Wiring board and method for manufacturing wiring board

Abstract

To provide a wiring board and a method for manufacturing the wiring board that suppresses the difficulty of current flow in a mesh wiring layer.SOLUTION: A wiring board (10) has a substrate (11) and a mesh wiring layer (20) that is disposed on the substrate (11) and includes a plurality of wires (21, 22). The substrate (11) has a transmittance of 85% or more for light rays of wavelengths from 400 nm to 700 nm. The wiring (21, 22) includes a surface roughness Ra, and the surface roughness Ra is equal to or less than 100 nm.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Embodiments of the present disclosure relate to a wiring board and a method for manufacturing the wiring board.

Background Art

[0002] Currently, high functionality, miniaturization, thinning, and weight reduction of portable terminal devices such as smartphones and tablets are progressing. Since these portable terminal devices use multiple communication bands, a plurality of antennas corresponding to the communication bands are required. For example, portable terminal devices are equipped with a plurality of antennas such as a telephone antenna, a WiFi (Wireless Fidelity) antenna, a 3G (Generation) antenna, a 4G (Generation) antenna, an LTE (Long Term Evolution) antenna, a Bluetooth (registered trademark) antenna, and an NFC (Near Field Communication) antenna. However, with the miniaturization of portable terminal devices, the mounting space for antennas is limited, and the degree of freedom in antenna design is narrowing. In addition, since the antenna is built in a limited space, the radio wave sensitivity is not always satisfactory.

[0003] For this reason, a film antenna that can be mounted in the display area of a portable terminal device has been developed. This film antenna is a transparent antenna in which an antenna pattern is formed on a transparent base material, and the antenna pattern is formed by a mesh-shaped conductor mesh layer including a conductor portion as a formed portion of an opaque conductor layer and a large number of openings as non-formed portions.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] In a conventional film antenna, a mesh wiring layer (conductor mesh layer) is mounted on a transparent substrate. In particular, in recent years, high-frequency electromagnetic waves have been used in film antennas. When high-frequency electromagnetic waves are used, the number of times electrons pass through the grain boundaries of the metal constituting the mesh wiring layer per unit time increases, making it difficult for current to flow and increasing the transmission loss.

[0006] This embodiment provides a wiring board and a method for manufacturing the wiring board capable of suppressing the difficulty of current flow in the mesh wiring layer.

Disclosure of the Invention

[0007] The wiring board according to this embodiment is a wiring board, comprising a substrate, and a mesh wiring layer disposed on the substrate and including a plurality of wirings. The substrate has a light transmittance of 85% or more for light rays with a wavelength of 400 nm or more and 700 nm or less. The wiring includes a surface roughness Ra, and the surface roughness Ra is 100 nm or less.

[0008] In the wiring board according to this embodiment, the wiring may include metal crystals, and the area average grain size of the metal crystals may be 300 nm or more.

[0009] In the wiring board according to this embodiment, the line width of the wiring may be 0.1 μm or more and 5.0 μm or less.

[0010] In the wiring board according to this embodiment, the mesh wiring layer may be an antenna.

[0011] In the wiring board according to this embodiment, the wiring may include gold, silver, copper, platinum, tin, aluminum, iron, or nickel.

[0012] In the wiring board according to this embodiment, the dielectric tangent of the substrate may be 0.002 or less.

[0013] In the wiring board according to the present embodiment, the thickness of the substrate may be 5 μm or more and 200 μm or less.

[0014] In the wiring board according to the present embodiment, the substrate may contain a cycloolefin polymer or a polynorbornene polymer.

[0015] In the wiring board according to the present embodiment, the mesh wiring layer may be present only in a part of the substrate.

[0016] In the wiring board according to the present embodiment, the surface roughness Ra may be 90 nm or less.

[0017] The method for manufacturing a wiring board according to the present embodiment is a method for manufacturing a wiring board, including a step of preparing a substrate and a step of forming a mesh wiring layer including a plurality of wirings on the substrate. The substrate has a light transmittance of 85% or more for light rays with a wavelength of 400 nm or more and 700 nm or less. The wiring includes a surface roughness Ra, and the surface roughness Ra is 100 nm or less.

[0018] In the method for manufacturing a wiring board according to the present embodiment, the wiring may contain metal crystals, and the area average particle diameter of the metal crystals may be 300 nm or more.

[0019] In the method for manufacturing a wiring board according to the present embodiment, the line width of the wiring may be 0.1 μm or more and 5.0 μm or less.

[0020] In the method for manufacturing a wiring board according to the present embodiment, the mesh wiring layer may be an antenna.

[0021] In the method for manufacturing a wiring board according to the present embodiment, the wiring may contain gold, silver, copper, platinum, tin, aluminum, iron, or nickel.

[0022] In the method for manufacturing a wiring board according to the present embodiment, the dielectric loss tangent of the substrate may be 0.002 or less.

[0023] In the method for manufacturing a wiring board according to the present embodiment, the thickness of the substrate may be 5 μm or more and 200 μm or less.

[0024] In the method for manufacturing a wiring board according to the present embodiment, the substrate may contain a cycloolefin polymer or a polynorbornene polymer.

[0025] In the method for manufacturing a wiring board according to the present embodiment, the mesh wiring layer may be present only in a part of the substrate.

[0026] In the method for manufacturing a wiring board according to the present embodiment, the surface roughness Ra may be 90 nm or less.

[0027] According to an embodiment of the present disclosure, it is possible to suppress the current from becoming difficult to flow in the mesh wiring layer.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0029] First, an embodiment will be described with reference to FIGS. 1 to 10. FIGS. 1 to 10 are diagrams showing this embodiment.

[0030] The following figures are shown schematically. Therefore, the size and shape of each part are exaggerated as appropriate for easy understanding. Also, it is possible to carry out appropriate modifications without departing from the technical idea. In each of the figures shown below, the same parts are denoted by the same reference numerals, and some detailed descriptions may be omitted. Also, the numerical values and material names of the dimensions of each member described in this specification are examples as embodiments and are not limited thereto, and can be appropriately selected and used. In this specification, terms specifying shapes and geometric conditions, such as terms like parallel, orthogonal, and perpendicular, include not only the strictly meant state but also substantially the same state.

[0031] Also, in the following embodiments, the "X direction" is a direction parallel to one side of the substrate. The "Y direction" is a direction perpendicular to the X direction and parallel to the other side of the substrate. The "Z direction" is a direction perpendicular to both the X direction and the Y direction and parallel to the thickness direction of the wiring board. Also, the "surface" is the surface on the plus side in the Z direction and is the surface on which wiring is provided with respect to the substrate. The "back surface" is the surface on the minus side in the Z direction and is the surface opposite to the surface on which wiring is provided with respect to the substrate.

[0032] [Configuration of Wiring Board] Referring to FIGS. 1 to 7, the configuration of the wiring board according to the present embodiment will be described. FIGS. 1 to 7 are diagrams showing the wiring board according to the present embodiment.

[0033] As shown in FIG. 1, the wiring board 10 according to the present embodiment is, for example, disposed on the display of an image display device. Such a wiring board 10 includes a substrate 11 having transparency and a mesh wiring layer (wiring pattern region) 20 disposed on the substrate 11. Further, a power supply unit 40 is electrically connected to the mesh wiring layer 20.

[0034] Among these, the substrate 11 is substantially rectangular in plan view, its longitudinal direction is parallel to the Y direction, and its short-side direction is parallel to the X direction. The substrate 11 has transparency and is substantially flat, and its thickness is substantially uniform as a whole. The length L1 of the substrate 11 in the longitudinal direction (Y direction) can be selected, for example, in the range of 2 mm or more and 300 mm or less, preferably in the range of 100 mm or more and 200 mm or less. The length L2 of the substrate 11 in the short-side direction (X direction) can be selected in the range of 2 mm or more and 300 mm or less, preferably, for example, in the range of 50 mm or more and 100 mm or less. Note that the corners of the substrate 11 may each have a rounded shape.

[0035] The material of the substrate 11 may be any material having transparency and electrical insulation in the visible light region. In this embodiment, the material of the substrate 11 is polyethylene terephthalate, but it is not limited thereto. As the material of the substrate 11, for example, polyester resins such as polyethylene terephthalate, acrylic resins such as polymethyl methacrylate, polycarbonate resins, polyimide resins, or polyolefin resins such as cycloolefin polymers, and organic insulating materials such as cellulose resin materials such as triacetyl cellulose are preferably used. Alternatively, as the material of the substrate 11, organic insulating materials such as cycloolefin polymers (for example, ZF-16 manufactured by Nippon Zeon Co., Ltd.) and polynorbornene polymers (manufactured by Sumitomo Bakelite Co., Ltd.) may be used. Further, as the material of the substrate 11, glass, ceramics, etc. can be appropriately selected according to the application. Although an example in which the substrate 11 is composed of a single layer is illustrated, it is not limited thereto, and a structure in which a plurality of base materials or layers are laminated may also be used. Also, the substrate 11 may be in the form of a film or a plate. For this reason, the thickness of the substrate 11 is not particularly limited and can be appropriately selected according to the application. As an example, the thickness (Z direction) T1 of the substrate 11 (see FIGS. 4 and 5) can be, for example, in the range of 5 μm or more and 200 μm or less.

[0036] Also, the dielectric tangent of the substrate 11 may be 0.002 or less, and preferably 0.001 or less. Note that there is no particular lower limit for the dielectric tangent of the substrate 11, but it may be more than 0. When the dielectric tangent of the substrate 11 is within the above range, particularly when the electromagnetic wave (for example, millimeter wave) transmitted and received by the mesh wiring layer 20 is a high frequency, the loss of gain (sensitivity) associated with the transmission and reception of the electromagnetic wave can be reduced. Note that the lower limit of the dielectric tangent of the substrate 11 is not particularly limited. The dielectric constant of the substrate 11 is not particularly limited, but it may be 2.0 or more and 10.0 or less.

[0037] The dielectric tangent of the substrate 11 can be measured in accordance with IEC 62562. Specifically, first, a test piece is prepared by cutting out the substrate 11 in a portion where the mesh wiring layer 20 is not formed. Alternatively, the substrate 11 on which the mesh wiring layer 20 is formed may be cut out and the mesh wiring layer 20 may be removed by etching or the like. The dimensions of the test piece shall be 10 mm to 20 mm in width and 50 mm to 100 mm in length. Next, the dielectric tangent is measured in accordance with IEC 62562. The dielectric constant and dielectric tangent of the substrate 11 can also be measured in accordance with ASTM D150.

[0038] Further, the substrate 11 may have a transmittance of visible light (light with a wavelength of 400 nm or more and 700 nm or less) of 85% or more, preferably 90% or more. Note that there is no particular upper limit to the transmittance of visible light of the substrate 11, but it may be, for example, 100% or less. By setting the transmittance of visible light of the substrate 11 within the above range, the transparency of the wiring substrate 10 can be increased, and the display 91 (described later) of the image display device 90 can be made easier to visually recognize. Note that visible light refers to light with a wavelength of 400 nm to 700 nm. Further, the transmittance of visible light being 85% or more means that when the absorbance of the substrate 11 is measured using a known spectrophotometer (for example, a spectroscope manufactured by JASCO Corporation: V-670), the transmittance is 85% or more in the entire wavelength range of 400 nm to 700 nm.

[0039] In the present embodiment, the mesh wiring layer 20 is composed of an antenna pattern region having a function as an antenna. In FIG. 1, a plurality (three) of mesh wiring layers 20 are formed on the substrate 11, each corresponding to a different frequency band. That is, the plurality of mesh wiring layers 20 have lengths L a that are different from each other and have lengths corresponding to specific frequency bands. Note that the lower the corresponding frequency band, the longer the length L of the mesh wiring layer 20 ais long. When the wiring board 10 is arranged, for example, on a display 91 (see FIG. 10 described later) of an image display device 90, each mesh wiring layer 20 may correspond to any one of a telephone antenna, a WiFi antenna, a 3G antenna, a 4G antenna, a 5G antenna, an LTE antenna, a Bluetooth (registered trademark) antenna, an NFC antenna, etc. Further, the mesh wiring layer 20 does not have to exist on the entire surface of the substrate 11, and may exist only in a partial region on the substrate 11.

[0040] Each mesh wiring layer 20 is substantially rectangular in plan view. The longitudinal direction of each mesh wiring layer 20 is parallel to the Y direction, and the short side direction thereof is parallel to the X direction. The length L of each mesh wiring layer 20 in the longitudinal direction (Y direction) a can be selected, for example, in the range of 3 mm or more and 100 mm or less, and the width W of each mesh wiring layer 20 in the short side direction (X direction) a can 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 a millimeter-wave antenna. When the mesh wiring layer 20 is a millimeter-wave antenna, the length L of the mesh wiring layer 20 a can be selected in the range of 1 mm or more and 10 mm or less, more preferably 1.5 mm or more and 5 mm or less.

[0041] In each mesh wiring layer 20, metal wires are formed in a lattice shape or a mesh shape and have a repeating pattern 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 X direction (second-direction wiring 22) and a portion extending in the Y direction (first-direction wiring 21).

[0042] As shown in FIG. 2, each mesh wiring layer 20 includes a plurality of first-direction wirings (antenna wirings) 21 having a function as an antenna, and a plurality of second-direction wirings (antenna connection wirings) 22 connecting the plurality of first-direction wirings 21. Specifically, 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 shape or a mesh shape. Each first-direction wiring 21 extends in a direction (longitudinal direction, Y direction) corresponding to the frequency band of the antenna, and each second-direction wiring 22 extends in a direction (width direction, X direction) orthogonal to the first-direction wiring 21. The first-direction wiring 21 has a length L a (the length of the mesh wiring layer 20 described above, see FIG. 1) and mainly functions as an antenna. On the other hand, the second-direction wiring 22 serves to suppress problems such as disconnection of the first-direction wirings 21 or loss of electrical connection between the first-direction wirings 21 and the power supply unit 40 by connecting these first-direction wirings 21 to each other.

[0043] As shown in FIG. 3, in each mesh wiring layer 20, a plurality of openings 23 are formed by being surrounded by adjacent first-direction wirings 21 and adjacent second-direction wirings 22. Further, the first-direction wirings 21 and the second-direction wirings 22 are arranged at equal intervals from each other. That is, the plurality of first-direction wirings 21 are arranged at equal intervals from each other, and the pitch P1 thereof can be in the range of, for example, 0.01 mm or more and 1 mm or less. Also, the plurality of second-direction wirings 22 are arranged at equal intervals from each other, and the pitch P2 thereof can be in the range of, for example, 0.01 mm or more and 1 mm or less. In this way, since the plurality of first-direction wirings 21 and the plurality of second-direction wirings 22 are each arranged at equal intervals, the size of the openings 23 does not vary within each mesh wiring layer 20, and the mesh wiring layer 20 can be made difficult to visually recognize with the naked eye. Also, the pitch P1 of the first-direction wirings 21 is equal to the pitch P2 of the second-direction wirings 22. For this reason, each opening 23 is substantially square in plan view, and the transparent substrate 11 is exposed from each opening 23. For this reason, by widening the area of each opening 23, the transparency of the entire wiring substrate 10 can be enhanced. Note that the length L3 of one side of each opening 23 can be in the range of, for example, 0.01 mm or more and 1 mm or less. Note that each first-direction wiring 21 and each second-direction wiring 22 are orthogonal to each other, but are not limited thereto, and may intersect at an acute angle or an obtuse angle with each other. Also, the shape of the opening 23 is preferably the same shape and the same size over the entire surface, but does not have to be uniform over the entire surface, such as being changed depending on the location.

[0044] As shown in FIG. 4, each first-direction wiring 21 has a cross section (X-direction cross section) perpendicular to its longitudinal direction that is substantially rectangular or substantially square. In this case, the cross-sectional shape of the first-direction wiring 21 is substantially uniform along the longitudinal direction (Y direction) of the first-direction wiring 21. Further, as shown in FIG. 5, the shape of the cross section (Y-direction cross section) perpendicular to the longitudinal direction of each second-direction wiring 22 is substantially rectangular or substantially square, and is substantially the same as the cross-sectional shape (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 substantially uniform along the longitudinal direction (X direction) of the second-direction wiring 22. The cross-sectional shapes of the first-direction wiring 21 and the second-direction wiring 22 do not necessarily have to be substantially rectangular or substantially square. The cross-sectional shapes of the first-direction wiring 21 and the second-direction wiring 22 may be, for example, a substantially trapezoidal shape in which the surface side (Z-direction plus side) is narrower than the back side (Z-direction minus side), or a shape in which the side surfaces located on both sides in the longitudinal direction are curved.

[0045] In the present embodiment, the line width W1 of the first-direction wiring 21 (the length in the X direction, see FIG. 4) and the line width W2 of the second-direction wiring 22 (the length in the Y direction, see FIG. 5) are not particularly limited and can be appropriately selected according to the application. For example, the line width W1 of the first-direction wiring 21 can be selected in the range of 0.1 μm or more and 5.0 μm or less, and is preferably 0.2 μm or more and 2.0 μm or less. Further, the line width W2 of the second-direction wiring 22 can be selected in the range of 0.1 μm or more and 5.0 μm or less, and is preferably 0.2 μm or more and 2.0 μm or less. Furthermore, the height H1 of the first-direction wiring 21 (the length in the Z direction, see FIG. 4) and the height H2 of the second-direction wiring 22 (the length in the Z direction, see FIG. 5) are not particularly limited and can be appropriately selected according to the application, and can be selected, for example, in the range of 0.1 μm or more and 5.0 μm or less, and are preferably 0.2 μm or more and 2.0 μm or less.

[0046] FIG. 6 shows cross-sections in the width direction (X direction, Y direction) of the first-direction wiring 21 and the second-direction wiring 22. The first-direction wiring 21 and the second-direction wiring 22 each have a front surface 24a, a back surface 24b, and two side surfaces 24c, 24d. Among these, the front surface 24a is located on the side (Z-direction plus side) where the first-direction wiring 21 and the second-direction wiring 22 are visible to an observer during use. The back surface 24b is on the opposite side of the front surface 24a and is located on the substrate 11 side (Z-direction minus side). Also, the two side surfaces 24c, 24d are located between the front surface 24a and the back surface 24b, and are respectively located on both sides in the width direction (X direction, Y direction) of the first-direction wiring 21 and the second-direction wiring 22. In this case, the front surface 24a and the side surfaces 24c, 24d are respectively substantially orthogonal, and the back surface 24b and the side surfaces 24c, 24d are respectively substantially orthogonal, but it is not limited to this, and they may intersect at an acute angle or an obtuse angle. Also, the front surface 24a, the back surface 24b, and the side surfaces 24c, 24d respectively extend linearly, but it is not limited to this, and the front surface 24a, the back surface 24b, or the side surfaces 24c, 24d may be curved respectively.

[0047] FIG. 7 is a schematic diagram showing an enlargement of the vicinity of the front surface 24a of the first-direction wiring 21 and the second-direction wiring 22. As shown in FIG. 7, for the first-direction wiring 21 and the second-direction wiring 22, the size of crystal grains appearing in the cross-section in their width direction (X direction, Y direction) can be measured by the EBSD method.

[0048] The EBSD method is a method for analyzing crystal grains based on an electron diffraction pattern (hereinafter also referred to as an EBSD pattern) obtained when an electron beam is irradiated on a sample from a direction significantly inclined with respect to the surface of the sample using a scanning electron microscope (hereinafter also referred to as SEM) or the like. As a measuring apparatus, for example, a combination of a Schottky field emission scanning electron microscope and an EBSD detector can be used. As the EBSD detector, for example, an OIM (Orientation Imaging Microscopy) detector manufactured by TSL Solutions Co., Ltd. can be used.

[0049] As a pretreatment before performing the EBSD method, cross-section processing of the sample may be performed using the FIB (focused ion beam) method. Also, as a pretreatment before performing the FIB method, carbon may be applied to the sample surface as a protective film with a thickness of 200 nm or more. This protective film may be composed of components such as Pt, PtPd, and Os. As a method for applying the protective film, either sputtering or evaporation may be used. The protective film prevents damage to the surface of the processed area during processing by the FIB method, and the film thickness of the protective film can be appropriately adjusted according to the processing conditions. As the FIB apparatus used for the FIB method, any apparatus may be used as long as it is equipped with a system capable of picking up from any location, including micro-sampling. For example, NB5000 manufactured by Hitachi High-Tech can be used. Note that the final film thickness after thinning the cross-section of the observation site should be 300 nm or more, and there is no problem with a thicker thickness. The final width after thinning the cross-section of the observation site may be, for example, 30 μm. Although it depends on the system installed in the FIB apparatus, a wider final width is more efficient.

[0050] An example of the conditions for the scanning electron microscope used in the EBSD method is as follows. · Observation magnification: 30,000 times (assuming the reference for x1 magnification is 120 mm × 90 mm) · Acceleration voltage: 15 kV · Working distance: 15 mm · Sample tilt angle: 70 degrees An example of the conditions for crystal analysis by the EBSD method is as follows. · Step size: 25 nm Analysis conditions: Using the crystal orientation analysis software OIM (Ver7.3) manufactured by TSL Solutions Co., Ltd., the following analysis is performed. When the number of crystal grains appearing in the measurement region to be analyzed is less than 100, images may be acquired at multiple positions on the cross-section of the sample while shifting the measurement target region, and the obtained multiple images may be concatenated to generate an image in which 100 or more crystal grains appear. Data with a reliability index (Confidence Index: CI value) defined by the crystal orientation analysis software OIM (Ver7.3) manufactured by TSL Solutions Co., Ltd. below a predetermined value is excluded and analysis is performed. For example, data with a CI value of 0.2 or less is excluded. This can eliminate the influence of the base material existing on the front and back of the sample, the protective film used for pretreatment, the grain boundaries existing in the sample cross-section, and amorphous. As another method, it is also possible to regard a portion having a contrast of a certain level or more from the Image Quality image as a crystal and perform data extraction. It is assumed that there is no twin grain boundary, and only normal grain boundaries are counted.

[0051] The area average particle size of the metal crystal 29 included in the first direction wiring 21 and the second direction wiring 22 may be 300 nm or more, and preferably 400 nm or more. Although there is no particular upper limit for the area average particle size of the metal crystal 29, for example, it may be 1000 nm or less. When the area average particle size of the metal crystal 29 is 300 nm or more, as will be described later, the density of the metal crystal 29 becomes relatively low, so the total area of the grain boundaries decreases, electron diffusion at the grain boundaries decreases, it is possible to suppress the difficulty of current flow, and the transmission loss of electromagnetic waves can be reduced.

[0052] Note that the particle size d of the metal crystal 29 p refers to, for example, the size of the metal crystal 29 in a cross-sectional view as shown in FIG. 7. In other words, it may be the diameter of a circle having the same area as the size of the metal crystal 29 observed when observing the first direction wiring 21 and the second direction wiring 22 from a direction parallel to the longitudinal direction of the first direction wiring 21 and the second direction wiring 22. The area average particle size of the metal crystal 29 is strictly the particle size d for all the metal crystals 29 included in the first direction wiring 21 and the second direction wiring 22 p is examined, and its average value is calculated. However, considering the size of the metal crystal 29 and the like, the particle size d of the metal crystal 29 within the first direction wiring 21 and the second direction wiring 22 p is the particle size d of a quantity of metal crystals 29 expected to represent the overall tendency pExamine them, and the average value may be used as the area average particle size of the metal crystal 29. For example, for the particle size d of 5 to 50 or more metal crystals 29 per 3 μm to 30 μm in the longitudinal direction of the first-direction wiring 21 and the second-direction wiring 22 p Examine them, and the average value may be used as the area average particle size of the metal crystal 29.

[0053] The location for measuring the area average particle size of the metal crystal 29 shall be at a location away from the end when the size required for measurement is smaller than the measurement surface on a measurement surface such as the cross-section of the first-direction wiring 21 and the second-direction wiring 22. For example, when the positions in the width direction of the first-direction wiring 21 and the second-direction wiring 22 can be measured, measure at a location close to the center, separated from the width-direction end by a length of 10% or more of the width of the first-direction wiring 21 and the second-direction wiring 22. When the positions in the thickness direction of the first-direction wiring 21 and the second-direction wiring 22 can be measured, measure at a location close to the center, separated from the thickness-direction end by a length of 10% or more of the thickness of the first-direction wiring 21 and the second-direction wiring 22. Also, as described above, several points may be measured and their average value may be used as the area average particle size.

[0054] Also, as shown in FIG. 7, the surface roughness Ra of the first-direction wiring 21 and the second-direction wiring 22 may be 100 nm or less, preferably 90 nm or less. Note that there is no particular lower limit for the surface roughness Ra of the first-direction wiring 21 and the second-direction wiring 22, but it may be, for example, 5 nm or more. When the surface roughness Ra of the first-direction wiring 21 and the second-direction wiring 22 is 100 nm or less, as will be described later, particularly in the case of high-frequency electromagnetic waves, electrons mainly flow on the surfaces of the first-direction wiring 21 and the second-direction wiring 22 due to the skin effect. Therefore, the smoother the surface, that is, the smaller the surface roughness Ra, the more the transmission loss of the electromagnetic wave can be reduced. The surface roughness Ra is the arithmetic average roughness measured using a non-contact roughness meter. As the non-contact roughness meter, a laser microscope VK-X250 (control unit) manufactured by Keyence Corporation can be used.

[0055] Here, the surface roughness Ra of the first-direction wiring 21 and the second-direction wiring 22 refers to the surface roughness Ra of the outer surfaces of the first-direction wiring 21 and the second-direction wiring 22. Specifically, it refers to the surface roughness Ra of the surface 24a of the first-direction wiring 21 and the second-direction wiring 22. Also, although it is preferable that the entire surface 24a satisfies the above range, it is not limited thereto, and the surface roughness Ra of a part of the surface 24a may satisfy the above range. The location for measuring the surface roughness Ra of the first-direction wiring 21 and the second-direction wiring 22 shall be a location on the surface 24a that is away from the width-direction end portions. For example, it is measured at a location close to the center that is away from the width-direction end portions by a length of 10% or more of the width of the first-direction wiring 21 and the second-direction wiring 22. Also, it may be a single point, but several points may be measured and used as their average value.

[0056] In addition, in the present embodiment, as described above, (i) the area average grain size of the metal crystals 29 included in the first-direction wiring 21 and the second-direction wiring 22 is 300 nm or more, and (ii) it is preferable that the surface roughness Ra of the first-direction wiring 21 and the second-direction wiring 22 is 100 nm or less. However, it is not limited thereto, and only one of the above conditions (i) or (ii) may be satisfied.

[0057] The materials of the first-direction wiring 21 and the second-direction wiring 22 may be any metal materials having conductivity. In the present embodiment, the materials of the first-direction wiring 21 and the second-direction wiring 22 are copper, but it is not limited thereto. As the materials of the first-direction wiring 21 and the second-direction wiring 22, for example, metal materials (including alloys) such as gold, silver, copper, platinum, tin, aluminum, iron, and nickel can be used. Also, the first-direction wiring 21 and the second-direction wiring 22 may be plating layers formed by an electrolytic plating method.

[0058] Also, as shown in FIGS. 4 and 5, an easy-adhesion layer 15 is formed on the substrate 11. The easy-adhesion layer 15 enhances the adhesiveness between the substrate 11 and the first-direction wiring 21 and the second-direction wiring 22, and is formed over substantially the entire surface of the substrate 11. The easy-adhesion layer 15 is composed of an insulating film. As materials for such an easy-adhesion layer 15, for example, acrylic resins such as polymethyl (meth)acrylate and polyethyl (meth)acrylate, copolymers with their modified resins, polyesters, polyvinyl alcohol, polyvinyl acetate, polyvinyl acetal, polyvinyl butyral and other polyvinyl resins and their copolymers, colorless transparent resins such as polyurethane, epoxy resin, polyamide, and chlorinated polyolefin can be used. Also, the thickness of the easy-adhesion layer 15 can be appropriately set within the range of 10 nm or more and 800 nm or less. Note that the easy-adhesion layer 15 only needs to be formed at least on the mesh wiring layer 20 on the surface of the substrate 11.

[0059] A adhesion layer 16 is formed on the easy-adhesion layer 15. This adhesion layer 16 is positioned between the first-direction wiring 21 and the second-direction wiring 22 and the easy-adhesion layer 15. The adhesion layer 16 enhances the adhesion between the substrate 11 and the first-direction wiring 21 and the second-direction wiring 22, and is formed in the same planar shape as the first-direction wiring 21 and the second-direction wiring 22. That is, the adhesion layer 16 has a lattice shape or a mesh shape in plan view. As materials for such an adhesion layer 16, for example, metal oxides such as titanium, titanium oxide, nickel, nickel oxide, indium-zinc oxide (IZO), and indium-tin oxide (ITO) can be used. Also, the thickness of the adhesion layer 16 can be selected within the range of 10 nm or more and 100 nm or less. Note that the adhesion layer 16 does not necessarily have to be provided.

[0060] Furthermore, a protective layer 17 is formed on the surface of the substrate 11 so as to cover the first-direction wiring 21, the second-direction wiring 22, and the easily adherent layer 15. The protective layer 17 protects the first-direction wiring 21 and the second-direction wiring 22 and is formed over substantially the entire surface of the substrate 11. As the material of the protective layer 17, acrylic resins such as polymethyl (meth)acrylate and polyethyl (meth)acrylate, modified resins thereof, and copolymers, polyesters, polyvinyl alcohol, polyvinyl acetate, polyvinyl acetal, polyvinyl butyral and other polyvinyl resins and their copolymers, polyurethanes, epoxy resins, polyamides, colorless and transparent insulating resins such as chlorinated polyolefins can be used. Also, the thickness of the protective layer 17 can be selected in the range of 0.3 μm or more and 10 μm or less. Note that the protective layer 17 only needs to be formed so as to cover at least the mesh wiring layer 20 of the substrate 11.

[0061] The overall aperture ratio At of the mesh wiring layer 20 can be, for example, in the range of 87% or more and less than 100%. By setting the overall aperture ratio At of the wiring substrate 10 within this range, the conductivity and transparency of the wiring substrate 10 can be ensured. Note that the aperture ratio refers to the ratio (%) of the area of the opening region (the region where the substrate 11 is exposed without the presence of metal portions such as the first-direction wiring 21 and the second-direction wiring 22) to the unit area of a predetermined region (for example, the entire area of the mesh wiring layer 20).

[0062] Referring back to FIG. 1, the power supply unit 40 is electrically connected to the mesh wiring layer 20. The power supply unit 40 is composed of a conductive thin plate-like member having a substantially rectangular shape. The longitudinal direction of the power supply unit 40 is parallel to the X direction, and the short side direction of the power supply unit 40 is parallel to the Y direction. Further, the power supply unit 40 is disposed at the longitudinal end (Y-direction negative side end) of the substrate 11. As the material of the power supply unit 40, for example, metal materials (including alloys) such as gold, silver, copper, platinum, tin, aluminum, iron, and nickel can be used. When the wiring substrate 10 is incorporated into the image display device 90 (see FIG. 10), the power supply unit 40 is electrically connected to the wireless communication circuit 92 of the image display device 90. Note that the power supply unit 40 is provided on the surface of the substrate 11, but is not limited thereto, and part or all of the power supply unit 40 may be located outside the periphery of the substrate 11. Further, by forming the power supply unit 40 flexibly, the power supply unit 40 can be wound around the side surface or the back surface of the image display device 90 so as to be electrically connected on the side surface or the back surface side.

[0063] [Method of manufacturing a wiring substrate] Next, with reference to FIGS. 8A-8E and FIGS. 9A-9E, a method of manufacturing a wiring substrate according to the present embodiment will be described. FIGS. 8A-8E and FIGS. 9A-9E are cross-sectional views showing a method of manufacturing a wiring substrate according to the present embodiment.

[0064] First, as shown in FIG. 8A, the substrate 11 is prepared, and an easy adhesion layer 15 and an adhesion layer 16 are sequentially formed over substantially the entire surface of the substrate 11. As a method of forming the easy adhesion layer 15, roll coating, gravure coating, gravure reverse coating, microgravure coating, slot die coating, die coating, knife coating, inkjet coating, dispenser coating, kiss coating, or spray coating may be used. As a method of forming the adhesion layer 16, vapor deposition, sputtering, or plasma CVD may be used.

[0065] Next, as shown in FIG. 8B, a conductive layer 51 is formed over substantially the entire surface of the substrate 11 and on the adhesion layer 16. In the present embodiment, the thickness of the conductive layer 51 is 200 nm. However, it is not limited thereto, and the thickness of the conductive layer 51 can be appropriately selected within the range of 10 nm or more and 1000 nm or less. In the present embodiment, the conductive layer 51 is formed by sputtering using copper. As a method for forming the conductive layer 51, a plasma CVD method may also be used.

[0066] Next, as shown in FIG. 8C, a photocurable insulating resist 52 is supplied over substantially the entire surface of the substrate 11 and on the adhesion layer 16. Examples of the photocurable insulating resist 52 include organic resins such as epoxy resins.

[0067] Subsequently, a transparent imprint mold 53 having convex portions 53a is prepared (FIG. 8D). The mold 53 and the substrate 11 are brought close to each other, and the photocurable insulating resist 52 is spread between the mold 53 and the substrate 11. Next, light irradiation is performed from the mold 53 side to cure the photocurable insulating resist 52, thereby forming an insulating layer 54. As a result, a trench 54a having a shape in which the convex portions 53a are transferred is formed on the surface of the insulating layer 54. The trench 54a has a planar shape pattern corresponding to the first-direction wiring 21 and the second-direction wiring 22.

[0068] Thereafter, the mold 53 is peeled off from the insulating layer 54 to obtain the insulating layer 54 having the cross-sectional structure shown in FIG. 8E. The direction in which the mold 53 is peeled off from the insulating layer 54 is preferably the Y direction in which the longer first-direction wiring 21 extends.

[0069] In this way, by forming the trench 54a on the surface of the insulating layer 54 by the imprint method, the shape of the trench 54a can be made fine. Note that the present invention is not limited thereto, and the insulating layer 54 may be formed by photolithography. In this case, a resist pattern is formed by photolithography so as to expose the conductive layer 51 corresponding to the first-direction wiring 21 and the second-direction wiring 22.

[0070] At this time, residues of the insulating material may remain at the bottom of the trench 54a of the insulating layer 54. Therefore, wet treatment using an organic solvent such as a permanganate solution or N-methyl-2-pyrrolidone, or dry treatment using oxygen plasma is performed to remove the residues of the insulating material.

[0071] In this way, by removing the residues of the insulating material, a trench 54a exposing the conductive layer 51 can be formed as shown in FIG. 9A.

[0072] Next, as shown in FIG. 9B, the trench 54a of the insulating layer 54 is filled with the conductor 55. In the present embodiment, using the conductive layer 51 as a seed layer, the trench 54a of the insulating layer 54 is filled with copper by an electrolytic plating method. Note that the conductor 55 has a planar shape corresponding to the first-direction wiring 21 and the second-direction wiring 22.

[0073] When filling the trench 54a with the conductor 55 using the electrolytic plating method in this way, for example, by appropriately adjusting the plating solution used for electrolytic plating, (i) the area average grain size of the metal crystals 29 included in the conductor 55 (the first-direction wiring 21 and the second-direction wiring 22) can be set to 300 nm or more, and / or (ii) the surface roughness Ra of the conductor 55 (the first-direction wiring 21 and the second-direction wiring 22) can be set to 100 nm or less. For example, when the conductor 55 is made of copper and a copper sulfate bath mainly containing copper sulfate is used as the plating solution, by appropriately adjusting various components such as brighteners including copper sulfate, sulfuric acid, and surfactants contained in the plating solution, the crystal growth rate can be suppressed, and as a result, the area average grain size of the metal crystals 29 included in the conductor 55 can be increased, and the surface roughness Ra of the conductor 55 can be suppressed. In this way, when a plating solution mainly containing copper sulfate is used, compared with the case of using a plating solution mainly containing general copper cyanide, the area average grain size of the metal crystals 29 included in the conductor 55 can be increased, and the outer surface of the conductor 55 can be made smooth.

[0074] Subsequently, as shown in FIG. 9C, the insulating layer 54 is removed. In this case, the insulating layer 54 on the substrate 11 is removed by performing wet processing using an organic solvent such as a permanganate solution or N-methyl-2-pyrrolidone, or dry processing using oxygen plasma.

[0075] Next, as shown in FIG. 9D, the conductive layer 51 and the adhesion layer 16 on the surface of the substrate 11 are removed. At this time, wet processing using a copper etching solution such as an aqueous solution of ferric chloride, an aqueous solution of cupric chloride, an aqueous solution of ammonium peroxydisulfate, an aqueous solution of sodium peroxydisulfate, sulfuric acid, or hydrogen peroxide solution is performed to etch the conductive layer 51 and the adhesion layer 16 so that the surface of the substrate 11 is exposed. Further thereafter, a blackening layer may be formed on the surface of the conductor 55 (the first-direction wiring 21 and the second-direction wiring 22).

[0076] Thereafter, as shown in FIG. 9E, a protective layer 17 is formed so as to cover the easy-adhesion layer 15, the conductor 55, and the adhesion layer 16 on the substrate 11. As a method for forming the protective layer 17, 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, or flexographic printing may be used.

[0077] In this way, a wiring substrate 10 having the substrate 11 and the mesh wiring layer 20 disposed on the substrate 11 is obtained (FIG. 9E). In this case, the mesh wiring layer 20 includes the first-direction wiring 21 and the second-direction wiring 22. At this time, a power supply unit 40 may be formed by a part of the conductor 55. Alternatively, a flat power supply unit 40 may be separately prepared and this power supply unit 40 may be electrically connected to the mesh wiring layer 20.

[0078] [Operation of the Present Embodiment] Next, the operation of the wiring substrate having such a configuration will be described.

[0079] As shown in FIG. 10, the wiring board 10 is incorporated into an image display device 90 having a display 91. The wiring board 10 is disposed on the display 91. Examples of such an image display device 90 include portable terminal devices such as smartphones and tablets. The mesh wiring layer 20 of the wiring board 10 is electrically connected to the wireless communication circuit 92 of the image display device 90 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 90.

[0080] By the way, particularly in high-frequency electromagnetic waves that have been used in recent years, the number of times electrons pass through the grain boundaries of the metal constituting the mesh wiring layer 20 per unit time increases, so that the current is difficult to flow and the transmission loss may increase.

[0081] On the other hand, according to the present embodiment, (i) the area average grain size of the metal crystals 29 included in the first-direction wiring 21 and the second-direction wiring 22 is 300 nm or more, and / or (ii) the surface roughness Ra of the first-direction wiring 21 and the second-direction wiring 22 is 100 nm or less. As a result, the density of the metal crystals 29 becomes relatively low, so that the total area of the grain boundaries decreases, the electron diffusion at the grain boundaries decreases, it is possible to suppress the difficulty of current flow, and the transmission loss of the electromagnetic wave can be reduced. In addition, since the surfaces of the first-direction wiring 21 and the second-direction wiring 22 are smooth, the transmission loss of the electromagnetic wave can be reduced.

[0082] In recent years, the development of mobile terminal devices for fifth-generation communication, i.e., 5G (Generation), has been underway. When the mesh wiring layer 20 of the wiring board 10 is used as, for example, an antenna for 5G (especially a millimeter-wave antenna), the radio waves (millimeter waves) transmitted and received by the mesh wiring layer 20 are of higher frequency than, for example, the radio waves transmitted and received by an antenna for 4G. Generally, when an alternating current flows through a wiring, the higher the frequency, the less likely the current is to flow through the central part of the wiring, and the more likely the current is to flow on the surface of the wiring. This phenomenon where the current flows only on the surface when an alternating current flows through the wiring is called the skin effect. Also, the skin depth refers to the depth from the surface of the wiring at which the current is attenuated to 1 / e (about 0.37) times that of the current on the surface of the wiring where the current flows most easily. This skin depth δ (see Figure 6) can generally be obtained by the following formula.

[0083] [Number]

[0084] In the above formula, ω is the angular frequency (= 2πf), μ is the magnetic permeability (4π × 10 -7 [H / m] in a vacuum), and σ is the conductivity of the conductor constituting the wiring (5.8 × 10 7 [S / m] in the case of copper). The skin depth δ of a copper wiring is approximately 2.3 μm when the frequency is 0.8 GHz, approximately 1.3 μm when the frequency is 2.4 GHz, approximately 1.0 μm when the frequency is 4.4 GHz, and approximately 0.85 μm when the frequency is 6 GHz. Also, the radio waves (millimeter waves) transmitted and received by an antenna for 5G are of higher frequency (28 GHz to 39 GHz) than, for example, the radio waves transmitted and received by an antenna for 4G. For example, when the frequency of the current is 28 GHz to 39 GHz, δ is approximately 0.3 μm to approximately 0.4 μm.

[0085] Therefore, the smoother the surface of the mesh wiring layer 20, that is, the smaller the surface roughness Ra, the more effectively the increase in the skin resistance of the wiring can be suppressed, and the transmission loss generated during radio wave transmission and reception can be reduced. On the other hand, when the surface roughness Ra of the wiring is large as a comparative example, the skin resistance of the wiring increases, and there is a possibility of transmission loss occurring during radio wave transmission and reception. In particular, when the radio wave (millimeter wave) transmitted and received by the mesh wiring layer 20 is a high frequency, by suppressing the surface roughness Ra of the first-direction wiring 21 and the second-direction wiring 22 to 100 nm or less, the skin resistance of the first-direction wiring 21 and the second-direction wiring 22 can be reduced. Therefore, it is possible to prevent the skin resistance of the first-direction wiring 21 and the second-direction wiring 22 from hindering the flow of current in the mesh wiring layer 20.

[0086] Moreover, according to the present embodiment, the line widths of the first-direction wiring 21 and the second-direction wiring 22 are 0.1 μm or more and 5.0 μm or less. Thereby, the first-direction wiring 21 and the second-direction wiring 22 can be made difficult to be seen by the naked eye, and the visibility of the display 91 can be prevented from being deteriorated.

[0087] In addition, in the present embodiment, since the dielectric tangent of the substrate 11 is 0.002 or less, the dielectric loss generated during radio wave transmission and reception can be reduced, particularly when the radio wave (millimeter wave) transmitted and received by the mesh wiring layer 20 is a high frequency.

[0088] Moreover, according to the present embodiment, since the first-direction wiring 21 and the second-direction wiring 22 are made of a plating layer, the height H1 of the first-direction wiring 21 and the height H2 of the second-direction wiring 22 can be increased.

[0089] In addition, according to the present embodiment, since the easy adhesion layer 15 is formed on the substrate 11, the adhesiveness between the substrate 11 and the first-direction wiring 21 and the second-direction wiring 22 can be enhanced. Further, since the adhesion layer 16 is formed on the easy adhesion layer 15, the adhesion between the substrate 11 and the first-direction wiring 21 and the second-direction wiring 22 can be further enhanced.

[0090] Also, according to this embodiment, since the protective layer 17 is formed on the substrate 11 so as to cover the first-direction wiring 21 and the second-direction wiring 22, the first-direction wiring 21 and the second-direction wiring 22 can be protected from external impacts and the like.

[0091] Also, according to this embodiment, the mesh wiring layer 20 has a function as an antenna. The mesh wiring layer 20 as this antenna can be disposed on the outermost surface side of the image display device 90. Therefore, the communication performance can be improved as compared with the case where the antenna is built in the image display device 90. Further, since a plurality of mesh wiring layers 20 as antennas can be arranged in the plane of the image display device 90, the communication performance can be further improved.

[0092] In particular, when the mesh wiring layer 20 is used as an antenna, it is possible to suppress a decrease in the performance as an antenna, specifically, antenna performance such as S11. Here, S11 refers to, for example, a value obtained by dividing the power reflected from the input terminal of the antenna by the power incident on the input terminal of the antenna. S11 can be measured, for example, using a network analyzer.

[0093] In this embodiment, the case where the mesh wiring layer 20 has a function as an antenna has been described as an example, but the present invention is not limited thereto. The mesh wiring layer 20 may perform functions such as hovering (a function that allows the user to operate without directly touching the display), fingerprint authentication, a heater, and noise cut (shielding). Even in such a case, the current can easily flow through the mesh wiring layer 20.

[0094] In this embodiment, both the first-direction wiring 21 and the second-direction wiring 22 are described by taking as an example the case where (i) the area average particle diameter of the metal crystals 29 included in the first-direction wiring 21 and the second-direction wiring 22 is 300 nm or more and / or (ii) the surface roughness Ra of the first-direction wiring 21 and the second-direction wiring 22 is 100 nm or less. However, the present invention is not limited to this. Even if only one of the first-direction wiring 21 and the second-direction wiring 22 satisfies (i) the area average particle diameter of the metal crystals 29 included in the first-direction wiring 21 and the second-direction wiring 22 is 300 nm or more and / or (ii) the surface roughness Ra of the first-direction wiring 21 and the second-direction wiring 22 is 100 nm or less, it is acceptable.

[0095] [Examples] Next, specific examples in this embodiment will be described.

[0096] (Fabrication of Mesh Pattern) Wiring boards of the examples and comparative examples were prepared as follows.

[0097] (Example 1) On a substrate made of a PET film, a copper mesh pattern was fabricated by electrolytic plating using a plating solution mainly composed of copper sulfate. As a result, a wiring board 100 including a substrate 101 and a mesh wiring layer 102 was obtained (see FIG. 11). The size of the mesh wiring layer 102 was 2 mm in width × 7.5 mm in length, and a solid copper region 103 with the same width of 2 mm and a length of 1 mm was formed at the terminal end of the 7.5-mm length. The mesh wiring layer 102 and the solid copper region 103 were electrically connected. Further, a copper solid region (ground) 104 with a width of 6 mm or more and a length of 6 mm or more was formed by opening a width of 1 to 2 mm from the solid copper region 103. The mesh wiring layer 102 had a lattice shape, and the solid regions 103 and 104 were solid. The width of each wiring was 1 μm both in the width direction and the length direction of the mesh wiring layer 102. The height of each wiring was 1 μm, and the pitch of each wiring was 100 μm. The height of the solid regions 103 and 104 was 1 μm.

[0098] (Example 2) A wiring board of Example 2 was fabricated in the same manner as in Example 1, except that various components of the plating solution were different when fabricating the mesh wiring layer 102 and the solid areas 103 and 104.

[0099] (Comparative Example 1) A wiring board of Comparative Example 1 was fabricated in the same manner as in Example 2, except that various components of the plating solution were different when fabricating the mesh wiring layer 102 and the solid areas 103 and 104.

[0100] For the wiring boards 100 of the examples and comparative examples, the area average grain size of copper crystals and the surface roughness Ra of the wiring were measured respectively. The area average grain size of copper crystals was analyzed by the SEM-EBSD method. Also, the surface roughness Ra of the wiring was measured using a laser microscope (VK-X250 (control unit), VK-X260 (measurement unit) manufactured by Keyence Corporation, laser wavelength 408 nm).

[0101] Using a vector network analyzer (8722ES manufactured by Agilent Technologies), the G signal of the coaxial cable was connected to the solid copper area 104 with a width of 6 mm or more and a length of 6 mm or more, the S signal was connected to the solid area 103 at the end of the mesh pattern, and the S11 of 8 - 12 GHz of the mesh wiring layer 102 was measured.

[0102] As a result, those having a peak of -10 dB or less were evaluated as "◎" (excellent), those having a peak of -8 dB or less were evaluated as "○" (good), and those not showing a peak of -8 dB or less were evaluated as "×" (poor). The above evaluation results are shown in Table 1.

[0103]

Table 1

[0104] It is also possible to appropriately combine a plurality of components disclosed in the above embodiments and modification examples as needed. Alternatively, some components may be deleted from all the components shown in the above embodiments and modification examples.

Claims

1. A wiring board, comprising: a substrate; and a mesh wiring layer disposed on the substrate and including a plurality of wirings, wherein the wirings include a plurality of metal crystals disposed adjacent to each other via grain boundaries in a cross-sectional view, and an area average particle size of the metal crystals is 300 nm or more.

2. The wiring board according to claim 1, wherein the substrate has transparency.

3. The wiring board according to claim 1 or 2, wherein an aperture ratio of the mesh wiring layer is 87% or more.

4. The wiring board according to any one of claims 1 to 3, wherein the wiring includes a surface roughness Ra, and the surface roughness Ra is 100 nm or less.

5. The wiring board according to any one of claims 1 to 4, wherein a line width of the wiring is 0.1 µm or more and 5.0 µm or less.

6. The wiring board according to any one of claims 1 to 5, wherein the mesh wiring layer is an antenna.

7. The wiring board according to any one of claims 1 to 6, wherein the wiring includes gold, silver, copper, platinum, tin, aluminum, iron, or nickel.

8. The wiring board according to any one of claims 1 to 7, wherein a dielectric loss tangent of the substrate is 0.002 or less.

9. The wiring board according to any one of claims 1 to 8, wherein a thickness of the substrate is 5 µm or more and 200 µm or less.

10. The wiring board according to any one of claims 1 to 9, wherein the substrate includes a cycloolefin polymer or a polynorbornene polymer.

11. The wiring board according to any one of claims 1 to 10, wherein the mesh wiring layer exists only in a part of the substrate.

12. The wiring board according to any one of claims 1 to 11, wherein the surface roughness Ra is 90 nm or less.

13. A method for manufacturing a wiring board, comprising: a step of preparing a substrate; and a step of forming a mesh wiring layer including a plurality of wirings on the substrate, wherein the wirings include a plurality of metal crystals disposed adjacent to each other via grain boundaries in a cross-sectional view, and an area average particle size of the metal crystals is 300 nm or more.

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