JP2011124550A - Electronic circuit board and manufacturing method of the same - Google Patents

Abstract

An electronic circuit board having an insulating layer excellent in both thermal conductivity and adhesion is provided.
An electronic circuit board is formed by laminating a metal base, a second resin layer containing an inorganic filler, a second resin layer containing no inorganic filler, and a metal foil for forming a wiring pattern. To do. Since the 2nd resin layer 103 does not contain an inorganic filler, adhesiveness with the metal foil 104 can be improved. Moreover, the adhesiveness between both can be improved by forming the 1st resin layer 102 and the 2nd resin layer 103 with the same resin. Further, a first coating film for the second resin layer 103 is formed on the metal foil 104, and a second coating film for the first resin layer 102 is formed without going through the solvent removal step. A solvent removal process is performed simultaneously on the film and the second coating film. Thereby, the adhesiveness between the 1st resin layer 102 and the 2nd resin layer 103 can further be improved.
[Selection] Figure 1

Description

  The present invention relates to an electronic circuit board using a heat dissipation board and a method for manufacturing the same.

  2. Description of the Related Art Conventionally, an electronic circuit board using a heat dissipation substrate formed of metal or the like and an insulating layer formed of resin or the like is known. FIG. 2 is a cross-sectional view showing an example of the structure of the electronic circuit board 200.

  In the example of FIG. 2, an insulating layer 202 is formed on a metal base 201, and further a metal foil 203 as a wiring pattern is formed. On the electronic circuit board 200, a mounting circuit 204 is provided using a plurality of electronic components 205 such as an IC (integrated circuit) and a transistor. Each electronic component 205 is electrically connected to a wiring pattern formed of the metal foil 203. Although the mounting circuit 204 generates heat during operation, this heat is directly radiated from the electronic component 205, is conducted to the metal base 201 through the insulating layer 202, and is also radiated from the metal base 201. For this reason, in the electronic circuit board 200 using the metal base 201, a high heat dissipation effect can be obtained.

  In such an electronic circuit board 200, it is desired that the thermal conductivity of the insulating layer 202 be sufficiently high in order to sufficiently exhibit the heat dissipation effect of the metal base 201. For example, techniques disclosed in Patent Documents 1 to 3 are known as techniques for obtaining the insulating layer 202 having excellent thermal conductivity.

  Patent Documents 1 and 2 disclose an insulating film having improved thermal conductivity by containing an inorganic filler.

  Patent Document 3 discloses an insulating film in which both a thermal conductivity and an insulating property are improved by providing a layer having a high inorganic filler content and a layer having a low content.

Japanese Patent Laid-Open No. 4-323889 (paragraph [0004] column) JP-A-5-167212 (column [0006] column) JP-A-6-310825 (column [0017] column)

  Here, when the insulating film contains an inorganic filler, the thermal conductivity improves as the content of the inorganic filler increases. For this reason, in order to obtain excellent thermal conductivity, it is desirable to contain as much inorganic filler as possible in the insulating film.

  However, when an insulating film containing an inorganic filler is used as the insulating layer 202, there is a drawback that the adhesion between the insulating layer 202 and the metal foil 203 is lowered. Such a defect becomes more remarkable as the content of the inorganic filler is larger.

  In recent years, the mounting circuit 204 has a tendency to increase in density, and for this reason, the wiring pattern of the electronic circuit board 200 tends to be miniaturized. As the wiring pattern becomes finer, the metal foil 203 is more easily peeled off during pattern formation. Therefore, there is an increasing demand for improving the adhesion between the insulating layer 202 and the metal foil 203. On the other hand, the higher the density of the mounting circuit 204, the greater the amount of heat radiation, so it is necessary to ensure excellent thermal conductivity.

  Then, an object of this invention is to provide the electronic circuit board which has an insulating layer excellent in both heat conductivity and adhesiveness, and its manufacturing method in view of such a situation.

  In order to achieve this object, the present inventor has studied the structure and manufacturing method of the insulating layer of the electronic circuit board, and has completed the present invention.

  That is, the invention according to claim 1 is an electronic circuit board having a heat dissipation substrate, an insulating layer provided on the heat dissipation substrate, and a conductive foil for forming a wiring pattern provided on the insulating layer. The insulating layer is formed on the heat dissipation substrate, the first resin layer containing an inorganic filler, and the first resin layer and the conductive foil are in direct contact with them. An electronic circuit board having a formed second resin layer containing no inorganic filler is provided.

  The invention according to claim 2 is characterized in that, in addition to the structure according to claim 1, the first resin layer contains 50 to 80% by volume of the inorganic filler.

  The invention described in claim 3 is characterized in that, in addition to the structure described in claim 1 or 2, the resin of the insulating layer is liquid crystal polyester.

  Furthermore, the invention according to claim 4 is an electronic circuit board having a heat dissipation substrate, an insulating layer provided on the heat dissipation substrate, and a conductive foil for forming a wiring pattern provided on the insulating layer. The insulating layer forming step includes a first step of forming a first coating film containing a solvent and a resin and no inorganic filler on the surface of the conductive foil, and the first coating step. A second step of forming a second coating film containing the solvent, the resin and the inorganic filler on the surface of the film; and a third step of simultaneously removing the solvent contained in the first coating film and the second coating film. And an electronic circuit board manufacturing method including the steps.

  According to invention of Claim 1, while comprising an insulating layer with the 1st resin layer containing an inorganic filler, and the 2nd resin layer which does not contain an inorganic filler, so that a 2nd resin layer and conductive foil may contact | connect directly. Since it formed, the adhesiveness of these 2nd resin layers and conductive foil can be improved.

  According to invention of Claim 2, since the 1st resin layer contains 50-80 volume% of inorganic fillers, the adhesiveness between a 1st resin layer and a 2nd resin layer can fully be made high.

  According to the invention of claim 3, since the resin of the insulating layer is liquid crystal polyester, excellent thermal conductivity can be obtained.

  According to invention of Claim 4, after forming the 2nd coating film on the 1st coating film, the solvent of both coating films is removed simultaneously, and the layer which contains an inorganic filler, and the layer which does not contain are formed integrally Therefore, the adhesion of these layers can be sufficiently increased.

It is sectional drawing which shows the structure of the electronic circuit board which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the structure of the conventional electronic circuit board.

Embodiments of the present invention will be described below.
Embodiment 1 of the Invention

FIG. 1 shows a first embodiment of the present invention. In the first embodiment, the metal base 101 is used as an example of the heat dissipation substrate, and the metal foil 104 is used as an example of the conductive foil.
<Structure of electronic circuit board>

  As shown in FIG. 1, the electronic circuit board 100 according to the first embodiment has a laminated structure in which a metal base 101, a first resin layer 102, a second resin layer 103, and a metal foil 104 are laminated in this order. . Here, the first resin layer 102 and the second resin layer 103 constitute an insulating layer 105.

  The metal base 101 (corresponding to the heat dissipation substrate of the present invention) is formed of a metal plate made of, for example, aluminum, copper, stainless steel, or an alloy thereof. As the metal base 101, the same one as the conventional one can be used. The thickness of the metal base 101 is 2 mm, for example. The metal base 101 does not need to be a flat plate, and can be bent, for example.

  The first resin layer 102 is a resin layer containing an inorganic filler. In the first embodiment, liquid crystal polyester is used as the resin of the first resin layer 102. By using liquid crystal polyester, excellent thermal conductivity can be obtained. Moreover, what is mentioned later can be used as an inorganic filler. The thickness of the first resin layer 102 is, for example, 100 μm. As for content of an inorganic filler, it is desirable to set it as 50-80 volume%, for example. If there is too little inorganic filler, the thermal conductivity of the first resin layer 102 will be insufficient, and if there is too much inorganic filler, peeling will easily occur between the first resin layer 102 and the second resin layer 103. is there.

  The second resin layer 103 is a resin layer that does not contain an inorganic filler. In the first embodiment, in order to obtain excellent thermal conductivity, liquid crystal polyester is used as the resin of the second resin layer 103. In order to further improve the thermal conductivity, it is desirable to make the second resin layer 103 thin, and therefore it is desirable to set the thickness to 5 μm or less, for example. On the other hand, in order to sufficiently increase the adhesion between the second resin layer 103 and the metal foil 104, it is desirable to make the thickness of the second resin layer 103 sufficiently thicker than the unevenness of the metal foil 104, Therefore, for example, it is desirable that the thickness is 0.1 μm or more.

  Insulating materials for forming the first resin layer 102 and the second resin layer 103 may be different materials, but in the first embodiment, the same liquid crystal polyester composition is used for both. In the case of using different materials, it is desirable to select these insulating materials so that the strength against peeling between the first resin layer 102 and the second resin layer 103 is sufficiently high.

  For example, a copper foil or the like is used as the metal foil 104 (corresponding to the conductive foil of the present invention). A wiring pattern of a mounting circuit is formed on the metal foil 104 by etching or the like, for example. 2 is mounted on the electronic circuit board 100 using this wiring pattern (not shown in FIG. 1). As the metal foil 104, the same one as in the past can be used. The thickness of the metal foil 104 is, for example, 70 μm.

Hereinafter, the main configuration of the first embodiment will be described in detail.
<Liquid crystal polyester>

  The liquid crystalline polyester exhibits optical anisotropy when melted, and forms an anisotropic melt at a temperature of 450 ° C. or lower. In the first embodiment, the first resin layer 102 and the second resin layer 103 are formed using a solution obtained by dissolving liquid crystal polyester in a solvent.

This liquid crystalline polyester has a structural unit represented by the following formula (1) (hereinafter referred to as structural unit (1)) and a structural unit represented by the following formula (2) (hereinafter referred to as structural unit (2)). And the structural unit represented by the following formula (3) (hereinafter referred to as the structural unit (3)), and the total content of all the structural units (the mass of each structural unit constituting the liquid crystal polyester is represented by each structural unit) The content of each structural unit is determined as a substance amount equivalent (mole) by dividing by the formula amount, and the content of the structural unit (1) is 30 to 80 mol% with respect to the total value). The content of the structural unit (2) is preferably 35 to 10 mol%, and the content of the structural unit (3) is preferably 35 to 10 mol%.
(1) —O—Ar ¹ —CO—
(2) —CO—Ar ² —CO—
⁽³⁾ -X-Ar 3 -Y-

Here, Ar ¹ represents 1,4-phenylene, 2,6-naphthalene or 4,4′-biphenylene. Ar ² represents 1,4-phenylene, 1,3-phenylene or 2,6-naphthalene. Ar ³ represents 1,4-phenylene or 1,3-phenylene. X represents —NH—, and Y represents —O— or —NH—.

  The structural unit (1) is a structural unit derived from an aromatic hydroxy acid, the structural unit (2) is a structural unit derived from an aromatic dicarboxylic acid, the structural unit (3) is an aromatic diamine, and an aromatic amine having a hydroxyl group (hydroxyl group). These are structural units derived from aromatic amino acids, but instead of these, ester-forming derivatives thereof may be used.

  Examples of ester-forming derivatives of carboxylic acids include those having a high reactive activity such as acid chlorides and acid anhydrides that promote the reaction in which the carboxyl group generates a polyester, and the carboxyl group is transesterified. Examples include those that form esters with alcohols, ethylene glycol, or the like that generate polyester by reaction.

  Examples of the ester-forming derivative of a phenolic hydroxyl group (phenolic hydroxyl group) include those in which a phenolic hydroxyl group forms an ester with a carboxylic acid so that a polyester is produced by a transesterification reaction.

  Examples of the ester-forming derivative of an amino group include those in which an amino group forms an ester with a carboxylic acid so that a polyester is produced by a transesterification reaction.

  Examples of the repeating structural unit of the liquid crystalline polyester used in the present invention include the following, but are not limited thereto.

  Examples of the structural unit (1) include structural units derived from p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, 4-hydroxy-4′-biphenylcarboxylic acid, and the like. Units may be included in all structural units. Among these structural units, it is preferable to use a liquid crystal polyester containing a structural unit derived from 2-hydroxy-6-naphthoic acid. The structural unit (1) is preferably from 30 to 80 mol%, more preferably from 40 to 70 mol%, still more preferably from 45 to 65 mol%, based on all structural units. When the structural unit (1) exceeds 80 mol%, the solubility tends to be remarkably lowered, and when it is less than 30 mol%, the liquid crystallinity tends not to be exhibited.

  Examples of the structural unit (2) include structural units derived from terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid, and two or more structural units may be included in all structural units. Good. Among these structural units, from the viewpoint of solubility, it is preferable to use a liquid crystal polyester containing a structural unit derived from isophthalic acid. The structural unit (2) is preferably from 35 to 10 mol%, more preferably from 30 to 15 mol%, and more preferably from 27.5 to 17.5 mol%, based on all structural units. Further preferred. If the structural unit (2) exceeds 35 mol%, the liquid crystallinity tends to be reduced, and if it is less than 10 mol%, the solubility tends to decrease.

  Examples of the structural unit (3) include 3-aminophenol, 4-aminophenol, 1,4-phenylenediamine, 1,3-phenylenediamine, and structural units derived from aminobenzoic acid. The structural unit may be contained in all structural units. Among these structural units, it is preferable to use a liquid crystalline polyester containing a structural unit derived from 4-aminophenol from the viewpoint of reactivity. The structural unit (3) is preferably from 35 to 10 mol%, more preferably from 30 to 15 mol%, and more preferably from 27.5 to 17.5 mol%, based on all structural units. Further preferred. If the structural unit (3) exceeds 35 mol%, the liquid crystallinity tends to decrease, and if it is less than 10 mol%, the solubility tends to decrease.

  The structural unit (3) is preferably used in substantially the same amount as the structural unit (2). However, the polymerization degree of liquid crystalline polyester can also be controlled by setting the structural unit (3) to −10 mol% to +10 mol% with respect to the structural unit (2).

  The manufacturing method of liquid crystalline polyester used by this invention is not specifically limited. For example, an aromatic hydroxy acid corresponding to the structural unit (1), an aromatic amine having a hydroxyl group corresponding to the structural unit (3), a phenolic hydroxyl group and an amino group of the aromatic diamine with an excessive amount of fatty acid anhydride. Examples include acylation to obtain an acylated product, and esterification (polycondensation) of the obtained acylated product and the aromatic dicarboxylic acid corresponding to the structural unit (2) to melt polymerization.

  As the acylated product, a fatty acid ester obtained by acylation in advance may be used (see JP 2002-220444 A and JP 2002-146003 A).

  In the acylation reaction, the amount of fatty acid anhydride added is preferably 1 to 1.2 times equivalent to the total content of phenolic hydroxyl groups and amino groups, more preferably 1.05 to 1. .1 equivalent. If the amount of fatty acid anhydride added is less than 1 equivalent, acylated products and raw material monomers tend to sublimate during transesterification (polycondensation), and the reaction system tends to become clogged. Conversely, the amount of fatty acid anhydride added Is more than 1.2 times equivalent, the resulting liquid crystal polyester tends to be remarkably colored.

  The acylation reaction 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 in the acylation reaction is not particularly limited, and examples thereof include acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, pivalic anhydride, anhydrous 2-ethylhexanoic acid, and monochloroacetic anhydride. , Dichloroacetic anhydride, trichloroacetic anhydride, monobromoacetic anhydride, dibromoacetic anhydride, tribromoacetic anhydride, monofluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, glutaric anhydride, maleic anhydride, succinic anhydride, β- Examples thereof include bromopropionic acid, and two or more of these may be used in combination. From the viewpoint of price and handleability, acetic anhydride, propionic anhydride, butyric anhydride, and isobutyric anhydride are preferable, and acetic anhydride is more preferable.

  In the transesterification, the acyl group of the acylated product is preferably 0.8 to 1.2 times the carboxyl group.

  The transesterification is preferably performed while increasing the temperature at 130 to 400 ° C. at a rate of 0.1 to 50 ° C./min, and at 150 to 350 ° C. while increasing the temperature at a rate of 0.3 to 5 ° C./min. It is more preferable.

  When transesterifying a fatty acid ester obtained by acylation with a carboxylic acid, the equilibrium is shifted according to Le Chatelier-Brown's law (equilibrium transfer principle). The product is preferably distilled out of the system, for example, by evaporation.

  The acylation reaction and transesterification may be performed in the presence of a catalyst. As this 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. Among these 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).

  Such a catalyst is usually added at the time of introduction of monomers, and it is not always necessary to remove it after acylation. If this catalyst is not removed, transesterification can be carried out as it is.

  Polycondensation by transesterification is usually performed by melt polymerization, but melt polymerization and solid phase polymerization may be used in combination. The solid phase polymerization is preferably carried out by a known solid phase polymerization method after the polymer is extracted from the melt polymerization step and then pulverized into powder or flakes. Specifically, for example, a method of heat treatment in a solid state at 20 to 350 ° C. for 1 to 30 hours under an inert atmosphere such as nitrogen can be used. The solid phase polymerization may be performed with stirring, or may be performed in a standing state without stirring. In addition, by providing an appropriate stirring mechanism, the melt polymerization tank and the solid phase polymerization tank can be made the same reaction tank. After the solid phase polymerization, the obtained liquid crystalline polyester may be pelletized and molded by a known method.

Manufacture of liquid crystalline polyester can be performed using a batch apparatus, a continuous apparatus, etc., for example.
<Solvent>

  The solvent used for the liquid crystal polyester solution of the first resin layer 102 and the second resin layer 103 is preferably an aprotic solvent. As this solvent, a solvent in which the liquid crystal polyester can be dissolved is desirable, but a solvent that does not dissolve can be used. Although the usage-amount of a solvent is not specifically limited, Although it can select suitably according to a use, It is preferable to use 0.01-100 mass parts of liquid crystal polyester for 100 mass parts of solvents. If the liquid crystal polyester is less than 0.01 parts by mass, the solution viscosity tends to be too low to uniformly coat, and conversely if the liquid crystal polyester exceeds 100 parts by mass, the viscosity tends to increase. From the viewpoint of workability and economy, the liquid crystalline polyester is more preferably 1 to 50 parts by mass, and further preferably 2 to 40 parts by mass with respect to 100 parts by mass of the solvent.

  Examples of the aprotic solvent include halogen solvents such as 1-chlorobutane, chlorobenzene, 1,1-dichloroethane, 1,2-dichloroethane, chloroform, 1,1,2,2-tetrachloroethane, diethyl ether, tetrahydrofuran, Ether solvents such as 1,4-dioxane, ketone solvents such as acetone and cyclohexanone, ester solvents such as ethyl acetate, lactone solvents such as γ-butyrolactone, carbonate solvents such as ethylene carbonate and propylene carbonate, triethylamine, Amine solvents such as pyridine, nitrile solvents such as acetonitrile and succinonitrile, amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, tetramethylurea and N-methylpyrrolidone , Nitromethane, nitro-based solvents such as nitrobenzene, dimethyl sulfoxide, sulfide-based solvent such as sulfolane, hexamethylphosphoramide, and phosphoric acid-based solvent such as tri-n- butyl phosphate and the like.

Among these, a solvent containing no halogen atom is preferably used from the viewpoint of influence on the environment, and a solvent having a dipole moment of 3 to 5 is preferably used from the viewpoint of solubility. Specifically, amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, tetramethylurea and N-methylpyrrolidone, and lactone solvents such as γ-butyrolactone are more preferably used. -Dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone are more preferably used.
<Inorganic filler>

  In Embodiment 1, an inorganic filler is contained in the first resin layer 102 made of a liquid crystal polyester composition. The content of the inorganic filler, the particle size, etc. are not particularly limited.

As the inorganic filler, those having a thermal conductivity of usually 10 W / (m · K) or more, preferably 30 W / (m · K) or more are used, and examples thereof include metal oxides, metal nitrides and metal carbides. One or more selected compounds can be used. The inorganic filler is preferably selected from oxides, nitrides and carbides of elements up to the seventh column of each of Groups II, III and IV of the Periodic Table. Specifically, for example, one or more kinds of beryllium oxide, magnesium oxide, aluminum oxide, thorium oxide, zinc oxide, silicon nitride, aluminum nitride, silicon carbide and the like can be used.
<Other ingredients>

  In the liquid crystal polyester composition as the first resin layer 102 and the second resin layer 103, additives such as a coupling agent, an anti-settling agent, an ultraviolet absorber, and a heat stabilizer are added within a range not impairing the object of the present invention. You may contain 1 type (s) or 2 or more types.

In addition, the liquid crystal polyester 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. One type or two or more types of resins other than liquid crystal polyester such as an elastomer such as a thermoplastic resin, a copolymer of glycidyl methacrylate and polyethylene may be contained.
<Method for producing liquid crystal polyester layer>

  In producing the liquid crystal polyester layer (that is, the first resin layer 102 and the second resin layer 103), first, a solution obtained by dissolving the liquid crystal polyester in a solvent is filtered by a filter or the like as necessary. By removing fine foreign substances contained therein, a liquid crystal polyester solution for the second resin layer 103 is obtained. And the liquid crystal polyester solution for the 1st resin layer 102 is obtained by adding an inorganic filler to the liquid crystal polyester solution same as this.

  Subsequently, a liquid crystal polyester solution for the second resin layer 103 (that is, a liquid crystal polyester solution that does not contain an inorganic filler) is placed on a support substrate (the metal foil 104 can be used in the first embodiment), for example, a roller. The surface is cast so that the surface is flat and uniform by various means such as a coating method, a dip coating method, a spray coating method, a spinner coating method, a curtain coating method, a slot coating method, and a screen printing method. Further, a liquid crystal polyester solution for the first resin layer 102 (that is, a liquid crystal polyester solution containing an inorganic filler) is cast by the same method so that the surface is flat and uniform.

  When the liquid crystal polyester solution for the first resin layer 102 is cast and the inorganic filler settles and reaches the solution for the second resin layer 103, the adhesion between the second resin layer 103 and the metal foil 104 is increased. May fall. Further, if the density of the inorganic filler in the first resin layer 102 increases near the interface with the second resin layer 103 without reaching the solution for the second resin layer 103, the first resin layer 102 and the second resin layer 103 There is a possibility that the adhesion between the two resin layers 103 may be lowered. For this reason, when casting the first resin layer 102 and the second resin layer 103, it is desirable that the viscosity of the liquid crystal polyester is sufficiently high so that the inorganic filler does not settle. For this purpose, it is desirable that the temperature during casting of the liquid crystal polyester solution is sufficiently low.

  Thereafter, the solvent of the first resin layer 102 and the second resin layer 103 is removed. In this Embodiment 1, after forming the 2nd resin layer 103, the 1st resin layer 102 is formed without passing through a solvent removal process, and the solvent of the 1st resin layer 102 and the 2nd resin layer 103 is changed simultaneously after that. Remove. Thus, by integrally forming the liquid crystal polyester solution of the first resin layer 102 and the second resin layer 103, peeling at the interface between the resin layers 102 and 103 is less likely to occur.

  As a method for removing the solvent, a method for evaporating the solvent is known, and examples of the method for evaporating the solvent include methods such as heating, decompression, and ventilation. In the first embodiment, it is desirable to remove the solvent, that is, to dry the liquid crystal polyester composition by heating. Drying by heating is excellent in terms of production efficiency and handleability. Further, if air drying is used in addition to heat drying, production efficiency can be further increased.

  After the drying step, for example, a heat treatment step at 200 to 400 ° C. for 30 minutes to 5 hours may be performed.

  The liquid crystalline polyester film of the present invention has low corrosivity and is easy to handle, and the insulating layer obtained using this composition has a vertical direction (casting direction) and a horizontal direction (perpendicular to the casting direction). Direction) is small, the mechanical strength is excellent, and the liquid crystal polyester originally has high-frequency characteristics and low water absorption.

  Examples of the present invention will be described below. In addition, this invention is not limited to an Example.

Hereafter, the manufacturing method of the Example sample and comparative example sample which were used by evaluation of this Example is demonstrated.
(1) Manufacture of liquid crystal polyester

  First, 1976 g (10.5 mol) of 2-hydroxy-6-naphthoic acid and 1474 g (9. 4-hydroxyacetanilide) were added to a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer and a reflux condenser. 75 mol), 1620 g (9.75 mol) of isophthalic acid and 2374 g (23.25 mol) of acetic anhydride. Then, 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 this temperature (150 ° C.).

Thereafter, while distilling off by-product acetic acid and unreacted acetic anhydride, the temperature was raised to 300 ° C. over 170 minutes. The time point at which an increase in torque was observed was regarded as completion of the reaction, and the contents were taken out. The taken out contents were cooled to room temperature and pulverized with a pulverizer to obtain a liquid crystal polyester powder having a relatively low molecular weight. It was 235 degreeC when the flow start temperature of the obtained powder was measured with the flow tester "CFT-500 type | mold" by Shimadzu Corporation. This liquid crystal polyester powder was subjected to solid phase polymerization by subjecting it to a heat treatment at 223 ° C. for 3 hours in a nitrogen atmosphere. The flow starting temperature of the liquid crystal polyester after solid phase polymerization was 270 ° C.
(2) Manufacture of liquid crystal polyester solution

  2200 g of the liquid crystal polyester obtained in the above (1) was added to 7800 g of N, N-dimethylacetamide (DMAc) and heated at 100 ° C. for 2 hours to obtain a liquid crystal polyester solution. The solution viscosity at this time was 320 cP (centipoise). This solution viscosity is a value when measured at a measurement temperature of 23 ° C. using a B-type viscometer “TVL-20 type” (rotor No. 21, rotation speed 5 rpm) manufactured by Toki Sangyo Co., Ltd.

In this example, the liquid crystal polyester composition thus obtained is used as a liquid crystal polyester solution for the second resin layer 103.
(3) Manufacture of electronic circuit boards

  An inorganic filler is added to the liquid crystal polyester solution (solid content 22% by mass) obtained in the above (2), and the liquid crystal polyester solution is stirred with a centrifugal defoamer for 5 minutes, whereby the liquid crystal polyester solution for the first resin layer 102 is Prepared. Here, the following two types of liquid crystal polyester solutions A and B were prepared.

  Solution A: As the inorganic filler, spherical α-alumina powder having a volume average particle size of 0.3 μm (aluminum oxide “Sumicorundum AA-03” manufactured by Sumitomo Chemical Co., Ltd.) was used.

  Solution B: As an inorganic filler, spherical α-alumina powder having a volume average particle size of 5 μm (aluminum oxide “Sumicorundum AA-5” manufactured by Sumitomo Chemical Co., Ltd.) was used.

  In each liquid crystal polyester solution, the filling amount of the inorganic filler was 50% by volume with respect to the total of the liquid crystal polyester and the inorganic filler.

Subsequently, these two types of liquid crystal polyester solutions A and B were used to produce the following two types of example samples and two types of comparative example samples.
<Example 1>

  First, on the copper foil having a thickness of 70 μm, the liquid crystal polyester solution obtained in the above (2) (that is, a liquid crystal polyester solution containing no inorganic filler) was applied so that the thickness after removing the solution was 2 μm. Without passing through the removal step, the above-described solution A (that is, a liquid crystal polyester solution containing an inorganic filler having a volume average particle size of 0.3 μm) was applied so that the thickness after solution removal was 100 μm. Then, after drying this at 40 degreeC for 1 hour, it heat-processed at 320 degreeC for 3 hours. Thereby, a laminated film of the metal foil 104, the second resin layer 103, and the first resin layer 102 was obtained.

Thereafter, an aluminum alloy plate (that is, metal base 101) having a thermal conductivity of 140 W / (m · K) and a thickness of 2.0 mm was overlaid on the laminated film. At this time, the surface of the first resin layer 102 (that is, the surface on which the second resin layer 103 was not formed) was in contact with the surface of the aluminum alloy plate. Then, the aluminum alloy plate and the liquid crystal polyester film were thermally bonded by performing heat treatment at a pressure of 19.6 MPa (200 kgf / cm ² ) and a temperature of 340 ° C. for 20 minutes.

The evaluation sample of Example 1 was completed as described above.
<Example 2>

First, in the same manner as in Example 1, the liquid crystal polyester solution (without inorganic filler) obtained in (2) above was applied so that the thickness after removing the solution was 2 μm. Then, without passing through the solution removal step, the above-mentioned solution B (that is, a liquid crystal polyester solution containing an inorganic filler having a volume average particle size of 5 μm) was applied so that the thickness after solution removal was 100 μm. Thereafter, the evaluation sample of Example 2 was completed in the same manner as in Example 1.
<Comparative Example 1>

  First, the above solution A is applied onto a copper foil having a thickness of 70 μm so that the thickness after removal of the solution becomes 100 μm, dried at 40 ° C. for 1 hour, and then heat treated at 320 ° C. for 3 hours. did.

Then, an aluminum alloy plate having a thermal conductivity of 140 W / (m · K) and a thickness of 2.0 mm was overlaid on the laminated film. At this time, the surface of the liquid crystal polyester film (the surface on which the copper foil was not formed) was in contact with the surface of the aluminum alloy plate. Then, the aluminum alloy plate and the liquid crystal polyester film were thermally bonded by performing heat treatment at a pressure of 19.6 MPa (200 kgf / cm ² ) and a temperature of 340 ° C. for 20 minutes.

Thus, as Comparative Example 1, the same evaluation sample as in Example 1 was obtained without the second resin layer 103 (that is, the resin layer containing no inorganic filler) and under other conditions.
<Comparative Example 2>

  First, the above-mentioned solution B was applied onto a copper foil having a thickness of 70 μm so that the thickness after removing the solution was 100 μm. Thereafter, in the same manner as in Comparative Example 1, an evaluation sample of Comparative Example 2 was produced.

Thus, as Comparative Example 2, the same evaluation sample as in Example 2 was obtained without the second resin layer 103 (that is, the resin layer containing no inorganic filler) and other conditions.
(4) Evaluation test

The following evaluation test was performed on the electronic circuit board obtained as described above.
<Peel strength test>

For each of the evaluation samples of Examples 1 and 2 and Comparative Examples 1 and 2, a conductive pattern having a width of 10 mm was formed by etching the metal foil. And about each of these evaluation samples, the peel strength (unit: N / cm) at the time of peeling at a speed | rate of 50 mm / min was measured so that metal foil might become perpendicular | vertical.
<Measurement of thermal resistance>

  Each evaluation sample of Examples 1 and 2 and Comparative Examples 1 and 2 was prepared to a substrate size of 30 mm × 40 mm, and each metal foil was etched, whereby a pad portion of 14 mm × 10 mm (a part where electronic components were soldered) A conductive pattern was formed. And with respect to each evaluation sample, a commercially available transistor (transistor “TO-220” manufactured by Toshiba Corporation) was mounted as an electronic component by soldering. Further, each evaluation sample was fixed on a water cooling device via a heat dissipating grease. Thereafter, the transistor was energized to generate heat, and the surface temperature of the transistor and the surface temperature of the water cooling device at this time were measured. After the measurement, the thermal resistance (unit: ° C./W) was calculated using the following formula.

  (Thermal resistance) = {(surface temperature of transistor) − (surface temperature of water cooling device)} / (load power)

  Table 1 shows the results of these evaluation tests.

  As shown in Table 1, the peel strength of Example 1 was 20.7 N / cm, while the peel strength of Comparative Example 1 was 6.4 N / cm. Further, the peel strength of Example 2 was 24.4 N / cm, whereas the peel strength of Comparative Example 2 was 20 N / cm. From these comparison results, the peel strength is improved by providing the resin layer having no inorganic filler (that is, the second resin layer 103 of the first embodiment), that is, according to this example, the electronic circuit board is improved. It was found that adhesion was improved.

  The thermal resistance of Example 1 was 0.28 ° C./W, whereas the thermal resistance of Comparative Example 1 was 0.26. The thermal resistance of Example 2 was 0.30 ° C./W, while the thermal resistance of Comparative Example 2 was 0.28 ° C./W. From these comparison results, it was found that the thermal resistance hardly deteriorates even when a resin layer having no inorganic filler is provided, that is, excellent thermal conductivity can be obtained in the electronic circuit board by this example.

  As can be seen from the above evaluation results, according to this example, it was possible to obtain an electronic circuit board having high thermal conductivity and being difficult to peel off.

  The present invention can be widely applied to electronic circuit boards incorporated in various electric products, automobiles, machine tools, and other devices / equipment.

100 …… Electronic circuit board 101 …… Metal base (Heat dissipation board)
102 …… First resin layer 103 …… Second resin layer 104 …… Metal foil (conductive foil)
105 …… Insulating layer 200 …… Electronic circuit board 201 …… Metal base 202 …… Insulating layer 203 …… Metal foil 204 …… Mounting circuit 205 …… Electronic component

Claims (4)

An electronic circuit board having a heat dissipation substrate, an insulating layer provided on the heat dissipation substrate, and a conductive foil for forming a wiring pattern provided on the insulating layer,
The insulating layer is
A first resin layer containing an inorganic filler formed on the heat dissipation substrate;
An electronic circuit board comprising: a second resin layer which is formed so as to be in direct contact with the first resin layer and the conductive foil and does not contain an inorganic filler.   The electronic circuit board according to claim 1, wherein the first resin layer contains 50 to 80% by volume of the inorganic filler.   The electronic circuit board according to claim 1, wherein the resin of the insulating layer is liquid crystal polyester. A method for producing an electronic circuit board, comprising: a heat dissipation substrate; an insulating layer provided on the heat dissipation substrate; and a conductive foil for forming a wiring pattern provided on the insulating layer,
The step of forming the insulating layer includes
A first step of forming a first coating film containing a solvent and a resin and no inorganic filler on the surface of the conductive foil;
A second step of forming a second coating film containing the solvent, the resin and the inorganic filler on the surface of the first coating film;
And a third step of simultaneously removing the solvent contained in the first coating film and the second coating film.

Images