flexible belt-like sheet formed of a synthetic resin, and has one side in the longitudinal direction of the surface (upper side in FIG. 3) as a connection surface that faces the bottom surface of the camera module 50. As shown in FIG. 3, the plurality of connection electrode portions 2 are formed at portions on the surface of the insulating film base 3 that face each other with respect to the external electrodes 51 that are dispersedly exposed on the bottom surface of the camera module 50. The The surface of the connection electrode portion 2 protrudes from the surface of the cover lay 5, and the formation method will be described later.

  The plurality of conductive wires 4 are copper foils printed and wired on the insulating film base 3, and are drawn out from the formation site of each connection electrode 2 to the other side of the insulating film base 3 along the longitudinal direction of the insulating film base 3. .

  The coverlay 5 is formed by adhering insulating ink or insulating film to the entire surface on the surface (surface shown in FIG. 3) side of the insulating film base 3 excluding the connection electrode portion 2. By attaching the coverlay 5 to the surface of the insulating film base 3 excluding the connection electrode portion 2, the conductive wire 4 is not oxidized, and when the FPC 1 is connected to the bottom surface of the camera module 50, The drawn conductive wire 4 does not make erroneous contact with the other external electrode 51 exposed on the bottom surface of the camera module 50 or the external electrode 52 exposed around the bottom surface. On the other side of the FPC 1, the connecting portion formed at the other end of the conductive wire 4 is exposed from the cover lay 5, contacts a contact of an FPC connector (not shown), and on the other side where the FPC 1 is connected to the camera module 50. Electrical connection is made to the pattern of the printed wiring board via an FPC connector.

  As shown in FIGS. 1 and 2, the connection electrode portion 2 surrounded by the cover lay 5 is formed of a bump electrode including a thick plating layer 6 and a surface plating layer 7 applied to the surface thereof. The thick plating layer 6 is a plating layer thicker than the thickness of the cover lay 5 of 20 to 35 μm so that the surface of the connection electrode portion 2 protrudes from the surface of the cover lay 5 to the opposing external electrode 51 side. Here, copper plating of the same material as that of the conductive wire 4 is formed on the conductive wire 4 exposed at the site where the connection electrode portion 2 is formed. Since thick plating of the same material as that of the underlying conductive wire 4 is performed, the thick plating can be easily performed on the conductive wire 4.

  The surface plating layer 7 on the thick plating layer 6 includes a 0.2 to 0.3 μm gold plating 7b that is thin with respect to the 5 to 6 μm conductive particles 11 contained in the anisotropic conductive adhesive 10, and its underlayer. Is formed by applying a hard nickel base plating 7a. When the anisotropic conductive adhesive 10 is interposed between the connection electrode portion 2 and the external electrode 51 by the surface plating layer 7 and heated and pressurized, the conductive particles 11 contained in the anisotropic conductive adhesive 10 are good. A part of the conductive gold plating 7b is pushed into contact with the conductive gold plating 7b and is in contact with the hard base plating 7a, so that it is sandwiched between the external electrodes 51 and electrically connected with a sufficient contact pressure.

  The thickness of the nickel base plating 7a is preferably about several μm at the maximum, and has a certain hardness when thickened on the insulating film base 3 so as to serve as a plating layer thicker than the thickness of the coverlay 5 described above. As a result, cracks occur and the flexibility of the FPC 1 itself is also impaired. On the other hand, the copper plating constituting the thick plating layer 6 is softer than the nickel base plating 7a, and even if the plating thickness is thicker than the coverlay 5, the flexibility of the FPC 1 is maintained.

  The surface plating layer 7 is usually applied to the surface of the electrode in the electrical connection between the electrodes using the conventional anisotropic conductive adhesive 10, and according to the present embodiment, the plating step Even if only the thick plating step is added before, even the connection electrode portion 2 surrounded by the coverlay 5 can be structured to be electrically connected.

  When the FPC 1 configured in this way is connected to the camera module 50, the anisotropic conductive adhesive 10 is applied to one side surface in the longitudinal direction of the FPC 1 shown in FIG. 3 where the plurality of connection electrode portions 2 are exposed. Adhere. The anisotropic conductive adhesive 10 may be attached to the connection electrode portion 2 with either an anisotropic conductive film (ACF) or an anisotropic conductive adhesive paste (ACP). An anisotropic conductive film (ACF) is a film having a three-layer structure in which a front separator and a rear separator are attached to the front and back of an adhesive layer serving as a binder formed by dispersing a large number of conductive particles 11. Is attached to the surface of the FPC 1 where the connection electrode portion 2 is exposed, and the surface separator is peeled off. In the case of an anisotropic conductive adhesive paste (ACP), the paste-like anisotropic conductive adhesive 10 is directly attached to the surface of the FPC 1 where the connection electrode portion 2 is exposed by printing or the like.

  Subsequently, as shown in FIG. 2, the connection electrode portions 2 of the FPC 1 are opposed to the plurality of external electrodes 51 exposed on the bottom surface of the camera module 50 through the anisotropic conductive adhesive 10, Pressurize while heating between FPC1. The pressurizing time is, for example, 5 seconds at 190 ° C. and 15 seconds at 170 ° C. During the pressurization, the connection electrode portion 2 formed by the bump electrode protrudes from the surrounding cover lay 5, so that the anisotropic conductive adhesive 10 sandwiched between the external electrode 51 and the connection electrode portion 2 is pressurized. .

  The conductive particles 11 contained in the anisotropic conductive adhesive 10 adhering to the connection electrode part 2 by the heating and pressurizing steps are sandwiched between the external electrode 51 and the connection electrode part 2 to make the two conductive. . At the same time, the thermosetting binder is cured by being heated, and the external electrode 51 and the connection electrode portion 2 are physically fixed while maintaining the above-described pressure state.

  On the other hand, between the electrodes adjacent to each other in the arrangement direction of the connection electrode portion 2 or the external electrode 51, there is no conductive particle 11 having an outer shape larger than the insulation interval, so that the insulation between the connection electrode portion and the external electrode 51 in the arrangement direction is Kept.

  According to the above-described embodiment, the bump electrode is formed by applying the surface plating layer 7 on the thick plating layer 6, but if a good electrical connection using the anisotropic conductive adhesive 10 is possible, The surface plating layer 7 does not necessarily need to be applied, and the thick plating layer 6 may be another metal material as long as it is metal plating.

  Further, in the above-described embodiment, the surface of the connection electrode portion 2 is protruded from the surface of the cover lay 5 by the thick plating layer 6, but for example, the opposing external electrode 51 is slightly from the bottom surface of the electronic component 50. The surface of the bump electrode (connection electrode portion 2) is slightly smaller than the surface of the coverlay 5 if the anisotropic conductive adhesive 10 can be sandwiched between the connection electrode portion 2 and the connection electrode portion 2 in a sufficiently pressurized state. The height may be as low as possible.

  The present invention is suitable for a flexible printed wiring board connected to an external electrode exposed around an electronic component using an anisotropic conductive adhesive.

It is a principal part longitudinal cross-sectional view of FPC1 which concerns on one embodiment of this invention. 3 is a longitudinal sectional view of a main part showing a state in which an FPC 1 is connected using an anisotropic conductive adhesive 10. FIG. It is a partial abbreviation top view of FPC1. It is a perspective view of the camera module 50 which connects FPC1. 4 is a bottom view of the camera module 50. FIG. It is a principal part longitudinal cross-sectional view which shows the state which connected the flexible printed wiring board 60 which used the bump electrode which printed the silver paste 63 as the connection electrode part 64 to the electronic component 50 which the external electrode 51 disperses and exposes. It is sectional drawing which shows the state which connects the conventional flexible printed wiring board 104 and the electronic component 101. FIG. 2 is a plan view of a flexible printed wiring board 104 and an electronic component 101. FIG.

Explanation of symbols

1 Flexible Printed Circuit Board (FPC)
2 Connection electrode (bump electrode)
3 Insulating film base 4 Conductive wire 5 Coverlay 6 Metal plating layer (thick plating layer)
7 Surface plating layer 7a Base plating 7b Gold plating 50 Electronic parts (camera module)
51 External electrode

Claims (4)

An insulating film base (3);
A plurality of connection electrode portions (2) formed at portions on the insulating film base (3) respectively facing the plurality of external electrodes (51) exposed around the electronic component (50);
A plurality of conductive wires (4) drawn from each connection electrode portion (2) onto the insulating film base (3);
A coverlay (5) that leaves the connection electrode portion (2) and covers the surfaces of the insulating film base (3) and the conductive wire (4);
With
A flexible printed wiring board that connects the external electrode (51) and the connection electrode portion (2) arranged opposite to each other using an anisotropic conductive adhesive (10),
The connection electrode portion (2) is formed of a bump electrode in which a metal plating layer (6, 7) is applied on the conductive wire (4), and the surface of the bump electrode is external electrode (at least near the surface of the cover lay (5)). 51) A flexible printed wiring board characterized by protruding toward the side. The plurality of connection electrode portions (2) are formed at portions facing the plurality of external electrodes (51) that are dispersedly exposed on the bottom surface of the electronic component (50), respectively. Flexible printed circuit board. The bump electrode includes a surface plating layer (7) obtained by applying gold plating (7b) to a nickel base plating (7a), and a thick plating layer (7) provided between the surface plating layer (7) and the conductive wire (4). The flexible printed wiring board according to claim 1 or 2, wherein the thickness of the thick plating layer (6) is substantially equal to that of the coverlay (5). The flexible printed wiring board according to claim 3, wherein the thick plating layer (6) is made of the same metal material as the conductive wire (4).

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