Insulating material for circuit substrate, and method for manufacturing the same, and metal foil-clad laminate

Abstract

To provide an insulating material for a circuit substrate, which has excellent dielectric characteristics in a high frequency area, has low coefficients of linear expansion all in a MD direction, a TD direction, and a ZD direction, is easily manufactured and has excellent productivity, and a method for manufacturing the same and a metal foil-clad laminate.SOLUTION: An insulating material for a circuit substrate, comprising a laminate having a thermoplastic liquid crystal polymer film and a woven fabric of an inorganic fiber, wherein the thermoplastic liquid crystal polymer film contains an inorganic filler, and the laminate is a dry laminate in which the thermoplastic liquid crystal polymer film and the woven fabric are thermocompression bonded.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an insulating material for circuit boards, a method for producing the same, and a metal foil-clad laminate. [Background technology]

[0002] Conventionally, varnish-impregnated composite materials have been known as insulating materials for circuit boards, which are produced by impregnating glass cloth with a varnish containing a thermosetting resin such as an epoxy resin, an inorganic filler, a solvent, and the like, and then hot-press molding the impregnated glass cloth (see, for example, Patent Documents 1 and 2). However, this manufacturing method has poor process tolerance during manufacturing, resulting in poor productivity, in terms of, for example, the resin flow during varnish impregnation and the curing property during hot-press molding. Furthermore, thermosetting resins are prone to absorbing moisture, and the dimensions change as a result of this moisture absorption, resulting in poor dimensional accuracy (heated dimensional accuracy) of the resulting varnish-impregnated composite materials.

[0003] On the other hand, liquid crystal polymers (LCPs; Liquid Crystal Polymers) are polymers that exhibit liquid crystallinity in a molten state or in a solution state. In particular, thermotropic liquid crystal polymers that exhibit liquid crystallinity in a molten state have excellent properties such as high gas barrier properties, high film strength, high heat resistance, high insulation, low water absorption, and low dielectric properties in high frequency ranges. Therefore, the practical application of films using liquid crystal polymers is being considered for gas barrier film material applications, electronic material applications, and electrical insulating material applications. As a liquid crystal polymer film having such properties, a liquid crystal polymer film obtained by inflation molding a thermoplastic liquid crystal polymer, which is a copolymer of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, has been disclosed (see, for example, Patent Document 3).

[0004] However, films using liquid crystal polymers have high anisotropy in the in-plane molecular orientation of the film, and large in-plane anisotropy in the dimensional change due to heating. To improve this, a biaxially stretched liquid crystal polymer film formed from a blend of a liquid crystal polymer and at least one thermoplastic resin selected from polyethersulfone, polyetherimide, polyamideimide, polyetheretherketone, polyarylate, and polyphenylene sulfide has been disclosed (see, for example, Patent Document 4).

[0005] On the other hand, as an insulating material for circuit boards using a liquid crystal polymer, a varnish-impregnated composite material is known, which is obtained by impregnating glass cloth with a varnish containing a liquid crystal polymer, an inorganic filler, a solvent, etc., and then hot-press molding (see, for example, Patent Document 5). Also, as an insulating material for circuit boards that does not use the varnish impregnation process, a laminated film is known, which is obtained by hot-pressing a liquid crystal polymer film and glass cloth (see, for example, Patent Documents 6 and 7). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-052955 [Patent Document 2] Japanese Patent Application Publication No. 2019-199562 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-263577 [Patent Document 4] Japanese Patent Application Laid-Open No. 2004-175995 [Patent Document 5] Japanese Patent Application Laid-Open No. 2010-103339 [Patent Document 6] Japanese Patent Application Publication No. 09-309150 [Patent Document 7] Japanese Patent Application Laid-Open No. 2005-109042 Summary of the Invention [Problem to be solved by the invention]

[0007] Insulating materials for circuit boards made from liquid crystal polymers have been attracting attention in recent years as insulating materials for circuit boards such as flexible printed circuit boards (FPCs), flexible printed circuit board laminates, and fiber-reinforced flexible laminates in the upcoming 5th generation mobile communication systems (5G) and millimeter wave radar, due to their excellent high-frequency characteristics and low dielectric constant.

[0008] The technology of Patent Document 4 mentioned above successfully suppresses the linear expansion coefficient of the film in the machine direction (MD; longitudinal direction) and transverse direction (TD; horizontal direction) to 5 to 25 ppm / K by biaxially stretching a thermoplastic resin blend. However, the linear expansion coefficient of the film in the ZD direction (thickness direction) still exceeds 200 ppm / K. For example, in rigid substrate applications requiring multilayer lamination, there is a strong demand for a reduction in the linear expansion coefficient of the film in the ZD direction (thickness direction). Moreover, the biaxially stretched film obtained in Patent Document 4 contains a large amount of thermoplastic resin such as polyarylate, resulting in reduced heat resistance, dielectric properties, tensile strength, etc., and therefore poor practicality in terms of the basic performance required for an insulating material for circuit boards.

[0009] Furthermore, the technology described in Patent Document 5 employs a varnish impregnation process, which results in limited process tolerance during manufacturing, resulting in poor productivity in terms of, for example, resin flow during varnish impregnation and curing during hot press molding. Furthermore, there are limitations on the thickness of the thermoplastic liquid crystal polymer film, resulting in limited flexibility in product configuration. Furthermore, the drying of the varnish-impregnated substrate, disposal of residual solvents, and the equipment burden required for these, such as drying ovens, are also significant. Meanwhile, the technologies described in Patent Documents 6 and 7 reduce the thermal expansion coefficient in the in-plane direction by thermocompression bonding the liquid crystal polymer film and glass cloth. However, no consideration or addressing has been given to the linear expansion coefficient in the ZD direction (thickness direction).

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an insulating material for circuit boards that has excellent dielectric properties in the high frequency range, a small coefficient of linear expansion in all of the MD, TD, and ZD directions, and is easy to manufacture with excellent productivity, a method for manufacturing the same, and a metal foil-clad laminate, etc. [Means for solving the problem]

[0011] As a result of intensive research to solve the above problems, the inventors discovered that a specific dry laminated laminate obtained by thermocompression bonding a thermoplastic liquid crystal polymer film and an inorganic fiber woven fabric can solve the above problems, and thus completed the present invention.

[0012] That is, the present invention provides various specific embodiments as shown below. (1) An insulating material for circuit boards, comprising a laminate having a thermoplastic liquid crystal polymer film and a woven fabric of inorganic fibers, the thermoplastic liquid crystal polymer film containing an inorganic filler, and the laminate being a dry laminate in which the thermoplastic liquid crystal polymer film and the woven fabric are thermocompression-bonded.

[0013] (2) The insulating material for circuit boards according to (1), wherein the thermoplastic liquid crystal polymer film is a melt-extruded film. (3) The insulating material for circuit boards according to (1) or (2), wherein the thermoplastic liquid crystal polymer film is a T-die melt-extruded film.

[0014] (4) The insulating material for circuit boards according to any one of (1) to (3), wherein the inorganic filler contains silica. (5) The insulating material for circuit boards according to any one of (1) to (4), wherein the inorganic filler has a median diameter (d50) of 0.01 μm or more and 50 μm or less. (6) The insulating material for circuit boards according to any one of (1) to (5), wherein the thermoplastic liquid crystal polymer film contains the inorganic filler in an amount of 1% by mass or more and 45% by mass or less relative to the total amount of the film.

[0015] (7) The insulating material for circuit boards according to any one of (1) to (6), wherein the woven fabric has a thickness of 10 μm or more and 300 μm or less. (8) The insulating material for circuit boards according to any one of (1) to (7), wherein the woven fabric of inorganic fibers is glass cloth.

[0016] (9) The insulating material for circuit boards according to any one of (1) to (8), having an average coefficient of linear expansion at 23 to 200°C, measured by a TMA method in accordance with JIS K7197, of 5 ppm / K or more and 25 ppm / K or less in the in-plane direction and 10 ppm / K or more and 100 ppm / K or less in the thickness direction. (10) Relative permittivity ε at 36 GHz measured by the cavity resonator contact method in accordance with JIS K6471 r The insulating material for circuit boards according to any one of (1) to (9), wherein the value of the elastic modulus is 3.0 or more and 3.7 or less. (11) The insulating material for circuit boards according to any one of (1) to (10), having a dielectric loss tangent tanδ of 0.0010 or more and 0.0050 or less at 36 GHz measured by a cavity resonator vibration method in accordance with JIS K6471.

[0017] (12) A method for producing an insulating material for circuit boards, comprising the steps of preparing a thermoplastic liquid crystal polymer film containing an inorganic filler, preparing a woven fabric of inorganic fibers, and laminating the thermoplastic liquid crystal polymer film and the woven fabric, heating and pressurizing the laminate to form a dry laminate in which the thermoplastic liquid crystal polymer film and the woven fabric are thermocompression-bonded.

[0018] (13) The method for producing an insulating material for circuit boards according to (12), wherein the step of preparing the thermoplastic liquid crystal polymer film includes a step of preparing a resin composition containing the thermoplastic liquid crystal polymer and the inorganic filler, and a film production step of molding the resin composition to produce the thermoplastic liquid crystal polymer film containing the inorganic filler.

[0019] (14) A metal foil-clad laminate comprising the insulating material for circuit boards according to any one of (1) to (11) above and a metal foil provided on one and / or both sides of the insulating material for circuit boards. [Effects of the Invention]

[0020] According to one aspect of the present invention, it is possible to provide an insulating material for circuit boards that has excellent dielectric properties in the high frequency range, a small coefficient of linear expansion in all of the MD, TD, and ZD directions, and is easy to manufacture with excellent productivity, a method for manufacturing the same, and a metal foil-clad laminate, etc. Furthermore, according to one aspect of the present invention, a high-performance insulating material for circuit boards can be realized without a varnish impregnation process, and therefore insulating materials for circuit boards can be supplied stably with good reproducibility and at low cost. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic cross-sectional view showing an insulating material 100 for a circuit board according to one embodiment. [Figure 2] 1 is a flowchart showing a method for manufacturing an insulating material 100 for a circuit board according to an embodiment. [Figure 3] 1 is a schematic diagram showing a metal foil-clad laminate 200 according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown. However, the following embodiments are merely examples for explaining the present invention, and the present invention is not limited thereto. In other words, the present invention can be implemented with any modifications within the scope of the gist of the present invention. In this specification, for example, a numerical range such as "1 to 100" includes both the lower limit "1" and the upper limit "100." The same applies to other numerical ranges.

[0023] (Insulating material for circuit boards) 1 is a schematic cross-sectional view showing a main portion of an insulating material 100 for circuit boards according to this embodiment. The insulating material 100 for circuit boards according to this embodiment includes a laminate having a layered structure (three-layer structure) in which a thermoplastic liquid crystal polymer film 11, an inorganic fiber woven fabric 21, and a thermoplastic liquid crystal polymer film 12 are arranged at least in this order. In this laminate, the thermoplastic liquid crystal polymer film 11 is provided on the side 21a of the woven fabric 21, and the thermoplastic liquid crystal polymer film 12 is provided on the side 21b of the woven fabric 21. As described below, these thermoplastic liquid crystal polymer films 11 and 12 are thermocompression bonded to the woven fabric 21, thereby forming a dry-laminate laminate L having a three-layer structure. Although this embodiment illustrates a three-layer dry laminate L, it goes without saying that the present invention can also be implemented with a two-layer dry laminate L in which either the thermoplastic liquid crystal polymer film 11 or the thermoplastic liquid crystal polymer film 12 is omitted, or with a four or more layer dry laminate L in which thermoplastic liquid crystal polymer films 11, 12 or woven fabric 21 are further laminated.

[0024] In this specification, "arranged at least in this order" not only refers to an embodiment in which the thermoplastic liquid crystal polymer films 11 and 12 are placed directly on the surface of the woven fabric 21 (e.g., surface 21a or surface 21b) as in this embodiment, but also includes an embodiment in which any layer (e.g., a primer layer, an adhesive layer, etc.) not shown is interposed between the surfaces 21a and 21b of the woven fabric 21 and the thermoplastic liquid crystal polymer films 11 and 12, and the thermoplastic liquid crystal polymer films 11 and 12 are arranged at a distance from the surfaces 21a and 21b of the woven fabric 21.

[0025] The thermoplastic liquid crystal polymer films 11 and 12 are formed by molding a thermoplastic liquid crystal polymer into a film shape. In this specification, the term "film" does not include woven fabrics and nonwoven fabrics (hereinafter, these may be collectively referred to as "fabric"). As the thermoplastic liquid crystal polymer films 11 and 12, melt-extruded films such as T-die melt-extruded films are preferably used. Compared to woven fabrics and nonwoven fabrics made of thermoplastic liquid crystal polymer fibers, melt-extruded films of thermoplastic liquid crystal polymer are available at low cost and with uniform quality.

[0026] The thickness of the thermoplastic liquid crystal polymer films 11, 12 can be appropriately set according to requirements and is not particularly limited. Considering handleability and productivity during melt extrusion molding, the thickness is preferably 5 μm to 300 μm, more preferably 10 μm to 250 μm, and even more preferably 20 μm to 200 μm. The thicknesses of the thermoplastic liquid crystal polymer films 11, 12 may be the same or different. This embodiment employs a dry laminate L in which the thermoplastic liquid crystal polymer films 11, 12 and the woven fabric 21 are thermocompression-bonded, which is advantageous in that it allows the use of thick thermoplastic liquid crystal polymer films 11, 12 (e.g., thickness of 200 μm or more), which could not be applied using the varnish impregnation process of the prior art.

[0027] The thermoplastic liquid crystal polymer used here can be any known one in the art, and the type is not particularly limited. Liquid crystal polymers are polymers that form an optically anisotropic molten phase, and representative examples include thermotropic liquid crystal compounds. The properties of the anisotropic molten phase can be confirmed by known methods such as polarized light inspection using crossed polarizers. More specifically, the anisotropic molten phase can be confirmed by using a Leitz polarizing microscope to observe a sample placed on a Leitz hot stage at 40x magnification under a nitrogen atmosphere.

[0028] Specific examples of thermoplastic liquid crystal polymers include, but are not limited to, those obtained by polycondensation of monomers such as aromatic or aliphatic dihydroxy compounds, aromatic or aliphatic dicarboxylic acids, aromatic hydroxycarboxylic acids, aromatic diamines, aromatic hydroxyamines, and aromatic aminocarboxylic acids. The thermoplastic liquid crystal polymer is preferably a copolymer. Specific examples include, but are not limited to, aromatic polyamide resins obtained by polycondensation of monomers such as aromatic hydroxycarboxylic acids, aromatic diamines, and aromatic hydroxyamines; and aromatic polyester resins obtained by polycondensation of monomers such as aromatic diols, aromatic carboxylic acids, and aromatic hydroxycarboxylic acids. These may be used alone or in any combination and ratio of two or more. The thermoplastic liquid crystal polymer film 11 and the thermoplastic liquid crystal polymer film 12 may be made of the same type of thermoplastic liquid crystal polymer or different types of thermoplastic liquid crystal polymers.

[0029] Among these, aromatic polyester resins that exhibit thermotropic liquid crystal-like properties and have a melting point of 250°C or higher, preferably 280°C to 380°C, are preferably used. Examples of such aromatic polyester resins include aromatic polyester resins that are synthesized from monomers such as aromatic diols, aromatic carboxylic acids, and hydroxycarboxylic acids and exhibit liquid crystallinity when melted. Representative examples include, but are not limited to, polycondensates of ethylene terephthalate and parahydroxybenzoic acid, polycondensates of phenol, phthalic acid, and parahydroxybenzoic acid, and polycondensates of 2,6-hydroxynaphthoic acid and parahydroxybenzoic acid. The aromatic polyester resins may be used alone or in any combination and ratio of two or more.

[0030] A preferred embodiment is an aromatic polyester resin having a basic structure of 6-hydroxy-2-naphthoic acid and its derivatives (hereinafter sometimes simply referred to as "monomer component A") and at least one monomer component (hereinafter sometimes simply referred to as "monomer component B") selected from the group consisting of parahydroxybenzoic acid, terephthalic acid, isophthalic acid, 6-naphthalenedicarboxylic acid, 4,4'-biphenol, bisphenol A, hydroquinone, 4,4-dihydroxybiphenol, ethylene terephthalate, and derivatives thereof. Such aromatic polyester resins have linear molecular chains regularly aligned in the molten state to form an anisotropic molten phase, typically exhibiting thermotropic liquid crystal-like properties and possessing excellent basic performance in terms of mechanical properties, electrical properties, high-frequency properties, heat resistance, moisture absorption, etc.

[0031] Furthermore, the aromatic polyester resin of the preferred embodiment described above can have any configuration as long as it contains monomer component A and monomer component B as essential units. For example, it may contain two or more types of monomer component A, or three or more types of monomer component A. The aromatic polyester resin of the preferred embodiment described above may also contain another monomer component (hereinafter simply referred to as "monomer component C") other than monomer component A and monomer component B. That is, the aromatic polyester resin of the preferred embodiment described above may be a binary or higher polycondensate consisting of only monomer component A and monomer component B, or a ternary or higher polycondensate consisting of monomer component A, monomer component B, and monomer component C. Examples of other monomer components include those other than the above-mentioned monomer component A and monomer component B, specifically, aromatic or aliphatic dihydroxy compounds and derivatives thereof; aromatic or aliphatic dicarboxylic acids and derivatives thereof; aromatic hydroxycarboxylic acids and derivatives thereof; aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids and derivatives thereof; but are not particularly limited thereto. The other monomer components may be used alone or in any combination and ratio of two or more.

[0032] In this specification, the term "derivative" refers to a monomer component described above into which a modifying group such as a halogen atom (e.g., fluorine atom, chlorine atom, bromine atom, or iodine atom), an alkyl group having 1 to 5 carbon atoms (e.g., methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, s-butyl group, or t-butyl group), an aryl group such as a phenyl group, a hydroxyl group, an alkoxy group having 1 to 5 carbon atoms (e.g., methoxy group, ethoxy group), a carbonyl group, or -O-, -S-, or -CH- has been introduced (hereinafter, this may be referred to as a "monomer component having a substituent"). Here, the "derivative" may be an ester-forming monomer such as an acylation product, ester derivative, or acid halide of the monomer components A and B, which may have the modifying group described above.

[0033] Particularly preferred embodiments include binary polycondensates of parahydroxybenzoic acid and its derivatives with 6-hydroxy-2-naphthoic acid and its derivatives; ternary or higher polycondensates of parahydroxybenzoic acid and its derivatives, 6-hydroxy-2-naphthoic acid and its derivatives, and monomer component C; and ternary or higher polycondensates of parahydroxybenzoic acid and its derivatives, 6-hydroxy-2-naphthoic acid and its derivatives, and terephthalic acid, isophthalic acid, 6-naphthalenedicarboxylic acid, 4,4'-biphenol, bisphenol A, hydroquinone, 4,4-dihydroxybiphenol. and ternary or higher polycondensates composed of parahydroxybenzoic acid and its derivatives, 6-hydroxy-2-naphthoic acid and its derivatives, and one or more selected from the group consisting of terephthalic acid, isophthalic acid, 6-naphthalenedicarboxylic acid, 4,4'-biphenol, bisphenol A, hydroquinone, 4,4-dihydroxybiphenol, ethylene terephthalate, and their derivatives, and one or more monomer components C. These can be obtained as having a relatively low melting point compared to, for example, homopolymers of parahydroxybenzoic acid, and therefore, thermoplastic liquid crystal polymers using these have excellent moldability when thermocompressed to an adherend.

[0034] To lower the melting point of the aromatic polyester resin, improve the moldability of the thermoplastic liquid crystal polymer films 11 and 12 when thermocompression-bonded to an adherend, or to obtain high peel strength when thermoplastic liquid crystal polymer films 11 and 12 are thermocompression-bonded to a metal foil, the molar ratio of the monomer component A to the aromatic polyester resin is preferably 10 mol% to 70 mol%, more preferably 10 mol% to 50 mol%, even more preferably 10 mol% to 40 mol%, and more preferably 15 mol% to 30 mol%. Similarly, the molar ratio of the monomer component B to the aromatic polyester resin is preferably 30 mol% to 90 mol%, more preferably 50 mol% to 90 mol%, even more preferably 60 mol% to 90 mol%, and more preferably 70 mol% to 85 mol%. Furthermore, the content of the monomer component C that may be contained in the aromatic polyester resin is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 5% by mass or less, and preferably 3% by mass or less, calculated as a molar ratio.

[0035] The aromatic polyester resin can be synthesized by any known method, and is not particularly limited. Known polycondensation methods for forming ester bonds using the above-mentioned monomer components, such as melt polymerization, melt acidolysis, and slurry polymerization, can be used. When using these polymerization methods, an acylation or acetylation step may be carried out according to a conventional method.

[0036] The thermoplastic liquid crystal polymer films 11 and 12 further contain an inorganic filler. By containing the inorganic filler, the thermoplastic liquid crystal polymer films 11 and 12 can be realized with a reduced linear expansion coefficient, and in particular, in this embodiment, the linear expansion coefficient in the ZD direction (thickness direction) is effectively reduced, making them particularly useful in rigid substrate applications that require multilayer lamination, for example.

[0037] The inorganic filler used here can be any known filler in the art, and the type is not particularly limited. Examples include kaolin, calcined kaolin, calcined clay, uncalcined clay, silica (e.g., natural silica, fused silica, amorphous silica, hollow silica, wet silica, synthetic silica, aerosil, etc.), aluminum compounds (e.g., boehmite, aluminum hydroxide, alumina, hydrotalcite, aluminum borate, aluminum nitride, etc.), magnesium compounds (e.g., magnesium aluminometasilicate, magnesium carbonate, magnesium oxide, magnesium hydroxide, etc.), calcium compounds (e.g., calcium carbonate, Examples of inorganic fillers include, but are not limited to, inorganic fillers such as calcium hydroxide, calcium sulfate, calcium sulfite, and calcium borate, molybdenum compounds (e.g., molybdenum oxide and zinc molybdate), talc (e.g., natural talc and calcined talc), mica, titanium oxide, zinc oxide, zirconium oxide, barium sulfate, zinc borate, barium metaborate, sodium borate, boron nitride, aggregated boron nitride, silicon nitride, carbon nitride, strontium titanate, barium titanate, and stannates such as zinc stannate. These may be used alone or in combination of two or more. Among these, silica is preferred from the viewpoint of dielectric properties, etc. The thermoplastic liquid crystal polymer film 11 and the thermoplastic liquid crystal polymer film 12 may contain the same type of inorganic filler or different types of inorganic fillers.

[0038] The inorganic filler used here may be subjected to a surface treatment known in the art. The surface treatment can improve moisture resistance, adhesive strength, dispersibility, etc. Examples of surface treatment agents include, but are not limited to, silane coupling agents, titanate coupling agents, sulfonate esters, carboxylate esters, and phosphate esters.

[0039] The median diameter (d50) of the inorganic filler can be appropriately set depending on the required performance and is not particularly limited. From the viewpoints of kneading and handling during preparation, the effect of reducing the linear expansion coefficient, etc., the d50 of the inorganic filler is preferably 0.01 μm to 50 μm, more preferably 0.03 μm to 50 μm, and even more preferably 0.1 μm to 50 μm. The inorganic fillers contained in the thermoplastic liquid crystal polymer films 11 and 12 may have the same or different d50s.

[0040] The content of the inorganic filler can be appropriately set according to the required performance, taking into account the balance of the other essential and optional components. From the viewpoints of kneading and handling during preparation, the effect of reducing the linear expansion coefficient, etc., the total content of the inorganic filler, calculated as solid content relative to the total amount of the thermoplastic liquid crystal polymer films 11 and 12, is preferably 1% by mass or more and 45% by mass or less, more preferably 3% by mass or more and 40% by mass or less, and even more preferably 5% by mass or more and 35% by mass or less. In this embodiment, a dry-laminate laminate L is used in which the thermoplastic liquid crystal polymer films 11 and 12 containing the inorganic filler are thermocompression-bonded to the inorganic fiber woven fabric 21. Therefore, the inorganic filler filling ratio can be kept relatively small to obtain the desired linear expansion coefficient in the MD, TD, and ZD directions. As a result, the thermoplastic liquid crystal polymer content can be maintained relatively high, thereby maintaining high dielectric properties in the high frequency range.

[0041] The thermoplastic liquid crystal polymer films 11 and 12 may contain resin components other than the thermoplastic liquid crystal polymer described above, such as thermosetting resins or thermoplastic resins, to the extent that the effects of the present invention are not excessively impaired. Furthermore, the thermoplastic liquid crystal polymer films 11 and 12 may contain additives known in the art, such as release improvers such as higher fatty acids having 10 to 25 carbon atoms, higher fatty acid esters, higher fatty acid amides, higher fatty acid metal salts, polysiloxanes, and fluororesins; colorants such as dyes and pigments; organic fillers; antioxidants; heat stabilizers; light stabilizers; ultraviolet absorbers; flame retardants; antistatic agents; surfactants; rust inhibitors; antifoaming agents; and fluorescent agents, to the extent that the effects of the present invention are not excessively impaired. These additives may be used alone or in combination of two or more. These additives may be added to the molten resin composition prepared during the film formation of the thermoplastic liquid crystal polymer films 11 and 12. The content of these resin components and additives is not particularly limited, but from the viewpoint of moldability and thermal stability, it is preferably 0.01 to 10 mass% each of the total amount of the thermoplastic liquid crystal polymer films 11 and 12, more preferably 0.1 to 7 mass% each, and even more preferably 0.5 to 5 mass% each.

[0042] The inorganic fiber woven fabric 21 is a fabric woven from inorganic fibers. By thermocompression bonding the inorganic fiber woven fabric 21 to the thermoplastic liquid crystal polymer films 11 and 12, the linear expansion coefficients in the MD and TD directions can be effectively reduced. Examples of inorganic fibers include, but are not limited to, glass fibers such as E-glass, D-glass, L-glass, M-glass, S-glass, T-glass, Q-glass, UN-glass, NE-glass, and spherical glass; inorganic fibers other than glass such as quartz; and ceramic fibers such as silica. For the inorganic fiber woven fabric 21, a woven fabric that has been subjected to a fiber-opening or clogging treatment is preferred from the viewpoint of dimensional stability. Among these, glass cloth is preferred from the viewpoints of mechanical strength, dimensional stability, water absorption, and the like. Glass cloth that has been subjected to a fiber-opening or clogging treatment is preferred from the viewpoint of improving thermocompression bonding with the thermoplastic liquid crystal polymer films 11 and 12. Furthermore, glass cloth that has been surface-treated with a silane coupling agent such as epoxy silane or amino silane can also be used. The woven fabric 21 may be used singly or in appropriate combination of two or more types.

[0043] The thickness of the woven fabric 21 can be appropriately set depending on the required performance and is not particularly limited. From the viewpoints of lamination property, processability, mechanical strength, etc., the thickness is preferably 10 to 300 μm, more preferably 10 to 200 μm, and even more preferably 15 to 180 μm.

[0044] The total thickness of the insulating material for circuit boards 100 (dry laminated laminate L) can be appropriately set depending on the required performance and is not particularly limited. From the viewpoints of lamination property, processability, mechanical strength, etc., it is preferably 30 to 500 μm, more preferably 50 to 400 μm, even more preferably 70 to 300 μm, and particularly preferably 90 to 250 μm.

[0045] By adopting the above-described configuration, the insulating material 100 for circuit boards of this embodiment has the remarkable effects of having a small linear expansion coefficient in all of the MD, TD, and ZD directions, excellent dielectric properties in the high frequency range, ease of manufacture, and excellent productivity.

[0046] The average coefficient of linear expansion in the MD direction (CTE, α2, 23 to 200°C) of the insulating material 100 for circuit boards of this embodiment is not particularly limited, but from the viewpoint of improving adhesion to metal foil, it is preferably 5 ppm / K to 25 ppm / K, more preferably 7 ppm / K to 24 ppm / K, and even more preferably 9 ppm / K to 23 ppm / K. Similarly, the average coefficient of linear expansion in the TD direction (CTE, α2, 23 to 200°C) is preferably 5 ppm / K to 25 ppm / K, more preferably 7 ppm / K to 24 ppm / K, and even more preferably 9 ppm / K to 23 ppm / K. On the other hand, the average coefficient of linear expansion in the ZD direction (CTE, α2, 23 to 200°C) is preferably 10 ppm / K to 100 ppm / K, more preferably 15 ppm / K to 98 ppm / K, and even more preferably 20 ppm / K to 95 ppm / K. In this specification, the linear expansion coefficient is measured by the TMA method in accordance with JIS K7197, and the average linear expansion coefficient refers to the average value of the linear expansion coefficients measured by the same method from 23 to 200°C. The linear expansion coefficient measured here refers to the value obtained when the insulating material 100 for circuit boards is heated at a heating rate of 5°C / min (first heating), cooled to the measurement ambient temperature (23°C) (first cooling), and then heated a second time at a heating rate of 5°C / min (second heating) to determine the value after thermal history has been removed. Other detailed measurement conditions are the same as those described in the examples below.

[0047] On the other hand, the dielectric properties of the insulating material 100 for circuit boards of this embodiment can be appropriately set according to the desired performance, and are not particularly limited. r The dielectric constant ε (36GHz) is preferably 3.0 or more and 3.7 or less, more preferably 3.0 to 3.5. Similarly, the dielectric loss tangent tanδ (36GHz) is preferably 0.0010 or more and 0.0050 or less, more preferably 0.0010 or more and 0.0045 or less. In this specification, the dielectric constant ε rThe dielectric loss tangent tanδ is a value measured at 36 GHz by a cavity resonator vibration method in accordance with JIS K 6471. Other detailed measurement conditions are in accordance with the conditions described in the examples below.

[0048] (Method of manufacturing insulating material for circuit boards) 2 is a flowchart showing an example of a method for manufacturing the insulating material 100 for circuit boards according to this embodiment. This manufacturing method includes at least a step (S1) of preparing the above-described thermoplastic liquid crystal polymer films 11, 12 containing an inorganic filler, a step (S2) of preparing a woven fabric 21 of inorganic fibers, and a step (S3) of laminating the thermoplastic liquid crystal polymer films 11, 12 and the woven fabric 21, and applying heat and pressure to form a dry-laminate laminate L in which the thermoplastic liquid crystal polymer films 11, 12 and the woven fabric 21 are thermocompression-bonded.

[0049] In step S1, thermoplastic liquid crystal polymer films 11 and 12 containing inorganic filler are prepared. Such films can be commercially available or can be produced by methods known in the art. A preferred embodiment includes, for example, a method in which a resin composition containing the above-mentioned thermoplastic liquid crystal polymer and inorganic filler is prepared (S1a), and this resin composition is formed into a film (S1b) to obtain the thermoplastic liquid crystal polymer films 11 and 12 containing inorganic filler.

[0050] The resin composition may be prepared according to a conventional method and is not particularly limited. The above-mentioned components can be produced and processed by known methods such as kneading, melt kneading, granulation, extrusion molding, pressing, or injection molding. When melt kneading, commonly used kneading devices such as single-screw or twin-screw extruders and various kneaders can be used. When supplying the components to these melt kneading devices, the liquid crystal polymer, other resin components, inorganic fillers, additives, etc. may be dry-blended in advance using a mixing device such as a tumbler or Henschel mixer. During melt kneading, the cylinder setting temperature of the kneading device may be appropriately set and is not particularly limited, but is generally preferably in the range of from the melting point of the liquid crystal polymer to 360°C, and more preferably from the melting point of the liquid crystal polymer + 10°C to 360°C.

[0051] During preparation of the resin composition, additives known in the art may be added, within limits that do not excessively impair the effects of the present invention. For example, release improvers such as higher fatty acids having 10 to 25 carbon atoms, higher fatty acid esters, higher fatty acid amides, higher fatty acid metal salts, polysiloxanes, and fluororesins; colorants such as dyes and pigments; organic fillers; antioxidants; heat stabilizers; light stabilizers; ultraviolet absorbers; flame retardants; antistatic agents; surfactants; rust inhibitors; antifoaming agents; and fluorescent agents. These additives may be used alone or in combination of two or more. The content of the additives is not particularly limited, but from the viewpoints of moldability and thermal stability, it is preferably 0.01 to 10% by mass, more preferably 0.1 to 7% by mass, and even more preferably 0.5 to 5% by mass, based on the total amount of the resin composition in terms of solid content.

[0052] Although there is no particular limitation on the method for producing the thermoplastic liquid crystal polymer films 11 and 12, a melt extrusion method is preferably used. In one preferred embodiment, the resin composition described above is extruded into a film form from a T-die by a melt extrusion film production method using a T-die (hereinafter, sometimes simply referred to as "T-die melt extrusion"), and then the T-die melt extruded film is pressurized and heated as necessary to obtain the desired thermoplastic liquid crystal polymer films 11 and 12.

[0053] The conditions for melt extrusion may be appropriately set depending on the type and composition of the resin composition used, the desired performance of the target melt-extruded film, etc., and are not particularly limited. Generally, the set temperature of the cylinder of the extruder is preferably 230 to 360°C, more preferably 280 to 350°C. Similarly, the slit gap of the T-die, for example, may be appropriately set depending on the type and composition of the resin composition used, the desired performance of the target melt-extruded film, etc., and is not particularly limited, but is generally preferably 0.1 to 1.5 mm, more preferably 0.1 to 0.5 mm.

[0054] The thickness of the resulting melt-extruded film can be appropriately set according to requirements and is not particularly limited. In consideration of handleability and productivity during T-die melt extrusion molding, the thickness is preferably 10 μm or more and 500 μm or less, more preferably 20 μm or more and 300 μm or less, and even more preferably 30 μm or more and 250 μm or less.

[0055] The melting point (melting temperature) of the melt-extruded film is not particularly limited, but from the viewpoints of the heat resistance and processability of the film, the melting point (melting temperature) is preferably 200 to 400°C. In particular, from the viewpoint of improving thermocompression bonding to metal foil, the melting point (melting temperature) is preferably 250 to 360°C, more preferably 260 to 355°C, even more preferably 270 to 350°C, and particularly preferably 275 to 345°C. In this specification, the melting point of the melt-extruded film refers to the peak melting temperature measured by differential scanning calorimetry (DSC) using a DSC8500 (manufactured by PerkinElmer) in a temperature range of 30 to 400°C, heated at a heating rate of 20°C / min (first heating), cooled at a heating rate of 50°C / min (first cooling), and then heated a second time (second heating) at a heating rate of 20°C / min to determine the value after thermal history has been eliminated. Other measurement conditions are as described in the Examples below.

[0056] When the above resin composition is subjected to T-die melt extrusion, a T-die melt extruded film is typically obtained that has a linear expansion coefficient (CTE, α2) in the machine direction (MD; longitudinal direction) of -40 to 40 ppm / K and a linear expansion coefficient (CTE, α2) in the transverse direction (TD; transverse direction) of 50 to 120 ppm / K. These physical properties are obtained because the main chains of the liquid crystal polymer tend to be easily oriented in the MD during T-die melt extrusion and because an anisotropic molten phase of the liquid crystal polymer is present during T-die melt extrusion.

[0057] Thus, in step S1, a T-die melt-extruded film having a high degree of orientation (high anisotropy) is likely to be formed. Even in the case of such a T-die melt-extruded film having a high degree of orientation, the orientation (anisotropy) is alleviated during thermocompression bonding, which will be described later, and therefore the film can be used as it is as the thermoplastic liquid crystal polymer film 11, 12. However, the orientation (anisotropy) can be reduced by further performing a pressurizing and heating step as necessary.

[0058] The heat-pressure treatment may be carried out using a method known in the art, such as contact heat treatment or non-contact heat treatment, and the type is not particularly limited. For example, heat setting can be carried out using known equipment such as a non-contact heater, oven, blower, heat roll, cooling roll, heat press, or double-belt heat press. If necessary, a release film or porous film known in the art may be placed on the surface of the T-die melt-extruded film before the heat treatment. Furthermore, when carrying out this heat treatment, from the viewpoint of controlling orientation, a preferred method is a thermocompression molding method in which a release film or porous film is placed on the front and back of the T-die melt-extruded film, and the film is thermocompressed while sandwiched between the pair of endless belts of a double-belt press, and then the release film or porous film is removed. The thermocompression molding method may be carried out with reference to, for example, JP 2010-221694 A. The processing temperature when a T-die melt-extruded film using the resin composition is thermocompressed between the pair of endless belts of a double-belt press is preferably above the melting point of the liquid crystal polymer but not higher than 70°C above the melting point, more preferably above +5°C above the melting point but not higher than 60°C above the melting point, and even more preferably above +10°C above the melting point but not higher than 50°C above the melting point. The thermocompression bonding conditions can be appropriately set depending on the desired performance and are not particularly limited. They are preferably performed under conditions of a surface pressure of 0.5 to 10 MPa and a heating temperature of 250 to 430°C, more preferably under conditions of a surface pressure of 0.6 to 8 MPa and a heating temperature of 260 to 400°C, and even more preferably under conditions of a surface pressure of 0.7 to 6 MPa and a heating temperature of 270 to 370°C. On the other hand, when a non-contact heater or oven is used, the thermocompression bonding is preferably performed under conditions of, for example, 200 to 320°C for 1 to 20 hours.

[0059] The thickness of the thermoplastic liquid crystal polymer films 11 and 12 prepared in step S1 can be appropriately set according to requirements and is not particularly limited. Considering handleability and productivity during pressure and heat treatment, the thickness is preferably 5 μm to 300 μm, more preferably 10 μm to 250 μm, and even more preferably 20 μm to 200 μm. The thicknesses of the thermoplastic liquid crystal polymer films 11 and 12 may be the same or different. This embodiment employs a dry laminate L in which the thermoplastic liquid crystal polymer films 11 and 12 and the woven fabric 21 are thermocompression-bonded, which is advantageous in that it allows the use of thick thermoplastic liquid crystal polymer films 11 and 12 (e.g., thicknesses of 200 μm or more), which could not be applied using the varnish impregnation process of the prior art.

[0060] The melting point (melting temperature) of the thermoplastic liquid crystal polymer films 11 and 12 prepared in step S1 is not particularly limited, but from the viewpoints of the heat resistance and processability of the film, the melting point (melting temperature) is preferably 200 to 400°C, and from the viewpoint of improving the thermocompression bonding to metal foil in particular, the melting point (melting temperature) is preferably 250 to 360°C, more preferably 260 to 355°C, even more preferably 270 to 350°C, and particularly preferably 275 to 345°C. In this specification, the melting point of the thermoplastic liquid crystal polymer films 11 and 12 means a value measured under the same measurement conditions as the melting point of the melt-extruded film.

[0061] In step S2, inorganic fiber woven fabric 21 is prepared. A commercially available product can be used as the woven fabric 21, or it can be produced by a method known in the art. Step S2 may be performed prior to, simultaneously with, or after step S1.

[0062] In step S3, the thermoplastic liquid crystal polymer films 11, 12 and the woven fabric 21 are laminated together and heated and pressurized to form a dry laminate L in which the thermoplastic liquid crystal polymer films 11, 12 and the woven fabric 21 are thermocompression-bonded together. In step S3, the thermoplastic liquid crystal polymer films 11, 12 and the woven fabric 21 are thermocompression-bonded together to form the dry laminate L. Compared to the varnish impregnation process of the prior art, this provides a large process tolerance during manufacturing, excellent productivity, and increased freedom in product configuration.

[0063] A preferred embodiment of step S3 involves stacking the thermoplastic liquid crystal polymer film 11, the woven fabric 21, and the thermoplastic liquid crystal polymer film 12 in this order to form a laminate, and then using a press or double-belt press to sandwich and heat and press the laminate, thereby thermoforming it. The processing temperature during thermocompression bonding can be set appropriately depending on the required performance and is not particularly limited, but is preferably 200 to 400°C, more preferably 250 to 360°C, and even more preferably 270 to 350°C. The processing temperature during thermocompression bonding is measured at the surface temperature of the thermoplastic liquid crystal polymer films 11 and 21 of the laminate. The pressure conditions can be set appropriately depending on the desired performance and are not particularly limited, but are, for example, 1 to 240 minutes at a surface pressure of 0.5 to 10 MPa, and more preferably 1 to 120 minutes at a surface pressure of 0.8 to 8 MPa.

[0064] (Metal foil laminate) 3 is a schematic diagram showing an example of a metal foil-clad laminate 200 of this embodiment. The metal foil-clad laminate 200 of this embodiment is a double-sided metal foil-clad laminate including the above-mentioned insulating material for circuit boards 100 (dry laminated laminate L) and metal foils 31, 32 provided on both surfaces of this insulating material for circuit boards 100. Note that although a double-sided metal foil-clad laminate is shown in this embodiment, the present invention can also be implemented in an embodiment in which the metal foil 31 (metal foil 32) is provided on only one surface of the insulating material for circuit boards 100.

[0065] The material of the metal foils 31 and 32 is not particularly limited, but examples include gold, silver, copper, copper alloys, nickel, nickel alloys, aluminum, aluminum alloys, iron, and iron alloys. Among these, copper foil, aluminum foil, stainless steel foil, and copper-aluminum alloy foil are preferred, with copper foil being more preferred. While any copper foil manufactured by rolling or electrolysis can be used, electrolytic copper foil or rolled copper foil, which has a relatively high surface roughness, is preferred. The thickness of the metal foils 31 and 32 can be appropriately set depending on the desired performance and is not particularly limited. It is typically 1.5 to 1000 μm, more preferably 2 to 500 μm, even more preferably 5 to 150 μm, and particularly preferably 7 to 100 μm. The metal foils 31 and 32 may be subjected to surface treatments such as chemical surface treatments such as acid cleaning, as long as the effects of the present invention are not impaired. The type and thickness of the metal foils 31 and 32 may be the same or different.

[0066] The method for providing the metal foils 31, 32 on the surface of the insulating material 100 for circuit boards can be performed according to a conventional method and is not particularly limited. Any of the following methods may be used: a method of laminating the metal foils 31, 32 on the insulating material 100 for circuit boards and adhering or pressing the two layers together; a physical method (dry method) such as sputtering or vapor deposition; a chemical method (wet method) such as electroless plating or electrolytic plating after electroless plating; or a method of applying a metal paste. The metal foil-clad laminate 200 can also be obtained by hot-pressing a laminate obtained by laminating the insulating material 100 for circuit boards and one or more metal foils 31, 32 using, for example, a multi-stage press, a multi-stage vacuum press, a continuous molding machine, an autoclave molding machine, or the like.

[0067] One preferred lamination method is to overlap the insulating material 100 for circuit boards and the metal foils 31 and 32 to form a laminate in which the metal foils 31 and 32 are placed on the insulating material 100 for circuit boards, and then to thermocompress the laminate while sandwiching it between a pair of endless belts of a double-belt press. As described above, the insulating material 100 for circuit boards used in this embodiment has sufficiently reduced anisotropy in the linear expansion coefficients in the MD and TD directions, so that it can obtain high peel strength to the metal foils 31 and 32. In addition, the linear expansion coefficient in the ZD direction is also sufficiently reduced, so that it is particularly useful in rigid board applications requiring multilayer lamination.

[0068] The temperature during thermocompression bonding of the metal foils 31 and 32 can be set appropriately depending on the required performance and is not particularly limited. However, it is preferably at least 50°C lower than the melting point of the liquid crystal polymer and not more than 50°C higher than the melting point, more preferably at least 40°C lower than the melting point and not more than 40°C higher than the melting point, even more preferably at least 30°C lower than the melting point and not more than 30°C higher than the melting point, and particularly preferably at least 20°C lower than the melting point and not more than 20°C higher than the melting point. The temperature during thermocompression bonding of the metal foils 31 and 32 is measured at the surface temperature of the insulating material 100 for circuit boards described above. The bonding conditions can be set appropriately depending on the desired performance and are not particularly limited. For example, when using a double-belt press, it is preferable to perform the bonding under conditions of a surface pressure of 0.5 to 10 MPa and a heating temperature of 200 to 360°C.

[0069] The metal foil-clad laminate 200 of this embodiment may have a different or additional laminate structure, so long as it comprises a two-layer thermocompression-bonded body of the insulating material 100 for circuit boards and the metal foils 31 and 32. For example, the laminate may have a multilayer structure having at least the two-layer structure described above, such as a two-layer structure of metal foil 31 / insulating material for circuit boards 100; a three-layer structure such as metal foil 31 / insulating material for circuit boards 100 / metal foil 32 or insulating material for circuit boards 100 / metal foil 31 / insulating material for circuit boards 100; or a five-layer structure such as metal foil 31 / insulating material for circuit boards 100 / metal foil 32 / insulating material for circuit boards 100 / metal foil 31. Furthermore, multiple (e.g., 2 to 50) metal foil-clad laminates 200 may be laminated and thermocompression-bonded.

[0070] In the metal foil-clad laminate 200 of this embodiment, the peel strength between the insulating material 100 for circuit boards and the metal foils 31 and 32 is not particularly limited. However, from the viewpoint of providing a higher peel strength, it is preferably 1.0 (N / mm) or more, more preferably 1.1 (N / mm) or more, and even more preferably 1.2 (N / mm) or more. As described above, the metal foil-clad laminate 200 of this embodiment can achieve a higher peel strength than conventional techniques, thereby suppressing peeling between the insulating material 100 for circuit boards and the metal foils 31 and 32, for example, during the heating process of substrate manufacturing. Furthermore, since manufacturing conditions with excellent process tolerance and productivity can be applied to obtain peel strength equivalent to that of conventional techniques, deterioration of the basic performance of the liquid crystal polymer can be suppressed while maintaining peel strength equivalent to that of conventional techniques.

[0071] The metal foil-clad laminate 200 of this embodiment can be used as a material for circuit boards such as electronic circuit boards and multilayer boards by, for example, pattern-etching at least a portion of the metal foils 31 and 32. The metal foil-clad laminate 200 of this embodiment also has excellent dielectric properties in the high frequency range, a small linear expansion coefficient in all of the MD, TD, and ZD directions, excellent dimensional stability, and is easy to manufacture and highly productive, making it a particularly useful material as an insulating material for flexible printed circuit boards (FPCs) and the like in fifth-generation mobile communication systems (5G), millimeter-wave radar, and the like. [Example]

[0072] The features of the present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto. That is, the materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the spirit of the present invention. Furthermore, the values ​​of various production conditions and evaluation results in the following examples represent preferred upper or lower limits in the embodiments of the present invention, and preferred numerical ranges may be defined by combining the above-mentioned upper or lower limits with the values ​​of the following examples or values ​​between the examples.

[0073] Example 1 Synthesis of Liquid Crystal Polymers A reactor equipped with a stirrer and a vacuum distillation apparatus was charged with p-hydroxybenzoic acid (74 mol%), 6-hydroxy-2-naphthoic acid (26 mol%), and 1.025 times the molar amount of acetic anhydride relative to the total amount of monomers. The reactor was heated to 150 °C under a nitrogen atmosphere and held for 30 minutes. After that, the temperature was rapidly raised to 190 °C while distilling off the by-product acetic acid and held for 1 hour to obtain an acetylated reaction product. The resulting acetylated reaction product was heated to 320 °C over 3.5 hours, then the pressure was reduced to 2.7 kPa over approximately 30 minutes to carry out melt polycondensation. The pressure was then gradually reduced to normal pressure to obtain a liquid crystalline polymer solid. The resulting liquid crystalline polymer solid was pulverized and granulated using a twin-screw extruder at 300 °C to obtain pellets of an aromatic polyester liquid crystalline polymer (PEs-LCP, molar ratio 74:26) composed of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid.

[0074] Preparation of Resin Composition 80 parts by mass of the obtained liquid crystal polymer pellets and 20 parts by mass of fused silica (trade name: Denka fused silica FB-5D, manufactured by Denka Co., Ltd.) were each supplied, and mixed, reacted, and granulated at 300°C using a twin-screw extruder to obtain the resin composition (pellets) of Example 1.

[0075] Manufacturing of thermoplastic liquid crystal polymer film The obtained pellets of the resin composition of Example 1 were used to form a film at 300°C by a T-die casting method, to obtain a thermoplastic liquid crystal polymer film of Example 1 having a melting point of 280°C and a thickness of 50 µm.

[0076] Manufacturing of insulating materials for circuit boards A glass cloth (IPC No. #1037) was sandwiched between the pair of thermoplastic liquid crystal polymer films of Example 1 obtained, and a thermocompression treatment was performed at 300°C for 5 minutes using a heat press machine, thereby obtaining an insulating material for circuit boards of Example 1 having a melting point of 280°C and a layer thickness of 100 μm.

[0077] Examples 2 to 13 The insulating materials for circuit boards of Examples 2 to 13 were obtained in the same manner as in Example 1, except that the type and content ratio of the inorganic filler used, the type and thickness of the woven inorganic fiber fabric used, and the thickness of the insulating material for circuit boards were changed as shown in Table 1.

[0078] (Comparative Example 1) An insulating material for circuit boards of Comparative Example 1 was obtained in the same manner as in Example 1, except that the blending of fused silica was omitted.

[0079] (Comparative Example 2) An insulating material for circuit boards of Comparative Example 2 was obtained in the same manner as in Example 1, except that the sandwiching of the glass cloth was omitted.

[0080] (Comparative Example 3) An insulating material for circuit boards of Comparative Example 3 was obtained in the same manner as in Example 1, except that the blending of fused silica and the sandwiching of glass cloth were omitted.

[0081] <Performance evaluation> Performance evaluation was carried out on the insulating materials for circuit boards of Examples 1 to 13 and Comparative Examples 1 to 3. The results are shown in Table 1. The measurement conditions were as follows:

[0082] [Median diameter of inorganic filler (d50)] Measurement method: Laser diffraction / scattering method Measuring equipment: LA-500 (Horiba Ltd.) Measurement sample: Inorganic filler dispersed in water using ultrasonic waves Calculation method: Create a particle size distribution of inorganic filler based on volume, The median diameter (d50) was calculated.

[0083] [Linear expansion coefficient] Measuring equipment: TMA 4000SE (NETZSCH) Measurement method: Tensile mode Measurement conditions: Sample size 20mm x 4mm x thickness 50μm Temperature range: 23~200℃ (2nd RUN) Heating rate: 5℃ / min Atmosphere: Nitrogen (flow rate 50 ml / min) Test load 5gf *The value from the 2nd run was used to see the value after eliminating the thermal history.

[0084] [Relative permittivity ε r , dielectric tangent tanδ(36GHz) electrical properties] Measurement method: Cylindrical cavity resonator method Measurement environment: Temperature 23°C, relative humidity 50% Measurement conditions: Sample size 15mm x 15mm x thickness 200μm Cavity 36GHz

[0085] [Table 1] [Industrial Applicability]

[0086] The insulating material for circuit boards of the present invention can be widely and effectively used in applications such as electronic circuit boards, multilayer boards, high heat dissipation boards, flexible printed wiring boards, antenna boards, optoelectronic hybrid boards, and IC packages. In particular, because of its excellent high-frequency characteristics and low dielectric properties, it can be widely and effectively used in particular as an insulating material for flexible printed wiring boards (FPCs) in fifth-generation mobile communication systems (5G), millimeter-wave radar, and the like. [Explanation of symbols]

[0087] 11. Thermoplastic liquid crystal polymer film 12. Thermoplastic liquid crystal polymer film 21. Inorganic fiber woven fabric 21a...plane 21b...plane 31 Metal foil 32 Metal foil 100 Insulating materials for circuit boards 200 ···Metal foil-clad laminate L Dry laminated laminate

Claims

1. A laminate having a thermoplastic liquid crystal polymer film and a woven fabric of inorganic fibers, The thermoplastic liquid crystal polymer film contains an inorganic filler, The laminate is a dry laminate in which the thermoplastic liquid crystal polymer film and the woven fabric are thermocompression-bonded. Insulating material for circuit boards.

2. The thermoplastic liquid crystal polymer film is a melt-extruded film. The insulating material for circuit boards according to claim 1 .

3. The thermoplastic liquid crystal polymer film is a T-die melt-extruded film. The insulating material for circuit boards according to claim 1 or 2.

4. The inorganic filler contains silica. The insulating material for circuit boards according to any one of claims 1 to 3.

5. The inorganic filler has a median diameter (d50) of 0.01 μm or more and 50 μm or less. The insulating material for circuit boards according to any one of claims 1 to 4.

6. The thermoplastic liquid crystal polymer film contains the inorganic filler in an amount of 1% by mass or more and 45% by mass or less relative to the total amount of the film. The insulating material for circuit boards according to any one of claims 1 to 5.

7. The woven fabric has a thickness of 10 μm or more and 300 μm or less. The insulating material for circuit boards according to any one of claims 1 to 6.

8. The woven fabric of the inorganic fibers is glass cloth. The insulating material for circuit boards according to any one of claims 1 to 7.

9. The average linear expansion coefficient at 23 to 200°C measured by the TMA method in accordance with JIS K7197 is 5 ppm / K or more and 25 ppm / K or less in the in-plane direction and 10 ppm / K or more and 100 ppm / K or less in the thickness direction. The insulating material for circuit boards according to any one of claims 1 to 8.

10. Relative permittivity ε at 36 GHz measured by the cavity resonator contact method in accordance with JIS K6471 r is 3.0 or more and 3.7 or less The insulating material for circuit boards according to any one of claims 1 to 9.

11. The dielectric loss tangent tanδ at 36 GHz measured by the cavity resonator contact method in accordance with JIS K6471 is 0.0010 or more and 0.0050 or less. The insulating material for circuit boards according to any one of claims 1 to 10.

12. preparing a thermoplastic liquid crystal polymer film containing an inorganic filler; providing a woven fabric of inorganic fibers; a step of laminating the thermoplastic liquid crystal polymer film and the woven fabric, and applying heat and pressure to form a dry laminate in which the thermoplastic liquid crystal polymer film and the woven fabric are thermocompression-bonded; A method for manufacturing insulating materials for circuit boards.

13. The step of preparing the thermoplastic liquid crystal polymer film includes: a composition preparation step of preparing a resin composition containing the thermoplastic liquid crystal polymer and the inorganic filler; a film production step of molding the resin composition to form the thermoplastic liquid crystal polymer film containing the inorganic filler. A method for producing the insulating material for circuit boards according to claim 12.

14. The insulating material for a circuit board according to any one of claims 1 to 11, and a metal foil provided on one and / or both sides of the insulating material for a circuit board. Metal foil laminate.

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