TWI571183B - A flexible circuit board, and a flexible circuit board - Google Patents

Description

Bent structure of flexible circuit board and flexible circuit board

The present invention relates to a flexible circuit board having a bent portion and a bent portion structure of the flexible circuit board, and more particularly, it has durability and good flexibility for bending. The flexible circuit board and the bent portion structure of the flexible circuit board.

A flexible circuit board (flexible printed circuit board) having a resin layer and a wiring made of a metal foil is bendable and can be used as a movable portion in a hard disk, a hinge portion of a mobile phone, or a sliding slide. The head, the print head of the printer, the optical pickup unit, and the movable portion of the notebook PC are widely used in various electronic and electrical equipment. In recent years, in particular, miniaturization, thinning, and high functionality of such devices have been made, and it has been proposed to fold the flexible circuit board into a small space for storage in a limited space, or to perform various operations such as an electronic device. Flexibility. Therefore, in order to correspond to an operation such as bending with a smaller radius of curvature in the curved portion or frequent repeated bending, it is necessary to improve mechanical properties such as further strength of the flexible circuit board.

In general, it is not so much a resin layer, but the wiring is a bad cause for bending or bending with a small radius of curvature, and the strength is poor. If it becomes unbearable, it will occur in a part of the wiring. It is broken or broken, and it cannot be utilized as a circuit board. Therefore, for example, in order to reduce the bending stress on the wiring in the hinge portion, a flexible circuit board that is wired so as to be inclined with respect to the rotation axis is formed (see Patent Document 1), or a spiral in the direction of the rotation of the hinge portion. A method of reducing the damage due to a change in the diameter of the spiral portion due to the opening and closing operation by increasing the number of turns of the spiral portion (see Patent Document 2) has been proposed. However, in these methods, the design of the flexible circuit substrate is limited.

On the other hand, the intensity (I) of the (200) plane obtained by the X-ray diffraction of the rolled surface of the rolled copper foil (the X-ray diffraction in the thickness direction of the copper foil) is relative to the X-ray of the fine powder copper. When the intensity (I ₀ ) of the (200) plane obtained by the diffraction is I/I ₀ > 20, the flexibility is reported (refer to Patent Documents 3 and 4). That is, the more the cube orientation of the recrystallized assembly structure belonging to copper is, the more the bendability of the copper foil is improved. Therefore, the above-mentioned parameter (I/I ₀ ) is used to specify the degree of development of the cube assembly structure as a flexible A copper foil of a wiring material of a circuit board is known. Further, the rolled copper alloy foil obtained by atomizing and recrystallizing the element in a concentration in the range of solid solution in the range of copper, Fe, Ni, Al, Ag, etc., is easy to be sheared along the slip surface. A good report has been proposed (see Patent Document 5).

In addition, in the case of using a copper foil containing impurities such as oxygen or silver, the flexible circuit board which is required to have a high bending property is a copper foil having a purity of about 99% to 99.9% by mass. In the present invention, the purity is expressed by mass concentration unless otherwise specified. In addition, in the test level, there is an example in which refined copper having a purity of about 99.5% or oxygen-free copper containing no oxide is used as a conductor widely used as a wire (see Patent Documents 3 and 4). The impure substance of refined copper contains hundreds of ppm of oxygen (mostly contained as copper oxide), silver, iron, sulfur, phosphorus, and the like. The oxygen-free copper is usually copper having a purity of about 99.96 to 99.995%, and copper which is greatly reduced to 10 ppm or less. In the above-mentioned Patent Documents 3 and 4, it has been reported that the copper foil produced by the oxygen-free copper has better bending fatigue characteristics than the fine copper foil, and depends on the presence or absence of copper oxide. Among them, when the purity of the copper is further increased, it is necessary to remove impurities such as silver, phosphorus, and sulfur.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2002-171033

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2002-300247

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2001-58203

[Patent Document 4] Japanese Patent No. 3009383

[Patent Document 5] Japanese Patent Laid-Open Publication No. 2007-107036

According to the above-described situation, the inventors of the present invention have a durable flexible circuit board that does not have any restriction on the design of the flexible circuit board and that has a bending resistance or a curvature having a small radius of curvature. As a result of careful study, it has been found that a flexible circuit substrate having excellent bending durability or flexibility can be obtained by using a metal foil having a crystal structure of a face-centered cubic lattice system which is highly aligned and has a large elongation at break. The present invention has been completed.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a flexible circuit board which is excellent in durability, and in particular to provide a reverse bending of a radius of curvature such as a hinge portion or a sliding sliding portion such as a mobile phone or a small electronic device. A flexible circuit board having excellent durability and excellent flexibility, such as an overly demanding use condition.

Further, another object of the present invention is to provide durability and excellent bending property in an overly harsh condition such as a hinge portion or a sliding sliding portion of a mobile phone or a small electronic device or the like, which is particularly small in a curved portion having a small radius of curvature. The curved portion structure of the flexible circuit board.

The present invention has been intensively studied in order to solve the problems of the above-described conventional techniques, and the following constitutions are intended as the gist.

(1) A flexible circuit board comprising a resin layer and a wiring formed of a metal foil, and a flexible circuit board having a bent portion at least one portion of the wiring, characterized in that the metal foil is It consists of a metal having a face-centered cubic structure, and the basic crystal axis of the unit cell of the face-centered cubic structure <100> is opposite to the thickness direction of the metal foil and two orthogonal axes existing in a certain direction in the foil surface. The preferential alignment field within 10° of the azimuth difference is 50% or more in area ratio, and the elongation at break of the metal foil in the normal direction of the cross section P of the wiring which is cut by the ridge line in the curved portion toward the thickness direction of the metal foil It is 3.5% or more and 20% or less.

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

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

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

(5) The flexible circuit board according to any one of (1) to (4) wherein the cross section P of the wiring is rotated from (100) to (110) with [001] as a ribbon axis. Any face included in the range from (20 1 0) to (1 20 0) in the direction forms the principal orientation.

(6) The flexible circuit board of (5), wherein the cross section P of the wiring is in a solid triangle of the (100) standard projection image, and is located at a point (20 1 0) indicating the (20 1 0) Point any face on the connected line segment.

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

The flexible circuit board of any one of (1) to (7), wherein the resin layer is composed of polyimine.

The flexible circuit board of any one of (1) to (8), wherein any one selected from the group consisting of sliding bending, bending bending, hinge bending, and slip bending is formed. The method of repeating the bending portion of the action is used.

(10) An electronic device comprising the flexible circuit board according to any one of the above (1) to (9).

(11) A curved portion structure of a flexible circuit board, comprising a resin layer and a wiring formed of a metal foil, and a bent portion structure of the flexible circuit board having a bent portion at at least one portion of the wiring The metal foil is composed of a metal having a face-centered cubic structure, and the basic crystal axis of the unit cell of the face-centered cubic structure is <100> with respect to the thickness direction of the metal foil, and some existing in the foil surface. The two orthogonal axes in one direction, the priority alignment field within 10° of the azimuth difference is 50% or more in area ratio, and the cross section P of the wiring which is cut toward the thickness direction of the metal foil by the ridge line in the curved portion The elongation at break of the metal foil in the line direction is 3.5% or more and 20% or less.

According to the present invention, the metal foil constituting the wiring in the bent portion when the flexible circuit board is bent is less likely to cause metal fatigue, and has excellent durability against stress and deformation. Therefore, it is possible to provide a flexible circuit board having excellent strength and excellent bending properties even in the case of bending or bending with a small radius of curvature, without any restriction on the design of the flexible circuit board, and It is an electronic device with high durability, such as a thin mobile phone, a thin display, a hard disk, a printer, or a DVD device.

The wiring included in the flexible circuit board of the present invention is formed of a metal foil made of a metal having a face-centered cubic lattice crystal structure. For a metal having a crystal structure of a face-centered cubic lattice system, for example, copper, aluminum, nickel, silver, rhodium, palladium, platinum, gold, or the like is known, and these may be any, but based on the metal foil. Copper, aluminum, and nickel are suitable for use, and copper foil which is mainly used as a wiring of a flexible circuit board is most common.

The present invention provides a flexible circuit board excellent in bending durability or flexibility, and in particular, a flexible circuit board having excellent fatigue characteristics in a high deformation range such as a curvature radius of 2 mm or less. In order to achieve the object, in the present invention, even if i) the metal foil is highly aligned, and ii) in the bent portion, the metal foil has a large elongation at break in the principal stress direction, and is not formed as in this case. A flexible circuit board which is resistant to fatigue damage at the time of high bending as shown in the invention. That is, by satisfying both of i) and ii) at the same time, it is possible to obtain a flexible circuit board which is resistant to fatigue damage at the time of high bending. Specifically, it must be: i) the basic crystal axis of the unit cell of the face-centered cubic structure <100> with respect to the thickness direction of the metal foil and the two orthogonal axes existing in a certain direction in the foil surface, respectively. The area of the preferential alignment within 10° is 50% or more in area ratio, and ii) the elongation at break of the metal foil in the normal direction of the cross section P of the wiring which is cut in the thickness direction of the metal foil by the ridge line in the curved portion is 3.5% or more and 20% or less.

When the metal foil is a polycrystalline body as seen in a general electrolytic foil or a rolled foil, high elongation at break can be obtained, but the high deformation fatigue obtained in the present invention does not become a high fatigue property. Circuit board. On the other hand, even if the aggregate structure is developed and the degree of alignment is large and the elongation at break is small, the flexible circuit board having the characteristics obtained by the present invention cannot be obtained in the same manner.

In the present invention, for the first time, it is known that a metal foil having a large aggregate structure and a large degree of alignment is used, and in particular, the elongation at break of the metal foil in the flexible circuit substrate having high bending characteristics is an important factor.

The metal foil may be either a calendered foil or an electrolytic foil, but a rolled foil is preferred in terms of obtaining high alignment. In the case of a face-centered cubic metal, the rolling conditions and the heat treatment conditions are designed, whereby a metal foil having a highly aligned cubic aggregate structure having a <100> main orientation in the rolling direction and the foil surface normal direction can be produced.

Not limited to the use of the flexible circuit board, the mechanical properties of the metal foil having a strong cubic orientation are characterized by an anisotropy in elongation at break. The elongation at break takes a very small value when stretching in the <100> direction. In general, the more the degree of alignment increases and the smaller the thickness of the metal foil, the smaller the elongation at break in the tensile test in the <100> direction. The basic crystal axis of the unit cell of the face-centered cubic structure is <100>, and the thickness direction of the metal foil (the normal direction of the foil surface) and the two directions existing in the foil surface (the one is the rolling direction) are positive. When the priority alignment field within 10° of each azimuth difference is 95% or more in area ratio, and the general rolled copper foil having a thickness of 18 μm or less (hereinafter referred to as "conveniently rolled copper" for convenience Foil"), the elongation at break in the direction of the principal stress in the bent portion did not reach 3.5%. The term "elongation at break" as used herein refers to the use of a test piece having a width which is sufficiently larger than the thickness of the metal foil, typically in the range of 5 to 15 mm in width, to a relative length of 10%/min. The deformation speed is stretched until the fracture at the time of the tensile test. In the present invention, it is assumed that the elongation at break of the metal foil is determined by the measurement method shown in the following examples, and the value is obtained by laminating the resin layer to obtain a flexible circuit board.

In the case of rolling the copper foil, the direction of rolling of the recrystallized aggregate structure, that is, the longitudinal direction of the metal foil is <100> orientation. In a general flexible circuit board, the longitudinal direction of the circuit is matched with the longitudinal direction of the copper foil from the viewpoint of improving the yield when the substrate is taken out. Therefore, in the general utilization form in which the longitudinal direction of the circuit is bent, since the principal stress direction coincides with the <100> direction, the conventional rolled copper foil is not subjected to fatigue which is highly resistant to repeated bending. characteristic.

In the method of improving the fatigue characteristics of the flexible circuit board used in the orientation relationship as described above, in the present invention, the purity of the metal foil to be used is improved. In the flexible circuit board used for the high-bending use known to date, a copper foil containing an impurity such as oxygen or silver, which is intentionally or unavoidably used, is used. For example, as disclosed in Patent Document 5, it is possible to make the shear deformation along the slip surface easier or to suppress the increase in resistance. However, these impurity elements reduce the energy of the laminated defects. The present inventors focused on this point. That is, if the delamination defect energy is lowered, the dislocations are easily expanded, and cross slippage is less likely to occur, and particularly when stretching in the <100> direction, stretching is less likely to occur.

Therefore, in the present invention, a metal foil (preferably a copper foil) exhibiting a predetermined preferential orientation as described below and preferably having a purity of 99.999% or more is used, whereby elongation at break in the <100> direction can be obtained. The increase is 3.5% or more, and as a result, the fatigue characteristics when the reverse deformation is applied in the high deformation field are improved. It is preferable to use a metal foil having a high purity, but it is most suitable for use in the case of manufacturing cost of 99.999% or 99.9999%. Further, even in the case of a copper foil having a purity of less than 99.999%, in an oxygen-free copper foil having a low oxygen concentration, as shown in the following examples, although it is a narrow condition, it is a face-centered cubic structure depending on rolling and heat treatment conditions. When one of the basic crystal axes <100>, for example, the [001] axis is 98% or more and 99.8% or less in the range of the thickness direction of the metal foil (the normal direction of the foil surface) within 10 degrees of the azimuth difference, there is In the field in which the elongation at break is 3.5% or more, the bending fatigue resistance is improved. For this reason, although the current point is not clear, in the oxygen-free copper foil obtained by heat treatment to obtain a predetermined aggregate structure, it is presumed that there is an appropriate size, and the rolling direction in which the relative volume ratio is dispersed is <212> Azimuth recrystallizes the residual structure and increases the elongation at break in the <100> direction.

In the flexible circuit board of the present invention, the three-dimensional crystal orientation of the metal foil is defined for the sample coordinate system of the metal foil constituting the circuit, and the aggregated degree of the aggregate structure is the following range. That is, one of the basic crystal axes <100> of the face-centered cubic structure, for example, the [001] axis is used in a field in which the thickness direction of the metal foil (the normal direction of the foil surface) is within 10 degrees with respect to the azimuth difference. Preferably, the ratio is 50% or more, preferably 75% or more, more preferably 98% or more, and the other basic crystal axis, for example, the [100] axis, is in a horizontal foil surface on the surface of the metal foil. A preferred alignment of 50% or more, preferably 85% or more, and more preferably 99% or more of the area within 10° of the azimuth difference. In the present invention, the accumulation degree of the aggregate structure as described above may be at least in the curved portion, but the so-called class having the degree of accumulation as described above, which is more suitable for all of the metal foil laminated on the resin layer. The single crystal metal foil is not restricted in the wiring design, and is preferable. Wherein, since the crystal orientation of the center located in the preferential alignment is referred to as the main orientation of the aggregate structure, the metal used in the present invention may be referred to as the main orientation of the metal foil having a thickness direction of <100>, and the metal foil The foil face has a main orientation of <100>.

The priority of the preferential alignment of the collective organization, that is, the index indicating the degree of alignment or the degree of accumulation, may be based on the diffraction intensity of the X-ray and the statistical data of the local three-dimensional orientation data obtained by the diffraction of the electron beam. Indicators of objective data.

For example, when the metal foil is a copper foil, the intensity (I) from the (002) perpendicular to the crystal ribbon axis obtained by X-ray diffraction (here, according to the general marking method in the X-ray diffraction) The strength of the (200) plane), the copper foil having the intensity (I ₀ ) of the (200) plane obtained by the X-ray diffraction of the fine powder copper is I/I ₀ ≧25, and wiring having a predetermined pattern is formed. Preferably, I/I ₀ is in the range of 33 to 150, more preferably in the range of 50 to 150. Here, the parameter I/I ₀ indicates the orientation of the crystal axis of (100) and (110), that is, the alignment of the common axis [001], and represents an objective index of the degree of development of the cube assembly. Next, when the metal foil is a rolled copper foil, it is strongly processed at a rolling ratio of a certain value or more, and then heated to recrystallize, the rolled foil surface is set to a (001) main orientation, and the foil surface is rolled in the direction. The orientation of the recrystallized cube set to (100) the main orientation is developed. The more the cube orientation of the recrystallized assembly of copper belongs to, the more the bending fatigue life of the copper foil is improved. In the flexible circuit board of the present invention, when the I/I _{0 is} less than 25, the improvement of the bending fatigue life of the wiring is not sufficiently satisfactory. If the I/I ₀ is 33 or more, the improvement of the bending fatigue life becomes more complicated. obvious. Here, the X-ray diffraction in the thickness direction of the copper foil refers to the alignment in the surface of the copper foil (in the case of a rolled copper foil, the rolling surface), and the strength (I) of the (200) plane is represented by X-ray. The intensity integral value of the (200) plane obtained by diffraction. Further, the strength (I ₀ ) indicates the intensity integral value of the (200) plane of the fine powder copper (the copper powder test material of the Kanto Chemical Co., Ltd. grade I, 325 mesh).

In order to obtain I/I _{0 of} 25 or more, it is only necessary to obtain a recrystallized aggregate structure of the copper foil, and the means is not particularly limited, but is a metal foil which is subjected to an intermediate burning condition or a cold rolling processing rate. The type or the concentration of the impurities is optimized, whereby a rolled structure of a large aggregate of crystal grains and a rolled copper foil of I/I ₀ ≧25 can be obtained. Further, for example, after the copper layer is laminated on the resin layer and the rolled copper foil, the copper foil may be heated at a temperature of 300 to 360 ° C for a load of 5 minutes or more. Recrystallized assembly of copper foil.

Further, in order to define the aggregate organization in terms of the degree of integration of the three dimensions, it is also possible to specify the area ratio of the priority alignment field within 10 degrees with respect to the main orientation of the aggregate organization. In other words, the crystal plane of the predetermined surface of the metal foil may be, for example, an electron beam diffraction method such as an EBSP (Electron Back Scattering Pattern) method or an ECP (Electron Channeling Pattern) method, or an X-ray such as a Micro Laue method. Confirm by the diffraction method or the like. The EBSP method analyzes crystals based on a diffraction image called a pseudo-Kikuchi line, which is diffracted by each crystal plane generated when a convergent electron beam is irradiated onto the surface of the sample to be measured, and is determined based on the orientation data and the measurement. The position information of the point is used to measure the crystal orientation distribution of the measurement object, and the crystal orientation of the aggregate structure in the micro domain can be analyzed compared to the X-ray diffraction method. For example, the crystal orientations can be specified in each of the microscopic fields, and the maps can be mapped together, and the inclination (azimuth difference) of the plane orientation between the map points is equal to or less than a certain value. The distribution of the fields (crystal grains) of the same plane orientation is revealed, whereby the orientation map image can be obtained. Further, the orientation plane having an orientation within a predetermined angle with respect to a specific plane orientation may be included, and the orientation may be defined, and the ratio of the existence of each plane orientation may be extracted by an area ratio. In the EBSP method, in order to exhibit an area ratio of a region within a certain angle from a specific orientation, it is necessary to at least be larger than the field of circuit bending in the flexible circuit substrate of the present invention, in order to exhibit an area ratio. The electronic wire is scanned in detail in a manner that is sufficient to obtain a sufficient number of points. However, in the metal foil to be used in the present invention, the size of the target metal is considered, and in the field of 0.005 mm ² or more, In order to exhibit an average area ratio, it is sufficient to measure 1000 points or more.

However, the present invention differs from the inventions described in Patent Documents 3 and 4 in that the orientation of the invention of the patent documents is only defined by the normal direction of the foil measured by the X-ray. In contrast, the present invention is defined by a third dimension. In order to obtain high fatigue properties for bending, in particular, the main deformation, the principal stress direction, that is, the <100> accumulation degree in the foil surface, is extremely important. Further, in the present invention, the size of the recrystallized grains, that is, the crystal grains having a cubic orientation is preferably 25 μm or more on the average.

Further, in the present invention, in particular, when high flexibility is required, the metal foil forming the flexible circuit board may be a rolled copper foil having a thickness of 5 to 18 μm, and a rolled copper foil having a thickness of 9 to 12 μm is preferably used. When the rolled copper foil is thicker than 18 μm, it is difficult to obtain a flexible circuit board having excellent fatigue characteristics in a high deformation range having a curvature radius of 2 mm or less. Further, when the thickness is thinner than 5 μm, it is difficult to laminate the metal foil and the resin layer, and it is difficult to form a homogeneous flexible circuit board.

Different from the first method for improving the fatigue characteristics of the flexible circuit substrate described above, in the present invention, the second elongation at break of the face-centered cubic metal foil for improving the single crystal close to the height alignment In the case of the square policy, the <100> direction in which the elongation at break is small does not become the principal stress direction, and the wiring structure of the flexible circuit board is designed. Specifically, the following methods are listed.

As described in the first aspect, by designing the rolling and recrystallization conditions, it is possible to produce a metal foil having a highly aligned cubic aggregate structure having a <100> main orientation in both the rolling direction and the normal direction of the foil surface. Further, in terms of wiring, the direction in which the circuit is cut is shifted from the rolling direction, that is, the <100> direction by a predetermined angle, and the circuit is obliquely drawn, whereby the bending elongation is large in the direction of the principal stress. Flexible circuit board. By the method as described above, the elongation at break of the metal foil in the normal direction (the principal stress direction in the curved portion) of the cross section P of the wiring which is cut in the thickness direction of the metal foil by the ridge line in the curved portion is 3.5. Above %, the above-mentioned section P must have a principal orientation in any plane included in the range of (20 1 0) to (1 20 0) with [001] as the ribbon axis. Here, the relationship between the ribbon axis and the plane orientation is shown in Fig. 1. (20 1 0) and (1 20 0) are in the relationship of [001] as the common axis, that is, the ribbon axis, and are located at (001) as the axis (100) to (110) [by (100) To the rotation surface of (010)]. That is, when it is displayed on the inverse pole map of the normal direction of the cross section P, the faces of (001), (20 1 0), and (110) are as shown in Fig. 2 . Based on the symmetry, on the inverse pole map, (1 20 0) is represented at the same position as (20 1 0). The metal of the metal foil in the present invention has a face-centered cubic structure. The crystal axis of the unit cell is [100], [010], [001], but in the present invention, if there is a <100> preferential orientation in the thickness direction of the metal foil (vertical direction with respect to the surface of the metal foil), Marking the axis as [001], that is, marking the orientation of the foil surface as (001), but even if the axis is replaced based on the symmetry of the face-centered cubic structure, it is equivalent to In the invention.

Then, the main direction in the foil surface must be 2.9° to the main direction of the bending portion, that is, the normal direction of the cross section of the wiring when the ridge line in the curved portion is cut in the thickness direction (for the perpendicular line to the wiring cross section P). The angle of 87.1 ° [(20 1 0) to (1 20 0)] is preferably an angle of 5.7 ° to 84.3 ° [(10 1 0) to (1 10 0)], more preferably 11.4 ° to 78.6. The angle of °[(510) to (150)], and more preferably the angle of 26.6° to 63.4° [(210) to (120)], is most suitable for 30° or 60° [(40 23 0) or (23 40 0)] is appropriate. Here, the inside of [ ] indicates the plane orientation of the section P corresponding to the respective angles. However, the symmetry of the crystal may be described as having a normal line with respect to the wiring cross section P at an angle of 2.9 to 45° with respect to the basic crystal axis <100> in the plane of the metal foil.

Here, the cross section P of the wiring when the ridge line in the curved portion is cut in the thickness direction is, for example, shown in FIG. 3, and when the flexible circuit board is bent into a U shape, a ridge line L is formed on the outer side thereof. The wiring portion among the cross sections obtained when the ridgeline L is cut toward the thickness direction d of the flexible circuit board. In addition, the ridge line L is a vertex phase formed when the flexible circuit board is bent, and the cross section of the flexible circuit board is viewed along the bending direction (the thick black arrow in FIG. 3). Linked line. Among them, for example, a case where the ridge line L such as a sliding curve to be described later moves on the flexible circuit board is also included. In addition, in the third figure, the resin layer 1 is outside and the wiring 2 is bent inward (the side in which the circle having the radius of curvature is inscribed is inside), but the wiring 2 may be folded outward. The way of music is self-evident.

In various applications, the metal foil is primarily subjected to tensile or compressive stresses when subjected to a forced displacement of a certain curvature. Which part of the flexible circuit board subjected to bending is subjected to stretching or compression depending on the composition of the metal foil and the resin, but is more than the neutral axis (or neutral surface) of stretching and compression. The farthest portion of the curved outer side is too severe due to metal damage, and it is generally seen that the tensile stress in the normal direction of the cross section of the wiring when the ridge line in the curved portion is cut in the thickness direction becomes the principal stress. That is, the principal stress direction of the wiring in the bent portion is a direction indicated by an arrow 21 in FIG. 3, and typically a wiring cross section P which is cut toward the thickness direction of the metal foil with respect to the ridge line of the curved portion. The lines are in the same direction and intersect perpendicularly to the [001] axis aligned toward the thickness direction of the metal foil.

In consideration of the mechanical properties of the metal foil in the flexible circuit board, the stress-deformation characteristic when the metal foil is simply stretched toward the principal stress direction indicated by the arrow 21 in Fig. 3 is an important characteristic. Here, as shown in the examples of (c) and (d) of FIG. 4, it is assumed that the [100] axis of the metal foil having a crystal structure having a face-centered cubic structure is curved so as to be orthogonal to the ridge line. In the case where the cross section of the wiring which is cut in the thickness direction of the flexible circuit board in the ridge line of the curved portion is the (100) plane, the cross section P of the wiring when the ridge line in the curved portion is cut in the thickness direction is as shown in FIG. 1 . As shown, [001] is the band axis and the range of (20 1 0) to (1 20 0) in the direction of rotation from (100) to (010) (the two arrows in the figure) is included. If any face exhibits a main orientation, the elongation at break can be increased. In the first graph, the range of (20 1 0) to (1 20 0) is shown, but there is a surface equivalent to the surface included in the range in the face-centered cubic crystal structure. Therefore, the equivalent faces of the cross section of the wiring and the range of (20 1 0) to (1 20 0) are different from each other, and are included in the present invention.

In the second aspect, the cross section P of the wiring when the ridge line in the curved portion is cut in the thickness direction has a main orientation in a specific orientation between (20 1 0) and (1 20 0), and is preferentially aligned, thereby being broken. The reason for the elongation rise is that when a tensile stress is applied to the normal direction of the section P, that is, the principal stress direction, among the metals having the face-centered cubic structure, among the eight {111} belonging to the slip surface, Since the Schmid factor has the largest main slip surface as 4 faces, the shear slip becomes good and local work hardening does not occur easily. In a general rolled copper foil, generally, the longitudinal direction of the metal foil corresponds to the rolling direction, and as shown in Fig. 4 (c) or (d), an electric circuit is formed along its main orientation <100>. For example, the embodiment of Patent Document 5 corresponds to the form of Fig. 4(d). As described above, when the cross-sectional orientation of the wiring when the ridge line in the curved portion is cut in the thickness direction is (100), when the bending is performed, the Schmid factor of the eight slip surfaces becomes equivalent. The slip system acts at the same time, and the locality is easy to accumulate dislocations. According to the difference from the conventional technique shown above, the bending resistance of the flexible circuit board using the second method is superior to the general use form in which the longitudinal direction of the circuit is bent.

The most preferable orientation of the cross section P in the flexible circuit board is 30° or 60° with respect to the main deformation direction of the curved portion, that is, the cross-sectional normal direction of the wiring when the ridge line in the curved portion is cut in the thickness direction. However, this is to make the direction of stress coincide with the stable orientation of the stretch. When the above mechanism is considered, if the cross section P of the wiring at least when the ridge line in the curved portion is cut in the thickness direction is [001] as the ribbon axis, the specificity between (20 1 0) and (1 20 0) The orientation has a main orientation and has a priority alignment.

That is, the second-party metal foil of the present invention has a face-centered cubic structure, the thickness direction of the metal foil has a main orientation of <100>, and the foil surface of the metal foil has a main orientation of <100>, and is provided with The normal direction of the cross section P of the wiring when the ridge line in the curved portion is cut in the thickness direction has a main orientation in a specific orientation between (20 1 0) and (1 20 0), and is preferentially aligned. At this time, the normal direction of the cross section P preferably has a main orientation in a specific orientation between (10 1 0) and (1 10 0) for preferential alignment, and more preferably (510) to (110). The specific orientation between the specific orientations has a principal orientation and is preferentially aligned. More preferably, the specific orientation between the (210) and (110) has a principal orientation for preferential alignment. The most suitable system has a central orientation near (40 23 0). For priority alignment. In the case of a metal foil in which the foil surface is preferentially oriented with (001) as the main orientation, for example, [001] and [100] in the foil surface are equivalent, and the flexible circuit board of the present invention is in the bent portion. The main orientation of the cross section P of the wiring when the ridge line is cut in the thickness direction may also be described as a specific orientation between (1 20 0) and (110), preferably at a specific orientation between (120) and (110). It has a main orientation and is preferentially aligned. It is most suitable to describe that it has a main orientation in the vicinity of (23 40 0) and is preferentially aligned.

Further, the thickness direction of the metal foil has a main orientation of <100>, and the metal foil has a main orientation of <100> in the foil surface, and the cross section P of the wiring when the ridge line in the curved portion is cut in the thickness direction is (20) The specific orientation between 1 0) and (1 20 0) has a principal orientation, which can also be said to be an inverse pole representation on the stereo triangle of the (100) standard projection map shown in FIG. The cross-sectional direction of the wiring when the ridge line in the portion is cut in the thickness direction is any surface on the line segment connecting the point indicating (20 1 0) and the point indicating (110). Further, in the flexible circuit board according to the second aspect, the wiring is formed of a material in which the thickness direction of the metal foil is 3 (2) axis of the [001] axis, and it may be said that when the ridge line in the curved portion is cut in the thickness direction The profile normal of the wiring has an angle ranging from 2.9 to 87.1 between the [100] axis in the foil face.

Then, by the second method as described above, it is possible to form the elongation at break of the metal foil in the direction of the principal stress in the curved portion to 3.5% or more, and it is less likely to cause a reverse deformation such as a curvature radius of 2 mm or less, or even A flexible circuit board which is less prone to metal fatigue and has high flexibility. Further, in the present invention, by combining the first method and the second method, it is possible to more reliably obtain a flexible circuit board having excellent metal fatigue characteristics and flexibility, and elongation at break of the metal foil in the main stress direction. It can be formed to be 3.5% or more, preferably 4% or more, and more preferably 9% or more. Wherein, the upper limit of the elongation at break, the basic crystal axis of the unit cell of the face-centered cubic structure <100>, the thickness direction of the metal foil (the normal direction of the foil surface) and a direction existing in the foil surface (its The two orthogonal axes of the rolling direction, the preferential alignment field within 10° of the azimuth difference is 50% by area ratio, and the thickness of 18 μm is the upper limit of the rolled foil which can be obtained within the scope of the present invention. It can be specified to be 20% or less, but if the basic crystal axis of the unit crystal lattice of copper is <100>, the orientation direction difference with respect to the thickness direction of the copper foil and the two orthogonal axes existing in a certain direction in the foil surface When the preferential alignment field within 10° accounts for 95% or more of the area ratio and the thickness is 12 μm or less, the upper limit of the elongation at break is 15% or less.

In the resin layer of the flexible circuit board of the present invention, the type of the resin forming the resin layer is not particularly limited, and it can be exemplified by a user in a general flexible circuit board, and examples thereof include polyimine and polyfluorene. Amine, polyester, liquid crystal polymer, polyphenylene sulfide, polyether ether ketone, and the like. Among them, since it exhibits good flexibility as a circuit board and also has excellent heat resistance, it is preferably a polyimine or a liquid crystal polymer.

The thickness of the resin layer can be appropriately set in accordance with the use, shape, and the like of the flexible circuit board. However, from the viewpoint of flexibility, it is preferably in the range of 5 to 75 μm, and preferably in the range of 9 to 50 μm. The range of 10 to 30 μm is optimal. When the thickness of the resin layer is less than 5 μm, the insulation reliability is lowered. On the other hand, when it is more than 75 μm, the thickness of the entire circuit board may become too thick when it is mounted on a small machine or the like, and bending may occur. Reduced sex.

In addition, when the flexible circuit board is applied to a sliding sliding portion of a mobile phone or the like, a cover member made of a cover film or the like is bonded to a wiring formed of a metal foil. In this case, in this case, it is preferable to design the cover material and the resin layer in consideration of the balance of the stress applied to the wiring. According to the knowledge of the inventors of the present invention, for example, a polyimide having a tensile modulus of 4 to 6 GPa at 25 ° C and a thickness of 14 to 17 μm is used as the resin layer, and has a thickness of 8 to 17 μm. Two layers of an adhesive layer made of a thermosetting resin and a polyimide layer having a thickness of 7 to 13 μm, and a cover film having a tensile modulus of 2 to 4 GPa of the entire adhesive layer and the polyimide layer as a cover. The composition of the material, or a polyimide having a tensile modulus of 6 to 8 GPa at 25 ° C and a thickness of 12 to 15 μm as a resin layer, and having a thermosetting resin having a thickness of 8 to 17 μm A cover film having a thickness of 7 to 13 μm and a polyimide film having a thickness of 7 to 13 μm is used as a coating material having a tensile modulus of 2 to 4 GPa in the entire layer of the adhesive layer and the polyimide layer.

Regarding the means for laminating the resin layer and the metal foil, for example, when the resin layer is composed of polyimide, the metal foil can be laminated on the polyimide film or the thermoplastic polyimide. Combination (so-called stacking). For the polyimide film to be used in the stacking method, for example, "Kapton" (Toray DuPont Co., Ltd.), "Apical" (Zhongyuan Chemical Industry Co., Ltd.), "Upilex" (Ubehing) Production Co., Ltd.) and so on. When the polyimide film and the metal foil are subjected to heat and pressure bonding, a thermoplastic thermoplastic polyimide resin showing thermoplasticity may be incorporated therein. Further, from the viewpoint of easy control of the thickness of the resin layer, the bending property, and the like, the metal foil may be coated with a polyimide film solution (also referred to as a polyamic acid solution) to be dried and hardened. And the layered body (so-called casting method).

The resin layer may be formed by laminating a plurality of resins, or may be formed by laminating two or more kinds of polyimine layers having different linear expansion coefficients, etc., but it is preferably from the viewpoint of ensuring heat resistance or flexibility at this time. In order to prevent the epoxy resin or the like from being used as an adhesive, it is preferable that all of the resin layers are substantially formed of polyimide. In the case of a case of a single polyimine and a case of a plurality of polyimine, the tensile modulus of the resin layer is preferably 4 to 10 GPa, more preferably 5 to 8 GPa.

In the flexible circuit board of the present invention, the linear expansion coefficient of the resin layer is preferably in the range of 10 to 30 ppm/°C. When the resin layer is composed of a plurality of resins, the coefficient of linear expansion of the entire resin layer may be within this range. In order to satisfy the conditions as described above, for example, a low-expandable polyimine layer having a linear expansion coefficient of 25 ppm/° C. or less, preferably 5 to 20 ppm/° C., and a coefficient of linear expansion of 26 ppm/° C. or more are used. The resin layer composed of a highly linear expandable polyimide layer of preferably 30 to 80 ppm/° C. can be formed to have a thickness ratio of 10 to 30 ppm/° C. by adjusting the thickness ratio. The ratio of the thickness of the preferred low linear expansion polyimide layer to the high linear expansion polyimide layer is in the range of 70:30 to 95:5. Further, the low-expansion polyimine layer is a main resin layer of the resin layer, and the high-expansion polyimine layer is preferably formed in contact with the metal foil. Among them, the coefficient of linear expansion is a sample obtained by using a polyamidimide in which the ruthenium imidization reaction is sufficiently completed, and is heated to 250 ° C using a thermomechanical analyzer (TMA), and then cooled at a rate of 10 ° C / minute. The average linear expansion coefficient in the range of -100 ° C was obtained.

Further, the flexible circuit board of the present invention includes a resin layer and a wiring formed of a metal foil, and has a bent portion for any user. In other words, the movable part in the hard disk, the hinge part or the sliding sliding part of the mobile phone, the printing head of the printer, the optical pickup part, the movable part of the notebook PC, etc. A machine or the like is widely used, and the circuit board itself is bent, twisted, or deformed in accordance with the operation of the loaded machine, and a bent portion is formed in any of them. In particular, since the flexible circuit board of the present invention has a curved portion structure excellent in bending durability, it is suitable for frequent bending with repeated operations such as sliding bending, bending bending, hinge bending, and slip bending, or Corresponding to the miniaturization of the loaded machine, the radius of curvature is 0.38 to 2.0 mm for the bending behavior, 1.25 to 2.0 mm for the sliding bending, 3.0 to 5.0 mm for the hinge bending, and 0.3 to 2.0 for the sliding bending. In the case of strict use conditions such as mm, it is particularly effective in sliding applications with a narrow gap of 0.3 to 1 mm and a strict bending performance.

Regarding the manufacturing method of the flexible circuit substrate in the present invention, i) obtains a rolled metal which exhibits a cubic aggregate structure in which the [001] axis is finally aligned toward the foil surface normal (the perpendicular to the surface of the metal foil). The composite in which the foil and the resin layer are bonded to the foil surface of the metal foil, the metal is oriented in the direction of the principal stress of the design, that is, the normal direction of the cross section of the wiring when the ridge line in the curved portion is cut in the thickness direction, and the metal The [100] main orientation in the foil surface has an angle of 2.9° to 87.1°, and the ridge line of the curved portion is formed to be wired, or ii) the metal foil constituting the wiring is formed to have a purity of 99.999% or more, or iii) The methods of i) and ii) are sufficient.

At this time, the metal foil does not necessarily have to present the cubic aggregate structure from the beginning, and the cubic aggregate structure can also be formed by heat treatment, for example, in the manufacturing process of the flexible circuit substrate, specifically, in the formation of the resin layer. Heat treatment is performed to form a cube assembly. That is, by performing heat treatment, the basic crystal axis of the unit cell is <100> toward the thickness of the metal foil in such a manner that the area of the <100> axis within 10° of the azimuth difference is occupied by 50% or more. The direction is preferentially aligned, and the surface of the basic crystal axis <100> is preferentially oriented horizontally with respect to the surface of the metal foil having an area ratio of less than 10% by the <100> axis. Can be aligned. The recrystallized aggregate structure of the rolled copper foil has a general calender plane orientation of {100} and a calendering direction of <100>. Therefore, the (001) main orientation is formed in terms of the rolling surface orientation. In addition, when a metal foil having a purity of 99.999% or more is used, even if a circuit is formed and wired in any orientation, the elongation at break can be secured by 3.5% or more, and a flexible circuit board having a large design range can be formed.

In the case where the second method is used, more specifically, as shown in FIG. 3, when, for example, the flexible circuit board is bent into a U shape, the outer side thereof is formed (inscribed with an inscribed circle having a radius of curvature) The ridgeline L is formed on the opposite side. However, the ridgeline L may have a slope in a range of α=2.9 to 87.1 (°) in a state orthogonal to the [100] axis of the metal foil on which the wiring is formed. An example of the state shown above is shown in (a) and (b) of Fig. 4. Incidentally, (c) and (d) of Fig. 4 are in a state in which the ridge lines are orthogonal to each other with respect to the [100] axis (α = 0). Here, if α is less than 2.9°, a clear effect is not confirmed in the bendability. If α is 11.4 to 78.6 (°), the bending durability of the bent portion structure is further improved. In the present invention, in the case of the above α=2.9°, the cross section P of the wiring when the ridge line is cut in the thickness d direction corresponds to the (20 1 0) plane, and when α=45, the profile P Corresponding to the (110) plane, if α = 87.1, the profile P corresponds to the (1 20 0) plane. Further, in the face-centered cubic structure, [100] and [010] are equivalent, so the orthogonal axis of the foil in-plane of [100] shown in Fig. 4 (a) and (b) forms an angle α with the ridge line. The angular range is consistent with the angular extent of [100] and the normal of the section P, and the angular extent of [100] and the ridgeline.

Further, the width, shape, pattern, and the like of the wiring are not particularly limited, and may be appropriately designed according to the use of the flexible circuit board, the mounted electronic device, or the like, but the bending of the curved portion of the present invention is durable. Since it is excellent, even in the case where the second method is employed, it is not necessary to perform diagonal wiring with respect to the rotation axis of the hinge portion for the purpose of, for example, reducing the bending stress on the wiring, and it is possible to perform the diagonally along the opposite bending portion. The ridge lines are in the orthogonal direction of the wiring, that is, the wiring at the minimum required minimum distance. (a) and (b) of FIG. 4 show a flexible circuit board used for, for example, a hinge portion of a mobile phone, and a resin layer 1, a wiring 2 formed of a metal foil, and a terminal 3 of a connector. . In any of (a) and (b) of FIG. 4, the position of the ridge line L in the curved portion is displayed in the vicinity of the center, and the ridge line L has a [100] axis direction with respect to the metal foil forming the wiring 2 (90+). α) ° angle. Here, Fig. 4(a) shows an example in which wiring is formed obliquely in the middle of the connector terminals 3 at both ends and in the vicinity of the ridge line L, but the connector terminal 3 may be formed as shown in Fig. 4(b). Wiring is performed at the shortest distance. In addition, in the case where the position of the ridge line L in the curved portion is fixed as in the case of a folding mobile phone, the ridge line L in the curved portion such as a slide type mobile phone may be moved to slide and slide. (The bold arrow direction in Figure 4 (b)). In the flexible circuit board of the present invention, the wiring layer made of a metal foil is provided on at least one surface of the resin layer. However, if necessary, a metal foil may be provided on both surfaces of the resin layer.

As described above, the metal foil which constitutes the wiring in the curved portion when the flexible circuit board is bent is a metal foil which is formed to have a high degree of alignment and is elongated in the principal stress and the main deformation direction. When a high-bending reverse bending having a small bending radius is performed, local stress concentration due to crystal anisotropy is less likely to occur, and two effects such as dislocation accumulation are less likely to occur, and metal fatigue is less likely to occur. Durability against stress and deformation is not restricted by the design of the flexible circuit board, and it has strength that can withstand bending even if it is repeatedly bent or has a small radius of curvature, and has excellent flexibility. Circuit board.

[Examples]

Hereinafter, the present invention will be more specifically described based on examples and comparative examples. The type of the copper foil used in the examples and the like and the synthesis of the polyaminic acid solution are as follows.

[copper foil A]

Commercially available rolled copper foil, purity 99.9%, thickness 9 μm.

[copper foil B]

Commercially available electrolytic copper foil, purity 99.9%, thickness 9 μm.

[copper foil C]

Oxygen-free copper foil, purity 99.99%, thickness 9μm, process condition A.

Mass ppm oxygen: 2, silver: 18, phosphorus: 2.1, sulfur: 4, iron: 1.5

[copper foil D]

Refined copper foil, purity 99.999%, thickness 9μm, process condition A.

Mass ppm oxygen: 2, silver: 5, phosphorus: 0.01, sulfur: 0.01, iron 0.002

[copper foil E]

Refined copper foil, purity 99.9999%, thickness 9μm, process condition A.

Mass ppm oxygen: <1, silver: 0.18, phosphorus: <0.005, sulfur: <0.005, iron: 0.002

[copper foil F]

Refined copper foil, purity 99.9999%, thickness 9μm, process condition B.

Mass ppm oxygen: <1, silver: 0.18, phosphorus: <0.005, sulfur: <0.005, iron: 0.002

[copper foil G]

Refined copper foil, purity 99.9999%, thickness 9μm, process condition C.

Mass ppm oxygen: <1, silver: 0.18, phosphorus: <0.005, sulfur: <0.005, iron: 0.002

[copper foil H]

Commercially available rolled copper foil, purity 99.9%, thickness 12 μm.

[Manufacturing method of copper foil]

Copper foil A and copper foil H are commercially available rolled copper foils, and copper foil B is a commercially available electrolytic copper foil produced by a copper sulfate bath. These copper foils which are commercially available as high-bend products have a purity of 99.9%, which is higher in the case of commercial products. The copper foil C to the copper foil G are processed by the inventors of the present invention, and the copper material of a predetermined purity is cast and solidified in a graphite mold, and is subjected to calendering to form a predetermined thickness. The thickness of the ingot was 10 mm, and after rolling down to 1 mm by cold, the copper foil C, the copper foil D, and the copper foil E were calendered to 9 μm after being blunt at 300 ° C for 30 minutes. Until (process condition A). Further, the copper foil F was subjected to cold rolling (process condition B) until the middle was burned to 9 μm. Further, the copper foil G was subjected to inter-cooling at 800 ° C, and cold rolling was carried out until 9 μm (process condition C).

[Synthesis of polyaminic acid solution]

(Synthesis Example 1)

N,N-dimethylacetamide was placed in a reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen. In the reaction vessel, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) was dissolved while being stirred in a vessel. Next, pyromellitic dianhydride (PMDA) was added. The input was carried out so that the total amount of the monomer input was 15% by weight. Thereafter, stirring was continued for 3 hours to obtain a resin solution of polyamic acid a. The resin solution of the polyamic acid a had a solution viscosity of 3,000 cps.

(Synthesis Example 2)

N,N-dimethylacetamide was placed in a reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen. 2,2'-Dimethyl-4,4'-diaminobiphenyl (m-TB) was introduced into the reaction vessel. Next, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) were added. The total amount of the monomer input was 15% by weight, and the molar ratio (BPDA: PMDA) of each acid anhydride was 20:80. Thereafter, stirring was continued for 3 hours to obtain a resin solution of poly-proline b. The resin solution of the polyaminic acid b had a solution viscosity of 20,000 cps.

[Example 1]

The above-mentioned prepared polyamic acid solution a was applied to seven types of copper foils of copper foil A to copper foil G, and dried (cured to form a thermoplastic polyimide having a film thickness of 2 μm) and coated thereon. The polyaminic acid b is dried (cured to form a low thermal expansion polyimine having a film thickness of 9 μm), and the polyamic acid a is coated thereon and dried (hardened to form a thermoplastic having a film thickness of 2 μm) The polyimine layer is formed into a polyimine layer composed of a three-layer structure by heating at a temperature of 300 to 360 ° C for a load of 5 minutes or more. Next, the length of the copper foil in the rolling direction (MD direction) was 250 mm, and the direction in which the direction perpendicular to the rolling direction (the TD direction) was a rectangular shape having a width of 150 mm was cut out, as shown in FIG. A single-sided copper-clad laminate 4 having a polyimide layer (resin layer) 1 having a thickness of 13 μm and a copper foil 2 having a thickness of 9 μm. The tensile modulus of the entire resin layer at this time was 7.5 GPa.

In the single-sided copper-clad laminate 4 obtained as described above, colloidal vermiculite is used for the rolling surface 2a of each of the copper foils A to the copper foils G, and after mechanical and chemical polishing, the orientation is performed by the EBSP apparatus. Analysis. The apparatus used was FE-SEM (S-4100) manufactured by Hitachi, Ltd., EBSP apparatus manufactured by TSL Corporation, and software (OIM Analysis 5.2). The measurement field is in the field of about 800 μm × 1600 μm, and the acceleration voltage is 20 kV and the measurement phase interval is 4 μm. The evaluation of the alignment is expressed by the ratio of the measurement direction of the thickness direction of the foil and the rolling direction of the foil of <100> within 10° to the total measurement point. The number of measurements was carried out for five different samples of each individual, and the percentage of the decimal point was rounded off. Further, using the obtained data, the crystal grain size was evaluated as a crystal grain boundary when the difference in orientation of adjacent crystal grains was 15 or more, and the average particle diameter was determined for the polycrystalline system. The results are shown in Table 1.

It is understood that the rolled copper foil other than the copper foil B is formed with a cubic aggregate structure, and both the copper foil surface orientation and the rolling direction have a principal orientation of {001}<100>. This is based on the fact that the calendered copper foil is recrystallized by the heat of the polyimine hardening to form a recrystallized aggregate structure. However, the degree varies depending on the type, and the orientation of the cube orientation with respect to the copper foils A, C, D, and E is extremely high. The degree of orientation of the cube orientation is not dependent on the purity of the copper foil having a purity of 99.9% or more, and the dependence on the copper foil processing method is large. These copper foils are formed in a field of view of 800 × 1600 μm, and the entire field of view is composed of granules having a cubic orientation, and is formed into a structure in which crystal grains of 5 μm or less having different orientations are dispersed in an island shape. The area ratio of the island-shaped structure is small, and is 2% or less. Therefore, the recrystallized grains having the cube orientation have the same orientation and are integrated, and the size of the recrystallized grains is 9 μm in the thickness direction and the foil thickness, in the foil surface. It is 800 μm or more. Further, since the area ratio of the recrystallized grains having the cubic orientation of the copper foil F and the copper foil G is not high, they exist independently of each other, and the average particle diameter in the foil surface is 25 μm and 20 μm, respectively. On the other hand, the electrolytic copper foil B was a polycrystalline body having an average particle diameter of 1 μm, and almost no alignment property was observed.

Next, a predetermined mask is coated on the copper foil 2 side of the single-sided copper-clad laminate 4 obtained above, and is etched using a ferric chloride/copper chloride-based solution, as shown in Fig. 6 (wherein the wiring direction) The angle between H and the MD direction is 0°), and the wiring direction H (H direction) of the linear wiring 2 having a line width (1) of 150 μm is parallel to the MD direction (<100> axis), and the space is A wiring pattern was formed in such a manner that the wide (s) was 250 μm. Then, according to JIS 6471, a test having a width of 15 mm in the longitudinal direction and a direction perpendicular to the wiring direction H in the wiring direction H of the circuit board is obtained in accordance with JIS 6471. The flexible circuit board 5 is used.

Using the test flexible circuit board obtained above, the MIT bending test was performed in accordance with JIS C5016. The mode diagram of the test is shown in Figure 7. The apparatus was manufactured by Toyo Seiki Seisakusho Co., Ltd. (STROGRAPH-R1), and one end of the test flexible circuit board 5 in the longitudinal direction was fixed to a holding jig of the bending test apparatus, and the other end was fixed by a weight to the holding part. In the case where the radiant speed is 150 times/min, the radians are rotated by 135±5 degrees, and the radius of curvature is 0.8 mm, and the conduction of the wiring 2 of the circuit board 5 is blocked. The number of times is the number of bends.

In this test condition, since the ridge line formed in the curved portion is curved so as to be orthogonal to the wiring direction H of the wiring 2 of the test flexible circuit board 5, the principal stress and the main deformation system applied to the copper circuit are applied. It is a tensile stress and tensile deformation parallel to the rolling direction. When the circuit was observed from the thickness direction of the copper foil after the bending test, it was confirmed that cracks were formed in the vicinity of the ridge line of the curved portion substantially perpendicularly to the rolling direction to form a broken line. The results of the bending life are shown in Table 1. The bending life of Table 1 is an average of the results of preparing five test flexible circuit boards for each type of copper foil.

As can be seen from the results shown in Table 1, the bending fatigue life is determined by the same processing method, and the bending fatigue life of the copper foil C, the copper foil D, and the copper foil E which are substantially equal in the degree of alignment is determined by the cumulative degree of the cubic aggregate structure. Very different.

Next, in order to investigate the dominating factor of the bending life, the tensile test was performed in parallel with the principal stress of the bending, the main deformation direction, that is, the rolling direction. In order to investigate the characteristics of the copper foil monomer, the resin layer was dissolved by the single-sided copper-clad laminate 4 before etching, and a tensile test of the copper foil alone was carried out. It was confirmed that the structure of the copper foil did not change during the dissolution of the polyimine.

The tensile test was cut into a length of 150 mm in the rolling direction (MD direction) of the copper foil, and cut into a sample having a width of 10 mm in a direction perpendicular to the rolling direction in the foil surface, and the length direction was between punctuation. The measurement was performed at a distance of 100 mm and a tensile speed of 10 mm/min. In the measurement, seven samples were prepared for each type of copper foil, and the fracture stress (breaking strength) obtained by the measurement and the average value of the elongation at break were shown in Table 1.

As a result, in the copper foil in which the aggregate structure was developed, it was found that the fracture strength was not related to the fracture strength, but the elongation at break was correlated with the bending fatigue life. Further, the copper foil B has a large strength and a large elongation at break, but this reflects a fine polycrystal which is a crystal grain. However, since the copper foil B is not developed due to the assembly structure, the fatigue life is inferior. In addition, when the copper foil C having an equal accumulation degree of 99.99% of the cubic aggregate structure is compared with the copper foil D having a purity of 99.999%, the bending fatigue property of the copper foil D is large, which is an excellent result. The two copper foils have the same oxygen concentration, and the amount of dispersion of the internal copper oxide is also small. Since they are equivalent, they are not caused by the difference in copper oxide, but are caused by the difference in the elongation at break due to the difference in purity.

As described above, it is understood from the results shown in the first embodiment that in order to obtain better characteristics than the general high-bending copper foil, it is necessary to have a basic crystal axis <100> in the thickness direction of the metal foil and a certain one existing in the foil surface. The two orthogonal axes of the direction have a main orientation in such a manner that the priority alignment field within 10° of each of the orientation differences accounts for 50% or more in area ratio, and is cut toward the thickness direction of the metal foil by the ridge line in the curved portion. The elongation at break of the metal foil in the normal direction of the cross section P of the wiring is 3.5% or more. In addition, it is known that the purity is extremely high at 99.999% or more, and the orientation of the cube is developed to form a flexible circuit board in which the elongation at break is increased, and the principal stress and the main deformation are applied in the direction, and the fatigue life is long.

[Embodiment 2]

Next, a single-sided copper-clad laminate using the copper foil A and the copper foil E produced in the same manner as in the first embodiment, as shown in Fig. 6, a linear wiring 2 having a line width (1) of 150 μm The wiring direction H (H direction) has an angle of 30° and 45° with respect to the MD direction ([100] axis), and a wiring pattern is formed with a space width (s) of 250 μm. Then, according to JIS 6471, a test having a width of 15 mm in the direction perpendicular to the wiring direction H and 150 mm in the longitudinal direction along the wiring direction H of the circuit board is obtained in accordance with JIS 6471. The flexible circuit board 5 is used. Fig. 6 shows an example in which the angle between the wiring direction H of the test flexible circuit board 5 and the MD direction is cut at an angle of 45°.

The fatigue test of the repeated bending was carried out under the same conditions as in Example 1 with respect to the test flexible circuit board 5 obtained above. In addition, the resin layer is dissolved by the single-sided copper-clad laminate 4 before etching in such a manner that the angle between the wiring direction H and the MD direction of the test flexible circuit board 5 is the same, and the calendering is performed in the longitudinal direction. A 150 mm × 10 mm sample cut in a direction having an angle of 30° and 45° was subjected to a tensile test in the same manner as in Example 1. That is, the principal stress and the main deformation direction of the fatigue test of the copper foil are consistent with the tensile direction of the tensile test, and the cubic assembly of the copper foil A and the copper foil E are highly developed, so fatigue test and stretching are performed. In the test, the main deformation and the principal stress were received in the same crystal orientation. The results of the fatigue test and the tensile test are shown in Table 2.

From the test results shown in Table 2, higher fatigue characteristics were obtained by shifting the principal stress and the main deformation direction by <100> orientation. In these orientations, the elongation at break is also significantly greater than the <100> orientation, especially at 30°, and both the elongation at break and the fatigue life become longer.

As a result of the above-described Example 2, it is understood that there is a high correlation between the fatigue life of the relatively high-deformation curved circuit board which is repeatedly bent and the elongation at break of the copper foil constituting the wiring when the copper foil is highly aligned. As seen in Example 1, higher strength and ductility are obtained in polycrystalline bodies, but are not effective in high bending applications. Therefore, the relationship between the fatigue life as shown above and the elongation at break under conditions of a highly concentrated aggregate structure is an important role for the slip system, not limited to copper, even for the face centered cubic orientation with the same slip system. If the metal is also established, if the metal with different delamination energy is different, the estimated elongation at break is also larger, and the fatigue life can be expected to become larger.

[Example 3]

The polyacrylic 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 μm, and dried (cured to form a thermoplastic polyimide having a film thickness of 2 μm). And coating the polyaminic acid b thereon and drying it (curing to form a low thermal expansion polyimine having a film thickness of 8 μm), and applying polyacrylic acid a thereon to dry (harden) Thereafter, a thermoplastic polyimide having a film thickness of 2 μm was formed, and as shown in the following conditions a to d, a polyimine layer was formed under a heating condition of a load of 10 minutes at a temperature of a maximum temperature of 180 to 240 ° C. Resin layer).

Then, it was cut in such a manner that the length of the copper foil in the rolling direction (MD direction) was 250 mm and the direction perpendicular to the rolling direction (TD direction) was a rectangular shape having a width of 150 mm, and the thickness was 12 μm. A single-sided copper-clad laminate 4 of Example 3 of a bismuth imide layer (resin layer) 1 and a copper foil 2 having a thickness of 12 μm.

The copper foil side of the single-sided copper-clad laminate 4 obtained above is covered with a predetermined mask, and is etched using a ferric chloride/copper chloride-based solution, and has a line width of 150 μm and a space width of 250 μm according to the IPC specification. Low-speed IPC test wiring 2 for wiring. In the production process, the maximum temperature of the heating conditions at the time of forming the polyimide layer is 180 ° C (condition a), 200 ° C (condition b), 220 ° C (condition c), and 240 ° C (condition d). In addition, the wiring direction (H direction) of the linear wiring 2 is 0°, 2°, 2.9°, 5.7°, 9.5°, 11.4°, and 14° with respect to the rolling direction (MD direction). 22 level angles of 18.4°, 25°, 26.6°, 30°, 40°, 45°, 55°, 60°, 63.4°, 78.6°, 80°, 82.9°, 87.1°, 88°, and 90° In a manner, wiring patterns are formed separately.

Then, as shown in Fig. 8(b), an epoxy-based adhesive was used on the surface of the wiring pattern side, and a cover material 7 (CVK-0515KA manufactured by Ozawa Seisakusho Co., Ltd.: thickness: 12.5 μm) was laminated. The thickness of the adhesive layer 6 composed of the adhesive was 15 μm in the portion where the copper foil circuit was absent, and 6 μm in the portion where the copper foil circuit was present. Then, it was cut out so as to be 15 cm in the longitudinal direction along the wiring direction (H direction) and 8 mm wide in the direction perpendicular to the wiring direction, thereby obtaining a test for forming an IPC test sample. Flexible circuit board.

On the other hand, in order to investigate the characteristics of the copper foil monomer, a tensile test was performed as shown below. The angle of the angle between the wiring direction H and the MD direction of the test flexible circuit board 5 is the same as the level of 22, and the resin layer is dissolved by the single-sided copper-clad laminate 4 before etching to form a copper foil. The monomer was prepared into a rectangular sample having a length of 150 mm and a width of 10 mm cut in such a manner that the longitudinal direction was at an angle of 22 degrees with respect to the rolling direction. At this time, it was confirmed that the structure of the copper foil did not change during the dissolution of the polyimine. The tensile test was carried out in the longitudinal direction at a distance between the punctuation of 100 mm and a tensile speed of 10 mm/min.

Further, in the sample for performing the analysis by the EBSP, the single-sided copper-clad laminate produced by the heat treatment conditions of the conditions a to d was produced to have a relative rolling direction of 0° and 2.9°. A total of 20 samples without a wiring pattern cut at five angles of 30°, 63.4°, and 78.6° were used. In order to prepare the IPC test sample and the heat history, the simulated heat treatment was applied under the same conditions as the circuit formation etching, and the cover material was laminated under the same conditions. However, these effects on the copper foil structure were slight, and the copper foil structure was determined after the heat treatment conditions of the conditions a to d at the time of formation of the polyimide.

Next, 20 copper foils H having the four-level heat treatment conditions and five angular angle conditions produced by the EBSP measurement described above are polished in the thickness direction of the substrate, and have a surface horizontal to the foil surface before polishing. The foil surface of the copper foil H is exposed. In addition, colloidal vermiculite was used for final grinding, and EBSP was used to evaluate the structure of copper foil H. The measurement area was 0.8 mm × 1.6 mm, and the measurement interval was set to 4 μm. That is, the number of measurement points in the 1 field is 80000 points. As a result, it was found that the sample obtained by heat treatment under the heat treatment conditions of the condition a to the condition d was formed with a cubic aggregate structure, and had a principal orientation of {001}<100> toward the copper foil surface orientation and the rolling direction. Then, based on the obtained results, the thickness direction and the rolling direction of the copper foil were counted by the number of points within the unit lattice axis <001> of 10°, and the ratio to the total number of dots was calculated, and the average value was obtained. The results are shown in Table 3. The ratio of the samples in the same heating conditions was not more than 1%, and the same heat treatment conditions were used to provide the total degree of accumulation shown in Table 3 throughout the copper foil. It can be seen that the higher the maximum heat treatment temperature and the higher the heat history, the more the recrystallization proceeds, and the higher the accumulation degree of the cubic recrystallized aggregate structure. Further, as a result of the orientation analysis in the foil surface, the main orientation of the sample cut out at five angles of 0°, 2.9°, 30°, 63.4°, and 78.6° with respect to the rolling direction has [100], [20 1 0], [40 23 0], [120], [150], roughly as indicated. On the other hand, using the obtained EBSP data, the evaluation of the crystal grain size when the orientation difference of the adjacent crystal grains is 15° or more is analyzed as the crystal grain boundary in the normal direction of the foil surface, and the polycrystalline body is obtained. The average particle size. The results are shown in Table 3.

In the eighth diagram, as shown in the schematic diagram, the IPC test is a test in which the slip of one of the bending forms used in the mobile phone or the like is simulated. In the IPC test system, as shown in Fig. 8, the curved portion is provided at the determined gap length 8, and the one side is fixed by the fixing portion 9, and the sliding operation portion 10 on the opposite side is tested as a reciprocating motion as shown. Therefore, in the field of the stroke amount in the portion to be reciprocated, the substrate is subjected to repeated bending. In the present embodiment, the polyimine layer (resin layer) 1 is set to the outside, and the gap length is set to 1 mm, that is, the bending radius is set to 0.5 mm, and the stroke is set to 38 mm to perform the reverse slip. test. In the test, the measurement of the electric resistance of the circuit of the flexible circuit board for the test was performed, and the degree of progress of the fatigue crack of the copper foil circuit was monitored by the increase in electric resistance. In the present embodiment, the number of strokes in which the resistance of the circuit reaches twice the initial value is taken as the circuit breaking life.

In the test, the four heat treatment conditions of the above conditions a to d were carried out for a total of 88 levels of wiring patterns having an angle of 22 levels. In each of the test levels, four test pieces were measured, and the average of the number of strokes after the circuit was broken was obtained. When the copper foil after the rupture life of the circuit is observed by a scanning electron microscope and the copper foil is cut in the thickness direction perpendicular to the sliding direction, a difference in degree is observed, but on the resin layer side. The surface of each of the copper foils on the side of the cover material is cracked, and in particular, a plurality of cracks are introduced into the surface of the copper foil on the resin layer side corresponding to the outer side of the curved portion.

Table 4 shows the average value of the circuit breaking life at each level and the elongation at break in the tensile test. In the angle column of Table 4, the surface index of the wiring in the longitudinal direction (wiring direction) of the circuit, that is, the cross-section P of the wiring when the ridge line in the curved portion is cut in the thickness direction is displayed only in the case of the low-index direction.

It is understood that the fracture life (fatigue life) in the IPC test is largely dependent on the angle formed by the longitudinal direction of the circuit (H direction) and the rolling direction (MD direction), that is, the wiring profile when the ridge line in the curved portion is cut toward the thickness direction. The normal direction is at an angle to [100]. This orientation dependence appears under condition b, condition c, and condition d. The higher the degree of accumulation of the cube orientation, the greater the fatigue life for repeated bending, and the greater the orientation dependence. Regarding the orientation dependence, it was confirmed that the thickness direction of the metal foil was such that the area of the copper [001] within 10 degrees of the azimuth difference was within 50% of the area evaluated by the EBSP method, and the <001> main The orientation is preferentially aligned toward the thickness direction of the metal foil, and the area occupied by the EBSP method is occupied by the EBSP method in a range of 10 degrees or less from the [100] axis of copper, [100] main The orientation appears when the orientation is preferentially aligned in the foil side. In particular, when the thickness direction and the rolling direction indicate the condition c having an area ratio of 75% or more and 85% or more and a cube orientation is high, the fatigue life is large and the effect of the orientation dependency is large. The thickness direction and the rolling direction indicate that the area ratio is 98% or more and 99% or more, and the condition d of the cube orientation is extremely high, and the fatigue life is larger and the effect of orientation dependence is greater.

When the results of condition b, condition c, and condition d are reviewed in detail, the normal direction of the wiring cross section P when the ridge line in the curved portion is cut in the thickness direction, that is, the principal stress direction is <100> main of the copper foil. The azimuth offset is higher in the fatigue life of the relatively curved circuit. In the IPC test of the present embodiment, it is seen that the main deformation direction of the curved portion, that is, the normal direction of the cross section of the wiring when the ridge line in the curved portion is cut in the thickness direction, has 2.9 to 87.1. The angle of the situation. When the surface line is indicated by the surface index, the cross section P of the wiring when the ridge line in the curved portion is cut in the thickness direction is [001] as the crystal ribbon axis, and (20 1 0) passes through (110) to (1 20 0). The scope. Among them, the larger the effect is the main deformation direction of the curved portion, that is, when the angle is 11.4 to 78.6° with respect to the normal direction of the cross section of the wiring when the ridge line in the curved portion is cut in the thickness direction. The cross section P of the wiring when the ridge line in the curved portion is cut in the thickness direction is expressed by the surface index, and [001] is the crystal ribbon axis, and (510) is passed through the range of (110) to (150). The bending characteristic is the same as the main deformation direction of the curved portion, that is, the normal direction of the cross section of the wiring when the ridge line in the curved portion is cut in the thickness direction, and has an angle of 26.6° to 63.4°, which is the most excellent. When it is 30° and 60°. If expressed by the surface index, the profile P is [001] as the ribbon axis, and (210) is passed from (110) to (120), and the most excellent is located at (40 23 0) and (23 40 0) When nearby.

When these results are compared with the elongation at break, it is understood that the basic crystal axis <100> of the unit cell of the face-centered cubic structure is orthogonal to the thickness direction of the metal foil and in one direction existing in the foil surface. In the case where the main alignment direction is 50% or more in area ratio, the main alignment direction of the axis is a cross section P of the wiring which is cut toward the thickness direction of the metal foil by the ridge line in the curved portion. The metal foil in the line direction has an elongation at break of 3.5% or more, and has good bending fatigue characteristics with respect to bending caused by principal stress and main deformation in its orientation. On the other hand, when the area ratio of the <100> preferential alignment field is 49% or less, even if the elongation at break in the direction is 3.5% or more, good bending fatigue characteristics cannot be obtained.

[Example 4]

The polyacrylic acid solution a was applied in the same manner as in Example 1 except that the copper foil C having a purity of 99.99% was subjected to heat treatment (preheat treatment) at a temperature of 5 ° C to 400 ° C for 30 minutes in an Ar gas flow. And dried (hardened to form a thermoplastic polyimide having a film thickness of 2 μm), coated with polylysine b, and dried (cured to form a low thermal expansion polyimine having a film thickness of 9 μm) Further, the polyamic acid a is coated thereon and dried (cured to form a thermoplastic polyimide having a film thickness of 2 μm), and the load is 5 minutes or more in an integrated time via a temperature of 300 to 360 ° C. A polyimine layer composed of a three-layer structure is formed under heating conditions. Then, the rolling direction (MD direction) of the copper foil is cut to a length of 250 mm, and the direction orthogonal to the rolling direction (TD direction) is a rectangular shape having a width of 150 mm. As shown in FIG. 5, A single-sided copper-clad laminate 4 having a polyimide layer (resin layer) 1 having a thickness of 13 μm and a copper foil 2 having a thickness of 9 μm was obtained. The tensile modulus of the entire resin layer at this time was 7.5 GPa.

In the single-sided copper-clad laminate 4 obtained as described above, colloidal vermiculite was used for the rolling surface 2a of the copper foil 2, and after mechanical and chemical polishing, the orientation analysis was performed by an EBSP apparatus. The apparatus used was FE-SEM (S-4100) manufactured by Hitachi, Ltd., EBSP apparatus manufactured by TSL Corporation, and software (OIM Analysis 5.2). The measurement field was a field of about 800 μm × 1600 μm, and the acceleration voltage was 20 kV at the time of measurement, and the measurement phase interval was 4 μm. The evaluation of the orientation is expressed by the ratio of the measurement point of <100> within 10° to the measurement point of the whole with respect to the thickness direction of the foil and the rolling direction of the foil. The number of measurements was carried out for five samples of different varieties, and the decimal point of the percentage was rounded off to the second place. Further, using the obtained data, the crystal grain size was evaluated as the crystal grain boundary when the orientation of the adjacent crystal grains was 15 or more, and the average particle diameter was determined for the polycrystalline body. The results are shown in Table 5.

It can be seen that the copper foil C is formed with a cubic assembly structure, and both the copper foil surface orientation and the rolling direction have a principal orientation of {001}<100>. This is because the calendered copper foil is recrystallized by heat during the preliminary heat treatment and the polyimine hardening to form a recrystallized aggregate structure. Here, the higher the preliminary heat treatment temperature, the larger the degree of alignment of {001}<100>. In addition, the orientation other than the <100> orientation was confirmed by the EBSP apparatus as described above, and the orientation in the rolling direction was <212>, and the recrystallized orientation in which the diameter of the circle was 5 μm or less was dispersed into an island shape. However, in the copper foil which was subjected to preliminary heat treatment at 400 ° C, almost no island-like structure as shown above was observed. Among them, since the area ratio of the confirmed island-like structure is small and is 2% or less, the recrystallized grains having the cubic orientation have the same orientation and are integrated. Further, the size of the recrystallized grains was 9 μm in the thickness direction and the thickness of the foil, and was 800 μm or more in the foil surface.

Next, a predetermined mask is coated on the copper foil 2 side of the single-sided copper-clad laminate 4 obtained above, and is etched using a ferric chloride/copper chloride-based solution, as shown in Fig. 6 (but the wiring direction H) The angle formed by the MD direction is 0°), and the wiring direction H (H direction) of the linear wiring 2 having a line width (1) of 150 μm is parallel to the MD direction (<100> axis), and the space is wide. A wiring pattern was formed in such a manner that the web (s) was 250 μm. Next, a test having a width of 15 mm along the wiring direction H of the circuit board, 150 mm in the longitudinal direction, and a direction perpendicular to the wiring direction H is obtained in accordance with JIS 6471, as shown in the sampling for the bending resistance test described later. The flexible circuit board 5 is used.

Using the test flexible circuit board obtained above, the MIT bending test was performed in accordance with JIS C5016. The mode diagram of the test is shown in Figure 7. The apparatus was manufactured by Toyo Seiki Seisakusho Co., Ltd. (STROGRAPH-R1), and one end of the test flexible circuit board 5 in the longitudinal direction was fixed to the holding jig of the bending test apparatus, and the other end was fixed by a weight to the holding part. In the case of the vibration of 150 times/min, the rotation is 135±5 degrees, and the curvature is 0.8 mm, and the conduction of the wiring 2 of the circuit board 5 is blocked. The number of times is the number of bends.

In the test condition, the ridge line formed in the curved portion is curved so as to be orthogonal to the wiring direction H of the wiring 2 of the test flexible circuit board 5, so that the principal stress and the main deformation applied to the copper circuit become Tensile stress and tensile deformation parallel to the rolling direction. When the circuit was observed from the thickness direction of the copper foil after the bending test, it was confirmed that a broken line was generated in the vicinity of the ridge line of the curved portion so as to be substantially perpendicular to the rolling direction. The results of the bending life are shown in Table 5. The bending life of Table 5 is an average of the results of preparing five test flexible circuit boards for each of the preliminary heat treatment temperatures of the copper foils. As is clear from the results shown in Table 5, the bending fatigue life is particularly large when the cumulative degree of the cubic aggregate structure is 98.0% or more and 99.8%.

Next, in order to investigate the dominating factor of the bending life, the tensile test was performed in parallel with the principal stress of the bending, the main deformation direction, that is, the rolling direction. In order to investigate the characteristics of the copper foil monomer obtained by the preliminary heat treatment temperature, the resin layer was dissolved by the single-sided copper-clad laminate 4 before etching, and a tensile test of the copper foil alone was carried out. It was confirmed that there was no change in the structure of the copper foil during the dissolution of the polyimine.

The tensile test was carried out by cutting into a length of 150 mm in the rolling direction (MD direction) of the copper foil and cutting into a width of 10 mm in the vertical direction of the foil surface, with a distance between the punctuation of 100 mm and a tensile speed of 10 mm in the longitudinal direction. /min. The measurement was performed. In the measurement, seven samples were prepared for each preliminary heat treatment temperature of each copper foil, and the fracture stress (breaking strength) and the average value of the elongation at break obtained by the measurement were shown in Table 5.

Contrary to the results so far, the elongation at break is larger in the field where the degree of accumulation (%) of <100> is 98.0% or more and 99.8% or less, and the degree of accumulation increases. On the other hand, in the copper foil in which the island-like structure has disappeared, the elongation at break becomes small. This system is presumed to be related to the slip surface. It has been confirmed from the above that the elongation at break is strongly correlated with the bending fatigue life. In other words, it is known that the aggregated degree (%) is 98.0% or more and 99.8% or less, and the aggregate structure is highly developed, and the elongation at break is 3.5% or more, and the bending fatigue life is increased.

On the other hand, a copper foil was produced under the same conditions using a fine copper containing 0.035 mass% of oxygen and a purity of 99.9% under the same conditions, and the test was carried out under the same conditions. As a result, even if the <100> accumulation degree (%) was 98.0% or more, the same was The elongation at break decreases as the degree of accumulation increases, and 3.5% or more of the copper foil is not obtained, and the fatigue life of 1000 or more times is not obtained.

[Industrial availability]

The flexible circuit board of the present invention can be widely used in various electronic and electrical equipment, and the circuit board itself is bent, twisted, or deformed in accordance with the operation of the loaded machine, and is suitable for having a bent portion in either case. Come and use it. In particular, since the flexible circuit board of the present invention has a curved portion structure excellent in bending durability, it is suitable for being frequently bent when repeated operations such as sliding bending, bending bending, hinge bending, and sliding bending, or In order to achieve a miniaturization of the loaded machine, a curved portion having a very small radius of curvature is formed. Therefore, it is suitable for use in various electronic devices, such as thin mobile phones, thin displays, hard disks, printers, and DVD devices that require durability.

1. . . Resin layer

2. . . Wiring (metal foil)

2a. . . Calendering surface

2b. . . side

3. . . Connector terminal

4. . . Single-sided copper laminate

5. . . Flexible circuit board for testing

6. . . Next layer

7. . . Covering material

8. . . Long gap

9. . . Fixed part

10. . . Slip operation

twenty one. . . Normal direction of section P

L. . . Ridge line

P. . . Cross section of the wiring when cut from the ridge line in the curved portion in the thickness direction

Fig. 1 is a view showing a relationship between a crystal ribbon axis in a crystal structure of a cubic lattice system and a surface rotated about a crystal ribbon axis.

Figure 2 is a solid triangle of the (100) standard projection.

Fig. 3 is a cross-sectional explanatory view showing a state in which the flexible circuit board is bent.

Fig. 4 is a plan explanatory view showing the relationship between the wiring in the flexible circuit board and the crystal axis of the metal foil, and (a) and (b) showing the flexible circuit board of the present invention, (c) and (d) A flexible circuit substrate showing a conventional technique.

Fig. 5 is a squint explanatory view of a single-sided copper clad laminate.

Fig. 6 is a plan explanatory view showing a state in which a test flexible circuit substrate is obtained from a single-sided copper-clad laminate in the embodiment of the present invention.

Fig. 7 is an explanatory view of the MIT bending test apparatus.

Fig. 8(a) is an explanatory view of an IPC bending test apparatus, and Fig. 8(b) is a cross-sectional view taken along line X-X' of the test flexible circuit board used in the IPC bending test.

1. . . Resin layer

2. . . Wiring (metal foil)

2a. . . Calendering surface

2b. . . side

4. . . Single-sided copper laminate

Claims (9)

A flexible circuit board comprising a resin layer and a wiring formed of a metal foil, and a flexible circuit board having a bent portion at least one portion of the wiring, wherein the metal foil is made of a purity of 99.9 a rolled copper foil having a thickness of not less than 5 μm and not more than 18 μm, wherein the rolled copper foil has a face-centered cubic structure, and a basic crystal axis of a unit lattice having a face-centered cubic structure is <100> relative to a rolled copper foil. In the thickness direction and the two orthogonal axes existing in one direction in the foil surface, the preferential alignment field within 10° of the azimuth difference is 50% or more in area ratio, and the normal direction of the foil surface of the rolled copper foil The crystal grain size at the time of viewing is 25 μm or more, and the elongation at break of the rolled copper foil in the normal direction of the cross section P of the wiring which is cut in the thickness direction of the rolled copper foil by the ridge line in the curved portion is 3.5% or more and 20%. the following. The flexible circuit board according to the first aspect of the invention, wherein the metal foil is made of a rolled copper foil having a purity of 99.999 mass% or more. The flexible circuit board according to claim 1 or 2, wherein the cross section P of the wiring is from (100) to the rotation direction of (100) to (110) by (001) Any face included in the range of 1 0) to (1 20 0) forms the principal orientation. The flexible circuit board of claim 3, wherein the cross section P of the wiring is in a solid triangle of the (100) standard projection image, and is located at a point representing (20 1 0) and a point representing (110) Linked line Any face on the segment. The flexible circuit board according to claim 1 or 2, wherein the wiring is formed in a direction orthogonal to a ridge line in the opposite curved portion. The flexible circuit board of claim 1 or 2, wherein the resin layer is composed of polyimide. The flexible circuit board according to claim 1 or 2, wherein the bending portion is formed with any reversing action selected from the group consisting of sliding bending, bending bending, hinge bending, and slip bending. The way to use it. An electronic device characterized by being mounted with a flexible circuit substrate according to any one of claims 1 to 7. A curved portion structure of a flexible circuit board, comprising a resin layer and a wiring formed of a metal foil, and a curved portion structure of a flexible circuit board having a bent portion at least one portion of the wiring, and characterized in that The metal foil is composed of a rolled copper foil having a purity of 99.9% by mass or more and a thickness of 5 μm or more and 18 μm or less, and the rolled copper foil has a face-centered cubic structure and a basic crystal axis of a unit cell having a face-centered cubic structure. <100> In the thickness direction of the rolled copper foil and the two orthogonal axes existing in one direction in the foil surface, the preferential alignment field within 10 degrees of the azimuth difference is 50% or more in area ratio, and is rolled by When the foil surface of the copper foil is viewed in the normal direction, the crystal grain size is 25 μm or more. In addition, the elongation at break of the rolled copper foil in the normal direction of the cross section P of the wiring which is cut in the thickness direction of the rolled copper foil by the ridge line in the curved portion is 3.5% or more and 20% or less.