JP2024091769A - Resin sheet and metal base substrate - Google Patents

Abstract

The present invention provides a resin sheet having excellent insulation durability and a metal base substrate including the resin sheet.
[Solution] The resin sheet of the present invention is obtained by curing a thermosetting resin composition containing (A) a thermosetting resin, (B) a phenoxy resin having a mesogenic structure in its molecule, and (C) thermally conductive particles, and has a thermal conductivity and moisture absorption rate that satisfy the following formulas.
Formula: Thermal conductivity ≧ 0.77 × moisture absorption rate + 17
18.0≦Thermal conductivity (W/m·K)≦25.0
0.28≦moisture absorption rate (%)≦0.40
[Selection diagram] None

Description

The present invention relates to a resin sheet and a metal base substrate including the resin sheet.

Heat dissipation is required for insulating materials used in electrical and electronic devices. Various developments have been made to improve the heat dissipation properties of insulating materials.

One example of this type of technology is the technology described in Patent Document 1. Patent Document 1 describes a thermosetting resin composition that uses bisphenol A type epoxy resin as the thermosetting resin and scaly or spherical boron nitride particles as the thermally conductive particles.

JP 2015-193504 A

However, the conventional technology described in Patent Document 1 could result in reduced insulation durability.

The present inventors have discovered that a resin sheet which is made of a thermosetting resin composition containing specified components, and which has a thermal conductivity and moisture absorption rate which are in a relationship not satisfied by conventional resin sheets, and which has an excellent balance between these properties, both of which are within specified ranges, has excellent insulation durability.
According to the present invention,
[1]
(A) a thermosetting resin;
(B) a phenoxy resin having a mesogen structure in the molecule;
(C) thermally conductive particles;
A resin sheet obtained by curing a thermosetting resin composition comprising:
A resin sheet is provided, the thermal conductivity and moisture absorption rate of which satisfy the following formulas.
Formula: Thermal conductivity ≧ 0.77 × moisture absorption rate + 17
18.0≦Thermal conductivity (W/m·K)≦25.0
0.28≦moisture absorption rate (%)≦0.40
According to the present invention, there is also provided the following resin sheet.
[2]
The resin sheet according to [1], wherein the thermosetting resin (A) includes at least one selected from an epoxy resin, a cyanate resin, a maleimide resin, a phenolic resin, and a benzoxazine resin.
[3]
The resin sheet according to [2], wherein the epoxy resin includes an epoxy resin having a mesogen structure.
[4]
The resin sheet according to any one of [1] to [3], wherein the phenoxy resin (B) contains a structural unit derived from a phenol compound and a structural unit derived from an epoxy compound.
[5]
The resin sheet according to any one of [1] to [4], wherein the thermally conductive particles (C) include at least one selected from silica, alumina, aluminum nitride, boron nitride, silicon nitride, silicon carbide, and magnesium oxide.
[6]
The thermally conductive particles (C) contain the boron nitride,
The resin sheet according to [5], wherein the boron nitride includes monodisperse particles, granular particles, agglomerated particles, or a mixture thereof, of scaly boron nitride.
[7]
The resin sheet according to any one of [1] to [6], further comprising an organosiloxane compound (D).
[8]
The resin sheet according to any one of [1] to [7], further comprising a curing accelerator (E).
According to the present invention,
[9]
A first metal substrate;
An insulating layer made of the resin sheet according to any one of [1] to [8];
A metal base substrate is provided comprising, in order, a first metal layer and a second metal layer.

The present invention provides a resin sheet with excellent insulation durability, and a metal base substrate including the resin sheet.

1 is a schematic cross-sectional view showing a configuration of a metal base substrate according to an embodiment of the present invention.

The following describes an embodiment of the present invention with reference to the drawings. In all drawings, similar components are given similar reference symbols and descriptions are omitted where appropriate. In addition, "~" indicates "above" to "below" unless otherwise specified.

The resin sheet of the present embodiment is obtained by curing a thermosetting resin composition containing (A) a thermosetting resin, (B) a phenoxy resin having a mesogen structure in its molecule, and (C) thermally conductive particles, and has a thermal conductivity and a moisture absorption rate that satisfy the following formulas.
Formula: Thermal conductivity ≧ 0.77 × moisture absorption rate + 17
18.0≦Thermal conductivity (W/m·K)≦25.0
0.28≦moisture absorption rate (%)≦0.40
The resin sheet of the present embodiment is made of a thermosetting resin composition containing predetermined components, and has thermal conductivity and moisture absorption rate within predetermined ranges, which satisfy the above formula, and therefore has excellent insulation durability.

The insulating layer (resin sheet) constituting the metal base substrate contains various components such as resin, and even if the moisture absorption rate of each of these components is improved, there is a limit to the improvement of the moisture absorption rate as a composite material. Since the moisture absorption rate affects the insulation, reducing the moisture absorption rate is an important issue. On the other hand, the insulating layer (resin sheet) contains thermally conductive particles to provide heat dissipation, and the inventor has found a phenomenon in which the moisture absorption rate increases at the interface between the thermally conductive particles and the resin. However, since the thermally conductive particles are essential components, there is a trade-off between the improvement of the thermal conductivity and the moisture absorption rate, and there is room for improvement in the long-term insulation durability.
The present inventors have conducted extensive research in order to simultaneously improve thermal conductivity and moisture absorption rate, and have found that in a thermosetting resin composition comprising (A) a thermosetting resin, (B) a phenoxy resin having a mesogen structure in its molecule, and (C) thermally conductive particles, by setting the thermal conductivity and moisture absorption rate within specific ranges and further satisfying the above formula, the thermal conductivity and moisture absorption rate are improved and the composition also has excellent long-term insulation durability, thereby completing the present invention.

[Thermosetting resin (A)]
The thermosetting resin composition constituting the resin sheet of the present embodiment contains a thermosetting resin (A). The thermosetting resin (A) does not contain a phenoxy resin (B).

Thermosetting resin (A) may be a thermosetting compound that contains a mesogenic structure (mesogenic skeleton) in the molecule, or a thermosetting compound that does not contain a mesogenic structure in the molecule.

Thermosetting resin (A) may include, for example, epoxy resin, cyanate resin, maleimide resin, phenol resin, benzoxazine resin, polyimide resin, unsaturated polyester resin, melamine resin, silicone resin, acrylic resin, and phenol derivatives or derivatives thereof, and may contain at least one of these.

In this embodiment, the thermosetting resin (A) preferably contains at least one selected from epoxy resins, cyanate resins, bismaleimide resins, phenolic resins, and benzoxazine resins, and more preferably contains at least one or both of an epoxy resin and a cyanate resin.

These thermosetting resins can be any monomer, oligomer, or polymer that has two or more reactive functional groups in one molecule, and there are no particular limitations on the molecular weight or molecular structure.

(Epoxy resin)
As the epoxy resin, known ones can be used within the scope of the effects of the present invention. For example, glycidyl ethers of bisphenol A type, F type, S type, AD type, etc., hydrogenated bisphenol A type glycidyl ether, phenol novolac type glycidyl ether, cresol novolac type glycidyl ether, bisphenol A type novolac type glycidyl ether, naphthalene type glycidyl ether, biphenol type glycidyl ether, dihydroxypentadiene type glycidyl ether, triphenylmethane type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, hydroquinone type glycidyl ether, etc. can be mentioned, and at least one of them can be used.

From the viewpoint of the effects of the present invention, the epoxy resin preferably contains at least one selected from naphthalene-type glycidyl ethers, biphenol-type glycidyl ethers, dihydroxypentadiene-type glycidyl ethers, and hydroquinone-type glycidyl ethers.
The epoxy resin may preferably contain an epoxy resin containing a mesogenic skeleton, which can further increase the thermal conductivity (heat dissipation) during curing.

When an epoxy resin containing a mesogenic skeleton is cured, it is believed that the mesogenic skeleton forms a higher-order structure (liquid crystal phase or crystalline phase). It is believed that the thermal conductivity (heat dissipation) is further increased when heat is transmitted through this higher-order structure. The presence of a higher-order structure in the cured product can be examined by observation with a polarizing microscope.

The mesogenic skeleton may be any skeleton that facilitates liquid crystallinity or crystallinity through intermolecular interactions. The mesogenic skeleton preferably includes a conjugated structure. Specific examples of the mesogenic skeleton include a biphenyl skeleton, a phenylbenzoate skeleton, an azobenzene skeleton, a stilbene skeleton, a naphthalene skeleton, an anthracene skeleton, and a phenanthrene skeleton.
The epoxy resin particularly preferably contains a condensed polycyclic aromatic hydrocarbon skeleton, and particularly preferably contains a naphthalene skeleton.

For example, in the case of a biphenyl skeleton (-C ₆ H ₄ -C ₆ H ₄ -), the central carbon-carbon single bond in the structure may "rotate" due to thermal motion at high temperatures, which may result in a decrease in liquid crystallinity. Similarly, in the case of a phenylbenzoate skeleton (-C ₆ H ₄ -COO-C ₆ H ₄ -), the ester bond may rotate at high temperatures. However, in the case of a condensed polycyclic aromatic hydrocarbon skeleton such as a naphthalene skeleton, in principle, there is no decrease in liquid crystallinity due to such rotation. In other words, when an epoxy resin contains a condensed polycyclic aromatic hydrocarbon skeleton, it is easier to further improve heat dissipation properties in a high-temperature environment.

In addition, by using a naphthalene skeleton as the polycyclic aromatic hydrocarbon skeleton, the above-mentioned advantages can be obtained while preventing the epoxy resin from becoming too rigid. This is because the naphthalene skeleton is relatively small as a mesogen skeleton. The fact that the epoxy resin does not become too rigid is preferable in terms of preventing cracks and the like caused by the stress being more easily relaxed during curing of the thermosetting resin composition of this embodiment.

The epoxy resin preferably contains a di- or higher-functional epoxy resin. In other words, it is preferable that one molecule of the epoxy resin contains two or more epoxy groups. The number of functional groups of the epoxy resin is preferably 2 to 6, and more preferably 2 to 4.
From the viewpoint of the effects of the present invention, the epoxy resin in the present embodiment preferably contains one or more resins selected from those represented by the following formulas.

The epoxy equivalent of the epoxy resin is, for example, 100 to 200 g/eq, preferably 105 to 190 g/eq, and more preferably 110 to 180 g/eq. By using an epoxy resin with an appropriate epoxy equivalent, it is possible to control the curing property and optimize the physical properties of the cured product.

In one embodiment, the epoxy resin preferably further contains another epoxy resin that is liquid or semi-solid at room temperature (23° C.). Specifically, it is preferable that a part or all of the epoxy resin is liquid or semi-solid at 23° C.
The use of a liquid or semi-solid epoxy resin is preferable in terms of ease of forming a cured product in a desired shape.
The thermosetting resin composition of the present embodiment may contain only one type of epoxy resin, or may contain two or more types of epoxy resins.

In this embodiment, the epoxy resin is, for example, 5% by mass to 40% by mass, preferably 7% by mass to 35% by mass, and more preferably 10% by mass to 30% by mass, relative to the resin component (100% by mass) of the thermosetting resin composition not including the thermally conductive particles (D). This allows a resin sheet to be obtained that satisfies the required thermal conductivity and moisture absorption rate and has superior insulation durability.

(Cyanate resin)
As the cyanate resin, known ones can be used within the scope of the effects of the present invention. The cyanate resin can include one or more selected from, for example, novolac type cyanate resin; bisphenol type cyanate resin such as bisphenol A type cyanate resin, bisphenol E type cyanate resin, tetramethylbisphenol F type cyanate resin; naphthol aralkyl type cyanate resin obtained by reacting naphthol aralkyl type phenol resin with cyanogen halide; dicyclopentadiene type cyanate resin; and biphenylene skeleton-containing phenol aralkyl type cyanate resin. Among these, from the viewpoint of the effects of the present invention, it is more preferable to include at least one of novolac type cyanate resin and naphthol aralkyl type cyanate resin, and it is particularly preferable to include novolac type cyanate resin.
As the novolac type cyanate resin, for example, one represented by the following general formula (I) can be used.

The average repeating unit n of the novolac cyanate resin represented by general formula (I) is any integer. The average repeating unit n is not particularly limited, but is preferably 1 or more, and more preferably 2 or more. When the average repeating unit n is equal to or more than the above lower limit, the heat resistance of the novolac cyanate resin is improved, and the elimination and volatilization of low molecular weight compounds during heating can be further suppressed. In addition, the average repeating unit n is not particularly limited, but is preferably 10 or less, and more preferably 7 or less. When n is equal to or less than the above upper limit, the melt viscosity can be suppressed from increasing, and the moldability of the resin sheet can be improved.

As the cyanate resin, naphthol aralkyl type cyanate resin represented by the following general formula (II) is also preferably used. The naphthol aralkyl type cyanate resin represented by the following general formula (II) is obtained by condensing a naphthol aralkyl type phenol resin obtained by reacting naphthols such as α-naphthol or β-naphthol with p-xylylene glycol, α,α'-dimethoxy-p-xylene, 1,4-di(2-hydroxy-2-propyl)benzene, etc., with a cyanogen halide. The repeating unit n in general formula (II) is preferably an integer of 10 or less. When the repeating unit n is 10 or less, a more uniform resin sheet can be obtained. In addition, intramolecular polymerization is less likely to occur during synthesis, and separation during washing with water is improved, which tends to prevent a decrease in yield.

In the above general formula (II), each R independently represents a hydrogen atom or a methyl group, and n represents an integer of 1 to 10.

The content of the cyanate resin is, for example, 10% by mass to 70% by mass, preferably 20% by mass to 60% by mass, based on the resin component (100% by mass) of the thermosetting resin composition not including the thermally conductive particles (C). This allows a resin sheet to be obtained that satisfies the required thermal conductivity and moisture absorption rate and has excellent insulation durability.

(Maleimide resin)
The maleimide resin is preferably, for example, a maleimide resin having at least two maleimide groups in the molecule.

Examples of maleimide resins having at least two maleimide groups in the molecule include 4,4'-diphenylmethane bismaleimide, m-phenylene bismaleimide, p-phenylene bismaleimide, 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane, bis-(3-ethyl-5-methyl-4-maleimidophenyl)methane, 4-methyl-1,3-phenylene bismaleimide, N,N'-ethylene dimaleimide, N,N'-hexamethylene dimaleimide, bis(4-maleimidophenyl)ether, bis(4-maleimidophenyl)sulfone, 3,3-dimethyl-5,5-diethyl-4,4-diphenylmethane bismaleimide, bisphenol A diphenyl ether bismaleimide, and other resins having two maleimide groups in the molecule, biphenyl aralkyl maleimide, polyphenylmethane maleimide, and other resins having three or more maleimide groups in the molecule.

(Phenol resin)
Examples of the phenol resin include novolac-type phenol resins such as phenol novolac resin, cresol novolac resin, and bisphenol A novolac resin, and resol-type phenol resins, etc. One of these may be used alone, or two or more of them may be used in combination.
Among the phenolic resins, phenolic novolac resins are preferred.

(Benzoxazine resin)
Specific examples of the benzoxazine resin include o-cresolaniline type benzoxazine resin, m-cresolaniline type benzoxazine resin, p-cresolaniline type benzoxazine resin, phenol-aniline type benzoxazine resin, phenol-methylamine type benzoxazine resin, phenol-cyclohexylamine type benzoxazine resin, phenol-m-toluidine type benzoxazine resin, phenol-3,5-dimethylaniline type benzoxazine resin, bisphenol A-aniline type benzoxazine resin, bisphenol A-amine type benzoxazine resin, bisphenol F-aniline ... Examples of the benzoxazine resin include aniline type benzoxazine resin, bisphenol S-aniline type benzoxazine resin, dihydroxydiphenylsulfone-aniline type benzoxazine resin, dihydroxydiphenylether-aniline type benzoxazine resin, benzophenone type benzoxazine resin, biphenyl type benzoxazine resin, bisphenol AF-aniline type benzoxazine resin, bisphenol A-methylaniline type benzoxazine resin, phenol-diaminodiphenylmethane type benzoxazine resin, triphenylmethane type benzoxazine resin, and phenolphthalein type benzoxazine resin.

From the viewpoint of the effects of the present invention, the content of the thermosetting resin (A) is, for example, preferably 0.1% by mass to 70% by mass, more preferably 0.5% by mass to 65% by mass, and even more preferably 1% by mass to 60% by mass, relative to the resin component (100% by mass) of the thermosetting resin composition not including the thermally conductive particles (D).

[Phenoxy resin (B)]
The thermosetting resin composition constituting the resin sheet of the present embodiment contains a phenoxy resin (B) having a mesogen structure in the molecule.

An example of the mesogenic structure-containing phenoxy resin is one that contains a structural unit derived from a phenol compound and a structural unit derived from an epoxy compound in the molecule, and at least one of these structural units contains a compound having a mesogenic structure.
Other examples of the mesogenic structure-containing phenoxy resin include those that contain, in the molecule, a structural unit derived from a mesogenic structure-containing phenol compound.

An example of the mesogenic structure-containing phenoxy resin can be produced by a known method, for example, by reacting a polyfunctional phenolic compound having two or more hydroxyl groups in the molecule with a polyfunctional epoxy compound having two or more epoxy groups in the molecule.

That is, the phenoxy resin may contain a reaction compound of a polyfunctional phenol compound and a polyfunctional epoxy compound. Either or both of these polyfunctional phenol compounds and polyfunctional epoxy compounds have a mesogenic structure.

Other examples of the mesogenic structure-containing phenoxy resin can be produced by known methods, for example, by subjecting a mesogenic structure-containing phenolic compound having two or more phenol groups in the molecule to an addition polymerization reaction in epichlorohydrin.
That is, the phenoxy resin may include an addition polymer of a phenol compound having a mesogen structure.

The phenoxy resin can be produced without a solvent or in the presence of a reaction solvent. The reaction solvent used can be an aprotic organic solvent, such as methyl ethyl ketone, dioxane, tetrahydrofuran, acetophenone, N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylacetamide, sulfolane, or cyclohexanone. After the reaction is complete, the resin can be obtained as a solution in a suitable solvent by performing solvent replacement or the like. The phenoxy resin obtained by the solvent reaction can also be made into a solvent-free solid resin by performing a solvent removal process using an evaporator or the like.

As reaction catalysts that can be used in the production of the phenoxy resin, conventionally known polymerization catalysts such as alkali metal hydroxides, tertiary amine compounds, quaternary ammonium compounds, tertiary phosphine compounds, quaternary phosphonium compounds, and imidazole compounds are preferably used.

The weight average molecular weight (Mw) of the phenoxy resin is usually 500 to 200,000. It is preferably 1,000 to 100,000, and more preferably 2,000 to 50,000. Mw is measured by gel permeation chromatography and is converted using a standard polystyrene calibration curve.

In this embodiment, the mesogenic structure has, for example, a structure represented by the following general formula (1) or (2).
-A1-x-A2-...(1)
-x-A1-x-... (2)

In the general formula (1) and general formula (2), A1 and A2 each independently represent an aromatic group, a condensed aromatic group, an alicyclic group, or an alicyclic heterocyclic group, and x each independently represents a direct bond or a divalent linking group selected from the group consisting of -O-, -C=C-, -C≡C-, -CO-, -CO-O-, -CO-NH-, -CH=N-, -CH=N-N=CH-, -N=N-, and -N(O)=N-.

Here, A1 and A2 are preferably each independently selected from a hydrocarbon group having 6 to 12 carbon atoms and a benzene ring, a hydrocarbon group having 10 to 20 carbon atoms and a naphthalene ring, a hydrocarbon group having 12 to 24 carbon atoms and a biphenyl structure, a hydrocarbon group having 12 to 36 carbon atoms and having three or more benzene rings, a hydrocarbon group having 12 to 36 carbon atoms and a condensed aromatic group, and an alicyclic heterocyclic group having 4 to 36 carbon atoms. A1 and A2 may be unsubstituted or may be a derivative having a substituent.

Specific examples of A1 and A2 in the mesogenic structure include phenylene, biphenylene, naphthylene, anthracenylene, cyclohexyl, pyridyl, pyrimidyl, and thiophenylene. These may be unsubstituted or may be derivatives having a substituent such as an aliphatic hydrocarbon group, a halogen group, a cyano group, or a nitro group.

For example, x, which corresponds to a bonding group (linking group) in the mesogenic structure, is preferably a direct bond or a divalent substituent selected from the group consisting of -C=C-, -C≡C-, -CO-O-, -CO-NH-, -CH=N-, -CH=N-N=CH-, -N=N- or -N(O)=N-.

Here, a direct bond means a single bond, or A1 and A2 in the mesogenic structure are linked to each other to form a ring structure. For example, the structure represented by the general formula (1) may contain a naphthalene structure.

As the polyfunctional phenol compound, for example, a mesogen structure-containing compound represented by the following general formula (A) can be used. These may be used alone or in combination of two or more types.

In the general formula (A), ^R1 and ^R3 each independently represent a hydroxy group, ^R2 and ^R4 each independently represent one selected from a hydrogen atom, a linear or cyclic alkyl group having 1 to 6 carbon atoms, a phenyl group, and a halogen atom, a and c each independently represent an integer of 1 to 3, and b and d each independently represent an integer of 0 to 2. However, a+b and c+d each independently represent an integer of 1 to 3. a+c may be 3 or more.

As the polyfunctional epoxy compound, for example, a mesogen structure-containing compound represented by the following general formula (B) can be used. These may be used alone or in combination of two or more types.

In the general formula (B), ^R5 and ^R7 each independently represent a glycidyl ether group, ^R6 and ^R8 each independently represent one selected from a hydrogen atom, a linear or cyclic alkyl group having 1 to 6 carbon atoms, a phenyl group, and a halogen atom, e and g each independently represent an integer of 1 to 3, and f and h each independently represent an integer of 0 to 2, with the proviso that e+f and g+h each independently represent an integer of 1 to 3.

In addition, R in the general formula (A) and general formula (B) represents -A1-x-A2-, -x-A1-x-, or -x-. The two benzene rings in the general formula (A) may be linked to each other to form a condensed ring.

Specific examples of ^R2 , ^R4 , ^R6 and ^R8 include a hydrogen atom, a methyl group, an ethyl group, a propyl group, a butyl group, a chlorine atom, a bromine atom and the like, and among these, a hydrogen atom or a methyl group is particularly preferred.

As the polyfunctional epoxy compound containing a mesogenic structure, for example, an addition polymer of the compound represented by the general formula (B) may be used. These may be used alone or in combination of two or more kinds.

Among the polyfunctional phenol compounds and polyfunctional epoxy compounds, polyfunctional phenol compounds having three or more hydroxyl groups in the molecule and polyfunctional epoxy compounds having two or more epoxy groups in the molecule may be used.

That is, the phenoxy resin may include a branched reaction compound between a polyfunctional phenol compound having three or more hydroxyl groups in the molecule and a polyfunctional epoxy compound having two or more epoxy groups in the molecule.
The polyfunctional phenol compound having three or more hydroxy groups in the molecule can include, for example, polyphenols or polyphenol derivatives.

The polyphenol is a compound containing three or more phenolic hydroxy groups in the molecule. In addition, it is preferable that the polyphenol has the mesogenic structure in the molecule. For example, the mesogenic structure may be a biphenyl skeleton, a phenylbenzoate skeleton, an azobenzene skeleton, a stilbene skeleton, or the like.

Note that polyphenol derivatives include compounds in which the substituents at substitutable positions of a polyphenol compound having three or more phenolic hydroxy groups and a mesogenic structure are changed to other substituents.

In this embodiment, the branched reaction compound can be obtained using one or more of the polyfunctional phenol compounds, including a polyfunctional phenol compound having at least three hydroxy groups in the molecule, and one or more of the polyfunctional epoxy resins.

For example, a combination of a trifunctional phenol compound and a difunctional epoxy compound, or a combination of a trifunctional phenol compound, a difunctional phenol compound and a difunctional epoxy compound may be used.
As the trifunctional phenol compound, for example, resveratrol represented by the following chemical formula can be used.

As the bifunctional phenol compound, for example, one in which the hydroxy groups of ^R1 and ^R3 are bonded to the para-position of each benzene ring can be used.

Furthermore, the bifunctional epoxy compound may be one in which the glycidyl ether groups of ^R5 and ^R7 are bonded to the para-position of each benzene ring.

In addition, when the bifunctional phenol compound has a naphthalene ring as a condensed ring, the hydroxyl groups of ^R1 and ^R3 can be bonded to any one of the 1st and 4th positions, the 1st and 5th positions, the 1st and 6th positions, the 2nd and 3rd positions, the 2nd and 6th positions, or the 2nd and 7th positions of the naphthalene ring. In addition, when the bifunctional epoxy compound has a naphthalene ring as a condensed ring, the glycidyl ether groups of ^R5 and ^R7 can be bonded to any one of the 1st and 4th positions, the 1st and 5th positions, the 1st and 6th positions, the 2nd and 3rd positions, the 2nd and 6th positions, or the 2nd and 7th positions of the naphthalene ring.

The above-mentioned branched reactive compound (branched phenoxy resin) can be obtained by combining a trifunctional phenolic compound and a bifunctional epoxy compound, or by combining a trifunctional phenolic compound, a bifunctional phenolic compound, and a bifunctional epoxy compound.

On the other hand, among the polyfunctional phenol compounds and polyfunctional epoxy compounds, bifunctional phenol compounds and bifunctional epoxy compounds may be used. These may be used alone or in combination of two or more.

That is, the phenoxy resin can include a linear reaction compound of a bifunctional phenolic compound having two hydroxyl groups in the molecule and a bifunctional epoxy compound having two epoxy groups in the molecule.

The bifunctional phenol compound may be one in which the hydroxyl groups of ^R1 and ^R3 are bonded to the para-position of the respective benzene rings, and the bifunctional epoxy compound may be one in which the glycidyl ether groups of ^R5 and ^R7 are bonded to the para-position of the respective benzene rings.

In addition, when the bifunctional phenol compound has a naphthalene ring as a condensed ring, the hydroxyl groups of ^R1 and ^R3 can be bonded to any one of the 1st and 4th positions, the 1st and 5th positions, the 1st and 6th positions, the 2nd and 3rd positions, the 2nd and 6th positions, or the 2nd and 7th positions of the naphthalene ring. In addition, when the bifunctional epoxy compound has a naphthalene ring as a condensed ring, the glycidyl ether groups of ^R5 and ^R7 can be bonded to any one of the 1st and 4th positions, the 1st and 5th positions, the 1st and 6th positions, the 2nd and 3rd positions, the 2nd and 6th positions, or the 2nd and 7th positions of the naphthalene ring.
By using such a difunctional phenol compound and a difunctional epoxy compound in combination, the above-mentioned linear reaction compound (linear phenoxy resin) can be obtained.

The branched phenoxy resin and the linear phenoxy resin may have an epoxy group or a hydroxy group at the molecular terminal and an epoxy group or a hydroxy group inside the molecule. By having an epoxy group at the terminal or inside, a crosslinking reaction can be formed, thereby improving heat resistance.
Furthermore, by having a rigid, electron-conjugated, straight-chain structural unit, the heat dissipation characteristics can be improved.

The amount of the phenoxy resin (B) is, for example, 5% by mass to 60% by mass, preferably 10% by mass to 50% by mass, and more preferably 15% by mass to 40% by mass, relative to the resin component (100% by mass) of the thermosetting resin composition not including the thermally conductive particles (D). This allows a resin sheet to be obtained that satisfies the required thermal conductivity and moisture absorption rate and has superior insulation durability.

[Thermal conductive particles (C)]
The thermosetting resin composition constituting the resin sheet of the present embodiment contains thermally conductive particles (C).
The thermally conductive particles (C) may include, for example, highly thermally conductive inorganic particles having a thermal conductivity of 20 W/m·K or more. The highly thermally conductive inorganic particles may include, for example, at least one selected from silica, alumina, aluminum nitride, boron nitride, silicon nitride, silicon carbide, and magnesium oxide. These may be used alone or in combination of two or more.

The boron nitride may include monodisperse particles, agglomerated particles, or a mixture thereof, of scaly boron nitride. The scaly boron nitride may be granulated. By using agglomerated particles of scaly boron nitride, the thermal conductivity can be further increased. The agglomerated particles may be sintered or non-sintered.

The content of the thermally conductive particles (C) is 100% by mass to 400% by mass, preferably 150% by mass to 350% by mass, and more preferably 200% by mass to 300% by mass, relative to the resin component (100% by mass) of the thermosetting resin composition. By making the content equal to or greater than the lower limit, it is possible to improve thermal conductivity. By making the content equal to or less than the upper limit, it is possible to suppress deterioration of processability.

[Organosiloxane compound (D)]
The thermosetting resin composition constituting the resin sheet of the present embodiment can contain an organosiloxane compound (D) as necessary.

The organosiloxane compound (D) is an aliphatic hydrocarbon compound having a Si-OQ bond (Q is an alkyl group) at one end of the molecular chain. It is more preferable that the organosiloxane compound (D) has at least one functional group selected from an epoxy group, a glycidyl ether group, an amino group, an isocyanate group, a phenyl group, a carboxyl group, a hydroxyl group, an alkyl group, a vinyl group, and a mercapto group at the other end. This makes it possible to obtain a resin sheet with a lower moisture absorption rate and better insulation durability.
The organosiloxane compound (D) may include a compound represented by the following general formula (1).

In general formula (1), R each independently represents an alkoxy group having 1 to 3 carbon atoms or an alkyl group having 1 to 3 carbon atoms, and at least two R are alkoxy groups having 1 to 3 carbon atoms. All of R are preferably alkoxy groups having 1 to 3 carbon atoms, and more preferably alkoxy groups having 1 to 2 carbon atoms.
L represents a linear or branched alkylene group having 2 to 12 carbon atoms.

X represents an epoxy group, a glycidyl ether group, an amino group, an isocyanate group, a phenyl group, a carboxyl group, a hydroxyl group, an alkyl group, a vinyl group, or a mercapto group. From the viewpoint of the effects of the present invention, X is preferably an epoxy group, a glycidyl ether group, an amino group, an isocyanate group, an alkyl group having 1 to 3 carbon atoms, a phenyl group, or a mercapto group, and from the viewpoint of the pot life of the thermosetting resin composition, an epoxy group, a phenyl group, a glycidyl ether group, or a methyl group is more preferable.

Examples of compounds represented by general formula (1) include 3-aminopropyltriethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-mercaptopropyltriethoxysilane, 3-isocyanatopropyltriethoxysilane, glycidoxyoctyltriethoxysilane, decyltriethoxysilane, and phenyltriethoxysilane.

The thermosetting resin composition of this embodiment can contain 0.01 to 0.5 parts by mass of the organosiloxane compound (D) per 100 parts by mass of the thermally conductive particles (C), preferably 0.02 to 0.3 parts by mass, and more preferably 0.03 to 0.2 parts by mass. This allows a resin sheet to be obtained that satisfies the prescribed conditions for thermal conductivity and moisture absorption rate and has superior insulation durability.

(Cure Accelerator (E))
The thermosetting resin composition constituting the resin sheet of the present embodiment may contain a curing accelerator (E) as necessary.
The type and amount of the curing accelerator (E) are not particularly limited, but an appropriate one can be selected from the viewpoints of reaction rate, reaction temperature, storage property, and the like.

Examples of the curing accelerator (E) include imidazoles, organic phosphorus compounds, tertiary amines, phenolic compounds, organic acids, and the like. These may be used alone or in combination of two or more. Among these, from the viewpoint of improving heat resistance, it is preferable to use nitrogen atom-containing compounds such as imidazoles.

Examples of the imidazoles include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 2,4-diethylimidazole, 2-phenyl-4-methyl-5-hydroxyimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 1-cyanoethyl-2-phenylimidazole, and 1-cyanoethyl-2-phenylimidazolium trimellitate.

Examples of the tertiary amines include triethylamine, tributylamine, 1,4-diazabicyclo[2.2.2]octane, and 1,8-diazabicyclo(5,4,0)undecene-7.

Examples of the phenol compound include phenol resin, bisphenol A, nonylphenol, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, and allylphenol.
Examples of the organic acid include acetic acid, benzoic acid, salicylic acid, and p-toluenesulfonic acid.

The content of the curing accelerator (E) may be 0.01% by mass to 10% by mass, 0.02% by mass to 5% by mass, or 0.05% by mass to 1.5% by mass, based on 100% by mass of the total thermosetting resin.

The thermosetting resin composition of the present embodiment may contain other components in addition to the above-mentioned components. Examples of the other components include an antioxidant and a leveling agent.
The thermosetting resin composition of the present embodiment can be produced, for example, by the following method.

A resin varnish (a varnish-like thermosetting resin composition) can be prepared by dissolving, mixing, and stirring each of the above components in a solvent. This mixing can be performed using various mixers such as ultrasonic dispersion, high-pressure collision dispersion, high-speed rotation dispersion, bead mill, high-speed shear dispersion, and rotation-revolution dispersion.

The above solvents are not particularly limited, but include acetone, methyl isobutyl ketone, toluene, ethyl acetate, cyclohexane, heptane, cyclohexanone, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethylsulfoxide, ethylene glycol, cellosolve-based solvents, carbitol-based solvents, anisole, and N-methylpyrrolidone.

[Resin sheet]
The resin sheet of the present embodiment is obtained by curing the thermosetting resin composition, and has a thermal conductivity and a moisture absorption rate that satisfy the following formulas.
Formula: Thermal conductivity ≧ 0.77 × moisture absorption rate + 17
18.0≦Thermal conductivity (W/m·K)≦25.0
0.28≦moisture absorption rate (%)≦0.40

The resin sheet of this embodiment is made of the thermosetting resin composition having the above-mentioned composition, and has a relationship between thermal conductivity and moisture absorption rate that conventional resin sheets do not satisfy, and both are within a specified range, providing an excellent balance between these, resulting in excellent insulation durability. In other words, by optimizing the thermal conductivity and moisture absorption rate, which are in a trade-off relationship, the insulation durability of the resin sheet can be improved.

A specific form of the resin sheet includes a carrier substrate and a resin layer formed on the carrier substrate and made of the thermosetting resin composition of the present embodiment.
The resin sheet can be obtained, for example, by applying a varnish-like thermosetting resin composition onto a carrier substrate to obtain a coating film (resin layer) and then subjecting the coating film to a solvent removal treatment. The solvent content in the resin sheet can be 10 mass% or less based on the entire thermosetting resin composition. For example, the solvent removal treatment can be performed under conditions of 80°C to 200°C and 1 minute to 30 minutes.

In this embodiment, the carrier substrate may be, for example, a polymer film or a metal foil. Examples of the polymer film include, but are not limited to, polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polycarbonates, release papers such as silicone sheets, and heat-resistant thermoplastic resin sheets such as fluorine-based resins and polyimide resins. Examples of the metal foil include, but are not limited to, copper and/or copper-based alloys, aluminum and/or aluminum-based alloys, iron and/or iron-based alloys, silver and/or silver-based alloys, gold and gold-based alloys, zinc and zinc-based alloys, nickel and nickel-based alloys, and tin and tin-based alloys.

The resin substrate of this embodiment has an insulating layer made of the cured product of the above-mentioned thermosetting resin composition. This resin substrate can be used as a material for a printed circuit board on which electronic components such as LEDs and power modules are mounted.

(Metal base substrate)
A metal base board 100 of this embodiment will be described with reference to FIG.
FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a metal base substrate 100 .

As shown in FIG. 1, the metal base substrate 100 can include a metal substrate 101, an insulating layer 102 provided on the metal substrate 101, and a metal layer 103 provided on the insulating layer 102. The insulating layer 102 can be made of one selected from the group consisting of a resin layer made of the above-mentioned thermosetting resin composition, a cured product of the thermosetting resin composition, and a laminate. Each of these resin layers and laminates may be made of a thermosetting resin composition in a B-stage state before the circuit processing of the metal layer 103, and may be a cured product obtained by curing the resin composition after the circuit processing.

The metal layer 103 is provided on the insulating layer 102 and is subjected to circuit processing. Examples of metals constituting the metal layer 103 include one or more selected from copper, copper alloys, aluminum, aluminum alloys, nickel, iron, tin, and the like. Among these, the metal layer 103 is preferably a copper layer or an aluminum layer, and is particularly preferably a copper layer. By using copper or aluminum, the circuit processing properties of the metal layer 103 can be improved. The metal layer 103 may be a metal foil available in a plate form, or a metal foil available in a roll form.
The lower limit of the thickness of the metal layer 103 is, for example, 0.01 mm or more, and preferably 0.035 mm or more, so that the metal layer 103 can be applied to applications requiring a high current.

The upper limit of the thickness of the metal layer 103 is, for example, 10.0 mm or less, and preferably 5 mm or less. If it is less than this value, the circuit processability can be improved, and the substrate as a whole can be made thinner.

The metal substrate 101 has a role of dissipating heat accumulated in the metal base substrate 100. The metal substrate 101 is not particularly limited as long as it is a heat dissipating metal substrate, but may be, for example, a copper substrate, a copper alloy substrate, an aluminum substrate, or an aluminum alloy substrate, with a copper substrate or an aluminum substrate being preferred, and a copper substrate being more preferred. By using a copper substrate or an aluminum substrate, the heat dissipation properties of the metal substrate 101 can be improved.
The thickness of the metal substrate 101 can be appropriately set as long as the object of the present invention is not impaired.

The upper limit of the thickness of the metal substrate 101 is, for example, 20.0 mm or less, and preferably 5.0 mm or less. A thickness of less than this value can improve the workability of the metal base substrate 100 in external processing, cutting, and the like.

The lower limit of the thickness of the metal substrate 101 is, for example, 0.01 mm or more, and preferably 0.6 mm or more. By using a metal substrate 101 with a thickness of this value or more, the heat dissipation properties of the metal base substrate 100 as a whole can be improved.

In this embodiment, the metal base substrate 100 can be used for various substrate applications, but because it has excellent thermal conductivity and heat resistance, it can be used as a printed circuit board that uses LEDs and power modules.

The metal base substrate 100 can have a metal layer 103 that has been circuitized by etching or the like into a pattern. In this metal base substrate 100, a solder resist (not shown) may be formed on the outermost layer, and connection electrodes may be exposed so that electronic components can be mounted by exposure and development.

The above describes the embodiments of the present invention, but these are merely examples of the present invention, and various configurations other than those described above can be adopted as long as they do not impair the effects of the present invention.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

<Production of Thermosetting Resin Composition (Varnish Form)>
A varnish-like thermosetting resin composition was obtained by stirring each component and the solvent according to the blending ratio shown in Table 1. In Table 1, the content of the thermally conductive particles is expressed as a volume % relative to the resin component of the thermosetting resin composition not including the thermally conductive filler.

Details of each component in Table 1 are as follows. The amount of each component in Table 1 is expressed in parts by mass.

(Epoxy resin)
Epoxy resin 1: Epoxy resin represented by the following structural formula, product number "EPICLON HP-4700" manufactured by DIC Corporation

Epoxy resin 2: Tetramethylbiphenyl type epoxy resin represented by the following structural formula, product number "YX4000", manufactured by Mitsubishi Chemical Corporation

Epoxy resin 3: Dicyclopentadiene type epoxy resin represented by the following structural formula, product number "HP-7200", manufactured by DIC Corporation

Epoxy resin 4: Manufactured by DIC, epoxy resin with the following structural formula, product number "EPICLON 830"

(Cyanate resin)
Cyanate resin 1: Primaset "PT-30" manufactured by Lonza

(Phenoxy resin with mesogen structure in the molecule)
Phenoxy resin 1: Phenoxy resin having a mesogenic structure in the molecule obtained by the following synthesis procedure 23.5 parts by mass of epoxy resin (having a mesogenic structure, 4,4'-dihydroxybiphenyl diglycidyl ether), 72.5 parts by mass of a bisphenol compound (having a mesogenic structure, bifunctional phenol having the following structure, manufactured by Ueno Pharmaceutical Co., Ltd., HQPOB), 0.04 parts by mass of triphenylphosphine (TPP), and 3.9 parts by mass of a solvent (methyl ethyl ketone) were added to a reactor. Then, the mixture was reacted at a temperature of 120 to 150°C while removing the solvent. The reaction was stopped after confirming that the molecular weight reached the target molecular weight by GPC. As a result, a phenoxy resin having a molecular weight of 4500 was obtained.

(Cure Accelerator)
Curing accelerator 1: Novolac-type phenol compound (PR-51470, manufactured by Sumitomo Bakelite Co., Ltd.)

(Organosiloxane Compound)
Organosiloxane 1: 3-glycidoxypropyltriethoxysilane Organosiloxane 2: 3-isocyanatepropyltriethoxysilane Organosiloxane 3: glycidoxyoctyltriethoxysilane Organosiloxane 4: decyltriethoxysilane

(Thermal Conductive Particles)
Thermally conductive particles 1: Granular boron nitride prepared according to the following procedure was used.
[procedure]
Commercially available boron carbide powder was placed in a carbon crucible and nitrided under a nitrogen atmosphere at 2000°C for 10 hours. Next, commercially available diboron trioxide powder was added to the nitrided boron nitride powder and mixed in a blender for 1 hour (boron nitride:diboron trioxide=7:3 (mass ratio)). The resulting mixture was placed in a carbon crucible and fired under a nitrogen atmosphere at 2000°C for 10 hours.
Granular boron nitride was obtained in this manner.

<Measurement of physical properties of resin molded product of thermosetting resin composition>
(Thermal conductivity)
・Production of resin molded body

The obtained thermosetting resin composition containing the thermally conductive filler was sandwiched between 0.018 um copper foil and compression molded at 10 MPa, 180°C, and 90 minutes to obtain a resin molded body (thermal conductivity measurement sample 1). A sample with a diameter of 10 mm for measuring thermal diffusivity was cut out from the obtained molded body and used for measuring thermal diffusivity.

Specific Gravity of Resin Molded Product Specific gravity measurement was performed in accordance with JIS K 6911 (general test method for thermosetting plastics). Test pieces were cut from the above resin molded products to a size of 2 cm length x 2 cm width x 2 mm thickness. The unit of specific gravity (SP) is g/ ^cm3 .

Specific Heat of Resin Molded Article The specific heat (Cp) of the above-obtained resin molded article was measured by a DSC method.

Measurement of thermal conductivity of resin molded body A test piece with a diameter of 10 mm was cut out from the obtained resin molded body for measurement in the thickness direction. Next, the thermal diffusion coefficient (α) in the thickness direction of the plate-shaped test piece was measured by a non-steady method using a Xe flash analyzer TD-1RTV manufactured by ULVAC. The measurement was performed under the condition of air atmosphere and 25°C.
For the resin molded body, the thermal conductivity was calculated from the measured values of the thermal diffusion coefficient (α), specific heat (Cp), and specific gravity (SP) according to the following formula.
Thermal conductivity [W/m·K] = α [m ² /s] × Cp [J/kg·K] × Sp [g/cm ³ ]
In Table 1, the thermal conductivity of the resin molded body is indicated as "thermal conductivity."

(Volume Resistivity)
Measurement was carried out in accordance with JIS C 2139.
Specifically, a cured product for measurement, processed to an appropriate size, was placed in an oven at 30° C., and the volume resistivity was measured when it reached the target temperature (i.e., 30° C.).

(Moisture absorption rate)
The copper foil was removed from the obtained resin molded product by etching, and the product was left to stand for 48 hours under conditions of 30° C./90% RH, and the moisture absorption rate (%) was calculated from the change in weight before and after the treatment.

(Insulation durability)
Specifically, a resin molded product was prepared with a 25 mmφ ring electrode on one side and copper foil on the other side, and placed under 85°C/85% RH conditions with the ring electrode side as the anode and the copper foil side as the cathode, and the time it took for the product to become conductive when a DC voltage of 2 kV was applied was measured. Evaluation was based on the following criteria. (Evaluation criteria)
◯: No electrical conduction even after 100 hours or more. ×: Electrical conduction after less than 100 hours.

100 Metal base substrate 101 Metal substrate 102 Insulating layer 103 Metal layer

Claims (9)

(A) a thermosetting resin;
(B) a phenoxy resin having a mesogen structure in the molecule;
(C) thermally conductive particles;
A resin sheet obtained by curing a thermosetting resin composition comprising:
A resin sheet having a thermal conductivity and a moisture absorption rate that satisfy the following formulas.
Formula: Thermal conductivity ≧ 0.77 × moisture absorption rate + 17
18.0≦Thermal conductivity (W/m·K)≦25.0
0.28≦moisture absorption rate (%)≦0.40 The resin sheet according to claim 1, wherein the thermosetting resin (A) includes at least one selected from the group consisting of epoxy resins, cyanate resins, maleimide resins, phenolic resins, and benzoxazine resins. The resin sheet according to claim 2, wherein the epoxy resin includes an epoxy resin having a mesogenic structure. The resin sheet according to any one of claims 1 to 3, wherein the phenoxy resin (B) contains structural units derived from a phenol compound and structural units derived from an epoxy compound. The resin sheet according to any one of claims 1 to 4, wherein the thermally conductive particles (C) include at least one selected from silica, alumina, aluminum nitride, boron nitride, silicon nitride, silicon carbide, and magnesium oxide. The thermally conductive particles (C) contain the boron nitride,
The resin sheet according to claim 5 , wherein the boron nitride comprises monodisperse particles, granular particles, agglomerated particles, or a mixture thereof, of scaly boron nitride. The resin sheet according to any one of claims 1 to 6, further comprising an organosiloxane compound (D). The resin sheet according to any one of claims 1 to 7, further comprising a curing accelerator (E). A first metal substrate;
An insulating layer made of the resin sheet according to any one of claims 1 to 8;
a second metal layer, in that order.

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