JP4763068B2 - Flexible circuit board, manufacturing method thereof, and bent portion structure of flexible circuit board - Google Patents

Description

  The present invention relates to a flexible circuit board that is used with a bent portion in any one of them, a method for manufacturing the same, and a bent portion structure of the flexible circuit board. In addition, the present invention relates to a flexible circuit board excellent in flexibility, a manufacturing method thereof, and a bent portion structure of the flexible circuit board.

  Since a flexible circuit board (flexible printed circuit board) having a resin layer and a wiring made of metal foil can be used by being bent, a movable part in a hard disk, a hinge part of a mobile phone, Widely used in various electronic and electrical devices such as sliding slides, printer heads, optical pickups, and notebook PCs. In recent years, especially with the downsizing, thinning, and high functionality of these devices, the flexible circuit board can be folded and stored in a limited space or used in various movements of electronic devices. Corresponding flexibility is required. Therefore, it is necessary to improve the mechanical characteristics such as the strength of the flexible circuit board so that it can cope with the bending with a smaller radius of curvature at the bent portion and the operation in which the bending is frequently repeated. It has become.

  In general, it is the wiring rather than the resin layer that causes failure due to repeated bending and bending with a small radius of curvature. As a result, it cannot be used as a circuit board. Therefore, for example, in order to reduce the bending stress on the wiring in the hinge portion, the flexible circuit board (see Patent Document 1) wired so as to be inclined with respect to the rotation axis, or in the rotation direction of the hinge portion. A method has been proposed in which a spiral portion formed by spiraling one or more turns is formed and the change in the diameter of the spiral portion due to the opening / closing operation is reduced to reduce damage by increasing the number of turns (see Patent Document 2). . However, any of these methods restricts the design of the flexible circuit board.

On the other hand, the strength (I) of the (200) plane determined by X-ray diffraction (X-ray diffraction in the thickness direction of the copper foil) of the rolled copper foil was determined by X-ray diffraction of fine powder copper (200 ) It has been reported that when I / I ₀ > 20 with respect to the surface strength (I ₀ ), the film has excellent flexibility (see Patent Documents 3 and 4). That is, the flexibility of the copper foil improves as the cube orientation, which is the recrystallized texture of copper, develops. Therefore, a flexible circuit board in which the degree of development of the cube texture is defined by the parameter (I / I ₀ ) A copper foil suitable as a wiring material is known. In addition, the rolled copper foil has a crystal structure in which the proportion of crystal grains oriented in the orientation in which the main slip surface can be active with respect to bending deformation is 80% or more in area ratio as observed from the rolled surface. There is also a report that the bending strength is excellent (see paragraph 0013 of Patent Document 5). According to the description of the specification in this document, it is preferable that the cross section of the bent wiring is oriented in {100}. Can be interpreted.

JP 2002-171033 A JP 2002-300147 A JP 2001-58203 A Japanese Patent No. 3009383 JP 2007-107036 A

  Under such circumstances, the present invention is not limited in the design of the flexible circuit board, and has sufficient strength to withstand repeated bending and bending with a small radius of curvature. An excellent flexible circuit board is provided. As a result of intensive studies, the present inventors have surprisingly improved the bending strength when bent at a predetermined angle with respect to the crystal axis of the metal foil having a cubic crystal structure, In addition, new findings such as excellent flexibility were obtained. And based on such knowledge, it discovered that the flexible circuit board excellent in bending durability and flexibility was obtained, and completed this invention.

  Accordingly, the object of the present invention is to provide durability and excellent flexibility in harsh conditions such as hinge portions or slide sliding portions of mobile phones and small electronic devices, particularly in repeated bending portions having a small curvature radius. It is to provide a flexible circuit board.

  Another object of the present invention is to manufacture a flexible circuit board capable of obtaining a flexible circuit board having excellent bending durability and flexibility without being restricted by the design of the flexible circuit board. It is to provide a method.

  In addition, another object of the present invention is to provide durability and resistance to harsh conditions such as hinge portions or slide sliding portions of mobile phones, small electronic devices, etc., particularly in repeated bending portions having a small curvature radius. An object of the present invention is to provide an excellent flexible circuit board bent portion structure.

The present invention is summarized as follows as a result of intensive studies to solve the above-described problems of the prior art.
(1) Provided with a resin layer and a wiring formed of a metal foil, and at least one part of the wiring is accompanied by any one of repeating operations selected from the group consisting of sliding bending, bending bending, hinge bending, and sliding bending A flexible circuit board used with a bent portion,
The metal foil is made of a copper foil having a cubic crystal structure, and the cross section of the wiring when cut in the thickness direction from the ridgeline at the bent portion is (100) to (110) with [001] as the crystal zone axis. A flexible circuit board characterized by having a main orientation in any surface included in a range of (20 1 0) to (1 20 0) in the rotation direction.
(2) The cross section of the wiring when cut in the thickness direction from the ridgeline at the bent portion is connected by a point representing (20 10) and a point representing (110) in the stereo triangle of (100) standard projection drawing The flexible circuit board according to (1), wherein the flexible circuit board is any surface on a line segment.
(3) The strength (I) of the (200) plane determined by X-ray diffraction in the thickness direction of the copper foil is I with respect to the strength (I ₀ ) of the (200) plane determined by X-ray diffraction of fine powder copper. The flexible circuit board according to (1) or (2), wherein / I ₀ ≧ 25.
(4) with respect to two orthogonal axes in one direction of the unit base crystal axes of the lattice <100> is the thickness direction and the foil surface of the copper foil of the copper, is preferentially oriented area is within orientation difference 10 °, the area And the normal to the wiring cross section cut from the ridge line of the bent portion in the thickness direction of the copper foil is the <100> main direction in the foil plane and 2. The flexible circuit board according to (1) or (2), which has an angle of 9 to 87.1 °.
(5) a flexible circuit board according to any one of the copper foil, a rolled copper foil having a thickness of 5 to 100 [mu] m (1) ~ (4).
( 6 ) The flexible circuit board according to any one of (1) to ( 5 ), wherein a wiring is formed along a direction orthogonal to the ridgeline in the bent portion.
( 7 ) The flexible circuit board according to any one of (1) to ( 6 ), wherein the resin layer is made of polyimide.
( 8 ) Provided with a resin layer and a wiring formed of a metal foil, and at least one part of the wiring is accompanied by any one of repeating operations selected from the group consisting of sliding bending, bending bending, hinge bending, and sliding bending A bent portion structure of a flexible circuit board used with a bent portion,
The metal foil is made of a copper foil having a cubic crystal structure, and the cross section of the wiring when cut in the thickness direction from the ridgeline at the bent portion is (100) to (110) with [001] as the crystal zone axis. A bent portion structure of a flexible circuit board, characterized in that a principal direction is formed on any surface included in the range of (20 1 0) to (1 20 0) in the rotation direction of the flexible circuit board.
( 9 ) The cross section of the wiring when cut in the thickness direction from the ridgeline at the bent portion is connected by a point representing (20 10) and a point representing (110) in the stereo triangle of (100) standard projection drawing The bent part structure of a flexible circuit board according to ( 8 ), which is any surface on a line segment.
( 10 ) It is provided with a resin layer and a wiring formed of a metal foil, and at least one part of the wiring is accompanied by any one of repeating operations selected from the group consisting of sliding bending, bending bending, hinge bending, and sliding bending. A method of manufacturing a flexible circuit board used with a bent portion,
The metal foil is made of a copper foil having a cubic crystal structure, and the ridge line at the bent portion has an angle of 2.9 to 87.1 ° with one of the basic crystal axes <100> in the plane of the copper foil. A method of manufacturing a flexible circuit board, wherein wiring is formed on the substrate.
( 11 ) The strength (I) of the (200) plane determined by X-ray diffraction in the thickness direction of the copper foil is I with respect to the strength (I ₀ ) of the (200) plane determined by X-ray diffraction of fine powder copper. The method for producing a flexible circuit board according to ( 10 ), wherein / I ₀ ≧ 25.
( 12 ) The copper foil is a rolled copper foil, and the rolled copper foil has two orthogonal directions in which the basic crystal axis <100> of the unit cell having a face-centered cubic structure is a thickness direction of the copper foil and one direction in the foil surface. ( 11 ) The method for producing a flexible circuit board according to ( 11 ), wherein a cubic texture is exhibited by heat treatment so that a preferential orientation region having an azimuth difference of 10 ° or less with respect to an axis occupies 50% or more in area ratio. .
( 13 ) The method for manufacturing a flexible circuit board according to any one of ( 10 ) to ( 12 ), wherein the wiring is formed along a direction orthogonal to the ridgeline in the bent portion.
( 14 ) An electronic device on which the flexible circuit board according to any one of (1) to ( 7 ) is mounted.

  According to the present invention, when the flexible circuit board is bent, the shearing of the bent portion in the main strain direction is facilitated, so that an effect is obtained that the breakage hardly occurs. In addition, metal fatigue is less likely to occur due to repeated strain. Furthermore, metal fatigue is less likely to occur with respect to stress. Therefore, it is possible to provide a flexible circuit board having excellent flexibility with sufficient strength to withstand repeated bending and bending with a small radius of curvature without any restrictions on the design of the flexible circuit board. it can. As a result, highly durable electronic devices such as thin mobile phones, thin displays, hard disks, printers, and DVD devices can be realized.

FIG. 1 is a diagram illustrating a relationship between a crystal zone axis in a cubic crystal structure and a plane obtained by rotating around the crystal zone axis. FIG. 2 is a stereo triangle of (100) standard projection. FIG. 3 is an explanatory cross-sectional view showing a state in which the flexible circuit board is bent. FIG. 4 is an explanatory plan view showing the relationship between the wiring in the flexible circuit board and the crystal axis of the metal foil, (a) and (b) show the flexible circuit board according to the present invention, and (c) ) And (d) show a prior art flexible circuit board. FIG. 5 is a perspective explanatory view of a single-sided copper-clad laminate. FIG. 6 is an explanatory plan view showing a state in which a test flexible circuit board is obtained from a single-sided copper-clad laminate in the embodiment of the present invention. FIG. 7 shows an orientation mapping image of the metal foil according to the embodiment of the present invention by the EBSP method. FIG. 8 is an explanatory diagram of an MIT flex test apparatus. FIG. 9A is an explanatory view of an IPC bending test apparatus, and FIG. 9B is an XX ′ sectional view of a test flexible circuit board used in the IPC bending test.

  The wiring included in the flexible circuit board of the present invention is formed of a metal foil made of a metal having a cubic crystal structure. As a metal having a cubic crystal structure, for example, in the case of a face-centered cubic crystal, copper, aluminum, nickel, silver, rhodium, palladium, platinum, gold and the like are known, and in the case of a body-centered cubic crystal, Iron, chromium, molybdenum, tungsten, and the like are known, and any of these may be used, but copper, aluminum, and nickel are preferable because of their availability as a metal foil. Copper foils that are mainly used as are most common. The metal foil may be either a rolled foil or an electrolytic foil, but is preferably a rolled foil. For example, in the case of a copper foil, the thickness is 5 to 100 μm, preferably 5 to 20 μm. More preferably, it is a rolled copper foil of 5 to 12 μm. The rolled copper foil may contain an alloy element, but is preferably a complete solid solution.

  The metal foil that forms a circuit in the flexible circuit board of the present invention is made of a metal having a cubic crystal structure, and the cross section P of the wiring when cut in the thickness direction from the ridgeline at the bent portion, With [001] as the zone axis, it is necessary that the main orientation be formed on any plane included in the range of (20 1 0) to (1 20 0). Here, the relationship between the zone axis and the plane orientation is shown in FIG. (20 1 0) and (1 20 0) have a relationship in which [001] is a common axis, that is, a zone axis, from (100) to (110) with [001] as the axis [from (100) (010)] in the plane of rotation. That is, when this is shown on the reverse pole figure with respect to the cross-sectional P normal direction, the surfaces of (001), (20 10), and (110) are as shown in FIG. Due to symmetry, (1 20 0) is represented at the same position as (20 1 0) on the inverse pole figure. The metal of the metal foil in the present invention is cubic. The crystal axes of the unit cell are [100], [010], and [001]. In the present invention, <100> preferred orientation in the thickness direction of the metal foil (the direction perpendicular to the surface of the metal foil). In this case, this axis is expressed as [001], that is, the foil plane orientation is (001), but it is equivalent even if these axes are interchanged due to the symmetry of the cubic crystal, and these are of course included in the present invention.

  In addition, the metal foil in the present invention does not necessarily need to be a single crystal, but at least at the bent portion, it is necessary to preferentially orientate three-dimensionally to form a texture. The crystal orientation at the center of the preferential orientation is called the main orientation of the texture. There are several indexes that represent the priority of texture preferential orientation, that is, the degree of orientation or accumulation. In the present invention, the statistical data of X-ray diffraction intensity and local three-dimensional orientation data obtained by electron diffraction is used. An index based on objective data using. The range of the preferential orientation degree of the metal foil in the present invention is as described below.

  In the typical form of the flexible circuit board of the present invention, the three-dimensional crystal orientation of the metal foil is defined with respect to the sample coordinate system of the metal foil constituting the circuit. It is specified in the following range. That is, at least in the bent portion, the cubic metal has one of the basic crystal axes of the metal unit cell, for example, the [001] axis, with respect to the thickness direction of the metal foil (the direction perpendicular to the surface of the metal foil). , Exhibiting a preferential orientation such that a region within 10 ° in orientation difference occupies 50% or more, preferably 75% or more, and more preferably 98% or more by area ratio, and the surface of the metal foil (main surface or foil) In the foil plane in the horizontal direction with respect to the surface), the area where the other basic crystal axis is the main orientation and the difference in orientation is within 10 ° from the main orientation is 50% or more, preferably 85% or more. More preferably, the preferred orientation should be 99% or more. And, the main orientation in the foil plane is in the main strain direction of the bent portion, that is, in the normal direction of the cross section of the wiring cut from the ridge line in the bent portion in the thickness direction (with respect to the perpendicular to the wiring cross section P), It is necessary to have an angle of 2.9 ° to 87.1 ° [(20 1 0) to (1 20 0)], and preferably 5.7 ° to 84.3 ° ((10 1 0) to (1 100)], more preferably 11.4 ° to 78.6 ° [(510) to (150)], and more preferably 26.6 ° to 63.4 ° [(210) to (120)], most preferably 30 ° or 60 ° [(40 23 0) or (23 40 0)]. [] Represents the plane orientation of the cross section P corresponding to each angle.

  According to the present invention, when the circuit is bent, shearing in the principal stress direction of the bent portion is facilitated, the elongation at break is increased, breakage is less likely to occur, and against repeated strain or stress, Metal fatigue is less likely to occur, and a flexible circuit board with high flexibility is obtained. That is, in a preferred example of the flexible circuit board of the present invention, the metal foil has a face-centered cubic structure, the main surface of the metal foil is preferentially oriented with (001) as the main orientation, and the ridgeline at the bent portion The cross section P of the wiring when cut in the thickness direction is preferentially oriented with a main orientation in a specific orientation between (20 1 0) and (1 20 0), preferably from (10 1 0) to ( 1 10 0) is preferentially oriented with a main orientation in a specific orientation, and more preferably is preferentially oriented with a main orientation in a specific orientation between (510) and (110), more preferably ( It is desirable that the orientation is preferentially provided with a main orientation at a specific orientation between 210) and (110), and most preferably preferentially oriented with a central orientation in the vicinity of (40 230). In the case of a metal foil whose foil surface is preferentially oriented with (001) as the main orientation, the other unit cell axes (100) and (010) in the foil surface are equivalent, and the flexible circuit board in the present invention The main direction of the cross section P of the wiring when cutting in the thickness direction from the ridgeline at the bent portion of the wire can be described as a specific direction between (1200) and (110), preferably from (120) ( 110) can be described as having a preferential orientation with a main orientation in a particular orientation, and most preferably with a main orientation in the vicinity of (23400). .

  Here, the cross section P of the wiring when it is cut in the thickness direction from the ridgeline at the bent portion is, for example, as shown in FIG. 3, when the flexible circuit board is bent in a U shape, a ridgeline L is formed on the outside thereof. However, it refers to the wiring portion of the cross section obtained when the ridge line L is cut in the thickness direction d of the flexible circuit board. The ridge line L is an apex formed when the cross section of the flexible circuit board is viewed along the bending direction (thick arrow in FIG. 3) in a state where the flexible circuit board is bent. It is a connected line. In addition, the case where the ridgeline L moves a flexible circuit board, such as sliding bending mentioned later, for example, is also included. 3 shows a state in which the resin layer 1 is on the outside and the wiring 2 is bent inward (the side on which a circle having a radius of curvature is inscribed is inward), but the wiring 2 is bent outward. Of course, it may be.

  In various applications, when subjected to a forced displacement of a certain curvature, the metal foil is primarily subjected to tensile or compressive stress. Which part of the flexible circuit board that is bent is subjected to tension or compression depends on the configuration of the metal foil and the resin, but is bent from the neutral axis (or neutral surface) of tension and compression. It is common that the outermost part, which is the outermost part, is severe due to the destruction of the metal, and the tensile stress in the normal direction of the cross section of the wiring when cut in the thickness direction from the ridgeline at the bent part becomes the main stress. That is, the main stress direction of the wiring in the bent portion is the direction indicated by the arrow 21 in FIG. 3, and is typically the normal direction to the wiring cross section P cut from the ridge line of the bent portion in the thickness direction of the metal foil. And the direction perpendicular to the [001] axis oriented in the thickness direction of the metal foil.

  In the present invention, the normal line 21 to the wiring cross section P cut from the ridgeline of the bent portion in the thickness direction of the metal foil has an angle of 2.9 to 45 ° with the basic crystal axis <100> in the metal foil plane. Take. However, because of the symmetry of the crystal, as the scope of the present invention, the basic crystal axis <100> in the metal foil plane is relative to the normal line 21 with respect to the wiring cross section P cut from the ridgeline of the bent portion in the thickness direction of the metal foil. It can be described that the wiring is formed to have an angle of 2.9 to 87.1 °. Further, since the ridgeline of the bent portion and the normal line 21 to the wiring cross section P cut from the ridgeline in the thickness direction of the metal foil are orthogonal, and the main directions [100] and [010] in the metal foil plane are orthogonal, As the scope of the present invention, it can also be described that the wiring is formed so that the basic crystal axis <100> in the metal foil plane has an angle of 2.9 to 87.1 ° with respect to the ridgeline of the metal foil.

  When considering the mechanical characteristics of the metal foil in the flexible circuit board, the stress-strain characteristic when the metal foil is simply pulled in the main stress direction indicated by the arrow 21 in FIG. 3 is an important characteristic. Here, as shown in the examples of FIGS. 4C and 4D, the metal foil having a cubic crystal structure is bent so that a ridge line perpendicular to the [100] axis is formed. In this case, the cross section of the wiring cut in the thickness direction of the flexible circuit board from the ridge line at the bent portion becomes the (100) plane. As shown in FIG. 1, the cross section P of FIG. 1 is in the range of (20 1 0) to (1 200) in the rotational direction from (100) to (010) with [001] as the zone axis (both in the figure New knowledge was obtained that the bending fatigue life of the wiring would be extended if any of the planes included in the arrow) had a main orientation. Speaking from the viewpoint of such remarkable improvement in bending fatigue characteristics, the cross section P of the wiring forms a main orientation on any surface included in the range of (10 10) to (1 100). It is preferable that any of the planes included in the range of (510) to (150) has a main orientation, and any of the ranges included in the range of (210) to (120) It is more preferable that the main direction is formed on the surface, and it is most preferable that the main direction is formed at (40 230) or (23 40 0). In FIG. 1, the range from (20 1 0) to (1 20 0) is shown, but the cubic crystal structure has a plane equivalent to the plane included in this range. Therefore, an equivalent surface having a sign different from that of a surface whose wiring cross section is in the range of (20 1 0) to (1 20 0) is included in the present invention.

  In the present invention, the cross section P of the wiring when it is cut in the thickness direction from the ridge line in the bent portion has a main orientation in a specific orientation between (20 1 0) and (1 20 0) and is preferentially oriented. Thus, the fatigue characteristics with respect to repeated bending are excellent when the tensile stress is applied in the normal direction of the cross section P, that is, in the principal stress direction, for example, in the case of a metal having a face-centered cubic structure. This is because, among the two {111}, the main slip surface having the largest Schmid factor is four, so that the shear slip is good and local work hardening is difficult to occur. In normal rolled copper foil, the longitudinal direction of the metal foil corresponds to the rolling direction, and as shown in FIGS. 4C and 4D, it is normal to form a circuit along the main direction <100>. is there. For example, the Example of patent document 5 is equivalent to the form of FIG.4 (d). Thus, when the cross-sectional orientation of the wiring when cutting in the thickness direction from the ridgeline at the bent portion is (100), the eight Schmitt factors of the eight slip planes become equivalent when bent, and the eight slip systems become simultaneous. Dislocations tend to accumulate locally. Because of such a difference from the prior art, the flex circuit resistance of the flexible circuit board taking the form of the present invention is superior to that of the normal form.

  Regarding the cross section P in the flexible circuit board of the present invention, the most desirable orientation is 30 ° with respect to the main strain direction of the bent portion, that is, the normal direction of the cross section of the wiring when cutting from the ridge line in the bent portion in the thickness direction. Although it is 60 °, this is because the stress direction matches the stable orientation of tension. Considering the above mechanism, the thickness direction of the metal foil does not necessarily have to be the [001] main direction, and the cross section P of the wiring when cut in the thickness direction from the ridgeline at the bent portion is [001]. It is only necessary to have a preferential orientation with a main orientation in a specific orientation between (20 1 0) and (1 20 0), where is a zone axis.

In the present invention, the metal foil does not necessarily need to be a single crystal, but in order to obtain the effects as described above, it is desirable that a texture is formed that is preferentially oriented three-dimensionally and the degree of integration is higher. . For example, when the metal foil is a copper foil, the intensity (I) from (002) perpendicular to the above-mentioned zone axis determined by X-ray diffraction (here, according to a general notation method in X-ray diffraction, (200) plane The wiring having a predetermined pattern is formed from a copper foil having I / I ₀ ≧ 25 with respect to the strength (I ₀ ) of the (200) plane obtained by X-ray diffraction of fine powder copper. The I / I ₀ is preferably in the range of 33 to 150, more preferably in the range of 50 to 150. Here, the parameter I / I ₀ represents the degree of orientation of the zone axes of (100) and (110), that is, the common axis [001], and is an objective index indicating the degree of development of the cube texture. is there. When the metal foil is a rolled copper foil, it is strongly processed at a rolling rate of a certain level or higher, and then recrystallized by applying heat, so that the rolled foil surface is rolled into the (001) main orientation and foil plane. A recrystallized cube orientation with the direction as the (100) principal orientation develops. The bending fatigue life of the copper foil is improved as the cubic orientation, which is the recrystallized texture of copper, develops. In the flexible circuit board of the present invention, if I / I ₀ is less than 25, it is not possible to sufficiently improve the bending fatigue life of the wiring. If I / I ₀ is 33 or more, the bending fatigue life is remarkably improved. Become. However, when I / I ₀ exceeds 150, as described later, for example, when annealing is performed in order to obtain a recrystallized texture, the thermal history becomes too large, and the resin layer other than the wiring In addition, the interface state between the wiring and the resin layer may be adversely affected. The X-ray diffraction in the thickness direction of the copper foil confirms the orientation on the surface of the copper foil (rolled surface in the case of a rolled copper foil), and the strength (I) of the (200) plane is X-ray. The integrated intensity value of the (200) plane obtained by diffraction is shown. The intensity (I ₀₎ shows a fine powder of copper (manufactured by Kanto Chemical Co., Inc. copper powder reagent I grade, 325 mesh) in an intensity integral value of the (200) plane.

In order to increase I / I ₀ to 25 or more, a recrystallized texture of the copper foil may be obtained. There is no particular limitation on this means, but for example, as described in Patent Document 4 above The annealing immediately before the final cold rolling is performed under the condition that the average grain size of the recrystallized grains obtained by this annealing is 5 to 20 μm, and the degree of rolling in the next final cold rolling is 90% or more. By doing so, a rolled copper foil with I / I ₀ ≧ 25 can be obtained. In addition, for example, after a resin layer and a rolled copper foil are laminated to obtain a copper-clad laminate, the copper foil is subjected to a heating condition such that a temperature of 300 to 360 ° C. is loaded for an integrated time of 5 minutes or more. A recrystallized texture of copper foil may be obtained.

  Further, in order to define the texture with a three-dimensional degree of integration, the texture can be specified using the area ratio of the preferentially oriented region that falls within 10 ° with respect to the main orientation of the texture. That is, as to what crystal orientation the predetermined surface of the metal foil has, for example, X-ray diffraction method such as EBSP (Electron Back Scattering Pattern) method, ECP (Electron Channeling Pattern) method or X-ray method such as micro Laue method It can be confirmed by a line diffraction method or the like. In particular, the EBSP method analyzes a crystal from a diffraction image called a pseudo Kikuchi line that is diffracted from each crystal plane generated when a focused electron beam is irradiated on the surface of a sample to be measured. This is a method of measuring the crystal orientation distribution of the measurement object from the position information of the above, and it is possible to analyze the crystal orientation of the texture in a microscopic region than the X-ray diffraction method. For example, it is possible to specify the crystal orientation in each minute region, connect them and map them, and separate the ones whose tilt angle (azimuth difference) between each mapping point is below a certain value with the same color, An orientation mapping image can be obtained by highlighting the distribution of regions (crystal grains) having substantially the same plane orientation. It is also possible to define the orientation including the orientation plane having an orientation within a predetermined angle with respect to a specific plane orientation, and to extract the existence ratio of each plane orientation by the area ratio.

In the EBSP method, in order to obtain an area ratio of a region within a specific angle from a specific orientation, in order to obtain an area ratio at least in a region larger than the circuit bent region in the flexible circuit board of the present invention. It is necessary to scan the electron beam finely so as to obtain a sufficient number of points to obtain the average information. However, in the metal foil targeted by the present invention, in view of the size of the target circuit, 0. In an area of 005 mm ² or more, 1000 points or more may be measured in order to obtain an average area ratio.

  In the present invention, the cross section P of the wiring when the foil surface of the metal foil is preferentially oriented with (001) as the main orientation and is cut in the thickness direction from the ridgeline at the bent portion is from (20 10) to (120 000). ) Has a main direction in a specific direction, when the reverse pole is displayed on the stereo triangle of the (100) standard projection diagram shown in FIG. It can also be said that the cross-sectional orientation of the wiring at that time is any surface on the line segment connected by the point representing (20 10) and the point representing (110). In the flexible circuit board of the present invention, the wiring is formed from a 3 (2) axis-oriented material in which the thickness direction of the metal foil is the [001] axis, and is cut from the ridgeline at the bent portion in the thickness direction. It can also be said that the cross-sectional normal of the wiring has an angle in the range of 2.9 ° to 87.1 ° with the [100] axis in the foil plane.

  Regarding the resin layer of the flexible circuit board in the present invention, the type of resin forming the resin layer is not particularly limited, and examples thereof include those used in ordinary flexible circuit boards, such as polyimide, polyamide, Examples thereof include polyester, liquid crystal polymer, polyphenylene sulfide, polyether ether ketone, and the like. Of these, polyimide and liquid crystal polymer are preferred because they exhibit good flexibility when used as a circuit board and are excellent in heat resistance.

  The thickness of the resin layer can be appropriately set according to the use, shape, etc. of the flexible circuit board, but is preferably in the range of 5 to 75 μm and in the range of 9 to 50 μm from the viewpoint of flexibility. Is more preferable, and the range of 10 to 30 μm is most preferable. If the thickness of the resin layer is less than 5 μm, the insulation reliability may decrease. On the other hand, if it exceeds 75 μm, the thickness of the entire circuit board may be too thick when mounted on a small device, etc. A decline in sex is also possible.

  Regarding the means for laminating the resin layer and the metal foil, for example, when the resin layer is made of polyimide, the metal foil may be thermally laminated by applying or interposing a thermoplastic polyimide to the polyimide film (so-called laminating). Law). Examples of the polyimide film used in the laminating method include “Kapton” (Toray DuPont Co., Ltd.), “Apical” (Kanebuchi Chemical Industry Co., Ltd.), “Upilex” (Ube Industries Co., Ltd.), and the like. When the polyimide film and the metal foil are heat-bonded, a thermoplastic polyimide resin exhibiting thermoplasticity is preferably interposed. In addition, from the viewpoint of easy control of the thickness and bending characteristics of the resin layer, a polyimide precursor solution (also referred to as a polyamic acid solution) may be applied to the metal foil, and then dried and cured to obtain a laminate (so-called “so-called”). Cast method).

  The resin layer may be formed by laminating a plurality of resins. For example, two or more kinds of polyimides having different linear expansion coefficients may be laminated, and in that case, heat resistance and flexibility are ensured. In view of the above, it is desirable that substantially all of the resin layer is formed of polyimide without using an epoxy resin or the like as an adhesive.

  In the flexible circuit board of the present invention, the linear expansion coefficient of the resin layer is preferably in the range of 10 to 30 ppm / ° C. When the resin layer is made of a plurality of resins, the linear expansion coefficient of the entire resin layer may be in this range. In order to satisfy such conditions, for example, a low linear expansion polyimide layer having a linear expansion coefficient of 25 ppm / ° C. or less, preferably 5 to 20 ppm / ° C., and a linear expansion coefficient of 26 ppm / ° C. or more, preferably 30 to It is a resin layer composed of a high linear expansion polyimide layer of 80 ppm / ° C., and can be adjusted to 10 to 30 ppm / ° C. by adjusting the thickness ratio thereof. A preferred ratio of the thickness of the low linear expansion polyimide layer to the high linear expansion polyimide layer is in the range of 70:30 to 95: 5. The low linear expansion polyimide layer is the main resin layer of the resin layer, and the high linear expansion polyimide layer is preferably provided so as to be in contact with the metal foil. In addition, the linear expansion coefficient is obtained by using polyimide with the imidization reaction sufficiently completed as a sample, raising the temperature to 250 ° C. using a thermomechanical analyzer (TMA), cooling at a rate of 10 ° C./min, and 240 to 100 ° C. It can obtain | require from the average linear expansion coefficient in the range.

  Moreover, the flexible circuit board in this invention is equipped with the wiring formed from the resin layer and metal foil, and has a bending part in any one, and is used. In other words, it is widely used in various electronic and electrical devices such as movable parts in hard disks, hinges and slides of mobile phones, printer heads, optical pickups, movable parts of notebook PCs, etc., and the circuit board itself Is bent, twisted, or deformed according to the operation of the mounted device, and a bent portion is formed in either of them. In particular, since the flexible circuit board of the present invention has a bent portion structure with excellent bending durability, it is frequently bent with repeated operations such as sliding bending, bending bending, hinge bending, and sliding bending. In addition, in order to cope with the downsizing of devices to be mounted, the radius of curvature is 0.38 to 2.0 mm in bending behavior, 1.25 to 2.0 mm in sliding bending, and 3. 0 to 5.0 mm, suitable for severe use conditions such as 0.3 to 2.0 mm in slide bending, and in slide applications where bending performance is severe with a narrow gap of 0.3 to 1 mm Especially effective.

  One of the methods for producing a flexible circuit board in the present invention is that a rolled metal foil and a resin layer exhibit a cubic texture in which the [001] axis is finally oriented in the normal direction of the foil surface (perpendicular to the surface of the metal foil) And the metal foil surface, the principal stress direction of the design bending, that is, the normal direction of the cross section of the wiring when cutting from the ridge line at the bent portion in the thickness direction is manufactured. What is necessary is just to wire so that the ridgeline of a bending part may be formed at an angle of 2.9 ° to 87.1 ° with respect to the [100] main orientation. The metal foil does not necessarily have to exhibit a cubic texture from the beginning, and may be formed by a heat treatment, for example, a manufacturing process of a flexible circuit board, specifically, formation of a resin layer. A cubic texture may be formed by heat treatment in the process. That is, by heat treatment, one of the basic crystal axes <100> of the unit cell is given priority in the thickness direction of the metal foil so that the area within 10 ° from the <100> axis occupies an area ratio of 50% or more. In addition to the orientation, another one of the basic crystal axes <100> is preferentially oriented in the horizontal direction with respect to the surface of the metal foil so that the area within 10 ° from the <100> axis occupies an area ratio of 50% or more. You can make it. The recrystallized texture of the rolled copper foil usually has a rolling plane orientation of {100} and a rolling direction of <100>. Therefore, since the (001) main orientation is formed as the rolling plane orientation, the ridge line in the bent portion has an angle of 2.9 to 87.1 ° with one of the basic crystal axes <001> in the plane of the metal foil. In other words, wiring may be performed so that the ridgeline of the bent portion is formed with an angle of 2.9 ° to 87.1 ° in the rolling direction.

  As shown in FIG. 3, for example, when a flexible circuit board is bent in a U shape, a ridge line L is formed on the outer side (the side opposite to the side where an inscribed circle having a radius of curvature is formed). However, the ridgeline L may be inclined in a range of α = 2.9 to 87.1 (°) from a state orthogonal to the [100] axis of the metal foil forming the wiring. An example of such a state is shown in FIGS. Incidentally, (c) and (d) of FIG. 4 are states (α = 0) in which the ridge line is orthogonal to the [100] axis. Here, when α is less than 2.9 °, a clear effect on flexibility is not confirmed. When α = 11.4 to 78.6 (°), the bending durability of the bent portion structure is further improved. In the present invention, when α = 2.9 °, the cross section P of the wiring when cut from the ridge line in the thickness d direction corresponds to the (20 10) plane, and when α = 45, the cross section P corresponds to the (110) plane, and when α = 87.1, the cross section P corresponds to the (1 200) plane. In addition, in the cubic crystal, [100] and [010] are equivalent, and therefore, the angle α formed by the orthogonal axis in the foil plane of [100] and the ridge line as shown in FIGS. 4 (a) and 4 (b). The range coincides with the angle range formed by [100] and the cross-section P normal line, and the angle range formed by [100] and the ridge line.

  The width, shape, pattern, etc. of the wiring are not particularly limited, and may be appropriately designed according to the use of the flexible circuit board, the electronic device to be mounted, etc. For example, in order to reduce the bending stress on the wiring, it is not necessary to dare to wire in an oblique direction with respect to the rotation axis of the hinge portion, and the direction along the direction perpendicular to the ridgeline at the bent portion is not necessary. Wiring, that is, wiring with the minimum necessary minimum distance is possible. For example, FIGS. 4 (a) and 4 (b) are examples of a flexible circuit board used for a hinge portion of a mobile phone and the like, which has a resin layer 1, a wiring 2 formed from a metal foil, and a connector terminal 3. It is. 4A and 4B show the position of the ridge line L in the bent portion near the center, and this ridge line L is (with respect to the [100] axis direction of the metal foil forming the wiring 2 ( 90 + α) °. Here, FIG. 4A is an example in which the wiring is formed obliquely in the vicinity of the ridge line L in the middle of the connector terminals 3 at both ends. However, as shown in FIG. Wiring is also possible. In addition to the case where the position of the ridge line L in the bent portion is fixed as in a folding mobile phone, the slide sliding bend in which the ridge line L in the bent portion moves as in a slide type mobile phone (see FIG. 4 (b) may be the direction of the thick arrow).

  Moreover, although the flexible circuit board in this invention is equipped with the wiring which consists of metal foils on at least one surface of a resin layer, you may make it equip both surfaces of a resin layer with metal foil as needed. At this time, it is desirable that the cross section of the wiring when any metal foil is cut in the thickness direction from the ridge line at the bent portion is a predetermined surface in the present invention.

  Hereinafter, based on an Example and a comparative example, the present invention is explained more concretely. In addition, the synthesis | combination of the kind of copper foil used in the Example etc. and a polyamic-acid solution is as follows.

[Copper foil A]
Rolled copper foil (trade name BHYA-72F-HA) manufactured by Nikko Metal Co., Ltd., thickness 12 μm.
[Copper foil B]
Rolled copper foil (trade name ROFD-T4X) manufactured by Fukuda Metal Co., Ltd., thickness 12 μm.
[Copper foil C]
Rolled copper foil (trade name BHY-22B-T) manufactured by Nikko Metal Co., Ltd., thickness 18 μm.
[Copper foil D]
Furukawa Circuit Foil Co., Ltd. electrolytic copper foil (trade name U-WZ), thickness 9μm.

[Synthesis of polyamic acid solution]
(Synthesis Example 1)
N, N-dimethylacetamide was placed in a reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen. 2,2-bis [4- (4-aminophenoxy) phenyl] propane (BAPP) was dissolved in the reaction vessel with stirring. Next, pyromellitic dianhydride (PMDA) was added. The total amount of monomers charged was 15 wt%. Thereafter, stirring was continued for 3 hours to obtain a resin solution of polyamic acid a. The solution viscosity of this polyamic acid a resin solution was 3,000 cps.

(Synthesis Example 2)
N, N-dimethylacetamide was placed in a reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen. 2,2′-Dimethyl-4,4′-diaminobiphenyl (m-TB) was charged into the reaction vessel. Next, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) were added. The total amount of monomers charged was 15 wt%, and the molar ratio of each acid anhydride (BPDA: PMDA) was 20:80. Thereafter, stirring was continued for 3 hours to obtain a resin solution of polyamic acid b. The solution viscosity of this polyamic acid b resin solution was 20,000 cps.

[Example 1]
The polyamic acid solution a prepared above is applied to copper foil A and dried (after curing, a 2 μm-thick thermoplastic polyimide film is formed), and then polyamic acid b is applied and dried (after curing, a film thickness of 12 μm) Of low thermal thermal expansion polyimide), and further coated with polyamic acid a and dried (forms a 2 μm thick thermoplastic polyimide after curing), and the temperature of 300 to 360 ° C. is 5 minutes or more in accumulated time. A polyimide layer having a three-layer structure was formed through heating conditions that were loaded. Next, cut along the rolling direction (MD direction) of the copper foil A to a rectangular size of 250 mm in length and 150 mm in width in the direction orthogonal to the rolling direction (TD direction), as shown in FIG. A single-sided copper-clad laminate 4 having a polyimide layer (resin layer) 1 having a thickness of 16 μm and a copper foil 2 having a thickness of 12 μm was obtained.

About the obtained single-sided copper clad laminated board 4, intensity | strength (I) was calculated | required from the intensity | strength integral value of the (200) plane obtained by the X-ray diffraction of the rolling surface 2a of the copper foil 2, and this value was measured beforehand. It was 61 when I / I ₀ was calculated by dividing by the intensity (I ₀ ) obtained from the intensity integrated value of (200) plane of pure fine powder copper (copper powder reagent class I, 325 mesh manufactured by Kanto Chemical Co., Inc.). . For X-ray diffraction, a pole figure measuring device RINT-2000 type (manufactured by Rigaku Corporation) is used, an Mo-Kα target is used, the tube voltage is 60 kV, and the tube current is 200 mA. The intensity ratio was determined from the magnification with respect to the pure copper powder solidified diffraction intensity.

  Moreover, the crystal orientation of the rolling surface 2a of the copper foil by EBSP was measured using Hitachi FE-SEM (S-4100). The measurement area was an area of about 150 μm × 75 μm, and the measurement acceleration voltage was 20 kV and the measurement step interval was 0.5 μm. For measurement and analysis of EBSP, OIM Analysis 5.2 and EBSP analysis software OIM 4.6 manufactured by TSL were used. Also, the surface of the obtained copper clad laminate was ion-polished with a polisher (SM09010: JEOL), and the crystal orientation of the copper foil rolled surface 2a was confirmed. As a result, a strong orientation toward the (001) plane was confirmed in the reverse pole figure. It was done. Further, in the EBSP measurement, when an orientation having an orientation within 10 ° with respect to a specific orientation plane was extracted, the area ratio of the (001) plane occupied 50% or more of the total measurement area. The (001) plane was dominant. FIG. 7A is an inverse pole mapping image of the foil surface orientation of the rolled surface 2a obtained at this time. FIG. 7C shows a mapping color contour. Similarly, when the crystal orientation of the rolled (MD) orientation of the copper foil 2 was analyzed, strong orientation to the (100) plane was confirmed, and the area ratio of the (100) plane was 50% or more of the total measurement area. Therefore, the (100) plane was dominant in the rolling (MD) orientation. FIG. 7B is a reverse pole mapping image of the MD orientation of the copper foil. From these results, since both the rolling surface 2a and the side surface 2b of the copper foil 2 are dominant in the {100} plane, the copper [100] is mainly formed along the rolling direction (MD direction) of the copper foil 2. It can be said that it has an axis. In Examples and the like, unless otherwise specified, the MD main azimuth plane is expressed as (100), and the MD main azimuth is expressed as [100].

  Then, a predetermined mask is put on the copper foil 2 side of the single-sided copper clad laminate 4 obtained above, and etching is performed using an iron chloride / copper chloride solution. As shown in FIG. ) The wiring direction H (H direction) of the linear wiring 2 of 150 μm has an angle of 45 ° with respect to the MD direction ([100] axis), and a wiring pattern is formed with a space width (s) of 250 μm. did. And a test having a length of 15 cm in the longitudinal direction along the wiring direction H of the circuit board and a width of 1.5 cm in the direction perpendicular to the wiring direction H according to JIS 6471 so that it also serves as a sample for a bending resistance test described later. A flexible circuit board 5 was obtained.

  Using the test flexible circuit board 5 obtained above, an MIT flex test was performed according to JIS C5016. The equipment is manufactured by Toyo Seiki Seisakusho (STROGRAPH-R1), one end of the test flexible circuit board 5 in the longitudinal direction is fixed to the holding jig of the bending test apparatus, and the other end is fixed with a weight. The wire 2 on the circuit board 5 is cut off from conduction while being rotated to 135 ± 5 degrees alternately left and right at a vibration speed of 150 times / min. Was determined as the number of flexing. At this time, as shown in FIG. 6, the test was performed so that the ridge line L formed in the bent portion was orthogonal to the wiring direction H of the wiring 2 of the test flexible circuit board 5. It was confirmed that the wiring 2 was broken in the vicinity of the ridge line L of the bent portion at the 2200th time. The results are shown in Table 1.

Here, in the test flexible circuit board 5 according to this example, the wiring 2 is formed so that the wiring direction H is inclined by 45 ° with respect to the [100] axis of copper, and the ridge line in this bending test It can be said that the cross section of the wiring 2 when cut from L in the thickness direction of the circuit board 5 is the (110) plane. That is, in this example, the rolling surface 2a is the (001) surface and the side surface 2b is the (010) surface, so that the crystal structure of this copper foil is the MD direction of the copper foil surface ([100] In addition, as shown in Table 2, the angular relationship between the (100) plane and the (h ₂ k ₂ l ₂ ) plane is known as shown in Table 2. Therefore, it can be said that the cross section cut in the thickness direction of the circuit board 5 from the ridge line L in this embodiment is the (110) plane. The numerical values in Table 2 are Phys. Rev. 26, 390 (1925).

[Examples 2 to 5]
A polyimide layer was formed on the copper foil A in the same manner as in Example 1 to obtain a single-sided copper-clad laminate 4. And about the obtained single-sided copper clad laminated board 4, each test flexible was carried out similarly to Example 1 except having made the angle of the wiring direction H with respect to MD direction ([100] axis | shaft) shown in Table 1. Circuit board 5 was prepared. Using the obtained circuit board 5, the MIT bending test was conducted in the same manner as in Example 1. The results are shown in Table 1.

[Examples 6 to 8]
Single-sided copper-clad laminates 4 according to Examples 6 to 8 in the same manner as in Example 1 except that the heating integration time was set to 2 minutes in the heating conditions for forming the polyimide layer on the surface-treated surface of the copper foil A. Got. For each single-sided copper-clad laminate 4 obtained was 43 was determined the I / I ₀ in the same manner as in Example 1. The obtained single-sided copper clad laminate 4 was analyzed for the crystal orientation of the rolled surface 2a orientation (MD orientation) and side surface 2b orientation (TD orientation) of the copper foil by the EBSP method in the same manner as in Example 1. Since the {100} plane was dominant in each case, the single-sided copper-clad laminate 4 according to Examples 6 to 8 had a copper [100] axis in the rolling direction (MD direction) of the copper foil 2. It was confirmed to have.

  And about the single-sided copper clad laminated board 4 obtained above, it is for each test similarly to Example 1 except having made the angle of the wiring direction H with respect to MD direction ([100] axis | shaft) shown in Table 1. A flexible circuit board 5 was prepared. Using the obtained circuit board 5, the MIT bending test was performed in the same manner as in Example 1. The results are shown in Table 1.

[Examples 9 to 11]
Examples 9 to 11 were performed in the same manner as in Example 1 except that the copper foil B was used and the heating integration time in the heating condition when forming the polyimide layer on the surface-treated surface of the copper foil B was set to 2 minutes. Such a single-sided copper-clad laminate 4 was obtained. For each single-sided copper-clad laminate 4 obtained, it was 33 was determined the I / I ₀ in the same manner as in Example 1. Further, when the crystal orientations of the rolled surface 2a and side surface 2b of the copper foil were analyzed by the EBSP method for these single-sided copper clad laminates 4 in the same manner as in Example 1, the (100) plane was dominant. From this, it was confirmed that the single-sided copper clad laminate 4 according to Examples 9 to 11 has a [100] axis of copper in the rolling direction (MD direction) of the copper foil 2.

  And about the single-sided copper clad laminated board 4 obtained above, it is for each test similarly to Example 1 except having made the angle of the wiring direction H with respect to MD direction ([100] axis | shaft) shown in Table 1. A flexible circuit board 5 was prepared. Using the obtained circuit board 5, the MIT bending test was performed in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Examples 1-3]
For the single-sided copper clad laminate 4 obtained in the same manner as in Example 1, the angle of the wiring direction H with respect to the MD direction ([100] axis) is as shown in Table 1, A test flexible circuit board 5 was prepared. Using the obtained circuit board 5, the MIT bending test was conducted in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 4]
A single-sided copper-clad laminate 4 was obtained in the same manner as in Example 1 except that the heating time when the polyimide layer was formed on the surface-treated surface of the copper foil A was set to 2 minutes. For each single-sided copper-clad laminate 4 obtained was 43 was determined the I / I ₀ in the same manner as in Example 1. Further, when the crystal orientation of the rolled surface 2a orientation (MD orientation) and the side surface 2b orientation (TD orientation) of the copper foil was analyzed in the same manner as in Example 1, the (100) plane was dominant in both cases. The single-sided copper clad laminate 4 was confirmed to have a [100] axis of copper in the rolling direction (MD direction) of the copper foil 2. And about the obtained single-sided copper clad laminated board 4, each test was carried out similarly to Example 1, except that the angle of the wiring direction H with respect to the MD direction ([100] axis) was 0 ° as shown in Table 1. A flexible circuit board 5 was prepared and an MIT flex test was performed. The results are shown in Table 1.

[Comparative Example 5]
Each single-sided copper-clad laminate in the same manner as in Example 1 except that the copper foil B was used and the heating integrated time in the heating condition when forming the polyimide layer on the surface-treated surface of the copper foil B was 2 minutes. 4 was obtained. For each single-sided copper-clad laminate 4 obtained, it was 33 was determined the I / I ₀ in the same manner as in Example 1. Further, when the crystal orientations of the rolling surface 2a orientation (MD orientation) and the side surface 2b orientation (TD orientation) were analyzed in the same manner as in Example 1, the (100) surface was dominant, and these single-sided copper-clad The laminate 4 was confirmed to have a [100] axis of copper in the rolling direction (MD direction) of the copper foil 2. And about the obtained single-sided copper clad laminated board 4, each test was carried out similarly to Example 1, except that the angle of the wiring direction H with respect to the MD direction ([100] axis) was 0 ° as shown in Table 1. A flexible circuit board 5 was prepared and an MIT flex test was performed. The results are shown in Table 1.

[Comparative Example 6]
Each single-sided copper clad laminate 4 was obtained in the same manner as in Example 1 except that the copper foil C was used. For each resulting one-sided copper-clad laminate 4 was 10 was determined the I / I ₀ in the same manner as in Example 1. And about the obtained single-sided copper clad laminated board 4, each flexible circuit board for a test was carried out similarly to Example 1 except having made the angle of the wiring direction H with respect to MD direction into 0 degree as shown in Table 1. 5 was prepared and an MIT flex test was performed. The results are shown in Table 1.

[Comparative Example 7]
Each single-sided copper clad laminate 4 was obtained in the same manner as in Example 1 except that the copper foil D was used. For each single-sided copper-clad laminate 4 obtained was 7 was determined the I / I ₀ in the same manner as in Example 1. And about the obtained single-sided copper clad laminated board 4, each test was carried out similarly to Example 1, except that the angle of the wiring direction H with respect to the MD direction ([100] axis) was 0 ° as shown in Table 1. A flexible circuit board 5 was prepared and an MIT flex test was performed. The results are shown in Table 1.

[Example 12]
The polyamic acid solution a prepared in the same manner as in Synthesis Example 1 was applied to a rolled copper foil E having a purity of 99.9 mass% and a thickness of 12 μm and dried (after curing, a 2 μm-thick thermoplastic polyimide was formed) ), And the polyamic acid b is applied thereon and dried (after curing, a low thermal expansion coefficient polyimide film having a thickness of 12 μm is formed). Further, the polyamic acid a is applied thereon and dried (the film thickness after curing). 2 μm thermoplastic polyimide was formed), and a polyimide layer was formed through heating conditions such that a temperature of 180 to 240 ° C. was added for 10 minutes over an integrated time.

  Next, a polyimide layer (resin) having a thickness of 250 μm along the rolling direction (MD direction) of the copper foil and a rectangular size of 150 mm width in a direction orthogonal to the rolling direction (TD direction) and having a thickness of 12 μm. Layer) 1 and a single-sided copper-clad laminate 4 having a copper foil 2 having a thickness of 12 μm were obtained. A predetermined mask is placed on the copper foil side of the single-sided copper-clad laminate 4 obtained above, etching is performed using an iron chloride / copper chloride solution, and a straight line having a line width of 150 μm and a space width of 250 μm is based on the IPC standard. A low-speed IPC test circuit 2 having a wire shape was formed. In this manufacturing process, the maximum heating temperature during the formation of the polyimide layer is set to four levels of 180 ° C. (condition A), 200 ° C. (condition B), 220 ° C. (condition C), and 240 ° C. (condition D). Moreover, the wiring direction (H direction) of the linear wiring 2 is 0 °, 2 °, 2.9 °, 5.7 °, 9.5 °, 11.4 ° with respect to the rolling direction (MD direction). 14 °, 18.4 °, 25 °, 26.6 °, 30 °, 40 °, 45 °, 55 °, 60 °, 63.4 °, 78.6 °, 80 °, 82.9 °, Wiring patterns were formed so as to have angles of 22 levels of 87.1 °, 88 °, and 90 °, respectively. Next, a cover material 7 (CVK-0515KA manufactured by Arisawa Manufacturing Co., Ltd., thickness: 12.5 μm) was laminated on each circuit side surface using an epoxy adhesive. The thickness of the adhesive layer 6 made of an adhesive was 15 μm in a portion without a copper foil circuit, and 6 μm in a portion where a copper foil circuit was present. And it cut out so that it might be set to 15 cm in a longitudinal direction along the wiring direction (H direction), and 8 mm in width in the direction orthogonal to a wiring direction, and the flexible circuit board for a test for setting it as an IPC test sample was obtained.

  In addition, as a sample for performing a structural analysis by EBSP, a single-sided copper-clad laminate produced under the heat treatment conditions A to D is 0 °, 2.9 °, 30 °, 63.4 ° with respect to the rolling direction. A total of 20 samples without wiring patterns cut out at five angles of 78.6 ° were prepared. In order to align the thermal history with the IPC test sample, the same simulated heat treatment as the circuit formation etching was applied, and the cover material was laminated under the same conditions. However, these influences on the copper foil structure are minor, and it has been found later that the copper foil structure is determined by the heat treatment conditions A to D at the time of polyimide formation.

  Then, 20 copper foils E having four levels of heat treatment conditions and five levels of angle conditions prepared for EBSP measurement as described above are polished in the substrate thickness direction, and have a plane parallel to the foil surface before polishing. Thus, the foil surface of the copper foil E was exposed. Furthermore, it finished-polished using colloidal silica and evaluated the structure of the copper foil E by EBSP. The measurement area was 0.8 mm × 1.6 mm, and the measurement interval was 4 μm. That is, the number of measurement points in one area is 80000 points. As a result, all the samples heat-treated under the heat treatment conditions from Condition A to Condition D form a cube texture, and have a copper foil plane orientation and a main orientation of {001} <100> in the rolling direction. I understood. Based on the obtained results, the number of points where the unit cell axis <001> is within 10 ° is counted in the thickness direction and the rolling direction of the copper foil, and the ratio to the total number of points is calculated. The average value was obtained. The results are shown in Table 3. The variation between samples under the same heating condition is 1% or less, and it can be said that the same heat treatment condition has the integration degree shown in Table 3 over the entire surface of the copper foil. It was found that the higher the maximum heat treatment temperature and the greater the thermal history, the more recrystallization progressed and the higher the degree of integration of the cubic recrystallization texture. Further, as a result of orientation analysis in the foil plane, the cutting direction of the sample cut at five angles of 0 °, 2.9 °, 30 °, 63.4 °, and 78.6 ° with respect to the rolling direction. The main orientations of [100], [20 1 0], [40 23 0], [120], and [150] were almost as specified.

  The IPC test is a test simulating slide bending, which is one of the bending forms used for mobile phones and the like, as shown in the schematic diagram of FIG. The IPC test is a test in which a bent portion is provided with a determined gap length 8 as shown in FIG. 9, one side is fixed by the fixing portion 9, and the slide operating portion 10 on the opposite side is repeatedly reciprocated as shown in the drawing. . Therefore, the substrate is repeatedly bent in a region corresponding to the stroke amount of the reciprocating portion. In this example, the test was conducted by repeatedly sliding the polyimide layer (resin layer) 1 with the cap length being 1 mm, that is, the bending radius being 0.5 mm and the stroke being 38 mm. During the test, the electrical resistance of the circuit of the test flexible circuit board was measured, and the progress of fatigue cracks in the copper foil circuit was monitored by increasing the electrical resistance. In this example, the circuit breakage life was defined as the number of strokes at which the electrical resistance of the circuit reached twice the initial value.

  The test was conducted on a total of 88 levels in which a wiring pattern having a 22-level angle was formed under the four heat treatment conditions of the above conditions A to D. At each test level, four test pieces were measured, and the average number of strokes at which the circuit was broken was obtained. Regarding the copper foil after the circuit breaking life, when the cross section of the copper foil cut in the thickness direction so as to be orthogonal to the sliding direction is observed with a scanning electron microscope, there is a difference in degree, but the resin layer side and the cover material side It was observed that cracks occurred on the surfaces of the copper foils, and that many cracks were introduced on the surface of the copper foil on the resin layer side, which is outside the bent portion.

  Table 4 shows the average value of circuit break life at each level. In the angle column of Table 4, the surface index is also shown only in the case of the low index direction of the cross section P of the wiring when the circuit is cut in the length direction (wiring direction), that is, the ridgeline at the bent portion in the thickness direction. .

  The fatigue life in the IPC test is the angle between the circuit length direction (wiring direction) and the rolling direction, that is, the angle between [100] and the normal direction of the wiring cross section when cutting in the thickness direction from the ridgeline at the bent portion. It turned out to depend greatly on. This orientation dependency is manifested under conditions B, C, and D, and the higher the degree of cube orientation integration, the greater the fatigue life against repeated bending and the greater the orientation dependency. Regarding this orientation dependency, the <001> main direction is such that the area where the copper [001] is within an orientation difference of 10 ° occupies an area ratio of 50% or more in the evaluation by the EBSP method with respect to the thickness direction of the metal foil. [100] The orientation is preferentially oriented in the thickness direction of the metal foil, and the region within 10 ° of the orientation difference from the [100] axis of copper occupies an area ratio of 50% or more as evaluated by the EBSP method. It was confirmed that the main azimuth was expressed when preferentially oriented in the metal foil plane. In particular, in the case of the condition C in which the thickness ratio and the rolling direction show an area ratio of 75% or more and 85% or more, respectively, and the accumulation degree of the cube orientation is high, the fatigue life is large and the effect of orientation dependency is also obtained. In the condition D where the area ratio is 98% or more and 99% or more in the thickness direction and the rolling direction, respectively, and the accumulation degree of the cube orientation is extremely high, the fatigue life is further increased, and the effect of orientation dependency is obtained. I found it big.

  When the results of Condition B, Condition C, and Condition D are examined in detail, the normal direction of the wiring cross section when cutting in the thickness direction from the ridge line at the bent portion, that is, the main stress direction is from the <100> main direction of the copper foil. The misalignment has a higher fatigue life of the circuit against bending. In the IPC test of this example, the effect was observed with respect to the main strain direction of the bent portion, that is, with respect to the normal direction of the cross section of the wiring when cut from the ridge line in the bent portion in the thickness direction. It was a case having an angle of from 0 ° to 87.1 °. When this is expressed in terms of a plane index, the cross section P of the wiring when it is cut in the thickness direction from the ridgeline at the bent portion passes from (20 1 0) to (110) with [001] as the crystal zone axis, and (1 20 0 ). In particular, the effect is large at an angle of 11.4 ° to 78.6 ° with respect to the main strain direction of the bent portion, that is, with respect to the normal direction of the cross section of the wiring when cut from the ridge line in the bent portion in the thickness direction. It was a case. When this is expressed in terms of a plane index, the cross section P of the wiring when it is cut in the thickness direction from the ridgeline at the bent portion ranges from (510) to (110) to (150) with [001] as the zone axis. It is. When the bending characteristic has an angle of 26.6 ° to 63.4 ° with respect to the main strain direction of the bent portion, that is, with respect to the normal direction of the cross section of the wiring when cut from the ridgeline in the bent portion in the thickness direction The best results were obtained at 30 ° and 60 °. When this is expressed in terms of a plane index, the cross section P is in the range from (210) to (110) to (120) with [001] as the zone axis, and the most excellent are (40 230) and ( 23 40 0) When in the vicinity.

  When the cross-sectional orientation of the wiring when the thickness is cut from the ridgeline at the bent portion, which is a normal usage form of rolled copper foil, is taken as (100), the Schmid factors of the eight slip surfaces are equivalent when bent. , 8 slip systems work simultaneously, and dislocations accumulate easily. On the other hand, when taking a special form in which the cross-sectional orientation of the wiring takes an orientation other than (100) as in the present invention, the eight slip surfaces are composed of four main slip systems and four secondary slip systems. Therefore, at the initial stage of deformation, only four main slip systems work, dislocation accumulation hardly occurs, and fatigue characteristics are considered to be improved. The most desirable orientation is 30 ° or 60 ° with respect to the main strain direction of the bent portion, that is, the normal direction of the cross section of the wiring when cutting from the ridge line in the bent portion in the thickness direction. This is because it matches the stable orientation of

  Considering the above mechanism, the metal foil in the wiring needs to exhibit a cubic texture, but the cross section of the wiring cut in the thickness direction from the ridgeline in the bent portion shows [001] It is only necessary that the main azimuth is formed on any plane included in the range of (21 1 0) to (1 20 0) in the rotation direction from (100) to (110) as an axis. Even if the metal foil is rotated 90 ° in the plane of the foil, this is equivalent due to symmetry. Furthermore, since the above mechanism is established not only for copper but also for other face-centered cubic metals having the same sliding surface and sliding direction, a metal foil or surface such as aluminum, nickel, silver, rhodium, palladium, molybdenum, tungsten, etc. It is obvious that the same effect appears in the alloy foil having a centered cubic structure.

  The flexible circuit board according to the present invention can be widely used in various electronic and electrical devices. The circuit board itself is bent, twisted, or deformed according to the operation of the mounted device. , Suitable for use with a bent portion in either. In particular, since the flexible circuit board of the present invention has a bent portion structure with excellent bending durability, it is frequently bent with repeated operations such as sliding bending, bending bending, hinge bending, and sliding bending. Alternatively, it is suitable for the case where a bent portion is required in which the radius of curvature is required to be extremely small in order to cope with downsizing of the equipment to be mounted. Therefore, the flexible circuit board of the present invention can be suitably used for various electronic devices including a thin mobile phone, a thin display, a hard disk, a printer, and a DVD device that require durability.

1: Resin layer 2: Wiring (metal foil)
2a: Rolled surface
2b: Side surface 3: Connector terminal 4: Single-sided copper clad laminate 5: Test flexible circuit board 6: Adhesive layer 7: Cover material 8: Gap length 9: Fixing part 10: Slide operating part 21: Method of section P Line direction L: Ridge line P: Cross section of wiring when cut in the thickness direction from the ridge line at the bent portion

Claims (14)

A wiring layer formed of a resin layer and a metal foil, and at least one portion of the wiring is provided with a bending portion with any of repetitive operations selected from the group consisting of sliding bending, bending bending, hinge bending, and sliding bending. A flexible circuit board for use with
The metal foil is made of a copper foil having a cubic crystal structure, and the cross section of the wiring when cut in the thickness direction from the ridgeline at the bent portion is (100) to (110) with [001] as the crystal zone axis. A flexible circuit board characterized by having a main orientation in any surface included in a range of (20 1 0) to (1 20 0) in the rotation direction.   The cross section of the wiring when cut in the thickness direction from the ridgeline at the bent portion is a line segment connected by a point representing (20 10) and a point representing (110) in the stereo triangle of (100) standard projection drawing The flexible circuit board according to claim 1, wherein the flexible circuit board is any one of the upper surfaces. The intensity (I) of the (200) plane determined by X-ray diffraction in the thickness direction of the copper foil is I / I ₀ relative to the intensity (I ₀ ) of the (200) plane determined by X-ray diffraction of fine powder copper. The flexible circuit board according to claim 1, wherein ≧ 25. The preferentially oriented region in which the basic crystal axis <100> of the copper unit cell is within an orientation difference of 10 ° with respect to two orthogonal axes of the thickness direction of the copper foil and one direction in the foil surface is 50 in area ratio. %, And the normal to the wiring cross section cut in the thickness direction of the copper foil from the ridge line of the bent portion is the <100> main direction in the foil plane and 2.9 to 87. The flexible circuit board according to claim 1, wherein the flexible circuit board has an angle of 1 °. The flexible circuit board according to claim 1, wherein the copper foil is a rolled copper foil having a thickness of 5 to 100 μm. The flexible circuit board according to claim 1, wherein wiring is formed along a direction orthogonal to the ridge line in the bent portion . The flexible circuit board according to claim 1, wherein the resin layer is made of polyimide . A wiring layer formed of a resin layer and a metal foil, and at least one portion of the wiring is provided with a bending portion with any of repetitive operations selected from the group consisting of sliding bending, bending bending, hinge bending, and sliding bending. A bent portion structure of a flexible circuit board to be used,
The metal foil is made of a copper foil having a cubic crystal structure, and the cross section of the wiring when cut in the thickness direction from the ridgeline at the bent portion is (100) to (110) with [001] as the crystal zone axis. A bent portion structure of a flexible circuit board, characterized in that a principal direction is formed on any surface included in the range of (20 1 0) to (1 20 0) in the rotation direction of the flexible circuit board. The cross section of the wiring when cut in the thickness direction from the ridgeline at the bent portion is a line segment connected by a point representing (20 10) and a point representing (110) in the stereo triangle of (100) standard projection drawing The bent portion structure of a flexible circuit board according to claim 8, wherein the bent portion structure is any one of the upper surfaces . A wiring layer formed of a resin layer and a metal foil, and at least one portion of the wiring is provided with a bending portion with any of repetitive operations selected from the group consisting of sliding bending, bending bending, hinge bending, and sliding bending. A method of manufacturing a flexible circuit board to be used.
The metal foil is made of a copper foil having a cubic crystal structure, and the ridge line at the bent portion has an angle of 2.9 to 87.1 ° with one of the basic crystal axes <100> in the plane of the copper foil. A method of manufacturing a flexible circuit board, wherein wiring is formed on the substrate. The intensity (I) of the (200) plane determined by X-ray diffraction in the thickness direction of the copper foil is I / I ₀ relative to the intensity (I ₀ ) of the (200) plane determined by X-ray diffraction of fine powder copper. The method for manufacturing a flexible circuit board according to claim 10, wherein ≧ 25 . The copper foil is a rolled copper foil, and the rolled copper foil has a basic crystal axis <100> of a unit cell having a face-centered cubic structure with respect to two orthogonal axes of the thickness direction of the copper foil and one direction in the foil surface. The method for manufacturing a flexible circuit board according to claim 11, wherein the cubic texture is exhibited by heat treatment so that the preferential orientation region having an orientation difference within 10 ° occupies 50% or more in terms of area ratio . The manufacturing method of the flexible circuit board in any one of Claims 10-12 which forms wiring along the direction orthogonal to the ridgeline in a bending part . The electronic device carrying the flexible circuit board in any one of Claims 1-7.

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