JP2023048546A - Thermally conductive adhesive sheet - Google Patents

Abstract

[Problem] To provide a thermally conductive adhesive sheet capable of forming a cured sheet having excellent adhesion to an object to be bonded when press-bonded at a low pressure, and having excellent thermal conductivity of the formed cured sheet. A thermally conductive adhesive sheet having a thermally conductive sheet and an adhesive layer disposed on at least one surface of the thermally conductive sheet, wherein the thermally conductive sheet comprises a first thermosetting The adhesive layer contains a compound and a first thermally conductive filler, the adhesive layer contains a second thermosetting compound and a second thermally conductive filler, and the surface roughness Ra of the thermally conductive adhesive sheet on the adhesive layer side is 2.5 μm or more and satisfies predetermined requirements for deformation rate. [Selection figure] None

Description

The present invention relates to a thermally conductive adhesive sheet.

In recent years, electronic devices using semiconductor elements are rapidly becoming more sophisticated and smaller. Along with this, the amount of heat generated from semiconductor elements in electronic devices is increasing, and the need to release the generated heat to the outside is increasing.
A known method for releasing heat generated inside an electronic device to the outside is to use a heat sink. Also, in order to efficiently transfer heat to the heat sink, a method of bonding the device and the heat sink with a thermally conductive adhesive sheet is known. Such a thermally conductive adhesive sheet is required to have excellent insulation properties, excellent thermal conductivity, and excellent adhesiveness to an object to be adhered.

For example, in Patent Document 1, a resin composition layer containing a thermosetting compound and a filler, and an arithmetic mean surface roughness of a surface that is disposed on at least one surface of the resin composition layer and does not face the resin composition layer A multilayer resin sheet (thermally conductive adhesive sheet) having an adhesive layer having an Ra of 1.5 μm or less is disclosed.

JP 2019-014261 A

In recent years, in terms of heat dissipation, power modules have shifted to the transfer mold type, and a process of directly thermocompressing a power module device and a thermally conductive adhesive sheet may be adopted. In the case of the above process, it is required to reduce the pressure during thermocompression bonding in order to reduce the load on the power module device. That is, the requirements for a thermally conductive adhesive sheet are that it is possible to form a cured sheet that has excellent adhesion to an object to be bonded even when crimped at a low pressure (for example, 10 MPa), and that the formed cured sheet has thermal conductivity. It is to be superior to
The present inventors have studied the thermally conductive adhesive sheet disclosed in Patent Document 1, and have found that the resulting cured sheet does not always have sufficient thermal conductivity and adhesiveness, and that there is room for improvement. I found out.

Therefore, the present invention provides a thermally conductive adhesive sheet that can form a cured sheet having excellent adhesion to an object to be bonded when crimped at a low pressure, and that the formed cured sheet has excellent thermal conductivity. Make it an issue.

The present inventor has completed the present invention as a result of intensive studies in order to solve the above problems. That is, the inventors have found that the above problems can be solved by the following configuration.

[1] A thermally conductive adhesive sheet comprising a thermally conductive sheet and an adhesive layer disposed on at least one surface of the thermally conductive sheet,
The thermally conductive sheet comprises a first thermosetting compound and a first thermally conductive filler,
The adhesive layer contains a second thermosetting compound and a second thermally conductive filler,
The surface roughness Ra of the adhesive layer side of the thermally conductive adhesive sheet is 2.5 μm or more,
A thermally conductive adhesive sheet that satisfies requirement 1 below.
Requirement 1: The thickness of the thermally conductive adhesive sheet is X, and pressure is applied to the adhesive layer side surface of the thermally conductive adhesive sheet at a pressure of 10 MPa, a temperature of 180 ° C., and a treatment time of 5 minutes. The deformation rate calculated by 100×(XY)/X is 10% or more, where Y is the thickness of the cured sheet obtained by heat treatment at 180° C. for 90 minutes.
[2] The thermally conductive adhesive sheet according to [1], wherein the deformation rate is 20% or more.
[3] The thermally conductive adhesive sheet according to [1] or [2], wherein the second thermally conductive filler satisfies formula (1) described below.
[4] The thermally conductive adhesive sheet according to any one of [1] to [3], wherein the second thermally conductive filler has a particle size of 2.5 to 20 μm.
[5] The thermally conductive adhesive sheet according to any one of [1] to [4], wherein the first thermally conductive filler is agglomerated boron nitride having a particle size of 40 μm or more.
[6] the first thermally conductive filler is agglomerated boron nitride having a particle size of 40 μm or more;
The thermally conductive adhesive sheet according to any one of [1] to [5], wherein the second thermally conductive filler has a particle size of 2.5 to 20 μm.
[7] The thermally conductive adhesive sheet according to any one of [1] to [6], wherein the first thermosetting compound and the second thermosetting compound contain an epoxy compound.
[8] The thermally conductive adhesive sheet according to any one of [1] to [7], wherein the first thermosetting compound and the second thermosetting compound contain a phenol compound.

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to provide a thermally conductive adhesive sheet that can form a cured sheet that has excellent adhesion to an object to be bonded when press-bonded at a low pressure, and that the formed cured sheet has excellent thermal conductivity. .

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows an example of the embodiment of the heat conductive adhesive sheet of this invention. FIG. 4 is a diagram for explaining the state of the second thermally conductive filler when bonding the thermally conductive adhesive sheet of the present invention and an object to be bonded. FIG. 4 is a diagram for explaining the state of the second thermally conductive filler when bonding the thermally conductive adhesive sheet of the present invention and an object to be bonded. FIG. 4 is a diagram for explaining the state of the second thermally conductive filler when bonding the thermally conductive adhesive sheet of the present invention and an object to be bonded.

The present invention will be described in detail below.
The description of the constituent elements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

Hereinafter, the meaning of each description in this specification is expressed.
In the present specification, a numerical range represented by "to" means a range including the numerical values before and after "to" as lower and upper limits.
In this specification, when two or more kinds of a certain component are present, the "content" of the component means the total content of the two or more kinds of components.

<Heat conductive adhesive sheet>
The thermally conductive adhesive sheet of the present invention is a thermally conductive adhesive sheet comprising a thermally conductive sheet and an adhesive layer disposed on at least one surface of the thermally conductive sheet,
the thermally conductive sheet comprises a first thermosetting compound and a first thermally conductive filler;
The adhesive layer contains a second thermosetting compound and a second thermally conductive filler, the surface roughness Ra of the thermally conductive adhesive sheet on the adhesive layer side is 2.5 μm or more, and Requirement 1 described later is satisfied.

The thermally conductive adhesive sheet of the present invention can form a cured sheet having excellent adhesion to an object to be bonded when pressed under low pressure, and the formed cured sheet has excellent thermal conductivity. In addition, hereinafter, the excellent adhesiveness between the adhesive object and the formed cured sheet is simply referred to as "excellent adhesiveness", and the excellent thermal conductivity of the formed cured sheet is simply referred to as "thermal conductivity. It is also said to be excellent.
The present inventor presumes the mechanism by which the thermally conductive adhesive sheet of the present invention is excellent in adhesiveness and thermal conductivity as follows.

Since the thermally conductive sheet and the adhesive layer in the thermally conductive adhesive sheet of the present invention contain the first thermally conductive filler and the second thermally conductive filler, respectively, the thermally conductive sheet and the adhesive layer have high thermal conductivity.
The surface roughness Ra of the adhesive layer side of the thermally conductive adhesive sheet of the present invention is 2.5 μm or more, and this surface roughness is mainly derived from the second thermally conductive filler contained in the adhesive layer. It is thought that this is caused by the convex portion. Here, when the thermally conductive adhesive sheet of the present invention and an object to be bonded are pressure-bonded, the object to be bonded and the second thermally conductive filler are likely to come into contact with each other, and the second thermally conductive filler is formed on the surface of the cured sheet. 2 Increases the likelihood of the presence of thermally conductive fillers. As a result, the thermally conductive adhesive sheet of the present invention is considered to have excellent thermal conductivity.
On the other hand, the deformation rate of the thermally conductive adhesive sheet of the present invention measured by the method described later is 10% or more. When the deformation rate is 10% or more, the adhesive layer and the thermally conductive sheet are easily deformed during pressure bonding even when the surface roughness is as described above, and the interface between the adhesive object and the cured sheet to be formed is easily deformed. It is considered that gaps are unlikely to occur. As a result, the thermally conductive adhesive sheet of the present invention is considered to be excellent in adhesiveness as well.
Furthermore, when the deformation ratio is 10% or more, the second thermally conductive filler is pushed into the thermally conductive sheet (see FIGS. 2 to 4 described later), and the second thermally conductive filler and the first thermally conductive It is thought that contact with the filler is likely to occur. It is believed that the contact forms a thermally conductive path between the adhesive layer and the thermally conductive sheet, resulting in superior thermal conductivity.

Embodiments of the thermally conductive adhesive sheet of the present invention (hereinafter also simply referred to as "thermally conductive adhesive sheet") will be described below with reference to the drawings. Note that the thermally conductive adhesive sheet should not be construed as being limited by the embodiments shown below.

FIG. 1 is a cross-sectional view showing an example of an embodiment of a thermally conductive adhesive sheet. In addition, FIG. 1 schematically shows a part of the thermally conductive adhesive sheet.
As shown in FIG. 1 , the thermally conductive adhesive sheet 10 has a thermally conductive sheet 12 and an adhesive layer 14 .
The thermally conductive sheet 12 consists of a first thermosetting compound 12a and a first thermally conductive filler 12b. The adhesive layer 14 is composed of a second thermosetting compound 14a and a second thermally conductive filler 14b.
The surface roughness Ra of the thermally conductive adhesive sheet 10 on the adhesive layer 14 side is 2.5 μm or more. The unevenness generated on the surface of the adhesive layer 14 side is formed by the second thermally conductive filler 14b with respect to the convex portion, and the second thermally conductive filler 14b is formed on the surface of the thermally conductive adhesive sheet 10. part is exposed.
In addition, the thermally conductive adhesive sheet 10 satisfies Requirement 1, which will be described later.

In FIG. 1, the thermally conductive adhesive sheet 10 has an adhesive layer 14 only on one surface of the thermally conductive sheet 12. You may have the adhesion layer 14 on both surfaces. When the adhesive layer 14 is provided on both sides, the surface roughness Ra of both sides of the thermally conductive adhesive sheet 10 is 2.5 μm or more.
The surface roughness Ra of the adhesive layer 14 side of the thermally conductive adhesive sheet 10 is 2.5 μm or more, but 3.0 to 15.0 μm is preferable in terms of excellent adhesion and thermal conductivity. 0 to 10.0 μm is more preferable, and 5.0 to 7.5 μm is even more preferable.
In the present specification, the surface roughness Ra is based on JIS B 0601-2001 after observation at a magnification of 100 using a laser microscope (VK-9710) manufactured by Keyence Corporation. A value calculated by the attached analysis application. Say.

In FIG. 1, the unevenness on the surface of the thermally conductive adhesive sheet 10 on the adhesive layer 14 side is a mode in which the protrusions are formed due to the second thermally conductive filler 14b. The first thermally conductive filler 12b of the adhesive sheet 12 may contribute to the irregularities on the surface of the adhesive layer 14 side. In other words, although the interface between the thermally conductive sheet 12 and the adhesive layer 14 is flat in FIG. It may appear as unevenness on the surface of the adhesive sheet 10 on the side of the adhesive layer 14 .
In FIG. 1, the second thermally conductive filler 14b is partially exposed on the surface of the thermally conductive adhesive sheet 10 in the convex portion, but all of the second thermally conductive filler 14b is It may be exposed or may not be entirely exposed.

In FIG. 1, the first thermally conductive filler 12b and the second thermally conductive filler 14b have different particle sizes, but the relationship between the particle sizes is not particularly limited. In particular, the particle size of the first thermally conductive filler 12b is preferably larger than the particle size of the second thermally conductive filler 14b. The particle size of the first thermally conductive filler 12b and the second thermally conductive filler 14b will be described in detail later.

In FIG. 1, the thermally conductive sheet 12 is composed of the first thermosetting compound 12a and the first thermally conductive filler 12b, but the thermally conductive sheet 12 contains components other than the above components. You can Details will be described later.
In FIG. 1, the adhesive layer 14 is composed of the second thermosetting compound 14a and the second thermally conductive filler 14b, but the adhesive layer 14 may contain components other than those described above. . Details will be described later.

[Requirement 1]
The thermally conductive adhesive sheet satisfies Requirement 1 below.
Requirement 1: Let the thickness of the thermally conductive adhesive sheet be X, and apply pressure to the adhesive layer side surface of the thermally conductive adhesive sheet at a pressure of 10 MPa, a temperature of 180 ° C., a treatment time of 5 minutes, and then a temperature of 180 ° C. The deformation rate calculated by 100×(XY)/X is 10% or more, where Y is the thickness of the cured sheet obtained by heat treatment for 90 minutes.
The thickness X of the thermally conductive adhesive sheet and the thickness Y of the cured sheet are measured by preparing a cross-section perpendicular to the film surface of the sheet and observing the cross-section of the sheet with a scanning electron microscope (SEM). More specifically, the thickness is measured at arbitrary 10 points in observation of the cross section by SEM, and the thickness is calculated by averaging the thickness.

The thickness X of the thermally conductive adhesive sheet may be measured before applying pressure, but if it is difficult to prepare a cross section due to deformation, heat treatment (for example, 180 ° C. for 90 minutes) is performed to obtain a cured sheet. After that, a cross section of the cured sheet may be produced, and the thickness of the cured sheet may be used as the thickness X of the thermally conductive sheet.
Moreover, the thickness Y of the cured sheet may be measured by preparing a cross section after peeling from the adhesion object, or by preparing a cross section while attached to the adhesion object.
The preparation of the cross section may be performed according to known methods, for example, a method of preparing a cross section with a cross-section polisher after cleaving a thermally conductive adhesive sheet or a cured sheet, and a method of preparing a thin piece with a microtome.

In this specification, the thickness X of the thermally conductive adhesive sheet is obtained by performing a heat treatment at 180° C. for 90 minutes to form a cured sheet, embedding both sides of the thermally conductive adhesive sheet with a resin, and measuring the thickness with a microtome. The thickness measured by the above method is used using a sample whose cross section is cut with a cross section polisher and the cross section is prepared with a cross section polisher.
In this specification, the thickness Y of the cured sheet is measured by the above method using a sample whose cross section is cut with a microtome and whose cross section is prepared with a cross-section polisher.

The thickness X is preferably 40 to 500 μm, more preferably 70 to 350 μm, even more preferably 100 to 250 μm.
The thickness Y is preferably 35 to 450 μm, more preferably 60 to 300 μm, even more preferably 90 to 220 μm.

The deformation rate is 10% or more, preferably 14% or more, more preferably 16% or more, and even more preferably 20% or more, from the viewpoint of excellent adhesiveness and thermal conductivity. Although the upper limit is not particularly limited, an example is 40%, preferably 30% or less.
The deformation rate can be adjusted by various means. For example, the type of the first thermosetting compound, the type and content of the first thermally conductive filler, the type of the second thermosetting compound, and the type and content of the second thermally conductive sheet, which will be described in detail later. You can adjust the quantity.

The thermally conductive sheet and the adhesive layer are described below.

[Thermal conductive sheet]
The thermally conductive sheet includes a first thermosetting compound and a first thermally conductive filler. The thermally conductive sheet may contain a curing accelerator, which will be described later, and other components.
The properties of each component and the thermally conductive sheet are described below.

(First thermosetting compound)
The first thermosetting compound is not particularly limited as long as it is a thermosetting resin.
The thermally conductive sheet may contain two or more first thermosetting compounds as a main agent and a curing agent.

The first thermosetting compound may be a polymer or a monomer.
Examples of the first thermosetting compound include epoxy compounds, oxetane compounds, (meth)acrylic compounds, benzoguanamine compounds, rosin-modified maleic acid compounds, rosin-modified fumaric acid compounds, melamine compounds, urea compounds, and phenolic compounds.
Among them, as the first thermosetting compound, an epoxy compound or an active hydrogen group-containing compound (preferably a phenol compound) is preferable, and an epoxy compound or a phenol compound is more preferable.
The epoxy compound and the active hydrogen group-containing compound are described below.

(epoxy compound)
An epoxy compound is a compound having at least one epoxy group (oxiranyl group) in one molecule.
The epoxy group is a group obtained by removing one or more hydrogen atoms (preferably one hydrogen atom) from an oxirane ring. If possible, the epoxy group may further have a substituent (linear or branched alkyl group having 1 to 5 carbon atoms, etc.).

The number of epoxy groups possessed by the epoxy compound is preferably 2 or more, more preferably 2 to 40, still more preferably 2 to 10, and particularly preferably 2, in one molecule.
The epoxy compound preferably has a molecular weight of 150 to 10,000, more preferably 150 to 1,000, and even more preferably 200 to 290.

The epoxy group content of the epoxy compound is preferably 2.0 to 20.0 mmol/g, more preferably 5.0 to 15.0 mmol/g, even more preferably 5.5 to 14.0 mmol/g.
In addition, the said epoxy group content intends the number of epoxy groups which 1g of epoxy compounds have.
The epoxy compound also preferably has an aromatic ring group (preferably an aromatic hydrocarbon ring group).

The epoxy compound may or may not exhibit liquid crystallinity.
That is, the epoxy compound may be a liquid crystal compound. In other words, it may be a liquid crystal compound having an epoxy group.

Among them, the epoxy compound is preferably polyhydroxy aromatic ring type glycidyl ether (polyhydroxy aromatic ring type epoxy compound).
The polyhydroxy aromatic ring type glycidyl ether is an aromatic ring having two or more (preferably 2 to 6, more preferably 2 to 3, still more preferably 2) hydroxyl groups as substituents, and the two or more hydroxyl groups are , is a compound having a structure obtained by glycidyl etherification.
The aromatic ring may be either an aromatic hydrocarbon ring or an aromatic hetero ring, and is preferably an aromatic hydrocarbon ring. The above aromatic rings may be polycyclic or monocyclic. The number of ring members of the aromatic ring is preferably 5 to 15, more preferably 6 to 12, and more preferably 6.
The aromatic ring may or may not have a substituent other than a hydroxyl group.
Examples of the polyhydroxy aromatic ring-type glycidyl ether include 1,3-phenylene bis(glycidyl ether).

Other epoxy compounds include, for example, compounds comprising at least partially rod-shaped structures (rod-shaped compounds) and compound discotic compounds comprising at least partially discotic structures.
In addition, the epoxy compound is a resin type, and the epoxy compound alone or the epoxy compound and other compounds (compounds containing active hydrogen groups such as phenol compounds and amine compounds, and/or acid anhydrides, etc.) are polymerized. It may be a resin (epoxy resin) obtained by

When the first thermosetting compound contains an epoxy compound, the content thereof is preferably 1 to 40% by mass, more preferably 3 to 30% by mass, and 6 to 20% by mass, based on the total mass of the thermally conductive sheet. % is more preferred.
An epoxy compound may be used individually by 1 type, and may use 2 or more types.

(active hydrogen group-containing compound)
The active hydrogen group-containing compound is a compound having one or more (preferably two or more, more preferably 2 to 10) groups having active hydrogen (active hydrogen groups).
Examples of active hydrogen groups include hydroxyl groups, primary or secondary amino groups, and mercapto groups, among which hydroxyl groups are preferred.
The active hydrogen group-containing compound is preferably a polyol having 2 or more (preferably 3 or more, more preferably 3 to 6) hydroxyl groups.

Among them, the active hydrogen group-containing compound used in combination with the epoxy compound is preferably a phenol compound.
A phenolic compound is a compound having one or more (preferably two or more, more preferably three or more, still more preferably three to six) phenolic hydroxyl groups.

The phenol compound preferably has a triazine skeleton.
The phenol compound "having a triazine skeleton" means that the phenol compound has one or more (preferably 1 to 5) triazine ring groups.

Other active hydrogen group-containing compounds include, for example, benzenepolyols such as benzenetriol, biphenylaralkyl-type phenolic resins, phenolic novolak resins, cresol novolak resins, aromatic hydrocarbon-formaldehyde resin-modified phenolic resins, dicyclopentadiene phenol addition type Resins, phenol aralkyl resins, polyhydric phenol novolac resins synthesized from polyhydric hydroxy compounds and formaldehyde, naphthol aralkyl resins, trimethylolmethane resins, tetraphenylolethane resins, naphthol novolak resins, naphthol phenol cocondensation novolac resins, naphthol Cresol cocondensed novolak resin, biphenyl-modified phenol resin, biphenyl-modified naphthol resin, aminotriazine-modified phenol resin, or alkoxy group-containing aromatic ring-modified novolac resin is also preferable.

The lower limit of the hydroxyl group content of the active hydrogen group-containing compound is preferably 3.0 mmol/g or more, more preferably 4.0 mmol/g or more. The upper limit is preferably 25.0 mmol/g or less, more preferably 20.0 mmol/g or less.
In addition, the said hydroxyl group content intends the number of hydroxyl groups (preferably phenolic hydroxyl groups) which 1g of active hydrogen group containing compounds have.
Moreover, the active hydrogen group-containing compound may have an active hydrogen-containing group (such as a carboxylic acid group) capable of undergoing a polymerization reaction with the epoxy compound, in addition to the hydroxyl group. The lower limit of the active hydrogen content (total content of hydrogen atoms in hydroxyl groups, carboxylic acid groups, etc.) of the active hydrogen group-containing compound is preferably 3.0 mmol/g or more, more preferably 4.0 mmol/g or more. The upper limit is preferably 25.0 mmol/g or less, more preferably 20.0 mmol/g or less.
In addition, the content of the said active hydrogen intends the number of the active hydrogen atoms which 1g of active-hydrogen-group containing compounds have.

The upper limit of the molecular weight of the active hydrogen group-containing compound is preferably 2000 or less, more preferably 1500 or less, and even more preferably 1000 or less. 110 or more are preferable and, as for a lower limit, 300 or more are more preferable.

When the thermally conductive sheet contains an active hydrogen group-containing compound, the content thereof is preferably 1 to 40% by mass, more preferably 3 to 30% by mass, more preferably 5 to 20% by mass, based on the total mass of the thermally conductive sheet. % by mass is more preferred.
The active hydrogen group-containing compounds may be used alone or in combination of two or more.

When the first thermosetting compound contains an epoxy compound and an active hydrogen group-containing compound, the ratio of the content of the epoxy compound to the content of the active hydrogen group-containing compound is The equivalent ratio (“number of epoxy groups”/“number of active hydrogen groups”) to active hydrogen groups (preferably hydroxyl groups, more preferably phenolic hydroxyl groups) of the hydrogen group-containing compound is 30/70 to 70/30. is preferred, an amount of 40/60 to 60/40 is more preferred, and an amount of 45/55 to 55/45 is even more preferred.
When the first thermosetting compound contains an epoxy compound and/or an active hydrogen group-containing compound, the total content of the epoxy compound and the active hydrogen group-containing compound is 20 to 20 to all the thermosetting compound components. 100% by mass is preferable, 60 to 100% by mass is more preferable, and 90 to 100% by mass is even more preferable.

A 1st thermosetting compound may be used individually by 1 type as a thermosetting component, and may use 2 or more types.

(First thermally conductive filler)
The first thermally conductive filler preferably contains a material with high thermal conductivity.
Materials contained in the first thermally conductive fillers include inorganic materials, and the first thermally conductive fillers are preferably made of inorganic materials.
Inorganic materials include, for example, silicon oxide (silica, _SiO2 ), aluminum oxide (alumina, _Al2O3 ), aluminum nitride ( _AlN ), and boron nitride (BN). Among these, alumina, aluminum nitride, or boron nitride is preferable, alumina or boron nitride is more preferable, and boron nitride is even more preferable, from the viewpoint of thermal conductivity.
The crystal structure of the inorganic material is not particularly limited, and known structures can be used. For example, the crystal structure of boron nitride may be any of hexagonal system, cubic system, and rhombohedral system. Among them, the crystal structure of boron nitride is preferably a hexagonal system from the viewpoint of thermal conductivity.
The first thermally conductive filler may be in the form of composite particles made of a plurality of materials. For example, the first thermally conductive filler may be in the form of a core-shell structure in which the core and shell are made of different materials.

The shape of the first thermally conductive filler is not particularly limited, and may be spherical, columnar, plate-like, or scale-like, for example. Further, the first thermally conductive filler may be secondary particles (aggregated particles) formed by aggregating primary particles. Agglomerated particles are generally approximately spherical.
Among them, spherical particles or agglomerated particles are preferable, agglomerated particles are more preferable, and agglomerated particles made of boron nitride (aggregated boron nitride) are more preferable because they are superior to one or more of adhesiveness and thermal conductivity.

The particle size of the first thermally conductive filler is not particularly limited. Here, the particle diameter refers to the median diameter, and when using a commercially available product, the median diameter of the catalog value is adopted. When there is no catalog value, the median diameter measured using SEM or transmission electron microscope (TEM) is adopted.
The particle size of the first thermally conductive filler is preferably 20 μm or more, more preferably 40 μm or more, in terms of better thermal conductivity. Although the upper limit is not particularly limited, it may be 100 μm or less.
Also, the first thermally conductive filler is preferably agglomerated boron nitride having a particle size of 40 μm or more.

A 1st thermally conductive filler may be used individually by 1 type, and may be used in combination of multiple types.
The content of the first thermally conductive filler is preferably 30 to 90% by mass, more preferably 50 to 85% by mass, and even more preferably 65 to 80% by mass, relative to the total mass of the thermally conductive sheet.
The content of the first thermally conductive filler is preferably 20 to 90% by volume, more preferably 40 to 80% by volume, even more preferably 50 to 70% by volume, relative to the total volume of the thermally conductive sheet.

(Curing accelerator)
The thermally conductive sheet may contain a curing accelerator.
The type of curing accelerator to be used may be appropriately determined.
Examples of curing accelerators include triarylphosphines, tetraarylphosphonium salts, boron trifluoride amine complexes, and compounds described in paragraph 0052 of JP-A-2012-67225. In addition, 2-methylimidazole (trade name; 2MZ), 2-undecylimidazole (trade name; C11-Z), 2-heptadecylimidazole (trade name; C17Z), 1,2-dimethylimidazole (trade name) ; 1.2DMZ), 2-ethyl-4-methylimidazole (trade name; 2E4MZ), 2-phenylimidazole (trade name; 2PZ), 2-phenyl-4-methylimidazole (trade name; 2P4MZ), 1-benzyl -2-methylimidazole (trade name; 1B2MZ), 1-benzyl-2-phenylimidazole (trade name; 1B2PZ), 1-cyanoethyl-2-methylimidazole (trade name; 2MZ-CN), 1-cyanoethyl-2- undecylimidazole (trade name; C11Z-CN), 1-cyanoethyl-2-phenylimidazolium trimellitate (trade name; 2PZCNS-PW), 2,4-diamino-6-[2'-methylimidazolyl-(1 ')]-ethyl-s-triazine (trade name; 2MZ-A), 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine (trade name; C11Z -A), 2,4-diamino-6-[2′-ethyl-4′-methylimidazolyl-(1′)]-ethyl-s-triazine (trade name; 2E4MZ-A), 2,4-diamino- 6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazineisocyanuric acid adduct (trade name; 2MA-OK), 2-phenyl-4,5-dihydroxymethylimidazole (trade name; 2PHZ- PW), 2-phenyl-4-methyl-5-hydroxymethylimidazole (trade name; 2P4MHZ-PW), 1-cyanoethyl-2-phenylimidazole (trade name; 2PZ-CN), 2,4-diamino-6- [2′-methylimidazolyl-(1′)]-ethyl-s-triazine (trade name; 2MZA-PW) and 2,4-diamino-6-[2′-methylimidazolyl-(1′)]- Examples include imidazole-based curing accelerators such as ethyl-s-triazine isocyanuric acid adduct (trade name: 2MAOK-PW) (both manufactured by Shikoku Kasei Kogyo Co., Ltd.). Furthermore, the compounds described in paragraph 0052 of JP-A-2004-43405 can also be mentioned as triarylphosphine-based curing accelerators. Examples of phosphorus-based curing accelerators in which triphenylborane is added to triarylphosphine include compounds described in paragraph 0024 of JP-A-2014-5382. Examples of tetraarylphosphonium salts include compounds described in paragraph 0010 of JP-A-2003-020326 and compounds described in paragraph 0021 of JP-A-08-169892.
A single curing accelerator may be used alone, or two or more curing accelerators may be used.
For example, when the first thermosetting compound contains an epoxy compound, the content of the curing accelerator is preferably 0.01 to 10% by mass, preferably 0.10 to 5% by mass, based on the total amount of the epoxy compound. is more preferred.

(Other ingredients)
The thermally conductive sheet may contain other components than those mentioned above.
Other components include, for example, catalysts, dispersants, surface modifiers, and polymerization initiators (photopolymerization initiators, thermal polymerization initiators, etc.).

(Properties of thermally conductive sheet)
-Thickness-
The thickness of the thermally conductive sheet is preferably 30 to 500 μm, more preferably 50 to 300 μm, even more preferably 100 to 200 μm, from the standpoint that at least one of adhesion and thermal conductivity is excellent.
The thickness is calculated by observing the cross section of the thermally conductive adhesive sheet in accordance with the thickness measurement method described in Requirement 1 above. The thermally conductive sheet and the adhesive layer can be distinguished from each other by the elemental contrast derived from the difference in the contained thermosetting compound and/or thermally conductive filler, and the difference in the shape of the thermally conductive filler. good.

-The state of the thermally conductive sheet-
In general, the states of thermosetting compounds include A-stage, B-stage, and C-stage. Refer to JIS K6900:1994 for each stage.
In the present specification, the A stage refers to a state of being soluble and fusible in a specific solvent, and the B stage refers to a state in which the viscosity is 10 ⁴ Pa s to 10 at normal temperature (25 ° C.). At ¹⁰⁰ ° C., the viscosity is reduced from 5 Pa·s to 10 ² Pa·s to 10 ³ Pa·s. The viscosity is measured by dynamic viscoelasticity measurement (frequency of 1 Hz, load of 40 g, temperature increase rate of 3° C./min).
As for the state of the thermally conductive sheet, the A stage or the B stage is preferable, and the A stage is more preferable, in that the deformation rate described above can be adjusted within the preferable range.

[Adhesion layer]
The adhesive layer includes a second thermosetting compound and a second thermally conductive filler. The adhesive layer may contain a curing accelerator, which will be described later, and other components.
The properties of each component and the adhesive layer are described below.

(Second thermosetting compound)
The second thermosetting compound is not particularly limited as long as it is a thermosetting resin.
Examples and preferred aspects of the second thermosetting compound are the same as those of the first thermosetting compound, so description thereof is omitted. That is, the second thermosetting compound preferably contains a compound selected from the group consisting of epoxy compounds and phenol compounds.

(Second thermal conductive filler)
The second thermally conductive filler preferably contains a material with high thermal conductivity.
Materials contained in the second thermally conductive fillers include inorganic materials, and the second thermally conductive fillers are preferably made of inorganic materials.
Inorganic materials include, for example, silicon oxide (silica, _SiO2 ), aluminum oxide (alumina, _Al2O3 ), aluminum nitride ( _AlN ), and boron nitride (BN). Among these, alumina, aluminum nitride, or boron nitride is preferable, alumina or boron nitride is more preferable, and boron nitride is even more preferable, from the viewpoint of thermal conductivity.
The crystal structure, structure, shape, etc. of the inorganic material are the same as those of the first thermally conductive filler.
Among them, spherical alumina or agglomerated particles of boron nitride (aggregated boron nitride) are preferable, and agglomerated boron nitride is more preferable, because they are superior in one or more of adhesiveness and thermal conductivity.

The particle size of the second thermally conductive filler is not particularly limited. The definition of particle size is the same as that of the first thermally conductive filler.
The particle size of the second thermally conductive filler is preferably 2.5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm, in terms of superiority in one or more of adhesiveness and thermal conductivity. Although the upper limit is not particularly limited, it may be 100 μm or less, preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less.

The first thermally conductive filler and the second thermally conductive filler may be the same, but are preferably different. The difference between the first thermally conductive filler and the second thermally conductive filler may mean that the materials constituting the thermally conductive fillers are different, and the shape or particle size of the thermally conductive fillers may be different. In particular, it is preferable that at least the first thermally conductive filler and the second thermally conductive filler have different particle sizes. For example, it is also preferable that the particle size of the first thermally conductive filler is 40 μm or more, and the particle size of the second thermally conductive filler is 2.5 to 20 μm.
It is also preferable that the first thermally conductive filler is agglomerated boron nitride having a particle size of 40 μm or more, and the second thermally conductive filler has a particle size of 2.5 to 20 μm. is aggregated boron nitride having a particle size of 40 μm or more, and the second thermally conductive filler is more preferably aggregated boron nitride having a particle size of 2.5 to 20 μm.

In addition, the second thermally conductive filler preferably satisfies the following formula (1) in terms of being superior to one or more of adhesiveness and thermal conductivity.
0.8×a≦b≦1.5×a Formula (1)
In formula (1), a represents the thickness of the adhesive layer. A method for measuring the thickness of the adhesive layer will be described in detail later.
In formula (1), b represents the particle size of the second thermally conductive filler.
By satisfying the relationship of the above formula (1), convex portions are likely to be formed on the surface of the thermally conductive adhesive sheet on the adhesive layer side due to the second thermally conductive filler.

A 2nd thermally conductive filler may be used individually by 1 type, and may be used in combination of multiple types.
The content of the second thermally conductive filler is preferably 20 to 80% by mass, more preferably 40 to 80% by mass, even more preferably 50 to 70% by mass, relative to the total mass of the adhesive layer.
The content of the second thermally conductive filler is preferably 20 to 90% by volume, more preferably 30 to 70% by volume, and even more preferably 35 to 50% by volume, relative to the total volume of the adhesive layer.

(Curing accelerator)
The adhesive layer may contain a curing accelerator.
The type of curing accelerator to be used may be appropriately determined.
Examples of the curing accelerator are the same as those listed for the curing accelerator that may be contained in the thermally conductive sheet, and the preferred contents are also the same.

(Other ingredients)
The adhesive layer may contain other components than those mentioned above.
Other components include, for example, catalysts, dispersants, surface modifiers, and polymerization initiators (photopolymerization initiators, thermal polymerization initiators, etc.).

(Properties of adhesive layer)
-Thickness-
The thickness of the adhesive layer is preferably from 1 to 100 μm, more preferably from 5 to 50 μm, and even more preferably from 10 to 30 μm, because one or more of adhesion and thermal conductivity are excellent.
The thickness is calculated by observing the cross section of the thermally conductive adhesive sheet according to the thickness measuring method described in Requirement 1 and the thickness measuring method described in the thermally conductive sheet. More specifically, the thickness of the adhesive layer is calculated by subtracting the thickness of the thermally conductive sheet from the thickness of the thermally conductive adhesive sheet.

- State of adhesive layer -
As the state of the adhesive layer, the A stage or the B stage is preferable, and the A stage is more preferable, in that the above-mentioned deformation ratio can be adjusted within the preferable range.
Note that the A stage and the B stage are as described above.

<Method for producing thermally conductive adhesive sheet>
A method for manufacturing the thermally conductive adhesive sheet is not particularly limited, and a known method can be used.
For example, a thermally conductive sheet can be manufactured by the following procedure.
First, a composition for forming a thermally conductive sheet containing a solvent and components contained in the thermally conductive sheet is prepared, and a composition for forming an adhesive layer containing a solvent and components contained in the adhesive layer is prepared. A product is prepared (composition preparation step). Next, the composition for forming a thermally conductive sheet and the composition for forming an adhesive layer are each applied onto the temporary support, the contained solvent is removed by heating or the like, and the thermal conductive material formed on the temporary support is removed. A flexible sheet and an adhesive layer formed on the temporary support are obtained (formation step). Next, the thermally conductive sheet formed on the temporary support and the adhesive layer formed on the temporary support are laminated so that the thermally conductive sheet and the adhesive layer face each other (lamination step). , a thermally conductive adhesive sheet sandwiched between temporary supports is obtained.

In the above composition preparation step, the method for mixing the components is not particularly limited, and any known method can be used. The mixing device used for mixing is preferably a submerged disperser. and a homogenizer. One type of mixing device may be used alone, or two or more types may be used. Degassing may be performed before, after and/or at the same time as mixing.
Although the solvent is not particularly limited, it is preferably an organic solvent. Examples of organic solvents include cyclopentanone, cyclohexanone, ethyl acetate, methyl ethyl ketone, dichloromethane, and tetrahydrofuran.
, the content of the solvent is preferably 5 to 80% by mass, more preferably 15 to 70% by mass, and more preferably 20 to 50% by mass with respect to the composition for forming a thermally conductive sheet or the composition for forming an adhesive layer. More preferred.

In the above procedure, the temporary support is not particularly limited, and a known temporary support can be used. A resin film is preferable as the temporary support. The resin film used as the temporary support may be subjected to release treatment on the surface on which the thermally conductive sheet or the adhesive layer is formed.

In the forming step, the coating method is not particularly limited, and a known method can be used.
Moreover, in the forming step, the heating temperature and the heating time may be appropriately selected according to the boiling point of the solvent. For example, the heating temperature may be 50 to 150°C. The heating time is 0.5 to 30 minutes. Note that the heat conductive sheet and the adhesive layer may become a semi-cured sheet (stage A or stage B) by the heating. Further, after the forming step, roll pressing may be performed while heating.

In the lamination step, the lamination method is not particularly limited, but vacuum lamination or vacuum pressing (pressing treatment under reduced pressure) is preferable in that the formation of voids can be suppressed. During the above treatment, heating may be performed, and heating is preferred. Although the heating temperature is not particularly limited, 50 to 120°C is preferable.

In the above procedure, the thermally conductive sheet and the adhesive layer are laminated to produce the thermally conductive adhesive sheet. It may be a manufacturing method in which a composition is applied to form an adhesive layer.

<How to use the thermally conductive adhesive sheet>
By using the thermally conductive adhesive sheet of the present invention, a laminate in which an object to be bonded and a cured sheet are laminated can be obtained. As described above, according to the thermally conductive adhesive sheet of the present invention, it is possible to form a cured sheet having excellent adhesion to an object to be bonded, and the formed cured sheet has excellent thermal conductivity.
When obtaining the laminate, it is preferable to obtain a laminate with the object to be adhered by pressing the thermally conductive adhesive sheet and the object to be adhered together and subjecting them to heat treatment. Note that the heat treatment may be performed while pressure is applied, or may be performed without applying pressure after pressure bonding.
To explain the above operation in more detail, first, as shown in FIG. 2, a thermally conductive adhesive sheet 10 and an object to be bonded 20 are prepared. At this time, the surface of the thermally conductive adhesive sheet 11 on the adhesive layer side faces the object 20 to be adhered. In addition, in FIG. 2, only the 2nd thermally conductive filler 14b is illustrated for description. Next, as described above, the thermally conductive adhesive sheet and the object to be bonded are thermocompression bonded. At this time, as shown in FIG. 3, when the thermally conductive adhesive sheet 10 and the object to be bonded 20 come into contact with each other and further pressure is applied, the thermally conductive adhesive sheet 10 is easily deformed as described above. The second thermally conductive filler 14b is easily pushed in the direction of the arrow. Therefore, when further pressure is applied, as shown in FIG. 4 , the contact between the object to be bonded and the second thermally conductive filler 14b is maintained, and the second thermally conductive filler and the first thermally conductive filler 14b are kept in contact with each other. Since it becomes easy to make a contact with the filler, the thermal conductivity is improved. Furthermore, the area other than the area in contact with the second thermally conductive filler 14b of the object to be adhered becomes the area in contact with the binder obtained by curing the second thermally conductive compound, and as a result, the adhesion is ensured.
As a typical example when the deformability of the thermally conductive adhesive sheet is small, the filler does not move in the direction of the arrow shown in FIG. A gap is generated between the resin and the binder obtained as a result of this, resulting in an increase in thermal resistance.
The applied pressure is carried out at low pressure. The applied pressure is, for example, 10 MPa or less, and may be 5 MPa or less. Further, the heating temperature may be appropriately selected according to the first thermosetting compound and the second thermosetting compound. is more preferred.

Moreover, it is also preferable that the formed cured sheet is insulating (electrically insulating). In other words, the thermally conductive adhesive sheet is also preferably a thermally conductive insulating adhesive sheet.
For example, the volume resistivity of the cured sheet at 23° C. and 65% relative humidity is preferably 10 ¹⁰ Ω·cm or more, more preferably 10 ¹² Ω·cm or more, and even more preferably 10 ¹⁴ Ω·cm or more. Although the upper limit is not particularly limited, it is usually 10 ¹⁸ Ω·cm or less.

The object to be adhered may be appropriately selected depending on the purpose, but a circuit board, an integrated circuit, a power semiconductor circuit, a heat spreader, a lead frame, a heat sink, or copper foil is preferable.
In the case where the thermally conductive adhesive sheet has adhesive layers on both sides of the thermally conductive sheet, both sides of the thermally conductive sheet have objects to be bonded. The two bonding objects in this case are preferably selected from the bonding objects described above. That is, the laminate formed by thermocompression is preferably heat spreader/curing sheet/copper foil, lead frame/curing sheet/copper foil, lead frame/curing sheet/heat sink, and integrated circuit/curing sheet/heat spreader. mentioned.

The object to be adhered is preferably in direct or indirect contact with the heating element. A laminate formed of a thermally conductive adhesive sheet can efficiently conduct heat from a heating element and radiate it to the outside. The heating element is preferably an integrated circuit or a power semiconductor circuit, more preferably a power semiconductor circuit. That is, the thermally conductive adhesive sheet is preferably used for power module devices.

The thermocompression bonding method may be appropriately selected according to the bonding object. A specific example is heat press.
Further, circuit boards and the like including integrated circuits, power semiconductor circuits, and the like are often sealed (molded) with resin or the like for insulation, circuit protection, reliability improvement, and the like. Molding methods include compression molding and transfer molding. During molding, pressure may be applied while heating, but thermocompression bonding between the object to be bonded and the thermally conductive adhesive sheet may be performed at the same time as molding. In the case of transfer molding, the applied pressure is relatively low, but according to the thermally conductive adhesive sheet of the present invention, even with thermocompression bonding at low pressure, a cured sheet having excellent adhesiveness and heat dissipation is formed. can.

The present invention will be described in further detail based on examples below.
The materials, amounts used, proportions, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed as limited by the examples shown below.

<Preparation of thermally conductive adhesive sheet>
The thermally conductive adhesive sheets used in each example and each comparative example were obtained by forming a thermally conductive sheet and an adhesive layer using a thermally conductive sheet-forming composition and an adhesive layer-forming composition, respectively. It was produced by laminating.
The manufacturing method will be described below.

[Formation of Thermally Conductive Sheet]
A composition for forming a thermally conductive sheet was prepared according to the formulation shown in Table 1.
The prepared thermally conductive sheet-forming composition was evenly applied to the release surface of a release-treated polyester film (PET75 6501, manufactured by Lintec Co., Ltd., film thickness 75 μm, hereinafter also referred to as “temporary support”) with an applicator. , and 120° C. for 5 minutes to obtain a temporary support with a thermally conductive sheet. The resulting thermally conductive sheet was in A stage.
The amount of the thermally conductive sheet-forming composition applied was adjusted so as to achieve the thickness of the thermally conductive sheet shown in Table 3 below.

Each notation in Table 1 and its details are as follows.
・Cyclopentanone: cyclopentanone, manufactured by Nippon Zeon ・Epoxy compound 1: EXA-830LVP, manufactured by DIC ・Epoxy compound 2: Denacol EX-201, manufactured by Nagase ChemteX ・Phenol compound 1: the following compound

・Catalyst 1: TPP-MK (tetraphenylphosphonium tetra-p-tolylborate), manufactured by Hokko Chemical Industry Co., Ltd. ・Boron nitride 1: HP40MF100 (aggregated boron nitride particles, median diameter: 42 μm), manufactured by Mizushima Ferroalloy Co., Ltd. ・Nitriding Boron 2: HP40J2WP (aggregated boron nitride particles, median diameter: 20 μm), manufactured by Mizushima Ferroalloy Co., Ltd.

[Formation of adhesive layer]
A composition for forming an adhesive layer was prepared according to the formulation shown in Table 2.
In the same manner as described above, the prepared adhesive layer-forming composition was evenly applied to the release surface of the temporary support with an applicator and allowed to stand at 60° C. for 3 minutes to obtain a temporary support with an adhesive layer.
The coating amount of the adhesive layer-forming composition was adjusted so as to achieve the thickness of the thermally conductive sheet shown in Table 3 below.

Each notation in Table 2 and its details are as follows.
・Boron nitride 3: MGP (flat boron nitride particles, median diameter: 10 μm), manufactured by Denka ・Alumina 1: Sumicorundum AA-18 (spherical alumina particles, median diameter: 18 μm), manufactured by Sumitomo Chemical ・Alumina 2: Sumicorundum AA-10 (spherical alumina particles, median diameter: 10 μm), manufactured by Sumitomo Chemical Co., Ltd. Alumina 3: Sumicorundum AA-5 (spherical alumina particles, median diameter: 5 μm), manufactured by Sumitomo Chemical Co., Ltd. Alumina 4: Sumicorundum AA-07 (spherical alumina particles, median diameter: 0.7 μm), manufactured by Sumitomo Chemical Co., Ltd. Alumina 5: AS-30 (spherical alumina particles, median diameter: 22 μm), manufactured by Showa Denko Co., Ltd. Boron nitride 2, cyclopenta Non, Epoxy Compound 1, Phenolic Compound 1, and Catalyst 1 are the same as in Table 1 above.

[Preparation of Thermally Conductive Adhesive Sheet by Lamination]
A thermally conductive sheet was produced by laminating the thermally conductive sheet and the adhesive layer so that the combinations shown in Table 3 below were obtained.
More specifically, the obtained temporary support with the thermally conductive sheet and the temporary support with the adhesive layer were laminated with a vacuum laminator so that the thermally conductive sheet and the adhesive layer faced each other. By lamination, a thermally conductive adhesive sheet laminate having a temporary support, a thermally conductive sheet, an adhesive layer, and a temporary support in this order was obtained. Lamination was performed at 100°C.
In Examples 4 to 6, the surface on the side of the thermally conductive sheet and the release surface of the temporary support are opposed to the temporary support with the thermally conductive sheet before the lamination is performed. A temporary support was installed as in the above, and roll pressing was performed at 100°C. After that, the temporary support provided before the roll press was peeled off. The thermally conductive sheet after roll pressing was in B stage.
In Comparative Example 5, roll pressing was performed in the same manner as in Examples 4 to 6, except that the roll pressing was performed at 100°C. The thermally conductive sheet after roll pressing was in the C stage.

<Measurement and evaluation>
[Measurement of Thermally Conductive Sheet and Adhesive Layer Thickness]
The thicknesses of the thermally conductive sheet and the adhesive layer were measured by the method described above for the thermally conductive adhesive sheet laminate heat-treated at 180°C.

[Measurement of deformation rate]
The deformation rate is determined by the thickness of the thermally conductive adhesive sheet in the thermally conductive adhesive sheet laminate subjected to heat treatment at 180 ° C. (thickness X above) and the thermally conductive adhesive sheet laminate different from the sample whose thickness X was measured. After applying pressure to the body at a pressure of 10 MPa, a temperature of 180 ° C., and a treatment time of 5 minutes, the thickness of the cured sheet (hot press cured sheet) obtained by heat treatment at a temperature of 180 ° C. for a treatment time of 90 minutes ( The thickness Y) was measured, and the deformation rate was calculated by the method described above.

[Measurement of surface roughness]
The surface roughness Ra was measured by peeling off the temporary support on the adhesive layer side of the thermally conductive adhesive sheet laminate by the method described above.

[Thermal conductivity evaluation]
The temporary support was peeled off from the hot press-cured sheet obtained by the above method, and the thermal conductivity in the film thickness direction was evaluated by the following method.
First, using "LFA467" manufactured by NETZSCH, the thermal diffusivity in the thickness direction of the heat press-cured sheet was measured by the laser flash method.
Next, the density of the heat-press cured sheet was measured by the Archimedes method using a balance "XS204" manufactured by Mettler-Toledo Corporation and a "solid specific gravity measurement kit".
In addition, using "DSC320/6200" manufactured by Seiko Instruments Inc., the specific heat capacity of the heat-press cured sheet at 25°C was determined under the temperature rising condition of 10°C/min.
The obtained thermal diffusivity was multiplied by the density and the specific heat capacity to obtain the thermal conductivity (W/m·K) of the heat-press cured sheet.
Thermal conductivity was evaluated according to the following evaluation criteria based on the obtained thermal conductivity. A to C are practically preferable evaluations.

(Thermal conductivity evaluation criteria)
A: 16 W/m·K or more B: 13 W/m·K or more and less than 16 W/m·K C: 11 W/m·K or more and less than 13 W/m·K D: Less than 11 W/m·K

[Adhesion evaluation]
Adhesion was evaluated by the peel strength of the copper foil in the laminate obtained by thermocompression bonding the thermally conductive adhesive sheet and the copper foil so that the adhesive layer and the copper foil face each other. Specifically, the peel strength was evaluated by the following procedure.
The temporary support on the thermally conductive sheet side of the thermally conductive adhesive sheet laminate was peeled off, and the exposed thermally conductive sheet and the aluminum plate were bonded together. The laminate in this state was subjected to vacuum hot pressing for 1 minute under conditions of a hot plate temperature of 100° C. and a pressure of 20 MPa. Next, the temporary support on the adhesive layer side of the thermally conductive adhesive sheet laminate was peeled off, and the exposed adhesive layer and copper foil (CF-T8G-UN-35, manufactured by Fukuda Metal Foil Co., Ltd.) were bonded together. The laminate in this state was subjected to a vacuum hot press for 5 minutes at a hot plate temperature of 180° C. and a pressure of 10 MPa, and further cured at 180° C. for 90 minutes under normal pressure. By the above procedure, a sample for peel strength measurement having an aluminum plate, a heat-press hardened sheet, and a copper foil in this order was obtained.
The copper foil peel strength of the obtained sample was measured using a digital force gauge (ZTS-200N, manufactured by Imada Co., Ltd.) and a 90-degree peel test jig (P90-200N-BB, manufactured by Imada Co., Ltd.), according to JIS C. 6481:1996, the peel strength was measured. The peeling of the copper foil in the peel strength test was performed at an angle of 90° to the surface of the sample at a peeling speed of 50 mm/min.
Adhesion was evaluated according to the following evaluation criteria based on the measured peel strength. A to C are practically preferable evaluations.

(Adhesion evaluation criteria)
A: 5 N/cm or more B: 4 N/cm or more and less than 5 N/cm C: 3 N/cm or more and less than 4 N/cm D: Less than 3 N/cm

<Results>
Table 3 shows the configuration of the thermally conductive adhesive sheets used in each example and each comparative example, and the above measurement and evaluation results.
In Table 3, the content ratio of the first thermally conductive filler in the thermally conductive sheet represents the ratio with respect to the total area of the thermally conductive sheet. Also, the content ratio of the second thermally conductive filler in the adhesive layer represents the ratio with respect to the total volume of the adhesive layer.
In Table 3, the description of "B/A thickness ratio" in the measurement results represents the ratio of the thickness of the adhesive layer to the thickness of the thermally conductive sheet.

In Examples 1 to 3, the thermal conductivity of the thermally conductive adhesive sheets provided with adhesive layers on both sides of the thermally conductive sheet was evaluated, and the thermal conductivity was rated A or B. In addition, when copper foil was thermocompression bonded to both sides of the thermally conductive adhesive sheet, the peel strength of the copper foil was measured, and the adhesiveness on both sides was evaluated. was evaluated.

From the results in Table 3, it was confirmed that the thermally conductive adhesive sheet of the present invention exhibited desired effects.
From comparisons of Examples 1, 2 and 6 with other examples, it was confirmed that when the deformation rate is 20% or more, the adhesiveness and heat dissipation are superior.
From the comparison of Examples 7 and 16 with other examples, it was confirmed that when the second thermally conductive filler satisfies the above formula (1), the adhesiveness and heat dissipation are superior.
From the comparison between Example 19 and Examples 12 to 17, it was confirmed that when the particle size of the second thermally conductive filler is 2.5 to 20 μm, at least one of adhesion and heat dissipation is superior. .
From a comparison between Example 18 and Examples 12 to 17, it was confirmed that at least one of adhesiveness and heat dissipation is superior when the first thermally conductive filler is agglomerated boron nitride having a particle size of 40 μm or more. rice field.
From a comparison between Examples 18 and 19 and Examples 12 to 17, the first thermally conductive filler is agglomerated boron nitride having a particle size of 40 μm or more, and the second thermally conductive filler has a particle size of 2.0 μm or more. It was confirmed that at least one of adhesion and heat dissipation is superior when the thickness is 5 to 20 μm.

REFERENCE SIGNS LIST 10 thermally conductive adhesive sheet 12 thermally conductive sheet 12a first thermosetting compound 12b first thermally conductive filler 14 adhesive layer 14a second thermosetting compound 14b second thermally conductive filler

Claims (8)

A thermally conductive adhesive sheet comprising a thermally conductive sheet and an adhesive layer disposed on at least one surface of the thermally conductive sheet,
The thermally conductive sheet comprises a first thermosetting compound and a first thermally conductive filler,
the adhesive layer comprises a second thermosetting compound and a second thermally conductive filler;
The surface roughness Ra of the adhesive layer side of the thermally conductive adhesive sheet is 2.5 μm or more,
A thermally conductive adhesive sheet that satisfies requirement 1 below.
Requirement 1: The thickness of the thermally conductive adhesive sheet is X, and pressure is applied to the adhesive layer side surface of the thermally conductive adhesive sheet at a pressure of 10 MPa, a temperature of 180 ° C., and a treatment time of 5 minutes. The deformation rate calculated by 100×(XY)/X is 10% or more, where Y is the thickness of the cured sheet obtained by heat treatment at 180° C. for 90 minutes. 2. The thermally conductive adhesive sheet according to claim 1, wherein said deformation rate is 20% or more. The thermally conductive adhesive sheet according to claim 1 or 2, wherein the second thermally conductive filler satisfies the following formula (1).
0.8×a≦b≦1.5×a Formula (1)
In formula (1), a represents the thickness of the adhesive layer.
In formula (1), b represents the particle size of the second thermally conductive filler. The thermally conductive adhesive sheet according to any one of claims 1 to 3, wherein the second thermally conductive filler has a particle size of 2.5 to 20 µm. The thermally conductive adhesive sheet according to any one of claims 1 to 4, wherein the first thermally conductive filler is agglomerated boron nitride having a particle size of 40 µm or more. The first thermally conductive filler is agglomerated boron nitride having a particle size of 40 μm or more,
The thermally conductive adhesive sheet according to any one of claims 1 to 5, wherein the second thermally conductive filler has a particle size of 2.5 to 20 µm. The thermally conductive adhesive sheet according to any one of claims 1 to 6, wherein said first thermosetting compound and said second thermosetting compound comprise an epoxy compound. The thermally conductive adhesive sheet according to any one of claims 1 to 7, wherein said first thermosetting compound and said second thermosetting compound comprise a phenolic compound.

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