JP2022135197A - flexible printed wiring board - Google Patents

Abstract

To provide a flexible printed wiring board which is superior in uniformity of a thickness of a wiring layer and reduced in dimensional change.SOLUTION: A flexible printed wiring board of an embodiment herein disclosed comprises: a base film; a wiring layer laminated on at least on one face side of the base film and having one or more wiring lines; and one or more plated parts laminated apart from the wiring layer so as to be electrically isolated in a predetermined first region included in a wiring layer non-laminated region included in the at least one face side of the base film. In plan view, a first ratio of an area of a formation region of the one or more plated parts on the first region to an area of the first region is 25% or more and 75% or less. In the first region, the ratio of two linear expansion coefficients of first and second directions, which are in parallel with the base film, and orthogonal to each other, is 0.5 or more and 2.0 or less.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to flexible printed wiring boards.

Flexible printed wiring boards are widely used to form circuits of various electronic devices. In recent years, with the miniaturization of electronic equipment, the miniaturization of flexible printed wiring boards and the increase in wiring density thereof have been remarkable.

As such a small flexible printed wiring board, there has been proposed one comprising a sheet-like insulating base material and a wiring layer having wiring laminated on the surface of this base material by plating (Japanese Patent Application Laid-Open No. 2018- 195681).

JP 2018-195681 A

Here, in a flexible printed wiring board in which a wiring layer is formed by plating, there is a possibility that a wiring layer having an uneven thickness is formed.

On the other hand, in the flexible printed wiring board, the wiring layer may be covered with an insulating coating layer. In this case, the dimensions of the wiring board may change due to heating during coating. If the dimensions change in this way, there is a risk that problems such as misalignment of the through-holes (sinking) and mounting failures may occur.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a flexible printed wiring board in which wiring layer thickness uniformity is excellent and dimensional change is reduced.

A flexible printed wiring board according to one aspect of the present disclosure, which has been made to solve the above problems, includes a base film and a wiring layer having one or more wires laminated on at least one surface side of the base film wherein the at least one surface side of the base film includes a non-laminated area that is an area where the wiring layer is not laminated, the non-laminated area includes a first area, and the first One region further includes one or a plurality of plated portions stacked with a gap from the wiring layer so as to be electrically isolated, and the first region is a region within a shortest distance of 15 mm from the wiring layer. and a first ratio, which is a ratio of the area of the plating portion formation region on the first region to the area of the first region in plan view, is 25% or more and 75% or less, and A ratio of two linear expansion coefficients in a first direction and a second direction, which are directions parallel to the base film and perpendicular to each other, is 0.5 or more and 2.0 or less.

A flexible printed wiring board according to an aspect of the present disclosure has excellent thickness uniformity of the wiring layer and reduced dimensional change.

FIG. 1 is a schematic plan view showing a flexible printed wiring board according to one embodiment. FIG. 2 is a schematic end view showing the flexible printed wiring board in FIG. 1, and is a schematic end view in the direction of arrow AA in FIG. FIG. 3 is a schematic plan view showing an example of the arrangement of triangular gaps in a grid-like plated portion by the arrangement of the centers of gravity of the gaps. FIG. 4 is a schematic plan view showing another arrangement example of the triangular gaps in the grid-like plated portion by the arrangement of the centers of gravity of the gaps. 5 is a schematic end view for explaining the method of manufacturing the flexible printed wiring board of FIG. 1, and is a schematic end view viewed in the same direction as the arrow AA direction of FIG. 1. FIG. 6 is a schematic end view for explaining the manufacturing method of the flexible printed wiring board of FIG. 1, and is a schematic end view viewed in the same direction as the arrow AA direction of FIG. 1. FIG.

[Description of Embodiments of the Present Disclosure]
A flexible printed wiring board according to an aspect of the present disclosure is a flexible printed wiring board comprising a base film and a wiring layer having one or more wirings laminated on at least one side of the base film. and the at least one surface side of the base film includes a non-laminated region where the wiring layer is not laminated, the non-laminated region includes a first region, and is electrically isolated from the first region. The first region is a region with a shortest distance of up to 15 mm from the wiring layer, and when viewed from above, the first region A first ratio, which is a ratio of the area of the plating portion forming region on the first region to the area of one region, is 25% or more and 75% or less, and the first regions are parallel to the base film. and a ratio of two linear expansion coefficients in the first direction and the second direction, which are directions perpendicular to each other, is 0.5 or more and 2.0 or less.

Here, the inventors of the present invention obtained the following knowledge as a result of earnest research. That is, as the area of the plated portion occupied in the first region increases, the rigidity of the flexible printed wiring board as a whole increases and the dimensional change decreases, while the thickness variation of the wiring layer tends to increase. Conversely, as the area of the forming region of the plating portion occupied by the first region becomes smaller, the variation in the thickness of the wiring layer becomes smaller, while the rigidity of the flexible printed wiring board as a whole becomes smaller, resulting in a larger dimensional change. There is a tendency. In addition, the closer the coefficients of linear expansion in the two mutually orthogonal directions in the first region are, the smaller the dimensional change of the flexible printed wiring board tends to be.

Therefore, according to the knowledge described above, when the first ratio of the area of the formation region of the plated portion in the first region is equal to or less than the upper limit, variations in the thickness of the wiring layer can be reduced. Thereby, the flexible printed wiring board is excellent in thickness uniformity. When the first ratio is equal to or higher than the lower limit, dimensional change of the flexible printed wiring board as a whole is reduced. In addition, since the ratio of the coefficients of linear expansion in the two directions in the first region is within the above range, the coefficients of linear expansion in the two directions of the first region are relatively close to each other, and the flexible printed wiring The placement balance of the metal portion of the plate that is harder (higher in rigidity) than the base film is improved. Thus, even if the ratio of the linear expansion coefficients in the two directions is within the above range, the dimensional change of the flexible printed wiring board as a whole is reduced. Therefore, the flexible printed wiring board is excellent in the uniformity of the thickness of the wiring layer, and the dimensional change is reduced.

A difference between the first ratio and a second ratio, which is a ratio of the area of the wiring layer formation region to the area of the region surrounded by the periphery of the wiring layer in plan view, is within 10% in absolute value. Good.

Since the difference between the first ratio and the second ratio is within the above range, the area ratio of the wiring layer forming region and the area ratio of the plating portion forming region are relatively high. Since the values are close to each other, the arrangement balance of the metal portion that is harder (higher in rigidity) than the base film is further improved in the flexible printed wiring board. This further reduces the dimensional change of the flexible printed wiring board.

A coefficient of linear expansion in a third direction, which is a direction parallel to the base film and inclined at an angle of 45° to both the first direction and the second direction, with respect to the coefficient of linear expansion in the first direction in the first region is preferably 0.5 or more and 2.0 or less.

Since the ratio of the coefficient of linear expansion in the third direction to the coefficient of linear expansion in the first direction is within the above range, the coefficients of linear expansion in the three directions are relatively close to each other. This further reduces the dimensional change of the flexible printed wiring board.

The ratio of the Young's modulus in the second direction to the Young's modulus in the first direction in the first region is 0.1 or more and 10 or less, and the ratio of the Young's modulus in the third direction to the Young's modulus in the first direction in the first region is The Young's modulus ratio is preferably 0.1 or more and 10 or less.

Thus, the ratio of the Young's modulus in the second direction to the Young's modulus in the first direction is within the above range, and the ratio of the Young's modulus in the third direction to the Young's modulus in the first direction is within the above range. As a result, the Young's moduli in the three directions are relatively close to each other. This further reduces the dimensional change of the flexible printed wiring board.

It is preferable that the plated portion has a shape in which a plurality of linear portions that are inclined to each other in a plan view are connected.

Thus, the flexible printed wiring board in which the first ratio of the first region is within the above range and the ratio of the coefficients of linear expansion is within the above range is provided by the plating portion having the above shape. Easier to manufacture. Moreover, it becomes easy to produce the flexible printed wiring board in which the ratio of the Young's moduli is within the above range. Therefore, the thickness uniformity of the wiring layer is more reliably excellent, and the dimensional variation of the flexible printed wiring board is reduced.

It is preferable that the plated portion has a polygonal line shape, a wave shape, a lattice shape having polygonal gaps, or a combination of these shapes in plan view.

Thus, the flexible printed wiring board in which the first ratio of the first region is within the above range and the ratio of the coefficients of linear expansion is within the above range is provided by the plating portion having the above shape. Easier to manufacture. Moreover, it becomes easier to produce the flexible printed wiring board in which the Young's modulus ratio is within the above range. Therefore, the thickness uniformity of the wiring layer is more reliably improved, and the dimensional variation of the flexible printed wiring board is reduced.

Here, "the first region within a shortest distance of 15 mm from the wiring layer" means a region within a minimum distance of 15 mm from the region surrounded by the periphery of the wiring layer. "A region surrounded by the periphery of the wiring layer" means, when the wiring layer has one wiring that is not formed in a winding shape (that is, does not have a portion adjacent to each other in the width direction), this wiring (i.e., the wiring itself), and when the wiring layer has one wiring formed in a winding shape (i.e., having a portion adjacent in the width direction), the most edge and a virtual line segment connecting the edges of these peripheral edges at the shortest distance (including gaps in wiring), and when a wiring layer has multiple wiring , a plurality of peripheral edges of a plurality of wirings positioned at the extreme ends of these wirings, and an area drawn together with the peripheral edges by a virtual line segment connecting the edges of these peripheral edges at the shortest distance (a plurality of wirings and each wiring). (including gaps in wiring).

The “area of the plated portion formation region” means the area of the portion where the plated portion is formed in the first region. This area is the planar view area of the plated portion itself (not including the gap in the plated portion) formed in the first region. "The coefficient of linear expansion of the first region" means the value of the coefficient of linear expansion measured for a piece obtained by cutting the first region from the flexible printed wiring board. The “area of the wiring layer forming region” means the area of the wiring layer itself (not including the gap in the wiring) formed on the base film. The "ratio of two linear expansion coefficients in the first direction and the second direction" means the ratio of the second linear expansion coefficient to the linear expansion coefficient in the first direction. "Young's modulus of the first region" means the value of Young's modulus measured for the cut piece.

[Details of the embodiment of the present disclosure]
EMBODIMENT OF THE INVENTION Hereinafter, it explains in full detail, referring drawings for embodiment of the flexible printed wiring board which concerns on this indication, and its manufacturing method. In the present embodiment, the "front side" refers to the side on which the wiring layer is laminated in the thickness direction of the base film, and the front and back sides of the flexible printed wiring board in the usage state of the flexible printed wiring board. It is not determinative.

[Flexible printed wiring board]
As shown in FIGS. 1 and 2, a flexible printed wiring board 10 of the present embodiment includes a base film 3 having insulating properties and wiring 13 laminated on one side (surface side) of the base film 3. and a wiring layer 11 having the wiring layer 11 . One surface side (surface side) of the base film 3 includes a non-laminated area K, which is an area where the wiring layer 11 is not laminated, and the non-laminated area K includes a first area K1 described later. The flexible printed wiring board 10 further includes a plated portion 41 spaced apart from the wiring layer 11 in the first region K1. The flexible printed wiring board 10 may further include a cover film (covering layer) on the surface side of the base film 3 or the wiring layer 11 . In this embodiment, the non-laminated area K and the first area K1 are aligned. Further, FIG. 1 omits the specific shape of the plated portion 41 formed in the first region K1 of the non-laminated region K, but FIG. It is formed.

<Base film>
The base film 3 is an insulating synthetic resin layer. The base film 3 also has flexibility. This base film 3 is also a base material for forming the wiring layer 11 . The material for forming the base film 3 is not particularly limited as long as it has insulating properties and flexibility. Main components of this synthetic resin film include, for example, polyimide, polyethylene terephthalate, liquid crystal polymer, and fluororesin. A "main component" is a component with the largest content, and means, for example, a component that accounts for 50% by mass or more in the forming material. The base film 3 may contain a resin other than the exemplified resin such as polyimide, an antistatic agent, and the like.

Although the lower limit of the average thickness of the base film 3 is not particularly limited, it is preferably 3 μm, preferably 5 μm, and more preferably 10 μm. The upper limit of the average thickness of the base film 3 is not particularly limited, but is preferably 200 µm, more preferably 150 µm, and even more preferably 100 µm. If the average thickness of the base film 3 is less than the above lower limit, the insulating strength and mechanical strength of the base film 3 may become insufficient. On the other hand, if the average thickness of the base film 3 exceeds the above upper limit, the flexible printed wiring board 10 may become unnecessarily thick. Here, "average thickness" means an average value of thicknesses measured at arbitrary ten points.

<Wiring layer>
The wiring layer 11 is laminated on the surface side of the base film 3 directly or via another layer. Examples of the wiring 13 included in the wiring layer 11 include a signal line for sending signals, a current line for sending current for power supply, and a current line for sending current for generating a magnetic field. In the present embodiment, the case where the wiring 13 is a current line for generating a magnetic field, that is, a coil wire will be described, but the wiring 13 is not limited to this.

The wiring 13 is formed in a spiral shape (wound shape) and has a land portion 13a at its inner end portion. Note that the winding 13 may have a land portion at its outer end. Also, the wiring 13 may have two lands at the inner end and the outer end, respectively.

The wiring 13 is composed of a first conductive underlayer 23 laminated on the surface side of the base film 3 and a plating layer for wiring laminated on the opposite side (surface side) of the first conductive underlayer 23 to the base film 3. 25. The first conductive base layer 23 is formed by part of a conductive base layer M (see FIG. 5, for example), which will be described later.

Materials for forming the first conductive base layer 23 include, for example, copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), and alloys thereof. be done. Regarding these forming materials, in terms of suppressing thermal deterioration of the adhesion of the wiring layer 11 to the base film 3, the side of the first conductive underlying layer 23 in contact with the base film 3 (for example, polyimide) contains the above nickel and chromium. , titanium and silver (first layer). Furthermore, it is more preferable that the first conductive underlayer 23 includes a layer (first layer) containing at least one selected from nickel and chromium, which are easy to remove and easy to maintain insulation. Further, it is more preferable that the first conductive underlayer 23 includes a layer (second layer) containing copper as a main component on the upper side of the first layer (the side opposite to the base film 3). By arranging the layer containing copper as a main component, it is possible to shorten the work time when forming the wiring layer 11 by electroplating.

For example, the lower limit of the average thickness of the first layer is preferably 1 nm, more preferably 2 nm. The upper limit of the average thickness of the first layer is preferably 15 nm, more preferably 8 nm. If the average thickness is less than the lower limit, it may be difficult to suppress thermal deterioration of the adhesion of the wiring layer 11 to the base film 3 . On the other hand, if the average thickness exceeds the upper limit, the first layer will be difficult to remove, and the insulating properties of the wiring layer 11 may not be sufficiently maintained. This first layer can be formed by a sputtering method, an electroplating method, an electroless plating method, or the like.

For example, the lower limit of the average thickness of the second layer is preferably 0.1 μm, more preferably 0.2 μm. The upper limit of the average thickness of the second layer is preferably 2 μm, more preferably 1 μm. If the average thickness is less than the lower limit, the time required to form the wiring layer 11 by electroplating may become excessively long. On the other hand, if the average thickness exceeds the upper limit, the second layer will be difficult to remove, and there is a risk that sufficient insulation between the wirings 13 (between the windings in FIG. 1) cannot be maintained. The second layer is preferably formed by a sputtering method, an electroplating method, an electroless plating method, or the like, and may be formed by combining these methods. In particular, it is preferable to arrange the electroless copper plating layer on the uppermost surface side of the first conductive base layer 23, so that when the inner layer is formed by the sputtering method, it may occur due to this sputtering method. Defects etc. can be covered.

Examples of the first metal material for forming the wiring plating layer 25 include copper, aluminum, silver, gold, nickel, and alloys thereof. Among these, copper or a copper alloy is preferable from the viewpoint of improving conductivity and reducing costs. For example, the wiring plating layer 25 is formed in the same shape as the first conductive underlying layer 23 in plan view (viewed in a direction perpendicular to the base film 3).

The second ratio, which is the ratio of the area of the region where the wiring layer 11 is formed to the area of the region surrounded by the periphery of the wiring layer 11, is not particularly limited and is set as appropriate. For example, the lower limit of the second ratio is preferably 25%, more preferably 30%, and even more preferably 40%. The upper limit of the second ratio is preferably 75%, more preferably 70%, and even more preferably 60%. If the second ratio is less than the lower limit, the flexible printed wiring board 10 may undergo a large dimensional change. On the other hand, if the second ratio exceeds the upper limit, there is a possibility that the film thickness will vary greatly.

The lower limit of the average line width L of the wiring 13 is preferably 5 μm, more preferably 10 μm, and even more preferably 15 μm. The upper limit of the average line width L of the wiring 13 is preferably 100 μm, more preferably 75 μm, and even more preferably 50 μm. If the average line width L of the wiring 13 is less than the above lower limit, there is a risk that the electrical resistance of the wiring 13 will become too large and that the mechanical strength will be insufficient. On the other hand, if the average line width L of the wiring 13 exceeds the upper limit, there is a possibility that space saving cannot be achieved. Here, the "average line width" means a value obtained by averaging the maximum width of a cross section of one wiring 13 perpendicular to the longitudinal direction in the longitudinal direction. "Line width" means a dimension in a direction perpendicular to the longitudinal direction. The "average line width" is calculated by exposing the cross section of the wiring board 10 with a cross-section processing device such as a microtome, measuring the length of the widest portion of the wiring 13 with a microscope capable of measuring, and calculating the average value thereof. be done. In the following description, the "average line width" of other members is also a value measured in the same manner.

In addition, a land portion having vias (through holes, blind vias, filled vias) for connecting between the wirings 13, a land portion connecting to mounted parts, a land portion for connecting to other printed circuit boards and connectors, etc. The land portion of is excluded from the "line width" defined above and below. In addition, this land portion is also excluded from the "gap" and "thickness" defined below.

The lower limit of the average interval S between adjacent wirings 13 is preferably 5 μm, more preferably 10 μm, and even more preferably 15 μm. The upper limit of the average interval S of the wirings 13 is preferably 100 μm, more preferably 75 μm, and even more preferably 25 μm. If the average interval S of the wirings 13 is less than the above lower limit, a short circuit may occur. On the other hand, if the average interval S of the wirings 13 exceeds the above upper limit, there is a possibility that space saving cannot be achieved. Here, the "average spacing" is a value obtained by averaging the distance between adjacent surfaces of two wires 13 (two winding portions in FIG. 1) in the longitudinal direction (winding direction in FIG. 1) of the wires 13. means. A "gap" means a distance between opposing adjacent faces of two wirings 13 (two windings in FIG. 1). This "average spacing" can be obtained by exposing the cross section of the wiring board 10 with a cross-section processing device such as a microtome, and measuring the length of the smallest spacing in the gap between the wirings 13 (between the windings in FIG. 1). measured with a microscope or the like, and calculated as their average value. In the following description, the "average spacing" of other members is also a value measured in the same manner.

As a minimum of average thickness of wiring 13, 7 micrometers is preferred, 15 micrometers is more preferred, and 20 micrometers is still more preferred. The upper limit of the average thickness of the wiring 13 is preferably 100 μm, more preferably 80 μm, and even more preferably 60 μm. If the average thickness is less than the lower limit, the electrical resistance of the wiring 13 may increase. On the other hand, if the average thickness exceeds the upper limit, the line width must be increased to form the wiring 13, and space saving may not be achieved. Here, “average thickness” means an average value of thicknesses measured at arbitrary ten points of one wiring 13 . "Thickness" means the distance between the base film and the upper edge of the wiring 13 in the direction perpendicular to this base film. The "average thickness" is obtained by exposing the cross section of the wiring board 10 with a cross section processing device such as a microtome, measuring the thickness of the wiring 13 by observing the cross section at arbitrary ten points, and calculating the average value of the measurement results. can get. In addition, the "average thickness" of other members etc. below is also a value measured similarly to this.

The average thickness, maximum line width, etc. of the land portion 13a can be appropriately set.

<Plating part>
The one or more plated parts 41 are laminated on the first area K1 included in the non-laminated area K of the wiring layer 11 on the surface side of the base film 3 with a gap from the wiring layer 11 so as to be electrically isolated. . In this way, the plated portion 41 is a plated layer that is electrically isolated so as not to conduct, and corresponds to a non-wiring (dummy) wiring. The plating portion 41 has a second conductive base layer 43 and a non-wiring (dummy) plating layer 45 laminated on the second conductive base layer 43 . The first region K1 is a region within a shortest distance of 15 mm from the wiring layer 11 . As described above, depending on the dimensions of the base film in plan view, the non-laminated area K and the first area K1 may coincide with each other as in the present embodiment.

The second conductive base layer 43 is formed of a part of a conductive base layer M (see FIG. 5, for example), which will be described later. As the second conductive base layer 43, the same materials as the first conductive base layer 23 can be used. The average thickness of the second conductive base layer 43 can be set similarly to the first conductive base layer 23 .

Materials for forming the non-wiring plating layer 45 include the same materials as the first metal material described above.

The plating portion 41 is defined by the formation of the plating portion 41 in the first region K1 with respect to the area of the first region K1 when viewed in a plan view, that is, in a direction perpendicular to the base film 3 (a direction perpendicular to the paper surface of FIG. 1). It is formed so that the first ratio, which is the area ratio of the region, is 25% or more and 75% or less. The plating portion 41 can be formed on the outer non-laminated region, the inner non-laminated region, or both the inner and outer sides of the wiring layer 11 . In the present embodiment, as an example, a case where the plated portion 41 is formed in the non-laminated region K outside the wiring layer 11 will be described.

Here, regarding the first region K1, if at least a portion of the non-laminated region K of the wiring layer 11 is less than 15 mm from the wiring layer 11 at the shortest distance, this portion is limited to the periphery of the non-laminated region K. shall be a region. In addition, this portion has a region with a shortest distance of at least 1 mm or more from the wiring layer 11 (a region separated from the wiring layer 11 to the periphery by 1 mm or more).

The lower limit of the first ratio is 25% as described above, preferably 30%, more preferably 40%. The upper limit of the first ratio is 75% as described above, preferably 70%, more preferably 60%. If the first ratio is less than the lower limit, the dimensional change of the flexible printed wiring board 10 may not be sufficiently reduced. On the other hand, if the first ratio exceeds the upper limit, the flexible printed wiring board 10 may have inferior uniformity in the thickness of the wiring layer 11 .

The absolute value of the difference between the first ratio and the second ratio (the ratio of the area of the wiring layer 11 formation region to the area of the region surrounded by the periphery of the wiring layer 11 in plan view) is 10. % or less is preferable, and 5% or less is more preferable. If the difference does not satisfy the above range, the area occupied by the metal portion differs greatly between the lamination region of the wiring layer 11 and the lamination region of the plating portion 41, and as a result, the flexible printed wiring board 10 may undergo a large dimensional change. There is Note that the lamination region of the wiring layer 11 (or the wiring 13) is a region surrounded by the periphery of the wiring layer 11 (or the wiring 13) on the base film 3 and includes a gap in the wiring layer 11. Say. Further, the laminated region of the plated portion 41 is a region surrounded by the periphery of the plated portion 41 in the non-laminated region K and includes a gap in the plated portion 41, which is the first region K1 here. .

The plating portion 41 may be laminated on the base film 3 so that the first ratio in the first region K1 is within the above range. The formation area ratio (occupancy ratio) is not particularly limited and is set as appropriate. For example, even in regions other than the first region K1 in the non-laminated region K, the occupation ratio of the plated portion 41 in this region can be set within the above range.

The plated portion 41 has a linear expansion of 2 in a first direction (X direction in FIG. 1) and a second direction (Y direction in FIG. 2), which are directions parallel to and orthogonal to the base film 3 in the first region K1. It is formed so that the ratio of coefficients is 0.5 or more and 2.0 or less.

The ratio of the linear expansion coefficients in the first direction and the second direction ((linear expansion coefficient in the second direction) / (linear expansion coefficient in the first direction)), that is, the lower limit of the first linear expansion coefficient ratio is 0.5, preferably 0.7, more preferably 0.9. The upper limit of the first linear expansion coefficient ratio is 2.0 as described above, preferably 1.5, and more preferably 1.2. When the first linear expansion coefficient ratio is less than the lower limit and when the first linear expansion coefficient ratio exceeds the upper limit, the linear expansion coefficient balance between the first direction and the second direction (anisotropic ) may deteriorate and dimensional change may increase.

The linear expansion coefficients of the first region K1 in directions other than the two directions can be set as follows, for example. For example, a third direction ( Z direction in FIG. 1) linear expansion coefficient ratio ((third direction linear expansion coefficient) / (first direction linear expansion coefficient)), that is, the lower limit of the second linear expansion coefficient ratio is 0.5 Preferably, 0.7 is more preferable, and 0.9 is even more preferable. The upper limit of the second linear expansion coefficient ratio is preferably 2.0, more preferably 1.5, and even more preferably 1.2. When the second linear expansion coefficient ratio is less than the lower limit and when the second linear expansion coefficient ratio exceeds the upper limit, the coefficient of linear expansion is different between the first and second directions and the third direction. Further improvement of balance may become difficult.

Each linear expansion coefficient in the first direction, the second direction, and the third direction is not particularly limited, and can be appropriately set so as to satisfy the above ratios. For example, the lower limit of the coefficient of linear expansion in the first direction is preferably 14 ppm/K, more preferably 16 ppm/K, and even more preferably 25 ppm/K. The upper limit of the coefficient of linear expansion in the first direction is preferably 100 ppm/K, more preferably 50 ppm/K, and even more preferably 30 ppm/K. When the coefficient of linear expansion in the first direction is less than the lower limit or exceeds the upper limit, the difference in linear expansion coefficient between the lamination region of the wiring 13 and the lamination region of the plating portion 41 increases, The linear expansion coefficients in wiring board 10 may become unbalanced.

For example, the lower limit of the coefficient of linear expansion in the second direction is preferably 14 ppm/K, more preferably 16 ppm/K, and even more preferably 25 ppm/K. The upper limit of the coefficient of linear expansion in the second direction is preferably 100 ppm/K, more preferably 50 ppm/K, and even more preferably 30 ppm/K. When the coefficient of linear expansion in the second direction is less than the lower limit or exceeds the upper limit, the difference in linear expansion coefficient between the lamination region of the wiring 13 and the lamination region of the plating portion 41 increases, The linear expansion coefficients in wiring board 10 may become unbalanced.

For example, the lower limit of the coefficient of linear expansion in the third direction is preferably 14 ppm/K, more preferably 16 ppm/K, and even more preferably 25 ppm/K. The upper limit of the coefficient of linear expansion in the third direction is preferably 100 ppm/K, more preferably 50 ppm/K, and even more preferably 30 ppm/K. When the coefficient of linear expansion in the third direction is less than the lower limit or exceeds the upper limit, the difference in linear expansion coefficient between the lamination region of the wiring 13 and the lamination region of the plating portion 41 increases, The linear expansion coefficients in wiring board 10 may become unbalanced.

The coefficient of linear expansion in directions other than the first direction, the second direction, and the third direction in the first region K1 is not particularly limited. For example, the coefficients of linear expansion in directions other than the three directions in the first region K1 may be set to have the same relationship as the coefficients of linear expansion in the three directions.

In addition to the relationship between the linear expansion coefficients in the first region K1, for example, the relationship between the Young's moduli in the first direction, the second direction, and the third direction in the first region K1 can be appropriately set. For example, the ratio of the Young's modulus in the second direction to the Young's modulus in the first direction in the first region K1 ((Young's modulus in the second direction)/(Young's modulus in the first direction)), that is, the first Young's modulus ratio The lower limit is preferably 0.1, more preferably 0.2, and even more preferably 0.5. The upper limit of the first Young's modulus ratio is preferably 10, more preferably 5, and even more preferably 2. In addition, the ratio of the Young's modulus in the third direction to the Young's modulus in the first direction in the first region K1 ((Young's modulus in the third direction)/(Young's modulus in the first direction)), that is, the second Young's modulus The lower limit of the ratio is preferably 0.1, more preferably 0.2, and even more preferably 0.5. The upper limit of the second Young's modulus ratio is preferably 10, more preferably 5, and even more preferably 2. When the first Young's modulus ratio and the second Young's modulus ratio are less than the lower limit or exceed the upper limit, the balance of Young's modulus between the first direction, the second direction, and the third direction is further improved. Improvement may be difficult.

Each Young's modulus in the first direction, the second direction, and the third direction is not particularly limited, and can be appropriately set so as to satisfy the above ratios. For example, the lower limit of the Young's modulus in the first direction is preferably 4000 MPa, more preferably 10000 MPa, and even more preferably 20000 MPa. The upper limit of the Young's modulus in the first direction is preferably 100000 MPa, more preferably 70000 MPa, and even more preferably 50000 MPa. When the Young's modulus in the first direction is less than the lower limit or exceeds the upper limit, the difference in Young's modulus between the lamination region of the wiring 13 and the lamination region of the plating portion 41 becomes large, resulting in balance of Young's modulus. may get worse.

For example, the lower limit of the Young's modulus in the second direction is preferably 4000 MPa, more preferably 10000 MPa, and even more preferably 20000 MPa. The upper limit of the Young's modulus in the second direction is preferably 100000 MPa, more preferably 70000 MPa, and even more preferably 50000 MPa. When the Young's modulus in the second direction is less than the lower limit or exceeds the upper limit, the difference in Young's modulus between the lamination region of the wiring 13 and the lamination region of the plating portion 41 becomes large, resulting in balance of Young's modulus. may get worse.

For example, the lower limit of the Young's modulus in the third direction is preferably 4000 MPa, more preferably 10000 MPa, and even more preferably 20000 MPa. The upper limit of the Young's modulus in the third direction is preferably 100000 MPa, more preferably 70000 MPa, and even more preferably 50000 MPa. When the Young's modulus in the third direction is less than the lower limit or exceeds the upper limit, the difference in Young's modulus between the lamination region of the wiring 13 and the lamination region of the plating part 41 becomes large, resulting in balance of Young's modulus. may get worse.

The Young's modulus in directions other than the first direction, the second direction, and the third direction in the first region K1 is not particularly limited. For example, the Young's moduli in directions other than the three directions in the first region K1 may be set to have the same relationship as the Young's moduli in the three directions.

The shape of the plated portion 41 is not particularly limited as long as the area ratio and the linear expansion coefficient ratio are satisfied, and can be set as appropriate. Further, the shape of the plated portion 41 can be appropriately set, for example, so as to satisfy the ratio of Young's modulus. For example, the plated portion 41 may be formed to have a shape in which a plurality of linear portions that are inclined to each other in plan view (in the paper surface direction of FIG. 1) are connected.

Thus, the flexible printed wiring board in which the first ratio of the first region K1 is within the above range and the ratio of the coefficients of linear expansion is within the above range by virtue of the plated portion 41 having the above shape. 10 becomes easier to produce. Moreover, it becomes easy to produce the flexible printed wiring board 10 in which the Young's modulus ratio is within the above range. Therefore, the thickness uniformity of the wiring layer 11 is more reliably excellent, and the dimensional variation of the flexible printed wiring board 10 is reduced.

Examples of the shape of the plated portion 41 include a polygonal line shape, a wave shape, a grid shape having polygonal gaps, and a combination of these shapes in a plan view. With the plated portion 41 having these shapes, the flexible printed wiring board 10 in which the first ratio of the first region K1 is within the above range and the ratio of the linear expansion coefficients is within the above range is more improved. Easier to manufacture. In addition, it becomes easier to manufacture the flexible printed wiring board 10 in which the Young's modulus ratio is within the above range. Therefore, the thickness uniformity of the wiring layer 11 is more reliably excellent, and the dimensional variation of the flexible printed wiring board 10 is reduced.

Although illustration is omitted, the plated portion 41 having such a shape is formed, for example, as follows.

(Shape example 1 of plated part: lattice shape (honeycomb shape))
For example, a grid-like (honeycomb shape) shape having a plurality of hexagonal (e.g., regular hexagon) gaps in plan view, and these plural gaps form an acute angle (e.g., 60 ° or an obtuse angle) with each other in two directions ( Although illustration is omitted, it is formed so as to be arranged along, for example, the horizontal direction and the oblique direction from the lower left to the upper right in FIG. The width of the grid of the gaps, the size of the gaps, and the like are not limited, and may be determined so that the first ratio and the ratio of the coefficient of linear expansion are within the above range. For example, it is preferable that the width of the grid, the size of the gap, and the like be substantially uniform over the entire formation area of the plated portion. The fact that the width of the grid, the size of the gap, etc. are not limited in this way also applies to other grid shapes and corrugated shapes hereinafter.

(Shape example 2 of plated part: lattice shape (triangular shape 1))
For example, the plated portion 41 has a grid shape with a plurality of triangular (e.g., isosceles triangles, equilateral triangles) gaps, and the plurality of gaps are arranged in two directions perpendicular to each other (e.g., left-right direction and up-down direction in FIG. 1). formed to be arranged along. For example, as shown in FIG. 3, a plurality of triangles, which are shapes of gaps, are formed such that their respective centers of gravity G1 are arranged at respective positions shown in FIG. In FIG. 3, a plurality of centers of gravity G1 are arranged along two mutually orthogonal directions (horizontal direction and vertical direction) in FIG. They are arranged so as to be symmetrical with respect to each other with an imaginary straight line X1 passing through the plurality of centers of gravity G1 as an axis of symmetry. More specifically, in FIG. 3, a plurality of upward triangles having a center of gravity G1 and vertices facing upward and a plurality of downward triangles having a center of gravity G1 and vertices facing downward alternately. placed. In this case, the sides (bases) facing the upward vertices of adjacent upward triangles are intermittently (spaced from each other) on a straight line, and connecting these bases forms a straight line along the left-right direction in FIG. becomes. Similarly, the sides (bases) facing the downward vertices of adjacent downward triangles are intermittently (spaced apart) on a straight line. Become. In addition, a plurality of gravity centers G1 are arranged so that four adjacent gravity centers G1 form a quadrangle, and this rhombus is continuously repeated in the vertical and horizontal directions without gaps. The gaps between the triangles are formed according to the placement of these centers of gravity G1 and so that a grid is formed (that is, the triangles are spaced apart from each other). Also, the plurality of triangular gaps to be formed are arranged along the left-right direction and the up-down direction in FIG. 3 as a whole as described above.

(Shape example 3 of plated part: lattice shape (square shape 1))
For example, the plated portion 41 has a lattice shape with a plurality of square (for example, square) gaps, and the plurality of gaps form an acute angle (or an obtuse angle, for example, 45°) in two directions (not shown). 1 and diagonally from the lower left to the upper right). In this case, for example, each square has two sides (an upper side and a lower side in FIG. 1) along the horizontal direction of FIG. The upper sides of squares adjacent to each other in the left-right direction in FIG. Become. The same applies to the lower sides of the squares adjacent to each other in the horizontal direction. On the other hand, each square has two sides along the vertical direction in FIG. 1 (the left side and the right side in FIG. 1). It is not a straight line (the left sides are not aligned), and these left sides are offset to the left and right. The right side of the vertically adjacent squares is the same as the left side.

(Shape example 4 of plated part: corrugated shape 1)
For example, the plurality of plating portions 41 has a corrugated shape (zigzag shape) extending parallel to each other along one direction (not shown, but for example, the vertical direction in FIG. 1). The crests (for example, the vertices on the left side of FIG. 1) and the valleys (for example, the vertices on the right side of FIG. 1) of the mold-shaped plated portion are aligned on a straight line. becomes a straight line along Moreover, such a plurality of plated portions 41 are symmetrical with respect to the straight line connecting the peaks and symmetrical with respect to the straight line connecting the valleys.

(Shape example 5 of plated part: corrugated shape 2)
For example, the plurality of plated portions 41 has a corrugated shape (zigzag shape) extending in one direction (for example, the vertical direction in FIG. 1), and the center line between two (a pair of) corrugated plated portions adjacent to each other. (for example, the vertical direction in FIG. 1).

(Shape example 6 of plated part: lattice shape (triangular shape 2))
For example, the plated portion 41 has a grid shape with a plurality of triangular (e.g., isosceles triangles, equilateral triangles) gaps, and the plurality of gaps are arranged in two directions perpendicular to each other (e.g., left-right direction and up-down direction in FIG. 1). formed to be arranged along. More specifically, for example, as shown in FIG. 4, a plurality of triangular gaps are formed such that their respective centers of gravity G2 are arranged at respective positions shown in FIG. In FIG. 4, a plurality of centers of gravity G2 are arranged along two mutually orthogonal directions (horizontal direction and vertical direction) in FIG. They are arranged so as to be line-symmetrical with each other with an imaginary straight line X2 passing through the plurality of centers of gravity G2 as an axis of symmetry. More specifically, in FIG. 4, a plurality of upward triangles having a center of gravity G2 and vertices facing upward and a plurality of downward triangles having a center of gravity G2 and vertices facing downward alternately. placed. In this case, the sides (bases) facing the upward vertices of adjacent upward triangles are intermittently (spaced apart from each other) on a straight line, and connecting these bases forms a straight line along the left-right direction in FIG. becomes. Similarly, the sides (bases) facing the downward vertices of adjacent downward triangles are intermittently (spaced from each other) on a straight line, and connecting these bases forms a straight line along the left-right direction in FIG. Become. In addition, a plurality of gravity centers G2 are arranged such that six adjacent gravity centers G2 form a hexagon, and this hexagon is continuously repeated in the vertical and horizontal directions without gaps. The gaps between the triangles are formed according to the arrangement of these centers of gravity G2 and so that a grid is formed (that is, the triangles are spaced apart from each other). Also, the plurality of triangular gaps to be formed are arranged along the left-right direction and the up-down direction in FIG. 4 as a whole, as described above.

(Shape example 7 of plated part: grid shape (square shape 2))
For example, the plated portion 41 has a grid shape with a plurality of square (for example, square) gaps, and the plurality of gaps are arranged in two directions perpendicular to each other (not shown, but for example, the left-right direction and the up-down direction in FIG. 1). is formed to be arranged along the In this case, for example, each square has two sides (an upper side and a lower side in FIG. 1) along the horizontal direction of FIG. The upper sides of squares adjacent to each other in the left-right direction in FIG. Become. The same applies to the lower sides of the squares adjacent to each other in the horizontal direction. Similarly, each square has two sides (a left side and a right side in FIG. 1) extending vertically in FIG. The left sides of vertically adjacent squares in FIG. Become. The right side of the vertically adjacent squares is the same as the left side.

The gap shape, line shape, average line width, average interval, average thickness, etc. of each of the plated portions described above are not particularly limited, and can be appropriately set so as to satisfy the above ratio and linear expansion coefficient ratio. Moreover, these can be appropriately set so as to satisfy the above ratio of Young's moduli.

<Method for manufacturing flexible printed wiring board>
Next, a method for manufacturing the flexible printed wiring board 10 will be described.

The method for manufacturing the flexible printed wiring board 10 uses a resist pattern R and deposits a first metal on the conductive underlayer M of the base film 3 having the conductive underlayer M laminated on one surface side (surface side). A plating step of forming a wiring plating layer 25 and a non-wiring plating layer 45 by electroplating a material, and after the plating step, the wiring plating layer in the resist pattern R and the conductive base layer M. 25 and a removing step of removing non-laminated regions of the plating layer 43 for non-wiring. The wiring layer 11 having the wiring 13 is formed by a part of the conductive base layer M and the wiring plating layer 25, and the other part of the conductive base layer M and the non-wiring plating layer 45 are electrically connected to each other. An isolated plated portion 41 is formed.

[Conductive underlayer]
The conductive base layer M is laminated on the surface side of the base film 3 . As the conductive base layer M, one laminated in advance on the entire front surface side of the base film 3 is used. A part of the conductive underlayer M becomes the first conductive underlayer 23 , and the other part of the conductive underlayer M becomes the second conductive underlayer 43 .

Materials for forming the conductive underlayer M include, for example, copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), and alloys thereof. Regarding these forming materials, from the point of view of suppressing thermal deterioration of the adhesion of the wiring layer 11 to the base film 3, the side of the conductive underlying layer M that contacts the base film 3 (for example, polyimide) contains the above-mentioned nickel, chromium, and titanium. and silver (first layer) containing at least one selected from the group consisting of silver. Furthermore, it is more preferable that the conductive underlying layer M includes a layer (first layer) containing at least one selected from nickel and chromium, which are easy to remove and easy to maintain insulating properties. Further, it is more preferable that the conductive underlayer M includes a layer (second layer) containing copper as a main component on the upper side of the first layer (the side opposite to the base film 3). By arranging the layer containing copper as a main component, it is possible to shorten the work time when forming the wiring layer 11 by electroplating.

For example, the lower limit of the average thickness of the first layer is preferably 1 nm, more preferably 2 nm. The upper limit of the average thickness of the first layer is preferably 15 nm, more preferably 8 nm. If the average thickness is less than the lower limit, it may be difficult to suppress thermal deterioration of the adhesion of the wiring layer 11 to the base film 3 . On the other hand, if the average thickness exceeds the upper limit, the first layer will be difficult to remove, and the insulating properties of the wiring layer 11 may not be sufficiently maintained. This first layer can be formed by a sputtering method, an electroplating method, an electroless plating method, or the like.

For example, the lower limit of the average thickness of the second layer is preferably 0.1 μm, more preferably 0.2 μm. The upper limit of the average thickness of the second layer is preferably 2 μm, more preferably 1 μm. If the average thickness is less than the lower limit, the time required to form the wiring layer 11 by electroplating may become excessively long. On the other hand, if the average thickness exceeds the upper limit, the second layer will be difficult to remove, and there is a risk that sufficient insulation between the wirings 13 (between the windings in FIG. 1) cannot be maintained. The second layer is preferably formed by a sputtering method, an electroplating method, an electroless plating method, or the like, and may be formed by combining these methods. In particular, it is preferable that the electroless copper plating layer is arranged on the uppermost surface side of the conductive underlayer M, so that when the inner layer is formed by the sputtering method, defects that may occur due to the sputtering method. can be covered.

[Plating process]
This step includes a resist pattern forming step of forming a resist pattern R on the surface of the conductive underlayer M, and electroplating the first metal material on the conductive underlayer M using the formed resist pattern R. and a plating layer forming step of forming the wiring plating layer 25 of the wiring 13 and the non-wiring plating layer 45 of the plating portion 41 .

(Resist pattern forming step)
In this step, a resist pattern R is formed on the surface of the conductive base layer M as shown in FIG. Specifically, a resist film such as a photosensitive film is laminated on the surface of the conductive underlayer M, and the laminated resist film is exposed and developed to form a resist pattern R having a predetermined pattern. Examples of the method of laminating the resist film include a method of applying a resist composition to the surface of the conductive underlayer M, a method of laminating a dry film photoresist on the surface of the conductive underlayer M, and the like. The exposure and development conditions for the resist film can be appropriately adjusted according to the resist composition used. The opening of the resist pattern R can be appropriately set according to the shape of the wiring plating layer 25 and the non-wiring plating layer 45 to be formed.

(Plating layer forming step)
In this step, by electroplating the first metal material while energizing the conductive base layer M, a wiring plating layer 25 is formed on the non-laminated region of the resist pattern R in the conductive base layer M as shown in FIG. and a non-wiring plating layer 45 are formed.

[Removal process]
This step includes a peeling step of removing the resist pattern R from the conductive base layer M and an etching step of etching a non-laminated region (unnecessary region) of the wiring plating layer 25 and the non-wiring plating layer 45 in the conductive base layer M. and a step.

(Peeling process)
In this step, the resist pattern R is removed from the conductive underlying layer M. As shown in FIG. As the stripping solution, known ones can be used, for example, alkaline aqueous solutions such as sodium hydroxide and potassium hydroxide, organic acid solutions such as alkylbenzenesulfonic acid, organic amines such as ethanolamine, and polar solvents. Mixed liquid etc. are mentioned.

(Etching process)
In this step, the conductive base layer M is etched using the wiring plating layer 25 and the non-wiring plating layer 45 as masks. By this etching, as shown in FIG. 2, the wiring 13 in which the wiring plating layer 25 is laminated on the base film 3 with the first conductive base layer 23 interposed therebetween is obtained. Also, the plating portion 41 is obtained by laminating the non-wiring plating layer 45 on the base film 3 with the second conductive underlayer 43 interposed therebetween. An etchant that corrodes the metal forming the conductive base layer M is used for the etching. In this way, the so-called semi-additive method is preferably used in the production method.

<Advantages>
In the flexible printed wiring board 10, the thickness variation of the wiring layer 11 is reduced because the first ratio of the plating portion 41 in the first region K1 is equal to or less than the upper limit. Therefore, the flexible printed wiring board 10 is excellent in thickness uniformity. In addition to the first ratio being equal to or higher than the lower limit, the linear expansion coefficient of the first region K1 is within the above range, thereby reducing dimensional change of the flexible printed wiring board 10 . Therefore, the flexible printed wiring board 10 has excellent uniformity in the thickness of the wiring layer 11 and reduced dimensional change.

[Other embodiments]
It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is not limited to the configuration of the above-described embodiment, but is indicated by the scope of the claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims. be.

In the above embodiments, a flexible printed wiring board having a single base film and a wiring layer laminated on one side of the base film was described, but the flexible printed wiring board is made of a single base film. Wiring layers may be laminated on both sides. Moreover, the flexible printed wiring board may be a multilayer printed wiring board having a plurality of base films and each base film having a plurality of wiring layers on one side or both sides thereof.

Although the wiring layer has one wiring in the above embodiment, the wiring layer may have a plurality of wirings.

Although the wiring 13 has a coil shape in the above embodiment, the wiring 13 may have another shape.

In the above embodiment, the case where the wiring 13 has one wiring plating layer has been described, but a mode in which the wiring 13 has two or more wiring plating layers can also be adopted. In this case, for example, in the manufacturing method described above, after the removal step, the non-wiring plating layer 45 is not energized, and only the wiring plating layer 25 is energized to perform further electroplating, thereby forming the second wiring layer. can form a plating layer for In the case of having the third and subsequent wiring plating layers, the same electroplating as the formation of the second wiring plating layer may be repeated.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples.

As a model experiment, various plated portions were formed on the base film, and the characteristic values of laminates of this base film and the plated portion were evaluated.

<Preparation of sample>
(Experimental example 1)
A film (Upilex-S, manufactured by Ube Industries, Ltd.) in which a conductive underlayer is laminated on one side (surface side) of a base film was used. As the plated portion, a plated portion having the same shape as the above-described plated portion shape example 1 (lattice shape (honeycomb shape)) was produced. Specifically, as described above, a resist pattern having a plurality of openings corresponding to the plating portions is used on the conductive underlayer of the film, and the conductive underlayer is electrically connected to the conductive underlayer. After electroplating a copper material as the first metal material in an electroplating bath, a removal step was performed to form a non-wiring plating layer. In this electroplating, a square area of 200 μm long×200 μm wide in plan view in the conductive underlayer is set to have an average thickness of 10 μm and an average line width of 20 μm. The plated portion was formed by setting the size of the lattice gap (regular hexagon) so that the ratio of the area was 50%. After that, a square region of 200 μm long×200 μm wide was cut out from the obtained laminate along the periphery of the plated portion, and a sample of Experimental Example 1 was obtained.

(Experimental Examples 2 to 7)
In the same manner as in Experimental Example 1 except that the shape of the plated portion in the first region K1 is changed to the same shape as in Shape Examples 2 to 7 of the plated portion described above, Experimental Examples 2 to Experiment A sample of Example 7 was prepared.
Experimental example 2: Grid shape (triangular shape 1)
Experimental example 3: Grid shape (square shape 1)
Experimental example 4: Parallel corrugated shape (corrugated shape 1)
Experimental Example 5: Line-symmetric wave shape (wavy shape 2)
Experimental Example 6: Grid shape (triangular shape 2)
Experimental Example 7: Grid shape (square shape 2)

(Experimental example 8)
The sample of Experimental Example 8 was prepared in the same manner as in Experimental Example 1 except that the shape of the plated portion in the first region K1 was changed to a linear shape extending along the vertical direction of FIG. 1 so as to be parallel to each other. was made.

<Evaluation>
(linear expansion coefficient)
For the samples of Experimental Examples 1 to 8, thermal stress analysis by simulation was performed under the following conditions. The coefficient of thermal expansion in the Y direction (second direction) was measured. Also, for each sample, the coefficient of thermal expansion in the Z direction (third direction), which is inclined at an angle of 45° with respect to both the X and Y directions, was measured. The linear expansion coefficient in the X direction, the linear expansion coefficient in the Y direction, the linear expansion coefficient in the Z direction, and the ratio of the linear expansion coefficient ((linear expansion coefficient in the Y direction) / (linear expansion coefficient in the X direction) obtained for each sample , (linear expansion coefficient in the Z direction)/(linear expansion coefficient in the X direction)) are shown in Table 1.
・Thermal analysis conditions Atmospheric temperature: Decrease from 180°C to 20°C Coefficient of linear expansion of base film: 90×10 ^-6 [/K]
Coefficient of linear expansion of copper: 16.2 × 10 ^-6 [/K]

(Young's modulus)
For the samples of Experimental Examples 1 to 8, the Young's modulus in the X direction, Y direction and Z direction were measured by conducting thermal stress analysis by simulation similar to the above linear expansion coefficient under the following conditions. The ratio of Young's modulus in the X direction, Young's modulus in the Y direction, Young's modulus in the Z direction, and Young's modulus obtained for each sample ((Young's modulus in the Y direction)/(Young's modulus in the X direction), (Young's modulus in the Z direction modulus)/(Young's modulus in the X direction)) is shown in Table 2.
・Thermal analysis conditions Atmospheric temperature: Decrease from 180°C to 20°C Young's modulus of base film: 2000 [MPa]
Young's modulus of copper: 110000 [MPa]

As shown in Table 1, when the ratio of the coefficients of linear expansion in the two mutually orthogonal directions of the samples having the plated portion is 0.5 or more and 2.0 or less, the dimensional change of these samples is small. As a result, in the non-laminated region of the wiring layer in the base film, the occupancy ratio (area ratio) is 25% or more and 75% or less in the first region between the shortest distance of 15 mm from the wiring layer, and the linear expansion It is presumed that the dimensional change of the flexible printed wiring board is reduced by forming the plated portion so that the coefficient ratio is within the above range. In addition, it is presumed that the uniformity of the thickness of the flexible printed wiring board is also improved. In addition, since the ratio of the Y-direction linear expansion coefficient to the X-direction linear expansion coefficient (first linear expansion coefficient ratio) approaches 1, the dimensional change is further reduced. As the ratio of the linear expansion coefficient in the Z direction to the expansion coefficient (second linear expansion coefficient ratio) also approaches 1, it is presumed that the above dimensional change is further reduced. It was also found that the second linear expansion coefficient ratio tends to be closer to 1 than the first linear expansion coefficient ratio.

As shown in Table 2, in addition to the ratio of the Y-direction Young's modulus to the X-direction Young's modulus (first Young's modulus ratio) approaching 1, the ratio of the Z-direction Young's modulus to the X-direction Young's modulus ( As the second Young's modulus ratio) also approaches 1, it is presumed that the dimensional change of the flexible printed wiring board is further reduced.

The flexible printed wiring board according to the embodiment of the present disclosure is excellent in uniformity of thickness of the wiring layer and reduced in dimensional change. Therefore, it can be suitably used for small electronic devices and the like.

10 flexible printed wiring board 3 base film 11 wiring layer 13 wiring 13a land portion 23 first conductive base layer 25 wiring plating layer 41 plating portion 43 second conductive base layer 45 non-wiring plating layer K wiring layer is not laminated area (non-laminated area)
K1 First region L Average line width S Average spacing M Conductive base layer R Resist patterns G1, G2 Gravity centers X1, X2 of triangular gaps Virtual straight lines (symmetry axes)

Claims (6)

a base film;
A flexible printed wiring board comprising: a wiring layer having one or more wirings laminated on at least one surface side of the base film,
The at least one surface side of the base film includes a non-laminated region, which is a region where the wiring layer is not laminated,
The non-laminated region includes a first region, and the first region further includes one or more plated portions laminated with a gap from the wiring layer so as to be electrically isolated,
The first region is a region within a shortest distance of 15 mm from the wiring layer,
A first ratio, which is a ratio of the area of the plating portion formation region on the first region to the area of the first region in plan view, is 25% or more and 75% or less,
A flexible flexible having a ratio of two linear expansion coefficients in a first direction and a second direction, which are directions parallel to each other and orthogonal to each other, with respect to the base film in the first region is 0.5 or more and 2.0 or less printed wiring board. A difference between the first ratio and a second ratio, which is a ratio of the area of the wiring layer formation region to the area of the region surrounded by the periphery of the wiring layer in plan view, is within 10% in absolute value. The flexible printed wiring board according to claim 1. A coefficient of linear expansion in a third direction, which is a direction parallel to the base film and inclined at an angle of 45° to both the first direction and the second direction, with respect to the coefficient of linear expansion in the first direction in the first region 3. The flexible printed wiring board according to claim 1, wherein the ratio of is from 0.5 to 2.0. The ratio of the Young's modulus in the second direction to the Young's modulus in the first direction in the first region is 0.1 or more and 10 or less,
4. The flexible printed wiring board according to claim 3, wherein the ratio of the Young's modulus in the third direction to the Young's modulus in the first direction in the first region is 0.1 or more and 10 or less. The flexible printed wiring board according to any one of claims 1 to 4, wherein the plated portion has a shape in which a plurality of mutually inclined linear portions are connected in plan view. 6. The flexible printed wiring board according to claim 5, wherein the plated portion has a polygonal line shape, a wavy shape, a lattice shape with polygonal gaps, or a combination thereof in plan view.

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