Sheet, method for producing same, metal-clad laminate, circuit board, and antenna

Abstract

Provided is a sheet that undergoes small changes in relative permittivity due to temperature changes. The sheet has a change rate in relative permittivity in a temperature range of -50 to 150°C of 0.020 or less.

Description

Sheet, manufacturing method thereof, metal-clad laminate, circuit board and antenna

[0001] The present disclosure relates to a sheet, a method for manufacturing the same, a metal-clad laminate, a circuit board, and an antenna.

[0002] There is a demand for high-frequency printed wiring boards with low transmission loss, and substrates used in antennas for millimeter-wave radar for mobility applications, in particular, are required to have small changes in dielectric constant due to temperature changes.

[0003] Patent Documents 1 to 3 disclose the use of two or more types of fillers in combination with fluororesin as materials for electronic substrates.

[0004] JP 2020-050860 JP 2020-037662 JP 2023-028091

[0005] Changes in the dielectric properties of a dielectric due to changes in the temperature of the environment in which the dielectric is used have a significant impact on circuit and antenna performance. Therefore, it is preferable that the dielectric properties do not change significantly with temperature changes. The present disclosure aims to provide a sheet whose relative permittivity changes little with temperature changes in order to minimize the impact on antenna performance.

[0006] The present disclosure provides a sheet characterized by having a rate of change in relative dielectric constant of 0.020 or less in the temperature range of -50 to 150°C and containing two or more types of fillers. The sheet preferably has a coefficient of linear expansion (CTE) of 70 ppm / K or less. The sheet preferably has a dielectric loss tangent value of 0.0015 or less at 10 GHz. The sheet preferably has a thickness of 5 to 250 μm.

[0007] The sheet preferably contains a fluororesin. The fluororesin is preferably polytetrafluoroethylene. The filler preferably has a band gap of 2 eV or more. The content of the filler relative to the total amount of the sheet is preferably 30 mass% or more. The filler preferably contains at least two types selected from the group consisting of silica, alumina, boron nitride, and zirconium oxide. The filler preferably contains two types of filler: silica and alumina. The silica is preferably spherical particles. The silica is preferably silica particles treated with a silane coupling agent. The silane coupling agent preferably has an aminopropyl group. The silica particles preferably have an average particle size of 10 μm or less. The alumina preferably has an average particle size of 10 μm or less. The alumina is preferably blended in an amount of 10 to 50 mass% relative to the total amount of alumina and silica.

[0008] The present disclosure also provides a method for producing the above-mentioned sheet, characterized in that a film is formed by mixing a fluororesin and a filler.The present disclosure also provides a method for producing the above-mentioned sheet, characterized in that a film is formed using a composition essentially consisting of fluororesin particles and filler particles including at least silica particles and alumina particles.

[0009] The present disclosure also provides a metal-clad laminate having the above sheet as an essential layer and a metal foil layer on one or both sides thereof, the metal foil being preferably copper.

[0010] The present disclosure also relates to a circuit board having the metal laminate described above. The present disclosure also relates to an antenna formed from the circuit board described above. The antenna is preferably a millimeter-wave antenna for mobility.

[0011] The sheet of the present disclosure has a small change in relative dielectric constant due to temperature changes, and therefore has the excellent effect of not causing performance changes due to temperature changes in applications where temperature changes are large, such as antennas for millimeter-wave radar for mobility.

[0012] The present disclosure will be described in detail below. The present disclosure is a sheet characterized by a rate of change in dielectric constant of 0.020 or less in the temperature range of -50 to 150°C. In other words, the dielectric constant does not change over the wide temperature range of -50 to 150°C. Therefore, there is little change in the electrical properties of the sheet.

[0013] In recent years, there has been an increase in finely formed circuits, such as millimeter-wave radar antennas, and in such circuits, even a slight change in the dielectric constant can change the electrical characteristics, which can cause operational abnormalities.

[0014] High accuracy is required for communications in the field of mobility applications, so by using a sheet whose relative permittivity hardly changes over a wide temperature range as described above, communication errors can be prevented.

[0015] In other fields as well, as wiring boards are becoming increasingly dense and thin, it is becoming increasingly important to reduce the rate of change in relative dielectric constant in order to prevent operational abnormalities. The present disclosure aims to solve such problems that have not been solved by conventional techniques. In this disclosure, the rate of change in relative dielectric constant is a value measured by the method described in the examples.

[0016] The rate of change of the relative dielectric constant in the temperature range of −50 to 150° C. is preferably 0.020 or less, more preferably 0.018 or less, and even more preferably 0.016 or less. The lower limit is not particularly limited, but can be, for example, 0.001 or more.

[0017] The sheet of the present disclosure preferably has a coefficient of linear expansion (CTE) of 70 ppm / °C or less. A sheet with a low coefficient of linear expansion is preferred because it has excellent dimensional stability and stable performance even when used under conditions of large temperature changes. The CTE is more preferably 50 ppm / °C or less, and even more preferably 40 ppm / °C or less. The lower limit of the CTE is not particularly limited, but is preferably 10 ppm / °C or more, and more preferably 18 ppm / °C.

[0018] The sheet of the present disclosure preferably has a dielectric loss tangent value of 0.0015 or less at 10 GHz. This is preferable in that it has low dielectric loss and low loss. The dielectric loss tangent is a value measured at 20°C, more specifically, a value measured by the method described in the examples.

[0019] The dielectric loss tangent at 10 GHz is more preferably 0.0012 or less, and even more preferably 0.0011 or less. The lower limit of the dielectric loss tangent at 10 GHz is not particularly limited, but can be, for example, 0.00001 or more.

[0020] The sheet preferably has a thickness of 5 to 250 μm. By setting the thickness within the above range, it can be suitably used in metal-clad laminates. The sheet of the present disclosure can fully achieve its purpose even if it is thin. The thickness is more preferably less than 230 μm, and even more preferably less than 200 μm. Furthermore, it is more preferably thicker than 15 μm, and even more preferably thicker than 30 μm.

[0021] The sheet of the present disclosure is not particularly limited in composition, but preferably contains a resin and a filler. By using such a composition, the specific physical properties described above can be obtained. The resin and the filler are each described in detail below.

[0022] (Fluororesin) The composition of the present disclosure contains a fluororesin. Fluororesin has low dielectric properties and can therefore be suitably used for the purposes of the present disclosure.

[0023] The fluororesin that can be used in the present disclosure is not particularly limited, but examples include polytetrafluoroethylene (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 having a molecular weight of 300,000 or less [LMW-PTFE]. One type may be used, or two or more types may be mixed. From the viewpoint of low dielectric constant, polytetrafluoroethylene resin (PTFE) is particularly preferred. PTFE having fibrillar properties is preferred. Fibrillar PTFE refers to PTFE that can be paste-extruded from unsintered polymer powder.

[0024] PTFE may be modified polytetrafluoroethylene (hereinafter referred to as modified PTFE), may be homopolytetrafluoroethylene (hereinafter referred to as homoPTFE), or may be a mixture of modified PTFE and homoPTFE. Note that, from the viewpoint of maintaining good moldability of polytetrafluoroethylene, the content ratio of modified PTFE in polymeric PTFE is preferably 10% by mass or more and 98% by mass or less, more preferably 50% by mass or more and 95% by mass or less. The homo-PTFE is not particularly limited, and homo-PTFE disclosed in JP-A-53-60979, JP-A-57-135, JP-A-61-16907, JP-A-62-104816, JP-A-62-190206, JP-A-63-137906, JP-A-2000-143727, JP-A-2002-201217, WO 2007 / 046345 pamphlet, WO 2007 / 119829 pamphlet, WO 2009 / 001894 pamphlet, WO 2010 / 113950 pamphlet, WO 2013 / 027850 pamphlet, etc. can be suitably used. Among these, homo-PTFE having high stretchability and disclosed in JP-A-57-135, JP-A-63-137906, JP-A-2000-143727, JP-A-2002-201217, WO 2007 / 046345, WO 2007 / 119829, WO 2010 / 113950, etc. is preferred.

[0025] Modified PTFE is made up of TFE and monomer other than TFE (hereinafter referred to as modified monomer).Modified PTFE can include, but is not limited to, the one that is uniformly modified by modified monomer, the one that is modified at the beginning of polymerization reaction, or the one that is modified at the end of polymerization reaction.Modified PTFE is preferably the TFE copolymer obtained by subjecting TFE and a small amount of monomer other than TFE to polymerization within the range that does not significantly impair the properties of TFE homopolymer. The modified PTFE can be suitably used, for example, those disclosed in JP-A-60-42446, JP-A-61-16907, JP-A-62-104816, JP-A-62-190206, JP-A-64-1711, JP-A-2-261810, JP-A-11-240917, JP-A-11-240918, WO 2003 / 033555 pamphlet, WO 2005 / 061567 pamphlet, WO 2007 / 005361 pamphlet, WO 2011 / 055824 pamphlet, WO 2013 / 027850 pamphlet, etc. Among these, modified PTFE having high stretchability and disclosed in JP-A-61-16907, JP-A-62-104816, JP-A-64-1711, JP-A-11-240917, WO 2003 / 033555, WO 2005 / 061567, WO 2007 / 005361, WO 2011 / 055824, etc. are preferred.

[0026] The modified PTFE contains TFE units based on TFE and modified monomer units based on a modified monomer. The modified monomer units are a part of the molecular structure of the modified PTFE that is derived from the modified monomer. The modified PTFE preferably contains modified monomer units in an amount of 0.001 to 0.500 mass% of the total monomer units, and more preferably 0.01 to 0.30 mass%. The total monomer units are the parts derived from all monomers in the molecular structure of the modified PTFE.

[0027] The modified monomer is not particularly limited as long as it can be copolymerized with TFE, and examples thereof 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. The modified monomer used may be one kind or multiple kinds.

[0028] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorounsaturated compounds represented by the following general formula (1): CF ２ =CF-ORf...(1)

[0029] In the formula, Rf represents a perfluoroorganic group.

[0030] In this specification, a perfluoroorganic group is an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0031] An example of a perfluorovinyl ether is perfluoro(alkyl vinyl ether) (PAVE), which is represented by the above general formula (1) and in which Rf 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 the perfluoroalkyl group in PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group. Preferred PAVEs are perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE).

[0032] The perfluoroalkylethylene (PFAE) is not particularly limited, and examples thereof include perfluorobutylethylene (PFBE) and perfluorohexylethylene (PFHE).

[0033] The modifying monomer in the modified PTFE is preferably at least one selected from the group consisting of HFP, CTFE, VDF, PAVE, PFAE, and ethylene.

[0034] The fluororesin is preferably non-melt-processable. Non-melt-processable means that the resin does not have sufficient fluidity even when heated above its melting point, and cannot be molded by melt molding techniques commonly used for resins. PTFE falls into this category.

[0035] In the present disclosure, it is preferable to use such a non-melt-processable fluororesin and form it into a sheet by a molding method that fibrillates it. The molding method will be described later.

[0036] The PTFE preferably has an SSG of 2.0 to 2.3. The use of such PTFE facilitates the production of PTFE membranes with high strength (cohesion 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 portion increases, and the degree of entanglement between molecules increases. It is believed that when the degree of entanglement between molecules is high, the PTFE membrane is less likely to deform under an applied load and exhibits excellent mechanical strength. Furthermore, the use of PTFE with a large molecular weight facilitates the production of PTFE membranes with small average pore sizes.

[0037] The lower limit of the SSG is more preferably 2.05, and even more preferably 2.1. The upper limit of the SSG is more preferably 2.25, and even more preferably 2.2.

[0038] The standard specific gravity [SSG] was measured by preparing a sample in accordance with ASTM D-4895-89 and measuring the specific gravity of the obtained sample by the water displacement method.

[0039] In this embodiment, the molecular weight (number average molecular weight) of the PTFE constituting the PTFE powder is, for example, in the range of 2 million 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.

[0040] Methods for measuring the number average molecular weight of PTFE include a method determining it from standard specific gravity and a method measuring dynamic viscoelasticity in the melt. The method for determining it from standard specific gravity can be carried out by the water displacement method in accordance with ASTM D-792 using a sample molded in accordance with ASTM D-4895 98. The measurement method using dynamic viscoelasticity is explained, for example, by S. Wu in Polymer Engineering & Science, 1988, Vol. 28, 538 and the same document, 1989, Vol. 29, 273.

[0041] The refractive index of the PTFE is preferably in the range of 1.2 to 1.6. Having such a refractive index is preferable in terms of low dielectric constant. The refractive index can be adjusted to within the above range by adjusting the polarizability or 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.

[0042] The refractive index is a value measured using a refractometer (Abbemat 300).

[0043] The PTFE preferably has a maximum endothermic peak temperature (crystalline melting point) of 340±7°C.

[0044] The PTFE may be a low-melting-point PTFE having a maximum peak temperature of 338°C or lower on the endothermic curve on the crystalline melting curve measured by a differential scanning calorimeter, or a high-melting-point PTFE having a maximum peak temperature of 342°C or higher on the endothermic curve on the crystalline melting curve measured by a differential scanning calorimeter.

[0045] Low-melting-point PTFE is a powder produced by emulsion polymerization, has the aforementioned maximum endothermic peak temperature (crystalline melting point), a dielectric constant (ε) of 2.08 to 2.2, and a dielectric dissipation factor (tan δ) of 1.9 × 10 to 4.0 × 10. Commercially available products include Polyflon Fine Powder F201, F203, F205, F301, and F302 manufactured by Daikin Industries, Ltd.; CD090 and CD076 manufactured by Asahi Glass Industry Co., Ltd.; and TF6C, TF62, and TF40 manufactured by DuPont.

[0046] The high melting point PTFE powder is also a powder produced by emulsion polymerization, and has the above-mentioned maximum endothermic peak temperature (crystalline melting point), a dielectric constant (ε) of 2.0 to 2.1, and a dielectric loss tangent (tan δ) of 1.6×10 －４ ~2.2 × 10 －４ Commercially available products include Polyflon fine powders F104 and F106 manufactured by Daikin Industries, Ltd., CD1, CD141, and CD123 manufactured by Asahi Glass Co., Ltd., and TF6 and TF65 manufactured by DuPont.

[0047] The powder formed by secondary aggregation of both PTFE polymer particles usually preferably has an average particle size of 250 to 2000 μm. In particular, granulated powder obtained by granulation using a solvent is preferred from the viewpoint of improving the flowability when filling a mold during preforming.

[0048] Powdered PTFE satisfying the above-described parameters can be obtained by conventional manufacturing methods, such as those described in International Publication Nos. 2015-080291 and 2012-086710.

[0049] (Filler) The filler that can be used in the present disclosure is not particularly limited, and examples thereof include organic fillers selected from aramid fibers, polyphenyl esters, polyphenylene sulfide, polyimides, polyether ether ketones, polyphenylenes, polyamides, and wholly aromatic polyester resins, and inorganic fillers selected from ceramics, talc, mica, alumina, tin oxide, titanium oxide, silica, calcium carbonate, calcium oxide, magnesium oxide, zirconium oxide, potassium titanate, glass fibers, glass chips, glass beads, silicon carbide, calcium fluoride, boron nitride, barium sulfate, molybdenum disulfide, and potassium carbonate whiskers. The sheet of the present disclosure uses two or more of these fillers in combination.

[0050] Among these, fillers containing at least two selected from the group consisting of silica, alumina, boron nitride, and zirconium oxide are particularly preferred. The temperature change of the dielectric loss tangent and the dielectric constant is closely related to the band gap of the filler. Basically, a low dielectric loss tangent can be achieved by using a compound with a large band gap. Therefore, these compounds with a suitable band gap range are particularly suitable for use. The preferred band gap range is preferably 2 eV or more, followed by 3 eV or more, then 3.5 eV or more, and then 4 eV or more. It is more preferable to use a filler with a band gap of 4.5 eV or more, even more preferably 5 eV or more, and particularly preferably 6 eV or more. Furthermore, using a combination of two or more of these fillers is particularly preferred, as it allows for a sheet with a small temperature change of the dielectric constant. Of these, silica and alumina are most preferred. The band gap was calculated by measuring the diffuse reflectance spectrum using a UV-2600 UV-Visible Spectrophotometer (Shimadzu Corporation). The measurement results were called up as spectrum data in the band gap calculation Excel macro, and after selecting the "photometric value (transmittance / reflectance)" and "n value (type of transition process)," the range that could be approximated as a straight line near the inflection point was specified as the tangent, and the band gap value was calculated using a Tauc plot.

[0051] When silica and alumina are used in combination, both have large band gaps of 5 eV or more, and therefore, by using these in combination, it is possible to particularly reduce the temperature change in the relative dielectric constant.

[0052] When the filler is a combination of silica and alumina, the silica is preferably spherical silica particles, which are preferable in that they are easy to process uniformly during drilling and have a small specific surface area and therefore low transmission loss.

[0053] The spherical silica particles have a particle shape close to a perfect sphere, and specifically, the sphericity is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, and most preferably 0.95 or more. The sphericity is determined by taking a photograph with an SEM, and using the area and perimeter of the observed particle, the formula is (sphericity) = {4π × (area) ÷ (perimeter)}. ２ The closer to 1 the particle is, the closer it is to a perfect sphere. Specifically, the average value measured for 100 particles using an image processing device (Spectris Corporation: FPIA-3000) is used.

[0054] The spherical silica particles used in the present disclosure preferably have a D90 / D10 of 2 or more (preferably 2.3 or more, 2.5 or more) and a D50 of 10 μm or less when the volume is calculated from the smallest particle size. Furthermore, it is preferable that the D90 / D50 is 1.5 or more (more preferably 1.6 or more). It is preferable that the D50 / D10 is 1.5 or more (more preferably 1.6 or more). Furthermore, it is more preferable that the D50 is 5 μm or less. Since small-sized spherical silica particles can enter the gaps between large-sized spherical silica particles, excellent filling properties and high fluidity can be achieved. In particular, it is preferable that the particle size distribution has a higher frequency on the small particle size side compared to a Gaussian curve. The particle size can be measured using a laser diffraction / scattering particle size distribution analyzer. Furthermore, since coarse particles make it difficult to form a thin sheet, it is preferable that coarse particles having a particle size above a certain size have been removed using a filter or the like.

[0055] In the present disclosure, the surface area (m ２ / g) is a value based on the BET method, and can be measured using a "Macsorb HM model-1208" (manufactured by MACSORB) as a specific surface area measuring device. When the sheet of the present disclosure contains two or more types of fillers, the surface area measured for all of the blended fillers falls within the above-mentioned range.

[0056] The silica particles preferably have an average particle size of 10 μm or less. The average particle size of the silica particles is preferably 10 μm or less, since this reduces the 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 average particle size here is the D50 value measured using a laser analysis particle size distribution analyzer.

[0057] The silica particles may be treated with a silane coupling agent. By previously treating the surface, aggregation of the silica particles can be suppressed, and the silica particles can be well dispersed in the sheet.

[0058] The silane coupling agent is not particularly limited, and any known agent can be used. Specific examples include treatment with a silane coupling agent having a reactive functional group, such as epoxysilane, aminosilane, isocyanatesilane, vinylsilane, acrylicsilane, hydrophobic alkylsilane, phenylsilane, or fluorinated alkylsilane, plasma treatment, and fluorination treatment.

[0059] Examples of the silane coupling agent include epoxy silanes such as γ-glycidoxypropyltriethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, amino silanes such as aminopropyltriethoxysilane and N-phenylaminopropyltrimethoxysilane, isocyanate silanes such as 3-isocyanatepropyltrimethoxysilane, vinyl silanes such as vinyltrimethoxysilane, and acrylic silanes such as acryloxytrimethoxysilane. Among these, those having an aminopropyl group are preferred.

[0060] The spherical silica particles may be commercially available silica particles that satisfy the above-mentioned properties. Examples of commercially available silica particles include Denka fused silica FB grade (manufactured by Denka Company Ltd.), Denka fused silica SFP grade (manufactured by Denka Company Ltd.), Excelica (manufactured by Tokuyama Corporation), high-purity synthetic spherical silica particles Admafine (manufactured by Admatechs Co., Ltd.), Admanano (manufactured by Admatechs Co., Ltd.), and Admafuse (manufactured by Admatechs Co., Ltd.).

[0061] When the silica particles are treated with a silane coupling agent, the amount of the treatment is not particularly limited, but is preferably in the range of 0.1 to 1.5 mass %, more preferably in the range of 0.15 to 1.0 mass %, based on the amount of the coated silica particles.

[0062] The alumina has good electrical insulation and thermal conductivity. The shape and size of the alumina particles are not particularly limited, and any known alumina particles can be used. More specifically, the average particle size is preferably 10 μm or less. Alumina particles having an average particle size of 10 μm or less are preferred because they reduce the surface roughness of the sheet. The upper limit of the average particle size of the alumina particles is more preferably 5 μm or less, and even more preferably 4 μm or less. Furthermore, the lower limit of the average particle size of the alumina particles is not particularly limited, but is preferably 0.5 μm or more. An average particle size of less than 0.5 μm tends to cause filler aggregation, resulting in insufficient effectiveness. The average particle size is measured using the same method as for silica particles described above. The alumina particles may be surface-treated or untreated. Furthermore, the BET specific surface area (m2 / g) is preferably 1.0 to 5.0, more preferably 1.2 to 4.0, and particularly preferably 1.4 to 3.2. The oil absorption (ml / 100g) is preferably from 10 to 40, more preferably from 15 to 30, and particularly preferably from 20 to 27. The pH is preferably from 7 to 10, more preferably from 8 to 10, and particularly preferably 9.

[0063] The mixing ratio of the silane particles and alumina particles is not particularly limited, but for example, the amount of alumina mixed is preferably 10 to 50% by mass relative to the total amount of alumina and silica, more preferably 12 to 40% by mass, and even more preferably 13 to 35% by mass. By keeping the ratio within the above range, it is possible to obtain a sheet with a small change in dielectric constant with temperature, which is preferable.

[0064] The alumina particles may be commercially available alumina particles that satisfy the above-mentioned properties, such as LS-210B and LS-110F manufactured by Nippon Light Metal Co., Ltd.

[0065] The sheet of the present disclosure preferably contains a filler in a proportion of 30% by mass or more relative to the total amount of the sheet. This amount is preferable in that it achieves low thermal expansion while maintaining a low dielectric constant and low loss. The amount 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. The upper limit of the filler amount is not particularly limited, but is preferably 70% by mass or less, more preferably 68% by mass or less, and even more preferably 65% ​​by mass or less.

[0066] (Method for manufacturing the sheet) The sheet of the present disclosure can be obtained by mixing the above-mentioned fluororesin particles and filler and forming a film. The manufacturing method is not limited, but can be paste extrusion molding, powder rolling molding, etc.

[0067] As described above, it is preferable to use a non-melt-processable fluororesin as the fluororesin used in the sheet of the present disclosure. When such a fluororesin is used and is molded into a sheet, it is preferable to mold it by fibrillating powdered PTFE as a raw material.

[0068] The powdered PTFE preferably has a primary particle size of 0.05 to 10 μm. The use of such a powder offers the advantages of excellent moldability and dispersibility. The primary particle size here is a value measured in accordance with ASTM D 4895.

[0069] The above-mentioned powdered PTFE preferably contains 50% by mass or more, more preferably 80% by mass or more, of polytetrafluoroethylene resin with a secondary particle diameter of 500 μm or more.The PTFE with a secondary particle diameter of 500 μm or more within this range has the advantage of being able to produce a composite sheet with high strength.By using the PTFE with a secondary particle diameter of 500 μm or more, it is possible to obtain a composite sheet with lower resistance and excellent toughness.

[0070] The lower limit of the secondary particle diameter is more preferably 300 μm, and even more preferably 350 μm. The upper limit of the secondary particle diameter is more preferably 700 μm or less, and even more preferably 600 μm or less. The secondary particle diameter can be determined, for example, by a sieving method.

[0071] The powdered PTFE preferably has an average primary particle diameter of 50 nm or more, since a sheet with higher strength and excellent homogeneity can be obtained. 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 PTFE, the more suppressed the increase in paste extrusion pressure when using the powder for paste extrusion molding, and the better the moldability. The upper limit is not particularly limited, but may be 500 nm. From the viewpoint of productivity in the polymerization process, it is preferably 350 nm.

[0072] The average primary particle diameter can be determined by preparing a calibration curve of the transmittance of 550 nm projected light per unit length of an aqueous dispersion of PTFE obtained by polymerization, the polymer concentration of which is adjusted to 0.22% by mass, and the average primary particle diameter determined by measuring the unidirectional diameter in a transmission electron microscope photograph, and measuring the transmittance of the aqueous dispersion to be measured, and then using the calibration curve.

[0073] The PTFE used in the present disclosure may have a core-shell structure. Examples of PTFE with a core-shell structure include modified polytetrafluoroethylene particles, which contain 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 JP-A-2005-527652.

[0074] There are no particular limitations on the specific methods of paste extrusion molding and powder rolling molding, but the following describes general methods.

[0075] (Paste extrusion molding) The method for producing the sheet may include the steps of: mixing the PTFE powder obtained using a hydrocarbon surfactant with an extrusion aid (1a), paste extrusion molding the resulting mixture (1b), rolling the extrudate obtained by extrusion molding (1c), drying the rolled sheet (1d), and firing the dried sheet to obtain a molded product (1e). The paste extrusion molding can also be carried out by adding conventionally known additives such as pigments and fillers to the PTFE powder.

[0076] The extrusion aid is not particularly limited, and any commonly known extrusion aid can be used, such as hydrocarbon oil.

[0077] (Powder Rolling Molding) The sheet can also be formed by powder rolling molding. Powder rolling molding is a method of applying shear force to resin powder to fibrillate it and thereby form it into a sheet. This method may then include a step of sintering the powder to obtain a molded product. More specifically, the sheet can be obtained by a production method including the steps of: (1) applying shear force while mixing a raw material composition containing a fluororesin and a filler; (2) molding the mixture obtained by the step (1) into a bulk form; and (3) rolling the bulk mixture obtained by the step (2) into a sheet form. When forming a sheet by such powder rolling molding, it is preferable to mix and mold only the fluororesin particles and the inorganic filler.

[0078] When a sheet is produced by the powder rolling molding method, it is preferable to form a film using a composition that does not contain any liquid component and that is essentially composed of fluororesin particles and filler particles. Here, "substantially composed of fluororesin particles and filler particles" means that the content of components other than the fluororesin particles and the filler particles is 3 mass% or less based on the total amount of the composition.

[0079] The sheet of the present disclosure may be surface-treated to enhance adhesive strength with the copper foil. The specific method of surface treatment of the sheet is not particularly limited, and any known method can be used. Conventional discharge treatments such as plasma discharge treatment, corona discharge treatment, glow discharge treatment, and sputtering treatment can be used as the surface treatment of the sheet. Among these, plasma treatment is preferred.

[0080] Plasma treatment is a process in which the fluororesin on the outer surface of the sheet is etched by contacting the sheet with plasma, and oxygen atoms, nitrogen atoms, etc. are added to the outer surface of the 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.

[0081] Alternatively, the surface to be modified may be exposed to an atmosphere of an organic compound-containing inert gas, which is an inert gas containing an organic compound, and a high-frequency voltage is applied between electrodes to cause a discharge, thereby generating active species on the surface, and then the surface treatment may be performed by introducing a functional group of the organic compound or graft-polymerizing a polymerizable organic compound.

[0082] The organic compound in the organic compound-containing inert gas may be a polymerizable or non-polymerizable organic compound containing an oxygen atom, such as vinyl esters such as vinyl acetate and vinyl formate; acrylic esters such as glycidyl methacrylate; ethers such as vinyl ethyl ether, vinyl methyl ether, and glycidyl methyl ether; carboxylic acids such as acetic acid and formic acid; alcohols such as methyl alcohol, ethyl alcohol, phenol, and ethylene glycol; ketones such as acetone and methyl ethyl ketone; carboxylic esters such as ethyl acetate and ethyl formate; acrylic acids such as acrylic acid and methacrylic acid. Among these, vinyl esters, acrylic esters, and ketones are preferred, and vinyl acetate and glycidyl methacrylate are particularly preferred, as the modified surface is less likely to be deactivated, i.e., has a long life.

[0083] The concentration of the organic compound in the organic compound-containing inert gas varies depending on the type of organic compound, 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 even more preferably 0.30 to 1.0% by volume. The discharge conditions may be appropriately selected depending on the desired degree of surface treatment, the type of fluororesin, the type and concentration of the organic compound, etc. Usually, the discharge amount is 50 to 1500 W·min / m. ２ , preferably 70 W·min / m ２ More than 1400W・min / m ２ The discharge treatment is carried out within the following range: The treatment temperature can be any temperature within the range of 0° C. to 100° C. In view of concerns about stretching and wrinkling of the sheet, a temperature of 80° C. or less is preferred.

[0084] (Laminate) The sheet of the present disclosure can be used as a sheet for printed wiring boards by laminating it with other substrates.

[0085] The sheet of the present disclosure can be used by laminating it with a metal foil as a sheet for a circuit board. A laminate may be formed by adhering a metal foil to one or both sides of the above-mentioned sheet. The present disclosure also provides a metal clad laminate having the above-mentioned sheet as an essential layer and a metal foil layer on one or both sides.

[0086] Examples of metal foils used in the present disclosure include copper foil, gold foil, silver foil, platinum foil, ruthenium foil, etc. Among these, copper foil is preferred because of its low conductor loss.

[0087] The present disclosure also provides a copper clad laminate, characterized in that a copper foil is adhered to one or both sides of the above-mentioned sheet. As described above, the sheet of the present disclosure is particularly suitable for use in printed wiring boards, and therefore can be suitably used as such a copper clad laminate.

[0088] The copper foil preferably has an Rz of 2.0 μm or less. That is, the sheet of the present disclosure also has excellent adhesion to copper foil with a high smoothness of Rz of 2.0 μm or less. Furthermore, the copper foil only needs to have an Rz of 2.0 μm or less on at least the surface that adheres to the sheet, and the Rz value of the other surface is not particularly limited. The copper foil preferably has a high smoothness of Rz of 2.0 μm or less, preferably Rz of 1.6 μm or less, and even more preferably Rz of 1.0 μm or less. The Rz is the sum of the values ​​of the highest point (maximum peak height: Rp) and the deepest point (maximum valley depth: Rv). The surface roughness is the ten-point average roughness defined in JIS-B0601. In this specification, the Rz is a value measured using a surface roughness meter (product name: Surfcom 470A, manufactured by Tokyo Seiki Co., Ltd.) with a measurement length of 4 mm.

[0089] The thickness of the copper foil is not particularly limited, but is preferably in the range of 1 to 100 μm, more preferably in the range of 5 to 50 μm, and even more preferably in the range of 9 to 35 μm.

[0090] The copper foil is not particularly limited, and specific examples include rolled copper foil and electrolytic copper foil.

[0091] The copper foil having an Rz of 2.0 μm or less is not particularly limited, and commercially available products can be used. Examples of commercially available copper foils having an Rz of 2.0 μm or less include electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm / Rz 0.85 μm) (manufactured by Fukuda Metal Foil & Powder Co., Ltd.).

[0092] The copper foil may be surface-treated to enhance the adhesive strength to the sheet of the present disclosure.

[0093] The surface treatment is not particularly limited, but includes silane coupling treatment, plasma treatment, corona treatment, UV treatment, electron beam treatment, etc., with plasma treatment being preferred. The reactive functional group of the silane coupling agent is not particularly limited, but from the viewpoint of adhesion to the resin substrate, it is preferred that the silane coupling agent has at least one terminal group selected from an amino group, a (meth)acrylic group, a mercapto group, and an epoxy group. Furthermore, the hydrolyzable group is not particularly limited, but includes alkoxy groups such as a methoxy group and an ethoxy group. The copper foil used in the present disclosure may have a rust-preventing layer (such as an oxide film such as chromate), a heat-resistant layer, etc. formed thereon.

[0094] The surface-treated copper foil having a surface treatment layer of the above-mentioned silane compound on the copper foil surface can be produced by preparing a solution containing the silane compound and then surface-treating the copper foil with this solution.

[0095] The copper foil may have a roughened layer on its surface from the viewpoint of improving adhesion to a resin substrate, etc. If the roughened layer may deteriorate the performance required in the present disclosure, the amount of roughening particles electrodeposited on the copper foil surface may be reduced as needed, or the copper foil may not be roughened at all.

[0096] In order to improve various properties, one or more layers selected from the group consisting of a heat-resistant layer, a rust-proofing layer, and a chromate-treated layer may be provided between the copper foil and the surface-treated layer. These layers may be a single layer or multiple layers.

[0097] The metal-clad laminate of the present disclosure may further include a layer other than the metal foil and sheet, which is preferably at least one 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.

[0098] The layers other than the metal foil and sheet are not particularly limited as long as they are made of the above-mentioned resins, and the thickness of the layers other than the metal foil and sheet is preferably within the range of 12.5 to 260 μm.

[0099] In the metal-clad laminate of the present disclosure, the metal layer may be formed on one or both sides of the roll film. Methods for forming the metal layer include laminating (adhering) metal foil to the surface of the roll film, vapor deposition, plating, and the like. Methods for laminating metal foil include a heat press method. The heat press temperature may be from the melting point of the sheet minus 150°C to the melting point of the sheet plus 40°C. The heat press time is, for example, 1 to 30 minutes. The laminate can be produced using a heat press pressure of 0.1 to 10 MPa.

[0100] The metal-clad laminate of the present disclosure is not particularly limited in its application, and is used as a circuit substrate. A printed circuit board is a plate-shaped component that electrically connects electronic components such as semiconductors and capacitor chips while simultaneously arranging and fixing them in a limited space. The configuration of the printed circuit board formed from the present metal-clad laminate is not particularly limited. The printed circuit board may be any of a rigid board, a flexible board, and a rigid-flexible board. The printed circuit board may be any of a single-sided board, a board, a double-sided board, and a multilayer board (such as a built-up board). In particular, it can be suitably used for flexible boards and rigid boards. In particular, it can be suitably used as a printed circuit board for high frequencies of 10 GHz or more.

[0101] The circuit board is not particularly limited, and can be produced by a general method using the above-mentioned metal-clad laminate.

[0102] In the metal clad laminate of the present disclosure, the metal foil layer may be formed on one or both sides of the rolled sheet. Examples of methods for forming the metal foil layer include laminating (adhering) a metal foil to the surface of a rolled sheet, vapor deposition, and plating. Examples of methods for laminating the metal foil include a method using heat pressing. The heat pressing temperature may be from the melting point of the sheet minus 150°C to the melting point of the sheet plus 40°C. The heat pressing time is, for example, 1 to 30 minutes.

[0103] For example, a method for producing a copper clad laminate is characterized in that the above sheet and a metal foil are laminated together, heated at 180 to 390°C, and press-molded at a pressure of 0.5 to 5 MPa in a vacuum or in an inert gas atmosphere.

[0104] To obtain the above-described laminate configuration, the sheet of the present disclosure is used with copper foil adhered to one or both sides. As described above, the sheet of the present disclosure has excellent adhesive properties. Therefore, it also has excellent adhesion to copper foil with a high smoothness of Rz 2.0 μm or less.

[0105] Copper foils used in circuit boards have traditionally been given a certain degree of roughness on their surfaces to ensure adhesion to insulating layers. However, in high-frequency applications, the presence of roughness on the copper foil surface is undesirable because it causes loss of electrical signals. The above-mentioned laminate can achieve suitable adhesion even to highly smooth copper foils, making it a laminate that can be suitably used as a circuit board.

[0106] The laminate for a circuit board is also a laminate characterized by having a metal foil layer and the above-mentioned sheet. The laminate may further have a base layer. The base layer is not particularly limited, but preferably has a fabric layer made of glass fiber and a resin film layer.

[0107] The glass fiber fabric layer is a layer made of glass cloth, glass nonwoven fabric, or the like. Commercially available glass cloth can be used, and glass cloth treated with a silane coupling agent is preferred to enhance affinity with the fluororesin. Examples of glass cloth materials include E-glass, C-glass, A-glass, S-glass, D-glass, NE-glass, and low-dielectric-constant glass, with E-glass, S-glass, and NE-glass being preferred due to their ease of availability. The fiber weave may be plain weave or twill weave. The thickness of the glass cloth is typically 5 to 90 μm, preferably 10 to 75 μm, but it is preferable to use glass cloth that is thinner than the sheet to be used.

[0108] The laminate may use a glass nonwoven fabric as a fabric layer made of glass fibers. Glass nonwoven fabric is a fabric in which short glass fibers are fixed with a small amount of a binder compound (resin or inorganic substance), or a fabric in which the shape is maintained by entanglement of the short glass fibers without the use of a binder compound. Commercially available glass nonwoven fabrics can be used. The diameter of the short glass fibers is preferably 0.5 to 30 μm, and the fiber length is preferably 5 to 30 mm. Specific examples of binder compounds include resins such as epoxy resins, acrylic resins, cellulose, polyvinyl alcohol, and fluororesins, as well as inorganic substances such as silica compounds. The amount of binder compound used is typically 3 to 15 mass% relative to the short glass fibers. Examples of materials for the short glass fibers include E-glass, C-glass, A-glass, S-glass, D-glass, NE-glass, and low-dielectric-constant glass. The thickness of the glass nonwoven fabric is typically 50 to 1000 μm, preferably 100 to 900 μm. The thickness of the glass nonwoven fabric in this application refers to a value measured in accordance with JIS P8118:1998 using a digital gauge DG-925 (load 110 grams, face diameter 10 mm) manufactured by Ono Sokki Co., Ltd. In order to increase the affinity with the fluororesin, the glass nonwoven fabric may be treated with a silane coupling agent.

[0109] Since most glass nonwoven fabrics have a very high porosity of 80% or more, it is preferable to use a sheet that is thicker than a sheet made of fluororesin and compress it under pressure.

[0110] The glass fiber fabric layer may be a layer formed by laminating a glass cloth and a glass nonwoven fabric. This allows the properties of each to be combined to obtain suitable properties. The glass fiber fabric layer may be in the form of a prepreg impregnated with a resin.

[0111] The laminate may have a glass fiber fabric layer and a sheet bonded at the interface, or the glass fiber fabric layer may be partially or entirely impregnated with the sheet. Furthermore, the laminate may be a prepreg produced by impregnating a glass fiber fabric with a fluororesin composition. The prepreg thus obtained may further be laminated with a sheet of the present disclosure. In this case, the fluororesin composition used to produce the prepreg is not particularly limited, and the sheet of the present disclosure may also be used.

[0112] The resin film used as the substrate layer is preferably a heat-resistant resin film or a thermosetting resin film. Examples of heat-resistant resin films include polyimide, modified polyimide, liquid crystal polymer, and polyphenylene sulfide. Examples of thermosetting resins include those containing epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene ether, polyphenylene ether, and polybutadiene. The heat-resistant resin film and the thermosetting resin film may contain reinforcing fibers. While the reinforcing fibers are not particularly limited, glass cloth, particularly low-dielectric type fibers, are preferred.

[0113] The dielectric properties, linear expansion coefficient, water absorption coefficient, and other properties of the heat-resistant resin film and the 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 3.0 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 linear expansion coefficient 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.

[0114] The metal clad laminate of the present disclosure is not particularly limited in its application and is used as a circuit board. The present disclosure also relates to a circuit board having the above-mentioned metal clad laminate. A circuit board is a plate-shaped component that electrically connects electronic components such as semiconductors and capacitor chips while simultaneously arranging and fixing them in a limited space. The configuration of a circuit board formed from a sheet or metal clad laminate of the present disclosure is not particularly limited. The circuit board may be any of a rigid board, a flexible board, and a rigid-flexible board. The circuit board may be any of a single-sided board, a double-sided board, and a multilayer board (such as a pulled-up board). In particular, it is suitable for use as a flexible board or a rigid board. When the sheet of the present disclosure does not contain glass fiber or a cloth made of glass fiber, it is suitable for use as a flexible board. In particular, it is suitable for use as a printed circuit board for high frequencies of 10 GHz or more.

[0115] In this disclosure, a high-frequency circuit does not simply refer to a circuit that transmits only high-frequency signals, but also includes circuits that also have transmission lines on the same plane that transmit signals other than high-frequency signals, such as a transmission line that converts a high-frequency signal into a low-frequency signal and outputs the generated low-frequency signal to the outside, or a transmission line that supplies power to drive high-frequency compatible components. The circuit board can also be used as a circuit board for antennas, filters, etc. The present disclosure also relates to antennas formed from the circuit board. It is particularly suitable for use as a millimeter-wave antenna for mobility applications such as automobiles and aircraft.

[0116] The circuit board is not particularly limited, and can be produced by a general method using the above-mentioned metal clad laminate.

[0117] The sheet and metal clad laminate of the present disclosure are used as electric and electronic components, for example, antennas used in electronic devices and communication devices such as ETC, GPS, wireless LAN, and mobile phones, high-speed transmission connectors, CPU sockets, millimeter wave and quasi-millimeter wave radars such as collision prevention radars, RFID tags, capacitors, inverter parts, cable covering materials, insulating materials for secondary batteries such as lithium ion batteries, speaker diaphragms, etc.

[0118] Examples of high-speed communication compatible substrates include base station antenna substrates, antenna distribution substrates, substrates for RRH (Remote Radio Head), which is the radio part of a wireless base station, substrates for the control unit or baseband unit (BBU: Base Band Unit) of a wireless base station, transceiver substrates for high-speed communication, substrates for RNC (Radio Network Controller), substrates for high-speed transmitters, substrates for high-speed receivers, substrates for high-speed signal multiplexing circuits, substrates for Wi-Fi using the 60 GHz band, and substrates for data transfer used in data center servers. Examples of high-speed communication compatible substrates include antenna substrates, such as substrates for massive MIMO (massive multiple-input multiple-output) antennas aimed at high-capacity communication required by standards from 5G onwards. Further examples include receiving antennas for microwave spatial transmission wireless power supply. The sheet of the present disclosure has good adhesion to unroughened copper foil, which has low transmission loss. Therefore, when an antenna is obtained by processing a copper clad laminate containing the sheet of the present disclosure and unroughened copper foil, the gain is improved, making it particularly suitable for antennas.

[0119] The sheet of the present disclosure can be used not only as an insulator for a substrate but also as an insulator for a signal line coating material, for example, as an insulating coating material (e.g., insulating tube) for a waveguide for transmitting high-speed signals, a QSFP cable for a high-speed LAN, a coaxial cable for high-speed communication (e.g., an SFP+ cable, a QSFP+ cable, etc.), a coaxial cable for low loss, etc.

[0120] When using such high frequencies, materials used in electrical components such as connectors and communication devices such as casings are required to have stable electrical properties such as a low relative permittivity (εr) and a low dielectric loss tangent (tanδ). The sheet of the present disclosure can also be used as an insulating material for such materials.

[0121] The sheet of the present disclosure can also be used as an insulating material for connector printed wiring boards that require soldering. Because the sheet of the present disclosure has excellent heat resistance, problems are unlikely to occur even at high temperatures during soldering.

[0122] In dielectric waveguides, materials with low dielectric loss are required to transmit high-frequency millimeter waves or submillimeter waves with low loss. The sheet of the present disclosure can also be used as an insulating material for dielectric waveguides that transmit millimeter waves, submillimeter waves, etc. Examples of dielectric waveguides include cylindrical dielectric waveguides, rectangular dielectric waveguides, elliptical dielectric waveguides, tubular dielectric waveguides, image waveguides, insulator image waveguides, trapped image waveguides, rib guides, strip dielectric waveguides, inverted strip waveguides, H guides, and nonradiative dielectric waveguides (NRD guides).

[0123] In this disclosure, mobility refers to all means and methods related to movement and transportation, including automobiles in general, such as private cars, buses, taxis, and trucks, as well as two-wheeled vehicles such as motorcycles, bicycles, and mopeds, trains, senior cars, and compact one-seater personal mobility vehicles. Furthermore, mobility is not necessarily limited to vehicles that move on land, but may also be vehicles that move in the air or underwater.

[0124] The present disclosure will be specifically described below based on examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass", respectively.

[0125] (Examples 1-9, Comparative Examples 1-3) Sheet Fabrication Method (Paste Extrusion) PTFE powder (average particle size: 500 μm, apparent density: 460 g / L, standard specific gravity: 2.17), silica particles (manufactured by Admatechs Co., Ltd.: SC6500-SQ, average particle size: 2.1 μm), and alumina particles (manufactured by Nippon Light Metal Co., Ltd.: LS-210B (average particle size: 3.2 μm) or LS-110F (average particle size: 1.13 μm)) were weighed out in the proportions shown in Table 1 and mixed in a mixer in the presence of dry ice. The temperature during mixing was kept below -10°C. 21 wt% of oil (Isopar H) was added to the resulting mixed powder, mixed, and aged for approximately 5 hours. The aged composition was preformed at a pressure of 3 MPa, and the preformed compact was extruded at 40°C and 50 mm / min to obtain an extrusion sample. The extruded sample was rolled with two rolls (roll gap: set to 500-80 μm) to obtain a sample with a film thickness of 125 μm. This was dried at 200°C for 2 hours and calcined at 360°C for 15 minutes to obtain a sheet.

[0126] Comparative Example 4 A sheet was obtained in the same manner as in Examples 1 to 9 and Comparative Examples 1 to 3, except that zinc oxide particles (DW-4 manufactured by Hakusui Tech Co., Ltd., average particle size: 4 μm) were used instead of alumina particles.

[0127] (Example 10) Sheet production method (powder rolling molding) PTFE powder (average particle size: 500 μm, apparent density: 460 g / L, standard specific gravity: 2.17), silica particles (manufactured by Admatechs Co., Ltd.: SC6500-SQ, average particle size: 2.1 μm), alumina particles (manufactured by Nippon Light Metal Co., Ltd.: LS-210B (average particle size: 3.2 μm) or LS-110F (average particle size: 1.13 μm)) were weighed to the mass ratio shown in Table 1 and stirred with a Wonder Crusher at room temperature at 6 setting for 30 seconds twice. The resulting mixture was rolled with two rolls (roll gap: set to 100 μm, roll temperature: 100 ° C.) to obtain a sample with a film thickness of 130 μm. The sample was then baked at 360 ° C. for 15 minutes to obtain a sheet.

[0128] Each sample obtained was evaluated based on the following criteria. [Dielectric constant (Dk) of sheet] Using a split cylinder dielectric constant / dielectric loss tangent measuring device (manufactured by EM Lab), Dk at 10 GHz was measured in 10°C increments from -50°C to 150°C. The rate of change from -50°C to 150°C was calculated from the difference between the maximum and minimum measured Dk values.

[0129] [Dielectric Loss Tangent (Df) of Sheet] Df was measured at 20° C. and 10 GHz using a split cylinder type dielectric constant / dielectric loss tangent measuring device (manufactured by EM Lab).

[0130] [Coefficient of linear expansion (CTE)] TMA measurement was performed in tension mode using a TMA-7100 (Hitachi High-Tech Science Corporation). A sheet cut to a length of 20 mm, width of 5 mm, and thickness of 150 μm was used as a sample piece. The distance between chucks was set to 10 mm, and the coefficient of linear expansion was determined from the displacement of the sample at a heating rate of 2°C / min from 0 to 150°C while applying a load of 49 mN. The results are shown in Table 1.

[0131]

[0132] The sheet obtained in Example 1 was subjected to [sheet surface treatment], [sheet surface XPS measurement], and [peel strength measurement] under the following conditions. The elemental composition (atomic %) measured by XPS was: C1s: 43.4, N1s: 2.8, O1s: 7.1, F1s: 43.3, Si2p: 1.2. Furthermore, the peel strength was a high value of 11 N / cm, confirming high adhesiveness.

[0133] [Sheet Surface Treatment] A sheet was placed between the upper and lower electrodes in a treatment chamber (direct-type plasma surface treatment device, manufactured by Air Water Inc.), and the treatment chamber was filled with a mixed gas atmosphere of argon, helium, nitrogen, and oxygen. The sheet surface was then subjected to discharge plasma treatment for 36 seconds. The elemental composition of the surface-treated sheet was measured by XPS.

[0134] [XPS Measurement of Sheet Surface] Measurement was carried out using a scanning X-ray photoelectron spectroscopic analyzer (XPS / ESCA) PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.).

[0135] [Peel Strength Measurement] Copper foil (CF-T9DA-SV-18, manufactured by Fukuda Metal Foil Powder Co., Ltd., Rz = 0.85 μm, Rq = 0.05 μm) was placed on top and bottom of the surface-treated sheet so that the treated side was in close contact with the sheet, and a sample was prepared by heating and pressurizing using a vacuum heat press (360°C, 2.5 MPa, 300 s). The obtained sample was cut into 10 mm wide strips, and the peel strength was measured using a Tensilon universal testing machine (manufactured by Shimadzu Corporation) by gripping the unbonded portion of the strip sample with the upper and lower chucks of the Tensilon and pulling at a rate of 50 mm per minute, and the obtained value was taken as the peel strength.

[0136] From the above results, it can be seen that the sheet of the present disclosure maintains a low dielectric loss tangent and low CTE, while also having a low rate of change in relative dielectric constant of 0.020 or less in the temperature range of -50 to 150°C, and also has excellent adhesion to copper foil, and therefore has excellent performance as a substrate for use in high-frequency printed wiring boards, particularly as a substrate for use in antennas for millimeter-wave radar for mobility applications.

[0137] The sheet of the present disclosure can be suitably used in particular for high-frequency printed circuit boards.

Claims

1. A sheet characterized in that the rate of change of the relative dielectric constant in the temperature range of -50 to 150°C is 0.020 or less and that it contains two or more types of fillers.

2. The sheet according to claim 1, wherein the sheet has a coefficient of linear expansion (CTE) of 70 ppm / °C or less.

3. The sheet according to claim 1 or 2, which has a dielectric tangent value of 0.0015 or less at 10 GHz.

4. The sheet according to any one of claims 1 to 3, which has a thickness of 5 to 250 µm.

5. The sheet according to any one of claims 1 to 4, wherein the sheet contains a fluororesin.

6. The sheet according to claim 5, wherein said fluororesin is polytetrafluoroethylene.

7. The sheet according to any one of claims 1 to 6, wherein the filler has a band gap of 2 eV or more.

8. A sheet according to any one of claims 1 to 7, wherein the filler content in the total amount of the sheet is 30 mass % or more.

9. The sheet according to any one of claims 1 to 8, wherein the filler contains at least two types selected from the group consisting of silica, alumina, boron nitride and zirconium oxide.

10. The sheet according to any one of claims 1 to 9, wherein the filler is composed of two types of filler: silica and alumina.

11. The sheet according to claim 9 or 10, wherein the silica is in the form of spherical particles.

12. The sheet according to any one of claims 9 to 11, wherein the silica is silica particles treated with a silane coupling agent.

13. The sheet according to claim 12, wherein the silane coupling agent has an aminopropyl group.

14. The sheet according to any one of claims 9 to 13, wherein the silica particles have an average particle size of 10 μm or less.

15. A sheet according to any one of claims 9 to 14, wherein the alumina has an average particle size of 10 µm or less.

16. The sheet according to any one of claims 9 to 15, wherein the alumina is mixed in an amount of 10 to 50 mass % based on the total amount of alumina and silica.

17. A method for producing a sheet according to any one of claims 5 to 16, characterized in that a film is formed by mixing a fluororesin and a filler.

18. A method for producing the sheet according to any one of claims 5 to 17, characterized in that the film is formed using a composition consisting essentially of fluororesin particles and filler particles containing at least silica particles and alumina particles.

19. A metal-clad laminate comprising the sheet according to any one of claims 1 to 16 as an essential layer and having a metal foil layer on one or both sides.

20. The metal-clad laminate of claim 19, wherein said metal foil is copper.

21. A circuit board comprising the metal-clad laminate according to claim 19 or 20.

22. An antenna formed from the circuit board according to claim 21.

23. The antenna of claim 22, which is a millimeter wave antenna for mobility.

24. The sheet according to any one of claims 1 to 16, which is for use in circuit boards.

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