JP2009076663A - Flexible circuit board, method for manufacturing same, and electronic apparatus using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible circuit board capable of improving the bending property of the board at the bending portion of the flexible circuit board. <P>SOLUTION: This invention provides the flexible circuit board including: a base material containing a first portion and a second portion separated by the bending portion, wherein the base material has a first surface and a second surface, a plurality of thin portions on the second surface side of the bending portion that extend from near one end surface of the base material to near the other end surface in a direction that crosses the bending direction, and supporting portions located between a plurality of thin portions that adjoin each other, and furthermore the base material is composed of flexible material whose thin portion width in the bending direction is greater than that of the supporting portion in the bending direction; a circuit body composed of conductive material formed in the first surface of the base material to which the circuit body is adhered; and a cover layer arranged on the first surface to cover at least part of the surface of the circuit body. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a flexible circuit board, and more particularly to a flexible circuit board used in a bent state in applications such as connection between a liquid crystal display panel of a liquid crystal display device and a printed wiring board.

  A flexible circuit board produced by printing a circuit body on a flexible base material such as a polymer is used inside a display device such as a liquid crystal television or an electronic device such as a mobile phone because of its flexible properties. Widely used as wiring. In order to reduce the size and thickness of these electronic devices, the flexible circuit board is often used in a bent state or a bent state inside the device.

  The flexible circuit board can be bent easily, but since it is elastically deformed in the bent state, a repulsive force is generated to return from the bent state to the straight state. When this repulsive force is large, the assembling workability is deteriorated when the electronic equipment is assembled. Moreover, when it is connected to a printed circuit board or the like at both ends, the repulsive force may act in the direction in which the connection portion is peeled off, thereby reducing the long-term reliability of the connection portion.

  In order to cope with such a problem, conventionally, the following methods for improving the flexibility of the flexible circuit board have been proposed.

  Patent Document 1 states that “at least one of an insulating base material and a surface coating material in a bent portion of a flexible circuit board having a required circuit conductor and having a surface coating material is irradiated with an excimer laser beam or the like. A circuit board is described, in which bent grooves are formed with the required depth and width that do not reach the circuit conductor.

  Patent Document 2 includes “a flexible portion made of a conductive thin film that forms a circuit pattern, and a base material laminated portion in which a base material is laminated on the conductive thin film, and the conductive thin film is a single material at least in the flexible portion. A printed wiring board is described which is covered by an insulating material layer consisting of

  Also, instead of reducing the thickness of a specific portion of the flexible circuit board, a very thin base material is sold. <Kapton> polyimide film model number 50H available from DuPont has a thickness of 12.5 μm.

  There are several known methods for providing a cover layer on a circuit body formed on a flexible substrate in a desired pattern. Among them, a liquid solder resist having a certain degree of viscosity on a desired part of the circuit body surface by silk screen printing due to low cost of components and compatibility with a series of processes for producing a flexible circuit board. The method of apply | coating is used suitably. The applied solder resist is then cured by irradiation with ultraviolet rays or the like to form a cover layer.

JP 05-335696 A JP 2006-210771 A

  In the case where the bending portion has one folding groove, the folding groove may be configured to be long in the folding direction in order to sufficiently improve the flexibility. When a silk screen mask on which a desired pattern is formed is placed on a bent portion of a flexible circuit board having one bent groove, the substrate of the bent portion is bent because the substrate is thin, and the silk screen A situation occurs in which the mask cannot follow the substrate surface. For this reason, the distance between the silk screen mask and the surface of the base material is not constant, thickness unevenness occurs in the solder resist layer on the substrate, and the liquid solder resist is applied even to an unintended region on the base material. That happens. As a result, there arises a problem that the thickness of the cover layer obtained by curing the solder resist layer is not uniform or the cover layer cannot be formed with a desired pattern. This phenomenon is more noticeable as the folding groove becomes longer in the folding direction.

  Moreover, in the order of removing the base material in the bent portion after providing the cover layer, it is necessary to repeat the process of removing a part of the base material again for the base material that has been processed once. In this case, ablation with a laser beam is generally performed. However, since this step scans the substrate with the laser beam, only one substrate can be processed at a time, and the processing cost is not low. Further, since the debris of the base material removed by ablation adheres to the substrate, it is necessary to provide a cleaning process to remove the adhered smear. Although the bent portion can also be formed by etching, it is not preferable because a series of steps of applying, exposing, developing and removing the photoresist needs to be repeated.

  Thus, in the method of providing the liquid solder resist which becomes a cover layer on the surface of the base material after providing the bent portion in advance on the base material, there arises a problem in the quality of the printed solder resist layer.

  If a very thin base material is used so that the flexibility of the flexible circuit board does not become a problem, the rigidity of the entire flexible circuit board is lowered. For this reason, a flexible circuit board becomes difficult to handle, and there is a possibility that workability in a process of incorporating in an electronic device may be deteriorated.

  Therefore, an object of the present invention is to provide a flexible circuit board that improves the bendability at the bent portion without deteriorating the handleability of the flexible circuit board. A further object of the present invention is to provide a flexible circuit board capable of forming a cover layer with less thickness unevenness in a desired region by silk screen printing, and a method for manufacturing the flexible circuit board and its flexibility An object is to provide an electronic device using a circuit board.

In one embodiment of the present invention, the present invention is a substrate made of a conductive material including a first portion and a second portion separated by a bent portion, and the substrate has a first surface and a second surface. And a plurality of thin portions adjacent to the folding direction on the second surface side of the bent portion, the thin portions extending in a direction intersecting the bending direction, and the plurality of adjacent thin portions A base material made of a flexible material having a support portion between the thin-walled portions, the width of the thin-walled portion in the folding direction being larger than the width of the support portion in the folding direction;
A circuit body made of a conductive material formed in close contact with the first surface of the substrate;
A cover layer provided on the first surface so as to cover at least part of the surface of the circuit body;
A flexible circuit board is provided.

In another embodiment, the present invention is a base material including a first portion and a second portion separated by a bent portion, and the base material has a first surface and a second surface, and the bent portion And a base material made of a flexible material having one thin part on the second surface side and one or more support parts on the thin part,
A circuit body made of a conductive material formed in close contact with the first surface of the substrate;
A cover layer provided on the first surface of the base material so as to cover at least a part of the surface of the circuit body;
A flexible circuit board is provided.

  In one embodiment thereof, the present invention provides a method for manufacturing a flexible circuit board, which includes the following steps.

a. Preparing a substrate b. Forming a circuit body on the substrate c. A part of the base material is removed from the second surface side of the base material to be a bent portion, and from the vicinity of one side end surface of the base material to the vicinity of the other side end surface in a direction crossing the bending direction A plurality of thin wall portions that extend and a support portion between the plurality of thin wall portions adjacent to each other so that the width of the thin wall portion in the folding direction is larger than the width of the support portion in the folding direction. Forming into d. Providing a cover layer on the substrate surface so as to cover at least a part of the circuit body;

  Furthermore, the present invention provides, as another embodiment, a method for manufacturing a flexible circuit board including the following steps.

a. Preparing a substrate b. Forming a circuit body on the substrate c. Removing a part of the base material from the second surface side of the base material to be a bent portion to form one thin portion and one or more support portions in the thin portion; d. Providing a cover layer on the substrate surface so as to cover at least a part of the circuit body;

  According to the present invention, a flexible circuit board is provided in which the flexibility of the board is improved without impairing the handleability. Furthermore, the present invention provides a flexible circuit board in which the bending of a base material when applying a liquid solder resist by silk screen printing is reduced, and the deterioration of the quality of the obtained cover layer is effectively suppressed.

  Several embodiments of a flexible circuit board according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a top view of a first embodiment of a flexible circuit board according to the present invention. The flexible circuit board 10 includes a base material 12 made of a flexible material and an electrically conductive circuit body 14 provided on the surface of the base material. The base material 12 has a film-like form. The flexible circuit board 10 further has a cover layer 16 obtained by curing the solder resist on a part on the circuit body 14 and a part on the substrate 12.

  2 and 3 are a sectional view and a bottom view of the flexible circuit board 10 shown in FIG. 1, respectively. The base material 12 has a bent portion 20 at the approximate center of the bending direction 18 of the flexible circuit board 10, and a first portion 22 is provided at one end of the bending direction 18 and a second portion 24 is provided at the other end. Have. The bent portion 20 is a portion that gives higher flexibility to the base material 12 by partially deleting the material of the base material 12. The bending part 20 does not need to be in the geometric center of the base material 12 in the bending direction 18 and may be located so as to deviate to either the first part side or the second part side. The first portion 22 and the second portion 24 are portions that can be connected to a printed circuit board or the like to which the flexible circuit board 10 is electrically connected. The base material 12 further intersects the first surface 26 on which the circuit body 14 is formed, the second surface 28 that is the back surface thereof, and both the first surface 26 and the second surface 28, and is a flexible circuit board. 10 side end faces 30 and 31 substantially parallel to the bending direction 18.

  The substrate 12 may be a single layer substrate made of a single film or a multilayer film in which a plurality of films are laminated. Although the base material 12 can be formed from various materials that can impart flexibility to the base material, it is usually advantageous to form the base material 12 from an insulating resin material into a film form by an arbitrary forming method. is there. Examples of the resin material suitable for the substrate include polyimide resin, liquid crystal polymer, polyethylene terephthalate, and polyethylene naphthalate. In particular, a polyimide resin is suitable. The base material can be used in various thicknesses depending on the configuration and use of the flexible circuit board. When the base material becomes thin, the rigidity is lowered, and there is a possibility that the handleability may be compromised or the substrate may be easily damaged. When the substrate becomes thicker, it goes against weight reduction. The thickness of the substrate is typically about 15 μm or more, about 300 μm or more, more preferably about 25 μm or more, and about 125 μm or less. Further, the base material is usually formed as a long object, preferably wound around a core, stored and transported, and unwound and used when the flexible circuit board is manufactured.

  The bent portion 20 has a plurality of thin portions 32 extending in a direction perpendicular to the bending direction 18 of the base material 12 and ends at both side end portions 30 and 31 of the base material 12 sandwiched between the thin portions 32. The supporting portion 34 is provided on the second surface 28 side of the substrate 12.

  The thin portion 32 is a portion that is thinner than the thickness of the base material 12, and includes a third surface 36 that forms a plane substantially parallel to the second surface, and a side wall 38 that connects the third surface and the second surface. ing. In other words, the bent portion includes a plurality of grooves 39, and the grooves 39 are defined by a bottom surface (third surface 36) and two side walls 38 arranged to face each other. The thin portion 32 can be provided by chemically or physically removing a part of the substrate 12 on the second surface 28 side. The side walls 38 are inclined so as to be separated from each other as the two side walls 38 facing each other through the thin portion 32 move from the third surface 36 toward the second surface 28. A surface having such an inclination can be easily formed by forming the thin portion 32 by a chemical method by etching. The side wall 38 may be perpendicular to the second surface 28 of the substrate, but if the side wall 38 is inclined, the boundary between the support portion 34 and the thin portion 32 when the flexible circuit board 10 is folded. The change in rigidity at the end becomes gradual, and the flexible circuit board 10 can be prevented from bending sharply at the boundary. The inclination of the side wall 38 may be any inclination, but the inclination angle α is preferably an obtuse angle in order to prevent the flexible circuit board 10 from being sharply bent. The inclination angle α is preferably 100 degrees or more and 175 degrees or less. More preferably, the inclination angle α is 135 degrees or more. Note that the inclination angle α is an angle formed by the third surface 36 of the thin portion 32 and the side wall 38.

  The support part 34 is a part of the base material 12 having a thickness larger than that of the thin part 32. The upper end surface 40 of the support portion 34 is substantially flush with the second surface 28 of the substrate 12. That is, the support portion 34 is a portion that separates two adjacent grooves 39. When the liquid solder resist is applied by a printing process, which will be described later, the support part 34 comes into contact with the plane on which the base material 12 is disposed, and suppresses the bending of the first surface 26 of the base material 12 in that process. Thereby, the clearance gap in the bending part of a silk screen mask and the base material 12 can be made substantially constant. The upper end surface 40 is usually formed by using the second surface 28 of the substrate 12 as it is, but the upper end surface 40 may be configured to be lower than the second surface 28.

  The cross-sectional shape of the groove 39 defined by one thin portion 32 and two side walls 38 adjacent to each other across the thin portion 32 is not limited to the trapezoid as shown in FIG. 2, but is rectangular, V-shaped, thin A shape such as a U-shape in which the thickness of the portion continuously changes can be used. Depending on the cross-sectional shape of the groove 39, for example, in the case of a V-shaped cross-section, the thin-walled third surface 36 may not be substantially present. In the present embodiment, the thin portion 32 reaches the both end surfaces 30 and 31 of the base material 12, but the thin portion does not need to reach the both end surfaces 30 and 31. That is, a structure in which the thin portion 32 terminates in the vicinity of both side end faces 30 and 31 of the substrate 12 is also possible. The vicinity of the side end faces 30 and 31 is a position that is a finite length away from the side end faces 30 and 31 and the width of the base material 12 (the shortest distance between the side end faces 30 and 31 in the direction intersecting the bending direction). It is a position that is not farther than 1/3 of the distance.

  The width W in the bending direction 18 of the support portion 34 and the width X and thickness of the thin portion 32 in the bending direction 18 are appropriately set according to the situation in which the flexible circuit board 10 is used. The thinner the thin portion 32 is, the better the flexibility of the flexible circuit board 10 is. However, it is usually 25 μm or less, more preferably 15 μm or less. On the other hand, the thin portion 32 preferably has a thickness of 5 μm or more, more preferably 10 μm or more. If it is thinner than this, the substrate may be damaged during handling. Further, when the thin portion 32 is processed by etching, it is preferable that the thickness of the thin portion 32 is not more than half of the thickness of the substrate 12. This is because if the substrate 12 is provided with a through-hole or the like, if the etching is performed from both sides of the substrate 12, the through-hole can be processed simultaneously with the thin portion 32 processing.

  The width X of the thin-walled portion 32 varies depending on the situation in which it is used, but if it is too wide, the deflection of the first surface 26 of the substrate 12 is not sufficiently suppressed. If the width X of the thin portion 32 is too narrow, the flexibility of the substrate 12 cannot be effectively improved. Therefore, the width X of the thin portion is usually about 2 mm or less and about 0.1 mm or more. More preferably, it is about 0.9 mm or less, and is about 0.4 mm or more.

  In order to efficiently improve the flexibility, the width X of the thin portion is usually set wider than the support portion width W. The width X of the thin portion is a distance between points (lines) at which the two side walls 38 facing each other across the thin portion 32 intersect the second surface 28 or the upper end surface 40. Similarly, the width W of the support portion is defined as a distance between points (lines) where the upper end surface 40 of one support portion intersects the side wall 38 closest to the support portion 34.

  The width X of the thin portion 32 and the width W of the support portion 34 may be uniform over the entire bent portion 20 or may be uneven. If these are made uniform, the flexible circuit board 10 can be bent with a more uniform bending radius in the entire bent portion 20. Conversely, when it is desired to partially change the bending radius, it can be adjusted by setting these unevenly.

  The thin wall portion 32 can be formed by removing the base material by various physical and chemical methods known to those skilled in the art. These methods include laser ablation by indirect or direct exposure and etching that selectively dissolves a portion exposed from the photoresist layer formed on the substrate 12 with a solution. In order to form the thin portion 32 of the present invention, etching can be preferably used among them. When the thin portion 32 is formed by etching, it is efficient because the shape of the base material 12 other than the thin portion 32 can be processed simultaneously. Also, unlike ablation, there is no smear, so there is no need to add a smear removal step. In addition, when the side wall 38 of the thin portion 32 is provided with an inclination, the inclined side wall 38 can be easily formed from the dissolution characteristics of etching.

  The circuit body 14 is a conductive circuit formed in close contact with the base material 12 in an arbitrary pattern so that the flexible circuit board 10 can perform a desired electrical function. A plurality of circuit bodies 14 are formed on the first surface 26 of the substrate 12 so as to conduct between the first portion 22 and the second portion 24. The circuit body 14 can also be provided on the substrate 12 via an adhesive layer. The circuit body 14 can further have a pattern for arranging electronic components such as ICs on the circuit body 14. The circuit body 14 can also be formed on the second surface 28 of each of the first portion 22 and the second portion 24 of the substrate 12. In this case, in order to conduct the circuit body 14 on the first surface 26 and the circuit body 14 on the second surface 28, an interlayer conduction hole called a via hole can be provided in the base material 12.

  Although the circuit body 14 can be comprised from arbitrary electrically-conductive materials, copper, aluminum, etc. are used suitably. In addition, in order to increase the reliability of electrical connection with a printed circuit board or the like, another metal, for example, a metal made of gold or tin, is provided on the surface of the circuit body 14 which is an electrical connection part with another circuit board or the like A film can be formed.

  The circuit body can be used in various thicknesses depending on the configuration of the flexible circuit board, the configuration of the circuit body, etc., but is usually about 50 μm or less, preferably in the range of about 5 to 40 μm. More preferably, it is in the range of about 10 to 30 μm.

  A cover layer 16 is provided on the surface of the base material 12 except for both end portions serving as contacts with other substrates of the circuit body 14 so that the circuit bodies 14 are not short-circuited with each other by solder. The cover layer 16 can be provided so as to cover the entire surface of the base material 12, and so as to cover only an arbitrary region excluding an electrical junction with a printed circuit board or an IC chip as in this embodiment. It can also be provided.

  In the flexible circuit board of the present invention, the cover layer 16 is formed by applying a liquid solder resist onto a substrate by silk screen printing and then curing it. As the liquid solder resist, various existing solder resists such as photo-curing and thermosetting can be used. In the silk screen printing method, a silk screen mask prepared so that the liquid solder resist is applied only to a desired area is placed on the object (base material), and the liquid solder resist is passed through the silk screen mask. This is a method of transferring to the surface of an object (base material). Silk screen printing has the merit that the material cost is lower than the method of laminating a solder resist film, and a cover layer can be easily provided selectively only in an arbitrary region. In order to apply the solder resist uniformly and only in a desired region by silk screen printing, it is necessary to adhere the silk screen mask to the object to be printed. If the silk screen mask is not partially adhered to the object to be printed, the solder resist coating thickness may increase at that portion, or the solder resist may be applied to an unintended region in some cases. Therefore, if the support part 34 is arrange | positioned in the bending part 20 and the bending of the thin part 32 is suppressed, it will be effective in prevention of the fall of the quality of silk screen printing.

  The liquid solder resist printed on the substrate is then cured by heat or light to form the cover layer 16. The thickness of the cover layer 16 is appropriately set depending on the characteristics of the liquid solder resist used and the usage state of the flexible circuit board, but is usually 5 μm or more and 40 μm or less. In order to exhibit the effect of the present invention more effectively, it is preferable to make the flexibility of the cover layer 16 larger than the bending flexibility of the substrate 12. For this purpose, adjustment is possible by reducing the elastic modulus of the material constituting the cover layer 16 or by reducing the thickness or / and the coating area of the cover layer 16. This is because, by any method, a decrease in the flexibility of the flexible circuit board can be minimized without providing the cover layer 16 with a bent portion similar to the present invention.

  A reinforcing plate may be used in combination with the flexible circuit board 10 of the present invention as necessary. The reinforcing plate is usually attached to the surface of the base member 12 where the circuit body 14 is not provided in association with the pattern of the circuit body 14. The reinforcing plate is attached using an empty area in which the circuit body 14 and other functional elements are not formed. Therefore, the reinforcing plate can be arranged in any continuous or discontinuous pattern. For example, the reinforcing plate pattern includes, for example, a rectangle, an L shape, and a circle. Any pattern can be easily formed by using a conventional technique such as punching, preferably from a sheet-like reinforcing plate. Examples of the location of the reinforcing plate include a connector portion.

  FIG. 4 is a diagram schematically showing, as an example, a portion of a liquid crystal display device 70 using a flexible circuit board according to the present invention. A backlight 74 is disposed on the back surface of the liquid crystal panel 72, and a drive circuit board 76 for driving the liquid crystal panel is further provided behind the backlight. In order to electrically connect the drive circuit board 76 and the liquid crystal panel 72, the flexible circuit board 10 is used. The flexible circuit board 10 also has a circuit body 14 'on the second surface side, and the circuit body 14' and the circuit body 14 on the first surface side are electrically connected by a via hole (not shown). Yes. The flexible circuit board 10 is electrically and mechanically connected to the liquid crystal panel 72 at one end and the drive circuit board 76 at the other end, and is bent at the bent portion 20. Used in. In FIG. 4, the second surface 28 of the flexible circuit board 10 is used with the second surface 28 facing inward, but the second surface 28 may be used with the second surface 28 facing outward.

  FIG. 5 shows a bottom view of the flexible circuit board 10a according to the second embodiment of the present invention. In the present embodiment, the bent portion 20a has a plurality of groove-shaped thin portions 32a, and between the support portions 34a and between the support portions 34a, the first portion 22a, and the second portion 24a is a connecting portion (support portion) 46a. Are connected by In other words, in this embodiment, the thin portion 32 (groove 39) of the first embodiment is divided into two by the connecting portion (support portion) 46a.

  With such a configuration, the connecting portion contributes to suppressing the base material 12a from being bent sharply at the boundary between the support portion 34a and the thin portion 32a when bent. In addition, when the cover layer is printed, the connecting portion 46a also acts in the same manner as the support portion 34a, and effectively suppresses the bending of the first surface 26a.

  In FIG. 5, the plurality of connecting portions 46a are arranged in a straight line in the bending direction, but each connecting portion 46a may be arranged at a different position in the width direction of the base material 12a. Furthermore, a plurality of connecting portions 46a may be arranged in parallel.

  In the embodiment of FIG. 5, the width of each connecting portion 46a is approximately constant, but the width can be changed. For example, the width can be made narrowest at the center of the bending direction 18a of the connecting portion 46a, and the width can be increased as the distance from the supporting portion 34a is approached.

  6 and 7 show some examples of further embodiments of the present invention.

  FIG. 6 is a bottom view of the flexible circuit board 10b according to the third embodiment of the present invention. In the present embodiment, a plurality of island-shaped support portions 34b are arranged in two rows in the bending direction 18b of the flexible circuit board 10b in one thin portion 32b. In other words, the flexible circuit board 10b of the present embodiment includes one concave portion (thin wall portion 32b) and a plurality of pillars (island-like support portions 34b) in the bent portion 20b. The island shape is a state where the entire outer periphery 41b of the upper end surface 40b of one support portion 34b is in contact with the one side wall 38b of the thin portion 32b. With respect to the position in the bending direction 18b, the support portions 34b are arranged such that one row of the support portions 34b is positioned between two adjacent support portions 34b in adjacent rows. That is, the support portions 34b of the two adjacent rows are alternately arranged in the bending direction 18b. In this embodiment, since the area | region of a thin part can further be expanded compared with 1st and 2nd embodiment, the flexibility of a flexible circuit board can be improved more. In addition, since the support portions 34b are arranged alternately, the bent portions are compared with the case where the support portions 34b are arranged in a row or when the support portions in the two rows are aligned with respect to the position in the folding direction. Flexibility becomes more uniform in the bending direction.

  FIG. 7 is a bottom view of the flexible circuit board 10c according to the fourth embodiment of the present invention. The bent portion 20c has one thin portion 32c, and a plurality of support portions 34c are arranged on the thin portion 32c. As in the embodiment shown in FIG. 6, the support portions 34 c are alternately arranged with respect to the positions in the bending direction 18 c of the support portions 34 c in the adjacent rows. In the present embodiment, the support portion 34c extends from the one side end 30c or 31c of the base material 12c toward the center in the width direction of the base material 12c, and the tip ends near the center in the width direction of the base material 12c. . Also in the flexible circuit board of this embodiment, the bending property of the bent portion is further improved, and the bending rigidity of the bent portion becomes more uniform in the bending direction, particularly when the bending radius is small. Steep bending of the flexible circuit board 10c can be effectively prevented.

  The third and fourth embodiments can further include a connecting portion to connect between the support portions and / or the support portion and the first portion or the second portion. It is also possible to combine two or more of these embodiments. Of course, it is also possible to arrange the support portions in a form in which the support portions are not arranged alternately or in a row in the bending direction.

  Next, a preferred example of the method for producing a flexible circuit board of the present invention will be described using the flexible circuit board 10 of the first embodiment as an example.

  First, a base material 12 formed from an arbitrary material is prepared. In order to efficiently produce the flexible circuit board 10 of the present invention, it is preferable in terms of production efficiency that the long substrate 12 is continuously processed.

  Next, metallization processing is performed on one surface of the substrate 12 by sputtering. It is also possible to use a substrate whose surface has been previously metallized, in which case the metallization step can be omitted. Then, a copper (Cu) layer that becomes the circuit body 14 is deposited on the entire first surface 26 of the substrate 12 by copper sulfate plating. The thickness of copper is about 1-7 μm.

  Next, a photoresist is applied to both surfaces of the substrate 12 over the entire surface. As the photoresist, for example, a liquid resist or a dry film resist can be used. After applying the photoresist, exposure is performed through a photomask, and further development is performed. As a result of the exposure and development, the photoresist at the portion corresponding to the place where the circuit body 14 is to be formed is removed from the first surface 26 of the base material 12 and the photoresist remains at other portions. Further, the photoresist corresponding to the thin portion 32 of the bent portion 20 is removed from the second surface 28 of the base material 12 and the remaining photoresist remains.

  On the first surface 26 of the substrate 12, additional copper is deposited on the surface exposed from the photoresist (copper plating surface) by copper plating. Copper plating can be performed on the same conditions as said copper plating. By this additional plating step, a copper layer having a thickness of about 8 to 50 μm is obtained at the portion where the circuit body 14 is formed. At this stage, since the underlying copper plating surface remains on the entire surface of the substrate 12, the circuit bodies 14 are not electrically independent of each other.

  Subsequently, the thin portion 32 is formed. This can be formed, for example, by dissolving and removing the surface of the substrate 12 exposed from the photoresist with a strong alkaline etchant. As a result of this etching, a thin portion 32 having an inclined side wall 38 is formed. The thin portion 32 can be formed by, for example, laser ablation instead of etching.

  After the thin portion 32 is formed as described above, the photoresist is dissolved and removed from both surfaces of the substrate 12. Following this photoresist removal step, a portion of the copper layer is removed entirely from the first surface 26 of the substrate 12 by etching, so that each circuit body 14 is electrically independent.

  Thereafter, a liquid solder resist is applied to any part of the first surface 26 of the substrate 12 by silk screen printing. As the solder resist, a liquid solder resist having a viscosity suitable for the printing method to be used can be used. Moreover, a photocurable or thermosetting liquid solder resist can be appropriately selected and used. The liquid solder resist is applied to an arbitrary part on the substrate 12 by silk screen printing, and then the liquid solder resist is cured to form the cover layer 16.

  Finally, in order to improve the connectivity with the external substrate, a metal film by plating can be formed on the portion of the circuit body 14 exposed from the cover layer. The metal film can be formed from, for example, gold (Au) plating or tin (Sn) plating.

Example 1
The flexible circuit board 10 according to the first embodiment was manufactured according to the following procedure.

  A Cr / Ni seed layer is provided by sputtering on one side of a long polyimide substrate 12 (trade name “Kapton 100E”, manufactured by DuPont) having a width of 11 mm and a thickness of 25 μm, and a Cu layer is provided on the seed layer. It was. Then, 3-5 micrometers of copper layers were deposited on the whole surface by copper sulfate plating.

  Next, a photoreactive photoresist was applied on both sides of the substrate. The double-sided photoresist was exposed to ultraviolet light through a photomask and developed.

  The substrate was immersed in a plating tank, and about 15 μm of copper was deposited on the surface of the copper layer exposed from the photomask by copper sulfate plating.

  Subsequently, the substrate was dipped in a strong alkali solution, and the exposed substrate surface was etched to form a groove-like thin portion extending from one side end surface of the substrate to the other side end surface at the bent portion.

  After the photoresist was dissolved and removed from both sides of the base material, the metal part was entirely removed by etching to obtain mutually independent circuit bodies. Four lines having a line / space of about 75 μm / about 75 μm and a thickness of about 15 μm were formed on the first surface of the base material along the bending direction of the base material.

  A thermosetting liquid solder resist (Iupicoat manufactured by Ube Industries) was printed on the copper wiring and cured at 150 ° C. for 1 hour to obtain a cover layer having a thickness of 15 to 18 μm. Ni and Au plating were applied to the portion of the circuit body exposed from the cover layer. The base material was cut to obtain a flexible circuit board having a length of 130 mm and a width of 11 mm. The dimensions of each part of the bent portion of the obtained flexible circuit board were as shown in Table 1.

Solder Resist Print Spot Evaluation The cover layer was observed under a stereomicroscope with a magnification of 10 times for the solder resist coating spots on the obtained flexible circuit board. The case where the remarkable application spot was seen was judged as "impossible", and the thing without the application spot or not remarkable was judged as "possible". The evaluation results are shown in Table 1.

Bending strength measurement The bending strength of the flexible circuit board was measured as loop stiffness. The flexible circuit board having a width of 11 mm and a length of 130 mm produced as described above was bent into a loop shape and fixed to the test apparatus so that the loop length was 60 mm. At this time, it adjusted so that a bending part may become the approximate center of a loop. The loop stiffness was measured by crushing the loop at a speed of 3.5 mm / second until the height of the loop reached 10 mm. For the measurement, a loop step tester D type manufactured by Toyo Seiki Co., Ltd. was used. The measurement results are shown in Table 1.

Examples 2-4
Although the flexible circuit board was produced similarly to Example 1, each part dimension of the photomask was changed and what was shown in Table 1 as a dimension of each part of a bending part was obtained.

Comparative Example 1
Although the flexible circuit board was produced similarly to Example 1, the thin part was not provided in the bending part of the base material.

Comparative Examples 2 and 3
A flexible circuit board was produced in the same manner as in Example 1, but only one having the dimensions shown in Table 1 was formed as a thin portion.

1 is a top view of a flexible circuit board according to a first embodiment of the present invention. 1 is a cross-sectional view of a flexible circuit board according to a first embodiment of the present invention. 1 is a bottom view of a flexible circuit board according to a first embodiment of the present invention. It is a figure which shows the part of the liquid crystal display device using the flexible circuit board based on one Embodiment of this invention. It is a bottom view of the flexible circuit board based on the 2nd Embodiment of this invention. It is a bottom view of the flexible circuit board based on the 3rd Embodiment of this invention. It is a bottom view of the flexible circuit board based on the 4th Embodiment of this invention.

Explanation of symbols

10, 10a, 10b, 10c Flexible circuit board 12, 12a, 12b, 12c Base material 14, 14a, 14b, 14c Circuit body 16, 16a, 16b, 16c Cover layer 18, 18a, 18b, 18c Bending direction 20 , 20a, 20b, 20c Bent part 22, 22a, 22b, 22c First part 24, 24a, 24b, 24c Second part 26, 26a, 26b, 26c First surface 28, 28a, 28b, 28c Second surface 30 , 30a, 30b, 30c, 31, 31a, 31b, 31c Side end face 32, 32a, 32b, 32c Thin part 34, 34a, 34b, 34c Support part 36, 36a, 36b, 36c Third surface 38, 38a, 38b, 38c Side wall 39, 39a Groove 40, 40a, 40b, 40c Support surface 41b, 41c Outer periphery 46a Connecting portion ( Support part)
70 Liquid Crystal Display Device 72 Liquid Crystal Panel 74 Backlight 76 Drive Circuit Board

Claims (14)

A base material made of a conductive material including a first portion and a second portion separated by a bent portion, the base material having a first surface and a second surface, and the second surface of the bent portion A plurality of thin wall portions adjacent to each other in the folding direction, the thin wall portion extending in a direction intersecting with the bending direction, and a support portion between the plurality of thin wall portions adjacent to each other, A base material made of a flexible material in which the width of the thin portion in the folding direction is larger than the width of the support portion in the folding direction;
A circuit body formed in close contact with the first surface of the substrate;
A cover layer provided on the first surface so as to cover at least part of the surface of the circuit body;
A flexible circuit board.   The flexible circuit board according to claim 1, wherein the thin portion reaches at least one side end surface of the base material.   The flexible circuit board according to claim 1, wherein the thin-walled portion has a support portion so as to divide at least one of the plurality of thin-walled portions in a direction crossing the bending direction. A base material including a first portion and a second portion separated by a bent portion, the base material having a first surface and a second surface, and one thin wall on the second surface side of the bent portion And a base material made of a flexible material having one or more support parts on the thin part,
A circuit body made of a conductive material formed in close contact with the first surface of the substrate;
A cover layer provided on the first surface of the base material so as to cover at least a part of the surface of the circuit body;
A flexible circuit board.   The flexible circuit board according to claim 4, wherein the support portion includes a support surface, and the entire outer periphery of the support surface is in contact with the thin portion.   The flexible circuit board according to claim 4, wherein the thin portion has a support portion so as to divide the thin portion in a direction intersecting the bending direction.   The flexible circuit board according to any one of claims 1 to 6, wherein the cover layer is obtained by curing a liquid solder resist applied on the base material by silk screen printing.   The flexible circuit board according to claim 7, wherein the cover layer is provided after forming the thin portion.   The flexible circuit board according to claim 1, wherein a region occupied by the thin portion in the bent portion is wider than a region occupied by the support portion.   The flexible circuit board according to claim 1, wherein the thin portion is provided by etching.   The flexible circuit board according to any one of claims 1 to 10, wherein an angle formed between a side wall of the thin portion and a third surface of the thin portion is an obtuse angle.   The electronic device which has a flexible circuit board of any one of Claims 1-11. A method of manufacturing a flexible circuit board, including the following steps.
a. Preparing a substrate b. Forming a circuit body on the substrate c. A part of the base material is removed from the second surface side of the base material to be a bent portion, and from the vicinity of one side end surface of the base material to the vicinity of the other side end surface in a direction crossing the bending direction A plurality of thin wall portions that extend and a support portion between the plurality of thin wall portions adjacent to each other so that the width of the thin wall portion in the folding direction is larger than the width of the support portion in the folding direction. Forming into d. A step of providing a cover layer on the substrate surface so as to cover at least a part of the circuit body A method of manufacturing a flexible circuit board, including the following steps.
a. Preparing a substrate b. Forming a circuit body on the substrate c. Removing a part of the base material from the second surface side of the base material to be a bent portion to form one thin portion and one or more support portions in the thin portion; d. A step of providing a cover layer on the substrate surface so as to cover at least a part of the circuit body

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