JP2007165523A - Flexible wiring board and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible wiring board that strikes a balance between fine pitch wiring and flexibility compatible with flexible arrangement, with high connection reliability of an external connection terminal. <P>SOLUTION: Internal conductor patterns 12 and 13 are provided on the surface of a plurality of dielectric layers 11. The adjoining dielectric layers 11 are integrally connected and molded with one of both main surfaces of the substrate communicating each other by layer ends. Connections 11a are alternately provided on one of both main surfaces of the substrate. So, the plurality of dielectric layers constitute one dielectric sheet being bent multiple times. Part of the internal conductor patterns 12 and 13 extends as far as an adjoining dielectric layer 11 by exceeding the connection 11a, and consequently it is exposed on the main surface of the wiring board. The exposed parts of the internal conductor patterns 12 and 13 constitute external connection terminals 17a and 17b on the substrate main surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flexible wiring board and a method of manufacturing the same, and more particularly to a flexible wiring board used in high-density mounting equipment such as a mobile phone and connecting a plurality of boards in a flexible shape with a large number of wirings.

  With the recent increase in performance and functionality of electronic devices, the scale of LSIs and peripheral circuits that make up electronic devices has increased, and the number of wirings that connect LSIs and peripheral circuits also on circuit boards on which these devices are mounted Has increased. Furthermore, in mobile electronic devices such as mobile phones, notebook computers, PDAs, digital cameras, etc., in order to accommodate the increasing circuits and wiring in a compact housing, the density of the space between each of the substrates constituting the plurality of circuit blocks is increased. A flexible wiring board to be connected is frequently used.

  In such a flexible wiring board, flexibility is increasingly required in order to realize a more flexible board arrangement. The demand for flexibility is to realize more inter-board wiring according to the increase in the circuit scale of equipment, to support high-speed signal transmission according to the speeding up of LSI, to downsizing equipment and diversifying designs. Based on the correspondence of.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-57259) discloses a conventional flexible wiring board used for a foldable mobile phone, which has been increasing rapidly in recent years. FIG. 11 is a plan view showing an example of a conventional flexible wiring board. In the flexible wiring board 200, a plurality of wiring patterns 202 are formed on one surface of an insulating film base material 201 such as polyimide, and terminal portions 203a and 203b are formed on the wiring pattern 202 at a connection portion with another substrate. ing. Further, the flexible wiring board 200 is formed with a crank portion 204 so that the upper and lower housings can be freely opened and closed at the folding portion of the mobile phone.

  FIG. 12 is a cross-sectional view showing a configuration in which a conventional flexible wiring board is installed in a folding housing such as a mobile phone. The upper casing 205a and the lower casing 205b can be freely opened and closed with the folding portion 206 as a rotation axis. The circuit block board 207a and the circuit block board 207b of the upper and lower casings are interconnected by the flexible wiring board 200. The flexible wiring board 200 is arranged in a rounded shape so as to flexibly follow the opening and closing of the folding part 206. The crank portion 204 of the flexible wiring board 200 is provided to facilitate such a rounded arrangement.

  The terminal portions 203a and 203b of the flexible wiring board 200 are respectively connected to the ends of the wiring boards (rigid boards) 207a and 207b of the upper and lower casings. Usually, a connector is used for connection between the flexible wiring board and the rigid board. Connection is made by soldering or soldering.

  In the connector connection, a connector is provided on the rigid board side, a terminal part of the flexible wiring board is inserted into the connector, and a connector pin is pressed into the terminal part for connection. In the case of solder connection, a terminal electrode having the same arrangement as the terminal portion of the flexible wiring board is provided on the rigid board, and the corresponding terminals are aligned via solder and heated and pressed to perform connection. In connector connection, it is difficult to miniaturize connector pins, and also in solder connection, a solder bridge occurs between adjacent wirings. Therefore, there is a limit to the fine pitch of the terminal portion, and the pitch is about 0.3 mm.

As described above, since it is necessary to secure a certain terminal pitch for the connection between the flexible wiring board and the rigid board, as shown in FIG. 11, the pitch of the terminal portions 203a and 203b is significantly wider than the normal wiring pitch. On the other hand, in a portion where flexibility is required, such as the crank portion 204, the width is narrowed as narrow pitch wiring as much as possible.
JP 2005-57259 A

  As described above, as the performance of equipment increases, flexible wiring boards that connect a plurality of circuit blocks are required to accommodate a larger number of wires in a compact manner, and in response to the diversification of equipment forms. The compatibility with the flexibility corresponding to the flexible arrangement is required.

  In order to accommodate a large number of wirings in a conventional flexible wiring board, development has been carried out to form a wiring with a fine pitch and to accommodate a large number of wirings in one layer.

  On the other hand, there are multilayer flexible wiring boards in which multiple insulating film base materials are laminated with adhesive layers to form multilayer wiring. However, ensuring the thickness of the insulating film base material that can withstand external forces such as tension and the thickness of the adhesive layer Further, considering the thickness of the coverlay covering the surface wiring, for example, even a multilayer substrate with four wiring layers has a thickness of 0.4 mm, and the flexibility is lost as the number of layers increases, so flexibility is required. In general, the portion is composed exclusively of a single layer of flexible wiring.

  Therefore, in order to accommodate a large number of wirings in a compact manner, wirings with a fine pitch are formed.

  However, in a wiring layer with a narrow pitch, it is necessary to increase the film thickness in order to prevent an increase in wiring resistance due to the miniaturization of the wiring. If you try to miniaturize a thicker wiring layer, it will inevitably result in a wiring pattern with a high aspect ratio, but forming a wiring pattern with a high aspect ratio requires advanced etching and wiring forming technology, making it difficult to manufacture. .

  Next, the problem of dealing with flexibility will be considered. Since the conventional flexible wiring board has a film shape with a predetermined width, it can be bent in the thickness direction of the film as shown in FIG. 12, but it is bent in another direction (for example, the width direction of the film). It is not possible. Since there is only a degree of freedom in the planar bending direction, there is a problem that it becomes difficult to cope with the mobility of the substrate arrangement and rotation in a more complicated device.

  In addition, as described above, there is a limit to the fine pitch of the connection terminals with other substrates. Therefore, even if the wiring pitch is miniaturized, the width of the connection terminal portion increases as the number of wirings increases. Therefore, like the flexible wiring board 200, it is necessary to increase the pitch in the terminal portion. Therefore, it is necessary to increase the width of the terminal portion and to form a complicated outer shape with a narrowed width in the wiring portion, and it is necessary to provide an extended wiring portion for expanding the width to the terminal portion.

  As described above, depending on the arrangement and the movable range of the flexible wiring board in the device, it must have a complicated external shape with the connection terminal expanded to match the other substrate to be connected. It is necessary to custom design and manufacture a flexible wiring board having a complicated shape as shown in FIG.

  The present invention has been made in view of such points, and relates to a flexible wiring board of a completely new concept different from the conventional flexible wiring board, and corresponds to fine pitch wiring and more flexible arrangement that solve the conventional problems. An object of the present invention is to provide a flexible wiring board that has both flexibility and is easy to be generalized.

  The flexible wiring board of the present invention is a flexible wiring board having a plurality of wirings arranged in parallel, and is arranged along the opposing direction of both main surfaces of the board, and a plurality of dielectric layers stacked in the board width direction, and And an internal conductor pattern provided on the surfaces of the plurality of dielectric layers as the plurality of wirings.

  Adjacent dielectric layers are formed by connecting and forming the end portions of the layers on either one of the main surfaces of the substrate. The connecting portions of the adjacent dielectric layers are alternately provided on either one of the main surfaces of the substrate, so that the plurality of dielectric layers form a single dielectric sheet shape that is bent. A part of the inner conductor pattern is exposed to the main surface of the wiring board by extending to a dielectric layer adjacent to the dielectric layer beyond the connecting portion of the dielectric layer where the inner conductor pattern is formed. And the exposed part of the said internal conductor pattern comprises an external connection terminal in a board | substrate main surface.

  With the above configuration, the internal conductor pattern has a finely spaced wiring pitch in which the dielectric sheets are alternately folded, and a large number of wirings can be accommodated in a narrow flexible wiring board. Furthermore, the configuration in which a part of each internal conductor pattern is extended and exposed makes it possible to draw out the external connection terminals at a desired pitch while keeping the narrow substrate width in the external connection terminals.

  Therefore, in the flexible wiring board of the present invention, a large number of wirings can be accommodated and the width of the board can be reduced, so that not only bending in the thickness direction but also flexibility in bending in the width direction, freedom in the twisting direction, etc. Flexibility can be increased. In addition, the external connection terminals can have the same substrate width as that of the flexible wiring portion, and a wiring portion for extending the pitch at the terminals as in the prior art becomes unnecessary. Furthermore, since it is not necessary to make a complicated outer shape by using a thin substrate with a certain width and the flexibility is high, by preparing the flexible wiring substrate of the present invention that has been standardized to some extent, various It is possible to cope with the board arrangement in a simple device.

  In a preferred embodiment, the internal conductor pattern is provided in a strip shape inside the substrate sandwiched between connecting portions of both main surfaces of the dielectric layer.

  In a preferred embodiment, among all the substrate length direction portions of the flexible wiring substrate, at least the substrate length direction portion where the external connection terminal is provided, the adjacent dielectric layers are fixed, It is integrated in the substrate width direction.

  In a preferred embodiment, among all the board length direction parts of the flexible wiring board, at least in the board length direction part where flexibility is required, at least one board main surface side of the connection parts. The dielectric layer is separated by cutting the connecting portion.

  In a preferred embodiment, the inner conductor pattern is provided on both surfaces of the dielectric sheet.

  In a preferred embodiment, the inner conductor pattern on one surface of the dielectric sheet is shielded by the inner conductor pattern on the other surface.

  In a preferred embodiment, a part of the inner conductor pattern on both surfaces of the dielectric sheet is adjacent to the dielectric layer beyond a connecting portion of the dielectric layer on which the inner conductor pattern is formed. By extending up to the layer, it is exposed on both main surfaces of the wiring board, and the exposed portions of both internal conductor patterns constitute the external connection terminals on both main surfaces of the wiring board.

  In a preferred embodiment, the adjacent external connection terminals are arranged so as to be shifted from each other along the substrate width direction and the substrate length direction orthogonal to the opposing direction of the both main surfaces of the substrate.

  In a preferred embodiment, an external connection electrode pad connected to the external connection terminal is provided, and the external connection electrode pad is provided on the main surface of the substrate.

  In a preferred embodiment, the dimension of the external connection electrode pad in the substrate width direction is larger than the dimension of the external connection terminal in the substrate width direction.

  The flexible wiring board of the present invention can be produced, for example, by the following manufacturing method. The manufacturing method prepares a dielectric sheet having a predetermined length and width, and alternately forms a crest-side line and a trough-side line indicating that the dielectric sheet becomes a valley when viewed from one surface of the dielectric sheet. A first step that is virtually set parallel to the length direction and at a predetermined interval; and located on at least one surface of the dielectric sheet between the crest-side line and the trough-side line; A second step of forming a strip-shaped internal conductor pattern parallel to the mountain-side line / valley-side line; and the mountain-side line becomes a mountain shape when the dielectric sheet is viewed along the mountain-side line / valley-side line from the one surface. And a third step of forming a flexible wiring board having the mountain-shaped exposed surface as one main surface by alternately folding the valley-side lines into a valley shape. In the second step, the inner conductor pattern is formed such that a part of the inner conductor pattern extends outward beyond the peak line / valley line of the dielectric sheet, and the extension of the inner conductor pattern The part is exposed to the main surface of the wiring board after the third step to serve as an external connection terminal.

  In a preferred embodiment, in the third step, the substrate on which at least the external connection terminal is provided among all the substrate length direction portions of the flexible wiring substrate when the dielectric sheets are alternately folded. Adjacent dielectric sheets are fixed to each other in the longitudinal direction and integrated in the substrate width direction.

  In a preferred embodiment, after the third step, among all the substrate length direction portions of the printed wiring board, at least the substrate sheet in the substrate length direction portion where flexibility is required, The method further includes a step of partially cutting the mountain side line or the valley side line.

  In a preferred embodiment, in the second step, the extending portions of the adjacent internal conductor patterns are arranged so as to be shifted from each other along the peak line / valley line.

  In a preferred embodiment, the method further includes a fifth step of forming an external connection electrode pad connected to the external connection terminal on the main surface of the substrate.

  In a preferred embodiment, in the fifth step, the external connection electrode pad is formed wider in the substrate width direction than the external connection terminal.

  The flexible wiring board according to the present invention allows a large number of signal wirings to be accommodated in a narrow flexible wiring board without forming a fine wiring pattern, and exposes the internal conductor pattern while maintaining the narrow board width. Thus, the external terminals can be drawn out at a desired pitch. Accordingly, since the width of the substrate can be reduced, it is possible to bend or twist not only in the thickness direction but also in the width direction, thereby increasing flexibility. Further, the same substrate width can be provided including the external connection terminal portion, and the pitch extension wiring portion at the terminal portion as in the prior art becomes unnecessary. Furthermore, since it is not necessary to have a complicated external shape, a flexible wiring board that has been standardized to some extent and has been generalized can be used for board arrangements in various devices.

  Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, components having substantially the same function are denoted by the same reference numerals for the sake of simplicity. In addition, this invention is not limited to the following embodiment.

(Embodiment 1)
FIG. 1 is a diagram showing a basic configuration of flexible wiring board 100 according to Embodiment 1 of the present invention. In particular, the cross-sectional structure of the flexible wiring board 100 and the connection structure between the external terminals are shown in an easy-to-understand manner, and the actual flexible wiring board 100 is further extended in the length direction.

  The flexible wiring board 100 shown in FIG. 1 has a plurality of dielectric layers 11, and each dielectric layer 11 has its main surface arranged along the opposing direction (thickness direction) of both main surfaces of the substrate. A plurality of layers are stacked in the width direction of the flexible wiring board. Internal conductor patterns 12 and 13 are provided on the surface of the dielectric layer 11. The internal conductor patterns 12 and 13 are provided on both surfaces of the dielectric layer 11. Adjacent dielectric layers 11 are formed so that their layer ends communicate with each other on either one of the main surfaces 20 and 21 of the substrate. The connected layer ends constitute a connecting portion 11 a of the adjacent dielectric layer 11. The connection part 11a is continuously provided in the dielectric layer 11 to the full length along the length direction of the dielectric layer 11 (length direction of the flexible wiring board 100). The connecting portion 11 a is provided at both layer ends of each dielectric layer 11. The plurality of connecting portions 11a are alternately arranged on either one of the substrate main surfaces 20 and 21 along the substrate width direction. That is, the connection part 11a adjacent to the connection part 11a on the one substrate main surface 20 side is provided on the other board main surface 21, and the connection part 11a adjacent to the connection part 11a on the other substrate main surface 21 side is Provided on one substrate main surface 20.

  Thus, the plurality of dielectric layers as a whole are in the form of a single dielectric sheet 10 that is bent by being folded at the connection portion 11a, and the flexible wiring board is further formed from the folded dielectric sheet 10. Composed. The inner conductor patterns 12 and 13 are arranged in a strip shape along the longitudinal direction of the dielectric layer 11 constituting the dielectric sheet 10 in this way. Here, the layer longitudinal direction is the direction of the connecting ridge line of the connecting portion 11a, and specifically the length direction of the flexible wiring board. The substrate length direction is orthogonal to the substrate main surface facing direction and the substrate width direction.

  The dielectric layers 11 are fixed to each other with an insulating adhesive layer 16 disposed between the layers, and the internal conductor patterns 12 and 13 are covered with the insulating adhesive layer 16. Thereby, one board | substrate main surface 20 of the flexible wiring board 100 is comprised by the continuous body of the some connection part 11a fixed by the insulating contact bonding layer 16. FIG. Similarly, the other substrate main surface 21 of the wiring substrate 100 is constituted by a continuous body of a plurality of connecting portions 11 a fixed by an insulating adhesive layer 16.

  At least one of the plurality of internal conductor patterns 12 and 13 extends to the connection portion 11a where the surface of the dielectric layer 11 on which the internal conductor patterns 12 and 13 are formed becomes the connection outside. As a result, the extended ends of the inner conductor patterns 12 and 13 are exposed on one of the main surfaces 20 and 21. The internal conductor pattern 12 exposed on the main surfaces 20 and 21 of the wiring board 100 constitutes extraction electrodes 17a and 17b of the respective layers (internal conductors 12 and 13 of each dielectric layer 11). The lead electrodes 17a and 17b of each layer are arranged so that the positions exposed at a predetermined pitch in the length direction of the flexible wiring board are shifted for each layer. External connection electrode pads 18 are formed on the upper surfaces of the respective extraction electrodes 17a and 17b. The external connection electrode pad 18 has a long rectangular shape whose dimension in the substrate width direction is longer than that of the extraction electrode 17. Each external connection electrode pad 18 is connected to each extraction electrode 17a, 17b.

  The first feature of the flexible wiring board 100 in the present embodiment is as follows. That is, a plurality of internal conductor patterns 12 and 13 are laminated along the width direction of the flexible wiring board with the dielectric layer 11 in between. As a result, a large number of wirings can run in the length direction of the substrate at a minute pitch that is the sum of the thickness of the dielectric layer 11 and the thickness of the internal conductor patterns 12 and 13. For example, when the thickness of the dielectric layer 11 is 3 μm and the thickness of the internal conductor patterns 12 and 13 is 1 μm, it is possible to route wiring with a very high density of 3 to 4 μm. This is a high-density wiring 20 times or more even when compared with the 80 μm pitch at the tip level in the flexible wiring board. Even if it is going to achieve wiring density comparable to this by the multilayering of the conventional flexible wiring board, since 20 or more layers are required, it is not practical as an industrial product, and the total thickness of the board is far less than 1 mm. This results in an inflexible wiring board.

  The second feature of the flexible wiring board 100 in the present embodiment is as follows. That is, the internal conductor patterns 12 and 13 are covered with the insulating adhesive layer 16 and have a structure embedded in the wiring board 100. As a result, the internal conductor patterns 12 and 13 can be densely wired while maintaining a narrow pitch without being obstructed by the external connection electrode pads 18 formed on the main surface 20 of the wiring board 100. Become. In order to realize high-density wiring with a conventional flexible wiring board, the pitch of the terminal electrodes must be increased, and an extra wiring area is required to extend the pitch from the fine pitch wiring to the terminal portion. . On the other hand, the flexible wiring board 100 of the present embodiment having the second feature described above is simply exposed by shifting the lead electrodes 17a and 17b of the flexible wiring board 100 at a predetermined pitch in the length direction of the board. It can be easily expanded to a pitch that can be used for connection to other substrates.

  As described above, the present embodiment provides a flexible wiring board in which the wiring density is dramatically increased as compared with a conventional flexible wiring board. It is possible to solve the following technical problems that have hindered densification.

  Although there is a narrow pitch of wiring as an issue of high density, a thick wiring layer is required to prevent an increase in wiring resistance due to miniaturization of the wiring, and as a result, a high pattern that forms a high aspect ratio wiring pattern Etching technique is required. For example, when the wiring width is 20 μm, a wiring with a high aspect ratio of about 20 μm is required as a desired wiring thickness from the viewpoint of reducing the resistance of the wiring.

  On the other hand, in the present embodiment, the inner conductor patterns 12 and 13 are formed in a strip shape on the surface of each dielectric layer 11, and the pattern width is set to the thickness of the flexible wiring board 100 (both main surfaces 20, It is possible to widen up to about half of (21 opposed spacing). For example, when the thickness of the wiring board 100 is 1 mm, the width of the inner conductor patterns 12 and 13 can be 400 μm or more, and the thickness of the inner conductor patterns 12 and 13 can be reduced to 1 μm. However, it is possible to obtain a conductor cross-sectional area equal to or greater than that of a high aspect ratio wiring having a width of 20 μm and a thickness of 20 μm, and the resistance of the wiring can be easily reduced. Of course, since the internal conductor patterns 12 and 13 having a width of the order of 100 μm can be easily formed by a normal etching technique, the internal conductor pattern can be formed with a high yield without requiring a difficult high aspect ratio etching technique. .

  Next, the flexibility of the flexible wiring board of the present embodiment that can flexibly correspond to the device configuration will be described. In a conventional flexible wiring board, a wiring pattern is formed in a plane on an insulating film substrate, so that the width of the board increases as the number of wirings increases, and only the degree of freedom of bending in the thickness direction of the film can be obtained. In addition, the connection terminal portion must be expanded, and as shown in the flexible wiring board 200 shown in FIG. 11, there is a problem that a complicated external shape is required for each product depending on the device design.

  The flexibility of the flexible wiring board of this embodiment will be described with reference to FIG. External connection terminal portions 19 a and 19 b are provided at both ends of one main surface of the flexible wiring board 100. A plurality of internal conductor patterns 12 and 13 are arranged in parallel on the inner layer of the flexible wiring board 100. The inner conductor patterns 12 and 13 are provided in a strip shape on each dielectric layer 11. The internal conductor patterns 12 and 13 function as parallel wirings that electrically connect the external connection terminal portion 19a on one end side and the external connection terminal portion 19b on the other end side. The connection terminal portions 19a and 19b have the terminal structure described above with reference to FIG. That is, the flexible wiring board 100 has lead electrodes 17a and 17b in which a part of the inner conductor patterns 12 and 13 are drawn and exposed on the substrate surface. The lead electrodes 17a and 17b are arranged at a predetermined pitch in the length direction of the substrate, and the lead electrodes 17a and 17b are connected to the external connection electrode pad 18. The board width direction dimension of the external connection electrode pad 18 is larger than the board width direction dimension of the external connection terminals 17a and 17b.

  The external connection electrode pad 18 is formed over the entire width of the flexible wiring board in accordance with a terminal of a rigid board (not shown) to be connected. The rigid board and the flexible wiring board 100 are connected by, for example, inserting the connection terminal portions 19a and 19b into a connector mounted on the rigid board, or soldering the opposing terminals.

  As shown in FIG. 2, in the flexible wiring substrate 100, the connection terminal portions 19a and 19b and the flexible wiring portion 25 (flexible portion of the flexible wiring substrate 100) have the same width, which is similar to the conventional flexible wiring substrate. There is no need for extended wiring at the connection terminals. Further, as described above, the high-density wiring 20 times or more than that of the conventional flexible wiring board can be achieved, so that it is possible to fit within the conventional width of 1/20 or less when compared with the same number of wirings. For example, when 100 wirings are used, the width is over 8 mm when considered with a conventional 80 μm pitch flexible wiring board, but the flexible wiring board according to the present invention can be accommodated in a width of 0.4 mm. When the width is 8 mm, bending in the width direction is impossible and only bending in the film thickness direction is possible. However, the flexible wiring board of the present invention, which is extremely thin as 0.4 mm, is closer to a string shape rather than a film shape. In addition to being able to bend in the direction, there is a degree of freedom in the twisting direction as shown in FIG.

  Furthermore, the connection terminal portions 19a and 19b and the flexible wiring portion 25 (the substrate region in which the inner conductor patterns 12 and 13 are accommodated) have the same width, and the inner conductor patterns 12 and 13 can also be configured in a simple belt shape. Even if it is not made into the shape of a single item according to a device like a flexible wiring board, it has the flexibility which can respond to the board arrangement in a more flexible device. Therefore, it is possible to easily achieve standardized parts that could not be considered with a conventional flexible wiring board having a complicated outer shape. By standardizing the terminal pitch, number of wires, wiring length, etc., it becomes possible to respond flexibly without using custom shapes like conventional flexible wiring boards.

  Next, the connection reliability of the connection terminal portions 19a and 19b will be described. In the connection between the flexible wiring board and the rigid board, which is performed by connector connection, solder connection, or the like, the terminal portion of the flexible wiring board needs to have a certain level of strength to ensure the connection. In the case of a conventional flexible wiring board, a reinforcing plate is bonded to the back of the terminal portion to give strength. In particular, in the case of a thin dielectric sheet used in the present embodiment, a reinforcing plate is essential in the past.

  On the other hand, since the flexible wiring board in the present embodiment is a block in which a large number of dielectric layers 11 are laminated and fixed, it is possible to obtain strength that cannot be obtained with a single dielectric sheet, Even if there is no backing reinforcing plate, it is possible to reliably connect to another substrate.

  Further, the configuration in which the dielectric layers 11 stacked in the substrate width direction are connected and folded as a single sheet also plays an important role in connection reliability in the connection terminal portions 19a and 19b. First, the lead electrodes 17 of the inner conductor patterns 12 and 13 have a curved shape following the connecting portion 11a of the dielectric sheet, whereby the lead electrodes 17 are formed from the surface along the substrate thickness direction. The surface is gradually curved along the substrate main surface direction. Therefore, even if stress is applied to the extraction electrode 17 from the outside, a stress concentration point does not occur. Therefore, even if an external force is applied to a connection portion with another substrate, there is no fear of disconnection and high reliability can be obtained.

  For example, in a so-called end face electrode lead-out structure in which a conductor layer exposed on the end face of a dielectric layer is connected to an external electrode pad by simply laminating dielectric layers and conductor layers alternately, the conductor layer and the external electrode pad A corner that is substantially perpendicular to the connection point between the two is formed. Therefore, when stress is applied to the extraction electrode 17 from the outside, a stress concentration point is generated. For these reasons, conventionally, it is common sense to pay close attention to maintaining connection reliability when connecting to other boards.

  Furthermore, in the case of a configuration in which dielectric layers and conductor layers are simply laminated alternately (for example, a wiring board disclosed in JP-A-2004-327971), a large external force is applied to the connection terminal portion by bending of the flexible wiring board, Delamination occurs from the adhesive interface between the dielectric layer and the conductor layer, which is a problem in improving reliability. On the other hand, in the flexible wiring board of the present embodiment, each dielectric layer 11 is necessarily integrated as a sheet with the adjacent dielectric layer, so that interlayer separation can be suppressed.

  As described above, in the structure of the present embodiment, high connection reliability is obtained by the fact that the external connection terminal portions 19a and 19b are firmly connected and fixed and the whole is constituted by a communication-integrated sheet. It is possible.

  Next, a method of forming the flexible wiring board 100 shown in FIGS. 1 and 2 by alternately folding the dielectric sheets 10 will be described with reference to FIGS.

  3A, 3B, and 3C are respectively a plan view, a cross-sectional view at XY, and a bottom view of the dielectric sheet 10 before being folded. As shown in FIG. 3A, when the dielectric sheet 10 having a rectangular shape is folded later, a peak side line PP ′ that becomes a peak when viewed from one surface of the dielectric sheet 10 and a valley side line that becomes a valley Q-Q 'is virtually set. These peak side lines PP ′ and valley side lines QQ ′ are set along the length direction of the dielectric sheet 10. Furthermore, the peak line P-P 'and the valley line Q-Q' are set alternately, parallel to each other, and at a constant interval. Here, the length direction is the same direction as the length direction in the wiring board 100. The above is the first step.

  Next, the inner conductor patterns 12 and 13 are formed on both surfaces of the dielectric sheet 10. At that time, the inner conductor patterns 12 and 13 are formed in a strip shape along the length direction. Further, the inner conductor patterns 12 and 13 are arranged in parallel to these lines PP ′ and QQ ′ in the surface regions sandwiched between the adjacent peak side lines PP ′ and valley side lines QQ ′, respectively. To do. Furthermore, the internal conductor pattern 12 provided on one surface of the dielectric sheet 10 and the internal conductor pattern 13 provided on the other surface are arranged opposite to each other with the dielectric sheet 10 interposed therebetween.

  A lead electrode is formed by extending a part of any of the plurality of internal conductor patterns 12 and 13 to a position exceeding the adjacent peak side line PP ′ or valley side line QQ ′. 17a and 17b are formed. Here, a crest-side line PP ′ or a trough-side line QQ ′ is arranged on both sides of the internal conductor patterns 12 and 13, and one of these lines PP ′ and QQ ′ is selected. Then, the internal conductor patterns 12 and 13 are extended to the selected line to form lead electrodes 17a and 17b. Selection of the lines P-P 'and Q-Q' is carried out as follows. As shown in FIG. 4, the dielectric sheet 10 is folded alternately along the lines PP ′ and QQ ′ in the subsequent process. When the internal conductor patterns 12 and 13 are extended toward the lines P-P 'and Q-Q', the extension end is located inside the sheet of the dielectric sheet 10 in the bent state, and the outside of the sheet The case where it is located occurs. As the extending side of the inner conductor patterns 12 and 13, lines PP ′ and QQ ′ positioned outside the dielectric sheet 10 with the pattern extending ends bent are selected.

  Here, an aramid film having a thickness of 3 μm is used for the dielectric sheet 10, and the internal conductor patterns 12 and 13 are formed by depositing a copper thin film with a thickness of 1 μm on the dielectric sheet 10 and then etching by 150 μm. Are formed at intervals of 300 μm (interval between the peak line P-P ′ and the valley line Q-Q ′). The above is the second step.

  Next, as shown in FIG. 4, the dielectric sheet 10 is alternately and continuously folded along the peak side line PP ′ and the valley side line QQ ′. At this time, the dielectric sheet 10 is folded so that the peak line P-P 'has a peak shape and the valley side line Q-Q' has a valley shape as viewed from one surface of the dielectric sheet 10. As a result, a plurality of dielectric layers 11 composed of the portions superimposed on each other are formed. Here, the layer ends of the dielectric layer 11 are connected by a connecting portion 11 a formed by alternately folding the dielectric sheets 10. A plurality of connecting portions 11 a are provided, and each connecting portion 11 a is alternately arranged on one of the two layer ends of each dielectric layer 11. Furthermore, each dielectric layer 11 is fixed to each other by filling the insulating adhesive layer 16 between the dielectric layers 11. The above is the third step. In addition, when the insulating adhesive layer 16 is provided and the dielectric layers 11 are bonded, the material of the insulating adhesive layer 16 is suitably a thermosetting epoxy resin or a composite material containing a thermosetting epoxy resin as a composition. Each dielectric layer 11 can be easily bonded by heating at about 100 to 200 ° C.

  In this way, the wiring board 100 shown in FIG. 1 is completed. The thickness of the wiring board 100 is generally less than 300 μm, and the wiring pitch of the internal conductor pattern 12 embedded in the wiring board 100 is about 4 μm.

  As shown in FIG. 4, when the dielectric sheet 10 is folded, the extraction electrodes 17a and 17b are located on the outer side of the connection portion 11a and exposed to the main surfaces 20 and 21 of the wiring board 100.

  Since the exposed lead electrodes 17a and 17b have a small contact area, an external connection electrode pad 18 is further formed to match the terminal of the rigid substrate to be connected.

  As the external connection electrode pad 18, a copper pattern is formed on the substrate main surfaces 20, 21 by plating, for example. In addition, various conventional electrode forming techniques such as printing the conductive paste to form the external connection electrode pads 18 can be used.

(Embodiment 2)
5 and FIG. 6 are modifications of the flexible wiring board 100 according to the first embodiment as the flexible wiring board 110 according to the second embodiment of the present invention. Although the basic configuration is the same as that of the first embodiment, each of the dielectric layers 11 is fixed to each other in the connection terminal portions 19a and 19b, but the flexible portion 25 is a portion where flexibility is required in the entire length of the substrate. 2 is characterized in that a part of the connecting portion of the dielectric layer 11 is cut and the adjacent dielectric layers 11 are separated from each other.

  FIG. 5 shows a top view of the flexible wiring board 110 before being folded. Similar to FIG. 3, when folded after the dielectric sheet 10, a peak-side line PP ′ that becomes a mountain when viewed from one surface of the dielectric sheet 10 and a valley-side line Q-Q ′ that becomes a valley are virtually The inner conductor pattern 12 (13 is not shown) is formed. Here, in the flexible wiring part 25, the slit 26 is provided in the dielectric sheet 10 along the peak line P-P 'and is partially cut. When cutting, it is necessary to leave at least the connection terminal portions 19a and 19b without cutting.

  Similar to the first embodiment, the dielectric sheet 10 is alternately and continuously folded along the peak line P-P 'and the valley line Q-Q', and the dielectric layers 11 are fixed. At the time of fixing, the adjacent dielectric layers 11 are not fixed at the portion where the slit 26 is provided along the peak side line P-P ′ serving as the connecting portion.

  The flexible wiring board 110 formed in this way is shown in FIG. Since the connection terminal portions 19a and 19b are firmly fixed between the dielectric layers 11 and have sufficient strength for connection to the rigid substrate, the dielectric portions 11 are separated in the flexible portion 25. Even a sudden bend as shown in FIG. 6 can follow more flexibly because there is play in each dielectric layer 11. In FIG. 5, there is a portion that is left uncut in the flexible portion 25, that is, there is a portion that is not provided with the slit 26. By doing so, each dielectric layer 11 is separated. It can be bundled so that it does not become. Further, in FIG. 5, in the flexible portion 25, the slit 26 is provided in the dielectric sheet 10 along the peak line PP ′, and the slit 26 is partially cut, but in addition to this, the valley line QQ A slit may be provided in the dielectric sheet 10 along the line ′ and may be partially cut.

(Embodiment 3)
7 and 8 are diagrams showing the configuration of the flexible wiring board 120 according to Embodiment 3 of the present invention. The basic configuration is the same as that of the first embodiment in that the strip-like internal conductor pattern 12 is provided on one surface of the dielectric sheet 10 in particular. The present embodiment is characterized in that the internal conductor patterns 13 formed on the other surface of the dielectric sheet 10 are continuously connected to each other.

  Even in flexible wiring boards, higher density of wiring is required with higher integration of LSIs, while with higher speed of LSI, crosstalk between wirings and reduction of influence of external noise etc. Improvement is also required. Therefore, in the conventional flexible wiring board, measures such as inserting a ground wiring between the signal lines or using a differential signal line made up of a pair of signal lines to reduce common mode noise, etc. It was given. However, it is difficult to reliably suppress crosstalk with the ground line between the signal lines.

  In this embodiment, a flexible wiring board having a configuration in which a shield layer that covers a signal wiring is provided can be easily achieved while overcoming the above-mentioned problems that have been difficult with a conventional flexible wiring board and maintaining a high wiring density. It is to provide.

  As shown in FIGS. 7A to 7C, in the present embodiment, a plurality of strip-shaped first internal conductor patterns 12 are formed in parallel on one surface of the dielectric sheet 10. On the other hand, second inner conductor patterns 30 a and 30 b are formed on the other surface of the dielectric sheet 10.

  A part of the plurality of first internal conductor patterns 12 has an extraction electrode 17a. The configuration of the extraction electrode 17a has the same structure as that of the extraction electrode 17a in the first embodiment, and is exposed on one main surface 20 of the wiring substrate 120 formed by bending the dielectric sheet 10. . The second inner conductor patterns 30a and 30b formed on the other surface of the dielectric layer 11 cross each other over the entire longitudinal direction of the pattern beyond the peak line PP ′ and the valley line QQ ′. The second inner conductor patterns 30a and 30b are formed so as to cover the entire main part across the plurality of valley-side lines QQ ′ on the other surface of the dielectric sheet 10. ing. As a result, the plurality of second inner conductor patterns 13 provided in the first embodiment are connected to each other on the other main surface 21 of the wiring board 120 in the present embodiment, and this connected second The portions of the internal conductor patterns 30a and 30b are exposed on the other main surface 21 of the wiring board 120 and function as lead electrodes 17b.

  Here, by using the first inner conductor pattern 12 as a signal line and the second inner conductor patterns 30a and 30b as ground lines, the first inner conductor pattern constituting the signal line built in the wiring board 120 is used. 12 is substantially shielded by the second inner conductor patterns 30a and 30b. The internal conductor patterns 30a and 30b functioning as shields can be used as ground wiring and power supply wiring, respectively. The second internal conductor patterns 30a and 30b are wider than the first internal conductor pattern 12 used as signal lines. Since it is widely formed, it is suitable for power supply wiring through which a large amount of current flows.

(Embodiment 4)
In the first to third embodiments, a basic configuration of a wiring board in which a dielectric sheet is folded and a dielectric layer composed of overlapping portions and an internal conductor pattern formed on the main surface of the dielectric layer is internally layered Although various modifications have been described, in the present embodiment, a more specific method of folding the dielectric sheet will be described with reference to FIGS.

  FIGS. 9A to 9E show a process of forming the internal conductor pattern on the dielectric sheet before folding.

  First, as shown in FIG. 9A, a dielectric sheet 10 having a certain width is prepared. For example, an aramid film having a thickness of 3 μm and a width of 100 mm is used as the dielectric sheet 10.

  Next, as shown in FIG. 9B, a virtual folding peak side line is formed on the surface of the dielectric sheet 10 along the direction perpendicular to the paper surface of the dielectric sheet 10 (the length direction of the substrate). PP ′ and valley side line QQ ′ are provided. Here, the peak line P-P 'and the valley line Q-Q' are provided alternately, and are set in parallel with each other at a constant interval.

  In the present embodiment, the bending guide groove 50 is formed on the surface of the dielectric sheet 10 along the peak side line PP ′ and the valley side line QQ ′ in order to facilitate folding. In this case, the bending guide groove 50 of the peak line P-P ′ is provided on one surface of the dielectric sheet 10, and the bending guide groove 50 of the valley side line Q-Q ′ is formed on the other surface of the dielectric sheet 10. Provided.

  Thereafter, as shown in FIG. 9C, copper thin films 12 'and 13' are formed on both surfaces of the dielectric sheet 10 by 1 [mu] m by sputtering. Further, as shown in FIG. 9D, the internal conductor patterns 12 and 13 are formed by etching the copper thin films 12 'and 13' into a predetermined pattern shape. The internal conductor patterns 12 and 13 are formed in the sheet surface region surrounded by the peak line P-P 'and the valley line Q-Q'.

  Here, some of the internal conductor patterns 12 and 13 extend toward the adjacent peak side line PP ′ or the valley side line QQ ′ and further beyond the lines PP ′ and QQ ′. It is formed, and its extended end constitutes extraction electrodes 17a and 17b.

  Finally, as shown in FIG. 9 (e), after the semi-curable insulating sheet 16 'is formed on the dielectric sheet 10, only the semi-curable insulating sheet 16' in the upper region of the internal conductor patterns 12 and 13 is formed. The semi-curable insulating sheet 16 'is removed in a state where the is left selectively. As a result, the inner conductor patterns 12 and 13 are covered with the semi-curable insulating sheet 16 ', and the lead electrodes 17a and 17b are exposed from the semi-curable insulating sheet 16'. Here, the semi-curable insulating sheet 16 'uses a composite resin made of an inorganic filler and an epoxy resin.

  Next, a method for folding the dielectric sheet 10 on which the inner conductor pattern has been formed will be described with reference to FIGS. In FIGS. 10A to 10C, only the dielectric sheet 10 is shown, and the internal conductor patterns 12 and 13 and the semi-curable insulating sheet 16 ′ are omitted.

  First, as shown in FIG. 10A, a plate-like plate whose bottom surface is narrowed along the peak side line PP ′ and the valley side line QQ ′ (not shown) sequentially from the end of the dielectric sheet 10. The dielectric sheet 10 is folded while applying the jig 60. After all of the dielectric sheet 10 is folded, as shown in FIG. 10B, pressing is performed from both sides of the folded dielectric sheet 10 until the semi-curable insulating sheets 16 ′ (not shown) come into contact with each other. . Finally, after being heated in a pressed state at a temperature of 200 ° C. for about 60 minutes and then cooled to room temperature, the semi-curable insulating sheets 16 ′ are fixed to each other, thereby completing the wiring board 100. .

  By the way, the technology for folding a flexible wiring board is disclosed in documents such as JP-A-11-330639, JP-A-2002-319750, US Pat. No. 6,121,676, etc., and any document is a feature of the present invention. It does not disclose or suggest a high-density wiring board in which wiring patterns (internal conductor patterns) arranged at a narrow pitch along the substrate plane direction are internally provided.

  Japanese Patent Laid-Open No. 11-330639 discloses a technique for continuously folding a film-like wiring sheet into a rectangular parallelepiped shape. However, the prior art discloses an electronic component mounted on the surface of a wiring sheet. The object is to realize a mounting substrate that is housed as compactly as possible, and there is no description regarding the configuration of the wiring pattern, and there is no description that suggests the configuration of the wiring pattern in the present invention.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible. For example, the case where the inner conductor patterns 12 and 13 are formed in a strip shape between the peak side line PP ′ and the valley side line QQ ′ of the dielectric sheet 10 has been described. By forming the pattern, it is possible to obtain a higher-density wiring board within a design range that does not increase the wiring resistance. Further, although the example in which the dielectric sheet 10 is continuously folded at a predetermined interval has been described, the folding interval may be changed for the purpose of, for example, matching the characteristic parameters of the signal line.

  Moreover, although the example which provided the internal conductor patterns 12 and 13 on both surfaces of the dielectric material sheet 10 is shown, an internal conductor pattern may be formed only in one side in consideration of restrictions, such as manufacturing cost. Although there is a restriction that the number of wirings is reduced by being single-sided, the same effect can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, a flexible wiring board with a high density and a high freedom degree of arrangement can be provided.

It is a figure which shows the structure of the flexible wiring board 100 which concerns on Embodiment 1 of this invention. It is a figure which shows the aspect of the whole arrangement | positioning of the flexible wiring board 100 which concerns on Embodiment 1 of this invention. (A)-(c) is a figure which shows the formation method of the flexible wiring board 100 which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the structure of the flexible wiring board 100 which concerns on Embodiment 1 of this invention. It is a top view which shows the structure of the dielectric material sheet before folding shaping | molding in the formation process of the flexible wiring board 110 which concerns on Embodiment 2 of this invention. It is a figure which shows the aspect of the whole arrangement | positioning of the flexible wiring board 110 which concerns on Embodiment 2 of this invention. (A)-(c) is a figure which shows the formation method of the flexible wiring board 120 which concerns on Embodiment 3 of this invention. It is sectional drawing which shows the structure of the flexible wiring board 120 which concerns on Embodiment 3 of this invention. (A)-(e) is a figure which shows the formation method of the dielectric material sheet concerning Embodiment 4 of this invention. It is a figure explaining the folding method of the dielectric material sheet concerning Embodiment 4 of this invention. It is a top view which shows the structure of the conventional flexible wiring board 200. FIG. It is sectional drawing which shows the aspect of the mounting | wearing in the apparatus of the conventional flexible wiring board 200. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Dielectric sheet 11 Dielectric layer 11a Connection part 12, 13 Internal conductor pattern 16 Insulating adhesive layer 17a, 17b Lead electrode 18 External connection electrode pad 100, 110, 120 Flexible wiring board

Claims (16)

A flexible wiring board having a plurality of wirings arranged in parallel,
A dielectric layer that is disposed along the opposing direction of both main surfaces of the substrate and is laminated in the substrate width direction; and
An internal conductor pattern provided on the surface of the plurality of dielectric layers as the plurality of wirings;
With
Adjacent dielectric layers are connected and formed integrally with each other at one end of both main surfaces of the substrate.
Each of the connecting portions of the adjacent dielectric layers is alternately provided on either one of the main surfaces of the substrate, so that the plurality of dielectric layers form a single dielectric sheet that is bent,
A part of the inner conductor pattern is exposed to the main surface of the wiring board by extending to the dielectric layer adjacent to the dielectric layer beyond the connecting portion of the dielectric layer where the inner conductor pattern is formed. Then, the exposed portion of the internal conductor pattern constitutes an external connection terminal on the substrate main surface.
A flexible wiring board characterized by that. The inner conductor pattern is provided in a band shape inside the substrate sandwiched between the connecting portions of both main surfaces of the dielectric layer.
The flexible wiring board according to claim 1. Of all the board length direction parts of the flexible wiring board, at least the board length direction part where the external connection terminal is provided, the adjacent dielectric layers are fixed and integrated in the board width direction. Yes,
The flexible wiring board according to claim 1. Of all the board length direction parts of the flexible wiring board that are required to be flexible, at least one board main surface side connection part of the connection parts is cut. Adjacent dielectric layers are separated;
The flexible wiring board according to claim 1. The inner conductor pattern is provided on both surfaces of the dielectric sheet;
The flexible wiring board according to claim 1. The inner conductor pattern on one side of the dielectric sheet is shielded by the inner conductor pattern on the other side.
The flexible wiring board according to claim 5. A part of the inner conductor pattern on both surfaces of the dielectric sheet extends beyond the connecting portion of the dielectric layer where the inner conductor pattern is formed to the dielectric layer adjacent to the dielectric layer. Exposed on both main surfaces of the substrate, each exposed portion of the internal conductor pattern constitutes the external connection terminal on both main surfaces of the wiring substrate,
The flexible wiring board according to claim 5. The adjacent external connection terminals are shifted from each other along the substrate length direction orthogonal to the substrate width direction and the opposing direction of both surfaces of the substrate.
The flexible wiring board according to claim 1. An external connection electrode pad connected to the external connection terminal, the external connection electrode pad is provided on the substrate main surface;
The flexible wiring board according to claim 1. The substrate width direction dimension of the external connection electrode pad is larger than the substrate width direction dimension of the external connection terminal.
The flexible wiring board according to claim 9. A dielectric sheet having a predetermined length and width is prepared, and crest-side lines and trough-side lines indicating that the dielectric sheet is a valley when viewed from one surface thereof are alternately and parallel to the length direction of the dielectric sheet. And a first step of virtually setting a predetermined interval;
A second step of forming, on at least one surface of the dielectric sheet, a strip-shaped internal conductor pattern located between the adjacent crest-side line and the trough-side line and parallel to the crest-side line / valley-side line;
The dielectric sheet is alternately folded along the mountain side line / valley side line so that the mountain side line has a mountain shape and the valley side line has a valley shape when viewed from the one surface, so that the mountain-shaped exposed surface is A third step of forming a flexible wiring board as one main surface;
Including
In the second step, the inner conductor pattern is formed such that a part of the inner conductor pattern extends outward beyond the peak line / valley line of the dielectric sheet, and the extension of the inner conductor pattern Part is exposed to the main surface of the wiring board after the third step to be an external connection terminal,
A method for producing a flexible wiring board, comprising: In the third step, when the dielectric sheets are alternately folded, at least the substrate length direction portion where the external connection terminal is provided among all the substrate length direction portions of the flexible wiring board. The dielectric sheets are fixed together and integrated in the substrate width direction.
The method for producing a flexible wiring board according to claim 11. After the third step, among all the substrate length direction portions, at least the flexibility of the flexible wiring board is required to place the dielectric sheet along the peak line or the valley side line. A step of partially cutting
The method for producing a flexible wiring board according to claim 11. In the second step, the extending portions of the adjacent internal conductor patterns are arranged so as to be shifted from each other along the peak line / valley line.
The method for producing a flexible wiring board according to claim 11. A step of forming an external connection electrode pad connected to the external connection terminal on the main surface of the substrate;
The method for producing a flexible wiring board according to claim 11. In the step of forming the external connection electrode pads connected to the external connection terminals on the substrate main surface, the external connection electrode pads are formed wider in the substrate width direction than the external connection terminals.
The method for manufacturing a flexible wiring board according to claim 15.

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