KR101690491B1 - Flexible circuit board and structure of bend section of flexible circuit board - Google Patents

Abstract

In particular, the present invention provides a flexible circuit board having durability against severe conditions in repeated bent portions having a small radius of curvature and excellent bendability.
1. A flexible circuit board comprising a resin layer and a wiring formed of a metal foil and having a bent portion in at least one of the wiring lines, wherein the metal foil is made of a metal having a face-centered cubic structure, 100 > represents a preferred orientation region within an orientation difference of 10 degrees occupying 50% or more in area ratio with respect to two orthogonal axes in a thickness direction of the metal foil and in one thin direction, The breaking extension of the metal foil in the normal direction with respect to the end face P of the wiring cut in the thickness direction of the metal foil is 3.5% or more and 20% or less.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a flexible circuit board and a flex circuit structure of the flexible circuit board,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a flexible circuit board and a flex circuit structure of a flexible circuit board which are used with a bent portion at any position, and more particularly to a flexible circuit board having flexibility A circuit board, and a bent portion structure of a flexible circuit board.

 A flexible printed circuit board (flexible printed circuit board) comprising a wiring made of a resin layer and a metal foil can be folded and used. Therefore, a movable portion in a hard disk, a hinge portion, a sliding sliding portion, A head portion of a printer, an optical pickup portion, a moving portion of a notebook, and the like, as well as various electronic and electric devices. In recent years, flexibil- ity corresponding to various movements of electronic apparatuses and the like has been demanded, especially, by folding the flexible circuit board in a limited space and storing it in a limited space, especially with the miniaturization, thinning, and high- Therefore, it is necessary to further improve the mechanical properties such as the strength of the flexible circuit board so that the flexible circuit board can cope with a bending operation in which the bending radius becomes smaller or a bending operation is repeated frequently.

Generally, it is a wiring side rather than a resin layer that causes a failure due to repetition of bending or a decrease in strength against bending with a small radius of curvature. If these elements can not withstand this, cracking or breakage occurs in a part of the wiring, It becomes unavailable. Therefore, for example, in order to reduce the bending stress on the wiring in the hinge portion, a flexible circuit board obliquely wired with respect to a turning axis (see Patent Document 1) or a rotation of the hinge portion And a method of reducing the damage by reducing the change of the diameter of the helix due to the opening and closing operation by increasing the number of the helium waves (see Patent Document 2) have been proposed . However, in all of these methods, the design of the flexible circuit board is limited.

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 surface of the rolled copper foil was determined by the X- I ₀ > 20 with respect to I ₀ (see Patent Documents 3 and 4). That is, since the flexibility of the copper foil is improved as the cubic orientation, which is the recrystallized texture of copper, is developed, a preferable copper foil as the wiring material of the flexible circuit board, in which the development degree of the cubic texture is defined by the above parameter (I / I ₀ ) It is known. A rolled copper alloy foil obtained by annealing and recrystallizing the copper foil at a concentration in the range that the elements such as Fe, Ni, Al and Ag are dissolved in the copper, It has been reported that it is easy to deform and excellent in flexibility (refer to Patent Document 5).

A copper foil containing an impurity such as oxygen or silver may be used for a flexible circuit board requiring high bending properties. When the purity is copper, it is about 99% to 99.9% by mass. Unless otherwise stated in the present invention, the purity is expressed as mass concentration. In the test level, tough pitch copper having a purity of about 99.5%, which is widely used as a conductor of a cable, or oxygen-free copper not containing oxides is used (see Patent Documents 3 and 4). Tough pitch copper impurities include hundreds of ppm of oxygen (mostly included as copper oxide), silver, iron, sulfur, phosphorus and the like. Oxygen-free copper is usually copper with a purity of 99.96 to 99.995%, which is greatly reduced in oxygen to below 10 ppm. In the above-described Patent Documents 3 and 4, it is reported that the copper foil produced from oxygen-free copper has better bending fatigue characteristics than the tough pitch copper foil and the presence or absence of copper oxide. On the other hand, when the purity of these copper is further increased, it is necessary to remove impurities such as silver, phosphorus and sulfur.

Japanese Patent Application Laid-Open No. 2002-171033 Japanese Patent Application Laid-Open No. 2002-300247 Japanese Patent Application Laid-Open No. 2001-58203 Japanese Patent Publication No. 3009383 Japanese Patent Application Laid-Open No. 2007-107036

Under such circumstances, the present inventors have conducted intensive studies to obtain a flexible circuit board having durability against repeated bending or bending with a small radius of curvature, without restriction on the design of the flexible circuit board. As a result, It has been found that a flexible circuit board excellent in bending durability and flexibility can be obtained by using a metal foil having a crystal structure of a face-centered cubic system having a large breaking elongation, and completed the present invention.

Therefore, it is an object of the present invention to provide a flexible circuit board having excellent durability, and particularly to a harsh use condition accompanied by repeated bending with a small radius of curvature, such as a hinge portion or a slide sliding portion of a cellular phone, To provide a flexible circuit board which exhibits durability and is excellent in flexibility.

Another object of the present invention is to provide a flexible circuit board having durability against harsh conditions such as a hinge portion or a slide sliding portion of a cellular phone or a small electronic device, particularly a repeated bending portion having a small radius of curvature, To provide a bent structure.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the prior art, and as a result, the following constitution is devised.

(1) A flexible circuit board having a resin layer and a wiring formed of a metal foil and having a bent portion in at least one of wiring lines,

The metal foil is made of a metal having a face-centered cubic structure, and the basic crystal axes of the unit cell of the face-centered cubic structure are oriented along the thickness direction of the metal foil and two orthogonal axes in one direction existing in the foil surface The preferred orientation region within 10 deg. Of the azimuthal difference occupies 50% or more of the area ratio, and the rupture height of the metal foil in the normal direction to the cross section P of the wiring cut in the thickness direction of the metal foil from the ridge line at the bent portion Is not less than 3.5% and not more than 20%.

(2) The flexible circuit board according to (1), wherein the metal foil is a copper foil having a purity of 99.999 mass% or more.

(3) The flexible circuit board according to (1) or (2), wherein the metal foil is a copper foil and the crystal grain size when viewed in the normal direction of the slope is 25 m or more.

(4) The flexible circuit board according to any one of (1) to (3), wherein the thickness of the metal foil is 5 탆 or more and 18 탆 or less.

(5) The cross-section P of the wiring is divided into (20 1 0) to (20 20) in the rotation direction from (100) to (110) with [001] being the positive axis (1) to (4), wherein the main direction of the flexible printed circuit board is a principal direction on one side included in the range of the width of the flexible circuit board.

(6) The term (P) of the wiring is a surface on a line segment connected to a point representing (110) and a point representing (20 1 0) in a stereo triangle of the standard projection diagram, ≪ / RTI >

(7) The flexible circuit board according to any one of (1) to (6), wherein a wiring is formed along a direction orthogonal to the ridge line in the bent portion.

(8) The flexible circuit board according to any one of (1) to (7), wherein the resin layer is made of polyimide.

(9) The flexible circuit according to any one of (1) to (8), which is used to form a bent portion with any one of repeated operation selected from the group consisting of sliding bending, bending bending, hinge bending and slide bending Board.

(10) An electronic apparatus mounted with the flexible circuit board according to any one of (1) to (9) above.

(11) A bent structure of a flexible circuit board having a resin layer and a wiring formed of a metal foil and having a bent portion in at least one of the wiring,

The metal foil is made of a metal having a face-centered cubic structure and the basic crystal axes of the unit cell of the face-centered cubic structure are oriented in the thickness direction of the metal foil and the two orthogonal axes in any one direction existing in the thin- Of the metal foil in the normal direction with respect to the section P of the wiring cut in the thickness direction of the metal foil from the ridge in the bent portion occupies not less than 50% Or less of the width of the flexible circuit board.

According to the present invention, the metal foil constituting the wiring at the bent portion when the flexible circuit board is bent is less likely to cause metal fatigue and has excellent durability against stress and distortion. Therefore, there is no restriction on the design of the flexible circuit board, and it is possible to provide a flexible circuit board which has sufficient rigidity to withstand repeated bending and bending with a small radius of curvature and is excellent in flexibility, A high-durability electronic device including a thin display, a hard disk, a printer, and a DVD device can be realized.

Fig. 1 is a diagram showing the relationship between a positive major axis in a crystal structure of a cubic system and a plane obtained by rotating the main axis.
Figure 2 is a stereo triangle of the (100) standard projection.
3 is a cross-sectional explanatory view showing a state in which the flexible circuit board is bent.
(A) and (b) show a flexible circuit board according to the present invention, and (c) and (d) show a flexible printed circuit board according to the present invention, Shows a flexible circuit board of the prior art.
5 is a perspective view of a single-sided copper-clad laminate.
6 is a plan explanatory view showing a state in which a test flexible circuit board is obtained from a single-sided copper clad laminate in an embodiment of the present invention.
7 is an explanatory diagram of the MIT bending test apparatus.
Fig. 8 (a) is an explanatory view of the IPC bending test apparatus, and Fig. 8 (b) is a cross-sectional view taken along line XX 'of the flexible circuit board for testing used in the IPC bend test.

The wiring provided in the flexible circuit board of the present invention is formed by a metal foil made of a metal having a face-centered cubic system crystal structure. As the metal having a crystal structure of face-centered cubic system, for example, copper, aluminum, nickel, silver, rhodium, palladium, platinum, gold and the like are known, and any of these metals is preferable. Among them, a copper foil mainly used as a wiring of a flexible circuit board is the most common.

The present invention provides a flexible circuit board excellent in bending durability and flexibility, and in particular, to provide a flexible circuit board having excellent fatigue characteristics in a high warp region with a radius of curvature of 2 mm or less. In order to achieve this object, in the present invention, even if either of i) the metal foil is highly oriented and ii) the metal foil has a large breaking elongation in the principal stress direction in the bent portion, Which is resistant to fatigue failure of the flexible circuit board. That is, by satisfying both i) and ii) at the same time, a flexible circuit board which is resistant to fatigue fracture at high bending can be obtained. Concretely, i) preferred crystal orientation of the unit crystal lattice of the face-centered cubic structure is defined as a preferred orientation region within the orientation difference of 10 ° with respect to two orthogonal axes in either one of the thickness direction of the metal foil and the thin- Ii) the breaking elongation of the metal foil in the normal direction with respect to the cross-section P of the wiring cut in the thickness direction of the metal foil from the ridge in the bent portion needs to be not less than 3.5% and not more than 20%.

When the metal foil is a polycrystalline material such as that shown in a general electrolytic foil or a rolled foil, a high breaking elongation can be obtained. However, the flexible circuit board does not have a high fatigue property with respect to the high twist fatigue required in the present invention. On the other hand, when the texture is developed and the degree of orientation is increased but the elongation at break is small, a flexible circuit board having the characteristics required by the present invention can not be obtained.

The present invention has for the first time revealed that breaking of a metal foil in a flexible circuit board, which is particularly required to have a high bending property, is an important factor, provided that the metal foil is a metal foil having a developed texture and a high degree of orientation.

The metal foil may be either a rolled foil or an electrolytic foil, but it is preferably a rolled foil in order to obtain high orientation. In the case of the face-centered cubic metal, by studying the rolling conditions and the heat treatment conditions, it is possible to manufacture a metal foil having a highly oriented cubic texture having <100> kitchens in the rolling direction and the normal direction of the slab surface.

Regardless of the use of the flexible circuit board, the mechanical characteristics of the metal foil having a strong cube orientation are anisotropic in breaking elongation. The elongation at break is very small when stretched in the <100> direction. Generally, as the degree of orientation increases, and as the thickness of the metal foil decreases, the breaking elongation at the time of tensile test in the <100> direction decreases. The basic crystal axis <100> of the unit cell of the face-centered cubic structure is oriented in the direction of the thickness of the metal foil (the normal direction of the sloped face) and the two orthogonal axes in one direction (one of them is the rolling direction) (Hereinafter referred to as "conventional rolled copper foil" for simplicity) having a thickness of 18 탆 or less while the preferred orientation region within 10 ° occupies 95% or more in area ratio, Height does not reach 3.5%. The term "elongation at break" as used herein refers to a test piece having a width of 5 to 15 mm, typically having a width sufficiently larger than the thickness of the metal foil, and a tensile test is conducted at a warp rate of 10% / min It refers to the elongation from the fracture to the fracture. In the present invention, it is assumed that a value obtained after obtaining the flexible circuit board by obtaining the elongation at break of the metal foil by the measuring method described in the following embodiment and stacking it with the resin layer.

In the case of the rolled copper foil, the recrystallized texture is oriented in the rolling direction, that is, the <100> direction in the longitudinal direction of the metal foil. In a conventional flexible circuit board, when the substrate is taken out, the longitudinal direction of the circuit and the longitudinal direction of the copper foil coincide with each other in terms of increasing the yield. Therefore, in the conventional use mode of bending the longitudinal direction of the circuit, the principal stress direction coincides with the < 100 > direction, so that the conventional rolled copper foil can not obtain high fatigue characteristics with respect to the repeated bending.

As a method for improving the fatigue characteristics of a flexible circuit board used in such a bearing relationship, the present invention contemplates a high-purity metal foil to be used. In the flexible circuit board used for high flexing applications, a copper foil in which impurities such as oxygen or silver are intentionally or inevitably contained is used. This is, for example, as disclosed in Patent Document 5, for the purpose of facilitating shear deformation along a slip surface or suppressing an increase in electrical resistance. However, these impurity elements deteriorate the stacking defect energy. The present inventors paid attention to this point. That is, when the stacking defect energy is lowered, the dislocation tends to expand and cross slip does not easily occur, and in particular, it is difficult to elongate when stretched in the <100> direction.

Therefore, in the present invention, by using a metal foil (preferably a copper foil) having a predetermined preferential orientation as described below and preferably having a purity of 99.999% or more, the breaking elongation in the <100> direction is increased to 3.5% And as a result, the fatigue characteristic when the warp is repeatedly applied in the high warp region is enhanced. It is preferable that the purity of the metal foil is high, but it is most preferable to use 99.999% to 99.9999% from the viewpoint of production cost. In the case of an oxygen-free copper foil having a low oxygen concentration even in the case of a copper foil having a purity of lower than 99.999%, one of the basic crystal axes of the face-centered cubic structure, for example, [ 001] axis is 98% or more and 99.8% or less in the direction of the thickness direction (thin plane normal direction) of the metal foil, there is a region where the elongation at break is 3.5% or more and the flexural fatigue resistance is good It becomes. For this reason, although it is not clear at this time, in the anaerobic copper foil in which a predetermined texture is obtained by heat treatment, the presence of the recrystallized residual structure relative to the <212> orientation with respect to the rolling direction dispersed in an appropriate size and volume ratio, It is presumed that the elongation at break is increased.

In 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, and the degree of integration of the aggregate structure is in the following range. That is, a region where one of the basic crystal axes <100> of the face-centered cubic structure, for example, the [001] axis, is within 10 ° in the direction of the thickness of the metal foil Of the metal foil has a preferential orientation occupying not less than 75%, more preferably not less than 98%, and at the same time, within a thin plane which is a direction parallel to the surface of the metal foil, Of the region occupies 50% or more, preferably 85% or more, and more preferably 99% or more of the area ratio. In the present invention, at least the bending portion may have the degree of integration of the aggregate structure. Preferably, the metal foil laminated on the resin layer is a so-called single crystal-like metal foil having the above- It is preferable because it is not restricted by wiring design. On the other hand, since the crystal orientation at the center of the orientation is referred to as the kitchen surface of the texture, the metal foil used in the present invention has a <100> thickness in the thickness direction of the metal foil, It can be said to have a kitchen.

There are several indexes indicating the degree of preference of the preferred orientation of the texture, that is, the orientation degree or the degree of integration, and an index based on objective data using statistical data of X-ray diffraction intensity and local three-dimensional orientation data obtained by electron beam diffraction can be used .

For example, in the case where the metal foil is a copper foil, the strength (I) from the (002) plane perpendicular to the normal axis obtained by X-ray diffraction (here, the strength of the (200) plane according to the general notation in X- is, good to form the wiring having a predetermined pattern from I / I ₀ ≥25 is a copper foil with respect to the intensity (I ₀₎ of the (200) plane determined by X-ray diffraction of a copper fine powder, preferably from I / I ₀ 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 positive axes of (100) and (110), that is, the common axis, and is one of objective indices showing the degree of development of the cube assembly texture. When the metal foil is a rolled copper foil, it is strengthened at a certain rolling rate and then heat-recrystallized to form a recrystallized cubic body (100) on the kitchen (001) Defense develops. The flexural fatigue life of the copper foil is improved as the cubic orientation, which is the recrystallized texture of copper, develops. Can not be sufficiently expected to increase fatigue life of the wire winding is smaller than the flexible circuit substrate on which an I / I ₀ 25 of the present invention, if the I / I ₀ is more than 33 it is bent significantly improved fatigue life. On the other hand, the X-ray diffraction in the thickness direction of the copper foil is to confirm the orientation of the surface of the copper foil (rolled surface in the case of rolled copper foil) and the intensity I of the (200) The intensity integral of the surface is shown. The intensity (I ₀ ) represents the integral value of the intensity of the (200) plane of the fine powder copper (I grade copper powder, reagent grade 325 mesh, manufactured by Kanto Kagaku).

In order to increase the I / I ₀ to 25 or more, it is sufficient to obtain the recrystallized texture of the copper foil. However, this means is not particularly limited, and the intermediate annealing condition or the cold rolling rate may be varied depending on the type of metal foil or the impurity concentration by optimization, the crystal particles can be obtained in a rolled copper foil large texture, yet I / I ₀ ≥25. For example, after a copper clad laminate is obtained by laminating a resin layer and a rolled copper foil, the copper foil is subjected to heating conditions such that a temperature of 300 to 360 ° C is loaded for 5 minutes or more at an integration time, .

Also, in order to define the texture of the texture as a three-dimensional density, it may be specified using the area ratio of the preferred orientation area falling within 10 deg. On the kitchen of the texture. That is, the crystal orientation of the predetermined surface of the metal foil can be determined by an electron beam diffraction method such as EBSP (Electron Back Scattering Pattern) method or ECP (Electron Channeling Pattern) method, a micro-Laue method X-ray diffraction method. Among them, the EBSP method analyzes a crystal from a diffraction image called a pseudo-Kikuchi line diffracted from each crystal plane generated when a convergent electron beam is irradiated onto the surface of a sample to be measured, And the crystal orientation of the texture in a region that is smaller than the X-ray diffraction method can be analyzed. For example, the crystal orientation of each microdomain can be specified, and they can be mapped to each other. A gradient of the plane orientation between each mapping point (azimuth difference) is equal to or less than a constant value, (Crystal grains) having a grain boundary can be revealed to obtain a bearing mapping image. It is also possible to specify the orientation including the orientation face having a direction within a predetermined angle with respect to the specific face orientation, and to extract the existence ratio of each face orientation as the area ratio. In the EBSP method, in order to obtain an area ratio of a region within a certain angle from a specific orientation, at least a region larger than the circuit bending region of the flexible circuit substrate of the present invention is formed so as to have a sufficient score It is necessary to obtain the average information by scanning the electron beam. In the case of the metal foil to be used in the present invention, it is necessary to measure 1000 points or more in order to obtain an average area ratio in an area of 0.005 mm &lt; 2 & .

However, the organizational differences in the invention described in the present invention and Patent Documents 3 and 4 are that the defense regulations of the invention of these patent documents are only in the direction of the normal line measured by X-rays, while the present invention is defined in three dimensions . In order to obtain high fatigue characteristics with respect to bending, it is important that the <100> density in the main stress direction, that is, the slope, especially in the main bending when bent. In the present invention, it is preferable that the size of the recrystallized particles, that is, the crystal grains having the cubic orientation is 25 mu m or more in average value.

Further, in the present invention, when a high flexibility is required, it is preferable to use a rolled copper foil having a thickness of 5 to 18 탆, preferably a rolled copper foil having a thickness of 9 to 12 탆 . If the rolled copper foil is thicker than 18 占 퐉, it becomes difficult to obtain a flexible circuit board having excellent fatigue characteristics in a high warp region such as a radius of curvature of 2 mm or less. If the thickness is smaller than 5 占 퐉, handling in laminating the metal foil and the resin layer becomes difficult, and it is difficult to form a homogeneous flexible circuit board.

Unlike the first measure for improving the fatigue characteristic of the flexible circuit board described above, the second measure for improving the fracture elongation of the face-centered cubic metal foil that is close to the highly oriented single crystal is that the breaking extension is small > Direction of the flexible circuit board is not in the direction of principal stress, the wiring configuration of the flexible circuit board may be studied. Specifically, the following methods can be mentioned.

By studying rolling and recrystallization conditions as described in the first measure, it is possible to produce a metal foil having a highly oriented cube texture with a <100> kitchen in both the rolling direction and the thinnormal direction. Furthermore, by cutting the circuit at an angle from the rolling direction, that is, from the <100> direction by cutting the circuit at an angle, the flexible circuit board having a large breaking elongation in the direction of principal stress when bent is obtained. By this method, in order to make the breaking elongation of the metal foil in the normal direction (principal stress direction in the bent portion) to the cross-section P of the wiring cut in the thickness direction of the metal foil from the ridge in the bent portion to 3.5% P must be on the kitchen surface on either side included in the range from (20 1 0) to (120 0) with [001] as the major axes. Here, the relationship between the positive axis and the plane orientation is shown in Fig. (100) to (110) in the range of (100) to (010) in which [001] is the axis, ). That is, when these are plotted on the inverse pole diagram with respect to the normal orientation of the cross section P, the respective faces of (001), (20 1 0), and (110) become as shown in FIG. Due to the symmetry, (1 20 0) on the inverse poles is displayed at the same position as (20 1 0). The metal of the metal foil in the present invention is a face-centered cubic structure. In the present invention, when the <100> preferred orientation exists in the thickness direction of the metal foil (the direction perpendicular to the surface of the metal foil), the axis of the unit lattice is [001], [010] , I.e., the slope orientation is denoted by (001), which is equivalent to changing the axes due to the symmetry of the face-centered cubic structure, and these are, of course, included in the present invention.

(Relative to the perpendicular to the wiring cross-section P) of the wire when the kitchen top in the thin plane is cut in the main twist direction of the bent portion, that is, in the thickness direction from the ridge line at the bent portion, from 2.9 to 87.1 (20 1 0) to (120 0), preferably an angle of 5.7 ° to 84.3 ° [(10 10) to (10 0)], more preferably an angle of 11.4 More preferably from 26.6 ° to 63.4 ° [(210) to (120)], most preferably from 30 ° or 60 ° [(40 23 0) or (23 40 0)]. Here, [] represents the plane orientation of the section P corresponding to each angle. On the other hand, it can be described that the normal to the wiring cross-section P has an angle of 2.9 to 45 with the basic crystal axis <100> in the metal foil due to the symmetry of the crystal.

Here, the cross section P of the wiring when cut in the thickness direction from the ridge in the bent portion means that the ridge L is formed on the outside of the flexible circuit board when the flexible circuit board is bent in a U- And is a wiring portion in a cross section obtained when the wiring board is cut from the ridgeline (L) in the thickness direction (d) of the flexible circuit board. The ridgeline L is a line connecting a vertex formed when the end surface of the flexible circuit board is viewed along the bending direction (bold arrow in Fig. 3) in a state where the flexible circuit board is bent. On the other hand, for example, a case in which the ridge L moves the flexible circuit board, such as a sliding bending to be described later, is also included. 3, the resin layer 1 is on the outer side and the wiring 2 is curved inward (the side on which the circle having a radius of curvature is inward is referred to as the inner side) Of course it is a way.

For various applications, the metal foil is mainly subjected to tensile or compressive stresses when subjected to a forced displacement of a certain curvature. In flexed flexible circuit boards, which part is tensioned or compressed varies depending on the configuration of the metal foil and the resin, but the farthest part of the flexure from the neutral axis (or neutral plane) of tension and compression, And the tensile stress in the direction of the section normal line of the wiring when it is cut in the thickness direction from the ridgeline in the bent portion becomes the main stress. In other words, the principal stress direction of the wiring in the bent portion is the direction indicated by the arrow 21 in Fig. 3, and is typically the same as the normal direction to the wiring section P cut in the thickness direction of the metal foil from the ridge of the bent portion, Axis perpendicular to the [001] axis.

Considering the mechanical characteristics of the metal foil in the flexible circuit board, the stress warping characteristic when the metal foil is simply pulled in the direction of the main stress indicated by the arrow 21 in Fig. 3 becomes an important characteristic. As shown in the examples of FIGS. 4 (c) and 4 (d), when the metal foil having the crystal structure of the face-centered cubic system is bent to form a ridge orthogonal to the [100] axis of the metal foil, The cross section of the wiring cut in the thickness direction of the wiring substrate is a (100) plane. The cross section P of the wiring when cut in the thickness direction from the ridge line at the bent portion is [001] (Both arrows in the drawing) in the range from (20 1 0) to (120 0) in the rotating direction from (100) to (010) Can be improved. On the other hand, FIG. 1 shows a range of (20 1 0) to (120 0), but in the crystal structure of the face-centered cubic system, there is a plane equivalent to the plane included in this range. Therefore, the present invention encompasses planes whose cross-sections are equivalent to the planes whose cross-sections are included in the range of (20 1 0) to (120 0).

In the second measure, since the cross-section P of the wiring when cut in the thickness direction from the ridge in the bent portion is preferentially oriented with the kitchen at a specific orientation between (20 1 0) and (120 0) The reason why the elongation at break is improved is that when a tensile stress is applied in the normal direction of the cross section P, that is, in the principal stress direction, a Schmid factor among the eight {111} The reason for this is that since the largest main slip surface is four, the shear slip becomes good and local work hardening hardly occurs. In a conventional rolled copper foil, the longitudinal direction of the metal foil corresponds to the rolling direction, and as shown in Fig. 4 (c) or (d), a circuit is usually formed along the kitchen surface <100>. For example, the embodiment of Patent Document 5 corresponds to the form of Fig. 4 (d). When the cross-sectional orientation of the wiring when cut in the thickness direction from the ridgeline in the bent portion is set to (100), when the bent portion is bent, the slip surfaces of the eight slip surfaces are equivalent and eight slip systems act simultaneously, The potential is likely to accumulate. Due to the difference from this prior art, the flexural characteristics of the flexible circuit board employing the second strategy are superior to those of the conventional mode of bending in the longitudinal direction of the circuit.

Regarding the cross-section P in the flexible circuit board, the most preferred orientation is 30 ° or 60 ° with respect to the cross-sectional normal direction of the wiring when cut in the main twist direction of the bent portion, that is, in the thickness direction from the ridge in the bent portion, This is because the direction of stress coincides with the stable orientation of the tensile. Considering the above mechanism, at least the cross-section P of the wiring when cut in the thickness direction from the ridge line at the curved portion is a straight line extending from (20 1 0) to (120 0) It is only necessary to have a preferred orientation with a certain orientation on the kitchen.

That is, the second measure of the present invention is that the metal foil has a face-centered cubic structure, the thickness direction of the metal foil is on the kitchen of <100>, the inside of the foil surface of the metal foil has a kitchen of <100> A wiring such that the normal direction of the cross section P of the wiring when cut in the thickness direction from the ridge line is preferentially oriented in the specific orientation between (20 1 0) and (120 0) is provided. At this time, the normal direction of the cross-section P is preferably preferentially oriented with the kitchen at a specific orientation between (10 10) and (10 0), more preferably at (510) 110), more preferentially orientated with specific orientation between (210) and (110), most preferably with (40 23 0) in the center of gravity. [001] In the case of a metal foil whose foil face is preferentially oriented on the kitchen surface, for example, [001] and [100] in the foil face are equivalent, and from the ridge line in the bent portion of the flexible circuit board in the present invention, The top of the cross section P of the wiring at the time of cutting may be described as a specific orientation between (120O) and (110), and preferably, It may be described that it is preferable that the liquid crystal molecules are preferentially oriented with respect to the center of the liquid crystal molecules, and most preferably, (2340 0).

The cross section P of the wiring when the metal foil has a thickness of <100> in the thickness direction and the inside of the foil of the metal foil has a <100> kitchen and is cut in the thickness direction from the ridge line at the bent portion, (100) to (120 0) means that when an inverse pole is displayed on a stereo triangle of the standard projection shown in FIG. 2, The cross-sectional orientation of the wiring when cut in the thickness direction may be referred to as a plane on a line segment connected by a point representing (20 1 0) and a point representing (110). Further, the flexible circuit board in the second policy means is constituted so that the wiring is formed of a material in which the thickness direction of the metal foil is the (3) axis oriented with the [001] axis and the sectional normal line of the wiring when cut in the thickness direction from the ridge line at the bent portion May be said to have an angle in the range of 2.9 DEG to 87.1 DEG with respect to the [100] axis in the thin plane.

According to the second measure, the breaking extension of the metal foil in the principal stress direction in the bent portion can be made 3.5% or more, metal fatigue hardly occurs in repeated warpage or stress with a radius of curvature of 2 mm or less, A flexible circuit board is obtained. Further, in the present invention, by combining the above-described first policy and the second policy, a flexible circuit board excellent in metal fatigue characteristics and flexibility can be obtained more reliably, and the elongation of the metal foil in the principal stress direction is preferably 3.5% , It may be 4% or more, and more preferably 9% or more. On the other hand, with respect to the upper limit of the elongation at break, the basic crystal axis <100> of the unit cell of the face-centered cubic structure is parallel to the thickness direction of the metal foil (normal direction of the sloped surface) The upper limit of the rolled foil which can be taken in the range of the present invention is 20% or less, which is 50% in area ratio and 18 탆 in thickness, Of the unit crystal lattice occupies 95% or more in area ratio with respect to two orthogonal axes in the thickness direction of the copper foil and any one direction existing in the thin plane, , The upper limit of the elongation at break is 15% or less.

With respect to the resin layer of the flexible circuit board in the present invention, the type of the resin forming the resin layer is not particularly limited and those used in conventional flexible circuit boards are exemplified. For example, polyimide, polyamide, Polyester, liquid crystal polymer, polyphenylene sulfide, polyether ether ketone, and the like. Among them, polyimide and liquid crystal polymer are preferable because they exhibit good flexibility and excellent heat resistance when used as a circuit board.

The thickness of the resin layer can be appropriately set according to the use, shape, and the like of the flexible circuit board. It is preferably in the range of 5 to 75 mu m, more preferably in the range of 9 to 50 mu m, Is most preferable. If the thickness of the resin layer is less than 5 占 퐉, the insulation reliability may deteriorate. On the other hand, if the thickness exceeds 75 占 퐉, there is a fear that the thickness of the entire circuit board becomes too thick when mounted on a small- do.

Further, when the flexible circuit board is applied to a slide sliding portion of a cellular phone or the like, a cover member made of a cover lay film or the like is bonded and used on a wiring formed of a metal foil. In this case, It is preferable to design the constitution of the cover material and the resin layer in consideration of the balance of the stress. According to the knowledge of the present inventors, for example, polyimide having a tensile modulus at 25 ° C of 4 to 6 GPa and a thickness of 14 to 17 μm is used as a resin layer, and an adhesive layer made of a thermosetting resin having a thickness of 8 to 17 μm A cover layer film having two layers of a polyimide layer having a thickness of 7 to 13 占 퐉 and a tensile modulus of 2 to 4 GPa of the entirety of the adhesive layer and the polyimide layer as cover materials and a constitution in which the cover layer has a tensile modulus at 25 占 폚 of 6 To 8 GPa and a thickness in the range of 12 to 15 mu m as a resin layer and has two layers of an adhesive layer made of a thermosetting resin having a thickness of 8 to 17 mu m and a polyimide layer having a thickness of 7 to 13 mu m, And a cover layer film having a tensile modulus of 2 to 4 GPa as a whole of the polyimide layer as a cover material.

With respect to 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 lamination method). Examples of the polyimide film used in the lamination method include "Kapton" (Toray DuPont), "Apical" (Kaneka Kabushiki Kaisha), "UPILEX" (Ube Kosan Co., Ltd.), and the like. When the polyimide film and the metal foil are heat-pressed, it is preferable to interpose a thermoplastic polyimide resin exhibiting thermoplasticity. From the viewpoint of easy control of the thickness and bending property of the resin layer, a polyimide precursor solution (also referred to as a polyamic acid solution) is applied to a metal foil, followed by drying and curing to obtain a laminate (so-called casting method) .

The resin layer may be formed by laminating a plurality of resins, for example, two or more kinds of polyimides having different coefficients of linear expansion or the like may be laminated. At this time, an epoxy resin or the like is used as an adhesive from the standpoint of ensuring heat resistance and flexibility It is preferable that all of the resin layers are formed substantially of polyimide. The tensile modulus of the resin layer, including the case of a single polyimide and the case of a plurality of polyimides, is preferably 4 to 10 GPa, and more preferably 5 to 8 GPa.

In the flexible circuit board of the present invention, it is preferable that the linear expansion coefficient of the resin layer is in the range of 10 to 30 ppm / ° C. In the case where the resin layer is made of a plurality of resins, the coefficient of linear expansion of the entire resin layer may be in this range. In order to satisfy such a condition, for example, a low-thermal-expansion polyimide layer having a linear expansion coefficient of 25 ppm / ° C or less, preferably 5 to 20 ppm / ° C, and a linear expansion polyimide layer having a linear expansion coefficient of 26 ppm / A resin layer comprising a polyimide layer having a high thermal expansion coefficient of 80 ppm / ° C and adjusting the thickness ratio thereof to 10 to 30 ppm / ° C. The ratio of the thickness of the low-swellable polyimide layer to the thickness of the high-swelling polyimide layer is in the range of 70:30 to 95: 5. It is preferable that the low expansion polyimide layer is a main resin layer of the resin layer and the high linear expansion polyimide layer is in contact with the metal foil. On the other hand, the coefficient of linear expansion was obtained by raising the temperature to 250 DEG C using a thermomechanical analyzer (TMA), cooling at a rate of 10 DEG C / min, Lt; 0 &gt; C. &Lt; / RTI &gt;

In addition, the flexible circuit board of the present invention is provided with a resin layer and a wiring formed of a metal foil, and the flexible circuit board is used with a bent portion at any position. That is, it is widely used in various electronic appliances such as a moving part in a hard disk, a hinge part or a sliding part of a cellular phone, a head part of a printer, an optical pickup part, a moving part of a notebook computer, etc., and the circuit board itself is bent or twisted Or deformed according to the operation of the mounted device, so that a bent portion is formed at any position. Particularly, since the flexible circuit board of the present invention has a bending part structure with excellent bending durability, it can be applied to a case where the bending part frequently bends due to repetitive operations such as sliding bending, bending bending, hinge bending, slide bending, In a rigid use condition in which the radius of curvature is 0.38 to 2.0 mm in the bending behavior, 1.25 to 2.0 mm in the sliding bending, 3.0 to 5.0 mm in the hinge bending, and 0.3 to 2.0 mm in the sliding bending And is especially effective in slide applications where the demand for bending performance is tight in a narrow gap of 0.3 to 1 mm.

As one of the methods for producing the flexible circuit board in the present invention, i) a rolled metal foil having a cube aggregate structure in which the [001] axis is finally oriented to the thin-plane normal (water line to the surface of the metal foil) The direction of the normal line of the wiring when cut in the thickness direction from the ridgeline at the bent portion is set to be 2.9 ° to 2.9 ° with respect to the [100] kitchen in the thin metal foil, Or ii) the metal foil constituting the wiring is made to have a purity of 99.999% or more, or iii) the method of i) and ii) may be simultaneously adopted.

At this time, the metal foil does not necessarily have to show the cube assembly texture from the beginning, and the cube assembly texture may be formed by the heat treatment. For example, in the manufacturing process of the flexible circuit board, And the cube texture may be formed by heat treatment. That is, one of the basic crystal axes <100> of the unit lattice is preferentially oriented in the thickness direction of the metal foil so that the area within 10 ° of the azimuth difference from the <100> axis occupies 50% or more of the area ratio by the heat treatment, The other one of the basic crystal axes may be preferentially oriented in the horizontal direction with respect to the surface of the metal foil so that the area within 10 deg. The recrystallized texture of the rolled copper foil usually has a rolling surface orientation of {100} and a rolling direction of < 100 >. Therefore, a (001) kitchen top is formed as the rolled surface orientation. Further, when a metal foil having a purity of 99.999% or more is used, it is possible to secure a break elongation of 3.5% or more even if a circuit is formed in any orientation and wiring, and a flexible circuit board having a wide application range can be formed.

As shown in Fig. 3, for example, when the flexible circuit board is bent in a U-shape, the outer side (the side on which the inscribed circle having a radius of curvature is formed) A ridge L is formed on the other side of the metal foil so that the ridge L has a slope in the range of? = 2.9 to 87.1 (?) In a state where the ridge L is perpendicular to the [100] . Examples of such states are shown in Figs. 4 (a) and 4 (b). For reference, (c) and (d) of FIG. 4 show a state where the ridge line is orthogonal to the [100] axis (? = 0). Here, if? Is less than 2.9 占, a definite effect on the flexibility is not confirmed. When α = 11.4 to 78.6 (°), the bending durability of the bent portion structure is further improved. On the other hand, in the present invention, the cross section P of the wiring when cut in the thickness d direction from the ridge in the case of? = 2.9 corresponds to the (20 1 0) plane, Corresponds to the (110) plane, and when? = 87.1, the plane P corresponds to the (120) plane. In addition, since [100] and [010] are equivalent in the face-centered cubic structure, the angular range of the angle [alpha] formed by the ridge line and the orthogonal axis in the thin plane [100] as shown in Figs. The angle range between [100] and the section normal (P), and the angle range between [100] and the ridge line.

The width, shape, pattern, etc. of the wiring are not particularly limited and may be suitably designed according to the use of the flexible circuit board and the electronic equipment to be mounted. The bending structure of the present invention is excellent in bending durability, It is not necessary to perform wiring in a direction oblique to the pivot axis of the hinge portion in order to reduce the bending stress on the wiring. For example, it is unnecessary to conduct wiring in a direction orthogonal to the ridge line at the bent portion, It is possible to perform wiring with a minimum shortest distance. 4 (a) and 4 (b) show a flexible circuit board used for a hinge portion of a cellular phone or the like, for example, which has a resin layer 1, a wiring 2 formed of a metal foil and a connector terminal 3 Yes. 4A and 4B show the positions of the ridgelines L in the vicinity of the center at the bent portions. The ridgelines L are located in the vicinity of the center of the metal foil forming the wirings 2 with respect to the [100] 90 + alpha) degrees. 4 (a) shows an example in which wiring lines are formed obliquely in the vicinity of the ridge L in the middle of the connector terminals 3 at both ends. As shown in Fig. 4 (b) It is also possible to conduct wiring. On the other hand, in addition to the case where the position of the ridgeline L in the bent portion is fixed, such as a folding mobile phone, the sliding bending (Fig. 4 (b)) in which the ridgeline L in the bending portion, In the direction of the thick arrow shown in Fig. On the other hand, the flexible circuit board according to the present invention has a wiring made of a metal foil on at least one surface of the resin layer, and may include a metal foil on both sides of the resin layer as necessary.

As described above, the metal foil constituting the wiring at the bent portion at the time of bending the flexible circuit board is highly oriented, and the metal foil having the major stress and the large breaking elongation in the main twist direction is constituted, It is difficult to cause metal fatigue due to the two effects that locally stress concentration due to the anisotropy of crystal is hard to occur and dislocation accumulation is hard to occur even when repeated bending with small high bending is performed and excellent durability against stress and distortion It is possible to provide a flexible circuit board which is not restricted in the design of the flexible circuit board and which has strength enough to withstand repeated bending or bending with a small radius of curvature and has excellent bendability.

Example

Hereinafter, the present invention will be described more specifically based on examples and comparative examples. On the other hand, the kind of the copper foil used in Examples and the like and the synthesis of the polyamic acid solution are as follows.

[Copper A]

Commercial rolled copper foil, purity 99.9%, thickness 9 탆.

[Copper B]

Commercial electrolytic copper foil, purity 99.9%, thickness 9 탆.

[Copper C]

Anoxic copper foil, purity 99.99%, thickness 9 탆, process conditions A.

Impurities (mass ppm) oxygen: 2, silver: 18, phosphorus: 2.1, sulfur: 4, iron: 1.5

[Copper D]

Purified copper foil, purity 99.999%, thickness 9 탆, process conditions A.

Impurities (mass ppm) Oxygen: 2, silver: 5, phosphorus: 0.01, sulfur: 0.01, iron 0.002

[Copper E]

Purified copper foil, purity 99.9999%, thickness 9 탆, process conditions A.

Impurities (mass ppm) Oxygen: <1, silver: 0.18, phosphorus: <0.005, sulfur: <0.005, iron: 0.002

[Copper foil F]

Purified copper foil, purity 99.9999%, thickness 9 탆, process conditions B.

Impurities (mass ppm) Oxygen: <1, silver: 0.18, phosphorus: <0.005, sulfur: <0.005, iron: 0.002

[Copper G]

Purified copper foil, purity 99.9999%, thickness 9 mu m, process conditions C.I.

Impurities (mass ppm) Oxygen: <1, silver: 0.18, phosphorus: <0.005, sulfur: <0.005, iron: 0.002

[Copper H]

Commercial rolled copper foil, purity 99.9%, thickness 12 탆.

[Manufacturing method of copper foil]

The copper foil A and the copper foil H are commercially available rolled copper foil, and the copper foil B is a commercially available electrolytic copper foil made of a copper sulfate bath. All of these are copper foils commercially available as high-flex applications, and their purity is 99.9%, which is high for commercial products. The copper foil C to copper foil G is processed by the present inventors, and a copper material having a predetermined purity is cast and solidified in a graphite molding and rolled to a predetermined thickness. The copper ingot C, the copper foil D, and the copper foil E were subjected to intermediate annealing at 300 캜 for 30 minutes, followed by cold rolling to a thickness of 9 탆 Condition A). Further, the copper foil F was subjected to cold rolling to 9 mu m without intermediate annealing (process condition B). The copper foil G was subjected to an intermediate annealing temperature of 800 占 폚 and cold rolling was performed to 9 占 퐉 (process condition C).

[Synthesis of polyamic acid solution]

(Synthesis Example 1)

N, N-dimethylacetamide was added to a reaction vessel equipped with a thermocouple and a stirrer and capable of nitrogen introduction. To this reaction vessel, 2,2-bis [4- (4-aminophenoxy) phenyl] propane (BAPP) was dissolved in a vessel while stirring. Next, pyromellitic dianhydride (PMDA) was added. And the total amount of the monomers 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 added to a reaction vessel equipped with a thermocouple and a stirrer and capable of nitrogen introduction. 2,2'-Dimethyl-4,4'-diaminobiphenyl (m-TB) was added to the reaction vessel. Next, 3,3 ', 4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) and pyromellitic dianhydride (PMDA) were added. The amount of the monomer added 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 the resin solution of the polyamic acid b was 20,000 cps.

[Example 1]

The polyamic acid solution a prepared above was applied to seven kinds of copper foils from the copper foil A to the copper foil G and dried (after the curing, a thermoplastic polyimide having a thickness of 2 탆 was formed) (To form a thermally expandable polyimide film having a thickness of 9 mu m after curing), and further, a polyamic acid a is applied thereon and dried (forming a thermoplastic polyimide film having a thickness of 2 mu m after curing) Lt; RTI ID = 0.0 &gt; C &lt; / RTI &gt; for 5 minutes or more at an integration time of 5 minutes or more. Subsequently, the copper foil was cut into a rectangular shape having a length of 250 mm along the rolling direction (MD direction) and a width of 150 mm in the direction perpendicular to the rolling direction (TD direction), and as shown in Fig. 5, a polyimide layer (Resin layer) 1 and a copper foil 2 having a thickness of 9 mu m were obtained. The tensile modulus of the entire resin layer at that time was 7.5 GPa.

The single-sided copper-clad laminate 4 obtained above was mechanically and chemically polished with colloidal silica on the rolled surface 2a of each copper foil 2 from the copper foil A to the copper foil G, And analyzed. The device used was FE-SEM (S-4100) manufactured by Hitachi Seisakusho, EBSP device manufactured by TSL, and software (OIM Analysis 5.2). The measurement area was about 800 占 퐉 占 1600 占 퐉 and the acceleration voltage was 20 kV and the measurement step interval was 4 占 퐉. The evaluation of the orientation was expressed as a ratio to the total measurement point of the measurement point within the range of < 100 > within 10 DEG with respect to the thickness direction of the foil and the rolling direction of the foil. Measurements were performed on 5 different samples of each breed, and rounded off to the decimal point of the percentage. Further, using the obtained data, the crystal grain size was evaluated as a crystal grain boundary in which the azimuth difference of neighboring crystal grains was 15 deg. Or more, and the average grain size was determined for polycrystals. The results are shown in Table 1.

All of the rolled copper foils except for the copper foil B were found to have a cubic texture, and had a {100} < 100 > This is because the rolled copper foil was recrystallized by heat at the time of polyimide curing and a recrystallized texture was formed. However, the degree varies depending on the variety, and the orientations of the copper foils A, C, D, and E with respect to the cubic orientation were very high. The orientation degree of the cubic orientation was highly dependent on the processing method of the copper foil regardless of its purity in the copper foil having a purity of 99.9% or more. These copper foils had a structure in which the whole field of view was composed of particles having a cubic orientation in a field of 800 x 1600 mu m and crystal grains of 5 mu m or less in which orientation was different were dispersed in an island shape. Since the area ratio of the island-like structure is as small as 2% or less, the recrystallized grains having a cubic orientation are integrated with the same orientation, and the size of the recrystallized grains is 9 mu m like the thickness in the thickness direction, to be. The recrystallized grains having the cubic orientation of the copper foil F and the copper foil G were present independently of each other because the area ratio was not high, and the average grain sizes in the thin faces were 25 占 퐉 and 20 占 퐉, respectively. On the other hand, the electrolytic copper foil B was a polycrystal having an average particle diameter of 1 탆, and orientation was hardly recognized.

Next, a predetermined mask was placed on the copper foil 2 side of the single-sided copper-clad laminate 4 obtained above, and etching was performed using a ferric chloride / copper chloride-based solution. As shown in Fig. 6 ) And the MD direction is 0 占 and the wiring direction H (H direction) of the linear wiring 2 having the line width l of 150 占 퐉 is parallel to the MD direction (<100> axis) , And a wiring pattern was formed so that the space width s was 250 m. A flexible circuit board 5 for testing having a width of 150 mm in the longitudinal direction and a width of 15 mm in the direction orthogonal to the wiring direction H along the wiring direction H of the circuit board in accordance with JIS 6471, ).

Using the flex circuit board for test obtained above, an MIT bending test was carried out in accordance with JIS C5016. A schematic diagram of the test is shown in Fig. One end of the testing flexible circuit board 5 in the longitudinal direction was fixed to the nip jig of the bending test apparatus and the other end And bent with a radius of curvature of 0.8 mm while being alternately left and right by 135 +/- 5 degrees on the condition of a vibration speed of 150 times / minute about the nip portion, 2) was cut off as the number of bends.

In this test condition, since the ridgelines formed at the bent portion are bent so as to be orthogonal to the wiring direction H of the wiring 2 of the flexible circuit board 5 for test, the principal stress applied to the copper circuit, Tensile stress parallel to the rolling direction, and tensile warpage. When the circuit was observed in the thickness direction of the copper foil after the bending test, it was confirmed that cracks were broken and almost perpendicular to the rolling direction near the ridge line of the bent portion. Table 1 shows the results of flex life. The flex life of Table 1 is the average of the results of five flexible circuit boards prepared for each type of copper foil.

From the results shown in Table 1, it can be seen that the bending fatigue life of the copper foil C, the copper foil D and the copper foil E, which are produced by the same processing method and have substantially the same degree of orientation, are significantly different depending on the degree of integration of the cube assembly texture.

Next, in order to investigate the dominant factor of the bending life, the tensile test was performed in parallel with the principal stress of the bending, main twist direction, that is, the rolling direction. In order to investigate the characteristics of a single copper foil, a resin layer was dissolved from a single-sided copper clad laminate 4 before etching, and a tensile test was conducted on a single copper foil. It was confirmed that there was no change in the structure of copper foil during the dissolution of polyimide.

In the tensile test, a sample cut into a width of 10 mm in the rolling direction (MD direction) and a length of 150 mm in a thin plane in a direction perpendicular to the rolling direction was used. The distance between the gaps in the longitudinal direction was 100 mm and the tensile speed was 10 mm / min Respectively. Seven samples were prepared for each kind of the copper foil, and the breaking stress (breaking strength) and the average value of the breaking elongation obtained by measuring them were shown in Table 1.

As a result, it was found that the fracture strength of the copper foil in which the texture was developed did not depend on the breaking fatigue life. In addition, although the strength and breaking elongation of the copper foil B are both large, this reflects that the crystal grains are fine polycrystals. However, the result of the fatigue life of the copper foil B was poor because the texture was not developed. Further, when comparing the copper foil C having a purity of 99.99% and the copper foil D having a purity of 99.999%, the fatigue characteristics with respect to the bending of the copper foil D were remarkably excellent. Since the oxygen concentrations of these two copper foils are the same and the amount of copper oxide dispersed therein is also small, the difference is not caused by the copper oxide but by the difference in the elongation at break due to the different purity.

From the results shown in Example 1, it was found that, in order to obtain better characteristics than general copper foams for high bending, the basic crystal axis <100> is defined as the thickness direction of the metal foil and the two orthogonal axes The metal foil in the normal direction with respect to the end face P of the wiring cut in the thickness direction of the metal foil from the ridge line at the bent portion while having the kitchen top so that the preferred orientation area within 10 deg. Of the azimuthal difference occupies 50% It was found that the breaking elongation was required to be 3.5% or more. Also, it was found that the flexible circuit board having a very high purity of 99.999% or more and improved cubic orientation improves the elongation at break, and the fatigue life of the flexible circuit board is longer than that of the principal flexure in which principal stress and principal twist are applied.

[Example 2]

Next, as shown in Fig. 6, the single-sided copper-clad laminates using the copper foil A and the copper foil E produced in the same manner as in Example 1 were subjected to the wiring direction H of the linear wirings 2 having a line width l of 150 mu m, The wiring pattern was formed with a space width (s) of 250 占 퐉, while keeping the angle (H direction) at 30 占 and 45 占 with respect to the MD direction ([100] axis). A flexible circuit board 5 for testing having a width of 150 mm in the longitudinal direction and a width of 15 mm in the direction orthogonal to the wiring direction H along the wiring direction H of the circuit board in accordance with JIS 6471, ). Fig. 6 shows an example in which the angle formed by the wiring direction H of the flexible circuit board 5 for testing and the MD direction is cut at an angle of 45 [deg.].

The flexible flexible circuit board 5 obtained above was repeatedly subjected to bending fatigue tests under the same conditions as in Example 1. [ In addition, the resin layer was dissolved from the single-sided copper clad laminate 4 before etching so that the angle formed by the wiring direction H and the MD direction of the flexible circuit board 5 for testing became equal, And a sample of 150 mm x 10 mm cut out at an angle of 45 [deg.], A tensile test was carried out in the same manner as in Example 1. [ That is, the principal stress and the main warping direction in the fatigue test of the copper foil match the tensile direction of the tensile test, and both the copper foil A and the copper foil E have a highly cube aggregate structure. Therefore, in the fatigue test and the tensile test, The crystal orientation is subject to principal strain and principal stress. The results of the fatigue test and the tensile test are shown in Table 2.

From the test results shown in Table 2, it is possible to obtain high fatigue characteristics by making the principal stress and the main warping direction deviate from the <100> direction. In these orientations, the elongation at break is significantly larger than the < 100 > orientation, and particularly at 30 DEG, the elongation at break and the fatigue life are prolonged.

From the results of the above Example 2, it can be seen that there is a high correlation between the fatigue life of the flexible circuit board against repeated bending of high warpage and the breaking extension of the copper foil constituting the wiring when the copper foil is highly oriented . As shown in Example 1, a higher strength and ductility can be obtained in a polycrystal, but it is not effective in a high flexural application. Therefore, the relation between the fatigue life and the elongation at break under the condition of highly integrated aggregate structure plays an important role in the slip system, and is not limited to copper, but is also formed of a face-centered cubic bearing metal having the same slip system, If the metal has a different defect energy, the fracture elongation can be expected to be larger than that of the other, and the fatigue life can be expected to increase.

[Example 3]

The polyamic acid solution a prepared in the same manner as in Synthesis Example 1 was applied to a rolled copper foil H having a purity of 99.9 mass% and a thickness of 12 占 퐉 and dried (after forming a thermoplastic polyimide film having a thickness of 2 占 퐉) (After the curing, a polyimide having a thickness of 8 占 퐉 was formed to form a low heat-expandable polyimide), and polyamide acid a was coated thereon and dried (after curing, a thermoplastic To form a polyimide layer (resin layer), as shown in the following conditions a to d, under a heating condition in which a temperature of 180 to 240 占 폚 at the maximum temperature was added for 10 minutes as an integration time.

Next, a polyimide layer (resin layer) 1 having a thickness of 12 占 퐉 was cut out to have a length of 250 mm along the rolling direction (MD direction) of the copper foil and a width of 150 mm width in the direction perpendicular to the rolling direction (TD direction) And the copper foil 2 having a thickness of 12 mu m were obtained.

A predetermined mask was placed on the copper foil side of the single-sided copper-clad laminate 4 obtained above, and etching was carried out using a ferric chloride / copper chloride-based solution. Based on the IPC standard, a straight line wiring 150 mu m having a line width of 150 mu m and a space width of 250 mu m A low-speed IPC test wiring 2 was formed. In this manufacturing process, the maximum temperature of the heating conditions at the time of forming the polyimide layer was set to four levels of 180 占 폚 (condition a), 200 占 폚 (condition b), 220 占 폚 (condition c), and 240 占 폚 (condition d) 2.9 deg., 5.7 deg., 9.5 deg., 11.4 deg., 14 deg., 18.4 deg., 25 deg., And 10 deg. Relative to the rolling direction (MD direction) The wiring patterns are formed so as to have an angle of 22 levels of 26.6 °, 30 °, 40 °, 45 °, 55 °, 60 °, 63.4 °, 78.6 °, 80 °, 82.9 °, 87.1 °, 88 °, .

Next, as shown in Fig. 8 (b), a cover material 7 (CVK-0515KA, thickness: 12.5 mu m, manufactured by Arisawa Seisakusho Co., Ltd.) was laminated on each wiring pattern side surface with an epoxy adhesive. The thickness of the adhesive layer 6 made of an adhesive was 15 占 퐉 in the portion where the copper foil circuit was not provided and 6 占 퐉 in the portion where the copper foil circuit was present. And cut to 15 cm in the longitudinal direction and 8 mm in the direction orthogonal to the wiring direction along the wiring direction (H direction) to obtain a flexible circuit board for testing to be an IPC test sample.

On the other hand, in order to investigate the characteristics of the copper foil, a tensile test was conducted as follows. The resin layer is melted from the single-sided copper clad laminate (4) before etching so that the angle between the wiring direction (H) of the flexible circuit board for test (5) and the MD direction is equal to 22 levels, A rectangular sample having a length of 150 mm and a width of 10 mm cut out so as to have the 22-level angle with respect to the rolling direction in the longitudinal direction was prepared. At this time, it was confirmed that there was no change in the structure of the copper foil in the process of dissolving the polyimide. The tensile test was carried out in a longitudinal direction at a distance of 100 mm between the gauge points and at a tensile speed of 10 mm / min.

The single-sided copper-clad laminate produced under the heat treatment conditions of conditions a to d was used as a sample for performing the tissue analysis by EBSP. The single-sided copper-clad laminate was subjected to 5, 5, A total of 20 specimens without wiring patterns cut out at an angle of 20 were manufactured. In order to match the thermal history with the IPC test sample, a simulated heat treatment was applied under the same condition as the circuit formation etching, and the cover material was laminated under the same conditions. However, these effects on the copper foil texture are slight, and it has been revealed that the copper foil structure is determined by the heat treatment conditions a to d during the polyimide formation.

Twenty copper foils H having four levels of heat treatment conditions and five levels of angular conditions were polished in the substrate thickness direction as described above for the EBSP measurement, and the thinned surface of the copper foil H Lt; / RTI &gt; Further, the surface of the copper foil H was polished by using colloidal silica, and the structure of the copper foil H was evaluated by EBSP. The measurement area was 0.8 mm x 1.6 mm and the measurement interval was 4 m. That is, the measurement score of one area is 80000 points. As a result, it was found that all of the samples subjected to the heat treatment under the condition a to the condition d formed a cube texture, and had a {100} crystal plane of {100} in the rolling direction. Based on the obtained results, the number of points where the unit lattice axis &lt; 001 &gt; was within 10 DEG in the thickness direction and the rolling direction of the copper foil was counted, and the ratio to the total score was calculated to obtain an average value. The results are shown in Table 3. The deviation between the samples under the same heating conditions is 1% or less, and it can be said that the degree of integration shown in Table 3 is obtained over the entire surface of the copper foil under the same heat treatment conditions. It was found that the recrystallization progresses as the maximum heat treatment temperature and the heat history increase, and the degree of integration of the cube recrystallization texture increases. As a result of orientation analysis in the slab surface, the cutting directions of the sample cut at five angles of 0 deg., 2.9 deg., 30 deg., 63.4 deg., And 78.6 deg. Relative to the rolling direction were [100], [ ], [40 23 0], [120], and [150]. On the other hand, the obtained EBSP data was used to evaluate the crystal grain size in the direction of the normal of the slab, which was interpreted as the crystal grain boundaries in which the azimuth difference of the neighboring crystal grains was 15 degrees or more, and the average grain size was determined for the polycrystals. The results are shown in Table 3.

The IPC test is a test simulating slide bending, which is one of the bending patterns used in a cellular phone, as shown in the schematic diagram of Fig. As shown in Fig. 8, the IPC test is a test in which a bent portion is provided at a predetermined gap length 8, one side is fixed by the fixing portion 9, and the slide movable portion 10 on the opposite side is repeatedly reciprocated as shown in the figure. Therefore, the substrate is subjected to repeated bending in the region corresponding to the stroke amount of the reciprocating portion. In this embodiment, the polyimide layer (resin layer) 1 was placed outside and the gap length was 1 mm, that is, the bending radius was 0.5 mm and the stroke was 38 mm. During the test, the electric resistance of the circuit of the flexible circuit board for testing was measured, and the degree of progress of the fatigue crack of the copper foil circuit was monitored by the increase of electric resistance. In the present embodiment, the number of strokes in which the electric resistance of the circuit reaches twice the initial value is defined as the circuit breakage life.

The test was carried out for a total of 88 levels in which a wiring pattern having an angle of 22 levels was formed for the four heat treatment conditions of the above conditions a to d. At each test level, measurements were taken on four specimens and the average number of strokes broken was determined. A cross section of the copper foil cut in the thickness direction perpendicular to the slide direction with respect to the copper foil after the break life of the circuit was observed with a scanning electron microscope and a crack was observed on the surface of the copper foil on the resin layer side and on the cover material side, In particular, it was observed that a large number of cracks were introduced into the surface of the copper foil on the side of the resin layer contacting the outside of the bent portion.

Table 4 shows the average value of the circuit breakage life at each level and the break elongation in the tensile test. In the angle column of Table 4, the surface index was also shown only in the low exponential direction with respect to the longitudinal direction (wiring direction) of the circuit, that is, the end face P of the wiring when cut in the thickness direction from the ridge line at the curved portion .

The fracture life (fatigue life) in the IPC test is determined by the angle formed by the circuit longitudinal direction (H direction) and the rolling direction (MD direction), that is, from the ridge line at the bent portion, ] Depend on the angle formed between the two. The orientation dependency is expressed in the condition b, the condition c, and the condition d, and the higher the degree of integration of the cubic bearing, the greater the fatigue life with respect to the repeated bending and the greater the bearing dependency. Regarding this orientation dependency, the <001> kitchen was placed in the thickness direction of the metal foil so that the area in which the [001] of copper was within 10 ° of the azimuthal difference by the evaluation by the EBSP method, , And the area of the [100] orientation is preferentially oriented in the metal thin plane so that the area within 10 ° of the azimuth difference from the [100] axis of copper occupies an area ratio of 50% or more as evaluated by the EBSP method Lt; / RTI &gt; Particularly, in the case of the condition c in which the thickness direction and the rolling direction each have an area ratio of 75% or more and 85% or more, and the degree of integration of the cubic bearing is high, the fatigue life is large and the effect of orientation dependency becomes large. 98% or more, and 99% or more, and the fatigue life is further increased and the effect of the orientation dependency is greater in the condition d in which the degree of integration of the cubic bearing is very high.

When the results of the conditions b, c and d are examined in detail, the normal direction of the wiring cross-section P at the time of cutting in the thickness direction from the ridge in the bent portion, that is, The fatigue life of the circuit for deviation and bending is high. The effect shown in the IPC test of the present embodiment was in the case of having an angle of 2.9 ° to 87.1 ° with respect to the principal twist direction of the bent portion, that is, with respect to the normal line direction of the wiring when cut in the thickness direction from the ridge line at the bent portion. The surface index P is expressed by the surface index, and the cross-section P of the wiring when cut in the thickness direction from the ridgeline at the bent portion extends from (20 1 0) to (110) . Among them, the larger effect was in the case of having an angle of 11.4 ° to 78.6 ° with respect to the principal twist direction of the bent portion, that is, with respect to the normal line direction of the wiring when cut in the thickness direction from the ridge line at the bent portion. When expressed in face indexes, the cross-section P of the wiring when cut in the thickness direction from the ridge line at the bent portion is in the range from (510) to (110) and (150) with [001] as the major axis. The bending characteristic is higher when the bent portion has an angle of 26.6 DEG to 63.4 DEG with respect to the principal normal twist direction of the bent portion, that is, from the ridge line at the bent portion in the thickness direction, 60 °. The surface area P is a range from (210) to (120) with [001] as the major axis, and the most excellent ones are (40 23 0) and (23 40 0 ) When it was near.

When these results are compared with the elongation at break, it can be seen that the basic crystal axis <100> of the unit cell of the face-centered cubic structure has an azimuthal difference of 10 [deg.] With respect to two orthogonal axes in a thickness direction of the metal foil, Of the metal foil in the thickness direction of the metal foil cut from the ridge in the bent portion to the thickness of the metal foil in the normal direction with respect to the end face P of the wiring is 3.5 %, It was found that the bending fatigue characteristic with respect to the bending causing the principal stress and the main twist in the bearing was obtained. On the other hand, when the area ratio of the <100> preferred orientation region is 49% or less, satisfactory bending fatigue characteristics can not be obtained even if the elongation at break in the direction has a value of 3.5% or more.

[Example 4]

The copper foil C having a purity of 99.99% was subjected to a heat treatment (preliminary heat treatment) for 30 minutes at a temperature of 180 ° C to 400 ° C in an Ar gas stream at a temperature of five degrees, and the polyamic acid solution a was applied, (To form a thermoplastic polyimide film having a thickness of 2 m thereafter), and then a polyamic acid b was coated thereon and dried (to form a low heat-expandable polyimide film having a thickness of 9 m after curing) (Forming a thermoplastic polyimide film having a thickness of 2 占 퐉 after curing), and a polyimide layer having a three-layer structure is formed through a heating condition in which a temperature of 300 to 360 占 폚 is loaded for an accumulation time of 5 minutes or more Respectively. Subsequently, the copper foil was cut into a rectangular shape having a length of 250 mm along the rolling direction (MD direction) and a width of 150 mm in a direction perpendicular to the rolling direction (TD direction), and as shown in Fig. 5, (Resin layer) 1 and a copper foil 2 having a thickness of 9 mu m were obtained. The tensile modulus of the entire resin layer at that time was 7.5 GPa.

The single-sided copper-clad laminate 4 obtained above was mechanically and chemically polished on the rolled surface 2a of the copper foil 2 using colloidal silica, and then subjected to bearing analysis with an EBSP apparatus. The device used was FE-SEM (S-4100) manufactured by Hitachi Seisakusho, EBSP device manufactured by TSL, and software (OIM Analysis 5.2). The measurement area was about 800 占 퐉 占 1600 占 퐉, and the acceleration voltage was 20 kV and the measurement step interval was 4 占 퐉. The evaluation of the orientation was expressed as a ratio to the total measurement point of the measurement point within the range of < 100 > within 10 DEG with respect to the thickness direction of the foil and the rolling direction of the foil. Measurements were performed on 5 different samples of each breed, and rounded off to the second decimal place of the percentage. Further, using the obtained data, the crystal grain size was evaluated as a crystal grain boundary in which the azimuth difference of neighboring crystal grains was 15 deg. Or more, and the average grain size was determined for polycrystals. The results are shown in Table 5.

All of the copper foil C formed a cube texture, and it was found that the copper foil had a {100} < 100 > This is because the rolled copper foil was recrystallized by preliminary heat treatment and heat at the time of polyimide curing to form a recrystallized texture. Here, the degree of orientation of {001} < 100 > increases as the preliminary heat treatment temperature is higher. The orientation other than the <100> orientation was confirmed by the EBSP apparatus as described above, and as a result, the orientation of the recrystallization having a circle-equivalent diameter of 5 μm or less was dispersed in an island shape with respect to the rolling direction. However, in the copper foil subjected to the preliminary heat treatment at 400 캜, almost no such islands were observed. On the other hand, since the area ratio of the identified island-like structure is as small as 2% or less, the recrystallized grains having a cubic orientation are integrated with the same orientation. The size of the recrystallized grains was 9 탆, which is the same as the thickness in the thickness direction, and 800 탆 or more in the thinned surface.

Next, a predetermined mask is placed on the copper foil 2 side of the single-sided copper-clad laminate 4 obtained above, and etching is performed using a ferric chloride / copper chloride-based solution. As shown in FIG. 6 ) And the MD direction is 0 DEG) and the wiring direction H (H direction) of the linear wirings 2 having the line width l of 150 mu m is parallel to the MD direction (< 100 > axis) , And a space width (s) of 250 mu m. A flexible circuit board 5 for testing having a width of 150 mm in the longitudinal direction and a width of 15 mm in the direction orthogonal to the wiring direction H along the wiring direction H of the circuit board in accordance with JIS 6471, ).

Using the flex circuit board for test obtained above, an MIT bending test was carried out in accordance with JIS C5016. A schematic diagram of the test is shown in Fig. One end of the testing flexible circuit board 5 in the longitudinal direction was fixed to the nip jig of the bending test apparatus and the other end was fixed by using the product STROGRAPH-R1 manufactured by Toyo Seiki Seisakusho Co., Ltd. , The bending is performed so that the radius of curvature becomes 0.8 mm while rotating the nip portion at a vibration speed of 150 times / minute alternately left and right by 135 5 degrees, and when conduction of the wiring 2 of the circuit board 5 is blocked Was calculated as the number of bends.

In this test condition, since the ridgelines formed at the bent portion are bent so as to be orthogonal to the wiring direction H of the wiring 2 of the flexible circuit board 5 for test, the principal stress applied to the copper circuit, Tensile stress parallel to the rolling direction, and tensile warpage. When the circuit was observed in the thickness direction of the copper foil after the bending test, it was confirmed that the crack was broken almost perpendicularly to the rolling direction in the vicinity of the ridge line of the bent portion. Table 5 shows the results of flex life. The flex life of Table 5 is the average of the results of the test flexible circuit boards prepared for each 5 pre-heat treatment temperatures of the copper foil. From the results shown in Table 5, it can be seen that the flexural fatigue life becomes particularly large when the degree of integration of the cube texture is 98.0% or more and 99.8%.

Next, in order to investigate the dominant factor of the bending life, the tensile test was performed in parallel with the principal stress of the bending, main twist direction, that is, the rolling direction. In order to investigate the properties of the copper foil by the preliminary heat treatment temperature, the resin layer was dissolved from the single-sided copper clad laminate (4) before etching, and a tensile test was conducted by a single copper foil. It was confirmed that there was no change in the structure of copper foil during the dissolution of polyimide.

The tensile test was carried out using a specimen cut in a rolling direction (MD direction) of the copper foil with a length of 150 mm and a width of 10 mm in the vertical direction in the thin plane, and the distance between the gaps was 100 mm and the tensile speed in the longitudinal direction was 10 mm / min. Seven samples were prepared for each of the pre-heat treatment temperature of the copper foil, and the breaking stress (breaking strength) and the average value of the breaking elongation obtained by measuring these samples were shown in Table 5.

Contrary to the results thus far, the elongation at break increased with increasing degree of integration in the region where the <100> degree of integration (%) was 98.0% or more and 99.8% or less. On the other hand, in the copper foil in which the island-shaped structure was lost, the breaking elongation was reduced. This is presumed to be related to the sliding surface. From the above, it was confirmed that there is a strong correlation between the elongation at break and the bending fatigue life. That is, it was found that the flexural fatigue life is increased in the region where the <100> density (%) is 98.0% or more and 99.8% or less is highly developed and the elongation at break is 3.5% or more.

On the other hand, when the copper foil was manufactured under the same conditions in a tough pitch copper having a purity of 99.9% and containing 0.035 mass% of oxygen under the same conditions, the test was conducted under the same conditions. As a result, even if the <100> Was decreased as the degree of integration increased, so that a copper foil of 3.5% or more was not obtained and a fatigue life of 1000 times or more was not obtained.

The flexible circuit board according to the present invention can be widely used in various electronic and electric devices, and the circuit board itself is bent, twisted, bent, or deformed according to the operation of the mounted device, . Particularly, since the flexible circuit board of the present invention has a bending part structure excellent in bending durability, it can be used in cases such as frequent bending accompanied by repeated bending such as sliding bending, bending bending, hinge bending, slide bending, It is preferable in the case of forming a bent portion in which the radius of curvature is required to be very small in order to cope with the miniaturization of the device. Therefore, it can be suitably used for various electronic devices including thin type mobile phones, thin type displays, hard disks, printers, DVD devices, etc., which are required to have durability.

1 resin layer
2 wiring (metal foil)
2a rolled surface
2b side
3 connector terminal
4 single sided copper clad laminate
5 Flexible circuit board for test
6 adhesive layer
7 Cover material
8 Gap length
9 Fixing section
10 Slide moving part
21 Normal direction of section (P)
L ridge
Section of the wiring when cut in the thickness direction from the ridge in the P bent portion

Claims (11)

A flexible circuit board comprising a resin layer and a wiring formed of a metal foil and having bent portions in at least a part of the wiring,
Wherein the resin layer is made of polyimide, the thickness of the resin layer is 10 占 퐉 to 30 占 퐉,
Wherein the metal foil is a copper foil having a face-centered cubic structure and a purity of 99.999 mass% or more, and the basic crystal axis of the unit cell of the face-centered cubic structure is present in a thickness direction and a foil surface of the metal foil , The preferred orientation region within an orientation difference of 10 占 occupies 50% or more of the area ratio and the crystal grain size of the metal foil when viewed in the normal direction of the slope is 25 占 퐉 or more ,
Wherein the breaking extension of the metal foil in the normal direction to the end face (P) of the wiring cut in the thickness direction of the metal foil from the ridge in the bent portion is 3.5% or more and 20% or less. A flexible circuit board comprising a resin layer and a wiring formed of a metal foil and having bent portions in at least a part of the wiring,
Wherein the resin layer is made of polyimide, the thickness of the resin layer is 10 占 퐉 to 30 占 퐉,
Wherein the metal foil comprises a rolled foil of oxygen-free copper having a face-centered cubic structure and a purity of 99.99% by mass or more, and wherein a basic crystal axis of the unit cell of the face-centered cubic structure is in a thickness direction of the metal foil and in a foil surface The preferred orientation regions within an orientation difference of 10 degrees occupy 98% or more and 99.8% or less in area ratio with respect to two orthogonal axes in any one direction present, and the crystal grain size of the metal foil Lt; / RTI &gt;
Wherein the breaking extension of the metal foil in the normal direction to the end face (P) of the wiring cut in the thickness direction of the metal foil from the ridge in the bent portion is 3.5% or more and 20% or less. 3. The method according to claim 1 or 2,
Wherein the thickness of the metal foil is 5 占 퐉 or more and 18 占 퐉 or less. 3. The method according to claim 1 or 2,
The cross section P of the wiring is formed on one surface included in the range of (20 1 0) to (120 0) in the rotating direction from (100) to (110) with [001] Wherein the flexible printed circuit board is formed on the flexible printed circuit board. 5. The method of claim 4,
Characterized in that the cross section P of the wiring is a surface on a line segment connected by a point representing (110) and a point representing (110) in a stereo triangle of the (100) standard projection. Board. 3. The method according to claim 1 or 2,
Wherein the wiring is formed along a direction orthogonal to a ridge line in the bent portion. 3. The method according to claim 1 or 2,
Wherein the flexible circuit board is used to form a bent portion with any one of repetitive operations selected from the group consisting of sliding, bending, hinge bending and slide bending. An electronic apparatus comprising the flexible circuit board according to claim 1 or 2. A flex circuit structure of a flexible circuit board, comprising a resin layer and a wiring formed of a metal foil, wherein at least a part of the wiring is used with a bent portion,
Wherein the resin layer is made of polyimide, the thickness of the resin layer is 10 占 퐉 to 30 占 퐉,
Wherein the metal foil comprises a copper foil having a face-centered cubic structure and a purity of 99.999 mass% or more and a basic crystal axis of the unit cell of the face-centered cubic structure is in a thickness direction of the metal foil and in a direction The preferred orientation regions having an orientation difference of 10 DEG or less occupy 50% or more of the area ratio, and the crystal grain size of the metal foil in the normal direction of the slope is 25 占 퐉 or more,
Wherein a breaking extension of the metal foil in a normal direction to an end face (P) of the wiring cut in the thickness direction of the copper foil from the ridge in the bent portion is not less than 3.5% and not more than 20% rescue. A flex circuit structure of a flexible circuit board, comprising a resin layer and a wiring formed of a metal foil, wherein at least a part of the wiring is used with a bent portion,
Wherein the resin layer is made of polyimide, the thickness of the resin layer is 10 占 퐉 to 30 占 퐉,
Wherein the metal foil comprises a rolled foil of oxygen-free copper having a face-centered cubic structure and a purity of 99.99% by mass or more, and wherein the basic crystal axis of the unit cell of the face-centered cubic structure exists within the thin- , The preferred orientation region within an orientation difference of 10 占 occupies not less than 98% and not more than 99.8% in area ratio, and the metal foil has a crystal grain size of not less than 25 占 퐉 Lt;
Wherein a breaking extension of the metal foil in a normal direction to an end face (P) of the wiring cut in the thickness direction of the copper foil from the ridge in the bent portion is not less than 3.5% and not more than 20% rescue. delete

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