Flexible Printed Wiring Board and Method for Manufacturing the Same

Abstract

To provide a flexible printed wiring board which has excellent flexibility, can reduce electrical resistance, and can save space, and a manufacturing method thereof.SOLUTION: A flexible printed wiring board according to an embodiment of the present invention includes an insulating base film, and one or more wires laminated on at least one surface side of the base film, and the wire includes one or more first portions in the longitudinal direction thereof, and one or more second portions having an average thickness larger than the average thickness of the first portion other than the first portion. The ratio of the average thickness of the second portion to the average thickness of the first portion is 1.5 or more and 50 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a flexible printed wiring board and a method for manufacturing the same.

Background Art

[0002] Flexible printed wiring boards are widely used to form circuits in various electronic devices. In recent years, with the miniaturization of electronic devices, the miniaturization of flexible printed wiring boards and the increase in their wiring density have been remarkable.

[0003] As such a small flexible printed wiring board, one having a sheet-like insulating substrate and wirings laminated on the surface of this substrate by plating has been proposed (see Japanese Unexamined Patent Application Publication No. 2018-195681). In this flexible printed wiring board, the plating film thickness, that is, the thickness of the wiring is made uniform.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, in a flexible printed wiring board, as wirings, current lines for sending an electric current for power supply may be arranged. Since it is desired to flow as much current as possible through this current line, it is required that the electric resistance of the current line be small.

[0006] Flexible printed wiring boards are generally often used by being bent at a predetermined position. For this reason, it is desired to be easily bent, that is, to have excellent flexibility.

[0007] On the one hand, in the flexible printed wiring board that is required to be miniaturized as described above, space saving is required.

[0008] Therefore, an object of the present invention is to provide a flexible printed wiring board and a manufacturing method thereof that have excellent flexibility, can reduce electrical resistance, and can achieve space saving.

Means for Solving the Problems

[0009] A flexible printed wiring board according to an aspect of the present disclosure made to solve the above problems is a flexible printed wiring board including an insulating base film and one or more wirings laminated on at least one surface side of the base film, wherein at least one of the wirings has one or more first portions in its longitudinal direction and one or more second portions that are portions other than the first portions and have an average thickness greater than the average thickness of the first portions, and the ratio of the average thickness of the second portions to the average thickness of the first portions is 1.5 or more and 50 or less.

[0010] Also, a method for manufacturing a flexible printed wiring board according to another aspect of the present disclosure made to solve the above problems is a method for manufacturing a flexible printed wiring board including an insulating base film and one or more wirings laminated on at least one surface side of the base film, wherein at least one of the wirings has one or more first portions in its longitudinal direction and one or more second portions that are portions other than the first portions and have an average thickness greater than the average thickness of the first portions, the ratio of the average thickness of the second portions to the average thickness of the first portions is 1.5 or more and 50 or less, a first plating step of forming one or more first plated bodies by electroplating a first metal material on the conductive underlayer of the base film having the conductive underlayer laminated on at least one surface side using a first resist pattern, a first removal step of removing the non-laminated regions of the first plated bodies in the first resist pattern and the conductive underlayer after the first plating step, a second plating step of forming one or more second plated bodies by electroplating a second metal material on one or more longitudinal portions of the first plated bodies using a second resist pattern after the first removal step, and a second removal step of removing the second resist pattern after the second plating step, the first portion is formed as a first laminated portion having a part of the conductive underlayer and the first plated body, and the second portion is formed as a second laminated portion having a part of the conductive underlayer, the first plated body, and the second plated body.

[0011] Also, a method for manufacturing a flexible printed wiring board according to another aspect of the present disclosure made to solve the above problems is a method for manufacturing a flexible printed wiring board including an insulating base film and one or more wirings laminated on at least one surface side of the base film, wherein at least one of the wirings has one or more first portions in its longitudinal direction and one or more second portions that are portions other than the first portions and have an average thickness greater than the average thickness of the first portions, and the ratio of the average thickness of the second portions to the average thickness of the first portions is 1.5 or more and 50 or less. By electroplating a third metal material on the conductive underlayer of a base film having a conductive underlayer laminated on at least one surface side using a third resist pattern, a third plating step of forming one or more third plated bodies extending in the longitudinal direction is performed. After the third plating step, a third removal step of removing the third resist pattern is performed. After the third removal step, using a fourth resist pattern, a fourth plating step of electroplating a fourth metal material so as to include at least a non-laminated region of the third plated body on the conductive underlayer and be connected to the third plated body in the longitudinal direction is performed to form one or more fourth plated bodies extending in the longitudinal direction and having an average thickness greater than that of the third plated body. After the fourth plating step, a fourth removal step of removing the fourth resist pattern and the non-laminated regions of the third plated body and the fourth plated body in the conductive underlayer is provided. The first portion is formed as a third laminated portion having a part of the conductive underlayer and the third plated body, and the second portion is formed as a fourth laminated portion having a part of the conductive underlayer and the fourth plated body.

Effects of the Invention

[0012] The flexible printed wiring board according to one aspect of the present disclosure has excellent flexibility, can reduce electrical resistance, and can achieve space saving. The method for manufacturing a flexible printed wiring board according to another aspect of the present disclosure can manufacture a flexible printed wiring board having excellent flexibility, capable of reducing electrical resistance, and achieving space saving.

Brief Description of the Drawings

[0013]

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[0014] [Description of Embodiments of the Present Disclosure] A flexible printed wiring board according to one aspect of the present disclosure is a flexible printed wiring board including an insulating base film and one or more wirings laminated on at least one surface side of the base film, wherein at least one of the wirings has one or more first portions in its longitudinal direction and one or more second portions that are portions other than the first portions and have an average thickness greater than the average thickness of the first portions, and the ratio of the average thickness of the second portions to the average thickness of the first portions is 1.5 or more and 50 or less.

[0015] Here, as a measure for reducing the electrical resistance of the wiring, increasing the thickness of the wiring can be considered. However, if the thickness of the wiring is increased in this way, the flexibility of the flexible printed wiring board may decrease. In addition, if the thickness of the wiring is increased too much, the mounting portion may become too thick when the flexible printed wiring board is mounted, or the connection portion may become too thick when connecting to another wiring board, which may make it difficult to achieve thinning (space saving). On the other hand, as a measure for reducing the electrical resistance of the wiring and improving the flexibility of the wiring, increasing the line width of the wiring can be considered. However, if the line width of the wiring is increased in this way, there is a possibility that space saving cannot be achieved.

[0016] In contrast, in the flexible printed wiring board, the ratio of the average thickness of the second portions to the average thickness of the first portions is within the above range. Thus, since the average thickness of the first portions is smaller than the average thickness of the second portions, the flexibility of the flexible printed wiring board can be improved. Also, since the average thickness of the second portions is larger than that of the first portions, the electrical resistance of the wiring can be reduced. In addition, since the average thickness of the second portions is larger than that of the first portions, space saving of the flexible printed wiring board can be achieved more than when the line width of the wiring is increased. Therefore, the flexible printed wiring board has excellent flexibility, can reduce the electrical resistance, and can achieve space saving.

[0017] It is preferable that the average line width of the wiring is 3 μm or more and 100 μm or less, and the average interval is 3 μm or more and 100 μm or less.

[0018] In this way, by having the average line width and average interval of the wiring within the above ranges, it is possible to achieve more space saving of the flexible printed wiring board.

[0019] It is preferable that the ratio of the minimum cross-sectional area in the thickness direction of the second portion to the minimum cross-sectional area in the thickness direction of the first portion is 0.5 or more and 200 or less.

[0020] In this way, by having the ratio of the minimum cross-sectional area of the second portion to the minimum cross-sectional area of the first portion within the above range, it is possible to reduce the electrical resistance of the entire wiring (the sum of the electrical resistances of the first portion and the second portion) while achieving space saving.

[0021] It is preferable that the ratio of the average thickness to the minimum line width in the first portion is 0.3 or more and 5 or less, and the ratio of the average thickness to the minimum line width in the second portion is 0.5 or more and 10 or less.

[0022] In this way, by having the ratio of the average thickness to the minimum line width of the first portion within the above range and the ratio of the average thickness to the minimum line width of the second portion within the above range, it is possible to achieve more space saving of the flexible printed wiring board.

[0023] Moreover, a method for manufacturing a flexible printed wiring board according to different aspects of the present disclosure is a method for manufacturing a flexible printed wiring board including an insulating base film and one or more wirings laminated on at least one surface side of the base film, wherein at least one of the wirings has one or more first portions in its longitudinal direction and one or more second portions other than the first portions and having an average thickness greater than the average thickness of the first portions, the ratio of the average thickness of the second portions to the average thickness of the first portions being 1.5 or more and 50 or less. By using a first resist pattern and electroplating a first metal material on the conductive underlayer of the base film having the conductive underlayer laminated on at least one surface side, a first plating step of forming one or more first plated bodies is performed. After the first plating step, a first removal step of removing the non-laminated regions of the first plated bodies in the first resist pattern and the conductive underlayer is performed. After the first removal step, by using a second resist pattern and electroplating a second metal material on one or more longitudinal portions of the first plated body, a second plating step of forming one or more second plated bodies is performed. After the second plating step, a second removal step of removing the second resist pattern is provided. The first portion is formed as a first laminated portion having a part of the conductive underlayer and the first plated body, and the second portion is formed as a second laminated portion having a part of the conductive underlayer, the first plated body, and the second plated body.

[0024] According to the method for manufacturing the flexible printed wiring board, the above-described flexible printed wiring board can be manufactured. That is, it is possible to manufacture a flexible printed wiring board having excellent flexibility, capable of reducing electrical resistance, and capable of saving space.

[0025] Further, a method for manufacturing a flexible printed wiring board according to different aspects of the present disclosure is a method for manufacturing a flexible printed wiring board including an insulating base film and one or more wirings laminated on at least one surface side of the base film, wherein at least one of the wirings has one or more first portions in its longitudinal direction and one or more second portions other than the first portions and having an average thickness greater than the average thickness of the first portions, the ratio of the average thickness of the second portions to the average thickness of the first portions being 1.5 or more and 50 or less, a third plating step of forming one or more third plated bodies extending in the longitudinal direction by electroplating a third metal material on the conductive underlayer of the base film having the conductive underlayer laminated on at least one surface side using a third resist pattern, a third removing step of removing the third resist pattern after the third plating step, a fourth plating step of electroplating a fourth metal material using a fourth resist pattern after the third removing step so as to include at least a non-laminated region of the third plated body on the conductive underlayer and to be connected to the third plated body in the longitudinal direction, thereby forming one or more fourth plated bodies extending in the longitudinal direction and having an average thickness greater than that of the third plated body, and a fourth removing step of removing the fourth resist pattern and non-laminated regions of the third plated body and the fourth plated body in the conductive underlayer after the fourth plating step, wherein the first portion is formed as a third laminated portion having a part of the conductive underlayer and the third plated body, and the second portion is formed as a fourth laminated portion having a part of the conductive underlayer and the fourth plated body.

[0026] Here, the "average thickness" means the average value of the thickness measured at any ten points for each of the first part and the second part in one wiring. The "thickness" means the distance between the base film and the upper edge of the wiring in the direction perpendicular to this base film. The "line width" means the dimension in the direction perpendicular to the longitudinal direction in one wiring. The "interval" means the distance between the adjacent surfaces of two opposing wirings, and the "average interval" means the value obtained by averaging the distance between the adjacent surfaces in the longitudinal direction of the wiring. The "average line width" means the value obtained by averaging the maximum width of the wiring in the cross-section perpendicular to the longitudinal direction of the wiring in the longitudinal direction of the wiring. The "minimum cross-sectional area" means the minimum value of the cross-sectional area perpendicular to the longitudinal direction for each of the first part and the second part in one wiring. The "minimum line width" means the minimum value of the line width for each of the first part and the second part in one wiring. However, land portions such as land portions having vias (through holes, blind vias, field vias) for connecting between wirings, land portions for connecting to mounted components, and land portions for connecting to other printed circuit boards or connectors shall be excluded from the "thickness", "line width", "interval", and "cross-sectional area" defined above. Note that "wiring" corresponds to "wiring layer".

[0027] [Details of Embodiments of the Present Disclosure] Hereinafter, embodiments of a flexible printed wiring board and a method for manufacturing the same according to the present disclosure will be described in detail with reference to the drawings. In this embodiment, the "surface side" refers to the side on which the wiring is laminated among the thickness directions of the base film, and the front and back of this embodiment do not determine the front and back in the usage state of the flexible printed wiring board.

[0028] [First Embodiment] [Flexible Printed Wiring Board] As shown in FIGS. 1 and 2, the flexible printed wiring board 10 of the present embodiment mainly includes an insulating base film 3 and a plurality of wirings 11 laminated on one surface side (front surface side) of the base film 3. The flexible printed wiring board 10 may further include a cover film on the front surface side of the base film 3 or the wiring 11.

[0029] <Base film> The base film 3 is a layer made of a synthetic resin having insulating properties. The base film 3 also has flexibility. This base film 3 is also a base material for forming the wiring 11. The material for forming the base film 3 is not particularly limited as long as it has insulating properties and flexibility, but a low dielectric constant synthetic resin film formed in a sheet shape can be adopted. Examples of the main component of this synthetic resin film include polyimide, polyethylene terephthalate, liquid crystal polymer, fluororesin, etc. "Main component" means the component with the highest content, for example, a component occupying 50% by mass or more in the forming material. The base film 3 may contain other resins such as those exemplified like polyimide, antistatic agents, etc.

[0030] The lower limit of the average thickness of the base film 3 is not particularly limited, but 3 μm is preferable, 5 μm is preferable, and 10 μm is more preferable. The upper limit of the average thickness of the base film 3 is not particularly limited, but 200 μm is preferable, 150 μm is more preferable, and 100 μm is even more preferable. When 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 be insufficient. On the other hand, when 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, as described above, the average value of the thicknesses measured at any ten points.

[0031] <Wiring> The wiring 11 is laminated directly or via another layer on the surface side of the base film 3. The wiring 11 has a plurality of first portions 11a in its longitudinal direction (the left - right direction in FIGS. 1 and 2), and a second portion 11b which is a portion other than the first portion 11a and has an average thickness H2 greater than the average thickness H1 of the first portion 11a. The ratio of the average thickness H2 of the second portion 11b to the average thickness H1 of the first portion 11a is 1.5 or more and 50 or less.

[0032] The wiring 11 has a first conductive underlayer 13 laminated on the surface side of the base film 3, a first plating layer 15 laminated on the side (surface side) of the first conductive underlayer 13 opposite to the base film 3, and a plurality of second plating layers 17 partially laminated in the longitudinal direction on the side (surface side) of the first plating layer 15 opposite to the first conductive underlayer 13. The first laminated portion having the first conductive underlayer 13 and the first plating layer 15 constitutes the first portion 11a. The second laminated portion having the first conductive underlayer 13, the first plating layer 15, and the second plating layer 17 constitutes the second portion 11b. Examples of the wiring 11 include a signal line for sending a signal, a current line for sending a current for power supply, a current line for sending a current for magnetic field generation, etc. Also, FIG. 2 shows an aspect in which the wiring 11 is arranged on only one side of the base film 3, but it is more preferable to arrange the wiring 11 on both sides of the base film 3 in order to save more space.

[0033] Examples of the material for forming the first conductive underlayer 13 include copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), and alloys thereof. Regarding these forming materials, in terms of suppressing the thermal deterioration of the adhesion of the wiring 11 to the base film 3, it is preferable that the first conductive underlayer 13 includes a layer (first layer) containing at least one selected from the group consisting of nickel, chromium, titanium, and silver on the side in contact with the base film 3 (for example, polyimide). Further, it is more preferable that the first conductive underlayer 13 includes a layer (first layer) containing at least one selected from nickel and chromium, which are easy to remove and easy to maintain insulation. Also, it is more preferable that the first conductive underlayer 13 includes a layer (second layer) mainly composed of copper on the upper side of this first inner layer (the side opposite to the base film 3). By arranging the layer mainly composed of copper, it becomes possible to shorten the working time when forming the wiring 11 by electroplating.

[0034] For example, as the lower limit of the average thickness of the first layer, 1 nm is preferable, and 2 nm is more preferable. As the upper limit of the average thickness of the first layer, 15 nm is preferable, and 8 nm is more preferable. If the average thickness is less than the lower limit, it may be difficult to suppress the thermal deterioration of the adhesion of the wiring 11 to the base film 3. On the other hand, if the average thickness exceeds the upper limit, it becomes difficult to easily remove the first layer, and there is a possibility that the insulation between the wirings 11 cannot be sufficiently maintained. Note that this first layer can be formed by a sputtering method, an electroplating method, an electroless plating method, or the like.

[0035] For example, as the lower limit of the average thickness of the second layer, 0.1 μm is preferable, and 0.2 μm is more preferable. As the upper limit of the average thickness of the second layer, 2 μm is preferable, and 1 μm is more preferable. If the average thickness is less than the lower limit, the time required to form the wiring 11 by electroplating may become excessively long. On the other hand, if the average thickness exceeds the upper limit, it becomes difficult to easily remove the second layer, and there is a possibility that the insulation between the wirings 11 cannot be sufficiently maintained. Note that this 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. In particular, it is preferable that an electroless copper plating layer is disposed on the uppermost surface side of the first conductive base layer 13, so that when the inner layer is formed by the sputtering method, defects that may occur by this sputtering method can be covered.

[0036] As shown in FIG. 1, in the present embodiment, the first conductive base layer 13 is formed such that the line width of the region where the second plating layer 17 is laminated is smaller than the line width of other regions.

[0037] Examples of the first metal material for forming the first plating layer 15 include copper, aluminum, silver, gold, nickel, and alloys thereof. Among these, copper or a copper alloy is preferable from the viewpoints of good conductivity and cost reduction. For example, the first plating layer 15 is formed in the same shape as the first conductive base layer 13 when viewed in a direction perpendicular to the base film 3.

[0038] Examples of the second metal material for forming the second plating layer 17 include the same materials as the first metal material. As the second metal material, the same type as the first metal material is preferable. The second plating layer 17 may have the same width or a different width as the line width of the non-laminated region of the second plating layer 17 in the first plating layer 15 when viewed in a direction perpendicular to the base film 3, but it is more preferable to make it larger than the line width of the non-laminated region because the electrical resistance of the entire wiring 11 can be reduced.

[0039] When a plurality of wirings 11 are arranged adjacent to each other, the lower limit of the average line width L1 of these wirings 11 is preferably 3 μm, more preferably 5 μm, and even more preferably 10 μm. The upper limit of the average line width L1 of the wiring 11 is preferably 100 μm, more preferably 75 μm, and even more preferably 50 μm. When the average line width L1 of the wiring 11 is less than the above lower limit, there is a risk that the mechanical strength of the wiring 11 is insufficient. On the other hand, when the average line width L1 of the wiring 11 exceeds the above upper limit, there is a risk that sufficient space saving cannot be achieved. The "average line width" is a value calculated as the average value 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 largest-width portion in each wiring 11 with a microscope or the like capable of measurement. In addition, the "average line width" of other members and the like is also a value measured in the same manner hereinafter.

[0040] When a plurality of wirings 11 are arranged adjacent to each other, the lower limit of the average interval S1 between these wirings 11 is preferably 3 μm, more preferably 5 μm, and even more preferably 10 μm. The upper limit of the average interval S1 of the wiring 11 is preferably 100 μm, more preferably 75 μm, and even more preferably 50 μm. When the average interval S1 of the wiring 11 is less than the above lower limit, there is a risk of short circuit. On the other hand, when the average interval S1 of the wiring 11 exceeds the above upper limit, there is a risk that sufficient space saving cannot be achieved. The "average interval" is a value calculated as the average value 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-interval portion in the gap between each wiring 11 with a microscope or the like capable of measurement. In addition, the "average interval" of other members and the like is also measured in the same manner hereinafter.

[0041] The first plating layer 15 and the second plating layer 17 are much thicker than the first conductive base layer 13. Therefore, the thickness of the first portion 11a can be mainly determined by the thickness of the first plating layer 15. The thickness of the second portion 11b can be mainly determined by the thicknesses of the first plating layer 15 and the second plating layer 17.

[0042] (First portion) The average thickness H1 of the first portion 11a can be appropriately set such that the ratio of the average thickness H2 of the second portion 11b to the average thickness H1 of the first portion 11a is 1.5 or more and 50 or less. For example, as the lower limit of the average thickness H1 of the first portion 11a, 3 μm is preferable, 5 μm is more preferable, and 10 μm is even more preferable. As the upper limit of the average thickness H1 of the first portion 11a, 30 μm is preferable, 25 μm is more preferable, and 20 μm is even more preferable. When the average thickness H1 is less than the lower limit, the mechanical strength of the first portion 11a may be insufficient. On the other hand, when the average thickness H1 exceeds the upper limit, the flexibility of the first portion 11a may decrease. The "average thickness" is obtained for each first portion 11a by exposing the cross-section of the wiring board 10 with a cross-section processing device such as a microtome, measuring the thickness by observing the cross-section at ten arbitrary points in each first portion 11a, and calculating the average value of the measurement results. Incidentally, the "average thickness" of other members, etc. hereinafter is also a value measured in the same manner as this.

[0043] As the lower limit of the ratio (aspect ratio) of the average thickness H1 to the minimum line width (not shown) of the first portion 11a, 0.3 is preferable, 0.5 is more preferable, and 0.7 is even more preferable. As the upper limit of the above ratio, 5 is preferable, 2 is more preferable, and 1.0 is even more preferable. If the above ratio is less than the above lower limit, there is a possibility that sufficient space saving cannot be achieved. On the other hand, even if the above ratio exceeds the above upper limit, there is a possibility that sufficient space saving cannot be achieved. The "minimum line width" is a value measured for each first portion 11a by a microscope or the like capable of measuring the length of the smallest-width portion in each first portion 11a of each wiring 11 by exposing the cross-section of the wiring board 10 with a cross-section processing device such as a microtome. However, this "minimum line width" is the length of the smallest-width portion in the region excluding the defect region of each first portion 11a. Here, the defect region to be excluded from the measurement is a region that is recessed (defective) inward from at least one edge in the width direction when the microscopic observation is performed as described above. Specifically, this defect region is a region whose deepest part in the width direction has a length (width) of 1 / 4 or more of the average line width of other regions in the longitudinal direction of each first portion 11a (excluding the above defect region). The above average line width is measured in the same manner as the measurement method of the "average line width" described above. In addition, in the following, the "minimum line width" of other members and the like is also a value measured in the same manner as this.

[0044] The minimum line width of the first portion 11a can be appropriately set, for example, so as to satisfy the above aspect ratio. For example, as the lower limit of the minimum line width of the first portion 11a, 3 μm is preferable, 5 μm is more preferable, and 10 μm is even more preferable. As the upper limit of the minimum line width of the first portion 11a, 30 μm is preferable, 25 μm is more preferable, and 20 μm is even more preferable. If the above minimum line width is less than the above upper limit, there is a possibility that the mechanical strength of the first portion 11a is insufficient. On the other hand, if the above minimum line width exceeds the above upper limit, there is a possibility that sufficient space saving cannot be achieved.

[0045] The minimum cross-sectional area in the thickness direction of the first portion 11a can be appropriately set such that the ratio of the minimum cross-sectional area in the thickness direction of the second portion 11b to the minimum cross-sectional area in the thickness direction of the first portion 11a (minimum cross-sectional area of the second portion 11b / minimum cross-sectional area of the first portion 11a) is within a predetermined range. As the lower limit of this ratio, for example, 0.5 is preferable, and 0.7 is more preferable. As the upper limit of the above ratio, 200 is preferable, and 20 is more preferable. If the above ratio is less than the lower limit, the electrical resistance of the wiring 11 may become excessively large. On the other hand, if the above ratio exceeds the upper limit, the line width of the second portion 11b may become relatively too large, and it may not be possible to achieve sufficient space saving. The "minimum cross-sectional area" is calculated by the product of the above average thickness H1 and the above minimum line width. In the following, the "minimum cross-sectional area" of other members, etc. is also a value measured in the same way.

[0046] (Second portion) The average thickness H2 of the second portion 11b can be appropriately set such that the ratio of the average thickness H2 of the second portion 11b to the average thickness H1 of the first portion 11a described above is 1.5 or more and 50 or less. For example, as the lower limit of the average thickness H2 of the second portion 11b, 5 μm is preferable, 10 μm is more preferable, and 20 μm is even more preferable. As the upper limit of the average thickness H2 of the second portion 11b, 100 μm is preferable, 75 μm is more preferable, and 50 μm is even more preferable. If the above average thickness H2 is less than the upper limit, the electrical resistance of the wiring 11 may become excessively large. On the other hand, if the above average thickness H2 exceeds the upper limit, it becomes necessary to increase the line width to form the second portion 11b, and it may not be possible to achieve sufficient space saving.

[0047] As the lower limit of the ratio (aspect ratio) of the average thickness H2 to the minimum line width (not shown) of the second portion 11b, 0.5 is preferable, 1 is preferable, and 2 is more preferable. As the upper limit of the ratio, 10 is preferable, 7 is more preferable, and 5 is even more preferable. If the ratio is less than the lower limit, there is a possibility that sufficient space saving cannot be achieved. On the other hand, if the ratio exceeds the upper limit, there is a possibility that the wiring 11 is likely to be deformed or damaged during the formation of the wiring 11 and in the processes after the formation of the wiring 11 in the manufacture of the flexible printed wiring board 10.

[0048] The minimum line width of the second portion 11b can be appropriately set, for example, so as to satisfy the above aspect ratio. For example, as the lower limit of the minimum line width of the second portion 11b, 5 μm is preferable, 10 μm is more preferable, and 15 μm is even more preferable. As the upper limit of the minimum line width of the second portion 11b, 100 μm is preferable, 75 μm is more preferable, and 50 μm is even more preferable. If the minimum line width is less than the upper limit, there is a possibility that the mechanical strength of the second portion 11b is insufficient. On the other hand, if the minimum line width exceeds the upper limit, there is a possibility that sufficient space saving cannot be achieved.

[0049] As described above, the minimum cross-sectional area in the thickness direction of the second portion 11b can be appropriately set so that the ratio of the minimum cross-sectional area in the thickness direction of the second portion 11b to the minimum cross-sectional area in the thickness direction of the first portion 11a is within the above predetermined range.

[0050] (Ratio of the average thickness of the second portion to the average thickness of the first portion) The lower limit of the ratio of the average thickness H2 of the second part 11b to the average thickness H1 of the first part 11a is 1.5 as described above, more preferably 2, and even more preferably 3. The upper limit of the ratio is 50 as described above, more preferably 20, and even more preferably 5. If the ratio is less than the lower limit, there is a possibility that the electric resistance of the entire wiring cannot be reduced. Furthermore, there is a possibility that the flexibility cannot be improved. In addition, there is a possibility that sufficient space saving cannot be achieved. On the other hand, if the ratio exceeds the upper limit, there is a possibility that sufficient space saving cannot be achieved.

[0051] The region located above the first part 11a in the second part 11b, that is, the longitudinal sectional shape (cross-sectional shape in the longitudinal direction) of the end portion (boundary portion) adjacent to the first part 11a in the second plating layer 17 is not particularly limited and can be set as appropriate. For example, as shown in FIG. 2, the shape of this end portion may be rectangular.

[0052] In addition, as in the second portion 11b’ shown in FIG. 3, the longitudinal cross-sectional shape of the lower end edge 11b’a of the boundary portion in the second portion 11b’ may be curved. This shape can be formed by treating the portion 11b’ with an etching solution. By having the longitudinal cross-sectional shape of the lower end edge 11b’a be curved, it becomes possible to prevent breakage due to stress caused by temperature changes and breakage due to external forces when forming an insulating layer on the wiring board 10. Examples of such a curved shape include an arc shape having a radius of curvature R. When the longitudinal cross-sectional shape of the lower end edge 11b’a is an arc shape, the lower limit of the radius of curvature R is preferably 0.2 μm, more preferably 0.5 μm, and even more preferably 1.0 μm. The upper limit of the radius of curvature R is preferably 4 μm, more preferably 3 μm, and even more preferably 2 μm. If the radius of curvature R is less than the lower limit, it becomes difficult to relieve the stress and external forces, and there is a risk that it will be difficult to prevent the breakage. On the other hand, if the radius of curvature R exceeds the upper limit, there is a risk that the wiring 11 will be entirely etched by performing the process for forming this arc shape, and as a result, the overall electrical resistance of the wiring 11 may increase.

[0053] In addition to the above, as shown in the second portion 11b’’ of FIG. 4, the longitudinal cross-sectional shape of the upper end edge 11b’’b of the boundary portion in the second portion 11b’’ may be curved. This shape can be formed by treating the portion 11b’ with an etching solution. Since the longitudinal cross-sectional shape of the upper edge 11b’’b is curved, it is possible to prevent breakage due to stress caused by temperature changes and breakage due to external forces when forming an insulating layer on the wiring board 10. Examples of such a curved shape include an arc shape having a radius of curvature r. When the longitudinal cross-sectional shape of the upper edge 11b’’b is an arc shape, the lower limit of the radius of curvature r is preferably 0.2 μm, more preferably 0.5 μm, and even more preferably 1.0 μm. The upper limit of the radius of curvature r is preferably 4 μm, more preferably 3 μm, and even more preferably 2 μm. If the radius of curvature r is less than the lower limit, it becomes difficult to relieve the stress and external forces, and there is a risk that it becomes difficult to prevent the breakage. On the other hand, if the radius of curvature r exceeds the upper limit, there is a risk that the wiring 11 may be etched entirely by performing the process for forming this arc shape, and as a result, the overall electrical resistance of the wiring 11 may increase.

[0054] <Advantages> In the flexible printed wiring board 10, the ratio of the average thickness H2 of the second portion 11b to the average thickness H1 of the first portion 11a of the wiring 11 is 1.5 or more and 50 or less. Since the average thickness H1 of the first portion 11a is smaller than the average thickness H2 of the second portion 11b in this way, the flexibility of the flexible printed wiring board 10 can be improved. Also, since the average thickness H2 of the second portion 11b is larger than the average thickness H1 of the first portion 11b, the electrical resistance of the wiring 11 can be reduced. In addition, since the average thickness H2 of the second portion 11b is larger than the average thickness H1 of the first portion 11a, the flexible printed wiring board 10 can be made more space-saving than when the line width of the wiring 11 is increased. Therefore, the flexible printed wiring board 10 has excellent flexibility, can reduce the electrical resistance, and can be made more space-saving.

[0055] [Manufacturing Method of Printed Wiring Board] Next, a method for manufacturing a flexible printed wiring board according to the present embodiment will be described with reference to the flexible printed wiring board 10. FIGS. 5 to 7 are schematic end views for explaining the manufacturing method, and are schematic end views viewed in the same direction as the AA arrow direction in FIG. 1. FIGS. 8 and 9 are schematic end views for explaining the manufacturing method, and are schematic end views viewed in the same direction as the BB arrow direction in FIG. 2. The direction perpendicular to the paper surface of FIGS. 5 to 7 and the left-right direction of FIGS. 8 and 9 are the longitudinal directions.

[0056] The manufacturing method of the flexible printed wiring board 10 includes a first plating step of forming a first plated body X1 by electroplating a first metal material on the conductive base layer M of the base film 3 having a conductive base layer M laminated on one surface side (front surface side) using a first resist pattern R1, a first removing step of removing the non-laminated regions of the first plated body X1 in the first resist pattern R1 and the conductive base layer M after the first plating step, a second plating step of forming a plurality of second plated bodies X2 by electroplating a second metal material on a plurality of portions in the longitudinal direction of the first plated body X1 using a second resist pattern R2 after the first removing step, and a second removing step of removing the second resist pattern R2 after the second plating step. The first portion 11a is formed as a first laminated portion having a part of the conductive base layer M (first conductive base layer 13) and the second plated body X2. The second portion 11b is formed as a second laminated portion having a part of the conductive base layer M (first conductive base layer 13), the first plated body X1, and the second plated body X2.

[0057] <Conductive base layer> The conductive base layer M is laminated on the front surface side of the base film 3. As the conductive base layer M, one that is laminated on the entire front surface side of the base film 3 in advance is used. A part of the conductive base layer M (first conductive base layer 13) is arranged so as to be finally sandwiched between the base film 3 and the first portion 11a in the wiring 11.

[0058] Examples of the material for forming the conductive base layer M include copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), and alloys thereof. With respect to these forming materials, in terms of suppressing the thermal degradation of the adhesion of the wiring 11 to the base film 3, it is preferable that the conductive base layer M includes a layer (first layer) containing at least one selected from the group consisting of nickel, chromium, titanium, and silver on the side in contact with the base film 3 (for example, polyimide). Further, it is more preferable that the conductive base 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 insulation. Also, it is more preferable that the conductive base layer M includes a layer (second layer) mainly composed of copper on the upper side of this first inner layer (the side opposite to the base film 3). By arranging the layer mainly composed of copper, it becomes possible to shorten the working time when forming the wiring 11 by electroplating.

[0059] For example, as the lower limit of the average thickness of the first layer, 1 nm is preferable, and 2 nm is more preferable. As the upper limit of the average thickness of the first layer, 15 nm is preferable, and 8 nm is more preferable. If the average thickness is less than the lower limit, it may be difficult to suppress the thermal degradation of the adhesion of the wiring 11 to the base film 3. On the other hand, if the average thickness exceeds the upper limit, it may become difficult to easily remove the first layer, and there is a possibility that the insulation between the wirings 11 cannot be sufficiently maintained. Note that this first layer can be formed by a sputtering method, an electroplating method, an electroless plating method, or the like.

[0060] For example, as the lower limit of the average thickness of the second layer, 0.1 μm is preferable, and 0.2 μm is more preferable. As the upper limit of the average thickness of the second layer, 2 μm is preferable, and 1 μm is more preferable. When the average thickness is less than the lower limit, the time required to form the wiring 11 by electroplating may become excessively long. On the other hand, when the average thickness exceeds the upper limit, it becomes difficult to easily remove the second layer, and there is a possibility that the insulation between the wirings 11 cannot be sufficiently maintained. Note that this second layer is preferably formed by a sputtering method, an electroplating method, an electroless plating method, etc., and may be formed by combining these. In particular, it is preferable that an electroless copper plating layer is disposed on the uppermost surface side of the conductive base layer M, whereby when the inner layer is formed by a sputtering method, defects that may occur by this sputtering method can be covered.

[0061] <First plating step> This step includes a first resist pattern forming step of forming a first resist pattern R1 on the surface of the conductive base layer M, and a first plating body forming step of forming a plurality of first plating bodies X1 by electroplating a first metal material on the conductive base layer M using the formed first resist pattern R1.

[0062] (First resist pattern forming step) In this step, as shown in FIG. 5, a first resist pattern R1 is formed on the surface of the conductive base layer M. Specifically, a resist film such as a photosensitive film is laminated on the surface of the conductive base layer M, and the laminated resist film is exposed and developed to form a first resist pattern R1 having a predetermined pattern. Examples of the method for laminating the resist film include a method of coating a resist composition on the surface of the conductive base layer M, a method of laminating a dry film photoresist on the surface of the conductive base layer M, etc. The exposure and development conditions of the resist film can be appropriately adjusted according to the resist composition used. The opening of the first resist pattern R1 can be appropriately set according to the first plating body X1 to be formed, that is, the conductive base layer M of the wiring 11.

[0063] (First plating body forming step) In this step, while applying an electric current to the conductive base layer M, the first metal material is electroplated to form a plurality of first plating bodies X1 extending in the longitudinal direction in the non-laminated region of the resist pattern R1 in the conductive base layer M as shown in FIG. 6.

[0064] <First removal step> This step includes a first stripping step of stripping the first resist pattern R1 from the conductive base layer M and an etching step of etching the non-laminated region (unnecessary region) of the first plating body X1 in the conductive base layer M.

[0065] (First stripping step) In this step, the first resist pattern R1 is stripped from the conductive base layer M. As this stripping solution, known ones can be used, such as alkaline aqueous solutions such as sodium hydroxide and potassium hydroxide, organic acid-based solutions such as alkylbenzene sulfonic acid, and mixed solutions of organic amines such as ethanolamine and polar solvents.

[0066] (First etching step) In this step, the conductive base layer M is etched using the first plating body X1 as a mask. By this etching, a laminate in which the first plating body X1 is laminated on the base film 3 via the first conductive base layer 13 is obtained as shown in FIG. 7. An etching solution that etches the metal forming the conductive base layer M is used for the above etching. In this manufacturing method, thus, a so-called semi-additive method is preferably used.

[0067] <Second plating step> This step includes a step of forming a second resist pattern R2 so as to cover the exposed base film 3 and the regions where the second plating bodies X2 are not scheduled to be laminated on the first plating bodies X1 after the above-described first removal step, and using the formed second resist pattern R2, the second metal material is electroplated on a plurality of portions in the longitudinal direction of each first plating body X1 to form a plurality of second plating bodies X2 on each first plating body X1, respectively.

[0068] (Second resist pattern formation step) In this step, as shown in FIG. 8, a resist film such as a photosensitive film is laminated so as to cover the entire exposed base film 3, the first conductive underlayer 13, and the first plating body X1, and the area where the second plating body X2 is scheduled to be laminated in the laminated resist film is exposed and developed, thereby forming a second resist pattern R2 having a predetermined pattern. Examples of the method for laminating the resist film include a method of coating a resist composition so as to cover the above entirety, a method of laminating a dry film photoresist on the above entirety, and the like. The exposure and development conditions of the resist film can be appropriately adjusted according to the resist composition used and the like. The second resist pattern R2 masks the area where the second plating body X2 is not scheduled to be laminated in the first plating body X1 (here, the area having a larger line width than other areas). The opening of the second resist pattern R2 can be appropriately set according to the second plating body X2 to be formed, that is, the second plating layer 17 in the second portion 11b. The height of the second resist pattern R2 can be appropriately set according to the height of the second portion 11b.

[0069] (Second plating body formation step) In this step, by using the second resist pattern R2 and electroplating the second metal material while energizing the first plating body X1, as shown in FIG. 9, a plurality of second plating bodies X2 are respectively formed on each first plating body X1 so as to partially cover the first plating body X1 in the longitudinal direction (the left-right direction in FIG. 9) and partially cover the first conductive underlayer 13.

[0070] <Second removal step> In this process, the second resist pattern R2 is removed from the base film 3. Specifically, the second resist pattern R2 is peeled off from the base film 3. As this peeling liquid, the same one as the peeling liquid used in the first peeling step described above can be used. By this peeling, as shown in FIG. 2 with reference to FIG. 9, a first conductive base layer 13 is formed on the base film 3, a first plating body X1 (corresponding to the first plating layer 15) disposed over the entire first conductive base layer 13, and a second plating layer 17 disposed at a plurality of portions in the longitudinal direction of the first plating body X1 are laminated to obtain a laminate. A first laminated portion formed by the first conductive base layer 13 and the first plating layer 15 constitutes the first portion 11a, and a second laminated portion formed by the first conductive base layer 13, the first plating layer 15, and the second plating layer 17 constitutes the second portion 11b.

[0071] In addition, when forming the second portion 11b' having the longitudinal cross-sectional shape as shown in FIG. 3 described above, after the second removing step, the manufacturing method further adds a step of dissolving, with an etching liquid, a portion including the lower end edge of the boundary portion with the first portion 11a in the formed second plating body X2 (that is, the second plating layer 17 of the second portion 11b). It can be manufactured by utilizing the fact that the etching rate decreases due to a decrease in the fluidity of the etching liquid at the lower end edge with respect to the peripheral portion of the lower end edge. As the etching liquid used in this step, the same etching liquid as the etching liquid used in the first etching step described above is used.

[0072] Also, when forming the second portion 11b’’ having the longitudinal cross-sectional shape as shown in FIG. 4 described above, the manufacturing method may further include an upper edge dissolution step of partially dissolving the upper edge of the boundary portion with the first portion 11a in the formed second plating body X2 (i.e., the second plating layer 17 of the second portion 11b) with an etching solution after the above-described second removal step. By further adding a step of dissolving the portion including the upper edge of this boundary portion with the etching solution, it is possible to utilize the fact that the etching rate increases due to the improved fluidity of the etching solution at the lower edge with respect to the peripheral portion of the upper edge. As the etching solution used in this upper edge dissolution step, the same etching solution as the etching solution used in the above-described first etching step is used.

[0073] <Advantages> According to the manufacturing method of the flexible printed wiring board 10, the above-described flexible printed wiring board 10 can be manufactured. That is, it is possible to manufacture a flexible printed wiring board 10 having excellent flexibility, capable of reducing electrical resistance, and achieving space saving.

[0074] [Second Embodiment] Next, the flexible printed wiring board and its manufacturing method according to the second embodiment will be described. Components common to the first embodiment are denoted by the same reference numerals and the description thereof will be omitted.

[0075] [Flexible Printed Wiring Board] As shown in FIGS. 10 and 11, the flexible printed wiring board 20 of the present embodiment mainly includes an insulating base film 3 and wiring 21 laminated on one surface side (front surface side) of the base film 3. The flexible printed wiring board 20 may further include a cover film on the front surface side of the base film 3 or the wiring 21.

[0076] [Wiring] The wiring 21 is laminated directly on the surface side of the base film 3 or via another layer. The wiring 21 has a first portion 21a in its longitudinal direction and a second portion 21b which is a portion other than the first portion 21a and has an average thickness H21 greater than the average thickness H11 of the first portion 21a. The ratio of the average thickness H21 of the second portion 21b to the average thickness H11 of the first portion 21a is 1.5 or more and 50 or less.

[0077] The wiring 21 has a second conductive base layer 23 laminated on the surface side of the base film 3, a plurality of third plating layers 25 laminated on the side (surface side) of the second conductive base layer 23 opposite to the base film 3 and at a plurality of portions in its longitudinal direction, and a plurality of fourth plating layers 27 laminated on the side (surface side) of the second conductive base layer 23 opposite to the base film 3 and connected to the third plating layer 25 in its longitudinal direction (the left - right direction in FIGS. 10 and 11). The third laminated portion having the second conductive base layer 23 and the third plating layer 25 constitutes the first portion 21a. The fourth laminated portion having the second conductive base layer 23 and the fourth plating layer 27 constitutes the second portion 11b. Examples of the wiring 21 include a signal line for sending a signal, a current line for sending a current for power supply, and a current line for sending a current for magnetic field generation.

[0078] Examples of the material for forming the second conductive base layer 23 include the same materials as those for the first conductive base layer 13 in the above - described first embodiment. The average thickness of the second conductive base layer 23 can be set in the same manner as the average thickness of the first conductive base layer 13 in the above - described first embodiment.

[0079] Examples of the third metal material for forming the third plating layer 25 include the same materials as those for the first metal material in the above - described first embodiment. For example, the line width of the third plating layer 25 can be set to be the same as the line width of the second conductive base layer 23.

[0080] Examples of the fourth metal material for forming the fourth plating layer 27 include, for example, those similar to the first metal material of the first embodiment described above. As the fourth metal material, those of the same type as the third metal material are preferable. For example, the line width of the fourth plating layer 25 can be set to be the same as the line width of the second conductive base layer 23.

[0081] When a plurality of wirings 21 are arranged adjacent to each other, the average line width L11 and the average interval S11 of these wirings 21 can be set in the same manner as the average line width L1 and the average interval S1 of the wiring 11 in the first embodiment described above.

[0082] The third plating layer 25 and the fourth plating layer 27 are much thicker than the second conductive base layer 23. Therefore, the thickness of the first portion 21a can be mainly determined by the thickness of the third plating layer 25. The thickness of the second portion 21b can be mainly determined by the thickness of the fourth plating layer 27.

[0083] (First portion) The average thickness H11 of each first portion 21a, the ratio (aspect ratio) of the average thickness H21 to the minimum line width (not shown) of the first portion 21a, the minimum line width of the first portion 21a, and the minimum cross-sectional area in the thickness direction of the first portion 21a, etc. can be set in the same manner as the first portion 11a of the first embodiment described above.

[0084] (Second portion) The average thickness H21 of each second portion 21b, the ratio (aspect ratio) of the average thickness H21 to the minimum line width (not shown) of the second portion 21b, the minimum line width of the second portion 21b, and the minimum cross-sectional area of the second portion 21b, etc. can be set in the same manner as the second portion 11b of the first embodiment described above.

[0085] Although illustration is omitted, also in this embodiment, similar to the second part 11b' of the first embodiment described above, the lower edge 21b'a of the boundary part adjacent to the first part 21a in the second part 21b' may have a curved shape as shown in FIG. 3 described above. Also, although illustration is omitted, similar to the second part 11b'' of the first embodiment described above, the upper edge 21b''b of the boundary part adjacent to the first part 21a in the second part 21b'' may have a curved shape as shown in FIG. 4 described above.

[0086] (Ratio of the average thickness of the second part to the average thickness of the first part) The ratio of the average thickness H21 of the second part 21b to the average thickness H11 of the first part 21a can be set in the same manner as the ratio of the average thickness H2 of the second part 11b to the average thickness H1 of the first part 11a of the first embodiment described above. That is, as the lower limit of the above ratio, it is 1.5 as described above, more preferably 2, and even more preferably 3. As the upper limit of the above ratio, it is 50 as described above, more preferably 20, and even more preferably 5. Note that, similar to the first embodiment described above, when each wiring 21 has a plurality of first parts 21a, the average thickness H11 of each first part 21a is set so as to satisfy the above ratio with respect to the average thickness H21 of each second part 21b. Also, when each wiring 21 has a plurality of second parts 21b, the average thickness H21 of each second part 21b is set so as to satisfy the above ratio with respect to the average thickness H11 of the first part 21a (with respect to the average thickness H11 of each first part 21a for a plurality of first parts 21a).

[0087] <Advantages> When the flexible printed wiring board 20 has a ratio of the average thickness H21 of the second portion 21b to the average thickness H11 of the first portion 21a of the wiring 21 of 1.5 or more and 50 or less. Thus, since the average thickness H11 of the first portion 21a is smaller than the average thickness H21 of the second portion 21b, the flexibility of the flexible printed wiring board 20 can be improved. Also, since the average thickness H21 of the second portion 21b is larger than the average thickness H11 of the first portion 21b, the electrical resistance of the wiring 21 can be reduced. In addition, since the average thickness H21 of the second portion 21b is larger than the average thickness H11 of the first portion 21a, space saving of the flexible printed wiring board 20 can be achieved more than when the line width of the wiring 21 is increased. Therefore, the flexible printed wiring board 20 has excellent flexibility, can reduce the electrical resistance, and can achieve space saving.

[0088] [Method for manufacturing a printed wiring board] Next, a method for manufacturing a flexible printed wiring board according to the present embodiment will be described using the flexible printed wiring board 20. FIGS. 12 to 16 are schematic end faces for explaining the manufacturing method, and are schematic end face views viewed in the same direction as the CC arrow viewing direction of FIG. 11. The left - right direction in FIGS. 12 to 16 is the longitudinal direction.

[0089] The manufacturing method of the flexible printed wiring board 20 includes a third plating step of forming a third plated body X3 extending in the longitudinal direction by electroplating a third metal material on the conductive base layer M of the base film 3 having the conductive base layer M laminated on one surface side (front surface side) using the third resist pattern R3, a third removing step of removing the third resist pattern R3 after the third plating step, and after the third removing step, using the fourth resist pattern R4, electroplating a fourth metal material on the conductive base layer M so as to include at least the non-laminated region of the third plated body X3 and be connected in the longitudinal direction to both end edges of the third plated body X3 in the longitudinal direction, thereby forming a plurality of fourth plated bodies X4 extending in the longitudinal direction and having an average thickness larger than that of the third plated body X3; and a fourth removing step of removing the fourth resist pattern R4 and the non-laminated regions of the third plated body X3 and the fourth plated body X4 in the conductive base layer M after the fourth plating step. The first portion 21a is formed as a third laminated portion having a part of the conductive base layer M (second conductive base layer 23) and the third plated body X3. The second portion 21b is formed as a fourth laminated portion having a part of the conductive base layer M (second conductive base layer 23) and the fourth plated body X4.

[0090] <Conductive base layer> As the conductive base layer M, the same one as that used in the first embodiment can be used. Therefore, a detailed description of the conductive base layer M is omitted.

[0091] <Third plating step> This step includes a third resist pattern forming step of forming a third resist pattern R3 on the surface of the conductive base layer M, and a third plated body forming step of forming a plurality of third plated bodies X3 extending in the longitudinal direction by electroplating a third metal material on the conductive base layer M using the formed third resist pattern R3.

[0092] (Third resist pattern forming step) In this process, as shown in FIG. 12, a third resist pattern R3 is formed on the surface of the conductive base layer M. Specifically, in the same manner as the first resist pattern forming process of the first embodiment, a third resist pattern R3 having a predetermined pattern is formed. The third resist pattern R3 can be appropriately set according to the third plating layer 25 to be formed.

[0093] (Third plating body forming process) In this process, while energizing the conductive base layer M, the third metal material is electroplated, so that, as shown in FIG. 13, third plating bodies X3 extending in the longitudinal direction (the direction perpendicular to the plane of FIG. 13) are formed at intervals in the width direction in the non-laminated regions of the third resist pattern R3 in the conductive base layer M.

[0094] <Third removal process> In this process, the third resist pattern R3 is removed from the conductive base layer M. Specifically, the third resist pattern R3 is peeled off from the conductive base layer M. Examples of the peeling liquid include the same ones as those used in the first peeling process of the first embodiment. By this removal, as shown in FIG. 14, a laminate in which the third plating bodies X3 are laminated on the conductive base layer M is obtained.

[0095] <Fourth plating process> This process includes a fourth resist pattern forming process of forming a fourth resist pattern R4 so as to cover the exposed conductive base layer M and the third plating bodies X3 after the above-described third removal process, and a fourth plating body forming process of forming fourth plating bodies X4 extending in the longitudinal direction by electroplating a fourth metal material using the formed fourth resist pattern R4.

[0096] (Fourth resist pattern forming process) In this process, as shown in FIG. 16, a fourth resist pattern R4 is formed on the exposed conductive base layer M. Specifically, a resist film such as a photosensitive film is laminated so as to cover the entire exposed conductive base layer M and the third plating body X3, and at least the non-laminated region of the third plating body X3 in the laminated resist film and a region connected to the third plating layer X3 in the longitudinal direction (the left-right direction in FIG. 13) are exposed and developed, thereby forming a fourth resist pattern R4 having a predetermined pattern. As the method for laminating the resist film, the same method as the first resist pattern forming method of the first embodiment described above can be adopted. The fourth resist pattern R4 can be appropriately set according to the arrangement of the third plating layer 27 of the wiring 21 to be formed. The height of the fourth resist pattern R4 can be appropriately set so as to be greater than the height of the third resist pattern R3 and according to the height of the fourth plating layer 27 of the wiring 21.

[0097] (Fourth plating body forming process) In this process, while energizing the conductive base layer M, the fourth metal material is electroplated, so that, as shown in FIG. 16, the fourth metal material is electroplated in the non-laminated region of the fourth plating body X4 in the conductive base layer M so as to be connected to both end edges in the longitudinal direction of the third plating body X3 in the longitudinal direction (the left-right direction in FIG. 16), thereby forming a plurality of fourth plating bodies X4 extending in the longitudinal direction while being connected to both end edges in the longitudinal direction of each third plating body X3.

[0098] <Fourth removal process> This process includes a second stripping process of stripping the fourth resist pattern R4 from the conductive base layer M and a second etching process of etching the non-laminated regions (unnecessary regions) of the third plating body X3 and the fourth plating body X5 in the conductive base layer M.

[0099] (Second stripping process) In this process, the fourth resist pattern R4 is stripped from the conductive base layer M. Examples of the stripping solution include the same ones as those used in the first stripping process of the first embodiment described above.

[0100] (Second Etching Process) In this process, the conductive base layer M is etched using the third plating body X3 and the fourth plating body X4 as masks. By this etching, as shown in FIG. 11 with reference to FIG. 16, a third laminated portion (corresponding to the first portion 21a) is obtained in which the second conductive base layer 23 and the third plating body X3 (corresponding to the third plating layer 25) are laminated on the base film 3. Also, a fourth laminate (corresponding to the second portion 21b) is obtained in which the second conductive base layer 23 and the fourth plating body X4 (corresponding to the fourth plating layer 27) are laminated on the base film 3. An etching solution that etches the metal forming the second conductive base layer 23 is used for the above etching.

[0101] For example, when forming the second portion 21b' having a longitudinal cross-sectional shape as shown in FIG. 3 described above, the manufacturing method further includes a step of dissolving, with an etching solution, a portion including the lower edge of the lower edge of the boundary between the first portion 21a and the formed fourth plating body X4 (that is, the second plating layer 27 of the second portion 21b) after the fourth removing step. By this, a step of utilizing the fact that the etching rate decreases due to a decrease in the fluidity of the etching solution at the lower edge with respect to the peripheral portion of the lower edge may be further provided. As the etching solution used in this lower edge dissolving step, the same etching solution as the etching solution used in the second etching step is used. In addition, when forming the second portion 21b'' having a longitudinal cross-sectional shape as shown in FIG. 4 described above, the lower edge may be dissolved by controlling the etching amount in the second etching step in the fourth removing step.

[0102] Also, when forming the second portion 21b’’ having the longitudinal cross-sectional shape as shown in FIG. 4 described above, the manufacturing method may further include a lower-end edge dissolving step of partially dissolving the upper-end edge of the boundary portion between the first portion 21a and the formed fourth plating body X4 (i.e., the second plating layer 27 of the second portion 21b) in the etching solution after the above fourth removing step. As the etching solution used in this lower-end edge dissolving step, an etching solution similar to the etching solution used in the above second etching step is used. In addition, when forming the second portion 21b’’ having the longitudinal cross-sectional shape as shown in FIG. 4 described above, the upper-end edge may be dissolved by controlling the etching amount in the second etching step in the above fourth removing step.

[0103] <Advantages> According to the manufacturing method of the flexible printed wiring board 20, the above-described flexible printed wiring board 20 can be manufactured. That is, it is possible to manufacture a flexible printed wiring board 20 having excellent flexibility, capable of reducing the electrical resistance, and capable of saving space.

[0104] [Other Embodiments] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is not limited to the configuration of the above embodiments, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0105] In the above embodiment, a flexible printed wiring board having a single base film and a plurality of wirings laminated on one surface of the base film has been described. However, the flexible printed wiring board may have a plurality of wirings laminated on both surfaces of a single base film. Further, the flexible printed wiring board may be a multilayer printed wiring board having a plurality of base films, and each base film has a plurality of wirings on one surface or both surfaces.

[0106] In the above-described embodiment, the case where the flexible printed wiring board has a plurality of wirings has been described. However, the flexible printed wiring board may have only one wiring.

[0107] In the above-described embodiment, the case where the line width of the first portion is the same as the line width of the second portion has been described. However, these line widths may be different. For example, the line width of the first portion may be larger than the line width of the second portion. Also, for example, the line width of the second portion may be larger than the line width of the first portion. In this case, as the first portion and the second portion, rectangular ones when viewed in a direction perpendicular to the base film 3 can be respectively adopted.

[0108] In the above-described embodiment, the case where each wiring has one first portion and a plurality of second portions has been described. However, the wiring may have one first portion and one second portion, may have a plurality of first portions and one second portion, or may have a plurality of first portions and a plurality of second portions. For example, the line width of the first portion may be larger than the line width of the second portion.

[0109] In the above-described first embodiment, the case where the line width of the region where the second plating layer 15 is formed in the longitudinal direction is smaller than the others has been described as the shape of the first conductive base body 13. However, the line width of this region may be the same as that of other regions or may be larger than other regions.

[0110] In the second plating step of the above-described first embodiment, the case where the second resist pattern R2 masks only a partial region in the longitudinal direction of the first plated body X1 has been described. However, as the second resist pattern, in addition to the above partial region, one that masks the space between the regions where the second plated bodies X2 are laminated may also be used.

[0111] Also, as another embodiment of the structure shown in FIG. 11, as shown in FIG. 17, the first portion 21a and the second portion 21b may partially overlap. As a manufacturing method of this structure, this structure can be manufactured by changing the region of the resist pattern R4 shown in FIG. 15. Thereby, even if a misalignment occurs during the formation of the resist pattern R2, the wiring 11 can be manufactured without disconnection, the yield can be improved, and the distortion at the boundary between the first portion 21a and the second portion 21b can be alleviated, which is more preferable.

Industrial Applicability

[0112] The flexible printed wiring board according to the embodiment of the present disclosure, and the flexible printed wiring board manufactured by the manufacturing method thereof have excellent flexibility, can reduce the electrical resistance, and can save space. Therefore, it can be suitably used for small electronic devices and the like.

Description of Symbols

[0113] 10, 20 Flexible printed wiring board 3 Base film 11, 21 Wiring 11a, 21a First portion 11b, 21b Second portion 13 First conductive underlayer 15 First plating layer 17 Second plating layer 23 Second conductive underlayer 25 Third plating layer 27 Fourth plating layer H1, H11 Average thickness of the first portion H2, H21 Average thickness of the second portion L1, L11 Average line width of the wiring S1, S11 Average interval of the wiring M Conductive underlayer R1 First resist pattern R2 Second resist pattern R3 Third resist pattern R4 Fourth resist pattern X1 First plating body X2 Second plating body X3 Third plating body X4 Fourth plating body

Claims

1. A flexible printed wiring board comprising an insulating base film and a plurality of wirings laminated on at least one surface side of the base film, wherein both the average line width and the average interval of the plurality of wirings are 3 μm or more and 50 μm or less, at least one of the plurality of wirings has a first portion in its longitudinal direction and a second portion other than the first portion and having an average thickness greater than the average thickness of the first portion, the first portion has a conductive base layer and a single first plating layer laminated on the conductive base layer, the second portion has the conductive base layer, the first plating layer, and a second plating layer at least partially laminated on the first plating layer, or has the conductive base layer and a second plating layer laminated on the conductive base layer adjacent to the first plating layer, the ratio of the average thickness of the second portion to the average thickness of the first portion is 1.5 or more and 50 or less, the second portions are arranged on both sides of the first portion in the longitudinal direction of the wiring, the ratio of the average thickness to the minimum line width in the first portion is 0.5 or more and 1.0 or less, the ratio of the average thickness to the minimum line width in the second portion is 1 or more and 10 or less, the wiring is a portion excluding the land portion, a flexible printed wiring board that is flexibly deformable in the first portion.

2. The flexible printed wiring board according to claim 1, wherein the minimum line width of the second portion is 100 μm or less.

3. The flexible printed wiring board according to any one of claims 1 or 2, wherein the ratio of the minimum cross-sectional area in the thickness direction of the second portion to the minimum cross-sectional area in the thickness direction of the first portion is 0.5 or more and 200 or less.

4. A method for manufacturing a flexible printed wiring board comprising an insulating base film and a plurality of wirings laminated on at least one surface side of the base film, wherein both the average line width and the average interval of the plurality of wirings are 3 μm or more and 50 μm or less, at least one of the plurality of wirings has a first portion in its longitudinal direction and a second portion other than the first portion and having an average thickness greater than the average thickness of the first portion, the first portion has a conductive base layer and a single first plating body laminated on the conductive base layer, The second part has the conductive base layer, the first plating body, and a second plating body at least partially laminated on the first plating body. The ratio of the average thickness of the second part to the average thickness of the first part is 1.5 or more and 50 or less. The second parts are arranged on both sides of the first part in the longitudinal direction of the wiring. The ratio of the average thickness to the minimum line width in the first part is 0.5 or more and 1.0 or less. The ratio of the average thickness to the minimum line width in the second part is 1 or more and 10 or less, and the wiring is a part excluding the land portion. A first plating step of forming one or more of the first plating bodies extending in the longitudinal direction by electroplating a first metal material on the conductive base layer of a base film having the conductive base layer laminated on at least one surface side using a first resist pattern. A first removing step of removing the non-laminated region of the first plating body in the first resist pattern and the conductive base layer after the first plating step. A second plating step of forming one or more of the second plating bodies by electroplating a second metal material partially in the longitudinal direction on the first plating body using a second resist pattern after the first removing step. A second removing step of removing the second resist pattern after the second plating step. The first part is formed as a first laminated part having a part of the conductive base layer and the first plating body. The second part is formed as a second laminated part having a part of the conductive base layer, the first plating body, and the second plating body. A method for manufacturing a flexible printed wiring board that is flexibly deformable in the first part.

5. A method for manufacturing a flexible printed wiring board including an insulating base film and a plurality of wirings laminated on at least one surface side of the base film, The average line width and average interval of the plurality of wirings are 3 μm or more and 50 μm or less. At least one of the plurality of wirings has a first part in its longitudinal direction and a second part that is a part other than the first part and has an average thickness greater than the average thickness of the first part. The first part has a conductive base layer and a single third plating body laminated on the conductive base layer. The second part has the conductive base layer and a fourth plating body laminated on the conductive base layer adjacent to the third plating body. The ratio of the average thickness of the second portion to the average thickness of the first portion is 1.5 or more and 50 or less, the second portion is disposed on both sides of the first portion in the longitudinal direction of the wiring, the ratio of the average thickness to the minimum line width in the first portion is 0.5 or more and 1.0 or less, the ratio of the average thickness to the minimum line width in the second portion is 1 or more and 10 or less, and the wiring is a portion excluding the land portion, a third plating step of forming one or more of the third plated bodies extending in the longitudinal direction by electroplating a third metal material on the conductive base layer of the base film having the conductive base layer laminated on at least one surface side using a third resist pattern; a third removing step of removing the third resist pattern after the third plating step; after the third removing step, using a fourth resist pattern, electroplating a fourth metal material so as to include at least a non-laminated region of the third plated body on the conductive base layer and be connected to the third plated body in the longitudinal direction, thereby forming one or more of the fourth plated bodies extending in the longitudinal direction and having a larger average thickness than the third plated body; a fourth plating step; after the fourth plating step, a fourth removing step of removing the fourth resist pattern and non-laminated regions of the third plated body and the fourth plated body in the conductive base layer are provided, the first portion is formed as a third laminated portion having a part of the conductive base layer and the third plated body, the second portion is formed as a fourth laminated portion having a part of the conductive base layer and the fourth plated body, A method for manufacturing a flexible printed wiring board that is flexibly deformable in the first portion.

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