JP2002329940A - Insulation material for high frequency circuit board and high frequency circuit board using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply an insulation resin material usable for a high frequency circuit board which has a low dielectric tangent, a low linear expansion coefficient and high process accuracy. SOLUTION: The insulation resin material containing inorganic grains and resin is usable for the high frequency circuit board. It contains at least two kinds of inorganic grains having different mean grain sizes. Among the two or more kinds of inorganic grains, the mean grain size Ra of those having a maximum mean grain size and the mean grain size Rb of those having a minimum mean grain size meet the relation of 5<=Ra/Rb<100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an insulating material for a high-frequency circuit board and a high-frequency circuit board using the same.

[0002]

2. Description of the Related Art Wireless communication technologies such as mobile phones are rapidly developing. As wireless technology following mobile phones,
Bluetoot using 2.4 to 5.8GHz microwave band
h Standards have been formulated and are being launched in earnest. In addition, Intelligent Transport Information System (ITS: Intelligent Transpor
t System), high-frequency wireless technology using the millimeter-wave band above 30 GHz is being applied. As described above, the operating frequency band is increasingly shifting to the high frequency band.

[0003] The material of the high-frequency circuit board used for these transceivers is required to have higher dimensional accuracy than the conventional frequency band, so that high processing accuracy and excellent thermal dimensional stability are required. In addition, the dielectric loss must be small in the GHz band. In order to reduce the dielectric loss, the dielectric loss tangent (tan δ) must be small, and a material having a small tan δ is required as a high-frequency circuit wave substrate material. It is also required that the dielectric constant be low in order to reduce the signal delay at high frequencies.

[0004]

Conventionally, ceramics have been used as a material for a high-frequency circuit board, taking advantage of characteristics such as a low dielectric loss tangent and a low coefficient of linear expansion. However, since the circuit is manufactured by a method such as drilling or paste printing on the ceramic substrate, the processing accuracy is low. In addition, since ceramics are baked by high-temperature treatment of 800 ° C. or more after processing, large shrinkage at that time is disadvantageous in terms of processing accuracy.

[0005] On the other hand, a resin substrate containing an epoxy resin or the like as a main component is highly advantageous in terms of dimensional accuracy because the wiring can be formed by etching and the processing accuracy is high. . Further, in a build-up substrate using photolithography or laser processing for forming the through-hole, the processing accuracy of the through-hole is very high. In addition, resins generally have the advantage of being lighter in weight because of their lower dielectric constant and lower specific gravity than ceramics. However, the resin substrate has a high dielectric loss tangent at high frequencies and a coefficient of linear expansion that is at least 10 times larger than that of ceramics, so that it has been difficult to use it for high frequency applications.

As a means for improving the electrical and thermal characteristics of a resin substrate, a method of mixing various ceramic particles or inorganic particles with a resin has been considered. However, in order to give the resin a low dielectric loss tangent and a low coefficient of linear expansion, which are the characteristics of ceramics, it is necessary to fill a large amount of ceramic particles and inorganic particles. There was a difficulty to do it.

[0007]

That is, the present invention is an insulating material for a high-frequency circuit board containing inorganic particles and a resin, wherein the insulating material contains at least two kinds of particles having different average particle diameters as the inorganic particles. Is an insulating material for a high-frequency circuit board.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

As the inorganic particles used in the insulating material for a high-frequency circuit board of the present invention, the following can be arbitrarily used.

Preferred inorganic particles include alumina, beryllia, mullite, steatite, forsterite,
Examples include cordierite, zircon, silica, silicon nitride, aluminum nitride, silicon carbide, ordinary porcelain, glass ceramics, and the like. Any of these can be preferably used as an electric circuit insulating material, but silica is most preferable for the purpose of obtaining the insulating material for a high-frequency circuit board in the present invention. Silica has a relatively low dielectric constant and a low specific gravity among inorganic substances, and when filled in a resin, does not easily impair the characteristics of the resin such as a low dielectric constant and a low specific gravity. Also,
There is also an advantage that dielectric loss in a high frequency region is small, inexpensive, and various particle sizes are commercially available and easily available. In addition, silica having a high purity of 99% or more can be easily obtained, and the electrical characteristics can be strictly controlled.

The shape of the inorganic particles is preferably spherical or substantially spherical. This is because spherical particles have the smallest specific surface area and thus hardly cause particle agglomeration or decrease in resin fluidity during filling.

It is desirable that these inorganic particles be contained in the resin at a high filling rate. However, in order to obtain the effect of the present invention, a mixture of two or more kinds having different average particle diameters is used. Required. When filled with particles of a single particle size, if the particles are spherical or nearly spherical, filling at a high density will create a diamond-shaped void between the particles, and other particles will no longer enter this void I can't do that.
However, particles having a size equal to or smaller than the gap can further penetrate into the gap, and the filling rate can be easily improved.

In the present invention, when the average particle diameter of the inorganic particles having the maximum average particle diameter is defined as Ra and the minimum average particle diameter is defined as Rb, 5 ≦ Ra / Rb <100
It is also to satisfy. The size of the small sphere is not less than one-fifth of the size of the large sphere, so that it cannot penetrate efficiently. On the other hand, when the size of the large particles is 1/100 or less, the small particles are extremely easily aggregated, which makes mixing difficult. Therefore, the preferred average particle size of the small particles is 5 times the average particle size of the large particles.
More than 1/100 and less than 1/100.

The average particle diameter of the inorganic particles used as the large particles is preferably 0.1 μm or more and less than 10 μm. If it exceeds 10 μm, the processability of the through-holes decreases, and if the large particles become less than 0.1 μm,
The preferred size of the small particles is about 10 nm, which facilitates aggregation. The average particle diameter of the inorganic particles used as the small particles is preferably 20 nm or more and less than 2 μm. Particles smaller than 20 nm tend to cause agglomeration and thickening of the resin. When particles having a particle size of 2 μm or more are used as small particles, the preferred size of the large particles is about 10 μm, which lowers the processability of through holes.

As a method of measuring the particle size, a laser diffraction or scattering type particle size distribution meter can be used. Examples of laser diffraction and scattering type particle size distribution measuring devices include LA-920 manufactured by Horiba and SAL manufactured by Shimadzu.
D-1100, Nikkiso MICROTRAC-UPA1
There are 50 mag. From the particle size distribution determined by these devices, the particle size of 50% of the cumulative distribution, so-called D50 particle size, can be used as the average particle size.

In the present invention, the content Wa of the inorganic particles having the largest average particle size and the content Wb of the inorganic particles having the smallest average particle size are 0.05 ≦ Wb / (Wa) in weight ratio.
+ Wb) <0.5. That is, the amount of the small particles is preferably 5% or more and less than 50% of the total amount of the particles in weight ratio. If the amount is less than 5%, the effect of increasing the filling amount by entering the voids is hardly obtained.
At 0% or more, the volume occupied by particles smaller than the voids created by the large particles increases, and the effect of interpenetrating and increasing the filling amount decreases.

In addition to these large and small particles,
Further, particles having other particle diameters may be mixed, and even if three or more kinds are used, the effect of improving dispersibility can be obtained by mixing the particles by appropriately selecting the particle diameter and the compounding ratio.

In the present invention, the total content of inorganic particles Wi
Satisfies 0.45 ≦ Wi / (Wi + Wo) <0.85 as a weight ratio with respect to the total amount of resin solid content Wo. That is, the content is preferably 45% by volume or more and less than 85% by volume with respect to the total solid content (the total of the inorganic particles and the resin solid content) of the insulating material. If the amount is less than 45% by volume, the effect of improving the dielectric loss tangent and linear expansion coefficient of the resin by filling the inorganic particles is small, and if the amount is more than 85% by volume, it becomes difficult to uniformly mix the resin.

It is preferable that at least a part of the resin component contains a thermosetting resin. Since the high-frequency circuit board requires high heat resistance such as solder resistance, it is preferable to use a thermosetting resin.

As the thermosetting resin, generally used resins such as an epoxy resin, a phenol resin, a urea resin, a melamine resin, a polyimide resin, an unsaturated ester resin and an epoxy acrylate resin are preferably used.

The epoxy resin used in the present invention is preferably a compound having two or more epoxy groups in one molecule. Examples of such a compound include phenol, cresol, halogenated phenol, and alkylated phenols and formaldehyde. Novolak type epoxy resin obtained by reacting novolaks obtained by reacting with an acidic catalyst with epichlorohydrin, salicylaldehyde-phenol or cresol type epoxy resin, bisphenol A type, bisphenol F type, hydrogenated bisphenol A type, bromine Bisphenol A type or alicyclic glycidyl ether type epoxy resin, rubber modified epoxy resin, cycloaliphatic epoxy resin, heterocyclic epoxy resin, hydantoin type epoxy resin, triglycidyl isocyanurate, etc. There can be used singly or in combination.

When at least a part of the resin component contains a photosensitive resin, through holes required for the circuit board can be processed with high precision by photolithography.
As the photosensitive resin, any of a photocurable resin and a photosoluble resin can be suitably used.

Examples of the photocurable resin include (1) a monomer or oligomer having one or more radically polymerizable functional groups such as an unsaturated group in one molecule mixed with a suitable binder polymer, and a photopolymerization initiator or the like. (2) a polymer obtained by introducing a photosensitive group into a polymer and adding a photopolymerization initiator, and (3) a photosensitive compound such as an aromatic diazo compound or an aromatic azide compound to a suitable binder polymer. Examples thereof include a mixture thereof, and (4) a mixture containing an epoxy resin and a cationic photopolymerization initiator.

Examples of the photo-soluble resin composition include:
(1) a complex of a diazo compound with an inorganic salt or an organic acid, a mixture of a quinonediazide or the like with an appropriate polymer binder, and (2) a complex of a quinonediazide with an appropriate polymer binder.

From the viewpoint of heat resistance, a photocurable resin which is polymerized and cured by exposure to light is more preferable than a photosoluble resin. These photocurable resins can also obtain an insulating layer with higher heat resistance by processing the through-holes by pattern exposure and development and then further curing by heating.

Examples of the binder polymer used in the present invention include polyvinyl alcohol, poly (meth) acrylate, polystyrene, polyamide, polyester, polyurethane, fluororesin, silicone resin, polyacetal, and the like which can achieve the object of the present invention. Examples thereof include polyphenylene oxide, polysulfone, and polyimide. These can be used alone or as a mixture.

In the present invention, the photocurable resin preferably contains at least a photoradical initiator and a resin component having a photopolymerizable functional group. Benzophenone, acetophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-1,2-diphenylethan-1-one, 2-methyl-1- [4- (methylthio) phenyl] -2 as a photo radical initiator -Morpholinopropanone-1,2-benzyl-2-
Dimethylamino-1- (4-morpholinophenyl) -butanone
-1,2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1- [4- (2-hydroxyethoxy) phenyl] -2-hydroxy-2-methyl-1-propan-1-one Benzophenone or acetophenone derivatives, such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,4,6-
Acylphosphine derivatives such as trimethylbenzoyl) -phenylphosphine oxide, thioxanthone,
2-chlorothioxanthone, 4-diethylthioxanthone,
Thioxanthone derivatives such as 2-isopropylthioxanthone, bis (cyclopentadienyl) -bis (2,6-difluoro
And metallocene compounds such as -3- (pyr-1-yl) titanium. A benzoic acid-based or tertiary amine-based photopolymerization accelerator can be used in combination with these photopolymerization initiators.

Examples of the resin component having a photopolymerizable functional group include a polymer compound having a radical polymerizable functional group introduced into a main chain or a side chain thereof, and / or one or more photopolymerizable functional groups in one molecule. And a low molecular weight compound having the following formula: Examples of the polymer compound having a radical polymerizable functional group introduced into a main chain or a side chain thereof include a copolymer obtained by reacting (meth) acrylic acid with a copolymer containing (meth) acrylate having a glycidyl group, and further reacting the copolymer with an acid. An anhydride-reacted polymer, a carboxyl-containing polymer reacted with a (meth) acrylate-containing glycidyl compound or isocyanate compound, a maleic anhydride-containing copolymer with a hydroxyl-containing (meth) acrylate monomer or glycidyl Examples thereof include those obtained by reacting a (meth) acrylate monomer having a group, unsaturated polyester resins, and epoxy (meth) acrylate resins, and these can be used alone or in combination. These can be used as a binder polymer at the same time as being a photopolymerizable compound.

Specific examples of the low molecular weight compound having a radical polymerizable functional group such as an unsaturated group in one molecule include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, N-vinylpyrrolidone, Ilmorpholine, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, N, N-dimethylacrylamide, phenoxyethyl (meth) acrylate, cyclohexyl (meth) acrylate, trimethylol Propane (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, tris (hydroxyethyl) isocyanurate di (meth) Acrylate, tris can be exemplified a (hydroxyethyl) isocyanurate tri (meth) acrylate, which may be used alone or in combination.

By selecting an alkali-soluble binder polymer, it is possible to develop with an aqueous alkali solution instead of an organic developer having a large environmental load.

One of the preferred embodiments is that the photosensitive resin itself is thermosetting. Examples include epoxy acrylate resin (a resin obtained by adding (meth) acrylic acid to an epoxy resin and further reacting with an acid anhydride), and a photosensitive polyimide resin (a (meth) acrylate group is formed by esterifying a (meth) acrylate group with a polyimide precursor). Introduced through a bond, an ionic bond, etc.).

The epoxy acrylate resin is added to the epoxy group of the epoxy resin in the presence of an esterification catalyst at about 60 to 14
It can be produced by reacting acrylic acid or methacrylic acid in a temperature range of about 0 ° C. to perform esterification.

The photosensitive polyimide resin is prepared by reacting a tetracarboxylic anhydride with a (meth) acrylate compound having a hydroxyl group and then reacting with a diamine compound in the presence of a dehydration condensing agent, or a polyimide precursor (polyamic acid) and an amino acid. It can be produced by mixing a (meth) acrylate compound having a group.

The insulating material for a high-frequency circuit board of the present invention can be adjusted, for example, by the following method. First, two or more kinds of inorganic particles having an average particle diameter, a resin component, and a solvent are mixed. What is necessary is just to select suitably what dissolves a resin as a solvent, For example, methyl cellosolve, butyl cellosolve,
Methyl ethyl ketone, dioxane, acetone, cyclohexanone, cyclopentanone, isobutyl alcohol,
Isopropyl alcohol, tetrahydrofuran, dimethyl sulfoxide, γ-butyrolactone, toluene, chlorobenzene, benzyl alcohol, isophorone, methoxymethylbutanol, ethyl lactate, propylene glycol monomethyl ether and its acetate, N-methylpyrrolidone, and one or more of these. An organic solvent mixture is used.

If necessary, stabilizers, dispersants,
A precipitation inhibitor, a plasticizer, an antioxidant, etc. may be added. When a photosensitive resin is used, a sensitizer, a sensitization aid, a photopolymerization accelerator, a thermal polymerization inhibitor, an ultraviolet absorber, etc. May be added. These mixtures are mixed by a method such as a ball mill, an attritor, a roll mill, a kneader, and a sand mill to form a paste.

The insulating material for a high-frequency circuit board of the present invention obtained as described above is applied and dried to form an insulating layer of the high-frequency circuit board. In order to obtain electrical connection between layers, through holes are formed by a photolithographic technique.
The preferable thickness of the paste after drying is from 10 to 200 μm. If the thickness is larger than this, it becomes difficult to process through holes, and the effect of photocuring is reduced. When the thickness is less than 10 μm, sufficient mechanical strength and electrical insulation cannot be secured.

The case where a through hole is formed by photolithography will be described. A high-resolution through-hole pattern can be formed by exposing ultraviolet rays to a desired pattern using a photomask and then developing the photosensitive layer. For the development, an appropriate developer (water, alkali developer, organic solvent, or a mixture thereof) can be used depending on the type of the photosensitive resin component. The developing method is not particularly limited, and for example, a paddle method, a dip method, a spray method, and the like can be adopted.

After the through-hole processing, a heat treatment may be performed under appropriate conditions in order to improve the heat resistance of the obtained pattern.

Examples of a method for forming a circuit on the substrate obtained as described above include electroless plating for attaching a metal layer to be a circuit to the substrate, or a combination of electroless plating and electrolytic plating.

[0040]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited to these examples. Unless otherwise specified, all the following operations were performed in a yellow light room where ultraviolet light was blocked.

Synthesis Example 1 A phenol novolak type epoxy resin (175 g, Epicort 152, epoxy equivalent: 175, manufactured by Yuka Shell Co., Ltd.) and 40 g of propylene glycol monomethyl ether acetate were added to a 500 ml reaction vessel, and the temperature was raised to 110 ° C. A mixture of acrylic acid (54 g), hydroquinone monomethyl ether (0.1 g) and benzyltriethylammonium chloride (0.3 g) was added dropwise over about 1 hour. After the addition, the mixture was heated at 110 ° C. for about 10 hours, cooled to 60 ° C., and a mixture of 116 g of tetrahydrophthalic anhydride and 170 g of propylene glycol monomethyl ether acetate was added. After the addition, the temperature was raised to 110 ° C over about 2 hours, and 1
Heating was continued at 10 ° C. for about 10 hours to obtain an acrylic epoxy resin solution (1-A). To this solution was added 2-benzyl-2-
Dimethylamino-1- (4-morpholinophenyl)-
10 g of butanone-1 and 5 g of pentaerythritol hexaacrylate were added to obtain a resin (1-B).

Synthesis Example 2 2-propanol was added to a 1000 ml four-necked flask.
While maintaining the temperature at 80 ° C. in an oil bath and sealing with nitrogen and stirring, 60 g of methyl methacrylate, 80 g of styrene, and 60 g of methacrylic acid were mixed with N.N. 2 g of N-azobisisobutyronitrile was mixed, and the mixture was added dropwise using a dropping funnel over 30 minutes. After continuing the reaction for 4 hours, 2 g of hydroquinone monomethyl ether was added, the temperature was returned to room temperature, and the polymerization was completed. The thus obtained product was designated as resin (2-A). Next, the resin (2-A)
While maintaining the temperature at 75 ° C., 80 g of glycidyl methacrylate and 6 g of triethylbenzylammonium chloride were added and reacted for 3 hours. The product thus obtained was designated as resin 2-B. Here, the reaction rate of glycidyl methacrylate was determined from the change in polymer acid value before and after the reaction.
%Met. Therefore, the added amount was 0.73 molar equivalent. Dissolve 60 g of resin (2-B), 30 g of dipentaerythritol hexaacrylate, and 12 g of 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 in 125 g of propylene glycol monomethyl ether acetate. Resin (2-C) was used.

In 160 g of propylene glycol monomethyl ether acetate, 60 g of the resin (2-B), 30 g of dipentaerythritol hexaacrylate,
Resin (2-D) was prepared by dissolving 1.2 g of benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 and 30 g of partially alkyletherated hexamethylolmelamine.

Synthesis Example 3 82.2 g of bis [4- (3-aminophenoxy) phenyl] sulfone and bis (3-aminopropyl) tetramethyldisiloxane were placed in a 1000 ml four-necked flask.
49 g was added to 324 g of N-methyl-2-pyrrolidone at 20 ° C.
And dissolved. Thereafter, 31.6 g of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride and 21.4 g of pyromellitic anhydride were added and reacted at 55 ° C. for 4 hours. Thereafter, the mixture is cooled to 20 ° C., and N-phenylglycine is added.
93 g, Michler's ketone 0.14 g, diethylaminoethyl methacrylate 74.0 g, and N-methyl-2-pyrrolidone 83.1 g were added to obtain a photosensitive polyimide precursor composition (3-A).

The inorganic particles are silica particles having various average particle diameters. The silica particles used are as follows.

Reagent primary silica (manufactured by Kanto Kagaku) average particle size: 12 μm “Admafine” SO-C3 (manufactured by Admatech) 1 μm average particle size “Admafine” SO-C1 (manufactured by Admatech) 0 "Aerosil" OX50 (manufactured by Nippon Aerosil) having an average particle diameter of 40 nm. "Aerosil" 200 (manufactured by Nippon Aerosil) having an average particle diameter of 10 nm.

Examples 1 to 17, Comparative Examples 1 to 3 Resins (1-B), (2-C), (2-D) and (3-
A) and inorganic particles were blended in the compositions shown in Tables 1 to 4, respectively, and kneaded with a three-roll mill to obtain a photosensitive resin composition containing inorganic particles. Unless otherwise specified, all numerical values in this example are parts by weight.

These photosensitive resin compositions were applied on a substrate and dried in a hot air oven at 80 ° C. for 30 minutes. Exposure was performed with an ultra-high pressure mercury lamp through a photomask having a test pattern. Development was performed for a period of time during which the unexposed portion was dissolved with a 1% aqueous solution of sodium carbonate plus 10 seconds, and the pattern shape was observed.

Separately from the sample for pattern processing, each photosensitive resin composition was coated on an aluminum substrate, dried at 80 ° C. for 30 minutes, exposed to light over the entire surface, and then thermally cured at 180 ° C. for 60 minutes. A counter electrode was formed on the obtained film with an aluminum vapor-deposited film, and the dielectric loss tangent at 1 MHz was measured by a Hewlett-Packard impedance measuring device. The coefficient of linear expansion of the cured film was measured by TMA.

For Examples 1 to 5 and Comparative Example 1, samples were prepared by using two types of particles having different particle diameters and changing the ratio of inorganic particles to organic solids. The results are shown in Table 1. .
The weight ratio between particles A having an average particle diameter of 1 μm and particles B having an average particle diameter of 40 nm was kept constant at 90/10. As compared with Comparative Example 1 containing no inorganic particles, Examples 1 to 5 had a lower dielectric loss tangent and a lower coefficient of linear expansion, and the pattern workability was equivalent to that of Comparative Example 1. Although the dielectric loss tangent and the coefficient of linear expansion were lower as the weight ratio of the inorganic particles was higher, the pattern workability was slightly lowered in Example 4 where the inorganic particle ratio was the largest.

[0051]

[Table 1]

In Examples 6 to 9 and Comparative Examples 2 to 3, the weight ratio of the inorganic particles to the organic solid was kept constant, and the inorganic particles A
A sample was prepared in which the ratio of the inorganic particles B was changed, and the results are shown in Table 2. Although the inorganic particles had a high ratio of 80% by weight in the solid content, the coating film appearance and pattern processability were all good. The coating films of Comparative Examples 2 and 3 containing only one type of inorganic particles were non-uniform in cloudiness, poor in particle dispersibility, and poor in pattern processing. Further, Comparative Example 2,
In No. 3, the dielectric loss tangent was also large. This is presumed to be due to poor dispersion and an increase in defects in the film, resulting in an increase in loss.

[0053]

[Table 2]

With respect to Examples 10 to 13, samples in which the size of the inorganic particles was changed were prepared, and the results are shown in Table 3. Resin compositions in which the weight ratio of the inorganic particles to the organic solids and the blending ratio of the two types of particles were kept constant all gave good results.

[0055]

[Table 3]

In Examples 14 to 17, samples were prepared in which the weight ratio of the inorganic particles to the organic solids, the particle size of the two types of particles, and the mixing ratio were constant, and the type of resin was changed. The results are shown in FIG. Good results were obtained according to the present invention regardless of the type of resin.

[0057]

[Table 4]

[0058]

According to the present invention having the above structure, an insulating resin material suitable for a high-frequency circuit board can be obtained, and the obtained high-frequency circuit board has a higher processing accuracy than a ceramic substrate. It has a low dielectric constant and a low coefficient of linear expansion and a high heat resistance as compared with a general resin substrate, and thus was very suitable as a high-frequency circuit board.

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Claims (9)

[Claims] 1. An insulating material for a high-frequency circuit board comprising at least a photosensitive resin as an inorganic particle and a resin component, wherein the inorganic particle contains at least two kinds of particles having different average particle diameters. An insulating material for a high-frequency circuit, comprising: 2. Among two or more kinds of inorganic particles having different average particle diameters, the average particle diameter of the inorganic particles having the maximum average particle diameter is Ra, and the average particle diameter of the inorganic particles having the minimum average particle diameter is Ra. 2. The insulating material for a high-frequency circuit board according to claim 1, wherein, when Rb, 5 ≦ Ra / Rb <100 is satisfied. 3. The content Wa of the inorganic particles having the maximum average particle size and the content Wb of the inorganic particles having the minimum average particle size.
Is 0.05 ≦ Wb / (Wa + Wb) <
3. The insulating material for a high-frequency circuit board according to claim 2, wherein 0.5 is satisfied. 4. The total content Wi of the inorganic particles is 0.45 ≦ Wi /
2. The insulating material for a high-frequency circuit board according to claim 1, wherein (Wi + Wo) <0.85 is satisfied. 5. The insulating material for a high-frequency circuit board according to claim 1, wherein the insulating material contains at least silica as inorganic particles. 6. The insulating material for a high-frequency circuit board according to claim 1, wherein at least a thermosetting resin is contained as a resin component. 7. The insulating material for a high-frequency circuit board according to claim 1, wherein the photosensitive resin contains at least a photocurable resin. 8. The insulating material for a high-frequency circuit board according to claim 7, wherein the photocurable resin contains at least a photoradical initiator and a resin component having a photopolymerizable functional group. 9. A high-frequency circuit board using the insulating material according to claim 1.