Wiring circuit board and method for manufacturing same

Abstract

This wiring circuit board comprises a transparent substrate and a wiring layer formed on the transparent substrate. The wiring layer contains copper and has an intersection part and a wiring part. The width of the wiring part is between 1 μｍ and 10 μｍ, inclusive. The wiring part has a first surface which is apart from one surface of the transparent substrate in a first direction in which the one surface of the transparent substrate faces and which faces in the first direction. The first surface is formed such that, in a cross section of the wiring part orthogonal to a second direction in which said wiring part extends, at least a portion of the first surface bulges or sinks with respect to the first direction.

Description

Wiring circuit board and method for manufacturing the same

[0001] The present invention relates to a wiring circuit board in which wirings are formed on a transparent substrate and a method for manufacturing the same.

[0002] There is a wiring circuit board in which wirings are formed on a transparent substrate. Such a wiring circuit board is used in various devices such as a touch panel and a defroster device, and it is required to be recognized as transparent by a user who views the wiring circuit board. For example, Patent Document 1 describes a wiring board including a transparent base material and a conductive layer as an example of a wiring circuit board.

[0003] The transparent base material described in Patent Document 1 corresponds to the above-mentioned transparent substrate. The transparent base material is preferably a base material having a certain transmittance with respect to visible light, and is, for example, a plastic substrate or glass. Further, the conductive layer described in Patent Document 1 corresponds to the above-mentioned wiring. The conductive layer includes an adhesive layer and a metal layer, and is provided on at least one surface of the transparent base material.

[0004] Japanese Patent Application Laid-Open No. 2017-211826

[0005] The wirings formed on the transparent substrate are a factor that reduces the transparency of the wiring circuit board. For example, when a part of the wiring is composed of a metal layer as in the conductive layer described in Patent Document 1, the surface of the metal layer easily reflects light (external light) incident from an arbitrary direction. At this time, the light reflected on the surface of the metal layer reduces the transparency of the wiring circuit board. As a result, when a user views an object through the wiring circuit board, the visibility of the object is significantly reduced. In order to suppress the occurrence of reflection of external light in the metal layer, there is a method of making the color of the surface of the conductive layer black.

[0006] However, even when a process of making the color of the surface of the conductive layer black (hereinafter referred to as a blackening process) is performed, the generation of reflected light in the conductive layer cannot always be sufficiently reduced. Further, depending on the functions required for the conductive layer, the blackening process of the conductive layer cannot always be performed under appropriate conditions. Therefore, it is required to improve the transparency of the wiring circuit board without depending on the blackening process.

[0007] Furthermore, in recent years, the increasing diversity of devices used with circuit boards has sometimes necessitated lower resistance in the wiring of the circuit boards. In this case, increasing the width of the wiring can be considered to reduce resistance. However, such a wiring design reduces the transparency of the circuit board.

[0008] The object of the present invention is to provide a wiring circuit board that can achieve high transparency and a method for manufacturing the same.

[0009] A wiring circuit board according to one aspect of the present invention comprises a transparent substrate having one surface and a copper-containing wiring formed on the one surface of the transparent substrate, wherein the width of the wiring is 1 μm or more and 10 μm or less, and the wiring has a first surface that is spaced apart from the one surface of the transparent substrate and faces the first direction in a first direction toward which the one surface of the transparent substrate faces, and the first surface is formed such that at least a portion of the cross-section of the wiring perpendicular to a second direction toward which the wiring extends bulges or is recessed with respect to the first direction.

[0010] A method for manufacturing a wiring circuit board according to another aspect of the present invention includes the steps of: preparing a transparent substrate having one surface; and forming a wiring containing copper on the one surface of the transparent substrate, wherein the width of the wiring is 1 μm or more and 10 μm or less; the wiring has a first surface that is spaced apart from the one surface of the transparent substrate and faces the first direction in a first direction toward which the one surface of the transparent substrate faces; and the step of forming the wiring includes forming the wiring such that, in a cross-section of the wiring perpendicular to a second direction toward which the wiring extends, at least a portion of the first surface bulges or is recessed with respect to the first direction.

[0011] According to the present invention, a wiring circuit board with high transparency can be realized.

[0012] Figure 1 is an external perspective view of a wiring circuit board according to one embodiment of the present invention. Figure 2 is a cross-sectional view taken along line A-A inside the outlet of the wiring circuit board of Figure 1. Figure 3 is an enlarged cross-sectional view of a wiring circuit board according to one modified example. Figure 4 is a schematic cross-sectional view illustrating the manufacturing method of the wiring circuit boards of Figures 1 and 2. Figure 5 is a schematic cross-sectional view illustrating the manufacturing method of the wiring circuit boards of Figures 1 and 2. Figure 6 is a schematic cross-sectional view illustrating the manufacturing method of the wiring circuit boards of Figures 1 and 2. Figure 7 is a schematic cross-sectional view illustrating the manufacturing method of the wiring circuit boards of Figures 1 and 2. Figure 8 is a schematic cross-sectional view illustrating the manufacturing method of the wiring circuit boards of Figures 1 and 2. Figure 9 is a schematic cross-sectional view illustrating the manufacturing method of the wiring circuit boards of Figures 1 and 2. Figure 10 is a schematic cross-sectional view illustrating the manufacturing method of the wiring circuit boards of Figures 1 and 2. Figure 11 shows the transparency evaluation test results of sample A. Figure 12 shows the transparency evaluation test results of sample B. Figure 13 shows the transparency evaluation test results of sample C. Figure 14 shows the transparency evaluation test results of sample D. Figure 15 shows the transparency evaluation test results for sample E. Figure 16 shows the transparency evaluation test results for sample F. Figure 17 shows the transparency evaluation test results for sample G.

[0013] Hereinafter, a wiring circuit board according to one embodiment of the present invention and a method for manufacturing the same will be described with reference to the drawings. In the following description, the degree of agreement (degree of agreement) between the image of a predetermined space perceived by the user when the user looks at the predetermined space directly and the image of the predetermined space perceived by the user when the user looks at the predetermined space with the wiring circuit board in between will be referred to as the transparency of the wiring circuit board. The transparency of the wiring circuit board is considered to be higher the higher the degree of agreement between the two images. The degree of agreement between the two images includes the degree of agreement in brightness, contrast, hue, and contour of the two images perceived by the user.

[0014] 1. Diagram 1 of the wiring circuit board configuration is an external perspective view of a wiring circuit board 1 according to one embodiment of the present invention. The wiring circuit board 1 according to this embodiment basically has a configuration in which a wiring layer 20 and a cover insulating layer 90 are formed in that order on a transparent substrate 10.

[0015] The transparent substrate 10 has a light transmittance of, for example, 80% or more in the visible light region (for example, 380 nm to 780 nm) and is electrically insulating. The transparent substrate 10 according to this embodiment is formed of a cycloolefin polymer resin. The transparent substrate 10 may also be formed of an organic insulating material such as polyester resin, acrylic resin, polycarbonate resin, or polyimide resin. In addition, a glass substrate and a transparent ceramic substrate may be used as the transparent substrate 10. The transparent substrate 10 has a thickness of, for example, 20 μm to 200 μm.

[0016] The transparent substrate 10 has one surface and the other surface facing opposite directions. In the following description, the direction in which one surface of the transparent substrate 10 faces will be referred to as the upper side of the wiring circuit board 1, and the direction in which the other surface of the transparent substrate 10 faces will be referred to as the lower side of the wiring circuit board 1. The wiring layer 20 is formed in a mesh pattern on one surface of the transparent substrate 10. Note that the mesh pattern of the wiring layer 20 in the example of Figure 1 is merely one example. The present invention is not limited to the wiring layer 20 being formed in a mesh pattern. Details of the wiring layer 20 will be described later. The cover insulating layer 90 is formed on one surface of the transparent substrate 10 so as to cover the wiring layer 20. The cover insulating layer 90 according to this embodiment is formed of a transparent polyimide resin. The cover insulating layer 90 may be formed of other transparent synthetic resins such as epoxy resin, cycloolefin polymer resin, polycarbonate resin, polyethylene terephthalate resin, polystyrene resin, or polyethylene naphthalate resin. The cover insulating layer 90 has a thickness of, for example, 1 μm to 30 μm. Furthermore, in the wiring circuit board 1, the cover insulating layer 90 is not necessarily required.

[0017] 2. Details of the wiring layer 20 and the effects obtained by the configuration of the wiring layer 20 The wiring layer 20 contains one or more metals. In Figure 1, within the dashed-dotted outline, an enlarged plan view of a portion of the external perspective view of the wiring circuit board 1 (the portion within the frame of the thick dashed-dotted outline) is shown.

[0018] As shown in the callout in Figure 1, the wiring layer 20 is formed in a mesh-like manner in plan view. More specifically, the wiring layer 20 in this example includes a plurality of intersections 21 and a plurality of wiring sections 22 having a common length. The plurality of intersections 21 and the plurality of wiring sections 22 are formed such that, in plan view, four wiring sections 22 extend from each intersection 21 in four mutually orthogonal directions, and each wiring section 22 connects two intersections 21. As stated above, the present invention is not limited to the wiring layer 20 being formed in a mesh-like manner.

[0019] Figure 2 is a cross-sectional view taken along line A-A inside the outlet of the wiring circuit board 1 shown in Figure 1. As shown in Figure 2, the wiring layer 20 includes a configuration in which a seed layer 20a, a plating layer 20b, and a coating layer 20c are laminated together. In Figure 2, the cross-section of the wiring portion 22 of the wiring layer 20 is shown, but the cross-section of the intersection portion 21 has basically the same configuration as the cross-section of the wiring portion 22.

[0020] The seed layer 20a according to this embodiment has a structure in which, for example, a copper thin film is further laminated on a base layer. The base layer is composed of one or more laminated thin films. The one or more thin films constituting the base layer include thin films made of a metal or alloy containing one or more elements from titanium, molybdenum, tungsten, nickel, aluminum, and chromium. In addition to the above example, the base layer may also include a thin film made of indium tin oxide (ITO). On the base layer of the seed layer 20a, instead of the copper thin film described above, a thin film made of a metal or alloy containing one or more elements from gold, silver, platinum, lead, tin, nickel, cobalt, indium, rhodium, chromium, tungsten, and ruthenium may be formed.

[0021] Each thin film constituting the seed layer 20a is formed, for example, by sputtering or electroless plating. The seed layer 20a has a thickness of 0.01 μm or more and 1 μm or less. The plating layer 20b is made of a metal containing copper and is formed by electroplating. In this embodiment, the plating layer 20b is made of copper.

[0022] The coating layer 20c is a black metallic thin film formed to cover the sides of the seed layer 20a, the sides of the plating layer 20b, and the upper end surface of the plating layer 20b. Examples of materials constituting the coating layer 20c include metallic materials such as palladium, copper oxide, nickel, chromium, zinc, tin, or alloys containing any of these metals.

[0023] The coating layer 20c may be composed of a material other than metal. In this case, the coating layer 20c may be composed of a black resin material such as polyimide resin or epoxy resin, or it may be composed of a black ceramic material. The coating layer 20c according to this embodiment has a thickness T2 greater than 0 μm and 0.1 μm or less. In this embodiment, the coating layer 20c has a thickness of 0.05 μm.

[0024] In this embodiment, each wiring portion 22 of the wiring layer 20 has a width W of 1 μm to 10 μm. Furthermore, each wiring portion 22 has a thickness T1 of 1 μm to 10 μm in a direction perpendicular to one surface of the transparent substrate 10.

[0025] In this embodiment, the width W of the wiring section 22 refers to the maximum width of the wiring section 22 in any part of the wiring section 22, in a cross section perpendicular to the direction in which the wiring section 22 extends (the cross section in Figure 2). The thickness T1 of the wiring section 22 refers to the maximum thickness of the wiring section 22 in any part of the wiring section 22, in a cross section perpendicular to the direction in which the wiring section 22 extends (the cross section in Figure 2).

[0026] As described above, the width W of the wiring portion 22 is 1 μm or more and 10 μm or less. In this case, by having a width W of 1 μm or more for the wiring portion 22, a decrease in the reliability of the wiring circuit board 1 due to excessively reducing the cross-sectional area of ​​the wiring portion 22 is suppressed. Furthermore, by having a width W of 5 μm or less for the wiring portion 22, the transparency of the wiring circuit board 1 is improved compared to the case where a wiring portion 22 with a width W greater than 10 μm is provided on one surface of the transparent substrate 10. It is preferable that the width W of the wiring portion 22 is 1 μm or more and 5 μm or less.

[0027] Furthermore, in this embodiment, each wiring section 22 is formed such that its aspect ratio (the ratio of thickness T1 to width W (T1 / W)) is 1.0 or greater. In this case, compared to the case where the aspect ratio of the wiring section 22 is less than 1.0, it is possible to reduce the area in which the wiring section 22 is formed on one surface of the transparent substrate 10 while ensuring a certain amount of cross-sectional area for the seed layer 20a and the wiring layer 20 that function as conductors. As a result, the transparency of the wiring circuit board can be improved without increasing the resistance value of the wiring section 22.

[0028] Furthermore, in this embodiment, each wiring portion 22 is formed in an arc shape such that its upper end surface bulges upward in a cross section perpendicular to the direction in which the wiring portion 22 extends (cross section in Figure 2). That is, the upper end surface of the wiring portion 22 is not a flat surface. In this case, light incident on the upper end surface of the wiring portion 22 is dispersed and reflected by the bulge of the upper end surface. As a result, when viewing the wiring circuit board 1 from above, the reduction in transparency of the wiring circuit board 1 caused by the strong upward reflection of light incident on the upper end surface of the wiring portion 22 is suppressed. Therefore, the reduction in transparency of the wiring circuit board 1 caused by reflections or halation of surrounding materials in the wiring portion 22 is suppressed. As a result, the wiring circuit board 1 in Figures 1 and 2 has high transparency.

[0029] Furthermore, each wiring section 22 has a constriction in its lower half. More specifically, at least a portion of the lower half of the wiring section 22 is formed such that the width of the wiring section 22 gradually decreases as it approaches one surface of the transparent substrate 10.

[0030] In this case, the area of ​​the portion of the wiring portion 22 that contacts one surface of the transparent substrate 10 (hereinafter referred to as the substrate contact surface) is smaller than in the case where the wiring portion 22 does not have a constriction. By forming the substrate contact surface of the wiring portion 22 to be small in this way, the amount of light incident on the substrate contact surface is reduced. As a result, when a user views the wiring circuit board 1 from a position below the wiring circuit board 1, the strong downward reflection of light incident on the substrate contact surface of the wiring portion 22 is suppressed. Therefore, the amount of light that is incident on the user's eyes due to reflections of surrounding materials or halation in the wiring portion 22 is reduced.

[0031] As described above, in each wiring section 22, the sides of the seed layer 20a, the sides of the plating layer 20b, and the upper end surface of the plating layer 20b are covered with a black coating layer 20c. In this case, at least a portion of the light incident on the upper end surface and both sides of the wiring section 22 is absorbed by the black coating layer 20c. As a result, when a user views the wiring circuit board 1 from above, the amount of light reflected from the upper end surface or both sides of the wiring section 22 that directly enters the user's eyes is reduced.

[0032] Furthermore, as described above, the thickness T2 of the coating layer 20c is greater than 0 μm and 0.1 μm or less. In this case, the enlargement of the wiring portion 22 is reduced compared to the case where the coating layer 20c has a thickness T2 greater than 0.1 μm. As a result, the increase in the area occupied by the wiring layer 20 on one surface of the transparent substrate 10 due to the coating layer 20c is suppressed. Therefore, the decrease in the transparency of the wiring circuit board 1 due to the coating layer 20c is suppressed.

[0033] 3. Modifications (a) In the wiring circuit board 1 of Figures 1 and 2, the upper end surface of the wiring portion 22 is formed to bulge upward. However, the upper end surface of the wiring portion 22 may be formed in an arc shape so as to be concave upward.

[0034] Figure 3 is an enlarged cross-sectional view of the wiring circuit board 1 according to one modified example. The cross-sectional view in Figure 3 corresponds to the cross-sectional view in Figure 2. The wiring circuit board 1 according to one modified example has the same configuration as the wiring circuit board 1 in Figures 1 and 2, except for the shape of the upper end surface of the wiring portion 22.

[0035] As shown in Figure 3, the upper end surface of the wiring portion 22 in one modified example is concave upwards. In this case as well, light incident on the upper end surface of the wiring portion 22 is dispersed and reflected by the concave surface. As a result, when viewing the wiring circuit board 1 from above, the reduction in transparency of the wiring circuit board 1 caused by the strong upward reflection of light incident on the upper end surface of the wiring portion 22 is suppressed. Therefore, the wiring circuit board 1 in one modified example has high transparency, similar to the wiring circuit board 1 in Figures 1 and 2.

[0036] (b) In the wiring circuit board 1 according to this embodiment, the wiring layer 20 does not have to have a coating layer 20c. That is, the wiring layer 20 may be composed of a seed layer 20a and a plating layer 20b. In this case, the formation of the coating layer 20c becomes unnecessary in the manufacturing method of the wiring circuit board 1 described later. Therefore, the number of manufacturing steps for the wiring circuit board 1 can be reduced.

[0037] (c) In the wiring circuit board 1 according to this embodiment, the wiring layer 20 may have a configuration formed of a single layer. In this case, the wiring layer 20 may have a configuration formed of a single layer consisting only of copper, for example.

[0038] (d) In the wiring circuit board 1 of Figure 1, the wiring layer 20 is formed such that, in a plan view, four wiring sections 22 extend from each intersection 21 in four mutually orthogonal directions, and each wiring section 22 connects two intersections 21. In other words, the wiring layer 20 is formed such that a square pattern with a common shape is arranged on one surface of the transparent substrate 10 by the multiple intersections 21 and the multiple wiring sections 22. However, the shape (pattern) of the wiring layer 20 in a plan view is not limited to the example in Figure 1.

[0039] The wiring layer 20 may be formed such that a pattern of rhombuses, excluding squares, having a common shape due to a plurality of intersections 21 and a plurality of wiring portions 22, is arranged on one surface of the transparent substrate 10. Alternatively, the wiring layer 20 may be formed such that a pattern of regular hexagons, having a common shape due to a plurality of intersections 21 and a plurality of wiring portions 22, is arranged on one surface of the transparent substrate 10.

[0040] Further, the wiring layer 20 may be formed such that other polygonal patterns such as triangles or pentagons are arranged on one surface of the transparent substrate 10. Alternatively, the wiring layer 20 may be formed such that a plurality of types of polygonal patterns having different sizes are randomly arranged on one surface of the transparent substrate 10.

[0041] (e) Also, in each of the above examples, the wiring layer 20 is formed in a mesh shape on one surface of the transparent substrate 10, but the present invention is not limited to this. The fact that the shape of the wiring layer 20 is a mesh shape is merely an example of the wiring circuit board 1 according to the present embodiment.

[0042] In the wiring circuit board 1, the wiring layer 20 may be formed on one surface of the transparent substrate 10 in a pattern other than a mesh shape. The wiring layer 20 may be formed, for example, such that a single straight line extends on one surface of the transparent substrate 10, or may be formed such that a plurality of straight lines arranged at a predetermined interval extend parallel to each other in one direction. Alternatively, the wiring layer 20 may be formed on one surface of the transparent substrate 10 so as to exhibit a zigzag shape or a spiral shape.

[0043] (f) In the wiring circuit board 1 according to the present embodiment, each wiring portion 22 may be formed such that the aspect ratio is less than 1.0. In this case, the formation of the wiring portion 22 becomes easier compared to the case where the wiring portion 22 is formed such that the aspect ratio is 1.0 or more.

[0044] 4. Manufacturing method of the wiring circuit board 1 FIGS. 4 to 10 are schematic cross-sectional views for explaining the manufacturing method of the wiring circuit board 1 of FIGS. 1 and 2. The schematic cross-sectional views of FIGS. 4 to 10 correspond to the cross-sectional view taken along line A - A of FIG. 1 (FIG. 2). First, as shown in FIG. 4, a transparent substrate 10 having a flat one surface and the other surface is prepared. The transparent substrate 10 in this example is made of a cycloolefin polymer resin and has flexibility. Here, it is assumed that the transparent substrate 10 is arranged such that one surface of the transparent substrate 10 faces upward and the other surface of the transparent substrate 10 faces downward.

[0045] Next, as shown in FIG. 5, a seed layer 20a is formed so as to cover the entire one surface of the transparent substrate 10. The seed layer 20a in this example has a structure in which a copper thin film is laminated on an underlayer. In this case, for example, an underlayer made of indium tin oxide (ITO) is formed on one surface of the transparent substrate 10 by sputtering. Thereafter, a copper thin film is formed on the underlayer by sputtering.

[0046] Next, after a photoresist is applied to the surface of the seed layer 20a, an exposure process and a development process are performed. Thereby, as shown in FIG. 6, a plating resist layer 30 having openings 31 of a predetermined pattern is formed on the seed layer 20a. The opening 31 in this example is a mesh-like pattern. The plating resist layer 30 may be formed by attaching a dry film resist to the surface of the seed layer 20a and performing an exposure process and a development process instead of applying a photoresist to the surface of the seed layer 20a.

[0047] Here, the opening 31 is formed such that the opening area gradually decreases downward in the vicinity of the lower end of the opening 31 in order to form a constriction in the lower half of the wiring portion 22. The formation of such an opening 31 can be performed, for example, by adjusting the amount of light (exposure amount) irradiated to the photoresist during the exposure process.

[0048] Next, as shown in FIG. 7, a plating layer 20b is formed by electrolytic plating on the region of the seed layer 20a where the plating resist layer 30 is not formed, that is, the portion of the seed layer 20a exposed through the opening 31. Thereafter, as shown in FIG. 8, the plating resist layer 30 is removed.

[0049] When forming the plating layer 20b, a predetermined additive is mixed into the plating solution to adjust the shape of the upper end surface of the wiring portion 22. Here, the additive includes, for example, an accelerator and an inhibitor. The accelerator is a liquid that promotes the growth of the plating by adsorbing onto the surface to be treated. The inhibitor is a liquid that suppresses the growth of the plating by adsorbing onto the surface to be treated. By adjusting the mixing ratio of the accelerator and the inhibitor in the additive, it is possible to make the upper end surface of the plating layer 20b bulge upward, or to make the upper end surface of the plating layer 20b concave.

[0050] Next, as shown in Figure 9, the unwanted portion of the exposed seed layer 20a is removed, for example, by wet etching or dry etching. When removing the unwanted portion of the seed layer 20a, an etching resist may be formed on the upper surface of the exposed plating layer 20b.

[0051] Next, as shown in Figure 10, a coating layer 20c is formed to cover the surface (side) of the seed layer 20a and the surface (side and upper end) of the plating layer 20b that are exposed on one surface of the transparent substrate 10. In this example, the coating layer 20c is formed by replacing the surface of the seed layer 20a and the surface of the plating layer 20b with another metal (for example, palladium, copper oxide, nickel, chromium, zinc, or tin). Alternatively, the coating layer 20c may be formed by laminating a film made of a resin material or a ceramic material onto the surface of the seed layer 20a and the surface of the plating layer 20b.

[0052] As described above, the formation of the coating layer 20c creates a wiring layer 20 consisting of a seed layer 20a, a plating layer 20b, and a coating layer 20c, thus completing the wiring circuit board 1. In the wiring circuit board 1 according to this embodiment, a cover insulating layer 90 covering the wiring layer 20 may be formed on the transparent substrate 10 (Figure 2). Alternatively, a cover insulating layer 90 covering the wiring layer 20 may not be formed on the transparent substrate 10. The cover insulating layer 90 can be formed from, for example, polyimide resin or epoxy resin.

[0053] In the wiring circuit board 1, the wiring layer 20 has a pattern corresponding to the opening 31 of the plating resist layer 30 in Figure 6.

[0054] As described above, the transparent substrate 10 in this example is made of a cycloolefin polymer resin and is flexible. In this case, the wiring circuit board 1 can be manufactured by a roll-to-roll method.

[0055] In the roll-to-roll method, for example, a roll (hereinafter referred to as the "feed-out roll") on which a long transparent substrate 10 is wound is prepared, and the transparent substrate 10 is fed out from the feed-out roll. The fed-out transparent substrate 10 is then wound onto another roll (hereinafter referred to as the "wind-up roll"). At this time, each part of the transparent substrate 10 being transported between the feed-out roll and the wind-up roll is sequentially subjected to the multiple processes described above using Figures 4 to 10 and Figure 2. As a result, a large number of wiring circuit boards 1 can be manufactured with high efficiency.

[0056] The wiring circuit board 1 may be manufactured by a method other than the roll-to-roll method. For example, if the transparent substrate 10 is made of a material with poor flexibility such as glass, the wiring circuit board 1 may be manufactured by a single-wafer method in which processing is performed sequentially on a single sheet.

[0057] 5. Effects (a) In the wiring circuit board 1 according to this embodiment, the width W of each wiring portion 22 is 1 μm or more and 10 μm or less. Also, the upper end surface of the wiring portion 22 is either bulging or recessed. As a result, the wiring circuit board 1 has high transparency.

[0058] (b) In addition, in each wiring section 22, a covering layer 20c is formed so as to cover the side surface of the seed layer 20a, the side surface of the plating layer 20b, and the upper end surface of the plating layer 20b. As a result, the wiring circuit board 1 has higher transparency.

[0059] (c) In addition, each wiring section 22 has a constriction in the lower half. This improves the transparency of the wiring circuit board 1 when viewed from a position below the wiring circuit board 1.

[0060] (d) As described above, when manufacturing the wiring circuit board 1, the wiring layer 20 is formed by first forming a plating layer 20b on the seed layer 20a and then removing the unnecessary portion of the seed layer 20a. This method of forming wiring is called the semi-additive method. On the other hand, another example of a method for manufacturing the wiring circuit board 1 is the subtractive method. The subtractive method is a method in which a two-layer substrate is prepared, in which a metal layer is formed on a transparent substrate, and wiring is formed by etching a part of the metal layer in a predetermined pattern.

[0061] In this embodiment, as described above, the wiring layer 20 is formed by a so-called semi-additive method. Compared to the case where the wiring layer 20 is formed by a subtractive method, the semi-additive method allows for the formation of fine patterns on the plating layer 20b with high dimensional accuracy. Therefore, the increase in the area where the wiring layer 20 is formed due to the formation of the plating layer 20b in unintended areas on the transparent substrate 10 is suppressed.

[0062] 6. Transparency Evaluation Test As described above, in the wiring circuit board 1 according to this embodiment, the width W of each wiring portion 22 is 1 μm or more and 10 μm or less. Also, the upper end surface of the wiring portion 22 is either bulging or recessed. In the following description, both of the above conditions relating to the wiring portion 22 of the wiring circuit board 1 will be referred to as the transparency conditions.

[0063] The inventors primarily prepared seven wiring circuit boards 1 as Sample A, Sample B, Sample C, Sample D, Sample E, Sample F, and Sample G to confirm whether there is a difference in transparency between wiring circuit boards 1 that meet the transparency conditions and other wiring circuit boards 1 (wiring circuit boards 1 that do not meet the transparency conditions). The inventors also observed the cross-sectional shape of the wiring section 22 of each of the prepared samples A to G using a scanning electron microscope (SEM) and measured the dimensions of each part of the wiring section 22. Based on this, the inventors determined whether the sample met the above transparency conditions. Furthermore, the inventors visually observed each of the samples A to G and evaluated the transparency of each sample A to G.

[0064] Figures 11 to 17 show the transparency evaluation test results for samples A to G. Each of Figures 11 to 17 schematically shows an SEM image of the cross-section of the wiring section 22 of the sample corresponding to the drawing. Various measurement results regarding the shape of the wiring section 22 are also shown. Furthermore, each figure shows the transparency evaluation results when the sample is viewed from above and when the sample is viewed from below.

[0065] As shown in Figures 11 to 17, samples A to E among samples A to G satisfy the transparency conditions described above. All of these samples A to E had high transparency. On the other hand, samples F and G, which did not meet the transparency conditions, both had low transparency. Thus, the transparency evaluation test confirmed that the wiring circuit board 1 has high transparency by satisfying the transparency conditions.

[0066] No constriction was formed in the wiring section 22 of sample C. As a result, the transparency of sample C when viewed from below was slightly lower than that of samples A and B.

[0067] The thickness T2 of the coating layer 20c of the wiring section 22 in samples A and B was 0.1 μm or less. On the other hand, the thickness of the coating layer 20c of the wiring section 22 in sample D was greater than 0.1 μm. As a result, the transparency of sample D was slightly lower than that of samples A and B. Furthermore, the color of sample D was strongly green.

[0068] A coating layer 20c was formed on the wiring portion 22 of samples A and B. On the other hand, a coating layer 20c was not formed on the wiring portion 22 of sample E. As a result, the transparency of sample E was slightly lower than that of samples A and B. This is because light is reflected off the surface of the wiring portion 22 of sample E.

[0069] Furthermore, the transparency of the wiring circuit board 1 according to this embodiment also changes depending on the color of the wiring circuit board 1. Therefore, the inventors measured the color of each of the samples A to F prepared in the transparency evaluation test described above and investigated the range of preferred colors for improving the transparency of the wiring circuit board 1. As a result, the inventors determined that the preferred color of the wiring circuit board 1 is L ＊ a ＊ b ＊ In the color space, a ＊ is 0.2 or more and 0.7 or less and b ＊ We found that it is preferable for the value to be between -5.7 and -3.0.

[0070] 7. Other Embodiments (a) In the manufacturing method of the wiring circuit board 1 according to the above embodiment, the shape of the opening 31 formed in the plating resist layer 30 is adjusted in order to form a constriction in the lower half of the wiring portion 22. Specifically, the opening 31 is formed such that the opening area gradually decreases downwards near the lower end of the opening 31. However, the present invention is not limited thereto.

[0071] During the manufacturing of the wiring circuit board 1, instead of adjusting the shape of the opening 31 formed in the plating resist layer 30, the side surface of the plating layer 20b may be etched by a predetermined amount after the formation of the plating layer 20b and after the removal of the plating resist layer 30. This may result in the formation of a constriction in the lower half of the wiring portion 22.

[0072] (b) In the manufacturing method of the wiring circuit board 1 according to the above embodiment, a constriction does not need to be formed in the lower half of the wiring portion 22. In this case, there is no need to adjust the shape of the wiring portion 22, so the manufacturing of the wiring circuit board 1 is simplified.

[0073] (c) In the wiring circuit board 1 according to the above embodiment, a black seed layer 20a may be formed as part of the wiring portion 22. In this case, the transparency of the wiring circuit board 1 when viewed from below is improved compared to the case in which a seed layer 20a of a color other than black is formed.

[0074] (d) In the wiring circuit board 1 according to the above embodiment, the wiring layer 20 is formed by a so-called semi-additive method, but the present invention is not limited thereto. The wiring layer 20 may be formed by an additive method or by a subtractive method.

[0075] (e) In the wiring circuit board 1 according to the above embodiment, the upper end surface of the wiring layer 20 may be bulging or recessed. Therefore, if the wiring layer 20 includes a coating layer 20c, the upper end surface of the coating layer 20c may be bulging or recessed. Consequently, if the wiring layer 20 includes a coating layer 20c, the upper end surface of the plating layer 20b may be formed flat.

[0076] 8. Correspondence between parts of the embodiment and components of the claims Below, examples of the correspondence between components of the claims and components of the embodiments will be described. Various other elements having the configuration or function described in the claims can also be used as components of the claims.

[0077] In the above embodiment, the transparent substrate 10 is an example of a transparent substrate, the wiring portion 22 of the wiring layer 20 is an example of wiring, the aspect ratio of the wiring portion 22 is an example of the ratio of the thickness of the wiring to the width of the wiring, the direction in which one surface of the transparent substrate 10 faces, that is, the direction upward from the wiring circuit board 1 is an example of a first direction, the direction in which the wiring portion 22 extends is an example of a second direction, the upper end surface of the wiring portion 22 is an example of a first surface, and the wiring circuit board 1 is an example of a wiring circuit board.

[0078] Furthermore, the laminate consisting of the seed layer 20a and the plating layer 20b of the wiring layer 20 is an example of a conductor layer, the coating layer 20c of the wiring layer 20 is an example of a coating layer, the seed layer 20a is an example of a seed layer, the plating resist layer 30 is an example of a resist layer, and the plating layer 20b is an example of a plating layer.

[0079] 9. Summary of Embodiments (Section 1) The wiring circuit board according to Section 1 comprises a transparent substrate having one surface, and a copper-containing wiring formed on the one surface of the transparent substrate, wherein the width of the wiring is 1 μm or more and 10 μm or less, and the wiring has a first surface that is spaced apart from the one surface of the transparent substrate and faces the first direction in the first direction that the one surface of the transparent substrate faces, and the first surface is formed such that at least a part of the cross-section of the wiring perpendicular to the second direction in which the wiring extends bulges or is recessed with respect to the first direction.

[0080] In this wiring circuit board, wiring is formed on one surface of a transparent substrate. The width of the wiring is between 1 μm and 10 μm. In this case, having a wiring width of 1 μm or more suppresses the decrease in reliability of the wiring circuit board caused by excessively reducing the cross-sectional area of ​​the wiring. Furthermore, having a wiring width of 10 μm or less improves the transparency of the wiring circuit board compared to the case where wiring wider than 10 μm is provided on one surface of the transparent substrate.

[0081] Furthermore, in the cross-section of the wiring, at least a portion of the first surface of the wiring bulges or is concave with respect to the first direction. That is, the first surface of the wiring is not a flat surface intersecting the first direction. In this case, light incident on the first surface of the wiring is dispersed and reflected by the bulge or concave. As a result, when viewing the wiring circuit board in the direction opposite to the first direction, the reduction in transparency of the wiring circuit board caused by the strong reflection of light incident on the first surface of the wiring in a predetermined direction (e.g., the first direction) is suppressed. Therefore, the reduction in transparency of the wiring circuit board caused by reflections of surrounding materials or halation in the wiring is suppressed. As a result, a wiring circuit board with high transparency is realized.

[0082] Furthermore, in the above-described wiring circuit board, it is preferable that the ratio of the thickness of the wiring to the width of the wiring, the so-called aspect ratio of the wiring, is 1.0 or greater. In this case, compared to forming wiring with an aspect ratio smaller than 1.0 on one surface of the transparent substrate, it is possible to reduce the area where wiring is formed on one surface of the transparent substrate while ensuring a certain amount of cross-sectional area of ​​the wiring (area of ​​the cross-section perpendicular to the longitudinal direction of the wiring). In other words, it is possible to reduce the area occupied by wiring on one surface of the transparent substrate without reducing the cross-sectional area of ​​the conductor. As a result, the transparency of the wiring circuit board can be improved without increasing the resistance value of the wiring.

[0083] (Paragraph 2) In the wiring circuit board according to Paragraph 1, the wiring includes a conductor layer containing copper and a black coating layer that covers at least a part of the conductor layer and forms the first surface, and the coating layer may have a thickness of 0.1 μm or less.

[0084] In this case, at least a portion of the light incident on the first surface of the wiring is absorbed by the black coating layer. As a result, when a user views the wiring circuit board from a position opposite one side of the transparent substrate, in the opposite direction to the first direction, the amount of light reflected from the first surface of the wiring that directly enters the user's eyes is reduced. Therefore, the reduction in the transparency of the wiring circuit board due to reflected light from the wiring is suppressed.

[0085] Furthermore, compared to cases where the coating layer has a thickness greater than 0.1 μm, the increase in the size of the wiring is reduced. As a result, the increase in the area occupied by the wiring on one surface of the transparent substrate due to the coating layer is suppressed. Therefore, the reduction in the transparency of the wiring circuit board due to the coating layer is suppressed. Moreover, because the coating layer is thin, the occurrence of strong discoloration on the wiring circuit board is suppressed.

[0086] (3) In a wiring circuit board relating to paragraph 1 or 2, the wiring may have a constriction in the portion of the transparent substrate that is closer to the surface of the transparent substrate than the center of the wiring in the first direction, such that the width of the wiring gradually decreases as it approaches the surface of the transparent substrate.

[0087] Because the wiring is formed on one surface of the transparent substrate, the wiring has a substrate contact surface that contacts that surface of the transparent substrate. This substrate contact surface is called the second surface. The second surface is the surface that faces in the opposite direction to the first surface. The transparent substrate also has another surface that faces in the opposite direction to the aforementioned surface.

[0088] According to the above configuration, the wiring has a constriction in which the width of the wiring gradually decreases as it approaches one side of the transparent substrate. Therefore, the second surface is smaller than when the wiring does not have a constriction. By forming the second surface smaller, the amount of light incident on the second surface is reduced, and strong reflection of light from the second surface in a predetermined direction (for example, the direction opposite to the first direction) is suppressed. As a result, when a user views the wiring circuit board in the first direction from a position facing the other side of the transparent substrate, the amount of light that enters the user's eyes due to reflections of surrounding materials in the wiring or halation is reduced. Therefore, regardless of the viewing direction, a decrease in the transparency of the wiring circuit board is suppressed.

[0089] (Clause 4) A method for manufacturing a wiring circuit board according to Clause 4 includes the steps of: preparing a transparent substrate having one surface; and forming a wiring containing copper on the one surface of the transparent substrate, wherein the width of the wiring is 1 μm or more and 10 μm or less; the wiring has a first surface that is spaced apart from the one surface of the transparent substrate and faces the first direction in the first direction in which the one surface of the transparent substrate faces; and the step of forming the wiring includes forming the wiring such that, in a cross section of the wiring perpendicular to a second direction in which the wiring extends, at least a part of the first surface bulges or is recessed with respect to the first direction.

[0090] In the manufacturing method of the wiring circuit board, the wiring circuit board is manufactured by forming copper-containing wiring on one surface of a transparent substrate. In the manufactured wiring circuit board, the width of the wiring is 1 μm or more and 5 μm or less. In this case, by having a wiring width of 1 μm or more, the decrease in reliability of the wiring circuit board caused by excessively reducing the cross-sectional area of ​​the wiring is suppressed. Furthermore, by having a wiring width of 5 μm or less, the transparency of the wiring circuit board is improved compared to when wiring with a width greater than 5 μm is provided on one surface of the transparent substrate.

[0091] Furthermore, in the cross-section of the wiring, at least a portion of the first surface of the wiring bulges or is concave with respect to the first direction. That is, the first surface of the wiring is not a flat surface intersecting the first direction. In this case, light incident on the first surface of the wiring is dispersed and reflected by the bulge or concave. As a result, when viewing the wiring circuit board in the direction opposite to the first direction, the reduction in transparency of the wiring circuit board caused by the light incident on the first surface of the wiring being strongly reflected in a predetermined direction (e.g., the first direction) is suppressed. Therefore, the reduction in transparency of the wiring circuit board caused by reflections or halation of surrounding components of the wiring circuit board is suppressed. As a result, a wiring circuit board with high transparency is realized.

[0092] Furthermore, in the above-described wiring circuit board, it is preferable that the ratio of the thickness of the wiring to the width of the wiring, the so-called aspect ratio of the wiring, is 1.0 or greater. In this case, compared to forming wiring with an aspect ratio smaller than 1.0 on one surface of the transparent substrate, it is possible to reduce the area where wiring is formed on one surface of the transparent substrate while ensuring a certain amount of cross-sectional area of ​​the wiring (area of ​​the cross-section perpendicular to the longitudinal direction of the wiring). In other words, it is possible to reduce the area occupied by wiring on one surface of the transparent substrate without reducing the cross-sectional area of ​​the conductor. As a result, the transparency of the wiring circuit board can be improved without increasing the resistance value of the wiring.

[0093] (Clause 5) In the method for manufacturing a wiring circuit board according to Clause 4, the step of forming the wiring may include: forming a seed layer on one surface of the prepared transparent substrate; forming a resist layer having openings of a predetermined pattern on the seed layer; forming a plating layer in the openings by electroplating; removing the resist layer after the formation of the plating layer; and removing the exposed portion of the seed layer after the removal of the resist layer, thereby making the laminate of the seed layer and the plating layer at least a part of the wiring.

[0094] As described above, at least a portion of the wiring is formed by the semi-additive method. Compared to forming wiring by the subtractive method, the semi-additive method allows for the formation of fine patterns in the plating layer with high dimensional accuracy. Therefore, the increase in the wiring formation area due to the formation of the plating layer in unintended areas on the transparent substrate is suppressed.

Claims

1. A wiring circuit board comprising a transparent substrate having one surface, and a copper-containing wiring formed on the one surface of the transparent substrate, wherein the width of the wiring is 1 μm or more and 10 μm or less, and the wiring has a first surface that is spaced apart from the one surface of the transparent substrate and faces the first direction in a first direction toward which the one surface of the transparent substrate faces, and the first surface is formed such that at least a portion of the cross-section of the wiring perpendicular to the second direction toward which the wiring extends bulges or is recessed with respect to the first direction.

2. The wiring circuit board according to claim 1, wherein the wiring comprises a conductor layer containing copper and a black coating layer that covers at least a portion of the conductor layer and forms the first surface, and the coating layer has a thickness of 0.1 μm or less.

3. The wiring circuit board according to claim 1 or 2, wherein the wiring has a constriction in the portion of the transparent substrate that is closer to the surface of the transparent substrate than the center of the wiring in the first direction, such that the width of the wiring gradually decreases as it approaches the surface of the transparent substrate.

4. A method for manufacturing a wiring circuit board, comprising the steps of: preparing a transparent substrate having one surface; and forming a wiring containing copper on the one surface of the transparent substrate, wherein the width of the wiring is 1 μm or more and 10 μm or less; the wiring has a first surface that is spaced apart from the one surface of the transparent substrate and faces the first direction in a first direction toward which the one surface of the transparent substrate faces; and the step of forming the wiring includes forming the wiring such that, in a cross-section of the wiring perpendicular to a second direction toward which the wiring extends, at least a part of the first surface bulges or is recessed with respect to the first direction.

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