JP7516060B2 - Transparent antenna and RF tag - Google Patents

Description

The present invention relates to a transparent antenna and an RF tag.

For example, in automobiles, film antennas are known that are installed on the windshield to receive various radio waves such as television radio waves and FM radio waves, as well as radio waves related to position coordinate information from GPS (global positioning system) satellites used in car navigation systems.

Film antennas are also used for radio frequency identification (RFID), which is widely used in many industries, including transportation, delivery, manufacturing, waste management, mail tracking, airline baggage matching, and toll management. RFID tags and labels are useful for tracking deliveries from source to customer and through the customer's supply chain.

For such film antennas, a technology has been proposed that improves the invisibility of the conductive pattern by forming the antenna using a conductive pattern (see, for example, Patent Documents 1 to 5).

JP 2011-66610 A JP 2011-91788 A JP 2017-175540 A JP 2003-209421 A JP 2016-105624 A

As described in the above prior art, making the conductive pattern finer improves its invisibility. However, making the conductive pattern finer can make it difficult to join the conductive pattern that constitutes the antenna to the IC chip that is electrically connected to it.

Patent Document 4 discloses that when bonding an IC chip, a child antenna pattern is formed around the IC chip in advance, an IC chip label is produced, and then bonding is performed so that the child antenna pattern of the IC chip label is conductive with the parent antenna pattern formed on the substrate. Patent Document 5 discloses that an anisotropic conductive paste (ACP) is used to bond the IC chip and the conductive pattern that constitutes the antenna.

However, when using conductive thin wires with a line width of 5 μm or less as the pattern forming the antenna, particularly in order to improve the invisibility of the pattern, it can be difficult to join the conductive pattern constituting the antenna to the IC chip electrically connected to it.

The present invention was made in consideration of the above problems, and aims to provide a transparent antenna with excellent bonding properties with semiconductor elements and an RF tag equipped with the transparent antenna.

The inventors conducted extensive research to solve the above problems. As a result, they discovered that the above problems could be solved by adjusting the shape of the conductive pattern in the area where the anisotropic conductive adhesive comes into contact, and thus completed the present invention.

That is, the present invention is as follows.
[1]
A transparent substrate;
The optical fiber cable includes a bonding portion disposed on the transparent base material and an antenna portion electrically connected to the bonding portion,
the bonding portion has a first conductive pattern having a first conductive thin wire,
the antenna portion has a second conductive pattern having a second conductive thin wire,
A transparent antenna that satisfies one or more of the following conditions A to C.
Condition A: the line width _W1 of the first conductive thin wire is wider than the line width _W2 of the second conductive thin wire. Condition B: the height _T1 of the first conductive thin wire is higher than the height _T2 of the second conductive thin wire. Condition C: the occupancy area ratio _S1 of the first conductive pattern per unit area is larger than the occupancy area ratio _S2 of the second conductive pattern per unit area [2]
The line width _W1 is 0.5 μm or more and 200 μm or less,
The line width _W2 is 0.25 μm or more and 5.0 μm or less.
The transparent antenna according to [1].
[3]
The height _T1 is 0.06 μm or more and 1.0 μm or less,
The height _T2 is 0.05 μm or more and 0.95 μm or less.
The transparent antenna according to [1] or [2].
[4]
The pitch _P1 of the first conductive thin wires is smaller than the pitch _P2 of the second conductive thin wires,
The pitch _P1 is 1.0 μm or more and 10 μm or less,
The pitch _P2 is 60 μm or more and 300 μm or less.
The transparent antenna according to any one of [1] to [3].
[5]
The occupied area ratio _S1 is 30% or more and 80% or less,
The occupied area ratio _S2 is 0.1% or more and 7.0% or less.
The transparent antenna according to any one of [1] to [4].
[6]
[1] to [5], and a transparent antenna according to any one of the above.
a semiconductor element electrically connected to the joint of the transparent antenna;
RF tag.
[7]
The semiconductor element is electrically connected to the joint portion by an anisotropic conductive adhesive.
The RF tag described in [6].

The present invention provides a transparent antenna with excellent bonding properties for semiconductor elements and an RF tag equipped with the transparent antenna.

FIG. 2 is a plan view showing a straight type RF tag of the present embodiment. FIG. 2 is an enlarged view of S1a in FIG. FIG. 2 is a plan view showing a loop type RF tag of the present embodiment. FIG. 4 is an enlarged view of S1b in FIG. FIG. 5 is an enlarged view (a) of S2 in FIG. 2 and FIG. 4. FIG. 5 is an enlarged view (a) of S3 in FIG. 2 and FIG. 4. 1 is a schematic cross-sectional view showing a state in which a semiconductor element is bonded via an anisotropic conductive adhesive onto a bonding portion of an RF tag of this embodiment that mainly satisfies condition A. FIG. 10 is a schematic cross-sectional view showing a state in which a semiconductor element is bonded via an anisotropic conductive adhesive onto a bonding portion of an RF tag of this embodiment that mainly satisfies condition B. FIG. 13 is a schematic cross-sectional view showing a state in which a semiconductor element is bonded via an anisotropic conductive adhesive onto a bonding portion of an RF tag of this embodiment that mainly satisfies condition C. FIG. 1 is a schematic cross-sectional view of an RF tag according to an embodiment of the present invention.

The following describes in detail an embodiment of the present invention (hereinafter referred to as "the present embodiment"); however, the present invention is not limited to this embodiment, and various modifications are possible without departing from the gist of the present invention. In the drawings, the same elements are given the same reference numerals, and duplicated explanations are omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[Transparent antenna]
The transparent antenna of the present embodiment has a transparent substrate, a bonding portion disposed on the transparent substrate, and an antenna portion electrically bonded to the bonding portion, the bonding portion having a first conductive pattern having a first conductive thin wire, the antenna portion having a second conductive pattern having a second conductive thin wire, and satisfies one or more of the following conditions A to C.
Condition A: The line width _W1 of the first conductive thin wire is wider than the line width _W2 of the second conductive thin wire. Condition B: The height _T1 of the first conductive thin wire is higher than the height _T2 of the second conductive thin wire. Condition C: The occupancy area ratio _S1 of the first conductive pattern per unit area is higher than the occupancy area ratio _S2 of the second conductive pattern per unit area.

1 shows a plan view of an embodiment of an RF tag 100 including a transparent antenna 10 according to the present invention. The transparent antenna 10 according to the present invention has a transparent substrate 11, a current collector 12 and an antenna section 13 formed on the transparent substrate 11. The current collector 12 is electrically connected to the antenna section 13, and is a section that collects electricity generated by the antenna section 13 in response to a predetermined frequency toward the semiconductor element 14. The joint section 121 is a section of the current collector 12 that is joined to the semiconductor element 14. Hereinafter, there is no need to distinguish between the current collector 12 and its joint section 121, and when referring to both, the term "current collector 12 (joint section 121)" may be used. In addition, even when the term "current collector 12" is used, it does not mean any part of the current collector 12 other than the joint section 121.

2 shows an enlarged view of S1a in FIG. 1. In FIG. 2, the current collecting part 12 has a joint 121 with two or more ends facing each other. The semiconductor element 14 is electrically joined to this joint 121 by an anisotropic conductive adhesive or the like. The antenna part 13 is electrically connected to the joint 121, and can receive radio waves of a predetermined frequency and transmit an electrical signal to the semiconductor element 14, or transmit radio waves of a predetermined frequency according to the output of the semiconductor element 14. Although the current collecting part 12 is shown in FIG. 2 as being trapezoidal, the shape of the current collecting part 12 is not limited to this. As an example, the current collecting part 12 in FIG. 2 has an area equal to or several times the projected area of the semiconductor element in a plan view, and it is preferable that the current collecting part 12 is almost covered when the semiconductor element 14 is joined to the joint 121. In this case, it can be said that the current collecting part 12 is substantially composed of only the joint 121.

Figure 1 shows a straight-type transparent antenna 10 and RF tag 100 having two antenna parts 13 with a current collecting part 13 having a joint 121 between them, but the configuration of the current collecting part 12 (joint 121) and antenna part 13 is not limited to this. For example, the transparent antenna 10 and RF tag 100 of this embodiment may be a loop-type transparent antenna 10 and RF tag 100 in which the current collecting part 12 is loop-shaped and the antenna part 13 is installed around the loop-shaped current collecting part 12, as shown in Figure 3.

Figure 4 shows an enlarged view of S1b in Figure 3. As shown in Figure 4, the loop-type current collecting part 12 has a joint 121 where the tips of the loops face each other. The joint 121 is the tip of the current collecting part 12, and is where it is joined to the semiconductor element 14.

In addition, the transparent antenna of this embodiment is not limited to the configuration of a λ/2 dipole antenna, but may have other antenna configurations, such as a grounded λ/4 monopole antenna, and accordingly, the current collecting section 12 (joint section 121) and the antenna section 13 can take various forms.

Next, the bonding properties of the semiconductor element will be described. As described above, the semiconductor element 14 is electrically bonded to the bonding portion 121 by an anisotropic conductive adhesive or the like. The anisotropic conductive adhesive mainly contains a resin binder and conductive fine particles dispersed in the resin binder. By placing these between the electrodes and applying heat and pressure, the resin binder is spread and the conductive fine particles electrically bond the electrodes. Depending on the difference in the bonding process, the anisotropic conductive adhesive is known to be of the film type, paste type, liquid type, etc.

In such bonding, the anisotropic conductive adhesive needs to be spread to a thickness that allows the conductive fine particles to electrically bond the electrodes. Therefore, it is desirable for the anisotropic conductive adhesive to sufficiently wet and spread over the bonding area. However, if the anisotropic conductive adhesive seeps out and spreads too much over the peripheral area of the semiconductor element, it may cause poor appearance of the RF tag and may also cause unintended electrical bonding. In particular, when a transparent antenna is used, if metallic parts resulting from the anisotropic conductive adhesive are generated in the peripheral area of the semiconductor element, the metallic parts will be particularly noticeable, resulting in a loss of the product value of transparency. In addition, the miniaturization of semiconductor elements makes it more difficult to adjust the amount of anisotropic conductive adhesive used, and there is a tendency for the yield to decrease due to seepage.

In contrast, in this embodiment, the line width, height, or occupancy rate of the first conductive pattern 300 constituting the joint 121 is adjusted to provide the joint with a function of preventing the diffusion of the anisotropic conductive adhesive. More specifically, the line width of the first conductive pattern 300 is widened (condition A), the height is increased (condition B), or the occupancy rate is increased (condition C). Note that in the current collecting section 12, the line width, height, or occupancy rate of the first conductive pattern 300 in the joint 121 and other parts may be the same or different.

This makes it possible to prevent the anisotropic conductive adhesive from seeping out beyond the first conductive thin wires of the first conductive pattern 300, and allows for precise control of the position where the anisotropic conductive adhesive stops spreading between the patterns. In addition, the conductive fine particles 21 can more easily bond the first conductive pattern 300 and the semiconductor element 14. This reduces bonding defects and improves the stability of the wiring bonding.

In this embodiment, improving the bonding performance means improving the bonding reliability and suppressing the occurrence of poor appearance. Each configuration will be described in detail below.

[Transparent substrate]
In this embodiment, a transparent substrate 11 is used. Here, "transparent" means that the visible light transmittance is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. Here, the visible light transmittance can be measured in accordance with JIS K 7361-1:1997.

The transparent substrate 11 may be made of one type of material, or may be a laminate of two or more types of materials. In addition, when the substrate is a multilayer body in which two or more types of materials are laminated, the substrate may be a laminate of organic substrates or inorganic substrates, or a laminate of an organic substrate and an inorganic substrate.

Examples of the transparent substrate 11 include a single-layer sheet of a core layer, a laminate sheet having a core layer and a first outermost layer, a laminate sheet having a core layer and a second outermost layer, a laminate sheet having a first outermost layer and a second outermost layer, and a laminate sheet having a core layer, a first outermost layer and a second outermost layer. In addition, the above laminate sheets may further have other layers between the core layer and the first outermost layer, between the core layer and the second outermost layer, or between the first outermost layer and the second outermost layer.

When the transparent substrate 11 is a single-layer sheet of the core layer, the current collecting section 12 (joint section 121) and the antenna section 13 are formed on the surface of the core layer. When the transparent substrate 11 is a laminated sheet, the first outermost layer refers to the layer that constitutes the surface on which the current collecting section 12 (joint section 121) and the antenna section 13 are formed, and the second outermost layer refers to the back surface of the first outermost layer. The structure of each layer is described in detail below.

(Core layer)
The material constituting the core layer is not particularly limited, but is preferably one that contributes to improving the mechanical strength of the substrate. The material of such a core layer is not particularly limited, but for example, a transparent inorganic substrate such as glass; a transparent organic substrate such as an acrylic acid ester, a methacrylic acid ester, a polyethylene terephthalate, a polybutylene terephthalate, a polyethylene naphthalate, a polycarbonate, a polyarylate, a polyvinyl chloride, a polyethylene, a polypropylene, a polystyrene, a nylon, an aromatic polyamide, a polyether ether ketone, a polysulfone, a polyether sulfone, a polyimide, or a polyether imide. Among these, by using polyethylene terephthalate, the productivity (cost reduction effect) for manufacturing a transparent antenna is more excellent. In addition, by using polyimide, the heat resistance of the transparent antenna is more excellent. When using polyimide, it is more preferable to use a so-called transparent polyimide that has excellent light transmittance of visible light. Furthermore, by using polyethylene terephthalate and/or polyethylene naphthalate, the adhesion between the transparent substrate and the conductive thin wire is more excellent.

The core layer may be made of one type of material, or may be made of two or more laminated materials. In addition, when the core layer is a multilayer body in which two or more materials are laminated, the substrate may be made of organic substrates or inorganic substrates laminated together, or an organic substrate and an inorganic substrate laminated together.

The thickness of the core layer is preferably 5 μm or more and 500 μm or less, and more preferably 10 μm or more and 100 μm or less.

(First outermost layer)
When the transparent substrate 11 is a laminate, the first outermost layer is a layer that constitutes the surface on which the current collecting portion 12 (joint portion 121) and the antenna portion 13 are formed. The material that constitutes the first outermost layer is not particularly limited, but is preferably one that contributes to improving the adhesion between the core layer and each of the current collecting portion 12 (joint portion 121) and the antenna portion 13. In addition, when the transparent substrate 11 has a first outermost layer and a second outermost layer, but does not have a core layer, it is preferable that the first outermost layer contributes to improving the adhesion between the second outermost layer and each of the current collecting portion 12 (joint portion 121) and the antenna portion 13.

The components contained in such a first outermost layer are not particularly limited, but examples thereof include silicon compounds (e.g., (poly)silanes, (poly)silazanes, (poly)silthians, (poly)siloxanes, silicon, silicon carbide, silicon oxide, silicon nitride, silicon chloride, silicate salts, zeolites, silicides, etc.), aluminum compounds (e.g., aluminum oxide, etc.), magnesium compounds (e.g., magnesium fluoride), etc.

Among these, silicon compounds are preferred, and siloxanes are more preferred. By using such components, the transparency and durability of the transparent antenna tend to be further improved.

The silicon compound is not particularly limited, but examples thereof include condensation products of polyfunctional organosilanes, and polycondensates obtained by hydrolysis reaction of polyfunctional organosilanes or their oligomers with polyvinyl acetate.

Examples of polyfunctional organosilanes include, but are not limited to, bifunctional organosilanes such as dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diphenyldimethoxysilane, and diphenyldiethoxysilane; trifunctional organosilanes such as methyltrimethoxysilane, methyltriethoxysilane, and phenyltrimethoxysilane; and tetrafunctional organosilanes such as tetramethoxysilane and tetraethoxysilane.

The first outermost layer can be formed by applying a composition containing the components contained in the first outermost layer to the core layer and drying it. The first outermost layer may also be formed by a gas phase film formation method such as PVD or CVD. The composition for forming the first outermost layer may contain a dispersant, a surfactant, a binder, etc., as necessary.

The thickness of the first outermost layer is preferably 0.01 μm or more and 100 μm or less, more preferably 0.01 μm or more and 10 μm or less, and even more preferably 0.01 μm or more and 1 μm or less. By having the thickness of the first outermost layer within the above range, the adhesion is further improved, and the transparency and durability of the transparent antenna tend to be further improved.

By laminating the first outermost layer on the core layer, for example, when the current collecting section 12 (joint section 121) and the antenna section 13 are formed by sintering the metal components in the ink using a baking method such as plasma, it is possible to prevent etching of the core layer by the plasma or the like at the locations that are not covered by the current collecting section 12 (joint section 121) and the antenna section 13.

Furthermore, this first outermost layer preferably has an antistatic function to prevent disconnection of the current collecting section 12 (joint section 121) and the antenna section 13 due to static electricity. In order for the first outermost layer to have an antistatic function, it is preferable that the first outermost layer contains at least one of a conductive inorganic oxide and a conductive organic compound.

(Second outermost layer)
When the transparent substrate 11 is a laminate, the second outermost layer means the back side of the first outermost layer. The components contained in the second outermost layer are not particularly limited, but examples thereof include melamine-based compounds, alkyd-based compounds, fluorine-based compounds, silicone-based compounds, polyethylene wax, fatty acids, and fatty acid esters. Among these, melamine-based compounds, alkyd-based compounds, fluorine-based compounds, and silicone-based compounds are preferred, and melamine-based compounds and alkyd-based compounds are more preferred. By using such components, the transparency and durability of the transparent antenna tend to be further improved.

The thickness of the second outermost layer is preferably 0.01 μm or more and 100 μm or less, more preferably 0.01 μm or more and 10 μm or less, and even more preferably 0.01 μm or more and 1 μm or less. By having the thickness of the second outermost layer within the above range, the transparency and durability of the transparent antenna 10 tend to be further improved.

(Other layers)
The other layer disposed between the core layer and the first outermost layer, between the core layer and the second outermost layer, or between the first outermost layer and the second outermost layer is not particularly limited, and may be, for example, an easy-adhesion layer. The easy-adhesion layer is used for the purpose of improving the adhesion between the core layer and the first outermost layer, between the core layer and the second outermost layer, or between the first outermost layer and the second outermost layer.

[Joint]
The joint 121 is the tip of the current collecting part 12 and is a place where it is joined to the semiconductor element 14. The joint 121 (current collecting part 12) is electrically joined to the antenna part 13 and has a first conductive pattern 300. Here, the first conductive pattern 300 is a continuous pattern that has conductivity from any point in the pattern to any other point. Note that the current collecting part 12 may have one or more first conductive patterns 300 that are electrically independent. In addition, a portion of the current collecting part 12 where the first conductive pattern 300 is not formed is referred to as a first opening 301.

Figures 2 and 4 show enlarged views of the S1a portion of Figure 1 and the S1b portion of Figure 3. Figures 2 and 4 show an example in which the current collecting portion 12 (joint portion 121) formed of the first conductive pattern 300 made of a thick conductive thin wire and the antenna portion 13 formed of the second conductive pattern 400 made of a thinner conductive thin wire are electrically joined.

Figure 5 shows an enlarged view of part S2 in Figures 2 and 4 as one embodiment of the joint 121. In Figure 5, the first conductive pattern 300 is shown as a grid pattern formed by a plurality of first conductive thin wires crossing each other in a mesh-like pattern, but the first conductive pattern 300 is not limited to this and may be another pattern in which the first conductive thin wires cross and maintain conductivity. In addition, the first conductive pattern 300 may be a regular pattern or an irregular pattern. Furthermore, the first conductive thin wires may be straight or curved.

The shape of the first opening 301 is not particularly limited, but may be, for example, a triangle; a quadrangle such as a square, rectangle, or diamond; a pentagon; a hexagon; or a combination of multiple polygons.

The configuration of the current collecting section 12 is not particularly limited, but examples include a configuration in which a current collecting section 12 of a size that is almost hidden by the semiconductor element 14 is provided so as to connect multiple antenna sections 13 (see FIG. 1), a configuration in which a semiconductor element 14 is joined to a part of a loop-shaped current collecting section 12 and an antenna section 13 is provided on the outer periphery of the loop-shaped current collecting section 12 (see FIG. 3), and a configuration in which a current collecting section 12 is provided at an arbitrary position of one antenna section 13. In addition, the joining position (joint 121) of the semiconductor element 14 to the current collecting section 12 is not particularly limited, but a position where the tip of the current collecting section 12 faces is preferable.

[Antenna section 13]
The antenna section 13 is electrically connected to the current collecting section 12 (joint section 121) and has a second conductive pattern 400. Here, the second conductive pattern 400 is a continuous pattern having conductivity from any point in the pattern to any other point. The antenna section 13 may have a plurality of electrically independent second conductive patterns 400. In addition, a portion of the antenna section 13 where the second conductive pattern 400 is not formed is referred to as a second opening 401.

The antenna unit 13 has various shapes depending on the type. The type of antenna unit 13 is not particularly limited, but examples include electric field antennas such as dipole antennas and patch antennas that generate current due to changes in the electric field, and magnetic field antennas such as loop antennas that generate current due to changes in the magnetic field.

The external shape of the antenna section 13 may be any known shape. For example, a linear dipole antenna is not limited to a straight line type, and may have a variety of known shapes, such as a folded type, a meander type, a helical type, or a spiral type. Patch antennas may also have any shape, such as a polygon or a circle, or may have a shape with a notch. Furthermore, the antenna section 13 may be a combination of multiple of these shapes.

It is also preferable that the antenna section 13 has a second conductive pattern having a second conductive thin wire. FIG. 6 shows an enlarged view of the S3 portion of FIGS. 2 and 4 as one embodiment of the antenna section 13. In FIG. 6, the second conductive pattern 400 is shown as a grid pattern formed by a plurality of second conductive thin wires crossing each other in a mesh-like manner, but the second conductive pattern 400 is not limited thereto and may be another pattern in which the second conductive thin wires cross and maintain conductivity. The second conductive pattern 400 may be a regular pattern or an irregular pattern. Furthermore, the second conductive thin wires may be straight or curved.

The shape of the portion where the second conductive pattern 400 is not formed, i.e., the second opening 401, is not particularly limited, but may be, for example, a triangle; a quadrangle such as a square, rectangle, or diamond; a pentagon; a hexagon; or a combination of multiple types of polygons.

Figures 1 and 3 show examples of the configuration of an RF tag in which the antenna section 13 is an electric field antenna. In Figure 1, two antenna sections 13 are formed around a relatively small current collecting section 12 that is almost hidden by a semiconductor element 14, and in Figure 3, the antenna section 13 is formed so as to surround the loop-shaped current collecting section 12. In both Figures 1 and 3, the antenna section 13 has a rectangular outer shape. In Figures 1 and 3, the antenna section 13 is not formed by applying a conductive layer solidly on a flat surface, but is formed by a grid pattern formed by a second opening 401 and a second conductive pattern 400. This ensures the transparency of the area in which the antenna section is formed while ensuring the function of the antenna section 13 as an electric field antenna.

(First Conductive Pattern 300 and Second Conductive Pattern 400)
The first conductive pattern 300 and the second conductive pattern 400 include a conductive component. The conductive component is not particularly limited, but examples thereof include conductive metals and conductive polymers. The first conductive pattern 300 and the second conductive pattern 400 may also include a non-conductive component. The conductive metal is not particularly limited, but examples thereof include gold, silver, copper, and aluminum. Among these, silver or copper is preferred, and copper, which is relatively inexpensive, is more preferred. By using such a conductive metal, the conductivity of the transparent antenna tends to be even more excellent. In addition, known conductive polymers can be used, and examples thereof include polyacetylene and polythiophene.

The non-conductive components are not particularly limited, but include, for example, metal oxides, metal compounds, and organic compounds. More specifically, these non-conductive components are derived from the components contained in the ink described below, and include metal oxides, metal compounds, and organic compounds that remain in the conductive thin wires after baking among the components contained in the ink.

The content ratio of the conductive component in the first conductive pattern 300 and the second conductive pattern 400 is preferably 50 mass% or more, more preferably 60 mass% or more, and even more preferably 70 mass% or more, each independently. The upper limit of the content ratio of the conductive component is not particularly limited, but is 100 mass%. The content ratio of the non-conductive component in the first conductive pattern 300 and the second conductive pattern 400 is preferably 50 mass% or less, more preferably 40 mass% or less, and even more preferably 30 mass% or less, each independently. The lower limit of the content ratio of the non-conductive component is not particularly limited, but is 0 mass%.

(Line width W)
The line width W of the first conductive thin wire and the second conductive thin wire in the first conductive pattern 300 and the second conductive pattern 400 refers to the line width W when the conductive thin wire is projected onto the surface of the transparent substrate 11 from the surface side on which the conductive pattern of the transparent substrate 11 is arranged. In the conductive thin wire having a trapezoidal cross section, the width of the surface of the conductive thin wire in contact with the transparent substrate 11 is the line width W.

The line width _W1 of the first conductive thin wire is preferably 0.5 to 200 μm, more preferably 1 to 150 μm, and even more preferably 2 to 100 μm. When the line width _W1 of the first conductive thin wire is within the above range, the bonding property is improved and the antenna characteristics such as gain tend to be improved. In addition, when the line width _W1 of the first conductive thin wire is 200 μm or less, the visibility of the first conductive pattern 300 is further reduced and the transparency of the current collecting part 12 (bonding part 121) tends to be further improved.

The line width _W2 of the second conductive thin wire is preferably 0.25 to 7.5 μm, more preferably 0.25 to 5.0 μm, even more preferably 0.25 to 4.0 μm, and particularly preferably 0.50 to 3.0 μm. When the line width _W2 of the second conductive thin wire is 0.25 μm or more, the conductivity of the antenna portion 13 tends to be further improved. In addition, the decrease in conductivity due to oxidation or corrosion of the conductive thin wire surface can be sufficiently suppressed. On the other hand, when the line width _W2 of the second conductive thin wire is 10.0 μm or less, the visibility of the second conductive pattern 400 tends to be further reduced, and the transparency of the antenna portion 13 tends to be further improved.

As condition A, the line width W ₁ of the first conductive thin wire in this embodiment is preferably wider than the line width W ₂ of the second conductive thin wire. FIG. 7 shows a schematic cross-sectional view showing a state in which a semiconductor element is bonded via an anisotropic conductive adhesive onto a joint of an RF tag of this embodiment that mainly satisfies condition A. By widening the line width W ₁ , the anisotropic conductive adhesive is less likely to exceed the first conductive thin wire with a wide line width, and seepage is further suppressed. The difference (W ₁ -W ₂ ) is preferably 4 to 200 μm, more preferably 10 to 150 μm, and even more preferably 20 to 100 μm. By having the difference (W ₁ -W ₂ ) within the above range, the bondability tends to be further improved.

In addition, in the first conductive pattern 300 and/or the second conductive pattern 400, when the line width _W1 and/or the line width _W2 are not a constant value but have multiple values, it is preferable that all the line widths _W1 and/or the line widths _W2 satisfy the above range.

(Height T)
The height _T1 of the first conductive thin wire is preferably 0.06 to 1.0 μm, more preferably 0.08 to 0.9 μm, and even more preferably 0.11 to 0.8 μm. When the height _T1 is 0.06 μm or more, the conductivity tends to be further improved. In addition, the decrease in conductivity due to oxidation or corrosion of the conductive thin wire surface tends to be sufficiently suppressed. On the other hand, when the height _T1 is 1.0 μm or less, high transparency tends to be exhibited at a wide viewing angle.

The height _T2 of the second conductive thin wire is preferably 0.05 to 0.95 μm, more preferably 0.07 to 0.8 μm, and even more preferably 0.1 to 0.5 μm. When the height _T2 is 0.05 μm or more, the conductivity tends to be further improved. In addition, the decrease in conductivity due to oxidation or corrosion of the conductive thin wire surface tends to be sufficiently suppressed. On the other hand, when the height _T2 is 0.95 μm or less, high transparency tends to be exhibited at a wide viewing angle.

As condition B, the height T ₁ of the first conductive thin wire in this embodiment is preferably higher than the height T ₂ of the second conductive thin wire. FIG. 8 shows a schematic cross-sectional view of a semiconductor element bonded via an anisotropic conductive adhesive on the bonding portion of the RF tag of this embodiment that mainly satisfies condition B. By increasing the height T ₁ , the anisotropic conductive adhesive is less likely to exceed the first conductive thin wire with a large line width, and exudation is further suppressed. Furthermore, since the conductive fine particles 21 are more likely to fit into the first opening 301, the stability of the wiring bonding between the first conductive pattern 300 and the semiconductor element 14 tends to be further improved. The difference (T ₁ -T ₂ ) is preferably 0.01 to 0.9 μm, more preferably 0.05 to 0.8 μm, and even more preferably 0.1 to 0.7 μm. By having the difference (T ₁ -T ₂ ) within the above range, the bonding property tends to be further improved.

In addition, in the first conductive pattern 300 and/or the second conductive pattern 400, when the height _T1 and/or the height _T2 are not a constant value but are multiple values, it is preferable that all the heights _T1 and/or the heights _T2 satisfy the above range.

(Pitch P)
The pitch _P1 of the first conductive thin wires is preferably 0.5 to 25 μm, more preferably 1.0 to 10 μm, and even more preferably 2.0 to 7.0 μm. By having the pitch _P1 within the above range, the bonding property is improved and the antenna characteristics such as gain tend to be improved. The pitch P is the distance between the conductive thin wires.

The pitch _P2 of the second conductive thin wire is preferably 20 to 1000 μm, more preferably 40 to 750 μm, and even more preferably 60 to 300 μm. When the pitch _P2 is 20 μm or more, the transparency of the antenna portion 13 tends to be further improved. Furthermore, when the pitch _P2 is 1000 μm or less, the conductivity tends to be further improved.

As a condition D other than conditions A to C, the pitch P ₁ of the first conductive thin wires in this embodiment is preferably smaller than the pitch P ₂ of the second conductive thin wires. This results in the first conductive pattern being densely arranged. Therefore, the anisotropic conductive adhesive is less likely to exceed the densely arranged first conductive pattern, and exudation is further suppressed. Furthermore, the density of the first openings 301 in which the conductive fine particles 21 are accommodated also increases, so that the stability of the wiring bond between the first conductive pattern 300 and the semiconductor element 14 tends to be further improved. The difference (P ₂ -P ₁ ) is preferably 30 to 1000 μm or less, more preferably 50 to 500 μm or less, and even more preferably 100 to 300 μm. By having the difference (P ₂ -P ₁ ) within the above range, the visibility of the joint is reduced, and the design tends to be improved.

In addition, in the first conductive pattern 300 and/or the second conductive pattern 400, when the pitch _P1 and/or the pitch _P2 are not a constant value but are a plurality of values, it is preferable that all the pitches _P1 and/or the pitches _P2 satisfy the above range.

(Occupancy area ratio S)
The occupied area ratio _S1 of the first conductive pattern 300 is preferably 30 to 90%, more preferably 30 to 80%, further preferably 40 to 80%, and particularly preferably 50 to 80%. By having the occupied area ratio _S1 within the above range, the bondability is further improved, and the antenna characteristics such as gain tend to be further improved.

The occupied area ratio _S2 of the second conductive pattern 400 is preferably 0.1 to 7.0%, more preferably 0.5 to 5.0%, and even more preferably 1.0 to 3.0%. When the occupied area ratio _S2 is 0.1% or more, the characteristics of the antenna portion 13 tend to be further improved. In addition, when the occupied area ratio _S2 is 7.0% or less, the transparency of the antenna portion 13 tends to be further improved.

As condition C, the occupancy rate S ₁ of the first conductive pattern of this embodiment is preferably larger than the occupancy rate S ₂ of the second conductive pattern. FIG. 9 shows a schematic cross-sectional view showing a state in which a semiconductor element is bonded via an anisotropic conductive adhesive on a joint of an RF tag of this embodiment that mainly satisfies condition C. By increasing the occupancy rate S ₁ , the first conductive pattern is densely arranged. Therefore, the anisotropic conductive adhesive is less likely to exceed the densely arranged first conductive pattern, and exudation is further suppressed. Furthermore, the density of the first opening 301 in which the conductive fine particles 21 are accommodated is also increased, so that the stability of the wiring bond between the first conductive pattern 300 and the semiconductor element 14 tends to be further improved. In addition, FIG. 9 shows an example in which the line width W ₁ is narrowed to increase the occupancy rate S ₁ , but instead of or in addition to this, the occupancy rate S ₁ may be increased by narrowing the pitch P ₁ . The difference (S ₁ -S ₂ ) is preferably 3 to 50%, more preferably 9 to 50%, and even more preferably 15 to 50%. When the difference (S ₁ -S ₂ ) is within the above range, the visibility of the joint decreases, and the design tends to improve.

The "occupancy area ratio S of the conductive pattern" can be calculated for the region on the transparent substrate where the conductive pattern is formed by the following formula: The region on the transparent substrate where the conductive pattern is formed is the range shown by S2 and S3 in Fig. 6, excluding edges and the like where the conductive pattern is not formed.
Conductive pattern occupation area ratio S
= (area occupied by conductive pattern/area of transparent substrate 11) x 100

The line width, height, pitch, and area ratio of the conductive pattern can be confirmed by observing the surface or cross section of the transparent antenna with an electron microscope, laser microscope, optical microscope, or the like. Methods for adjusting the line width and pitch of the conductive pattern to the desired range include adjusting the grooves of the plate used in the transparent antenna manufacturing method described below, and adjusting the average particle size of the metal particles in the ink.

(shape)
The cross-sectional shapes of the first conductive thin wire and the second conductive thin wire can be defined by the width W and height T of the conductive thin wire. Based on the height T of the conductive thin wire, the heights from the interface between the transparent substrate 11 and the conductive thin wire are defined as 0.50T and 0.90T. Furthermore, the width of the conductive thin wire at a height of 0.50T is defined as W _0.50 , and the width of the conductive thin wire at a height of 0.90T is defined as W _0.90 . In this case, W _0.50 /W ₀ is preferably 0.70 to 0.99, more preferably 0.75 to 0.99 or less, and even more preferably 0.80 to 0.95. Furthermore, W _0.90 /W _0.50 is preferably 0.50 to 0.95, more preferably 0.55 to 0.90, and even more preferably 0.60 to 0.85. In the transparent antenna of this embodiment, it is preferable that _W0.50 / _W0 is greater than _W0.90 / _W0.50 . In other words, it is preferable that the width of the conductive thin wire gradually decreases from a height position at a thickness of 0.50T from the interface of the conductive thin wire on the transparent substrate 11 side toward a height position at a thickness of 0.90T.

As described below, the transparent antenna of this embodiment can be formed by a printing method using ink, and the conductive thin wire formed by this method has the characteristic shape described above. Other methods for forming conductive thin wires include methods using nanoimprinting and lithography, and methods using other nanowires, but the conductive thin wires created by these methods differ from the conductive thin wires formed by the printing method in terms of the shape described above.

(Sheet Resistance)
The sheet resistance of the first conductive pattern 300 and the second conductive pattern 400 is preferably 0.1 Ω/sq or more and 1,000 Ω/sq or less, more preferably 0.1 Ω/sq or more and 500 Ω/sq or less, even more preferably 0.1 Ω/sq or more and 100 Ω/sq or less, still more preferably 0.1 Ω/sq or more and 20 Ω/sq or less, and even more preferably 0.1 Ω/sq or more and 10 Ω/sq or less.

The sheet resistance of a transparent antenna can be measured by the following method. First, a portion of the transparent antenna with a conductive pattern disposed over the entire surface is cut out in a rectangular shape to obtain a measurement sample. A current collector for measuring sheet resistance, electrically connected to the conductive pattern, is formed at both ends of the obtained measurement sample, and the electrical resistance R (Ω) between the current collectors provided at both ends is measured. Using the above-mentioned electrical resistance R (Ω) and the width direction length L (mm) and depth direction length D (mm) corresponding to the distance between the current collectors of the measurement sample, the sheet resistance R _s (Ω/sq) can be calculated by the following formula.
_Rs = R/L x D

The sheet resistance of the transparent antenna 10 tends to decrease by increasing the height of the conductive thin wires. It can also be adjusted by selecting the type of metal material that makes up the conductive thin wires.

(Visible Light Transmittance)
The visible light transmittance _VT1 of the first conductive pattern 300 is preferably 30 to 80%, more preferably 40 to 75%, and further preferably 45 to 70%. Here, the visible light transmittance can be measured by calculating the transmittance in the visible light range (360 to 830 nm) in accordance with the total light transmittance of JIS K 7361-1:1997.

The visible light transmittance _VT2 of the second conductive pattern 400 is preferably 80% or more and 100% or less, and more preferably 90% or more and 100% or less.

The visible light transmittance of the transparent antenna 10 tends to improve by reducing the line width of the conductive pattern and increasing the occupied area rate.

[Method of manufacturing a transparent antenna]
The method for manufacturing the transparent antenna may include a pattern forming step of forming a pattern on the transparent substrate 11 using ink containing a metal component, and a firing step of firing the ink to form the current collecting portion 12 (bonding portion 121) and the antenna portion 13. The method may also include a surface treatment step of treating the surface of the transparent substrate 11.

[Surface treatment process]
In the surface treatment step, a first outermost layer can be provided on one surface of the core layer, and the surface roughness of the transparent substrate 11 can be adjusted.

The method for forming the first outermost layer is not particularly limited, but examples include a method in which the components that form the first outermost layer are formed on one side of the core layer using a vapor phase deposition method such as PVD or CVD. Another method includes a method in which a composition containing the components that form the first outermost layer is applied to one side of the core layer and dried to form the first outermost layer.

There are no particular limitations on the method for increasing the surface roughness of the transparent substrate 11, which is generally smooth. For example, a method may be used in which an easy-to-adhere layer with high surface roughness is provided between the core layer and the first outermost layer, and the first outermost layer is then formed on the easy-to-adhere layer. This allows the first outermost layer to reflect the surface roughness of the easy-to-adhere layer.

[Pattern Forming Process]
The pattern forming process is a process of forming a pattern using an ink containing a metal component. The pattern forming process is not particularly limited as long as it is a plate-based printing method using a plate having grooves of a desired conductive pattern, but includes, for example, a process of coating the surface of a transfer medium with ink, a process of placing the ink-coated transfer medium surface opposite the convex surface of a relief plate, pressing and contacting the surface to transfer the ink on the transfer medium surface to the convex surface of the relief plate, and a process of placing the transfer medium surface on which the ink remains opposite the surface of a transparent substrate 11, pressing and contacting the surface to transfer the ink remaining on the transfer medium surface to the surface of the transparent substrate 11. In addition, when a first outermost layer is formed on the transparent substrate 11, the ink is transferred to the surface of the first outermost layer.

(ink)
The ink used in the pattern formation process contains a conductive component and a solvent, and may contain, as necessary, a surfactant, a dispersant, a reducing agent, etc. When the conductive component is a metal component, the metal component may be contained in the ink as metal particles or as a metal complex.

The average primary particle size of the metal particles is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less. The lower limit of the average primary particle size of the metal particles is not particularly limited, but may be 1 nm or more. By making the average primary particle size of the metal particles 100 nm or less, the line width W of the obtained conductive thin wire can be made thinner. Note that the "average primary particle size" refers to the particle size of each individual metal particle (so-called primary particle), and is distinguished from the average secondary particle size, which is the particle size of an aggregate (so-called secondary particle) formed by gathering multiple metal particles together.

The metal particles are not particularly limited, but examples include metal oxides such as copper oxide, metal compounds, and core/shell particles in which the core is copper and the shell is copper oxide. The form of the metal particles can be appropriately determined from the viewpoint of dispersibility and sinterability.

The surfactant is not particularly limited, but examples include fluorine-based surfactants. By using such surfactants, the coatability of the ink on the transfer medium (blanket) and the smoothness of the coated ink are improved, and a more uniform coating film tends to be obtained. It is preferable that the surfactant is capable of dispersing metal components and is configured so as not to remain after firing.

The dispersant is not particularly limited, but examples thereof include dispersants that form a non-covalent bond or interact with the metal component surface, and dispersants that form a covalent bond with the metal component surface. Examples of functional groups that form a non-covalent bond or interact with the metal component surface include dispersants having a phosphate group. Use of such dispersants tends to further improve the dispersibility of the metal component.

Further, examples of the solvent include alcohol-based solvents such as monoalcohols and polyhydric alcohols; alkyl ether-based solvents; hydrocarbon-based solvents; ketone-based solvents; ester-based solvents; and the like. These may be used alone or in combination of one or more. For example, a monoalcohol having 10 or less carbon atoms may be used in combination with a polyhydric alcohol having 10 or less carbon atoms. By using such a solvent, the coating property of the ink on the transfer medium (blanket), the transfer property of the ink from the transfer medium to the letterpress, the transfer property of the ink from the transfer medium to the transparent substrate, and the dispersibility of the metal components tend to be further improved. Note that the solvent is preferably configured to be capable of dispersing the metal components and to be less likely to remain after firing.

[Firing process]
In the baking process, for example, the metal components in the ink transferred to the surface of the transparent substrate 11 are sintered to form the current collecting section 12 (joint section 121) and the antenna section 13. The baking method is not particularly limited as long as the metal components are fused to form a metal component sintered film. The baking may be performed, for example, in a baking furnace, or may be performed using plasma, a heating catalyst, ultraviolet light, vacuum ultraviolet light, an electron beam, infrared lamp annealing, flash lamp annealing, a laser, or the like. If the resulting sintered film is easily oxidized, it is preferable to bake in a non-oxidizing atmosphere. In addition, if the metal oxide or the like is difficult to reduce only by the reducing agent that may be contained in the ink, it is preferable to bake in a reducing atmosphere.

A non-oxidizing atmosphere is an atmosphere that does not contain oxidizing gases such as oxygen, and includes inert atmospheres and reducing atmospheres. An inert atmosphere is, for example, an atmosphere filled with inert gases such as argon, helium, neon, and nitrogen. A reducing atmosphere refers to an atmosphere in which reducing gases such as hydrogen and carbon monoxide are present. The ink coating film (dispersion coating film) may be baked by filling the baking furnace with these gases and forming a closed system. The baking furnace may also be a flow system in which the dispersion coating film is baked while flowing these gases. When the dispersion coating film is baked in a non-oxidizing atmosphere, it is preferable to once evacuate the baking furnace to remove the oxygen in the baking furnace and replace it with a non-oxidizing gas. The baking may be performed in a pressurized atmosphere or a reduced pressure atmosphere.

The baking temperature is not particularly limited, but is preferably 20°C to 400°C, more preferably 50°C to 300°C, and even more preferably 80°C to 200°C. A baking temperature of 400°C or less is preferable because it allows the use of a substrate with low heat resistance. Also, a baking temperature of 20°C or more is preferable because the formation of the sintered film proceeds sufficiently and the conductivity tends to be good. The obtained sintered film contains conductive components derived from metal components, and may also contain non-conductive components depending on the components used in the ink and the baking temperature.

[RF tag]
The RF tag 100 of this embodiment includes the transparent antenna 10 and a semiconductor element 14 electrically joined to a joint 121 of the transparent antenna 10. Fig. 9 shows a cross-sectional view of the RF tag 100 of this embodiment. As shown in Fig. 9, the semiconductor element 14 is preferably electrically joined to the joint 121 by an anisotropic conductive adhesive 15 such as an anisotropic conductive paste or an anisotropic conductive film.

Figures 1 and 2 show an RF tag 100 that is a passive tag that does not have a built-in battery and operates using radio waves received from a reader/writer as its energy source, but the RF tag 100 of this embodiment may also be an active tag that further has a built-in battery (not shown) and uses the power for transmission and reception and for the internal circuitry, or a semi-passive tag that has a built-in battery as a power source for other sensors and sensors. Note that in this embodiment, an RF tag refers to one that has the transparent antenna 10 and is capable of transmitting and receiving a specific frequency. Therefore, even if it is called an IC tag, it is included in the RF tag of this embodiment as long as it meets the above configuration.

The semiconductor element 14 may be a known one depending on the application of the RF tag 100. The configuration of the semiconductor element 14 is not particularly limited, but may have functional units such as a memory unit, a power supply rectification unit, a receiver unit, a control unit, and a transmitter unit.

An example of the operation of each functional unit and the RF tag 100 of this embodiment when it is a passive type will be described. First, the antenna unit 13 of the RF tag 100 receives radio waves from the reader/writer, and an electromotive force is generated by electromagnetic induction or the like. Then, this electromotive force activates the semiconductor element 14 of the RF tag 100. At that time, the power supply rectifier converts the AC input to the antenna unit 13 into DC and supplies power to the circuit of the semiconductor element 14. In parallel with this, the receiver demodulates the carrier wave received from the reader/writer into a signal sequence and sends the signal sequence to the control unit. The control unit reads/writes information to the memory unit and passes the information processing result as a signal sequence to the transmitter unit according to the signal sequence received from the receiver. Here, the memory unit stores various information such as product information according to the application of the RF tag. Finally, the transmitter modulates the signal sequence received from the control unit into a carrier wave and transmits it from the antenna unit 13. Then, the antenna of the reader/writer receives the carrier wave and performs information processing. In this embodiment, RFID refers to a system consisting of an RF tag and a reader/writer.

The frequency bands that can be used by the RF tag 100 of this embodiment are not particularly limited, but examples include LF band (medium wave band): 120 to 130 kHz, HF band (short wave band): 13.56 MHz, UHF band (ultra high frequency band): 900 MHz band, and microwave: 2.45 GHz band. The type of antenna unit 13 can be adjusted appropriately according to the frequency band to be used. For example, when using the HF band, a loop type antenna can be used, and when using the UHF band, a dipole type antenna can be used.

The transmission and reception methods that can be used by the RF tag 100 of this embodiment are not limited to the radio wave method described above, and may also include an electromagnetic coupling method in which high frequency waves are applied to coils on the transmitting and receiving sides, and information is transmitted through the mutual induction that occurs, or an electromagnetic induction method in which information is transmitted through a magnetic field generated near the antenna.

The diameter d of the conductive fine particles contained in the anisotropic conductive adhesive is preferably 3.0 to 10 μm, and more preferably 4.0 to 9.0 μm. When the diameter d of the conductive fine particles is within the above range, the bonding property tends to be further improved.

It is preferable that the pitch P ₁ of the first conductive pattern formed on current collecting portion 12 (joint portion 121), the thickness T ₁ thereof, and the diameter d of the conductive fine particles satisfy the following formula (1).
(P ₁ /2) ² < (d/2) ² - (d/2 - T ₁ ) ² Equation (5)

The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited in any way by the following examples.

Example 1
Polyethylene terephthalate (PET) was used as a core layer, and a composition containing silicon oxide nanoparticles and a conductive organosilane compound was applied to one side of the core layer and dried to form a first outermost layer containing silicon oxide and having a thickness of 50 nm, thereby obtaining substrate A.

Next, 20 parts by mass of cuprous oxide nanoparticles with a particle diameter of 21 nm, 4 parts by mass of a dispersant (manufactured by BYK-Chemie, product name: Disperbyk-145), 1 part by mass of a surfactant (manufactured by Seimi Chemical, product name: S-611), and 75 parts by mass of ethanol were mixed and dispersed to prepare an ink containing 20% by mass of cuprous oxide nanoparticles.

Then, ink was applied to the surface of the transfer medium, and the ink-coated transfer medium surface was placed opposite a plate having grooves of a conductive pattern, and pressed and brought into contact with each other to transfer a portion of the ink on the transfer medium surface to the convex surface of the plate. After that, the transfer medium surface coated with the remaining ink was placed opposite substrate A, and pressed and brought into contact with each other to transfer the ink in the desired conductive pattern onto substrate A. Next, the conductive pattern ink (dispersion coating film) was baked by flash lamp annealing in a room temperature environment using a Pulseforge 1300 manufactured by NovaCentrix.

As a result, the conductive pattern in the antenna portion was in a square grid shape, with a line width _W2 of 2.0 μm, a height _T2 of 0.5 μm, an opening pitch _P2 of 60 μm, and an occupied area ratio _S2 of 6%. The conductive pattern in the joint portion was in a square grid shape, with a line width _W1 of 3.0 μm, a height _T1 of 0.5 μm, an opening pitch _P1 of 6.0 μm, and an occupied area ratio _S1 of 75%. The antenna portion was a dipole antenna in which two rectangular conductive patterns with a vertical dimension of 49 mm in the long side direction and a horizontal dimension of 10 mm in the short side direction were provided at an interval of 2 mm so that the short sides faced each other, as shown in FIG. 1, and the gap between the joints formed between the two conductive patterns was 150 μm. In both the joint portion and the antenna portion, the conductive thin wire had a W _0.50 /W ₀ ratio greater than W _0.90 /W _0.50 .

Example 2
On the substrate A provided with the alignment mark, ink was transferred to the conductive pattern of the antenna part using the first plate and transfer medium. Next, after alignment was performed using the alignment mark, ink was transferred to the conductive pattern of the joint part using the second plate and transfer medium. As a result, a conductive pattern with a line width W ₂ of 3.0 μm, a height T ₂ of 0.5 μm, an opening pitch P ₂ of 60 μm, and an occupied area ratio S ₂ of 10% was formed as the antenna part. In addition, a conductive pattern with a line width W ₁ of 3.0 μm, a height T ₁ of 1.0 μm, an opening pitch P ₁ of 6.0 μm, and an occupied area ratio S ₁ of 75% was formed as the joint part. In this way, the antenna part and joint part were formed similarly to those in Example 1, except that they had the above line width and opening pitch, and the height of the conductive thin line was made different between the antenna part and the joint part. The dimensions of the joint part and the conductive thin line of the antenna part are shown in Table 1.

Example 3
Except for the fact that the conductive pattern in the antenna part had a line width _W2 of 3.0 μm, an antenna part and a joint part were formed similarly to those in Example 1. The dimensions of the conductive thin lines in the joint part and the antenna part are shown in Table 1.

Comparative Example 1
As the antenna part, a conductive pattern was formed with a line width _W2 : 3.0 μm, a height _T2 : 0.5 μm, an opening pitch _P2 : 60 μm, and an occupied area ratio _S2 of 6%. As the bonding part, a conductive pattern was formed with a line width _W1 : 3.0 μm, a height _T1 : 0.5 μm, an opening pitch _P1 : 6.0 μm, and an occupied area ratio _S1 of 6%, similar to the antenna part.
The dimensions of the conductive thin wires in the joint and antenna are shown in Table 1.

[Line width, pitch, and area ratio]
The line width, pitch, and occupied area ratio were calculated from planar photographs taken with an optical microscope.

[RF tag]
A semiconductor element was bonded to the bonding portion of the transparent antenna obtained as described above using an anisotropic conductive paste having conductive particles with an average particle size of 10 μm, to obtain an RF tag.

[Joint reliability]
As a result of measuring the radiation characteristics of the RF tags of Examples 1 to 3, a communication distance of 1.3 m was obtained at 920 MHz, and antenna characteristics equivalent to those of a metal dipole antenna made of copper foil with the same external dimensions were obtained (Evaluation of connection reliability as "good" in Table 1). On the other hand, the RF tag of Comparative Example 1 did not respond to communication at 920 MHz, and no antenna characteristics were obtained (Evaluation of connection reliability as "x" in Table 1). It was estimated that the RF tag of Comparative Example 1 had insufficient conductivity between the antenna part and the IC chip.

〔Poor appearance〕
The joints of Examples 1, 2, and 3 and Comparative Example 1 were observed from the back side of the transparent substrate with a digital microscope (VHX-100 manufactured by KEYENCE). There were no air bubbles trapped in the opening of the substrate of Example 1, and adhesion stability was ensured. Furthermore, there was no overflow of the anisotropic conductive paste from the joint to the antenna part, and the appearance was excellent (evaluated as ◯ in Table 1).
On the other hand, in the joint of Comparative Example 1, a large number of conductive particles that were not in contact with the conductive pattern were found, and further, the anisotropic conductive paste was observed protruding from the joint to the antenna part, impairing the appearance as a transparent RF tag (evaluated as × in Table 1).

The present invention has industrial applicability as an RF tag that can be used for RFID, in particular as an RF tag used in applications that require design that takes advantage of transparency.

10...transparent antenna, 11...transparent substrate, 12...current collecting portion, 123...joint portion, 13...antenna portion, 14...semiconductor element, 15...anisotropic conductive adhesive, 21...conductive fine particles, 22...resin binder, 100...RF tag, 300...first conductive pattern, 301...first opening, 400...second conductive pattern, 401...second opening.

Claims (6)

A transparent substrate;
The optical fiber cable includes a bonding portion disposed on the transparent base material and an antenna portion electrically connected to the bonding portion,
the bonding portion has a first conductive pattern having a first conductive thin wire,
the antenna portion has a second conductive pattern having a second conductive thin wire,
A transparent antenna that satisfies one or more of the following conditions A to C.
Condition A: the line width _W1 of the first conductive thin wire is wider than the line width W2 of the second conductive thin wire, the line width W1 _{is 0.5} μm or more and 200 μm or less, and the line width W2 _is 0.25 μm or more and 5.0 μm or less.
Condition B: The height _T1 of the first conductive thin wire is higher than the height _T2 of the second conductive thin wire. Condition C: The occupancy area ratio _S1 of the first conductive pattern per unit area is higher than the occupancy area ratio _S2 of the second conductive pattern per unit area. A transparent substrate;
The optical fiber cable includes a bonding portion disposed on the transparent base material and an antenna portion electrically connected to the bonding portion,
the bonding portion has a first conductive pattern having a first conductive thin wire,
the antenna portion has a second conductive pattern having a second conductive thin wire,
A transparent antenna that satisfies one or more of the following conditions A to C.
Condition A: The line width _W1 of the first conductive thin wire is wider than the line width _W2 of the second conductive thin wire.
Condition B: The height _T1 of the first conductive thin wire is higher than the height T2 of the second conductive thin wire, _the height _T1 is 0.06 μm or more and 1.0 μm or less , and the height _T2 is 0.05 μm or more and 0.95 μm or less.
Condition C: The occupancy area ratio S ₁ of the first conductive pattern per unit area is greater than the occupancy area ratio S ₂ of the second conductive pattern per unit area. A transparent substrate;
The optical fiber cable includes a bonding portion disposed on the transparent base material and an antenna portion electrically connected to the bonding portion,
the bonding portion has a first conductive pattern having a first conductive thin wire,
the antenna portion has a second conductive pattern having a second conductive thin wire,
The pitch _P1 of the first conductive thin wires is smaller than the pitch _P2 of the second conductive thin wires,
The pitch _P1 is 1.0 μm or more and 10 μm or less,
The pitch _P2 is 60 μm or more and 300 μm or less,
A transparent antenna that satisfies one or more of the following conditions A to C.
Condition A: The line width _W1 of the first conductive thin wire is wider than the line width _W2 of the second conductive thin wire.
Condition B: The height _T1 of the first conductive thin wire is greater than the height _T2 of the second conductive thin wire.
Condition C: The occupancy area ratio S ₁ of the first conductive pattern per unit area is greater than the occupancy area ratio S ₂ of the second conductive pattern per unit area. A transparent substrate;
The optical fiber cable includes a bonding portion disposed on the transparent base material and an antenna portion electrically connected to the bonding portion,
the bonding portion has a first conductive pattern having a first conductive thin wire,
the antenna portion has a second conductive pattern having a second conductive thin wire,
A transparent antenna that satisfies one or more of the following conditions A to C.
Condition A: The line width _W1 of the first conductive thin wire is wider than the line width _W2 of the second conductive thin wire.
Condition B: The height _T1 of the first conductive thin wire is greater than the height _T2 of the second conductive thin wire.
Condition C: The occupation area ratio S ₁ of the first conductive pattern per unit area is greater than the occupation area ratio S ₂ of the second conductive pattern per unit area, the occupation area ratio S ₁ is 30% or more and 80% or less , and the occupation area ratio S ₂ is 0.1% or more and 7.0% or less. A transparent antenna according to any one of claims 1 to 4 ;
a semiconductor element electrically connected to the joint of the transparent antenna;
RF tag. The semiconductor element is electrically connected to the joint portion by an anisotropic conductive adhesive.
The RF tag according to claim 5 .