Antenna, method for manufacturing an antenna, and method for using an antenna

Abstract

This invention provides an antenna with good antenna characteristics in a specific frequency band, a method for manufacturing the same, and a method for using the same. [Solution] An antenna for radar used in a frequency band of 70 GHz to 90 GHz, wherein the antenna is a patch array antenna, the antenna has a dielectric layer, the dielectric layer is a fluororesin sheet, the oxygen element ratio measured by X-ray photoelectron spectroscopy (XPS) on one or both sides of the fluororesin sheet is 3.0 atomic% or more, and the coefficient of linear expansion (CTE) of the fluororesin sheet is 100 ppm / °C or less.

Description

[Technical Field]

[0001] This disclosure relates to an antenna, a method for manufacturing an antenna, and a method for using an antenna. [Background technology]

[0002] There is a need for a planar antenna suitable for millimeter-wave communication. As such a planar antenna, a planar antenna equipped with a dielectric substrate is known (Patent Document 1). It is known that a resin substrate is used as such a substrate. For example, Patent Document 2 proposes a printed circuit board having a dielectric layer made of fluororesin. Patent Document 3 proposes a resin substrate containing a polymer having arylene groups. Patent Document 4 proposes a printed circuit board having a resin layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2004-320356 [Patent Document 2] Japanese Patent Publication No. 2015-8260 [Patent Document 3] Japanese Patent Publication No. 2016-32098 [Patent Document 4] International Publication No. 2020 / 059606 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] This disclosure aims to provide an antenna with good antenna characteristics in a specific frequency band, a method for manufacturing the same, and a method for using the same. [Means for solving the problem]

[0005] This disclosure relates to a radar antenna for use in the frequency band between 70 GHz and 90 GHz, wherein the relative radiation efficiency measured at a frequency of 82.5 GHz is 17.5 dB or higher.

[0006] The antenna is preferably a patch array antenna. The antenna has a plurality of antenna elements, and the plurality of antenna elements preferably consists of 8 to 16 rows of antenna element arrays, each of which consists of 16 to 64 antenna elements arranged in a straight line, and the 8 to 16 rows of antenna element arrays are arranged parallel to each other.

[0007] The antenna has a dielectric layer, the dielectric layer is a fluororesin sheet containing fluororesin and silica particles, and preferably the oxygen element ratio measured by X-ray photoelectron spectroscopy (XPS) on one or both sides of the fluororesin sheet is 3.0 atomic% or more, and the coefficient of linear expansion (CTE) of the fluororesin sheet is 100 ppm / °C or less. Preferably, the fluororesin is polytetrafluoroethylene. Furthermore, it is preferable that the nitrogen element ratio measured by X-ray photoelectron spectroscopy (XPS) on the same surface of the fluororesin sheet is 1.35 atomic% or more. Furthermore, it is preferable that the silicon element ratio measured by X-ray photoelectron spectroscopy (XPS) on the same surface of the fluororesin sheet is 0.5 atomic% or more. Furthermore, it is preferable that the static contact angle of water measured 1 second after droplet placement with a droplet volume of 2 μL on the same surface of the fluororesin sheet is 105° or less.

[0008] It is preferable that the silica particles are spherical silica. It is preferable to use silica particles treated with a silane coupling agent as the silica particles. It is preferable that the average particle size of the silica particles is 10 μm or less. It is preferable that the fluororesin sheet does not contain glass fibers. The silica particle content is preferably 30% by mass or more relative to the total amount of the fluororesin sheet. The silica particle content is preferably 50% by mass or more relative to the total amount of the fluororesin sheet. The silica particle content is preferably 50% by mass or more and 65% by mass or less relative to the total amount of the fluororesin sheet.

[0009] It is preferable that the dielectric loss tangent value of the fluororesin sheet at 10 GHz is 0.0015 or less. The thickness of the fluororesin sheet is preferably 5 to 250 μm.

[0010] The antenna is preferably formed from a metal-clad laminate in which the metal foil and the dielectric layer are essential layers. Preferably, the metal foil is copper foil. It is preferable that the surface roughness (Rz) of the copper foil is 1.0 μm or less. The surface roughness (Rq) of the copper foil is preferably 0.01 to 0.15 μm. Preferably, the copper foil and the dielectric layer are directly laminated together, and the peel strength at the interface between the copper foil and the dielectric layer is 0.5 kN / m or more. The aforementioned antenna is preferably a millimeter-wave antenna for mobility applications. The relative radiation efficiency measured at a frequency of 82.5 GHz is 18.0 dB or more and 20.0 dB or less. The antenna has a dielectric layer, and the dielectric layer is a fluororesin sheet containing a fluororesin and silica particles. The fluororesin is polytetrafluoroethylene, the silica particles are spherical silica, and the content of the silica particles is 50% by mass or more and 65% by mass or less based on the total amount of the fluororesin sheet. On one or both surfaces of the fluororesin sheet, the oxygen element ratio measured by X-ray photoelectron spectroscopy (XPS) is 3.0 atomic% or more and 25.0 atomic% or less. On the same surface of the fluororesin sheet, the silicon element ratio measured by X-ray photoelectron spectroscopy (XPS) is 0.5 atomic% or more and 10.0 atomic% or less. It is preferable that the linear expansion rate (CTE) of the fluororesin sheet is 31 ppm / °C or more and 70 ppm / °C or less.

[0011] The present disclosure is also a method for manufacturing the antenna, including a dielectric layer forming step of forming a dielectric layer. In the dielectric layer forming step, fluororesin particles and silica particles are mixed to form a film and surface-treated.

[0012] In the dielectric layer forming step, it is preferable to form a film and surface-treat using a composition substantially composed of the fluororesin particles and filler particles including at least the silica particles. It further includes a metal-clad laminate forming step of forming a metal-clad laminate. In the metal-clad laminate forming step, it is preferable to laminate the dielectric layer and a metal foil, heat at 18^0~390 °C, and press-mold under vacuum or in an inert gas atmosphere at a pressure of 0.5~5 MPa. It is preferable to further include an etching step of etching the metal-clad laminate.

[0013] The present disclosure is also a method for using the antenna, including a step of using the antenna in a frequency band of 70 GHz or more and 90 GHz or less. The present disclosure relates to an antenna for radar used in a frequency band of 70 GHz or higher and 90 GHz or lower, where the antenna is a patch array antenna, the antenna has a dielectric layer, the dielectric layer is a fluororesin sheet, on one or both surfaces of the fluororesin sheet, the oxygen element ratio measured by X-ray photoelectron spectroscopy (XPS) is 3.0 atomic% or higher, and the linear expansion coefficient (CTE) of the fluororesin sheet is 100 ppm / °C or lower. The antenna is also an antenna. The antenna has a plurality of antenna elements, the plurality of antenna elements are composed of 8 to 16 rows of antenna element arrays in which 16 to 64 antenna elements are arranged in a straight line, the 8 to 16 rows of antenna element arrays are preferably arranged parallel to each other. The fluororesin sheet preferably contains a fluororesin and silica particles. The fluororesin is preferably polytetrafluoroethylene. Furthermore, on one or both surfaces of the fluororesin sheet, the nitrogen element ratio measured by X-ray photoelectron spectroscopy (XPS) is preferably 1.35 atomic% or higher. Furthermore, on one or both surfaces of the fluororesin sheet, the silicon element ratio measured by X-ray photoelectron spectroscopy (XPS) is preferably 0.5 atomic% or higher. Furthermore, on one or both surfaces of the fluororesin sheet, the static contact angle of water measured 1 second after dropping 2 μL of liquid droplets is preferably 105° or lower. The silica particles are preferably spherical silica. As the silica particles, silica particles treated with a silane coupling agent are preferably used. The average particle size of the silica particles is preferably 10 μm or less. The fluororesin sheet preferably does not contain glass fibers. The silica particle content is preferably 30% by mass or more relative to the total amount of the fluororesin sheet. The silica particle content is preferably 50% by mass or more relative to the total amount of the fluororesin sheet. The silica particle content is preferably 50% by mass or more and 65% by mass or less relative to the total amount of the fluororesin sheet. It is preferable that the dielectric loss tangent value of the fluororesin sheet at 10 GHz is 0.0015 or less. It is preferable that the relative permittivity of the fluororesin sheet at 10 GHz is 2.8 or less. The thickness of the fluororesin sheet is preferably 5 to 250 μm. The antenna is preferably formed from a metal-clad laminate in which the metal foil and the dielectric layer are essential layers. Preferably, the metal foil is copper foil. It is preferable that the surface roughness (Rz) of the copper foil is 1.0 μm or less. The surface roughness (Rq) of the copper foil is preferably 0.01 to 0.15 μm. Preferably, the copper foil and the dielectric layer are directly laminated together, and the peel strength at the interface between the copper foil and the dielectric layer is 0.5 kN / m or more. A millimeter-wave antenna for mobility applications is preferable. The aforementioned fluororesin sheet contains fluororesin and silica particles. The fluororesin is polytetrafluoroethylene, The silica particles are spherical silica, The silica particle content is 50% by mass or more and 65% by mass or less relative to the total amount of the fluororesin sheet. On one or both sides of the fluororesin sheet, the oxygen element ratio measured by X-ray photoelectron spectroscopy (XPS) is 3.0 atomic% or more and 25.0 atomic% or less. On one or both sides of the fluororesin sheet, the silicon element ratio measured by X-ray photoelectron spectroscopy (XPS) is 0.5 atomic% or more and 10.0 atomic% or less. It is preferable that the coefficient of linear expansion (CTE) of the fluororesin sheet is 31 ppm / °C or more and 70 ppm / °C or less. This disclosure relates to a method for manufacturing the antenna described above, The process includes a dielectric layer formation step for forming the dielectric layer, In the dielectric layer formation step, fluororesin particles and silica particles are mixed to form a film, and then the surface is treated, which is also a method for manufacturing an antenna. In the dielectric layer formation step, it is preferable to form a film and perform surface treatment using a composition that substantially consists of fluororesin particles and filler particles containing at least the silica particles. The process further includes a metal-clad laminate forming step, In the metal-clad laminate formation process, it is preferable to laminate the dielectric layer and the metal foil, heat them at 180 to 390°C, and press-form them at a pressure of 0.5 to 5 MPa under vacuum or in an inert gas atmosphere. Preferably, the process further includes an etching step for etching the metal-clad laminate. This disclosure relates to the method of using the antenna described above, This also includes a method for using the antenna, which involves using the antenna in a frequency band between 70 GHz and 90 GHz. [Effects of the Invention]

[0014] The antennas of this disclosure, and antennas manufactured by the manufacturing method of this disclosure, exhibit good antenna characteristics in a specific frequency band. Furthermore, good antenna characteristics in a specific frequency band can be achieved by using the antennas of this disclosure. [Modes for carrying out the invention]

[0015] [antenna] The antenna of this disclosure will be described below. The antenna of this disclosure is a radar antenna used in the frequency band between 70 GHz and 90 GHz. Preferably, the antenna of this disclosure is a radar antenna used in the frequency band between 75 GHz and 85 GHz. Hereinafter, the "frequency band between 70 GHz and 90 GHz" may be referred to as the "predetermined frequency band". The antenna of this disclosure transmits and receives radio waves in the predetermined frequency band.

[0016] Because the antenna of this disclosure is used in a predetermined frequency band, it is suitably used as an antenna for millimeter-wave radar that transmits and receives radio waves in the millimeter-wave band (particularly the predetermined frequency band). Because radio waves in the millimeter-wave band (particularly the predetermined frequency band) have high directivity, the antenna of this disclosure is particularly suitably used as a millimeter-wave antenna for mobility applications such as collision avoidance.

[0017] In this disclosure, "mobility" refers to all means of transportation and movement, including all types of automobiles such as private cars, buses, taxis, and trucks; two-wheeled vehicles such as motorcycles, bicycles, and mopeds; and railways, mobility scooters, and compact, single-person personal mobility devices. Furthermore, it is not necessarily limited to those that move on land, but may also include those that move in the air and underwater, such as aircraft, drones, and ships.

[0018] The relative radiation efficiency of the antenna described herein, as measured at a frequency of 82.5 GHz, is 17.5 dB or higher. Hereinafter, "relative radiation efficiency measured at a frequency of 82.5 GHz" may be referred to as "prescribed relative radiation efficiency."

[0019] Here, the higher the predetermined relative radiation efficiency of the antenna, the more miniaturization and energy saving of the antenna can be promoted. In one example, when the energy used by the antenna is the same, an increase of approximately 1.8 dB in the predetermined relative radiation efficiency of the antenna tends to reduce the substrate size of the antenna by approximately 33%. In another example, when the substrate size of the antenna is the same, an increase of approximately 1.8 dB in the predetermined relative radiation efficiency of the antenna tends to reduce the energy used by the antenna by approximately 30%. The predetermined relative radiation efficiency of the antenna in this disclosure is 17.5 dB or higher, and since the predetermined relative radiation efficiency is higher than that of conventional products (see, for example, Comparative Example 1 described later), it can promote miniaturization and energy saving of the antenna.

[0020] From the viewpoint of increasing the predetermined relative radiation efficiency and promoting miniaturization and energy saving of the antenna, the predetermined relative radiation efficiency of the antenna is preferably 18.0 dB or higher, more preferably 18.5 dB or higher, even more preferably 19.0 dB or higher, and even more preferably 19.1 dB or higher. There is no particular upper limit specified for the predetermined relative radiation efficiency, but from the viewpoint of productivity, it is preferably 30.0 dB or lower, more preferably 20.0 dB or lower, and even more preferably 19.5 dB or lower.

[0021] In this disclosure, the predetermined relative radiation efficiency of the antenna is measured by performing a planar scanning near-field measurement using a vector network analyzer (MS46522B manufactured by Anritsu Corporation) under the following conditions: measurement range ±150 mm in the XY axis direction in the XY plane, movement step of 1 mm, distance of 50 mm between the receiving probe and the antenna under measurement, and measurement frequency of 82.5 GHz.

[0022] The antenna of this disclosure comprises, for example, a substrate, an antenna element, and a transmission line. Hereinafter, the "substrate equipped with the antenna element and the transmission line" may be referred to as an "antenna circuit board." The structure of the antenna of this disclosure is not particularly limited and can be appropriately selected from known structures.

[0023] The antennas of this disclosure are preferably patch antennas. Patch antennas are a type of antenna used in high frequency bands above microwaves. Patch antennas are also called microstrip antennas. Patch antennas are a general term for antennas formed using conductors printed on a dielectric substrate (a substrate having a dielectric layer). Patch antennas have the advantage of low manufacturing cost.

[0024] The antenna of this disclosure is more preferably a patch array antenna. A patch array antenna is a patch antenna that creates high directivity by arranging multiple antenna elements on a plane. The directivity of a patch array antenna can be changed by applying signals with different phases and amplitudes to each antenna element. For this reason, patch array antennas have recently been used in applications such as automotive radar antennas. As a method for controlling the directivity of a patch array antenna, for example, a method can be used in which a phase shifter or a variable attenuator is connected to each antenna element of the patch array antenna and these are controlled.

[0025] If the antenna of this disclosure is a patch array antenna, the patch array antenna has a substrate and a plurality of antenna elements provided on the substrate. The plurality of antenna elements are arranged in an array on the substrate.

[0026] The arrangement of antenna elements in a patch array antenna is, for example, an m × n arrangement. m and n are the number of antenna elements, and represent integers of 2 or more. m is preferably an integer of 16 or more. m is preferably an integer of 64 or less. n is preferably an integer of 8 or more. n is preferably an integer of 16 or less. The number of antenna elements can be appropriately selected according to the type, size, and performance of the antenna. A patch array antenna with an m × n arrangement of antennas has m × n antenna elements, where the m × n antenna elements form n rows of antenna elements arranged in a straight line, and the n rows of antenna elements are arranged parallel to each other. In the rows of antenna elements, the m antenna elements are arranged at predetermined intervals from each other. The n rows of antenna elements are arranged at predetermined intervals from each other. The m × n antenna elements are arranged, for example, in a triangular or square arrangement.

[0027] An example of an m×n arrangement of antenna elements in a patch array antenna is an arrangement of (integers between 16 and 64) × (integers between 8 and 16). A patch array antenna with an arrangement of (integers between 16 and 64) × (integers between 8 and 16) has multiple antenna elements, and these multiple antenna elements consist of 8 to 16 rows of antenna elements, each row containing 16 to 64 antenna elements arranged in a straight line, with the 8 to 16 rows of antenna elements arranged parallel to each other. In this arrangement, the multiple antenna elements consist of m×n elements (where m is an integer between 16 and 64, and n is an integer between 8 and 16).

[0028] More specifically, a 16x8 arrangement is a possible m×n configuration of antenna elements in a patch array antenna. A 16x8 patch array antenna has 128 antenna elements, which are arranged in eight rows of 16 antenna elements aligned in a straight line, with these eight rows of antenna elements arranged parallel to each other.

[0029] The antenna elements, transmission lines, and substrate of the antenna disclosed herein will be described below.

[0030] <Antenna element> An antenna element transmits and receives radio waves in a predetermined frequency band. The antenna element is provided, for example, on the surface of a substrate (e.g., one side or both sides). The antenna element is not particularly limited as long as it can transmit and receive radio waves in a predetermined frequency band, but from the viewpoint of efficiently receiving radio waves, it is preferable to use a phased array antenna. A phased array antenna is an antenna that enables transmission and reception in a desired direction by arranging a plurality of patch-shaped antenna elements in an array and controlling the phase of each antenna element. Regardless of the direction of the antenna, a phased array antenna can transmit or receive radio waves in a desired direction by electronically controlling the phase of each antenna element (beam steering).

[0031] Any known antenna element can be used without particular limitation. Examples of antenna elements include loop antenna structures, patch antenna structures, stacked patch antenna structures, patch antenna structures with parasitic elements, inverted F antenna structures, slot antenna structures, plane inverted F antenna structures, monopoles, dipoles, helical antenna structures, Yagi (Yagi-Uda) antenna structures, surface integrated waveguide structures, and antenna elements having resonant elements formed from hybrids of these designs. Different types of antenna elements may be used for different combinations of frequency bands.

[0032] The material constituting the antenna element is not particularly limited as long as it is a conductor. Examples of materials constituting the antenna element include metals such as titanium, silicon, niobium, indium, zinc, tin, gold, silver, copper, aluminum, cobalt, chromium, nickel, lead, iron, palladium, platinum, tungsten, zirconium, tantalum, ruthenium, and hafnium; as well as metal oxides such as ITO (indium and tin oxide), zinc oxide, and tin oxide. Furthermore, materials constituting the antenna element may include those containing two or more of these metals and metal oxides, as well as alloys mainly composed of these metals. Among these, copper is preferred as the material constituting the antenna element from the viewpoint of conductivity. When the antenna element is composed of a metal such as copper, the antenna element may be blackened by forming a film of nitrides, oxides, and sulfides of the metal.

[0033] <Transmission lines> The signals transmitted and received by the antenna element may be transferred to a transceiver circuit via a transmission line. When the antenna is equipped with a transmission line, the transmission line may be provided, for example, on the surface of a substrate (e.g., one side or both sides) or inside the substrate. Examples of transmission lines include coaxial cable paths, microstrip transmission lines, stripline transmission lines, edge-coupled microstrip transmission lines, edge-coupled stripline transmission lines, waveguide structures for transmitting signals in a predetermined frequency band (e.g., coplanar waveguides or grounded coplanar waveguides), and transmission lines formed from combinations of these types of transmission lines. The materials constituting the transmission line are not particularly limited, and the same materials as those constituting the antenna element can be used. The transmission line may include a feed line for supplying power to the antenna.

[0034] Here, we will explain the transmission loss in a power transmission line, which is an example of transmission loss. Power transmission line losses include conductor loss, dielectric loss, and radiated loss. Conductor loss is the loss due to the current flowing on the surface of the line when a conductor is used in the line. Since the current density is approximately inversely proportional to the height of the line, conductor loss tends to be inversely proportional to the height of the line. Dielectric loss occurs due to the electric field in the line volume when a dielectric is used in the line. Dielectric loss tends to be constant with respect to the height of the line. Radiated loss occurs in open-system lines due to discontinuities in the line, such as bends and branches. Radiated loss tends to increase as the height of the line increases. In the case of open-system lines such as microstrip lines, the power transmission line loss is the sum of the three losses: conductor loss, dielectric loss, and radiated loss.

[0035] As described above, the loss in a power transmission line is the sum of three losses: conductor loss, dielectric loss, and radiation loss. Therefore, reducing dielectric loss can reduce the loss in the power transmission line. To reduce dielectric loss, it is preferable to use a material with a small dielectric loss tangent for the dielectric layer for the following reasons. The dielectric layer and its dielectric loss tangent of the antenna disclosed herein will be described later. The dielectric loss tangent tanδ is a parameter that represents the loss of the dielectric layer. The dielectric loss tangent tanδ is the ratio of the real part to the imaginary part of the complex relative permittivity and is defined as shown in equation (1) below. The propagation constant γ of the transmission line is approximated by equation (2) below when the dielectric loss tangent tanδ is sufficiently smaller than 1. Therefore, dielectric loss α d This is expressed by equation (3) below. As can be understood from equation (3), dielectric loss α d To reduce this, it is preferable to use a material with a small dielectric loss tangent tanδ for the dielectric layer.

[0036]

number

[0037] As described above, the loss in a power transmission line is the sum of three losses: conductor loss, dielectric loss, and radiation loss. Therefore, reducing conductor loss can reduce the loss in the power transmission line. To reduce conductor loss, it is preferable to control the conductivity of the conductor for the following reasons. The metal-clad laminate for forming the antenna of this disclosure and its metal interface conductivity, which affect the conductivity of the conductor, will be described later. Conductivity σ is a parameter that represents the loss of the conductor. Since the conductor satisfies the equation "σ>>ωε", the surface impedance Z of the conductor is... S This is approximated by equation (4) below. Therefore, the surface resistance R S This is expressed by equation (5) below. Here, δ in equation (5) is the skin thickness, which is expressed by equation (6). Note that the skin thickness δ is the depth at which the electromagnetic field strength is 1 / e (=-8.68 dB) of the value at the conductor surface, and is inversely proportional to the square roots of the frequency and conductivity σ, respectively.

[0038]

number

[0039] <Circuit board> Examples of materials that make up the substrate include plastic materials. Examples of such plastic materials include fluororesins, polyester resins (e.g., polyethylene terephthalate), (meth)acrylic resins (e.g., polymethyl methacrylate), polycarbonate, triacetylcellulose, polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymer, and cyclic olefin polymers. These plastic materials may be used individually or in combination of two or more. From the viewpoint of improving the relative radiation efficiency of the antenna, fluororesins are preferred as the material that makes up the substrate, and polytetrafluoroethylene (PTFE) is more preferred.

[0040] The thickness of the substrate is preferably 5 to 250 μm, from the viewpoint of suppressing radiation loss of radio waves in a predetermined frequency band while mounting the antenna element. The substrate may be single-layer or multi-layer. Furthermore, the surface of the substrate may be subjected to known surface treatments. Examples of known surface treatments include corona discharge treatment, plasma treatment, electron beam treatment, undercoating treatment, and coating treatment.

[0041] The substrate may be a rigid substrate, a flexible substrate, or a rigid-flexible substrate. The substrate may also be a single-sided substrate, a double-sided substrate, or a multilayer substrate (e.g., a pull-up substrate). It can be particularly suitable for use with flexible substrates and rigid substrates. If the fluororesin sheet does not contain glass fibers or cloth made of glass fibers, it is suitable for use with flexible substrates. It can be particularly suitable for use as a high-frequency printed circuit board in a predetermined frequency band.

[0042] The substrate of the antenna of this disclosure has, for example, a dielectric layer. The substrate may consist only of the dielectric layer, or it may further have layers other than the dielectric layer. Examples of materials that constitute the dielectric layer include the plastic materials mentioned above. Among these, fluororesin is preferred as the material that constitutes the dielectric layer. Furthermore, the dielectric layer is preferably a fluororesin sheet. Below, a fluororesin sheet that can be suitably used as the dielectric layer of the antenna of this disclosure will be described.

[0043] (Fluororesin sheet) A smooth interface between the metal foil used to form antenna elements and circuits and the fluororesin sheet reduces transmission loss and improves antenna characteristics. Therefore, good adhesion between the fluororesin sheet and the metal foil with a smooth surface is required.

[0044] However, sheets made solely from fluororesin have a high coefficient of thermal expansion, which can cause warping of the substrate and defects in the circuit. In particular, sheets made solely from PTFE resin do not readily form functional groups containing oxygen, even after surface treatment, resulting in insufficient adhesion to smooth metal foils, and further improvements are needed. These problems arise because polytetrafluoroethylene resins do not readily generate functional groups on the surface, and even if functional groups do form, they tend to move from the surface into the interior of the resin due to molecular motion, making it difficult to obtain the effects of surface treatment.

[0045] Therefore, by applying a surface treatment such as plasma treatment to the surface of a fluororesin sheet containing fluororesin and silica particles, the oxygen element ratio on the surface of the fluororesin sheet is increased, thereby improving the adhesion between the fluororesin sheet and a metal foil with a smooth surface of Rz 1.0 μm or less.

[0046] By incorporating silica particles, when a fluororesin sheet is surface-treated, functional groups derived from the surface treatment can be added to the silica surface, thereby increasing the oxygen atom ratio on the surface of the fluororesin sheet. This improves the adhesion between the fluororesin sheet and the metal foil, resulting in better peel strength at the adhesive surface. Furthermore, by using a composite product of fluororesin and silica particles, the coefficient of thermal expansion of the fluororesin sheet can be further reduced. Such a fluororesin sheet can achieve both a low coefficient of thermal expansion and good peel strength.

[0047] The fluororesin sheet is preferably a fluororesin sheet containing fluororesin and silica particles, wherein the oxygen element ratio measured by X-ray photoelectron spectroscopy (XPS) is 3.0 atomic% or higher, and the coefficient of thermal expansion (CTE) is 100 ppm / °C or lower. As described above, by using a fluororesin sheet containing fluororesin and silica particles, the oxygen element ratio on the surface of the fluororesin sheet can be increased, thus enabling good adhesion to metal foils with smooth surfaces. In addition, the low coefficient of thermal expansion (CTE) can sufficiently suppress substrate warping and the occurrence of circuit defects.

[0048] Preferably, the oxygen atom ratio of the fluororesin sheet, as measured by X-ray photoelectron spectroscopy (XPS), is 3.0 atomic% or higher on one or both sides. In particular, the oxygen atom ratio of the sheet surface that adheres to the metal foil should be 3.0 atomic% or higher as measured by X-ray photoelectron spectroscopy (XPS). An oxygen atom ratio of 3.0 atomic% or higher allows the sheet to bond with the surface of the metal foil, improving the peel strength against the metal foil. The oxygen atom ratio is preferably 3.0 atomic% or higher, more preferably 5.0 atomic% or higher, and even more preferably 10.0 atomic% or higher. There is no specific upper limit, but considering the impact on productivity and other physical properties, it is preferable to have an upper limit of 25.0 atomic% or lower.

[0049] The above-mentioned X-ray photoelectron spectroscopy (XPS) measurements are specifically performed using a scanning X-ray photoelectron spectroscopy (XPS / ESCA) analyzer, the PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.).

[0050] The fluororesin sheet preferably has an oxygen atom ratio of 3.0 atomic% or more as measured by the above-mentioned X-ray photoelectron spectroscopy (XPS), and further preferably has a nitrogen atom ratio of 1.35 atomic% or more as measured by the same X-ray photoelectron spectroscopy (XPS). The above nitrogen atom ratio is more preferably 1.35 atomic% or more, even more preferably 2.5 atomic% or more, and most preferably 3.0 atomic% or more. By increasing the nitrogen atom ratio on the surface of the fluororesin sheet in this way, which contributes to adhesion, sufficient peel strength with metal foil can be obtained without impairing dielectric properties. There is no particular upper limit specified, but considering the impact on productivity and other physical properties, it is preferable to have a value of 25.0 atomic% or less.

[0051] The fluororesin sheet preferably has an oxygen element ratio of 3.0 atomic% or more as measured by the above-mentioned X-ray photoelectron spectroscopy (XPS), and further preferably has a silicon element ratio of 0.5 atomic% or more as measured by the same X-ray photoelectron spectroscopy (XPS). The silicon element ratio is more preferably 1.0 atomic% or more, even more preferably 1.5 atomic% or more, and most preferably 2.0 atomic% or more. A high silicon element ratio on the surface of the fluororesin sheet, which contributes to adhesion, exposes silica particles that can be surface-treated, thereby increasing the peel strength with the metal foil. There is no particular upper limit specified, but considering the impact on productivity and other physical properties such as strength, it is preferable to have a silicon element ratio of 10.0 atomic% or less.

[0052] The fluororesin sheet preferably has a static contact angle of 105° or less, more preferably 103° or less, and even more preferably 100° or less, on a surface where the oxygen element ratio measured by the above-mentioned X-ray photoelectron spectroscopy (XPS) is 3.0 atomic% or more, with a droplet volume of 2 μL and measured 1 second after application. Meeting these ranges allows new functional groups to be formed in the fluororesin sheet, increasing the peel strength with the metal foil. There is no specific lower limit, but considering productivity, etc., it is preferable that the static contact angle of water be 90° or more.

[0053] The static contact angle of water was measured using a contact angle meter (DropMaster, manufactured by Kyowa Interface Science Co., Ltd.) at 23°C, with a droplet volume of 2 μL, and 1 second after application.

[0054] The fluororesin sheet preferably has a coefficient of thermal expansion (CTE) of 100 ppm / °C or less. Being within this range is preferable because it results in a fluororesin sheet with low shrinkage and excellent dimensional stability. The coefficient of thermal expansion (CTE) is more preferably 70 ppm / °C or less, even more preferably 50 ppm / °C or less, and even more preferably 40 ppm / °C or less. There is no specific lower limit, but considering productivity, etc., the coefficient of thermal expansion (CTE) is preferably 10 ppm / °C or more, more preferably 18 ppm / °C or more, and even more preferably 31 ppm / °C or more.

[0055] In this specification, the coefficient of thermal expansion is determined by performing TMA measurement in tensile mode using a TMA-7100 (manufactured by Hitachi High-Tech Science Corporation). A fluororesin sheet cut to a length of 20 mm, width of 5 mm, and thickness of 150 μm is used as the sample piece. The distance between the chucks is set to 10 mm, and a load of 49 mN is applied while heating at a rate of 2 °C / min. The coefficient of thermal expansion is determined from the displacement of the sample from 0 to 150 °C.

[0056] The fluororesin sheet preferably has a dielectric loss tangent of 0.0015 or less at 10 GHz. This is preferable because it allows for low loss of electrical signals in the circuit. The dielectric loss tangent is more preferably 0.0012 or less, even more preferably 0.0011 or less, even more preferably 0.0010 or less, and particularly preferably 0.0009 or less. On the other hand, the lower limit of the dielectric loss tangent is preferably 0.00001.

[0057] The fluororesin sheet preferably has a relative permittivity of 3.5 or less at 10 GHz. This range is preferable because it results in low dielectric loss. The upper limit of the relative permittivity is more preferably 3.2, and even more preferably 3.1. On the other hand, the lower limit of the relative permittivity is preferably 2.0, and even more preferably 2.5.

[0058] The relative permittivity (Dk) and dielectric loss tangent (Df) in this specification were obtained by measuring Dk and Df at 25°C and 10GHz using a split-cylinder type dielectric constant / dielectric loss tangent measuring device (manufactured by EM lab).

[0059] The fluororesin sheet preferably has a thickness of 5 to 250 μm. The lower limit of the thickness is more preferably 15 μm or more, and even more preferably 30 μm or more. The upper limit of the thickness is more preferably 230 μm or less, and even more preferably 200 μm or less. The thickness can be selected considering the balance between the electrical properties of the laminate and the coefficient of thermal expansion.

[0060] As mentioned above, the fluororesin sheet contains fluororesin and silica particles. The fluororesin and silica particles will be described below.

[0061] (Fluororesin) Because fluororesins have low dielectric properties, they can be suitably used in fluororesin sheets.

[0062] The fluororesins that can be used for fluororesin sheets are not particularly limited, but examples include PTFE, tetrafluoroethylene (TFE) / hexafluoropropylene (HFP) copolymer (FEP), TFE / alkyl vinyl ether copolymer (PFA), TFE / HFP / alkyl vinyl ether copolymer (EPA), TFE / chlorotrifluoroethylene (CTFE) copolymer, TFE / ethylene copolymer (ETFE), polyvinylidene fluoride (PVdF), and tetrafluoroethylene (LMW-PTFE) with a molecular weight of 300,000 or less. These fluororesins may be used individually or mixed in combination of two or more types. Among these, PTFE is particularly preferred from the viewpoint of low dielectric properties and low coefficient of thermal expansion. PTFE with fibril properties is preferred. PTFE with fibril properties means PTFE that can be extruded as a paste from an uncalcined polymer powder.

[0063] PTFE may be modified polytetrafluoroethylene (hereinafter referred to as modified PTFE), homopolytetrafluoroethylene (hereinafter referred to as homoPTFE), or a mixture of modified PTFE and homoPTFE. The content of modified PTFE in polymer PTFE is preferably 10% to 98% by mass, and more preferably 50% to 95% by mass, from the viewpoint of maintaining good moldability of polytetrafluoroethylene.

[0064] Homo-PTFE is not particularly limited, and homo-PTFE disclosed in Japanese Patent Publication No. 53-60979, Japanese Patent Publication No. 57-135, Japanese Patent Publication No. 61-16907, Japanese Patent Publication No. 62-104816, Japanese Patent Publication No. 62-190206, Japanese Patent Publication No. 63-137906, Japanese Patent Publication No. 2000-143727, Japanese Patent Publication No. 2002-201217, International Publication No. 2007 / 046345, International Publication No. 2007 / 119829, International Publication No. 2009 / 001894, International Publication No. 2010 / 113950, International Publication No. 2013 / 027850, etc., can be suitably used. Among these, homo-PTFE disclosed in Japanese Patent Publication No. 57-135, Japanese Patent Publication No. 63-137906, Japanese Patent Publication No. 2000-143727, Japanese Patent Publication No. 2002-201217, International Publication No. 2007 / 046345, International Publication No. 2007 / 119829, International Publication No. 2010 / 113950, etc., which have high stretchability, is preferred.

[0065] Modified PTFE is composed of TFE and monomers other than TFE (hereinafter referred to as modified monomers). Modified PTFE can be uniformly modified with modified monomers, modified in the early stages of the polymerization reaction, or modified in the final stages of the polymerization reaction, but is not limited to these. Preferably, modified PTFE is a TFE copolymer obtained by polymerizing TFE along with a small amount of monomers other than TFE, within a range that does not significantly impair the properties of the TFE homopolymer.

[0066] Modified PTFE can preferably be those disclosed in, for example, Japanese Patent Publication No. 60-42446, Japanese Patent Publication No. 61-16907, Japanese Patent Publication No. 62-104816, Japanese Patent Publication No. 62-190206, Japanese Patent Publication No. 64-1711, Japanese Patent Publication No. 2-261810, Japanese Patent Publication No. 11-240917, Japanese Patent Publication No. 11-240918, International Publication Brochure No. 2003 / 033555, International Publication Brochure No. 2005 / 061567, International Publication Brochure No. 2007 / 005361, International Publication Brochure No. 2011 / 055824, International Publication Brochure No. 2013 / 027850, etc. Among these, modified PTFE disclosed in Japanese Patent Publication No. 61-16907, Japanese Patent Publication No. 62-104816, Japanese Patent Publication No. 64-1711, Japanese Patent Publication No. 11-240917, International Publication No. 2003 / 033555, International Publication No. 2005 / 061567, International Publication No. 2007 / 005361, International Publication No. 2011 / 055824, etc., which have high stretchability, is preferred.

[0067] Modified PTFE contains TFE units based on TFE and modified monomer units based on modified monomers. Modified monomer units are a part of the molecular structure of modified PTFE that originates from the modified monomer. Modified PTFE preferably contains 0.001 to 0.500% by mass of modified monomer units, and more preferably 0.01 to 0.30% by mass of total monomer units. Total monomer units are the parts of the molecular structure of modified PTFE that originate from all monomers.

[0068] The modified monomer is not particularly limited as long as it can copolymerize with TFE, and examples include perfluoroolefins such as hexafluoropropylene (HFP); chlorofluoroolefins such as chlorotrifluoroethylene (CTFE); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF); perfluorovinyl ether; perfluoroalkylethylene (PFAE); ethylene, etc. One or more modified monomers may be used.

[0069] Perfluorovinyl ethers are not particularly limited and include, for example, perfluorounsaturated compounds represented by the following general formula (A). CF2 = CF - ORf...(A) (In the formula, Rf represents a perfluoroorganic group.)

[0070] In this specification, a perfluoroorganic group is an organic group in which all hydrogen atoms bonded to a carbon atom are replaced with fluorine atoms. The above perfluoroorganic group may have an ether oxygen.

[0071] Examples of perfluorovinyl ethers include perfluoro(alkyl vinyl ether) (PAVE) in which Rf in the above general formula (A) is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5. Examples of perfluoroalkyl groups in PAVE include perfluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, and perfluorohexyl group. Perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE) are preferred PAVEs.

[0072] The perfluoroalkylethylene (PFAE) mentioned above is not particularly limited and includes, for example, perfluorobutylethylene (PFBE), perfluorohexylethylene (PFHE), and the like.

[0073] In modified PTFE, the modified monomer is preferably at least one selected from the group consisting of HFP, CTFE, VDF, PAVE, PFAE, and ethylene.

[0074] The above-mentioned fluororesin is preferably non-melt-processable. Non-melt-processable means that even when heated above its melting point, the resin does not have sufficient fluidity and cannot be molded using the melt molding methods commonly used for resins. PTFE falls into this category.

[0075] It is preferable to use such non-melt-processable fluororesin particles and to form a fluororesin sheet by a molding method that fibrillates them. This molding method will be described later.

[0076] The above-mentioned PTFE preferably has a standard specific gravity (SSG) of 2.0 to 2.3. Using such PTFE makes it easier to obtain PTFE films with high strength (cohesive force and puncture strength per unit thickness). PTFE with a large molecular weight has long molecular chains, making it difficult to form a structure in which the molecular chains are regularly arranged. In this case, the length of the amorphous region increases, and the degree of entanglement between molecules increases. When the degree of entanglement between molecules is high, the PTFE film is less likely to deform under applied load and is thought to exhibit excellent mechanical strength. Furthermore, using PTFE with a large molecular weight makes it easier to obtain PTFE films with a small average pore size.

[0077] The lower limit of the above SSG is more preferably 2.05, and even more preferably 2.1. The upper limit of the above SSG is more preferably 2.25, and even more preferably 2.2.

[0078] Standard specific gravity (SSG) is determined by preparing a sample in accordance with ASTM D-4895-89 and measuring the specific gravity of the obtained sample using the water displacement method.

[0079] In this embodiment, the molecular weight (number-average molecular weight) of the PTFE constituting the PTFE particles is, for example, in the range of 2 to 12 million. The lower limit of the molecular weight of PTFE may be 3 million or 4 million. The upper limit of the molecular weight of PTFE may be 10 million.

[0080] Methods for determining the number-average molecular weight of PTFE include determining it from standard specific gravity and determining it by dynamic viscoelasticity during melting. The method of determining it from standard specific gravity can be performed using a sample molded in accordance with ASTM D-4895 98 and the water displacement method in accordance with ASTM D-792. The method of determining it by dynamic viscoelasticity is described, for example, by S. Wu in Polymer Engineering & Science, 1988, Vol. 28, 538, and in the same publication, 1989, Vol. 29, 273.

[0081] The PTFE described above preferably has a refractive index within the range of 1.2 to 1.6. Having such a refractive index is preferable in that it is a low dielectric material. The refractive index can be set within the above range by methods such as adjusting the polarizability and the flexibility of the main chain. The lower limit of the refractive index is more preferably 1.25, more preferably 1.30, and most preferably 1.32. The upper limit of the refractive index is more preferably 1.55, more preferably 1.50, and most preferably 1.45.

[0082] The refractive index mentioned above was measured using a refractometer (Abbemat 300).

[0083] Furthermore, the PTFE described above preferably has a maximum endothermic peak temperature (crystal melting point) of 340±7℃.

[0084] The PTFE may be low-melting-point PTFE, where the maximum peak temperature of the endothermic curve on the crystal melting curve measured by differential scanning calorimeter is 338°C or lower, or high-melting-point PTFE, where the maximum peak temperature of the endothermic curve on the crystal melting curve measured by differential scanning calorimeter is 342°C or higher.

[0085] Low-melting-point PTFE powder is a powder particle produced by polymerization using an emulsion polymerization method, possessing the aforementioned maximum endothermic peak temperature (crystal melting point), a dielectric constant (ε) of 2.08 to 2.2, and a dielectric loss tangent (tan δ) of 1.9 × 10⁻¹⁰. -4~4.0×10 -4 Examples of commercially available products include Polyflon Fine Powder F201, F203, F205, F301, and F302 from Daikin Industries, Ltd.; CD090 and CD076 from Asahi Glass Industrial Co., Ltd.; and TF6C, TF62, and TF40 from DuPont.

[0086] High-melting-point PTFE powder is also a powder particle manufactured by polymerization using the emulsion polymerization method, and has the aforementioned maximum endothermic peak temperature (crystal melting point), a dielectric constant (ε) of 2.0 to 2.1, and a dielectric loss tangent (tanδ) of 1.6 × 10⁻¹⁰. -4 ~2.2×10 -4 The overall levels are low. Examples of commercially available products include Polyflon Fine Powder F104 and F106 from Daikin Industries, Ltd.; CD1, CD141, and CD123 from Asahi Glass Industrial Co., Ltd.; and TF6 and TF65 from DuPont.

[0087] Furthermore, the average particle size of the powder obtained by secondary aggregation of both PTFE polymerized particles is preferably 250 to 2000 μm. In particular, granulated powder obtained by granulation using a solvent is preferred because it improves fluidity when filling the mold during pre-molding.

[0088] PTFE particles in powder form that satisfy the parameters described above can be obtained by conventional manufacturing methods. For example, they can be manufactured by following the manufacturing methods described in International Publication No. 2015-080291 and International Publication No. 2012-086710, etc.

[0089] It is preferable to use PTFE powder with a primary particle size of 0.05 to 10 μm. Using such a material offers the advantage of excellent moldability and dispersibility. The primary particle size here is the value measured in accordance with ASTM D 4895.

[0090] The above-mentioned powdered PTFE preferably contains 50% by mass or more of polytetrafluoroethylene resin with a secondary particle size of 500 μm or larger, and more preferably 80% by mass or more. Having PTFE with a secondary particle size of 500 μm or larger within this range has the advantage of enabling the production of high-strength fluororesin sheets. Using PTFE with a secondary particle size of 500 μm or larger allows for the acquisition of sheets with lower resistance and greater toughness.

[0091] The lower limit of the secondary particle size is more preferably 300 μm, and even more preferably 350 μm. The secondary particle size is more preferably 700 μm or less, and even more preferably 600 μm or less. The secondary particle size can be determined, for example, by sieving.

[0092] The above-mentioned powdered PTFE preferably has an average primary particle diameter of 50 nm or more, as this yields a sheet with higher strength and superior homogeneity. More preferably, it is 100 nm or more, even more preferably 150 nm or more, and particularly preferably 200 nm or more. The larger the average primary particle diameter of the PTFE, the lower the increase in paste extrusion pressure when using the powder for paste extrusion molding, resulting in superior moldability. There is no particular upper limit to the average primary particle diameter, but it may be 500 nm or less. From the viewpoint of productivity in the polymerization process, it is preferable that the average primary particle diameter is 350 nm or less.

[0093] The above average primary particle diameter can be determined by creating a calibration curve using an aqueous dispersion of PTFE obtained by polymerization, adjusting the polymer concentration to 0.22% by mass, and comparing the transmittance of 550 nm projected light per unit length of the aqueous dispersion with the average primary particle diameter determined by measuring the directional diameter in transmission electron microscope images. The transmittance of the aqueous dispersion to be measured is then measured, and the average primary particle diameter can be determined based on the above calibration curve.

[0094] PTFE particles used in fluororesin sheets may have a core-shell structure. Examples of PTFE particles having a core-shell structure include modified polytetrafluoroethylene, which contains a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene. Examples of such modified polytetrafluoroethylene include the polytetrafluoroethylene described in Japanese Patent Publication No. 2005-527652.

[0095] (Silica particles) Fluoropolymer sheets must contain silica particles. While the shape of the silica particles is not particularly limited, spherical shapes are especially preferred. Spherical shapes are preferable because they allow for uniform processing during drilling, have a small specific surface area, and result in low transmission loss. In fluoropolymer sheets, the use of spherical silica is most preferable.

[0096] The spherical silica described above refers to particles whose shape is close to a perfect sphere. Specifically, a sphericity of 0.80 or higher is preferred, 0.85 or higher is more preferred, 0.90 or higher is even more preferred, and 0.95 or higher is most preferred. Sphericity is calculated by taking a picture with a scanning electron microscope (SEM) and using the area and perimeter of the observed particle as a value calculated using the formula (sphericity) = {4π × (area) ÷ (perimeter)²}. The closer to 1, the closer to a perfect sphere. Specifically, the average value measured for 100 particles using an image processing device (Spectris Corporation: FPIA-3000) is adopted.

[0097] For spherical silica used in fluororesin sheets, it is preferable that the D90 / D10 ratio is 2 or greater (preferably 2.3 or greater and 2.5 or greater) and the D50 ratio is 10 μm or less when the volume is accumulated from the smallest particle size. Furthermore, it is preferable that the D90 / D50 ratio is 1.5 or greater (more preferably 1.6 or greater). It is preferable that the D50 / D10 ratio is 1.5 or greater (more preferably 1.6 or greater). Furthermore, it is even more preferable that the D50 ratio is 5 μm or less. This allows smaller spherical silica particles to fill the gaps between larger spherical silica particles, resulting in excellent packing performance and high fluidity. In particular, it is preferable that the frequency of smaller particle sizes is higher in the particle size distribution compared to a Gaussian curve. The particle size can be measured using a laser diffraction scattering particle size distribution analyzer. In addition, since coarse particles make it difficult to thin the sheet, it is preferable that coarse particles with a particle size greater than a predetermined size are removed by filtering or the like.

[0098] The spherical silica described above preferably has a water absorption of 1.0% or less, and more preferably 0.5% or less. Water absorption is based on the mass of the silica particles when dry. Water absorption is measured by leaving a dry sample at 40°C and 80% RH for 1 hour, and then measuring the moisture generated by heating to 200°C using a Karl Fischer moisture analyzer.

[0099] Furthermore, the parameters of the spherical silica can also be measured using the method described above after burning off the fluororesin by heating the fluororesin sheet at 600°C for 30 minutes in an atmospheric environment, thereby extracting the spherical silica particles.

[0100] The silica particles described above are preferably surface-treated. By pre-treating the surface, interactions can be introduced between the silica particles, which can reduce the coefficient of thermal expansion of the fluororesin sheet.

[0101] The above surface treatment is not particularly limited, and any known treatment can be used. Specifically, examples include treatment with silane coupling agents such as epoxysilane, aminosilane, isocyanatesilane, vinylsilane, acrylicsilane, hydrophobic alkylsilane, phenylsilane, and fluorinated alkylsilane having reactive functional groups, plasma treatment, and fluorination treatment. Among these, treatment with a silane coupling agent is preferred.

[0102] It is preferable to use silica particles treated with a silane coupling agent as the silica particles contained in the fluororesin sheet. Treating the silica particles with a silane coupling agent lowers the coefficient of thermal expansion, which is advantageous in that it improves adhesion to the metal foil. Furthermore, by applying the silane coupling agent treatment, the polar functional groups present on the surface of the silica particles react, reducing the amount of polar functional groups and resulting in superior electrical properties. In addition, the functional groups contained in the silane coupling agent react with the surface of the metal foil, further increasing the peel strength with respect to the metal foil.

[0103] Examples of the silane coupling agents mentioned above include epoxysilanes such as γ-glycidoxypropyltriethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, aminosilanes such as aminopropyltriethoxysilane and N-phenylaminopropyltrimethoxysilane, isocyanatesilanes such as 3-isocyanatetopropyltrimethoxysilane, vinylsilanes such as vinyltrimethoxysilane, and acrylicsilanes such as acryloxytrimethoxysilane.

[0104] The average particle size of the silica particles is preferably 10 μm or less. This is preferable because it results in a lower surface roughness of the sheet. The upper limit of the average particle size of the silica particles is more preferably 8 μm or less, and even more preferably 5 μm or less. The lower limit of the average particle size of the silica particles is not particularly limited, but is preferably 0.5 μm or more. An average particle size of 0.5 μm or more tends to effectively suppress the aggregation of fillers. The average particle size here refers to the D50 value measured by a laser particle size distribution analyzer.

[0105] The silica particles used may be commercially available silica particles that satisfy the properties described above. Examples of commercially available silica particles include Denka Fused Silica FB Grade (manufactured by Denka Co., Ltd.), Denka Fused Silica SFP Grade (manufactured by Denka Co., Ltd.), Excelica (manufactured by Tokuyama Corporation), High-Purity Synthetic Spherical Silica Particles AdmaFine (manufactured by Admatex Co., Ltd.), Admanano (manufactured by Admatex Co., Ltd.), and AdmaFuse (manufactured by Admatex Co., Ltd.).

[0106] The silica particle content is preferably 30% by mass or more relative to the total amount of the fluororesin sheet. This content is preferable because it allows for a low coefficient of thermal expansion while maintaining a low dielectric constant and low loss. Furthermore, when PTFE is used as the fluororesin, PTFE does not readily form oxygen or nitrogen functional groups even after plasma treatment, but the presence of silica particles allows for the formation of surface-treated functional groups on the silica surface. As a result, the oxygen atom ratio on the surface of the fluororesin sheet can be increased, improving the adhesion between the fluororesin sheet and the metal foil, and further improving the peel strength of the adhesive surface. The silica particle content is more preferably 35% by mass or more, even more preferably 50% by mass or more, and even more preferably 55% by mass or more, relative to the total amount of the fluororesin sheet. There is no particular upper limit to the silica particle content, but the silica particle content is preferably 70% by mass or less, more preferably 68% by mass or less, and even more preferably 65% ​​by mass or less, relative to the total amount of the fluororesin sheet.

[0107] (Other ingredients) The fluororesin sheet of this disclosure may contain components other than fluororesin and silica particles (hereinafter sometimes referred to as "other components"). These other components are not particularly limited and may include, for example, fluorine-free thermosetting resins, fluorine-free thermoplastic resins, fillers other than silica particles, etc. It is preferable that the fluororesin sheet does not contain glass fibers. By not including glass fibers or cloth made of glass fibers, it is possible to make the fluororesin sheet into a thin film, and it also becomes more flexible, offering advantages in applications where bending is required.

[0108] Other fillers besides silica particles are not particularly limited and include organic fillers such as one or more selected from polyphenyl esters, polyphenylene sulfide, polyimide, polyether ether ketone, polyphenylene, polyamide, and fully aromatic polyester resins, and inorganic fillers such as one or more selected from ceramics, talc, mica, aluminum oxide, zinc oxide, tin oxide, titanium dioxide, calcium carbonate, calcium oxide, magnesium oxide, potassium titanate, calcium fluoride, boron nitride, barium sulfate, molybdenum disulfide, and potassium carbonate whiskers. Two or more of these may be used in combination.

[0109] <Laminate> The dielectric layer described above (for example, a fluororesin sheet) can be used in lamination with other substrates.

[0110] (Metal-clad laminate) A metal-clad laminate comprising a dielectric layer and a metal foil may be used to form the antenna of this disclosure. Examples of metal foils used in this disclosure include metal foils made of the same material as the material constituting the antenna element, and preferred examples include copper foil, gold foil, silver foil, platinum foil, ruthenium foil, etc. Among these, copper foil is preferred because it has low conductor loss.

[0111] The antenna of this disclosure may use a metal-clad laminate in which metal foil is bonded to one or both sides of a dielectric layer (more specifically, a fluororesin sheet). As the metal-clad laminate, a metal-clad laminate in which metal foil and a dielectric layer (more specifically, a fluororesin sheet) are essential layers is preferred. A fluororesin sheet containing fluororesin and silica particles has excellent adhesive properties. Therefore, it is more preferable that the metal-clad laminate is in which the surface-treated surface of the dielectric layer (more specifically, the fluororesin sheet) and the metal foil are directly laminated.

[0112] In obtaining the laminate structure described above, the fluororesin sheet is used with metal foil bonded to one or both sides. As described above, the fluororesin sheet usable as a dielectric layer in the antenna of this disclosure has excellent adhesive properties. Therefore, it also has excellent adhesion to metal foil with a high degree of smoothness, such as Rz 1.0 μm or less.

[0113] Conventionally, metal foils used in forming antenna circuit boards have a certain degree of surface irregularity to ensure adhesion to fluororesin sheets. However, in high-frequency applications, the presence of surface irregularities on the metal foil is undesirable because it causes loss of electrical signals. The above-described laminate can achieve suitable adhesion even to highly smooth metal foils and can be suitably used as an antenna circuit board.

[0114] The metal foil (preferably copper foil) has a surface roughness (Rz) of 1.0 μm or less. A surface roughness (Rz) of 1.0 μm or less is preferable because it results in a smooth interface between the metal foil and the fluororesin sheet, high metal interface conductivity, and low transmission loss. The metal foil only needs to have an Rz of 1.0 μm or less on at least the side that adheres to the fluororesin sheet, and the Rz of the other side is not particularly limited. The fluororesin sheet has excellent adhesion to metal foils with high smoothness, such as an Rz of 1.0 μm or less, more specifically, an Rz of 0.9 μm or less, and even more specifically, an Rz of 0.5 μm or less. There is no particular lower limit for the Rz of the metal foil, but considering productivity, it is preferable that the Rz of the metal foil is 0.2 μm or more.

[0115] The above Rz is the sum of the highest point (maximum peak height: Rp) and the deepest point (maximum valley depth: Rv). The above Rz is the ten-point average roughness as defined in JIS-B0601. In this specification, the above Rz is the value measured using a surface roughness meter (product name: Surfcom 470A, manufactured by Tokyo Seiki Co., Ltd.) with a measurement length of 4 mm.

[0116] The metal foil (preferably copper foil) has a surface roughness (Rq) of 0.01 to 0.15 μm. A Rq within this range is preferable because it allows for high metal interface conductivity and effectively reduces transmission loss. The metal foil only needs to have an Rq of 0.01 to 0.15 μm on at least the surface that adheres to the fluororesin sheet; the Rq of the other surface is not particularly limited. The Rq of the surface adhering to the fluororesin sheet is more preferably 0.015 to 0.1 μm, and even more preferably 0.03 to 0.08 μm. The above Rq is the root mean square height. In this specification, the above Rq is the value measured using a stylus-type surface roughness measuring instrument (product name: SE600A, manufactured by Kosaka Research Institute Co., Ltd.) with a measurement length of 4 mm.

[0117] The thickness of the metal foil is not particularly limited, but is preferably 1 to 100 μm, more preferably 5 to 50 μm, and even more preferably 9 to 35 μm.

[0118] The above-mentioned metal foils are not particularly limited, and specific examples include rolled metal foils and electrolytic metal foils.

[0119] The metal foil having an Rz of 1.0 μm or less and / or an Rq of 0.01 to 0.15 μm is not particularly limited, and commercially available foils can be used. Examples of such commercially available metal foils include electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm / Rz 0.85 μm / Rq 0.05 μm) (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.).

[0120] The above metal foil may be surface-treated to increase its peel strength with the fluororesin sheet.

[0121] The surface treatment of the metal foil is not particularly limited, but may include silane coupling treatment, plasma treatment, corona treatment, UV treatment, or electron beam treatment. The reactive functional group of the silane coupling agent is not particularly limited, but from the viewpoint of adhesion to resin substrates such as fluororesin sheets, it is preferable that it has at least one selected from amino groups, (meth)acrylic groups, mercapto groups, and epoxy groups at its terminal end. The hydrolyzable group is not particularly limited, but may include alkoxy groups such as methoxy groups and ethoxy groups. The metal foil may have a rust-preventive layer (such as an oxide film like chromate), a heat-resistant layer, etc., formed on it.

[0122] A surface-treated metal foil having a surface treatment layer of the silane compound described above on the surface of the metal foil can be manufactured by preparing a solution containing the silane compound and then using this solution to surface-treat the metal foil.

[0123] The above-mentioned metal foil may have a roughened layer on its surface, for example, to improve adhesion to the resin substrate. If the roughening treatment may reduce the performance required in this disclosure, the amount of roughened particles electrodeposited on the metal foil surface may be reduced or the roughening treatment may be omitted as needed.

[0124] Between the metal foil and the surface treatment layer, one or more layers selected from the group consisting of a heat-resistant treatment layer, a rust-preventive treatment layer, and a chromate treatment layer may be provided from the viewpoint of improving various properties. These layers may be a single layer or multiple layers.

[0125] In a metal-clad laminate, when the surface-treated surface of a dielectric layer (more specifically, a fluororesin sheet) and a metal foil (more specifically, a copper foil) are directly laminated, it is preferable that the peel strength at the interface between the metal foil (more specifically, a copper foil) and the dielectric layer (more specifically, a fluororesin sheet) is 0.5 kN / m or more. By using the dielectric layer (more specifically, a fluororesin sheet) described above, a peel strength of 0.5 kN / m or more can be achieved. By setting the peel strength to 0.5 kN / m or more, it can be suitably used as a metal-clad laminate. A peel strength of 0.7 kN / m or more is even more preferable. The upper limit of the peel strength is not particularly limited, but it may be 3.0 kN / m or less, or 1.4 kN / m or less. Note that the peel strength here refers to the peel strength measured under the conditions described in the examples.

[0126] Furthermore, in the case of a laminate in which metal foil is bonded to the surface-treated surface of a fluororesin sheet that has been surface-treated on only one side, a separate surface treatment may be applied to the untreated surface of the fluororesin sheet in order to improve the adhesion between the laminate and other materials.

[0127] The metal-clad laminate may further have layers other than metal foil and fluororesin sheets. Preferably, the layers other than metal foil and fluororesin sheets are layers of at least one resin selected from the group consisting of polyimide, modified polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene ether, polyphenylene ether, and polybutadiene.

[0128] The resin layer, other than the metal foil and fluororesin sheet, may contain reinforcing fibers. The reinforcing fibers are not particularly limited, but glass cloth, especially a low-dielectric type, is preferred.

[0129] The layers other than these metal foils and fluororesin sheets are not particularly limited as long as they are composed of the resins described above. Furthermore, it is preferable that the layers other than the metal foils and fluororesin sheets have a thickness of 12.5 to 260 μm.

[0130] Metal-clad laminates are used, for example, in the formation of antenna circuit boards.

[0131] Since the metal-clad laminate is used to form the antenna of this disclosure, a high metal interface conductivity is preferable. Preferably, it is 1.00 (1e7 S / m) or higher, more preferably 3.00 (1e7 S / m) or higher, and even more preferably 5.00 (1e7 S / m) or higher. There is no particular upper limit, but it is preferable to be 6.00 (1e7 S / m) or lower.

[0132] Since the metal-clad laminate is also used to form antenna circuit boards, it is preferable that the transmission loss be close to zero. The transmission loss at a frequency of 67 GHz is preferably -4.20 dB / 100 mm or more, more preferably -4.00 dB / 100 mm or more, and even more preferably -3.30 dB / 100 mm or more.

[0133] The above-mentioned fluororesin sheet has good adhesion to unroughened metal foil, which has low transmission loss. Since the gain is improved when an antenna is obtained by processing a metal-clad laminate containing the above-mentioned fluororesin sheet and unroughened metal foil, the metal-clad laminate containing the fluororesin sheet and unroughened metal foil is particularly suitable for use in the manufacture of the antenna of this disclosure.

[0134] The laminate for forming the antenna circuit board may further laminate a metal foil layer, the aforementioned fluororesin sheet, and a base layer. The base layer is not particularly limited, but examples include a fabric layer made of glass fibers, a resin film layer, and the like.

[0135] As the resin film used as the base layer, heat-resistant resin films and thermosetting resin films are preferred. Examples of heat-resistant resin films include polyimide, modified polyimide, liquid crystal polymer, and polyphenylene sulfide. Examples of thermosetting resins include epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene ether, polyphenylene ether, and polybutadiene. The heat-resistant resin film and thermosetting resin film may contain reinforcing fibers. The reinforcing fibers are not particularly limited, but glass cloth, especially low-dielectric type, is preferred.

[0136] The dielectric properties, coefficient of thermal expansion, and water absorption of the heat-resistant resin film and thermosetting resin film are not particularly limited, but for example, the dielectric constant at 20 GHz is preferably 3.8 or less, more preferably 3.4 or less, and even more preferably 3.2 or less. The dielectric loss tangent at 20 GHz is preferably 0.0030 or less, more preferably 0.0025 or less, and even more preferably 0.0020 or less. The coefficient of thermal expansion is preferably 100 ppm / °C or less, more preferably 70 ppm / °C or less, and even more preferably 40 ppm / °C or less. The water absorption is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.1% or less.

[0137] When laminating a metal-clad laminate, which requires a fluororesin sheet and a metal foil, with a substrate layer such as a resin film layer, the lamination can be achieved by bonding the fluororesin sheet layer side of the metal-clad laminate to the substrate layer. In this case, the fluororesin sheet layer side of the metal-clad laminate may be surface-treated before lamination to improve its adhesive performance. The surface treatment here is not particularly limited and can include the plasma treatment mentioned above.

[0138] In the above-described laminate, the layering order and manufacturing method of the metal foil layer, substrate, and the aforementioned fluororesin sheet are not particularly limited, and the layer configuration can be adapted to the purpose. Specifically, examples of the above-described layering order include those composed of a substrate layer / fluororesin sheet / metal foil layer, metal foil layer / fluororesin sheet / substrate layer / fluororesin sheet / metal foil layer, and metal foil layer / substrate layer / fluororesin sheet / substrate layer / metal foil layer. In addition, other layers may be included as needed.

[0139] [Antenna manufacturing method] The method for manufacturing an antenna according to this disclosure includes, for example, a dielectric layer formation step, a metal-clad laminate formation step, and an etching step.

[0140] <Dielectric layer formation process> In the dielectric layer formation process, a dielectric layer is formed. The following explanation will use the case where a fluororesin sheet is formed as the dielectric layer as an example. A fluororesin sheet, an example of a dielectric layer, can be obtained, for example, by mixing the aforementioned fluororesin particles and silica particles, forming a film, and then performing a surface treatment. The method of film formation is not limited to this, but can be carried out by paste extrusion molding, powder rolling molding, etc.

[0141] As mentioned above, it is preferable to use non-melt-processable fluororesin particles for use in fluororesin sheets. When using such fluororesin particles, it is preferable to form them into a sheet by fibrillating powdered PTFE as a raw material.

[0142] The specific methods for paste extrusion molding and powder rolling molding described above are not particularly limited, but general methods are described below.

[0143] (Film formation by paste extrusion molding) The above method for producing a fluororesin sheet may include the steps of: mixing powdered fluororesin particles, silica particles, and an extrusion aid obtained using a hydrocarbon surfactant (1a); paste extrusion molding of the obtained mixture (1b); rolling the extruded product obtained by extrusion molding (1c); drying the rolled sheet (1d); and firing the dried sheet to obtain a molded body (1e). The paste extrusion molding may also be carried out by adding conventionally known additives such as pigments and fillers to the fluororesin particles and silica particles.

[0144] The above-mentioned extrusion aids are not particularly limited and generally known ones can be used. Examples include hydrocarbon oils.

[0145] (Film formation by powder rolling) The above-mentioned fluororesin sheet can also be formed by powder rolling. Powder rolling is a method of forming a sheet by applying shear force to powdered fluororesin particles to cause fibrillation. The process may then include a step of firing to obtain a molded body. More specifically, it can be obtained by a manufacturing method having a step of applying shear force while mixing a raw material composition containing fluororesin particles and filler particles (1), a step of forming the mixture obtained in step (1) into a bulk (2), and a step of rolling the bulk mixture obtained in step (2) into a sheet (3). Furthermore, the process may include a step of firing the sheet obtained above at 200 to 400°C for 1 to 60 minutes (4). Step (2) may also be omitted.

[0146] When manufacturing a fluororesin sheet by the powder rolling molding method described above, it is preferable to use a composition that does not contain any liquid components and consists substantially of fluororesin particles and filler particles containing at least silica particles to form the film. "Substantially consisting of fluororesin particles and filler particles containing at least silica particles" means that the content of components other than fluororesin particles and the above-mentioned filler particles is 3% by mass or less of the total amount of the composition. The filler particles contain at least silica particles, and other preferred filler particles include aluminum oxide, zinc oxide, titanium oxide, calcium carbonate, magnesium oxide, etc. Furthermore, filler particles other than silica particles may not be used, one type may be used, or two or more types may be mixed and used. The amount of filler particles other than silica particles is preferably 0.1 to 80% by mass of the filler particles. In particular, it is preferable to mold a mixture of only fluororesin particles and silica particles.

[0147] The fluororesin sheet obtained by the above-described method for manufacturing fluororesin sheets, before surface treatment, preferably has an oxygen element ratio of 1.5 atomic% or more, as measured by X-ray photoelectron spectroscopy (XPS) at least on the surface to be treated. The presence of oxygen elements on the surface of the fluororesin sheet before surface treatment enables good adhesion to metal foils with smooth surfaces. Furthermore, this range is preferable in order to ensure that the oxygen element ratio of the fluororesin sheet after surface treatment, as measured by X-ray photoelectron spectroscopy (XPS), is within the above-described range. The oxygen element ratio is preferably 1.65 atomic% or more, more preferably 1.7 atomic% or more, and even more preferably 1.8 atomic% or more. There is no particular upper limit, but considering the impact on productivity and other physical properties, it is preferable to have a value of 4.9 atomic% or less. The method for achieving the above-described range for the oxygen element ratio of the fluororesin sheet before surface treatment is not particularly limited and can be controlled, for example, by adjusting the amount of silica particles blended or adjusting the molding method.

[0148] It is preferable that the silicon element ratio of the fluororesin sheet before surface treatment is 0.2 atomic% or higher, at least on the surface to be treated, as measured by X-ray photoelectron spectroscopy (XPS). The presence of silicon elements on the surface of the fluororesin sheet before surface treatment enables good adhesion with metal foils that have a smooth surface. This range is also preferable in order to ensure that the silicon element ratio of the fluororesin sheet after surface treatment, as measured by X-ray photoelectron spectroscopy (XPS), is preferably 0.5 atomic% or higher. The silicon element ratio is preferably 0.3 atomic% or higher, more preferably 0.5 atomic% or higher, and even more preferably 0.7 atomic% or higher. There is no particular upper limit, but considering the impact on productivity and other physical properties, it is preferable to have a silicon element ratio of 2.0 atomic% or lower. The silicon element ratio of the fluororesin sheet before surface treatment can be adjusted by adjusting the amount of silica particles added.

[0149] (Surface treatment) By performing a surface treatment on one or both sides of the fluororesin sheet obtained by the method described above, a fluororesin sheet that satisfies the above requirements can be obtained. Fluororesins are generally difficult to adhere to metal foils. Therefore, it is preferable to perform a surface treatment on the fluororesin sheet to improve its lamination properties. Such surface treatments are generally known to increase the amount of oxygen atoms on the resin surface.

[0150] The specific method for the surface treatment described above is not particularly limited and can be carried out by any known method. Surface treatment of the fluororesin sheet can be performed using conventional discharge treatments such as plasma discharge treatment, corona discharge treatment, glow discharge treatment, or sputtering. Among these, plasma treatment is preferred.

[0151] Plasma treatment is a process that involves bringing a plasma into contact with a fluororesin sheet to etch the fluororesin on its outer surface and add oxygen atoms, nitrogen atoms, etc., to the outer surface of the fluororesin sheet. For example, the surface free energy can be controlled by introducing oxygen gas, nitrogen gas, hydrogen gas, helium gas, argon gas, etc., into the discharge atmosphere.

[0152] Alternatively, the surface to be modified may be exposed to an atmosphere of an inert gas containing organic compounds, a high-frequency voltage applied between electrodes to induce a discharge, thereby generating active species on the surface, and then the surface treatment may be performed by introducing functional groups of organic compounds or by graft polymerization of polymerizable organic compounds.

[0153] Examples of organic compounds in the inert gas containing the organic compound include polymerizable or nonpolymerizable organic compounds containing oxygen atoms, such as vinyl esters like vinyl acetate and vinyl formate; acrylic acid esters like glycidyl methacrylate; ethers like vinyl ethyl ether, vinyl methyl ether, and glycidyl methyl ether; carboxylic acids like acetic acid and formic acid; alcohols like methyl alcohol, ethyl alcohol, phenol, and ethylene glycol; ketones like acetone and methyl ethyl ketone; carboxylic acid esters like ethyl acetate and ethyl formate; and acrylic acids like acrylic acid and methacrylic acid. Of these, vinyl esters, acrylic acid esters, and ketones are preferred because the modified surface is less likely to deactivate, has a long lifespan, and is easy to handle, with vinyl acetate and glycidyl methacrylate being particularly preferred.

[0154] The concentration of the organic compound in the inert gas containing the organic compound varies depending on its type, the type of fluororesin to be surface-treated, etc., but is usually 0.1 to 3.0% by volume, preferably 0.1 to 1.0% by volume, more preferably 0.15 to 1.0% by volume, and still more preferably 0.30 to 1.0% by volume. The discharge conditions may be appropriately selected according to the degree of the intended surface treatment, the type of fluororesin, the type and concentration of the organic compound, etc. Usually, the discharge amount is 50 W·min / m 2 or more and 1500 W·min / m 2 or less, preferably 70 W·min / m 2 or more and 1400 W·min / m 2 or less, and the discharge treatment is performed within this range. The treatment temperature can be any temperature within the range of 0°C or more and 100°C or less. It is preferably 80°C or less due to concerns such as elongation and wrinkles of the fluororesin sheet.

[0155] <Metal-clad laminate forming step> In the metal-clad laminate forming step, a metal-clad laminate is formed. In the metal-clad laminate, the metal foil layer may be formed on one side or both sides of the roll-shaped sheet. Examples of the method for forming the metal foil layer include a method of laminating (adhering) a metal foil on the surface of the roll-shaped sheet, a vapor deposition method, a plating method, etc. Examples of the method for laminating the above metal foil include a method by hot pressing. The hot pressing temperature is from the melting point of the sheet - 150°C to the melting point of the sheet + 40°C. The time of hot pressing is, for example, 1 to 30 minutes.

[0156] For example, a method of manufacturing a metal-clad laminate by laminating a dielectric layer (more specifically, a fluororesin sheet) and a metal foil, heating at 180 to 390°C, and press-forming under a pressure of 0.5 to 5 MPa under vacuum or in an inert gas atmosphere is suitable. By press-forming under such conditions, there is no deterioration of the dielectric layer and adhesion to the metal foil is also possible.

[0157] <Etching step> In the etching process, the metal-clad laminate is etched. By etching, an antenna pattern is printed onto the metal foil of the metal-clad laminate, forming an antenna circuit board, which is a printed circuit board. More specifically, based on the antenna pattern data, the metal foil of the metal-clad laminate is divided into a pattern region where the antenna pattern is formed and a non-pattern region where the antenna pattern is not formed. Using an etching solution, the metal foil in the non-pattern region is dissolved and removed, leaving the metal foil in the pattern region, thereby forming an antenna pattern composed of metal foil on the substrate. The antenna pattern includes, for example, an antenna element and a transmission path. In this way, an antenna equipped with an antenna circuit board having a substrate, an antenna element composed of metal foil, and a transmission path composed of metal foil is manufactured. Examples of etching solutions include acidic or alkaline chemicals, and more specifically, an aqueous solution of ferric chloride. After etching, the antenna circuit board may be washed and dried as needed. Alternatively, dry etching using gas may be performed instead of wet etching using an etching solution. Furthermore, the specific method of etching described above is not particularly limited and can be any known method.

[0158] [How to use the antenna] The method of using the antenna of this disclosure includes the step of using the antenna in a predetermined frequency band. Since the predetermined relative radiation efficiency of the antenna of this disclosure is high, at 17.5 dB or more, it is particularly suitable for use in a predetermined frequency band.

[0159] [Uses of antennas] The antenna disclosed herein is suitable for applications such as antennas for radomes, antennas for metasurfaces, and reflectors for metasurfaces. These applications also require low dielectric constant and low loss, making this antenna particularly suitable.

[0160] While embodiments of this disclosure have been described above, it will be understood that a variety of modifications to the form and details are possible without departing from the spirit and scope of the claims. [Examples]

[0161] The present disclosure will be described in detail below based on examples. However, the present disclosure is not limited to the following examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass," respectively.

[0162] Each sample obtained was evaluated based on the following criteria.

[0163] [Thickness of fluororesin sheet] The measurement was taken using a micrometer.

[0164] [XPS measurement of the surface of a fluororesin sheet] Measurements were performed using a scanning X-ray photoelectron spectroscopy (XPS / ESCA) analyzer, PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.).

[0165] [Coefficient of Thermal Expansion (CTE)] TMA measurements were performed in tensile mode using the TMA-7100 (manufactured by Hitachi High-Tech Science Corporation). A fluororesin sheet cut to a length of 20 mm, width of 5 mm, and thickness of 150 μm was used as the sample piece. The distance between the chucks was set to 10 mm, and while applying a load of 49 mN, the linear expansion coefficient was determined from the displacement of the sample from 0 to 150°C at a heating rate of 2°C / min.

[0166] [Dielectric constant and dielectric loss tangent of fluororesin sheets] The dielectric constant and dielectric loss tangent were measured at 25°C and 10GHz using a split-cylinder dielectric constant / dielectric loss tangent measuring device (manufactured by EM lab).

[0167] [Static contact angle of water] The static contact angle of the fabricated fluororesin sheet with water was measured using a contact angle meter (DropMaster, manufactured by Kyowa Interface Science Co., Ltd.) at 23°C, with a droplet volume of 2 μL, and the contact angle with water was measured 1 second after droplet placement.

[0168] [Peel strength] Samples were prepared by placing copper foil (Fukuda Metal Foil Powder Co., Ltd. CF-T9DA-SV-18, Rz=0.85μm, Rq=0.05μm) on top and bottom of a surface-treated fluororesin sheet so that the treated surface was in close contact with the fluororesin sheet, and then heating under pressure using a vacuum heat press (360℃, 2.5MPa, 300s). The obtained samples were cut into 10mm wide strips, and the peel strength was measured by gripping the unadhered portion of the strip sample with the upper and lower chucks of the Tensilon universal tester (Shimadzu Corporation) and pulling it at a speed of 50mm per minute. The obtained value was defined as the peel strength.

[0169] [Specified relative radiation efficiency of the antenna] The predetermined relative radiation efficiency of the antenna was measured in a millimeter-wave anechoic chamber. The right side of the millimeter-wave anechoic chamber was designated as the transmitting side, and the left side as the receiving side. A transmitting device, to which the antenna under test (one of the antennas described in Examples 1 to 10 and Comparative Example 1, described later) was connected, was installed on the right side of the millimeter-wave anechoic chamber. The reflection coefficient (S11) was measured using the transmitting device. A vector network analyzer (Anritsu Corporation "MS46522B") was used as the reflection coefficient measuring device, which also served as the transmitting device. A receiving probe was installed on the left side of the millimeter-wave anechoic chamber. A WR12 size separated waveguide was used as the receiving probe. Using two linear stages, the receiving probe was moved on the XY plane, and a planar scanning near-field measurement was performed. The measurement range in the XY axis direction on the XY plane was ±150 mm, and the movement step was 1 mm. The distance between the receiving probe and the antenna under test was 50 mm. Furthermore, to measure the polarization characteristics, the receiving probe was rotated 0 degrees and 90 degrees around its long axis. The measurement frequency was set to 82.5 GHz. The measured reflection coefficient (S11) was converted using the near-field-far-field transformation (PNFFFT) method of the planar scanning near-field measurement method and then converted using the pattern integration method of the upper half of the surface to calculate the relative radiation efficiency. From the value obtained by truncating the second decimal place of the predetermined relative radiation efficiency, it was determined whether or not the predetermined relative radiation efficiency was 17.5 dB or higher.

[0170] [Examples 1-10] <How to create sheets A-D> (Paste extrusion molding) PTFE powder (average particle size: 500 μm, apparent density: 460 g / L, standard specific gravity: 2.17) and silica particles shown in Table 1 were weighed in the mass ratio shown in Table 1 and mixed in a mixer in the presence of dry ice. The temperature during mixing was below -10°C. 18-23% of oil (IP Solvent 2028) was added to the resulting mixed powder, mixed, and allowed to mature for about 5 hours. The matured composition was pre-molded under a pressure of 3 MPa, and the pre-molded body was extruded at 40°C and 50 mm / min to obtain an extruded sample. The extruded sample was rolled using a double roll to obtain a sample with a film thickness of 125 μm, which was then passed through a drying roll at 200°C for 2 hours and baked at 360°C for 15 minutes to obtain a sheet. Furthermore, it was confirmed that a sample with a film thickness of 30 μm could be produced by adjusting the gap and pressure of the double roll.

[0171] <Method for creating Sheet AP> (Powder rolling) PTFE powder (average particle size: 500 μm, apparent density: 460 g / L, standard specific gravity: 2.17) and silica particles shown in Table 1 were weighed in the mass ratio shown in Table 1 and stirred in a Wonder Crusher at room temperature at setting 6 for 30 seconds twice. The resulting mixture was rolled using a double roll roller (roll gap: set to 100 μm, roll temperature: 100 °C) to obtain a sample with a film thickness of 130 μm, and then baked at 360 °C for 15 minutes to obtain a sheet.

[0172] As shown in Table 1, the silica used in the preparation of sheets A, AP, B, and C was spherical silica, SC6500-SQ (average particle size 2.1 μm), manufactured by Admatex, which was surface-treated with 3-aminopropyltriethoxysilane (treatment amount of 0.5% or 1% by mass relative to the mass of silica particles). As shown in Table 1, the silica used in the preparation of sheet D was spherical silica, SC6500-SQ (average particle size 2.1 μm), manufactured by Admatex, which was used without surface treatment.

[0173] [Table 1]

[0174] <Surface treatment of fluororesin sheets> Fluoropolymer sheets (each of the fabricated sheets A-D and AP) were placed between the upper and lower electrodes in a processing chamber (direct-type plasma surface treatment device, manufactured by Air Water Co., Ltd.) equipped with upper and lower electrodes. After creating the mixed gas atmosphere described below in the processing chamber, the fluoropolymer sheet surfaces were subjected to discharge plasma treatment for the processing times shown in Table 2. The elemental composition of the surface-treated fluoropolymer sheets was measured by XPS. (Processing atmosphere) GA: A mixed gas of argon, helium, and oxygen. GB: A mixture of argon, helium, nitrogen, and oxygen.

[0175] <Fabrication of double-sided copper-clad laminated boards> A surface-treated fluororesin sheet was topped with copper foil (Fukuda Metal Foil Powder Co., Ltd. CF-T9DA-SV-18, Rz=0.85μm, Rq=0.05μm) with the treated surface facing the sheet, and then inserted into a vacuum heat press. Under vacuum, the temperature was raised from room temperature to 360°C, and then pressurized at 3 MPa below 360°C to produce a double-sided copper-clad laminate.

[0176] <Etching process> The copper foil of a double-sided copper-clad laminate was etched with an aqueous ferric chloride solution to form a patch antenna pattern. The etched double-sided copper-clad laminate was washed with running clean water for 2 to 5 minutes, then washed again with distilled water, and dried in a constant temperature bath at 80±3°C for about 60 minutes. In this way, the patterned patch array antennas of Examples 1 to 10 were obtained.

[0177] The substrate size of the fabricated antenna was 61.5 mm in length and 24.5 mm in width. The patch antenna pattern fabricated by etching was as follows: The patch antenna pattern was arranged in a 16x8 configuration, and the antenna elements were square in shape with a length of 1.15 mm and a width of 1.30 mm. The rows of antenna elements were arranged parallel to the length of the substrate. In each row of antenna elements, 16 antenna elements were spaced 2.20 mm apart (distance between the centers of the antenna elements). The eight rows of antenna elements were spaced 1.90 mm apart (distance between the centers of the antenna elements). The antenna elements were arranged in a square configuration.

[0178] [Comparative Example 1] The antenna of Comparative Example 1 was fabricated in the same manner as the antennas of Examples 1 to 10, except that RO3003 (manufactured by Rogers) was used instead of the fabricated double-sided copper-clad laminate. RO3003 is a double-sided roughened copper-clad laminate of a composite sheet of fluororesin and filler. Analysis of RO3003 confirmed the presence of non-spherical inorganic fillers.

[0179] The results for Examples 1-10 and Comparative Example 1 are shown in Table 2.

[0180] [Table 2]

[0181] In addition to the measurements shown in Table 2, the following measurements were also performed.

[0182] [Metal interface conductivity measurement] From the fabricated double-sided copper-clad laminate, circular dielectric samples (without copper on both sides) and circular dielectric samples (with circular copper foil patterning on one side) were prepared, and the conductivity (1e7 S / m) at the metal layer interface in the frequency range of 14.5 GHz to 111.5 GHz was measured using the balanced disk resonator method. The average conductivity at the metal layer interface of the double-sided copper-clad laminate used to fabricate the antenna in Example 6 was 5.66 (1e7 S / m), which was equivalent to the result for the reference copper disk.

[0183] Furthermore, when the average conductivity of the metal layer interface was similarly measured using commercially available RO3003 (manufactured by Rogers), which is a double-sided copper-clad laminate made of a composite sheet of fluororesin and filler, it was found to be 0.56 (1e7 S / m). Therefore, it was clear that the double-sided copper-clad laminate used in the antenna fabrication of Example 6 has a higher metal interface conductivity than commercially available double-sided copper-clad laminates.

[0184] From the experimental results above, it was found that the predetermined relative radiation efficiency of the antennas in Examples 1 to 10 was 1.67 dB or more better than that of the antenna in Comparative Example 1, indicating that the antenna characteristics in the predetermined frequency band were excellent. [Industrial applicability]

[0185] The antenna of this disclosure can be suitably used as an antenna for a millimeter-wave radar for mobility applications such as collision avoidance.

Claims

1. An antenna for radar used in the frequency band between 70 GHz and 90 GHz, The aforementioned antenna is a patch array antenna, The antenna has a dielectric layer, The dielectric layer is a fluororesin sheet. On one or both sides of the fluororesin sheet, the oxygen element ratio measured by X-ray photoelectron spectroscopy (XPS) is 3.0 atomic% or more. An antenna in which the coefficient of linear thermal expansion (CTE) of the fluororesin sheet is 100 ppm / °C or less.

2. The aforementioned antenna has a plurality of antenna elements, The multiple antenna elements consist of 8 to 16 rows of antenna elements, each row having 16 to 64 antenna elements arranged in a straight line. The antenna according to claim 1, wherein the 8 to 16 rows of antenna elements are arranged parallel to each other.

3. The antenna according to claim 1 or 2, wherein the fluororesin sheet comprises fluororesin and silica particles.

4. The antenna according to claim 3, wherein the fluororesin is polytetrafluoroethylene.

5. Furthermore, the antenna according to claim 1 or 2, wherein the nitrogen element ratio measured by X-ray photoelectron spectroscopy (XPS) on one or both sides of the fluororesin sheet is 1.35 atomic% or more.

6. Furthermore, the antenna according to claim 1 or 2, wherein the silicon element ratio measured by X-ray photoelectron spectroscopy (XPS) on one or both sides of the fluororesin sheet is 0.5 atomic% or more.

7. Furthermore, the antenna according to claim 1 or 2, wherein on one or both sides of the fluororesin sheet, the static contact angle of water measured 1 second after droplet placement with a droplet volume of 2 μL is 105° or less.

8. The antenna according to claim 3, wherein the silica particles are spherical silica.

9. The antenna according to claim 3, wherein silica particles treated with a silane coupling agent are used as the silica particles.

10. The antenna according to claim 3, wherein the average particle size of the silica particles is 10 μm or less.

11. The antenna according to claim 1 or 2, wherein the fluororesin sheet does not contain glass fibers.

12. The antenna according to claim 3, wherein the silica particle content is 30% by mass or more relative to the total amount of the fluororesin sheet.

13. The antenna according to claim 3, wherein the silica particle content is 50% by mass or more relative to the total amount of the fluororesin sheet.

14. The antenna according to claim 3, wherein the silica particle content is 50% by mass or more and 65% by mass or less based on the total amount of the fluororesin sheet.

15. The antenna according to claim 1 or 2, wherein the dielectric loss tangent value of the fluororesin sheet at 10 GHz is 0.0015 or less.

16. The antenna according to claim 1 or 2, wherein the relative permittivity of the fluororesin sheet at 10 GHz is 2.8 or less.

17. The antenna according to claim 1 or 2, wherein the thickness of the fluororesin sheet is 5 to 250 μm.

18. The antenna according to claim 1 or 2, wherein the antenna is formed from a metal-clad laminate in which the metal foil and the dielectric layer are essential layers.

19. The antenna according to claim 18, wherein the metal foil is copper foil.

20. The antenna according to claim 19, wherein the surface roughness (Rz) of the copper foil is 1.0 μm or less.

21. The antenna according to claim 19, wherein the surface roughness (Rq) of the copper foil is 0.01 to 0.15 μm.

22. The antenna according to claim 19, wherein the copper foil and the dielectric layer are directly laminated, and the peel strength of the interface between the copper foil and the dielectric layer is 0.5 kN / m or more.

23. The antenna according to claim 1 or 2, which is a millimeter-wave antenna for mobility applications.

24. The aforementioned fluororesin sheet contains fluororesin and silica particles. The fluororesin is polytetrafluoroethylene, The silica particles are spherical silica, The silica particle content is 50% by mass or more and 65% by mass or less relative to the total amount of the fluororesin sheet. On one or both sides of the fluororesin sheet, the oxygen element ratio measured by X-ray photoelectron spectroscopy (XPS) is 3.0 atomic% or more and 25.0 atomic% or less. On one or both sides of the fluororesin sheet, the silicon element ratio measured by X-ray photoelectron spectroscopy (XPS) is 0.5 atomic% or more and 10.0 atomic% or less. The antenna according to claim 1 or 2, wherein the coefficient of linear expansion (CTE) of the fluororesin sheet is 31 ppm / °C or more and 70 ppm / °C or less.

25. A method for manufacturing an antenna according to claim 1 or 2, The process includes a dielectric layer formation step for forming the dielectric layer, A method for manufacturing an antenna, comprising the steps of forming a dielectric layer, mixing fluororesin particles and silica particles to form a film, and then performing a surface treatment.

26. The method for manufacturing an antenna according to claim 25, wherein in the dielectric layer formation step, a film is formed and surface treated using a composition substantially comprising the fluororesin particles and filler particles containing at least the silica particles.

27. The process further includes a metal-clad laminate forming step, The method for manufacturing an antenna according to claim 25, wherein in the metal-clad laminate formation step, the dielectric layer and the metal foil are laminated, heated at 180 to 390°C, and press-molded at a pressure of 0.5 to 5 MPa under vacuum or in an inert gas atmosphere.

28. The method for manufacturing an antenna according to claim 27, further comprising an etching step of etching the metal-clad laminate.

29. A method of using an antenna according to claim 1 or 2, A method for using an antenna, comprising the step of using the antenna in a frequency band of 70 GHz or more and 90 GHz or less.

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