JP2013243398A - Laminate for circuit board, metallic base circuit board, and method for manufacturing them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously attain high withstand voltage and high peel strength.SOLUTION: A method for manufacturing a laminate for a circuit board comprises the steps of: transferring an insulation layer 3' which is formed on a support 5, contains electrical insulating resin 3a' and an electrical insulating inorganic filler 3b and arbitrarily contains solvent from the support 5 to metal foil; and sticking the metal foil and a metal substrate together by sandwiching the insulation layer 3' between them.

Description

  The present invention relates to a laminated board for circuit boards, a metal base circuit board produced from the laminated board for circuit boards, and a method for producing them.

  A circuit board on which a semiconductor element is mounted is required to be downsized, high-density mounting, and high performance. In addition, with the miniaturization, high performance, and high power of semiconductor elements, circuit boards are required to be able to efficiently dissipate heat generated by the elements.

  As a circuit board that requires high heat dissipation, a circuit board in which a circuit pattern is formed by metallizing on a ceramic substrate such as aluminum and aluminum nitride is mainly used. However, circuit boards including ceramic substrates are difficult to increase in size and are expensive. Further, since ceramic is brittle, such a circuit board is not necessarily suitable for an application that is vibrated vigorously.

  The metal base circuit board has a structure in which an insulating layer and a circuit pattern are laminated in this order on a metal board. The metal base circuit board is prepared by, for example, preparing a so-called “metal base board”, in which a metal board and a metal foil are integrated with an insulating layer interposed therebetween, and the metal foil is formed into a circuit pattern. It is obtained by patterning. Since the metal base circuit board does not include a ceramic substrate, the above-described problem does not occur.

  In the metal base circuit board, the insulating layer serves to electrically insulate the circuit pattern from the metal board, and also serves to bond them together. Therefore, a resin is generally used for the insulating layer.

  However, the resin has a low thermal conductivity. Therefore, research is being conducted on metal base circuit boards to increase the thermal conductivity of the insulating layer.

  For example, Patent Document 1 describes a metal base substrate in which a metal foil and a metal substrate are integrated via an insulating layer containing 65 to 80% by volume of an inorganic filler and a dispersant. In this metal base substrate, a coating liquid made of a thermosetting resin containing an inorganic filler and a dispersant is applied onto a metal foil, and the coating film is heated until the thermosetting resin reaches the B stage. Is manufactured by superposing metal substrates on the insulating layer obtained by heating and heating them while applying pressure.

  Patent Document 2 describes a metal base substrate including a spherical inorganic filler whose insulating layer is 65 to 85% by volume. This document describes that excellent heat dissipation is achieved by using a plurality of types of spherical inorganic fillers having different average particle diameters and closely packing the inorganic filler. In this metal base substrate, an adhesive containing a spherical inorganic filler and a resin is applied onto the metal substrate, the coating film is heated until the resin reaches the B stage, and a metal foil is formed on the insulating layer obtained thereby. It is manufactured by layering and heating them under pressure.

Patent Document 3 describes a metal base substrate in which an insulating layer contains an inorganic filler. In this metal base substrate, as the inorganic filler, the thermal conductivity of boron nitride, diamond, beryllium oxide or the like is 3.0 × 10 ⁻³ cal / cm · sec · ° C. or more and the relative dielectric constant is 4.5 or less. Use what is. The metal base substrate is manufactured by applying a mixture of an inorganic filler and a thermosetting resin on a metal substrate, overlaying a metal foil on the metal substrate, and heating them.

JP-A-8-83963 JP-A-5-167212 Japanese Patent Laid-Open No. 7-320538

  The present inventors have found that there is room for improvement in the withstand voltage or the peel strength of the circuit pattern in the metal base circuit board obtained from the circuit board laminate according to the prior art.

  Therefore, an object of the present invention is to make it possible to simultaneously realize a high withstand voltage and a high peel strength.

  According to the first aspect of the present invention, an insulating layer formed on a support and containing an electrically insulating resin, an electrically insulating inorganic filler, and optionally a solvent is transferred from the support to the metal foil. There is provided a method for producing a laminated board for a circuit board, comprising a transferring step and a step of bonding the metal foil and a metal substrate with the insulating layer interposed therebetween.

  According to the second aspect of the present invention, an insulating layer formed on a support and containing an electrically insulating resin, an electrically insulating inorganic filler, and optionally a solvent is transferred from the support to the metal foil. There is provided a method of manufacturing a metal base circuit board including a transferring step, a step of bonding the metal foil and a metal substrate with the insulating layer interposed therebetween, and a step of patterning the metal foil.

  According to a third aspect of the present invention, a metal substrate, a metal foil facing the metal substrate, and an insulating layer interposed between the metal substrate and the metal foil and bonding them together, It contains an electrically insulating resin and an electrically insulating inorganic filler, and the volume ratio of the inorganic filler in the insulating layer is higher in the metal foil side region than in the metal substrate side region. A circuit board laminate having a smaller insulating layer is provided.

  According to a fourth aspect of the present invention, a metal substrate, a circuit pattern facing the metal substrate, an insulating layer interposed between the metal substrate and the circuit pattern, and bonding them together, It contains an electrically insulating resin and an electrically insulating inorganic filler, and the volume ratio of the inorganic filler in the insulating layer is greater in the region on the circuit pattern side than in the region on the metal substrate side. A metal-based circuit board with a smaller insulating layer is provided.

  According to the present invention, a high withstand voltage and a high peel strength can be realized simultaneously.

The perspective view which shows schematically the laminated board for circuit boards which concerns on 1 aspect of this invention. Sectional drawing along the II-II line of the laminated board for circuit boards shown in FIG. Sectional drawing which shows roughly an example of the metal base circuit board obtained from the laminated board for circuit boards shown in FIG.1 and FIG.2. Sectional drawing which shows schematically the 1st process in manufacture of the laminated board for circuit boards shown in FIG.1 and FIG.2. Sectional drawing which shows schematically the 2nd process in manufacture of the laminated board for circuit boards shown in FIG.1 and FIG.2. 3 is a graph showing the distribution of inorganic fillers in the insulating layer of the circuit board laminate according to Example 1. FIG. The graph which shows distribution of the inorganic filler in the insulating layer of the laminated board for circuit boards which concerns on the comparative example 1. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same referential mark is attached | subjected to the component which exhibits the same or similar function through all the drawings, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a perspective view schematically showing a laminated board for a circuit board according to one embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line II-II of the circuit board laminate shown in FIG.

  A circuit board laminate 1 shown in FIGS. 1 and 2 includes a metal substrate 2, an insulating layer 3, and a metal foil 4. 1 and 2, the X and Y directions are parallel to the main surface of the metal substrate 2 and perpendicular to each other, and the Z direction is a thickness direction perpendicular to the X and Y directions. In FIG. 1, a rectangular circuit board laminate 1 is depicted as an example, but the circuit board laminate 1 may have other shapes.

  The metal substrate 2 is made of, for example, a single metal or an alloy. As a material of the metal substrate 2, for example, aluminum, iron, copper, an aluminum alloy, or stainless steel can be used. The metal substrate 2 may further contain a nonmetal such as carbon. For example, the metal substrate 2 may contain aluminum combined with carbon. Moreover, the metal substrate 2 may have a single layer structure or a multilayer structure.

The metal substrate 2 has a high thermal conductivity. Typically, the metal substrate 2 has a thermal conductivity of 60 W · m ⁻¹ · K ⁻¹ or more.

  The metal substrate 2 may have flexibility or may not have flexibility. The thickness of the metal substrate 2 is in the range of 0.2 to 5 mm, for example.

  The insulating layer 3 is provided on the metal substrate 2. The insulating layer 3 contains a resin 3a and an inorganic filler 3b. The thickness of the insulating layer 3 is in the range of 50 to 200 μm, for example.

  The resin 3a included in the insulating layer 3 is electrically insulating. The resin 3a serves as a binder for bonding the inorganic fillers 3b. Further, the resin 3 a plays a role as an adhesive for bonding the metal foil 4 to the metal substrate 2. In addition, the resin 3a serves to flatten the surface of the insulating layer 3.

  The proportion of the resin 3a in the insulating layer 3 is, for example, in the range of 15 to 55% by volume, and typically in the range of 20 to 50% by volume. If this ratio is excessively reduced, the adhesive strength between the insulating layer 3 and the metal substrate 2 or the metal foil 4 is reduced, or it is difficult to make the surface of the insulating layer 3 flat. When this ratio is excessively increased, the thermal resistance of the circuit board laminate 1 increases.

  Examples of the resin 3a include epoxy resin, bismaleimide triazine resin (BT resin), polyphenylene oxide, hydrogenated styrene-butadiene resin, hydrogenated styrene-isobutylene resin, polyamideimide, silicone resin, silicone rubber, polyester, acrylic resin, or Acrylic rubber can be used. These can be used alone or in combination.

  Liquid crystalline polyester may be used as at least a part of the resin 3a. Liquid crystalline polyester is an electrically insulating material. Liquid crystalline polyester has a higher specific resistance value than many other resins.

  In addition, the liquid crystal polyester exhibits excellent thermal stability over a long period of time. Therefore, the use of liquid crystal polyester is used when an electric or electronic element that generates high heat, for example, a power element, particularly a power element using a silicon carbide substrate, is mounted on a metal base circuit board obtained from the circuit board laminate 1. Is particularly advantageous.

  The liquid crystal polyester typically has thermoplasticity. As the liquid crystalline polyester, for example, a material that exhibits optical anisotropy when melted and forms an anisotropic melt at a temperature of 450 ° C. or lower can be used. As such a liquid crystalline polyester, for example, those having structural units represented by the following general formulas (1) to (3) can be used.

In the following general formulas (1) to (3), Ar1 represents, for example, a phenylene group or a naphthylene group, Ar2 represents, for example, a phenylene group, a naphthylene group, or a group represented by the following general formula (4), and Ar3 represents Represents a group represented by, for example, a phenylene group or the following general formula (4), and X and Y each independently represent, for example, O or NH. The hydrogen atom bonded to the aromatic ring of Ar, Ar2 and Ar3 may be substituted with, for example, a halogen atom, an alkyl group or an aryl group. Further, in the following general formula (4), the Ar11 and Ar12, for example, each independently represent a phenylene group or a naphthylene group, Z represents represents O, and CO or SO _2.

-O-Ar1-CO- (1)
-CO-Ar2-CO- (2)
-X-Ar3-Y- (3)
-Ar11-Z-Ar12- (4)
In this liquid crystal polyester, the ratio of the structural unit represented by the general formula (1) to the total of the structural units represented by the general formulas (1) to (3) is, for example, 30 to 80 mol%. It is in the range. In this case, the ratio of the structural unit represented by the general formula (2) to the total of the structural units represented by the general formulas (1) to (3) is, for example, in the range of 10 to 35 mol%. Is in. In this case, the ratio of the structural unit represented by the general formula (3) to the total of the structural units represented by the general formulas (1) to (3) is, for example, 10 to 35 mol%. It is in the range.

  The structural unit represented by the general formula (1) is a structural unit derived from an aromatic hydroxycarboxylic acid, the structural unit represented by the general formula (2) is a structural unit derived from an aromatic dicarboxylic acid, and the general formula ( The structural unit represented by 3) is a structural unit derived from an aromatic diamine or an aromatic amine having a phenolic hydroxyl group. The above-mentioned liquid crystalline polyester is obtained by polymerizing these monomers using compounds that respectively derive such structural units (1) to (3) as monomers.

  From the viewpoint of facilitating the progress of the polymerization reaction for obtaining this liquid crystalline polyester, those ester-forming derivatives and amide-forming derivatives may be used instead of the above-mentioned monomers.

  As the ester-forming derivative or amide-forming derivative of the carboxylic acid, for example, the carboxyl group is a derivative having a high reaction activity such as an acid chloride or an acid anhydride so as to promote a reaction to form a polyester or polyamide. And those in which a carboxyl group forms an ester with alcohols, ethylene glycol, or the like so that a polyester or polyamide is produced by an ester exchange reaction or an amide exchange reaction.

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

  Examples of the amide-forming derivative of the amino group include those in which the amino group forms an ester with a carboxylic acid so that a polyamide is formed by an amide exchange reaction.

  Specific examples of the structural unit represented by the structural units (1) to (3) include the following. However, the structural units represented by the structural units (1) to (3) are not limited to these.

  Examples of the structural unit represented by the general formula (1) include aromatic hydroxycarboxylic acids selected from p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid and 4-hydroxy-4′-biphenylcarboxylic acid. Examples are derived structural units. Liquid crystalline polyester may contain only 1 type in these structural units, and may contain 2 or more types. In particular, it is preferable to use an aromatic liquid crystal polyester having a structural unit derived from p-hydroxybenzoic acid or a structural unit derived from 2-hydroxy-6-naphthoic acid.

  The ratio of the structural unit represented by the general formula (1) to the total of all the structural units is, for example, in the range of 30.0 to 80.0 mol%, preferably 35.0 to 40.0. It is in the range of mol%.

  When the ratio of the structural unit represented by the general formula (1) to all the structural units is increased, the solubility of the liquid crystal polyester in the aprotic solvent described later decreases. When this ratio is small, the polyester tends not to exhibit liquid crystallinity.

  Examples of the structural unit represented by the general formula (2) include a structural unit derived from an aromatic dicarboxylic acid selected from terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid. Liquid crystalline polyester may contain only 1 type in these structural units, and may contain 2 or more types. In particular, from the viewpoint of the solubility of the liquid crystal polyester in an aprotic solvent described later, it is preferable to use a liquid crystal polyester having a structural unit derived from isophthalic acid.

  The ratio of the structural unit represented by the general formula (2) to the total of all the structural units is, for example, in the range of 10.0 to 35.0 mol%, and preferably 30.0 to 32.5. It is in the range of mol%.

  When the ratio of the structural unit represented by the general formula (2) to all structural units is increased, the liquid crystallinity of the polyester tends to be lowered. When this ratio is reduced, the solubility of the polyester in the aprotic solvent tends to decrease.

  Examples of the structural unit represented by the general formula (3) include aromatic amine-derived structural units having a phenolic hydroxyl group such as 3-aminophenol and 4-aminophenol, 1,4-phenylenediamine, and 1, Mention may be made of structural units derived from aromatic diamines such as 3-phenylenediamine. Liquid crystalline polyester may contain only 1 type in these structural units, and may contain 2 or more types. Especially, it is preferable to use liquid crystalline polyester which has a structural unit derived from 4-aminophenol from a viewpoint of the polymerization reaction performed in manufacture of liquid crystalline polyester.

  The ratio of the structural unit represented by the general formula (3) to the total of all the structural units is, for example, in the range of 10.0 to 35.0 mol%, and preferably 30.0 to 32.5. It is in the range of mol%.

  When the ratio of the structural unit represented by the general formula (3) to all structural units is increased, the liquid crystallinity of the polyester tends to be lowered. When this ratio is reduced, the solubility of the liquid crystal polyester in the aprotic solvent tends to be lowered.

  In addition, it is preferable that the structural unit represented by General formula (3) and the structural unit represented by General formula (2) are substantially equivalent. The difference between the ratio of the structural unit represented by the general formula (3) to the total structural unit and the ratio of the structural unit represented by the general formula (2) to the total structural unit is set within a range of −10 to +10 mol%. Thus, the degree of polymerization of the aromatic liquid crystal polyester can also be controlled.

  The method for producing the liquid crystal polyester is not particularly limited. As a manufacturing method of this liquid crystal polyester, for example, an aromatic hydroxycarboxylic acid corresponding to the structural unit represented by the general formula (1) and an aromatic having a hydroxyl group corresponding to the structural unit represented by the general formula (3) Acylation of the phenolic hydroxyl group or amino group of the aromatic amine or aromatic diamine with an excess amount of fatty acid anhydride, and the resulting acylated product (ester-forming derivative or amide-forming derivative) with the general formula (2) The method of melt-polymerizing by transesterifying (polycondensation) with the aromatic dicarboxylic acid corresponding to the structural unit represented is mentioned.

  As the acylated product, a fatty acid ester obtained by acylation in advance may be used (for example, see JP-A No. 2002-220444 or JP-A No. 2002-146003).

  In the acylation reaction, the amount of fatty acid anhydride added is preferably 1.0 to 1.2 times equivalent to the total of the phenolic hydroxyl group and amino group, and is preferably 1.05 to 1.1. More preferably, it is a double equivalent.

  When the amount of fatty acid anhydride added is small, acylated products and raw material monomers sublimate during transesterification (polycondensation), and the reaction system tends to be clogged. Moreover, when there are many additives of a fatty acid anhydride, there exists a tendency for coloring of the aromatic liquid crystal polyester obtained to become remarkable.

  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 for the acylation reaction is not particularly limited. Examples of the fatty acid anhydride include acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, pivalic anhydride, 2-ethylhexanoic anhydride, monochloroacetic anhydride, dichloroacetic anhydride, trichloroacetic anhydride, and anhydrous Examples include monobromoacetic acid, dibromoacetic anhydride, tribromoacetic anhydride, monofluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, glutaric anhydride, maleic anhydride, succinic anhydride, and β-bromopropionic anhydride. These may be used alone or in combination of two or more.

  Among these, from the viewpoints of price and handleability, acetic anhydride, propionic anhydride, butyric anhydride and isobutyric anhydride are preferable, and acetic anhydride is more preferable.

  In the transesterification and amide exchange reactions, the acyl group of the acylated product is preferably 0.8 to 1.2 times equivalent to the carboxyl group.

  The transesterification and amide exchange reactions are preferably performed at 130 to 400 ° C. while increasing the temperature at a rate of 0.1 to 50 ° C./min, and at 150 to 350 ° C., 0.3 to 5 ° C./min. More preferably, the temperature is raised at a rate.

  When transesterification and amide exchange between the fatty acid ester obtained by the acylation and carboxylic acid or amine are carried out, the equilibrium is shifted, so that the by-product fatty acid and the unreacted fatty acid anhydride are evaporated to the outside of the system. It is preferable to distill off.

  The acylation reaction, transesterification and amide exchange reaction may be performed in the presence of a catalyst. As this catalyst, for example, a conventional catalyst for polyester polymerization can be used. Such catalysts include, for example, metal salt catalysts such as magnesium acetate, stannous acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate and antimony trioxide, and N, N-dimethylaminopyridine and N -Organic compound catalysts such as methylimidazole can be mentioned.

  Among the above 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 added at the time of monomer introduction. This catalyst may or may not be removed after acylation. If this catalyst is not removed, transesterification can be carried out continuously with acylation.

  The polymerization by the ester exchange and amide exchange reactions is usually performed by melt polymerization, but melt polymerization and solid phase polymerization may be used in combination. The solid phase polymerization can be performed by a known solid phase polymerization method after the polymer is extracted from the melt polymerization step and 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 given. The solid phase polymerization may be performed with stirring, or may be performed in a state of standing without stirring.

  In addition, melt polymerization and solid phase polymerization can also be performed in the same reaction tank by providing an appropriate stirring mechanism.

  After the solid phase polymerization, the obtained liquid crystal polyester may be formed into, for example, a pellet by a known method.

  The liquid crystalline polyester can be produced using a batch apparatus and / or a continuous apparatus.

  The liquid crystalline polyester preferably has a flow initiation temperature determined by the following method of 250 ° C. or higher, and more preferably 260 ° C. or higher. When such a liquid crystal polyester is used, it is between the insulating layer 3 and the metal foil 4 and between the insulating layer 3 and the metal substrate 2 as compared with the case where a liquid crystal polyester having a lower flow start temperature is used. A higher degree of adhesion can be obtained.

  In addition, the liquid crystalline polyester preferably has a flow start temperature of 300 ° C. or lower, and more preferably 290 ° C. or lower. Such a liquid crystal polyester tends to have higher solubility in a solvent as compared with a liquid crystal polyester having a higher flow start temperature.

  Here, the “flow start temperature” refers to the lowest temperature at which the melt viscosity of the aromatic 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.

  According to the book “Liquid Crystal Polymer -Synthesis / Molding / Application—” published in 1987 (Naoyuki Koide, pages 95 to 105, CMC, published June 5, 1987), liquid crystal polyester resin in the 1970s. Has been developed, the flow temperature (equivalent to the term “flow start temperature” used in the present specification) has been used as a measure of the molecular weight of liquid crystal polyester resin.

  The flow start temperature of the liquid crystalline polyester is controlled by, for example, extracting the polymer from the melt polymerization step, pulverizing the polymer into powder or flakes, and then adjusting the flow start temperature by a known solid phase polymerization method. Can be implemented easily.

  More specifically, for example, after the melt polymerization step, in an inert atmosphere such as nitrogen, at a temperature exceeding 210 ° C., more preferably at a temperature of 220 to 350 ° C., for 1 to 10 hours in a solid state. It is obtained by a method of heat treatment at The solid phase polymerization may be performed with stirring, or may be performed in a state of standing without stirring. For example, solid state polymerization may be performed at 225 ° C. for 3 hours in an inactive atmosphere such as nitrogen without being stirred.

  The inorganic filler 3b is distributed over almost the entire insulating layer 3. Typically, the inorganic filler 3b is distributed almost uniformly in each cross section perpendicular to the thickness direction of the insulating layer 3. And typically, in each cross section parallel to the thickness direction of the insulating layer, the density of the inorganic filler 3b decreases from the metal substrate 2 side toward the metal foil 4 side.

  The proportion of the inorganic filler 3b in the insulating layer 3 is, for example, in the range of 45 to 85% by volume, and typically in the range of 50 to 80% by volume. If this ratio is too small, the thermal resistance increases. If this ratio is excessively increased, the adhesive strength between the inorganic fillers 3b decreases, the adhesive strength between the insulating layer 3 and the metal substrate 2 or the metal foil 4 decreases, or the surface of the insulating layer 3 is flattened. It becomes difficult to make.

  The volume ratio of the inorganic filler 3b in the insulating layer 3 is smaller in the region on the metal foil 4 side than in the region on the metal substrate 2 side. This structure is obtained by, for example, measuring the amount or concentration of a specific element contained in the inorganic filler 3b in the thickness direction of the insulating layer 3 using a wavelength dispersion X-ray analyzer (WDX). Can be confirmed.

In the distribution obtained by this measurement, the distance from the metal substrate 2 with respect to the maximum value F _max of the frequency of the preceding element in an area where the distance from the metal substrate 2 is 10% or less of the thickness of the insulating layer 3 is the insulating layer 3. The ratio F _min / F _max of the minimum value F _min of the frequency of the previous element in the region of 90% to 100% of the thickness of the material is, for example, in the range of 0.75 to 0.95, typically 0 Within the range of .8 to 0.9.

If this ratio F _min / F _max is excessively increased, peeling of the circuit pattern obtained by patterning the metal foil 4 from the insulating layer 3 tends to occur, or the interface between the insulating layer 3 and the metal foil 4 The flatness of the is reduced. When the ratio F _min / F _max is excessively reduced, the adhesive strength between the C insulating layer 3 and the metal substrate 2 is lowered.

Note that a result obtained using WDX may include an error. Therefore, in such a case, in order to make the error sufficiently small, measurement may be performed at a plurality of positions, and an average value of the ratio F _min / F _max obtained from the measurement results may be used.

The inorganic filler 3b typically has higher thermal conductivity than the resin 3a and is excellent in insulation. The inorganic filler 3b has, for example, a thermal conductivity of 30 W · m ⁻¹ · K ⁻¹ or more.

  The inorganic filler 3b is made of, for example, a metal oxide such as aluminum oxide, magnesium oxide and zinc oxide, a metal hydroxide such as aluminum hydroxide, a metal nitride such as aluminum nitride, or a nonmetal compound such as boron nitride. . The inorganic filler 3b may include only one of these materials or may include two or more.

  The inorganic filler 3b may be spherical particles, non-spherical particles, or a mixture thereof, but is preferably spherical particles. Spherical particles have a smaller increase in viscosity when dispersed in a resin solution than particles having other shapes. Also, typically, spherical particles can be packed more densely than particles having other shapes.

  As the inorganic filler 3b, spherical secondary particles obtained by agglomerating non-spherical insulating fine particles may be used. The spherical secondary particles can be obtained, for example, by spray-drying a dispersion containing non-spherical insulating fine particles, a dispersion medium, and, if necessary, a binder.

  As at least a part of the inorganic filler 3b, particles obtained by subjecting the above-described particles to surface treatment may be used in order to improve the adhesion to the resin 3a and the dispersibility in the dispersion described later. Examples of surface treatment agents that can be used for this surface treatment include silane coupling agents, titanium coupling agents, aluminum or zirconium coupling agents, long chain fatty acids, isocyanate compounds, and, for example, epoxy groups, methoxy Mention may be made of polar polymers or reactive polymers containing silane groups, amino groups or hydroxyl groups.

  The average particle diameter of the inorganic filler 3b is, for example, in the range of 0.1 to 100 μm. Here, the “average particle diameter” means the average particle diameter of the particles measured by the laser diffraction scattering method.

  The metal foil 4 is provided on the insulating layer 3. The metal foil 4 faces the metal substrate 2 with the insulating layer 3 interposed therebetween.

  The metal foil 4 is made of, for example, a single metal or an alloy. As a material of the metal foil 4, for example, copper or aluminum can be used. The thickness of the metal foil 4 is, for example, in the range of 10 to 500 μm.

Next, the metal base circuit board 1 ′ obtained from the circuit board laminate 1 described above will be described.
FIG. 3 is a cross-sectional view schematically showing an example of a metal base circuit board 1 ′ obtained from the circuit board laminate 1 shown in FIGS. 1 and 2.

  A metal base circuit board 1 ′ shown in FIG. 3 includes a metal board 2, an insulating layer 3, and a circuit pattern 4 ′. The circuit pattern 4 ′ is obtained by patterning the metal foil 4 of the circuit board laminate 1 described with reference to FIGS. 1 and 2. This patterning can be obtained, for example, by forming a mask pattern on the metal foil 4 and removing the exposed portion of the metal foil 4 by etching. The metal base circuit board 1 ′ can be obtained, for example, by performing the above-described patterning on the metal foil 4 of the circuit board laminate 1 and performing processing such as cutting and drilling as necessary. it can.

  This metal base circuit board 1 'is excellent in heat dissipation and heat resistance, as will be described later. In addition, in the metal base circuit board 1 ′, the circuit pattern 4 ′ has a sufficient peel strength despite the high proportion of the inorganic filler in the insulating layer 3.

  The metal base circuit board 1 'is mounted on, for example, an automobile. In this case, the metal base circuit board 1 ′ is, for example, an electric power steering control unit, an LED (light-emitting diode) head-up display, an automatic transmission, an ABS (antilock braking system) module, an engine control control unit, or an LED meter panel. Can be used.

  The metal base circuit board 1 'can also be used in other applications, for example, LED lighting fixtures, display panels whose backlights include LEDs, or power systems such as elevators and trains.

  The circuit board laminate 1 and the metal base circuit board 1 ′ described above are manufactured by, for example, the following method. This will be described with reference to FIGS.

  FIG. 4 is a cross-sectional view schematically showing a first step in manufacturing the circuit board laminate 1 shown in FIGS. 1 and 2. FIG. 5 is a cross-sectional view schematically showing a second step in the manufacture of the circuit board laminate 1 shown in FIGS. 1 and 2.

  In manufacturing the circuit board laminate 1 shown in FIGS. 1 and 2, first, a transfer sheet 11 shown in FIG. 4 is prepared. The transfer sheet 11 includes a release film 5 and an insulating layer 3 ′ formed thereon.

  The release film 5 is a support that supports the insulating layer 3 ′ in a peelable manner. Although there is no restriction | limiting in particular in the shape of the release film 5, When forming insulating layer 3 'by a continuous type, what has a strip | belt shape as the release film 5 is typically used.

  As the release film 5, for example, resin films such as a polyester film, a polypropylene film, a fluororesin film, a nylon film, and a polymethylpentene film can be used alone or by laminating two or more kinds. Or you may use as a release film 5 what apply | coats a silicone resin to the surface of paper or a resin film.

  The release film 5 needs to have sufficient heat resistance and solvent resistance. Moreover, it is desirable that the release film 5 has a high gas permeability, specifically, a high ability to transmit the vaporized solvent. In this respect, it is preferable to use a polyester film, a polymethylpentene film, or a polypropylene film as the release film 5. The thickness of the release film 5 is preferably in the range of 30 to 150 μm from the viewpoint of strength and gas permeability.

  The release film 5 may include a transparent part. For example, the part of the release film 5 that supports the insulating layer 3 ′ may be substantially entirely transparent. When such a configuration is adopted, it is possible to confirm whether or not the insulating layer 3 ′ is defective by observation through the transparent portion.

  The insulating layer 3 'is a layer containing a resin 3a' and an inorganic filler 3b. The insulating layer 3 ′ is formed by applying a coating liquid containing a resin 3a ′, an inorganic filler 3b, and a solvent on the release film 5 and heating the coating film to remove at least a part of the solvent. can get.

  The resin 3a 'is, for example, the resin 3a, an uncured product thereof, or a mixture thereof. As this resin, it is preferable to use a resin having a relatively small molecular weight in consideration of solubility in the solvent.

  The insulating layer 3 ′ may contain a solvent or may not contain a solvent. The insulating layer 3 ′ containing the solvent has high toughness or flexibility, and does not easily cause brittle fracture even when the transfer sheet 11 is wound around a roll (not shown). Further, when a thermoplastic resin is used as the resin 3a ', the softening temperature of the resin 3a' becomes lower when the insulating layer 3 'contains a solvent. Therefore, the transfer described later can be performed at a lower temperature.

The insulating layer 3 ′ is manufactured, for example, by the following method.
First, the resin 3a ′ is dissolved in a solvent. As the solvent, a pure substance or a mixture may be used as long as the resin 3a ′ can be dissolved.

  Examples of the solvent include low boiling point solvents such as toluene, xylene, ethyl acetate, methyl ethyl ketone and acetone; cellosolves such as methyl cellosolve and butyl cellosolve, N-methylpyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide and High boiling polar solvents such as dimethyl sulfoxide; or mixtures containing two or more thereof can be used.

  When liquid crystal polyester is used as the resin 3a ', it is preferable to use an aprotic solvent containing no halogen atom as the solvent. Examples of such aprotic solvents include ether solvents such as diethyl ether, tetrahydrofuran and 1,4-dioxane; ketone solvents such as acetone and cyclohexanone; ester solvents such as ethyl acetate; γ-butyrolactone and the like. Lactone solvents; 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-dimethylacetamide, tetra Amide solvents such as methylurea and N-methylpyrrolidone; Nitro solvents such as nitromethane and nitrobenzene; Sulfide solvents such as dimethyl sulfoxide and sulfolane; Hexamethylphosphoric acid Phosphoric acid-based solvent such as bromide and tri n- butyl phosphate and the like.

  Among these, a solvent having a dipole moment of 3 to 5 is preferable from the viewpoint of solubility described above. Specifically, amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, tetramethylurea and N-methylpyrrolidone, and lactone solvents such as γ-butyrolactone are preferred, and N, N-dimethyl is preferred. Formamide, N, N-dimethylacetamide and N-methylpyrrolidone (NMP) are particularly preferred. Further, when a highly volatile solvent having a boiling point of 180 ° C. or less at 1 atm is used, the solvent is removed from the coating film after forming a coating film made of a dispersion containing the resin and the inorganic filler 3b. Easy to do. From this viewpoint, N, N-dimethylformamide (DMF) and N, N-dimethylacetamide (DMAc) are particularly preferable.

  This solution contains a resin such as liquid crystal polyester, for example, 10 to 50 parts by mass, preferably 20 to 40 parts by mass with respect to 100 parts by mass of the solvent. If the amount of resin is too small, a large amount of solvent must be removed from the coating. Therefore, the appearance defect of the insulating layer 3 ′ tends to occur. When the amount of the resin is excessively increased, the above-described solution or dispersion tends to increase in viscosity, and the handleability thereof decreases.

  Other components may be further dissolved in this solution. For example, you may add additives, such as coupling agents, such as a silane coupling agent and a titanium coupling agent, and an ion adsorption agent, to this solution.

  Next, the inorganic filler 3b is dispersed in the previous solution to obtain a dispersion containing a resin and the inorganic filler 3b as a coating liquid. The inorganic filler may be dispersed in the solution while being pulverized using, for example, a ball mill, three rolls, a centrifugal stirrer, a bead mill, or a homomixer.

  Here, the method of dispersing the inorganic filler 3b in a solution obtained by dissolving the resin 3a ′ in a solvent has been described. However, the resin 3a ′ is dissolved in a dispersion obtained by dispersing the inorganic filler 3b in a solvent. May be.

  Next, the coating solution is defoamed and applied to one main surface of the release film 5. The surface on which the dispersion liquid of the release film 5 is applied is smooth and is typically a flat surface. For the application of the coating liquid, for example, a roll coating method, a bar coating method, a screen printing method, a die scoring method or a comma coating method can be used. Application | coating of a coating liquid may be performed by a continuous type and may be performed by a single plate type.

  After forming a coating film on the release film 5 as described above, this coating film is dried. Thereby, the transfer sheet 11 including the insulating layer 3 ′ is obtained.

  In this method, the inorganic filler 3b is non-uniformly distributed in the coating film within the time from the application of the coating solution to the end of drying of the coating film. Specifically, the inorganic filler 3b is distributed so that the density decreases from the release film 5 side toward the opposite side. This distribution can be generated, for example, by causing the inorganic filler 3b to settle using gravity.

  Easiness of sedimentation of the inorganic filler 3b includes, for example, the average particle diameter of the inorganic filler 3b, the viscosity of the solution containing the resin 3a ′ and the solvent, the affinity with the solution of the inorganic filler 3b, and their specific gravity. Depends on the difference and the evaporation rate of the solvent. Specifically, the inorganic filler 3b having a small average particle size is less likely to settle than the inorganic filler 3b having a large average particle size. In addition, the inorganic filler 3b is unlikely to settle in a solution having a higher viscosity, a solution having a higher affinity with the inorganic filler 3b, or a solution having a small specific gravity difference from the inorganic filler 3b. And since the viscosity of a solution will become high when evaporation of a solvent progresses, when the evaporation rate of a solvent is made high, sedimentation of the inorganic filler 3b will become difficult to occur.

  The above-described coating film is dried, for example, so that a part of the solvent remains in the coating film. In this case, the coating film may be dried, for example, so that the amount of the solvent in the insulating layer 3 ′ is 1 to 25% with respect to the total of the solid content and the amount of the solvent at the time of drying.

  As described above, the insulating layer 3 ′ containing the solvent has high flexibility, and even when the transfer sheet 11 is wound around a roll, it is difficult to cause brittle fracture. Further, when the solvent is left in the insulating layer 3 ′ containing the solvent, the transfer described later can be performed at a lower temperature as compared with the case where the solvent is completely removed.

  The appropriate value of the solvent remaining amount in the insulating layer 3 ′ depends on the types of the resin and the inorganic filler. For example, when liquid crystal polyester and boron nitride are used as the resin and the inorganic filler, respectively, and N-methylpyrrolidone or N, N-dimethylacetamide is used as the solvent, the coating film is dried by the insulating layer 3 ′. It is preferable that the amount of the solvent is 5 to 25% of the amount of the solvent contained in the coating film before drying.

  Next, the insulating layer 3 'is transferred from the release film 5 onto the metal foil 4 to obtain the structure 12 shown in FIG.

  Specifically, first, the transfer sheet 11 and the metal foil 4 are overlapped so that the insulating layer 3 ′ is in contact with the metal foil 4. In this state, heat and pressure are applied to them. Thereby, the insulating layer 3 ′ is bonded to the metal foil 4.

Thereafter, the release film 5 is peeled from the metal foil 4. If the adhesive strength of the insulating layer 3 ′ to the metal foil 4 is higher than the adhesive strength of the insulating layer 3 ′ to the release film 5, the release film remains with the insulating layer 3 ′ left on the metal foil 4. Only 5 can be removed.
As described above, the structure 12 shown in FIG. 5 is obtained.

  In the structure 12 obtained by this method, the insulating layer 3 ′ has a uniform thickness. This will be described below.

  The insulating layer 3 ′ is formed on the release film 5 having a smooth surface. Therefore, in the transfer sheet 11 shown in FIG. 4, the first main surface of the insulating layer 3 ′ on the release film 5 side is smooth. The smoothness of the first main surface is also maintained in the structure 12 shown in FIG.

  Further, in the transfer sheet 11 shown in FIG. 4, the second main surface opposite to the first main surface of the insulating layer 3 ′ is inferior in smoothness compared to the first main surface. However, since the density of the inorganic filler 3b is low in the region adjacent to the second main surface, the surface shape is easily changed by applying heat and pressure. Therefore, in the structure 12 shown in FIG. 5, the second main surface is smooth.

  As described above, in the structure 12 shown in FIG. 5, the first and second main surfaces of the insulating layer 3 ′ are smooth. Therefore, in this structure 12, the variation in the thickness of the insulating layer 3 'due to the unevenness of the first or second main surface is small.

  After obtaining the structure 12 shown in FIG. 5 as described above, the insulating layer 3 ′ is completely dried. The insulating layer 3 ′ may be completely dried by heat applied during transfer. However, the temperature condition optimal for transfer and the temperature condition optimal for drying are usually different, and they are typically performed in separate steps.

  In addition, after drying, the insulating layer 3 ′ may be heat-treated at a higher temperature. In this way, the molecular weight of the resin can be adjusted.

  Next, the structure 12 and the metal substrate 2 described above are bonded together. Specifically, first, the structure 12 and the metal substrate 2 are overlaid so that the insulating layer 3 ′ is in contact with the metal substrate 2. In this state, heat and pressure are applied to them. Thereby, the insulating layer 3 ′ as the insulating layer 3 is bonded to the metal substrate 2. In this way, the circuit board laminate 1 shown in FIGS. 1 and 2 is obtained.

  Thereafter, the metal foil 4 is patterned. For example, a mask pattern is formed on the metal foil 4 and the exposed portion of the metal foil 4 is removed by etching. As a result, a circuit pattern 4 'shown in FIG. 3 is obtained. Furthermore, processing such as cutting and drilling is performed as necessary. As described above, the metal base circuit board 1 'shown in FIG. 4 is completed.

  In the circuit board laminate 1 obtained by the above-described method, as shown in FIG. 2, the density of the inorganic filler 3b decreases in the insulating layer 3 from the metal substrate 2 side to the metal foil 4 side. Distributed. Therefore, also in the metal base circuit board 1 ′ obtained from the circuit board laminate 1, the density of the inorganic filler 3b is directed from the metal board 2 side to the circuit pattern 4 ′ side as shown in FIG. It is distributed to decrease.

  As the proportion of the resin 3a in the insulating layer 3 increases, the adhesive strength increases. Therefore, in this metal base circuit board 1 ′, the circuit pattern 4 ′ has a higher adhesion strength to the insulating layer 3 than the metal board 2. Therefore, when the circuit board laminate 1 obtained by the above-described method is used for manufacturing the metal base circuit board 1, the peel strength of the circuit pattern 4 ′ becomes insufficient without reducing the amount of the inorganic filler 3b. Can be prevented. That is, it is possible to prevent the peel strength of the circuit pattern 4 'from becoming insufficient without sacrificing heat dissipation.

  As described above, when the above-described configuration is adopted, it is possible to prevent the peel strength of the circuit pattern 4 ′ from becoming insufficient. If the adhesive strength between the circuit pattern 4 ′ and the insulating layer 3 is high, even if the circuit pattern 4 ′ is formed more finely, it is difficult to peel off. That is, the above configuration is advantageous for miniaturization of the circuit pattern 4 '.

  Further, in a general metal base circuit board, when boron nitride is used as an inorganic filler, high heat dissipation and withstand voltage can be achieved, but on the other hand, the peel strength of the circuit pattern becomes insufficient. In particular, when the proportion of boron nitride in the insulating layer is large, for example, in the range of 45 to 85% by volume, the peel strength of the circuit pattern is greatly reduced. In contrast, when the configuration described with reference to FIGS. 1 to 5 is adopted, even if boron nitride is used as the inorganic filler 3b and the proportion of boron nitride in the insulating layer 3 is increased, the circuit It is possible to prevent the peel strength of the pattern 4 ′ from becoming insufficient. That is, the benefits of boron nitride can be enjoyed without the disadvantages associated with using boron nitride.

  As shown in FIG. 3, in this metal base circuit board 1 ', the metal substrate 2 has a larger contact area with the insulating layer 3 than the circuit pattern 4'. Therefore, the bonding strength between the metal substrate 2 and the insulating layer 3 is not required to be as high as the bonding between the circuit pattern 4 ′ and the insulating layer 3. Therefore, even if the inorganic filler 3b is distributed as described above, the peel strength of the insulating layer 3 from the metal substrate 2 does not become insufficient.

  Further, as described above, in the structure 12 shown in FIG. 5, the first and second main surfaces of the insulating layer 3 ′ are smooth, and the thickness of the insulating layer 3 ′ due to the unevenness of the first or second main surface. Variation is small. Therefore, also in the laminated board 1 for circuit boards obtained by the above method, both main surfaces of the insulating layer 3 are smooth and the variation in thickness is small. Therefore, according to the method described above, the withstand voltage does not become insufficient due to the variation in the thickness of the insulating layer 3.

  Furthermore, according to the method described above, excellent performance can be achieved with respect to adhesive strength, heat dissipation, and withstand voltage for the following reasons.

  In general, the drying of the coating proceeds from the surface. Moreover, the metal substrate and the metal foil are gas impermeable. Therefore, if the coating film formed on the metal substrate or metal foil is heated to dry, the dried surface and the metal substrate or metal foil prevent the release of the solvent existing deep in the coating film to the outside. It is done. As a result, voids may be generated in the insulating layer obtained from the previous coating film or between the insulating layer and the metal substrate or metal foil in this drying step or in a subsequent step involving heating. . Voids can reduce the adhesive strength between the insulating layer and the metal substrate or metal foil, as well as the heat dissipation and withstand voltage of the metal base circuit board.

  Voids may be removed by pressing at very high pressure. However, in practice, even if such pressing is performed, it is difficult to completely remove the voids.

  In the method described with reference to FIGS. 1 to 5, a coating film is formed on the release film 5, and a part of the solvent is removed from the coating film to obtain the insulating layer 3 '. The surface area on the first main surface side of the insulating layer 3 ′ has a higher density of the inorganic filler 3 b than the surface area on the second main surface side. That is, the former has higher gas permeability than the latter. In general, the release film 5 has higher gas permeability than the metal foil 4. Therefore, according to this method, in addition to being able to release the solvent from the exposed surface side of the insulating layer 3 ′ to the outside, it is possible to release the solvent from the insulating layer 3 ′ to the outside through the release film 5. Can do.

  In this method, the insulating layer 3 ′ is subjected to a drying process immediately after the insulating layer 3 ′ is transferred from the release film 5 onto the metal foil 4. That is, according to this method, the insulating layer 3 ′ is dried with the second main surface exposed before transfer, and the insulating layer 3 ′ is dried with the first main surface exposed after transfer. Can do.

  Therefore, according to this method, it is possible to suppress the solvent from remaining in the insulating layer 3 ′, and it is possible to prevent voids from being generated in the insulating layer 3 ′ due to the evaporated solvent. . That is, according to the method described above, excellent performance can be achieved with respect to adhesive strength, heat dissipation, and withstand voltage.

  In general, a thermoplastic resin has an extremely large average molecular weight as compared with a thermosetting resin. Therefore, the coating liquid containing the thermoplastic resin has a much higher viscosity than the coating liquid containing the thermosetting resin.

  When a coating film composed of a high-viscosity coating solution is subjected to a drying step, the surface of the coating film dries at a much faster rate than the deep part, and this dried surface prevents the deep part of the coating film from being dried. For this reason, when using the coating liquid containing a thermoplastic resin, compared with the case where the coating liquid containing a thermosetting resin is used, an excess amount of solvent tends to remain in the insulating layer.

  Some resins, such as liquid crystal polyester and polyamideimide, have low gas permeability. And as a solvent for dissolving these resins, a high boiling point solvent is often used. Therefore, when the coating liquid for forming the insulating layer contains liquid crystal polyester or polyamideimide and a high boiling point solvent, it is generally difficult to sufficiently remove the solvent from the insulating layer. That is, also in this case, an excessive amount of solvent tends to remain in the insulating layer.

  According to the method described with reference to FIGS. 1 to 5, as described above, the insulating layer 3 ′ is dried with the second main surface exposed before transfer, and the evaporated solvent is removed from the insulating layer 3 ′. It is possible to release the insulating layer 3 ′ through the release film 5 and to dry the insulating layer 3 ′ with the first main surface exposed after the transfer. Therefore, even when an excessive amount of solvent is likely to remain in the insulating layer, it is possible to suppress the unnecessary solvent from remaining in the insulating layer 3 ′, and insulation due to the vaporized solvent can be prevented. Generation of voids in the layer 3 ′ can be prevented. That is, excellent performance can be achieved with respect to adhesive strength, heat dissipation, and withstand voltage.

  In the method described with reference to FIGS. 1 to 5, when the insulating layer 3 ′ of the transfer sheet 11 contains a solvent, the transfer sheet 11 can be wound around a roll. The transfer sheet 11 wound on a roll is convenient for stocking. Since the transfer sheet 11 as the intermediate product does not include the metal substrate 2 and the metal foil 4, the use thereof increases the degree of freedom in manufacturing as will be described below.

  Unlike the metal substrate 2, the metal foil 4 can generally be wound up on a roll. Therefore, according to the method of applying the coating liquid on the metal foil 4, the continuous production is easy and the metal foil 4 on which the insulating layer 3 is formed can be stocked as an intermediate product. However, in this method, intermediate products must be stocked for each type of metal foil 4.

  Since the transfer sheet 11 does not include the metal substrate 2 and the metal foil 4, it is not necessary to stock each type of the metal substrate 2 and the metal foil 4. Therefore, the circuit board laminate 1 can be manufactured without having a large amount of intermediate products in stock.

  For example, when a copper foil having a thickness of about 500 μm is used as the metal foil 4, such a metal foil 4 is generally not provided in a state of being wound on a roll but provided as a plurality of sheets. Is done. In the method of intermittently applying the coating liquid onto the metal foil 4, it is difficult to manufacture the insulating layer 3 excellent in thickness uniformity with high productivity.

  The release film 5 has no dimensional restrictions. Therefore, the coating liquid can be continuously applied onto the release film 5, and the insulating layer 3 having excellent thickness uniformity can be easily manufactured with high productivity. The transfer of the insulating layer 3 ′ from the release film 5 to the metal foil 4 can be performed regardless of the dimensions of the metal foil 4. That is, when the transfer sheet 11 is used, the circuit board laminate 1 having excellent thickness uniformity of the insulating layer 3 can be manufactured with high productivity.

  Examples of the present invention will be described below.

<Manufacture of 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 and 1474 g (9.75 mol) of 4-hydroxyacetanilide, 1620 g (9.75 mol) of isophthalic acid, and 2374 g (23.25 mol) of acetic anhydride were charged. After sufficiently replacing the atmosphere in 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 at this temperature for 3 hours.

  Thereafter, while distilling off the distilled by-product acetic acid and unreacted acetic anhydride, the temperature was raised to 300 ° C. over 170 minutes, and when the increase in torque was observed, the reaction was considered to be complete. Was 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 by Shimadzu Corporation flow tester CFT-500. Moreover, this liquid crystalline polyester powder was heat-treated at 223 ° C. for 3 hours in a nitrogen atmosphere to cause solid phase polymerization. The flow starting temperature of the liquid crystal polyester after solid phase polymerization was 270 ° C.

<Preparation of liquid crystal polyester solution>
2200 g of liquid crystal polyester obtained by the above-mentioned method 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 viscosity of this solution was 320 cP. This viscosity is a value measured at 23 ° C. using a B-type viscometer (manufactured by Toki Sangyo, “TVL-20 type”, rotor No. 21 (rotation speed: 5 rpm)).

<Example 1>
Boron nitride (manufactured by Mizushima Alloy Iron Co., Ltd., “HP-40”, average particle size 15 μm) was added to the liquid crystal polyester solution obtained by the above-described method to prepare a dispersion. Here, boron nitride was added so that the proportion of the inorganic filler composed of boron nitride in the insulating layer obtained from this dispersion was 60% by volume.

  The dispersion was stirred for 5 minutes with a centrifugal stirring and defoaming machine, and then applied onto a release film. Here, a polyester film having a band shape and a thickness of 100 μm was used as the release film. Subsequently, this coating film was dried at 70 ° C. for 6 minutes, and further dried at 100 ° C. for 6 minutes. As a result, a transfer sheet comprising a release film and an insulating layer having a thickness of about 100 μm was obtained.

  In this transfer sheet, 10% of the solvent contained in the coating film before drying remained in the insulating layer. Further, even when the transfer sheet was wound on a roll, the insulating layer did not cause brittle fracture.

  Next, heat and pressure were applied to the transfer sheet and the metal foil by overlapping them and passing them between a pair of hot rolls. Here, a copper foil having a thickness of 70 μm was used as the metal foil. The transfer sheet and the metal foil were overlapped so that the insulating layer of the transfer sheet was in contact with the metal foil. The temperature of the heat roll on the transfer sheet side was set to 130 ° C., and the temperature of the heat roll on the metal foil side was set to 150 ° C. Thereby, the insulating layer and the metal foil were bonded together.

  After peeling off the release film, the laminate composed of the insulating layer and the metal foil was subjected to a drying treatment. Specifically, this laminate was heated to 300 ° C. over 10 hours, and then maintained at this temperature for 3 hours.

Next, the laminate and the metal substrate were overlapped so that an insulating layer was interposed between the metal substrate and the metal foil. Here, an aluminum substrate having a thickness of 2 mm was used as the metal substrate. And these were heat-processed and heat-bonded for 15 minutes at 330 degreeC, applying the pressure of 15 MPa.
As described above, a laminated board for a circuit board was manufactured.

  For the circuit board laminate, the density D of the insulating layer was measured. Further, based on the composition of the dispersion, the coating amount per unit area, and the like, the density D ′ of the insulating layer when the bubble content was assumed to be zero was calculated. Then, the ratio D / D 'between the density D and the density D' was subtracted from 1, and the percentage was calculated as the porosity. As a result, the porosity was 0%.

  Next, withstand voltage, T peel strength and thermal resistance were measured using this laminate for circuit board. Moreover, the heat resistance of this laminated board for circuit boards was evaluated. Furthermore, the distribution of the inorganic filler in the insulating layer was examined for this laminated board for circuit boards. Below, these measurement and evaluation methods are described.

Withstand voltage:
The circuit board laminate cut to a predetermined size was immersed in insulating oil, and an AC voltage was applied between the metal foil and the metal substrate at room temperature. The applied voltage was raised, and the lowest voltage that caused dielectric breakdown was taken as the withstand voltage.

T peel strength test:
The metal foil of the circuit board laminate cut to a predetermined size was partially removed by etching to form a metal foil pattern having a width of 10 mm. The metal foil pattern is pulled from the aluminum substrate at a speed of 50 mm / min while grasping one end of the metal foil pattern and applying a force so that the peeled portion of the metal foil pattern is perpendicular to the main surface of the metal substrate. I peeled it off. At this time, the force applied to the metal foil pattern was defined as T peel strength.

Thermal resistance:
The metal foil of the circuit board laminate cut to a size of 30 mm × 40 mm was partially removed by etching to form a 14 mm × 10 mm land. After the transistor (C2233) was attached to the land using solder, it was set in the water cooling device so that the metal substrate was in contact with the cooling surface of the cooling device through the silicone grease layer. Next, power P of 30 W was supplied to the transistor, and the temperature T1 of the transistor and the temperature T2 of the cooling surface of the cooling device were measured. The difference T1-T2 between the temperature T1 and the temperature T2 obtained in this way was determined, and the ratio (T1-T2) / P between the difference T1-T2 and the supplied power P was defined as the thermal resistance.

Heat-resistant:
The metal foil of the circuit board laminate cut to a size of 50 mm × 50 mm was partially removed by etching to form a rectangular land. This etching was performed so that each of the dimension of the area from which the metal foil was removed and the dimension of the land were 25 mm × 50 mm. Next, the land was brought into contact with a 300 ° C. solder bath for 4 minutes, and then the state of the metal foil was observed. When the metal foil swelled or peeled off, it was determined as unacceptable, and when neither the metal foil swelled nor peeled off was determined as acceptable.

Inorganic filler distribution:
The distribution of boron in the insulating layer of the circuit board laminate was measured in the thickness direction using WDX. Here, the section from the main surface on the metal substrate side of the insulating layer to the main surface on the metal foil side was subjected to line analysis at a pitch of 0.8 μm. Then, the measurement result was converted so that the average value was 1, and the boron distribution obtained thereby was regarded as the inorganic filler distribution.

  When each measurement and evaluation was performed under the above conditions, the withstand voltage was 7.0 to 8.0 kV, the T peel strength was 10.9 N / cm, the thermal resistance was 0.13 ° C./W, and the heat resistance was “ It was determined as “pass”. Further, the frequency of the inorganic filler in the distribution curve was 1.03 to 1.10 in the vicinity of the metal substrate, and 0.85 in the vicinity of the metal foil. The distribution curve obtained in this example is shown in FIG.

  6 is a graph showing the distribution of the inorganic filler in the insulating layer of the circuit board laminate according to Example 1. FIG.

  In FIG. 6, the horizontal axis represents the distance from the metal substrate as a relative value where the distance from the metal substrate to the copper foil is 1. In FIG. 6, the vertical axis represents the frequency of the inorganic filler.

  In FIG. 6, the curve represented by the solid line is the distribution curve of the inorganic filler. On the other hand, the broken line approximates the distribution curve with a straight line.

  As shown in FIG. 6, in the insulating layer of the circuit board laminate according to this example, the density of the inorganic filler decreased from the metal substrate side to the metal foil side.

<Comparative Example 1>
In this example, first, a dispersion was prepared by the same method as in Example 1. This dispersion was applied on a copper foil having a thickness of 70 μm instead of being applied on the release film. Next, this coating film was subjected to a drying treatment. Specifically, this coating film was heated to 300 ° C. over 10 hours, and then maintained at this temperature for 3 hours. Thereby, the laminated body which consists of an insulating layer and metal foil about 100 micrometers thick was obtained. Furthermore, the above laminate and an aluminum substrate having a thickness of 2 mm were thermally bonded by the same method as in Example 1. As described above, a laminated board for a circuit board was manufactured.

  The circuit board laminate was subjected to various measurements and evaluations in the same manner as in Example 1. As a result, the porosity is 2%, the withstand voltage is 4.0 to 7.0 kV, the T peel strength is 7.5 N / cm, the thermal resistance is 0.15 ° C./W, and the heat resistance is judged as “pass”. It was done. The frequency of the inorganic filler in the distribution curve was 0.90 in the vicinity of the metal substrate and 1.05 to 1.10. In addition, the distribution curve obtained in this example is shown in FIG.

  FIG. 7 is a graph showing the distribution of the inorganic filler in the insulating layer of the circuit board laminate according to Comparative Example 1.

  In FIG. 7, the horizontal axis represents the distance from the metal substrate as a relative value where the distance from the metal substrate to the metal foil is 1. In FIG. 7, the vertical axis represents the frequency of the inorganic filler.

  In FIG. 7, the curve represented by the solid line is the distribution curve of the inorganic filler. On the other hand, the broken line approximates the distribution curve with a straight line.

  As shown in FIG. 7, in the insulating layer of the circuit board laminate according to the present example, the density of the inorganic filler decreased from the metal foil side toward the metal substrate side.

<Example 2>
A resin solution was prepared by dissolving 20 parts by mass of polyamideimide resin (manufactured by Hitachi Chemical Co., Ltd., “HP5000”) in 100 parts by mass of N-methylpyrrolidone. To this resin solution, boron nitride similar to that used in Example 1 was added to prepare a dispersion. Here, boron nitride was added so that the proportion of the inorganic filler made of boron nitride in the insulating layer obtained from this dispersion was 70% by volume.

  The dispersion was stirred for 5 minutes with a centrifugal stirring and defoaming machine, and then applied onto a release film. Here, as the release film, a polyester film having a belt shape, having a surface subjected to release treatment with a silicone resin, and having a thickness of 100 μm was used. The coating was then dried at 70 ° C. for 10 minutes. As a result, a transfer sheet comprising a release film and an insulating layer having a thickness of about 100 μm was obtained.

  In this transfer sheet, 10% of the solvent contained in the coating film before drying remained in the insulating layer. Further, even when the transfer sheet was wound on a roll, the insulating layer did not cause brittle fracture.

  Next, heat and pressure were applied to the transfer sheet and the metal foil by overlapping them and passing them between a pair of hot rolls. Here, a copper foil having a thickness of 70 μm was used as the metal foil. The transfer sheet and the metal foil were overlapped so that the insulating layer of the transfer sheet was in contact with the metal foil. Moreover, the temperature of each heat roll was set to 150 degreeC. Thereby, the insulating layer and the metal foil were bonded together.

  After peeling off the release film, the laminate composed of the insulating layer and the metal foil was subjected to a drying treatment. Specifically, this insulating layer was dried at 170 ° C. for 1 hour.

Next, the laminate and the metal substrate were overlapped so that an insulating layer was interposed between the metal substrate and the metal foil. Here, an aluminum substrate having a thickness of 2 mm was used as the metal substrate. And these were heat-processed for 15 minutes at 250 degreeC, applying the pressure of 10 Mpa, and heat-bonded.
As described above, a laminated board for a circuit board was manufactured.

  The circuit board laminate was subjected to various measurements and evaluations in the same manner as in Example 1. As a result, the porosity was 0%, the withstand voltage was 7.0 kV, the T peel strength was 20.0 N / cm, and the thermal resistance was 0.18 ° C./W. Moreover, the density of the inorganic filler in the insulating layer decreased from the metal substrate side toward the metal foil side. The frequency of the inorganic filler in the distribution curve was about 1.10 near the metal substrate and about 0.80 near the metal foil.

<Comparative example 2>
In this example, first, a dispersion was prepared by the same method as in Example 2. This dispersion was applied on a copper foil having a thickness of 70 μm instead of being applied on the release film. Next, this coating film was subjected to a drying treatment. Specifically, this coating film was dried at 170 ° C. for 1 hour. Thereby, the laminated body which consists of an insulating layer and metal foil about 100 micrometers thick was obtained. Furthermore, the above laminate and an aluminum substrate having a thickness of 2 mm were thermally bonded by the same method as in Example 2. As described above, a laminated board for a circuit board was manufactured.

  The circuit board laminate was subjected to various measurements and evaluations in the same manner as in Example 1. As a result, the porosity was 3%, the withstand voltage was 2.0 to 5.0 kV, the T peel strength was 15.0 N / cm, and the thermal resistance was 0.20 ° C./W. Moreover, the density of the inorganic filler in the insulating layer decreased from the metal foil side toward the metal substrate side. Specifically, the frequency of the inorganic filler in the distribution curve was about 0.85 in the vicinity of the metal substrate and about 1.10.

<Example 3>
50 parts by mass of 100 parts by mass of a bisphenol A-based epoxy resin (manufactured by Adeka, “EP4100G”, epoxy equivalent 190) and 85 parts by mass of an acid anhydride curing agent (manufactured by Adeka, “EH3326”, oxidation 650) A resin solution was prepared by dissolving in a mixed solution of 50 parts by mass of toluene and 50 parts by mass of butyl cellosolve. Spherical alumina (“AS40” manufactured by Showa Denko KK, average particle diameter of 11 μm) was added to this resin solution to prepare a dispersion. Here, the spherical alumina was added so that the proportion of the inorganic filler made of spherical alumina in the insulating layer obtained from this dispersion was 75% by volume.

  The dispersion was stirred for 5 minutes with a centrifugal stirring and defoaming machine, and then applied onto a release film. Here, as the release film, a polyester film having a belt shape, having a surface subjected to release treatment with a silicone resin, and having a thickness of 100 μm was used. The coating was then dried at 70 ° C. for 10 minutes. As a result, a transfer sheet comprising a release film and an insulating layer having a thickness of about 100 μm was obtained.

  In this transfer sheet, 10% of the solvent contained in the coating film before drying remained in the insulating layer. Further, even when the transfer sheet was wound on a roll, the insulating layer did not cause brittle fracture.

  Next, heat and pressure were applied to the transfer sheet and the metal foil by overlapping them and passing them between a pair of hot rolls. Here, a copper foil having a thickness of 70 μm was used as the metal foil. The transfer sheet and the metal foil were overlapped so that the insulating layer of the transfer sheet was in contact with the metal foil. Moreover, the temperature of each heat roll was set to 80 degreeC. Thereby, the insulating layer and the metal foil were bonded together.

  After peeling off the release film, the laminate composed of the insulating layer and the metal foil was subjected to a drying treatment. Specifically, this insulating layer was dried at 100 ° C. for 10 minutes.

Next, the laminate and the metal substrate were overlapped so that an insulating layer was interposed between the metal substrate and the metal foil. Here, an aluminum substrate having a thickness of 2 mm was used as the metal substrate. And these were heat-processed for 60 minutes at 180 degreeC, applying the pressure of 5 Mpa, and heat-adhered.
As described above, a laminated board for a circuit board was manufactured.

  The circuit board laminate was subjected to various measurements and evaluations in the same manner as in Example 1. As a result, the porosity was 0%, the withstand voltage was 5.0 kV, the T peel strength was 20.0 N / cm, the thermal resistance was 0.20 ° C./W, and the heat resistance was determined as “pass”. Moreover, the density of the inorganic filler in the insulating layer decreased from the metal substrate side toward the metal foil side. The frequency of the inorganic filler in the distribution curve was about 1.10 near the metal substrate and about 0.85 near the metal foil.

<Comparative Example 3>
In this example, first, a dispersion was prepared by the same method as in Example 3. This dispersion was applied on a copper foil having a thickness of 70 μm instead of being applied on the release film. Next, this coating film was subjected to a drying treatment. Specifically, this coating film was dried at 100 ° C. for 10 minutes. Thereby, the laminated body which consists of an insulating layer and metal foil about 100 micrometers thick was obtained. Further, the above laminate and an aluminum substrate having a thickness of 2 mm were thermally bonded by the same method as in Example 3. As described above, a laminated board for a circuit board was manufactured.

  The circuit board laminate was subjected to various measurements and evaluations in the same manner as in Example 1. As a result, the porosity was 2%, the withstand voltage was about 2.0 kV, the T peel strength was 15.0 N / cm, and the thermal resistance was 0.25 ° C./W. Moreover, the density of the inorganic filler in the insulating layer decreased from the metal foil side toward the metal substrate side. Specifically, the frequency of the inorganic filler in the distribution curve was about 0.85 in the vicinity of the metal substrate and about 1.10.

[1]
Transferring an insulating layer formed on a support and containing an electrically insulating resin, an electrically insulating inorganic filler, and optionally a solvent, from the support onto a metal foil;
A method of manufacturing a laminated board for a circuit board, comprising a step of bonding the metal foil and a metal substrate with the insulating layer interposed therebetween.

[2]
The support has a band shape;
The method
Applying a coating solution containing the resin, the inorganic filler, and the solvent on the support along the length direction thereof to form a coating film;
Removing only a part of the solvent from the coating film to form the insulating layer;
Winding the insulating layer on the roll together with the support;
The method according to [1], further comprising a step of unwinding the wound insulating layer together with the support from the roll prior to transfer of the insulating layer.

[3]
The support includes a transparent portion;
The method according to [1] or [2], wherein the method further includes a step of confirming whether there is a defect in the insulating layer by observation through the transparent portion prior to transfer of the insulating layer.

[4]
Transferring an insulating layer formed on a support and containing an electrically insulating resin, an electrically insulating inorganic filler, and optionally a solvent, from the support onto a metal foil;
Bonding the metal foil and the metal substrate with the insulating layer interposed therebetween;
A method of manufacturing a metal base circuit board including a step of patterning the metal foil.

[5]
A metal substrate;
A metal foil facing the metal substrate;
An insulating layer interposed between the metal substrate and the metal foil and bonded to each other, containing an electrically insulating resin and an electrically insulating inorganic filler, occupying the insulating layer A laminated board for a circuit board comprising an insulating layer in which the volume ratio of the inorganic filler is smaller in the region on the metal foil side than in the region on the metal substrate side.

[6]
A metal substrate;
A circuit pattern facing the metal substrate;
An insulating layer interposed between the metal substrate and the circuit pattern and bonded to each other, containing an electrically insulating resin and an electrically insulating inorganic filler, occupying the insulating layer A metal base circuit board comprising an insulating layer in which the volume ratio of the inorganic filler is smaller in the region on the circuit pattern side than in the region on the metal substrate side.

  DESCRIPTION OF SYMBOLS 1 ... Laminated board for circuit boards, 1 '... Metal base circuit board, 2 ... Metal substrate, 3 ... Insulating layer, 3' ... Insulating layer, 3a ... Resin, 3a '... Resin, 3b ... Inorganic filler, 4 ... Metal Foil, 4 '... circuit pattern, 5 ... release film, 11 ... transfer sheet, 12 ... structure.

Claims (5)

A metal substrate;
A metal foil facing the metal substrate;
An insulating layer interposed between the metal substrate and the metal foil and bonded to each other, containing an electrically insulating resin and an electrically insulating inorganic filler, occupying the insulating layer A laminated board for a circuit board comprising an insulating layer in which the volume ratio of the inorganic filler is smaller in the region on the metal foil side than in the region on the metal substrate side. A metal substrate;
A circuit pattern facing the metal substrate;
An insulating layer interposed between the metal substrate and the circuit pattern and bonded to each other, containing an electrically insulating resin and an electrically insulating inorganic filler, occupying the insulating layer A metal base circuit board comprising an insulating layer in which the volume ratio of the inorganic filler is smaller in the region on the circuit pattern side than in the region on the metal substrate side. A step of applying a coating liquid containing an electrically insulating resin, an electrically insulating inorganic filler, and a solvent along a longitudinal direction on a support having a belt shape to form a coating film; and ,
Removing only a part of the solvent from the coating film, and forming an insulating layer distributed so that the density of the inorganic filler decreases from the support side toward the opposite side;
Winding the insulating layer on the roll together with the support;
A step of unwinding the wound insulating layer from the roll together with the support;
Transferring the insulating layer containing the resin, the inorganic filler, and the solvent from the support onto a metal foil;
A method of manufacturing a laminated board for a circuit board, comprising a step of bonding the metal foil and a metal substrate with the insulating layer interposed therebetween. The support includes a transparent portion;
The method according to claim 3, wherein the method further includes a step of confirming the presence or absence of a defect of the insulating layer by observation through the transparent portion prior to the transfer of the insulating layer. A step of applying a coating liquid containing an electrically insulating resin, an electrically insulating inorganic filler, and a solvent along a longitudinal direction on a support having a belt shape to form a coating film; and ,
Removing only a part of the solvent from the coating film, and forming an insulating layer distributed so that the density of the inorganic filler decreases from the support side toward the opposite side;
Winding the insulating layer on the roll together with the support;
A step of unwinding the wound insulating layer from the roll together with the support;
Transferring the insulating layer containing the resin, the inorganic filler, and the solvent from the support onto a metal foil;
A method for manufacturing a metal base circuit board, comprising: a step of bonding the metal foil and a metal substrate with the insulating layer interposed therebetween; and a step of patterning the metal foil.

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