JP7357582B2 - flexible printed wiring board - Google Patents

Description

The present disclosure relates to flexible printed wiring boards.

In recent years, as electronic devices have become smaller and lighter, electronic components such as planar coil elements have been miniaturized by using conductive patterns such as planar coils, and are mounted on flexible printed wiring boards.

In the production of the above-mentioned flexible printed wiring board, a photosensitive dry film, for example, is used as a material for forming an insulating layer in order to protect conductive circuits and maintain insulation between conductors (Japanese Patent Laid-Open No. 2002-156754) reference).

Japanese Patent Application Publication No. 2002-156754

A flexible printed wiring board according to an embodiment of the present disclosure includes a base film having an insulating property, a planar coil provided on both sides of the base film, and a flexible printed wiring board according to an embodiment of the present disclosure. A plurality of dummy wirings are provided on both surfaces in a state of electrical insulation from the planar coil, and an insulating layer is laminated on the base film, the planar coil, and the dummy wiring, and the dummy wiring on the front surface and the back surface of the base film are provided. The average intersection angle with the dummy wiring is 30 degrees or less.

FIG. 1 is a schematic plan view showing a flexible printed wiring board according to an embodiment of the present disclosure. FIG. 2 is a partial cross-sectional view taken along line AA of the flexible printed wiring board of FIG. FIG. 3 is a schematic plan view of the surface of the flexible printed wiring board of the example. FIG. 4 is a partial cross-sectional view of the flexible printed wiring board of the example.

[Problems that this disclosure seeks to solve]

The photosensitive dry film used as the material for forming the insulating layer is the photocurable and thermosetting resin composition kept in a semi-cured state. The above-mentioned photosensitive dry film is, for example, heat-pressed onto the circuit of a flexible printed wiring board, exposed to light, peeled off the support film, and developed to form a pattern, and then the patterned resin is cured by heating. An insulating layer is formed to insulate and protect the circuit. However, when a thermosetting resin is used to form such an insulating layer, there is a problem that the base film of the flexible printed wiring board is likely to warp due to heat shrinkage after the thermosetting resin is cured.

The present disclosure has been made based on the above-mentioned circumstances, and is aimed at preventing warping of the base film due to heat shrinkage after curing of the thermosetting resin when forming an insulating layer using a thermosetting resin. The purpose of the present invention is to provide a flexible printed wiring board that can suppress the noise.

[Effects of this disclosure]
In the flexible printed wiring board according to the present disclosure, when forming an insulating layer using a thermosetting resin, it is possible to suppress warpage of the base film of the flexible printed wiring board due to heat shrinkage after curing of the thermosetting resin.

[Description of embodiments of the present disclosure]
First, embodiments of the present disclosure will be listed and described.

A flexible printed wiring board according to one aspect of the present disclosure includes a base film having an insulating property, a planar coil provided on both sides of the base film, and a planar coil provided on both sides of the base film in an electrically insulated state from the planar coil. comprising a plurality of dummy wirings, and an insulating layer laminated on the base film, the planar coil, and the dummy wiring, wherein the average intersection angle between the dummy wiring on the front surface and the dummy wiring on the back surface of the base film is 30 degrees or less. be.

When forming an insulating layer using a thermosetting resin, the flexible printed wiring board can suppress warping of the base film of the flexible printed wiring board due to thermal contraction after the thermosetting resin is cured. The reason is assumed to be as follows. As shown in FIG. 4, which will be described later, in a flexible printed wiring board including a planar coil and a plurality of dummy wirings, the direction perpendicular to the main wiring direction of the plurality of wirings is the main contraction direction (the direction in which the contraction is most likely to occur). Therefore, if the circuit directions differ between the front and back surfaces of a flexible printed wiring board that includes a planar coil and a plurality of dummy wires on both sides, the main shrinkage direction will be different, making it easy for the base film to warp. In the flexible printed wiring board, the average intersection angle between the dummy wiring on the front surface and the dummy wiring on the back surface of the base film is 30 degrees or less. As a result, in the flexible printed wiring board, the difference in the main shrinkage direction between the front surface and the back surface of the flexible printed wiring board becomes small. Therefore, it is possible to suppress warping of the base film of the flexible printed wiring board due to thermal contraction of the thermosetting resin after curing. Here, the "crossing angle" refers to the crossing angle that is an acute angle among the angles formed by the dummy wiring on the front surface and the dummy wiring on the back surface. "Average intersection angle" refers to the average value of intersection angles at ten arbitrary locations.

It is preferable that the average line width of the plurality of dummy wirings is 5 μm or more and 50 μm. When the average line width of the plurality of dummy wirings is within the above range, the effect of suppressing warping of the base film of the flexible printed wiring board due to thermal contraction of the thermosetting resin after curing can be further enhanced.

It is preferable that the Young's modulus of the dummy wiring is 40,000 MPa or more and 130,000 MPa or less. When the Young's modulus of the dummy wiring is within the above range, desired wiring board strength can be obtained. Here, the above Young's modulus is a value measured in accordance with JIS-Z2280 (1993).

It is preferable that the base film has polyimide, polyethylene terephthalate, liquid crystal polymer, or fluororesin as a main component. When the base film has polyimide, polyethylene terephthalate, liquid crystal polymer, or fluororesin as a main component, desired insulation properties, flexibility, and low dielectric constant properties can be obtained. Here, the term "main component" means the component having the highest content.

It is preferable that the insulating layer contains a cured product of a photosensitive dry film. When the insulating layer contains a cured product of a photosensitive dry film, a desired insulating layer can be easily formed.

It is preferable that the ratio of the area of the wiring area of the dummy wiring to the area of the surface of the base film is 60% or more. When the area ratio of the wiring area of the dummy wiring is within the above range, it is possible to enhance the effect of suppressing warpage of the base film of the flexible printed wiring board due to thermal contraction of the thermosetting resin after curing. Here, the "wiring area of the dummy wiring" includes a region of the base film where the dummy wiring is provided and a region between adjacent dummy wirings.

It is preferable that the amount of warpage H (%) of the base film expressed by the following formula (1) of a rectangular test piece with a side length A in the wiring area of the dummy wiring is 0.50 or less.
H=(y2-y1)×100/A...(1)
(In formula (1), y2 is the maximum displacement amount of the component in the direction perpendicular to the surface of the base film, with the surface of the base film as a reference. y1 is the displacement amount of the component in the direction perpendicular to the surface of the base film. (This is the minimum value of the amount of displacement.)
When the amount of warpage H of the base film is within the above range, the flexible printed wiring board can have more stable quality.

[Details of embodiments of the present disclosure]
Hereinafter, flexible printed wiring boards according to each embodiment of the present disclosure will be explained in detail with reference to the drawings.

<Flexible printed wiring board>
The flexible printed wiring board 1 shown in FIGS. 1 and 2 includes a base film 2 having an insulating property, a planar coil 3 provided on both sides of the base film, and a state in which both sides of the base film 2 are electrically insulated from the planar coil. and an insulating layer 4 laminated on the base film 2, the planar coil 3, and the dummy wires 41. The base film 2 serves as a substrate for a flexible printed wiring board.

The flexible printed wiring board 1 has a plurality of dummy wires (hereinafter referred to as "dummy wires") arranged outside the planar coil 3 in the width direction, electrically insulated from the wires 5, and parallel to the wires 5. (also referred to as "wiring 41").

(Base film)
The base film 2 has electrical insulation properties. The base film 2 is a base material layer for forming the planar coil 3. The base film 2 has flexibility. Note that the "main component" refers to a component with the largest content ratio in terms of mass, for example, a component with a content of 50% by mass or more.

The base film 2 preferably contains polyimide, polyethylene terephthalate, liquid crystal polymer, or fluororesin as a main component. When the base film 2 has polyimide, polyethylene terephthalate, liquid crystal polymer, or fluororesin as its main component, desired performances such as insulation, flexibility, and low dielectric constant can be obtained.

The lower limit of the average thickness of the base film 2 is preferably 5 μm, more preferably 10 μm. On the other hand, the upper limit of the average thickness of the base film 2 is preferably 50 μm, more preferably 40 μm. If the average thickness of the base film 2 is less than the above lower limit, the dielectric strength of the base film 2 may be insufficient. On the other hand, if the average thickness of the base film 2 exceeds the above upper limit, the flexible printed wiring board 1 may become unnecessarily thick or have insufficient flexibility. In addition, in this specification, "average thickness" refers to the average value of thicknesses at arbitrary 10 points.

(Planar coil)
The planar coil 3 is a layer made of an electrically conductive conductor, and one strip of the planar coil 3 has a wiring structure in which it is spirally wound a plurality of times. The planar coil 3 is, for example, a laminate of a seed layer laminated on the base film 2 and an electroplated layer laminated on the seed layer. Furthermore, the planar coil 3 has a land portion 13 arranged at the peripheral edge of a hole in the base film 2 for forming a through hole.

Examples of the main components of the seed layer include copper, nickel, and silver. The seed layer is formed, for example, by electroless plating. Further, the seed layer may be a sintered body layer of metal particles obtained by applying ink containing metal particles to the surface of the base film 2 and sintering the metal particles, It may be a laminate of plated layers. Further, the electroplated layer is formed by electroplating. The main components of the electroplated layer include copper, nickel, silver, and the like.

The upper limit of the average thickness of the wiring 5 of the planar coil 3 is preferably 90 μm, more preferably 70 μm. If the average thickness of the wiring 5 exceeds the upper limit, there is a possibility that the demand for making the flexible printed wiring board 1 thinner is not met. On the other hand, the lower limit of the average thickness of the wiring 5 of the planar coil 3 is preferably 5 μm, more preferably 10 μm. If the average thickness is less than the lower limit, electrical resistance may increase. Further, the lower limit of the average thickness of the wiring 5 may be, for example, 30 μm or 40 μm.

The lower limit of the average line width of the wiring 5 of the planar coil 3 is preferably 5 μm, more preferably 10 μm. On the other hand, the upper limit of the average line width of the wiring 5 of the planar coil 3 is preferably 50 μm, more preferably 30 μm. If the average line width of the wiring 5 is less than the lower limit, it may not be easy to form the planar coil 3. Moreover, if the average line width of the wiring 5 is less than the lower limit, there is a possibility that the thickness of the planar coil 3 cannot be made sufficiently large. Conversely, if the average line width exceeds the upper limit, it may be difficult to obtain the desired wiring density. Note that the "average line width" refers to the average value of the widths of ten arbitrary points.

When the wires 5 of the planar coil 3 are arranged at the same pitch, the lower limit of the average pitch between adjacent wires 5 is preferably 10 μm, and more preferably 20 μm, for example. On the other hand, the upper limit of the average pitch is preferably, for example, 100 μm, more preferably 60 μm. If the average pitch is less than the lower limit, it may be difficult to form the planar coil 3. Conversely, if the average pitch exceeds the upper limit, it may be difficult to obtain the desired wiring density.

The lower limit of the average interval between adjacent wirings 5 of the planar coil 3 is preferably 5 μm, more preferably 10 μm. On the other hand, the upper limit of the average interval is preferably 50 μm, more preferably 30 μm. If the average interval is less than the lower limit, it may not be easy to form the planar coil 3. Conversely, if the average spacing exceeds the upper limit, it may be difficult to obtain the desired wiring density. Note that the "average interval" refers to the average value of the intervals of ten arbitrary points.

(dummy wiring)
The plurality of dummy wirings 41 are provided in an electrically insulated state from the planar coil 3. Specifically, the plurality of dummy wirings 41 are arranged in an area outside the planar coil 3 in the base film 2 at a distance from the planar coil 3, and are formed to be electrically isolated so as not to be electrically conductive. . By providing a plurality of dummy wirings 41 in this manner, the strength of the flexible printed wiring board can be increased. It is preferable that the plurality of dummy wirings 41 are all arranged in parallel on each of the front and back surfaces of the base film 2. In the present disclosure, "parallel" means that the angle between the two is 5° or less, preferably 3° or less.

The dummy wiring 41 constitutes a plurality of linear bodies. For example, like the planar coil 3, the plurality of dummy wirings 41 can be a laminate of a seed layer laminated on a base film and an electroplated layer laminated on this seed layer.

The average intersection angle between the dummy wiring 41 on the front surface and the dummy wiring 41 on the back surface of the base film 2 is 30 degrees or less. As described above, since the average intersection angle between the dummy wiring 41 on the front surface and the dummy wiring 41 on the back surface is 30 degrees or less, the flexible printed wiring board has a main shrinkage direction between the front surface and the back surface of the flexible printed wiring board. The difference becomes smaller. Therefore, it is possible to suppress warping of the base film of the flexible printed wiring board due to thermal contraction of the thermosetting resin after curing.

The lower limit of the average interval between the plurality of dummy wirings 41 and the planar coil 3 is preferably 5 μm. On the other hand, the upper limit of the average interval is preferably 50 μm, more preferably 30 μm. If the average interval is less than the lower limit, there is a risk that the plurality of dummy wirings 41 and the planar coil 3 will be short-circuited. On the other hand, if the average interval exceeds the upper limit, there is a possibility that the effect of improving the strength by the plurality of dummy wirings 41 will be insufficient.

The lower limit of the average line width of the dummy wiring 41 is preferably 5 μm, more preferably 10 μm. On the other hand, the upper limit of the average line width of the planar coil 3 is preferably 50 μm, more preferably 30 μm. If the average line width of the dummy wiring 41 is less than the lower limit, there is a possibility that the thickness of the dummy wiring 41 cannot be made sufficiently large. Conversely, if the average line width exceeds the upper limit, it may be difficult to obtain the desired wiring density.

When the dummy wires 41 are arranged at the same pitch, the lower limit of the average pitch between adjacent dummy wires 41 is preferably 10 μm, and more preferably 20 μm, for example. On the other hand, the upper limit of the average pitch is preferably, for example, 100 μm, more preferably 60 μm. If the average pitch is less than the lower limit, it may not be easy to form the dummy wiring 41. Conversely, if the average pitch exceeds the upper limit, it may be difficult to obtain the desired strength of the flexible printed wiring board.

It is preferable that the Young's modulus of the dummy wiring is 40,000 MPa or more and 130,000 MPa or less. When the Young's modulus of the dummy wiring is within the above range, desired wiring board strength can be obtained.

The area of the wiring area of the dummy wiring 41 on the base film 2 can be set as appropriate, but the lower limit of the area ratio of the wiring area of the dummy wiring 41 to the surface area of the base film 2 is preferably 60%, and 70% is preferable. More preferred. When the area ratio of the wiring area of the dummy wiring is within the above range, it is possible to enhance the effect of suppressing warpage of the base film of the flexible printed wiring board due to thermal contraction of the thermosetting resin after curing.

(insulating layer)
The insulating layer 4 is laminated on the planar coil 3, the plurality of dummy wirings 41, and the region of the base film 2 where the planar coil 3 and the plurality of dummy wirings 41 are not laminated. The insulating layer 4 mainly prevents damage and short circuits caused by contact of the planar coil 3 with other members. Therefore, it is preferable that the insulating layer 4 covers the entire outer surface of the planar coil 3 except for intentionally provided openings or notches.

The insulating layer 4 can be formed using a solder resist, a coverlay, etc., and it is preferable that the insulating layer contains a cured product of a photosensitive dry film. When the insulating layer contains a cured product of a photosensitive dry film, a desired insulating layer can be easily formed. Moreover, the effects of the present disclosure can be exhibited because the insulating layer contains a cured product of a photosensitive dry film. When using a photosensitive dry film for the insulating layer 4, by heating and pressing the photosensitive dry film from the outer surface of the planar coil 3, the photosensitive dry film flows, covering the outer surface of the planar coil 3 and , fills the gap between the planar coils 3.

The upper limit of the amount of warpage H (%) of the base film expressed by the following formula (1) of a rectangular test piece with a side length A in the wiring area of the dummy wiring is preferably 0.50, and 0. More preferably, it is .25 or less.
H=(y2-y1)×100/A...(1)
In the above formula (1), y2 is the maximum value of the amount of displacement in the direction component perpendicular to the surface of the base film, with the surface of the base film as a reference. y1 is the minimum value of the displacement in the direction component perpendicular to the surface of the base film.
When the amount of warpage H of the base film is within the above range, the flexible printed wiring board can have more stable quality.

[Method for manufacturing flexible printed wiring board]
Next, an example of a method for manufacturing the flexible printed wiring board 1 will be described. The method for manufacturing the flexible printed wiring board includes a step of installing a conductive pattern including a planar coil and a plurality of dummy wirings on an insulating base film (hereinafter also referred to as a conductive pattern installation step), and the above-mentioned conductive pattern installation step. Thereafter, a step of laminating an insulating layer on the base film and the planar coil (hereinafter also referred to as an insulating layer laminating step) is provided.

(Conductive pattern installation process)
In the conductive pattern installation step, a plurality of dummy wirings are installed on the surface of the base film at the same time as the planar coil. In the conductive pattern installation step, a conductive pattern including a planar coil and a plurality of dummy wirings is installed using, for example, a semi-additive method. Specifically, the conductive pattern installation step includes a step of laminating a seed layer on the surface of the base film, and after the seed layer lamination step, inverted shapes of the planar coil 3 and the plurality of dummy wirings 41 are formed on the surface of the seed layer. a step of electroplating the surface of the seed layer after the resist pattern forming step; and after the electroplating step, removing the resist pattern and the region of the seed layer that overlaps with the resist pattern. It has a process. The seed layer lamination step may be performed, for example, by electroless plating, or may be performed by applying ink containing metal particles and sintering the metal particles, and sintering and electroless plating of the metal particles. It may be done by both.

The dummy wiring on the front surface and the dummy wiring on the back surface of the base film are provided so that the average intersection angle is 30 degrees or less, as described above.

(Insulating layer lamination process)
In the insulating layer lamination step, the insulating layer 4 is laminated by curing a thermosetting resin. In this way, by laminating the insulating layer by curing the thermosetting resin in the insulating layer lamination step, it is possible to easily and easily form a flexible printed wiring board in which the insulating layer of the planar coil is prevented from being exposed to the outside. It can be manufactured reliably. In the insulating layer lamination step, for example, a photosensitive dry film having an average thickness smaller than the average thickness of the planar coil 3 is thermally laminated from the outer surface side of the planar coil 3 and the plurality of dummy wirings 41. By heating and pressing the photosensitive dry film from the outer surfaces of the planar coil 3 and the plurality of dummy wirings 41, the photosensitive dry film flows and covers the outer surfaces of the planar coil 3 and the plurality of dummy wirings 41. While covering, the gaps between the planar coils 3 and the gaps between the plurality of dummy wirings 41 are filled. This makes it possible to reduce the thickness of the insulating layer 4 and promote thinning of the flexible printed wiring board.

Next, the photosensitive dry film after thermal lamination is masked, and exposure is performed to irradiate light such as ultraviolet rays in accordance with required areas or wiring patterns. Thereafter, by performing a development step, the masked portions that were not irradiated with ultraviolet rays are dissolved and removed, and a solder resist film with high dimensional and shape accuracy can be formed. Thereafter, by performing thermosetting, the thermosetting resin component is cured and the resist film is stabilized. The temperature conditions for the thermosetting may be, for example, 85° C. and 60 minutes.

According to the flexible printed wiring board, when forming an insulating layer using a thermosetting resin, warping of the base film of the flexible printed wiring board due to heat shrinkage after curing of the thermosetting resin can be suppressed, and stability is achieved. You can get the quality you want.

[Other embodiments]
The embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is not limited to the configuration of the above embodiments, but is indicated by the claims, and is intended to include all changes within the meaning and range equivalent to the claims. Ru.

For example, in the flexible printed wiring board, the arrangement pattern of the planar coil wiring is not limited. Further, the flexible printed wiring board may include wiring other than the planar coil 3 with the plurality of dummy wirings 41 interposed therebetween.

In each of the above embodiments, a laminate of a seed layer and an electroplated layer, or a structure in which this laminate is coated with a coating layer has been described as a specific structure of the plurality of wirings, but the specific layer structure of the plurality of wirings is The configuration is not limited to the configuration described in the above embodiment. Furthermore, the configurations of the seed layer and the electroplated layer are not limited, and may be a laminate of two or more electroplated layers, for example.

In manufacturing the flexible printed wiring board, a planar coil may be laminated on the base film using a method other than the semi-additive method in the conductive pattern installation step.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Test Example 1 to Test Example 6]
As Test Examples 1 to 6, as shown in FIGS. 3 and 4, a line and space (L/S) of 20 μm/20 μm was formed on the surface side of a test piece of a rectangular polyimide base film 2 with each side of 200 μm. A flexible printed wiring board 10 was designed that includes a plurality of parallel, straight, copper wires 15. Arrow X indicates the main shrinkage direction (direction in which the base film 2 shrinks most easily). Further, in the flexible printed wiring board 10, a molded product 14 of photosensitive dry film resin having the same shape is arranged between a plurality of wirings 15. The average height of the wiring 15 and the molded product 14 made of epoxy-acrylic photosensitive dry film resin was 45 μm, and the average thickness of the base film 2 was 12.5 μm. Table 1 shows the physical properties of the materials used for the flexible printed wiring board 10. Next, on the back side of the base film 2 of Test Examples 1 to 6, a wiring pattern having the same shape as the above-mentioned front side wiring pattern (L/S = 20 μm/20 μm) and having an average crossing angle shown in Table 2 is applied. Designed a copper wiring pattern.

[evaluation]
(Young's modulus)
Young's modulus was measured for Test Examples 1 to 6 in accordance with JIS-Z2280 (1993). Table 1 shows the Young's modulus of the dummy wiring, photosensitive dry film resin, and base film obtained for each sample.

(linear expansion coefficient)
For Test Examples 1 to 6, the linear expansion coefficient of the dummy wiring was measured in accordance with JIS-Z2285 (2003). The linear expansion coefficients of the photosensitive dry film resin and base film were measured in accordance with JIS-K7197 (2012). Table 1 also shows the linear expansion coefficients of the dummy wiring, photosensitive dry film resin, and base film obtained for each sample.

(Amount of warpage of base film)
For Test Examples 1 to 6, the amount of warpage (%) of the base film 2 due to heat shrinkage when the temperature is changed from 180 ° C., which is the thermosetting temperature of the photosensitive dry film resin, to 20 ° C. (room temperature). Calculated. A rectangular test piece with a side length of 200 μm in the wiring area of the dummy wiring was used as the test piece. As mentioned above, the amount of warpage H (%) of the base film was calculated based on the following formula (1).
H=(y2-y1)×100/A...(1)
In formula (1), y2 is the maximum value of displacement in a direction component perpendicular to the surface of the base film with respect to the surface of the base film. y1 is the minimum value of the displacement in the direction component perpendicular to the surface of the base film.
Table 2 shows the amount of warpage (%) of the base film of the flexible printed wiring boards of Test Examples 1 to 6.

As shown in Table 1, in Test Examples 1 to 3 in which the average intersection angle between the front wiring and the back wiring in the base film was 30 degrees or less, 180°C, which is the thermosetting temperature of the photosensitive dry film resin, It can be seen that the amount of warpage (%) of the base film due to thermal shrinkage when the temperature is changed from .degree. C. to 20.degree. C. (room temperature) is 0.5% or less. The amount of warpage of this base film of 0.5% corresponds to a warpage of 0.1 mm with respect to the length of each coil substrate piece of 20 mm.

From the above, when forming an insulating layer using a thermosetting resin, the flexible printed wiring board can suppress warping of the base film of the flexible printed wiring board due to heat shrinkage after the thermosetting resin has cured. It was shown to be highly effective.

1, 10 Flexible printed wiring board 2 Base film 13 Land part 3 Planar coil 4 Insulating layer 5, 15 Wiring 14 Resin molded product 41 Dummy wiring X Main shrinkage direction

Claims (7)

A base film having insulation properties,
A planar coil provided on both sides of the base film,
a plurality of dummy wirings provided on both sides of the base film in a state of electrical insulation from the planar coil;
an insulating layer laminated on the base film, the planar coil, and the dummy wiring;
A flexible printed wiring board in which the average intersection angle between the dummy wiring on the front surface and the dummy wiring on the back surface of the base film is 30 degrees or less. The flexible printed wiring board according to claim 1, wherein the average line width of the plurality of dummy wirings is 5 μm or more and 50 μm. The flexible printed wiring board according to claim 1 or 2, wherein the Young's modulus of the dummy wiring is 40,000 MPa or more and 130,000 MPa or less. 4. The flexible printed wiring board according to claim 1, wherein the base film contains polyimide, polyethylene terephthalate, liquid crystal polymer, or fluororesin as a main component. The flexible printed wiring board according to any one of claims 1 to 4, wherein the insulating layer contains a cured product of a photosensitive dry film. The flexible printed wiring board according to any one of claims 1 to 5, wherein the ratio of the area of the wiring area of the dummy wiring to the area of the surface of the base film is 60% or more. Claims 1 to 3, wherein the amount of warpage H (%) of the base film expressed by the following formula (1) of a rectangular test piece with a side length A in the wiring area of the dummy wiring is 0.50 or less. The flexible printed wiring board according to any one of Item 6.
H=(y2-y1)×100/A...(1)
(In formula (1), y2 is the maximum displacement amount of the component in the direction perpendicular to the surface of the base film, with the surface of the base film as a reference. y1 is the displacement amount of the component in the direction perpendicular to the surface of the base film. (This is the minimum value of the amount of displacement.)

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