JP2965516B2 - Flexible wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible wiring board which is a functional component mainly used in the field of electric and electronic equipment.

[0002]

2. Description of the Related Art Hitherto, a wiring board having a high flexibility is commonly called a flexible wiring board, and is widely used in the field of electronic equipment and the like. FIG. 14 shows an example of this, and this flexible wiring board is made of a plastic film 4 (for a base layer).
The adhesive layer 8 is formed on the adhesive layer 8, and the metal electric circuit 3 is formed on the adhesive layer 8. On the other hand, the adhesive layer 8 is also formed on the plastic film 2 (for the cover layer).
The two plastic films 2 and 4 are laminated with the respective adhesive layers 8 facing each other. In addition, as the plastic films 2 and 4, it is common to use those cut out to a predetermined size from a strip-shaped raw plastic film stretched in two directions of a vertical direction and a horizontal direction.

A flexible wiring board is mounted inside an electronic device or the like after electronic components such as a semiconductor device are mounted thereon. Depending on an electronic device or the like to be used, the flexible wiring board bends. There are cases. For example, in a printer, a flexible wiring board used for wiring a print head (operating portion) and a motherboard (fixed portion) bends in accordance with the operation of the printer. For this reason, a flexible wiring board used in such an operation part is required to have sufficient flexibility and durability.

[0004] In response to this requirement, the physical properties of metal electric circuits have been studied. This is because, among the main components of the flexible wiring board, the plastic film originally has flexibility, and a problem is caused by a metal electric circuit which is another main component. Specifically, there are plastic deformation and elastic deformation in the deformation of the metal electric circuit, and the property of the plastic deformation has been improved to exhibit flexibility.

[0005]

However, a flexible wiring board on which a metal electric circuit having improved plastic deformation properties is formed has a problem that a warp called a curl is generated. As described above, in the flexible wiring board, there is a plastic film as another main component of the metal electric circuit, which is flexible, but has a plastic deformation property compared to the metal electric circuit. Is extremely small. That is, in a flexible wiring board having improved flexibility, a plastic film is easily elastically deformed, whereas a metal electric circuit is easily plastically deformed. As a result of bonding two members having such contradictory properties, curl occurs in the flexible wiring board. This will be described in accordance with the manufacturing process of the flexible wiring board. For example, as shown in FIGS. 17A and 17B, an adhesive layer 8 is formed on a plastic film 4 for a base layer, and this adhesive is formed. The copper foil 3a is placed on the layer 8. Then, as shown in FIG. 17 (C), when heating and pressing such as laminating, or after heating and pressing as shown in FIG. 17 (D), it is cooled to room temperature, and then the copper is removed by a subtractive method or the like. In the two steps of forming the metal electric circuit by performing the etching process on the foil 3a, tension is applied in the film surface direction as indicated by the arrow in the figure. Then, when the tension is removed, the plastic film 4 returns to its original length (elastic deformation), but the metal electric circuit 3 keeps the expanded state (plastic deformation). As a result, as shown in FIG. 17E, the flexible wiring board warps like a bimetal and curls. Usually, after the metal electric circuit 3 is formed, a plastic film is stuck thereon to form a cover layer, but even in this case, the curl still occurs.

[0006] The curled flexible wiring board has a problem in the precision of the shape, and causes a problem in mounting a semiconductor device or mounting the flexible wiring board in an electronic device.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a flexible wiring board having sufficient flexibility and durability, and suppressing curling.

[0008]

The outline of the present invention will be described. The flexible wiring board of the present invention specifies physical properties of a metal electric circuit in order to improve flexibility and durability. In addition, the flexible wiring board of the present invention,
In order to suppress the occurrence of curling, attention is paid not to the relationship between the metal electric circuit and the plastic film but to the relationship between the physical properties of the two plastic films disposed on both outermost layers of the laminate, and the physical properties are substantially matched. That is, the amount of deformation is balanced. Then, three means were developed as means for making the physical properties of the two plastic films substantially the same.

That is, first, the flexible wiring board according to claim 1 of the present invention has two vertical and horizontal directions.
A flexible wiring board in which two or more plastic films stretched in the direction are laminated, and a metal electric circuit is formed on at least one of the plastic films constituting the laminate, wherein the metal electric circuit is as follows: A), wherein the two plastic films disposed on both outermost layers of the laminate are the following two plastic films (B), and these two plastic films are transferred to both outermost layers of the laminate. Is arranged such that the front surface of one plastic film and the back surface of the other plastic film face each other. (A) The permanent strain when a stress is applied and removed is defined as a plastic deformation component, and the plastic deformation component when the stress is applied until the strain becomes 0.002 (mm / mm) is 0.0
003 (mm / mm) or more metal electric circuit. (B) On the film surface of the strip-shaped raw plastic film stretched in two directions with the length direction being the stretching longitudinal direction and the width direction being the stretching transverse direction, any one reference line parallel to the stretching direction is assumed. And 2 of the same shape
The two cutout scheduled areas are aligned with each other, and an arbitrary point of one of the two cutout planned areas and a corresponding one of the other cutout scheduled areas correspond to this point. Two plastic films cut out from these two cut-out planned areas, which are assumed to be on the reference line.

In the flexible wiring board according to the second aspect of the present invention, two or more plastic films stretched in two directions, a vertical direction and a horizontal direction, are laminated, and at least one of the plastic films constituting the laminate is formed. One is a flexible wiring board on which a metal electric circuit is formed, wherein the metal electric circuit is the above (A), and a plastic film disposed on both outermost layers of the laminate is as follows. By the method (C) shown, ellipsoids of respective coefficients of linear expansion in portions corresponding to each other on the film surface of each plastic film are created on coordinates, and the respective ellipsoids are set so that their center points and coordinate axes X and Y coincide with each other. maximum value of a difference of linear expansion coefficients of the plastic film obtained by superposing is, have a relationship that is ^{1.4 × 10 -5 (1 / ℃} ) or less The two plastic films are arranged on both outermost layers of the laminate, and the two plastic films are arranged in a state where the surface of one plastic film and the back surface of the other plastic film face each other. There is a configuration that there is. (C) A predetermined base point P is determined on the film surface of the plastic film, and the linear expansion coefficient in the angle θ direction is measured with the base point P as a center point and with reference to the axis of the plastic film stretching longitudinal direction passing through the base point P. I do. On the other hand, coordinates are prepared in which the axis of the plastic film stretching longitudinal direction is the Y axis and the axis of the plastic film stretching lateral direction is the X axis. In these coordinates, the intersection of the Y axis and the X axis is defined as a base point P for measuring the linear expansion coefficient, and the magnitude of the measured value of the linear expansion coefficient is defined as a distance r from the base point P. Are plotted in the measurement angle θ direction with respect to the Y axis. This plot is performed a plurality of times while changing the measurement angle θ, and an ellipsoid is created by drawing an analysis line over the base point P in the 360-degree direction so as to pass through the average point of the plotted points.

In the flexible wiring board according to the third aspect of the present invention, two or more plastic films stretched in two directions, a vertical direction and a horizontal direction, are laminated, and at least one of the plastic films constituting the laminate is formed. A flexible wiring board having a metal electric circuit formed thereon, wherein the metal electric circuit is the one described in (A) above, and two plastic films disposed on both outermost layers of the laminate are: According to the method (C), ellipsoids of respective coefficients of linear expansion in portions corresponding to each other on the film surface of each plastic film are created on coordinates, and the respective ellipsoids are set so that the center point and the coordinate axes X and Y coincide with each other. The total area of non-overlapping parts when
6.5 × 10 ⁻¹⁰ [(1 / ° C.) × (1 / ° C.)] or less, and the two plastic films are applied to both outermost layers of the laminate. The arrangement is such that the arrangement is such that the front surface of one plastic film and the back surface of the other plastic film face each other.

Here, the plastic deformation component will be described.

For materials such as metal foil, tension (stress σ)
Is added, a deformation amount corresponding to this is generated. This deformation amount is represented by a strain ε because the size of the material is generally considered. The strain ε is a ratio of the length when deformed (the length under stress) to the original length, and its defining equation (1) is shown below.

[0014]

[Number 1] ε (mm / mm) = ( Δl / l 0) = (l 1 -l o) / l 0 ... (1) l 0: stress load front of the length l _1: length in the stress load

A graph showing the relationship between the stress σ and the strain ε is shown by an SS curve (Stress-Strain C
urve) figure. An example of the SS curve of the metal foil is shown in the graphs of FIGS. In these SS curves, stress is gradually applied to the metal foil, and after the stress reaches a certain value, the stress is gradually reduced (removed). Therefore, two SS curves appear in one graph. In the figure, the direction of the SS curve (forward path) in which stress is gradually applied is indicated by a solid arrow, and the stress is gradually reduced (removed). ) Is indicated by a dotted arrow.

First, the graph of FIG. 7 shows that the strain ε is 0.0
7 shows an SS curve when a very small stress σ such as less than 005 is applied and removed. As shown in the figure, when such a small stress is applied, the SS curve becomes a straight line, and the straight line of the stress load (in the direction of the solid arrow) and the straight line of the stress removal (the direction of the dotted arrow) substantially overlap. When the stress becomes zero, the strain becomes zero. In this case, only the elastic deformation was observed in the metal foil. And
The inclination of the straight line corresponds to the elastic modulus of the metal foil.

The graphs of FIGS. 8, 9 and 10 are SS curves when the maximum stress applied in this order is further increased. As shown in the figure, as the applied stress increases, the outward path and the return path of the SS curve become different. In other words, when a stress is applied (outbound path), a straight line is formed in a region where the stress is small,
In the region where the stress is high, the straight line collapses and becomes a curve close to the asymptote. Then, when the stress is removed (return path), the straight line has the same inclination as the inclination of the straight line on the outward path. This inclination is an inclination corresponding to the elastic modulus of the metal foil, as described above. Then, as shown in the graphs of FIGS. 8 to 10, even if the applied stress is completely removed (stress: 0), the strain does not return to the original length and the strain remains. The distortion that remains after the stress is removed is called permanent distortion. The permanent set increases as the applied maximum stress increases. In other words, the permanent strain increases in the order of FIGS. 8, 9, and 10. This permanent strain represents the property of plastic deformation of the material, and in the present invention, this permanent strain is referred to as “plastic deformation component”.

In the present invention, the linear expansion coefficient α is
It is derived as in the following. That is, plus
When a tic film is heated, its plastic fill
Expands according to the unique properties of the system. At this time, plastic
Of change to temperature t when measuring film length p
If (∂p / ∂t), the film length p at 0 ° C. ₀
From this, the linear expansion coefficient α can be obtained by the following equation (2).
("Chemical Handbook-Basics II", The Chemical Society of Japan,
Published by Maruzen Publishing).

[0019]

(Equation 2)

However, the coefficient of linear expansion α in the present invention refers to that in the region below the glass transition temperature (Tg) of the plastic film. This is because the Tg of the plastic film which is the object of the present invention is in a temperature range exceeding room temperature (about 23 ° C.), and the curl is a problem in a temperature range near room temperature, where Tg or softening point is considered. The following linear expansion coefficients are of interest. In the case of a polyimide film, its Tg is 300 ° C. or higher, which is beyond the range of use, and Tg does not appear clearly. Therefore, there is little need to consider Tg.

In the present invention, the area C of the non-overlapping portion of the ellipsoid is defined by the following equation (3) which represents the integral value of the difference Δα _C between the linear expansion coefficients squared. That is, in the present invention, the area C of the non-overlapping portion of the ellipsoid and the integral value of the difference Δα _C between the squares of the linear expansion coefficient are synonymous. In the following formula (3), θ is a measurement angle of the coefficient of linear expansion, and is based on the axis in the stretching longitudinal direction. Also, Δα in the following equation (3)
_C (θ) is defined by the following equation (4).
The ellipsoid of the present invention includes a perfect circle.

[0022]

(Equation 3)

[0023]

(Equation 4)

In the present invention, the term "both outermost layers" of the "both outermost layers of the laminate" does not mean both outermost layers of the flexible wiring board, but means both outermost layers of the plastic film laminate. I do. Therefore, for example, when a flexible wiring board is formed by forming a shield layer or the like on a plastic film laminate by a coating method, a printing method, or the like, the shield layer is referred to as “both outermost layers” in the present invention. is not. As you can see from the previous explanation,

In the present invention, suppression of curl is defined as curl degree (%) defined as follows.
Is 5% or less. That is, the length of the long side of the minimum rectangle in which the flexible wiring board is inscribed is defined as the longest length L of the flexible wiring board. FIG. 12A shows an example of a minimum rectangle (rectangle) 21 in which the substantially rectangular (substantially boomerang) flexible wiring board 1a is inscribed. As shown in the drawing, the length of the long side of the rectangle 21 indicated by the dotted line is the longest length L in the flexible wiring board 1a.
Then, as shown in FIG. 12 (B), one end of the flexible wiring board 1a is fixed to the reference plane 6, and the maximum warp height h of the flexible wiring board 1a from the reference plane 6 is determined. h. Then, the ratio of the curl amount h to the longest length L of the flexible wiring board, that is, (h / L) × 100 is set to the curl level (%).

In the present invention, the front and back surfaces of the plastic film are determined appropriately. That is, since the two surfaces of the plastic film are clearly different in surface state (rear surface state) such as roughness and wettability, the front surface and the rear surface can be clearly distinguished. So, for example,
Assuming that one surface of the raw plastic film is a front surface and the other surface is a back surface, in the plastic film cut out from the raw plastic film, the surface having the same surface as the raw plastic film is the front surface, and the same back surface as the raw plastic film is similarly used. The surface provided with can be the back surface. Further, in two plastic films cut out from different raw material plastic films, surfaces in similar states can be respectively set as front surfaces or back surfaces.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an embodiment of the first aspect of the present invention.

As shown in the figure, a strip-shaped raw plastic film 10 is prepared which is stretched in two directions, with the longitudinal direction being the longitudinal direction and the transverse direction being the transverse direction. In the figure,
MD indicates the stretching longitudinal direction, and TD indicates the stretching transverse direction. Then, in this raw material plastic film 10, any one of the reference lines SL parallel to the above-mentioned stretching machine direction (MD).
, And two cut-out scheduled regions 2a and 4a of substantially the same shape (rectangular in the figure) are further assumed on this. However, the two cutout scheduled areas 2a, 4a
Are aligned with each other, and an arbitrary point in the cutout scheduled area 2a and a corresponding point in the cutout planned area 4a are on the reference line SL. In the figure, the center point is set as an arbitrary point of the two cutout scheduled areas 2a and a corresponding point of the cutout scheduled area 4a. Then, the two plastic films 2 and 4 are cut out from the two cutout areas 2a and 4a. The two plastic films 2 and 4 have the same surface 91 as the surface 91 of the raw plastic film 10. And
These two plastic films 2 and 4 are arranged on both outermost layers of the plastic film laminate with the front surface of one plastic film and the back surface of the other plastic film facing each other. This arrangement will be described in detail. As shown in FIG. 2A, the surface 91 of the plastic film 4 and the plastic film 2
The two plastic films 2 and 4 are arranged in a state where the rear surface 92 of the plastic film 2 faces. FIG. 2B is a cross-sectional view of FIG. 2A, and the same parts are denoted by the same reference numerals. 1 and 2, a metal electric circuit is not shown.

As described above, how to cut out the two plastic films disposed on both outermost layers of the plastic film laminate from the raw plastic film and how to dispose the two plastic films are specified. If this is the case, the physical properties of these two plastic films, such as the thermal shrinkage coefficient, the linear expansion coefficient, and the elastic modulus, can be made to substantially match. As a result, it is possible to balance the amount of deformation of both outermost layers of the plastic film laminate constituting the flexible wiring board, and curl is suppressed even if there is a difference in the deformation properties between the metal electric circuit and the plastic film. Become like In addition, since the flexibility and durability of the metal electric circuit and the plastic film do not change, the flexibility and durability of the flexible wiring board are sufficient.

Here, in the field of conventional flexible wiring boards, any plastic film cut out from a raw plastic film stretched in two directions is considered to have no difference in physical properties such as linear expansion coefficient. . However, when the present inventors examined the physical properties of the raw material plastic film in detail, they found that the conventional recognition was incorrect. That is, according to the study of the present inventors, the raw material plastic films differed in physical properties such as the coefficient of linear expansion at the portions. This is considered to be due to the fact that the stress applied during bidirectional stretching differs depending on each part of the raw plastic film. The present inventors further investigated the above physical properties, and found that the physical properties varied greatly in the width direction of the strip-shaped raw plastic film, but the change in the physical properties was small in the length direction of the raw plastic film. It is. And based on this knowledge,
We developed the above-mentioned cutting and arrangement methods.

Further, in the invention according to claim 1 of the present invention, the metal electric circuit has the plastic deformation component of 0.0003.
(Mm / mm) or more. This numerical value is a meaningful numerical value found by the present inventors from the relationship between the flexibility and durability of the flexible wiring board and the two plastic films used for both outermost layers of the laminate. In addition, this is claimed in claim 2
The same applies to the invention of the fifth aspect.

Next, the flexible wiring board according to claims 2 to 5 of the present invention will be described.

First, the inventions of the flexible wiring boards according to the second and third aspects are common in specifying the coefficient of linear expansion of the plastic film.
They differ in certain ways. As described in the section of the invention according to claim 1, each of the plastic films constituting the flexible wiring board has a different coefficient of linear expansion. When the study on the difference in the coefficient of linear expansion was continued, it was found that the bidirectionally stretched plastic film used for the flexible wiring board exhibited anisotropy in the coefficient of linear expansion.

More specifically, first, a predetermined base point P is defined on the film surface of the plastic film, the base point P is set as a center point, and an angle with respect to an axis of the plastic film stretching longitudinal direction passing through the base point P is set as a reference. The coefficient of linear expansion in the θ direction is measured. On the other hand, coordinates are prepared in which the axis of the plastic film stretching longitudinal direction is the Y axis and the axis of the plastic film stretching lateral direction is the X axis. In these coordinates, the intersection of the Y axis and the X axis is defined as a base point P for measuring the linear expansion coefficient, and the magnitude of the measured value of the linear expansion coefficient is defined as a distance r from the base point P. Are plotted in the measurement angle θ direction with respect to the Y axis. This plotting is performed a plurality of times while changing the measurement angle θ, and three points around the base point P are passed through the average point of the plotted points.
When an analysis line was drawn in the direction of 60 degrees, an ellipsoid as shown in FIG. 3 was obtained on the coordinates. In the figure, MD indicates an axis in the longitudinal direction of stretching (Y axis), and TD indicates an axis in the transverse direction of stretching (X axis). Further, a solid arrow A indicates the main axis of the crystal orientation of the plastic film, and similarly, a dotted arrow B indicates the sub-axis of the crystal orientation. Is a measurement angle of the linear expansion coefficient, and is based on MD. r represents the magnitude of the coefficient of linear expansion as a distance from the base point P, and its tip is plotted with a circle. Such a plot is called a polar coordinate plot. As can be seen from the ellipsoid (see FIG. 3) obtained from the polar coordinate plot, the crystal orientation principal axis direction of the plastic film is usually shifted obliquely from the longitudinal stretching direction, and the coefficient of linear expansion varies depending on the direction. (Anisotropic). As a result, it is considered that the analytical line of the coefficient of linear expansion of the bidirectionally stretched plastic film shows an ellipsoid.

Next, as shown in FIG. 4, the ellipsoids on the coordinates obtained for the two stretched plastic films (of the same material) are superimposed so that the center point and the coordinate axes coincide with each other. It can be seen that the coefficient of linear expansion differs in each part (each direction) and the crystal orientation direction also differs.

Then, a method for controlling the difference in the linear expansion characteristics of the plastic films thus obtained to suppress the curl of the flexible wiring board was examined. In the process, the difference (Δα) in the coefficient of linear expansion shown in FIG.
The idea of using the maximum value of 値 and the index of the area C of the non-overlapping part of the ellipsoid was obtained, and various experiments were repeated based on this idea. As a result, as the two plastic films disposed on both outermost layers of the two or more laminated plastic films constituting the flexible wiring board, the difference in linear expansion coefficient obtained by overlapping the ellipsoids created for each of the two plastic films is obtained. It has been found that the use of two plastic films having a relationship that the maximum value is 1.4 × 10 ⁻⁵ (1 / ° C.) or less suppresses the curling of the flexible wiring board (claim 2). . Similarly, even if the area C of the non-overlapping portion when the two ellipsoids are overlapped has a relationship of 6.5 × 10 ⁻¹⁰ [(1 / ° C.) × (1 / ° C.)] or less, it is flexible. It has been found that curling in the production of wiring boards is suppressed (claim 3).

It is necessary to satisfy at least one of the above two conditions only in the two plastic films disposed on both outermost layers of the laminate of the plastic films constituting the flexible wiring board, and in the intermediate layer. There is no need to consider the plastic film to be placed. That is, in the same manner as described above, the two plastic films used for the outermost layers of the laminate may have substantially the same linear expansion coefficient characteristics to balance the amount of deformation. As is clear from the above description, the maximum value (Δα) of the difference in the linear expansion coefficient ellipsoid and the area (C) of the non-overlapping portion indicate the relative relationship of the film located in the outermost layer. Therefore, the direction of the coordinate axis of the ellipsoid may be determined arbitrarily, and even in this case, as described above,
Exactly the same results are obtained as when the stretching direction of the film is set to the Y axis (claims 4 and 5).

Next, an example of an experimental result of deriving the predetermined value is shown in the graphs of FIGS. 5 and 6, respectively.
In this experiment, the curl amount was measured by the method described above, and the coefficient of linear expansion was determined by TMA (Thermal Mechanical Anatomical Analysis).
lysis, thermomechanical analysis). The maximum value of the difference (Δα) between the linear expansion coefficients and the area C of the non-overlapping part of the ellipsoid were derived by the method described later.

The graph in FIG. 5 shows the relationship between the maximum value of the ratio of curl amount to length [curl degree (%)] and the difference (Δα) in the coefficient of linear expansion. As shown in the figure, the two have a linear relationship, and the maximum value of the difference in the coefficient of linear expansion in which the occurrence of curl is reliably suppressed (the degree of curl is 5% or less) is 1.4 × 10
^-5 (1 / ° C).

On the other hand, the graph of FIG. 6 shows the relationship between the ratio of curl amount and length [degree of curl (%)] and the area C of the non-overlapping portion of the ellipsoid. As shown in the drawing, the two show a quadratic relationship, and the area C of the non-overlapping portion of the ellipsoid in which the occurrence of curl is reliably suppressed (curl degree is 5% or less) is 6.5 × 10 ^-10 [(1 / ° C) × (1 / ° C)]
It can be seen that it is.

It should be noted that the two indices of the maximum value of the difference (Δα) in the coefficient of linear expansion and the area (C) of the non-overlapping portion of the ellipsoid can be used at the same time, and this is preferable. Further, in the invention according to claim 1, the maximum value of the difference (Δα) between the coefficients of linear expansion and the area of a portion where the ellipsoid does not overlap with respect to the two plastic films disposed on both outermost layers of the laminate. By applying at least one of the conditions (C), it is possible to more effectively prevent the occurrence of curling.

Further, in the inventions according to the second to fifth aspects, similarly to the invention according to the first aspect, the arrangement of the two plastic films on both outermost layers of the laminated body is made different from the surface of one of the plastic films. This is an arrangement in a state in which the other plastic film faces the back surface. By doing so, for example, it is possible to cut out the plastic film for the cover layer and the plastic film for the base layer from the same raw material plastic film in a state in which the orientations are aligned. In the above, the cutting of the plastic film becomes easy. Conversely, if two plastic films are arranged in a state where the surfaces face each other, it is necessary to make the cutting method from the same raw material plastic film bilaterally symmetric, and the cutting becomes complicated. Further, by arranging the two plastic films so that the front surface and the rear surface face each other, the surface state and the wettability surface state (the front surface and the rear surface) of the laminate of the plastic films constituting the flexible wiring board can be improved. Back state)
Will be different. As a result, the front surface and the back surface of the flexible wiring board can be clearly distinguished, and for example, improvement in handleability and the like in a wiring process of the flexible wiring board can be expected.

Next, the present invention will be described specifically.

The flexible wiring board of the present invention will be described with reference to an example having a structure in which two plastic films 2 and 4 shown in FIG. 16 are laminated.

In the two plastic films 2 and 4, 2 is a plastic film for a cover layer and 4 is a plastic film for a base layer.

Examples of the types of the plastic films 2 and 4 include a polyimide film, a polyether nitrile film, a polyether sulfone film, a polyethylene terephthalate film, and a polyvinyl chloride film. Among these, polyethylene terephthalate film and polyimide film are preferable in consideration of heat resistance, dimensional stability, electric characteristics, mechanical strength characteristics, chemical resistance characteristics, price, etc.
A polyethylene terephthalate film is used. The thickness of the plastic film is usually 0.01 to
0.3 mm, preferably 0.025 to 0.125
mm. In order to more effectively prevent the occurrence of curling, it is preferable that the two plastic films disposed on the outermost layers have the same thickness.

The degree of stretching of the bidirectionally stretched plastic film is generally 1.5 to 15 times, preferably 2 to 9 times in the vertical direction and 3 to 8 times in the horizontal direction.

Then, as described above, whether the two plastic films 2 and 4 are cut out from the raw plastic film stretched in two directions by a specific method (Claim 1), The maximum value of the difference (Δα) between the coefficients of linear expansion when the ellipsoids are superimposed is 1.4 × 10 ⁻⁵ (1 /
C) or less (Claim 2), or the area C of the non-overlapping portion is 6.5 × 10 ⁻¹⁰ [(1 / ° C.) × (1 / ° C.)] or less (Claim 3). At least one of the two conditions must be met.

The method of cutting out the raw material plastic film according to claim 1 is as described above.

The above-described method of measuring the coefficient of linear expansion is based on the aforementioned T
In addition to the method of directly measuring by MA, for example, there is a method of measuring the ultrasonic wave propagation velocity of a plastic film developed by the present inventors. That is, there is a correlation between the elastic modulus of the plastic film and the ultrasonic wave propagation speed, and since the elastic modulus can be an index indicating the linear expansion coefficient, the ultrasonic wave propagation speed is determined by SST [Sonic Sheet Teste].
r, an ultrasonic propagation velocity measuring device (available from Nomura Trading Co., Ltd.)], the linear expansion coefficient of each part of the plastic film can be measured. The method using the ultrasonic wave propagation velocity has an advantage that the time required for the measurement is extremely short, about 2 minutes, and the measurement accuracy is substantially the same as that of the TMA method, and that no skill is required. Note that the measurement temperature in the measurement by SST is preferably about 23 ° C. ± 2 ° C.

The difference (Δα) between the linear expansion coefficients can be derived as follows. That is, first,
An ellipsoid of the coefficient of linear expansion of a plastic film is created by polar plotting according to the procedure described above (see FIG. 3). The radius r of the ellipsoid can be expressed as a function of the measured angle of linear expansion coefficient: θ (rad) as in the following equation (5). In the following equation (5), ξ indicates the eccentricity, which is defined by the following equation (6). Also,
a is the major axis radius of the ellipsoid and is the maximum value of r (r _max ). On the other hand, b is the minor axis radius of the ellipsoid, which is the minimum value of r (r _min ).

[0053]

(Equation 5)

[0054]

(Equation 6)

The radii of the ellipsoids of the two plastic films disposed on both outermost layers are defined as r ₁ and r.
Assuming that ₂ , the difference (Δα) in the coefficient of linear expansion is given by the following equation (7).
Can be represented by

[0056]

(Equation 7)

According to the equation (7), when the measurement angle θ is compared over 0 to 360 degrees (0 to 2π rad), the maximum value is the maximum value of the difference (Δα) between the linear expansion coefficients of the two plastic films. Value (Δα _max ). The maximum value (Δα _max ) can be derived using a computer programmed based on the above equations (5), (6), and (7).

On the other hand, the derivation of the area C of the non-overlapping part of the two ellipsoids is performed, for example, by the following equation (3) that defines the area C.
Can be derived by the following integration formula (8), which is one of the approximation formulas. In addition, approximation of the above equation (3) by other equations is not limited.

[0059]

(Equation 8)

Further, the metal electric circuit 3 is formed on the plastic film 4 serving as the base layer. Examples of the types of the metals include metals such as copper, gold, stainless steel, and aluminum, and metals such as Be, Ni, Co, Ag, Pb, and C.
An alloy to which r or the like is added is given. Further, these metals or alloys include those in which non-metal elements (for example, C, O, etc.) which are unavoidably mixed exist. Among these, copper alloys (> 99.9) are used because mechanical properties such as strength and elastic modulus, electrical properties such as electrical conductivity, and price are excellent.
% Cu, 0.0002 to 0.06% O ₂ , and other materials such as tough pitch copper), which are commonly used.

In the present invention, when the metal electric circuit 3 applies a stress until the strain becomes 0.002 (mm / mm), the plastic deformation component is 0.0003 (mm / mm).
This is necessary as described above.
A metal electric circuit having such physical properties can be formed by appropriately selecting the types of the above metals and alloys. The normal range of the plastic deformation component when a stress is applied until the strain becomes 0.002 (mm / mm) is 0.0003 to 0.0015, and particularly preferably 0.0004 to 0.0010. It is.

Here, the plastic deformation component and the flexibility of the metal electric circuit will be described using a metal foil as an example.

FIG. 11 shows SS curves of two types of metal foils A and B. These have different plastic deformation components. In the figure, a is the plastic deformation component (permanent strain) of the metal foil A when the stress is removed after the stress is applied, and b is the same when the stress is removed after the stress is applied. Plastic deformation component of metal foil B (permanent strain)
And c is the amount of distortion (deformation) when stress is applied to the metal foils A and B. Also, in the same figure, the direction of the stage of applying stress (outward path) is indicated by a solid arrow, and the direction of the stage of removing stress (return path) is indicated by a dotted arrow. As shown in the figure, when comparing two types of metal foils A and B with the same amount of strain (deformation amount), it is understood that the smaller the plastic deformation component, the smaller the stress generated from the metal foil. Note that the stress generated from the metal foil is generated as a reaction of the stress applied to the metal foil for deformation, and that a small value means excellent flexibility. In the same figure, specifically, when the amount of strain is S (mm / mm), the stress of the metal foil A is α, and similarly, the stress of the metal foil B is β, and the stress β
Is larger than the stress α (β> α). The plastic deformation component A of the metal foil A is larger than the plastic deformation component B of the metal foil B. Therefore, the metal foil A having a large plastic deformation component
Can be said to be superior in flexibility to the metal foil B having a small plastic deformation component.

Although the relationship between the plastic deformation component and the flexibility has been described using a metal foil as an example, the above relationship holds even when the metal foil is attached to a plastic film to form an electric circuit. . Also, not limited to metal foil,
For example, the above relationship holds even when a metal thin film is formed on a plastic film by an electroplating method, a sputtering method, or the like, and is formed in an electric circuit.

For reference, the SS curve of a general plastic film is shown in the graph of FIG. In the figure, the solid arrow indicates the direction of the path (outgoing path) that increases the stress, and the dotted arrow indicates the direction of the path (return path) that reduces (removes) the stress. As shown in the drawing, the SS curve of the plastic film is substantially a straight line, and when it is removed after applying a stress, it returns to a substantially original length,
It can be seen that the plastic deformation component is substantially zero. From this, it can be said that a plastic film has an extremely small plastic deformation component with respect to a metal electric circuit, and the deformation is substantially elastic deformation.

Next, the flexible wiring board of the present invention
It is manufactured using the above-described materials, for example, as shown in FIG.

That is, first, as shown in FIG. 14A, the adhesive layer 8 is formed on the surface of the base layer plastic film 4. The adhesive layer 8 is formed, for example, by applying an adhesive on the plastic film 4 and then drying it, or by attaching the adhesive applied on the separator to the plastic film 4 and then removing the separator. Can be formed. Next, a metal thin film 3a is formed on the adhesive layer 8. This thin film can be formed, for example, by disposing a metal foil such as a copper foil on the adhesive layer 8 and performing roll lamination. The metal foil film 3a can also be formed by an electroplating method or a sputtering method. In this case, the formation of the adhesive layer 8 can be omitted and the metal foil film 3a can be formed directly on the plastic film 4. Then, as shown in FIG. 1B, the metal thin film 3 is processed by a known method such as a printing method, a subtractive method, an additive method, etc., to form a metal electric circuit 3 in a predetermined circuit pattern. On the other hand, a plastic film 2 for a carver layer is prepared, and an adhesive layer 8 is formed on the back surface in the same manner as described above. When the adhesive layer 8 is formed on the back surface of the base layer plastic film 4, the adhesive layer 8 is formed on the cover layer plastic film 2 on the front surface. Then, as shown in FIG. 2C, the two are laminated with the surface of the plastic film 4 for the base layer and the back surface of the plastic film 2 for the carver layer facing each other. This lamination is performed by, for example, a pressure bonding method using a hot press or a lamination method using at least one of heat and pressure after temporarily attaching by roll lamination. The lamination method and conditions are appropriately determined depending on the types of the plastic film, the adhesive and the like.

FIG. 15 shows an example of the press-fitting method using the hot press.
Shown in In the figure, two hot plates 11a and 11b
They are arranged vertically facing each other. The upper heating plate 11a is connected to and fixed to the support rod 12a. The lower heating plate 11b is connected to a driving unit (not shown) via a support rod 12b, and is capable of moving up and down.
The plastic film 2 and the plastic film 4 are disposed between the two hot plates 11a and 11b with the adhesive layer 8 and the metal electric circuit 3 facing each other. In this state, by operating the drive unit to move the lower hot plate 11b upward as indicated by the arrow,
The above plastic film 2 and plastic film 4
Are pressed and laminated with the metal electric circuit 3 sandwiched therebetween.

Thus, FIG. 14D or FIG.
A flexible wiring board as shown in FIG. 6 can be manufactured. In addition, curl occurs when the metal electric circuit 3 is formed on the base layer plastic film 4,
In the present invention, the curling is suppressed by laminating the plastic film for the carver layer, and the flexible wiring board has a flat shape. In the lamination, the pressure and temperature conditions common to the pressure bonding method and the roll lamination method are usually 40 to 300 ° C. × 1.
-100 kg / cm ² , preferably 50-200 ° C. × 8
７０70 kg / cm ² .

Here, claim 2 or claim 3 of the present invention
In the invention according to the above, for each plastic film,
Measuring the linear expansion coefficient and performing a polar coordinate plot to create an ellipsoid of the linear expansion coefficient, and satisfying at least one of the condition of the maximum value of the difference in the linear expansion coefficient and the condition of the area of the non-overlapping portion of the ellipsoid. Investigation is the most basic method, but has the problem of lack of practicality. In order to solve this problem, the present inventors have developed the following method based on the knowledge obtained by examining the characteristics of the coefficient of linear expansion of the raw plastic film.

That is, in the belt-shaped raw plastic film, a region that satisfies at least one of the above two conditions relating to the coefficient of linear expansion is checked in advance, and the plastic film 2 for the cover layer and the plastic film for the base layer are determined from this region. The film 4 is cut out.

FIG. 18 shows an example of the characteristic of the linear expansion coefficient in the width direction of the strip-shaped raw plastic film 5 stretched in two directions. In the figure, the raw plastic film 5 is divided into eight strips parallel to the length direction (MD direction), and the relative position is determined based on a center line CL parallel to the length direction (MD direction). (-4, -3, -2, -1, 1, 2,
Each part is represented by (3, 4,). In each part, the ellipsoid of the coefficient of linear expansion is shown, and the main axes of crystal orientation are indicated by dotted arrows. And MD in a figure shows extending | stretching longitudinal direction and TD shows extending | stretching transverse direction. As shown in the drawing, as the distance from the center line CL of the raw plastic film 5 increases, the crystal orientation main axis shifts from the longitudinal direction of stretching. In this figure, there is no significant difference such as the difference in the coefficient of linear expansion in the portion (−3, −2, −1, 1, 2, 3) near the center line of the raw plastic film. Satisfy at least one of the following. Therefore, as shown in the figure, the relative positions (−3) to (−1) are the cutout portions for the cover layer, and the relative positions (1) to (3) are the cutout portions for the base layer. By combining the plastic films thus obtained and disposing them on both outermost layers with the front surface of one plastic film and the back surface of the other plastic film facing each other to produce a flexible wiring board, curling can be prevented. The figure shows a combination of the plastic film for the cover layer cut out from the relative position (-3) and the plastic film for the base layer cut out from the relative position (2).

The classification of the raw material plastic film is merely an example, and is actually determined as appropriate according to the size and the degree of stretching of the raw material plastic film. For example, in the case of a raw plastic film having a width of 2 to 6 m, the width of the section (band width) is 200 to
If it is 1000 mm, the number of divisions will be 6 to 10 sections.
Specifically, for example, when the width of the raw plastic film is 2 m, the width of the section (band width) can be 200 mm and the section can be divided into 10 sections. When the width of the raw plastic film is 6 m, the width of the division (band width) is 1000 mm and the film can be divided into six sections. For the reason that workability is good, for example, when the raw plastic film is 5 m, it is preferable that the division width (width of the band) is 500 mm and the division is made into ten sections.

As described above, the ellipsoid of the linear expansion coefficient of each part of the raw plastic film is examined in advance, the characteristics of the linear expansion coefficient are grasped and standardized, and the raw plastic film satisfying at least one of the above two conditions is obtained. By cutting out the plastic film from a predetermined part of the film, the maximum value of the difference in linear expansion coefficient and the area of the non-overlapping part of the ellipsoid can be determined without having to create an ellipsoid of linear expansion coefficient every time the plastic film is selected. It becomes possible to set it to a predetermined value or less. As a result, it is possible to improve the production efficiency of the flexible wiring board in which the curl is suppressed.

The method of manufacturing the flexible wiring board of the present invention has been described by taking an example in which two plastic films are laminated, but the present invention is not limited to this.
The present invention can be applied to a laminate of three or more plastic films. As described above, in this case, it is necessary to satisfy the predetermined condition of the present invention only in the two plastic films disposed on both outermost layers of the laminate of the plastic films constituting the flexible wiring board. It is not necessary to consider the plastic film disposed on the intermediate layer.

The thickness of the flexible wiring board according to the present invention is appropriately determined depending on its use and the like, but is generally 50 to 800 μm, preferably 100 to 600 μm.
μm. In addition, the shape is not particularly limited, and is appropriately determined depending on its use and the like. The size of the flexible wiring board is not particularly limited, and is appropriately determined according to the application. For example, the maximum length L of the flexible wiring board defined above (see FIG. 12A) is 10 to 1000 mm. , Preferably 30 to 600
mm may be used.

The flexibility of the flexible wiring board according to the present invention is appropriately determined according to its shape and use. For example, the flexibility of a rectangular (band-shaped) flexible wiring board is measured using a compression tester shown in FIG. In the figure, reference numeral 22 denotes an upper fixed plate on which a load cell (load detector) 25 is disposed above itself.
A lower movable plate 24 that is connected to a drive unit (linear motor) 23 and that can move up and down is provided so as to face the lower side of the upper fixed plate 22. First, the flexible wiring board 1 is connected to the upper fixed plate 22 and the lower movable plate 24.
Are placed in a state of being bent in a U-shape in the lateral direction in the direction of the long side. Then, the lower movable plate 24 is raised by operating the drive unit 23, and the bent flexible wiring board 1 is sandwiched and compressed between the upper fixed plate 22 and compressed by a predetermined amount to a predetermined bending radius R. Of the load cell 25
Is measured, and the flexibility (repulsion) is calculated and evaluated from the following equation. The bending radius R is
Since the distance between the upper fixed plate 22 and the lower movable plate 24 at the time of measurement is twice the bending radius R of the flexible wiring board 1, it can be calculated from the above distance.

[0078]

[Equation 9] Repulsive force (g / cm) = Repelled force detection value (g) / Length (cm) of short side (width) of flexible wiring board

The flexibility of the flexible wiring board (rectangular shape) measured in this manner is usually represented by a bending radius R = 5 mm.
Repulsive force 2g / cm to bending radius R = 15mm and repulsive force 6
00 g / cm, preferably the bending radius R
= 5 mm and rebound force of 4 g / cm to bending radius R = 15 mm and repulsion force of 400 g / cm.

Although the above-described evaluation method of flexibility is for a rectangular flexible wiring board, it can be applied to a flexible wiring board having a shape other than a rectangle. For example, in a flexible wiring board having a substantially rectangular shape (substantially boomerang shape) as shown in FIG. 12A, a part of the flexible wiring board is cut into a rectangle, and the flexibility can be evaluated in the same manner as described above using this part as a sample. . In this case, the flexibility can be objectively evaluated by unifying (standardizing) the shape of the cutout portion and the sample in advance.

[0081]

As described above, the flexible wiring board of the present invention specifies the physical properties of the metal electric circuit to ensure flexibility and durability, and is disposed on both outermost layers of the plastic film laminate. By specifying the two plastic films and specifying the mode of their arrangement, the physical properties of the outermost layers are made substantially the same, and the deformation amounts thereof are balanced. By doing so, the curling of the flexible wiring board is suppressed even if the metal electric circuit and the plastic film have different deformation properties. Moreover, since the flexibility and durability of the metal electric circuit and the plastic film are not impaired,
The flexible wiring board of the present invention has high performance having three characteristics of flexibility, durability, and curl suppression. Therefore, the flexible wiring of the present invention is optimal for a portion where frequent bending operations are performed, such as a connection portion between a print head of a printer and a motherboard. Also,
The flexible wiring board of the present invention has high precision in shape, and if electronic components are mounted or mounted using the flexible wiring board, automatic mounting by a machine or the like can be performed with high accuracy.

Next, examples will be described together with comparative examples.

[0083]

Example 1 A strip-like polyethylene terephthalate film (thickness: 0.05 m) stretched in two directions, longitudinal and transverse.
m, manufactured by Toray Industries, Inc.) as a raw plastic film. Then, in the raw plastic film, one reference line parallel to the stretching longitudinal direction is imagined, and two rectangular cutouts are formed on the reference plastic line in a state where the reference lines pass through respective center points and are aligned with each other. Assuming the planned area, these 2
A rectangular plastic film (film-A, film-B) having a size of 100 × 200 mm was cut out from one of the cutout areas (see FIG. 1). This film-
The SS curve of A is shown in the graph of FIG. In addition, this SS curve is based on ASTM D-882-83,
The measurement was performed by applying a stress up to a strain amount of 0.002 (mm / mm). As shown, Film-A
It can be seen that has almost no plastic deformation component and undergoes substantially elastic deformation. Similarly, for film-B, S-
An S-curve was made, which was the same as Film-A.

These two films-A and film-B
The maximum value of the difference in the coefficient of linear expansion between the front surface of the film-A and the back surface of the film-B and the area of the non-overlapping portion of the ellipsoid were measured by the method described below. As a result, the maximum value of the difference between the linear expansion coefficients is 0.2 × 10 ^−5.
(1 / ° C.), and the total area of the non-overlapping portions of the ellipsoid was 2.1 × 10 ⁻¹⁰ [(1 / ° C.) × (1 / ° C.)].

Next, a polyester-based thermosetting adhesive was prepared, and a flexible wiring board was produced according to the above-described method (see FIG. 14). That is, first, film-A
The above adhesive was applied to the surface of the base layer (for the base layer) and then dried to form an adhesive layer having a thickness of 0.03 mm. Next,
On this adhesive layer, a copper foil (tough pitch copper, thickness 0.03
5 mm, BHY-02-T, manufactured by Nippon Mining Co., Ltd.). The SS curve of this copper foil is shown in the graph of FIG.
In addition, this SS curve is based on ASTM D-882-83.
The stress was applied until the strain amount became 0.002 (mm / mm). As can be seen from the figure, this copper foil has a plastic deformation component of 0.0 in the above case.
005 (mm / mm), which is equal to or more than the predetermined value of the present invention. Then, the film-A and the copper foil were joined by a laminating roll whose surface was set at 120 ° C., and heated under pressure (conditions: 110 ° C. × 2 h × 10 kg / cm ² ) to bond the two. Then, the copper foil was processed by a subtractive method to form an electric circuit with a predetermined circuit pattern. In addition, curling occurred in the formation of the electric circuit. On the other hand, an adhesive layer having a thickness of 0.03 mm was formed on the back surface of Film-B in the same manner as for Film-A. And the surface of the film-A and the film-
Both films were pressed and laminated by a hot press (see FIG. 15) with the back surface of B facing. The condition of this crimping is 15
It is 0 ° C. × 1 h × 30 kg / cm ² .

For the flexible wiring board thus obtained, the curl amount h was measured by the above-mentioned method, but no curl occurrence was confirmed and the measurement was not possible. That is, the curl generated during the formation of the metal electric circuit was eliminated by forming the cover layer, and the flexible wiring board became flat. Further, the flexibility and durability of this flexible wiring board were examined. The flexibility was measured by the above-described method (FIG. 13), and as a result, the bending radius R was 5 mm and the repulsive force was 26 g / cm. On the other hand, as an evaluation of durability, a flexure and ductility test (Flexura) specified in IPC-FC-250A is used.
l Fatigue and Ductility, F
Cycles to Failure (Flexible Printed Wiring)
e) is the mandrel diameter; 0.125 '' (3.2 m
m). As a result, the number of flexural breaks was 820.

[0087]

Comparative Example 1 The same belt-shaped polyethylene terephthalate film (thickness: 0.05 mm) as in Example 1 was used as a raw material plastic film. Then, as shown in FIG.
In the above-mentioned raw material plastic film, assuming two cut-out planned areas of a rectangle arranged in the width direction, a size of 100 × 200 mm is obtained from these two cut-out planned areas.
Of rectangular plastic films (Film-C and Film-D). These two films-C,
About film-D, a film-
The maximum value of the difference in the coefficient of linear expansion in the state where the front surface of C and the back surface of Film-D faced each other and the total area of the non-overlapping portions of the ellipsoid were measured. As a result, the maximum value of the difference between the coefficients of linear expansion is 1.8 × 10 ⁻⁶ (1 / ° C.), and the total area of the non-overlapping portions of the ellipsoid is 7.4 × 10 ⁻¹⁰ [(1 / ° C. )
× (1 / ° C.)].

Then, a flexible wiring board was produced in the same manner as in Example 1 using these Film-C (for the base layer) and Film-D (for the cover layer).

The flexible wiring board thus obtained was examined for curl occurrence, flexibility and durability in the same manner as in Example 1. As a result, the flexibility is a repulsion force of 27 g / cm at a bending radius R = 5 mm,
As for the durability, the number of bending breaks was 820, which was almost the same as that of Example 1. However, regarding the occurrence of curl, the curl generated during the formation of the electric circuit remained after the formation of the cover layer, the curl amount h was 19 mm, and the curl degree was 9.5%.

[0090]

Example 2 As a copper foil, a strain amount of 0.002 (mm / m
m) the plastic deformation component when stress is applied up to 0.00)
What was 03 (mm / mm) was used. Other than this,
A flexible wiring board was manufactured in the same manner as in Example 1.

This flexible wiring board was examined for curl occurrence, flexibility, and durability in the same manner as in Example 1. As a result, the curl amount h was measured,
As in Example 1, no curl could be observed and measurement could not be performed. That is, the curl generated during the formation of the metal electric circuit is eliminated by forming the cover layer,
The flexible wiring board became flat. The flexibility was sufficient, with a bending radius R of 5 mm and a repulsion of 29.5 g / cm. The number of times of flexural breakage (durability) was 760 times, which was almost the same as that in Example 1.

[0092]

Example 3 A strip-shaped polyethylene terephthalate film (thickness: 0.05 m) stretched in two directions, vertical and horizontal.
m, manufactured by Toray Industries, Inc.) as a raw material plastic film, from which plastic films (film-1, film-2) having a size of 100 × 200 mm were cut out. Then, with the front surface of the film-1 and the back surface of the film-2 facing each other, the coefficient of linear expansion is measured by the TMA method described above, and an ellipsoid of the coefficient of linear expansion is created by a polar coordinate plot. Then, both were overlapped. This is shown in the graph of FIG. From this graph, the linear expansion coefficient of Film-1 and Film-2 was determined using a control computer attached to TMA, which was programmed based on the above equations (4), (5) and (6). As a result of calculating the maximum value of the difference,
0.53 × 10 ⁻⁵ (1 / ° C.), which was below a predetermined value. The measurement of the coefficient of linear expansion by TMA was performed as described below in order to eliminate the influence of hygroscopic expansion.
That is, the above plastic film is heated at 150 ° C. for 60 hours.
For 3 minutes to dry.
While cooling to 0 ° C., the length of the plastic film and the temperature of the plastic film were measured simultaneously and continuously, and the coefficient of linear expansion was determined based on the above equation (2) for the region below Tg.

Next, using the film-1 (for the base layer) and the film-2 (for the cover layer), according to Example 1, the surface of the film-1 and the rear surface of the film-2 face each other. A flexible wiring board was manufactured. In addition,
At this time, the metal electric circuit was formed from the same copper foil as in Example 1 using the same adhesive and manufacturing method as in Example 1.
This flexible wiring board was examined for curl occurrence, flexibility, and durability in the same manner as in Example 1. As a result, the curl amount h was 3.9 mm, and the curl degree was 2.
0%, curling was suppressed. The flexibility is a rebound of 27 g / cm at a bending radius R of 5 mm,
The number of flexural breaks (durability) was 830 times, which was almost the same as in Example 1.

[0094]

Comparative Example 2 The polyethylene terephthalate film used in Example 3 was newly resized to 100 × 200 m.
m of plastic film (film-3). On the other hand, the same film-1 as in Example 3 was prepared. Then, an ellipsoid having a linear expansion coefficient was prepared in the same manner as in Example 1, and both were superposed. This is shown in the graph of FIG. From this graph, the maximum value of the difference between the coefficients of linear expansion of Film-1 and Film-3 was calculated in the same manner as in Example 3.
77 × 10 ⁻⁵ (1 / ° C.), which exceeded the predetermined value.

Then, in the same manner as in Example 1, a flexible wiring board was produced using Film-1 and Film-3 with the front surface of Film-1 and the back surface of Film-3 facing each other. The metal electric circuit at this time was formed by using the same copper foil as in Example 1 using the same adhesive and manufacturing method as in Example 1. Then, the flexibility and the durability were examined in the same manner as in Example 1. As a result, the flexibility was a repulsion force of 27.5 g / cm at a bending radius of R = 5 mm, and the number of flexural breaks (durability) was 800. Yes, almost the same as Example 1. However, as a result of measuring the curl amount h of the flexible wiring board in the same manner as in Example 1, the curl amount h was 1
3.5 mm, the degree of curl was 6.8%, and curl occurred.

[0096]

EXAMPLE 4 A strip-shaped polyimide film (thickness: 0.125 mm, manufactured by Du Pont-Toray Co., Ltd.) stretched in two directions, lengthwise and widthwise, was used as a raw material plastic film, and a 200 × 360 mm plastic film (film-4, Film-5) was cut out. Then, in the same manner as in Example 3 using the above-described TMA,
The linear expansion coefficient was measured in a state where the front surface of No. 4 and the back surface of the film 5 faced each other, and an ellipsoid of the linear expansion coefficient was prepared by a polar coordinate plot, and both were superimposed. This is shown in the graph of FIG. From this graph, the area C of the non-overlapping part of the ellipsoids of Film-4 and Film-5 is 3.44 × 10
⁻¹⁰ [(1 / ° C.) × (1 / ° C.)], which was lower than the predetermined value. The calculation of the area is based on the above-described integration equation (8).
The measurement was performed using a control computer attached to a TMA measuring device programmed based on the above. In this calculation, m = 720 and Δθ = (2π / 720) ≒ 0.
00873 (rad).

Next, the above-mentioned film-4 (for the base layer)
And a film-5 (for the cover layer), and a flexible wiring board was produced in the same manner as in Example 1 with the surface of the film-4 facing the backside of the film-5.
The metal electric circuit at this time was formed by using the same copper foil as in Example 1 using the same adhesive and manufacturing method as in Example 1. Then, the curl amount h of the flexible wiring board was measured in the same manner as in Example 1, and as a result, the curl amount h was 8.3 m.
m, the degree of curl was 2.3%, and curl generation was suppressed. Further, as a result of examining the flexibility in the same manner as in Example 1, the bending radius R was 5 mm and the repulsive force was 160 g / cm. Regarding durability, IPC-FC-24
Flexural test (Flexural F
atgrup Test (Cy attest)
les to Failure) with a radius of curvature of 5 m.
m and evaluated. As a result, the number of bending breaks is 9 ×
It was ¹⁰⁶ times.

[0098]

Comparative Example 3 From the polyimide film used in Example 4, a new plastic film (film-6) having a size of 200 × 360 mm was cut out. On the other hand, the same film-4 as in Example 4 was prepared. Then, in the same manner as in Example 4, an ellipsoid having a coefficient of linear expansion was formed in a state where the front surface of the above-mentioned film-4 and the back surface of the film-6 faced each other, and both were overlapped. This is shown in the graph of FIG. Based on this graph, the area of the non-overlapping portion of the ellipsoids of the linear expansion coefficients of the film-4 and the film-6 was calculated in the same manner as in Example 4, and as a result, 7.71 × 10 ^-10 [(1 / ℃) × (1 /
° C)], which exceeded the predetermined value.

Next, in the same manner as in Example 4, using the film-4 (for the base layer) and the film-6 (for the cover layer), the front surface of the film-4 and the back surface of the film-6 face each other. In this state, a flexible wiring board was produced. Then, the curl amount h of the flexible wiring board was measured in the same manner as in Example 1. As a result, the curl amount h was 25.2 mm, the curl degree was 7.0%, and curl occurred.
Further, as a result of examining the flexibility and the durability in the same manner as in Example 4, the flexibility was determined to be a repulsion force 166 at a bending radius R = 5 mm.
g / cm, and the durability (the number of times of flexural breakage) was 8.3 × 10 ⁶ times as determined with a radius of curvature of 5 mm.

[0100]

EXAMPLE 5 A polyethylene terephthalate film (thickness: 0.125 mm, manufactured by Toray Industries, Inc.) stretched in two directions, lengthwise and widthwise, was used as a raw material plastic film. ) Was cut out. Also, a polyethylene terephthalate film (thickness: 0.250 mm, manufactured by Toray Industries, Inc.) stretched in two directions was used as a raw material plastic film, and a plastic film (film-10) having a size of 200 × 360 mm was cut out therefrom. Then, an ellipsoid having a coefficient of linear expansion was created in the same manner as in Example 3, and the three members were overlapped. Note that this stacking method is a stacking method in a state where the front surface of the film-7 and the back surface of the film-8 face each other. These ellipsoids are shown in the graph of FIG. From this graph, the maximum value of the difference between the respective coefficients of linear expansion was calculated in the same manner as in Example 3. As a result, the maximum value of the difference between the coefficient of linear expansion of Film-7 and Film-8 is
0.54 × 10 ⁻⁵ (1 / ° C.), and the maximum value of the difference between the linear expansion coefficients of Film-7 and Film-10 was 4.49 × 1.
0 ^-5 (1 / ° C.), for Film-8 and Film-10
The maximum value of the difference between the linear expansion coefficients is 3.94 × 10 ⁻⁵ (1 /
° C).

Next, the above-mentioned film-7, film-
8. A flexible wiring board was produced using Film-10. That is, as shown in FIG. 29, first, as shown in FIG.
5 mm) was prepared, and was temporarily attached to the front surface of the film 7 and the back surface of the film 8 with a roll to form an adhesive layer 8 1. Then, on each adhesive layer, a thickness of 0.035 m was obtained by a subtractive method in the same manner as in Example 1.
m of copper electric circuit 3 was formed. In addition, film-10
An adhesive layer 8 was formed on the front and back surfaces of the substrate using a sheet-like polyester-based thermosetting adhesive in the same manner as described above.
Then, as shown in FIG. 29, via the film-10,
In a state where the front surface of the film-7 and the back surface of the film-8 face each other, these three members are temporarily pressure-bonded by roll lamination, and then cured in a pressure cooker (condition: 110 ° C × 2h × 10
kg / cm ² ) to produce a flexible wiring board having a film three-layer structure as shown in FIG. 30, the same parts as those in FIG. 29 are denoted by the same reference numerals. In addition, in this flexible wiring board, the film-
7 and film-8, and as described above, the maximum value of the difference between the two coefficients of linear expansion is 0.54 × 10 ⁻⁵ (1 / ° C.), which is below the predetermined value of the present invention. .

The curl amount h of the flexible wiring board having the three-layer film structure was measured in the same manner as in Example 1. As a result, the curl amount h was 5.0 mm, the curl degree was 1.4%, and the curl amount was 1.4%. Was suppressed. Further, as a result of examining the flexibility in the same manner as in Example 1, the flexibility was a rebound force of 360 g / cm at a bending radius R of 15 mm.

[0103]

Comparative Example 4 The polyethylene terephthalate film (thickness 0.125 mm) used in Example 5 was newly added.
A plastic film (film-9) having a size of 200 × 360 mm was cut out. On the other hand, the same film-7 and film-10 as in Example 5 were prepared. Then, in the same manner as in Example 5, an ellipsoid having a linear expansion coefficient was created, and the three members were overlapped.
This is shown in the graph of FIG. From this graph, the maximum value of the difference in the coefficient of linear expansion was calculated in the same manner as in Example 1.
As a result, the maximum value of the difference between the linear expansion coefficients of the film 7 and the film 9 was 1.66 × 10 ⁻⁵ (1 / ° C.). The maximum value is
4.17 × 10 ⁻⁵ (1 / ° C.). As described above, the maximum value of the difference between the coefficients of linear expansion of Film-7 and Film-10 is 4.49 × 10 ⁻⁵ (1 / ° C.).

Next, the above-mentioned film-7, film-
9, a flexible wiring board was produced in the same manner as in Example 5, except that Film-9 was used instead of Film-8. As a result, the curl amount h was measured in the same manner as in Example 1.
9 mm, the degree of curl was 5.3%, and curl occurred. Further, as a result of examining the flexibility in the same manner as in Example 1, it was found that the bending radius R was 15 mm and the repulsive force was 370 g / cm.

[0105]

Example 6 A raw plastic film (made of polyethylene terephthalate, thickness 0.05 mm) stretched in two directions, longitudinal and transverse, was prepared. This width is 4 m. Then, as shown in FIG. 18, this was divided into eight sections in a belt shape parallel to the length direction (stretched longitudinal direction). This category (obi)
Is 500 mm in width. In this raw material (raw material) plastic film, the linear expansion coefficients of the respective sections were measured in the same manner as in Example 3, and the combination of the relative positions was examined. 4 × 10 ^-5 (1
/ ° C) The following conditions are satisfied in relative positions (−3) to
The range (area) was (3). Then, as shown in the figure, a plastic film (film-11) for the cover layer having a size of 80 × 200 mm is cut out from the relative position (−3), and the size is 80 × 200 mm from the relative position (2).
Plastic film for base layer (Film-12)
I cut it out. This film-11 and film-12
When the difference in the coefficient of linear expansion between the back surface of the film 11 and the front surface of the film 12 was measured, the maximum value was 1.1 × 10 ⁻⁵ (1 / ° C.). Was.

Then, in the same manner as in Example 3, a flexible wiring board was produced using Film-11 and Film-12 with the back surface of Film-11 facing the front surface of Film-12. Then, the curl amount h of this flexible wiring board was measured in the same manner as in Example 1, and as a result,
The curl amount h is 7.6 mm, and the curl degree is 3.8%.
And the occurrence of curling was suppressed. As a result of examining the flexibility and durability in the same manner as in Example 1, the flexibility was a rebound of 27 g / cm at a bending radius R of 5 mm,
The number of flexural breaks (durability) was 810 times, and
And about the same.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention.

FIG. 2A is a perspective view showing how to stack two plastic films in the above embodiment, and FIG. 2B is a cross-sectional view thereof.

FIG. 3 is a polar plot diagram showing an ellipsoid of a linear expansion coefficient of a plastic film stretched in two directions.

FIG. 4 is a polar plot in which two linear expansion coefficients ellipsoids are superimposed.

FIG. 5 is a graph showing the relationship between the maximum value of the difference in the coefficient of linear expansion and the degree of curling.

FIG. 6 is a graph showing the relationship between the area of a non-overlapping portion of a linear expansion coefficient ellipsoid and the degree of curl.

FIG. 7 is a graph showing an SS curve of a material.

FIG. 8 is another graph showing the SS curve of the material.

FIG. 9 is another graph showing the SS curve of the material.

FIG. 10 is another graph showing an SS curve of a material.

FIG. 11 is a graph showing SS curves of two metal foils.

FIG. 12A is a schematic diagram showing the longest length of a flexible wiring board, and FIG. 12B is an explanatory diagram for measuring the curling amount of the flexible wiring board.

FIG. 13 is an explanatory diagram showing an example of measuring the flexibility of a flexible wiring board.

FIG. 14A is a cross-sectional view showing a state in which an adhesive layer is formed on a base film and then a copper foil is placed thereon, and FIG.
FIG. 3 is a cross-sectional view showing a state in which the copper foil is formed in an electric circuit, FIG. 4C is a cross-sectional view showing a state in which a plastic film for a base layer and a plastic film for a cover layer are laminated, and FIG. It is sectional drawing which shows the structure of the flexible wiring board obtained in this way.

FIG. 15 is an explanatory view showing an example of a hot press in the above manufacturing method.

FIG. 16 is a cross-sectional view illustrating an example of a flexible wiring board.

17A is a cross-sectional view of a plastic film for a base layer, FIG. 17B is a cross-sectional view showing a state where an adhesive layer is formed on the plastic film for a base layer, and FIG. It is a cross-sectional view showing a state where tension is applied when a metal thin film is formed on the adhesive layer,
(D) is a cross-sectional view showing a state in which tension is applied when the metal thin film is formed on the metal electric circuit, and (E) is a cross-sectional view.
FIG. 4 is a cross-sectional view showing a state in which curl has occurred in a laminate of the plastic film and a metal electric circuit.

FIG. 18 is an explanatory view showing a state in which a plastic film is cut out from a raw plastic film in an example of the present invention.

FIG. 19 is a graph showing an SS curve of a general plastic film.

FIG. 20 is a graph showing an SS curve of a plastic film used in an example of the present invention.

FIG. 21 is a graph showing an SS curve of a copper foil used in an example of the present invention.

FIG. 22 is an explanatory diagram showing a state in which a plastic film is cut out from a raw plastic film in a comparative example.

FIG. 23 is a polar plot diagram in which two linear expansion coefficients ellipsoids are overlapped in one embodiment of the present invention.

FIG. 24 is a polar coordinate plot in which two ellipsoids of linear expansion coefficient in a comparative example are superimposed.

FIG. 25 is a polar plot diagram in which two ellipsoids of linear expansion coefficient are overlapped in another embodiment of the present invention.

FIG. 26 is a polar coordinate plot in which two ellipsoids of a linear expansion coefficient in another comparative example are superimposed.

FIG. 27 is a polar coordinate plot in which ellipsoids of three linear expansion coefficients are overlapped in another example of the present invention.

FIG. 28 is a polar plot diagram in which three ellipsoids of linear expansion coefficients are superimposed in another comparative example.

FIG. 29 is a cross-sectional view showing a state in which a flexible wiring board in which three layers of plastic films are laminated is manufactured.

FIG. 30 is a cross-sectional view showing a structure of a flexible wiring board in which three layers of plastic films are laminated.

[Explanation of symbols]

2: Plastic film for cover layer 2a: Planned area for cutting plastic film for cover layer 4: Plastic film for base layer 4a: Planned area for cutting plastic film for cover layer 91: Surface 10: Strip-shaped raw plastic film SL: Reference line MD: Stretching longitudinal direction TD: Stretching transverse direction

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H05K 1/02 H05K 1/03

Claims (5)

(57) [Claims] 1. A flexible wiring board in which two or more plastic films stretched in two directions, a vertical direction and a horizontal direction, are laminated, and a metal electric circuit is formed on at least one of the plastic films constituting the laminate. Wherein the metal electric circuit is the following (A), and the two plastic films disposed on both outermost layers of the laminate are the following two (B) plastic films. A flexible wiring board, wherein the arrangement of two plastic films on both outermost layers of the laminate is such that the surface of one plastic film and the back surface of the other plastic film face each other. (A) The permanent strain when a stress is applied and removed is defined as a plastic deformation component, and the plastic deformation component when the stress is applied until the strain becomes 0.002 (mm / mm) is 0.0
003 (mm / mm) or more metal electric circuit. (B) On the film surface of the strip-shaped raw plastic film stretched in two directions with the length direction being the stretching longitudinal direction and the width direction being the stretching transverse direction, any one reference line parallel to the stretching direction is assumed. And 2 of the same shape
The two cutout scheduled areas are aligned with each other, and an arbitrary point of one of the two cutout planned areas and a corresponding one of the other cutout scheduled areas correspond to this point. Two plastic films cut out from these two cut-out planned areas, which are assumed to be on the reference line. 2. A flexible wiring board in which two or more plastic films stretched in two directions, a vertical direction and a horizontal direction, are laminated, and a metal electric circuit is formed on at least one of the plastic films constituting the laminated body. Wherein the metal electric circuit is that of (A) according to claim 1, and the two plastic films disposed on both outermost layers of the laminate are each formed by a method (C) shown below. Ellipsoids of respective coefficients of linear expansion in portions corresponding to each other on the film surface of the plastic film are formed on coordinates, and the respective ellipsoids obtained by superimposing the ellipsoids so that the center point and the coordinate axes X and Y coincide with each other. The maximum value of the difference between the linear expansion coefficients of the plastic films is 1.4 × 10 ⁻⁵ (1
/ ° C) or less, and the arrangement of these two plastic films on both outermost layers of the laminate is such that the surface of one plastic film and the back surface of the other plastic film A flexible wiring board, wherein the flexible wiring board is arranged in a state of facing each other. (C) A predetermined base point P is determined on the film surface of the plastic film, and the linear expansion coefficient in the angle θ direction is measured with the base point P as a center point and with reference to the axis of the plastic film stretching longitudinal direction passing through the base point P. I do. On the other hand, coordinates are prepared in which the axis of the plastic film stretching longitudinal direction is the Y axis and the axis of the plastic film stretching lateral direction is the X axis. In these coordinates, the intersection of the Y axis and the X axis is defined as a base point P for measuring the linear expansion coefficient, and the magnitude of the measured value of the linear expansion coefficient is defined as a distance r from the base point P. Are plotted in the measurement angle θ direction with respect to the Y axis. This plot is performed a plurality of times while changing the measurement angle θ, and an ellipsoid is created by drawing an analysis line over the base point P in the 360-degree direction so as to pass through the average point of the plotted points. 3. A flexible wiring board in which two or more plastic films stretched in two directions, a longitudinal direction and a lateral direction, are laminated, and a metal electric circuit is formed on at least one of the plastic films constituting the laminated body. Wherein the metal electric circuit is that of (A) according to claim 1 and the two plastic films disposed on both outermost layers of the laminate are the method (C) according to claim 2. )), Ellipsoids of respective linear expansion coefficients at portions corresponding to each other on the film surface of each plastic film are created on the coordinates, and the ellipsoids are overlapped so that the center point and the coordinate axes X and Y coincide with each other. The total area of non-overlapping parts in the case is 6.5 × 10 ⁻¹⁰ [(1 / ° C.) ×
(1 / ° C.)], and the two plastic films are arranged on both outermost layers of the laminate, and the surface of one plastic film and the other plastic film A flexible wiring board, wherein the flexible wiring board is arranged so as to face the rear surface of the flexible wiring board. 4. A flexible wiring board in which two or more plastic films stretched in two directions, a longitudinal direction and a lateral direction, are laminated, and a metal electric circuit is formed on at least one of the plastic films constituting the laminated body. Wherein the metal electric circuit is that of (A) according to claim 1, and the two plastic films disposed on both outermost layers of the laminate are each formed by a method (D) shown below. Ellipsoids of respective coefficients of linear expansion in portions corresponding to each other on the film surface of the plastic film are formed on coordinates, and the respective ellipsoids obtained by superimposing the ellipsoids so that the center point and the coordinate axes X and Y coincide with each other. The maximum value of the difference between the linear expansion coefficients of the plastic films is 1.4 × 10 ⁻⁵ (1
/ ° C) or less, and the arrangement of these two plastic films on both outermost layers of the laminate is such that the surface of one plastic film and the back surface of the other plastic film A flexible wiring board, wherein the flexible wiring board is arranged in a state of facing each other. (D) A predetermined base point P is defined on the film surface of the plastic film, the base point P is set as a center point, an arbitrary direction on the plastic film surface passing through the base point P is determined, and the film surface is determined with reference to this axis. The linear expansion coefficient in the angle θ direction above is measured. On the other hand, the axis in the arbitrary direction is set as the Y axis, and the axis in
Prepare coordinates to be used as axes. And at these coordinates,
The point of intersection of the Y axis and the X axis is the base point P for measuring the coefficient of linear expansion.
The magnitude of the measured value of the coefficient of linear expansion is defined as a distance r from the base point P, and the tip point of the distance r is plotted in the measurement angle θ direction with the Y axis as a reference. This plot is performed a plurality of times while changing the measurement angle θ, and an ellipsoid is created by drawing an analysis line over the base point P in the 360-degree direction so as to pass through the average point of the plotted points. 5. A flexible wiring board in which two or more plastic films stretched in two directions, a longitudinal direction and a lateral direction, are laminated, and a metal electric circuit is formed on at least one of the plastic films constituting the laminated body. Wherein the metal electric circuit is that of (A) according to claim 1, and the two plastic films disposed on both outermost layers of the laminate are the method (D) according to claim 4. )), Ellipsoids of respective linear expansion coefficients at portions corresponding to each other on the film surface of each plastic film are created on the coordinates, and the ellipsoids are overlapped so that the center point and the coordinate axes X and Y coincide with each other. The total area of non-overlapping parts in the case is 6.5 × 10 ⁻¹⁰ [(1 / ° C.) ×
(1 / ° C.)], and the two plastic films are arranged on both outermost layers of the laminate, and the surface of one plastic film and the other plastic film A flexible wiring board, wherein the flexible wiring board is arranged so as to face the rear surface of the flexible wiring board.