Conductive film

Abstract

A conductive film (1) comprises a translucent substrate (2) and a first wiring (10) positioned on the substrate (2). The first wiring (10) has a conductive layer (11) and a metal layer (12) laminated on the conductive layer (11). The conductive layer (11) includes a first layer (11a) and a second layer (11b) laminated on the first layer (11a). The sheet resistance value of the second layer (11b) is smaller than the sheet resistance value of the first layer (11a).

Description

Conductive film

[0001] The present disclosure relates to a conductive film used as a wiring board or the like.

[0002] In electrical equipment, a wiring board with wiring formed on a substrate is used. The wiring board is used as a touch sensor substrate provided with sensor electrodes or as a mounting substrate on which electronic components such as circuit elements are mounted. For example, as an electrical device using a wiring board as a touch sensor substrate, a touch panel provided with a touch sensor substrate in which fine wiring serving as sensor electrodes is formed in a mesh shape on a transparent film substrate is known. The fine wiring is, for example, metal wiring such as copper wiring with a line width on the order of micrometers.

[0003] As a technique for forming fine wiring on the order of micrometers, there is a technique of forming a groove in the insulating substrate itself or in an insulating layer on the substrate and embedding the wiring in the groove. As this type of technique, for example, the imprint method is known. The imprint method is a technique of transferring a fine concavo-convex structure using a mold member (mold) having a fine concavo-convex structure to an insulating substrate made of a resin material or a resin insulating layer on the substrate to form a fine groove, and embedding the wiring in this groove.

[0004] As this type of wiring board, Patent Document 1 discloses a conductive film including a substrate made of a resin material and wiring embedded in a groove formed in the substrate. In the conductive film disclosed in Patent Document 1, the wiring has a laminated structure of a conductive layer and a metal layer.

[0005] International Publication No. 2024 / 11269

[0006] However, the conductive film disclosed in Patent Document 1 has a problem that the sheet resistance value of the conductive layer is high in the wiring in which the conductive layer and the metal layer are laminated. For example, when a conductive film was produced by the method disclosed in Patent Document 1, the sheet resistance value of the conductive layer in the wiring was about 3.0 Ω / sq. Thus, when the sheet resistance value of the conductive layer is high in the wiring in which the conductive layer and the metal layer are laminated, the sheet resistance value as the wiring also becomes high.

[0007] This disclosure is made to solve these problems and aims to provide a conductive film having wiring with low sheet resistance.

[0008] To achieve the above objective, one embodiment of a conductive film according to the present disclosure comprises a light-transmitting substrate and wiring located on the substrate, wherein the wiring has a conductive layer and a metal layer laminated on the conductive layer, and the conductive layer includes a first layer and a second layer laminated on the first layer, wherein the sheet resistance of the second layer is smaller than the sheet resistance of the first layer.

[0009] This makes it possible to create a conductive film with wiring that has low sheet resistance.

[0010] Figure 1 is a diagram showing a conductive film according to an embodiment. Figure 2 is a partial cross-sectional view of the conductive film according to an embodiment. Figure 3 is a diagram illustrating a method for manufacturing a conductive film according to an embodiment. Figure 4 is a diagram illustrating the process of forming the first conductive layer in the method for manufacturing a conductive film according to an embodiment. Figure 5 is a diagram illustrating the process of forming the second conductive layer in the method for manufacturing a conductive film according to an embodiment. Figure 6 is a cross-sectional SEM image showing the conductive layer and its surrounding region in an actually manufactured conductive film. Figure 7A is a diagram showing the results of metal composition analysis in a conductive layer manufactured using a catalyst in an actually manufactured conductive film. Figure 7B is a diagram showing the results of metal composition analysis in a conductive layer manufactured without using a catalyst in an actually manufactured conductive film. Figure 8 is a diagram showing the film thickness and sheet resistance value when CuNi plating films corresponding to the first and second layers of the conductive layer are manufactured.

[0011] The embodiments of this disclosure will be described below with reference to the drawings. The embodiments described below are all specific examples of this disclosure. Therefore, the numerical values, shapes, materials, components, arrangement and connection configurations of components, as well as the processes (steps) and their order, shown in the following embodiments are examples and are not intended to limit this disclosure. Accordingly, any components in the following embodiments that are not described in the independent claims representing the highest-level concepts of this disclosure will be described as optional components.

[0012] Please note that each figure is a schematic diagram and not necessarily a strictly accurate representation. Therefore, the scale and other aspects may not necessarily be consistent across all figures. In addition, the same reference numerals are used for substantially identical components in each figure, and redundant explanations are omitted or simplified. Furthermore, in this specification, the terms "up" and "down" do not necessarily refer to the absolute upward (vertically upward) and downward (vertically downward) directions in spatial perception.

[0013] (Embodiment) First, the configuration of the conductive film 1 according to the embodiment will be described using Figures 1 and 2. Figure 1 is a diagram showing the conductive film 1 according to the embodiment. Figure 2 is a partial cross-sectional view of the conductive film 1 according to the embodiment. Figure 2 shows the cross section along line II-II in Figure 1.

[0014] In this embodiment, the conductive film 1 is a wiring substrate on which wiring is formed as a conductor. Specifically, the conductive film 1 is a flexible wiring substrate in the form of a flexible film. Furthermore, the conductive film 1 is a light-transmitting wiring substrate that can transmit light. For example, the conductive film 1 is a transparent wiring substrate on which fine wiring is formed.

[0015] As shown in Figure 1, the conductive film 1 has a first wiring 10 and a second wiring 20 as wiring. In this embodiment, the first wiring 10 and the second wiring 20 are formed on the same plane. That is, the first wiring 10 and the second wiring 20 are integral. However, the first wiring 10 and the second wiring 20 may be located on different planes and formed to intersect in three dimensions.

[0016] The first wiring 10 extends in a first direction, and the second wiring 20 extends in a second direction that intersects the first direction. In this embodiment, the first wiring 10 and the second wiring 20 are not orthogonal, but they may be.

[0017] Multiple first wirings 10 and second wirings 20 are formed. For example, the first wirings 10 and second wirings 20 are formed across the entire conductive film 1 in a mesh-like manner. The first wirings 10 and second wirings 20 are fine wirings with a line width on the order of micrometers. As an example, the line width of each of the first wirings 10 and second wirings 20 is 100 μm or less, and in this embodiment, it is 10 μm or less.

[0018] As shown in Figure 2, the conductive film 1 has a substrate 2 and an insulating layer 3 formed on top of the substrate 2. However, the insulating layer 3 is not required. In other words, the conductive film 1 may consist only of the substrate 2 on which the first wiring 10 and the second wiring 20 are formed.

[0019] Substrate 2 is an insulating substrate having insulating properties. For example, substrate 2 is an insulating resin substrate made of an insulating resin material. Alternatively, substrate 2 is a flexible sheet-like film substrate and serves as the base film for conductive film 1.

[0020] In this embodiment, the substrate 2 is translucent. Specifically, the substrate 2 is a film substrate that is translucent to at least visible light and is made of a translucent insulating resin material. In this case, the substrate 2 may be a transparent resin substrate made of a transparent resin material with a high transmittance such that the other side can be seen through it.

[0021] As the translucent resin material constituting the substrate 2, for example, PET (polyethylene terephthalate) resin, polyimide resin, cycloolefin resin, polycarbonate resin, or acrylic resin can be used.

[0022] The insulating layer 3 is located above the substrate 2. In this embodiment, the insulating layer 3 is formed directly above the substrate 2. Therefore, the upper surface of the substrate 2 is in contact with the lower surface of the insulating layer 3.

[0023] The insulating layer 3 is a resin layer made of an insulating resin material. In this embodiment, the insulating layer 3 is made of a light-transmitting insulating resin material. Specifically, the insulating layer 3 is made of a transparent insulating resin material. The resin material constituting the insulating layer 3 is a thermosetting resin or an ultraviolet-curable resin. Examples of resin materials that can be used to constitute the insulating layer 3 include PET resin, polyimide resin, cycloolefin resin, polycarbonate resin, or acrylic resin. The insulating layer 3 may be fixed to the substrate 2 by a transparent adhesive layer (not shown) or the like. The insulating layer 3 functions, for example, as a protective film.

[0024] The substrate 2 has grooves 2a. The grooves 2a are provided on the upper surface of the substrate 2. The grooves 2a are groove-shaped recesses formed so as to be recessed in the upper surface of the substrate 2, and are formed in an elongated shape. Specifically, the grooves 2a are formed in a straight or curved shape. In this embodiment, the grooves 2a are straight and are formed on only one surface of the substrate 2. The grooves 2a are formed in correspondence with the first wiring 10. For example, multiple grooves 2a are formed on the substrate 2 so as to be parallel to each other at predetermined intervals. Although not shown, grooves corresponding to the second wiring 20 are also formed on the substrate 2. The grooves corresponding to the second wiring 20 are the same as the grooves 2a corresponding to the first wiring 10.

[0025] The groove 2a has a bottom surface and side surfaces that are continuously connected to the bottom surface. In this embodiment, the cross-sectional shape of the groove 2a when cut in a cross section perpendicular to the longitudinal direction of the groove 2a is rectangular. Therefore, in this cross section, the groove 2a has a planar bottom surface and a pair of side surfaces, each planar and facing each other. In the groove 2a, the side surfaces are erected on the bottom surface. Specifically, the side surfaces are perpendicular to the bottom surface. The substrate 2 having the groove 2a may be formed by an imprint method, or it may be formed by cutting out the surface of a flat substrate with a laser scribe or the like.

[0026] The first wiring 10 is provided on one side of the substrate 2. In this embodiment, the first wiring 10 is positioned in a groove 2a provided on one side of the substrate 2. In other words, the first wiring 10 is embedded inside the groove 2a. As shown in Figure 2, the cross-sectional shape of the groove 2a is rectangular, so the cross-sectional shape of the first wiring 10 is rectangular.

[0027] The first wiring 10 is a metal wiring and has a conductive layer 11 and a metal layer 12 laminated on the conductive layer 11. In this embodiment, the conductive layer 11 and the metal layer 12 are formed inside the groove 2a of the substrate 2. Specifically, the conductive layer 11 is formed along the inner surface of the groove 2a. That is, the conductive layer 11 is formed as a thin film so as to cover the bottom and side surfaces of the groove 2a without completely filling the groove 2a. The metal layer 12 laminated on the conductive layer 11 is formed so as to fill the groove 2a whose inner surface is covered with the conductive layer 11. The metal layer 12 is the main wiring layer of the first wiring 10 and constitutes most of the groove 2a. Therefore, the metal layer 12 is thicker than the conductive layer 11. As an example, the metal layer 12 occupies more than 80% of the first wiring 10 in the cross-sectional view in Figure 2.

[0028] The conductive layer 11 is the base layer when forming the metal layer 12. Specifically, when the metal layer 12 is formed by a plating method, the conductive layer 11 serves as a seed layer when forming the metal layer 12.

[0029] The conductive layer 11 includes a first layer 11a and a second layer 11b laminated on the first layer 11a. In this embodiment, the conductive layer 11 has a two-layer structure consisting of a first layer 11a and a second layer 11b, and the first layer 11a and the second layer 11b are in contact. The first layer 11a is the lower layer of the conductive layer 11, and the second layer 11b is the upper layer of the conductive layer 11.

[0030] The sheet resistance of the second layer 11b is smaller than that of the first layer 11a. In other words, the sheet resistance of the first layer 11a is larger than that of the second layer 11b. That is, the second layer 11b is a low-sheet-resistance layer in the conductive layer 11, and the first layer 11a is a high-sheet-resistance layer in the conductive layer 11. For example, the sheet resistance of the first layer 11a is more than twice that of the second layer 11b, but this is not limited to that.

[0031] The first layer 11a and the second layer 11b are made of a conductive material. In this embodiment, the conductive layer 11 is a metal layer (metal film) made of a metallic material. Specifically, both the first layer 11a and the second layer 11b contain copper (Cu) and nickel (Ni). However, the first layer 11a and the second layer 11b may also contain metals other than copper and nickel.

[0032] The first layer 11a and the second layer 11b are CuNi plating films, formed, for example, by an electroless plating method. However, the first layer 11a and the second layer 11b do not necessarily have to be formed by an electroless plating method. For example, the first layer 11a and the second layer 11b may be formed by a sputtering method or the like.

[0033] The first layer 11a is a Ni-rich layer containing more nickel than copper. On the other hand, the second layer 11b is a Cu-rich layer containing more copper than nickel. Therefore, if we define the composition ratio of copper to nickel (number of Cu atoms ÷ number of Ni atoms) as the "Cu / Ni composition ratio," the Cu / Ni composition ratio of the Ni-rich first layer 11a is less than 1, and the Cu / Ni composition ratio of the Cu-rich second layer 11b is greater than 1. Thus, the Cu / Ni composition ratio of the second layer 11b is greater than the Cu / Ni composition ratio of the first layer 11a. In this case, it is desirable that the Cu / Ni composition ratio of the second layer 11b be 3 or greater.

[0034] Since the resistivity of copper is lower than that of nickel, the sheet resistance of the second layer 11b, which is a Cu-rich layer, is lower than the sheet resistance of the first layer 11a, which is a Ni-rich layer. For example, if the first layer 11a and the second layer 11b are CuNi plated films, the sheet resistance of the first layer 11a is between 2 and 7 times the sheet resistance of the second layer 11b.

[0035] In this way, by including the second layer 11b, which has a low sheet resistance, in the conductive layer 11, the sheet resistance of the conductive layer 11 can be reduced. Specifically, the sheet resistance of the conductive layer 11 is between 0 Ω / sq and 1.5 Ω / sq.

[0036] On the other hand, by including the Ni-rich first layer 11a in the conductive layer 11, the adhesion between the first layer 11a and the substrate 2 can be improved due to the adhesion effect of nickel. This improves the reliability of the first wiring 10 formed on the substrate 2.

[0037] The thickness of the first layer 11a and the second layer 11b is less than 1 μm. For example, the thickness of the first layer 11a and the second layer 11b is 0.010 μm or more and 0.500 μm or less. The thickness of the first layer 11a and the thickness of the second layer 11b may be the same or different. In this embodiment, the thickness of the first layer 11a and the thickness of the second layer 11b are different. Specifically, the thickness of the upper layer, the second layer 11b, is greater than the thickness of the lower layer, the first layer 11a. In other words, the thickness of the lower layer, the first layer 11a, is thinner than the thickness of the upper layer, the second layer 11b.

[0038] Furthermore, the interface between the first layer 11a and the second layer 11b has an uneven surface. That is, the upper surface of the first layer 11a and the lower surface of the second layer 11b have an uneven surface. This uneven surface is composed of countless recesses and countless protrusions of random depth and height. The surface roughness Ry of this uneven surface is on the order of nanometers, specifically between 10 nm and 50 nm.

[0039] The metal layer 12 laminated on the conductive layer 11 is made of a metal material such as copper, aluminum, or silver. In the present embodiment, the metal layer 12 contains copper. Specifically, the metal layer 12 is a copper wiring containing copper as a main component. In this case, the metal layer 12 may be composed of pure copper or a copper alloy.

[0040] The metal layer 12 is a plating film formed by a plating method using the conductive layer 11 as a seed layer. Specifically, the metal layer 12 is formed using the second layer 11b (low sheet resistance layer), which is the uppermost layer of the conductive layer 11, as a seed layer. In the present embodiment, the metal layer 12 is an electrolytic plating film formed by an electrolytic plating method. Specifically, the metal layer 12 is a Cu plating film composed of copper.

[0041] Note that the second wiring 20 has the same structure as the first wiring 10. Specifically, the second wiring 20 is a copper wiring, and includes a conductive layer having a two-layer structure of a first layer and a second layer each formed of a CuNi plating film formed by electroless plating, and a metal layer which is a Cu plating film formed by electrolytic plating on the conductive layer.

[0042] Further, in the present embodiment, a fine particle layer 2b exists below the conductive layer 11 of the first wiring 10. Specifically, the fine particle layer 2b exists below the first layer 11a of the conductive layer 11. The conductive layer 11 and the substrate 2 are in contact with each other via the fine particle layer 2b. That is, the conductive layer 11 and the fine particle layer 2b are in contact with each other. Specifically, the first layer 11a of the conductive layer 11 and the fine particle layer 2b are in contact with each other.

[0043] The fine particle layer 2b is a part of the substrate 2 which is a resin substrate. Specifically, the fine particle layer 2b is an upper layer (surface layer) of the substrate 2 existing near the surface of the substrate 2. Therefore, the fine particle layer 2b contains the resin material constituting the substrate 2. The thickness of the fine particle layer 2b is thinner than the thickness of the conductive layer 11. As an example, the thickness of the fine particle layer 2b is 30 nm or more and 150 nm or less. Note that the thickness of the fine particle layer 2b may be less than 30 nm or may exceed 150 nm. Also, the fine particle layer 2b may not be provided.

[0044] Further, the interface between the conductive layer 11 and the fine particle layer 2b has an uneven structure. Specifically, the interface between the first layer 11a of the conductive layer 11 and the fine particle layer 2b has an uneven structure. That is, the lower surface of the first layer 11a of the conductive layer 11 and the upper surface of the fine particle layer 2b have an uneven structure. In the present embodiment, since the fine particle layer 2b is a part of the substrate 2 which is a resin substrate, the interface between the first layer 11a of the conductive layer 11 and the substrate 2 (resin) has an uneven structure. This uneven structure is composed of innumerable recesses and innumerable protrusions with random depths and heights. The surface roughness Ry of this uneven structure is on the order of nanometers, specifically, 10 nm or more and 50 nm or less. Thus, the interface between the conductive layer 11 and the fine particle layer 2b has a nano-anchor structure due to the uneven structure.

[0045] The fine particle layer 2b is a layer containing metal fine particles 4 that absorb light. The metal fine particles 4 not only absorb light but also scatter and reflect light. Specifically, the metal fine particles 4 absorb, scatter, and reflect visible light.

[0046] The metal fine particles 4 are nano-particles with a particle size on the order of nanometers. The metal fine particles 4 which are nano-particles can absorb visible light of a specific wavelength by localized surface plasmon resonance. Further, the metal fine particles 4 which are nano-particles have the property of showing different light attenuation depending on the particle size.

[0047] In the fine particle layer 2b, a plurality of metal fine particles 4 exist randomly. The particle size of the plurality of metal fine particles 4 present in the fine particle layer 2b is 10 nm or more and 30 nm or less. Note that the fine particle layer 2b may contain metal fine particles 4 with a particle size of 10 nm or less. The fine particle layer 2b is a layer in which the metal fine particles 4 with a particle size of 10 nm or more and 30 nm or less among the plurality of metal fine particles 4 present in the fine particle layer 2b occupy the majority (for example, 50% or more). In the fine particle layer 2b, the cross-sectional density of the metal fine particles 4 with a particle size of 10 nm or more is 1×10 ３ particles / μm ２ ~3×10 ３ particles / μm ２ and is.

[0048] In this embodiment, the metal nanoparticles 4 contain copper and nickel. Specifically, the metal nanoparticles 4 are nanoparticles made of a copper-nickel alloy formed by the growth of copper and nickel around palladium particles (Pd particles) with a particle size of several nanometers.

[0049] Although the metal nanoparticles 4 may be present in areas other than the nanoparticle layer 2b, the density of metal nanoparticles 4 in the nanoparticle layer 2b is highest in the conductive film 1. Specifically, the density of metal nanoparticles 4 in the nanoparticle layer 2b is higher than the density of metal nanoparticles 4 in the substrate 2 or the conductive layer 11. In this embodiment, the metal nanoparticles 4 are present only in the nanoparticle layer 2b. In other words, the density of metal nanoparticles 4 in the substrate 2 or the conductive layer 11 is zero.

[0050] Next, a method for manufacturing the conductive film 1 according to the embodiment will be described using Figure 3. Figure 3 is a diagram illustrating the method for manufacturing the conductive film 1 according to the embodiment.

[0051] First, a substrate 2 having grooves 2a is prepared. For example, a substrate 2 having grooves 2a can be manufactured by the imprint method. In this case, first, as shown in Figure 3(a), a substrate 2 made of thermoplastic resin is prepared, the temperature is raised to soften the substrate 2, and a mold member 100, which will serve as a transfer plate, is pressed onto the substrate 2 to form grooves 2a. After that, the mold member 100 is removed. This makes it possible to manufacture a substrate 2 having grooves 2a, as shown in Figure 3(b).

[0052] Alternatively, the substrate 2 having grooves 2a may be fabricated using a photo-imprint method with a photocurable resin instead of a thermal imprint method with a thermoplastic resin. In this case, liquid photocurable resin is sandwiched between a first mold member and a second mold member, which serve as a transfer plate, and the photocurable resin is cured by irradiation with light (ultraviolet light). After that, the first mold member and the second mold member are removed. This allows grooves 2a to be formed in the substrate 2 made of photocurable resin. Alternatively, the substrate 2 may be formed using a thermosetting resin instead of a photocurable resin.

[0053] Next, as shown in Figure 3(c), a first layer 11a is formed on the inner surface of the groove 2a. Specifically, the first layer 11a is formed not only on the inner surface of the groove 2a, but also on the entire surface of the substrate 2 other than the groove 2a. In other words, the first layer 11a is formed over the entire surface of the substrate 2. In this embodiment, the first layer 11a, which is made of a CuNi plating film, was formed by electroless plating. Details of this process will be described later.

[0054] Next, as shown in Figure 3(d), a second layer 11b is formed on the first layer 11a. The second layer 11b is formed over the entire surface of the first layer 11a. In other words, the second layer 11b is formed over the entire surface of the first layer 11a. In this embodiment, the second layer 11b, which is made of a CuNi plating film, was formed by electroless plating. Details of this process will be described later.

[0055] Next, as shown in Figure 3(e), a metal layer 12 is formed on the second layer 11b. Specifically, the metal layer 12 is formed over the entire surface of the second layer 11b so as to fill the groove 2a. In this embodiment, the metal layer 12 was formed by electroplating. Specifically, the second layer 11b was used as a seed layer, and a metal layer 12 consisting of a Cu plating film was formed on the second layer 11b.

[0056] Next, as shown in Figure 3(f), a portion of the substrate 2 on which the first layer 11a, the second layer 11b, and the metal layer 12 are formed is removed to form the first wiring 10, which consists of a conductive layer 11 made up of the first layer 11a and the second layer 11b and a metal layer 12. Specifically, the first layer 11a, the second layer 11b, and the metal layer 12 are removed until the surface of the substrate 2 in the portion where the groove 2a is not formed is exposed. In other words, unnecessary portions of the first layer 11a, the second layer 11b, and the metal layer 12 are removed so as to leave the first layer 11a, the second layer 11b, and the metal layer 12 embedded in the groove 2a. This makes it possible to obtain a substrate 2 in which the first wiring 10, in which the metal layer 12 is formed on top of the conductive layer 11 which has a laminated structure of the first layer 11a and the second layer 11b, is embedded in the groove 2a.

[0057] Although not shown in the figures, an insulating layer 3 having grooves into which the second wiring 20 is embedded is then formed on the substrate 2 on which the first wiring 10 is formed. This makes it possible to produce the conductive film 1 shown in Figures 1 and 2.

[0058] Here, the steps of forming the first layer 11a of the conductive layer 11 (step 3(c) in Figure 3) and forming the second layer 11b of the conductive layer 11 (step 3(d) in Figure 3) will be explained in detail using Figures 4 and 5. Figure 4 is a diagram illustrating the step of forming the first layer 11a of the conductive layer 11 in the method for manufacturing the conductive film 1 according to the embodiment. Figure 5 is a diagram illustrating the step of forming the second layer 11b of the conductive layer 11 in the method for manufacturing the conductive film 1 according to the embodiment.

[0059] In the process of forming the first layer 11a, first, as shown in Figure 4(a), ultraviolet light is irradiated onto the surface of the substrate 2 on which the groove 2a is formed. This breaks the C=C bonds present in the surface layer of the substrate 2. In this embodiment, a low-pressure mercury lamp was used to irradiate the entire surface of the substrate 2 with ultraviolet light having two peak wavelengths of 185 nm and 256 nm.

[0060] Next, as shown in Figure 4(b), an alkaline treatment is performed. Specifically, the substrate 2 irradiated with ultraviolet light is immersed in an aqueous NaOH solution. By performing this alkaline treatment after irradiation with ultraviolet light, the C=C bonds present in the surface layer of the substrate 2 can be broken, and functional groups can be introduced. This allows for the formation of a modified layer 2s near the surface of the substrate 2, in which the surface layer of the substrate 2 has been modified. The thickness t of the modified layer 2s formed at this time is 30 nm to 150 nm.

[0061] Next, as shown in Figure 4(c), the catalyst 4a is supported on the substrate 2. In this embodiment, palladium particles (Pd particles) with a particle size of φ5 nm were used as the catalyst 4a.

[0062] Specifically, first, the substrate 2 is cleaned using a cleaner. Then, the substrate 2 is treated with PdCl ２ Pd particles are supported on the substrate 2 as catalyst 4a by immersion in an aqueous solution.

[0063] In this case, since the modified layer 2s is formed near the surface of the substrate 2, the catalyst 4a (Pd particles) can penetrate not only the surface of the substrate 2 but also into the interior of the substrate 2. Specifically, the catalyst 4a can penetrate into the interior of the modified layer 2s.

[0064] Next, as shown in Figure 4(d), a first layer 11a is formed on the substrate 2. In this embodiment, the first layer 11a was formed by electroless plating. Specifically, the substrate 2 on which the catalyst 4a is supported is immersed in a CuNi plating solution. As a result, copper and nickel are deposited and grow by a catalytic reaction of the catalyst 4a (Pd particles) supported on the substrate 2, and a CuNi plating film, which is an electroless plating film, is formed on the substrate 2 as the first layer 11a. In this embodiment, since a Ni-rich layer is formed as the first layer 11a, a Ni-rich CuNi plating solution with more Ni components than Cu components was used as the CuNi plating solution.

[0065] Furthermore, when forming this CuNi plating film, the catalyst 4a is scattered even inside the modified layer 2s of the substrate 2, so copper and nickel are deposited by the catalyst 4a present inside the modified layer 2s. In other words, copper and nickel grow with the catalyst 4a (Pd particles) as nuclei, forming countless metal nanoparticles 4 made of a copper-nickel alloy. As a result, the modified layer 2s, which is the surface layer of the substrate 2, becomes a nanoparticle layer 2b containing countless metal nanoparticles 4.

[0066] In this way, by performing electroless plating on the substrate 2 on which the catalyst 4a is supported, a first layer 11a consisting of a plating film is deposited on the substrate 2 by the catalyst 4a, and a fine particle layer 2b containing metal fine particles 4 is also formed. In other words, as the plating film that becomes the first layer 11a is deposited on the substrate 2, metal fine particles 4 made of the same metal as the plating film grow below the first layer 11a. That is, the metal that constitutes the first layer 11a and the metal that constitutes the metal fine particles 4 are the same. In this embodiment, both the metal that constitutes the first layer 11a and the metal that constitutes the metal fine particles 4 are copper-nickel alloys.

[0067] Furthermore, both the first layer 11a and the fine particle layer 2b are formed by the simultaneous growth of metal deposited by the catalyst 4a. However, the first layer 11a is formed by the unrestricted growth of copper and nickel, resulting in a dense, film-like alloy film. On the other hand, the fine particle layer 2b is thought to be composed of countless metal fine particles 4 because the copper and nickel grow within the resin substrate 2 under restricted conditions. For this reason, the interface between the first layer 11a and the fine particle layer 2b is thought to have an uneven structure. In addition, the film-like structure of the fine particle layer 2b is coarser than that of the first layer 11a. The surface of the first layer 11a also has an uneven structure. This uneven structure has a surface roughness Ry of 10 nm to 50 nm.

[0068] Next, the process of forming the second layer 11b will be explained using Figure 5. The second layer 11b is also formed by electroless plating, similar to the first layer 11a.

[0069] Specifically, in the step of forming the second layer 11b, first, as shown in Figure 5(a), the catalyst 4a is supported on the first layer 11a. In this embodiment, palladium particles (Pd particles) with a particle size of φ5 nm were used as the catalyst 4a. Specifically, the substrate 2 on which the first layer 11a is formed is made of PdCl ２ The Pd particles are supported on the first layer 11a as catalyst 4a by immersion in an aqueous solution.

[0070] Next, as shown in Figure 5(b), a second layer 11b is formed on top of the first layer 11a. In this embodiment, the second layer 11b was formed by electroless plating. Specifically, the first layer 11a on which the catalyst 4a is supported is immersed in a CuNi plating solution. As a result, copper and nickel are deposited and grow by a catalytic reaction of the catalyst 4a (Pd particles) supported on the first layer 11a, and a CuNi plating film, which is an electroless plating film, is laminated on top of the first layer 11a as the second layer 11b. In this embodiment, since a Cu-rich layer is formed as the second layer 11b, a Cu-rich CuNi plating solution with more Cu component than Ni component was used.

[0071] Furthermore, by forming the second layer 11b on top of the first layer 11a, which has an uneven surface structure, the interface between the first layer 11a and the second layer 11b also becomes an uneven structure. In addition, the surface of the second layer 11b also has an uneven structure. These uneven structures have a surface roughness Ry of 10 nm to 50 nm.

[0072] Furthermore, by supporting the catalyst 4a on the first layer 11a and forming the second layer 11b by electroless plating, a catalyst layer is present between the first layer 11a and the second layer 11b. In other words, the conductive layer 11 further has a catalyst layer located between the first layer 11a and the second layer 11b. In this embodiment, since Pd particles are used as the catalyst 4a, this catalyst layer will contain Pd.

[0073] In this embodiment, the second layer 11b in the conductive layer 11 was formed using catalyst 4a, but this is not limited to this. In other words, the second layer 11b may be formed without using catalyst 4a. In this case, if catalyst 4a is used as in this embodiment, the second layer 11b can be formed without using formalin, but if catalyst 4a is not used, it is preferable to form the second layer 11b using formalin.

[0074] Although not shown in the diagram, after forming the first layer 11a and the second layer 11b on the substrate 2, a baking process is performed. This relieves the internal stress in the fine particle layer 2b, the first layer 11a, and the second layer 11b, and also dehydrates them. The heating temperature for the baking process is, for example, 100°C.

[0075] Figure 6 is a cross-sectional SEM (Scanning Electron Microscope) image of a portion of the conductive film 1 actually fabricated using the method described above. Figure 6 shows the conductive layer 11 and its surrounding region.

[0076] As shown in Figure 6, it can be seen that a first layer 11a and a second layer 11b are formed on the substrate 2. It can also be confirmed that the first layer 11a of the conductive layer 11 and the substrate 2 are in contact via the fine particle layer 2b. Furthermore, it can be confirmed that the interface between the first layer 11a and the fine particle layer 2b has an uneven structure, and that the interface between the first layer 11a and the second layer 11b also has an uneven structure.

[0077] Furthermore, Figures 7A and 7B show the results of the metal composition analysis in the conductive layer 11 of the actually fabricated conductive film 1. Figure 7A shows the results when the second layer 11b was formed using catalyst 4a without using formalin, and Figure 7B shows the results when the second layer 11b was formed using formalin without using catalyst 4a.

[0078] As shown in Figures 7A and 7B, it can be seen that both the first layer 11a and the second layer 11b of the conductive layer 11 contain copper (Cu), nickel (Ni), and phosphorus (P). Furthermore, if we define the composition ratio of copper to nickel as the "Cu / Ni composition ratio," it can be seen that the Cu / Ni composition ratio of the second layer 11b is higher than that of the first layer 11a. It can also be seen that the Cu / Ni composition ratio of the second layer 11b is 3 or more, while the Cu / Ni composition ratio of the first layer 11a is less than 3.

[0079] Figure 8 shows the thickness of the CuNi plating film and the sheet resistance value when multiple CuNi plating films corresponding to the first layer 11a and the second layer 11b are fabricated using the method described above. In this example, the CuNi plating film corresponding to the second layer 11b was fabricated with a Cu / Ni composition ratio of 10, and the CuNi plating film corresponding to the first layer 11a was fabricated with a Cu / Ni composition ratio of 1.5.

[0080] As a result, it can be seen that by making the Cu / Ni composition ratio greater than 2, a Cu-rich Cu film can be formed with a low sheet resistance. Specifically, it can be seen that a CuNi plated film with a sheet resistance of 1.1 Ω / sq or less can be formed.

[0081] Furthermore, it can be seen that by making the Cu / Ni composition ratio less than 2 and making it Ni-rich, a CuNi plating film with a high sheet resistance can be formed. Specifically, it can be seen that a CuNi plating film with a sheet resistance of 2.55 Ω / sq or higher can be formed.

[0082] Furthermore, as shown in Figure 8, the sheet resistance of a Ni-rich CuNi plating film is approximately 2.3 to 7.0 times higher than that of a CuNi plating film formed with a Cu-rich material. Additionally, the film thickness of a Ni-rich CuNi plating film is thinner than that of a CuNi plating film formed with a Cu-rich material.

[0083] Furthermore, from the distribution of Cu / Ni composition ratio and sheet resistance obtained in this embodiment, it was found that if the Cu / Ni composition ratio is x and the sheet resistance is y, then the Cu / Ni composition ratio and the sheet resistance can be expressed as functions of x and y. Specifically, it was found that the Cu / Ni composition ratio (x) and the sheet resistance (y) can be approximated by a linear function. As a result, the sheet resistance can be predicted from the Cu / Ni composition ratio.

[0084] As described above, the conductive film 1 according to this embodiment comprises a light-transmitting substrate 2 and a first wiring 10 located on the substrate 2. The first wiring 10 has a conductive layer 11 and a metal layer 12 laminated on the conductive layer 11. The conductive layer 11 includes a first layer 11a and a second layer 11b laminated on the first layer 11a, and the sheet resistance value of the second layer 11b is smaller than the sheet resistance value of the first layer 11a.

[0085] This configuration makes it possible to lower the sheet resistance of the conductive layer 11. Specifically, the sheet resistance of the conductive layer when manufactured by the method disclosed in Patent Document 1 was approximately 3.0 Ω / sq, but in the conductive film 1 of this embodiment, the sheet resistance of the conductive layer 11 could be reduced to 1.5 Ω / sq or less. In other words, the sheet resistance of the conductive layer 11 of the conductive film 1 of this embodiment could be reduced to less than half that of the conductive layer of the conductive film disclosed in Patent Document 1.

[0086] Thus, in the conductive film 1 according to this embodiment, the sheet resistance value of the conductive layer 11 can be reduced, and therefore the sheet resistance value of the first wiring 10, which is composed of the conductive layer 11 and the metal layer 12, can also be reduced. Therefore, a conductive film 1 having a first wiring 10 with low sheet resistance can be realized. In other words, a conductive film 1 having a first wiring 10 with low wiring resistance can be realized.

[0087] Furthermore, in the conductive film 1 according to this embodiment, the metal layer 12 of the first wiring 10 contains copper, and both the first layer 11a and the second layer 11b of the conductive layer 11 contain copper and nickel.

[0088] This configuration allows for the formation of a metal layer 12 as a conductive film containing copper, using a conductive layer 11 containing copper and nickel as a base layer. For example, the conductive layer 11 containing copper and nickel can be used as a seed layer to form a metal layer 12 consisting of a copper plating film by a plating method.

[0089] Furthermore, in the conductive film 1 according to this embodiment, the Cu / Ni composition ratio of the second layer 11b is greater than that of the first layer 11a, which contains copper and nickel.

[0090] This makes the sheet resistance of the second layer 11b smaller than that of the first layer 11a, thus lowering the sheet resistance of the conductive layer 11. Furthermore, by making the Cu / Ni composition ratio of the first layer 11a smaller than that of the second layer 11b (i.e., by making the first layer 11a a Ni-rich layer), the adhesion between the first layer 11a and the substrate 2 can be improved due to the adhesion effect of nickel. In other words, the adhesion between the conductive layer 11 and the substrate 2 can be improved compared to the case where the conductive layer 11 is composed only of a Cu-rich layer. This improves the reliability of the first wiring 10 formed on the substrate 2.

[0091] Furthermore, in the conductive film 1 according to this embodiment, the Cu / Ni composition ratio of the second layer 11b is preferably 3 or more.

[0092] This significantly reduces the sheet resistance of the second layer 11b, which is composed of Cu and Ni, and thus significantly reduces the sheet resistance of the conductive layer 11. As a result, the sheet resistance of the first wiring 10 can also be significantly reduced.

[0093] Furthermore, in the conductive film 1 according to this embodiment, the thickness of the second layer 11b is greater than the thickness of the first layer 11a.

[0094] This makes it easy to make the sheet resistance of the second layer 11b smaller than that of the first layer 11a.

[0095] Furthermore, in the conductive film 1 according to this embodiment, a groove 2a is provided on the upper surface of the substrate 2, and the first wiring 10 is arranged in the groove 2a.

[0096] This configuration allows the first wiring 10, which has a laminated structure of a conductive layer 11 and a metal layer 12, to be embedded in the groove 2a of the substrate 2.

[0097] Furthermore, in the conductive film 1 according to this embodiment, the substrate 2 has a fine particle layer 2b containing light-absorbing metal fine particles 4 as an upper layer of the substrate 2, and the interface between the conductive layer 11 and the fine particle layer 2b has an uneven structure.

[0098] In this configuration, light incident from the back side of the first wiring 10 is absorbed by the microparticle layer 2b containing metal microparticles 4, and is also diffusely reflected by the uneven structure at the interface between the conductive layer 11 and the microparticle layer 2b. Furthermore, light incident from the back side of the first wiring 10 is also scattered by the metal microparticles 4 contained in the microparticle layer 2b. Thus, in the conductive film 1 according to this embodiment, the microparticle layer 2b is formed as a low-reflectivity layer with low reflectivity at the interface between the substrate 2 and the conductive layer 11. This makes it possible to reduce the reflectivity at the interface between the substrate 2 and the conductive layer 11. Therefore, when the conductive film 1 is viewed from the back side, it becomes difficult to recognize the first wiring 10.

[0099] (Modification) The conductive film 1 relating to the present disclosure has been described above based on embodiments, but the present disclosure is not limited to the above embodiments.

[0100] For example, in the above embodiment, the single-component metals constituting the first layer 11a and the second layer 11b in the conductive layer 11 were Cu and Ni, but are not limited to these. For example, the single-component metals constituting the first layer 11a and the second layer 11b may be Co, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Pb, Bi, etc. Also, in the above embodiment, the alloy or additive component (a component that is intentionally alloyed or added) constituting the first layer 11a and the second layer 11b was P, but are not limited to this. For example, the alloy or additive component metals constituting the first layer 11a and the second layer 11b may be Fe, Cr, Mn, Zn, W, B, C, Si, etc.

[0101] Furthermore, in the above embodiment, the first wiring 10 was provided on only one side of the substrate 2, but this is not limited to this. Specifically, the first wiring 10 may be provided on both sides of the substrate 2. In other words, the conductive layer 11 and the metal layer 12 may be provided on both sides of the substrate 2. Thus, the conductive layer 11 and the metal layer 12 only need to be provided on at least one side of the substrate 2. The second wiring 20 may also be provided on both sides of the substrate 2.

[0102] Furthermore, in the above embodiment, the first wiring 10 and the second wiring 20 intersect in a three-dimensional manner, but this is not limited to this. For example, the first wiring 10 and the second wiring 20 may be formed in the same layer. In the above embodiment, the three-dimensionally intersecting first wiring 10 and the second wiring 20 are insulated from each other via the insulating layer 3. However, contact portions (vias) may be formed at some of the multiple intersections of the first wiring 10 and the second wiring 20. In other words, the first wiring 10 and the second wiring 20 may be electrically connected.

[0103] Furthermore, although the above embodiment states that the second wiring 20 has the same structure as the first wiring 10, it is not limited to this. In other words, the second wiring 20 may have a different structure from the first wiring 10. Also, the second wiring 20 may be made of a different metal material than the first wiring 10. In this case, the first wiring 10 and the second wiring 20 can be insulated via the insulating layer 3, with the second wiring 20 being an upper layer wiring formed on the insulating layer 3 above the first wiring 10, and the first wiring 10 being a lower layer wiring formed below the insulating layer 3.

[0104] Furthermore, in the above embodiment, the conductive film 1 is a light-transmitting wiring substrate and can be used as a touch sensor substrate in a touch panel, for example, but is not limited to this. For example, the conductive film 1, which is a light-transmitting wiring substrate, may be used as a mounting substrate in a display device having a plurality of LED elements arranged in a matrix, or as a connecting substrate for electrically connecting electronic components, or as an antenna substrate having wiring formed in a predetermined pattern as a pattern antenna such as a 5G antenna, or as a heater substrate using wiring as heating wires.

[0105] Furthermore, although the conductive film 1 had a first wiring 10 and a second wiring 20 formed on it in the above embodiment, it is not limited to this. For example, the conductive film 1 may have only the first wiring 10. In this case, the first wiring 10 was formed in a groove 2a formed in the substrate 2, but it is not limited to this, and may be formed on the surface of the substrate 2 where no groove 2a is formed.

[0106] Furthermore, although the conductive film 1 was used as a wiring substrate with wiring in the above embodiment, it is not limited to this. Specifically, the conductive film 1 may be used for purposes other than a wiring substrate. In this case, the conductive film 1 may have a configuration in which only the conductive layer 11 is formed on the substrate 2 via a fine particle layer 2b.

[0107] Furthermore, in the above embodiment, the first wiring 10 of the conductive film 1 was composed of a conductive layer 11 having a first layer 11a and a second layer 11b and a fine particle layer 2b, but is not limited to this. For example, the conductive layer 11 may not have a second layer 11b and may consist only of the first layer 11a. In this case, the first wiring 10 is composed of a conductive layer 11 consisting only of the first layer 11a and a fine particle layer 2b. In this case, the sheet resistance value of the conductive layer 11 (= first layer 11a) is lower than the sheet resistance value of the fine particle layer 2b. Note that this embodiment (a configuration in which the sheet resistance value of the first layer 11a is lower than the sheet resistance value of the fine particle layer 2b, and the conductive layer 11 does not have a second layer 11b) is not included in claim 1 of the claims at the time of filing this application, but is included as one of the technologies of this disclosure.

[0108] Furthermore, this disclosure also includes forms obtained by applying various modifications to the above embodiments that a person skilled in the art could conceive, and forms realized by arbitrarily combining the components and functions of the embodiments without departing from the spirit of this disclosure. In addition, this disclosure also includes any combination of two or more claims from the multiple claims described in the claims of this application, provided that they are not technically contradictory. For example, if the cited claims described in the claims of this application are made into a multi-claim or multi-multi-claim so as to refer to all of the higher-level claims without technically contradictory, then all combinations of claims included in that multi-claim or multi-multi-claim are also included in this disclosure.

[0109] The conductive film relating to this disclosure can be used in various electrical devices, including touch panels.

[0110] 1 Conductive film 2 Substrate 2a Groove 2b Fine particle layer 2s Modified layer 3 Insulating layer 4 Metal fine particles 4a Catalyst 10 First wiring 11 Conductive layer 11a First layer 11b Second layer 12 Metal layer 20 Second wiring 100 Mold component

Claims

1. A conductive film comprising a light-transmitting substrate and wiring located on the substrate, wherein the wiring has a conductive layer and a metal layer laminated on the conductive layer, the conductive layer includes a first layer and a second layer laminated on the first layer, and the sheet resistance value of the second layer is smaller than the sheet resistance value of the first layer.

2. The conductive film according to claim 1, wherein the metal layer contains copper, the first layer contains copper and nickel, and the second layer contains copper and nickel.

3. The conductive film according to claim 2, wherein the Cu / Ni composition ratio, which is the ratio of copper to nickel in the second layer, is greater than the Cu / Ni composition ratio, which is the ratio of copper to nickel in the first layer.

4. The conductive film according to claim 2, wherein the Cu / Ni composition ratio, which is the ratio of copper to nickel in the second layer, is 3 or more.

5. The conductive film according to claim 1, wherein the sheet resistance value of the conductive layer is 0 Ω / sq or more and 1.5 Ω / sq or less.

6. The conductive film according to claim 1, wherein the thickness of the second layer is greater than the thickness of the first layer.

7. The conductive film according to claim 1, wherein the conductive layer further comprises a catalyst layer located between the first layer and the second layer, and the catalyst layer contains Pd.

8. The conductive film according to claim 1, wherein a groove is provided on the upper surface of the substrate, and the wiring is arranged in the groove.

9. The conductive film according to claim 1, wherein the substrate has a microparticle layer containing light-absorbing metal microparticles as an upper layer of the substrate, and the interface between the conductive layer and the microparticle layer has an uneven structure.

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