JP2007194459A - Flexible circuit substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make addition of excessive member for the countermeasure of disconnection unnecessary, and to prevent the breakage of an electrode pattern upon bending with high reliability. <P>SOLUTION: A wiring pattern formed of copper foil 105 of the rear surface side is electrically connected to a front surface side non electrolysis gold plating layer 104 through a through-hole 110, and, further, is electrically connected to the mounting land unit 206 of a main substrate 200. A rear surface side cover layer 109 is provided in a region inside of the rear surface side non-electrolysis gold plating layer 107. When the flexible substrate 100 is bent, the same is bent at the position of boundary Q of a mounting land 111 substantially. The wiring pattern is formed of the rear surface side copper foil 105 covered by the rear surface side cover layer 109 whereby the wiring pattern will not be disconnected thereby permitting the securing of reliability for bending. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flexible circuit board, and more particularly to a flexible circuit board used by being bent inside a housing of an electronic device or the like.

  For example, electronic devices that perform communication through an optical communication network are provided. The housing of such an electronic device is required to be further downsized in response to the demand for space saving, while the performance required for the electronic device is becoming increasingly sophisticated, and the electronic components mounted in the housing of the electronic device are It is getting more. As a means for solving the two conflicting propositions of miniaturization and high-density mounting, a plurality of circuit boards are three-dimensionally arranged in a casing, and each circuit board is a flexible board (hereinafter referred to as a flexible board). A form of electrical connection with a substrate) is generalized.

  In a conventional general form using a flexible substrate, a configuration in which the flexible substrate is bent at an acute angle while paying attention to the flexibility of the flexible substrate has not been adopted. In general, it can be said that a flexible substrate is generally applied to a movable part of an electronic device and expected to be durable.

On the other hand, with the miniaturization of the housing of the electronic device, a configuration has been proposed in which a flexible substrate is bent at an acute angle and a plurality of circuit substrates are connected in the shortest distance. Since the copper foil provided as a conductor on the flexible substrate is soft, it can be bent. Furthermore, if a rolled copper foil is used as the conductor, the reliability with respect to repeated bending is improved. Moreover, if the copper foil part is protected by the cover lay, the curvature radius of the copper foil part becomes large when the cover lay part is bent at an acute angle, and the reliability of the copper foil is further improved.
However, for example, a cover lay cannot be provided in a mounting land portion provided to connect a flexible substrate to a counterpart substrate, and a copper foil is exposed depending on the configuration. If the flexible substrate is bent in such a region, the copper foil may be disconnected.

  FIG. 5 is a main part configuration diagram for explaining a configuration example of a flexible substrate and a mechanism of disconnection. In the drawing, 400 is a flexible substrate, 401 is a flexible material, 402 is a copper foil, 403 is a nickel plating layer, 404 is An electroless gold plating layer, 405 is a surface side adhesive layer, 406 is a surface side cover lay, 407 is a back surface side adhesive layer, 408 is a back surface side cover lay, and 409 is a mounting land portion.

  The flexible substrate 400 of FIG. 5 includes a mounting land portion 409 that serves as a connection portion for a connection destination circuit board. Here, the surface on which the mounting land portion 409 is provided is the front surface, and the surface opposite to the mounting land portion 409 is the back surface. Further, the front end side (left side in FIG. 5) of the mounting land portion 409 of the flexible substrate 400 is defined as the outside, and the opposite direction (right side in FIG. 5) is defined as the inside. The same applies to embodiments of the present invention described later.

A copper foil 402 is laminated on the surface side of the flexible material 401, and a wiring pattern is formed by the copper foil 402. And the surface side coverlay 406 by the insulators, such as a polyimide for protecting the copper foil 402, is formed on the copper foil 402 via the surface side adhesive layer 405.
However, the surface side coverlay 406 is not formed on the mounting land portion 409 in order to electrically connect the flexible substrate 400 to another circuit substrate. In this case, in the mounting land portion 409, it is necessary to protect the copper foil 402 with another one in order to prevent oxidation of the copper foil 402.

  In general, in the mounting land portion 409, an electroless gold plating layer 404 is formed on the surface of the copper foil 402 via the nickel plating layer 403 in order to prevent the copper foil 402 from being oxidized. The nickel plating layer 403 is provided to improve the adhesion between the electroless gold plating layer 404 and the copper foil 402.

The electroless gold plating layer 404 may be formed to a thickness that does not expose at least the copper foil 402 to prevent oxidation, and generally has a thickness of 0.1 μm or less. On the other hand, the thickness of the nickel plating layer 403 is 3.0 to 8.0 μm. Incidentally, the thickness of the copper foil 402 is about 18 μm.
Further, on the back side of the flexible material 401, a back side coverlay 408 is laminated via a back side adhesive layer 407. On the back side, the back side coverlay 408 covers the entire area.

FIG. 6 is a diagram for explaining a configuration example of the flexible substrate 400 shown in FIG. 5 and the main substrate 200 connecting the flexible substrate 400. In FIG. 6, 200 is the main substrate, 201 is the main board base material, 202 Is a copper foil, 203 is a nickel plating layer, 204 is an electroless gold plating layer, 205 is a resist, and 206 is a mounting land portion.
The main substrate 200 has a wiring pattern formed of a copper foil 202 on the surface of a main board base 201 made of, for example, a glass epoxy material. The region excluding the mounting land portion 206 and the electrode portions other than the mounting land portion 206 is protected by the resist 205. In the region where the resist 205 is not formed, the electroless gold plating layer 204 is formed on the nickel plating layer 203 as in the case of the flexible substrate 400 described above.

  FIG. 7 is a diagram for explaining a state when the flexible board is connected to the main board. The mounting land part 409 of the flexible board 400 and the mounting land part of the main board 200 as shown in FIG. A configuration in which 206 is connected by solder 300 is shown. In this state, for example, the flexible substrate 400 is bent at an acute angle in the direction of arrow A in order to be mounted inside the housing of the electronic device.

  In this case, the flexible substrate 400 is bent at the inner outer edge portion (position P1 in FIG. 7) of the solder 300 that covers the mounting land portion 409. Since the region where the solder 300 is applied and the region covered with the surface side coverlay 406 are mechanically strong, the flexible substrate 400 is not bent, and other regions, ie, the surface side coverlay 406 are not bent. The flexible substrate 400 bends at the position P1 of the inner outer edge of the solder 300 in a region where no solder exists.

At the position P1 where the flexible substrate 400 is bent, the nickel plating layer 403 and the electroless gold plating layer 404 are formed on the pattern made of the copper foil 402.
In this configuration, since the nickel plating layer 403 is bent at an acute angle when the flexible substrate 400 is bent, the copper foil 402 and the nickel plating layer 403 are cracked, and in the worst case, the wiring pattern of the copper foil 402 is disconnected. It will occur.

FIG. 8 is a diagram for explaining a configuration example when the connection substrate of FIG. 7 is reinforced with an adhesive. In the figure, reference numeral 301 denotes an adhesive.
In order to cope with the occurrence of cracks in the copper foil 402 and the nickel plating layer 403, the solder 300 is applied in the region where the electroless gold plating layer 404 is exposed through the nickel plating layer 403 in the example of FIG. Adhesive 301 is applied and fixed so as to cover the unexposed area.

  However, if the adhesive 301 is used, the number of manufacturing steps increases, which is irrational. In this configuration, when the flexible substrate 400 is bent at an acute angle in the direction of arrow A, the bent position is the inner outer edge (position P2) of the application area of the adhesive 301. In this case, it does not bend at the inner outer edge portion (position P1) of the mounting land portion 409 as shown in FIG. 7 and is not suitable for high-density mounting.

In addition, the flexible substrate 400 may be bent in the direction of arrow B. In this case, the top and bottom of FIG. 7 or FIG. 8 is reversed at the time of mounting, and the flexible substrate 400 is placed below the main substrate 200 and the flexible substrate 400 is bent upward.
However, in this case, the position at which the flexible substrate 400 bends is further away from the mounting land portion 409 in the inner direction, making it unsuitable for high-density mounting.

  Regarding the connection configuration of the flexible substrate as described above, for example, Patent Document 1 discloses an electrode terminal so that the conductive pattern does not break when used by being connected to a lead electrode of an electrical component substrate and bent. A flexible substrate in which another cover film is further coated on the boundary portion between the cover and the cover film is disclosed.

  Patent Document 2 discloses a conductive connection method that reinforces a connection portion by electrically connecting a flexible substrate to a terminal of a liquid crystal panel substrate with a conductive adhesive, and then covering the flexible substrate with an ultraviolet curable resin and curing it with ultraviolet rays. ing.

Further, in Patent Document 3, a part of nickel plating and gold plating on a flexible substrate is covered with a cover lay, and an exposed region excluding a region connected as an electrode is protected by a terminal mold made of silicon resin. There has been disclosed a flexible circuit board in which stress that tends to concentrate on a bent portion in the vicinity of an edge is dispersed.
JP 2005-050971 A JP-A-5-061063 JP 2004-193466 A

  As described above, in the case of adopting a configuration in which a flexible substrate is bent at an acute angle and a plurality of circuit boards are connected at the shortest distance in response to a demand for downsizing and high-density mounting of an electronic device, the flexible substrate is bent at an acute angle. In some cases, cracks may occur in the nickel plating layer or the copper foil, causing problems such as disconnection.

  Moreover, in the flexible circuit board of the said patent document 1, the curvature radius at the time of bending becomes large by coat | covering another cover film in the boundary part of an electrode terminal part and a cover film. However, the configuration in which another cover film is further applied becomes unreasonable due to an increase in manufacturing steps. Further, if the cover film is covered in the direction of the outer side, the cover film is bent at a position where the cover film is not covered, so that there is a risk of disconnection. That is, the flexible substrate of Patent Document 1 can be bent only in a certain direction with the cover film covering side as the inside, and there is a problem that the versatility is poor.

  In addition, the conductive connection method of Patent Document 2 reinforces the connection portion between the flexible substrate and the external circuit with a UV curable resin, so that it is necessary to apply the UV curable resin after connection and cure it with ultraviolet rays, which increases the number of steps. Further, the conductive connection method of Patent Document 2 is essentially for protecting the connection portion between the flexible substrate and the external circuit, and cannot be applied to measures against disconnection due to bending of the flexible substrate.

  Furthermore, in order to disperse the stress which tends to concentrate on the bending location near the edge of the cover film, the flexible substrate of Patent Document 3 needs to be provided with a silicon resin for terminal molding. In this case, after the electrode terminal portion of the flexible substrate is connected to the electrical component substrate, the number of steps for applying the silicon resin of the terminal mold increases, which is irrational.

  The present invention has been made in view of the above-described circumstances. By using the electronic device by bending it at an acute angle inside a housing or the like of the electronic device, the housing can be miniaturized and the housing can be mounted at high density. It is an object of the present invention to provide a flexible substrate that does not require an extra member to be taken as a measure against disconnection, and that can prevent the electrode pattern from being damaged at the time of bending with high reliability.

  The flexible circuit board of the present invention has a first surface and a second surface opposite to the first surface, which is connected to a connected body having a mounting electrode portion. The flexible circuit board has a mounting land portion and a wiring portion. The mounting land portion has an electrode portion connected to the mounting electrode of the connected body on the first surface and the wiring portion on the second surface. It has a lead electrode portion that is electrically connected to the wiring pattern. The electrode portion and the lead electrode portion are connected by a through hole, and no wiring is drawn from the electrode portion to the first surface.

The wiring pattern extends to the mounting land portion on the second surface, and the flexible circuit board has a cover lay that protects the wiring pattern extending to the mounting land portion.
In addition, the electrode portion, the lead electrode portion, and the wiring pattern of the mounting land portion have a multilayer metal structure of copper / nickel / gold.

  According to the present invention, it is possible to reduce the size of the housing and achieve high-density mounting inside the housing by bending it at an acute angle inside the housing or the like of the electronic device. Therefore, it is possible to prevent the electrode pattern from being damaged at the time of bending with high reliability.

  In particular, according to the present invention, an electrode is drawn out to the back surface side through a through hole to form a wiring pattern, and a coverlay is disposed instead of a nickel layer at a position on the back surface side that would otherwise be bent. Thereby, even when the flexible substrate is bent, the hard nickel layer is not bent, and the wiring pattern such as the copper foil on which the nickel layer is laminated is not broken. At this time, it is not necessary to provide extra members such as a UV curable resin for reinforcing or stress dispersion, silicon resin, or other cover film, and a rational and highly reliable configuration can be provided. it can.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an embodiment of a flexible circuit board according to the present invention. In the figure, 100 is a flexible board (flexible board), 101 is a flexible material, 102 is a surface side copper foil, and 103 is a surface side nickel plating. 104, front side electroless gold plating layer, 105 back side copper foil, 106 back side nickel plating layer, 107 back side electroless gold plating layer, 108 back side adhesive layer, 109 back side coverlay, Reference numeral 110 denotes a through hole (via hole), and 111 denotes a mounting land portion.

  In a region to be the mounting land portion 111 of the flexible substrate 100, the surface side copper foil 102 is laminated on the surface of the flexible material 101, and the surface side electroless gold plating layer 104 is disposed thereon via the surface side nickel plating layer 103. Is formed. The surface-side nickel plating layer 103 is provided to improve the adhesion between the surface-side electroless gold plating layer 104 and the surface-side copper foil 102.

  A through hole 110 is provided in the mounting land portion 111. On the back surface side of the mounting land portion 111, a back surface side copper foil 105 is provided on the flexible material 101, and a wiring pattern is formed by the back surface side copper foil 105. That is, the wiring pattern formed by the back-side copper foil 105 is electrically connected to the front-side electroless gold plating layer 104 through the through-hole 110, and is further electrically connected to a mounting land portion of the main board described later. . The inside of the through hole 110 has a three-layer structure of copper / nickel / gold although not shown.

Further, a back side coverlay 109 for protecting the back side copper foil 105 is provided in a region inside the back side electroless gold plating layer 107 and the back side nickel plating layer 106. The back side coverlay 109 is laminated and fixed to the back side copper foil 105 by the back side adhesive layer 108.
Here, the inner edge of the region where the surface-side copper foil 102, the surface-side nickel plating layer 103, and the surface-side electroless gold plating layer 104 are laminated is defined as q. The edge q exists on a line in the depth direction of the paper surface of FIG. A surface passing through q and orthogonal to the surface direction of the flexible material 101 is defined as a boundary Q.

The boundary Q is a boundary across which the wiring pattern of the back side copper foil 105 crosses. At this time, in this embodiment, the back surface side coverlay 109 covers at least a part of the region corresponding to the back surface side of the electrode region of the mounting land portion 111, and particularly corresponds to the back surface side of the mounting land portion 111. Of the boundary line between the region and another region, a region including at least the boundary Q across which the wiring pattern connected to the through hole 110 crosses is covered.
The region corresponding to the back surface side of the mounting land portion 111 is a region on the back surface side in which the electrode region of the mounting land portion 111 is projected in a direction orthogonal to the surface direction of the flexible substrate 100.

FIG. 2 is a diagram for explaining a configuration example of the flexible substrate 100 shown in FIG. 1 and a main substrate 200 that connects the flexible substrate 100.
The main substrate 200 has the same configuration as that of FIG. 6 described in the conventional example. That is, a wiring pattern is formed by the copper foil 202 on the main board base 201 made of glass epoxy material or the like. The region excluding the mounting land portion 206 and the electrode portions other than the mounting land portion 206 is protected by the resist 205. In the region where the resist 205 is not applied, an electrode made of the electroless gold plating layer 204 is formed on the nickel plating layer 203 as in the case of the flexible substrate 100 described above.

  The mounting land portion 111 of the flexible substrate 100 has a structure equivalent to or smaller than the mounting land portion 206 of the main substrate 200, and the flexible substrate 100 and the main substrate 200 are electrically connected to each other by the respective mounting land portions 111 and 206. Is done.

  FIG. 3 is a diagram for explaining a state when the flexible board is connected to the main board and mounted. The mounting land portion 111 of the flexible board 100 as shown in FIG. A configuration in which the mounting land portion 206 is connected by solder 300 is shown. In this state, for example, the flexible substrate 100 is bent at an acute angle in order to be mounted inside a housing of an electronic device.

In the configuration of the present embodiment, when the flexible substrate 100 is bent, the flexible substrate 100 is bent substantially at the position of the boundary Q of the mounting land portion 111.
Since the boundary line Q of the flexible substrate 100 is at the inner end position of the front surface side nickel plating layer 103, the front surface side nickel plating layer 103 and the rear surface side nickel plating layer 106 are not bent. Further, since the wiring pattern is formed of the back surface side copper foil 105 covered with the back surface side coverlay 109, the wiring pattern is not disconnected and the reliability of bending can be ensured.

  Further, in the above configuration, it is assumed that the position of the flexible substrate 100 and the main substrate 200 is relatively shifted due to a decrease in alignment accuracy between the main substrate 200 and the flexible substrate 100. For example, in FIG. 3, the flexible substrate 100 is connected to the main substrate 200 while being shifted to the right (inside). At this time, the surface side electroless gold plating layer 104 of the flexible substrate 100 is applied to the solder 300. An uncovered part occurs.

  In such a case, when the flexible substrate 100 is bent immediately inside the connection portion by the solder 300, the possibility of cracks in the surface-side nickel plating layer 103 cannot be denied. However, even in such a case, the front-side nickel-plated layer 103 is not directly laminated on the wiring by the back-side copper foil 105, so the electrical connection characteristics between the flexible substrate 100 and the main substrate 200 are There will be no impact.

  FIG. 4 is a plan view of the main part in the vicinity of the mounting land portion of the flexible board, FIG. 4A is a diagram showing the surface side (mounting land side) of the flexible board, and FIG. 4B is the mounting land of the flexible board. It is a figure which shows the back surface side (non-connection side) of a part. In FIG. 4, 112 is a front surface side coverlay applied to the front surface side of the flexible substrate, 120 is an electrode portion formed on the land mounting portion on the front surface side, 120 'is another electrode portion, and 121 is a lead electrode on the back surface side Part.

As shown in FIG. 4A, the mounting land portion 111 is formed on the surface side of the flexible substrate 100, and the electrode portion 120 is patterned. The electrode portion 120 has a multilayer metal structure including the surface-side copper foil 102, the surface-side nickel plating layer 103, and the surface-side electroless gold plating layer 104. The electrode part 120 is solder-connected to the mounting land part 206 of the main board 200.
Further, in the example of FIG. 4, since another electrode portion 120 ′ is provided inside the mounting land portion 111 on the front side of the flexible substrate 100, a surface side coverlay 112 is provided to protect this. .

The electrode part 120 on the front surface side is drawn out to the back surface side through the through hole 110. The extraction electrode portion 121 shown in FIG. 4B is obtained by extracting the electrode portion 120 of FIG. The lead electrode portion 121 has a multilayer metal structure composed of a back side copper foil 105, a back side nickel plating layer 106, and a back side electroless gold plating layer 107.
Each electrode part 120 is formed with a dimension of about 0.5 to 0.7 mm (width) × 1 mm or less (length), for example.

As shown in FIG. 4A, the entire surface of the mounting land portion 111 is exposed without being covered by the front surface side coverlay 112 on the front surface side. In this case, the surface side cover lay 112 covers the position of the boundary Q of the inner end edge portion of the mounting land portion 111.
On the other hand, on the back surface side, a portion of the back surface region corresponding to the mounting land portion 111 is covered by the cover lay 109 on the back surface side except for some predetermined regions. The coverlay 109 is provided so as to surround the region where the extraction electrode part 121 is arranged beyond the position of the boundary Q.

That is, as described above, the cover lay 109 on the back surface side covers at least a part of the region corresponding to the back surface side of the electrode region of the mounting land portion 111, and particularly the region corresponding to the back surface side of the mounting land portion 111. And a region including at least the boundary Q crossed by the wiring pattern connected to the through hole 110 among the boundaries between the other regions.
In this case, the entire area may be covered with the cover lay 109 on the back surface side, but in this example, it is necessary to raise the temperature from the back surface side when soldering the front surface side. Therefore, the coverlay 109 is not provided in that portion.

It is a section lineblock diagram showing one embodiment of a flexible circuit board by the present invention. It is a figure for demonstrating the structural example of the flexible substrate shown in FIG. 1, and the main board | substrate which connects a flexible substrate. It is a figure for demonstrating a state when a flexible substrate is connected and mounted with respect to the main substrate. It is a principal part top view of the mounting land part vicinity of a flexible substrate. It is a principal part block diagram for demonstrating the structural example of a flexible substrate, and the mechanism of a disconnection. It is a figure for demonstrating the structural example of the main board | substrate which connects a flexible substrate shown in FIG. 5, and a flexible substrate. It is a figure for demonstrating a state when a flexible substrate is connected with respect to the main substrate. It is a figure for demonstrating the structural example when the connection board | substrate of FIG. 7 is reinforced with an adhesive agent.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Flexible board, 101 ... Flexible material, 102 ... Surface side copper foil, 103 ... Surface side nickel plating layer, 104 ... Surface side electroless gold plating layer, 105 ... Back side copper foil, 106 ... Back side nickel plating layer, 107 ... back side electroless gold plating layer, 108 ... back side adhesive layer, 109 ... back side cover lay, 110 ... through hole, 111 ... mounting land part, 112 ... front side cover lay, 120 ... electrode part, 121 ... extraction electrode , 200 ... main board, 201 ... main board base material, 202 ... copper foil, 203 ... nickel plating layer, 204 ... electroless gold plating layer, 205 ... resist, 206 ... mounting land, 300 ... solder, 301 ... adhesive , 400 ... flexible substrate, 401 ... flexible material, 402 ... copper foil, 403 ... nickel plating layer, 404 ... electroless gold plating layer, 405 ... surface side Chakuzaiso, 406 ... surface coverlay, 407 ... rear surface-side adhesive layer, 408 ... rear surface side cover lay, 409 ... mounting land portion.

Claims (3)

A flexible circuit board having a first surface and a second surface opposite to the first surface connected to a connected body having a mounting electrode portion,
A mounting land portion and a wiring portion;
The mounting land portion has an electrode portion connected to the mounting electrode of the connected body on the first surface, and a lead electrode portion electrically connected to the wiring pattern of the wiring portion on the second surface,
The electrode part and the lead electrode part are connected by a through hole,
A flexible circuit board, wherein no wiring is drawn from the electrode portion to the first surface. The wiring pattern extends to the mounting land portion on the second surface,
The flexible circuit board according to claim 1, further comprising a cover lay that protects a wiring pattern extending to the mounting land portion.   The flexible circuit board according to claim 1, wherein the electrode portion of the mounting land portion, the lead electrode portion, and the wiring pattern have a multilayer metal structure of copper / nickel / gold.

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