JP5791488B2 - Resin composition for heat conductive sheet, heat conductive sheet and power module - Google Patents

Description

  The present invention relates to a resin composition for a heat conductive sheet, a heat conductive sheet, and a power module, and more particularly to the manufacture of a heat conductive sheet that transfers heat from a heat generating member of an electric / electronic device such as a power module to a heat radiating member. The present invention relates to a resin composition for a heat conductive sheet to be used, and a heat conductive sheet and a power module manufactured using the resin composition for a heat conductive sheet.

  A member that transmits heat generated from a heat generating portion of an electric / electronic device to a heat radiating member is required to be excellent in thermal conductivity and electrical insulation. As a member satisfying such requirements, a heat conductive sheet in which an inorganic filler is dispersed in a cured product of a thermosetting resin is widely used. Various inorganic fillers are known for use in this heat conductive sheet. Among them, hexagonal boron nitride (h-BN) is chemically stable in addition to heat conductivity and electrical insulation. In addition, since it is non-toxic and relatively inexpensive, it is optimal for use in a heat conductive sheet.

  Hexagonal boron nitride has a molecular structure similar to graphite. Further, commercially available hexagonal boron nitride has a scaly crystal structure as shown in FIG. 4 and is also referred to as scaly boron nitride. In FIG. 4, the direction of the arrow represents the direction of heat conduction, and the thickness of the arrow represents the magnitude of heat conduction. This scaly boron nitride has thermal anisotropy that the thermal conductivity in the major axis direction (crystal direction) is high and the thermal conductivity in the minor axis direction (layer direction) is low. The thermal conductivity in the (plane direction) is said to be several to several tens of times in the c-axis direction (thickness direction). Therefore, in the sheet thickness direction, the scale-like boron nitride dispersed in the cured product of the thermosetting resin is upright in the sheet, that is, by orienting the major axis direction of the scale-like boron nitride parallel to the sheet thickness direction. Development of thermal conductive sheets with dramatically improved thermal conductivity has been carried out.

  Generally, a heat conductive sheet is a known resin composition containing scaly boron nitride and a thermosetting resin, such as a press molding method, an injection molding method, an extrusion molding method, a calender molding method, a roll molding method, a doctor blade molding method, etc. It is manufactured by forming into a sheet by the forming method and then curing. However, in such a method, the scale-like boron nitride collapses in the sheet due to the pressure and flow during molding into a sheet, that is, as shown in FIG. 5, in the cured product 4 of the thermosetting resin. Therefore, the major axis direction of the scaly boron nitride 2 is easily oriented parallel to the sheet surface direction. Since such a heat conductive sheet is excellent in the heat conductivity in the sheet surface direction, the heat conductivity is not sufficient in the usage form in which the sheet thickness direction is a heat conduction path.

  Therefore, various methods have been proposed to increase the thermal conductivity in the sheet thickness direction. For example, a method has been proposed in which secondary particles obtained by agglomerating scaly boron nitride are produced, and a thermally conductive sheet is produced using a resin composition containing the secondary particles (for example, Patent Documents 1 and 2). reference). By using such secondary particles, it is possible to suppress the scaly boron nitride from falling in the thermally conductive sheet.

Japanese Patent No. 3654743 International Publication No. 2009/041300

The conventional thermal conductive sheet using secondary particles obtained by aggregating flaky boron nitride improves the thermal conductivity in the sheet thickness direction by controlling the orientation of the flaky boron nitride. not enough. In particular, in the power module, the amount of heat generation has increased in recent years with an increase in capacity and miniaturization. From the viewpoint of improving heat dissipation, it is still possible to improve the thermal conductivity in the thickness direction of the thermal conductive sheet. It has been demanded.
On the other hand, there is a method of blending spherical aluminum nitride (AlN) in place of secondary particles obtained by agglomerating scaly boron nitride, but the relative dielectric constant (about 9) of aluminum nitride is the relative dielectric constant of boron nitride. Since it is higher than (about 4) and is significantly different from the relative dielectric constant (about 4) of the thermosetting resin, the electrical insulation is greatly reduced.

The present invention has been made to solve the above-described problems, and provides a resin composition for a heat conductive sheet that provides a heat conductive sheet excellent in heat conductivity and electrical insulation in the sheet thickness direction. The purpose is to do.
Moreover, an object of this invention is to provide the heat conductive sheet excellent in the heat conductivity and electrical insulation of a sheet | seat thickness direction.
Furthermore, an object of this invention is to provide the power module excellent in heat dissipation and electrical insulation.

  As a result of intensive studies to solve the above problems, the present inventors have found that the degree of crystallinity of secondary particles obtained by aggregating scaly boron nitride is closely related to the agglomeration force and thermal conductivity of secondary particles. Based on the knowledge that it is related, the use of secondary particles with a crystallinity in a predetermined range not only controls the orientation of the flaky boron nitride, but also improves the thermal conductivity of the secondary particles themselves. I found out that I could make it.

That is, the present invention is a resin composition for a thermally conductive sheet comprising an epoxy resin and a filler , wherein the filler is composed only of secondary particles of scaly boron nitride, and the secondary particles are 3 A resin composition for a heat conductive sheet, comprising 60% by mass or more of secondary particles having a crystallinity of 7 or less.
Further, the present invention is a thermally conductive sheet containing a filler in a cured epoxy resin, wherein the filler consists only of secondary particles of scaly boron nitride, and the secondary particles are 3 or more. A heat conductive sheet comprising 60% by mass or more of secondary particles having a crystallinity of 7 or less.
Furthermore, the present invention provides a power semiconductor element mounted on one heat radiating member, another heat radiating member that radiates heat generated in the power semiconductor element to the outside, and heat generated in the power semiconductor element. A power module comprising: the heat conductive sheet that transmits from a heat radiating member to the other heat radiating member.

  ADVANTAGE OF THE INVENTION According to this invention, the resin composition for heat conductive sheets which gives the heat conductive sheet excellent in the heat conductivity of a sheet thickness direction and electrical insulation can be provided. Moreover, according to this invention, the heat conductive sheet excellent in the heat conductivity and electrical insulation of a sheet | seat thickness direction can be provided. Furthermore, according to this invention, the power module excellent in heat dissipation and electrical insulation can be provided.

It is sectional drawing of the heat conductive sheet in Embodiment 2. FIG. FIG. 6 is a cross-sectional view of a power module in a third embodiment. It is a graph showing the relationship between the crystallinity degree of the secondary particle in Examples 1-5 and Comparative Examples 1-4, and the thermal conductivity of a sheet | seat thickness direction. It is a figure which shows the crystal structure of scaly boron nitride. It is sectional drawing of the conventional heat conductive sheet containing scaly boron nitride. It is sectional drawing of the conventional heat conductive sheet containing a secondary particle.

Embodiment 1 FIG.
The resin composition for a heat conductive sheet of the present embodiment (hereinafter abbreviated as “resin composition”) includes a thermosetting resin and scaly boron nitride secondary particles. Here, in the present specification, “secondary particles of flaky boron nitride” means isotropic aggregation and sintering of flaky boron nitride (hereinafter sometimes referred to as “primary particles”). Means that the scaly boron nitrides are bound together.
The secondary particles desirably have a large cohesive force in order to prevent the primary particles from collapsing during the production of the heat conductive sheet and causing the primary particles to fall within the sheet. Moreover, in order to improve the thermal conductivity in the thickness direction of the thermal conductive sheet, it is also desirable that the secondary particles themselves have a high thermal conductivity.

  As a result of detailed studies on the agglomeration force and thermal conductivity of the secondary particles, the present inventors found that the agglomeration force and thermal conductivity of the secondary particles are closely related to the crystallinity of the secondary particles. I found out. Based on such knowledge, in the resin composition of the present embodiment, it is necessary to regulate the crystallinity of the secondary particles to 3 or more and 7 or less in order to increase both the cohesive force and thermal conductivity of the secondary particles. is there. When the degree of crystallinity of the secondary particles is less than 3, the binding force between the primary particles becomes weak, and the cohesive force of the secondary particles is reduced. As a result, the secondary particles collapse during the production of the heat conductive sheet, and the primary particles tend to fall in the sheet. On the other hand, when the degree of crystallinity of the secondary particles exceeds 7, heat conduction is inhibited by the phonons of the scaly boron nitride, so that the thermal conductivity of the secondary particles decreases. As a result, the heat conductivity in the thickness direction of the heat conductive sheet is not sufficiently improved.

  Further, all the secondary particles may have a crystallinity of 3 or more and 7 or less, but 60% by mass or more of all the secondary particles have a crystallinity of 3 or more and 7 or less. If it has, if the heat conductive sheet is manufactured, the effect of improving the heat conductivity in the sheet thickness direction can be sufficiently obtained. When the secondary particles having a crystallinity of 3 or more and 7 or less are less than 60% by mass, the effect of improving the thermal conductivity in the sheet thickness direction cannot be sufficiently obtained.

Here, the crystallinity of the secondary particles can be determined by measuring the X-ray diffraction pattern of the secondary particles. Specifically, it can be calculated by obtaining the diffraction peak areas of the (100) plane, (101) plane and (102) plane in X-ray diffraction and substituting them into the following (Equation 1).
Crystallinity = [(100) + (101)] / (102) (Formula 1)
In the above formula 1, (100), (101), and (102) represent the diffraction peak areas of each surface. In general, the degree of crystallinity of the secondary particles increases as the crystallinity decreases, and decreases as the crystallinity increases. With perfect crystallinity, the degree of crystallinity of secondary particles is about 1.6.

The calculation of the degree of crystallinity of the secondary particles is preferably performed by sampling several points (preferably 10 points) and obtaining an average value of the degree of crystallinity obtained from each sample.
When calculating the crystallinity of the secondary particles in the resin composition, the secondary particles of the raw material may be used as a sample. Moreover, when calculating the crystallinity degree of the secondary particle in a heat conductive sheet, it heat-processes about 5 to 10 hours at the temperature of 500 to 800 degreeC in an air atmosphere using an electric furnace. Then, secondary particles obtained by ashing may be used as a sample.

  The average major axis of the scaly boron nitride (primary particles) constituting the secondary particles is preferably 15 μm or less, more preferably 0.1 μm or more and 10 μm or less. Here, when measuring the average major axis of the scaly boron nitride constituting the secondary particles in the resin composition, the secondary particles of the raw material were used as samples, and several photographs were taken that were enlarged several thousand times with an electron microscope. Thereafter, the major axis of the scaly boron nitride is actually measured, and the measured value can be averaged. In addition, when measuring the average major axis of the flaky boron nitride constituting the secondary particles in the thermal conductive sheet, several photographs were taken of the thermal conductive sheet that had been polished several thousand times with an electron microscope. Then, the major axis of the scaly boron nitride is actually measured, and the measured value can be averaged. If the average major axis is in the above range, the scaly boron nitride aggregates in all directions, so that secondary particles having isotropic thermal conductivity are obtained. On the other hand, when the average major axis of the flaky boron nitride is larger than 15 μm, the flaky boron nitride does not aggregate isotropically, so that anisotropy may appear in the thermal conductivity of the secondary particles (that is, in a specific direction). Only the thermal conductivity of can be high). As a result, the thermal conductivity in the sheet thickness direction may not be sufficiently improved.

The shape of the secondary particles is not particularly limited, but is preferably spherical. If the secondary particles are spherical, the fluidity of the resin composition can be ensured even if the blending amount of the secondary particles is increased.
The average particle size of the secondary particles is preferably 20 μm or more and 180 μm or less, more preferably 40 μm or more and 130 μm or less. Here, when measuring the average particle diameter of the secondary particles in the resin composition, the secondary particles of the raw material can be used as a sample, and this sample can be obtained by performing particle size distribution measurement by a laser diffraction / scattering method. Moreover, when measuring the average particle diameter of the secondary particles in the heat conductive sheet, the heat conductive sheet is heat-treated in an air atmosphere at a temperature of 500 ° C. to 800 ° C. for about 5 to 10 hours using an electric furnace. Then, the secondary particles obtained by ashing can be used as a sample, and this sample can be obtained by measuring the particle size distribution by the laser diffraction / scattering method. When the average particle size of the secondary particles is less than 20 μm, a heat conductive sheet having desired heat conductivity may not be obtained. On the other hand, when the average particle size of the secondary particles exceeds 180 μm, it becomes difficult to mix and disperse the secondary particles in the resin composition, and workability and moldability may be hindered.
Moreover, when the maximum particle diameter of the secondary particle with respect to the thickness of the heat conductive sheet to manufacture is too large, there exists a possibility that electrical insulation may fall along an interface. Therefore, the maximum particle size of the secondary particles is preferably about 90% or less of the thickness of the heat conductive sheet to be manufactured.

  The secondary particles can be produced by aggregating a slurry containing scaly boron nitride by a known method such as a spray drying method and then sintering. Here, the sintering temperature is not particularly limited, but is generally about 2,000 ° C. Moreover, since the conditions in this method vary depending on the type of raw material used, it is difficult to define uniquely. Therefore, it is necessary to appropriately adjust the secondary particles so as to have the above characteristics according to the raw material to be used.

  The content of the secondary particles is preferably 20% by volume or more and 80% by volume or less in the solid content (thermal conductive sheet) of the resin composition. In particular, when the content of secondary particles in the solid content of the resin composition is 30% by volume or more and 65% by volume or less, the secondary particles are easily mixed and dispersed in the resin composition, and workability and moldability are improved. While being favorable, the heat conductivity of a heat conductive sheet improves further. When the content of the secondary particles is less than 20% by volume, a heat conductive sheet having desired heat conductivity may not be obtained. On the other hand, when the content of the secondary particles exceeds 80% by volume, it is difficult to mix and disperse the secondary particles in the resin composition, and workability and moldability may be hindered.

  It does not specifically limit as a thermosetting resin, A well-known thing can be used in the said technical field. Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, phenol resins, melamine resins, silicone resins, and polyimide resins. Among these, epoxy resins are preferable because they are excellent in characteristics such as heat resistance and adhesiveness. Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, orthocresol novolac type epoxy resin, phenol novolac type epoxy resin, alicyclic aliphatic epoxy resin, and glycidyl-aminophenol type epoxy resin. It is done. These resins can be used alone or in combination of two or more.

When an epoxy resin is used as the thermosetting resin, examples of the curing agent include alicyclic acid anhydrides such as methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, and hymic anhydride; fats such as dodecenyl succinic anhydride Aromatic anhydrides; aromatic anhydrides such as phthalic anhydride and trimellitic anhydride; organic dihydrazides such as dicyandiamide and adipic dihydrazide; tris (dimethylaminomethyl) phenol; dimethylbenzylamine; 1,8-diazabicyclo (5 , 4, 0) Undecene and its derivatives; imidazoles such as 2-methylimidazole, 2-ethyl-4-methylimidazole and 2-phenylimidazole. These hardening | curing agents can be used individually or in combination of 2 or more types.
The compounding amount of the curing agent needs to be appropriately set according to the type of the thermosetting resin and the curing agent to be used, but is generally 0.1 parts by mass or more with respect to 100 parts by mass of the thermosetting resin. It is 200 parts by mass or less.

The resin composition of this Embodiment can contain a coupling agent from a viewpoint of improving the adhesive force of the interface of a secondary particle and the hardened | cured material of a thermosetting resin. Examples of coupling agents include γ-glycidoxypropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltri And methoxysilane. These coupling agents can be used alone or in combination.
The blending amount of the coupling agent needs to be appropriately set according to the type of the thermosetting resin and the coupling agent to be used, but is generally 0.01 mass with respect to 100 parts by mass of the thermosetting resin. Part to 1 part by mass.

The resin composition of the present embodiment includes various fillers different from the above secondary particles for the purpose of improving thermal conductivity and electrical insulation and improving the balance between thermal conductivity and electrical insulation. Can be included. Examples of the filler include fused silica (SiO ₂ ), crystalline silica (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), boron nitride (BN), aluminum nitride (AlN), silicon carbide (SiC), and the like. It is done. These can be used alone or in combination.
The blending amount of the filler is not particularly limited as long as the effects of the present invention are not impaired, and may be set as appropriate according to the type of filler to be used.

The resin composition of the present embodiment can contain a solvent from the viewpoint of adjusting the viscosity of the composition. It does not specifically limit as a solvent, What is necessary is just to select suitably according to the kind of thermosetting resin to be used, the compounding quantity of each component, etc. Examples of such a solvent include toluene and methyl ethyl ketone. These can be used alone or in combination of two or more.
The amount of the solvent is not particularly limited as long as it can be kneaded, but generally 40 parts by mass or more and 85 parts by mass with respect to 100 parts by mass in total of the thermosetting resin, secondary particles, and optional fillers. Or less.

The manufacturing method of the resin composition of this Embodiment containing the above structural components is not specifically limited, It can carry out according to a well-known method. For example, the resin composition can be manufactured as follows.
First, a predetermined amount of a thermosetting resin and an amount of a curing agent necessary for curing the thermosetting resin are mixed. Next, after adding a solvent to this mixture, secondary particles and optional fillers are added and premixed. In addition, when the viscosity of a resin composition is low, it is not necessary to add a solvent. Next, a resin composition can be obtained by kneading the preliminary mixture using a three roll or a kneader. In addition, what is necessary is just to add a coupling agent before a kneading | mixing process, when mix | blending a coupling agent with a resin composition.

  The resin composition of the present embodiment manufactured as described above has the secondary particles at the time of manufacturing the heat conductive sheet by blending the secondary particles having a predetermined crystallinity at a specific ratio. Can be prevented from collapsing and the primary particles fall in the sheet, and the thermal conductivity of the secondary particles themselves can be improved. Sex sheet can be given. Moreover, since the secondary particle is formed from scaly boron nitride, this resin composition can provide a heat conductive sheet excellent in electrical insulation.

Embodiment 2. FIG.
The thermally conductive sheet of the present embodiment is formed by molding the above resin composition into a sheet and then curing. That is, the thermally conductive sheet of the present embodiment includes scaly boron nitride secondary particles in a cured product of a thermosetting resin. Here, the secondary particles include 60% by mass or more of secondary particles having a crystallinity of 3 or more and 7 or less.

Hereinafter, the thermally conductive sheet of the present embodiment will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of a thermally conductive sheet in the present embodiment. In FIG. 1, a heat conductive sheet 1 is composed of a cured product 2 of a thermosetting resin and secondary particles 3 dispersed in the cured product 2 of the thermosetting resin. The secondary particles 3 are composed of scaly boron nitride (primary particles) 4.

The heat conductive sheet 1 of this Embodiment can be manufactured by apply | coating said resin composition to a base material and drying, and heating and hardening a coating dried material. Further, if necessary, the coated and dried product may be heated and cured while being pressed at a predetermined press pressure.
Here, it does not specifically limit as a base material, For example, well-known releasable base materials, such as a resin sheet and a film by which the release process was carried out, are mentioned. Moreover, when forming the heat conductive sheet 1 directly on a heat radiating member, you may use a heat radiating member as a base material. Here, although it does not specifically limit as a heat radiating member, For example, a lead frame, a heat sink, a heat spreader etc. are mentioned.
It does not specifically limit as a coating method of a resin composition, Well-known methods, such as a doctor blade method, can be used.
The applied resin composition may be dried at ambient temperature, but may be heated to 80 ° C. or higher and 150 ° C. or lower as needed from the viewpoint of promoting volatilization of the solvent.

When pressurizing the coated dried product, the pressing pressure is not particularly limited, but is preferably 0.5 MPa or more and 50 MPa or less, more preferably 1.9 MPa or more and 30 MPa or less. The pressing time is not particularly limited, but is generally 5 minutes or more and 60 minutes or less.
The curing temperature of the coated and dried product may be appropriately set according to the type of thermosetting resin to be used, but is generally 150 ° C. or higher and 250 ° C. or lower. Moreover, although hardening time is not specifically limited, Generally it is 2 minutes or more and 24 hours or less.

  The heat conductive sheet of the present embodiment manufactured as described above has a secondary ratio in the production of the heat conductive sheet by blending secondary particles having a predetermined crystallinity at a specific ratio. While suppressing the collapse of the particles and the primary particles falling in the sheet, it is possible to improve the thermal conductivity of the secondary particles themselves, and therefore excellent thermal conductivity in the sheet thickness direction. . Moreover, since this secondary particle is formed from scaly boron nitride, this heat conductive sheet is also excellent in electrical insulation.

Embodiment 3 FIG.
The power module of the present embodiment includes a heat conductive sheet obtained from the above resin composition. That is, the power module according to the present embodiment includes a power semiconductor element mounted on one heat radiating member, the other heat radiating member that radiates heat generated in the power semiconductor element to the outside, and heat generated in the semiconductor element. The heat conductive sheet is transmitted from the heat radiating member to the other heat radiating member.

Hereinafter, the power module of the present embodiment will be described with reference to the drawings.
FIG. 2 is a cross-sectional view of the power module of the present embodiment. In FIG. 2, the power module 10 includes a lead frame 12 that is one heat radiating member, a heat sink 14 that is the other heat radiating member, a heat conductive sheet 11 disposed between the lead frame 12 and the heat sink 14, A power semiconductor element 13 and a control semiconductor element 15 mounted on the lead frame 12 are provided. The power semiconductor element 13 and the control semiconductor element 15 and the power semiconductor element 13 and the lead frame 12 are wire-bonded by a metal wire 16. The parts other than the external connection part of the lead frame 12 and the external heat dissipation part of the heat sink 14 are sealed with a sealing resin 17.

In this power module, members other than the heat conductive sheet 11 are not particularly limited, and those known in the technical field can be used. For example, as the power semiconductor element 13, one formed of silicon can be used, but it is preferable to use one formed of a wide band gap semiconductor having a larger band gap than silicon. Examples of the wide band gap semiconductor include silicon carbide, gallium nitride-based materials, and diamond.
Since the power semiconductor element 13 formed of a wide band gap semiconductor has high voltage resistance and high allowable current density, the power semiconductor element 13 can be downsized. And by using the power semiconductor element 13 reduced in size as described above, the power module incorporating the power semiconductor element 13 can be reduced in size.
In addition, since the power semiconductor element 13 formed of a wide band gap semiconductor has high heat resistance, it leads to miniaturization of heat radiating members such as the lead frame 12 and the heat sink 14, thereby enabling further miniaturization of the power module. Become.
Furthermore, since the power semiconductor element 13 formed of a wide band gap semiconductor has low power loss, the efficiency of the element can be increased.

The method for incorporating the heat conductive sheet 11 into the power module is not particularly limited, and can be performed according to a known method. For example, when the heat conductive sheet 11 is manufactured separately, the heat conductive sheet 11 is sandwiched between the heat sink 14 and the lead frame 12 on which various parts such as the power semiconductor element 13 are mounted, and then transferred mold. What is necessary is just to arrange | position to the metal mold | die for shaping | molding, to pour sealing resin 17 into a metal mold | die using a transfer mold molding apparatus, and to seal by pressurizing and heating.
Further, when the heat conductive sheet 11 is directly formed on the heat sink 14, the lead frame 12 on which various components such as the power semiconductor element 13 are mounted is disposed on the heat conductive sheet 11, and then this is used as a transfer mold molding die. The sealing resin 17 may be poured into a mold using a transfer mold molding device, and sealed by pressurization and heating.
In addition, although the sealing method by the transfer mold method was described above, other known methods (for example, a press molding method, an injection molding method, an extrusion molding method) and the like may be used.

  In particular, when the heat conductive sheet 11 is incorporated into the power module, the heat conductive sheet 11 in which the thermosetting resin is in a B stage state (semi-cured state) is prepared in advance, and this is connected to the lead frame 12 and the heat sink 14. It is preferable that the heat conductive sheet 11 is produced by heating to 150 ° C. or higher and 250 ° C. or lower while being pressed with a predetermined press pressure. According to this method, the adhesion of the lead frame 12 and the heat sink 14 to the heat conductive sheet 11 can be improved.

  The power module of the present embodiment manufactured as described above has a heat conductive sheet excellent in heat conductivity and electric insulation in the sheet thickness direction, and thus has high heat dissipation and electric insulation. .

Hereinafter, although an Example and a comparative example demonstrate the detail of this invention, this invention is not limited by these.
The secondary particles used in the following examples and comparative examples are sintered at about 2,000 ° C. after a slurry containing scaly boron nitride (primary particles) is aggregated by a known method such as a spray drying method. Manufactured by. X-ray diffraction patterns were measured for various secondary particles produced by changing raw materials and production conditions, and the crystallinity was calculated. In addition, the average major axis of primary particles and the average particle size of secondary particles were determined by the above methods. Table 1 shows the characteristics of the produced secondary particles.

Example 1
100 parts by mass of liquid bisphenol A type epoxy resin (thermosetting resin, Epicoat 828 manufactured by Japan Epoxy Resin Co., Ltd.) and 1-cyanoethyl-2-methylimidazole (curing agent, Curazole 2PN-CN manufactured by Shikoku Kasei Kogyo Co., Ltd.) After mixing with 1 part by mass, 166 parts by mass of methyl ethyl ketone (solvent) was further added and mixed and stirred. Next, secondary particles No. were added to this mixture. 287 parts by mass of C was added and mixed. Next, this mixture was kneaded with three rolls to obtain secondary particles No. A resin composition in which C was uniformly dispersed was obtained.

Next, after applying this resin composition onto a 105 μm thick copper foil (heat radiating member) by a doctor blade method, the resin composition is heated and dried at 110 ° C. for 15 minutes, so that the heat in a B stage state with a thickness of 100 μm. A conductive sheet was obtained.
Next, the two B-stage heat conductive sheets formed on the copper foil are stacked so that the heat conductive sheet side is on the inside, then heated at 120 ° C. for 1 hour, and further heated at 160 ° C. for 3 hours. By doing this, the thermosetting resin was completely cured to obtain a heat conductive sheet sandwiched between two copper foils.

(Example 2)
Secondary particle No. Secondary particle No. Except having used D, it carried out similarly to Example 1, and obtained the heat conductive sheet pinched | interposed into the resin composition and two copper foils.
(Example 3)
Secondary particle No. Secondary particle No. A heat conductive sheet sandwiched between a resin composition and two copper foils was obtained in the same manner as in Example 1 except that E was used.
Example 4
Secondary particle No. Secondary particle No. Except having used F, it carried out similarly to Example 1, and obtained the heat conductive sheet pinched | interposed into the resin composition and two copper foils.
(Example 5)
Secondary particle No. Secondary particle No. Except having used G, it carried out similarly to Example 1, and obtained the heat conductive sheet pinched | interposed into the resin composition and two copper foils.

(Comparative Example 1)
Secondary particle No. Secondary particle No. Except having used A, it carried out similarly to Example 1, and obtained the heat conductive sheet pinched | interposed into the resin composition and two copper foils.
(Comparative Example 2)
Secondary particle No. Secondary particle No. Except having used B, it carried out similarly to Example 1, and obtained the heat conductive sheet pinched | interposed into the resin composition and two copper foils.
(Comparative Example 3)
Secondary particle No. Secondary particle No. Except having used H, it carried out similarly to Example 1, and obtained the heat conductive sheet pinched | interposed into the resin composition and two copper foils.
(Comparative Example 4)
Secondary particle No. Secondary particle No. Except having used I, it carried out similarly to Example 1, and obtained the heat conductive sheet pinched | interposed into the resin composition and two copper foils.

  About the heat conductive sheet obtained by said Example and comparative example, the heat conductivity of the sheet | seat thickness direction was measured with the laser flash method. The measurement result of this thermal conductivity is based on the thermal conductivity obtained with the thermal conductive sheet of Comparative Example 1, and the relative value of the thermal conductivity obtained with the thermal conductive sheet of each Example or each Comparative Example. It is shown in Table 2 as (value of [thermal conductivity obtained with thermal conductive sheet of each example or comparative example] / [thermal conductivity obtained with thermal conductive sheet of comparative example 1]).

Moreover, the dielectric breakdown electric field (BDE) was evaluated about said heat conductive sheet. The dielectric breakdown electric field (BDE) of the thermal conductive sheet is the breakdown voltage (BDV) measured by applying a voltage at a constant boost of 1 kV / sec to the thermal conductive sheet sandwiched between copper foils in oil. ) Divided by the thickness of the thermally conductive sheet. The result of this dielectric breakdown electric field (BDE) is based on the BDE obtained with the heat conductive sheet of Example 1, and the relative value of BDE obtained with the heat conductive sheet of each Example or Comparative Example ([each It is shown in Table 2 as (value of BDE obtained with the heat conductive sheet of Example or Comparative Example) / [BDE obtained with the heat conductive sheet of Example 1]).
In Table 2, the blending amounts and the like of the constituent components used in the above examples and comparative examples are also summarized. Moreover, about the compounding quantity, it represented using the mass part.

As shown in Table 2, the thermal conductive sheets of Examples 1 to 5 using secondary particles having a crystallinity of 3 or more and 7 or less had high thermal conductivity in the sheet thickness direction. On the other hand, the heat conductive sheets of Comparative Examples 1 to 4 using secondary particles having a crystallinity of less than 3 or more than 7 had low heat conductivity in the sheet thickness direction. This is because when the degree of crystallinity of the secondary particles is less than 3, the cohesive force of the secondary particles is remarkably reduced, and the secondary particles are collapsed during the production of the heat conductive sheet. This is considered to be caused by the vertical orientation (see FIG. 6). On the other hand, if the degree of crystallinity of the secondary particles exceeds 7, the cause is considered to be a decrease in the thermal conductivity of the secondary particles.
Based on the results of the above Examples 1 to 5 and Comparative Examples 1 to 4, a graph showing the relationship between the crystallinity of secondary particles and the thermal conductivity in the sheet thickness direction is shown in FIG. As shown in FIG. 3, it can be seen that there is a close relationship between the crystallinity of the secondary particles and the thermal conductivity in the sheet thickness direction.

(Example 6)
Secondary particle No. In place of C, the secondary particle No. 114.8 parts by mass of B and secondary particle No. Except having used 172.8 mass parts of D, it carried out similarly to Example 1, and obtained the heat conductive sheet pinched | interposed into the resin composition and two copper foils.
(Example 7)
Secondary particle No. In place of C, the secondary particle No. 57.4 parts by mass of B and secondary particle No. Except having used 229.6 mass parts of D, it carried out similarly to Example 1, and obtained the heat conductive sheet pinched | interposed into the resin composition and two copper foils.
(Example 8)
Secondary particle No. In place of C, the secondary particle No. 28.7 parts by mass of B and secondary particle No. Except having used 258.3 mass parts of D, it carried out similarly to Example 1, and obtained the heat conductive sheet pinched | interposed into the resin composition and two copper foils.

Example 9
While the amount of methyl ethyl ketone (solvent) was 78 parts by mass, the secondary particle No. Secondary particle No. A heat conductive sheet sandwiched between the resin composition and two copper foils was obtained in the same manner as in Example 1 except that D was used and the amount thereof was 82 parts by mass.
(Example 10)
While the amount of methyl ethyl ketone (solvent) was 102 parts by mass, the secondary particle No. Secondary particle No. A heat conductive sheet sandwiched between the resin composition and two copper foils was obtained in the same manner as in Example 1 except that D was used and the amount thereof was 127 parts by mass.
(Example 11)
While the amount of methyl ethyl ketone (solvent) was 234 parts by mass, secondary particle No. Secondary particle No. A heat conductive sheet sandwiched between the resin composition and two copper foils was obtained in the same manner as in Example 1 except that D was used and the amount thereof was 446 parts by mass.

(Comparative Example 5)
Secondary particle No. In place of C, the secondary particle No. 129.2 parts by mass of B and secondary particle No. Except having used 157.9 mass parts of D, it carried out similarly to Example 1, and obtained the heat conductive sheet pinched | interposed into the resin composition and two copper foils.

About the heat conductive sheet obtained by said Example and comparative example, the heat conductivity and dielectric breakdown electric field (BDE) of the sheet thickness direction were evaluated. These evaluations are shown in Table 3 as relative values using the same criteria as described above.
In Table 3, the blending amounts of the constituent components used in the above Examples and Comparative Examples are also summarized. Moreover, about the compounding quantity, it represented using the mass part.

  As shown in Table 3, the heat conductive sheet in which the ratio of the secondary particles having a crystallinity of 3 or more and 7 or less in the entire secondary particles is 60% by mass or more is the heat conduction in the sheet thickness direction. While the rate was high, the thermal conductive sheet having this ratio of 55% by mass had low thermal conductivity in the sheet thickness direction in the sheet thickness direction (comparison between Examples 6 to 8 and Comparative Example 5). . Moreover, the heat conductive sheet whose secondary particle content is 30 to 70% by volume had high heat conductivity in the sheet thickness direction (Examples 9 to 11).

Next, using the heat conductive sheet of Examples 1-11, it sealed with sealing resin by the transfer molding method, and produced the power module.
In this power module, after attaching a thermocouple to the lead frame and the central part of the copper heat sink, the power module was operated and the temperatures of the lead frame and the heat sink were measured. As a result, all the power modules using the heat conductive sheets of Examples 1 to 11 had a small temperature difference between the lead frame and the heat sink and were excellent in heat dissipation.

  As can be seen from the above results, according to the present invention, it is possible to provide a resin composition for a thermally conductive sheet that provides a thermally conductive sheet excellent in thermal conductivity and electrical insulation in the sheet thickness direction. Moreover, according to this invention, the heat conductive sheet excellent in the heat conductivity and electrical insulation of a sheet | seat thickness direction can be provided. Furthermore, according to this invention, the power module excellent in heat dissipation and electrical insulation can be provided.

  DESCRIPTION OF SYMBOLS 1 Thermal conductive sheet, 2 Hardened | cured material of thermosetting resin, 3 Secondary particle, 4 Scale-like boron nitride, 10 Power module, 11 Thermal conductive sheet, 12 Lead frame, 13 Power semiconductor element, 14 Heat sink, 15 Control Semiconductor element, 16 metal wire, 17 sealing resin.

Claims (11)

A resin composition for a thermally conductive sheet comprising an epoxy resin and a filler ,
The filler is composed only of secondary particles of scaly boron nitride,
The said secondary particle contains 60 mass% or more of secondary particles which have a crystallinity degree of 3-7, The resin composition for heat conductive sheets characterized by the above-mentioned.   The resin composition for a heat conductive sheet according to claim 1, wherein the secondary particles have an average particle size of 20 μm to 180 μm.   The resin for a heat conductive sheet according to claim 1 or 2, wherein the content of the secondary particles in the solid content of the resin composition for the heat conductive sheet is 20% by volume or more and 80% by volume or less. Composition.   4. The resin composition for a heat conductive sheet according to claim 1, wherein an average major axis of the scaly boron nitride constituting the secondary particles is 15 μm or less. A thermally conductive sheet containing a filler in a cured epoxy resin,
The filler is composed only of secondary particles of scaly boron nitride,
The heat conductive sheet, wherein the secondary particles contain 60% by mass or more of secondary particles having a crystallinity of 3 or more and 7 or less.   The thermally conductive sheet according to claim 5, wherein the secondary particles have an average particle diameter of 20 μm to 180 μm.   The heat conductive sheet according to claim 5 or 6, wherein the content of the secondary particles in the heat conductive sheet is 20% by volume or more and 80% by volume or less.   The heat conductive sheet according to any one of claims 5 to 7, wherein an average major axis of the scaly boron nitride constituting the secondary particle is 15 µm or less.   A power semiconductor element mounted on one heat dissipation member; another heat dissipation member that radiates heat generated in the power semiconductor element to the outside; and heat generated in the power semiconductor element from the one heat dissipation member to the other A power module comprising the thermally conductive sheet according to any one of claims 5 to 8, which is transmitted to a heat radiating member.   The power module according to claim 9, wherein the power semiconductor element is formed of a wide band gap semiconductor.   The power module according to claim 10, wherein the wide band gap semiconductor is silicon carbide, a gallium nitride-based material, or diamond.

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