JP6500339B2 - Heat dissipation sheet, coating liquid for heat dissipation sheet, and power device - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a heat dissipation sheet suitably used for power semiconductor devices. The heat-dissipating sheet of the present invention comprises a specific boron nitride secondary particle and a specific plate-like boron nitride particle, and further, a heat-dissipating sheet coating solution containing these boron nitride secondary particle and plate-like particle, and a heat-dissipating sheet The present invention relates to a power device apparatus used.

In recent years, power semiconductor devices used in various fields such as railways, automobiles, and general home appliances are from conventional Si power semiconductors to SiC, AlN, GaN, etc. for further miniaturization, cost reduction, and high efficiency. Transition to power semiconductors using
A power semiconductor device is generally used as a power semiconductor module in which a plurality of semiconductor devices are disposed on a common heat sink and packaged.

  Although various issues are pointed out toward practical use of such power semiconductor devices, one of the problems is the problem of heat radiation from the devices. In general, power semiconductor devices are heated to a high temperature by operating at high power and high density, which affects the reliability of the power semiconductor devices. In addition, there is a concern that the heat generation associated with the switching of the device may lower the reliability.

  In recent years, particularly in the electric and electronic fields, heat generation accompanying the densification of integrated circuits has become a major issue, and how to dissipate heat is an urgent issue.

  As one method for solving this problem, a ceramic substrate with high thermal conductivity such as an alumina substrate or an aluminum nitride substrate is used as a heat dissipation substrate on which a power semiconductor device is mounted. However, there is a problem that these substrates are difficult to be multi-layered, the processability is bad, and the cost is very high. On the other hand, although the heat dissipation sheet using resin is characterized by being excellent in processability and capable of being laminated, there is a problem that the thermal conductivity which is an index of heat dissipation is very low.

Therefore, as a thermosetting resin constituting the resin component of the composition, a high thermal conductivity epoxy resin is used, or the high thermal conductivity resin and the high thermal conductivity inorganic filler are combined to form a composition. It is practiced to make things highly heat conductive. For example, Patent Document 1 describes a composition in which spherical boron nitride aggregates are blended as a filler. This composition is usually applied to a copper substrate as a coating solution which is dispersed or dissolved in a suitable organic solvent to adjust its viscosity to an appropriate level.
However, as described below, conventionally, as a heat dissipation sheet using a resin, one having thermal conductivity comparable to that of a ceramic substrate has not been developed yet.

  In conventional compositions, boron nitride (BN) is used as a filler. Boron nitride (BN) is an insulating ceramic, c-BN having a diamond structure, h-BN (hexagonal boron nitride) having a graphite structure, α-BN, β-BN having an irregular layer structure, etc. Crystal forms are known. Among them, h-BN having a graphite structure has the same layer structure as graphite, and is characterized by being relatively easy to synthesize and excellent in thermal conductivity, solid lubricity, chemical stability, and heat resistance. Are widely used in the field of electrical and electronic materials.

In addition, h-BN is attracting attention as such a heat conductive filler for a heat radiating member, taking advantage of its high thermal conductivity despite the fact that it is insulating. It is believed that a heat dissipating sheet can be formed. In addition to the above-mentioned patent documents 1, the art which uses boron nitride powder conventionally is known, for example, boron nitride powder which has specific particle diameter and particle size distribution as such boron nitride is known. (See, for example, Patent Document 2). In addition to this, a technique using two types of mixed boron nitride having different particle properties such as surface area, particle size, tap density and the like (see, for example, Patent Document 3) is known.

  In addition, h-BN powder is known as a material excellent in thermal conductivity, and after washing the crude hexagonal boron nitride powder, it is heat-treated at 1200 to 1850 ° C. in an inert gas flow, A technique for producing highly crystalline boron nitride is known (see, for example, Patent Document 4). In this technique, a crystallite size (La) of 100 planes of crystallites of boron nitride is grown. Further, Patent Document 5 describes that by subjecting the crude hexagonal boron nitride powder to a specific treatment, a hexagonal boron nitride powder having a large particle diameter and excellent lubricity can be obtained. In addition, Patent Document 6 similarly mixes a compound having lanthanum as a main component with the crude hexagonal boron nitride powder, and heat-processes it in a specific temperature range in a non-oxidizing gas atmosphere to obtain a crystallite of 002 plane. A hexagonal boron nitride powder obtained by growing the size (Lc) is described, and this hexagonal boron nitride powder is described to be excellent in dispersibility and to have high crystallinity.

  However, h-BN has a plate-like particle shape and exhibits high thermal conductivity in the plate surface direction (C plane direction or (002) plane direction) (usually, the thermal conductivity is about 250 W / mK or so) ), Because it exhibits only low thermal conductivity (generally, about 2 to 3 W / mK as thermal conductivity) in the plate thickness direction (C-axis direction), it is compounded in a resin and the substrate surface as a composition coating solution Is coated to form a coating, this is heated to be B-staged, and main curing is performed to produce a heat dissipation sheet. In the produced heat dissipation sheet, the plate-like BN particles are in the film surface direction of the coating Although the heat-radiating sheet thus formed has excellent thermal conductivity in the film surface direction, it has a problem that it exhibits only low thermal conductivity in the thickness direction.

In the past, in order to improve the thermal conductivity anisotropy of such BN particles, attempts have been made to increase the heat dissipation properties in the sheet thickness direction of heat conduction by using secondary particles in which primary particles of boron nitride are gathered. It has been done.
Furthermore, it is proposed to mix together with spherical boron nitride secondary particles so as to prevent the plate-like boron nitride particles from being oriented (Patent Documents 7 and 8).

Japanese Patent Application Publication No. 2008-510878 JP, 2008-189818, A Japanese Patent Publication No. 2010-505729 Japanese Patent Application Laid-Open No. 61-7260 Unexamined-Japanese-Patent No. 9-263402 Patent No. 5171798 gazette Patent No. 5092050 JP, 2009-144072, A

However, in order to suppress the orientation of the plate-like boron nitride particles, the spherical boron nitride secondary particles mixed in the above document do not have high crushing strength. Therefore, the spherical boron nitride secondary particles are crushed in the pressing step in forming the sheet to eliminate the voids formed in the sheet, and as a result, the plate-like boron nitride is oriented in the sheet length direction As a result, the thermal conductivity can not be effectively enhanced even in the thickness direction of the sheet.
An object of the present invention is to provide a heat dissipation sheet having high thermal conductivity also in the thickness direction of the sheet.

  The inventors of the present invention conducted intensive studies to solve the above problems, and as a result, using the secondary particles of boron nitride having a card house structure and the boron nitride plate-like particles as a filler to be contained in the heat dissipation sheet Found to solve. That is, the boron nitride secondary particles having a card house structure do not crush even in the pressing step for eliminating the voids in the sheet, whereby the plate-like boron nitride particles used in combination are not oriented in the sheet longitudinal direction. By this, it discovered that the thermal radiation sheet which has the high thermal conductivity and high voltage resistance which improves the reliability of a power device can be provided.

The present invention has been achieved based on such findings, and the gist of the present invention is as follows.
[1] A heat dissipation sheet containing secondary boron nitride particles having a card house structure and plate-like boron nitride particles.
[2] The heat dissipation sheet according to [1], wherein the length of the plate-like boron nitride particles in the long axis direction is 3 μm or more.
[3] The heat dissipation sheet according to [1] or [2], wherein the plate-like boron nitride particles have an intensity ratio I (100) / I (004) of 100 axes to 004 axes smaller than 3.0 in XRD measurement. .
[4] The content ratio of the boron nitride secondary particles and the plate-like boron nitride particles represented by boron nitride secondary particles / (boron nitride secondary particles + plate-like boron nitride particles) is 0.1 or more The thermal radiation sheet in any one of [1]-[3] which is 0.98 or less.
[5] The boron nitride secondary particle according to any one of [1] to [4], wherein the intensity ratio I (100) / I (004) of 100 axis and 004 axis is 3.0 or more in XRD measurement. Heat dissipation sheet as described. [6] The heat dissipation sheet according to any one of [1] to [5], wherein the boron nitride secondary particles are particles containing a resin.
[7] A laminated heat dissipation sheet in which the heat dissipation sheet according to any one of [1] to [6] is laminated on a support.
[8] A power device apparatus including the heat dissipation sheet according to any one of [1] to [7].

According to the heat-radiating sheet of the present invention, the boron nitride secondary particles having the contained card house structure are not crushed even in the pressing step for eliminating the voids in the sheet. Therefore, the heat dissipation sheet of the present invention has high thermal conductivity and high voltage resistance, and can impart high reliability when applied to a power device.
Moreover, the manufacturing cost of a thermal radiation sheet can be lowered | hung by using cheap plate-like boron nitride together.

(A) It is a SEM photograph which shows the cardhouse structure of a boron nitride secondary particle, (b) It is a schematic diagram of the cardhouse structure in the cross section of a boron nitride secondary particle. It is a SEM photograph of boron nitride secondary particles in an example (drawing substitute photograph).

  Hereinafter, the present invention will be described in detail, but the present invention is not interpreted as being limited to the following description, and can be implemented arbitrarily within the scope of the present invention.

[1. Heat dissipation sheet]
The heat-radiating sheet of the present invention includes two types of boron nitride particles: boron nitride secondary particles having a card house structure (hereinafter, also simply referred to as boron nitride secondary particles) and plate-like boron nitride particles.
The card house structure is, for example, ceramics 43 no. 2 (issued in 2008 by the Japan Ceramics Association), which is a structure in which plate-like particles are laminated in a complicated manner without being oriented. More specifically, the boron nitride secondary particles having a card house structure are an aggregate of boron nitride primary particles, and a boron nitride secondary particle having a structure in which a flat portion and an end portion of the primary particles are in contact with each other. It is a particle (see FIGS. 1 (a) and (b)).
The boron nitride secondary particles having a card house structure have a very high breaking strength due to their structure, and do not crush even in the pressing step performed at the time of forming the heat dissipation sheet. Therefore, by combining and using plate-like boron nitride particles, it has become possible to cause plate-like boron nitride particles normally oriented in the longitudinal direction of the heat dissipation sheet to be present in random directions. As a result, the inventors have found that high thermal conductivity can be achieved not only in the longitudinal direction of the heat dissipation sheet but also in the thickness direction.

[1-1. Boron nitride secondary particles]
The boron nitride secondary particles used in the present invention have a cardhouse structure. Although the card house structure is as described above, the boron nitride secondary particles are preferably boron nitride 2 having a card house structure in which the boron nitride primary particles are plate-like and the flat surface portion and the end surface portion are in contact. It is a secondary particle, more preferably a boron nitride secondary particle having a cardhouse structure in which a primary surface of boron nitride is in a polygonal shape and a flat surface portion and an end surface portion are in contact with each other.
The aggregation form of the boron nitride secondary particles can be confirmed by a scanning electron microscope (SEM).

<Peak intensity ratio>
The boron nitride secondary particles generally have a peak intensity ratio I (100) / I (004) of 100 axis and 004 axis in the XRD measurement of usually 3.0 or more, preferably 3.1 or more, more preferably 3.2 The above, particularly preferably 3.3 or more. Usually, there is no upper limit, but it is 10 or less.
By being in this range, it is indicated that primary particles constituting the boron nitride secondary particles are randomly oriented, and such secondary particles have very high breaking strength. Therefore, the secondary boron nitride particles are not crushed even if pressure is applied in the pressing step for eliminating the voids in the sheet when the heat dissipating sheet is formed. Thereby, the plate-like boron nitride particles mixed together can be randomly oriented, and the heat conductivity in the thickness direction of the heat dissipation sheet can be enhanced.
The peak intensity ratio can be calculated from the intensity ratio of the corresponding peak intensities measured by powder X-ray diffraction measurement. The sample to be subjected to the measurement may be boron nitride secondary particles in which primary particles are aggregated, or may be boron nitride particles in which a resin described later is contained. Moreover, X-ray-diffraction measurement can also be performed in the state of a molded object (heat dissipation sheet).

<Breaking strength>
The fracture strength of the boron nitride secondary particles is usually 2.5 MPa or more, preferably 3.0 MPa or more, more preferably 3.5 MPa or more, still more preferably 4.0 MPa or more, and usually 20 MPa or less, preferably 15 MPa or less, More preferably, it is 10 MPa or less. If it is larger than the above upper limit, the particle strength is too strong, so the surface smoothness is lost when formed into a molded product, and the thermal conductivity tends to decrease, and if smaller than the above lower limit, the molded product is produced The particles tend to be deformed by pressure, and thermal conductivity tends not to be improved.
The breaking strength can be calculated from the following equation by compression testing one particle according to JIS R 1639-5. Usually, particles are measured at 5 points or more, and the average value is adopted.
Formula: Cs = 2.48P / πd ²
Cs: fracture strength (MPa)
P: Destructive test force (N)
d: Particle size (mm)
However, the particles may be deformed and the fracture strength can not be calculated, and may be expressed as 10% strength. In this case, the concept of the fracture strength is not applied.

<Specific surface area>
The specific surface area of the boron nitride secondary particles is usually 1 m ² / g or more, preferably 3 m ² / g to 50 m ² / g, more preferably 5 m ² / g to 40 m ² / g. Below this lower limit, it is difficult for the capillary phenomenon to work, and above this upper limit, the primary particles are too small, and it is difficult to form resin-encapsulated boron nitride particles described later.
The specific surface area can be measured by the BET one-point method (adsorbed gas: nitrogen).

<Average crystallite diameter>
The average crystallite diameter of the boron nitride secondary particles determined from the (002) plane peak by powder X-ray diffraction (XRD) is usually 375 Å or more, preferably 380 Å or more, more preferably 390 Å or more, still more preferably 400 Å or more And is usually 5000 Å or less, preferably 2000 Å or less, and more preferably 1000 Å or less. If it is larger than the above upper limit, the primary particles constituting the secondary particles grow too much, so the gaps in the secondary particles increase and the capillary phenomenon becomes difficult to occur, so it is difficult to form resin-encapsulated boron nitride particles described later . If it is less than the above lower limit, grain boundaries in primary particles constituting secondary particles increase, so that phonon scattering tends to occur at grain boundaries, and there is a tendency for low thermal conductivity.
Here, the "average crystallite diameter" refers to the crystallite diameter determined by the Scherrer formula from the (002) plane peak obtained by powder X-ray diffraction measurement. The sample to be subjected to the measurement may be boron nitride secondary particles in which primary particles are aggregated, or may be boron nitride particles in which a resin described later is contained.

<Size of primary boron nitride particles>
As another expression of the boron nitride secondary particles used in the present invention, the major axis of the boron nitride primary particles is usually grown to 0.5 to 10 μm, and radially grown from the center side to the surface side of the secondary particles It can also form a sea urchin-like appearance. The major axis of the boron nitride primary particles constituting the boron nitride secondary particles is preferably 0.6 to 5 μm, more preferably 0.8 to 3 μm, and still more preferably 1.0 to 3. It is a particle in which 0 μm h-BN is aggregated.
The major axis is an enlargement of one particle obtained by scanning electron microscope (SEM) measurement, and the primary particle constituting one particle is an average of the maximum length of primary particles that can be observed on an image. Value.

<Pore diameter>
The boron nitride secondary particles preferably have a pore diameter of 10 nm or more, more preferably 30 nm or more, and further 50 nm or more from the viewpoint of facilitating the introduction of the resin into the boron nitride secondary particles by capillary phenomenon. preferable. On the other hand, the pore diameter is preferably 10 μm or less, more preferably 5 μm or less, and still more preferably 3 μm or less. The pore diameter can be measured by mercury porosimetry.
<Pore volume>
The boron nitride secondary particles are preferably boron nitride secondary particles in which a resin described later is contained. Since the boron nitride secondary particles in which the resin is contained introduce the resin into the voids by capillary action, the boron nitride secondary particles before the resin is contained requires an appropriate pore volume.
The total pore volume of the boron nitride secondary particles is usually 0.05 ml / g or more, preferably 0.1 ml / g or more, more preferably 0.15 ml / g or more, still more preferably 0.2 ml / g or more . On the other hand, it is usually 5 ml / g or less, preferably 3 ml / g or less, more preferably 2 ml / g or less, and still more preferably 1.5 ml / g or less.
If the total pore volume is small, the inside of the boron nitride secondary particles is dense, so it is possible to reduce the interface that inhibits the heat conduction, but the resin in the void of the boron nitride secondary particles It becomes difficult for the resin to fill the voids of the boron nitride secondary particles sufficiently. On the other hand, even when the total pore volume is too large, the space between the voids is usually too large, so that the capillary phenomenon is less likely to occur and the resin is less likely to be taken into the boron nitride secondary particles.
The total pore volume of the boron nitride secondary particles can be measured by mercury porosimetry.

<Volume-based maximum particle diameter D _max , average particle diameter D ₅₀ >
The boron nitride secondary particles generally have a volume-based maximum particle diameter D _max (which may be simply referred to as “maximum particle diameter” in this specification), usually 2 μm or more, and preferably 3 μm or more. More preferably, it is 5 μm or more, and particularly preferably 10 μm or more. Also, it is usually 300 μm or less, preferably 200 μm or less, more preferably 100 μm or less, and particularly preferably 80 μm or less.

  When the maximum particle diameter of the boron nitride secondary particles (hereinafter, also simply referred to as a filler) is less than or equal to the above upper limit, the interface between the matrix resin and the filler decreases, so the thermal resistance decreases and high thermal conductivity can be achieved. In addition, it is possible to form a high quality film free from surface roughness and the like. When the maximum particle diameter is smaller than the above lower limit, the effect of improving the thermal conductivity as the thermally conductive filler required for the power semiconductor device is reduced. When high thermal conductivity fillers are used, in order to express thermal conductivity as a composite material, the interface adhesion between the thermal conductive filler and the resin, the adhesion between the composite material and the substrate, etc. are important. It is believed that the interface is the most responsible for heat transfer damping. In particular, a heat dissipation sheet with a thickness of 200 μm to 300 μm is often applied as a heat dissipation sheet for power semiconductor devices, but the effect of the above-mentioned interface on the thickness of the sheet becomes remarkable It is considered that the size of the conductive filler is 1/10 or less. Therefore, from the viewpoint of thermal conductivity, the volume-based maximum particle diameter of the filler is preferably larger than the above lower limit. When the volume-based maximum particle diameter of the filler exceeds the above upper limit, the filler protrudes on the surface of the heat-radiating sheet after curing, the surface shape of the heat-radiating sheet is deteriorated, and adhesion when producing a laminated sheet with a copper substrate The tendency is that the resistance is lowered and the withstand voltage characteristics are lowered. On the other hand, when the maximum particle diameter of the filler is too small, the influence of the above-mentioned interface on the thermal conductivity becomes remarkable, and the number of heat conduction paths required due to the small filler particles increases. The probability of connecting from one side to the other side in the thickness direction of the sheet is small, and even when combined with a matrix resin with high thermal conductivity, the effect of improving the thermal conductivity in the thickness direction of the heat dissipation sheet becomes insufficient. The interface area of the filler and the filler tends to be large, and the withstand voltage characteristics tend to be lowered.

  In general, it is assumed that the heat dissipation sheet for power semiconductor devices is used at a high temperature of 200 ° C. to 300 ° C. in order to further improve performance such as speeding up and capacity increase. In order to extend the life of peripheral members and ensure reliability such as high thermal conductivity and withstand voltage characteristics even when used at high temperatures above 0 ° C, the maximum particle diameter of the blended filler is relative to the thickness of the heat dissipation sheet It is usually 1/10 or more, preferably 1/5 or more, more preferably 1/4 or more, and usually 1/2 or less, preferably 1/3 or less.

Also, the volume-based average particle diameter D _{50 of the} boron nitride secondary particles (hereinafter sometimes referred to simply as “average particle diameter”) is not particularly limited, but the value of the above-mentioned volume-based maximum particle diameter For the same reason as in the above, it is usually 1 μm or more, preferably 2 μm or more, more preferably 3 μm or more, and still more preferably 5 μm or more. Also, it is usually 250 μm or less, preferably 150 μm or less, more preferably 90 μm or less, and still more preferably 70 μm or less. By the average particle size D ₅₀ in the above range, a sufficient thermal conductivity in the thickness direction of the heat radiation sheet, the withstand voltage characteristics can be obtained a good heat dissipation sheet.

The above maximum particle size and average particle size are, for example, dispersed in an appropriate solvent, and specifically, boron nitride secondary particles are dispersed in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer For the sample, the particle size distribution is measured by a laser diffraction / scattering type particle size distribution measuring apparatus LA-920 manufactured by Horiba, Ltd., and the maximum particle size and the average particle size of the boron nitride secondary particles are determined from the obtained particle size distribution. be able to.
The average particle diameter and the maximum particle diameter of the resin-incorporated boron nitride secondary particles, which will be described later, can be similarly dispersed in an appropriate solvent and measured with the same apparatus as described above.

  The manufacturing method of the boron nitride spherical secondary particles is not limited as long as it has a cardhouse structure and preferably satisfies the above-mentioned physical properties. The details of the method for producing boron nitride secondary particles are exemplified below.

[1-2. Method of producing boron nitride secondary particles]
The method for producing the boron nitride secondary particles is not particularly limited, but in order to form a card house structure, in particular, boron nitride as a raw material (hereinafter, it may be described as raw BN powder together with a pulverized one thereof) ) Is crushed in a crushing step, and then granulated by aggregating in a granulation step, and it is preferable to go through a heating step of further heat treatment. More specifically, the raw material BN powder was once dispersed in a medium to form a slurry of the raw material BN powder (hereinafter sometimes referred to as "BN slurry"), and then subjected to a grinding treatment, and then obtained. It is preferable to heat-process in order to crystallize to spherical particle | grains using a slurry and to crystallize the granulated aggregated BN granulated particle.

Raw material BN powder
When producing boron nitride secondary particles (hereinafter, also referred to as aggregated BN particles), it is possible to use particles of boron nitride described below as a raw material. However, the raw material of the agglomerated BN particles of the present invention is not particularly limited to the following.
More specifically, commercially available h-BN, commercially available .alpha. And .beta.-BN, BN prepared by the reduction nitriding method of a boron compound and ammonia, BN synthesized from a boron compound and a nitrogen-containing compound such as melamine, boro Any of sodium hydrogen and BN prepared from ammonium chloride can be used without any limitation, but h-BN is particularly preferably used.

  From the viewpoint of h-BN crystal growth, it is preferable that oxygen be present in the raw material BN powder such as h-BN as a raw material to some extent, and the total oxygen content in the raw material BN powder is 1% by mass or more and 10% by mass or less The total oxygen content in the raw material BN powder is preferably 3% by mass to 10% by mass, and more preferably 3% by mass to 9% by mass.

The raw material BN powder having a total oxygen content in the above range has small primary particle diameter and many undeveloped crystals, so crystals tend to grow by heat treatment. It is preferable to grow BN crystals by heat-treating BN granulated particles in which raw material BN powder is aggregated by granulation, but primary particles of BN crystal are obtained by using raw material BN powder in the range of the total oxygen content. Is grown to form a cardhouse structure in the normal direction so that the a-axis points out, that is, the flat and end portions of the BN primary particles are radial on the surface of the agglomerated BN particles from which BN primary particles can be obtained. It can be arranged to be in contact.
The agglomerated BN particles arrange the primary particles radially on the surface and in such a manner that the flat surface portion and the end surface portion of the BN primary particles are in contact with each other, whereby the resin reaches the central portion in the boron nitride secondary particles by capillary action. It also has the advantage of being easy to introduce.

When the total oxygen content of the raw material BN powder is less than the above lower limit, the crystal growth of the C surface is not sufficiently performed because the purity and crystallinity of the raw material BN itself are good, and the BN primary particles are radially emitted on the aggregated BN particle surface And, it can not be disposed in the card house structure, conversely, if the above upper limit is exceeded, the oxygen content becomes high even after heat treatment, and high thermal conductivity can not be achieved when used as a heat dissipation sheet Unfavorable.
As a method of adjusting the total oxygen content of raw material BN powder to the said range, the method of performing the heating temperature at the time of BN heating at the low temperature of 2500 degrees C or less, etc. are mentioned.

Moreover, a commercial item can also be used as a raw material BN powder whose total oxygen content is the said suitable range, For example, h-BN "ABN" by Nisshin Lifratec, h-BN "AP170S" by MARUKA, etc. Can be mentioned.
The oxygen content of the raw material BN powder can be measured by an inert gas melting-infrared absorption method using an HORIBA oxygen / nitrogen analyzer.

Moreover, as other physical properties of the raw material BN powder, for example, the total pore volume of the raw material BN powder is usually 1.0 cm ³ / g or less, preferably 0.3 cm ³ / g or more and 1.0 cm ³ / g Or less, more preferably 0.5 cm ³ / g or more and 1.0 cm ³ / g or less.
The specific surface area of the raw material BN powder is usually 20 m ² / g or more, preferably 20 m ² / g to 500 m ² / g, and more preferably 50 m ² / g to 200 m ² / g.
When the total pore volume is 1.0 cm ³ / g or less, granulation of high sphericity is possible when the raw material BN powder is dense and it is used as primary particles constituting agglomerated BN particles It becomes. In addition, when the specific surface area is 20 m ² / g or more, the dispersed particle diameter in the BN slurry used in the spheroidization by granulation can be reduced, which is preferable.

  The total pore volume of the raw material BN powder can be measured by the mercury intrusion method, and the specific surface area can be measured by the BET one-point method (adsorbed gas: nitrogen).

Preparation of BN Slurry
The medium used to prepare the BN slurry is not particularly limited, and water and / or various organic solvents can be used, but water (pure water) is used in view of easiness of spray drying, simplification of the apparatus, etc. It is preferred to use.
If the amount of water used is too large, the load at the time of spray drying will increase and if it is too small, uniform dispersion will be difficult. It is preferable to make it 10 mass times.

  The viscosity of the BN slurry at 25 ° C. and 1 atm is usually 100 mPa · s or more, preferably 300 mPa · s or more. Also, it is usually 3000 mPa · s or less, preferably 2000 mPa · s or less. It becomes easy to manufacture the boron nitride secondary particle which is easy to contain resin by being this range.

<Surfactant>
Various surfactants may be added to the BN slurry from the viewpoint of the dispersion stability (aggregation suppression) of the BN particles as well as suppressing the increase in viscosity of the slurry during the pulverization treatment described later.
As surfactant, anionic surfactant, cationic surfactant, nonionic surfactant etc. can be used, These may be used individually by 1 type, and 2 or more types are mixed, You may use it.

When a surfactant is added to the BN slurry and used, the concentration of the surfactant in the BN slurry is usually 0.1% by mass or more and 10% by mass or less, particularly 0.5% by mass or more and 5% by mass or less It is preferred to use. When the concentration of the BN slurry is the above lower limit or more, the above-mentioned effect by adding the surfactant can be sufficiently obtained, and by being below the above upper limit, BN having a high content of the raw material BN powder After the slurry is prepared, it is possible to reduce the influence of residual carbon when granulated and subjected to heat treatment.
The surfactant may be added before the following pulverizing treatment, or may be added after the pulverizing treatment.

<Binder>
The BN slurry preferably contains a binder in order to effectively granulate the raw material BN powder into agglomerated particles. The binder acts to firmly bind the raw material BN powder, which is inherently non-adhesive, to stabilize the shape of the granulated particles.

  The binder used for the BN slurry may be any binder as long as it can improve the adhesion between BN powders, but granulated particles are heat-treated after aggregation, so heat resistance to high temperature conditions in this heat treatment step It is preferable to have.

As such a binder, metal oxides are preferable, and specifically, aluminum oxide, magnesium oxide, yttrium oxide, calcium oxide, silicon oxide, silicon oxide, boron oxide, cerium oxide, zirconium oxide, titanium oxide and the like are preferably used. Among these, aluminum oxide and yttrium oxide are preferable from the viewpoints of thermal conductivity and heat resistance as oxides, bonding strength for bonding BN powders, and the like. The binder may be a liquid binder such as alumina sol, or a binder such as an organic metal compound which is converted to a metal oxide by firing may be used.
One of these binders may be used alone, or two or more thereof may be mixed and used.

  The amount of binder used (in the case of liquid binder, the amount used as solid content) is usually 1% by mass or more and 30% by mass or less, preferably 1% by mass or more and 20% by mass or less based on the raw material BN powder in the BN slurry. It is the mass% or less, more preferably 5 mass% or more and 20 mass% or less. If the amount of binder used is less than the above lower limit, the effect of binding the BN powders will be small, and there is a possibility that the granulated particles can not maintain the shape after granulation, and if it exceeds the above upper limit The content of BN decreases and not only influences the crystal growth, but when used as a thermally conductive filler, the effect of improving the thermal conductivity may be reduced.

<Crushing treatment>
The BN slurry may be used as it is in a granulation step by spray drying, but prior to granulation, it is preferable to pulverize the raw material BN powder in the slurry to make it finer, and aggregation is achieved by making it finer You will be able to do it smoothly.
That is, depending on the particle diameter of the raw material BN powder, when the raw material BN powder is dispersed as it is in a medium, since the BN powder is flat particles, there is a tendency that many particles not granulated in the aggregation step. However, miniaturization and efficient aggregation can be performed.

  For pulverization, usual pulverization methods such as bead mill, ball mill and pin mill can be used, but bead mill is preferable from the viewpoint of being able to carry out mass circulation pulverization as slurry and controlling the pulverized particle size easily. In addition, since the viscosity of the BN slurry is increased by pulverizing the BN particles into fine particles, it is preferable that the BN slurry can be crushed even at a high concentration and high viscosity, and additionally, the temperature increase of the BN slurry as the crushing proceeds Preferably, a cooling system is provided as it occurs. As such an apparatus, for example, "OB mill" manufactured by Freundt Turbo, "Star Mill LMZ series" manufactured by Ashizawa Finetech, etc. may be mentioned.

Granulation (aggregation)
Although there is no restriction in particular in order to obtain granulated particles which are agglomerated BN particles from BN slurry, a spray dry method is suitably used. In the spray drying method, granulated particles of a desired size are produced by the concentration of the slurry serving as the raw material, the amount of liquid feed per unit time introduced into the apparatus, and the pressure and pressure of the pressure of the fed slurry. It is also possible to obtain spherical granulated particles. There is no limitation on the spray-drying apparatus used for the spheroidization, but in order to obtain larger spherical BN granulated particles, a rotary disc is most suitable. As such an apparatus, the spray dryer F series by Ogawara Chemical Industries, Ltd., the spray dryer "MDL-050M" by Fujisaki Electric Co., etc. are mentioned.

The maximum particle size of the granulated particles obtained by granulation is an average particle size on a volume basis in order to set the range of the maximum particle size on a volume basis to be larger than 25 μm and 200 μm or less as aggregated BN particles of the present invention after heat treatment. D ₅₀ in the normal 1μm or more, particularly 10μm or 150μm or less, it is preferable that especially 10μm or 100μm or less. Here, the average particle diameter D ₅₀ based on volume of the granulated particles, for example, can be measured by Nikkiso Co., Ltd. "Microtrac HRA".

<Heat treatment>
The granulated particles of boron nitride obtained by the above granulation are preferably further heat-treated in a non-oxidizing gas atmosphere.
Here, the non-oxidizing gas atmosphere is an atmosphere such as nitrogen gas, helium gas, argon gas, ammonia gas, hydrogen gas, methane gas, propane gas, carbon monoxide gas and the like. The crystallization rate of the agglomerated BN particles differs depending on the type of the atmosphere gas used here. For example, in the case of argon gas, the crystallization rate becomes slow, and the heat treatment time is extended for a long time. In order to carry out crystallization in a short time, in particular, nitrogen gas or a mixed gas in which nitrogen gas and another gas are used in combination is preferably used. Proper selection of the heat treatment conditions is also important for radially arranging the primary particles of boron nitride on the surface, with the specific surface area and the total pore volume of the agglomerated BN particles in a specific range.

  The heat treatment temperature is usually 1300 ° C. to 2500 ° C., preferably 1300 ° C. to 2300 ° C., more preferably 1400 ° C. to 2200 ° C. When the heat treatment temperature is less than the lower limit described below, the crystallization of h-BN is insufficient, and the thermal conductivity improvement effect when it is used as a thermally conductive filler is reduced. When the heat treatment temperature exceeds the above upper limit, the added binder component melts and decomposes, the aggregated BN particles aggregate, and there is a possibility that the original shape can not be maintained or BN is decomposed.

  The heat treatment time is usually 1 hour or more and 50 hours or less, more preferably 3 hours or more and 40 hours or less, and particularly preferably 5 hours or more and 30 hours or less. Furthermore, it is preferable to introduce a holding step for at least 3 hours at 1300 ° C. to 1500 ° C. within the above heat treatment time. By introducing the holding step in the above temperature range, h-BN can be crystallized more efficiently, so the upper heat treatment temperature tends to be able to be reduced. If the heat treatment time is less than the above lower limit, crystallization is insufficient, and if it exceeds the above upper limit, h-BN may be partially decomposed.

  The heat treatment is preferably performed in a non-oxidizing gas atmosphere, and for this purpose, the furnace is generally heated while being drawn by a vacuum pump, and exhausting is performed until the decomposition gas accompanying heating is reduced, It is preferable to continue heating to a desired temperature while introducing a non-oxidizing gas. As a standard of the temperature which exhausts with a vacuum pump, after heating temperature rising to 200-500 ° C, for example, around 400 ° C for about 30-60 minutes, exhausting is continued for about 30-60 minutes, maintaining the temperature, It is preferable to perform evacuation until the degree of vacuum is 10 Pa or less, and then introduce a non-oxidizing gas. Although the flow rate of the non-oxidizing gas depends on the size of the furnace, there is usually no problem if it is 2 L (liter) or more. Thereafter, while introducing a non-oxidizing gas, the temperature is raised to about 1500 ° C. at 50 to 100 ° C./hour, and thereafter, the temperature is raised from 1500 ° C. to a predetermined heat treatment temperature at 30 to 50 ° C./hour. After heating at this temperature during the heat treatment time, it is preferable to lower the temperature to room temperature at about 5 to 50 ° C./minute.

For example, when heat treatment is performed in a nitrogen gas atmosphere, radial growth is performed under the conditions of about 2000 ° C. for about 5 hours, and in the case of an argon gas atmosphere, about 2000 ° C. for about 5 to 15 hours. Can.
The baking furnace to which the heat treatment is applied includes batch furnaces such as muffle furnaces, tubular furnaces and atmosphere furnaces, rotary kilns, screw conveyor furnaces, tunnel furnaces, belt furnaces, pusher furnaces, and continuous furnaces such as vertical furnaces. It can be used properly depending on

Immediately after the production of the agglomerated BN particles, the obtained particles may be further agglomerated to fail to satisfy the particle diameter range suitable for the present invention. Therefore, the agglomerated BN particles may be crushed so as to satisfy the range of particle sizes suitable for the present invention, if necessary.
The method of grinding the agglomerated BN particles is not particularly limited, and a method of stirring and mixing with a grinding medium such as zirconia beads or a conventionally known grinding method such as jet injection can be applied.

<Classification>
The agglomerated BN particles after the above heat treatment are preferably classified in order to increase the average particle diameter and to suppress the increase in viscosity when blended into the composition. This classification is usually performed after the heat treatment of the granulated particles, but may be performed on the granulated particles before the heat treatment and then subjected to the heat treatment.

Classification may be either wet or dry, but dry classification is preferable from the viewpoint of suppressing the decomposition of h-BN. In particular, when the binder has water solubility, dry classification is particularly preferably used.
In dry classification, there is classification by a sieve, or air classification classified by difference between centrifugal force and fluid drag, but from the viewpoint of classification accuracy, wind classification is preferable, and a swirling current classifier, forced vortex centrifugal It can carry out using classifiers, such as a formula classifier and a semi-free-vortex centrifugal classifier. Among these, particles to be classified such as a swirling flow classifier to classify small particles in the submicron to single micron region, and a semi-free-vortex centrifugal classifier to classify relatively large particles larger than that It may be properly used according to the particle diameter of.

  In order to obtain agglomerated BN particles having a volume-based maximum particle diameter of 25 μm or more and 200 μm or less, classification operation for removing fine particles and / or semi-free vortex centrifugal classification may be performed using a swirling flow classifier. preferable.

<Shape of boron nitride secondary particles>
As described above, the raw material BN powder is granulated, and heat treatment is carried out to grow h-BN crystals while maintaining its shape, and as a further aspect of the above-mentioned physical properties, the surface is usually It becomes possible to arrange boron nitride primary particles (hereinafter sometimes referred to as “BN primary particles”) of 0.05 μm or more and 5 μm or less, and aggregate particles having a cardhouse structure can be obtained. Preferably, the boron nitride secondary particles may have a cardhouse structure in which the flat portion of the plate-like BN primary particle and the end face are in contact with each other. More preferably, the flat portion and the end face of the polygonal boron primary particle It can be set as the boron nitride secondary particle which has the card house structure which the part is contacting. . More preferably, it can be expressed as another form of the above-mentioned physical property that the agglomerated BN particles are spherical. Here, "spherical" means that the aspect ratio (the ratio of the major axis to the minor axis) is 1 or more and 2 or less, preferably 1 or more and 1.5 or less. The agglomerated BN particles are particles granulated by aggregating raw material BN powder to be described later, and the granulated particles are preferably “spherical” and “spherical” is a primary particle. It is not preferred that the shape is spherical. The aspect ratio of the agglomerated BN particles can be selected by arbitrarily selecting 200 or more particles from the image taken with a scanning electron microscope (SEM), calculating the ratio of the major axis to the minor axis, and calculating the average value. decide.

In addition, although BN primary particles having an average particle diameter of 0.05 μm or more exist on the surface of the aggregated BN particles, “0.05 μm or more” of “BN primary particles having an average particle diameter of 0.05 μm or more” means It refers to the length corresponding to the particle diameter of BN primary particles. The crystal size of this BN primary particle is observed at a magnification of about 20,000 times using a scanning electron microscope (SEM) to measure the maximum particle size of any 100 particles observed on the surface. Then, it can measure by finding an average value.

In agglomerated BN particles, how crystals are grown is one of the important requirements in the application as a high thermal conductivity filler.
In the present invention, by obtaining the boron nitride secondary particles having a card house structure by such specific crystal growth, it is said that the thermal conductivity isotropy, the kneading property with the matrix resin, and the collapse resistance are excellent. Play an effect.

  As a method of preparing aggregated BN particles, h-BN powder having a total oxygen content of usually 1% by mass or more and 10% by mass or less is used as a raw material, and heat treatment conditions are controlled as described above. It becomes possible to manufacture.

  Specifically, in agglomerated BN particles, the crystal growth direction of h-BN is radial to the sphere from the center, ie, the primary particles of BN crystal grow in the normal direction so that the a-axis is directed outward, and In the case of using raw material h-BN having a total oxygen content of less than 1% by mass, while having a card house structure, crystal growth (c-plane of h-BN is directed outward in the circumferential direction As a result, it is considered that a card house structure can not be obtained, the specific surface area is small, and the total pore volume is also large.

[1-3. Plate-like boron nitride particles]
The heat dissipation sheet of the present invention contains plate-like boron nitride particles. The plate-like boron nitride particles are not particularly limited, but the peak intensity ratio I (100) / I (004) in the 100-axis and 004-axis in the XRD measurement is usually 3.0 or less, preferably 2.95 or less, in particular Preferably it is 2.9 or less, More preferably, it is 2.85 or less. Usually, the lower limit is not limited, but is 1.0 or more.

<Size of plate-like boron nitride particles>
The size average length in the long axis direction of the plate-like boron nitride particles is usually 3 μm to 300 μm, preferably 6 μm to 200 μm, more preferably 7 μm to 150 μm, and particularly preferably 8 μm to 100 μm. When I (100) / I (004) and the size in the long axis direction are in this range, the thermal conductivity in the sheet thickness direction can be enhanced by mixing with the above-mentioned secondary particles of boron nitride, preferable. If the thickness is out of this range, the number of voids increases, the heat conductivity may not be enhanced, and the voltage resistance may not be enhanced.
Commercially available products exist as plate-like boron nitride satisfying the above range, and commercially available products include Denka boron nitride SGP, MGP, GP, HGP, SP-2 and the like manufactured by Denka Co., and PT-110 and PT- manufactured by Momentive. 120, PT-140, PT-180, PT-160, PT-180 and the like. With regard to I (100) / I (004), commercially available plate-like boron nitrides that satisfy the range exist as commercially available products, and may be selected appropriately. On the other hand, when the size in the long axis direction is large, the size can be reduced by classification or the like to be in the above range.
In addition, the size average length of the plate-like boron nitride particles in the long axis direction is an average value observed for 20 or more particles with an electron microscope.

The weight content ratio of the boron nitride secondary particles and the plate-like boron nitride particles in the heat dissipation sheet is not particularly limited, but the boron nitride secondary particles / (boron nitride secondary particles + plate-like boron nitride particles) are usually 0. It is 1 or more and 0.98 or less, preferably 0.2 or more and 0.95 or less, more preferably 0.3 or more and 0.9 or less, and particularly preferably 0.4 or more and 0.85 or less.
By setting it as the said range, a boron nitride secondary particle and plate-shaped boron nitride particle are contained in a thermal radiation sheet by a suitable ratio, and high heat conduction is carried out by arranging plate-shaped boron nitride particles in a random direction. Rates can be achieved.

[1-4. Matrix resin]
In the heat dissipating sheet, usually, the heat transfer agent is the above-mentioned filler, ie, boron nitride secondary particles and plate-like boron nitride particles. However, the heat dissipating sheet for power semiconductor devices has a high heat conductivity of 10 W / mK or more. Therefore, it is desirable that the thermal conductivity of the matrix resin used for the heat dissipating sheet is also high.
In order to obtain high thermal conductivity by complexation with the filler, the thermal conductivity of the matrix resin is preferably 0.2 W / mK or more, and particularly preferably 0.22 W / mK or more.

  The thermal conductivity of the matrix resin in the heat dissipation sheet is determined by using only the curing agent in the coating liquid and the matrix resin and the organic solvent among the components constituting the heat dissipation sheet coating liquid. The cured film is formed according to a common curing method, and this cured film is a value determined by the following method.

<Method of measuring thermal conductivity of matrix resin>
The thermal diffusivity, specific gravity, and specific heat of the cured film of the matrix resin are measured using the following apparatus, and the thermal conductivity is determined by multiplying these three measured values.
(1) Thermal diffusivity: "I-phase mobile 1u" manufactured by I-phase
(2) Specific gravity: manufactured by METTLER TOLEDO "balance XS-204"
(Use of solid specific gravity measurement kit)
(3) Specific heat: Seiko Instruments Inc. "DSC320 / 6200"

  As a matrix resin, any of a curable resin and a thermoplastic resin can be used without limitation. The curable resin may be any one that is crosslinkable such as thermosetting, light curing, electron beam curing, etc. However, in view of heat resistance, water absorption, dimensional stability, etc., thermosetting resin is preferable. Used.

As a thermosetting resin and a thermosetting resin, what was illustrated by WO2013 / 081061 can be used, for example. Among these, it is preferable to use a thermosetting resin, and in particular, it is preferable to use an epoxy resin.
The epoxy resin is preferably a phenoxy resin having at least one skeleton selected from the group consisting of a naphthalene skeleton, a fluorene skeleton, a biphenyl skeleton, an anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton and a dicyclopentadiene skeleton. Among them, a phenoxy resin having a fluorene skeleton and / or a biphenyl skeleton is particularly preferable because heat resistance is further enhanced, and in particular, it has at least one skeleton of biphenol A skeleton, bisphenol F skeleton and biphenyl skeleton. It is preferable that it is a phenoxy resin.

The content of the matrix resin in the heat dissipation sheet is usually 2 wt% or more, preferably 5 wt% or more, more preferably 7 wt% or more, and usually 70 wt% or less, preferably 60 wt% or less, more preferably 40 wt% or less .
The content of boron nitride (boron nitride secondary particles and plate-like boron nitride particles) in the heat dissipation sheet is usually 30 wt% or more, preferably 40 wt% or more, more preferably 50 wt% or more, and usually 99 wt% or less Preferably it is 98 wt% or less, More preferably, it is 95 wt% or less.
The content of the boron nitride secondary particles in the heat dissipation sheet is usually 3 wt% or more, preferably 10 wt% or more, more preferably 15 wt% or more, and usually 97 wt% or less, preferably 95 wt% or less, more preferably It is 90 wt% or less.
In addition, the content of plate-like boron nitride particles in the heat dissipation sheet is usually 3 wt% or more, preferably 10 wt% or more, more preferably 15 wt% or more, and usually 97 wt% or less, preferably 95 wt% or less, more preferably It is 90 wt% or less.
By containing the matrix resin and the boron nitride in the above range in the heat dissipation sheet, high thermal conductivity can be exhibited.

[1-5. Resin-containing boron nitride secondary particles]
The boron nitride secondary particles contained in the heat dissipation sheet may be boron nitride secondary particles containing a resin.
The boron nitride secondary particles have an adequate pore volume due to having a cardhouse structure, and the resin can be introduced into the boron nitride secondary particles by capillary action.
By using resin-incorporated boron nitride secondary particles, it is possible to eliminate absorption of the solvent in the boron nitride secondary particles and voids in the boron nitride secondary particles, achieving high thermal conductivity and high voltage resistance. can do.

  The weight ratio of the encapsulated resin in the resin-encapsulated boron nitride secondary particles is usually 5 wt% to 50 wt%, preferably 8 wt% to 45 wt%, more preferably 10 wt% to 40 wt%, particularly preferably 15 wt%. % Or more and 35 wt% or less. If it is above the upper limit value, the resin will stick out of the boron nitride secondary particles, making the particles easy to aggregate and difficult to handle. On the other hand, when the content is below the lower limit, the boron nitride secondary particles can not be sufficiently covered with the resin, and the absorption amount of the solvent can not be sufficiently suppressed in the composition, which makes it difficult to form a slurry.

  The encapsulated resin contained in the boron nitride secondary particles has a solubility in water of usually 5 wt% or less, preferably 4 wt% or less, more preferably 3 wt% or less, particularly preferably 2 wt% or less. This is because the basal plane of boron nitride is hydrophobic. In order to introduce the resin into the inside of the boron nitride secondary particles by capillary phenomenon, the solvent to be used is non-water-soluble, and further, the inclusion resin is also required to be dissolved in the non-water-soluble solvent. That is, the resin required for the contained resin is preferably a hydrophobic resin. In addition, even after the non-water-soluble solvent is removed, the hydrophobic resin is desirable in order to increase the adhesion between the boron nitride and the encapsulating resin even when the encapsulating resin fills the inside of the boron nitride secondary particles.

The resin contained in the boron nitride particles preferably contains a curable resin, and preferably contains an epoxy resin. Furthermore, it is preferable to include a phenoxy resin having at least one or more skeletons in the group consisting of bisphenol A skeleton, bisphenol F skeleton and biphenyl skeleton. By including these resins, good heat dissipation can be obtained when the heat dissipation sheet is formed.
Further, a surfactant can be added to the contained resin. The amount of surfactant added is usually 0.001 to 5% by mass, preferably 0.005 to 3% by mass, based on the total amount of the encapsulating resin. If the addition amount of the surfactant is less than the above lower limit, the inclusion resin may not sufficiently penetrate into the boron nitride secondary particles, and if it exceeds the above upper limit, the adhesion between the boron nitride and the inclusion resin is poor, which is not preferable. .
In addition, a curing agent described later and other additives may be contained in the encapsulating resin. The content etc. can refer to the description mentioned later.
Moreover, different functions can be imparted to the heat dissipation sheet by using the internal resin and the matrix resin as different resins, which is preferable.

In order to produce the resin-encapsulated boron nitride secondary particles, any method may be used as long as the resin can be introduced into the boron nitride secondary particles, but the resin is introduced into the boron nitride secondary particles using capillary action. When using, it is preferable to use a solvent. Although the solvent to be used is not particularly limited, an organic solvent is preferable because the basal surface of boron nitride has a hydrophobic surface.

As the organic solvent, for example, alcohol solvents, aromatic solvents, amide solvents, alkane solvents, ethylene glycol ether and ether / ester easer, propylene glycol ether and ether / ester solvents, ketone exemplified below From among the system solvents and the ester solvents, it can be suitably selected and used in consideration of the solubility of the resin and the like.
As a specific example of the organic solvent, those exemplified in WO2013 / 081061 can be used.
The organic solvents may be used alone or in any combination of two or more in any proportion.

<Other inorganic substances>
The resin-encapsulated boron nitride secondary particles may optionally contain an inorganic substance other than boron nitride, and one or more inorganic fillers selected from silica, alumina, aluminum nitride, silicon nitride, and magnesium oxide. May be contained.
The content of these inorganic fillers is usually 50 wt% or less, preferably 40 wt% or less, more preferably 30 wt% or less. Moreover, it is usually 0.5 wt% or more.

[1-6. Other ingredients]
<Hardening agent>
The matrix resin contained in the heat dissipation sheet may contain a curing agent, if necessary.
The curing agent used in the present invention indicates a substance that contributes to the crosslinking reaction between the crosslinking groups of the matrix resin, such as the epoxy group of the epoxy resin.
In the epoxy resin, as needed, a curing agent for epoxy resin and a curing accelerator are used together.

  The curing accelerator may be appropriately selected according to the type of matrix resin and curing agent used. For example, as a curing accelerator for the acid anhydride curing agent, for example, boron trifluoride monoethylamine, 2-ethyl-4-methylimidazole, 1-isobutyl-2-methylimidazole, 2-phenyl-4-methylimidazole It can be mentioned. One of these may be used alone, or two or more may be mixed and used. These curing accelerators are usually used in the range of 0.1 to 5 parts by mass with respect to 100 parts by mass of the epoxy resin.

There is no restriction | limiting in particular as a hardening agent, According to the kind of thermosetting resin to be used, it selects and uses. When the thermosetting resin is an epoxy resin, any one generally known as an epoxy resin curing agent can be used. For example, amine curing agents such as phenolic curing agents, aliphatic amines, polyether amines, alicyclic amines and aromatic amines, acid anhydride curing agents, amide curing agents, tertiary amines, imidazoles and the like Derivatives, organic phosphines, phosphonium salts, tetraphenylboron salts, organic acid dihydrazides, halogenated boron amine complexes, polymercaptan-based curing agents, isocyanate-based curing agents, blocked isocyanate-based curing agents and the like can be mentioned.
As specific examples of the curing agent, those exemplified in WO2013 / 081061 can be used.
One of these curing agents may be used alone, or two or more thereof may be mixed and used in any combination and ratio.
Among the curing agents, imidazole or a derivative thereof or a dicyandiamine compound is suitably used.
The content of the curing agent is usually 0.1 to 60 parts by mass, preferably 0.5 to 40 parts by mass with respect to 100 parts by mass of the matrix resin.

  In particular, when the curing agent is a phenolic curing agent, an amine curing agent, or an acid anhydride curing agent, the equivalent ratio of the epoxy group in the epoxy resin to the functional group in the curing agent is usually 0.8 to 1 It is preferable to use in the range of .5. If the content is out of this range, unreacted epoxy groups and functional groups of the curing agent may remain, and desired physical properties may not be obtained.

In addition, the curing agent is an amide type curing agent, tertiary amine, imidazole and derivatives thereof, organic phosphines, phosphonium salt, tetraphenyl boron salt, organic acid dihydrazide, boron halide amine complex, polymercaptan type curing agent, isocyanate type In the case of a curing agent, a block isocyanate type curing agent, etc., it is preferably used in a range of usually 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the epoxy resin.
Moreover, in the case of the dicyan diamine compound, it is preferable to use in 0.1-10 mass parts with respect to 100 mass parts of epoxy resins, and 0.5-6 mass parts is more preferable normally.

[Other additives]
In order to further improve the functionality, the heat dissipation sheet may contain various additives (other additives) as long as the effects of the present invention are not impaired. Other additives include, for example, functional resins obtained by adding functionality to the above matrix resin, such as liquid crystalline epoxy resin, nitride particles such as aluminum nitride, silicon nitride, and fibrous boron nitride, alumina, fibrous Insulating metal oxides such as alumina, zinc oxide, magnesium oxide, beryllium oxide and titanium oxide, insulating carbon components such as diamond and fullerene, resin curing agents, resin curing accelerators, viscosity modifiers, dispersion stabilizers .

Furthermore, as other additives, coupling agents such as silane coupling agents and titanate coupling agents, as additives for improving the adhesion to the substrate and the adhesion between the matrix resin and the inorganic filler, and storage Examples thereof include UV inhibitors for improving stability, antioxidants, plasticizers, flame retardants, colorants, dispersants, flow improvers, adhesion improvers with a substrate, and the like.
In addition, the heat dissipating sheet can also contain thermoplastic oligomers from the viewpoint of improving the fluidity at the time of molding and the adhesion with the base material.

In addition, a surfactant, an emulsifier, a low-elasticity agent, a diluent, an antifoaming agent, an ion trap agent, etc. which improve the dispersibility of each component in a composition or a coating liquid can also be added.
Any of these may be used alone, or two or more may be mixed and used in any combination and ratio.
As specific examples of the additive, those exemplified in WO 2013/081061 can be used, and the addition amount can also be in the range described in WO 2013/081061.

[2. Coating fluid for heat dissipation sheet]
Another embodiment of the present invention is a coating solution for a heat dissipation sheet, which comprises two types of boron nitride particles: boron nitride secondary particles having a card house structure and plate-like boron nitride particles. Moreover, the coating liquid for heat dissipation sheets may contain a matrix resin, a solvent and other additives. In order to disperse and mix these constituent materials, paint shakers, bead mills, planetary mixers, stirring type dispersing machines, revolution-revolution stirring mixers, three-rolls, kneaders, and single- or twin-screw kneaders are generally used. It is preferable to mix using a suitable kneading apparatus or the like.

The solid content concentration of the heat-dissipating sheet coating solution is usually 5 wt% or more, preferably 10 wt% or more, more preferably 15 wt% or more, and particularly preferably 20 wt% or more. Also, it is usually 90 wt% or less, preferably 80 wt% or less, more preferably 70 wt% or less, and particularly preferably 60 wt% or less.
When the solid content concentration of the coating liquid for heat release sheet is above this upper limit, the slurry is too thick, and the leveling properties deteriorate, so that a uniform coating film can not be formed. On the other hand, below the lower limit, in order to obtain a desired dry film thickness for the heat dissipation sheet, it is necessary to increase the wet film thickness. When the wet film thickness is increased, not only the manufacturing cost for drying the film becomes high but also the tact time becomes long. Furthermore, the occurrence of unevenness in drying may occur.

The heat sink sheet coating solution can use additives (inorganic materials other than the above-mentioned boron nitride, a curing agent, a dispersing agent, etc.) which can be added to the above-mentioned matrix resin.
The order of mixing the respective components of the heat sink sheet coating solution is also arbitrary as long as there is no particular problem such as reaction or precipitation, and any two components of the composition and the composition coating liquid or The three or more components may be premixed, and then the remaining components may be mixed, or all may be mixed at one time.

[3. Manufacturing method of molded body]
Various molded articles can be manufactured using the coating liquid for heat dissipation sheets.
As a method of molding this molded body, a method generally used for molding of a resin composition can be used.
For example, it can be molded by curing the heat dissipation sheet coating liquid in a desired shape, for example, in a state of being filled in a mold. An injection molding method, an injection compression molding method, an extrusion molding method, and a compression molding method can be used as a manufacturing method of such a molded object.
Moreover, when the coating liquid for heat dissipation sheets contains a thermosetting resin composition such as an epoxy resin or a silicone resin, molding of the molded body, that is, curing can be performed under curing temperature conditions corresponding to the respective compositions.

Moreover, when the coating liquid for thermal radiation sheet contains a thermoplastic resin composition, shaping | molding of a molded object can be performed on the conditions more than the melting temperature of a thermoplastic resin, and predetermined | prescribed shaping | molding speed and pressure. Moreover, a molded object can also be obtained by shaving off the coating material for thermal radiation sheet | seats to a desired shape from the solid-like material which shape | molded hardened | cured.
Hereinafter, the method of manufacturing the heat dissipation sheet of the present invention will be specifically described.

<Coating process>
First, a coating film is formed on the surface of the substrate with the coating liquid for heat dissipation sheet.
That is, a coating film is formed by a dip method, a spin coat method, a spray coat method, a blade method, or any other method using the coating liquid for heat dissipation sheet. By using a coating apparatus such as a spin coater, a slit coater, a die coater, or a blade coater for coating the composition coating liquid, it is possible to uniformly form a coating of a predetermined film thickness on the substrate. preferable.
In addition, although the copper foil of the below-mentioned thickness is generally used as a board | substrate, it is not limited to a copper board | substrate at all.

<Drying process>
The coating film formed by applying the heat sink sheet coating solution is generally 10 to 150 ° C., preferably 25 to 100 ° C., more preferably 30 to 90 ° C. for removing the solvent and low molecular components. Particularly preferably, drying can be performed at any temperature of 40 to 80 ° C. However, it is desirable not to exceed the boiling point of the solvent. If it is above the upper limit of this temperature range, the coating film surface may be roughened due to the convection of the solvent at the time of solvent removal. In addition, when the heat-dissipating sheet coating solution contains a thermosetting resin, the coating solution may be cured, and the resin may not flow in the subsequent press process, and the void may not be removed. If the temperature is below the lower limit of this temperature range, the solvent can not be removed effectively, which may take time to remove the solvent. The drying time is usually 5 minutes to 10 days, preferably 10 minutes to 3 days, more preferably 20 minutes to 1 day, and particularly preferably 30 minutes to 4 hours to form a dried film.
If the drying time is too short, the solvent can not be sufficiently removed, and the residual solvent may be a void in the heat dissipation sheet. If the drying time is too long, the productivity can not be increased and the manufacturing process cost may be increased.

<Pressure process>
After the drying step, a pressure step may be performed. In the sheet forming step, the purpose is to join the boron nitrides to form a heat path, the purpose to eliminate voids and voids in the sheet, the purpose to adhere to the substrate, and the resin in the boron nitride particles to be bonded in the sheet It is desirable to apply pressure for the purpose of The pressing step is usually 10 kgf / cm ^{2 to} 2000 kgf / cm ² , preferably 50 kgf / cm ^{2 to} 1000 kgf / cm ² , more preferably 80 kgf / cm ^{2 to} 800 kgf / cm ² , particularly preferably to a dried film on a copper substrate. It should be carried out by applying a load of ^{100kgf / cm 2 ~500kgf / cm 2} . By setting the weight at the time of pressure application to the above upper limit or less, it is possible to obtain a sheet having high thermal conductivity without voids or the like in the sheet without breakage of the boron nitride secondary particles. Further, by setting the weight to the above lower limit or more, the contact between the agglomerated BN particles is improved and the heat conduction path is easily formed, so that a sheet having high heat conductivity can be obtained.
In the pressing step, it is desirable to heat the composition film coated and dried on a copper substrate usually at 25 to 300 ° C., preferably 40 to 250 ° C., more preferably 50 to 200 ° C., particularly preferably 60 to 160 ° C. . By performing the sheet forming process in this temperature range, heating can reduce the melt viscosity of the resin in the dried film, and voids and voids in the sheet can be eliminated. If the temperature is higher than this range, the organic component may be decomposed or the residual solvent may be vapor to form a void.
The pressurizing step is usually 30 seconds to 4 hours, preferably 1 minute to 2 hours, more preferably 3 minutes to 1 hour, and particularly preferably 5 minutes to 45 minutes. Above this upper limit time, the manufacturing process time of the heat dissipation sheet may be too long, and the production cost may be high. Below this lower limit time, the voids and voids in the sheet can not be removed sufficiently, which may affect the heat transfer performance and the withstand voltage characteristics.

The curing process for allowing the curing reaction to be carried out completely may be carried out under pressure or without pressure, but in the case of pressure, the same conditions as the above-mentioned pressure process for the same reasons as above. It is desirable to The pressing process and the curing process may be performed simultaneously.
In particular, in the sheet forming step through the pressing step and the curing step, it is preferable to apply pressure in the above-mentioned range to perform pressing and curing so as to be within the range of compression ratio described later.

In the manufacture of the heat-radiating sheet, there is a tendency that the effects of the present invention can be easily exhibited by forming the dry film into a sheet by thus applying a large weight.
When a heat dissipation sheet is manufactured using boron nitride secondary particles having no card house structure by XRD measurement, the boron nitride secondary particles are crushed by a pressing process, and the low thermal conductive surface is oriented in the sheet in-plane direction In addition, since the plate-like boron nitride particles are oriented in the longitudinal direction of the sheet, only low thermal conductivity can be obtained in the sheet thickness direction. On the other hand, by containing specific boron nitride secondary particles and specific plate-like boron nitride particles having high fracture strength in the heat dissipation sheet, the structure of the boron nitride secondary particles is unlikely to be crushed in the pressing step, Plate-like boron nitride particles may be randomly present in the sheet, and the sheet may be thermally conductive even in the thickness direction of the sheet.

The heat-radiating sheet is produced by sheeting under a large load as described above, and in particular, the ratio of the sheet thickness before curing and the thickness of the cured sheet after being completely cured by applying a weight ( When the compression ratio (1- (hardened sheet thickness) / (unhardened sheet thickness)) calculated from (hardened sheet thickness) / (pre-hardened sheet thickness) is 0.2 or more and 0.8 or less, High thermal conductivity of 10 W / mK to 50 W / mK is expressed in the thickness direction. The compression ratio is more preferably 0.3 or more and 0.7 or less, still more preferably 0.4 or more and 0.7 or less, and particularly preferably 0.5 or more and 0.7 or less. By setting the compression ratio to the upper limit or less, it is possible to obtain a sheet having high thermal conductivity without voids in the sheet without destroying the boron nitride secondary particles. Further, by setting the compression ratio to the above lower limit or more, the contact between the boron nitride secondary particles becomes good and the heat conduction path is easily formed, so that a sheet having high thermal conductivity can be obtained.
The thermal conductivity of the heat-radiating sheet of the present invention obtained by curing with such a compression ratio is more preferably 15 to 40 W / mK, particularly preferably 20 to 40 W / mK.
Moreover, it is preferable that the said heat dissipation sheet is 3.0 or more in intensity ratio I (100) / I (004) of 100 axis | shaft and 004 axis | shaft by XRD measurement. Within the above range, the secondary boron nitride particles are not crushed even in the pressing step, and the plate-like boron nitride particles are randomly oriented, and high thermal conductivity can be achieved in the thickness direction of the heat dissipation sheet.

[4. Laminated heat dissipation sheet]
Another embodiment of the present invention is a laminated heat dissipating sheet formed by laminating a heat dissipating sheet on a support. The support is not particularly limited, but in order to increase the thermal conductivity, it is particularly preferred to use a copper foil, for example, one manufactured by the above-described method for producing a heat dissipating sheet and laminated and integrated with a copper foil preferable.

The thickness of the heat dissipating sheet of the present invention or the laminated heat dissipating sheet is not particularly limited, but it is preferably 100 to 300 μm, particularly preferably 150 to 250 μm. If the thickness of the heat dissipation sheet is less than the above lower limit, the thickness of the cured film is too thin, the withstand voltage characteristics deteriorate, and the dielectric breakdown voltage becomes low, which is not preferable. It is not preferable because thinning can not be achieved.
In addition, the thickness of the copper foil is preferably 30 to 200 μm, particularly 30 to 150 μm, in order to ensure sufficient heat dissipation.

[5. Power device equipment]
The heat dissipating sheet or the laminated heat dissipating sheet can be mounted on a power device as a heat dissipating substrate. The power device apparatus provided with the heat dissipation sheet and the laminated heat dissipation sheet can achieve high output and high density with high reliability due to the heat dissipation effect by high thermal conductivity. In the power semiconductor device device, conventionally known members can be appropriately adopted as members such as aluminum wiring, sealing material, package material, heat sink, thermal paste, and solder other than the heat dissipation sheet or laminated heat dissipation sheet.

Hereinafter, the present invention will be described in more detail by way of production examples.
<Production Example 1 of boron nitride secondary particles>
BN-A agglomerated particles were prepared by the method described below.
In order to produce BN-A agglomerated particles, as a raw material, the half width of the (002) plane peak obtained by powder X-ray diffraction measurement is 2θ = 0.67 °, and the oxygen concentration is 7.5 mass% h -BN (hereinafter described as raw material h-BN powder) was used.
・ Preparation of agglomerated particles from BN slurry
[Slurry A]
Slurry A having a viscosity of 810 mPa · s was prepared by the following composition.
Slurry A composition Raw material h-BN powder: 10000 g
Pure water: 0 g
Binder (Takiceram M160L, manufactured by Taki Chemical Co., Ltd., solid concentration 21% by mass): 1
1496 g
Surfactant (Kao Co., Ltd. surfactant "ammonium lauryl sulfate": solid concentration 14% by mass): 250 g
[Slurry preparation]
A predetermined amount of raw material h-BN powder was weighed into a resin-made bottle, and then a predetermined amount of pure water and a binder were sequentially added. Further, after a predetermined amount of surfactant was added, zirconia ceramic balls were added and the mixture was stirred by a pot mill rotary table. Stirring was carried out until the desired viscosity was reached for 1 to 5 hours.
[Granulation]
Granulation from BN slurry was performed using FOC-20 manufactured by Ogawara Kako Co., Ltd.
It implemented by disc rotation speed 20000-23000 rpm, and the drying temperature of 80 degreeC.

[Preparation of BN-A Aggregated Particles]
The BN granulated particles were heat-treated at 2000 ° C. for 5 hours under nitrogen gas flow.
The temperature elevation and temperature lowering during the heat treatment were performed as follows.
After evacuation at room temperature, nitrogen gas was introduced and pressure was restored, and while the nitrogen gas was introduced as it was, the temperature was raised to 2000 ° C. at 83 ° C./hour and held for 5 hours after reaching 2000 ° C. Then, it cooled to room temperature and obtained BN-A aggregation particle | grains.
[Classification]
Furthermore, the BN agglomerated particles after the above heat treatment were lightly crushed using a mortar and a pestle, and then classified using a sieve with an opening of 90 μm. After classification, the average crystallite diameter of BN-A agglomerated particles, D ₅₀ , and peak intensity ratio of (100) plane to (004) plane by XRD measurement were measured. The measurement results are shown in Table 1. Moreover, the SEM photograph of BN-A is shown in FIG. It can be seen from FIG. 2 that the BN secondary particles produced are boron nitride secondary particles having a cardhouse structure.

<Manufacture of heat dissipation sheet>
The manufactured BN secondary particles, plate-like boron nitride, and an epoxy resin are added to water and mixed to prepare a slurry for a heat dissipation sheet. The prepared slurry is applied in a sheet form on a copper plate and dried to remove water, whereby a heat dissipation sheet is obtained.

The boron nitride secondary particles having a card house structure produced according to the above-described production example exhibit very advantageous effects by being contained in the heat dissipation sheet as a filler together with the plate-like boron nitride particles. First, the boron nitride secondary particles having a card house structure have a very high breaking strength due to their structure, and do not crush even in the pressing step performed at the time of forming the heat-radiating sheet. Therefore, by combining and using plate-like boron nitride particles, it has become possible to cause plate-like boron nitride particles normally oriented in the longitudinal direction of the heat dissipation sheet to be present in random directions. As a result, it is possible to provide a heat dissipating sheet capable of achieving high thermal conductivity also in the thickness direction.
In addition, by not collapsing boron nitride secondary particles having a card house structure even in the pressing step, it is possible to obtain a heat dissipation sheet having high thermal conductivity and high voltage resistance when contained in a heat dissipation sheet. is there. The heat dissipation sheet can provide high reliability when applied to a power device.

Claims (8)

A heat dissipation sheet having a card house structure, primary particles arranged radially on the surface of secondary particles, and secondary particles of boron nitride having a breaking strength of 20 MPa or less and plate-like boron nitride particles . The heat sink sheet according to claim 1, wherein the length of the plate-like boron nitride particles in the long axis direction is 8 μm or more and 100 μm or less .   The heat dissipation sheet according to claim 1 or 2, wherein the plate-like boron nitride particles have an intensity ratio I (100) / I (004) of 100 axes to 004 axes smaller than 3.0 as measured by XRD.   The content ratio of the boron nitride secondary particles and the plate-like boron nitride particles represented by boron nitride secondary particles / (boron nitride secondary particles + plate-like boron nitride particles) is 0.1 or more and 0.98. The heat dissipation sheet according to any one of claims 1 to 3, which is the following.   The heat dissipation according to any one of claims 1 to 4, wherein the boron nitride secondary particles have an intensity ratio I (100) / I (004) of 100 axes to 004 axes of 3.0 or more as measured by XRD. Sheet.   The heat dissipation sheet according to any one of claims 1 to 5, wherein the boron nitride secondary particles are particles containing a resin.   The lamination | stacking heat-radiation sheet by which the heat-radiation sheet of any one of Claims 1-6 is laminated | stacked on a support body.   The power device apparatus containing the thermal radiation sheet of any one of Claims 1-7.