Wiring board, laminate for image display device, and image display device

Abstract

To provide a wiring board, a laminate for an image display unit, and an image display unit capable of suppressing degradation of antenna performance.SOLUTION: In an image display unit 60, a wiring board 10, which together with the first transparent adhesive layer (first adhesive layer) 95 and the second transparent adhesive layer (second adhesive layer) 96 constitutes the laminate 70 for the image display unit, has a dielectric layer 12 having a substrate 11 including a first side 11a and a second side 11b located opposite the first side 11a, and a mesh wiring layer 20 disposed on the first side 11a of the dielectric layer 12. The substrate 11 is transparent. The dielectric tangent of the dielectric layer 12 is 0.002 or less. The moisture content in the dielectric layer 12 is between 0.01% and 0.1% by weight.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] Embodiments of this disclosure relate to a wiring board, a laminate for an image display device, and an image display device. [Background technology]

[0002] Currently, mobile devices such as smartphones and tablets are becoming more sophisticated, smaller, thinner, and lighter. Because these devices utilize multiple communication bands, they require multiple antennas corresponding to each band. For example, mobile devices are equipped with multiple antennas, including antennas for telephone communication, Wi-Fi (Wireless Fidelity), 3G (Generation), 4G (Generation), LTE (Long Term Evolution), Bluetooth (registered trademark), and NFC (Near Field Communication). However, with the miniaturization of mobile devices, the space available for antenna installation is limited, restricting the design flexibility of antennas. Furthermore, because antennas are integrated into a limited space, radio wave sensitivity is not always satisfactory.

[0003] For this reason, film antennas that can be mounted on the display area of ​​mobile devices have been developed. In this film antenna, an antenna pattern is formed on a transparent substrate, and the antenna pattern is formed by a mesh-like conductive mesh layer consisting of a conductive part that forms an opaque conductive layer and a number of openings that do not form the layer. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2011-66610 [Overview of the project] [Problems that the invention aims to solve]

[0005] This embodiment aims to provide a wiring board, a laminate for an image display device, and an image display device that can suppress the degradation of antenna performance. [Means for solving the problem]

[0006] A first aspect of the present disclosure is a wiring substrate comprising a dielectric layer having a substrate including a first surface and a second surface located opposite to the first surface, and a mesh wiring layer disposed on the first surface side of the dielectric layer, wherein the substrate is transparent, the dielectric loss tangent of the dielectric layer is 0.002 or less, and the moisture content in the dielectric layer is 0.01% by weight or more and 0.1% by weight or less.

[0007] A second aspect of this disclosure is a wiring substrate according to the first aspect described above, wherein the dielectric layer may further include a primer layer disposed on the first surface of the substrate.

[0008] A third aspect of the present disclosure is a wiring board according to the first or second aspect described above, wherein the wiring board may have a millimeter-wave transmitting and receiving function, and the mesh wiring layer may function as an array antenna.

[0009] A fourth aspect of this disclosure is that, in each of the first to third aspects described above, a dummy wiring layer electrically independent from the mesh wiring layer may be provided around the mesh wiring layer.

[0010] A fifth aspect of this disclosure is a wiring board according to the fourth aspect described above, wherein a plurality of dummy wiring layers may be provided, and the aperture ratio of the mesh wiring layer and the dummy wiring layer may increase in stages from the mesh wiring layer toward the dummy wiring layer which is further away from the mesh wiring layer.

[0011] A sixth aspect of the present disclosure is that each of the wiring substrates according to the first to fifth aspects described above may further include a protective layer disposed on the first surface side of the dielectric layer and covering the mesh wiring layer, wherein the dielectric loss tangent of the protective layer may be 0.002 or less, and the moisture content in the protective layer may be 0.01% by weight or more and 0.1% by weight or less.

[0012] A seventh aspect of the present disclosure is a laminate for an image display device, comprising a wiring substrate according to each of the first to fifth aspects described above, a first adhesive layer located on the first surface side of the substrate, and a second adhesive layer located on the second surface side of the substrate, wherein a portion of the substrate is disposed in a portion of the region between the first adhesive layer and the second adhesive layer, the dielectric loss tangent of the first adhesive layer is 0.002 or less, and the moisture content in the first adhesive layer is 0.01% by weight or more and 0.1% by weight or less.

[0013] An eighth aspect of the present disclosure comprises a wiring board according to the sixth aspect described above, a first adhesive layer located on the first surface side of the board, and a second adhesive layer located on the second surface side of the board, wherein a portion of the board is disposed in a portion of the region between the first adhesive layer and the second adhesive layer.

[0014] A ninth aspect of the present disclosure comprises a laminate for an image display device according to the seventh or eighth aspect described above, and a display device laminated on the laminate for the image display device. [Effects of the Invention]

[0015] According to the embodiments of this disclosure, the degradation of antenna performance can be suppressed. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a plan view showing an image display device according to one embodiment. [Figure 2] Figure 2 is a cross-sectional view (cross-sectional view along line II-II in Figure 1) showing an image display device according to one embodiment. [Figure 3]FIG. 3 is a plan view showing a wiring board according to an embodiment. [Figure 4] FIG. 4 is an enlarged plan view showing a mesh wiring layer of a wiring board according to an embodiment. [Figure 5] FIG. 5 is a cross-sectional view (a cross-sectional view taken along line V-V in FIG. 4) showing a wiring board according to an embodiment. [Figure 6] FIG. 6 is a cross-sectional view (a cross-sectional view taken along line VI-VI in FIG. 4) showing a wiring board according to an embodiment. [Figure 7] FIGS. 7(a)-(f) are cross-sectional views showing a method for manufacturing a wiring board according to an embodiment. [Figure 8] FIGS. 8(a)-(c) are cross-sectional views showing a method for manufacturing a laminate for an image display device according to an embodiment. [Figure 9] FIG. 9 is a cross-sectional view showing a laminate for an image display device according to a modified example. [Figure 10] FIG. 10 is a plan view showing a wiring board according to a first modified example. [Figure 11] FIG. 11 is an enlarged plan view showing a wiring board according to a first modified example. [Figure 12] FIG. 12 is a plan view showing a wiring board according to a second modified example. [Figure 13] FIG. 13 is an enlarged plan view showing a wiring board according to a second modified example. [Figure 14] FIG. 14 is a plan view showing a wiring board according to a third modified example.

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] First, an embodiment will be described with reference to FIGS. 1 to 8. FIGS. 1 to 8 are diagrams showing this embodiment.

[0018] The following figures are schematic representations. Therefore, the size and shape of each part are exaggerated as appropriate for ease of understanding. Furthermore, they can be modified as appropriate without departing from the technical concept. In the following figures, the same parts are denoted by the same reference numerals, and some detailed explanations may be omitted. Also, the numerical values ​​such as dimensions and material names of each component described in this specification are examples of embodiments and are not limiting; they can be selected and used as appropriate. In this specification, terms that specify shapes and geometric conditions, such as parallel, orthogonal, and perpendicular, are interpreted to include not only their strict meaning but also substantially equivalent states.

[0019] In the following embodiments, "X direction" refers to the direction parallel to one side of the image display device. "Y direction" refers to the direction perpendicular to the X direction and parallel to the other side of the image display device. "Z direction" refers to the direction perpendicular to both the X and Y directions and parallel to the thickness direction of the image display device. "Front surface" refers to the surface on the positive Z direction side, which is the light-emitting surface side of the image display device and faces the observer. "Back surface" refers to the surface on the negative Z direction side, which is the surface opposite to the light-emitting surface and the surface facing the observer of the image display device.

[0020] The configuration of the image display device according to this embodiment will be described with reference to Figures 1 and 2.

[0021] As shown in Figures 1 and 2, the image display device 60 according to this embodiment comprises an image display device laminate 70 and a display device 61 laminated on the image display device laminate 70. The image display device laminate 70 comprises a wiring board 10, a first transparent adhesive layer (first adhesive layer) 95, and a second transparent adhesive layer (second adhesive layer) 96.

[0022] The wiring board 10 comprises a dielectric layer 12 having a substrate 11 and a mesh wiring layer 20. The dielectric layer 12 may further have a primer layer 15. As shown in Figure 2, the substrate 11 of the dielectric layer 12 includes a first surface 11a and a second surface 11b located on the opposite side of the first surface 11a. The primer layer 15 is disposed on the first surface 11a of the substrate 11. The mesh wiring layer 20 is disposed on the side of the first surface 11a of the dielectric layer 12. Specifically, the mesh wiring layer 20 is disposed on the primer layer 15. A power supply unit 40 is electrically connected to the mesh wiring layer 20. Furthermore, a communication module 63 is disposed on the Z-minus side relative to the display device 61. The laminate for image display device 70, the display device 61, and the communication module 63 are housed in a housing 62.

[0023] In the image display device 60 shown in Figures 1 and 2, radio waves of a predetermined frequency can be transmitted and received via a communication module 63, enabling communication. The communication module 63 may include any of the following: a millimeter-wave antenna, a telephone antenna, a WiFi antenna, a 3G antenna, a 4G antenna, a 5G antenna, an LTE antenna, a Bluetooth® antenna, an NFC antenna, etc. Examples of such an image display device 60 include mobile terminal devices such as smartphones and tablets.

[0024] As shown in Figure 2, the image display device 60 has a light-emitting surface 64. The image display device 60 includes a wiring board 10 located on the side of the light-emitting surface 64 (i.e., the positive Z-direction side) relative to the display device 61, and a communication module 63 located on the opposite side of the light-emitting surface 64 (i.e., the negative Z-direction side) relative to the display device 61.

[0025] The display device 61 is, for example, an organic EL (Electro-Luminescence) display device. The display device 61 may also include, for example, a metal layer (not shown), a support substrate, a resin substrate, a thin-film transistor (TFT), and an organic EL layer. A touch sensor (not shown) may be placed on the display device 61. Note that the display device 61 is not limited to an organic EL display device. For example, the display device 61 may be another display device that has the function of emitting light itself, or it may be a micro-LED display device that includes a micro-LED element. Furthermore, the display device 61 may be a liquid crystal display device that includes a liquid crystal.

[0026] Furthermore, a wiring board 10 is placed on the display device 61 via a second transparent adhesive layer 96. A cover glass 75 is placed on the wiring board 10 via a first transparent adhesive layer 95. A decorative film and a polarizing plate (not shown) may be placed between the first transparent adhesive layer 95 and the cover glass 75.

[0027] The first transparent adhesive layer 95 is an adhesive layer that directly or indirectly adheres the wiring substrate 10 to the cover glass 75. This first transparent adhesive layer 95 is located on the first surface 11a side of the substrate 11. In this embodiment, the first transparent adhesive layer 95 is in contact with the mesh wiring layer 20 of the wiring substrate 10. The first transparent adhesive layer 95 has optical transparency and may be an OCA (Optical Clear Adhesive) layer. An OCA layer is a layer made, for example, as follows: First, a liquid curable adhesive layer composition containing a polymerizable compound is applied to a release film such as polyethylene terephthalate (PET). Next, an OCA sheet is obtained by curing this using, for example, ultraviolet light (UV). After laminating this OCA sheet to the object, the OCA layer is obtained by peeling off the release film. The material of the first transparent adhesive layer 95 may be an acrylic resin, a silicone resin, or a urethane resin. In particular, the first transparent adhesive layer 95 may contain an acrylic resin. In this case, it is preferable that the second transparent adhesive layer 96 contains an acrylic resin. This substantially eliminates the difference in refractive index between the first transparent adhesive layer 95 and the second transparent adhesive layer 96, and more reliably suppresses the reflection of visible light at the interface B4 between the first transparent adhesive layer 95 and the second transparent adhesive layer 96.

[0028] The first transparent adhesive layer 95 may have a visible light transmittance of 85% or more, and preferably 90% or more. There is no particular upper limit to the visible light transmittance of the first transparent adhesive layer 95, but it may be, for example, 100% or less. By setting the visible light transmittance of the first transparent adhesive layer 95 within the above range, the transparency of the laminate 70 for the image display device can be increased, making the display device 61 of the image display device 60 easier to see. Visible light refers to light rays with a wavelength of 400 nm or more and 700 nm or less. Furthermore, a visible light transmittance of 85% or more means that when the absorbance is measured on the component to be measured (for example, the first transparent adhesive layer 95), the transmittance is 85% or more in the entire wavelength range from 400 nm to 700 nm. Absorbance can be measured using a known spectrophotometer (for example, a spectrometer manufactured by JASCO Corporation: V-670).

[0029] The dielectric loss tangent of the first transparent adhesive layer 95 is preferably 0.002 or less. This effectively suppresses the first transparent adhesive layer 95 from affecting the transmission and reception of radio waves in the mesh wiring layer 20. As a result, a decrease in antenna performance can be suppressed. The lower limit of the dielectric loss tangent of the first transparent adhesive layer 95 is not particularly limited, but it may be greater than 0. By having the dielectric loss tangent of the substrate 11 within the above range, the loss of gain (i.e., decrease in sensitivity) associated with the transmission and reception of electromagnetic waves can be reduced, especially when the electromagnetic waves (e.g., millimeter waves) transmitted and received by the mesh wiring layer 20 are at high frequencies. The dielectric loss tangent of the first transparent adhesive layer 95 can be measured in accordance with IEC 62562 by the same method as the method for measuring the dielectric loss tangent of the substrate 11, as described later.

[0030] In the first transparent adhesive layer 95, the acid value measured in accordance with JIS K 0070:1992 is preferably 1 or less. The acid value refers to the number of milligrams of potassium hydroxide (KOH) required to neutralize 1 g of the sample (mgKOH / g).

[0031] Here, migration may occur over time between the mesh wiring layer 20 and the layer in contact with the mesh wiring layer 20. In this case, for example, the metallic components of the mesh wiring layer 20 may diffuse into the first transparent adhesive layer 95 that is in contact with the mesh wiring layer 20. Furthermore, the higher the acid value of the first transparent adhesive layer 95, the greater the amount of metallic components that diffuse into the first transparent adhesive layer 95. That is, the metallic components of the mesh wiring layer 20 may diffuse into the first transparent adhesive layer 95 by ionization (dissolution) of the metal by the acidic molecules in the first transparent adhesive layer 95. In this case, the higher the acidity of the first transparent adhesive layer 95, the greater the amount of metal that is ionized. In other words, the higher the acid value of the first transparent adhesive layer 95, the greater the amount of metal that is ionized. Therefore, the higher the acid value of the first transparent adhesive layer 95, the greater the amount of metallic components that diffuse into the first transparent adhesive layer 95. Furthermore, if metal components diffuse into the first transparent adhesive layer 95, the dielectric loss of the first transparent adhesive layer 95 increases. In this case, the first transparent adhesive layer 95 may adversely affect the transmission and reception of radio waves in the mesh wiring layer 20. This may lead to a decrease in antenna performance. In particular, when the mesh wiring layer 20 transmits and receives millimeter waves, the increased dielectric loss of the first transparent adhesive layer 95 may significantly reduce antenna performance. In this specification, "acidic molecule" means a molecule containing an acidic functional group that is bonded to an organic polymer or organic low molecular weight molecule. Specific examples of acidic functional groups include hydroxyl groups, aldehyde groups, carboxyl groups, sulfate groups, nitrate groups, halogen groups, or phosphoric acid groups. The unit of a molecule is defined as one molecule containing an acidic functional group.

[0032] In contrast, by having an acid value of 1 or less in the first transparent adhesive layer 95, as measured in accordance with JIS K 0070:1992, migration between the mesh wiring layer 20 and the first transparent adhesive layer 95 can be suppressed. This suppresses an increase in dielectric loss of the first transparent adhesive layer 95. Therefore, it is possible to prevent the first transparent adhesive layer 95 from adversely affecting the transmission and reception of radio waves in the mesh wiring layer 20. As a result, a decrease in antenna performance can be suppressed.

[0033] Furthermore, if the acid value measured in accordance with JIS K 0070:1992 in the first transparent adhesive layer 95 is 1 or less, the amount of acidic molecules in the first transparent adhesive layer 95 can be reduced. This suppresses the absorption of moisture from the atmosphere into the first transparent adhesive layer 95 by the acidic molecules within the first transparent adhesive layer 95.

[0034] Preferably, the content of metal elements in the first transparent adhesive layer 95 is 0.1% by weight or more and 1% by weight or less. A metal element content of 0.1% by weight or more in the first transparent adhesive layer 95 enhances the adhesion between the first transparent adhesive layer 95 and the mesh wiring layer 20. Furthermore, a metal element content of 1% by weight or less in the first transparent adhesive layer 95 effectively reduces dielectric loss in the first transparent adhesive layer 95. This effectively suppresses the first transparent adhesive layer 95 from affecting the transmission and reception of radio waves in the mesh wiring layer 20. Therefore, a decrease in antenna performance can be suppressed. Additionally, a metal element content of 1% by weight or less in the first transparent adhesive layer 95 ensures the transparency of the first transparent adhesive layer 95. Therefore, the invisibility of the wiring substrate 10 can be maintained. The metal element content can be measured using an emission spectrometer (Hitachi High-Tech Science Corporation, high-resolution ICP emission spectrometer, PS3500DDII).

[0035] The moisture content in the first transparent adhesive layer 95 is preferably 0.01% by weight or more and 0.1% by weight or less. A moisture content of 0.01% by weight or more in the first transparent adhesive layer 95 enhances its flexibility. Furthermore, a moisture content of 0.1% by weight or less effectively reduces dielectric loss in the first transparent adhesive layer 95. This effectively suppresses the first transparent adhesive layer 95 from affecting the transmission and reception of radio waves in the mesh wiring layer 20. Therefore, a decrease in antenna performance can be suppressed. The moisture content can be measured using a moisture meter (Carl Fischer moisture meter, CA-310, manufactured by Nitto Seikou Analytech Co., Ltd.).

[0036] Next, the wiring board 10 will be described. As described above, the wiring board 10 is positioned on the light-emitting surface 64 side relative to the display device 61. In this case, the wiring board 10 is located between the first transparent adhesive layer 95 and the second transparent adhesive layer 96. More specifically, a portion of the substrate 11 of the wiring board 10 is positioned in a portion of the area between the first transparent adhesive layer 95 and the second transparent adhesive layer 96. In this case, the first transparent adhesive layer 95, the second transparent adhesive layer 96, the display device 61, and the cover glass 75 each have a larger area than the substrate 11 of the wiring board 10. In this way, by positioning the substrate 11 of the wiring board 10 in a portion of the image display device 60 rather than the entire surface in a plan view, the overall thickness of the image display device 60 can be reduced.

[0037] As described above, the wiring board 10 comprises a substrate 11, a dielectric layer 12 having a primer layer 15 disposed on the first surface 11a of the substrate 11, and a mesh wiring layer 20 disposed on the primer layer 15 of the dielectric layer 12. The power supply unit 40 is electrically connected to the mesh wiring layer 20. The power supply unit 40 is electrically connected to the communication module 63 via a power supply line (not shown). Furthermore, a portion of the wiring board 10 is not positioned between the first transparent adhesive layer 95 and the second transparent adhesive layer 96, but protrudes outward (i.e., to the negative side in the Y direction) from between the first transparent adhesive layer 95 and the second transparent adhesive layer 96. Specifically, the region of the wiring board 10 where the power supply unit 40 is provided protrudes outward. This facilitates the electrical connection between the power supply unit 40 and the communication module 63. On the other hand, the region of the wiring board 10 where the mesh wiring layer 20 is provided is located between the first transparent adhesive layer 95 and the second transparent adhesive layer 96. Details of the wiring board 10 will be described later.

[0038] The second transparent adhesive layer 96 is an adhesive layer that directly or indirectly adheres the display device 61 to the wiring board 10. This second transparent adhesive layer 96 is located on the second surface 11b side of the substrate 11. The second transparent adhesive layer 96, like the first transparent adhesive layer 95, has optical transparency and may be an OCA (Optical Clear Adhesive) layer. The material of the second transparent adhesive layer 96 may be an acrylic resin, silicone resin, or urethane resin, etc. In particular, the second transparent adhesive layer 96 may contain an acrylic resin. This substantially eliminates the difference in refractive index between the first transparent adhesive layer 95 and the second transparent adhesive layer 96, and more reliably suppresses the reflection of visible light at the interface B4 between the first transparent adhesive layer 95 and the second transparent adhesive layer 96.

[0039] The second transparent adhesive layer 96 may have a transmittance of 85% or more for visible light (i.e., light with a wavelength of 400 nm to 700 nm), and preferably 90% or more. There is no particular upper limit to the transmittance of visible light of the second transparent adhesive layer 96, but it may be, for example, 100% or less. By setting the transmittance of visible light of the second transparent adhesive layer 96 within the above range, the transparency of the laminate 70 for the image display device is increased, making the display device 61 of the image display device 60 easier to see.

[0040] In such a laminated image display device 70, the difference between the refractive index of the primer layer 15 and the refractive index of the first transparent adhesive layer 95 is 0.1 or less, preferably 0.05 or less. Furthermore, the difference between the refractive index of the primer layer 15 and the refractive index of the substrate 11 is 0.1 or less, preferably 0.05 or less. Here, refractive index refers to the absolute refractive index, which can be determined based on Method A of JIS K-7142. For example, if the material of the first transparent adhesive layer 95 is an acrylic resin (refractive index 1.49), the refractive index of the primer layer 15 should be 1.39 or more and 1.59 or less. Examples of such materials include fluororesins, silicone resins, polyolefin resins, polyester resins, acrylic resins, polycarbonate resins, polyimide resins, cellulose resins, and the like.

[0041] In this way, by keeping the difference between the refractive index of the primer layer 15 and the refractive index of the first transparent adhesive layer 95 to 0.1 or less, the reflection of visible light at the interface B1 between the primer layer 15 and the first transparent adhesive layer 95 is suppressed, making it difficult for the observer to see the substrate 11 on which the primer layer 15 is provided. Furthermore, by keeping the difference between the refractive index of the primer layer 15 and the refractive index of the substrate 11 to 0.1 or less, the reflection of visible light at the interface B2 between the primer layer 15 and the substrate 11 is suppressed, making it difficult for the observer to see the substrate 11.

[0042] Furthermore, in the laminate 70 for the image display device, the difference between the refractive index of the substrate 11 and the refractive index of the first transparent adhesive layer 95 is 0.1 or less, and preferably 0.05 or less. Also, the difference between the refractive index of the second transparent adhesive layer 96 and the refractive index of the substrate 11 is 0.1 or less, and preferably 0.05 or less. Moreover, the difference between the refractive index of the first transparent adhesive layer 95 and the refractive index of the second transparent adhesive layer 96 is preferably 0.1 or less, and more preferably 0.05 or less. For example, if the material of the first transparent adhesive layer 95 and the material of the second transparent adhesive layer 96 are acrylic resins (refractive index 1.49), the refractive index of the substrate 11 is set to 1.39 or more and 1.59 or less. As mentioned above, examples of such materials include fluororesins, silicone resins, polyolefin resins, polyester resins, acrylic resins, polycarbonate resins, polyimide resins, cellulose resins, and the like.

[0043] In this way, by keeping the difference between the refractive index of the second transparent adhesive layer 96 and the refractive index of the substrate 11 to 0.1 or less, the reflection of visible light at the interface B3 between the second transparent adhesive layer 96 and the substrate 11 is suppressed, making it difficult for the observer to see the substrate 11 with the naked eye. Furthermore, by keeping the difference between the refractive index of the first transparent adhesive layer 95 and the refractive index of the second transparent adhesive layer 96 to 0.1 or less, the reflection of visible light at the interface B4 between the first transparent adhesive layer 95 and the second transparent adhesive layer 96 is suppressed, making it difficult for the observer to see the first transparent adhesive layer 95 and the second transparent adhesive layer 96 with the naked eye.

[0044] In particular, it is preferable that the material of the first transparent adhesive layer 95 and the material of the second transparent adhesive layer 96 are the same material. This makes it possible to further reduce the difference in refractive index between the first transparent adhesive layer 95 and the second transparent adhesive layer 96, and to suppress the reflection of visible light at the interface B4 between the first transparent adhesive layer 95 and the second transparent adhesive layer 96.

[0045] In Figure 2, the thickness T3 of the first transparent adhesive layer 95 and the thickness T4 of the second transparent adhesive layer 96 may be 1.5 times or more the thickness T1 of the substrate 11, preferably 2 times or more, and more preferably 2.5 times or more. By making the thickness T3 of the first transparent adhesive layer 95 or the thickness T4 of the second transparent adhesive layer 96 sufficiently thicker than the thickness T1 of the substrate 11, the first transparent adhesive layer 95 or the second transparent adhesive layer 96 deforms in the thickness direction in the region overlapping with the substrate 11, absorbing the thickness of the substrate 11. This prevents the formation of steps in the first transparent adhesive layer 95 or the second transparent adhesive layer 96 at the periphery of the substrate 11, making it difficult for observers to recognize the presence of the substrate 11.

[0046] The thickness T3 of the first transparent adhesive layer 95 and the thickness T4 of the second transparent adhesive layer 96 are preferably 10 times or less the thickness T1 of the substrate 11, and more preferably 5 times or less. This prevents the thickness T3 of the first transparent adhesive layer 95 or the thickness T4 of the second transparent adhesive layer 96 from becoming too thick, thereby reducing the overall thickness of the image display device 60.

[0047] In Figure 2, the thickness T3 of the first transparent adhesive layer 95 and the thickness T4 of the second transparent adhesive layer 96 may be the same. In this case, the thickness T3 of the first transparent adhesive layer 95 and the thickness T4 of the second transparent adhesive layer 96 may each be 1.5 times or more the thickness T1 of the substrate 11, and preferably 2.0 times or more. That is, the sum of the thickness T3 of the first transparent adhesive layer 95 and the thickness T4 of the second transparent adhesive layer 96 (i.e., T3 + T4) is 3 times or more the thickness T1 of the substrate 11. In this way, by making the sum of the thicknesses T3 and T4 of the first transparent adhesive layer 95 and the second transparent adhesive layer 96 sufficiently thick relative to the thickness T1 of the substrate 11, the first transparent adhesive layer 95 and the second transparent adhesive layer 96 deform (shrink) in the thickness direction in the region overlapping with the substrate 11. As a result, the first transparent adhesive layer 95 and the second transparent adhesive layer 96 absorb the thickness of the substrate 11. Therefore, it is possible to suppress the occurrence of steps in the first transparent adhesive layer 95 or the second transparent adhesive layer 96 at the periphery of the substrate 11, making it difficult for observers to recognize the presence of the substrate 11.

[0048] When the thickness T3 of the first transparent adhesive layer 95 and the thickness T4 of the second transparent adhesive layer 96 are the same, the thickness T3 of the first transparent adhesive layer 95 and the thickness T4 of the second transparent adhesive layer 96 may be 5 times or less the thickness T1 of the substrate 11, and preferably 3 times or less. This prevents the thicknesses T3 and T4 of both the first transparent adhesive layer 95 and the second transparent adhesive layer 96 from becoming too thick, and allows the overall thickness of the image display device 60 to be reduced.

[0049] Specifically, the thickness T1 of the substrate 11 may be, for example, 2 μm or more, 10 μm or more, and preferably 15 μm or more. By setting the thickness T1 of the substrate 11 to 2 μm or more, the strength of the wiring substrate 10 can be maintained, and the first directional wiring 21 and second directional wiring 22 of the mesh wiring layer 20, described later, can be made less susceptible to deformation. Alternatively, the thickness T1 of the substrate 11 may be, for example, 200 μm or less, 50 μm or less, and preferably 25 μm or less. By setting the thickness T1 of the substrate 11 to 200 μm or less, the occurrence of steps between the first transparent adhesive layer 95 and the second transparent adhesive layer 96 at the periphery of the substrate 11 can be suppressed, making it difficult for observers to recognize the presence of the substrate 11. Furthermore, by setting the thickness T1 of the substrate 11 to 50 μm or less, the occurrence of steps between the first transparent adhesive layer 95 and the second transparent adhesive layer 96 at the periphery of the substrate 11 can be further suppressed, making it even more difficult for observers to recognize the presence of the substrate 11.

[0050] The thickness T3 of the first transparent adhesive layer 95 may be, for example, 15 μm or more, and preferably 20 μm or more. The thickness T3 of the first transparent adhesive layer 95 may be, for example, 500 μm or less, preferably 300 μm or less, and more preferably 250 μm or less. The thickness T4 of the second transparent adhesive layer 96 may be, for example, 15 μm or more, and preferably 20 μm or more. The thickness T4 of the second transparent adhesive layer 96 may be, for example, 500 μm or less, preferably 300 μm or less, and more preferably 250 μm or less.

[0051] Referring again to Figure 2, the cover glass 75 is placed directly or indirectly on the first transparent adhesive layer 95. This cover glass 75 is a light-transmitting glass component. The cover glass 75 is plate-shaped, and its shape may be rectangular in plan view. The thickness of the cover glass 75 may be, for example, 200 μm or more and 1000 μm or less, and preferably 300 μm or more and 700 μm or less. The length of the cover glass 75 in the longitudinal direction (i.e., the Y direction) may be, for example, 20 mm or more and 500 mm or less, preferably 100 mm or more and 200 mm or less. The length of the cover glass 75 in the short direction (i.e., the X direction) may be 20 mm or more and 500 mm or less, preferably 50 mm or more and 100 mm or less.

[0052] As shown in Figure 1, the shape of the image display device 60 is approximately rectangular in plan view, with its longitudinal direction parallel to the Y direction and its transverse direction parallel to the X direction. The length L4 of the longitudinal direction (i.e., Y direction) of the image display device 60 can be selected within the range of, for example, 20 mm to 500 mm, preferably 100 mm to 200 mm. The length L5 of the transverse direction (i.e., X direction) of the image display device 60 can be selected within the range of, for example, 20 mm to 500 mm, preferably 50 mm to 100 mm. The planar shape of the image display device 60 may also be a rectangle with rounded corners.

[0053] Next, the configuration of the wiring board will be described with reference to Figures 3 to 6. Figures 3 to 6 are diagrams showing the wiring board according to this embodiment.

[0054] As shown in Figure 3, the wiring board 10 according to this embodiment is a substrate used in the image display device 60 (see Figures 1 and 2) described above. The wiring board 10 is located on the light-emitting surface 64 side of the display device 61 and can be placed between the first transparent adhesive layer 95 and the second transparent adhesive layer 96. As described above, such a wiring board 10 comprises a substrate 11, a dielectric layer 12 having a primer layer 15 disposed on the first surface 11a of the substrate 11, and a mesh wiring layer 20 disposed on the first surface 11a side of the dielectric layer 12. The dielectric layer 12 is in contact with the mesh wiring layer 20. The power supply unit 40 is electrically connected to the mesh wiring layer 20. Note that the dielectric layer 12 does not necessarily have a primer layer 15, and the dielectric layer 12 may be composed only of the substrate 11.

[0055] The dielectric layer 12 substrate 11 has a roughly rectangular shape in plan view, with its first direction parallel to the Y direction and its second direction parallel to the X direction. The substrate 11 is transparent and roughly flat, and its thickness is roughly uniform overall. The length L1 of the substrate 11 in the first direction (i.e., the Y direction) can be selected within a range of, for example, 3 mm to 300 mm. The length L2 of the substrate 11 in the second direction (i.e., the X direction) (see Figure 1) can be selected within a range of, for example, 3 mm to 300 mm. The planar shape of the substrate 11 may be a rectangle with rounded corners.

[0056] The substrate 11 material can be any material that has transparency in the visible light region and electrical insulation properties. Preferably, the substrate 11 material is an organic insulating material such as polyester resin, acrylic resin, polycarbonate resin, polyimide resin, polyolefin resin, cellulose resin, or fluororesin material. Polyester resin may be polyethylene terephthalate, etc. Acrylic resin may be polymethyl methacrylate, etc. Polyolefin resin may be cycloolefin polymer, etc. Cellulose resin may be triacetylcellulose, etc. Fluororesin material may be PTFE or PFA, etc. For example, the substrate 11 material may be an organic insulating material such as cycloolefin polymer (e.g., ZF-16 manufactured by Nippon Zeon Co., Ltd.) or polynorbornene polymer (manufactured by Sumitomo Bakelite Co., Ltd.). Furthermore, glass or ceramics may be appropriately selected as the substrate 11 material depending on the application. Although the illustration shows a substrate 11 composed of a single layer, it is not limited to this, and may have a structure in which multiple substrates or layers are laminated. Furthermore, the substrate 11 may be a film-like material or a plate-like material.

[0057] The dielectric loss tangent of the substrate 11 may be 0.002 or less, and preferably 0.001 or less. The lower limit of the dielectric loss tangent of the substrate 11 is not particularly limited, but it may be greater than 0. By having the dielectric loss tangent of the substrate 11 within the above range, the loss of gain (i.e., decrease in sensitivity) associated with the transmission and reception of electromagnetic waves can be reduced, especially when the electromagnetic waves (e.g., millimeter waves) transmitted and received by the mesh wiring layer 20 are at high frequencies.

[0058] The relative permittivity of the substrate 11 is not particularly limited, but it is preferably between 2 and 10. Having a relative permittivity of 2 or higher allows for a wider range of material choices for the substrate 11. Furthermore, having a relative permittivity of 10 or lower reduces the gain loss associated with electromagnetic wave transmission and reception. That is, when the relative permittivity of the substrate 11 is high, the influence of the substrate 11's thickness on electromagnetic wave propagation increases. Also, if there is an adverse effect on electromagnetic wave propagation, the dielectric loss tangent of the substrate 11 increases, potentially leading to a greater gain loss associated with electromagnetic wave transmission and reception. In contrast, having a relative permittivity of 10 or lower reduces the influence of the substrate 11's thickness on electromagnetic wave propagation. Therefore, the gain loss associated with electromagnetic wave transmission and reception can be reduced. In particular, when the electromagnetic waves (e.g., millimeter waves) transmitted and received by the mesh wiring layer 20 are high-frequency, the gain loss associated with electromagnetic wave transmission and reception can be reduced.

[0059] The dielectric loss tangent and relative permittivity of the substrate 11 can be measured in accordance with IEC 62562. Specifically, first, a test specimen is prepared by cutting out a portion of the substrate 11 where the mesh wiring layer 20 is not formed. The dimensions of the test specimen shall be a width of 10 mm to 20 mm and a length of 50 mm to 100 mm. Next, the dielectric loss tangent or relative permittivity is measured in accordance with IEC 62562.

[0060] In this embodiment, the substrate 11 is transparent. In this specification, "transparent" means that the transmittance of visible light (i.e., light with a wavelength of 400 nm to 700 nm) is 85% or more. The substrate 11 may have a visible light transmittance of 85% or more, but it is preferably 90% or more. There is no particular upper limit to the visible light transmittance of the substrate 11, but it may be, for example, 100% or less. By setting the visible light transmittance of the substrate 11 within the above range, the transparency of the wiring board 10 is increased, making the display device 61 of the image display device 60 easier to see.

[0061] Next, the primer layer 15 of the dielectric layer 12 will be described. The primer layer 15 plays a role in improving the adhesion between the mesh wiring layer 20 and the substrate 11. In this embodiment, the primer layer 15 is provided over substantially the entire first surface 11a of the substrate 11. This eliminates the need for patterning of the primer layer 15. Therefore, the number of process steps can be reduced. The primer layer 15 may also be provided only in the area of ​​the first surface 11a of the substrate 11 where the mesh wiring layer 20 is provided.

[0062] This primer layer 15 contains a polymer material. This effectively improves the adhesion between the mesh wiring layer 20 and the substrate 11. In this case, a colorless, transparent polymer material can be used as the material for the primer layer 15.

[0063] The primer layer 15 preferably contains an acrylic resin or a polyester resin. This more effectively improves the adhesion between the mesh wiring layer 20 and the substrate 11. When the primer layer 15 contains an acrylic resin, examples of acrylic resins include polymers whose monomer components are acrylic acid, methacrylic acid, and their derivatives. As acrylic resins, for example, polymers may be used that copolymerize monomers copolymerizable with monomers such as acrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methacrylic acid, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl acrylate, acrylamide, acrylonitrile, hydroxyl acrylate, etc., as the main components (e.g., styrene, divinylbenzene, acrylonitrile, etc.). In addition to the monomers mentioned above, dimers having two acrylic or methacrylic groups per molecule, or polyfunctional urethane acrylates may be added to the main component resin, or organic molecules having two or more epoxy groups per molecule may be added to the main component resin. This allows the acrylic resin to be crosslinked, thereby curing the resin and forming the primer layer 15. The cured primer layer has excellent adhesion. It is also possible to exhibit excellent water resistance, acid resistance, alkali resistance, solvent resistance, or combinations thereof. Therefore, it is possible to suppress the decrease in adhesion between the mesh wiring layer 20 and the substrate 11 during wiring formation or over time.

[0064] Furthermore, if the primer layer 15 contains a polyester resin, the primer layer 15 can be formed by curing, for example, a hydroxyl group-containing polyester resin by crosslinking it with a curing agent that reacts with hydroxyl groups. Examples of hydroxyl group-containing polyester resins include polyester polyols, and examples of curing agents include polyisocyanates and / or polyisocyanate prepolymers. The primer layer 15 formed by curing a polyester polyol and a polyisocyanate and / or polyisocyanate prepolymer has excellent adhesion. It can also exhibit excellent water resistance, acid resistance, alkali resistance, or solvent resistance, or a combination thereof. Therefore, it is possible to suppress the deterioration of adhesion between the mesh wiring layer 20 and the substrate 11 over time. In addition, the primer layer 15 formed by curing a polyester polyol and a polyisocyanate and / or polyisocyanate prepolymer has excellent heat resistance. Therefore, the primer layer 15 is less susceptible to the effects of heat generated during each film formation process performed after its formation, and the occurrence of whitening or cracks in the primer layer 15 due to heat can be suppressed.

[0065] Furthermore, examples of preferred polyisocyanates and / or polyisocyanate prepolymers include IPDI-based, XDI-based, and HDI-based polyisocyanate and / or polyisocyanate prepolymers. By using these, yellowing of the primer layer 15 can be suppressed. Here, IPDI-based refers to isophorone diisocyanate and its modified form, XDI-based refers to xylylene diisocyanate and its modified form, and HDI-based refers to hexamelletin diisocyanate and its modified form. Examples of modified forms include trimethylolpropane (TMP) adduct, isocyanurate, biuret, and allophanate.

[0066] Furthermore, the polymer material of the primer layer 15 may be cured by crosslinking it by irradiating it with visible light, ultraviolet light, X-rays, electron beams, alpha rays, beta rays, gamma rays, etc. This can improve the scratch resistance and heat resistance of the primer layer 15.

[0067] Furthermore, the primer layer 15 may have a transmittance of 85% or more for visible light (light with a wavelength of 400 nm to 700 nm), and preferably 90% or more. There is no particular upper limit to the transmittance of visible light of the primer layer 15, but it may be, for example, 100% or less. By setting the transmittance of visible light of the primer layer 15 within the above range, the transparency of the wiring board 10 can be increased, making the display device 61 of the image display device 60 easier to see.

[0068] The thickness T2 (length in the Z direction, see Figure 5) of the primer layer 15 is preferably 0.05 μm or more and 0.5 μm or less. A thickness T2 of 0.05 μm or more of the primer layer 15 effectively improves the adhesion between the mesh wiring layer 20 and the substrate 11. Furthermore, a thickness T2 of 0.5 μm or less of the primer layer 15 ensures the transparency of the wiring substrate 10.

[0069] Next, we will describe the mesh wiring layer 20.

[0070] In this embodiment, the mesh wiring layer 20 consists of an antenna pattern that functions as an antenna. This mesh wiring layer 20 functions as an array antenna. When the mesh wiring layer 20 functions as an array antenna in this way, the performance of a millimeter-wave antenna that transmits and receives highly directional millimeter waves can be improved. An array antenna is an antenna in which a plurality of antenna elements (radiating elements) are arranged regularly, and in which the amplitude and phase of the excitation of the elements can be controlled independently.

[0071] Three mesh wiring layers 20 are formed on the substrate 11 (see Figure 1). Furthermore, as shown in Figure 3, the mesh wiring layers 20 may not be present across the entire surface of the substrate 11, but only in a portion of the substrate 11. Each mesh wiring layer 20 may have the same shape as the others. In this case, each mesh wiring layer 20 has a length (i.e., length in the Y direction) L. a Error and width (length in the X direction) W aIt is preferable that the errors are within 10% each. This effectively improves the performance of the millimeter-wave antenna.

[0072] This mesh wiring layer 20 corresponds to a predetermined frequency band. That is, the mesh wiring layer 20 has a length (length in the Y direction) L a The length corresponds to a specific frequency band. Note that the lower the frequency band, the longer the mesh wiring layer L 20. a The length will increase. The mesh wiring layer 20 may support any of the following in addition to the millimeter wave antenna: telephone antenna, WiFi antenna, 3G antenna, 4G antenna, 5G antenna, LTE antenna, Bluetooth® antenna, NFC antenna, etc. The lengths of multiple mesh wiring layers 20 may differ from each other, and each may support a different frequency band. Alternatively, each mesh wiring layer 20 may perform functions such as hovering, fingerprint authentication, heating, and noise reduction (shielding). The hovering function refers to a function that allows the user to operate the display without directly touching it.

[0073] The mesh wiring layer 20 has a base end portion 20a on the power supply unit 40 side and a tip end portion 20b connected to the base end portion 20a. The base end portion 20a is connected to the power supply unit 40. The shape of the base end portion 20a and the shape of the tip end portion 20b are both approximately rectangular in plan view. In this case, the length of the tip end portion 20b (i.e., distance in the Y direction) is longer than the length of the base end portion 20a (i.e., distance in the Y direction), and the width of the tip end portion 20b (i.e., distance in the X direction) is wider than the width of the base end portion 20a (i.e., distance in the X direction).

[0074] The mesh wiring layer 20 has its longitudinal direction parallel to the Y direction and its short direction parallel to the X direction. The length L of the mesh wiring layer 20 in the longitudinal direction (i.e., the Y direction) a For example, it can be selected within a range of 3 mm to 100 mm. The width W of the leading edge portion 20b of the mesh wiring layer 20 in the short direction (i.e., the X direction) acan be selected, for example, in the range of 1 mm or more and 10 mm or less. In particular, the mesh wiring layer 20 may be an antenna for millimeter waves. When the mesh wiring layer 20 is an antenna for millimeter waves, the length L of the mesh wiring layer 20 a can be selected in the range of 1 mm or more, more preferably 1.5 mm or more. When the mesh wiring layer 20 is an antenna for millimeter waves, the length L of the mesh wiring layer 20 a can be selected in the range of 10 mm or less, more preferably 5 mm or less.

[0075] The mesh wiring layer 20 has a pattern shape in which metal wires are arranged in a lattice or mesh pattern. This pattern shape is repeatedly arranged in the X direction and the Y direction. That is, the mesh wiring layer 20 has a pattern shape composed of a portion extending in the first direction (for example, the Y direction) (that is, the first direction wiring 21) and a portion extending in the second direction (for example, the X direction) (that is, the second direction wiring 22).

[0076] As shown in FIG. 4, the mesh wiring layer 20 has a plurality of wirings. Specifically, the mesh wiring layer 20 has a plurality of first direction wirings (wirings) 21 having a function as an antenna and a plurality of second direction wirings (wirings) 22 connecting the plurality of first direction wirings 21. The plurality of first direction wirings 21 and the plurality of second direction wirings 22 are integrally formed as a whole to form a lattice or mesh shape. Each first direction wiring 21 extends linearly in the longitudinal direction (that is, the Y direction) of the mesh wiring layer 20. Each second direction wiring 22 extends linearly in the width direction (that is, the X direction) of the mesh wiring layer 20. The first direction wiring 21 has a length L a (see FIG. 3) to mainly exhibit the function as an antenna. Here, the length L a is the length of the mesh wiring layer 20 described above. On the other hand, the second direction wiring 22 serves to suppress problems such as disconnection of the first direction wiring 21 or loss of electrical connection between the first direction wiring 21 and the power supply unit 40 by connecting the first direction wirings 21 to each other.

[0077] In the mesh wiring layer 20, multiple openings 23 are formed by being surrounded by adjacent first-directional wirings 21 and adjacent second-directional wirings 22. Furthermore, the first-directional wirings 21 and second-directional wirings 22 are arranged at equal intervals from each other. That is, the multiple first-directional wirings 21 are arranged at equal intervals from each other, and their pitch P1 can be, for example, in the range of 0.01 mm to 1 mm. Similarly, the multiple second-directional wirings 22 are arranged at equal intervals from each other, and their pitch P2 can be, for example, in the range of 0.01 mm to 1 mm. In this way, because the multiple first-directional wirings 21 and multiple second-directional wirings 22 are arranged at equal intervals, there is no variation in the size of the openings 23 within the mesh wiring layer 20, making the mesh wiring layer 20 difficult to see with the naked eye. In addition, the pitch P1 of the first-directional wirings 21 is equal to the pitch P2 of the second-directional wirings 22. Therefore, each opening 23 is approximately square in plan view, and the transparent primer layer 15 and substrate 11 are exposed through each opening 23. By increasing the area of ​​each opening 23, the overall transparency of the wiring board 10 can be increased. The length L3 of one side of each opening 23 can be, for example, in the range of 0.01 mm to 1 mm. Although each first directional wiring 21 and each second directional wiring 22 are orthogonal to each other, they are not limited to this and may intersect at acute or obtuse angles. Furthermore, while it is preferable for the shape and size of the openings 23 to be the same across the entire surface, they do not need to be uniform across the entire surface, for example, by varying them in different locations.

[0078] As shown in Figure 5, each first-direction wiring 21 has a shape in which the cross section perpendicular to its longitudinal direction (i.e., the X-direction cross section) is approximately rectangular or approximately square. In this case, the cross-sectional shape of the first-direction wiring 21 is approximately uniform along its longitudinal direction (i.e., the Y-direction). As shown in Figure 6, each second-direction wiring 22 has a shape in which the cross section perpendicular to its longitudinal direction (i.e., the Y-direction cross section) is approximately rectangular or approximately square, and has approximately the same shape as the cross-sectional shape (i.e., the X-direction cross section) of the first-direction wiring 21 described above. In this case, the cross-sectional shape of the second-direction wiring 22 is approximately uniform along its longitudinal direction (i.e., the X-direction). The cross-sectional shapes of the first-direction wiring 21 and the second-direction wiring 22 do not necessarily have to be approximately rectangular or approximately square. For example, the cross-sectional shape of the first direction wiring 21 and the cross-sectional shape of the second direction wiring 22 may be a roughly trapezoidal shape where the front side (i.e., the positive Z-direction side) is narrower than the back side (i.e., the negative Z-direction side), or a shape in which the sides located on both sides in the width direction are curved.

[0079] In this embodiment, the line width W1 of the first directional wiring 21 (see Figure 5) and the line width W2 of the second directional wiring 22 (see Figure 6) are not particularly limited and can be appropriately selected according to the application. Here, the line width W1 of the first directional wiring 21 is the width in a cross section perpendicular to its longitudinal direction (i.e., the length in the X direction), and the line width W2 of the second directional wiring 22 is the width in a cross section perpendicular to its longitudinal direction (i.e., the length in the Y direction). For example, the line width W1 of the first directional wiring 21 can be selected in the range of 0.1 μm to 5.0 μm, and is preferably 0.2 μm to 2.0 μm. Also, the line width W2 of the second directional wiring 22 can be selected in the range of 0.1 μm to 5.0 μm, and is preferably 0.2 μm to 2.0 μm.

[0080] The height H1 of the first directional wiring 21 (see Figure 5) and the height H2 of the second directional wiring 22 (see Figure 6) are not particularly limited and can be appropriately selected depending on the application. Here, the height H1 of the first directional wiring 21 and the height H2 of the second directional wiring 22 are the lengths in the Z direction. The height H1 of the first directional wiring 21 and the height H2 of the second directional wiring 22 can be selected in a range of, for example, 0.1 μm or more and 5.0 μm or less, and it is preferable that they be 0.2 μm or more and 2.0 μm or less.

[0081] The material of the first directional wiring 21 and the second directional wiring 22 may be any conductive metallic material. In this embodiment, the material of the first directional wiring 21 and the second directional wiring 22 is copper, but is not limited to this. The material of the first directional wiring 21 and the second directional wiring 22 may be, for example, a metallic material such as gold, silver, copper, platinum, tin, aluminum, iron, or nickel, or an alloy containing these metals. Furthermore, the first directional wiring 21 and the second directional wiring 22 may be a plated layer formed by an electroplating method.

[0082] The overall aperture ratio At of the mesh wiring layer 20 may be, for example, in the range of 87% or more and less than 100%. By setting the overall aperture ratio At of the mesh wiring layer 20 within this range, the conductivity and transparency of the wiring substrate 10 can be ensured. Preferably, the overall aperture ratio At of the mesh wiring layer 20 is 95% or more and less than 100%. This ensures the conductivity of the wiring substrate 10 while also increasing its transparency. The aperture ratio refers to the ratio (%) of the area of ​​the aperture region to the unit area of ​​a predetermined region (for example, the entire area of ​​the mesh wiring layer 20). The aperture region refers to the area where there are no metal parts such as the first direction wiring 21 and the second direction wiring 22, and the substrate 11 is exposed.

[0083] Incidentally, when a bending resistance test is performed on the wiring board 10, the increase in the resistance value of the mesh wiring layer 20 may be 20% or less, or it may be 10% or less. The bending resistance test is a test in which the wiring board 10 is bent 180° around the circumference of a 1 mm diameter cylinder and then straightened 100 times using a cylindrical mandrel bending tester.

[0084] Specifically, the test is performed as follows: First, the electrical resistance between the longitudinal ends of the mesh wiring layer 20 is measured. This resistance is denoted as R0 (Ω). Next, the wiring board 10 is wrapped around the cylinder of a cylindrical mandrel bending tester so that the longitudinal ends of the wiring board 10 are facing 180° opposite directions. Then, the wiring board 10 is removed from the cylinder and flattened. This process is repeated 100 times. After that, the electrical resistance between the longitudinal ends of the mesh wiring layer 20 is measured again. This resistance is denoted as R1 (Ω). The increase in resistance is calculated as ((R1-R0) / R0) × 100 (%). By keeping this increase in resistance to 20% or less, the durability of the wiring board 10 can be improved when the wiring board 10 is used in a curved or bent position.

[0085] Although not shown in the figures, a protective layer may be formed on the primer layer 15 so as to cover the mesh wiring layer 20. The protective layer protects the mesh wiring layer 20 and is formed so as to cover at least the mesh wiring layer 20 of the substrate 11. As the material for the protective layer, a colorless, transparent insulating resin such as polymethyl (meth)acrylate, polyethyl (meth)acrylate, acrylic resins and their modified resins and copolymers, polyester, polyvinyl alcohol, polyvinyl acetate, polyvinyl acetal, polyvinyl butyral, polyvinyl resins and their copolymers, polyurethane, epoxy resin, polyamide, or chlorinated polyolefin can be used.

[0086] Referring again to Figure 3, the power supply unit 40 is electrically connected to the mesh wiring layer 20. This power supply unit 40 consists of a substantially rectangular conductive thin plate-like member. The longitudinal direction of the power supply unit 40 is parallel to the X direction, and the short direction of the power supply unit 40 is parallel to the Y direction. The power supply unit 40 is also located at the longitudinal end of the substrate 11 (i.e., the negative Y-direction end). The material of the power supply unit 40 can be, for example, a metallic material such as gold, silver, copper, platinum, tin, aluminum, iron, or nickel, or an alloy containing these metals. When the wiring board 10 is incorporated into the image display device 60 (see Figures 1 and 2), this power supply unit 40 is electrically connected to the communication module 63 of the image display device 60 via a power supply line (not shown). Although the power supply unit 40 is provided on the first surface 11a of the substrate 11, it is not limited to this, and part or all of the power supply unit 40 may be located outside the periphery of the substrate 11. Furthermore, by flexibly forming the power supply unit 40, it may be configured to wrap around the side or back of the image display device 60. In this case, the power supply unit 40 may be electrically connected to the communication module 63 on the side or back of the image display device 60.

[0087] Multiple first-direction wirings 21 are electrically connected to the power supply section 40 on the positive side in the Y direction. In this case, the power supply section 40 is formed integrally with the mesh wiring layer 20. The thickness (length in the Z direction) of the power supply section 40 can be the same as the height H1 of the first-direction wiring 21 (see Figure 5) and the height H2 of the second-direction wiring 22 (see Figure 6), and can be selected, for example, in the range of 0.1 μm to 5.0 μm.

[0088] In such a wiring substrate 10, the dielectric loss tangent of the dielectric layer 12 described above is 0.002 or less. This effectively suppresses the dielectric layer 12 from affecting the transmission and reception of radio waves in the mesh wiring layer 20. Therefore, a decrease in antenna performance can be suppressed. The lower limit of the dielectric loss tangent of the dielectric layer 12 is not particularly limited, but it may be greater than 0. By having the dielectric loss tangent of the dielectric layer 12 within the above range, the loss of gain (i.e., decrease in sensitivity) associated with the transmission and reception of electromagnetic waves can be reduced, especially when the electromagnetic waves (e.g., millimeter waves) transmitted and received by the mesh wiring layer 20 are at high frequencies. The dielectric loss tangent of the dielectric layer 12 can be measured in accordance with IEC 62562 by the same method as the method for measuring the dielectric loss tangent of the substrate 11 described above.

[0089] Furthermore, the acid value of the dielectric layer 12, measured in accordance with JIS K 0070:1992, is 1 or less. As described above, migration may occur over time between the mesh wiring layer 20 and the layer in contact with the mesh wiring layer 20. In this case, for example, the metallic components of the mesh wiring layer 20 may diffuse into the dielectric layer 12 that is in contact with the mesh wiring layer 20. Also, the higher the acid value of the dielectric layer 12, the greater the amount of metallic components that diffuse into the dielectric layer 12. When metallic components diffuse into the dielectric layer 12, the dielectric loss of the dielectric layer 12 increases. In this case, the dielectric layer 12 may adversely affect the transmission and reception of radio waves in the mesh wiring layer 20. Therefore, the antenna performance may deteriorate.

[0090] In contrast, the acid value of the dielectric layer 12, measured in accordance with JIS K 0070:1992, is 1 or less, which suppresses migration between the mesh wiring layer 20 and the dielectric layer 12. This suppresses an increase in dielectric loss in the dielectric layer 12. Therefore, it is possible to prevent the dielectric layer 12 from adversely affecting the transmission and reception of radio waves in the mesh wiring layer 20. As a result, a decrease in antenna performance can be suppressed.

[0091] Furthermore, the content of metal elements in the dielectric layer 12 is preferably 0.1% by weight or more and 1% by weight or less. A metal element content of 0.1% by weight or more in the dielectric layer 12 enhances the adhesion between the dielectric layer 12 and the mesh wiring layer 20. Additionally, a metal element content of 1% by weight or less in the dielectric layer 12 effectively reduces dielectric loss in the dielectric layer 12. This effectively suppresses the dielectric layer 12 from affecting the transmission and reception of radio waves in the mesh wiring layer 20. Therefore, a decrease in antenna performance can be suppressed. Furthermore, a metal element content of 1% by weight or less in the dielectric layer 12 ensures the transparency of the dielectric layer 12. Therefore, the invisibility of the wiring substrate 10 can be maintained.

[0092] The moisture content in the dielectric layer 12 is preferably 0.01% by weight or more and 0.1% by weight or less. A moisture content of 0.01% by weight or more in the dielectric layer 12 enhances its flexibility. Furthermore, a moisture content of 0.1% by weight or less effectively reduces dielectric loss in the dielectric layer 12. This effectively suppresses the dielectric layer 12 from affecting the transmission and reception of radio waves in the mesh wiring layer 20. Therefore, a decrease in antenna performance can be suppressed.

[0093] [Manufacturing method for wiring boards] Next, the manufacturing method of the wiring board 10 and the manufacturing method of the laminated body 70 for an image display device according to this embodiment will be described with reference to Figures 7(a)-(f) and 8(a)-(c). Figure 7(a)-(f) is a cross-sectional view showing the manufacturing method of the wiring board 10 according to this embodiment. Figure 8(a)-(c) is a cross-sectional view showing the manufacturing method of the laminated body 70 for an image display device according to this embodiment.

[0094] First, prepare a transparent substrate 11.

[0095] Next, as shown in Figure 7(a), a dielectric layer 12 is fabricated by forming a primer layer 15 on the substrate 11. In this case, the primer layer 15 may be formed over substantially the entire surface 11a of the substrate 11. Methods for forming the primer layer 15 may include roll coating, gravure coating, gravure reverse coating, microgravure coating, slot die coating, die coating, knife coating, inkjet coating, dispenser coating, kiss coating, spray coating, screen printing, offset printing, and flexographic printing.

[0096] Next, a mesh wiring layer 20 is formed on the primer layer 15 of the dielectric layer 12, which includes a plurality of first directional wirings 21 and a plurality of second directional wirings 22 that connect the plurality of first directional wirings 21.

[0097] In this process, first, as shown in Figure 7(b), a metal foil 51 is laminated over substantially the entire surface of the primer layer 15. In this embodiment, the thickness of the metal foil 51 may be 0.1 μm or more and 5.0 μm or less. In this embodiment, the metal foil 51 may contain copper.

[0098] Next, as shown in Figure 7(c), a photocurable insulating resist 52 is supplied to substantially the entire surface of the metal foil 51. Examples of this photocurable insulating resist 52 include organic resins such as acrylic resin and epoxy resin.

[0099] Next, as shown in Figure 7(d), the insulating layer 54 is formed by photolithography. In this case, the photocurable insulating resist 52 is patterned by photolithography to form the insulating layer 54 (resist pattern). At this time, the insulating layer 54 is formed so that the metal foil 51 corresponding to the first directional wiring 21 and the second directional wiring 22 is exposed.

[0100] Next, as shown in Figure 7(e), the metal foil 51 located on the surface of the primer layer 15 that is not covered by the insulating layer 54 is removed. In this process, the metal foil 51 is etched so that the surface of the primer layer 15 is exposed by performing a wet treatment using ferric chloride, cupric chloride, strong acids such as sulfuric acid and hydrochloric acid, persulfates, hydrogen peroxide, aqueous solutions thereof, or combinations thereof.

[0101] Next, as shown in Figure 7(f), the insulating layer 54 is removed. In this case, the insulating layer 54 on the metal foil 51 is removed by wet treatment using a permanganate solution, N-methyl-2-pyrrolidone, an acid or alkaline solution, or by dry treatment using oxygen plasma.

[0102] In this way, a wiring substrate 10 is obtained, which has a dielectric layer 12 having a substrate 11 and a mesh wiring layer 20 disposed on the first surface 11a side of the dielectric layer 12. In this case, the mesh wiring layer 20 includes first-direction wiring 21 and second-direction wiring 22. Subsequently, the wiring substrate 10 is cut to the desired size.

[0103] Next, the first transparent adhesive layer 95, the wiring board 10, and the second transparent adhesive layer 96 are laminated together. First, as shown in Figure 8(a), an OCA sheet 90 is prepared, which includes, for example, a release film 91 made of polyethylene terephthalate (PET) and an OCA layer 92 (first transparent adhesive layer 95 or second transparent adhesive layer 96) laminated on the release film 91. At this time, the OCA layer 92 may be a layer obtained by coating the release film 91 with a liquid curable adhesive layer composition containing a polymerizable compound and curing it using, for example, ultraviolet light (UV). This curable adhesive layer composition contains a polar group-containing monomer.

[0104] Next, as shown in Figure 8(b), the OCA layer 92 of the OCA sheet 90 is bonded to the wiring board 10. This sandwiches the wiring board 10 between the OCA layer 92.

[0105] Subsequently, as shown in Figure 8(c), the release film 91 is peeled off from the OCA layer 92 of the OCA sheet 90 bonded to the wiring board 10, thereby obtaining the first transparent adhesive layer 95 (OCA layer 92), the wiring board 10, and the second transparent adhesive layer 96 (OCA layer 92) which are laminated together.

[0106] In this way, a laminate 70 for an image display device is obtained, comprising a first transparent adhesive layer 95, a second transparent adhesive layer 96, and a wiring substrate 10.

[0107] Subsequently, by stacking the display device 61 on the image display device laminate 70, an image display device 60 is obtained, comprising the image display device laminate 70 and the display device 61 stacked on the image display device laminate 70 (see Figure 1).

[0108] Next, we will describe the operation of this embodiment, which has the above configuration.

[0109] As shown in Figures 1 and 2, the wiring board 10 is incorporated into an image display device 60 having a display device 61. At this time, the wiring board 10 is placed on the display device 61. The mesh wiring layer 20 of the wiring board 10 is electrically connected to the communication module 63 of the image display device 60 via the power supply unit 40. In this way, radio waves of a predetermined frequency can be transmitted and received via the mesh wiring layer 20, and communication can be performed using the image display device 60.

[0110] According to this embodiment, the dielectric loss tangent of the dielectric layer 12 is 0.002 or less. This effectively suppresses the dielectric layer 12 from affecting the transmission and reception of radio waves in the mesh wiring layer 20. As a result, a decrease in antenna performance can be suppressed. In particular, when the electromagnetic waves (e.g., millimeter waves) transmitted and received by the mesh wiring layer 20 are high frequency, the gain loss (i.e., decrease in sensitivity) associated with the transmission and reception of electromagnetic waves can be reduced.

[0111] Furthermore, the moisture content in the dielectric layer 12 is between 0.01% by weight and 0.1% by weight. By having a moisture content of 0.01% by weight or more in the dielectric layer 12, the flexibility of the dielectric layer 12 can be increased. In addition, by having a moisture content of 0.1% by weight or less in the dielectric layer 12, dielectric loss in the dielectric layer 12 can be effectively reduced. This effectively suppresses the dielectric layer 12 from affecting the transmission and reception of radio waves in the mesh wiring layer 20. Therefore, a decrease in antenna performance can be suppressed.

[0112] Furthermore, according to this embodiment, the wiring board 10 comprises a dielectric layer 12 having a substrate 11 and a mesh wiring layer 20 disposed on the first surface 11a side of the dielectric layer 12. The substrate 11 is transparent. Furthermore, the mesh wiring layer 20 has a conductive portion as a part for forming an opaque conductive layer and a mesh-like pattern with a large number of openings 23. Therefore, the transparency of the wiring board 10 is ensured. As a result, when the wiring board 10 is placed on the display device 61, the display device 61 can be seen through the openings 23 of the mesh wiring layer 20, and the visibility of the display device 61 is not hindered.

[0113] Next, a modified example of the laminated image display device 70 will be described.

[0114] Figure 9 shows a modified example of a laminate for an image display device. The modified example shown in Figure 9 differs in that a protective layer 17 is formed on the primer layer 15 so as to cover the mesh wiring layer 20 and the power supply section 40. The other components are substantially the same as those shown in Figures 1 to 8 described above. In Figure 9, the same reference numerals are used for parts that are the same as those shown in Figures 1 to 8, and detailed explanations are omitted.

[0115] In the modified example shown in Figure 9, the wiring board 10 is positioned on the first surface 11a side of the dielectric layer 12 and further includes a protective layer 17 that covers the mesh wiring layer 20. This protective layer 17 is formed on the surface of the primer layer 15. The protective layer 17 covers the mesh wiring layer 20 and the power supply unit 40. That is, the protective layer 17 is in contact with the mesh wiring layer 20 and the power supply unit 40. The protective layer 17 protects the mesh wiring layer 20 and the power supply unit 40 and may be formed over substantially the entire surface of the primer layer 15.

[0116] The thickness T5 of the protective layer 17 may be between 0.05 μm and 1.8 μm. A thickness T5 of 0.05 μm or more enhances the abrasion resistance and weather resistance of the protective layer 17. Furthermore, a thickness T5 of 1.8 μm or less prevents the thickness of the wiring board 10 and the laminate for the image display device 70 from becoming too thick, thus reducing the overall thickness of the image display device 60. In this specification, the thickness T5 of the protective layer 17 refers to the distance in the Z direction from the surface of the power supply unit 40 to the surface of the protective layer 17.

[0117] The dielectric loss tangent of the protective layer 17 is preferably 0.002 or less. This effectively suppresses the protective layer 17 from affecting the transmission and reception of radio waves in the mesh wiring layer 20. As a result, a decrease in antenna performance can be suppressed. The lower limit of the dielectric loss tangent of the protective layer 17 is not particularly limited, but it may be greater than 0. By having the dielectric loss tangent of the protective layer 17 within the above range, the loss of gain (i.e., decrease in sensitivity) associated with the transmission and reception of electromagnetic waves can be reduced, especially when the electromagnetic waves (e.g., millimeter waves) transmitted and received by the mesh wiring layer 20 are at high frequencies. The dielectric loss tangent of the protective layer 17 can be measured in accordance with IEC 62562 by the same method as the method for measuring the relative permittivity of the substrate 11.

[0118] Furthermore, it is preferable that the acid value of the protective layer 17, measured in accordance with JIS K 0070:1992, be 1 or less. This suppresses the occurrence of migration between the mesh wiring layer 20 and the protective layer 17. As a result, it is possible to suppress the increase in dielectric loss of the protective layer 17. Consequently, it is possible to prevent the protective layer 17 from adversely affecting the transmission and reception of radio waves in the mesh wiring layer 20. As a result, it is possible to prevent a decrease in antenna performance.

[0119] The content of metal elements in the protective layer 17 is preferably 0.1% by weight or more and 1% by weight or less. A metal element content of 0.1% by weight or more in the protective layer 17 enhances the adhesion between the protective layer 17 and the mesh wiring layer 20. Furthermore, a metal element content of 1% by weight or less in the protective layer 17 effectively reduces dielectric loss in the protective layer 17. This effectively suppresses the protective layer 17 from affecting the transmission and reception of radio waves in the mesh wiring layer 20. Therefore, a decrease in antenna performance can be suppressed. Additionally, a metal element content of 1% by weight or less in the protective layer 17 ensures the transparency of the protective layer 17. Therefore, the invisibility of the wiring substrate 10 can be maintained.

[0120] The moisture content in the protective layer 17 is preferably 0.01% by weight or more and 0.1% by weight or less. A moisture content of 0.01% by weight or more in the protective layer 17 enhances its flexibility. Furthermore, a moisture content of 0.1% by weight or less effectively reduces dielectric loss in the protective layer 17. This effectively suppresses the protective layer 17 from affecting the transmission and reception of radio waves in the mesh wiring layer 20. Therefore, a decrease in antenna performance can be suppressed.

[0121] As the material for the protective layer 17, colorless and transparent insulating resins such as polymethyl (meth)acrylate, polyethyl (meth)acrylate, acrylic resins and their modified resins and copolymers, polyester resins, polyvinyl alcohol, polyvinyl acetate, polyvinyl acetal, polyvinyl butyral and their copolymers, polyurethane resins, epoxy resins, polyamide resins, and chlorinated polyolefins can be used.

[0122] The protective layer 17 preferably contains an acrylic resin or a polyester resin. This improves the adhesion between the first directional wiring 21 and the second directional wiring 22, or the adhesion between the first directional wiring 21 and the second directional wiring 22, thereby increasing the abrasion resistance and weather resistance of the first directional wiring 21 and the second directional wiring 22. It also maintains the invisibility and antenna performance of the wiring board 10.

[0123] Furthermore, it is preferable that the protective layer 17 contains silicon dioxide. The silicon dioxide may be added to the resin as a powder. Alternatively, it may be formed as a film that is substantially free of resin by methods such as vapor deposition, sputtering, or CVD. This improves the slipperiness of the surface of the protective layer 17 and the anti-reflective properties of the protective layer 17.

[0124] Methods for forming such a protective layer 17 may include roll coating, gravure coating, gravure reverse coating, microgravure coating, slot die coating, die coating, knife coating, inkjet coating, dispenser coating, kiss coating, spray coating, screen printing, offset printing, and flexographic printing.

[0125] In this modified example as well, the protective layer 17 can suppress adverse effects on the transmission and reception of radio waves in the mesh wiring layer 20. Therefore, a decrease in antenna performance can be suppressed.

[0126] Next, we will describe a modified example of a wiring board.

[0127] Figures 10 and 11 show a first modified example of the wiring board. The modified example shown in Figures 10 and 11 differs in that a dummy wiring layer 30 is provided around the mesh wiring layer 20, while the other configurations are substantially the same as those shown in Figures 1 to 9 described above. In Figures 10 and 11, the same reference numerals are used for parts that are the same as those shown in Figures 1 to 9, and detailed explanations are omitted.

[0128] In the wiring board 10 shown in Figure 10, a dummy wiring layer 30 is provided around the mesh wiring layer 20. Unlike the mesh wiring layer 20, this dummy wiring layer 30 does not substantially function as an antenna.

[0129] As shown in Figure 11, the dummy wiring layer 30 is composed of repeating dummy wiring 30a having a predetermined unit pattern shape. That is, the dummy wiring layer 30 contains multiple dummy wiring 30a of the same shape, and each dummy wiring 30a is electrically independent from the mesh wiring layer 20 (i.e., the first direction wiring 21 and the second direction wiring 22). Furthermore, the multiple dummy wiring 30a are regularly arranged throughout the entire area of ​​the dummy wiring layer 30. The multiple dummy wiring 30a are spaced apart from each other in the planar direction and are positioned protruding from the substrate 11. That is, each dummy wiring 30a is electrically independent from the mesh wiring layer 20, the power supply unit 40 and other dummy wiring 30a. The shape of each dummy wiring 30a is approximately L-shaped in plan view.

[0130] In this case, the dummy wiring 30a has a shape in which a part of the unit pattern shape of the mesh wiring layer 20 (see Figure 4) described above is missing. This makes it difficult to visually recognize the difference between the mesh wiring layer 20 and the dummy wiring layer 30, and makes the mesh wiring layer 20 placed on the substrate 11 less visible.

[0131] As shown in Figure 11, the dummy wiring 30a extends parallel to the first direction wiring 21 or the second direction wiring 22. Specifically, the dummy wiring 30a includes a first portion 31a that extends parallel to the first direction wiring 21 and a second portion 32a that extends parallel to the second direction wiring 22. The first portion 31a has a shape in which a part of the first direction wiring 21 is missing. Similarly, the second portion 32a has a shape in which a part of the second direction wiring 22 is missing. Note that the other configurations of the first portion 31a and the second portion 32a are the same as those of the first direction wiring 21 and the second direction wiring 22, so a detailed explanation is omitted here. In this way, because the dummy wiring 30a extends parallel to the first direction wiring 21 or the second direction wiring 22, the mesh wiring layer 20 placed on the substrate 11 can be made even less visible. The aperture ratio of the dummy wiring layer 30 may be the same as or different from that of the mesh wiring layer 20, but it is preferable that it be close to the aperture ratio of the mesh wiring layer 20.

[0132] In this way, by providing a dummy wiring layer 30 electrically independent of the mesh wiring layer 20 around the mesh wiring layer 20, the outer edge of the mesh wiring layer 20 can be obscured. As a result, the mesh wiring layer 20 can be made less visible on the surface of the image display device 60, making it difficult for users of the image display device 60 to recognize the mesh wiring layer 20 with the naked eye.

[0133] Figures 12 and 13 show a second modified example of the wiring board. The modified example shown in Figures 12 and 13 differs in that multiple dummy wiring layers 30A and 30B with different aperture ratios are provided around the mesh wiring layer 20, while the other configurations are substantially the same as those shown in Figures 1 to 11 described above. In Figures 12 and 13, the same reference numerals are used for parts that are the same as those shown in Figures 1 to 11, and detailed explanations are omitted.

[0134] In the wiring board 10 shown in Figure 12, multiple (in this case, two) dummy wiring layers 30A and 30B (i.e., a first dummy wiring layer 30A and a second dummy wiring layer 30B) with different aperture ratios are provided around the mesh wiring layer 20. Specifically, the first dummy wiring layer 30A is arranged around the mesh wiring layer 20, and the second dummy wiring layer 30B is arranged around the first dummy wiring layer 30A. Unlike the mesh wiring layer 20, these dummy wiring layers 30A and 30B do not substantially function as antennas.

[0135] As shown in Figure 13, the first dummy wiring layer 30A is composed of repeating dummy wiring 30a1 having a predetermined unit pattern shape. The second dummy wiring layer 30B is composed of repeating dummy wiring 30a2 having a predetermined unit pattern shape. That is, dummy wiring layers 30A and 30B each contain multiple dummy wirings 30a1 and 30a2 of the same shape, and each dummy wiring 30a1 and 30a2 is electrically independent from the mesh wiring layer 20. Furthermore, the dummy wirings 30a1 and 30a2 are regularly arranged throughout the entire area of ​​dummy wiring layers 30A and 30B, respectively. Each dummy wiring 30a1 and 30a2 is spaced apart from each other in the planar direction and is positioned protruding from the substrate 11. Each dummy wiring 30a1 and 30a2 is electrically independent from the mesh wiring layer 20, the power supply unit 40, and other dummy wirings 30a1 and 30a2. The shapes of each dummy wire 30a1 and 30a2 are roughly L-shaped when viewed from above.

[0136] In this case, the dummy wirings 30a1 and 30a2 have a shape in which a part of the unit pattern shape of the mesh wiring layer 20 (see Figure 4) described above is missing. This makes it difficult to visually recognize the difference between the mesh wiring layer 20 and the first dummy wiring layer 30A, and the difference between the first dummy wiring layer 30A and the second dummy wiring layer 30B, thereby making the mesh wiring layer 20 placed on the substrate 11 less visible. As shown in Figure 13, the dummy wirings 30a1 and 30a2 extend parallel to the first directional wiring 21 or the second directional wiring 22. Specifically, the dummy wiring 30a1 includes a first portion 31a1 that extends parallel to the first directional wiring 21 and a second portion 32a1 that extends parallel to the second directional wiring 22. The dummy wiring 30a2 includes a first portion 31a2 extending parallel to the first direction wiring 21 and a second portion 32a2 extending parallel to the second direction wiring 22.

[0137] The area of ​​each dummy wire 30a1 in the first dummy wiring layer 30A is larger than the area of ​​each dummy wire 30a2 in the second dummy wiring layer 30B. In this case, the line width of each dummy wire 30a1 is the same as the line width of each dummy wire 30a2, but this is not limited to this, and the line width of each dummy wire 30a1 may be thicker than the line width of each dummy wire 30a2. The other configurations of the dummy wires 30a1 and 30a2 are the same as the configuration of the dummy wire 30a in the first modified example, so a detailed explanation is omitted here.

[0138] In this modified example, it is preferable that the aperture ratios of the mesh wiring layer 20 and the multiple dummy wiring layers 30A and 30B increase in a stepwise manner from the mesh wiring layer 20 toward the dummy wiring layers 30A and 30B that are further away from the mesh wiring layer 20. In other words, it is preferable that the aperture ratio of each dummy wiring layer gradually increases from those closer to the mesh wiring layer 20 toward those further away. In this case, it is preferable that the aperture ratio of the first dummy wiring layer 30A is greater than the aperture ratio of the mesh wiring layer 20. It is also preferable that the aperture ratio of the second dummy wiring layer 30B is greater than the aperture ratio of the first dummy wiring layer 30A. This makes the outer edges of the mesh wiring layer 20 and the dummy wiring layers 30A and 30B even more indistinct. As a result, the mesh wiring layer 20 can be made even less visible on the surface of the image display device 60.

[0139] In this way, by arranging dummy wiring layers 30A and 30B that are electrically independent from the mesh wiring layer 20, the outer edge of the mesh wiring layer 20 can be made more indistinct. As a result, the mesh wiring layer 20 can be made less visible on the surface of the image display device 60, making it difficult for users of the image display device 60 to recognize the mesh wiring layer 20 with the naked eye. In addition, three or more dummy wiring layers with different aperture ratios may be provided around the mesh wiring layer 20.

[0140] Figure 14 shows a third modified example of the wiring board. The modified example shown in Figure 14 differs in the planar shape of the mesh wiring layer 20, but the other components are substantially the same as those shown in Figures 1 to 13 described above. In Figure 14, the same reference numerals are used for parts that are the same as those shown in Figures 1 to 13, and detailed explanations are omitted.

[0141] Figure 14 is an enlarged plan view showing the mesh wiring layer 20 according to the third modified example. In Figure 14, the first directional wiring 21 and the second directional wiring 22 intersect diagonally (i.e., not at a right angle), and the shape of each opening 23 is rhombus in plan view. Neither the first directional wiring 21 nor the second directional wiring 22 are parallel to either the X or Y direction, but either one of the first directional wiring 21 or the second directional wiring 22 may be parallel to either the X or Y direction.

[0142] [Examples] Next, a specific example of this embodiment will be described.

[0143] (Example 1) A wiring board with the configuration shown in Figure 2 was fabricated. In this case, a polyethylene terephthalate substrate with a thickness of 100 μm was used as the substrate for the dielectric layer. A polyester resin with a thickness of 0.1 μm was used as the primer layer for the dielectric layer. Copper wiring was formed on the polyester resin as first-direction wiring and second-direction wiring. Furthermore, an acrylic resin with a thickness of 25 μm was used as the protective layer.

[0144] Next, the dielectric loss tangent of the dielectric layer was measured. The dielectric loss tangent of the dielectric layer was measured according to the method compliant with IEC 62562. Specifically, a test specimen was prepared by cutting out the dielectric layer from the portion where the mesh wiring layer was not formed. The dimensions of the test specimen were 1 mm in width and 100 mm in length. The dielectric loss tangent of the test specimen was then measured according to IEC 62562. In the wiring substrate according to Example 1, the dielectric loss tangent of the dielectric layer was 0.0017 at 20 GHz.

[0145] Next, the moisture content in the dielectric layer was measured. The moisture content in the dielectric layer was measured using a moisture meter (Carl Fischer moisture meter, CA-310, manufactured by Nitto Seikou Analytech Co., Ltd.). In the wiring board according to Example 1, the moisture content in the dielectric layer was 0.01% by weight.

[0146] Next, the acid value of the dielectric layer was measured. The acid value of the dielectric layer was measured according to the method compliant with JIS K 0070:1992. Specifically, first, the dielectric layer in contact with the mesh wiring layer was cut out. Next, the dielectric layer was peeled from the mesh wiring layer to prepare a test specimen. Then, the acid value of the test specimen was measured according to JIS K 0070:1992. In the wiring substrate according to Example 1, the acid value of the dielectric layer was 0.2.

[0147] Next, an antenna performance evaluation test was conducted. First, the wiring board under evaluation was attached to the input terminal of a network analyzer (KEYSIGHT E5080B ENA Vector Network Analyzer). A 28GHz helical antenna (Candox Systems) was attached as a standard antenna to the output terminal of the network analyzer. Next, S21 at 28GHz was measured. Furthermore, the standard antenna was attached to both the input and output terminals, and S21 at 28GHz was measured again. Finally, using the case with the standard antenna attached to both terminals as a baseline, the extent to which S21 changed when the wiring board was attached to the input terminal was evaluated.

[0148] (Example 2) Except for the moisture content in the dielectric layer being 0.08% by weight and the acid value of the dielectric layer being 0.9, a wiring board was fabricated in the same manner as in Example 1, and an antenna performance evaluation test was performed.

[0149] (Comparative Example 1) Except for the dielectric loss tangent of the dielectric layer being 0.003, a wiring board was fabricated in the same manner as in Example 1, and an antenna performance evaluation test was performed.

[0150] (Comparative Example 2) A wiring board was fabricated in the same manner as in Example 1, except that the moisture content in the dielectric layer was 0.31% by weight and the acid value of the dielectric layer was 2.5, and an antenna performance evaluation test was performed.

[0151] The results are shown in Table 1. In the performance column of Table 1, "A (excellent)" means that the S21 at 28 GHz was not significantly degraded compared to the standard antenna. "B (poor)" means that the S-parameters (S21) at 28 GHz were significantly degraded compared to the standard antenna.

[0152] [Table 1]

[0153] As a result, as shown in Table 1, the S-parameters (S21) at 28 GHz were significantly degraded compared to the standard antenna in the wiring boards of Comparative Examples 1 and 2. In contrast, the S21 at 28 GHz was not significantly degraded compared to the standard antenna in the wiring boards of Examples 1 and 2. Therefore, it was found that the wiring board according to this embodiment can effectively suppress the degradation of antenna performance.

[0154] The multiple components disclosed in the above embodiments and each of their variations can be combined as needed. Alternatively, some components may be removed from all the components shown in the above embodiments and each of their variations.

Claims

1. A wiring board, A dielectric layer having a substrate including a first surface and a second surface located opposite the first surface, The dielectric layer comprises a mesh wiring layer disposed on the first surface side of the dielectric layer, The substrate is transparent, The dielectric loss tangent of the dielectric layer is 0.002 or less. The moisture content in the dielectric layer is 0.01% by weight or more and 0.1% by weight or less. A wiring board in which the content of metal elements in the dielectric layer is 0.1% by weight or more and 1% by weight or less.

2. The wiring substrate according to claim 1, wherein the dielectric layer further comprises a primer layer disposed on the first surface of the substrate.

3. The wiring board according to claim 1, wherein the wiring board has millimeter-wave transmitting and receiving capabilities, and the mesh wiring layer functions as an array antenna.

4. The wiring board according to claim 1, wherein a dummy wiring layer is provided around the mesh wiring layer, electrically independent from the mesh wiring layer.

5. The wiring board according to claim 4, wherein a plurality of dummy wiring layers are provided, and the aperture ratio of the mesh wiring layer and the dummy wiring layer increases in stages from the mesh wiring layer toward the dummy wiring layer which is further away from the mesh wiring layer.

6. The wiring substrate according to claim 1, further comprising a protective layer disposed on the first surface side of the dielectric layer and covering the mesh wiring layer, wherein the dielectric loss tangent of the protective layer is 0.002 or less, and the moisture content in the protective layer is 0.01% by weight or more and 0.1% by weight or less.

7. A wiring board according to any one of claims 1 to 5, A first adhesive layer located on the first surface side of the substrate, The substrate comprises a second adhesive layer located on the second surface side, A portion of the substrate is placed in a portion of the region between the first adhesive layer and the second adhesive layer. The dielectric loss tangent of the first adhesive layer is 0.002 or less. A laminate for an image display device, wherein the moisture content in the first adhesive layer is 0.01% by weight or more and 0.1% by weight or less.

8. The wiring board according to claim 6, A first adhesive layer located on the first surface side of the substrate, The substrate comprises a second adhesive layer located on the second surface side, A laminate for an image display device, wherein a portion of the substrate is disposed in a portion of the region between the first adhesive layer and the second adhesive layer.

9. A laminate for an image display device according to claim 7, An image display device comprising a display device formed by stacking the aforementioned stacked image display device bodies.

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