JP2010103339A - High frequency circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency circuit board which includes an insulating layer (LCP substrate) which is excellent in solder thermal resistance, while sufficiently maintaining the characteristics of liquid crystal polyester, such as dielectric characteristics or the like. <P>SOLUTION: The high frequency circuit board includes an insulating layer consisting of: a sheet (A) which is made of inorganic fiber and/or carbon fiber; and liquid crystal polyester (B) which is solvent-soluble and whose flow beginning temperature is ≥250°C. Preferably, the liquid crystal polyester (B) has a structural unit derived from aromatic amine which has phenolic hydroxy group, and the sheet (A) is a glass cloth. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a high frequency circuit board.

  In recent years, information transmission apparatuses such as network devices are increasingly demanded for high-speed signal transmission. In order to increase the speed of such a signal, it is necessary to improve the signal propagation speed and realize low transmission in the high frequency range for the high frequency circuit board used in the information transmission apparatus. For this reason, development of a high-frequency circuit board having a low dielectric constant and low dielectric loss has been studied.

  In order to improve such low dielectric constant and low dielectric loss characteristics, it is important to improve the dielectric characteristics of the insulating layer in the high-frequency circuit board. Conventionally, epoxy resin and polyimide resin have been applied to the resin material constituting the insulating layer of such a high-frequency circuit board, but these resins are highly hygroscopic and the dielectric constant tends to change in the high-frequency range. Had. Therefore, a high-frequency circuit board having an insulating layer (LCP substrate) formed by laminating a plurality of films made of liquid crystal polyester using liquid crystal polyester having low water absorption and excellent dielectric properties in a high frequency region is described above. It is disclosed in Patent Document 1 that the above problem can be solved.

JP 2000-269616 A

However, the LCP substrate disclosed in Patent Document 1 may cause a blistered appearance abnormality on the surface of the LCP substrate, for example, when heat treatment such as solder reflow is performed. There was a case.
Under such circumstances, the object of the present invention is to have an LCP substrate as an insulating layer that is excellent in durability against solder reflow (solder heat resistance) while sufficiently maintaining the characteristics of liquid crystal polyester such as dielectric properties and low water absorption. The object is to provide a high-frequency circuit board.

As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, the present invention provides the following <1>.
<1> A high-frequency circuit board comprising an insulating layer made of a sheet (A) made of inorganic fibers and / or carbon fibers and a liquid-soluble polyester (B) which is soluble in a solvent and has a flow start temperature of 250 ° C. or higher.

Furthermore, the present invention provides the following <2> to <7> as preferred embodiments according to the above <1>.
<2> The liquid crystalline polyester (B) has a structural unit represented by the following formula (1), a structural unit represented by the formula (2), and a structural unit represented by the formula (3). The structural unit represented by the formula (1) is 30.0 to 45.0 mol%, and the structural unit represented by the formula (2) is 27.5 to 35.0 mol based on the total of all the structural units. %, The high frequency circuit board according to <1>, wherein the structural unit represented by the formula (3) is composed of 27.5 to 35.0 mol%;
⁽¹⁾ -O-Ar 1 -CO-
(2) —CO—Ar ² —CO—
⁽³⁾ -X-Ar 3 -Y-
(In the formula, Ar ¹ is phenylene, naphthylene; Ar ² is phenylene, naphthylene, or a group represented by the following formula (4); Ar ³ is phenylene or a group represented by the following formula (4); X and Y each independently represents O or NH, wherein the hydrogen atom bonded to the aromatic ring of Ar ¹ , Ar ² and Ar ³ may be substituted with a halogen atom, an alkyl group or an aryl group. Good.)
^{(4) -Ar 11 -Z-Ar} 12 -
(In the formula, Ar ¹¹ and Ar ¹² each independently represent phenylene or naphthylene. Z represents O, CO, or SO _2. )
<3> The high-frequency circuit board according to <2>, wherein at least one of X and Y of the structural unit represented by the formula (3) is NH;
<4> The total of the structural units derived from p-hydroxybenzoic acid and the structural units derived from 2-hydroxy-6-naphthoic acid is 30.0 to 45.0 mol% in the liquid crystal polyester (B), 4- The total number of structural units derived from aminophenol is 27.5 to 35.0 mol%, structural units derived from terephthalic acid, structural units derived from isophthalic acid, and structural units derived from 2,6-naphthalenedicarboxylic acid is 27. <1> high-frequency circuit board comprising 5 to 35.0 mol%;
<5> The high-frequency circuit board according to any one of <1> to <4>, wherein an adhesion amount of the liquid crystalline polyester (B) with respect to a total weight of the insulating layer is in a range of 25 to 75% by weight.
<6> The insulating layer is formed by impregnating a solution composition containing the liquid crystalline polyester (B) and a solvent into a sheet (A) made of inorganic fibers and / or carbon fibers having a thickness of 10 to 200 μm. The high-frequency circuit board according to any one of <1> to <5>;
<7> The high-frequency circuit board according to any one of <1> to <6>, wherein the sheet is a glass cloth;

  ADVANTAGE OF THE INVENTION According to this invention, the high frequency circuit board which has the insulating layer (LCP board | substrate) excellent in solder heat resistance can be provided, fully maintaining the characteristics of liquid crystalline polyester, such as a dielectric property and low water absorption. Since the high-frequency circuit board can realize an information transmission device excellent in high-speed signal processing, the industrial value is extremely high.

In the high-frequency circuit board of the present invention, the insulating layer is composed of a sheet (A) composed of inorganic fibers and / or carbon fibers, and a solvent-soluble liquid crystal polyester (B) having a flow start temperature of 250 ° C. or higher. It is characterized by.
Hereinafter, a liquid crystal polyester forming such an insulating layer, a sheet made of inorganic fibers and / or carbon fibers, a method for manufacturing an insulating layer (LCP substrate) using these, and a high-frequency circuit board provided with the insulating layer will be sequentially described. .

<Liquid crystal polyester (B)>
The liquid crystal polyester (B) used in the present invention is a polyester having the characteristics of exhibiting optical anisotropy at the time of melting and forming an anisotropic melt at a temperature of 450 ° C. or lower.
As the liquid crystalline polyester used in the present invention, a structural unit represented by the following formula (1) (hereinafter referred to as “formula (1) structural unit”) and a structural unit represented by the following formula (2) (hereinafter, "Formula (2) structural unit") and a structural unit represented by the following formula (3) (hereinafter referred to as "formula (3) structural unit"), Formula (1) 30.0-45.0 mol% of structural units, Formula (2) 27.5-35.0 mol% of structural units, Formula (3) 27.5-35.0 mol% of structural units Those consisting of are preferred.
⁽¹⁾ -O-Ar 1 -CO-
(2) —CO—Ar ² —CO—
⁽³⁾ -X-Ar 3 -Y-
(In the formula, Ar ¹ is phenylene, naphthylene; Ar ² is phenylene, naphthylene, or a group represented by the following formula (4); Ar ³ is phenylene or a group represented by the following formula (4); X and Y each independently represents O or NH, wherein the hydrogen atom bonded to the aromatic ring of Ar ¹ , Ar ² and Ar ³ may be substituted with a halogen atom, an alkyl group or an aryl group. Good.)
^{(4) -Ar 11 -Z-Ar} 12 -
(In the formula, Ar ¹¹ and Ar ¹² each independently represent phenylene or naphthylene. Z represents O, CO, or SO _2. )

  The structural unit of the formula (1) is a structural unit derived from an aromatic hydroxycarboxylic acid, and examples of the aromatic hydroxycarboxylic acid include parahydroxybenzoic acid, metahydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, Examples include 2-hydroxy-3-naphthoic acid and 1-hydroxy-4-naphthoic acid.

  The structural unit (2) is a structural unit derived from an aromatic dicarboxylic acid, and examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 1,5-naphthalenedicarboxylic acid. , Diphenyl ether-4,4′-dicarboxylic acid, diphenylsulfone-4,4′-dicarboxylic acid, diphenyl ketone-4,4′-dicarboxylic acid and the like.

The structural unit (3) is a structural unit derived from an aromatic diol, an aromatic amine having a phenolic hydroxyl group, or an aromatic diamine. Examples of the aromatic diol include hydroquinone, resorcin, 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, bis (4-hydroxyphenyl) ether, and bis- (4-hydroxyphenyl) ketone. And bis- (4-hydroxyphenyl) sulfone.
Examples of the aromatic amine having a phenolic hydroxyl group include p-aminophenol and 3-aminophenol. Examples of the aromatic diamine include 1,4-phenylenediamine and 1,3-phenylenediamine. Etc.

The liquid crystalline polyester (B) used in the present invention is solvent-soluble, and such solvent-soluble means that it dissolves in a solvent at a temperature of 50 ° C. at a concentration of 1% by weight or more. The solvent in this case is any one of suitable solvents used for preparing a solution composition described later, and details will be described later.
As the solvent-soluble liquid crystal polyester (B), the structural unit derived from an aromatic amine having a phenolic hydroxyl group and / or a structural unit derived from an aromatic diamine is included as the structural unit of the formula (3). Those are preferred. That is, as the structural unit of the formula (3), a structural unit in which at least one of X and Y is NH (a structural unit represented by the following formula (3 ′), hereinafter referred to as “formula (3 ′) structural unit”). When it contains, since there exists a tendency for the solvent solubility with respect to the suitable solvent (aprotic polar solvent) mentioned later, it is preferable. In particular, it is preferable that substantially all the structural units of the formula (3) are the structural units of the formula (3 ′). In addition to sufficiently improving the solvent solubility of the liquid crystal polyester, the formula (3 ′) structural unit is advantageous in that the liquid crystal polyester (B) has a lower water absorption.
(3 ′) — X—Ar ³ —NH—
(In the formula, Ar ³ and X have the same meanings as the formula (3)).
It is more preferable that the structural unit of the formula (3) is contained in the range of 30.0 to 32.5 mol% with respect to the total of all the structural units, and by doing so, the solvent solubility is further improved. Thus, the liquid crystal polyester having the structural unit of the formula (3 ′) as the structural unit of the formula (3) is more soluble in a solvent and has a low water absorption, and moreover, an insulating layer can be produced using the solution composition. It also has the advantage of being easy. Among the structural units of the formula (3 ′), 4-aminophenol is preferable in consideration of the solvent solubility of the liquid crystal polyester (B) and the availability and economy of the compound that derives the structural unit. Particular preference is given to structural units derived from 4-aminophenol (3 ′).

  The structural unit (1) is preferably contained in the range of 30.0 to 45.0 mol%, more preferably 35.0 to 40.0 mol%, based on the total of all the structural units. The liquid crystal polyester containing the structural unit of the formula (1) at such a molar fraction tends to be more excellent in solubility in a solvent while sufficiently maintaining liquid crystallinity. Furthermore, considering the availability of the aromatic hydroxycarboxylic acid from which the structural unit of formula (1) is derived, the aromatic hydroxycarboxylic acid may be p-hydroxybenzoic acid and / or 2-hydroxy-6-naphthoic acid. Is preferred.

  The structural unit (2) is preferably contained in the range of 27.5 to 35.0 mol%, more preferably 30.0 to 32.5 mol%, based on the total of all the structural units. The liquid crystal polyester containing the structural unit of the formula (2) at such a molar fraction tends to be more excellent in solubility in a solvent while sufficiently maintaining liquid crystallinity. Furthermore, considering the availability of the aromatic dicarboxylic acid derived from the structural unit of formula (2), the aromatic dicarboxylic acid is selected from the group consisting of terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid. It is preferable that it is at least one kind.

  Moreover, in the point that liquid crystalline polyester (B) expresses higher liquid crystallinity, the molar fraction of the formula (2) structural unit and the formula (3) structural unit is [formula (2) structural unit] / [formula (3) Structural unit], a range of 0.9 / 1.0 to 1.0 / 0.9 is preferable.

Next, the manufacturing method of liquid crystalline polyester (B) is demonstrated easily.
The liquid crystal polyester (B) can be produced by various known methods. When producing a suitable liquid crystal polyester (B) comprising the structural unit (1), the structural unit (2) and the structural unit (3), the compound (monomer) derived from these structural units is converted into an ester-forming compound. A method for producing a liquid crystal polyester (B) by polymerization after conversion to an amide-forming derivative is preferred because the operation is simple.

The ester-forming / amide-forming derivatives will be described with examples.
As an ester-forming / amide-forming derivative of a monomer having a carboxyl group, such as an aromatic hydroxycarboxylic acid or an aromatic dicarboxylic acid, an acid is used so that the carboxyl group promotes a reaction to form a polyester or polyamide. Form esters with alcohols, ethylene glycol, etc., such as those with highly reactive groups such as chlorides, acid anhydrides, and the like, such that the carboxyl group generates polyester or polyamide by transesterification / amide exchange reaction And the like.
Examples of ester-forming and amide-forming derivatives of monomers having a phenolic hydroxyl group, such as aromatic hydroxycarboxylic acids and aromatic diols, are those in which the phenolic hydroxyl group is carboxylated so as to produce polyesters and polyamides by transesterification. Examples include those forming esters with acids.
Examples of the amide-forming derivative of a monomer having an amino group, such as an aromatic diamine, include those in which an amino group forms an amide with a carboxylic acid so that a polyamide is formed by an amide exchange reaction. Can be mentioned.

Among these, in order to more easily produce the liquid crystal polyester (B), an aromatic hydroxycarboxylic acid, an aromatic diol, an aromatic amine having a phenolic hydroxyl group, a phenolic hydroxyl group such as an aromatic diamine, and / or an amino group. Is converted to an ester-forming / amide-forming derivative (acylated product) with a fatty acid anhydride, and the acyl group of the acylated product and the carboxy group of the monomer having a carboxy group are transesterified. A method of producing liquid crystal polyester (B) by polymerizing in such a way that amide exchange occurs is particularly preferable.
Such a production method is described in, for example, Japanese Patent Application Laid-Open No. 2002-220444 or Japanese Patent Application Laid-Open No. 2002-146003, and the liquid crystal polyester (B) is produced according to the production method described in these publications. be able to.

  In acylation, the addition amount of fatty acid anhydride is preferably 1.0 to 1.2 times equivalent to the total of phenolic hydroxyl group and amino group, and 1.05 to 1.1 times equivalent. More preferably. When the addition amount of the fatty acid anhydride is less than 1.0 times equivalent, the acylated product and other monomers tend to sublime at the time of polymerization and the reaction system tends to be blocked, and when the amount exceeds 1.2 times equivalent, The liquid crystal polyester obtained tends to be markedly colored.

The acylation is preferably performed at 130 to 180 ° C. for 5 minutes to 10 hours, more preferably at 140 to 160 ° C. for 10 minutes to 3 hours.
The fatty acid anhydride used for the acylation is preferably acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, or a mixture of two or more selected from these, particularly preferably anhydrous, from the viewpoint of price and handleability. Acetic acid.

The polymerization following acylation is preferably carried out at 130 to 400 ° C. while raising the temperature at a rate of 0.1 to 50 ° C./min, and at 150 to 350 ° C. at a rate of 0.3 to 5 ° C./min. More preferably.
Moreover, in superposition | polymerization, it is preferable that the acyl group of an acylation thing is 0.8-1.2 times equivalent of a carboxyl group.

  In the acylation and / or polymerization, in order to shift the equilibrium, it is preferable to distill out by-produced fatty acids and unreacted fatty acid anhydrides by evaporating them.

The acylation and polymerization may be performed in the presence of a catalyst. As the catalyst, those conventionally known as polyester polymerization catalysts can be used, such as magnesium acetate, stannous acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate, antimony trioxide and the like. And organic compound catalysts such as N, N-dimethylaminopyridine and N-methylimidazole.
However, when the catalyst containing metal remains in the liquid crystal polyester, when the insulating layer is formed using the liquid crystal polyester, there is a risk of deteriorating the electrical properties (dielectric constant, etc.) of the insulating layer. Among these, organic compound catalysts (heterocyclic compounds containing two or more nitrogen atoms) such as N, N-dimethylaminopyridine and N-methylimidazole are preferably used (see JP 2002-146003 A).
The catalyst is usually charged together with the monomer and it is not always necessary to remove it after acylation. If the catalyst is not removed, the polymerization can be transferred directly from the acylation.

  The liquid crystal polyester (B) obtained by such polymerization can be used as it is in the present invention as long as its flow start temperature is 250 ° C. or higher, but for further improvement of characteristics such as liquid crystallinity. Thus, it is preferable to increase the molecular weight, and it is preferable to perform solid-state polymerization for increasing the molecular weight. A series of operations relating to this solid phase polymerization will be described. The relatively low molecular weight liquid crystal polyester obtained by the above polymerization is taken out and pulverized into powder or flakes. Subsequently, solid phase polymerization can be performed by an operation in which the pulverized liquid crystal polyester is heat-treated in a solid state at 20 to 350 ° C. for 1 to 30 hours in an atmosphere of an inert gas such as nitrogen, for example. The solid phase polymerization may be performed while stirring or in a state of standing without stirring. From the viewpoint of obtaining a liquid crystalline polyester (B) having a suitable flow start temperature described later, the preferred conditions for the solid phase polymerization will be described in detail. The reaction temperature is preferably higher than 210 ° C, more preferably 220 ° C. It is the range of -350 degreeC. The reaction time is preferably selected from 1 to 10 hours.

  The liquid crystal polyester (B) used in the present invention needs to have a flow start temperature of 250 ° C. or higher. The higher the flow initiation temperature, the better the solder heat resistance. In addition, when the flow start temperature is higher, a wiring pattern is formed on the insulating layer using the liquid crystal polyester (B) to manufacture a high-frequency circuit board, and therefore, the space between the wiring pattern (conductor layer) and the insulating layer is increased. In addition, there is an advantage that a higher degree of adhesion can be obtained. In addition, the flow start temperature here means the temperature at which the melt viscosity of the liquid crystal polyester is 4800 Pa · s or less under a pressure of 9.8 MPa in the evaluation of the melt viscosity by a flow tester. The flow initiation temperature is well known to those skilled in the art as a measure of the molecular weight of liquid crystal polyester (Naoyuki Koide, “Liquid Crystal Polymer—Synthesis / Molding / Application—”, pages 95 to 105, CMC. , Issued June 5, 1987).

  Thus, although the flow start temperature of liquid crystal polyester (B) is so preferable that it is high, this flow start temperature needs to be made into the range which does not impair the solvent solubility of this liquid crystal polyester (B) remarkably, From such a point, The flow initiation temperature is preferably 300 ° C. or lower. If the flow start temperature is 300 ° C. or lower, the solubility of the liquid crystalline polyester in the solvent is sufficiently good, and when the solution composition described below is obtained, the viscosity does not increase significantly. It tends to be easy to handle. Considering these viewpoints, a liquid crystal polyester having a flow start temperature of 260 ° C. or higher and 290 ° C. or lower is more preferable. In order to control the flow start temperature of the liquid crystal polyester within such a suitable range, the polymerization conditions for the solid phase polymerization may be optimized as appropriate.

<Solution composition>
In order to obtain the insulating layer of the high-frequency circuit board of the present invention, it is preferable to use a solution composition containing the liquid crystal polyester (B) and a solvent, particularly a solution composition in which the liquid crystal polyester (B) is dissolved in a solvent.
As the liquid crystal polyester (B) used in the present invention, when the above-described preferred liquid crystal polyester, particularly the liquid crystal polyester (B) containing the structural unit (3 ′) is used, the liquid crystal polyester (B) contains a halogen atom. It exhibits sufficient solubility in non-protic solvents.
Here, the aprotic solvent not containing a halogen atom is, for example, an ether solvent such as diethyl ether, tetrahydrofuran or 1,4-dioxane; a ketone solvent such as acetone or cyclohexanone; an ester solvent such as ethyl acetate; -Lactone solvents such as butyrolactone; carbonate solvents such as ethylene carbonate and propylene carbonate; amine solvents such as triethylamine and pyridine; nitrile solvents such as acetonitrile and succinonitrile; N, N-dimethylformamide, N, N- Amide solvents such as dimethylacetamide, tetramethylurea and N-methylpyrrolidone; Nitro solvents such as nitromethane and nitrobenzene; Sulfur solvents such as dimethylsulfoxide and sulfolane, hexamethylphosphoric acid amide, and tri-n-butylphosphoric acid It includes phosphorus-based solvents are. In addition, the solvent solubility of the above-mentioned liquid crystalline polyester indicates that it is soluble in at least one aprotic solvent selected from these.

  Among the exemplified solvents, it is preferable to use an aprotic polar solvent having a dipole moment of 3 or more and 5 or less among the exemplified solvents in that the solvent solubility of the liquid crystal polyester (B) is further improved and a solution composition is easily obtained. . Specifically, amide solvents and lactone solvents are preferable, and N, N′-dimethylformamide (DMF), N, N′-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP) are more preferably used. preferable. Further, if the solvent is a highly volatile solvent having a boiling point of 180 ° C. or less at 1 atm, there is an advantage that the sheet is easily removed after impregnating the solution composition. From this viewpoint, DMF and DMAc are particularly preferable. In addition, the use of such an amide-based solvent has an advantage that a conductor layer is easily formed on the insulating layer because unevenness in thickness or the like hardly occurs during the production of the insulating layer.

When the aprotic solvent as described above is used in the solution composition, 20 to 50 parts by weight, preferably 22 to 40 parts by weight of the liquid crystal polyester (B) is dissolved with respect to 100 parts by weight of the aprotic solvent. It is preferable to do so. When the content of the liquid crystal polyester (B) with respect to the solution composition is in such a range, when the insulating layer is produced, the efficiency of impregnating the solution composition into the sheet is further improved. When removing by drying, there is a tendency that inconveniences such as uneven thickness of the insulating layer are unlikely to occur.
In addition, the solution composition includes polypropylene, polyamide, polyester, polyphenylene sulfide, polyether ketone, polycarbonate, polyether sulfone, polyphenyl ether and a modified product thereof, polyether imide, and the like as long as the object of the present invention is not impaired. 1 type or 2 or more types of resins other than liquid crystal polyester, such as thermoplastic resins such as glycidyl methacrylate and polyethylene copolymers; thermosetting resins such as phenol resins, epoxy resins, polyimide resins, and cyanate resins. It may be added. However, even when such other resins are used, it is preferable that these other resins are also soluble in the solvent used in the solution composition.

Furthermore, for the purpose of improving the dimensional stability, thermal conductivity, etc., the solution composition has a silica, alumina, titanium oxide, barium titanate, strontium titanate, as long as the effects of the present invention are not impaired. Inorganic fillers such as aluminum hydroxide and calcium carbonate; Organic fillers such as cured epoxy resin, cross-linked benzoguanamine resin and cross-linked acrylic polymer; various additives such as silane coupling agents, antioxidants and ultraviolet absorbers are used alone or in combination The above may be added. However, it is necessary to select the kind and amount of use of such additives so as not to significantly deteriorate the dielectric properties of the obtained insulating layer.
Moreover, this solution composition may remove the fine foreign material contained in a solution by the filtration process using a filter etc. as needed.
Further, the solution composition may be subjected to defoaming treatment as necessary.

<Sheet made of inorganic fiber and / or carbon fiber>
The sheet (A) used in the present invention is a breathable paper, woven fabric, nonwoven fabric sheet or the like, and is made of inorganic fibers and / or carbon fibers. Here, as an inorganic fiber, it is a ceramic fiber represented by glass, and a glass fiber, an alumina type fiber, a silicon containing ceramic type fiber etc. are mentioned. Among these, since the availability is good, a sheet mainly made of glass fiber, that is, a glass cloth is preferable for use as the sheet (A).

As said glass cloth, what consists of alkali-containing glass fiber, an alkali free glass fiber, and a low dielectric glass fiber is preferable. Moreover, as a fiber constituting the glass cloth, a ceramic fiber or carbon fiber made of a ceramic other than glass may be mixed in a part thereof. The fibers constituting the glass cloth may be surface-treated with a coupling agent such as an aminosilane coupling agent, an epoxysilane coupling agent, or a titanate coupling agent.
As a method for producing a glass cloth composed of these fibers, the fibers forming the glass cloth are dispersed in water, and if necessary, a paste such as an acrylic resin is added, and after making with a paper machine, drying is performed. The method of obtaining a nonwoven fabric by this and the method of using a well-known weaving machine can be mentioned.

Plain weave, satin weave, twill weave, Nanako weave, etc. can be used as the weaving method of the fibers. The weaving density is 10 to 100/25 mm, and the mass per unit area of the glass cloth is preferably 10 to 300 g / m ² . The thickness of the glass cloth is usually about 10 to 200 μm, and more preferably 10 to 180 μm.

  It is also possible to use a glass cloth that is easily available from the market. Various glass cloths are commercially available as insulating impregnation base materials for electronic components, and can be obtained from Asahi Schwer, Nitto Boseki, Arisawa Seisakusho, etc. In addition, in a commercially available glass cloth, the thing of suitable thickness includes the thing of 1035, 1078, 2116, 7628 by IPC name.

<Method for manufacturing insulating layer of high-frequency circuit board>
The insulating layer of the high-frequency circuit board of the present invention is manufactured using a resin-impregnated base material formed from the liquid crystal polyester (B) as exemplified and the sheet (A) (preferably glass cloth). A resin-impregnated substrate obtained by impregnating the sheet with a solution composition containing the liquid crystalline polyester (B) and then removing the solvent by drying is particularly preferable. The adhesion amount of the liquid crystalline polyester to the resin-impregnated base material after removing the solvent is preferably 25 to 75% by weight and preferably 30 to 70% by weight based on the weight of the obtained resin-impregnated base material. More preferred. Further, the insulating layer of the high-frequency circuit board must have an appropriate thickness and not have anisotropy in electrical characteristics. In the insulating layer of Patent Document 1, a liquid crystal polyester film obtained by extrusion molding is used. By using a plurality of sheets and heat-pressing them by overlapping them, the anisotropy of the electrical characteristics is lowered and a bonding film having an appropriate thickness is formed. However, in this method, liquid crystal polyester films having different orientation directions are overlapped with each other, so that voids (bubbles) may be formed in the overlapping portion. When the bonding film in which such voids are generated is heat-treated by solder reflow or the like, the voids expand, and a bulging appearance abnormality (defect) occurs. The insulating layer of the high-frequency circuit board of the present invention can be formed with an appropriate thickness by using the sheet (A), and the sheet is impregnated with a solution composition in which liquid crystalline polyester is dissolved. By doing so, the liquid crystal polyester is sufficiently filled in the sheet. Therefore, when this resin-impregnated base material is formed, generation of voids that are disadvantageous to solder heat resistance is sufficiently prevented, so that it is presumed that no blistering defect is generated even in solder reflow or the like.

Here, the manufacturing method of the high frequency circuit board at the time of using a suitable glass cloth as said sheet | seat (A) is demonstrated.
The glass cloth can be impregnated with the solution composition typically by preparing a dipping tank charged with the solution composition and immersing the glass cloth in the dipping layer. Here, if the content of the liquid crystal polyester (B) in the solution composition used, the time for dipping in the dipping bath, and the speed of pulling up the glass cloth impregnated with the solution composition are appropriately optimized, the above-mentioned preferred liquid crystal polyester The amount of adhesion can be easily controlled.

  Thus, the glass cloth impregnated with the solution composition can produce a resin-impregnated base material by removing the solvent. Although the method for removing the solvent is not particularly limited, it is preferably carried out by evaporation of the solvent in terms of simple operation, and heating, reduced pressure, ventilation or a combination of these is used. Further, in the production of the resin-impregnated base material, after the solvent is removed, heat treatment may be further performed. According to such heat treatment, the liquid crystal polyester (B) contained in the resin-impregnated base material after the solvent removal can be further increased in molecular weight. Examples of the treatment conditions relating to this heat treatment include a method of heat treatment at 240 to 330 ° C. for 1 to 30 hours in an atmosphere of an inert gas such as nitrogen. From the viewpoint of obtaining a high-frequency circuit board having better heat resistance, it is preferable that the heating temperature is higher than 250 ° C., and even more preferable that the heating temperature is higher. It is the range of 260-320 degreeC. The treatment time of the heat treatment is preferably selected from 1 to 10 hours from the viewpoint of productivity.

Next, the obtained resin-impregnated base material is used as an insulating layer, and a high-frequency circuit board can be manufactured by laminating a conductor layer containing copper on at least one surface of the insulating layer, preferably on both surfaces.
As a method of laminating the conductor layer, a method of laminating a metal foil containing copper on the insulating layer, a method of forming a conductor layer by coating fine particles (copper fine particles) made of copper or a copper alloy on the insulating layer, etc. Is mentioned.
As such a conductor layer, one made of copper or a copper alloy can be used, but it is preferable to manufacture a high-frequency circuit board using a copper foil in terms of simple operation. The copper foil expresses excellent conductivity and can be said to be excellent in terms of economy.

Examples of the method of laminating the copper foil include a method of bonding the copper foil and the insulating layer using an adhesive, and a method of thermally bonding the copper foil and the insulating layer by hot pressing.
When an adhesive is used, a commercially available epoxy resin-based adhesive or acrylic resin-based adhesive can be used as the adhesive, but the use of such an adhesive is insufficient for the heat resistance of the adhesive. Therefore, the method of bonding the copper foil and the resin-impregnated base material by hot pressing is particularly preferable.
The treatment conditions in the case of hot pressing can be optimized as appropriate depending on the size and shape of the insulating layer to be used or the thickness and type of the copper foil to be used, but it is particularly preferable to hot press under vacuum. In addition, it is preferable that the processing conditions in this hot press determine processing temperature and processing pressure so that the obtained high frequency circuit board may express favorable surface smoothness. This treatment temperature can be based on the temperature condition of the heat treatment used when producing the insulating layer used in the hot press. Specifically, when the maximum temperature of the temperature conditions according to the heat treatment used was T _max [° C.] in making the insulating layer, it is preferred to hot pressing at a temperature above the T _max, T _max +5 It is more preferable to heat press at a temperature of [° C.] or higher. The upper limit of the temperature relating to the hot press is selected so as to be lower than the decomposition temperature of the liquid crystal polyester (B) contained in the insulating layer to be used, but it is preferable that the upper limit of the temperature is 30 ° C. or lower. . In addition, the decomposition temperature here is calculated | required by using liquid crystal polyester (B) to be used for well-known means, such as a thermogravimetry. The processing time for the hot press is selected from 1 to 30 hours, and the press pressure is selected from 1 to 30 MPa.
Further, in such heat fusion of the copper foil and the insulating layer by hot pressing, a plurality of the above resin-impregnated base materials may be used as the insulating layer. Even in this case, voids or the like do not occur in the overlapping portion between the resin-impregnated substrates using the liquid crystal polyester (B). The reason for this is not necessarily clear, but is a unique finding based on the study of the present inventors.

Hereinafter, the copper fine particle coating method related to the lamination of the conductor layers will be briefly described.
As the coating method, a plating method, a screen printing method, a sputtering method, or the like can be used. Among these, a plating method is preferable as the coating method, and specifically, electroless plating or electrolytic plating is preferably used.
Also, in order to further improve the properties of the conductor layer obtained by such plating method, it is preferable to heat-treat the conductor layer after plating, and the temperature condition of the hot press is also related to the temperature condition of the heat treatment. A condition equivalent to the condition described as the condition is adopted.

<Method for manufacturing wiring pattern>
A predetermined wiring pattern is formed on the conductor layer on the high-frequency circuit board thus obtained. To form the wiring pattern, a commercially available etching resist or dry film can be used as the masking. In the masked conductor layer and the unmasked conductor layer, the latter conductor layer is removed by an etching process called a wet method (chemical treatment). As a chemical | medical agent used for an etching process, ferric chloride aqueous solution is mentioned, for example.
Next, the etching resist and the dry film are removed from the masked conductor layer with acetone or a sodium hydroxide aqueous solution. In this way, a predetermined wiring pattern can be formed on the conductor layer.

  According to the present invention, even if the high-frequency circuit board subjected to the etching process as described above is subjected to, for example, heat treatment or the like, no blistering defect is generated on the surface of the high-frequency circuit board. . Also for this reason, it is presumed that the high-frequency circuit board of the present invention includes an insulating layer in which generation of voids is sufficiently prevented. If a high-frequency circuit board having an insulating layer having voids is subjected to heat treatment by solder reflow or the like, the gas (gas) in the voids expands and rises to the surface, resulting in blistering defects. become. Moreover, when the chemical | medical agent used for this etching process osmose | permeates to a void and retains in this void, generation | occurrence | production of the blistering-like defect by heat processing will become remarkable. The insulating layer of the high-frequency circuit board according to the present invention can exhibit such an effect because voids that are disadvantageous to the occurrence of blistering defects are sufficiently prevented.

The wiring pattern thus formed is also a concept included in the high-frequency circuit board of the present invention. In addition, a concept in which a plurality of high-frequency circuit boards on which the wiring patterns obtained in this way are formed is also included in the high-frequency circuit board of the present invention. Even in this case, it is possible to satisfactorily prevent the occurrence of voids or the like in the overlapping portion of the high-frequency circuit boards.
Furthermore, a resin film such as a cover film may be laminated on the high frequency circuit board of the present invention for the purpose of protecting the conductive layer on the high frequency circuit board.
Further, a through hole may be formed. As this method, a processing method using a drill or a processing method using a laser such as a carbon dioxide laser, a YAG laser, or an excimer laser can be employed. In addition, it is preferable to remove chemically the cutting waste of the liquid crystalline polyester adhering to the inside of the hole due to heat generated during the formation of the through hole using a general-purpose commercially available drug.

  The insulating layer according to the high-frequency circuit board of the present invention is extremely capable of maintaining the excellent dielectric property that the frequency dependence of the dielectric constant is small even in the high-frequency region above the GHz band that the liquid crystal polyester (B) has. It has excellent solder heat resistance. Therefore, the high-frequency circuit board provided with such an insulating layer is extremely useful for use in an information transmission apparatus, particularly for use of a printed wiring board or the like constituting the information transmission apparatus.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.

Example 1
[Manufacture of high-frequency circuit boards]
(1) Preparation of Aromatic Liquid Crystal Polyester In a reactor equipped with a stirrer, torque meter, nitrogen gas inlet tube, thermometer and reflux condenser, 1976 g (10.5 mol) of 2-hydroxy-6-naphthoic acid, 4 -1474 g (9.75 mol) of hydroxyacetanilide, 1620 g (9.75 mol) of isophthalic acid and 2374 g (23.25 mol) of acetic anhydride were charged. After sufficiently replacing the inside of the reactor with nitrogen gas, the temperature was raised to 150 ° C. over 15 minutes under a nitrogen gas stream, and the mixture was refluxed for 3 hours while maintaining the same temperature.
Thereafter, the temperature was raised to 300 ° C. over 170 minutes while distilling off the by-product acetic acid and unreacted acetic anhydride, and the time when an increase in torque was observed was regarded as the completion of the reaction, and the contents were taken out. The taken out contents were cooled to room temperature and pulverized with a coarse pulverizer to obtain a polyester powder. When the obtained polyester powder was evaluated by Shimadzu Corporation flow tester CFT-500, the flow initiation temperature was 235 ° C. The polyester powder was subjected to solid phase polymerization such as heating at 223 ° C. for 3 hours in a nitrogen atmosphere to obtain a liquid crystal polyester (B) in powder form. The liquid crystal polyester (B) had a flow start temperature of 270 ° C.

(2) Preparation of Aromatic Liquid Crystalline Polyester Solution 2200 g of the liquid crystal polyester (B) obtained in (1) above was added to 7800 g of N, N′-dimethylacetamide (DMAc) and heated at 100 ° C. for 2 hours to obtain a solution composition. I got a thing. The solution viscosity of this solution composition was 320 cP at 23 ° C. This melt viscosity was measured at a measurement temperature of 23 ° C. using a B-type viscometer (manufactured by Toki Sangyo, “TVL-20 type”, rotor No. 21 (rotation speed: 5 rpm)).

(3) Production of resin-impregnated base material Glass cloth (manufactured by Arisawa Manufacturing Co., Ltd .; thickness 96 μm, IPC name 2116) is impregnated with the solution composition obtained in (2) above, and further a hot air dryer (set temperature 160 ° C.) The resin-impregnated base material was obtained by evaporating the solvent using In the obtained resin-impregnated base material, the amount of liquid crystal polyester adhered to the glass cloth was about 35% by weight, the thickness was 100 μm (thickness distribution in the width direction of the base material), and the thickness variation was 3%.

(4) Production of high-frequency circuit board The resin-impregnated base material obtained in (4) above was subjected to heat treatment for 3 hours using a hot air dryer (set temperature: 290 ° C) in a nitrogen atmosphere. Two heat-treated resin-impregnated base materials were stacked, and a copper foil (3EC-VLP Mitsui Kinzoku Co., Ltd. (18 μm)) was further stacked on both surfaces thereof. The obtained laminate is hot-pressed with a high-temperature vacuum press (KVHC-PRESS 300 mm, manufactured by Kitagawa Seiki) under the conditions of 340 ° C., 20 minutes, and 5 MPa to thermally bond the copper foil and the resin-impregnated base material. Thus, a high frequency circuit board was obtained.

[Evaluation of high-frequency circuit board]
(5) Evaluation of dielectric constant The copper foil laminated | stacked on both surfaces of the high frequency circuit board obtained by said (4) was removed using ferric chloride aqueous solution (Kida Co., Ltd. 40 degree | times Baume). The dielectric constant of the resin-impregnated substrate remaining after removing the copper foil was measured by the Fabry-Perot method. In addition, the measurement frequency at the time of this dielectric constant measurement is four levels, 30 GHz, 50 GHz, 70 GHz, and 90 GHz. The results are shown in Table 1.
As shown in the table, since the frequency dependency is small and a small value is shown, it is possible to provide a high-frequency circuit board in a high-frequency region above the GHz band.

(6) Evaluation of solder heat resistance The copper foil was removed in the same manner as in (4) for the high-frequency circuit board obtained in (4). Thereafter, a 50 mm square test piece was prepared based on JIS C6481. The produced test piece was stored for 1 hour in a furnace set in an atmosphere of 121 ° C., 2 atm, 100% RH. Thereafter, it was immersed in a solder bath at 288 ° C. for 10 seconds, and the surface appearance was inspected to visually confirm that there was no discoloration or swelling or peeling of the copper foil part. The results are shown in Table 1.

(Example 2)
A high frequency circuit board was manufactured in the same manner as in Example 1 except that the glass cloth used in Example 1 was changed to a glass cloth (manufactured by Arisawa Seisakusho; thickness 45 μm, IPC name 1078). The adhesion amount of the liquid crystal polyester on the resin-impregnated base material was about 55% by weight, the thickness was 55 μm (thickness distribution in the width direction of the base material), and the thickness variation was 3%. Table 1 shows the results of evaluating the dielectric constant and solder heat resistance of the insulating layer of the obtained high-frequency circuit board in the same manner as in Example 1.

  The insulating layer composed of the liquid crystal polyester (B) and the glass cloth (sheet (A)) has a low frequency dependence of dielectric constant even if it is treated with a ferric chloride aqueous solution to process a copper foil. It was found to be excellent in solder heat resistance and extremely excellent as a high-frequency circuit board.

Claims (7)

  A high-frequency circuit board comprising an insulating layer comprising a sheet (A) made of inorganic fiber and / or carbon fiber and a liquid-soluble polyester (B) which is soluble in a solvent and has a flow start temperature of 250 ° C. or higher. The liquid crystalline polyester (B) has a structural unit represented by the following formula (1), a structural unit represented by the formula (2), and a structural unit represented by the formula (3), The structural unit represented by the formula (1) is 30.0 to 45.0 mol%, the structural unit represented by the formula (2) is 27.5 to 35.0 mol%, the formula 2. The high-frequency circuit board according to claim 1, wherein the structural unit represented by (3) is composed of 27.5 to 35.0 mol%.
⁽¹⁾ -O-Ar 1 -CO-
(2) —CO—Ar ² —CO—
⁽³⁾ -X-Ar 3 -Y-
(In the formula, Ar ¹ is phenylene, naphthylene; Ar ² is phenylene, naphthylene, or a group represented by the following formula (4); Ar ³ is phenylene or a group represented by the following formula (4); X and Y each independently represents O or NH, wherein the hydrogen atom bonded to the aromatic ring of Ar ¹ , Ar ² and Ar ³ may be substituted with a halogen atom, an alkyl group or an aryl group. Good.)
^{(4) -Ar 11 -Z-Ar} 12 -
(In the formula, Ar ¹¹ and Ar ¹² each independently represent phenylene or naphthylene. Z represents O, CO, or SO _2. )   The high frequency circuit board according to claim 2, wherein at least one of X and Y of the structural unit represented by the formula (3) is NH.   The liquid crystal polyester (B) has a total of 30.0 to 45.0 mol% of structural units derived from p-hydroxybenzoic acid and structural units derived from 2-hydroxy-6-naphthoic acid, and 4-aminophenol. The total number of structural units derived from 27.5 to 35.0 mol%, structural units derived from terephthalic acid, structural units derived from isophthalic acid, and structural units derived from 2,6-naphthalenedicarboxylic acid is 27.5 to The high-frequency circuit board according to claim 1, comprising 35.0 mol%.   5. The high-frequency circuit board according to claim 1, wherein an adhesion amount of the liquid crystal polyester (B) with respect to a total weight of the insulating layer is in a range of 25 to 75% by weight.   The insulating layer is formed by impregnating a solution composition containing the liquid crystalline polyester (B) and a solvent into a sheet (A) made of inorganic fibers and / or carbon fibers having a thickness of 10 to 200 μm. The high-frequency circuit board according to any one of claims 1 to 5,   The high-frequency circuit board according to claim 1, wherein the sheet is a glass cloth.