JP2024146562A - Heat dissipation resin sheet - Google Patents

Abstract

The present invention provides a heat-dissipating resin sheet that can improve thermal conductivity while also improving the flexibility of the heat-dissipating resin sheet before curing. The heat-dissipating resin sheet includes an epoxy resin having a mesogen skeleton and a cyanate ester compound having a melting point of 40° C. or less. [Selected Figures] None

Description

The present invention relates to a heat dissipation resin sheet.

The amount of heat generated by electronic devices is increasing due to miniaturization and high performance, and there is a growing demand for high heat dissipation resin sheets used in electronic devices. The thermal conductivity of a heat dissipation resin sheet can be improved by increasing the inorganic filler filling rate, but increasing the inorganic filler filling rate causes a problem of reduced flexibility, for example in the B-stage state before curing. If the flexibility of a heat dissipation resin sheet decreases, it becomes more susceptible to problems such as cracks occurring when rolled up during storage or during the process of mounting on a substrate, etc.

It has also been considered to increase the thermal conductivity of heat dissipation resin sheets by using a matrix resin, and the use of an epoxy resin having a mesogenic skeleton has been considered. Although an epoxy resin having a mesogenic skeleton is easy to increase thermal conductivity, it is prone to crystallization, which reduces fluidity and handling properties. For this reason, for example, Patent Document 1 discloses an epoxy resin composition that contains, in addition to an epoxy resin having a mesogenic skeleton, a phenolic curing agent having a specific structure, a curing accelerator, and a latent catalyst in order to achieve high thermal conductivity while improving handling and moldability.

For example, Patent Document 2 discloses a high heat dissipation insulating resin sheet that contains an epoxy resin, a curing agent, and an inorganic filler, and that has excellent thermal conductivity and flexibility by oligomerizing the epoxy resin to a certain amount of dimers and trimers. Patent Document 2 also shows that an epoxy resin having a mesogenic skeleton can be used as the epoxy resin.

International Publication No. 2021/161360 JP 2012-67205 A

As described above, Patent Document 1 discloses that the fluidity of the resin is increased to improve the handling and moldability. However, the fluidity of the resin is improved only by reacting the epoxy resin with a curing agent once during curing to oligomerize the resin, and does not disclose that the flexibility of the heat dissipating resin sheet before curing or in the B-stage state is improved.
Furthermore, if dimers and trimers are oligomerized to a certain amount as in Patent Document 2, the manufacturing process becomes complicated and is not practical.In addition, since Patent Document 2 uses an amine curing agent or a phenol novolac-based curing agent as the curing agent, it is considered that there is room for improvement in thermal conductivity.

The present invention aims to provide a heat dissipation resin sheet that can improve thermal conductivity while also maintaining good flexibility of the heat dissipation resin sheet before curing, without complicating the manufacturing process.

As a result of intensive research, the present inventors have found that the above-mentioned problems can be solved by incorporating a cyanate ester having a melting point of 40° C. or less in a heat dissipation resin sheet in addition to an epoxy resin having a mesogenic skeleton, and have completed the present invention as described below. That is, the present invention provides the following [1] to [6].
[1] A heat dissipating resin sheet comprising an epoxy resin having a mesogenic skeleton and a cyanate ester compound having a melting point of 40° C. or lower.
[2] The heat dissipating resin sheet according to the above [1], wherein the cyanate ester compound has a skeleton containing an aromatic ring.
[3] The heat dissipating resin sheet according to the above [1] or [2], wherein the molecular weight of the cyanate ester compound is 500 or less. [4] The heat dissipating resin sheet according to any one of the above [1] to [3], wherein the epoxy resin has a biphenyl skeleton.
[5] The heat dissipating resin sheet according to any one of the above [1] to [4], which contains an inorganic filler.
[6] A cured product of the heat dissipation resin sheet according to any one of [1] to [5] above.

The present invention provides a heat dissipation resin sheet that improves thermal conductivity while also improving the flexibility of the heat dissipation resin sheet before curing, without complicating the manufacturing process.

Hereinafter, the present invention will be described with reference to embodiments.
The heat-dissipating resin sheet of the present invention contains an epoxy resin having a mesogenic skeleton and a cyanate ester compound having a melting point of 40° C. or lower.

<Epoxy resin>
The heat dissipating resin sheet of the present invention contains an epoxy resin having a mesogenic skeleton. The mesogenic skeleton is a molecular structure capable of exhibiting liquid crystallinity, and improves the alignment after curing, which makes it easier to increase the thermal conductivity of the heat dissipating resin sheet after curing. The epoxy resin having a mesogenic skeleton preferably has two or more epoxy groups in one molecule, and the number of epoxy groups in one molecule is more preferably 2 to 4, and even more preferably 2. The number of epoxy groups being 2 makes it easier to improve the alignment after curing, which makes it easier to increase the thermal conductivity.

An example of a structure having a mesogenic skeleton is the structure of the following formula (1).
In formula (1), each * is independently either a bond to a group containing an epoxy group or a bond to a linking group bonded to another mesogenic skeleton. k is an integer of 0 to 4, and each Y is independently either -R, -OR, a halogen atom, -CN, _-NO2 , or _-COCH3 . R is an aliphatic hydrocarbon group having 1 to 8 carbon atoms. X is at least one type selected from the group represented by formula (A) below.

In group (A), n is an integer of 0 to 4, s is an integer of 0 to 7, m is an integer of 0 to 8, l is an integer of 0 to 12, and r is an integer of 0 to 8. Y is as described above.

In formula (1), the bonding position indicated by * is preferably the para position relative to X, that is, the structure represented by formula (1) is preferably the following formula (1-1).
In formula (1-1), *, X, Y, and k are as defined above.

In formulas (1) and (1-1), Y is preferably a halogen atom or an alkyl group, more preferably an alkyl group. The halogen atom is any one of a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The alkyl group may be linear or may have a branched or cyclic structure, but is preferably linear.
Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, and an n-octyl group, and of these, a methyl group is preferred.
k is preferably an integer of 0 to 2. n is preferably an integer of 0 to 2. s is preferably an integer of 0 to 5, and more preferably an integer of 0 to 2. m is preferably an integer of 0 to 4, and more preferably an integer of 0 to 2. l is preferably an integer of 0 to 6, and more preferably an integer of 0 to 3. r is preferably an integer of 0 to 4, and more preferably an integer of 0 to 2, and most preferably an integer of 0.

In formula (1) or formula (1-1), the mesogenic skeleton is preferably a skeleton in which X is a single bond or a group containing -COO-, and more preferably a biphenyl skeleton in which X is a single bond or a phenylbenzoate skeleton in which X is a group containing -COO-.

In formulas (1) and (1-1), the group containing an epoxy group bonded to * is preferably an organic group containing an epoxy group having about 2 to 20 carbon atoms, more preferably an organic group containing an epoxy group having 3 to 12 carbon atoms, and even more preferably a group represented by the following formula (2). When the group containing an epoxy group is a group represented by the following formula (2), it becomes easy to synthesize an epoxy resin having a mesogenic skeleton.

In formula (2), * represents a bond bonded to the aromatic ring of the mesogenic skeleton. ^R1 represents a linear or branched alkylene group having 1 to 10 carbon atoms. Examples of the linear or branched alkylene group include a methylene group, a methylmethylene group, a dimethylmethylene group, an ethylene group, a propylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, a heptamethylene group, an octamethylene group, a nonamethylene group, and a decamethylene group. Of these, a methylene group is preferred.

In addition, it is preferable that in the above formulas (1) and (1-1), each of the *'s in the epoxy resin having a mesogenic skeleton is bonded to a group represented by formula (2). Therefore, the epoxy resin having a mesogenic skeleton preferably has a structure represented by the following formula (1-2).
In the formula (1-2), R ¹ , X, Y and k are as described above.

In addition, in the above formulas (1) and (1-1), the linking group bonded to * may be an organic group having about 1 to 24 carbon atoms, preferably an organic group having 3 to 16 carbon atoms, and more preferably an organic group having 4 to 12 carbon atoms.
In the above formulas (1) and (1-1), when at least one of the *'s is bonded to a linking group that is linked to another mesogenic skeleton, the epoxy resin having a mesogenic skeleton will have a plurality of mesogenic skeletons in one molecule, and in this case, it is preferable that there are two mesogenic skeletons in one molecule. In the above formulas (1) and (1-1), the "another mesogenic skeleton" may be any of the skeletons represented by formulas (1) and (1-1), respectively. The two or more mesogenic skeletons in one molecule may be the same or different from each other, but are preferably the same from the viewpoint of ease of production.

In the above formulas (1) and (1-1), it is also preferred that one of the *'s is bonded to a group containing an epoxy group, and the other * is bonded to a linking group that is linked to another mesogenic skeleton. In this case, the group containing an epoxy group is as described above, and is preferably a group represented by formula (2). Therefore, it is also preferred that the epoxy resin having a mesogenic skeleton has a structure represented by the following formula (1-3). The structure represented by the following formula (1-3) has a linking group represented by ^R2 , which makes it easier to improve thermal conductivity.

In formula (1-3), X, Y, k, and ^R1 are as described above. ^R2 is a divalent organic group, and the number of carbon atoms in ^R2 is, for example, 1 to 24, preferably 2 to 16, and more preferably 3 to 12.
More specifically, ^R2 is a hydrocarbon group which may have a heteroatom such as an oxygen atom, a nitrogen atom, a sulfur atom, etc. As the heteroatom, an oxygen atom is preferable, and among them, an oxygen atom constituting an ether bond is preferable.
In addition, in the formula (1-3), R ² is preferably a group represented by *-O-R ⁴ -O-* from the viewpoint of ease of synthesis. Here, * is a bond to the phenyl ring, and R ⁴ is an aliphatic hydrocarbon group having 1 to 24 carbon atoms, preferably a saturated aliphatic hydrocarbon group. R ⁴ may be linear or may have a branched structure or a cyclic structure, but is preferably linear. The number of carbon atoms in R ⁴ is, for example, 1 to 24, preferably 2 to 16, more preferably 3 to 12, and even more preferably 6 to 12.
^R4 is preferably a linear or branched alkylene group. Specific examples of ^R4 include ethylene, propylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, octamethylene, nonamethylene, decamethylene, undecamethylene, dodecamethylene, tridecamethylene, tetradecamethylene, pentadecamethylene, hexadecamethylene, and heptadecamethylene groups, and among these, octamethylene is particularly preferred.

As an epoxy resin having a mesogenic skeleton, a compound represented by the following formula (2-1) or formula (2-2) is particularly preferred. Among these, from the viewpoint of ease of manufacturing the epoxy resin, a compound represented by formula (2-1) is preferred, and from the viewpoint of improving thermal conductivity, a compound represented by formula (2-2) is preferred.

In formula (2-1), ^R6 is independently an alkyl group or a hydrogen atom. The alkyl group is as described above, and is preferably a methyl group.

In addition, in formula (2-2), R ⁴ is as defined above.

The epoxy resin having a mesogenic skeleton may be in a prepolymer state obtained by reacting a part of it with a curing agent or the like. The curing agent may be a cyanate ester compound described later, but is not limited to cyanate ester compounds and may be any of phenol-based curing agents, amine-based curing agents, acid anhydride-based curing agents, mercaptan-based curing agents, imidazole-based curing agents, etc.

The weight average molecular weight of the epoxy resin having a mesogenic skeleton is preferably less than 10,000, more preferably not more than 5,000, and even more preferably not more than 3,000. The weight average molecular weight of the epoxy resin having a mesogenic skeleton is not particularly limited, but may be, for example, 200 or more, and preferably 250 or more.
The weight average molecular weight is a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC). In the gel permeation chromatography (GPC) measurement, tetrahydrofuran is preferably used as an eluent. However, when the molecular weight is a low molecular weight of 1000 or less, the weight average molecular weight may be calculated from the structural formula. In addition, in the heat dissipation resin sheet, the epoxy resin may react by curing, but the weight average molecular weight means the weight average molecular weight of the epoxy resin in the state before curing.

The epoxy equivalent of the epoxy resin having a mesogenic skeleton is not particularly limited, but is, for example, 100 g/eq or more and 1000 g/eq or less. The epoxy equivalent of the epoxy resin is preferably 120 g/eq or more, more preferably 140 g/eq or more, and is preferably 500 g/eq or less, more preferably 400 g/eq or less. The epoxy equivalent can be measured, for example, according to the method specified in JIS K 7236.

In the heat dissipation resin sheet, the content of the epoxy resin having a mesogenic skeleton is, for example, 15 mass % or more and 80 mass % or less, preferably 25 mass % or more and 75 mass % or less, more preferably 30 mass % or more and 70 mass % or less, and even more preferably 45 mass % or more and 65 mass % or less, based on the total amount of the components of the heat dissipation resin sheet excluding the inorganic filler described later.
The mesogenic skeleton-containing epoxy resin may be used alone or in combination of two or more kinds.

The heat dissipation resin sheet may contain an epoxy resin having no mesogenic skeleton in addition to the epoxy resin having a mesogenic skeleton. The epoxy resin having no mesogenic skeleton may have one or more epoxy groups, preferably two or more.
From the viewpoint of thermal conductivity, the content of the epoxy resin having no mesogenic skeleton is preferably smaller, and is, for example, less than 100 parts by mass, preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and further preferably 15 parts by mass or less, relative to 100 parts by mass of the epoxy resin having a mesogenic skeleton. The less the epoxy resin having no mesogenic skeleton, the better, and the content may be 0 parts by mass or more, but it is preferable that no epoxy resin having no mesogenic skeleton is contained.
The heat dissipation resin sheet may contain a resin other than the epoxy resin as long as the effect of the present invention is not impaired. Such a resin may be a thermosetting resin or a resin other than a thermosetting resin.

<Cyanate ester compound>
The cyanate ester compound contained in the heat dissipating resin sheet of the present invention has a melting point of not more than 40° C. If the melting point of the cyanate ester exceeds 40° C., the flexibility of the heat dissipating resin sheet before curing or in a B-stage state decreases, and there is a risk of cracks occurring when, for example, the sheet is wound into a roll.
From the viewpoint of improving flexibility at around room temperature, the melting point of the cyanate ester compound is preferably 35° C. or lower, more preferably 30° C. or lower. The melting point of the cyanate ester compound is not particularly limited in terms of the lower limit, but may be, for example, 0° C. or higher.
The melting point of the cyanate ester compound can be measured by DSC.

The cyanate ester compound is a compound that functions as a curing agent for epoxy resins and has a cyanate ester group (-OCN). A part of the cyanate ester group is trimerized during curing to form a triazine skeleton, which forms a molecular structure with high alignment together with the epoxy resin after curing, making it easier to improve thermal conductivity.
In addition, the cyanate ester compound preferably has two or more cyanate ester groups in one molecule from the viewpoint of improving the curability, and more preferably has two cyanate ester groups in one molecule from the viewpoint of increasing the alignment of the molecular structure to easily improve the thermal conductivity and to easily lower the melting point.

The cyanate ester compound preferably has a skeleton containing an aromatic ring, and more preferably has a skeleton containing a phenyl ring. By having a skeleton containing an aromatic ring, it becomes easier to further improve the thermal conductivity after curing. In addition, the cyanate ester compound preferably has a cyanate ester group directly bonded to the aromatic ring, and more preferably directly bonded to the phenyl ring. By directly bonding the cyanate ester group to the aromatic ring, it becomes easier to increase the reactivity of the cyanate ester group, and trimerization and curing by heating become easier to proceed.

The molecular weight of the cyanate ester compound is preferably 500 or less. A molecular weight of 500 or less lowers the melting point, which makes it easier to improve the flexibility of the heat dissipation resin sheet before curing or in the B-stage state. The molecular weight of the cyanate ester compound is more preferably 400 or less, and even more preferably 320 or less. The molecular weight of the cyanate ester compound is not particularly limited, but may be, for example, 150 or more, or may be 200 or more.

The cyanate ester compound is preferably a bisphenol-type cyanate ester. The bisphenol-type cyanate ester has a bisphenol skeleton and preferably has a structure in which one cyanate ester group is directly bonded to each phenyl group of the bisphenol skeleton. Examples of bisphenol-type cyanate ester resins include bisphenol E-type cyanate ester resins and bisphenol F-type cyanate ester resins, and among these, bisphenol E-type cyanate ester resins are preferred. The cyanate ester compounds may be used alone or in combination of two or more types.

The cyanate ester compound is preferably contained in the heat dissipating resin sheet so that the equivalent ratio (OCN/epoxy group) is preferably 0.25 or more, more preferably 0.3 or more, even more preferably 0.4 or more, and even more preferably 0.6 or more. By adjusting the content of the cyanate ester compound so that the equivalent ratio is a certain level or more, the curing of the heat dissipating resin sheet can be appropriately promoted by heating or the like. In addition, the equivalent ratio is preferably 2.5 or less, more preferably 2.0 or less, even more preferably 1.6 or less, and even more preferably 1.2 or less. By setting the equivalent ratio to the above upper limit or less, the epoxy resin having a mesogen skeleton is appropriately arranged after curing, making it easier to improve thermal conductivity.
The equivalent ratio (OCN/epoxy group) referred to here is the ratio of the cyanate ester groups of the cyanate ester compound blended into the heat dissipation resin sheet to the epoxy groups of the epoxy resin blended into the heat dissipation resin sheet, and in the case of curing by semi-curing or the like, it is the equivalent ratio before curing.

The heat dissipation resin sheet of the present invention may contain a curing agent other than the cyanate ester compound, as long as the effect of the present invention is not significantly impaired. The curing agent other than the cyanate ester compound is a compound that can react with the epoxy resin to cure the epoxy resin.
The content of the curing agent other than the cyanate ester compound in the heat dissipating resin sheet is, for example, less than 50 equivalent %, preferably 30 equivalent % or less, and more preferably 10 equivalent % or less, assuming that the total amount of the curing agent contained in the heat dissipating resin sheet is 100 equivalent %. The heat dissipating resin sheet of the present invention does not need to contain a curing agent other than the cyanate ester compound, and therefore the blending amount of the curing agent other than the cyanate ester compound may be 0 equivalent % or more.

<Inorganic filler>
The heat dissipating resin sheet of the present invention preferably contains an inorganic filler. The inorganic filler is preferably a thermally conductive filler. By containing the inorganic filler, which is a thermally conductive filler, the heat dissipating resin sheet can be given high thermal conductivity. The inorganic filler may be dispersed in a resin component containing an epoxy resin having a mesogen skeleton and a matrix component containing a curing agent such as a cyanate ester compound.

From the viewpoint of increasing the thermal conductivity while ensuring the insulating properties of the thermally conductive resin composition, the thermal conductivity of the insulating inorganic filler is, for example, 10 W/(m·K) or more, preferably 15 W/(m·K) or more, and more preferably 20 W/(m·K) or more. The thermal conductivity of the thermally conductive filler is not particularly limited, but may be, for example, 2000 W/(m·K) or less, or 1000 W/(m·K) or less.
The thermal conductivity of the inorganic filler can be measured, for example, by a periodic heating thermoreflectance method using a thermal microscope manufactured by Bethel Corporation on a cross section of the filler cut with a cross section polisher.

In addition, the inorganic filler is preferably electrically insulating, and is preferably a filler having an electrical resistivity of, for example, 10 ⁸ [Ω·m] or more. High electrical insulation properties make it suitable for use in electronic devices such as substrates. Therefore, the inorganic filler is preferably a thermally conductive filler having electrical insulation properties.

Examples of inorganic fillers include metals, metal oxides, metal nitrides, metal hydroxides, carbon materials, oxides other than metals, nitrides, and carbides. The shape of the inorganic filler may be any shape such as scale, sphere, crushed, irregular, polyhedral, or fibrous, or may be aggregated particles formed by aggregation of primary particles. For example, boron nitride, which will be described later, is preferably used as aggregated particles.
In the inorganic filler, examples of metals include aluminum, copper, nickel, etc., examples of metal oxides include aluminum oxide, magnesium oxide, zinc oxide, etc., such as alumina, and examples of metal nitrides include aluminum nitride. Examples of metal hydroxides include aluminum hydroxide. Furthermore, examples of carbon materials include spherical graphite, scaly graphite, and carbon fibers. Examples of oxides, nitrides, and carbides other than metals include quartz, boron nitride, and silicon carbide. Among these, from the viewpoint of ensuring electrical insulation, metal oxides, metal nitrides, metal hydroxides, oxides, nitrides, and carbides other than metals are preferred, and among these, metal oxides, metal hydroxides, and nitrides are preferred. Specifically, aluminum oxide, aluminum hydroxide, and boron nitride are more preferred.
The inorganic fillers may be used alone or in combination of two or more of the above.

The average particle size of the inorganic filler is preferably 0.1 μm or more and 200 μm or less, more preferably 0.5 μm or more and 150 μm or less, and even more preferably 1 μm or more and 110 μm or less.
It is also preferable to use, for example, a small particle size filler having an average particle size of 0.1 μm or more and 5 μm or less in combination with a large particle size filler having an average particle size of more than 5 μm and 200 μm or less in combination as the inorganic filler. By using inorganic fillers with different average particle sizes, the filling rate of the inorganic filler in the heat dissipating resin sheet can be increased.
The average particle size of the inorganic filler can be measured by observation using an electron microscope, etc. More specifically, for example, the particle sizes of 50 arbitrary thermally conductive fillers can be measured using an electron microscope or an optical microscope, and the average value (arithmetic mean value) can be regarded as the average particle size.
When the inorganic filler is, for example, an agglomerated particle as described above, the average particle size of the agglomerated particles may be within the above range.

The content of the inorganic filler is not particularly limited, but from the viewpoint of improving the heat dissipation, it is, for example, 30 mass% or more, preferably 50 mass% or more, more preferably 70 mass% or more, and even more preferably 85 mass% or more in the heat dissipation resin sheet. In the present invention, even if the content of the inorganic filler is increased, the flexibility of the heat dissipation resin sheet can be prevented from being impaired by using specific components in the epoxy resin and the curing agent as described above.
The content of the inorganic filler is not particularly limited, but in order to contain a certain amount or more of the epoxy resin and the cyanate ester compound, the content is 98% by mass or less, preferably 96% by mass or less, more preferably 95% by mass or less, and even more preferably 93% by mass or less.

(Cure Accelerator)
The heat dissipating resin sheet of the invention may contain a curing accelerator. By containing a curing accelerator, the curing property of the heat dissipating resin sheet of the invention can be enhanced. The curing accelerator is not particularly limited, and examples thereof include imidazole-based curing accelerators and tertiary amine-based curing accelerators. Among them, it is preferable to use an imidazole-based curing accelerator. Examples of the imidazole-based curing accelerator include 1-cyanoethyl-2-phenylimidazole in which the 1-position of imidazole is protected with a cyanoethyl group, and imidazole-based curing accelerators in which basicity is protected with isocyanuric acid. Examples of commercially available products include 2MA-OK, 2MZ, 2MZ-P, 2PZ, 2PZ-PW, 2P4MZ, C11Z-CNS, 2PZ-CN, 2PZ-CNS, 2PZCNS-PW, 2MZ-A, 2MZA-PW, C11Z-A, 2E4MZ-A, 2MAOK-PW, 2PZ-OK, 2MZ-OK, 2PHZ, 2PHZ-PW, 2P4MHZ, 2P4MHZ-PW, 2E4MZ-BIS, VT, VT-OK, MAVT, and MAVT-OK (all manufactured by Shikoku Chemical Industry Co., Ltd.).
These curing accelerators may be used alone or in combination of two or more.
The content of the curing accelerator is, for example, 0.1 parts by mass or more and 10 parts by mass or less, preferably 0.2 parts by mass or more and 5 parts by mass or less, and more preferably 0.5 parts by mass or more and 3 parts by mass or less, relative to 100 parts by mass of the total amount of the epoxy resin having a mesogenic skeleton and the cyanate ester compound.

(Coupling Agent)
The heat dissipating resin sheet of the present invention may contain a coupling agent. Examples of the coupling agent include a silane coupling agent and a titanium coupling agent, and the silane coupling agent is preferred.
As the silane coupling agent, known ones can be used without any particular limitation, and examples thereof include dimethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, n-decyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane.
The silane coupling agents may be used alone or in combination of two or more kinds.
By including a silane coupling agent in the heat dissipating resin sheet, the inorganic filler can be easily dispersed, and as a result, the inorganic filler can be highly packed, resulting in high thermal conductivity.
The content of the coupling agent in the heat dissipating resin sheet is, for example, 0.1 mass % or more and 10 mass % or less, preferably 0.3 mass % or more and 5 mass % or less, and more preferably 0.5 mass % or more and 3 mass % or less, based on the total amount of the heat dissipating resin sheet.

[Other ingredients]
In addition to the above components, the heat dissipating resin sheet of the present invention may contain other additives such as a flame retardant, an antioxidant, a tackifier, a plasticizer, a thixotropy imparting agent, a colorant, etc. In addition, a solvent may be blended into the heat dissipating resin sheet in its manufacturing method, and it is preferable that the blended solvent partly remains in the heat dissipating resin sheet.

As described in the manufacturing method below, the heat dissipation resin sheet of the present invention is made of a curable resin composition containing an epoxy resin having a mesogenic skeleton and a cyanate ester compound, and may be uncured or semi-cured and in a B-stage state. When the heat dissipation resin sheet is in an uncured or B-stage state, it has high adhesion to other members and can be adhered to other members with high adhesive strength.

[Thickness]
The thickness of the heat dissipation resin sheet is not particularly limited, but is, for example, 10 μm or more and 500 μm or less. If the thickness is 10 μm or more, a certain level of heat dissipation can be ensured, and if the thickness is 500 μm or less, it is easy to make the electronic device to which the heat dissipation resin sheet is applied, such as a circuit board or a semiconductor device, thin. The thickness of the heat dissipation resin sheet is preferably 80 μm or more, more preferably 100 μm or more, and preferably 400 μm or less, more preferably 260 μm or less.

[Thermal conductivity]
The thermal conductivity of the heat dissipation resin sheet is preferably 7 W/(m·K) or more. When the thermal conductivity is 7 W/(m·K) or more, the heat dissipation is good. In addition, from the viewpoint of heat dissipation, the thermal conductivity is more preferably 8 W/(m·K) or more, and even more preferably 9 W/(m·K) or more. As described above, when the thermal conductivity is increased, the heat dissipation is excellent, and when used as a circuit board or a board with built-in components, the heat generated by the electronic components mounted on the circuit board or the electronic components embedded inside the heat dissipation resin sheet can be efficiently released to the outside. In addition, the upper limit of the thermal conductivity of the heat dissipation resin sheet is not particularly limited, but in practical use, it is about 30 W/(m·K).
The thermal conductivity of the heat dissipating resin sheet can be determined as described in the examples described later.

(Method of manufacturing heat dissipation resin sheet)
The heat dissipation resin sheet can be obtained by forming the curable resin composition into a sheet. The curable resin composition can be obtained by mixing an epoxy resin having a mesogenic skeleton, a cyanate ester compound having a melting point of 40° C. or less, and optionally blending a resin other than the epoxy resin having a mesogenic skeleton, a curing agent other than the cyanate ester compound, an inorganic filler, a curing accelerator, a coupling agent, and other additives other than these. The curable resin composition may also be diluted with a dilution solvent such as an organic solvent by adding the dilution solvent.

The method for forming the curable resin composition into a sheet is not particularly limited, but for example, the curable resin composition may be applied or laminated on a support such as a release sheet, metal foil, or substrate, and dried by heating or the like as necessary to form the composition into a sheet. Note that the term "sheet-like" or "sheet" refers to something that is thin and flat, with a thickness that is small relative to its length and width, and the concept of a sheet also includes something that is formed into a film or layer on another member such as a support.

(How to use the heat dissipation resin sheet)
The heat dissipating resin sheet may be cured and used as a cured product for various purposes. The heat dissipating resin sheet may be laminated on an adherend such as a metal base plate or other substrate in the uncured or semi-cured state described above, and then cured to be adhered to the adherend.
The heat dissipation resin sheet can be used for various applications requiring heat dissipation, but is preferably used as a heat dissipation resin sheet for electronic devices, and more preferably used in semiconductor devices. The semiconductor device is preferably a power module. The power module is used, for example, in inverters. The power module is used, for example, in industrial equipment such as elevators and uninterruptible power supplies (UPS), but the applications are not particularly limited.
More specifically, the heat dissipation resin sheet may be used as a part of a circuit board, or as a sealant for electronic components for embedding electronic components such as semiconductor chips inside. Among these, it is preferable to use it as a sealant.

When used as the above-mentioned sealing material, electronic components may be embedded inside the heat dissipation resin sheet. Specifically, the heat dissipation resin sheet may be laminated on one side of a support to which electronic components or electronic components and a substrate are fixed, and the heat dissipation resin sheet may be laminated on the support while embedding the electronic components or electronic components and a substrate inside the heat dissipation resin sheet. The heat dissipation resin sheet with the electronic components embedded therein as described above is cured by heating to become a cured product, and may be used, for example, as a substrate with built-in components.
The heat dissipating resin sheet with the electronic components embedded therein may be peeled off from the support as appropriate, and then laminated onto another member, such as another substrate, and then cured.

The heating temperature when curing the heat dissipation resin sheet is not particularly limited, but may be, for example, in the range of 70°C to 240°C, preferably 120°C to 220°C, and more preferably 160°C to 200°C, and the heating time may be, for example, 5 minutes to 300 minutes, preferably 10 minutes to 250 minutes, and more preferably 15 minutes to 200 minutes. When heating for curing, appropriate pressure may be applied, for example, the sheet may be heated and cured under pressurized or negative pressure, which makes it easier to adhere to other members with high adhesive strength when cured.

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

The methods for measuring and evaluating each physical property are as follows.
[Melting point]
The melting point of the cyanate ester compound was measured using a differential scanning calorimeter (DSC) (apparatus name "EXTEAR DSC6100", manufactured by SII NanoTechnology Inc.) at a temperature increase rate of 10° C./min. The value measured as the temperature of the endothermic peak was taken as the melting point.

[Sheet property evaluation]
The heat dissipation resin sheets obtained in each of the Examples and Comparative Examples, each having a width of 200 mm and a length of 300 m, were wrapped around a cylindrical core having a diameter of 90 mm in an environment of 25° C., and the sheet properties were evaluated based on the presence or absence of cracks. Sheets that did not crack were rated as “A”, and sheets that did crack were rated as “B”.

[Thermal conductivity]
The heat dissipation resin sheets obtained in each Example and Comparative Example were press-cured at 100°C for 1 hour and then at 200°C for 1 hour while maintaining a pressure of 1 MPa in a vacuum press. The thermal conductivity of the cured heat dissipation resin sheet in the thickness direction was measured using a laser flash thermal constant measurement device (NETZSCH "LFA447"). Thermal conductivity of 7 W/(m K) or more was evaluated as "A", and thermal conductivity of less than 7 W/(m K) was evaluated as "B".

The components used in the examples and comparative examples are as follows.
(Epoxy resin)
Epoxy A: an epoxy resin having a mesogenic skeleton of the following structure, molecular weight 682
Epoxy B: "YL6121HA", manufactured by Mitsubishi Chemical Corporation, an epoxy resin having a mesogen skeleton of the following structure, molecular weight 326
Epoxy C: "YD-127", manufactured by Nippon Steel Chemical Co., Ltd., bisphenol A type epoxy resin

(Hardening agent)
Cyanate A: "P-201" manufactured by Mitsubishi Gas Chemical Company, Inc., a cyanate ester compound having the following structure, molecular weight 264, melting point: 29°C
Cyanate B: "TA", manufactured by Mitsubishi Gas Chemical Company, a cyanate ester compound having the following structure, molecular weight 278, melting point: 80° C.

Acid anhydride: "Rikacid MH-700", New Japan Chemical Co., Ltd. Curing accelerator: "2PHZ-PW", Shikoku Chemical Industry Co., Ltd. Coupling agent: "KBM-573", Shin-Etsu Chemical Co., Ltd., N-phenyl-3-aminopropyltrimethoxysilane

(Inorganic filler)
Alumina 1: "AA-03" manufactured by Sumitomo Chemical Co., Ltd., polyhedral alumina, average particle size 0.3 μm
Alumina 2: "AA-3" manufactured by Sumitomo Chemical Co., Ltd., polyhedral alumina, average particle size 3 μm
Alumina 3: "AA-18", manufactured by Sumitomo Chemical Co., Ltd., polyhedral alumina, average particle size 18 μm

[Example 1]
A dilution of the thermosetting resin composition was obtained by adding each component shown in Table 1 and a solvent, methyl ethyl ketone, so that the solid content was 80 mass %. The obtained dilution of the thermosetting resin composition was applied onto a support made of a release PET sheet and dried at 90°C for 10 minutes to form a thin film of the thermosetting resin composition on the release PET sheet, thereby obtaining a heat dissipation resin sheet having a thickness of 100 µm.

[Examples 2 to 4, Comparative Examples 1 to 3]
The same procedure as in Example 1 was carried out except that the composition was changed as shown in Table 1.

As shown in the above examples, the heat dissipation resin sheet of each example contained an epoxy resin having a mesogenic skeleton and a cyanate ester compound having a melting point of 40°C or less, and was therefore able to maintain high thermal conductivity while also having good flexibility.
In contrast, Comparative Example 1 contained an epoxy resin having a mesogen skeleton and a cyanate ester compound, and thus was able to increase the thermal conductivity, but was unable to improve flexibility because the melting point of the cyanate ester compound was higher than 40° C. In addition, Comparative Examples 2 and 3 did not contain either an epoxy resin having a mesogen skeleton or a cyanate ester compound, and therefore were unable to achieve a sufficiently high thermal conductivity.

Claims (6)

A heat dissipating resin sheet containing an epoxy resin with a mesogenic skeleton and a cyanate ester compound with a melting point of 40°C or less. The heat dissipation resin sheet according to claim 1, wherein the cyanate ester compound has a skeleton containing an aromatic ring. The heat dissipation resin sheet according to claim 1, wherein the molecular weight of the cyanate ester compound is 500 or less. The heat dissipation resin sheet according to claim 1, wherein the epoxy resin has a biphenyl skeleton. The heat dissipation resin sheet according to claim 1, which contains an inorganic filler. A cured product of the heat dissipation resin sheet according to any one of claims 1 to 5.