Flexible printed wiring board and method for manufacturing the same

Abstract

A flexible printed wiring board according to one aspect of the present disclosure is a flexible printed wiring board comprising a base film and a wiring layer, wherein the wiring layer comprises a plurality of wirings provided on at least one side of the base film, wherein the average line width of the wirings is 30 μm or less, and the average spacing is 30 μm or less, and the wirings comprise a copper-based plating layer, wherein the resistivity of the copper-based plating layer is greater than 1.68×10 ‑8 Ω·m.

Description

Technical Field

[0001] The present disclosure relates to a flexible printed wiring board and a method for manufacturing the same. This application claims priority based on Japanese application No. 2020-066298 filed on April 1, 2020, and incorporates all the contents described in the above Japanese application. Background Art

[0002] 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.

[0003] As such a small flexible printed wiring board, a flexible printed wiring board having a sheet-shaped insulating substrate and a coil-shaped wiring layer stacked on the surface of the substrate by plating has been proposed (see Japanese Patent Application Publication No. 2018-195681).

[0004] On the other hand, as a plating solution for electroplating to form wiring in a flexible printed wiring board, a plating solution containing copper ions, sulfuric acid, chloride ions, and hydroxycarboxylic acid has been proposed (see Japanese Patent Application Laid-Open No. 7-102392).

[0005] Prior Art Literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-195681

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 7-102392 Summary of the invention

[0009] A flexible printed wiring board according to one aspect of the present disclosure is a flexible printed wiring board comprising a base film and a wiring layer, wherein the wiring layer comprises a plurality of wirings provided on at least one side of the base film, wherein the average line width of the wirings is 30 μm or less, the average spacing is 30 μm or less, the wirings comprise a copper-based plating layer, and the resistivity of the copper-based plating layer is greater than 1.68×10 -8 Ω·m.

[0010] A method for manufacturing a flexible printed wiring board according to another aspect of the present disclosure is a method for manufacturing a flexible printed wiring board having a base film and a wiring layer, wherein the wiring layer has a plurality of wirings provided on at least one side of the base film, the average line width of the wirings is 30 μm or less, the average spacing is 30 μm or less, the wirings have a copper-based plating layer, and the resistivity of the copper-based plating layer is greater than 1.68×10 -8Ω·m, the manufacturing method comprises: a step of laminating a conductive base layer on at least one side of a base film; a step of forming a resist pattern on the surface of the conductive base layer; a step of forming a copper-based plating layer by electroplating the opening of the resist pattern on the conductive base layer in a plating solution; and a step of removing the resist pattern and the conductive base layer in the region where the copper-based plating layer is not laminated, wherein the plating solution contains a first organic compound, a second organic compound and a third organic compound, wherein the first organic compound contains disodium 3,3'-dithiobis(1-propanesulfonic acid), the second organic compound contains polyethylene glycol, and the third organic compound contains a nitrogen-containing organic compound. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic end view showing a flexible printed wiring board according to an embodiment.

[0012] Figure 2 is a schematic end view showing a flexible printed wiring board according to an embodiment.

[0013] Figure 3 It is used to illustrate Figure 1 Schematic end view of a method for manufacturing a flexible printed wiring board.

[0014] Figure 4 It is used to illustrate Figure 1 Schematic end view of a method for manufacturing a flexible printed wiring board. DETAILED DESCRIPTION

[0015] [Technical Problems to be Solved by the Present Disclosure]

[0016] Here, in order to meet various design specifications in a flexible printed wiring board, it is sometimes required to increase the resistance of the wiring. In this regard, in the flexible wiring board as described above, in order to increase the resistance of the wiring, it is necessary to reduce the line width of the wiring or increase the length. However, under the current situation of miniaturization as described above, if such a size change is made, it is worried that it will be difficult to achieve miniaturization or to meet other design specifications other than resistance.

[0017] Therefore, an object of the present invention is to provide a flexible printed wiring board and a method for manufacturing the same which can be miniaturized and adapted to various design specifications.

[0018] [Effects of the present disclosure]

[0019] A flexible printed wiring board according to one aspect of the present disclosure can be miniaturized and adapted to various design specifications. 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 be miniaturized and adapted to various design specifications.

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

[0021] A flexible printed wiring board according to one aspect of the present disclosure is a flexible printed wiring board comprising a base film and a wiring layer, wherein the wiring layer comprises a plurality of wirings provided on at least one side of the base film, wherein the average line width of the wirings is 30 μm or less, the average spacing is 30 μm or less, the wirings comprise a copper-based plating layer, and the resistivity of the copper-based plating layer is greater than 1.68×10 -8 Ω·m.

[0022] The flexible printed wiring board is miniaturized by making the average line width and average spacing of the wiring within the above ranges. In addition, by making the wiring have a copper-based plating layer, the resistance of the wiring can be increased when compared with the same size. Therefore, the flexible printed wiring board can be miniaturized and adapt to various design specifications.

[0023] The resistivity of the copper-based plating layer can also be 1.73×10 -8 Ω·m or more and 2.10×10 -8 Ω·m or less.

[0024] By setting the resistivity of the copper-based plating layer to 1.73×10 -8 Ω·m or more, it can be more widely adapted to various design specifications. -8 Ω·m or less, it is possible to suppress an unnecessary increase in resistance.

[0025] The resistivity of the copper-based plating layer can also be 1.76×10 -8 Ω·m or more and 1.93×10 -8 Ω·m or less.

[0026] By setting the resistivity of the copper-based plating layer to 1.76×10 -8 Ω·m or more, it can be more widely adapted to various design specifications. -8 When the value is Ω·m or less, an unnecessary increase in resistance can be further suppressed.

[0027] The copper-based plating contains sulfur, nitrogen and carbon. The sulfur content in the copper-based plating can be greater than 0.0001 mass % and less than 0.005 mass %, the nitrogen content can be greater than 0.0001 mass % and less than 0.005 mass %, and the carbon content can be greater than 0.001 mass % and less than 0.01 mass %.

[0028] By setting the contents of sulfur, nitrogen, and carbon to be within the above ranges, the resistivity can be more reliably set to be within the above ranges.

[0029] The average diameter of copper crystal grains in the copper-based plating layer may be 0.05 μm or more and 100 μm or less.

[0030] By setting the average diameter of the copper crystal grains to be within the above range, the resistivity can be more reliably set to be within the above range.

[0031] Alternatively, the wiring also includes a first conductive base layer in contact with the above-mentioned one side of the base film, the copper-based plating layer is arranged on the opposite side of the surface of the first conductive base layer in contact with the base film, and the first conductive base layer includes: a first layer in contact with the above-mentioned one side of the base film; and a second layer arranged on the opposite side of the surface of the first layer in contact with the base film.

[0032] When the first layer contains at least one selected from the group consisting of nickel, chromium, titanium, and silver, thermal degradation of the adhesion of the wiring layer to the base film can be suppressed.

[0033] When the second layer contains 50 mass % or more of copper, the working time can be shortened when forming a copper-based plating layer on the surface of the second layer by electroplating.

[0034] In addition, a method for manufacturing a flexible printed wiring board according to a different aspect of the present disclosure is a method for manufacturing a flexible printed wiring board having a base film and a wiring layer, wherein the wiring layer has a plurality of wirings provided on at least one side of the base film, the average line width of the wirings is 30 μm or less, the average spacing is 30 μm or less, the wirings have a copper-based plating layer, and the resistivity of the copper-based plating layer is greater than 1.68×10 -8 Ω·m, the manufacturing method comprises: a step of laminating a conductive base layer on at least one side of a base film; a step of forming a resist pattern on the surface of the conductive base layer; a step of forming a copper-based plating layer by electroplating the opening of the resist pattern on the conductive base layer in a plating solution; and a step of removing the resist pattern and the conductive base layer in the region where the copper-based plating layer is not laminated, wherein the plating solution contains a first organic compound, a second organic compound and a third organic compound, wherein the first organic compound contains disodium 3,3'-dithiobis(1-propanesulfonic acid), the second organic compound contains polyethylene glycol, and the third organic compound contains a nitrogen-containing organic compound.

[0035] The third organic compound may include at least one selected from the group consisting of a copolymer of diallyl ammonium and sulfur dioxide, a polyvinyl imidazolium quaternary ammonium compound, a copolymer of vinyl pyrrolidone and vinyl imidazolium quaternary ammonium compound, and a quaternized polyamine.

[0036] In the plating solution, the content of the first organic compound may be 0.0001 mass % to 1 mass %, the content of the second organic compound may be 0.004 mass % to 5 mass %, and the content of the third organic compound may be 0.0001 mass % to 0.5 mass %.

[0037] 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 that can be miniaturized and adapted to various design specifications can be manufactured.

[0038] Here, "line width" means the dimension of a wiring in a direction perpendicular to the length direction, and "average line width" means the value obtained by measuring the maximum width of the wiring in five cross sections perpendicular to the length direction of the wiring at random in the length direction of the wiring and averaging them. "Interval" means the distance between adjacent surfaces of two opposing wirings, and "average interval" means the value obtained by measuring the distance between the adjacent surfaces at five random points in the length direction of the wiring and averaging them.

[0039] However, the pad portions having via holes (through holes, blind holes, filled via holes) for connecting each wiring, the pad portions connected to the mounting components, the pad portions for connecting to other printed circuit boards and connectors, etc. are excluded from the above-mentioned "line width" and "interval". "Resistivity" means the resistivity value of the copper-based plating at 20°C. "Average diameter" means the value obtained by cutting a cross section of the wiring in the thickness direction along the length direction of the wiring with a length of 200μm using a FIB (Focused Ion Beam) device, observing the cross section using a FIB device, SEM (Scanning Electron Microscope) or a metal microscope, measuring the long and short diameters of the crystals present in the copper-based plating in the cross section and averaging them.

[0040] [Details of the embodiments of the present disclosure]

[0041] 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 of the stacked wiring layer 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.

[0042] [Flexible printed wiring board]

[0043] like Figure 1 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 having a plurality of wirings 13 stacked on one side (surface side) of 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.

[0044] <Base film>

[0045] The base film 3 is a layer made of synthetic resin with insulating properties. The base film 3 is also flexible. The base film 3 is also a substrate for forming the wiring layer 11. As the forming material of the base film 3, there is no particular limitation as long as it has insulating properties and flexibility, and 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 largest content, for example, it means 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.

[0046] The lower limit of the average thickness of the base film 3 is not particularly limited, and may be 3 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the base film 3 is not particularly limited, and may be 200 μm, 150 μm, or 100 μm. When the average thickness of the base film 3 is less than 3 μm, there is a concern that the insulation strength and mechanical strength of the base film 3 are insufficient. On the other hand, when the average thickness of the base film 3 exceeds 200 μm, there is a concern that the flexible printed wiring board 10 is unnecessarily thickened. Here, "average thickness" means the average value of the thickness measured at any ten points.

[0047] <Wiring Layer>

[0048] The wiring layer 11 is stacked directly or via other layers on the surface side of the base film 3. Examples of the wiring 13 included in the wiring layer 11 include signal lines for transmitting signals, current lines for transmitting current for power supply, and current lines for transmitting current for generating a magnetic field.

[0049] The wiring 13 is formed of a first conductive base layer 23 stacked on the surface side of the base film 3 and a copper-based plating layer 25 stacked on the side (surface side) of the first conductive base layer 23 opposite to the base film 3 .

[0050] The lower limit of the average line width L of the wiring 13 may be 1 μm, 3 μm, or 5 μm. The upper limit of the average line width L of the wiring 13 may be 30 μm, 20 μm, or 10 μm. When the average line width L of the wiring 13 is less than 1 μm, there is a concern that the mechanical strength of the wiring 13 is insufficient. On the other hand, when the average line width L of the wiring 13 exceeds 30 μm, there is a concern that sufficient miniaturization may not be achieved. The "average line width" is a value obtained by exposing a cross section perpendicular to the length direction of the wiring board 10 at five locations in each wiring using a cross-section processing device such as a slicer, measuring the length of the widest part of the wiring 13 using a microscope, etc., and calculating the value as the average of these measured values.

[0051] When a plurality of wirings 13 are arranged adjacent to each other, the lower limit of the average spacing S of these wirings 13 may be 1 μm, 3 μm, or 5 μm. The upper limit of the average spacing S of the wirings 13 may be 30 μm, 20 μm, or 10 μm. When the average spacing S of the wirings 13 is less than 1 μm, there is a concern that a short circuit may occur. On the other hand, when the average spacing S of the wirings 13 exceeds 30 μm, there is a concern that sufficient miniaturization may not be achieved. The "average spacing" is a value obtained by exposing a cross section perpendicular to the length direction of the wiring board 10 at five locations of each wiring using a cross-section processing device such as a slicer, and measuring the length of the smallest portion of the gap between two wirings 13 using a microscope, etc., and calculating the value as the average of these measured values.

[0052] The lower limit of the average thickness of the wiring 13 can be 1μm, 3μm, or 5μm. The upper limit of the average thickness of the wiring 13 can be 30μm, 20μm, or 10μm. When the average thickness is less than 1μm, there is a concern that the mechanical strength is insufficient. On the other hand, when the average thickness exceeds 30μm, there is a concern that the flexibility of the wiring 13 is reduced. Here, "thickness" means the distance from the upper surface of the base film to the upper edge of the wiring 13 in the cross-sectional view of the base film 3 in the vertical direction (thickness direction) of the top view. "Average thickness" means the average value of the thickness measured at any ten points of a wiring 13. Specifically, it is obtained by exposing any ten places of a cross-section perpendicular to the length direction of the wiring 13 through a cross-sectional processing device such as a slicer, measuring the thickness by cross-sectional observation, and calculating the average value of the measured values. It should be noted that the "average thickness" of other components below is also a value measured in the same way.

[0053] The first conductive base layer 23 is composed of a conductive base layer M described later (for example, see Figure 3 ) is formed as a part of the first conductive base layer 23. Examples of the material for forming the first conductive base layer 23 include copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), and alloys thereof. Figure 2As shown, the first conductive base layer 23 may also include a first layer 231 and a second layer 232. 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, the first conductive base layer 23 may also include a layer (first layer 231) containing at least one selected from the group consisting of nickel, chromium, titanium and silver on the side in contact with the base film 3 (for example, polyimide). Furthermore, it is more preferred that the first conductive base layer 23 includes a layer (first layer 231) containing at least one selected from nickel and chromium that are easy to remove and easy to maintain insulation. In addition, it is more preferred that the first conductive base layer 23 includes a layer (second layer 232) containing copper as a main component on the upper side of the first layer 231 (the side opposite to the base film 3). By configuring the layer containing copper as a main component, the working time can be shortened when the wiring layer 11 is formed by electroplating. "Main component" is the component with the largest content, for example, it means a component that accounts for 50% by mass or more in the second layer 232.

[0054] For example, the lower limit of the average thickness of the first layer 231 may be 1 nm or 2 nm. The upper limit of the average thickness of the first layer 231 may be 15 nm or 8 nm. When the average thickness is less than 1 nm, 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 15 nm, it is difficult to easily remove the first layer 231, and it is feared that the insulation of the wiring layer 11 cannot be sufficiently maintained. It should be noted that the first layer 231 can be formed by sputtering, electroplating, electroless plating, or the like.

[0055] For example, as the lower limit of the average thickness of the second layer 232, it can be 0.1μm or 0.2μm. As the upper limit of the average thickness of the second layer 232, it can be 2μm or 1μm. When the average thickness is less than 0.1μm, there is a concern that the time to form the wiring layer 11 by electroplating is too long. On the other hand, when the average thickness exceeds 2μm, it is difficult to easily remove the second layer 232, and there is a concern that the insulation of the wiring layer 11 cannot be fully maintained. It should be noted that the second layer 232 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, thereby, when a layer located further inside is formed by sputtering, defects that may be generated by the sputtering method can be covered.

[0056] The copper-based plating layer 25 contains copper. The resistivity of the copper-based plating layer 25 is greater than 1.68×10 -8 Ω·m. Here, the resistivity of the plating layer formed of pure copper is usually 1.68×10 -8 Therefore, the copper-based plating layer 25 has a higher resistivity than a pure copper plating layer.

[0057] As mentioned above, the resistivity is greater than 1.68×10 -8 Ω·m, which can be 1.73×10 -8 Ω·m or more, and can also be 1.76×10 -8 Ω·m or more. The upper limit of the resistivity can be 2.10×10 -8 Ω·m, or 1.93×10 -8 Ω·m, can also be 1.84×10 -8 Ω·m. When the resistivity is less than 1.68×10 -8 Ω·m, it may be difficult to fully meet various design specifications. On the other hand, when the resistivity exceeds 2.10×10 -8 Here, the resistivity is a value measured by a four-terminal method at 20°C.

[0058] The copper content in the copper-based plating layer 25 may be 99.0% by mass or more, 99.5% by mass or more, or 99.9% or more.

[0059] The copper-based plating layer 25 may contain additives other than copper. For example, the copper-based plating layer 25 may contain sulfur (atom), nitrogen (atom), and carbon (atom). By making the copper-based plating layer 25 contain the above-mentioned elements (atoms), the resistivity can be more reliably set within the above-mentioned range.

[0060] When the copper-based plating layer 25 contains sulfur, nitrogen and carbon, the lower limit of the sulfur content in the copper-based plating layer 25 can be 0.0001 mass%, 0.0002 mass% or 0.0003 mass%. As the upper limit of the sulfur content, it can be 0.005 mass%, 0.004 mass% or 0.003 mass%. When the sulfur content is less than 0.0001 mass%, it is worried that it is difficult to set the resistivity more reliably within the above range. On the other hand, when the sulfur content exceeds 0.005 mass%, it is also worried that it is difficult to set the resistivity more reliably within the above range. The sulfur content can be measured based on high-frequency combustion-infrared absorption method (e.g., JIS G1215-4 (2018), JIS H1070 (2013)).

[0061] When the copper-based plating layer 25 contains sulfur, nitrogen and carbon, the lower limit of the nitrogen content in the copper-based plating layer 25 can be 0.0001 mass%, 0.0002 mass% or 0.0003 mass%. The upper limit of the nitrogen content can be 0.005 mass%, 0.004 mass% or 0.003 mass%. When the nitrogen content is less than 0.0001 mass%, it is difficult to set the resistivity more reliably within the above range. On the other hand, when the nitrogen content exceeds 0.005 mass%, it is also difficult to set the resistivity more reliably within the above range. The nitrogen content can be measured based on the inert gas transport melting-thermal conductivity method (e.g., JIS G1228 (2006)).

[0062] When the copper-based plating layer 25 contains sulfur, nitrogen and carbon, the lower limit of the content of carbon in the copper-based plating layer 25 can be 0.001 mass%, 0.002 mass% or 0.003 mass%. As the upper limit of the content of carbon, it can be 0.01 mass%, 0.009 mass% or 0.008 mass%. When the content of carbon is less than 0.001 mass%, it is worried that it is difficult to set the resistivity more reliably within the above range. On the other hand, when the content of carbon exceeds 0.01 mass%, it is also worried that it is difficult to set the resistivity more reliably within the above range. Here, the content of carbon can be measured based on high-frequency combustion-infrared absorption method (for example JIS Z 2615 (2015), JIS G 1211-3 (2018)).

[0063] As compounds that are the supply sources of sulfur, nitrogen and carbon, there are no particular limitations as long as they contain at least one of them and can make the copper-based plating 25 contain sulfur, nitrogen and carbon in the above-mentioned respective contents. For example, as compounds containing sulfur and carbon, organic compounds containing sulfur (sulfur-containing organic compounds, hereinafter also referred to as "first organic compounds") can be listed. As the first organic compound, for example, 3,3'-dithiobis(1-propanesulfonic acid) disodium (SPS) can be listed. For example, as compounds containing carbon, organic compounds (hereinafter also referred to as "second organic compounds") can be listed. As the second organic compound, polyethylene glycol (PEG) can be listed. As PEG, it can be PEG with a weight average molecular weight of more than 1000. Here, the weight average molecular weight is measured by GPC (gel permeation chromatography). For example, as compounds containing nitrogen and carbon, organic compounds containing nitrogen (nitrogen-containing organic compounds, hereinafter also referred to as "third organic compounds") can be listed. As the third organic compound, there can be cited copolymers of diallyl ammonium and sulfur dioxide, polyvinyl imidazolium quaternary ammonium compounds (PVI quaternary ammonium compounds), copolymers of vinyl pyrrolidone and vinyl imidazolium quaternary ammonium compounds, quaternized polyamines, etc. Among them, for example, SPS, PEG, and copolymers of diallyl ammonium and sulfur dioxide can be used in combination so that the contents of sulfur, nitrogen, and carbon in the copper-based plating layer 25 are within the above ranges.

[0064] The copper-based plating layer 25 may contain copper, sulfur, nitrogen, and carbon in the above-mentioned respective contents, and the remainder may be inevitable impurities. Here, the inevitable impurities refer to impurities whose content in the copper-based plating layer 25 is less than 0.0001 mass %.

[0065] The material (forming material) for forming the copper-based plating layer 25 includes a first metal material. The first metal material is a copper-based metal material. The copper content in the first metal material may be 99.0 mass % or more, 99.5 mass % or more, or 99.9 mass % or more.

[0066] The formation material may contain sulfur, nitrogen, and carbon in addition to the first metal material. The contents of each of sulfur, nitrogen, and carbon in the formation material may be set within the above ranges.

[0067] In order to set the sulfur, nitrogen, and carbon contents in the copper-based plating layer 25 to the above-mentioned contents, the contents of the first organic compound, the second organic compound, and the third organic compound in the plating solution are preferably adjusted as follows.

[0068] The lower limit of the content of the first organic compound in the plating solution may be 0.0001 mass %, 0.0005 mass %, or 0.001 mass %, and the upper limit of the content of the first organic compound in the plating solution may be 1 mass %, 0.1 mass %, or 0.05 mass %.

[0069] The lower limit of the content of the second organic compound in the plating solution may be 0.004 mass %, 0.02 mass %, or 0.04 mass %, and the upper limit of the content of the second organic compound in the plating solution may be 5 mass %, 1 mass %, or 0.5 mass %.

[0070] The lower limit of the content of the third organic compound in the plating solution may be 0.0001 mass %, 0.0005 mass %, or 0.001 mass %, and the upper limit of the content of the third organic compound in the plating solution may be 0.5 mass %, 0.1 mass %, or 0.005 mass %.

[0071] The contents of the first organic compound, the second organic compound, and the third organic compound in the plating solution can also be adjusted as described above, so that the contents of sulfur, nitrogen, and carbon in the plating solution are respectively adjusted to 0.00005 mass % to 0.005 mass % for sulfur, 0.000001 mass % to 0.001 mass % for nitrogen, and 0.01 mass % to 0.5 mass % for carbon.

[0072] Such a forming material can be used as a plating solution used in the method for producing the flexible printed wiring board described later.

[0073] The lower limit of the average diameter of the copper crystal grains in the copper-based plating layer 25 may be 0.05 μm, 0.1 μm, or 0.5 μm. The upper limit of the average diameter of the copper crystal grains may be 100 μm, 50 μm, or 10 μm. When the average diameter of the copper crystal grains is less than 0.05 μm, it is feared that it may be difficult to more reliably set the resistivity within the above range. On the other hand, when the average diameter of the copper crystal grains exceeds 100 μm, it is also feared that it may be difficult to more reliably set the resistivity within the above range. Here, the average diameter is measured by the method described in the embodiments described later.

[0074] The average diameter of the copper crystal grains can be appropriately adjusted by changing the addition of components other than the copper component in the forming material, for example, by changing the type of the above-mentioned organic compound, the amount thereof added, the electrical density during electroplating, and the like.

[0075] <Advantages>

[0076] The flexible printed wiring board 10 is miniaturized by making the average line width L and the average spacing S of the wiring 13 within the above ranges. In addition, by making the wiring 13 have a copper-based plating layer 25, the resistance of the wiring can be increased when compared with the same size. Therefore, the flexible printed wiring board 10 can be miniaturized and adapt to various design specifications.

[0077] [Method for manufacturing flexible printed wiring board]

[0078] 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 .

[0079] The method for manufacturing a flexible printed wiring board 10 comprises: a plating step of electroplating a conductive base layer M of a base film on which a conductive base layer M is laminated on at least one side (surface side) of a base film 3 in a plating solution using a resist pattern R1, thereby forming a copper-based plating layer 25; and a removal step of removing a region of the resist pattern R1 and the conductive base layer M where the copper-based plating layer 25 is not laminated. The plating solution contains sulfur, nitrogen, and carbon. The content of sulfur in the plating solution is 0.00005 mass % or more and 0.005 mass % or less, the content of nitrogen is 0.000001 mass % or more and 0.001 mass % or less, and the content of carbon is 0.01 mass % or more and 0.5 mass % or less.

[0080] <Conductive Base Layer>

[0081] The conductive base layer M is laminated on the surface side of the base film 3. The conductive base layer M is a layer laminated in advance on the entire surface side of the base film 3. A part of the conductive base layer M serves as the first conductive base layer 23.

[0082] As the forming material of the conductive base layer M, for example, copper (Cu), silver (Ag), gold (Au), nickel (Ni), titanium (Ti), chromium (Cr), and alloys thereof, 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, the conductive base layer M may also include a layer (first layer 231) containing at least one selected from the group consisting of nickel, chromium, titanium, and silver on the side in contact with the base film 3 (for example, polyimide). Furthermore, it is more preferred that the conductive base layer M includes a layer (first layer 231) containing at least one selected from nickel and chromium that are easy to remove and easy to maintain insulation. In addition, it is more preferred that the conductive base layer M includes a layer (second layer 232) with copper as the main component on the upper side of the first layer 231 (the side opposite to the base film 3). By configuring this layer with copper as the main component, the operation time can be shortened when the wiring layer 11 is formed by electroplating.

[0083] For example, the lower limit of the average thickness of the first layer 231 may be 1 nm or 2 nm. The upper limit of the average thickness of the first layer 231 may be 15 nm or 8 nm. When the average thickness is less than 1 nm, 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 15 nm, it is difficult to easily remove the first layer 231, and it is feared that the insulation of the wiring layer 11 cannot be sufficiently maintained. It should be noted that the first layer 231 can be formed by sputtering, electroplating, electroless plating, or the like.

[0084] For example, as the lower limit of the average thickness of the second layer 232, it can be 0.1μm or 0.2μm. As the upper limit of the average thickness of the second layer 232, it can be 2μm or 1μm. When the average thickness is less than 0.1μm, there is a concern that the time to form the wiring layer 11 by electroplating is too long. On the other hand, when the average thickness exceeds 2μm, it is difficult to easily remove the second layer 232, and there is a concern that the insulation of the wiring layer 11 cannot be fully maintained. It should be noted that the second layer 232 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 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.

[0085] <Plating process>

[0086] This step includes: a resist pattern forming step of forming a resist pattern R1 on the surface of the conductive base layer M; and a copper-based plating layer forming step of electroplating a first metal material on the conductive base layer M using the formed resist pattern R1 to form a copper-based plating layer 25 .

[0087] (Resist Pattern Formation Step)

[0088] In this process, if Figure 3 As shown, a resist pattern R1 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 R1 having a predetermined pattern. As a stacking method of the 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 R1 can be appropriately set according to the copper-based plating layer 25 to be formed.

[0089] (Copper-based plating layer forming step)

[0090] In this step, the plating solution contains sulfur, nitrogen and carbon. The content of sulfur in the plating solution is 0.00005 mass % or more and 0.005 mass % or less, the content of nitrogen is 0.000001 mass % or more and 0.001 mass % or less, and the content of carbon is 0.01 mass % or more and 0.5 mass % or less. As such a plating solution, a plating solution containing the above-mentioned forming materials can be used.

[0091] In this step, for example, as a plating solution, a first metal material, for example, a copper source such as a copper salt, and a mixture of a first organic compound, a second organic compound, and a third organic compound are used in such a manner that the contents of sulfur, nitrogen, and carbon are within a certain range. In this step, the first metal material is electroplated while the conductive base layer M is energized using the plating solution, thereby Figure 4 As shown, the copper-based plating layer 25 is formed in the region of the conductive base layer M where the resist pattern R1 is not stacked.

[0092] In order to set the contents of sulfur, nitrogen, and carbon in the plating solution to the respective contents, the lower limit of the content of the first organic compound in the plating solution may be 0.0001 mass %, 0.0005 mass %, or 0.001 mass %, as described above. The upper limit of the content of the first organic compound in the plating solution may be 1 mass %, 0.1 mass %, or 0.05 mass %, as described above.

[0093] In order to set the contents of sulfur, nitrogen, and carbon in the plating solution to the above contents, the lower limit of the content of the second organic compound in the plating solution may be 0.004 mass %, 0.02 mass %, or 0.04 mass % as described above.

[0094] As described above, the upper limit of the content of the second organic compound in the plating solution may be 5% by mass, 1% by mass, or more preferably 0.5% by mass.

[0095] In order to set the contents of sulfur, nitrogen, and carbon in the plating solution to the above contents, the lower limit of the content of the third organic compound in the plating solution may be 0.0001 mass %, 0.0005 mass %, or 0.001 mass %, and the upper limit of the content of the third organic compound in the plating solution may be 0.5 mass %, 0.1 mass %, or 0.005 mass %.

[0096] For example, in the electroplating of this process, by adjusting the current density, the resistivity of the copper-based plating layer can be adjusted in more detail. The current density can be appropriately set according to the content of the above-mentioned organic compound in the above-mentioned plating solution, etc. In addition, by adjusting the current density, the average diameter of the copper crystal grains in the copper-based plating layer 25 can be adjusted as described above.

[0097] <Removal process>

[0098] This step includes a peeling step of peeling the resist pattern R1 from the conductive base layer M and an etching step of etching a region (unnecessary region) in the conductive base layer M where the copper-based plating layer 25 is not laminated.

[0099] (Peeling process)

[0100] In this step, the resist pattern R1 is peeled off from the conductive base layer M. As the stripping solution, a known stripping solution can be used, for example, an alkaline aqueous solution such as sodium hydroxide and potassium hydroxide, an organic acid solution such as alkylbenzenesulfonic acid, a mixed solution of organic amines such as ethanolamine and a polar solvent, etc.

[0101] (Etching process)

[0102] In this step, the conductive base layer M is etched using the copper-based plating layer 25 as a mask. Figure 1 As shown, the wiring 13 is obtained in which the first conductive base layer 23 and the copper-based plating layer 25 are stacked on the base film 3. The etching is performed using an etching solution that corrodes the metal forming the conductive base layer M. In this manufacturing method, the so-called semi-additive method is preferably used.

[0103] <Advantages>

[0104] 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 which can be miniaturized and can adapt to various design specifications can be manufactured.

[0105] [Other embodiments]

[0106] The embodiments disclosed this time should be considered to be illustrative in all aspects and not restrictive. The scope of the present invention is not limited to the configuration of the embodiments but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0107] In the embodiments, 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 be a flexible printed wiring board having 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 via the pad portion.

[0108] In the 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 at intervals.

[0109] In the embodiment, the case where the wiring layer includes the wiring having the above-mentioned specific copper-based plating layer has been described, but an aspect in which the wiring layer includes other wirings in addition to such wirings may be adopted.

[0110] [Example]

[0111] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

[0112] <Sample Preparation>

[0113] (Examples 1 to 4, Comparative Examples 1 to 3)

[0114] A film (Upilex (registered trademark)-S, manufactured by Ube Industries, Ltd.) having a conductive base layer laminated on one side (surface side) of the base film was used. As a material for forming a copper-based plating layer, a plating solution was used in which SPS, PEG, and a copolymer of diallyl ammonium and sulfur dioxide were mixed in the amounts shown in Table 1 in addition to 75 g / L of copper sulfate and 190 g / L of sulfuric acid. In Table 1, "-" indicates that no addition was made. Using these films and plating solutions, a conductive base layer having the above-mentioned structure was formed on the conductive base layer of the film. Figure 1 A wiring layer having wiring as shown. Specifically, the above-mentioned resist pattern is used to conduct the conductive base layer while electroplating is performed on the conductive base layer in an electroplating tank at each current density shown in Table 1 using a plating solution, thereby forming a copper-based plating layer. Then, the removal process is performed as described above to obtain wiring boards of Examples 1 to 4 and Comparative Examples 1 to 3 having wiring with an average line width of 15 μm, an average interval of 15 μm, and an average thickness of 15 μm. The contents (concentrations) of sulfur, nitrogen, and carbon in the copper-based plating layer of each wiring board obtained, the average diameter of copper crystal grains, and the resistivity of the copper-based plating layer are measured as follows.

[0115] <Determination of sulfur, nitrogen and carbon content>

[0116] The copper-based plating layer was peeled off and collected, and then measured by the following method.

[0117] (Sulfur and carbon content)

[0118] The sulfur and carbon contents in the copper-based plating layer are measured based on the high-frequency combustion-infrared absorption method. The device used is the CSLS600 (manufactured by LECO). The sulfur content is measured according to the determination method of JIS H1070 (2013). The carbon content is measured according to JIS Z 2615 (2015) on the basis of JIS G 1211-3 (2018) in accordance with the general principles of carbon quantitative methods for metal materials.

[0119] (Nitrogen content)

[0120] The nitrogen content in the copper-based plating layer was measured by an inert gas transport melting-thermal conductivity method. The device used was a TC600 (manufactured by LECO). The nitrogen content was measured in accordance with Appendix 4 of JIS G1228 (2006).

[0121] (Average diameter of copper grains)

[0122] As described above, the average diameter of copper crystal grains in the copper-based plating layer of each wiring board was measured by observing a cross section cut out using a FIB apparatus.

[0123] (Resistivity)

[0124] The resistivity of the copper-based plating layer of each wiring board of Examples 1 to 4 and Comparative Examples 1 to 3 was measured by a four-probe method.

[0125]

[0126] In Examples 1 to 4 in which the sulfur content was 0.0001 mass % to 0.005 mass %, the nitrogen content was 0.0001 mass % to 0.005 mass %, and the carbon content was 0.001 mass % to 0.01 mass %, the resistivity of the copper-based plating layer exceeded 1.68×10 -8 Ω·m. On the other hand, in Comparative Examples 1, 2, and 3 in which sulfur, nitrogen, and carbon were all 0.00001 mass %, the resistivity of the copper-based plating layer was 1.68×10 -8 Ω·m or less.

[0127] Description of Reference Numerals

[0128] 10Flexible printed wiring board 3Base film

[0129] 11 wiring layer 13 wiring

[0130] 23 first conductive base layer 231 first layer

[0131] 232 second layer 25 copper plating

[0132] L Average line width S Average spacing

[0133] M conductive base layer R1 resist pattern.

Claims

1. A flexible printed wiring board comprising a base film and a wiring layer, wherein the wiring layer has a plurality of wirings provided on at least one surface of the base film, The average line width of the wiring is less than 30 μm, and the average spacing is less than 30 μm. The wiring has a copper-based plating layer, The resistivity of the copper-based coating is greater than 1.68×10 -8 Ω·m, The copper-based plating layer contains sulfur, nitrogen and carbon. The copper-based plating layer has a sulfur content of 0.0001 mass % to 0.005 mass %, a nitrogen content of 0.0001 mass % to 0.005 mass %, and a carbon content of 0.001 mass % to 0.01 mass %.

2. The flexible printed wiring board according to claim 1, wherein The resistivity of the copper-based coating is 1.73×10 -8 Ω·m or more and 2.10×10 -8 Ω·m or less.

3. The flexible printed wiring board according to claim 2, wherein The resistivity of the copper-based coating is 1.76×10 -8 Ω·m or more and 1.93×10 -8 Ω·m or less.

4. The flexible printed wiring board according to any one of claims 1 to 3, wherein The average diameter of copper crystal grains in the copper-based plating layer is 0.05 μm or more and 100 μm or less.

5. The flexible printed wiring board according to any one of claims 1 to 3, wherein The wiring further includes a first conductive base layer in contact with the one side of the base film, The copper-based plating layer is provided on the opposite side of the surface of the first conductive base layer that contacts the base film. The first conductive substrate layer comprises: a first layer in contact with the one side of the base film; and The second layer is provided on the opposite side of the surface of the first layer in contact with the base film.

6. The flexible printed wiring board according to claim 5, wherein The first layer contains at least one selected from the group consisting of nickel, chromium, titanium, and silver.

7. The flexible printed wiring board according to claim 5, wherein The second layer contains 50 mass % or more of copper in the second layer.

8. A method for manufacturing a flexible printed wiring board, the flexible printed wiring board comprising a base film and a wiring layer, the wiring layer having a plurality of wirings provided on at least one surface of the base film, The average line width of the wiring is less than 30 μm, and the average spacing is less than 30 μm. The wiring has a copper-based plating layer, The resistivity of the copper-based coating is greater than 1.68×10 -8 Ω·m, The copper-based plating layer contains sulfur, nitrogen and carbon. The copper-based plating layer has a sulfur content of 0.0001 mass % or more and 0.005 mass % or less, a nitrogen content of 0.0001 mass % or more and 0.005 mass % or less, and a carbon content of 0.001 mass % or more and 0.01 mass % or less, The manufacturing method comprises: A step of laminating a conductive base layer on at least one side of the base film; forming a resist pattern on the surface of the conductive base layer; a step of forming a copper-based plating layer by electroplating the opening of the resist pattern on the conductive base layer in a plating solution; and a step of removing the resist pattern and the region of the conductive base layer where the copper-based plating layer is not laminated, The plating solution contains a first organic compound, a second organic compound and a third organic compound, The first organic compound comprises disodium 3,3'-dithiobis(1-propanesulfonate), The second organic compound comprises polyethylene glycol, The third organic compound includes a nitrogen-containing organic compound.

9. The method for manufacturing a flexible printed wiring board according to claim 8, wherein: The third organic compound is one or more selected from the group consisting of a copolymer of diallyl ammonium and sulfur dioxide, a polyvinyl imidazolium quaternary ammonium compound, a copolymer of vinyl pyrrolidone and vinyl imidazolium quaternary ammonium compound, and a quaternized polyamine.

10. The method for manufacturing a flexible printed wiring board according to claim 8 or 9, wherein: In the plating solution, The content of the first organic compound is 0.0001 mass % or more and 1 mass % or less, The content of the second organic compound is 0.004 mass % or more and 5 mass % or less, The content of the third organic compound is 0.0001 mass % or more and 0.5 mass % or less.

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