Flexible printed wiring board and its manufacturing method

Abstract

To provide a flexible printed wiring board and a manufacturing method thereof that can reduce the electrical resistance of the entire wiring and also save space.SOLUTION: A flexible printed wiring board according to an embodiment of the present invention includes an insulating base film, and a plurality of wires laminated on at least one surface side of the base film, and the plurality of wires have one or more first wires and one or more second wires having an average thickness larger than the average thickness of the first wires in the same plane. The ratio of the average thickness of the second wire to the average thickness of the first wire 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 manufacturing method thereof. [Background technology]

[0002] Flexible printed wiring boards are widely used to configure circuits in various electronic devices. In recent years, as electronic devices have become smaller, flexible printed wiring boards have become smaller and their wiring density has increased significantly.

[0003] As such a small flexible printed wiring board, one having a sheet-like insulating base material and wiring laminated on the surface of the base material by plating has been proposed (see JP 2018-195681 A). In this flexible printed wiring board, the plating film thickness, i.e., the thickness of the wiring, is made uniform. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-195681 A Summary of the Invention [Problem to be solved by the invention]

[0005] Here, in a flexible printed wiring board, signal lines, current lines, etc. may be arranged as wiring. For example, since it is desired to pass as much current as possible through the current lines, when a flexible printed wiring board has current lines and signal lines, it is desired that the current lines have smaller electrical resistance than the signal lines.

[0006] On the other hand, in flexible printed wiring boards, which are desired to be miniaturized as described above, space saving is also desired.

[0007] For this reason, when a flexible printed wiring board has a plurality of current lines, it is desired that the electrical resistance of the current lines as a whole be small while the line width of the entire wiring be small, that is, space saving is required.

[0008] It is therefore an object of the present invention to provide a flexible printed wiring board capable of reducing the electrical resistance of the entire wiring and saving space, and a method for manufacturing the same. [Means for solving the problem]

[0009] A flexible printed wiring board according to one embodiment of the present disclosure, made to solve the above problems, is a flexible printed wiring board comprising an insulating base film and a plurality of wirings laminated on at least one side of the base film, wherein the plurality of wirings include, within the same surface, one or more first wirings and one or more second wirings having an average thickness greater than the average thickness of the first wirings, and the ratio of the average thickness of the second wirings to the average thickness of the first wirings is 1.5 or more and 50 or less.

[0010] Further, a manufacturing method for a flexible printed wiring board according to another embodiment of the present disclosure made to solve the above-mentioned problems is a manufacturing method for 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 plurality of wirings including one or more first wirings and one or more second wirings each having an average thickness greater than an average thickness of the first wirings within the same surface, a ratio of an average thickness of the second wirings to an average thickness of the first wirings is 1.5 or more and 50 or less, and a first metal material is electroplated on the conductive underlayer layer of the base film having a conductive underlayer laminated on at least one surface side of the base film using a first resist pattern, The method includes a first plating step of forming a first plated body and a second plated body; a first removal step of removing, after the first plating step, the first resist pattern and non-laminated areas of the first plated body and the second plated body in the conductive base layer; a second plating step of forming one or more third plated bodies by electroplating the second plated body with a second metal material 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, wherein the first wiring is formed as a first laminate having a portion of the conductive base layer and the first plated body, and the second wiring is formed as a second laminate having another portion of the conductive base layer, the second plated body, and the third plated body.

[0011] In addition, a manufacturing method for a flexible printed wiring board according to another embodiment of the present disclosure made to solve the above problem is a manufacturing method for 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 plurality of wirings having one or more first wirings and one or more second wirings each having an average thickness greater than the average thickness of the first wirings in the same surface, the ratio of the average thickness of the second wirings to the average thickness of the first wirings being 1.5 or more and 50 or less, and using a third resist pattern, electroplating a third metal material on the conductive base layer of the base film having a conductive base layer laminated on at least one surface side to form one or more fourth plated bodies. The method includes a third plating step, a third removal step of removing the third resist pattern after the third plating step, a fourth plating step of electroplating a fourth metal material in the non-laminated area of ​​the fourth plated body on the conductive base layer using the fourth resist pattern after the third removal step to form one or more fifth plated bodies having an average thickness larger than that of the fourth plated body, and a fourth removal step of removing the fourth resist pattern and the non-laminated area of ​​the fourth plated body and the fifth plated body on the conductive base layer after the fourth plating step, wherein the first wiring is formed as a third laminate having a portion of the conductive base layer and the fourth plated body, and the second wiring is formed as a fourth laminate having another portion of the conductive base layer and the fifth plated body. Effect of the Invention

[0012] A flexible printed wiring board according to one aspect of the present disclosure can reduce the electrical resistance of the entire wiring and can also save space. A method for manufacturing a flexible printed wiring board according to another aspect of the present disclosure can manufacture a flexible printed wiring board that can reduce the electrical resistance of the entire wiring and can also save space. [Brief description of the drawings]

[0013] [Figure 1]FIG. 1 is a schematic cross-sectional view showing a flexible printed wiring board according to a first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. [Diagram 3] FIG. 3 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. [Figure 4] FIG. 4 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. [Diagram 5] FIG. 5 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. [Figure 6] FIG. 6 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. [Figure 7] FIG. 7 is a schematic cross-sectional view showing a flexible printed wiring board according to the second embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. [Figure 9] FIG. 9 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. [Figure 10] FIG. 10 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. [Figure 11] FIG. 11 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. [Figure 12] FIG. 12 is a schematic cross-sectional view for explaining a method for manufacturing the flexible printed wiring board of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] [Description of the embodiments of the present disclosure] A flexible printed wiring board according to one embodiment of the present disclosure is a flexible printed wiring board comprising an insulating base film and a plurality of wirings laminated on at least one side of the base film, wherein the plurality of wirings include, within the same surface, one or more first wirings and one or more second wirings having an average thickness greater than the average thickness of the first wirings, and the ratio of the average thickness of the second wirings to the average thickness of the first wirings is 1.5 or more and 50 or less.

[0015] In the flexible printed wiring board, the ratio of the average thickness of the second wiring to the average thickness of the first wiring is within the above range, so that the electrical resistance of the second wiring can be made smaller than the electrical resistance of the first wiring when compared at the same line width. In addition, the line width of the second wiring can be made smaller than the line width of the first wiring when compared at the same electrical resistance. Therefore, the flexible printed wiring board can reduce the electrical resistance of the entire wiring and can achieve space saving.

[0016] The first wiring preferably has an average line width of 3 μm or more and 100 μm or less, and an average interval of 3 μm or more and 100 μm or less.

[0017] In this manner, by having the average line width and average spacing of the first wiring be within the above ranges, it is possible to further reduce the space required for the flexible printed wiring board.

[0018] The second wiring preferably has an average line width of 5 μm or more and 100 μm or less, and an average interval of 5 μm or more and 100 μm or less.

[0019] In this manner, by having the average line width and average spacing of the second wiring be within the above ranges, it is possible to further reduce the space required for the flexible printed wiring board.

[0020] It is preferable that a ratio of a minimum cross-sectional area in a thickness direction of the second wiring to a minimum cross-sectional area in a thickness direction of the first wiring is 0.5 or more and 200 or less.

[0021] In this way, by having the ratio of the minimum cross-sectional area in the thickness direction of the second wiring to the minimum cross-sectional area in the thickness direction of the first wiring be within the above range, the electrical resistance of the first wiring and the electrical resistance of the second wiring are relatively close to each other, and yet the flexible printed wiring board can be made more space-saving.

[0022] It is preferable that the ratio of the average thickness to the minimum line width in the first wiring is 0.3 or more and 5 or less, and the ratio of the average thickness to the minimum line width in the second wiring is 0.5 or more and 10 or less.

[0023] In this way, since the ratio of the average thickness to the minimum line width of the first wiring is within the above range, and the ratio of the average thickness to the minimum line width of the second wiring is within the above range, it is possible to further reduce the space required for the flexible printed wiring board.

[0024] A method for manufacturing a flexible printed wiring board according to another embodiment of the present disclosure is 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 plurality of wirings including one or more first wirings and one or more second wirings each having an average thickness greater than an average thickness of the first wirings within the same surface, a ratio of an average thickness of the second wirings to an average thickness of the first wirings being 1.5 or more and 50 or less, and using a first resist pattern, electroplating a first metal material onto a conductive base layer of the base film having a conductive base layer laminated on at least one surface side thereof, thereby forming one or more first plated bodies. the first plating step of forming a first plated body and a second plated body; a first removal step of removing, after the first plating step, the first resist pattern and non-laminated areas of the first plated body and the second plated body in the conductive base layer; a second plating step of forming one or more third plated bodies by electroplating the second plated body with a second metal material 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, wherein the first wiring is formed as a first laminate having a portion of the conductive base layer and the first plated body, and the second wiring is formed as a second laminate having another portion of the conductive base layer, the second plated body, and the third plated body.

[0025] According to the method for manufacturing a flexible printed wiring board, the flexible printed wiring board described above can be manufactured, that is, a flexible printed wiring board that can reduce the electrical resistance of the entire wiring and can also save space can be manufactured.

[0026] A method for producing a flexible printed wiring board according to another embodiment of the present disclosure is a method for producing 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 plurality of wirings including one or more first wirings and one or more second wirings each having an average thickness greater than an average thickness of the first wirings within the same surface, a ratio of an average thickness of the second wirings to an average thickness of the first wirings being 1.5 or more and 50 or less, and a third plating step of forming one or more fourth plated bodies by electroplating a third metal material on the conductive base layer of the base film having a conductive base layer laminated on at least one surface side of the base film using a third resist pattern. the third removal step of removing the third resist pattern after the third plating step; a fourth plating step of forming one or more fifth plated bodies having an average thickness larger than that of the fourth plated body by electroplating a fourth metal material in the non-laminated areas of the fourth plated body on the conductive base layer using the fourth resist pattern after the third removal step; and a fourth removal step of removing the fourth resist pattern and the non-laminated areas of the fourth plated body and the fifth plated body on the conductive base layer after the fourth plating step, wherein the first wiring is formed as a third laminate having a portion of the conductive base layer and the fourth plated body, and the second wiring is formed as a fourth laminate having another portion of the conductive base layer and the fifth plated body.

[0027] According to the method for manufacturing a flexible printed wiring board, the flexible printed wiring board described above can be manufactured, that is, a flexible printed wiring board that can reduce the electrical resistance of the entire wiring and can also save space can be manufactured.

[0028] Here, "average thickness" means the average value of thicknesses measured at any ten points in one wiring. "Thickness" means the distance between the base film and the upper edge of the wiring in a direction perpendicular to the base film. "Width" means the dimension of one wiring in a direction perpendicular to the longitudinal direction. "Spacing" means the distance between adjacent surfaces of two opposing wirings, and "average spacing" means the average value of the distance between the adjacent surfaces in the longitudinal direction of the wiring. "Average line width" means the average value of the maximum width of the wiring in a cross section perpendicular to the longitudinal direction of the wiring in the longitudinal direction of the wiring. "Minimum cross-sectional area" means the minimum value of the cross-sectional area of ​​one wiring perpendicular to the longitudinal direction of this wiring. "Minimum line width" means the minimum value of the line width within one wiring. However, land parts having vias (through holes, blind vias, filled vias) for connecting each wiring, land parts for connecting with mounted components, land parts for connecting with other printed circuit boards or connectors, etc. shall be excluded from the "thickness," "line width," "spacing," and "cross-sectional area" stipulated above. "Wiring" corresponds to "wiring layer."

[0029] [Details of the embodiment of the present disclosure] Hereinafter, an embodiment of a flexible printed wiring board and a manufacturing method thereof according to the present disclosure will be described in detail with reference to the drawings. In this embodiment, the "front side" refers to the side on which wiring is laminated in the thickness direction of the base film, and the front and back of this embodiment do not determine the front and back of the flexible printed wiring board when used.

[0030] [First embodiment] [Flexible Printed Wiring Boards] 1, a 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 wirings 11.

[0031] <Base film> The base film 3 is a layer made of synthetic resin having insulating properties. The base film 3 is also flexible. This base film 3 is also a substrate 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-permittivity synthetic resin film formed in a sheet shape can be used. Examples of the main component of this synthetic resin film include polyimide, polyethylene terephthalate, liquid crystal polymer, and fluororesin. The "main component" refers to the component with the highest content, for example, a component that occupies 50% by mass or more of the forming material. The base film 3 may contain other resins other than the exemplified resins such as polyimide, antistatic agents, etc.

[0032] The lower limit of the average thickness of the base film 3 is not particularly limited, but is preferably 3 μm, more 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 lower limit, the insulating strength and mechanical strength of the base film 3 may be insufficient. On the other hand, if the average thickness of the base film 3 exceeds the upper limit, the flexible printed wiring board 10 may be unnecessarily thick. Here, the "average thickness" means the average value of thicknesses measured at any ten points, as described above.

[0033] <Multiple Wires> The multiple wirings 11 are laminated directly or via another layer on the front surface side of the base film 3. The multiple wirings 11 have, in the same plane (here, in the same plane on the front surface side), multiple first wirings 13 and multiple second wirings 15 having an average thickness H2 larger than the average thickness H1 of the first wirings. The ratio of the average thickness H2 of the second wirings 15 to the average thickness H1 of the first wirings 13 is 1.5 or more and 50 or less.

[0034] (1st wiring) The first wiring 13 has a first conductive underlayer 13a laminated on the front surface side of the base film 3, and a first plating layer 13b laminated on the side (front surface side) of the first conductive underlayer 13a opposite to the base film 3. Examples of the first wiring 13 include a signal line for transmitting a signal, a current line for transmitting a current for power supply, and a current line for transmitting a current for generating a magnetic field.

[0035] Examples of materials for forming the first conductive underlayer 13a include copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), alloys thereof, and stainless steel. With regard to these forming materials, in terms of suppressing thermal deterioration of the adhesion of the first wiring 13 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 (e.g., polyimide). Furthermore, it is more preferable that the first conductive underlayer 13a includes a layer (first layer) containing at least one selected from nickel and chromium, which are easy to remove and easy to maintain insulation. It is also more preferable that the first conductive underlayer 13a includes a layer (second layer) mainly composed of copper on the upper side of this first layer (the side opposite to the base film 3). By disposing this layer mainly composed of copper, it is possible to shorten the work time when forming the first wiring 13 by electroplating.

[0036] 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 first wiring 13 to the base film 3. On the other hand, if the average thickness exceeds the upper limit, the first layer may be difficult to remove, and the insulation between the first wirings 13 may not be sufficiently maintained. The first layer may be formed by a sputtering method, an electroplating method, an electroless plating method, or the like.

[0037] 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 11 by electroplating may be excessively long. On the other hand, if the average thickness exceeds the upper limit, the second layer is difficult to remove, and the insulation between the first wirings 13 may not be sufficiently maintained. The second layer is preferably formed by a sputtering method, an electroplating method, an electroless plating method, or the like, or may be formed by a combination of these. In particular, it is preferable that an electroless copper plating layer is disposed on the uppermost surface side of the first conductive underlayer 13a, and thus, when an inner layer is formed by a sputtering method, defects that may occur due to the sputtering method can be covered.

[0038] Examples of the first metal material for forming the first plating layer 13b include copper, aluminum, silver, gold, nickel, and alloys thereof. Among these, copper or a copper alloy is preferred from the viewpoints of improving electrical conductivity and reducing costs. For example, the first plating layer 13b is formed in the same shape as the first conductive underlayer 13a when viewed in a direction perpendicular to the base film 3.

[0039] Since first plating layer 13b is much thicker than first conductive underlayer 13a, the thickness of first wiring 13 can be determined mainly by the thickness of first plating layer 13b.

[0040] The average thickness H1 of the first wiring 13 can be appropriately set so that the ratio of the average thickness H2 of the second wiring 15 to the average thickness H1 of the first wiring 13 is 1.5 or more and 50 or less. For example, the lower limit of the average thickness H1 of the first wiring 13 is preferably 3 μm, more preferably 5 μm, and even more preferably 10 μm. The upper limit of the average thickness H1 of the first wiring 13 is preferably 30 μm, more preferably 25 μm, and even more preferably 20 μm. If the average thickness H1 does not meet the lower limit, the mechanical strength of the first wiring 13 may be insufficient. In addition, the electrical resistance of the first wiring 13 may become excessively large, and a predetermined current may not be able to flow. On the other hand, if the average thickness H1 exceeds the upper limit, it becomes necessary to increase the line width to form the first wiring 13, and there is a risk that sufficient space saving cannot be achieved. The "average thickness" is obtained for each first wiring 13 by exposing a 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 any ten points in each first wiring 13, and calculating the average value of the measurement results. Note that, in the following, the "average thickness" of other members, etc. is a value measured in the same manner.

[0041] The lower limit of the ratio (aspect ratio) of the average thickness H1 to the minimum line width (not shown) of the first wiring 13 is preferably 0.3, more preferably 0.5, and more preferably 0.7. The upper limit of the ratio is preferably 5, more preferably 2, and even more preferably 1.0. If the ratio is less than the lower limit, there is a risk that sufficient space saving cannot be achieved. On the other hand, if the ratio exceeds the upper limit, there is a risk that sufficient space saving cannot be achieved. In addition, there is a risk that the flexibility of the wiring board 10 decreases and the wiring board 10 may break during bending. The "minimum line width" is a value measured for each first wiring 13 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 narrowest part of each first wiring 13 with a microscope or the like. However, this "minimum line width" is the length of the narrowest part in the area of ​​the first wiring 13 excluding the defective area. Here, the defective area to be excluded from the measurement is an area that is recessed (missing) inward from at least one edge in the width direction when observed with a microscope as described above. Specifically, this defective area is an area whose deepest part in the width direction has a length (width) that is ¼ or more of the average line width of other areas (other than the above-mentioned defective area) in the longitudinal direction of the first wiring 13. The above-mentioned average line width is measured in the same manner as the measurement method of the "average line width" described later. Note that, in the following, the "minimum line width" of other members, etc. is also a value measured in the same manner.

[0042] The minimum line width of the first wiring 13 can be appropriately set so as to satisfy, for example, the aspect ratio. For example, the lower limit of the minimum line width of the first wiring 13 is preferably 3 μm, more preferably 5 μm, and even more preferably 10 μm. The upper limit of the minimum line width of the first wiring 13 is preferably 30 μm, more preferably 25 μm, and even more preferably 20 μm. If the minimum line width is less than the lower limit, the mechanical strength of the first wiring 13 may be insufficient. On the other hand, if the minimum line width exceeds the upper limit, sufficient space saving may not be achieved.

[0043] When a plurality of first wirings 13 are arranged adjacent to each other, the lower limit of the average line width L1 of the first wirings 13 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 first wirings 13 is preferably 100 μm, more preferably 75 μm, and even more preferably 50 μm. If the average line width L1 of the first wirings 13 does not meet the lower limit, the mechanical strength may be insufficient. On the other hand, if the average line width L1 of the first wirings 13 exceeds the 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, measuring the length of the widest part of each first wiring 13 with a microscope or the like that can measure it. In the following, the "average line width" of other members, etc. is also a value measured in the same manner.

[0044] When a plurality of first wirings 13 are arranged adjacent to each other, the lower limit of the average interval S1 of the first wirings 13 is preferably 3 μm, more preferably 5 μm, and even more preferably 10 μm. The upper limit of the average interval S1 of the first wirings 13 is preferably 100 μm, more preferably 75 μm, and even more preferably 50 μm. If the average interval S1 of the first wirings 13 does not meet the lower limit, a short circuit may occur. On the other hand, if the average interval S1 of the first wirings 13 exceeds the upper limit, there is a risk that sufficient space saving cannot be achieved. The "average interval" is a value calculated as the average value of the lengths of the smallest intervals in the gaps between the first wirings 13, which are exposed by a cross-section processing device such as a microtome and measured by a microscope or the like that can measure the length of the smallest interval. In the following, the "average interval" of other members, etc. is measured in the same manner.

[0045] The minimum cross-sectional area in the thickness direction of the first wiring 13 can be appropriately set so that the ratio of the minimum cross-sectional area in the thickness direction of the second wiring 15 to the minimum cross-sectional area in the thickness direction of the first wiring 13 (minimum cross-sectional area of ​​the second wiring 15 / minimum cross-sectional area of ​​the first wiring 13) is within a predetermined range. The lower limit of this ratio is preferably 0.5, more preferably 0.7. The upper limit of the ratio is preferably 200, more preferably 20, and even more preferably 5. If the ratio does not meet the lower limit, the line width of the first wiring 13 may become relatively too large, and sufficient space saving may not be achieved. On the other hand, if the ratio exceeds the upper limit, the line width and interval of the second wiring 15 may become relatively too large, and sufficient space saving may not be achieved. The "minimum cross-sectional area" is calculated by the product of the average thickness H1 and the minimum line width. In the following, the "minimum cross-sectional area" of other members, etc. is also a value measured in the same manner.

[0046] (2nd wiring) The second wiring 15 has a thin second conductive underlayer 15a laminated on the front surface side of the base film 3, a second plating layer 15b laminated on the side (front surface side) of the second conductive underlayer 15a opposite the base film 3, and a third plating layer 15c laminated on the base film 3 so as to cover the second conductive underlayer 15a and the second plating layer 15b. Examples of the second wiring 15 include an operating power line of a connected device and a ground line.

[0047] The second conductive underlayer 15a may be formed from the same material as the first conductive underlayer 13a described above. The average thickness of the second conductive underlayer 15a is set to the same thickness as the average thickness of the first conductive underlayer 13a described above.

[0048] The second plating layer 15b is formed together with the first plating layer 13b using the first metal material for forming the first plating layer 13b of the first wiring 13 described above. That is, the metal material for forming the second plating layer 15b is the first metal material described above. For example, the second plating layer 13b is formed in the same shape as the second conductive underlayer 15a when viewed in a direction perpendicular to the base film 3.

[0049] Examples of the second metal material for forming the third plating layer 15c include copper, aluminum, silver, gold, nickel, and alloys thereof. Among these, copper or a copper alloy is preferred from the viewpoint of improving conductivity and reducing costs. The second metal material is preferably the same as the first metal material described above. For example, the third plating layer 15c is formed in a shape having a line width larger than that of the second conductive underlayer 15a and the second plating layer 15b when viewed in a direction perpendicular to the base film 3.

[0050] Since the second plating layer 15b and the third plating layer 15c are much thicker than the second conductive base layer 15a, the thickness of the second wiring 15 can be determined mainly by the thicknesses of the second plating layer 15b and the third plating layer 15c.

[0051] The average thickness H2 of the second wiring 15 can be appropriately set so that the ratio of the average thickness H2 of the second wiring 15 to the average thickness H1 of the first wiring 13 described above is 1.5 or more and 50 or less. For example, the lower limit of the average thickness H2 of the second wiring 15 is preferably 5 μm, more preferably 10 μm, and even more preferably 20 μm. The upper limit of the average thickness H2 of the second wiring 15 is preferably 100 μm, more preferably 75 μm, and even more preferably 50 μm. If the average thickness H2 does not meet the lower limit, the mechanical strength of the second wiring 15 may be insufficient. In addition, the electrical resistance of the second wiring 15 may become excessively large, and a predetermined current may not be able to flow. On the other hand, if the average thickness H2 exceeds the upper limit, it becomes necessary to increase the line width to form the second wiring 15, and there is a risk that sufficient space saving cannot be achieved.

[0052] The lower limit of the ratio (aspect ratio) of the average thickness H2 to the minimum line width (not shown) of the second wiring 15 is preferably 0.5, more preferably 1, and even more preferably 2. The upper limit of the ratio is preferably 10, more preferably 7, and even more preferably 5. If the ratio is below the lower limit, sufficient space saving may not be achieved. On the other hand, if the ratio exceeds the upper limit, sufficient space saving may not be achieved.

[0053] The minimum line width of the second wiring 15 can be appropriately set so as to satisfy, for example, the aspect ratio. For example, the lower limit of the minimum line width of the second wiring 15 is preferably 5 μm, more preferably 10 μm, and even more preferably 15 μm. The upper limit of the minimum line width of the second wiring 15 is preferably 100 μm, more preferably 75 μm, and even more preferably 50 μm. If the minimum line width is less than the lower limit, the mechanical strength of the second wiring 15 may be insufficient. On the other hand, if the minimum line width exceeds the upper limit, sufficient space saving may not be achieved. In addition, the flexibility of the wiring board 10 may decrease, and cracks or the like may occur during bending.

[0054] When a plurality of second wirings 15 are arranged adjacent to each other, the lower limit of the average line width L2 of the second wirings 15 is preferably 5 μm, more preferably 10 μm, and even more preferably 15 μm. The upper limit of the average line width L2 of the second wirings 15 is preferably 100 μm, more preferably 75 μm, and even more preferably 50 μm. If the average line width L2 of the second wirings 15 is less than the lower limit, the mechanical strength of the second wirings 15 may be insufficient. On the other hand, if the average line width L2 of the second wirings 15 exceeds the upper limit, sufficient space saving may not be achieved. In the embodiment shown in FIG. 1, the average line width L2 of the second wirings 15 is set to be larger than the average line width L1 of the first wirings 13.

[0055] When a plurality of second wirings 15 are arranged adjacent to each other, the lower limit of the average interval S2 of the second wirings 15 is preferably 5 μm, more preferably 10 μm, and even more preferably 15 μm. The upper limit of the average interval S2 of the second wirings 15 is preferably 100 μm, more preferably 75 μm, and even more preferably 50 μm. If the average interval S2 of the second wirings 15 does not meet the lower limit, a short circuit may occur. On the other hand, if the average interval S2 of the second wirings 15 exceeds the upper limit, sufficient space saving may not be achieved. In the embodiment shown in FIG. 1, the average interval S2 of the second wirings 15 is set to be the same as the average interval S1 of the first wirings 13.

[0056] As described above, the minimum cross-sectional area of ​​the second wiring 15 in the thickness direction can be appropriately set so that the ratio of the minimum cross-sectional area of ​​the second wiring 15 to the minimum cross-sectional area of ​​the first wiring 13 in the thickness direction is within the above-mentioned specified range.

[0057] (The ratio of the average thickness of the second wiring to the average thickness of the first wiring) The lower limit of the ratio of the average thickness H2 of the second wiring 15 to the average thickness H1 of the first wiring 13 is 1.5, preferably 2, and more preferably 3, as described above. The upper limit of the ratio is 50, preferably 20, and more preferably 5, as described above. If the ratio does not meet the lower limit, the electrical resistance of the entire wiring may not be reduced. In addition, sufficient space saving may not be achieved. On the other hand, if the ratio exceeds the upper limit, sufficient space saving may not be achieved.

[0058] <Advantages> In the flexible printed wiring board 10, the ratio of the average thickness H2 of the second wirings 15 to the average thickness H1 of the first wirings 13 is 1.5 or more and 50 or less, so that the electrical resistance of the second wirings 15 can be made smaller than the electrical resistance of the first wirings 13 when compared at the same line width. In addition, the line width of the second wirings 15 can be made smaller than the line width of the first wirings 13 when compared at the same electrical resistance. Therefore, the flexible printed wiring board 10 can reduce the electrical resistance of the entire wiring and can achieve space saving.

[0059] [Printed wiring board manufacturing method] Next, a method for manufacturing a flexible printed wiring board according to this embodiment will be described using the flexible printed wiring board 10.

[0060] The manufacturing method of the flexible printed wiring board 10 includes a first plating step of electroplating a first metal material on the conductive underlayer M of the base film 3 having the conductive underlayer M laminated on one side (front side) thereof using a first resist pattern R1 to form a plurality of first plated bodies X1 and second plated bodies X2, a first removal step of removing the first resist pattern R1 and non-laminated regions of the first plated bodies X1 and the second plated bodies X2 in the conductive underlayer M after the first plating step, a second plating step of electroplating the second metal material on the second plated body X2 using a second resist pattern R2 after the first removal step to form a third plated body X3, and a second removal step of removing the second resist pattern R2 after the second plating step. The first wiring 11 is formed as a first laminate having a part (first conductive underlayer 13a) of the conductive underlayer M and the first plated body X1. The second wiring 15 is formed as a second laminate having another part of the conductive base layer M (the second conductive base layer 15a), the second plated body X2, and the third plated body X3.

[0061] <Conductive base layer> The conductive underlayer M is laminated on the front surface side of the base film 3. This conductive underlayer M is used after being laminated in advance over the entire surface side of the base film 3. A part of the conductive underlayer M will eventually become the first conductive underlayer 13a of the first wiring 13, and another part of the conductive underlayer M will eventually become the second conductive underlayer 15a of the second wiring 15.

[0062] Examples of materials for forming the conductive underlayer M include copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), alloys thereof, and stainless steel. With regard to these forming materials, in order to suppress thermal deterioration of the adhesion of the first wiring 13 and the second wiring 15 to the base film 3, it is preferable that the conductive underlayer 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 (e.g., polyimide). Furthermore, it is more preferable that the conductive underlayer 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. It is also more preferable that the conductive underlayer M includes a layer (second layer) mainly composed of copper on the upper side of this first layer (the side opposite to the base film 3). By disposing this layer mainly composed of copper, it is possible to shorten the work time when forming the first wiring 13 and the second wiring 15 by electroplating.

[0063] 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 first wiring 13 and the second wiring 15 to the base film 3. On the other hand, if the average thickness exceeds the upper limit, the first layer is difficult to remove, and the insulation between the first wiring 13 and the second wiring 15 may not be sufficiently maintained. The first layer may be formed by a sputtering method, an electroplating method, an electroless plating method, or the like.

[0064] 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 11 by electroplating may be excessively long. On the other hand, if the average thickness exceeds the upper limit, the second layer is difficult to remove, and the insulation between the first wiring 13 and the second wiring 15 may not be sufficiently maintained. The second layer is preferably formed by a sputtering method, an electroplating method, an electroless plating method, or the like, or may be formed by a combination of these. In particular, it is preferable that an electroless copper plating layer is disposed on the uppermost surface side of the conductive underlayer M, and thus, when an inner layer is formed by a sputtering method, defects that may occur due to the sputtering method can be covered.

[0065] <First plating process> This process includes a first resist pattern formation process of forming a first resist pattern R1 on the surface of the conductive base layer M, and a first and second plating body formation process of forming a first plating body X1 and a second plating body X2 by electroplating a first metal material onto the conductive base layer M using the formed first resist pattern R1.

[0066] (First resist pattern forming process) In this step, as shown in FIG. 2, 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 applying a resist composition to the surface of the conductive base layer M, and a method of laminating a dry film photoresist on the surface of the conductive base layer M. The exposure and development conditions of the resist film can be appropriately adjusted depending on the resist composition used, etc. The openings of the first resist pattern R1 can be appropriately set depending on the first plating body X1 and the second plating body X2 to be formed, that is, the first plating layer 13b of the first wiring 13 and the second plating layer 15b of the second wiring 15 to be formed.

[0067] (First and second plating body forming process) In this process, the first metal material is electroplated while passing current through the conductive base layer M, thereby forming a plurality of first plated bodies X1 and second plated bodies X2 in the non-laminated area of ​​the first resist pattern R1 in the conductive base layer M as shown in Fig. 3. The first plated bodies X1 and second plated bodies X2 are arbitrarily set except that they have the same thickness. The shapes of the first plated bodies X1 and second plated bodies are not particularly limited, and for example, the cross-sectional shape may be set to a rectangular shape.

[0068] <First removal process> This process includes a first peeling process for peeling off the first resist pattern R1 from the conductive base layer M, and a first etching process for etching the non-laminated areas (unnecessary areas) of the first plating body X1 and the second plating body X2 in the conductive base layer M.

[0069] (First peeling process) In this step, the first resist pattern R1 is peeled off from the conductive underlayer M. A known peeling solution can be used, for example, an alkaline aqueous solution of sodium hydroxide, potassium hydroxide, or the like, an organic acid solution of alkylbenzenesulfonic acid, or the like, or a mixture of an organic amine, such as ethanolamine, and a polar solvent.

[0070] (First etching process) In this process, the conductive underlayer M is etched using the first plated body X1 and the second plated body X2 as a mask. This etching produces a laminate in which the first plated body X1 is laminated on the base film 3 via the first conductive underlayer 13a, and a laminate in which the second plated body X2 is laminated on the base film 3 via the second conductive underlayer 15a, as shown in FIG. An etching solution that corrodes the metal that forms the conductive underlayer M is used for the etching. In this manufacturing method, a so-called semi-additive method is preferably used.

[0071] <Second plating process> The second plating process includes, after the above-mentioned first removal process, a process of forming a second resist pattern R2 to cover the exposed base film 3 and first plating body X1, and a third plating body formation process of forming a third plating body X3 by electroplating the second plating body X2 with the above-mentioned second metal material using the formed second resist pattern R2.

[0072] (Second resist pattern forming process) In this process, as shown in FIG. 5, a resist film such as a photosensitive film is laminated so as to cover the entire exposed base film 3, the first conductive underlayer 13a, the first plating body X1, the second conductive underlayer 15a, and the second plating body X2, and the area of ​​the laminated resist film that overlaps with the second plating body X2 is exposed and developed to form a second resist pattern R2 having a predetermined pattern. Examples of the method of laminating the resist film include a method of applying a resist composition so as to cover the entire surface, and a method of laminating a dry film photoresist over the entire surface. The exposure and development conditions of the resist film can be appropriately adjusted depending on the resist composition used. The opening of the second resist pattern R2 can be appropriately set so that the second plating body X2 is formed in this opening and depending on the third plating body X3 to be formed, i.e., the third plating layer 15c of the second wiring 15. The height of the second resist pattern R2 can be appropriately set depending on the height of the third plating layer 15c of the second wiring 15.

[0073] (Third plating body formation process) In this process, the second metal material is electroplated while current is passed through the first plating body X1 and the second plating body X2, thereby forming a third plating body X3 in the non-laminated area of ​​the second resist pattern R2 so as to cover the second conductive base layer 15a and the second plating body X2, as shown in FIG. 6.

[0074] <Second removal process> In this step, 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 the peeling solution, the same one as that used in the first peeling step described above can be used. By this peeling, as shown in FIG. 1 with reference to FIG. 6, a first laminate (corresponding to the first wiring 13) formed by laminating the first conductive underlayer 13a and the first plated body X1 (corresponding to the first plating layer 13b) on the base film 3, and a second laminate (corresponding to the second wiring 15) formed by laminating the second conductive underlayer 15a, the second plated body X2 (corresponding to the second plating layer 15b), and the third plated body X3 (corresponding to the third plating layer 15c) on the base film 3 are obtained.

[0075] <Advantages> According to the manufacturing method of the flexible printed wiring board 10, it is possible to manufacture the above-mentioned flexible printed wiring board 10. That is, it is possible to manufacture a flexible printed wiring board 10 that can reduce the electrical resistance of the entire wiring and can achieve space saving.

[0076] [Second embodiment] Next, a flexible printed wiring board and a manufacturing method thereof according to a second embodiment will be described. Configurations common to the first embodiment will be denoted by the same reference numerals, and descriptions thereof will be omitted.

[0077] [Flexible Printed Wiring Boards] 7, a flexible printed wiring board 20 of the present embodiment mainly includes an insulating base film 3 and a plurality of wirings 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 wirings 21.

[0078] <Multiple Wires> The multiple wirings 21 are laminated on the front surface side of the base film 3 directly or via another layer. The multiple wirings 21 have, in the same plane (here, in the same plane on the front surface side), one or more first wirings 23 and one or more second wirings 25 having an average thickness H21 larger than the average thickness H11 of the first wirings 23. The ratio of the average thickness H21 of the second wirings 25 to the average thickness H11 of the first wirings 23 is 1.5 or more and 50 or less.

[0079] (1st wiring) The first wiring 23 may have a similar configuration to the first wiring 13 of the first embodiment described above. Therefore, detailed description of the first wiring 23 will be omitted. That is, the first wiring 23 has a third conductive base layer 23a and a fourth plating layer 23b similar to the first conductive base layer 13a and the first plating layer 13b of the first wiring 13. The material for forming the third conductive base layer 23a may be the same as the material for forming the first conductive base layer 13a of the first embodiment described above. The third metal material for forming the fourth plating layer 23b may be the same as the first metal material for forming the first plating layer 13b of the first embodiment described above.

[0080] The average thickness H11 of the first wiring 23, the ratio of the average thickness H11 to the minimum line width (not shown), the minimum line width, the average line width L11, the average spacing S11, the minimum cross-sectional area in the thickness direction, etc. can be set in the same manner as the first wiring 13 of the first embodiment described above.

[0081] (2nd wiring) The second wiring 25 has a thin fourth conductive underlayer 25a laminated on the front surface side of the base film 3, and a fifth plating layer 25b laminated on the side (front surface side) of the fourth conductive underlayer 25a opposite to the base film 3. Examples of the second wiring 25 include an operating power line of a connected device, a ground line, etc.

[0082] The line width and interval of the fourth conductive underlayer 25a are larger than those of the third conductive underlayer 23a of the first wiring 23. The remaining configuration of the fourth conductive underlayer 25a can be the same as that of the second conductive underlayer 15a of the second wiring 15 of the first embodiment described above. Therefore, detailed description of the remaining second conductive underlayer lines 25a will be omitted. That is, the fourth conductive underlayer 25a is formed by a part of the conductive underlayer M (see, for example, FIG. 8) described later other than the region where the third conductive underlayer 23a is formed. The material for forming the fourth conductive underlayer 25a is preferably the same as that for forming the third conductive underlayer 23a.

[0083] The fourth metal material for forming the fifth plating layer 25b may be the same as the first metal material for forming the first plating layer 13b in the first embodiment described above. The fourth metal material is preferably the same as the third metal material for forming the fourth plating layer 23b of the first wiring 23. For example, the fifth plating layer 25b is formed in the same shape as the fourth conductive underlayer 25a when viewed in a direction perpendicular to the base film 3.

[0084] Since the fifth plating layer 25b is much thicker than the fourth conductive base layer 25a, the thickness of the second wiring 25 can be determined mainly by the thickness of the fifth plating layer 25b.

[0085] The average thickness H21 of the second wiring 25, the ratio of the average thickness H21 to the maximum line width (not shown), the minimum line width, the average line width L21, the average spacing S21, the minimum cross-sectional area in the thickness direction, etc. can be set in the same manner as the second wiring 15 of the first embodiment described above.

[0086] (Average thickness of second wiring compared to average thickness of first wiring) The lower limit of the ratio of the average thickness H21 of the second wiring 25 to the average thickness H11 of the first wiring 23 is 1.5, preferably 2, and more preferably 3, as described above. The upper limit of the ratio is 50, preferably 20, and more preferably 5, as described above. If the ratio is below the lower limit, there is a risk that sufficient space saving cannot be achieved. On the other hand, if the ratio exceeds the upper limit, there is also a risk that sufficient space saving cannot be achieved. In addition, the flexibility of the wiring board 20 is reduced, and cracks or the like may occur during bending.

[0087] <Advantages> In the flexible printed wiring board 20, the ratio of the average thickness H21 of the second wirings 25 to the average thickness H11 of the first wirings 23 is 1.5 or more and 50 or less, so that the electrical resistance of the second wirings 25 can be made smaller than the electrical resistance of the first wirings 23 when compared at the same line width. In addition, the line width of the second wirings 25 can be made smaller than the line width of the first wirings 23 when compared at the same electrical resistance. Therefore, the flexible printed wiring board 20 can reduce the electrical resistance of the entire wiring and can achieve space saving.

[0088] [Printed wiring board manufacturing method] Next, a method for manufacturing a flexible printed wiring board according to this embodiment will be described using the flexible printed wiring board 20.

[0089] The manufacturing method of the flexible printed wiring board 20 includes a third plating step of 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 side (front side) thereof using a third resist pattern R3 to form a plurality of fourth plated bodies X4, a third removal step of removing the third resist pattern R3 after the third plating step, a fourth plating step of electroplating a fourth metal material on the non-laminated region of the fourth plated body X4 on the conductive base layer M using the fourth resist pattern R4 after the third removal step to form a plurality of fifth plated bodies X5 having an average thickness larger than that of the fourth plated body X4, and a fourth removal step of removing the fourth resist pattern R4 and the non-laminated region of the fourth plated body X4 and the fifth plated body 5 on the conductive base layer M after the fourth plating step. The first wiring 21 is formed as a third laminate having the third conductive base body M3 and the fourth plated body X4, which are part of the conductive base layer M. The second wiring 25 is formed as a fourth laminate having a fourth conductive base body M4, which is another part of the conductive base layer M, and a fifth plating body X5.

[0090] <Conductive base layer> The conductive underlayer M is the same as that used in the first embodiment, and therefore a detailed description of the conductive underlayer M will be omitted.

[0091] <Third plating process> This process includes a third resist pattern formation process of forming a third resist pattern R3 on the surface of the conductive base layer M, and a fourth plating body formation process of forming a fourth plating body X4 by electroplating a third metal material onto the conductive base layer M using the formed third resist pattern R3.

[0092] (Third resist pattern forming process) In this step, a third resist pattern R3 is formed on the surface of the conductive base layer M as shown in FIG. 8. Specifically, a third resist pattern R3 having a predetermined pattern is formed in the same manner as the first resist pattern forming step of the first embodiment. The openings of the third resist pattern R3 can be appropriately set according to the fourth plating body X4 to be formed, i.e., the fourth plating layer 23b of the first wiring 23 to be formed. The openings of the third resist pattern R3 can be appropriately set so that a space for forming the second wiring 25 remains on the conductive base layer.

[0093] (Fourth plating body formation process) In this process, the third metal material is electroplated while passing an electric current through the conductive base layer M, thereby forming a fourth plating body X4 in the non-laminated area of ​​the third resist pattern R3 on the conductive base layer M, as shown in Figure 9.

[0094] <Third removal process> In this step, 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. The peeling liquid used here may be the same as the peeling liquid used in the first peeling step of the first embodiment. This removal results in a laminate in which the fourth plated body X4 is laminated on the conductive base layer M, as shown in FIG.

[0095] <Fourth plating process> This process includes, after the third removal process described above, a process of forming a fourth resist pattern R4 to cover the exposed conductive base layer M and the fourth plating body X4, and a fifth plating body formation process of forming a fifth plating body X5 by electroplating a fourth metal material using the formed fourth resist pattern R4.

[0096] (Fourth resist pattern forming process) In this step, as shown in FIG. 11, 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 fourth plating body X4, and the non-laminated area of ​​the laminated resist film of the fourth plating body X4 is exposed and developed to form a fourth resist pattern R4 having a predetermined pattern. As a method for laminating the resist film, a method similar to the first resist pattern forming method of the first embodiment described above can be adopted. The opening of the fourth resist pattern R4 can be appropriately set according to the fifth plating body X5 to be formed, that is, the fifth plating layer 25b of the second wiring 25. The height of the fourth resist pattern R4 can be appropriately set so as to be greater than the third resist pattern R3 and according to the height of the fifth plating layer 25b of the second wiring 25.

[0097] (Fifth plating body formation process) In this process, the fourth metal material is electroplated while current is passed through the conductive base layer M, thereby forming a fifth plated body X5 having an average thickness greater than that of the fourth plated body X4 in the non-laminated area of ​​the conductive base layer M, as shown in Figure 12.

[0098] <4th removal process> This process includes a second peeling process for peeling the fourth resist pattern R4 from the conductive base layer M, and a second etching process for etching the non-laminated areas (unnecessary areas) of the fourth plated body X4 and the fifth plated body X5 in the conductive base layer M.

[0099] (Second peeling process) In this step, the fourth resist pattern R4 is stripped from the conductive underlayer M. As the stripping liquid, the same one as the stripping liquid used in the first stripping step of the first embodiment described above can be used.

[0100] (Second etching process) In this step, the conductive underlayer M is etched using the fourth plated body X4 and the fifth plated body X5 as a mask. This etching produces a third laminate (corresponding to the first wiring 23) in which the third conductive underlayer M3 (corresponding to the third conductive underlayer 23a) and the fourth plated body X4 (corresponding to the fourth plating layer 23b) which are parts of the conductive underlayer M are laminated on the base film 3, and a fourth laminate (corresponding to the second wiring 25) in which the fourth conductive underlayer M4 (corresponding to the fourth conductive underlayer 25a) and the fifth plated body X5 (corresponding to the fifth plating layer 25b) which are other parts of the conductive underlayer M are laminated on the base film 3, as shown in FIG. 7 with reference to FIG. 12. An etching solution that corrodes the metal that forms the conductive underlayer M is used for the etching.

[0101] <Advantages> According to the manufacturing method of the flexible printed wiring board 20, it is possible to manufacture the above-mentioned flexible printed wiring board 20. That is, it is possible to manufacture a flexible printed wiring board 20 that can reduce the electrical resistance of the entire wiring and can also save space.

[0102] [Other embodiments] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is not limited to the configurations of the above-described embodiments, but is indicated by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0103] In the above embodiment, a flexible printed wiring board having a single base film and a plurality of wirings laminated on one side of the base film has been described, but the flexible printed wiring board may have a plurality of wirings laminated on both sides of a single base film. Also, the flexible printed wiring board may be a multilayer printed wiring board having a plurality of base films, each of which has a plurality of wirings on one or both sides.

[0104] In the above embodiment, a case has been described in which the multiple wirings have multiple first wirings and multiple second wirings, but the multiple wirings may have one first wiring and one second wiring, one first wiring and multiple second wirings, or multiple first wirings and one second wiring.

[0105] In the above first embodiment, the case has been described where the thickness of first plating layer 13b of first wiring 13 is the same as the thickness of second plating layer 15b of second wiring 13, but these thicknesses may be different.

[0106] In the above first embodiment, the case where the line width of the second wiring 15 is larger than that of the first wiring 13 has been described, but the line width of the second wiring 15 may be the same as that of the first wiring 13 or may be smaller than that of the first wiring 13.

[0107] In the above first embodiment, the first conductive base body 13a and the first plating layer 13b of the first wiring 13 are formed in the same shape, but these shapes may be different. Also, the second conductive base body 15a and the second plating layer 15b of the second wiring 15 are formed in the same shape, but these shapes may be different.

[0108] In the second plating process of the first embodiment described above, the second resist pattern R2 masks not only all of the first plating bodies X1 but also the spaces between all of the second plating bodies X2. Alternatively, the second resist pattern may be one that masks only all of the first plating bodies X1 and does not mask the spaces between the second plating bodies X2.

[0109] In the above second embodiment, the third conductive base layer 23a and the fourth plating layer 23b of the first wiring 23 are formed in the same shape, but these shapes may be different. Also, the fourth conductive base layer 25a and the fifth plating layer 25b of the second wiring 25 are formed in the same shape, but these shapes may be different.

[0110] In the above first and second embodiments, the case where the average line width of the second wiring is larger than the average line width of the first wiring has been described, but the average line width of the second wiring may be the same as the average line width of the first wiring, or may be smaller than the average line width of the first wiring.

[0111] In the above first and second embodiments, the case where the average interval between the second wirings is the same as the average interval between the first wirings has been described. However, the average interval between the second wirings may be different from the average interval between the first wirings. [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 can reduce the electrical resistance of the entire wiring and can also save space, and therefore can be suitably used in small electronic devices, etc. [Explanation of symbols]

[0113] 10, 20 Flexible printed wiring board 3 Base film 11, 21 Wiring 13, 23 1st wiring 13a First conductive underlayer 13b First plating layer 15, 25 2nd wiring 15a Second conductive underlayer 15b Second plating layer 15c 3rd plating layer 23a Third conductive underlayer 23b 4th plating layer 25a 4th conductive underlayer 25b 5th plating layer H1, H11 Average thickness of the first wiring H2, H21 Average thickness of second wiring L1, L11 Average line width of the first wiring L2, L21 Average line width of second wiring S1, S11 Average spacing of the first wiring S2, S21 Average spacing of second wiring M Conductive base layer R1 First resist pattern R2 Second resist pattern R3 Third resist pattern R4 4th resist pattern X1 First plating body X2 Second plating body X3 3rd plating body X4 4th plating body X5 5th 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 of the base film, the plurality of wirings includes, in the same plane, a plurality of first wirings and a plurality of second wirings having an average thickness larger than an average thickness of the first wirings; a ratio of an average thickness of the second wiring to an average thickness of the first wiring is 1.5 or more and 50 or less; The first wiring and the second wiring each have a conductive base layer and a plating layer laminated on the conductive base layer, the average thickness of the conductive underlayer constituting the first wiring is equal to the average thickness of the conductive underlayer constituting the second wiring; the thickness of the plating layer constituting the second wiring is greater than the thickness of the plating layer constituting the first wiring, the line width of the conductive underlayer constituting the second wiring is larger than the line width of the conductive underlayer constituting the first wiring, A flexible printed wiring board, in which the distance between the conductive base layers constituting a pair of adjacent second wirings in the plurality of second wirings is larger than the distance between the conductive base layers constituting a pair of adjacent first wirings in the plurality of first wirings.

2. 2. The flexible printed wiring board according to claim 1, wherein the first wiring has an average line width of 3 μm or more and 100 μm or less and an average interval of 3 μm or more and 100 μm or less.

3. 3. The flexible printed wiring board according to claim 1, wherein the second wiring has an average line width of 5 μm or more and 100 μm or less and an average interval of 5 μm or more and 100 μm or less.

4. a ratio of an average thickness to a minimum line width in the first wiring is 0.3 or more and 5 or less; 4. The flexible printed wiring board according to claim 1, wherein a ratio of an average thickness to a minimum line width of the second wiring is 0.5 or more and 10 or less.

5. A method for producing a flexible printed wiring board according to any one of claims 1 to 4, comprising the steps of: a third plating step of electroplating a third metal material on the first conductive underlayer laminated on at least one surface side of the base film using a third resist pattern to form a plurality of fourth plated bodies; a third removal step of removing the third resist pattern after the third plating step; a fourth plating step of electroplating a fourth metal material in the non-laminated region of the fourth plated body on the first conductive underlayer using a fourth resist pattern after the third removal step, thereby forming a plurality of fifth plated bodies having an average thickness larger than that of the fourth plated body; a fourth removal step of removing the fourth resist pattern and non-laminated regions of the fourth plated body and the fifth plated body in the first conductive base layer after the fourth plating step; Equipped with the first wiring is formed as a third laminate having a part of the first conductive underlayer and the fourth plating body; A method for manufacturing a flexible printed wiring board, in which the second wiring is formed as a fourth laminate having another portion of the first conductive base layer and the fifth plated body.

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