Flexible printed wiring board and method for manufacturing the same

Abstract

A flexible printed wiring board comprises: a base film having a hole for forming a through hole; and a coil-shaped wiring layer stacked on at least one side of the base film, the wiring layer having: a pad portion arranged on the inner peripheral surface of the hole and the peripheral edge of the hole in the base film; and a winding portion arranged in a spiral shape with the pad portion as the inner end or the outer end, the winding portion having a first winding portion as the outermost periphery and a second winding portion closer to the inner side than the outermost periphery, and the ratio of the average thickness of the pad portion to the average thickness of the second winding portion is greater than 1.1 and less than 5.

Description

Technical Field

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

[0002] This application claims the benefit of Japanese Application No. 2020-003240 filed on January 10, 2020, and incorporates all of the contents described in the aforementioned Japanese Application. Background Art

[0003] Flexible printed wiring boards are widely used to form circuits of various electronic devices. In recent years, with the miniaturization of electronic devices, the miniaturization of flexible printed wiring boards and the increase in wiring density have been remarkable.

[0004] As such a small flexible printed wiring board, a flexible printed wiring board having a sheet-like insulating substrate and a coil-shaped wiring layer laminated on the surface of the substrate by plating is proposed (see Japanese Patent Publication No. 2018-195681). In this flexible printed wiring board, the thickness of the plating film, that is, the thickness of the wiring layer, is made uniform.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-195681 Summary of the invention

[0008] One embodiment of the present disclosure involves a flexible printed wiring board, which is a flexible printed wiring board comprising a base film having a hole for forming a through hole and a coil-shaped wiring layer stacked on at least one side of the base film, wherein the wiring layer comprises: a pad portion, which is arranged on the inner peripheral surface of the hole and the peripheral edge of the hole in the base film; and a winding portion, which is arranged in a spiral shape with the pad portion as the inner end or the outer end, and the winding portion comprises a first winding portion as the outermost periphery and a second winding portion which is closer to the inner side than the outermost periphery, and the ratio of the average thickness of the pad portion to the average thickness of the second winding portion is greater than 1.1 and less than 5.

[0009] Another embodiment of the present disclosure relates to a method for manufacturing a flexible printed wiring board, the flexible printed wiring board comprising: a base film having a hole for forming a through hole; and a coil-shaped wiring layer stacked on at least one side of the base film, the wiring layer comprising: a pad portion arranged on the inner peripheral surface of the hole and the peripheral edge of the hole in the base film; and a winding portion arranged in a spiral shape with the pad portion as the inner end or the outer end, the winding portion comprising a first winding portion as the outermost periphery and a second winding portion further inward than the outermost periphery, the average thickness of the pad portion relative to the average thickness of the second winding portion being greater than 1.1 and less than 5, the method for manufacturing the flexible printed wiring board comprising: a first plating step of electroplating a first metal material on the conductive base layer of the base film having a hole for forming a through hole and having a conductive base layer stacked on at least one side by using a resist pattern, thereby forming a base film having the pad a first plated body having a lower pad layer of the pad portion and a lower winding layer of the winding portion; a removing process, after the first plating process, removing the resist pattern and the non-laminated area of ​​the first plated body in the conductive base layer; and a second plating process, after the removing process, forming a second plated body having an upper pad layer of the pad portion and an upper winding layer of the winding portion by electroplating a second metal material on the first plated body, wherein in the first plating process, the first metal material is electroplated on the conductive base layer in a manner that the second plating amount for forming the lower pad layer is larger than the first plating amount for forming the innermost part of the lower winding layer, the pad portion is formed by a portion of the conductive base layer, the lower pad layer and the upper pad layer, and the winding portion is formed by another portion of the conductive base layer, the lower winding layer and the upper winding layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 1 is a schematic plan view showing a flexible printed wiring board according to the first embodiment.

[0011] Figure 2 It is shown Figure 1 Schematic cross-sectional view of a flexible printed wiring board.

[0012] Figure 3 It is used to illustrate Figure 1 and Figure 2 A schematic cross-sectional view of a method for manufacturing a flexible printed wiring board is shown along Figure 1 The AA arrow direction is the same as the schematic cross-sectional view observed in the direction.

[0013] Figure 4 It is used to illustrate Figure 1 and Figure 2 A schematic cross-sectional view of a method for manufacturing a flexible printed wiring board is shown along Figure 1 The AA arrow direction is the same as the schematic cross-sectional view observed in the direction.

[0014] Figure 5 It is used to illustrate Figure 1 and Figure 2 A schematic cross-sectional view of a method for manufacturing a flexible printed wiring board is shown along Figure 1 The AA arrow direction is the same as the schematic cross-sectional view observed in the direction. DETAILED DESCRIPTION

[0015] Technical problems to be solved by the present disclosure

[0016] Here, in a flexible printed wiring board, if poor conduction occurs or resistance is too high, there is a concern that poor connection may occur. Therefore, the flexible printed wiring board is required to have excellent connection reliability.

[0017] In view of the above, an object of the present invention is to provide a flexible printed wiring board having excellent connection reliability and a method for manufacturing the same.

[0018] Effects of the present disclosure

[0019] A flexible printed wiring board according to one aspect of the present disclosure is excellent in connection reliability. A method for manufacturing a flexible printed wiring board according to another aspect of the present disclosure is capable of manufacturing a flexible printed wiring board having excellent connection reliability.

[0020] [Description of Embodiments of the Present Disclosure]

[0021] One embodiment of the present disclosure involves a flexible printed wiring board, which is a flexible printed wiring board comprising a base film having a hole for forming a through hole and a coil-shaped wiring layer stacked on at least one side of the base film, wherein the wiring layer comprises: a pad portion, which is arranged on the inner peripheral surface of the hole and the peripheral edge of the hole in the base film; and a winding portion, which is arranged in a spiral shape with the pad portion as the inner end or the outer end, and the winding portion comprises a first winding portion as the outermost periphery and a second winding portion which is closer to the inner side than the outermost periphery, and the ratio of the average thickness of the pad portion to the average thickness of the second winding portion is greater than 1.1 and less than 5.

[0022] Here, in a flexible printed wiring board having a wiring layer with a coil-shaped winding portion, when the average thickness of the pad portion in the wiring layer is small, the amount of metal stacked on the inner peripheral surface of the above-mentioned hole becomes smaller, and there is a concern that poor conduction is likely to occur in the through hole.

[0023] In contrast, in the flexible printed wiring board, since the above ratio is within the above range, the average thickness of the above pad portion is sufficiently large, and the amount of metal laminated on the inner peripheral surface of the above hole can be increased. Therefore, poor conduction in the through hole can be reduced. Therefore, the connection reliability of the flexible printed wiring board is excellent.

[0024] It is preferred that the ratio of the average thickness of the first winding portion to the average thickness of the second winding portion be 1.1 or more and 5 or less.

[0025] Since the ratio is within the range, the average thickness of the first winding portion at the outermost circumference becomes sufficiently large, and the resistance of the first winding portion can be reduced. Therefore, the resistance of the wiring layer can be reduced.

[0026] The flexible printed wiring board may further include one or more dummy wiring layers arranged at a distance from the wiring layer in a region outside the wiring layer in the base film.

[0027] As described above, since the flexible printed wiring board includes the dummy wiring layer, it is easy to form a wiring layer having a large average thickness in the first winding portion at the outermost periphery. Therefore, the connection reliability of the flexible printed wiring board is further improved.

[0028] It is preferred that the ratio of the second area of ​​the stacked region of the dummy wiring layer in the base film to the first area of ​​the region between the wiring layer and the outside thereof at the shortest distance of 2 mm is 20% or more and less than 50%.

[0029] As described above, since the ratio of the second area to the first area is within the above range, it is easier to form a wiring layer having a large average thickness in the first winding portion at the outermost periphery. Therefore, the connection reliability of the flexible printed wiring board is further improved.

[0030] In addition, different schemes of the present disclosure involve a method for manufacturing a flexible printed wiring board, the flexible printed wiring board comprising: a base film having a hole for forming a through hole; and a coil-shaped wiring layer stacked on at least one side of the base film, the wiring layer comprising: a pad portion arranged on the inner peripheral surface of the hole and the peripheral edge of the hole in the base film; and a winding portion arranged in a spiral shape with the pad portion as the inner end or the outer end, the winding portion comprising a first winding portion as the outermost periphery and a second winding portion further inner than the outermost periphery, the ratio of the average thickness of the pad portion to the average thickness of the second winding portion being greater than 1.1 and less than 5, the method for manufacturing the flexible printed wiring board comprising: a first plating step of electroplating a first metal material on the conductive base layer of the base film having a hole for forming a through hole and having a conductive base layer stacked on at least one side by using a resist pattern, thereby forming a base film having the solder pad portion A first plated body having a lower pad layer of the pad portion and a lower winding layer of the winding portion; a removal process, after the first plating process, removing the resist pattern and the non-laminated area of ​​the first plated body in the conductive base layer; and a second plating process, after the removal process, forming a second plated body having an upper pad layer of the pad portion and an upper winding layer of the winding portion by electroplating a second metal material on the first plated body, wherein in the first plating process, the first metal material is electroplated on the conductive base layer in a manner that the second plating amount for forming the lower pad layer is larger than the first plating amount for forming the lower winding layer further inside the outermost periphery, the pad portion is formed by a portion of the conductive base layer, the lower pad layer and the upper pad layer, and the winding portion is formed by another portion of the conductive base layer, the lower winding layer and the upper winding layer.

[0031] According to the manufacturing method of the flexible printed wiring board, the above-mentioned flexible printed wiring board can be manufactured. That is, a flexible printed wiring board with excellent connection reliability can be manufactured.

[0032] Preferably, the flexible printed wiring board further comprises a dummy wiring layer which is arranged at a distance from the wiring layer in an outer area of ​​the wiring layer in the base film, and in the first plating step, a dummy plating body is formed on the conductive base layer in addition to the first plating body, and the electrically isolated dummy wiring layer is formed by a part of the non-laminated area of ​​the pad portion and the winding portion in the conductive base layer and the dummy plating body.

[0033] Since the dummy plated body is formed in the first plating step, it is easy to form a wiring layer having a large average thickness in the first winding portion at the outermost periphery. Therefore, according to the manufacturing method of the flexible printed wiring board, a flexible printed wiring board with better connection reliability can be manufactured.

[0034] Here, the "outermost periphery of the winding portion" refers to a portion whose inner side is opposite to other portions of the winding portion. The "average thickness" refers to the average values ​​of the thicknesses measured at any ten points for each of the pad, the first winding portion, and the second winding portion. The "thickness" refers to the distance between the base film and the upper edge of the wiring layer in the direction perpendicular to the base film. In addition, hereinafter, the "line width" refers to the dimension of the winding portion in the direction perpendicular to the length direction (winding direction). The "interval" refers to the distance between adjacent faces in the winding portion, and the "average interval" refers to the value obtained by averaging the distances between the adjacent faces in the length direction. The "average line width" refers to the value obtained by averaging the maximum width of the winding portion in a section perpendicular to the length direction in the length direction.

[0035] [Details of the embodiments of the present disclosure]

[0036] Hereinafter, the embodiment of the flexible printed wiring board and the manufacturing method thereof involved in the present disclosure will be described in detail with reference to the accompanying drawings. It should be noted that in this embodiment, the "surface side" refers to the side where the wiring layer is stacked in the thickness direction of the base film, and the surface and back side of this embodiment do not determine the surface and back side of the flexible printed wiring board in the use state.

[0037] [First embodiment]

[0038] 〔Flexible printed wiring board〕

[0039] like Figure 1 and Figure 2 As shown, the flexible printed wiring board 10 of this embodiment mainly includes a base film 3 having insulating properties and a wiring layer 11 stacked on one side (surface side) of the base film 3. The flexible printed wiring board 10 also includes a dummy wiring layer 41 arranged at a distance from the wiring layer 11 in the outer area of ​​the wiring layer 11 in the base film 3. The flexible printed wiring board 10 may also include a cover film on the surface side of the base film 3 or the wiring layer 11.

[0040] <Base film>

[0041] The base film 3 is a layer made of synthetic resin with insulation. The base film 3 is also flexible. The base film 3 is also a substrate for forming the wiring layer 11. The base film 3 has a hole 3a for forming the through hole 20. The forming material of the base film 3 is not particularly limited as long as it has insulation and flexibility, but a synthetic resin film with a low dielectric constant formed in a sheet shape can be used. As the main component of the synthetic resin film, for example, polyimide, polyethylene terephthalate, liquid crystal polymer, fluororesin, etc. can be listed. The "main component" is the component with the highest content, which refers to, for example, a component that accounts for more than 50% by mass in the forming material. The base film 3 may also contain other resins other than the resins exemplified by polyimide, antistatic agents, etc.

[0042] The lower limit of the average thickness of the base film 3 is not particularly limited, but is preferably 3 μm, preferably 5 μm, and more preferably 10 μm. The upper limit of the average thickness of the base film 3 is not particularly limited, but is preferably 200 μm, more preferably 150 μm, and further preferably 100 μm. When the average thickness of the base film 3 is less than the above lower limit, there is a concern that the insulation strength and mechanical strength of the base film 3 are not sufficient. On the other hand, when the average thickness of the base film 3 exceeds the above upper limit, there is a concern that the flexible printed wiring board 10 is unnecessarily thickened. Here, as above, "average thickness" refers to the average value of the thickness measured at any ten points.

[0043] The through hole 20 may be formed at a suitable position and in a suitable size.

[0044] <Wiring Layer>

[0045] The wiring layer 11 is stacked on the surface side of the base film 3 directly or through other layers. The wiring layer 11 is coil-shaped. The wiring layer 11 has a pad portion 13 and a winding portion 15, the pad portion 13 is arranged on the inner peripheral surface of the hole 3a for forming the above-mentioned through hole 20 and the peripheral portion of the above-mentioned hole 3a in the above-mentioned base film 3, and the winding portion 15 is arranged in a spiral shape with the pad portion 13 as the inner end. The above-mentioned winding portion 15 has a first winding portion 15a as the outermost periphery and a second winding portion 15b that is closer to the inner side than the above-mentioned outermost periphery. The ratio of the average thickness H2 of the above-mentioned pad portion to the average thickness H1 of the above-mentioned second winding portion 15b is greater than 1.1 and less than 5. The ratio of the average thickness H3 of the above-mentioned first winding portion 15a to the average thickness H1 of the above-mentioned second winding portion 15b is not particularly limited. For example, in the present embodiment, the ratio is greater than 1.1 and less than 5. It should be noted that the wiring layer 11 may have the pad portion 13 as the outer end portion. In addition, the wiring layer 11 may have two pad portions as the inner end portion and the outer end portion, respectively.

[0046] The pad portion 13 is formed by a first conductive base layer 23 stacked on the surface side of the base film 3 and a lower pad layer 25 stacked on the side (surface side) of the first conductive base layer 23 opposite to the base film 3. The first conductive base layer 23 is also stacked on the inner peripheral surface of the hole 3a. The winding portion 15 is formed by a second conductive base layer 33 stacked on the surface side of the base film 3, a lower winding layer 35 stacked on the side (surface side) of the second conductive base layer 33 opposite to the base film 3, and an upper winding layer 37 stacked on the side (surface side) of the lower winding layer 35 opposite to the second conductive base layer 33. The upper winding layer 37 is formed so that the average thickness of the region constituting a part of the pad portion 13 in the upper winding layer 37 and the average thickness of the region constituting a part of the first winding portion 15a are greater than the average thickness of the region constituting a part of the second winding portion 15b in the upper winding layer 37. As the wiring layer 11 , for example, a coil wire for transmitting a current for generating a magnetic field can be cited.

[0047] As the forming material of the first conductive base layer 23 and the second conductive base layer 33, for example, copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), alloys thereof, stainless steel, etc. can be cited. With regard to these forming materials, in order to suppress the thermal degradation of the adhesion of the wiring layer 11 to the base film 3, preferably, the first conductive base layer 23 and the second conductive base layer 33 include a layer (first layer) containing at least one selected from the group consisting of the above-mentioned nickel, chromium, titanium and silver on the side in contact with the base film 3 (for example, polyimide). Furthermore, more preferably, the first conductive base layer 23 and the second conductive base layer 33 include a layer (first layer) containing at least one selected from nickel and chromium that are easy to remove and easy to maintain insulation. In addition, more preferably, the first conductive base layer 23 and the second conductive base layer 33 include a layer (second layer) containing copper as a main component on the upper side of the first layer (the side opposite to the base film 3). By providing this layer containing copper as a main component, it is possible to shorten the working time when forming the wiring layer 11 by electroplating.

[0048] 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. When the average thickness is less than the lower limit, there is a concern that it is difficult to suppress the thermal degradation of the adhesion of the wiring layer 11 to the base film 3. On the other hand, when the average thickness exceeds the upper limit, there is a concern that it is difficult to easily remove the first layer and the insulation of the wiring layer 11 cannot be fully maintained. It should be noted that the first layer can be formed by sputtering, electroplating, electroless plating, etc.

[0049] For example, the lower limit of the average thickness of the second layer is preferably 0.1 μm, and more preferably 0.2 μm. The upper limit of the average thickness of the second layer is preferably 2 μm, and more preferably 1 μm. When the average thickness is less than the lower limit, there is a concern that the time for forming the wiring layer 11 by electroplating becomes too long. On the other hand, when the average thickness exceeds the upper limit, there is a concern that it is difficult to easily remove the second layer and the insulation between the winding parts 15 cannot be fully maintained. It should be noted that the second layer is preferably formed by sputtering, electroplating, non-electrolytic plating, etc., and can also be formed by combining these methods. In particular, it is preferred to configure a non-electrolytic copper plating layer on the uppermost surface side of the first conductive base layer 23 and the second conductive base layer 33, thereby, when a layer located further inside is formed by sputtering, defects that may be generated by the sputtering method can be covered.

[0050] As the first metal material for forming the lower pad layer 25 and the lower winding layer 35, for example, copper, aluminum, silver, gold, nickel, and alloys thereof can be cited. Among them, copper or copper alloys are preferred from the viewpoint of improving conductivity and reducing costs. For example, when viewed in a direction perpendicular to the base film 3, the lower pad layer 25 and the lower winding layer 35 are formed in the same shape as the first conductive base layer 23 and the second conductive base layer 33.

[0051] As the second metal material for forming the upper pad layer 27 and the upper winding layer 37, for example, the same material as the first metal material can be cited. As the second metal material, the same type of material as the first metal material is preferred. For example, when viewed in a direction perpendicular to the base film 3, the upper pad layer 27 and the upper winding layer 37 are formed to have a line width greater than that of the lower pad layer 25 and the lower winding layer 35.

[0052] (Pad part)

[0053] The average thickness H2 of the pad portion 13 can be appropriately set in such a manner that the ratio of the average thickness H2 of the pad portion 13 to the average thickness H1 of the second winding portion 15b is greater than 1.1 and less than 10. For example, the lower limit of the average thickness H2 of the pad portion 13 is preferably 5 μm, more preferably 10 μm, and further preferably 20 μm. The upper limit of the average thickness H2 of the pad portion 13 is preferably 100 μm, more preferably 75 μm, and further preferably 50 μm. When the above-mentioned average thickness H2 is less than the above-mentioned lower limit, there is a concern that it is difficult to make the above-mentioned first metal material and the above-mentioned second metal material adhere to the inner circumferential surface of the hole 3a in a sufficient amount (coating amount). On the other hand, when the above-mentioned average thickness H2 exceeds the above-mentioned upper limit, there is a concern that the amount of adhesion of the above-mentioned first metal material and the above-mentioned second metal material to the inner circumferential surface of the hole 3a will increase excessively. Average thickness H2 is obtained by exposing the cross section of wiring board 10 using a cross-section processing device such as a slicer, measuring the thickness of ten arbitrary points in pad portion 13 based on cross-section observation, and calculating the average value of the measurement results.

[0054] The maximum line width of the pad portion 13 , the ratio of the average thickness H2 to the maximum line width (aspect ratio), and the like can be appropriately set.

[0055] (Winding part)

[0056] The lower limit of the average line width L of the winding portion 15 is preferably 5 μm, more preferably 10 μm, and further preferably 15 μm. The upper limit of the average line width L of the winding portion 15 is preferably 100 μm, more preferably 75 μm, and further preferably 50 μm. When the average line width L of the winding portion 15 is less than the above lower limit, there is a concern that the resistance of the winding portion 15 becomes too large and the mechanical strength is insufficient. On the other hand, when the average line width L of the winding portion 15 exceeds the above upper limit, there is a concern that space saving cannot be achieved. The "average line width" is a value obtained by exposing the cross section of the wiring board 10 using a cross-section processing device such as a slicer, measuring the length of the widest part in the winding portion 15 using a microscope, etc., and calculating the value as their average value.

[0057] The lower limit of the average spacing S of the winding parts 15 is preferably 5μm, more preferably 10μm, and further preferably 15μm. The upper limit of the average spacing S of the winding parts 15 is preferably 50μm, and further preferably 25μm. When the average spacing S of the winding parts 15 is less than the above lower limit, there is a concern that a short circuit will occur. On the other hand, when the average spacing S of the winding parts 15 exceeds the above upper limit, there is a concern that space saving cannot be achieved. The "average spacing" is a value obtained by exposing the cross section of the wiring board 10 using a cross-section processing device such as a slicer, measuring the length of the smallest portion of the gap between the winding parts 15 using a microscope, etc., and calculating the value as their average value.

[0058] The lower winding layer 35 and the upper winding layer 37 are much thicker than the second conductive base layer 33. Therefore, the thickness of the winding portion 15 can be mainly determined by the thickness of the lower winding layer 35 and the upper winding layer 37.

[0059] Second winding section

[0060] The average thickness H1 of the inner second winding portion 15b in the winding portion 15 can be appropriately set in such a manner that the ratio of the average thickness H2 of the pad portion 13 and the average thickness H3 of the outermost first winding portion 15a to the average thickness H1 of the second winding portion 15b is greater than 1.1 and less than 5. For example, the lower limit of the average thickness H1 of the second winding portion 15b is preferably 10μm, more preferably 15μm, and further preferably 20μm. The upper limit of the average thickness H1 of the second winding portion 15b is preferably 100μm, more preferably 80μm, and further preferably 60μm. When the above-mentioned average thickness H1 is less than the above-mentioned lower limit, there is a concern that the resistance of the second winding portion 15b becomes larger. On the other hand, when the above-mentioned average thickness H1 exceeds the above-mentioned upper limit, there is a concern that the line width needs to be increased in order to form the second winding portion 15b, and space saving cannot be achieved. The "average thickness" is obtained by exposing the cross section of the wiring board 10 using a cross-section processing device such as a slicer, measuring the thickness based on cross-section observation at any ten points in the second winding portion 15, and calculating the average value of the measurement results. It should be noted that the "average thickness" of other components, etc., is also a value measured in the same manner as above.

[0061] The lower limit of the ratio (aspect ratio) of the average thickness H1 of the second winding portion 15b to the minimum line width (not shown) is preferably 0.3, preferably 0.5, and more preferably 0.7. The upper limit of the above ratio is preferably 5, more preferably 3, and further preferably 2. When the above ratio is less than the above lower limit, there is a concern that space saving cannot be achieved. On the other hand, when the above ratio exceeds the above upper limit, there is also a concern that space saving cannot be achieved. "Minimum line width" refers to the minimum value of the line width of the second winding portion 15b. The "minimum line width" is the following value: the cross section of the wiring board 10 is exposed by a cross-section processing device such as a slicer, and the value is measured by a microscope that can measure the length of the smallest width portion in the second winding portion 15b. However, the "minimum line width" is the length of the smallest width portion in the area other than the defective area of ​​the second winding portion 15b. Here, the defective area to be excluded from the measurement is an area that is recessed (missing) from at least one end edge in the width direction to the inside when observed with a microscope as described above. Specifically, the defective region is a region where the deepest portion in the width direction has a length (width) of 1 / 4 or more relative to the average line width of other regions (other than the above-mentioned defective region) in the length direction (winding direction) of the second winding portion 15b. The above-mentioned average line width is measured in the same manner as the above-mentioned "average line width" measurement method. It should be noted that, hereinafter, the "minimum line width" of other components is also a value measured in the same manner as above.

[0062] ·First winding part

[0063] The average thickness H3 of the outermost first winding portion 15a can be appropriately set in such a manner that the ratio of the average thickness H3 of the first winding portion 15a to the average thickness H1 of the second winding portion 15b is greater than 1.1 and less than 5. For example, the lower limit of the average thickness H3 of the first winding portion 15a is preferably 10 μm, more preferably 20 μm, and further preferably 30 μm. The upper limit of the average thickness H3 of the first winding portion 15a is preferably 120 μm, more preferably 100 μm, and further preferably 80 μm. When the above-mentioned average thickness H3 is less than the above-mentioned lower limit, there is a concern that the resistance of the first winding portion 15a becomes higher. On the other hand, when the above-mentioned average thickness H3 exceeds the above-mentioned upper limit, there is a concern that the line width needs to be increased in order to form the first winding portion 15a, and space saving cannot be achieved.

[0064] The lower limit of the ratio (aspect ratio) of the average thickness H3 of the first winding portion 15a to the minimum line width (not shown) is preferably 0.5, preferably 0.7, and more preferably 1. The upper limit of the above ratio is preferably 7, more preferably 5, and further preferably 3. When the above ratio is less than the above lower limit, there is a concern that space saving cannot be achieved. On the other hand, when the above ratio exceeds the above upper limit, there is also a concern that space saving cannot be achieved.

[0065] (Ratio of the average thickness of the land portion to the average thickness of the second winding portion)

[0066] As described above, the lower limit of the ratio of the average thickness H2 of the pad portion 13 to the average thickness H1 of the second winding portion 15b is 1.1, preferably 1.3, more preferably 1.5, and further preferably 2. As described above, the upper limit of the above ratio is 5, preferably 4, and more preferably 3. When the above ratio is less than the above lower limit, there is a concern that the first metal material and the second metal material are difficult to adhere to the inner peripheral surface of the hole 3a in a sufficient amount (coating amount). On the other hand, when the above ratio exceeds the above upper limit, the amount of the first metal material and the second metal material attached to the inner peripheral surface of the hole 3a increases excessively, and the flexible printed wiring board 10 is unnecessarily thickened.

[0067] (Ratio of the average thickness of the first winding portion to the average thickness of the second winding portion)

[0068] As described above, the lower limit of the ratio of the average thickness H3 of the first winding portion 15a to the average thickness H1 of the second winding portion 15b is 1.1, preferably 1.3, more preferably 1.5, and further preferably 2. As described above, the upper limit of the above ratio is 5, preferably 4, and more preferably 3. When the above ratio is less than the above lower limit, there is a concern that the resistance of the wiring layer 11 cannot be sufficiently reduced. On the other hand, when the above ratio exceeds the above upper limit, there is a concern that the sufficient flexibility of the flexible printed wiring board 10 will be reduced.

[0069] <Dummy Wiring Layer>

[0070] The dummy wiring layer 41 is a wiring layer formed so as to be electrically isolated without being electrically connected. The dummy wiring layer 41 includes a third conductive base layer 43 and a dummy plating layer 45 stacked on the third conductive base layer 43 .

[0071] As described above, since the flexible printed wiring board 10 includes the dummy wiring layer 41, it is easy to increase the average thickness H3 of the outermost first winding portion 15a of the winding portion 15 located near the dummy wiring layer 41. Specifically, when forming the upper winding layer 37, the plating amount of the outermost portion located near the dummy wiring layer 41 can be made larger than that of the inner portion. Therefore, it is easy to form the flexible printed wiring board 10 with better connection reliability.

[0072] The third conductive base layer 43 is composed of a conductive base layer M described later (for example, see Figure 3). The third conductive base layer 43 may be formed as a part of the first conductive base layer 23 and the second conductive base layer 33. The average thickness of the third conductive base layer 43 may be set in the same manner as the first conductive base layer 23 and the second conductive base layer 33.

[0073] As a material for forming the dummy plating layer 45 , the same materials as the above-mentioned first metal material can be cited.

[0074] Since the thickness of the dummy plating layer 45 is much greater than the thickness of the third conductive base layer 43, the thickness of the dummy wiring layer 41 can be determined by the thickness of the dummy plating layer 45. For example, the average thickness of the dummy wiring layer 41 can be set to the same level as the average thickness of the lower pad layer 25 and the lower winding layer 35 described above.

[0075] The lamination area of ​​the dummy wiring layer 41 in the base film 3 can be appropriately set. For example, the lower limit of the ratio of the second area of ​​the lamination region of the dummy wiring layer 41 in the base film 3 to the first area of ​​the region from the wiring layer 11 to the outside thereof at the shortest distance of 2 mm is preferably 20%, and more preferably 25%. The upper limit of the above ratio is preferably less than 50%, and more preferably 40%. When the above ratio is less than the above lower limit, there is a concern that the resistance of the wiring layer 11 cannot be sufficiently reduced. On the other hand, when the above ratio exceeds the above upper limit, there is also a concern that the resistance of the wiring layer 11 cannot be sufficiently reduced. In addition, there is a concern that poor conduction cannot be sufficiently reduced.

[0076] The shape of the dummy wiring layer 41 is not particularly limited and can be set appropriately. For example, when viewed in a direction perpendicular to the base film 3, the dummy wiring layer 41 can be set to a linear shape, other shapes, etc. The shape can be set appropriately, for example, to a shape that satisfies the above-mentioned area ratio. Figure 1 In the illustrated embodiment, the dummy wiring layer 41 has a plurality of linear bodies.

[0077] <Advantages>

[0078] In the flexible printed wiring board 10, the ratio of the average thickness H2 of the pad portion 13 to the average thickness H1 of the second winding portion 15b of the winding portion 15 is 1.1 or more and 5 or less. Since the above ratio is within the above range, the average thickness H2 of the pad portion 13 is sufficiently large, and the amount of metal stacked on the inner peripheral surface of the hole 3a can be increased. Therefore, the conduction failure in the through hole 20 can be reduced. Therefore, the connection reliability of the flexible printed wiring board 10 is excellent.

[0079] In the present embodiment, the ratio of the average thickness H3 of the first winding portion 15a of the winding portion 15 to the average thickness H1 of the second winding portion 15b is greater than 1.1 and less than 5. Since the above ratio is within the above range, the average thickness H3 of the first winding portion 15a at the outermost periphery becomes large enough to reduce the resistance of the first winding portion 15a. Therefore, the resistance of the wiring layer 11 can be reduced.

[0080] [Manufacturing method of printed wiring board]

[0081] Next, a method for manufacturing the flexible printed wiring board according to the present embodiment will be described using the flexible printed wiring board 10 .

[0082] The manufacturing method of the flexible printed wiring board 10 includes: a first plating process, by using an anti-etching pattern R, electroplating a first metal material on the above-mentioned conductive base layer M of the base film 3 having a hole 3a for forming a through hole 20 and a conductive base layer M stacked on one side (surface side), thereby forming a first plated body X1 having a lower pad layer 25 of the above-mentioned pad portion 13 and a lower winding layer 35 of the above-mentioned winding portion 15; a removal process, after the above-mentioned first plating process, removing the above-mentioned anti-etching pattern R and the non-stacked area of ​​the above-mentioned first plated body X1 in the above-mentioned conductive base layer M; and a second plating process, after the above-mentioned removal process, by electroplating a second metal material on the above-mentioned first plated body X1, a second plated body X3 (not shown) having an upper pad layer 27 of the above-mentioned pad portion 13 and an upper winding layer 37 of the above-mentioned winding portion 15 is formed. The pad portion 13 is formed by a portion of the conductive base layer M, the lower pad layer 25 and the upper pad layer 27 , and the winding portion 15 is formed by another portion of the conductive base layer M, the lower winding layer 35 and the upper winding layer 37 .

[0083] In this embodiment, in the first plating step, the first metal material is plated on the conductive base layer M in a manner such that the second plating amount for forming the lower pad layer 25 is larger than the first plating amount for forming the innermost part of the lower winding layer.

[0084] Furthermore, in the present embodiment, in the first plating step, in addition to forming the first plated body X1, a dummy plated body X2 corresponding to the dummy plated layer 45 is formed on the conductive base layer M. The electrically isolated dummy wiring layer 41 is formed by a portion of the non-laminated region of the first plated body X1 in the conductive base layer M and the dummy plated body X2. In this way, since the dummy plated body X2 is formed in the first plating step, it is easy to form the wiring layer 11 having a large average thickness H3 of the first winding portion 15a at the outermost periphery. Therefore, a flexible printed wiring board 10 having a more excellent connection reliability can be manufactured.

[0085] <Conductive Base Layer>

[0086] The conductive base layer M is laminated on the surface side of the base film 3. The conductive base layer M is a layer previously laminated on the entire surface side of the base film 3. A portion of the conductive base layer M becomes the first conductive base layer 23, and another portion of the conductive base layer M becomes the second conductive base layer 33. In addition, another portion of the conductive base layer M becomes the third conductive base layer 43.

[0087] As the forming material of the conductive base layer M, for example, copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), their alloys, stainless steel, etc. can be cited. With regard to these forming materials, in order to suppress the thermal degradation of the adhesion of the wiring layer 11 to the base film 3, preferably, the conductive base layer M includes a layer (first layer) containing at least one selected from the group consisting of the above-mentioned nickel, chromium, titanium and silver on the side in contact with the base film 3 (for example, polyimide). Furthermore, more preferably, the conductive base layer M includes a layer (first layer) containing at least one selected from nickel and chromium that are easy to remove and easy to maintain insulation. In addition, more preferably, the conductive base layer M includes a layer (second layer) with copper as the main component on the upper side of the first layer (the side opposite to the base film 3). By configuring this layer with copper as the main component, when the wiring layer 11 is formed by electroplating, the working time can be shortened.

[0088] 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. When the average thickness is less than the lower limit, there is a concern that it is difficult to suppress the thermal degradation of the adhesion of the wiring layer 11 to the base film 3. On the other hand, when the average thickness exceeds the upper limit, there is a concern that it is difficult to easily remove the first layer and the insulation of the wiring layer 11 cannot be fully maintained. It should be noted that the first layer can be formed by sputtering, electroplating, electroless plating, etc.

[0089] For example, the lower limit of the average thickness of the second layer is preferably 0.1 μm, and more preferably 0.2 μm. The upper limit of the average thickness of the second layer is preferably 2 μm, and more preferably 1 μm. When the average thickness is less than the lower limit, there is a concern that the time for forming the wiring layer 11 by electroplating becomes too long. On the other hand, when the average thickness exceeds the upper limit, there is a concern that it is difficult to easily remove the second layer and the insulation between the winding parts 15 cannot be fully maintained. It should be noted that the second layer is preferably formed by sputtering, electroplating, non-electrolytic plating, etc., and can also be formed by a combination of these methods. In particular, it is preferred to configure a non-electrolytic copper plating layer on the uppermost surface side of the conductive base layer M, thereby, when a layer located further inside is formed by sputtering, defects that may be generated by the sputtering method can be covered.

[0090] <First plating step>

[0091] This process includes: an anti-etching pattern forming process, forming an anti-etching pattern R on the surface of the conductive base layer M; and a first plated body forming process, by using the formed anti-etching pattern R, electroplating a first metal material on the conductive base layer M, thereby forming a first plated body X1 having a lower pad layer 25 of the pad portion 13 and a lower winding layer 35 of the winding portion 15, and a dummy plated body X2 of a dummy plating layer 45 serving as a dummy wiring layer 41.

[0092] (Resist Pattern Formation Step)

[0093] In this process, if Figure 3 As shown, a resist pattern R is formed on the surface of the conductive base layer M. Specifically, a resist film such as a photosensitive film is stacked on the surface of the conductive base layer M, and the stacked resist film is exposed and developed to form a resist pattern R having a predetermined pattern. As a stacking method of the above-mentioned resist film, for example, a method of applying a resist composition to the surface of the conductive base layer M, a method of stacking a dry film photoresist on the surface of the conductive base layer M, etc. can be cited. The exposure and development conditions of the resist film can be appropriately adjusted according to the resist composition used, etc. The opening of the resist pattern R can be appropriately set according to the first plated body X1 and the dummy plated body X2 to be formed, that is, the lower pad layer 25 and the lower winding layer 35 of the wiring layer 11 and the dummy plating layer 45 of the dummy wiring layer 41.

[0094] (First Plated Body Forming Step)

[0095] In this process, the conductive base layer M is energized and the first metal material is electroplated. Figure 4As shown, a first plated body X1 and a dummy plated body X2 are formed in a non-laminated area of ​​the resist pattern R in the conductive base layer M. When the first plated body X1 is formed, the inner peripheral surface of the hole 3a is coated with the first metal material. In this process, the plating condition is set so that the second plating amount for forming the lower pad layer 25 is greater than the first plating amount on the inner side of the above-mentioned outermost periphery of the lower winding layer 35. In addition, in this process, the plating condition is set so that the third plating amount for forming the outermost periphery of the lower winding layer 35 is greater than the above-mentioned first plating amount.

[0096] For example, in the electroplating of this process, the above-mentioned plating conditions can be adjusted by adjusting the jet flow rate of the plating solution in the electroplating tank, the amount of air bubbling, etc. For example, the lower limit of the above-mentioned jet flow rate is preferably 15L / min, and more preferably 20L / min. The upper limit of the above-mentioned jet flow rate is preferably less than 50L / min, and more preferably 40L / min. When the above-mentioned jet flow rate is less than the above-mentioned lower limit, there is a concern that the resistance of the wiring layer 11 cannot be fully reduced. On the other hand, when the above-mentioned jet flow rate exceeds the above-mentioned upper limit, there is also a concern that the resistance of the wiring layer 11 cannot be fully reduced. In addition, there is a concern that poor conduction of the through hole 20 occurs.

[0097] For example, the lower limit of the air flow rate in the air bubbling is preferably 15 L / min, more preferably 20 L / min. The upper limit of the above air flow rate is preferably 50 L / min, more preferably 40 L / min. When the above air flow rate is less than the above lower limit, there is a concern that the resistance of the wiring layer 11 cannot be sufficiently reduced. On the other hand, when the above air flow rate exceeds the above upper limit, there is also a concern that the resistance of the wiring layer 11 cannot be sufficiently reduced. In addition, there is a concern that poor conduction of the through hole 20 occurs.

[0098] Through the first plating process, Figure 4 As shown, on the conductive base layer M of the base film 3, a first plated body X1 is formed, in which the average thickness of the inner end portion (equivalent to the lower pad layer 25) is greater than the average thickness of the inner side of the outermost circumference (equivalent to the inner side of the outermost circumference of the lower winding layer 35), and the average thickness of the outermost circumference (equivalent to the outermost circumference of the lower winding layer 35) is greater than the average thickness of the inner side. In addition, on the conductive base layer M of the base film 3, a dummy plated body X2 (equivalent to the dummy plated layer 45) is also formed.

[0099] <Removal process>

[0100] This step includes a stripping step of stripping the resist pattern R from the conductive base layer M and an etching step of etching a non-laminated region (unnecessary region) of the first plated body X1 and the dummy plated body X2 in the conductive base layer M.

[0101] (Peeling process)

[0102] In this step, the resist pattern R is peeled off from the conductive base layer M. As the stripping solution, a known stripping solution can be used, for example, alkaline aqueous solutions such as sodium hydroxide and potassium hydroxide, organic acid solutions such as alkylbenzenesulfonic acid, and mixed solutions of organic amines such as ethanolamine and polar solvents.

[0103] (Etching process)

[0104] In this step, the conductive base layer M is etched using the first plated body X1 and the dummy plated body X2 as masks. Figure 5 As shown, a first laminated body in which a first plated body X1 is laminated on a base film 3 via a first conductive base layer 23 and a second conductive base layer 33 is obtained. In addition, a second laminated body in which a dummy plated body X2 is laminated on a base film 3 via a third conductive base layer 43 is obtained. In the above etching, an etching liquid that corrodes the metal forming the conductive base layer M is used. In this manufacturing method, as described above, the so-called semi-additive method is preferably used.

[0105] <Second plating step>

[0106] In this process, after the above-mentioned removal process, the third plated body X3 (not shown) having the upper pad layer 27 of the pad portion 13 and the upper winding layer 37 of the winding portion 15 is formed by conducting with the first plated body X1 and electroplating the second metal material. In this process, for example, the second metal material is electroplated on the first plated body X1 under predetermined constant plating conditions. Thus, the plating amount of the first plated body X1 can be made constant as a whole (thickness). Through this second plating process, refer to Figure 5 And if Figure 2 As shown, a first laminate (equivalent to the wiring layer 11) is obtained by laminating the first conductive base layer 23 and the second conductive base layer 33 on the base film 3, a first plated body X1 having a lower pad layer 25 and a lower winding layer 35, and a second plated body X3 (not shown) having an upper pad layer 27 and an upper winding layer 37. In addition, a second laminate (equivalent to the dummy wiring layer 41) is obtained by laminating the third conductive base layer 43 and the dummy plated body X2 (equivalent to the dummy plated layer 45) on the base film 3.

[0107] <Advantages>

[0108] According to the manufacturing method of the flexible printed wiring board 10, the above-mentioned flexible printed wiring board 10 can be manufactured. That is, the flexible printed wiring board 10 with excellent connection reliability can be manufactured.

[0109] [Other embodiments]

[0110] The embodiments disclosed this time should be considered as illustrative in all aspects and not restrictive. The scope of the present invention is not limited to the configuration of the above-mentioned embodiments, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0111] In the above embodiment, a flexible printed wiring board having a single base film and a wiring layer stacked on one side of the base film is described, but the flexible printed wiring board may also have wiring layers stacked on both sides of a single base film. In addition, the flexible printed wiring board may also be a multilayer printed wiring board having a plurality of base films, each of which has a plurality of wiring layers on one side or both sides. In this case, the wiring layers on both sides may be connected by means of a pad portion.

[0112] In the above-described embodiment, a case where one wiring layer is stacked on a base film is described. However, a plurality of wiring layers may be stacked on a base film with spaces therebetween.

[0113] In the above-mentioned embodiment, the case where the dummy wiring layer is provided is described, but it is also possible to adopt a scheme where the dummy wiring layer is not provided.

[0114] Example

[0115] Hereinafter, the present disclosure will be further specifically described through examples, but the present disclosure is not limited to the following examples.

[0116] <Sample Preparation>

[0117] A film (Upilex-S, manufactured by Ube Industries, Ltd.) was used in which a conductive base layer was laminated on one side (surface side) of a base film having holes for forming through holes. Figure 1 and Figure 2 A wiring layer in the shape of a coil of a prescribed shape as shown in the figure and a dummy wiring layer having a linear body. Specifically, the above-mentioned resist pattern is used to conduct with the conductive base layer and electroplate a copper material as the first metal material on the conductive base layer in an electroplating tank, thereby forming a first plated body for the wiring layer and a dummy plated body for the dummy wiring layer. In this electroplating, except for setting the injection flow rate of the plating solution in the above-mentioned electroplating tank and the amount of air for air bubbling as shown in the following Table 1, the rest are set to the same conditions. Next, the copper material identical to the first metal material is electroplated as the second metal material on the first plated body in the above-mentioned electroplating tank under prescribed constant conditions, and samples of Experimental Examples 1 to 4 are prepared as shown in Table 1.

[0118] <Evaluation>

[0119] (Average Thickness)

[0120] For the samples of Experimental Examples 1 to 4, the average thickness H1 of the second winding portion that is closer to the innermost part than the outermost part in the winding portion, the average thickness H2 of the pad portion, and the average thickness H3 of the first winding portion that is the outermost part in the winding portion were measured. Specifically, the cross section of each sample was exposed using a cross-section processing device such as a slicer, and the thickness of the second winding portion, the pad portion, and the first winding portion was measured at any ten points based on cross-section observation, and the average values ​​of the measurement results were calculated, thereby obtaining the average thickness H1 of the second winding portion, the average thickness H2 of the pad portion, and the average thickness H3 of the first winding portion. After the measurement, the ratio of the average thickness H2 of the pad portion to the average thickness H1 of the second winding portion and the ratio of the average thickness H3 of the first winding portion to the average thickness H1 of the second winding portion were calculated. The results are shown in Table 1.

[0121] (Ratio of the second area to the first area)

[0122] For the samples of Experimental Examples 1 to 4, the ratio of the second area of ​​the laminated region of the dummy wiring layer in the base film to the first area of ​​the region 2 mm outside the wiring layer was measured. The ratio was calculated by measuring the area of ​​the dummy wiring layer and the area of ​​the exposed portion of the conductive base layer after the resist was formed. The results are shown in Table 1.

[0123] (Continuity)

[0124] The samples of Experimental Examples 1 to 4 were subjected to electrical inspection. As a result, the open-circuited portions were judged as defective. The results are shown in Table 1.

[0125] (Resistance reduction rate)

[0126] The electrical resistance of the samples of Experimental Examples 1 to 4 was measured by electrical inspection. The reduction rate of the resistance of Experimental Examples 1 to 4 relative to the resistance (baseline) of Experimental Example 4 was calculated. The results are shown in Table 1.

[0127]

[0128] As shown in Table 1, it is shown that poor conduction can be reduced by setting the ratio of the average thickness H2 of the pad portion to the average thickness H1 of the second winding portion to be greater than 1.1 and less than 5. In addition, it is shown that the resistance can be reduced by setting the ratio of the average thickness H3 of the first winding portion to the average thickness H1 of the second winding portion to be greater than 1.1 and less than 5.

[0129] Industrial Applicability

[0130] 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 are excellent in connection reliability and can therefore be suitably used in small electronic devices and the like.

[0131] Description of Reference Numerals

[0132] 10: Flexible printed wiring board

[0133] 3: Basement membrane

[0134] 3a: Hole

[0135] 11: Wiring layer

[0136] 13: Pad

[0137] 15: Winding part

[0138] 20: Through hole

[0139] 23: First conductive base layer

[0140] 25: Lower pad layer

[0141] 27: Upper pad layer

[0142] 33: Second conductive base layer

[0143] 35: Lower winding layer

[0144] 37: Upper winding layer

[0145] 41: Virtual wiring layer

[0146] 43: The third conductive base layer

[0147] 45: Virtual coating

[0148] H1: Average thickness of the second winding part

[0149] H2: Average thickness of the pad

[0150] H3: Average thickness of the first winding part

[0151] L: Average wire width of the winding part

[0152] S: Average spacing of winding parts

[0153] M: Conductive base layer

[0154] R: Resist pattern

[0155] X1: First plated body

[0156] X2: Dummy plated body.

Claims

1. A flexible printed wiring board comprising: a base film having a hole for forming a through hole; and a coil-shaped wiring layer laminated on at least one side of the base film, The wiring layer has: a pad portion disposed on an inner peripheral surface of the hole and a peripheral edge portion of the hole in the base film; and The winding portion is arranged in a spiral shape with the pad portion as an inner end portion or an outer end portion, The winding portion includes a first winding portion as an outermost circumference and a second winding portion located inside the outermost circumference. The ratio of the average thickness of the pad portion to the average thickness of the second winding portion is 1.1 or more and 5 or less, The pad portion includes a conductive base layer and a lower pad layer, the conductive base layer and the lower pad layer are stacked on the inner peripheral surface of the hole and the peripheral portion of the hole in the base film, the first winding portion includes the conductive base layer and a first lower winding layer, the conductive base layer and the first lower winding layer are stacked on the base film, The second winding portion includes the conductive base layer and a second lower winding layer, and the conductive base layer and the second lower winding layer are stacked on the base film. The thickness of the portion of the lower pad layer that is laminated on the periphery of the hole in the base film and the first lower winding layer is greater than the thickness of the second lower winding layer. A ratio of an average thickness of the first winding portion to an average thickness of the second winding portion is greater than or equal to 1.1 and less than or equal to 5.

2. The flexible printed wiring board according to claim 1, wherein The flexible printed wiring board further includes a dummy wiring layer disposed at a distance from the wiring layer in a region outside the wiring layer in the base film.

3. The flexible printed wiring board according to claim 2, wherein A ratio of a second area of ​​the stacked region of the dummy wiring layer in the base film to a first area of ​​a region between the first winding portion and the outside of the first winding portion at a shortest distance of 2 mm is 20% or more and less than 50%.

4. A method for manufacturing a flexible printed wiring board, The flexible printed wiring board comprises: a base film having a hole for forming a through hole; and a coil-shaped wiring layer stacked on at least one side of the base film. The wiring layer comprises: a pad portion arranged on the inner peripheral surface of the hole and the peripheral edge of the hole in the base film; and a winding portion arranged in a spiral shape with the pad portion as the inner end or the outer end. The winding portion includes a first winding portion as an outermost circumference and a second winding portion located inside the outermost circumference. The ratio of the average thickness of the pad portion to the average thickness of the second winding portion is 1.1 or more and 5 or less, The ratio of the average thickness of the first winding portion to the average thickness of the second winding portion is 1.1 or more and 5 or less, The method for manufacturing the flexible printed wiring board comprises: A first plating step of electroplating a first metal material on a base film having a hole for forming a through hole and having a conductive base layer laminated on at least one side thereof by using a resist pattern, thereby forming a first plated body having a lower pad layer of the pad portion and a lower winding layer of the winding portion; a removing step of removing the resist pattern and a non-laminated area of ​​the first plated body in the conductive base layer after the first plating step; as well as a second plating step, after the removal step, forming a second plated body having an upper pad layer of the pad portion and an upper winding layer of the winding portion by electroplating a second metal material on the first plated body, In the first plating step, the first metal material is plated on the conductive base layer in such a manner that a second plating amount of a portion stacked at the peripheral portion of the hole in the base film for forming the lower pad layer is larger than a first plating amount on the inner side of the outermost periphery for forming the lower winding layer, and a third plating amount on the outermost periphery for forming the lower winding layer is larger than the first plating amount, The pad portion is formed by a portion of the conductive base layer, the lower pad layer, and the upper pad layer. The winding portion is formed by another portion of the conductive base layer, the lower winding layer, and the upper winding layer. The conductive base layer and the lower pad layer are stacked on the inner peripheral surface of the hole and the peripheral edge portion of the hole in the base film.

5. The method for manufacturing a flexible printed wiring board according to claim 4, wherein: The flexible printed wiring board further includes a dummy wiring layer disposed in a region outside the wiring layer in the base film at a distance from the wiring layer. In the first plating step, a dummy plated body is formed on the conductive base layer in addition to the first plated body. The electrically isolated dummy wiring layer is formed by a part of the non-laminated region of the pad portion and the winding portion in the conductive base layer and the dummy plated body.

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