JP2012209318A - Flexible printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible printed wiring board (FPC) that facilitates connection between conductors 2 of the FPC at an opening part and visual inspection of a connection state thereof.SOLUTION: An FPC 10 has, for example, signal wiring 12 and ground wiring 13 of a wiring pattern formed on one main surface of a base film 11, and also has a coverlay film 15 joined with the base film 11 in one body with an adhesive layer 14 interposed. Then a ground layer 16 is joined to a top surface of the coverlay film 15 with an adhesive 17. The ground layer 16 is formed on the coverlay film 15 while a tongue piece 18 for connection cut and formed in a predetermined place thereof is bent in an opening part 19 and connected to the ground wiring 13. Alternatively, translucent resin 21 is bonded to the tongue piece 18 for connection by, for example, thermocompression bonding etc.

Description

  The present invention relates to a flexible printed wiring board, and more particularly to a flexible printed wiring board that facilitates visual inspection of the connection state between conductor layers.

  BACKGROUND OF THE INVENTION Flexible printed wiring boards (hereinafter also referred to as FPC: Flexible Printed Circuit) are widely used in electronic devices such as portable devices, network devices, servers, and testers. Furthermore, taking advantage of its excellent flexibility, it is also used to connect a movable part such as a thermal print head and a control part. Usually, the basic structure (single-layer structure) of an FPC is a circuit (wiring) pattern of a conductor layer formed on the surface of a resin base film, which is an insulator layer, and an adhesive layer, which is an insulator layer covering the conductor layer And a resin coverlay film. Further, a ground layer is attached on the coverlay film in order to prevent electromagnetic interference between the conductor layers or between the wirings.

  Hereinafter, a conventional FPC in which a ground layer is attached to the single-layer structure will be described with reference to FIGS. Here, FIG. 6 shows the main part of two different examples of FPC, (a) is a plan view of the main part, and (b) and (c) are YY arrow cross sections in (a) of the two examples of FPC. FIG. And FIG. 7 is principal part sectional drawing according to the manufacturing process with which it uses for description of the manufacturing method of the said FPC.

  As shown in FIG. 6, a signal wiring 102 and a ground wiring 103 made of a wiring pattern are formed on the main surface of the base film 101. A coverlay film 105 covers the wiring pattern and is bonded to the base film 101 via an adhesive layer 104 that fills the space between these wiring patterns, for example. A ground layer 106 is attached to the surface of the coverlay film 105. An opening 107 is appropriately formed on the ground wiring 103, and the ground wiring 103 is connected to the ground layer 106 through the opening 107.

  Here, in the example shown in FIG. 6B, the blind plating layer 108 is formed so as to cover the surface of the ground wiring 103 and the surface of the ground layer 106 exposed to the opening 107 by, for example, electrolytic plating. Electrical connection to layer 106 is made. In the example shown in FIG. 6C, the opening 107 is filled with the conductive paste 109, and the ground wiring 103 and the ground layer 106 are electrically connected.

  In the manufacture of the FPC, as shown in FIG. 7A, the signal wiring 102 and the ground wiring 103 having a required wiring pattern are formed on one main surface of the base film 101. Here, the copper foil of the single-sided copper-clad laminate in which the copper foil is stuck to one side of the resin base film 101 is selectively etched to form a wiring pattern. Then, for example, a semi-cured adhesive layer 104 such as a hot melt adhesive is laminated on one side of a resin coverlay film 105 having a ground layer 106 made of, for example, a single-sided copper-clad laminate, and opened at a predetermined position. A portion 107 is formed. The opening 107 is provided in the adhesive layer 14, the coverlay film 105, the ground layer 106, and the like by, for example, punching, drilling, laser processing, or the like. Then, the coverlay film 104 and the base film 101 described above are aligned (FIG. 7A).

  Next, after the base film 101 and the cover lay film 105 are overlaid, the cover lay film 105 is joined and integrated with the base film 101 via the adhesive layer 104 by heating and pressing at a predetermined pressure by hot pressing (FIG. 7). (B)). In this hot press, the adhesive layer 104 is first softened, and a part thereof flows to fill between the wiring patterns of the signal wiring 102 and the ground wiring 103. The opening 107 is arranged at a predetermined position of the ground wiring 103.

  Thereafter, in the example shown in FIG. 6B, the blind plating layer 108 is formed by, for example, electrolytic plating using the ground wiring 103 and the ground layer 106 as a power feeding layer. Alternatively, in the example shown in FIG. 6C, the conductive paste 109 is printed and filled in the opening 107. In this way, the FPC in the prior art is manufactured.

  A method for connecting conductor layers in an FPC by blind plating is described in, for example, Patent Document 1. A method for connecting conductor layers in an FPC with a conductor paste such as solder is described in Patent Document 2, for example.

JP 2010-278067 A JP 2001-085835 A

  By the way, in the step of forming the opening 107 of the flexible printed wiring board, burrs or protrusions may occur on the side wall of the coverlay film 105. In this case, blind plating is hindered by such a side wall, and a problem is likely to occur in the electrical connection between the ground wiring 103 and the ground layer 106. Further, in filling the opening 107 with the conductive paste 109, air gas may remain as bubbles at the bottom of the opening 107. Also in this case, a problem is likely to occur in the electrical connection between the ground wiring 103 and the ground layer 106. Such defects lead to defective products of flexible printed wiring board products.

  Therefore, it is effective in production control to inspect the connection state of the ground wiring 103 and the ground layer 106 and to select and remove the defective connection in advance at the stage of the manufacturing process of the flexible printed wiring board, for example, before the outer shape processing process. become. Inspection / selection in the middle stage of production of a flexible printed wiring board product can appropriately produce a lot out of a flexible printed wiring board having a defect in connection between the ground wiring 103 and the ground layer 106. Then, in the final stage of the manufacture, an electrical inspection check of the ground wiring 103 and the ground layer 106 of the flexible printed wiring board having a defective connection is not necessary.

  However, in the conventional flexible printed wiring board, it is difficult to inspect and select the connection state between the ground wiring 103 and the ground layer 106 during the manufacturing process. For example, when the opening 107 shown in FIG. 6A is visually inspected from above with an optical microscope or the like, the metal-made blind plating layer 108 or the conductive paste 109 has a non-translucent property, and the connection portion This is because the bottom of the opening 107 is not visible. Here, a destructive inspection in which the opening 107 is cut and its cross section is examined is possible, but in this case, only a production lot can be confirmed.

  As described above, in the conventional flexible printed wiring board, the quality control of the connection at the opening 107 of the ground wiring 103 and the ground layer 106 is not easy in the manufacturing process. Here, by improving the reliability of the manufacturing technique, it is possible to reduce the defects of the connection and improve the quality. However, the manufacturing technology becomes expensive. In any case, since the conventional flexible printed wiring board cannot easily perform quality control of the connection in the opening 107 between the two conductor layers seen in the ground wiring 103 and the ground layer 106, for example, its manufacturing cost is low. There was a limit to the reduction.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a flexible printed wiring board that facilitates the connection in the opening between the conductors 2 layers of the flexible printed wiring board and the visual inspection of the connection state. And And the cost reduction of a flexible printed wiring board is made easy.

  In order to achieve the above object, in the flexible printed wiring board according to the present invention, the first conductor layer disposed on one main surface of the first insulator layer, the first conductor layer being covered, In the flexible printed wiring board which has the 2nd insulator layer joined to the 1st insulator layer, and the 2nd conductor layer arranged on the 2nd insulator layer, the 2nd above-mentioned conductor The layer is formed by cutting a connection tongue formed by cutting the second conductor layer into an opening provided in the second insulator layer, and electrically connecting the first conductor layer to the first conductor layer. 2 on the insulator layer.

  According to the configuration of the present invention, the connection at the opening between the conductors 2 of the flexible printed wiring board and the visual inspection of the connection state are facilitated. And cost reduction of a flexible printed wiring board is promoted.

An example of the flexible printed wiring board concerning embodiment of this invention is shown, (a) is a principal part top view, (b) is XX arrow sectional drawing in (a). (A) thru | or (d) are principal part enlarged plan views which show the modification of the flexible printed wiring board concerning embodiment of this invention. (A) thru | or (c) is principal part sectional drawing according to a manufacturing process with which it uses for description of the manufacturing method of a flexible printed wiring board same as the above. (A) And (b) is a principal part top view in one manufacturing process with which it uses for description of a manufacturing method same as the above. (A) thru | or (c) is a partial expanded sectional view of the opening part which shows the modification of the connection between 2 conductor layers in a flexible printed wiring board same as the above. The principal part of the flexible printed wiring board of two different examples in a prior art is shown, (a) is those principal part top views, (b) and (c) are in (a) of the flexible printed wiring board of the two examples. YY arrow sectional drawing. (A) And (b) is principal part sectional drawing according to a manufacturing process with which it uses for description of the manufacturing method of a flexible printed wiring board same as the above.

  A flexible printed wiring board according to an embodiment of the present invention will be described with reference to FIGS. Here, parts that are the same or similar to each other are denoted by common reference numerals, and a duplicate description is partially omitted. However, the drawings are schematic and ratios of dimensions and the like are different from actual ones.

  As shown in FIG. 1, in the FPC 10 of the present embodiment, for example, signal wiring 12 and ground wiring 13 (first conductor layer) of a wiring pattern are formed on one main surface of the base film 11, and the adhesive layer 14 is interposed therebetween. A coverlay film 15 is integrally joined to the base film 11. A ground layer 16 (second conductor layer) is bonded to the surface of the coverlay film 15 with an adhesive 17. The ground layer 16 is formed on the cover lay film 15 by connecting a tongue piece 18 for connection cut into a predetermined portion thereof, bent into an opening 19 and connected to the ground wiring 13.

  In the FPC 10 of the above embodiment, the base film 11 is formed of a thermosetting resin such as a polyimide resin having a film thickness of 5 μm to 30 μm, for example. Similarly, the coverlay film 15 is formed of a thermosetting resin such as a polyimide resin having a film thickness of 3 μm to 25 μm, for example. In addition, thermosetting resin epoxy resin, phenol resin, acrylic resin, polyester resin, and the like are used as the film material. Alternatively, a thermoplastic resin such as a thermoplastic polyimide resin or a polyethylene terephthalate (PET) resin may be used. The first conductor layer or the second conductor layer is formed of a metal foil such as a copper foil having a thickness of 10 μm to 35 μm, for example.

  The adhesive layer 14 is formed of, for example, a thermosetting polyimide resin or epoxy resin having a film thickness of 1 μm to 15 μm, corresponding to the thickness and pattern shape of the signal wiring 12 and the ground wiring 13. In addition, thermosetting resins such as alkyd, urethane, phenol, and melamine can be used. Alternatively, thermoplastic resins such as acrylic, polyamide, polyethylene, polystyrene, polypropylene, polyester, vinyl acetate, and rubber can be used.

  In the flexible printed wiring board 10 shown in FIG. 1, a plurality of strip lines, signal wirings 12 and ground wirings 13 are arranged in a wiring pattern, and two signal wirings 12 can cope with LVDS (Low Voltage Differential Signaling). Shown as a pair of transmission lines. In addition, the first conductor layer or the second conductor layer can take various forms or shapes. For example, the second conductor layer may be an external terminal in addition to the ground layer, or may be a wiring pattern. Depending on the aspect of the conductor layer or the shape associated therewith, various modifications as shown in FIG. 2 occur in the connecting tongue 18 and the opening 19, for example.

  For example, in FIG. 2A, the first connecting tongue piece 18a and the second connecting tongue piece 18b are folded in parallel in the rectangular opening 19 similar to the case of FIG. Connect to conductor layer. In FIG. 2B, the first connecting tongue piece 18a and the second connecting tongue piece 18b face each other in the rectangular opening 19 and are bent and connected to the first conductor layer. In FIG. 2C, the connecting tongue 18 is bent in the direction of the short axis in the elliptical opening 19 and connected to the first conductor layer. In FIG. 2D, the connecting tongue piece 18 is bent in the major axis direction in the elliptical opening 19 and connected to the first conductor layer. In addition, the planar shape of the connecting tongue pieces 18, 18 a, 18 b may be a curved shape other than a rectangle.

  Next, the manufacturing method of FPC10 in this embodiment is demonstrated. As shown in FIG. 3A, for example, in a single-sided copper-clad laminate in which a copper foil is attached to one side of a base film 11 made of a thermosetting resin by heating and pressing, copper on the main surface of the base film 11 is used. The foil is selectively etched into the required wiring pattern. In this way, for example, the signal wiring 12 and the ground wiring 13 are formed on one main surface of the base film 11. Here, the line widths of the signal wiring 12 and the ground wiring 13 are appropriately set, and are, for example, about 20 μm to 100 μm and 400 μm to 1 mm, respectively.

  Then, an adhesive layer 14 made of, for example, a sheet-like hot melt adhesive is attached to one surface of the coverlay film 15, and an opening 19 is formed at a predetermined position by, for example, punching. Here, as for the dimension of the opening part 19, the long side of a rectangle is about 1 mm-2 mm, for example, and the short side is about 0.3 mm-0.5 mm.

  Further, a connecting tongue piece 18 is cut and formed at a predetermined location of a metal foil such as a copper foil that becomes the ground layer 16. The connecting tongue 18 can be formed into various planar shapes by various methods. For example, press processing of copper foil, laser processing, etc. are suitable. Alternatively, when the dimension of the connecting tongue 18 becomes fine, it is preferable to use, for example, a photolithography technique and a selective etching technique of a metal foil that becomes the ground layer 16. In any case, the connecting tongue 18 is formed by cutting a part of the ground layer 16 so that the base portion is integrated with the ground layer 16 and the tongue tip is a free end.

  In the photolithography technique, a photoresist film is formed on a metal foil by applying a known photoresist coating solution such as roll coating or laminating a photosensitive dry film. Then, an etching mask having a notch pattern is formed by exposing the photoresist film and developing the photoresist film. Alternatively, it can be formed by selective film formation by a screen printing method. Then, using this etching mask, the metal foil is selectively wet etched with a chemical solution to cut and form the connecting tongue piece 18.

  In the notch formation of the connecting tongue 18, the slit-shaped defining portion 16a is provided in the ground layer 16 in a required pattern shape except for the tongue piece base as shown in FIG. The slit-shaped defining portion 16a can be formed with high accuracy by using the photolithography technique and the selective etching technique for the ground layer 16 described above. In addition, it can be formed at a low cost by using a cutting process such as a router process including a cutter. Alternatively, as shown in FIG. 4B, a linear defining portion 16b is provided in the ground layer 16 in a required pattern except for the tongue piece base. The linear defining portion 16a can be formed by, for example, laser scribing or pressing.

  Next, the coverlay film 15 and the metal foil are aligned so that the connecting tongue 18 formed on the metal foil to be the ground layer 16 is positioned at an appropriate position of the opening 19. Then, they are overlapped, and the connecting tongue piece 18 is attached to the other surface of the cover lay film 15 in which the opening 19 is formed via a thermosetting resin adhesive 17 such as an epoxy resin. A metal foil formed with is attached. Then, this metal foil is patterned on the ground layer 16. Here, the adhesive 17 has a thickness of about 2 μm.

  Thereafter, the cover lay film 15 having the adhesive layer 14 and the ground layer 16 attached to both surfaces thereof and the above-described base film 11 are aligned (FIG. 3A). Then, the heat-resistant elastic sheet 20 is superposed and arranged together with the base film 11 and the coverlay film 15. Here, the base film 11 is placed on, for example, a flat plate (not shown), and the elastic sheet 20 is laid on the ground layer 16 (FIG. 3B). The elastic sheet 20 is made of, for example, synthetic rubber or natural rubber.

  In the superposed state, the heat-resistant elastic sheet 20 is heated to an appropriate temperature and pressed with a predetermined pressure. For example, it is heated and pressurized at a predetermined pressure by a vacuum roll laminating method. By such pressing of the elastic sheet 20, the connecting tongue 18 is bent into the opening 19 and connected to the ground wiring 13 in the opening 13. Further, the cover lay film 15 is joined and integrated with the base film 11 through the adhesive layer 14 (FIG. 3C). Here, in the heating and pressurization, first, the adhesive layer 14 is softened, and a part thereof flows to fill between the wiring patterns of the signal wiring 12 and the ground wiring 13. When the adhesive layer 14 and the adhesive 17 are made of a thermosetting resin, these are thermoset.

  Thereafter, the elastic sheet 20 is peeled from the ground layer 16 and the base film 11 is removed from a flat plate (not shown). In this way, the FPC 10 having the structure shown in FIG. 1 is manufactured.

  Note that the manufacturing method of the FPC 10 shown in FIG. 3 shows a case where the alignment accuracy between the opening 19 of the connecting tongue 18 and the ground wiring 13 is extremely high. Actually, after the joining and integration, the connecting tongue piece 18 is displaced with respect to the opening 19 or the ground wiring 13 within an allowable range.

  The FPC 10 can be manufactured by various other manufacturing methods. For example, the connecting tongue piece 18 and the opening 19 may be formed in the state where the adhesive layer 14 and the ground layer 16 made of metal foil are adhered to both surfaces of the cover lay film 15, respectively. Here, what laminated | stacked the semi-hardened adhesive bond layer 14 on the other surface of the coverlay film 15 which has the ground layer 16 which consists of a single-sided copper clad laminated board can be used. In the formation of the connecting tongue piece 18 and the opening 19, laser processing that can selectively etch the adhesive layer 14, the resin material of the coverlay film 15, and the metal material of the ground layer 16 can be suitably used. Alternatively, the ground layer 16 may be wet-etched using the etching mask described above, and the adhesive layer 14 and the coverlay film 15 may be laser processed.

  In the FPC 10 shown in FIG. 1, the translucent resin 21 may be formed by being attached to at least the connecting tongue piece 18. In this case, the translucent resin 21 is thermocompression bonded to the connecting tongue piece 18. The translucent resin 21 is preferably an elastomer resin having elasticity such as silicone rubber and urethane rubber. By forming the translucent resin 21, the connection tongue piece 18 is stabilized in connection with the ground wiring 13 in the opening 19 for a long period of time.

  The connection can be easily stabilized by, for example, a modification of the connection between the two conductor layers shown in FIG. In FIG. 5A, blind plating as described in the prior art is added to the FPC 10 shown in FIG. 1, and the surface of the connecting tongue piece 18 is plated together with the surface of the ground wiring 13 and the ground layer 16 exposed at the opening 19. Layer 22 is formed. 5B, in the FPC 10 shown in FIG. 1, the solder 23 is melted and attached to the tip of the connecting tongue 18 that is bent into the opening 19. Similarly, in FIG. 5C, the conductive paste 24 is applied to the tip of the connecting tongue 18 that is bent into the opening 19 in the FPC 10 shown in FIG.

  In the embodiment described above, the case of FPC in which two conductor layers are formed is described, but a multilayer wiring board having three or more conductor layers can be formed in the same manner. In this case, a multilayer wiring board having a desired number of layers can be very easily obtained by laying up the FPC structure as shown in FIG. 1 with the adhesive layer interposed therebetween. The flexible printed wiring board 10 described above can also be used as a flexible flat cable.

  In the present embodiment, the connecting tongue 18 integrated with the ground layer 16 is mechanically pressed by the elastic sheet 20, bent into the opening 19, and connected to the ground wiring 13. Here, even if the burrs or protrusions described in the prior art are formed on the side wall of the cover lay film 15 in the opening portion 19, they are mechanically deformed by the pressing force. For this reason, in the connection of the connecting tongue 18 to the ground wiring 13, the generation of the burrs or protrusions is less likely to be a hindrance to the connection as compared with the conventional blind plating. Further, in the connection with the ground wiring 13 at the opening 19 by the connecting tongue 18 of the present embodiment, no bubbles remain in the opening 19 as described in the prior art. In this way, in the present embodiment, occurrence of problems in the electrical connection between the ground wiring 13 and the ground layer 16 is greatly reduced.

  Moreover, in the flexible printed wiring board of this embodiment, the inspection / sorting in the middle of its manufacture becomes extremely easy. Then, it is possible to effectively remove in advance connection problems. This is because, for example, when the connecting tongue 18 in the opening 19 shown in FIG. 1A is visually inspected from above with an optical microscope or the like, the connecting tongue 18 is moved downward into the opening 19. This is because the folded form can be easily visually recognized. In particular, one side of the edge 25 of the connecting tongue 18 can be easily recognized, and the connection state in the opening 19 can be confirmed. Here, by visually observing the step from the surface of the ground layer 16 at the edge 25 located below the connecting tongue piece 18, the connection with the ground wiring 13 is confirmed.

  The visual recognition of the connection at the edge 25 is similarly easy even in the case of the modification of the connection between the two conductor layers shown in FIG. This is because even if the plating layer 22, the solder 23, or the conductor paste 24 is formed on the edge 25, a stepped portion is formed on the edge 25, and this is easily visually recognized as one side.

  In this way, the flexible printed wiring board of this embodiment can be easily produced and managed. And the manufacturing technology becomes cheap, the limit of the manufacturing cost reduction is removed, and the cost reduction of the flexible printed wiring board is promoted.

  Although the preferred embodiments of the present invention have been described above, the above-described embodiments do not limit the present invention. Those skilled in the art can make various modifications and changes in specific embodiments without departing from the technical idea and technical scope of the present invention.

  For example, the translucent resin 21 mentioned in the above embodiment may be formed on the surface of the ground layer 16 together with the connecting tongue piece 18.

  Moreover, in the said embodiment, the coverlay film 15 and the ground layer 16 may be thermocompression-bonded without the adhesive agent 17 being interposed.

  Further, the adhesive layer 14 may be configured to join and integrate the base film 11 and the coverlay film 15 in a form that does not fill between the wiring patterns. Alternatively, the cover layer film 15 may be directly thermocompression bonded and integrated with the wiring pattern of the first conductor layer and the base film 11 without the insertion of the adhesive layer 14.

  Further, a conductive plating layer having oxidation resistance may be formed on the surface of the first conductor layer or the surface of the second conductor layer.

  DESCRIPTION OF SYMBOLS 10 ... Flexible printed wiring board, 11 ... Base film (1st insulator layer), 12 ... Signal wiring, 13 ... Ground wiring (1st conductor layer), 14 ... Adhesive layer (2nd insulator layer) , 15 ... Coverlay film (second insulator layer), 16 ... Ground layer (second conductor layer), 16a ... Slit-like definition part, 16b ... Linear definition part, 17 ... Adhesive, DESCRIPTION OF SYMBOLS 18 ... Connection tongue, 18a ... 1st connection tongue, 18b ... 2nd connection tongue, 19 ... Opening part, 20 ... Elastic sheet, 21 ... Translucent resin, 22 ... Plating layer, 23 ... solder, 24 ... conductor paste, 25 ... edge

Claims (4)

A first conductor layer disposed on one main surface of the first insulator layer; a second insulator layer covering the first conductor layer and bonding to the first insulator layer; and A flexible printed wiring board having a second conductor layer disposed on the second insulator layer;
The second conductor layer is electrically connected to the first conductor layer by bending a connecting tongue formed by cutting the second conductor layer into an opening provided in the second insulator layer. And the flexible printed wiring board characterized by being formed on the said 2nd insulator layer.   The flexible printed wiring board according to claim 1, wherein a resin having translucency is formed so as to cover the connecting tongue bent in the opening.   2. A conductive plating layer is formed on the surface of the connecting tongue bent into the opening, the first conductor layer of the opening, and the second conductor layer. The flexible printed wiring board as described in.   2. The flexible device according to claim 1, wherein a tip of the bent connecting tongue and the first conductor layer of the opening are connected to each other by solder or conductor paste in the opening. Printed wiring board.

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