TW202302763A - Thermally conductive resin composition, thermally conductive resin sheet, multilayer heat dissipation sheet, heat-dissipating circuit board, and power semiconductor device - Google Patents

Abstract

The present invention provides a thermally conductive resin sheet which has good withstand voltage performance and good thermal conductivity coefficient, while exhibiting excellent reflow resistance after moisture absorption. A thermally conductive resin composition according to one embodiment of the present invention contains a thermoplastic resin and boron nitride agglomerated particles; and if A1 is the intraparticle pore volume of the boron nitride agglomerated particles and B1 is the interparticle volume, both determined by means of a mercury intrusion method, B1/(A1 + B1) is 0.60 or more. A thermally conductive resin sheet is obtained from this composition. A thermally conductive resin sheet according to another embodiment of the present invention is formed from a resin composition that contains a thermoplastic resin and boron nitride agglomerated particles; with respect to the pore size distribution curve as determined by measurement of the residual ash, which is obtained by heating the thermally conductive resin sheet at 700 DEG C for 5 hours, by means of a mercury intrusion method, if a peak that has the maximum value at a pore diameter of less than 5 [mu]m is taken as the first peak, and a peak that has the maximum value at a pore diameter of not less than 5 [mu]m is taken as the second peak, the second peak top height is 1.0 mL/g or more and the second peak top diameter is 15 [mu]m or more.

Description

Thermally conductive resin composition, thermally conductive resin sheet, laminated heat sink, heat-radiating circuit board, and power semiconductor device

The present invention relates to a thermally conductive resin composition, a thermally conductive resin sheet, a laminated heat sink formed by laminating a metal layer for heat dissipation on the surface of the thermally conductive resin sheet, and a conductive circuit formed on the surface of the thermally conductive resin sheet. The heat-dissipating circuit substrate formed by it.

In recent years, power semiconductor devices used in various fields such as railways, automobiles, industrial applications, and general household appliances are gradually changing from the previous Si power semiconductors to SiC and AlN in order to achieve smaller size, lower cost, and higher efficiency. , GaN and other power semiconductor transitions. In general, a power semiconductor device is used as a power semiconductor module in which a plurality of semiconductor devices are arranged on a common heat sink and packaged.

Facing the practical application of such power semiconductor devices, various problems have been pointed out. One of them is the heating problem from the device. By operating the power semiconductor device at high temperature, high output and high density can be realized. On the other hand, there is a concern that the reliability of the power semiconductor device may be lowered due to heat generated by switching of the device or the like.

In recent years, especially in the electrical and electronic fields, the heat generated along with the high density of integrated circuits has become a major problem, and how to dissipate heat has become an urgent issue. As one method to solve 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 for mounting a power semiconductor device. However, ceramic substrates have problems such as being easy to crack when receiving an impact, and difficult to thin and miniaturize.

Therefore, as a substitute product of the above-mentioned ceramic substrate, a thermally conductive resin sheet containing a resin and an inorganic filler has been studied. Among them, hexagonal boron nitride has attracted attention as an inorganic filler from the viewpoint of thermal conductivity and the like. However, since the hexagonal boron nitride particles are plate-shaped, the thermal conductivity in the plane direction (ab-axis direction) is high, but the thermal conductivity in the thickness direction (c-axis direction) is low. When the hexagonal boron nitride is blended into a resin and formed into a sheet, the hexagonal boron nitride is easily aligned in the flow direction of the resin composition, that is, the plane direction of the sheet, so the obtained thermal conductivity The thermal conductivity in the surface direction of the permanent resin sheet is high, but the thermal conductivity in the thickness direction becomes low.

In order to improve the anisotropy of the thermal conductivity of the thermally conductive resin sheet, the industry has studied a method of reducing the alignment of the particles by using aggregated boron nitride particles obtained by aggregating boron nitride particles. For example, Patent Documents 1 and 2 propose spherical agglomerates, which are obtained by spray-drying boron nitride particles bound by a binder. Also, Patent Document 3 proposes hexagonal boron nitride particles in which primary particles of hexagonal boron nitride are assembled in a pinecone shape. Furthermore, Patent Document 4 proposes a granulated powder comprising spherical secondary particles formed by aggregating flaky boron nitride, and the density of the primary particles in the core of the secondary particles is lower than that of the shell The density of primary particles in the section. In addition, Patent Document 5 proposes boron nitride aggregated particles in which primary particles of hexagonal boron nitride are aggregated, and the primary particles of the boron nitride aggregated particles have a house of cards. structure. prior art literature patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2006-257392 Patent Document 2: Japanese Patent Application Publication No. 2008-510878 Patent Document 3: Japanese Patent Application Laid-Open No. 09-202663 Patent Document 4: Japanese Patent Laid-Open No. 2016-044098 Patent Document 5: Japanese Patent Laid-Open No. 2015-006985

[Problem to be solved by the invention]

Conventional thermally conductive resin sheets have insufficient withstand voltage performance and thermal conductivity.

Moreover, the heat conductive resin sheet used as a power semiconductor device is required to have resistance to the reflow process. The reflow step is one of the steps in assembling the power semiconductor module. In this reflow step, the metal members are joined to each other by rapidly raising the temperature of the members to melt the solder. In recent years, with the high output and high density of power semiconductor devices, the operating temperature has continued to rise, thus requiring the solder used in the above reflow step to have heat resistance, and high temperature solder that requires a reflow temperature of 290°C is commonly used. Therefore, in the reflow step, the step of cooling after heating up to around 290° C. where the high-temperature solder starts to flow is repeated. In addition, there are cases where moisture absorption of the member before the reflow step greatly accelerates the deterioration of the member in the reflow step, resulting in a significant drop in withstand voltage performance.

Therefore, an object of the present invention is to provide a thermally conductive resin sheet having good voltage resistance performance and thermal conductivity, and excellent moisture absorption and reflow resistance. Furthermore, in this specification, "resistance to moisture absorption and reflow" refers to a laminate made of a thermally conductive resin sheet and a metal plate, which is subjected to high-temperature and high-humidity conditions (such as 85°C, 85%RH for 3 days) Carry out a reflow test (for example, 290°C) after being stored under low temperature. After the moisture absorption reflow test, it also has a high withstand voltage, and there will be no interface peeling with the metal plate and foaming from the thermally conductive resin sheet. caused deformation. [Technical means to solve the problem]

A thermally conductive resin composition according to an aspect of the present invention is a resin composition comprising a thermoplastic resin and aggregated boron nitride particles, where the volume of pores in the particles of the aggregated boron nitride particles measured by mercury porosimetry is set to When A ₁ and the particle interstitial volume are defined as B ₁ , B ₁ /(A ₁ +B ₁ ) is 0.60 or more. In addition, the thermally conductive resin sheet according to another aspect of the present invention contains a resin composition containing a thermoplastic resin and boron nitride aggregated particles, and the thermally conductive resin sheet is heated at 700° C. for 5 hours by mercury porosimetry. In the pore size distribution curve obtained by measuring the residual ash content at the time, the peak with the maximum value in the range of pore diameters less than 5 μm is set as the first peak, and the peak with the maximum value in the range of pore diameters above 5 μm is set as the first peak. When it is the second peak, the height of the second peak top is 1.0 mL/g or more, and the diameter of the second peak top is 15 μm or more. [Effect of Invention]

The thermally conductive resin sheet obtained from the thermally conductive resin composition according to one aspect of the present invention has good withstand voltage performance and thermal conductivity, and is excellent in moisture absorption and reflow resistance. In addition, the thermally conductive resin sheet according to another aspect of the present invention has good withstand voltage performance and thermal conductivity, and is also excellent in moisture absorption reflow resistance.

Hereinafter, an example of the embodiment of the present invention will be described in detail. However, this invention is not limited to the following embodiment, Various changes can be added and implemented within the range of the summary.

<First Embodiment> 1. Resin Composition A thermally conductive resin sheet according to a first embodiment of the present invention includes a thermally conductive resin composition comprising a thermoplastic resin and boron nitride aggregated particles. , when the intraparticle pore volume of the above-mentioned boron nitride aggregated particles measured by mercury intrusion porosimetry is A ₁ , and the particle interstitial volume is B ₁ , B ₁ /(A ₁ +B ₁ ) is 0.60 or more . Each component will be described in detail below.

(1) Thermoplastic resin The above-mentioned thermoplastic resin used in the thermally conductive resin composition of this embodiment is preferably under the reflow conditions of the heat-dissipating circuit board, for example, under the conditions of 290°C and 5 minutes, and it is not easy to produce the resin caused by the decrease of the elastic modulus. The recovery of flow, plastic deformation, and thermal recovery strain. In order to satisfy this point, it is preferable that the glass transition temperature (Tg) of the said thermoplastic resin is 300 degreeC or more, or a melting point (Tm) is 300 degreeC or more.

When the above-mentioned thermoplastic resin is a resin composition comprising a combination of two or more thermoplastic resins and resins compatible with each other, the glass transition temperature (Tg) of the resin composition is preferably 300°C or higher, Alternatively, the melting point (Tm) of the resin composition is preferably above 300°C. On the other hand, when the above-mentioned thermoplastic resin is a combination of two or more thermoplastic resins and a resin composition containing resins that are incompatible with each other, the glass transition of the thermoplastic resin that is the main component of the resin composition The temperature (Tg) is preferably 300°C or higher, or the melting point (Tm) of the thermoplastic resin which is the main component of the resin composition is preferably 300°C or higher. Here, the so-called "main component" refers to the resin with the highest mass ratio in the resin composition, which means more than 50% by mass of the resin composition, of which 60% by mass or more, of which 70% by mass or more, of which 80% by mass % or more, of which more than 90% by mass, of which more than 95% by mass (including 100% by mass) of resin.

In view of the above, the thermoplastic resin preferably contains an amorphous thermoplastic resin with a glass transition temperature (Tg) of 300°C or higher and/or a crystalline thermoplastic resin with a melting point (Tm) of 300°C or higher. Among them, it is preferable that an amorphous thermoplastic resin with a glass transition temperature (Tg) of 300°C or higher and/or a crystalline thermoplastic resin with a melting point (Tm) of 300°C or higher are the main components of the above-mentioned thermoplastic resin, that is, account for the above-mentioned thermoplastic resin. More than 50% by mass of the resin as a whole. Among them, it is more preferably at least 60% by mass, even more preferably at least 70% by mass, even more preferably at least 80% by mass, and even more preferably at least 90% by mass (including 100% by mass).

Furthermore, in the present invention, the term "amorphous thermoplastic resin" refers to a thermoplastic resin that does not have a melting point. On the other hand, "crystalline thermoplastic resin" refers to a thermoplastic resin having a melting point.

Examples of heat-resistant amorphous thermoplastic resins available as commercially available materials include polycarbonate resin (Tg: 152°C), modified polyphenylene ether resin (Tg: 211°C), polycarbonate resin ( Tg: 190°C), polyphenylene resin (Tg: 220°C), polyether resin (Tg: 225°C), polyetherimide resin (Tg: 217°C), etc. However, the glass transition temperatures of these commercially available heat-resistant amorphous thermoplastic resins are far from 300°C or higher. Also, thermoplastic polyimide resins having a glass transition temperature of 300° C. or higher are commercially available. However, since the moldable temperature of the thermoplastic polyimide resin is very high, and the melt viscosity at the moldable temperature is very high, it is difficult to fill a large amount of boron nitride aggregated particles. Furthermore, since imide groups are included in the molecular structure, hygroscopicity is high, and it is unfavorable to be used as the main component of the thermoplastic resin of this embodiment from these points.

From the above, the thermoplastic resin used in the thermally conductive resin composition of the present embodiment is preferably a resin mainly composed of a crystalline thermoplastic resin having a melting point of 300° C. or higher. By using a crystalline thermoplastic resin having a melting point of 300° C. or higher as a main component, sufficient heat resistance durability can be obtained as a substrate of a power semiconductor device. Also, even if a large amount of aggregated boron nitride particles are filled, formability is good, and voids inside the sheet caused by the shape of the aggregated particles or internal voids, or sheets caused by moisture absorption of the resin component or aggregated particles can be sufficiently reduced Pores inside the material, so the insulation becomes good. In addition, crystalline thermoplastic resins with a melting point above 300°C are less prone to flow, plastic deformation, and recovery of thermal recovery strain caused by the decrease in elastic modulus under reflow conditions, so the resistance to moisture absorption and reflow also changes. well.

In addition, the melting point of a thermoplastic resin can be measured by the method stipulated in JIS K-7121 "Measurement method of transition temperature of plastics - Calculation method of melting temperature". Specifically, the melting point of a thermoplastic resin is obtained by using a differential scanning calorimeter (DSC: for example, "DSC-7" manufactured by PerkinElmer, etc.), taking 10 mg of a sample as a sample, and measuring The thermoplastic resin composition was heated from -40°C to 380°C at a heating rate of 10°C/min, kept at 380°C for 1 minute, then cooled to -40°C at a cooling rate of 10°C/min, and kept at the same temperature for 1 minute Thereafter, the temperature (Tpm) at the top of the melting peak when the temperature was raised again at 10° C./min was read as the melting point (Tm). As the crystalline thermoplastic resin in this embodiment, at least an endothermic peak due to crystal melting can be clearly confirmed, and the temperature of the apex of the main peak within the peak is 300° C. or higher. Furthermore, in the case of measuring the resin composition with boron nitride aggregated particles added using a differential scanning calorimeter (DSC), in addition to the degradation of the thermoforming of the matrix resin due to the addition of boron nitride aggregated particles In addition to the case, the melting point will not produce a big difference.

From the viewpoint of moisture absorption reflow resistance at 290°C, the melting point of the crystalline thermoplastic resin is more preferably 310°C or higher, more preferably 320°C or higher, and still more preferably 30°C or higher. On the other hand, the upper limit of the melting point is not particularly limited. Among them, from the viewpoint of moldability and productivity, it is more preferably 380°C or lower, especially preferably 370°C or lower, and even more preferably 360°C or lower.

By setting the melting point of the thermoplastic resin above 300° C., the modulus of elasticity of the resin material is less likely to decrease even at 290° C. under the reflow condition. Therefore, the flow deformation of the resin in the reflow step can be suppressed, and the elastic strain of the resin layer is also difficult to recover, so that the deterioration of the surface appearance of the thermally conductive resin sheet or the uneven thickness of the thermally conductive resin sheet can be suppressed, and it is possible to obtain Thermally conductive resin sheet with sufficient strength. In addition, since the modulus of elasticity of the resin material is not likely to decrease at 290°C, even if the resin composition absorbs moisture in a hot and humid environment and there is moisture in the resin composition, it will not In the step, the moisture in the resin composition is not easy to expand, and the thermally conductive resin sheet is not easy to generate foaming, so the withstand voltage performance and thermal conductivity become good.

Furthermore, it is considered that the foaming in the thermally conductive resin sheet in the reflow process is related to the withstand voltage performance and thermal conductivity, for example, as follows. If the moisture in the resin composition expands due to the reflow process or the process of mounting to the module, it will exist inside the thermally conductive resin sheet, near the interface between the metal layer for heat dissipation and the thermally conductive resin sheet, or between the conductive circuit pattern and the thermally conductive The case where foaming occurs near the interface of the permanent resin sheet. For example, when foaming occurs inside the thermally conductive resin sheet, there is a possibility that the withstand voltage performance may be significantly lowered. When there is a metal material for heat dissipation layered on the surface of the thermally conductive resin sheet, if foaming occurs near the interface between the metal material for heat dissipation and the thermally conductive resin sheet, the metal material for heat dissipation will be peeled off and the thermal conductivity will be significant. risk of reduction. Also, when a conductive circuit pattern is formed on the other surface of the thermally conductive resin sheet, if foaming occurs near the interface between the conductive circuit pattern and the thermally conductive resin sheet, the conductive circuit pattern may peel or fall off, or There is a possibility that an abnormality occurs in the circuit, or the thermal conductivity of the thermally conductive resin sheet decreases significantly.

Specific examples of heat-resistant crystalline thermoplastic resins include polybutylene terephthalate resin (PBT, melting point: 224°C), polyamide 6 (nylon 6, melting point: 225°C), polyamide 6 (nylon 6, melting point: 225°C), Amide 66 (nylon 66, melting point: 265°C), liquid crystal polymer (LCP, melting point: 320°C to 344°C), polyetherketone resin (melting point: 303°C to 400°C), polytetrafluoroene resin (PTFE , melting point: 327℃), tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin (PFA, melting point: 302℃～310℃), tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP, melting point: 250℃～290 ℃), etc.

As the crystalline thermoplastic resin used in the present embodiment, liquid crystal polymers, polyether ketone resins, PTFE, and PFA are preferable in terms of having a melting point of 300° C. or higher. Among these crystalline thermoplastic resins having a melting point of 300° C. or higher, liquid crystal polymers and/or polyetherketone resins are particularly preferred from the viewpoint of moldability and the like. Furthermore, among these, polyether ketone resin is preferable from the viewpoint of the adhesiveness with the metal layer for heat dissipation represented by a copper plate.

The polyether ketone resins usable in this embodiment are collectively referred to as thermoplastic resins having repeating units represented by the following formula (1) (in which m and n are 1 or 2).

[chemical 1]

Examples of polyetherketone-based resins include polyetherketone (PEK; m=1, n=1, melting point 373°C), polyetheretherketone (PEEK; m=2, n=1, melting point 343°C), polyetheretherketone (PEEK; m=2, n=1, melting point 343°C), Ether ketone ketone (PEKK; m=1, n=2, melting point 303°C-400°C), polyetheretherketone ketone (PEEKK; m=2, n=2, melting point 358°C), polyetheretherketone ketone ( PEKEKK; a copolymer comprising structural units of m=1, n=1 and structural units of m=1, n=2, melting point 387° C.) and the like. All can be obtained as commercially available raw materials.

Among the polyether ketone resins, comprehensively considering that the melting point is sufficiently high, and the molding processing temperature is relatively low so that the molding cycle can be shortened, the continuous heat-resistant temperature has been confirmed to be above 200°C, and it can be used for heat-resistant applications without hindrance, There are various grades of melt viscosity related to molding processability, the chemical stability of the structure is the highest among polyether ketone resins, the hot water resistance and chemical resistance are also excellent, and the price is disclosed for a wide range of applications, etc. Aspects, polyetheretherketone (PEEK) can be used particularly preferably.

In the case of using polyetheretherketone (PEEK) as the crystalline thermoplastic resin of this embodiment, it may be blended with other thermoplastic resins. The types of other thermoplastic resins are not particularly limited. Among them, other thermoplastic resins are preferably compatible resins that have the effect of supplementing the performance that is lacking when only polyether ether ketone is used for the application of the present embodiment.

The compatible resin is more preferably polyetherimide (PEI). If PEEK and PEI are combined, not only the crystallinity of PEEK (crystal melting heat) can be adjusted, but also the glass transition temperature ( The Tg of PEEK is 143°C, whereas the Tg of PEI is 217°C). Furthermore, since PEI is an amorphous resin, even if PEEK and PEI are combined, the melting point of the resin itself will not change. Furthermore, in the present invention, by using the non-crystalline PEI having an imide group, the adhesion to metal materials for heat dissipation such as copper plates can be improved.

Assuming that the total amount of the resin composition is 100% by mass, the amount of PEI added is preferably 50% by mass or less. By setting the amount of PEI added to 50% by mass or less, the crystallinity of PEEK maintains the heat resistance in the moisture absorption reflow test, and the adhesion to the metal material for heat dissipation becomes good.

Various commercially available products can be used for PEEK. For example, "KetaSpire (registered trademark)" manufactured by Solvay, "VESTAKEEP (registered trademark)" manufactured by Daicel-Evonik, "Victrex PEEK" manufactured by Victrex, etc. are available from various companies with various melt viscosities. These PEEK raw materials can be used in a single grade, or blended with different grades such as melt viscosity.

The melt viscosity of the crystalline thermoplastic resin in this embodiment is not particularly limited. Among them, since a relatively large amount of boron nitride aggregated particles is blended, the melt viscosity of the above-mentioned crystalline thermoplastic resin is preferably 0.60 kPa·s or less, more preferably 0.30 kPa·s or less, in order to facilitate thermoforming. By setting the melt viscosity within the above range, the deterioration of the raw material can be suppressed without setting the temperature of the molding machine too high. On the other hand, the lower limit of the melt viscosity is not particularly limited. Among them, 0.01 kPa·s or more is preferable. Furthermore, the melt viscosity is a value measured under the conditions of a shear rate of 1000 s ⁻¹ and a temperature of 400° C. according to ASTM D3835.

From the viewpoint of long-term durability in a heated environment, the mass average molecular weight (Mw) of the crystalline thermoplastic resin is preferably at least 48,000, more preferably at least 49,000, and even more preferably at least 50,000. On the other hand, from the viewpoint of moldability, it is preferably 120,000 or less, more preferably 110,000 or less, and even more preferably 100,000 or less.

In terms of molding processability or the difficulty of forming voids with the added boron nitride aggregated particles, the MFR (Melt mass-flow rate) of the crystalline thermoplastic resin is preferably 8 g/10 minutes or more, more preferably 9 g/10 minutes or more, and even more preferably 10 g/10 minutes or more. On the other hand, from the viewpoint of long-term durability in a heated environment, it is preferably not more than 180 g/10 minutes, more preferably not more than 170 g/10 minutes, and even more preferably not more than 160 g/10 minutes . In addition, MFR is a value measured at 380°C and 5 kgf in accordance with JIS K7210:2014.

(2) Boron nitride aggregated particles In the boron nitride aggregated particles of the present embodiment, the pore volume in the particles of the above-mentioned boron nitride aggregated particles measured by mercury porosimetry is A ₁ , and the particle interstitial volume is In the case of B ₁ , B ₁ /(A ₁ +B ₁ ) is preferably 0.60 or more. In addition, in the present invention, the intraparticle pore volume and the interparticle interstitial volume of boron nitride aggregated particles were obtained by the methods described in the examples in accordance with JIS R1655:2003, respectively. Specifically, first, 200 mg of boron nitride aggregated particles were prepared, and mercury intrusion and exit curves were measured by mercury intrusion porosimetry. Next, as illustrated in FIG. 1 , a pore size distribution curve with the pore diameter as the horizontal axis and the logarithmic differential pore volume as the vertical axis was created. Usually, the peak a from the inner pores of the particles is observed within the range of less than 5 μm, preferably more than 0.1 μm and less than 5 μm, and is usually observed at the range of more than 5 μm, preferably more than 5 μm and less than 100 μm. Peak b of interparticle pores. Read the diameter at which the logarithmic differential pore volume takes the minimum value with respect to the pore diameter (cut diameter, X in FIG. 1 ) between these peaks a and b. The integral value of the mercury intrusion and exit curve at the region where the pore diameter is larger than the split diameter (dashed arrow in Fig. 1) becomes the particle interstitial volume. In addition, the integrated value of the mercury intrusion and exit curve in the entire measurement area becomes the total pore volume, and the value obtained by subtracting the above-mentioned particle interstitial volume from the total pore volume is the intraparticle pore volume.

In Fig. 2, the pore volume in the particles is excluding the closed pores which are not filled with mercury and the like which exist in the pores α inside the aggregated particles. The pore volume in the particles is a value determined by the density, average aspect ratio, and particle thickness of the boron nitride primary particles that constitute the aggregated particles, and is related to the mechanical properties of the boron nitride aggregated particles or the thermal conductivity inside the aggregated particles, etc. . If the pore volume in the particles is appropriately reduced, there will not be too many voids in the aggregated particles that increase the thermal resistance, so there is a tendency to effectively improve the heat conduction inside the aggregated particles. Furthermore, the strength of the aggregated particles can be improved. For example, when a sheet is produced by press molding, the aggregated particles themselves will not be crushed or excessively deformed, and the isotropy of the aggregated particles can be maintained. Therefore, The decrease in thermal conductivity in the thickness direction of the thermally conductive resin sheet can be effectively suppressed. On the other hand, if the pore volume in the particles is appropriately increased, it is possible to sufficiently ensure that the resin penetrates into the internal pores of the aggregated particles, thereby suppressing the generation of pores in the thermally conductive resin sheet, so there is a tendency for the withstand voltage performance to become better. .

From the above point of view, the particle internal pore volume A ₁ is preferably at least 0.30 mL/g, more preferably at least 0.35 mL/g, still more preferably at least 0.40 mL/g, still more preferably at least 0.42 mL/g. In addition, the particle internal pore volume _A1 is preferably 0.80 mL/g or less, more preferably 0.70 mL/g or less, further preferably 0.60 mL/g or less, still more preferably 0.55 mL/g or less, especially preferably 0.50 mL/g or less. Below mL/g.

In Fig. 3, the particle interstitial volume refers to the pores β existing between aggregated particles, and generally indicates the degree of accumulation caused by the shape, particle size, and distribution of aggregated particles. However, regarding boron nitride aggregated particles, in addition to the above, it also refers to the alignment state of the primary particles on the surface of the aggregated particles (primary particles are aligned in the radial direction of the aggregated particles or aligned in the direction of the circumferential surface of the aggregated particles, etc.) ), or the density, average aspect ratio, or particle thickness of primary particles on the surface, and furthermore, it is also related to the density, average aspect ratio, or particle thickness of primary particles constituting the aggregated particles as a whole. The reason is that, in the case where the size of the primary particles is too large and lacks compactness, etc., the strength of the aggregated particles themselves is insufficient, so that the particles are destroyed or the surface primary particles fall off during various operations before being blended with the resin. In measurement by mercury porosimetry, fragments of particles generated by such crushing or isolated primary particles may fill the gaps between aggregated particles.

Here, the particle interstitial volume will be described in more detail using FIGS. 4 to 7 . For example, as shown in Fig. 4 and Fig. 5, when there is a structure in which the thickness direction (c-axis direction) of the primary particles near the outermost surface of the aggregated particles coincides with the radiation direction of the aggregated particles, the interstitial volume of the particles becomes smaller. tendency. Such aggregated particles have the following advantages: when the thermally conductive resin sheet is produced by the wet coating method, the coatability is good, and it is easy to obtain a sheet with less remaining pores; The nearby primary particles exist in such a way as to cover the aggregated particles, so that the thermal resistance at the interface between the surface of the aggregated particles and the resin, or at the contact interface of a plurality of aggregated particles increases. Also, when a plurality of aggregated particles are filled in the thermally conductive resin sheet in contact with each other, the aggregated particles shown in FIG. 4 and FIG. 5 pass through the thickness direction of the primary particle (c axial direction) to achieve heat conduction. Since the thermal conductivity in the thickness direction of the primary particles is low, the thermal conductivity in the thickness direction of the thermally conductive resin sheet is limited. Also, for example, when the primary particles constituting the aggregated particles are too large and lack compactness, the volume of the particle interstitial will also become small. Since the strength of such aggregated particles is insufficient, for example, when a sheet is produced by press molding, the aggregated particles may be broken or surface primary particles may fall off. Since the isolated primary particles are flat or scaly, the thickness direction (c-axis direction) of the particles may be aligned with the surface direction of the sheet, resulting in a decrease in thermal conductivity in the thickness direction of the thermally conductive resin sheet.

On the other hand, for example, as shown in FIG. 6 and FIG. 7 , in the vicinity of the outermost surface of aggregated particles, there is a structure in which the plane direction (ab-axis direction) of primary particles coincides with the radiation direction of aggregated particles, and the aligned When primary particles exist densely on the surface, the volume of interparticle spaces tends to increase. Compared with the aggregated particles in which the primary particles near the outermost surface cover the aggregated particles, when such aggregated particles are filled in such a manner that a plurality of aggregated particles are in contact with each other in the thermally conductive resin sheet, the distance between the particles The contact area increases. Therefore, since the thermal resistance between particles falls, the thermal conductivity of the thickness direction of a thermally conductive resin sheet becomes high. Also, if the particle interstitial volume is large, assuming that the particle internal pore volume, average particle size, and particle size distribution are the same, the contact surface of a plurality of aggregated particles is shown in Figure 9 through sheet forming and other pressurization steps. It shows that deformation occurs, and the polyhedrons contact each other to increase the contact area, forming a state of surface contact, so the thermal resistance between the particles is further reduced. Also, for example, when the primary particles constituting the aggregated particles are moderately small and dense, the interparticle interstitial volume also becomes large. Since such aggregated particles have good strength, it is possible to prevent the aggregated particles from being broken or the surface primary particles fall off during molding. Thereby, since primary particle isolation|separation can be suppressed, the thermal conductivity of the thickness direction of a thermally conductive resin sheet can be made favorable.

From the above viewpoints, the particle interstitial volume B ₁ is preferably at least 0.50 mL/g, more preferably at least 0.55 mL/g, still more preferably at least 0.60 mL/g, still more preferably at least 0.65 mL/g. Furthermore, it is preferably at least 0.70 mL/g, more preferably at least 0.75 mL/g, still more preferably at least 0.80 mL/g, still more preferably at least 0.85 mL/g. Also, the particle interstitial volume B ₁ is preferably 1.0 mL/g or less, more preferably 0.95 mL/g or less, still more preferably 0.90 mL/g or less.

B ₁ /(A ₁ +B ₁ ) in this embodiment represents the ratio of the particle interstitial volume to the total pore volume. B ₁ /(A ₁ +B ₁ ) is preferably at least 0.60, more preferably at least 0.62, still more preferably at least 0.64, still more preferably at least 0.66. Also, B ₁ /(A ₁ +B ₁ ) is preferably less than 1.00, more preferably at most 0.90, further preferably at most 0.80, still more preferably at most 0.75, and most preferably at most 0.70. As described above, the strength of aggregated particles, the alignment state of primary particles, etc. represented by the pore volume in the particles or the interstitial volume between particles affect the withstand voltage performance or thermal conductivity. The inventors of the present invention have found that the balance of the volume of pores in particles and the volume of interstices between particles affects them. More specifically, by setting B ₁ /(A ₁ + B ₁ ) within the above range, the aggregated particles have sufficient strength, so that the aggregated particles can be prevented from disintegrating during molding, and since the primary particles on the surface of the aggregated particles It is radially aligned, so it can fully form the heat conduction path between the aggregated particles. In addition, if B ₁ /(A ₁ +B ₁ ) is within the above range, it has a structure that can be called "hard on the inside and soft on the outside", that is, in the state where the inside of the aggregated particles is dense and maintains a structure with isotropic thermal conductivity The region where the primary particles on the surface of the aggregated particles are radially aligned is moderately deformed during molding, so the contact area between adjacent aggregated particles increases, and the thermal conductivity in the thickness direction of the thermally conductive resin sheet can be further improved. Also, if B ₁ /(A ₁ +B ₁ ) is within the above range, the inside of the aggregated particles will be dense, and the resin will sufficiently permeate the particles, so the generation of voids during molding can be suppressed, and the withstand voltage performance can be further improved.

Examples of the boron nitride aggregated particles having a B ₁ /(A ₁ +B ₁ ) of 0.60 or more include aggregated particles having a house of cards structure. In addition, B ₁ /(A ₁ +B ₁ ) can be adjusted to 0.60 or more by performing physical surface roughening treatment or chemical surface roughening treatment after boron nitride aggregated particles are obtained by a known method. Since boron nitride aggregated particles commercially available from various companies use boron nitride primary particles that crystallize relative to each other during granulation, stable stacking of primary particle faces (ab faces) is preferentially generated, and thus aggregated particles are the most There are many "cabbage structures" in which the thickness direction of primary particles near the outer surface coincides with the radiation direction of aggregated particles. Since the primary particles in the vicinity of the outermost surface of the aggregated particles of the "cabbage structure" exist so as to cover the aggregated particles, it is difficult for B ₁ /(A ₁ +B ₁ ) to be 0.60 or more. Therefore, in the case of using the aggregated particles of the "cabbage structure", it is preferable to carry out the adjustment by performing the above-mentioned surface roughening treatment.

The shape of the boron nitride aggregated particles in this embodiment is preferably spherical. The term "spherical" means that the aspect ratio (the ratio of the major axis to the minor axis) is usually 1 to 2, preferably 1 to 1.75, more preferably 1 to 1.5, and more preferably 1 to 1.4. The aspect ratio can be obtained by arbitrarily selecting 200 or more particles from an image obtained by photographing a cross section of a thermally conductive resin sheet with a scanning electron microscope (SEM), and obtaining the respective major diameter and The average value was calculated from the ratio of the short diameter.

In addition, "circularity" measured using a particle image analyzer (manufactured by Malvern Instruments Ltd., Morpholog G3S) can be used as an index of "sphericality". The same measurement is to observe the projected plane image (two-dimensional image) of the particles, and the degree of "sphericity" can be evaluated by increasing the number of measurements and averaging. The above-mentioned circularity has an upper limit of 1, and is preferably at least 0.90, more preferably at least 0.92, further preferably at least 0.94, and still more preferably at least 0.96.

From the viewpoint of enhancing thermal conductivity, the aggregated structure of boron nitride aggregated particles is preferably a house of cards structure. Furthermore, the aggregated structure of boron nitride aggregated particles can be confirmed by a scanning electron microscope (SEM).

The so-called house of cards structure refers to the complex layering of plate-shaped particles without alignment, which is described in "Ceramics 43 No. 2" (published by the Japan Ceramics Association in 2008). More specifically, it means that the flat part of the primary particle that forms the aggregated particle is firmly bonded or bonded to the end face of the other primary particle present in the aggregated particle, and that the scale-like or flat-shaped primary particles each face random directions. Structure in aggregated particles. A schematic diagram of the structure of the house of cards is shown in FIG. 8 . The aggregated particles of the house of cards structure have the above-mentioned structure and relatively high sphericity as the aggregated particles, so the fracture strength is very high, and they will not be crushed even in the pressurization step performed when the thermally conductive resin sheet is formed. . Therefore, primary particles generally aligned in the longitudinal direction of the thermally conductive resin sheet can be made to exist in random directions. Therefore, if aggregated particles with a house of cards structure are used, the ratio of the ab planes of the primary particles to be aligned in the thickness direction of the thermally conductive resin sheet can be further increased, so that heat can be effectively conducted in the thickness direction of the sheet, and the thickness can be further increased. direction of thermal conductivity.

Furthermore, boron nitride aggregated particles having a house of cards structure can be produced, for example, by the method described in International Publication No. 2015/119198. The aggregated boron nitride particles in this embodiment are preferably not subjected to treatment such as ball milling to apply force to the surface.

When boron nitride aggregated particles having a house of cards structure are used, the particles may be surface treated with a surface treatment agent. As an example of the surface treatment agent, well-known surface treatment agents, such as a silane coupling treatment agent, can be used. In general, boron nitride aggregated particles do not exhibit direct affinity or adhesion with thermoplastic resins in many cases, and this is also the case when boron nitride aggregated particles having a house of cards structure are used. It is considered that by using chemical treatment to improve the adhesiveness of the interface between the boron nitride aggregated particles and the matrix resin, the decrease in thermal conductivity at the interface can be further reduced.

The boron nitride aggregated particles of this embodiment can increase the particle size compared to the case where primary particles are used as they are. By increasing the particle size of the boron nitride aggregated particles, the heat transfer path between the boron nitride aggregated particles separated by the thermoplastic resin with low thermal conductivity can be reduced, so the thermal resistance in the heat transfer path in the thickness direction can be reduced case of increase.

From the above point of view, the lower limit of the volume-based maximum particle diameter Dmax (hereinafter also referred to as "maximum particle diameter") of boron nitride aggregated particles is preferably 20 μm or more, more preferably 30 μm or more, and still more preferably More than 50 μm. On the other hand, the upper limit of the maximum particle diameter Dmax is preferably 300 μm or less, more preferably 200 μm or less, further preferably 100 μm or less, and even more preferably 90 μm or less.

Also, the lower limit of the volume-based average particle diameter D50 of boron nitride aggregated particles is preferably at least 10 μm, more preferably at least 20 μm, and still more preferably at least 30 μm. On the other hand, the upper limit of the average particle diameter D50 is preferably 200 μm or less, more preferably 100 μm or less, further preferably 80 μm or less, and even more preferably 60 μm or less.

By setting the maximum particle size of boron nitride aggregated particles below the upper limit, when the matrix resin contains boron nitride aggregated particles, the interface between the matrix resin and the boron nitride aggregated particles becomes smaller, resulting in a smaller thermal resistance. , can achieve high thermal conductivity, and can form a high-quality film without surface roughness. By setting the maximum particle diameter to be equal to or greater than the above-mentioned lower limit, a sufficient effect of improving thermal conductivity as boron nitride aggregated particles required for a power semiconductor device can be obtained.

Also, it is considered that when the size of boron nitride aggregated particles is 1/10 or less relative to the thickness of the thermally conductive resin sheet, the thermal resistance of the interface between the matrix resin and boron nitride aggregated particles is greater than the thickness of the thermally conductive resin sheet. The impact becomes apparent. Especially in the case of power semiconductor devices, thermally conductive resin sheets with a thickness of 100 μm to 300 μm are often used. Therefore, from the perspective of thermal conductivity, it is also preferable to use the largest volume basis of boron nitride aggregated particles The particle diameter Dmax is larger than the above-mentioned lower limit. Also, by making the maximum particle diameter Dmax of the boron nitride aggregated particles not less than the above-mentioned lower limit, not only the increase in thermal resistance due to the interface between the boron nitride aggregated particles and the matrix resin can be suppressed, but also the number of heat conduction paths required between the particles can be suppressed. As the thickness decreases, the connection probability from one side to the other side increases in the thickness direction of the thermally conductive resin sheet. Furthermore, by setting the maximum particle diameter Dmax of boron nitride aggregated particles to be equal to or greater than the above-mentioned lower limit, the interface area between the matrix resin and boron nitride aggregated particles becomes smaller than when using the same mass of particles whose Dmax is smaller than the above-mentioned lower limit. Therefore, in the thermally conductive resin sheet, it is possible to reduce the occurrence of voids that tend to appear at the interface between the matrix resin and the boron nitride aggregated particles, and it is easy to obtain excellent withstand voltage characteristics. On the other hand, by making the volume-based maximum particle diameter Dmax of the aggregated boron nitride particles not more than the above upper limit, the aggregated boron nitride particles are suppressed from protruding from the surface of the thermally conductive resin sheet, and a good surface without surface roughness can be obtained. Therefore, when making a sheet bonded to a copper substrate, it has sufficient adhesion and can obtain excellent withstand voltage characteristics.

The ratio of the size (Dmax) of boron nitride aggregated particles to the thickness of the thermally conductive resin sheet (Dmax/thickness) is preferably from 0.3 to 1.0, more preferably from 0.35 to 0.95, and even more preferably from 0.4 above or below 0.9.

In addition, the maximum particle diameter Dmax and the average particle diameter D50 of boron nitride aggregated particle can be measured by the following method, for example. For samples obtained by dispersing boron nitride aggregated particles in a solvent, specifically, for samples obtained by dispersing boron nitride aggregated particles in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer, The particle size distribution is measured using a laser diffraction/scattering particle size distribution measuring device LA-920 (manufactured by Horiba Manufacturing Co., Ltd.), and the maximum particle size Dmax and average particle size D50 of boron nitride aggregated particles can be obtained from the obtained particle size distribution. . In addition, the maximum particle diameter and the average particle diameter can also be obtained using a dry-type particle size distribution measuring device such as Morpholog G3S (manufactured by Malvern). Regarding the maximum particle diameter Dmax and the average particle diameter D50 of boron nitride aggregated particles added to thermoplastic resins, the thermoplastic resin can also be removed by dissolving in a solvent (including a heating solvent) or swelled to reduce the interaction with boron nitride. The adhesion strength of the aggregated particles is removed physically, and then the resin component is heated in the atmosphere to be ashed and removed, and measured by the same method as above.

(3) Content of each ingredient The lower limit of the content of the thermoplastic resin in 100% by mass of the resin composition of the present embodiment is preferably at least 15% by mass, more preferably at least 20% by mass. On the other hand, the upper limit of the thermoplastic resin content is preferably at most 40% by mass, more preferably at most 35% by mass. In addition, the lower limit of the content of boron nitride aggregated particles in 100% by mass of the resin composition of the present embodiment is preferably at least 60% by mass, more preferably at least 65% by mass. On the other hand, the upper limit of the content of boron nitride aggregated particles is preferably at most 85% by mass, more preferably at most 80% by mass. When the content of the aggregated boron nitride particles is equal to or greater than the above lower limit, the effect of improving the thermal conductivity or the effect of controlling the linear expansion coefficient by the aggregated boron nitride particles can be favorably exhibited. On the other hand, by making content of boron nitride aggregated particle below the said upper limit, the moldability of a resin composition, or the interface adhesiveness with a different material becomes favorable.

In general, the formulation ratio of the thermally conductive resin composition is often specified based on the respective volume fractions of the matrix resin and boron nitride aggregated particles (therefore, the area ratio in the cross section of the thermally conductive resin sheet). The thermal conductivity in the thickness direction of the thermally conductive resin sheet is not only dependent on the volume fraction, but also related to various factors such as the above-mentioned preferred particle size, the alignment state of the particles, and the shape of the particles. Therefore, in the present invention, the actual In terms of convenience in preparation, the mass fraction is used. Especially in the case of using boron nitride agglomerated particles with a house of cards structure, the internal structure of the particles is a house of cards structure, and a plurality of protrusions along the radial direction are formed on the surface of the particles in the state of so-called chestnut-shaped or gold flat sugar-shaped protrusions. Aligned flat boron nitride primary particles and the protrusions of adjacent house of card particles are in physical contact with each other, thereby forming a heat transfer path with small thermal resistance in the thickness direction. Therefore, it may not be easy to determine the respective volume fractions of the matrix resin and the thermally conductive filler when observing with a normal scanning electron microscope (SEM). Furthermore, if the addition amount of the aggregated boron nitride particles having the house of cards structure characteristic of the present invention is gradually increased, the particles do not form spherical particles with each other under the action of the pressure applied when the resin composition is heated and pressurized. The point contact of mutual contact means that the part where the particles contact each other deforms, and the contact part is observed to be in a state of linear or planar contact. In such a contact state, by adding boron nitride having a house-of-cards structure, a thermal conduction path can be efficiently formed. However, in this case, it is not easy to determine the respective volume fractions of the matrix resin and boron nitride aggregated particles by SEM observation.

The resin composition of this embodiment may contain other components than the thermoplastic resin and boron nitride aggregated particles. However, from the viewpoint of improving thermal conductivity, it is preferable not to contain other components. Examples of other components include phosphorus-based and various antioxidants other than phenol-based, process stabilizers other than phenol acrylate-based, heat stabilizers, hindered amine-based radical scavengers (HAAS), impact modifiers, and processing aids. additives, metal deactivators, copper poisoning inhibitors, antistatic agents, flame retardants, silane coupling agents, etc. to improve the affinity of the interface between boron nitride aggregated particles and thermoplastic resins, and can also be expected to improve the resin Additives, extenders, etc. for the effect of the bonding strength between the sheet and the metal plate. When using these additives, the addition amount should just be the range of the amount used based on these purposes normally.

2. Thermally conductive resin sheet The thermally conductive resin sheet according to this embodiment has the following features: it contains the above-mentioned resin composition, has excellent moisture absorption reflow resistance, and is less prone to interfacial peeling due to thermal expansion and thermal contraction when producing a laminate with a metal plate.

The thermal conductivity of the thermally conductive resin sheet in the thickness direction at 25°C is preferably at least 16 W/m·K, more preferably at least 18 W/m·K, still more preferably at least 19 W/m·K, and furthermore More preferably at least 20 W/m・K. By making the thermal conductivity in the thickness direction more than the above-mentioned lower limit value, it can be preferably used also for power semiconductor devices and the like that operate at high temperatures. The thermal conductivity can be determined by the type of thermoplastic resin and physical properties such as melt viscosity, the value, structure and content of B ₁ /(A ₁ + B ₁ ) of boron nitride aggregated particles, and the mixing method of thermoplastic resin and boron nitride aggregated particles , the conditions in the following heating and kneading steps, etc. are adjusted.

In addition, thermal conductivity can be measured by the following method. First, thermal diffusivity a (mm ² /sec) in the thickness direction of the resin sheet at a measurement temperature of 25° C. was measured by a laser flash method. Since there is no JIS standard for thermal diffusivity and thermal conductivity in resin-based materials, it is measured according to JIS R1611:2010 (method for measuring thermal diffusivity, specific heat capacity, and thermal conductivity of precision ceramics by flash method). In addition, in JIS R1611:2010, there is a regulation that "the thickness of the sample is not less than 0.5 mm and not more than 5 mm", so the thickness of the resin sheet is adjusted to be not less than 0.5 mm for measurement. When the thickness of the resin sheet is less than 0.5 mm, multiple sheets can be stacked, and the overall thickness can be adjusted to be more than 0.5 mm for measurement. Then, the density ρ (g/m ³ ) of the resin sheet was obtained by the Archimedes method in accordance with JIS K6268. Furthermore, according to JIS K7123, the specific heat capacity c (J/(g·K)) at 25 degreeC was measured using the DSC measuring apparatus. From these respective measured values, the thermal conductivity in the sheet thickness direction at 25° C. was determined as “H=a×ρ×c”.

The lower limit of the thickness of the thermally conductive resin sheet is preferably at least 50 μm, more preferably at least 60 μm, and still more preferably at least 70 μm. On the other hand, the upper limit of the thickness is preferably at most 300 μm, more preferably at most 200 μm, and still more preferably at most 160 μm. Sufficient withstand voltage characteristics can be secured by setting the thickness of the thermally conductive resin sheet to 50 μm or more. On the other hand, by setting the thickness to 300 μm or less, miniaturization or thinning can be achieved especially when the thermally conductive resin sheet is used in a power semiconductor device or the like, and it is comparable to an insulating thermally conductive layer using a ceramic material. Ratio, the effect of reducing the thermal resistance in the thickness direction brought about by thinning can be obtained.

In order to reduce the anisotropy of thermal conductivity and increase the thermal conductivity in the thickness direction, the thermally conductive resin sheet of this embodiment preferably reduces the alignment of the primary particles of boron nitride aggregated particles. Regarding the orientation of the primary particles, when measuring the thermally conductive resin sheet by the X-ray diffraction method, the diffraction peak intensity of the (002) plane can be determined as I(002), and the (100) plane When the intensity of the diffraction peak is set to I(100), the ratio "I(002)/I(100)" is evaluated. The above ratio "I(002)/I(100)" is preferably 20 or less, more preferably 17 or less, still more preferably 15 or less. When the above ratio exceeds 20, the boron nitride aggregated particles are disintegrated in the melting and kneading step, or the boron nitride aggregated particles are excessively crushed in the press molding step, and the boron nitride aggregated particles are parallel to or placed in the direction of the surface of the thermally conductive resin sheet. The smaller the angle, the more primary particles. In this case, even if the content of boron nitride aggregated particles is increased, it is difficult to increase the thermal conductivity in the thickness direction. In addition, the lower limit of the said ratio "I(002)/I(100)" is not specifically limited. For example, in the case of using boron nitride agglomerated particles with a house-of-card structure that has a relatively high isotropy so that boron nitride primary particles are rarely aligned in a specific direction, the ratio "I(002)/I(100 )" is about 4.5 to 6.6, therefore, if the intentional alignment operation is excluded, 4.5 is considered to be the lower limit.

In the thermally conductive resin sheet of the present embodiment, regarding boron nitride aggregated particles contained in the residual ash when heated at 700°C for 5 hours, the pore volume in the particles measured by the mercury porosimetry was set as A ₂ is A 2 , and when the particle interstitial volume is B ₂ , A ₂ /A ₁ is preferably at least 0.70, and B ₂ /B ₁ is preferably at most 0.85. A ₂ /A ₁ of 0.70 or higher indicates that the state of the primary particles inside the aggregated particles does not change significantly before and after sheet forming, so the strength of the aggregated particles is relatively high. Therefore, A ₂ /A ₁ being 0.70 or more means that the original structure of the internal thermal conductivity path forming boron nitride aggregated particles is sufficiently maintained even after the sheet is formed. It can also be said that, although deformation due to pressurization during molding occurs, isolated primary particles are rarely generated due to crushing of aggregated particles. If the generation of isolated primary particles is less, it will bring about the effect of reducing the thermal resistance in the thickness direction. The reason why isolated primary particles hinder effective heat conduction in the thickness direction is that since the primary particles are flat or scaly particles, in the formed sheet, the thickness direction (c-axis direction) of the particles is aligned to The face direction of the sheet. On the other hand, B ₂ /B ₁ being 0.85 or less indicates that relatively large deformation occurs on the surface of aggregated particles before and after sheet forming. As shown in FIG. 9 , the deformation occurs because polyhedrons on the contact surfaces of a plurality of aggregated particles contact each other to increase the contact area and form a state such as surface contact. Therefore, a high thermal conductivity can be obtained by making boron nitride aggregated particles exist in the sheet in a state where both A ₂ /A ₁ and B ₂ /B ₁ satisfy the above numerical range.

From the above viewpoint, A ₂ /A ₁ is preferably at least 0.70, more preferably at least 0.72, still more preferably at least 0.75, still more preferably at least 0.80. Also, A ₂ /A ₁ is preferably at most 1.0, more preferably at most 0.90, still more preferably at most 0.88. On the other hand, B ₂ /B ₁ is preferably at most 0.85, more preferably at most 0.80, still more preferably at most 0.75, still more preferably at most 0.70. Furthermore, it is preferably 0.65 or less, more preferably 0.60 or less, and still more preferably 0.50 or less. Also, B ₂ /B ₁ is preferably at least 0.40, more preferably at least 0.45.

The in-particle pore volume _A2 of the boron nitride aggregated particles contained in the residual ash is preferably at least 0.20 mL/g, more preferably at least 0.25 mL/g, still more preferably at least 0.30 mL/g, and still more preferably at least 0.30 mL/g. More than 0.32 mL/g, preferably more than 0.34 mL/g. In addition, the particle internal pore volume A ₂ is preferably 0.60 mL/g or less, more preferably 0.50 mL/g or less, still more preferably 0.45 mL/g or less, still more preferably 0.40 mL/g or less.

The particle interstitial volume _B2 of boron nitride aggregated particles contained in the residual ash is preferably at least 0.35 mL/g, more preferably at least 0.40 mL/g, still more preferably at least 0.45 mL/g, still more preferably at least 0.50 mL/g or more. Also, the particle interstitial volume B ₂ is preferably 0.80 mL/g or less, more preferably 0.70 mL/g or less, still more preferably 0.65 mL/g or less.

Also, the circularity of boron nitride aggregated particles contained in the residual ash is preferably at least 0.85, more preferably at least 0.90, still more preferably at least 0.92, and still more preferably at least 0.94.

3. Manufacturing method of thermally conductive resin sheet Hereinafter, an example of the manufacturing method of the thermally conductive resin sheet of this embodiment is demonstrated. As an example of the manufacturing method of the heat conductive resin sheet of this embodiment, the method including a mixing process and a press molding process is mentioned, for example.

As a conventional production method, there is a method in which a slurry obtained by dispersing matrix resin and boron nitride aggregated particles in a solvent is applied to a substrate to obtain a thermally conductive resin film (wet coating method). However, bubbles are included when applied to the substrate, or foaming due to residual solvent in the coating film occurs when the solvent is not sufficiently dried, and the withstand voltage performance may be lowered. In particular, when using aggregated boron nitride particles whose pore volume in particles is _A1 and particle interstitial volume is _B1 , _B1 /( _A1 + _B1 ) is 0.60 or more. In some cases, the primary particles on the surface of the aggregated particles become radial, so the surface of the aggregated particles becomes more concave-convex, the slurry tends to become viscous, and bubbles are more likely to be generated when kneading with the resin or when it is applied to the substrate. Bubbles are likely to remain, and the withstand voltage performance is likely to decrease. In addition, in the above-mentioned wet coating method, if the addition amount of boron nitride aggregated particles is increased to improve thermal conductivity, streaks may be generated during coating, and productivity may be deteriorated. In particular, when using boron nitride aggregated particles in which the above-mentioned B ₁ /(A ₁ +B ₁ ) is 0.60 or more, the streaks are likely to occur.

In the production method of this embodiment, the sheet is formed by applying pressure at a temperature at which the thermoplastic resin exhibits fluidity, and the thermoplastic resin is pressed into the voids in the boron nitride aggregated particles, so that it is difficult to contain boron nitride in the sheet. bubble. Moreover, in this embodiment, since a sheet can be obtained without using a solvent, foaming by a residual solvent does not generate|occur|produce. Therefore, according to the manufacturing method of this embodiment, the withstand voltage performance of a thermally conductive resin sheet can be made favorable. In addition, since the production method of this embodiment does not go through the coating step, even if the above-mentioned boron nitride aggregated particles whose B ₁ /(A ₁ + B ₁ ) is 0.60 or more are used, there will be no problems caused by coating, such as Streaks and the like were generated, and the productivity was good.

Also as described in the examples of Patent Documents 4 and 5, since the previous mainstream is to use thermosetting resin as the matrix resin, wet coating method is often used as the manufacturing method of the thermally conductive resin sheet. It is considered that in this wet coating method, if there are many irregularities on the surface of the aggregated particles, the above-mentioned disadvantages will occur in many cases, so it is preferable to have as few irregularities on the surface of the aggregated particles as possible (that is, the above-mentioned B Aggregated particles in which the ratio of ₁ /(A ₁ +B ₁ ) is less than 0.60). On the other hand, from the viewpoint of thermal conductivity, it is preferable that the primary particles on the surface of aggregated particles are radial, and the ratio of B ₁ /(A ₁ +B ₁ ) of such particles is often greater than 0.60. In this way, in the case of using the previous manufacturing method, the relationship between the improvement of withstand voltage performance and productivity and the improvement of thermal conductivity and the volume _A1 of the pores in the particle and the volume _B1 between the particles of boron nitride aggregated particles is a trade-off relationship. , which is a trade-off relationship in B ₁ /(A ₁ +B ₁ ). According to the production method of this embodiment, aggregated particles having a ratio of B ₁ /(A ₁ +B ₁ ) of 0.60 or more can be used without considering the disadvantages of the wet coating method, so that the withstand voltage performance and Productivity becomes good, and thermal conductivity improves.

(1) Mixing step In the mixing step, the powder containing thermoplastic resin and boron nitride aggregated particles are stirred and mixed at room temperature. Regarding the above-mentioned boron nitride aggregated particles, the pore volume in the particles of the boron nitride aggregated particles When A ₁ is used and the particle interstitial volume is B ₁ , B ₁ /(A ₁ +B ₁ ) is 0.60 or more. As a conventional production method, there is a method of heating, melting and kneading matrix resin and boron nitride aggregated particles. However, boron nitride aggregated particles may be sheared and broken by this melt-kneading. In particular, when boron nitride aggregated particles having a ratio of B ₁ /(A ₁ +B ₁ ) of 0.60 or more are used, there are many unevennesses on the surface, so shear fracture is likely to occur. Therefore, in the present embodiment, without heating, melting and kneading, boron nitride aggregated particles having a ratio of B ₁ /(A ₁ + B ₁ ) of 0.60 or more between the powder containing the thermoplastic resin are heated at room temperature Stirring and mixing are not easy to cause shear damage of aggregated particles, and can improve the thermal conductivity of the obtained sheet.

(2) Press forming step In the pressure forming step, the mixture obtained in the above mixing step is heated and pressurized to form a sheet.

As the press molding method, various known press devices for thermoplastic resin molding can be used. From the viewpoint of preventing resin deterioration during heating and pressing, it is particularly preferable to use a vacuum pressurizing device that can reduce the amount of oxygen in the pressurizing machine during heating, or a pressurizing device equipped with a nitrogen replacement device.

In the pressure forming step, based on the purpose of forming the above-mentioned molten kneaded product into a sheet with uniform thickness, and by bonding the added boron nitride aggregated particles to each other, the surface of the particles at the joint is deformed to form a heat flow path For the purpose of removing pores or voids in the sheet, etc., it is preferable to set the pressing pressure. From this point of view, the pressure in the pressure forming step is usually 8 MPa or higher, preferably 9 MPa or higher, more preferably 10 MPa or higher, based on the actual pressure applied to the sample. Moreover, it is preferably at most 50 MPa, more preferably at most 40 MPa, and still more preferably at most 30 MPa. By setting the pressure at the time of this pressurization to be equal to or less than the above-mentioned upper limit, it is possible to prevent boron nitride aggregated particles from being crushed, and it is possible to obtain a thermally conductive resin sheet having high thermal conductivity. In addition, by setting the pressing pressure to be more than the above lower limit, the contact between the boron nitride aggregated particles becomes good, the heat conduction path is easily formed, and a sheet with high thermal conductivity can be obtained, and the number of resin flakes can be reduced. Therefore, it can be made into a thermally conductive resin sheet with a high dielectric breakdown voltage even after the moisture absorption reflow test.

The set temperature of the pressurizing device in the press molding step is preferably the temperature at which the thermoplastic resin exhibits fluidity, for example, the melting point of the thermoplastic resin as the main component + 30° C. or higher. For example, when polyetherketone resin is used as the main component, the set temperature of the pressurizing device is preferably 370°C to 440°C, more preferably 380°C or higher or 420°C or lower. By performing press molding at a temperature within this range, good thickness uniformity can be imparted to the obtained thermally conductive resin sheet, and high thermal conductivity can be generated by good contact between the added boron nitride aggregated particles sex. If the molding temperature is 370°C or higher, the viscosity of the resin is low enough to perform molding processing, and sufficient thickness uniformity can be imparted to the thermally conductive resin sheet formed. On the other hand, if the set temperature of the press machine is 440° C. or lower, deterioration of the resin itself or deterioration of the physical properties of the molded thermally conductive resin sheet can be suppressed.

The pressing time is usually at least 30 seconds, preferably at least 1 minute, more preferably at least 3 minutes, and still more preferably at least 5 minutes. Moreover, it is preferably 1 hour or less, more preferably 30 minutes or less, and still more preferably 15 minutes or less. By being below the above upper limit, the manufacturing process time of the thermally conductive resin sheet can be suppressed, and the cycle time can be shortened compared with a thermally conductive resin sheet using a heat-resistant thermosetting resin, thereby tending to suppress production costs. Moreover, by being more than the said lower limit, the thickness uniformity of a thermally conductive resin sheet can fully be obtained, internal voids or voids can be fully removed, and the nonuniformity of thermal conductivity and withstand voltage characteristic can be prevented.

4. Laminated heat sink The laminated heat sink of this embodiment is formed by layering a metal layer for heat dissipation including a heat dissipation material on one surface of the thermally conductive resin sheet of this embodiment. The heat dissipation material is not particularly limited as long as it includes a material with good thermal conductivity. Among them, in order to improve the thermal conductivity when forming a laminate, it is preferable to use a metal material for heat dissipation, and it is more preferable to use a flat metal material. The material of the metal material is not particularly limited. Among them, a copper plate, an aluminum plate, an aluminum alloy plate, etc. are preferable in terms of good thermal conductivity and relatively low price.

In the case of using a flat metal material as the metal material for heat dissipation in a laminated heat sink, in order to ensure sufficient heat dissipation, the thickness of the metal material is preferably 0.03 to 6 mm, more preferably 0.1 mm or more or 5 mm. mm or less.

Regarding the bonding with the metal material for heat dissipation, the surface of the metal material on the side where the thermally conductive resin sheet is laminated can be roughened by soft etching, weathering plating treatment, oxidation-reduction treatment, etc. to ensure the durability of the bonding Plating treatment of various metals and metal alloys, organic surface treatment including amine-based, mercapto-based silane coupling treatment, or surface treatment using organic-inorganic composite materials. By performing these surface treatments, the initial adhesive force, the durability of the adhesive force, and the effect of suppressing interfacial peeling after the moisture absorption reflow test can be improved.

On the other hand, the side of the metal material for heat dissipation that is opposite to the side where the thermally conductive resin sheet is laminated does not need to be a simple flat plate. In order to ensure the contact area with the cooling medium that is gas or liquid, processing to increase the surface area, etc., can be performed. . Examples of the processing for increasing the surface area include: roughening the surface by blasting to increase the surface area; directly forming a V-shape on the metal material for heat dissipation by cutting or pressurizing, The method of grooves such as rectangles or various shapes of concavities and convexities; the metal layer for heat dissipation that includes a flat metal material is further bonded by casting, diffusion bonding, or bolt fastening, welding, welding, etc. Another metal material processed to increase the surface area; or embedding metal pins, etc. Furthermore, it is also conceivable to directly press-laminate a thermally conductive resin sheet on a metal layer for heat dissipation having a cavity through which a cooling medium passes. However, since the pressurization pressure of the heat-conducting resin sheet and the heat-dissipating metal plate is relatively high, in such cases, it is preferable to laminate and integrate the plate-shaped metal material and the heat-conducting resin sheet in a subsequent step. In the step, it is integrated with the metal plate that undergoes grooving processing or the metal layer that has a cavity for the circulation of the refrigerant by welding, welding, bolting, and the like.

For the lamination and integration of the metal material for heat dissipation and the thermally conductive resin sheet in the laminated heat sink, pressure molding as a batch process can be preferably adopted. In this case, the range of the pressurization equipment, pressurization conditions, etc. is the same as the above-mentioned press molding conditions for obtaining a thermally conductive resin sheet.

5. Heat dissipation circuit board The heat-dissipating circuit board of this embodiment has the above-mentioned laminated heat-dissipating sheet. That is, the heat-dissipating circuit board has a structure in which the metal layer for heat dissipation is laminated on one surface of the heat-conductive resin sheet of the present embodiment, and the heat-dissipating resin sheet is formed on the other surface opposite to the metal material for heat dissipation by For example, an etching process or the like forms a circuit board.

As the composition of the heat-dissipating circuit board, it is more preferable to integrate "metal material for heat dissipation/thermally conductive resin sheet/conductive circuit". As the state before circuit etching, for example, the following can be cited: In the integrated structure of "metal material for heat dissipation/thermally conductive resin sheet/metal material for conductive circuit formation", the metal material for conductive circuit formation is flat and formed Formed on the entire surface or a part of one side of the thermally conductive resin sheet.

The material of the metal material for forming a conductive circuit is not particularly limited. Among them, in general, it is preferable to form a copper thin plate with a thickness of 0.05 mm or more and 1.2 mm or less from the viewpoint of good electrical conductivity, etching property, and cost.

The dielectric breakdown voltage of the heat-dissipating circuit board is preferably at least 40 kV/mm, more preferably at least 50 kV/mm, still more preferably at least 60 kV/mm, still more preferably at least 80 kV/mm. By making the dielectric breakdown voltage 40 kV/mm or higher, for example, a thermally conductive resin sheet with a thickness of 100 μm can also obtain a dielectric breakdown voltage of 4 kV or higher. If the dielectric breakdown voltage is 80 kV/mm or higher, the thickness is 50 μm A dielectric breakdown voltage of 4 kV or higher can also be obtained, so it is possible to use a thinner thermally conductive resin layer that is advantageous in terms of thermal resistance while having sufficient withstand voltage performance, and it is possible to suppress the occurrence of dielectric breakdown when a high voltage is applied.

6. Power semiconductor devices The thermally conductive resin sheet of this embodiment or the laminated heat sink of this embodiment can be preferably used as a heat sink for a power semiconductor device, and a highly reliable power semiconductor module can be realized. The power semiconductor device is a power semiconductor device using the above-mentioned thermally conductive resin sheet or the above-mentioned laminated heat sink, and the above-mentioned thermally conductive resin sheet or the above-mentioned laminated heat sink is mounted on the power semiconductor device as a heat-dissipating circuit board. The power semiconductor device device can achieve high output and high density on the basis of high reliability through the heat dissipation effect based on high thermal conductivity. In power semiconductor device devices, conventionally known components such as aluminum wiring, sealing materials, packaging materials, heat sinks, heat radiation paste, and solder other than thermally conductive resin sheets or laminated heat sinks can be appropriately used.

<Second Embodiment> 1. Resin composition A thermally conductive resin sheet according to a second embodiment of the present invention contains a resin composition containing a thermoplastic resin and boron nitride aggregated particles.

(1) Thermoplastic resin The thermoplastic resin of this embodiment is the same as the thermoplastic resin described in the above-mentioned first embodiment, and the physical properties and resin types of preferable thermoplastic resins in this embodiment are also the same as those of the above-mentioned first embodiment.

(2) Boron nitride agglomerated particles The boron nitride aggregated particles of this embodiment are the same as the boron nitride aggregated particles described in the above-mentioned first embodiment, and the physical properties and structure of preferable boron nitride aggregated particles in this embodiment are also the same as those of the above-mentioned first embodiment. Furthermore, in this embodiment, the circularity of boron nitride aggregated particles in the resin composition has 1 as the upper limit, and is preferably more than 0.945, more preferably 0.95 or more, and still more preferably 0.96 or more.

(3) Content of each ingredient The content of the thermoplastic resin and boron nitride aggregated particles in the resin composition of this embodiment is the same as that of the above-mentioned first embodiment. Moreover, the resin composition of this embodiment may contain other components other than a thermoplastic resin and boron nitride aggregated particle. However, from the viewpoint of improving thermal conductivity, it is preferable not to contain other components. The other components are those exemplified in the above-mentioned first embodiment.

2. Thermally conductive resin sheet The thermally conductive resin sheet of this embodiment has the following features: it contains the above-mentioned resin composition, has high thermal conductivity in the thickness direction, is excellent in resistance to moisture absorption and reflow, and is less prone to thermal expansion and Interfacial peeling caused by shrinkage.

A thermally conductive resin sheet containing a resin composition containing boron nitride aggregated particles was heated at 700°C for 5 hours to remove the resin component. Regarding the ash content, after measuring the mercury intrusion and exit curve by mercury intrusion porosimetry, the pore diameter was prepared. As the horizontal axis, the pore size distribution curve with the logarithmic differential pore volume as the vertical axis is usually less than 5 μm, preferably 0.1 μm or more and less than 5 μm, and usually 5 μm or more, preferably 5 μm or more A peak is observed in the range below 100 μm. In the present invention, the peak having a maximum value in the range of less than 5 μm, preferably 0.1 μm or more and less than 5 μm is set as the first peak, and the peak is 5 μm or more, preferably 5 μm or more and 100 μm The peak having the maximum value in the range below was set as the second peak. The range below 5 μm includes the peak a caused by the inner pores of the boron nitride aggregated particles, and the range above 5 μm includes the peak b caused by the interparticle gap of the boron nitride aggregated particles.

In the present invention, the maximum values of the first peak and the second peak are respectively referred to as the first peak top height and the second peak top height. Also, the pore diameters at which the first peak and the second peak show maximum values are referred to as the first peak top diameter and the second peak top diameter, respectively.

In addition, as the case where there are multiple peaks in the range of 5 μm or more, it is considered that there are the following cases: in the residual ash, those with two particle size distributions are mixed and used as boron nitride aggregated particles; Boron aggregated particles also contain fillers other than boron nitride; or peaks caused by fragments generated by the disintegration of boron nitride aggregated particles during the forming process or primary particles detached from the aggregated particles. In these cases, it is considered that the height of the second peak top is often smaller than that of the present embodiment, and it is considered that it is difficult to obtain high thermal conductivity.

In order to improve the thermal conductivity of the thermally conductive resin sheet, it is preferable to use aggregated particles having a structure in which the primary particles near the outermost surface of the aggregated particles are aligned with the radiation direction of the aggregated particles, and the aggregated particles are in surface contact with each other after sheeting. In this state, the vicinity of the surface is deformed, and the disintegration of the aggregated particles themselves or the shedding of the primary particles accompanying the disintegration is less, and the contact area between the aggregated particles becomes larger. From this point of view, it is preferable that the diameter of the second peak top is larger.

The second peak top diameter is preferably at least 15 μm, more preferably at least 16 μm, and still more preferably at least 17 μm. On the other hand, from the viewpoint of increasing the contact area by bringing the aggregated particles into surface contact with each other, thereby reducing the thermal resistance between the aggregated particles, the second peak diameter is preferably 30 μm or less, more preferably 30 μm or less. Below 25 μm. If the diameter of the second peak is large, only the part of the resin exists between a plurality of aggregated particles. Therefore, if viewed locally, the part with a large thermal resistance exists in a relatively large volume. Generally speaking, the heat sink has a high In terms of thermal conductivity, it leaves a bad impression. However, when aggregated boron nitride particles are used as a thermally conductive filler, particularly house-of-card-type aggregated boron nitride particles in which the primary particles constituting the aggregated particles are firmly bonded to each other, the aggregated boron nitride particles are not stable even after the sheet is formed. It is important to maintain the firm combination of the primary particles inside the aggregated particles. In order to maintain effective heat transfer between the primary particles inside the aggregated particles, it is preferable to avoid excessive deformation or crushing of the aggregated particles in the sheet. There is a case where a single primary particle detaches from excessively deformed or crushed aggregated particles, or a case where a plurality of primary particles detach in a bonded state. When such particles are generated, the height of the second peak top becomes smaller, or the diameter of the second peak top becomes smaller, or the second peak tends to become a wider shape.

The second peak top height is preferably at least 1.0 mL/g, more preferably at least 1.2 mL/g, still more preferably at least 1.5 mL/g. The upper limit of the second peak height is not particularly limited. Since the second peak height of boron nitride aggregated particle raw materials with high circularity and relatively narrow particle size distribution is about 3.5, it is preferably 3.2 mL/g or less. , more preferably 3.0 mL/g or less, further preferably 2.7 mL/g or less, still more preferably 2.5 mL/g or less. The second peak height is an index showing the uniformity of the surface contact state of the aggregated particles in the sheet. As described above, in the sheet, the aggregated particles are preferably deformed near the surface so that the aggregated particles are brought into surface contact with each other. When it is close to the state of point contact, high thermal conductivity of the entire sheet cannot be obtained. In this case, the height of the second peak becomes smaller. The fact that the second peak top height is equal to or greater than the above-mentioned lower limit means that the aggregated particles in the sheet are in a relatively uniform surface-to-face contact state accompanied by relatively uniform deformation, and the particle interstitial volume becomes relatively uniform.

In addition, the thermally conductive resin sheet according to the present embodiment preferably has a smaller first peak diameter, that is, has a structure in which interparticle gaps are smaller and aggregated particles are dense. It is considered that when the diameter of the first peak top is small, the particle gaps of boron nitride agglomerated particles as a raw material itself are small, and as a result, the particle gaps from the raw material also remain small after sheet forming. It is believed that boron nitride aggregated particles with small particle gaps have a structure in which the primary particles form a dense combination, and it is easy to obtain high thermal conductivity inside the aggregated particles. The smaller diameter of the first peak reflects that the above-mentioned aggregated particles will not be excessively deformed or crushed even if they are subjected to pressure during sheet processing, and the primary particle will not fall off. It is considered that if the first The smaller the peak top diameter, the better the thermal conductivity is likely to be. Furthermore, it is also considered that the aggregated particles are excessively deformed or disintegrated due to pressurization during sheet forming, and as a result, the diameter of the first peak top becomes smaller. In this case, the height of the second peak top and the height of the second peak The top diameter is outside the above range. From the above point of view, the first peak top diameter is preferably 0.4 μm or less, more preferably 0.38 μm or less. On the other hand, from the viewpoint of sufficiently ensuring that the resin penetrates into the internal pores of the aggregated particles, suppressing the generation of voids in the thermally conductive resin sheet and improving the withstand voltage performance, the first peak top diameter is preferably 0.1 μm or more, more preferably It is 0.15 μm or more, and more preferably 0.2 μm or more.

Also, the first peak top height is preferably at least 0.25 mL/g, more preferably at least 0.3 mL/g, and still more preferably at least 0.4 mL/g. The upper limit of the first peak height is not particularly limited, but is preferably 0.7 mL/g or less, more preferably 0.65 mL/g or less, further preferably 0.6 mL/g or less. If the first peak top height is not more than the above-mentioned upper limit, the pore volume inside the aggregated particles does not become too large, and primary particles capable of efficiently conducting heat inside the aggregated particles are moderately present. On the other hand, the fact that the first peak top height is equal to or greater than the above-mentioned lower limit indicates that the internal voids of the aggregated particles themselves used as raw materials are moderately present. Such aggregated particles are considered to cause moderate deformation near the surfaces of the aggregated particles in the sheet, and surface contact is likely to occur. In addition, as the case where the height of the first peak top is lower than the above-mentioned lower limit value, it is considered that the first peak may be observed as a broad peak. In this case, it is considered that the three-dimensional structure of the primary particles constituting the aggregated particles used as a raw material is significantly different, or that deformation and destruction due to pressure during sheet forming also spread to the inside of the aggregated particles.

As described above, the strength of aggregated particles, the alignment state of primary particles after flaking, and the like are indicated by the first peak top height, first peak top diameter, second peak top height, and second peak top diameter. The inventors of the present invention found that, among these factors, the second peak height and the second peak diameter affect the withstand voltage performance and thermal conductivity. The height of the second peak and the diameter of the second peak within the above range indicate that aggregated particles with sufficient strength are used, and if such a thermally conductive resin sheet is used, the aggregated particles are less disintegrated during molding, etc. And the house-of-cards-shaped boron nitride aggregated particles whose primary particles on the surface of the aggregated particles are radially aligned are used as the raw material, which can fully form the heat conduction path between the aggregated particles. Furthermore, the inventors of the present invention also found that, among these factors, the first peak top diameter and the second peak top diameter affect the withstand voltage performance and thermal conductivity. If the diameter of the first peak top and the second peak top diameter are within the above range, it has a structure that can be called "hard inside and soft outside", that is, in the state where the interior of the aggregated particles is dense and maintains a structure with isotropic thermal conductivity The region where the primary particles on the surface of the aggregated particles are radially aligned is moderately deformed during molding, so the contact area between adjacent aggregated particles increases, and the thermal conductivity in the thickness direction of the thermally conductive resin sheet can be further improved.

Examples of aggregated particles of boron nitride having a first peak height, a first peak diameter, a second peak height, and a second peak diameter within the above ranges include aggregated particles having a house of cards structure. In addition, after boron nitride aggregated particles are obtained by a known method, physical surface roughening treatment or chemical surface roughening treatment can be performed for adjustment. Usually, commercially available boron nitride aggregated particles use boron nitride primary particles that are relatively crystallized during granulation. Therefore, stable primary particle faces (ab faces) are preferentially stacked, and the outermost portion of the aggregated particles There are many "cabbage structures" in which the thickness direction of primary particles near the surface is consistent with the radiation direction of aggregated particles. Since the primary particles near the outermost surface of the aggregated particles of the "cabbage structure" exist in the form of covering the aggregated particles, and the strength of the aggregated particles itself is relatively low, so in the measurement of the heated ash content of the sheet, the second The height of the 2 peak and the diameter of the second peak tend to become smaller. Therefore, in the case of using the aggregated particles of the "cabbage structure", the above-mentioned surface roughening treatment can be performed for adjustment.

The thermal conductivity of the thermally conductive resin sheet of the present embodiment in the thickness direction at 25°C is preferably at least 18 W/m·K, more preferably at least 19 W/m·K, still more preferably at least 20 W/m·K above. By making the thermal conductivity in the thickness direction more than the above-mentioned lower limit value, it can be preferably used also for power semiconductor devices and the like that operate at high temperatures. The thermal conductivity can be determined by the type of thermoplastic resin and physical property values such as melt viscosity, the value of the first peak height, the first peak diameter, the second peak height and the second peak diameter in the thermally conductive resin sheet, nitrogen The structure and content of the boron nitride aggregated particles, the mixing method of the thermoplastic resin and the boron nitride aggregated particles, and the conditions in the following heating and kneading step were adjusted.

Also, from the viewpoint of suppressing excessive deformation of the aggregated particles and improving the thermal conductivity of the sheet, the circularity of the boron nitride aggregated particles contained in the residual ash in this embodiment is preferably greater than 0.945, and more preferably Preferably, it is more than 0.95. In addition, when the aggregated particles are in surface contact with each other, the thermal conductivity of the sheet becomes good, so the circularity is preferably at most 0.99, more preferably at most 0.98, and still more preferably at most 0.97.

3. Manufacturing method of thermally conductive resin sheet As an example of the manufacturing method of the heat conductive resin sheet of this embodiment, the method including a mixing process and a press molding process is mentioned, for example.

As the boron nitride aggregated particles whose second peak diameter becomes large as measured by the heated ash content of the sheet, those with radial primary particles on the surface of the aggregated particles and with many irregularities on the surface of the aggregated particles can be selected. If such boron nitride aggregated particles are used in the conventional production method (wet coating method), it is possible to reduce the interfacial heat when the aggregated particles come into contact with each other by pressing the sheet under pressure. However, the slurry tends to become viscous, and air bubbles are more likely to be generated when it is mixed with resin or applied to the substrate. Therefore, air bubbles are likely to remain in the resin film, and the withstand voltage performance is prone to decrease. Also, when such boron nitride aggregated particles are used, streaks are likely to be generated during coating, and productivity may be deteriorated.

In the production method of this embodiment, the sheet is formed by applying pressure at a temperature at which the thermoplastic resin exhibits fluidity, and the thermoplastic resin is pressed into the voids in the boron nitride aggregated particles, so that it is difficult to contain boron nitride in the sheet. bubble. Moreover, in this embodiment, since a sheet can be obtained without using a solvent, foaming by a residual solvent does not generate|occur|produce. Therefore, according to the manufacturing method of this embodiment, the withstand voltage performance of a thermally conductive resin sheet can be made favorable. In addition, since the production method of the present embodiment does not go through the coating step, even if boron nitride aggregated particles whose second peak diameter as measured by the heating ash of the sheet is used as a raw material, there is no occurrence of Problems caused by coating, such as streaks, etc., are good in productivity.

As mentioned above, since the previous mainstream is to use thermosetting resin as the matrix resin, wet coating method is often used as the manufacturing method of the thermally conductive resin sheet. It is considered that in this wet coating method, if there are many irregularities on the surface of the aggregated particles, the above-mentioned disadvantages will occur in many cases. Agglomerated particles where the diameter of the second peak top measured by the heated ash of the sheet becomes smaller). On the other hand, from the viewpoint of thermal conductivity, it is preferable that the primary particles on the surface of aggregated particles are radial, and the ratio of B ₁ /(A ₁ +B ₁ ) of such particles is often greater than 0.60. Thus, in the case of using the conventional manufacturing method, there is a trade-off relationship between the improvement of withstand voltage performance and productivity and the improvement of thermal conductivity in terms of the second peak top diameter. According to the production method of the present embodiment, aggregated particles such as those whose second peak diameter becomes large as measured by the heating ash content of the sheet can be used without considering the disadvantages in the wet coating method, so it is possible to use The withstand voltage performance and productivity are improved, and the thermal conductivity is improved.

(1) Mixing step In the mixing step, the powder containing thermoplastic resin and boron nitride aggregated particles are stirred and mixed at normal temperature. As a conventional production method, there is a method of heating, melting and kneading matrix resin and boron nitride aggregated particles. However, when boron nitride agglomerated particles having a large second peak diameter as measured by the heated ash content of the sheet are used, the surface has many irregularities, so shear fracture is likely to occur. Therefore, in the present embodiment, without heating, melting and kneading, a powder containing a thermoplastic resin and boron nitride having a larger second peak diameter as measured by the heating ash content of the sheet The agglomerated particles are stirred and mixed at room temperature, so that the shear damage of the agglomerated particles is not easy to occur, and the thermal conductivity of the obtained sheet can be improved.

(2) Press forming step In the pressure forming step, the mixture obtained in the above mixing step is heated and pressurized to form a sheet. A preferred press molding method in this embodiment is the same as that in the above-mentioned first embodiment.

4. Laminated heat sinks, heat-dissipating circuit substrates, and power semiconductor devices Similar to the above-mentioned first embodiment, the thermally conductive resin sheet of this embodiment is suitably used as a laminated heat sink, a heat-dissipating circuit board, and a power semiconductor device.

＜Description of sentences＞ In the present invention, when expressed as "X~Y" (X, Y are arbitrary numbers), unless otherwise specified, it means "more than X but less than Y" and also includes "preferably greater than X". ” or “preferably less than Y”. In addition, when expressed as "more than X" (X is any number) or "below Y" (Y is any number), it also includes "preferably greater than X" or "preferably less than Y". main meaning. In the present invention, the term "sheet" includes concepts of sheet, film, and tape. [Example]

Hereinafter, the present invention will be described in more detail by means of examples. However, the present invention is not limited to the following examples unless the gist is exceeded.

<Examples 1-3 and Comparative Examples 1-4> Materials used, production methods, measurement conditions, and evaluation methods of the thermally conductive resin sheets in Examples 1-3 and Comparative Examples 1-4 are as follows.

[use material] (thermoplastic resin) Thermoplastic resin 1: Polyetheretherketone "KetaSpire KT-880FP" (manufactured by Solvay Co., Ltd., melting point: 343°C, melt viscosity: 0.15 kPa・s (400°C), average particle size (D50): 30.0 to 45.0 μm, MFR : 86 g/10 minutes, mass average molecular weight (Mw): 58000).

(thermosetting resin) Thermosetting resin 1: Epoxy resin composition (bisphenol F type epoxy resin (manufactured by Mitsubishi Chemical Corporation, mass average molecular weight in terms of polystyrene: 60000) 8.74 parts by mass, hydrogenated bisphenol A type liquid epoxy 10.93 parts by mass of resin (manufactured by Mitsubishi Chemical Corporation), 2.62 parts by mass of p-aminophenol-type liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation), 5.73 parts by mass of phenolic resin-based hardener "MEH-8000H" (manufactured by Meiwa Kasei Co., Ltd.) , 0.48 parts by mass of 1-cyanoethyl-2-undecylimidazole "C11Z-CN" (manufactured by Shikoku Chemicals, molecular weight: 275) as a curing catalyst.

Aggregated boron nitride particles (thermally conductive filler) Thermally conductive fillers used as aggregated boron nitride particles are as follows. Thermally conductive filler 1: Boron nitride agglomerated particles having a house of cards structure (B ₁ /(A ₁ + B ₁ )=0.664, average particle diameter (D50): 35 μm, maximum particle diameter Dmax: 90 μm) Thermally conductive filler 2 : Boron nitride agglomerated particles having a house of cards structure (B ₁ /(A ₁ + B ₁ )=0.662, average particle size (D50): 35 μm, maximum particle size Dmax: 90 μm) Thermally conductive filler 3: Has a house of cards Structured boron nitride aggregated particles (B ₁ /(A ₁ + B ₁ )=0.648, average particle size (D50): 35 μm, maximum particle size Dmax: 90 μm) Thermally conductive filler 4: Nitriding with house of cards structure Boron aggregated particles (B ₁ /(A ₁ +B ₁ )=0.516, average particle diameter (D50): 34 μm, maximum particle diameter Dmax: 90 μm) Thermally conductive filler 5: Boron nitride aggregated particles having a house of cards structure ( B ₁ /(A ₁ +B ₁ )=0.556, average particle diameter (D50): 40 μm, maximum particle diameter Dmax: 90 μm) Thermally conductive filler 6: Has cabbage structure (among primary particles near the outermost surface of aggregated particles Boron nitride aggregated particles (“PTX25” (manufactured by Momentive, B ₁ /(A ₁ +B ₁ )=0.441, average particle diameter (D50) 25 μm, specific surface area 7 m ² /g)

Thermally conductive fillers 1 and 2 were produced by the method described below. Furthermore, regarding the thermally conductive fillers 1 and 2, the (raw material), (preparation of slurry), (granulation) to (thermal decomposition) described below were carried out as the same batch, and only (the boron nitride aggregated particle The furnace treatment at 2000°C in the item of production) is carried out successively as another batch.

(raw material) Hexagonal boron nitride (hereinafter referred to as " Raw material "h-BN powder"): 10000 g, binder ("Takiceram M160L" manufactured by Taki Chemical Co., Ltd., solid content concentration: 21% by mass): 11496 g, and surfactant (manufactured by Kao Co., Ltd. Surfactant "ammonium lauryl sulfate": solid content concentration: 14% by mass): 250 g as a raw material.

(Preparation of slurry) Measure the above-mentioned amount of raw material h-BN powder into a resin bottle, and then add the above-mentioned amount of binder. Furthermore, after adding the above-mentioned amount of surfactant, zirconia ceramic balls were added, and stirred for 1 hour on the rotary table of a pot mill to obtain a BN slurry. The viscosity of the slurry is 810 mPa·s.

(granulation) Using a spray dryer (FOC-20 manufactured by Daheyuan Chemical Machinery Co., Ltd.), the above-mentioned BN slurry was spray-dried under the conditions of a disc rotation speed of 20000-23000 rpm and a drying temperature of 80 ° C to obtain spherical BN granules particle.

(Thermal decomposition) Under the air atmosphere, the above-mentioned BN granulated particles were heat-treated at 700° C. for 5 hours to obtain precursor particles.

(Production of Boron Nitride Aggregated Particles) Fill the above-mentioned precursor particles in a disk shape into a circular graphite crucible with a cover, and replace the furnace with nitrogen gas at room temperature at room temperature, and raise the temperature at 83°C/hour while nitrogen gas is flowing. After reaching 2000° C. and reaching 2000° C., it was maintained in this state for 5 hours while flowing nitrogen gas, and then cooled to room temperature. Take out the calcined product from the crucible, remove the part of the calcined product that is in contact with graphite, crush it manually with a mortar and pestle, and then process it with a roller mill to obtain spherical boron nitride agglomerated particles with a house of cards structure . The boron nitride aggregated particles obtained were sieved using a sieve with a mesh size of 90 μm, and only the particles that passed through the sieve were used as thermally conductive fillers. Furthermore, for thermally conductive fillers 1 and 2, after the above-mentioned furnace treatment at 2000°C, manual crushing and roller mill treatment were also carried out respectively, but the treatment after the furnace treatment at 2000°C was regarded as another batch Repeated implementation will not affect the determination results of mercury porosimetry.

Regarding the thermally conductive filler 3, a mixture of 5000 g each of hexagonal boron nitride having an oxygen concentration of 5% by mass and 5000 g of hexagonal boron nitride having an oxygen concentration of 7.5% by mass was used as a raw material. Manufactured in the same way as thermal conductive filler 1. The thermally conductive filler 4 uses spherical aggregated particles having a structure in which the thermally conductive filler 2 is dry-processed for 30 minutes by a bead mill using nylon balls having a diameter of 10 mm, thereby aggregating the particles The primary particles on the surface are bent so as to cover the aggregated particles. As shown in FIG. 5 , according to the SEM observation image of the aggregated particles alone, it was judged that the aggregated particles themselves were not disintegrated or damaged, and the internal house of cards structure was also maintained. Also, for the thermally conductive filler 5, in addition to using 10,000 g of hexagonal boron nitride with an oxygen concentration of 7.5% by mass as a raw material, spherical aggregated particles having the following structure were also used: by the same method as the thermally conductive filler 1 After production, dry processing was performed for 30 minutes by using a bead mill with nylon balls with a diameter of 10 mm, whereby the primary particles on the surface of the aggregated particles were bent so as to cover the aggregated particles. According to the SEM observation image of the aggregated particles alone, the filler 5 also judged that the aggregated particles themselves were not disintegrated or damaged, and the internal house of cards structure was also maintained.

[Preparation of thermally conductive resin sheets of Examples 1-3 and Comparative Examples 1-3] Mix the powder of the matrix resin and the powder of the thermally conductive filler at room temperature, and use a high-temperature vacuum pressurization device (manufactured by Kitagawa Seiki Co., Ltd.) to pressurize the obtained powder at a pressurization temperature of 395°C and a pressurization surface pressure of 10 MPa. The bulk mixture was pressurized for 10 minutes to obtain a 15 cm square and 150 μm thick thermally conductive resin sheet and a 15 cm square and 500 μm thick thermally conductive resin sheet. At this time, the thickness of the sheet is adjusted by adjusting the amount of powder. However, only in Example 2, pressurization was performed for 10 minutes at a pressurization temperature of 395° C. and a pressurization surface pressure of 20 MPa. Then, the thermally conductive resin sheet with a thickness of 150 μm was used as a sample for the following moisture absorption reflow test, and the thermally conductive resin sheet with a thickness of 500 μm was used as a sample for measuring the thermal conductivity described below.

Here, the above-mentioned 10 minutes means preheating the inside of the vacuum press to 150°C, putting the above-mentioned powder mixture as a press-in composition into it, and applying several times to the molten kneaded product while operating the vacuum pump. For the lighter pressure of MPa, set the internal temperature of the press to 395°C. After heating up for 40 minutes, set the press surface pressure to 10 MPa, and then carry out pressurization for 10 minutes. After 10 minutes, the internal temperature of the press was set to 150° C. again, and the vacuum was released when the internal temperature was close to 150° C., and the thermally conductive resin sheet was taken out.

The above-mentioned so-called press-in composition refers to the composition required for one pressurization in the batch. The composition is placed on the lower plated plate with a thickness of 6 mm, and the outer sides are 20 cm in length and width. A frame-shaped spacer with an opening of 15 cm×15 cm, in which a powdered mixture of the quality required to obtain a compressed tablet with a thickness of 150 μm or a compressed tablet with a thickness of 500 μm is spread, and then spread in the spacer at 15 cm The above-mentioned opening of ×15 cm is embedded in a cover plate with a thickness of 5.85 mm (in the case of a sample thickness of 150 μm) or a thickness of 5.50 mm (in the case of a sample thickness of 500 μm), and a cover plate of 14.6 cm in length and width x 14.6 cm, and placed Upper plated plate.

[Manufacturing of the thermally conductive resin sheet of Comparative Example 4] The thermally conductive filler is added so that the total amount of the epoxy resin composition and the thermally conductive filler becomes 100% by mass, and the total solid content concentration of the epoxy resin composition and the thermally conductive filler becomes 62.8% by mass. Method A mixed solution of methyl ethyl ketone and cyclohexanone (mixing ratio (volume ratio) 1:1) was added and mixed at 37.2% by mass to obtain a coating slurry (coating liquid for sheet). When mixing these, after stirring by hand, stir for 2 minutes using a self-rotating and revolving mixer "Defoaming Rentaro AR-250". The coating slurry obtained above was coated on a polyethylene terephthalate film (hereinafter also referred to as "PET film") with a thickness of 38 μm by the doctor blade method, and heat-dried at 60°C for 120 minutes Thereafter, pressurization was performed at a pressurization temperature of 42° C. and a pressurization surface pressure of 15 MPa for 10 minutes to obtain an uncured epoxy resin sheet-like molded body. This epoxy resin sheet-like molded body was used as a sample for a moisture absorption reflow test.

Also, a thermally conductive resin sheet having a thickness of 500 μm used in the measurement of the thermal conductivity described below was produced by the following method. Cut the above-mentioned unhardened epoxy resin sheet-shaped molded body into 10 cm×10 cm, and laminate 4 pieces of the molded body as a press-in structure, which is used in Examples 1-3 and Comparative Examples 1-3 The spacer and the cover plate were pressed at a pressing temperature of 175°C and a pressing surface pressure of 10 MPa for 1 hour in the same manner as in the case of obtaining a sheet with a thickness of 500 μm to obtain a thermally conductive resin sheet with a thickness of 500 μm. Furthermore, the excess thickness of the laminated uncured epoxy resin sheet molded body is absorbed in the void volume between the sheet size 10 cm x 10 cm and the spacer size 15 cm x 15 cm.

<Measurement conditions, evaluation methods> The thermally conductive resin sheets of thermally conductive fillers 1-6, Examples 1-3, and Comparative Examples 1-4 were measured and evaluated by the following methods.

[Physical properties of aggregated particles (raw material powder)] (Dmax and D50) The maximum particle diameter Dmax and the average particle diameter D50 of boron nitride aggregated particles were measured by the following methods. For a sample obtained by dispersing 20 mg of boron nitride aggregated particles in 10 mL of pure water medium containing sodium hexametaphosphate by ultrasonic waves, laser diffraction/scattering particle size distribution analyzer LA-920 (Horiba Manufacturing Co., Ltd.) to measure the particle size distribution, and obtain the maximum particle size Dmax and average particle size D50 of boron nitride aggregated particles based on the obtained particle size distribution.

(Intra-particle pore volume A ₁ , particle interstitial volume B ₁ and B ₁ /(A ₁ + B ₁ )) Intra-particle pore volume A ₁ (mL/g) and particle interstitial volume B ₁ (mL/g) of boron nitride aggregated particles g) were measured according to JIS R1655: 2003 "Test method for pore size distribution of molded articles of precision ceramics by mercury porosimetry". Specifically, using the AutoPore IV manufactured by Micromeritics as a mercury porosimeter, 200 mg of the sample was filled into the measurement cell, and after 10 minutes of decompression treatment under reduced pressure (50 μmHg or less), the The total pore volume, again, is determined by the mercury intrusion and exit curve. Create a pore size distribution curve with the pore diameter as the horizontal axis and the logarithmic differential pore volume as the vertical axis. Assuming the pore is a cylinder, read the logarithmic differential pore volume relative to the pore diameter between the peak a representing the inner pores of the particles and the peak b representing the pores between particles. Minimum diameter (division diameter). The particle interstitial volume B ₁ (mL/g) was calculated from the integral value of the mercury intrusion and exit curve in the region where the pore diameter was larger than the cut diameter. Also, the above-mentioned particle interstitial volume B ₁ was subtracted from the total pore volume to obtain the intra-particle pore volume A ₁ (mL/g). From the measurement results, "B ₁ /(A ₁ +B ₁ )" was calculated. In addition, when filling the sample into the groove of the mercury porosimeter, in particular, operations such as tapping are not performed, but the measurement itself is to press mercury with a relatively high specific gravity, so it will be independent of the initial stage of the sample. The filling condition depends only on the measurement results of the properties of boron nitride aggregated particles. There are boron nitride agglomerated particles destroyed by the above-mentioned mercury intrusion, but such particles do not satisfy the requirements of the present invention.

(circularity) The circularity of thermally conductive fillers 2 to 5 was measured using a particle image analyzer (manufactured by Malvern, Morpholog G3S). Furthermore, for any of the above boron nitride aggregated particles, it is conceivable that the following particles exist: boron nitride particles that remain in the state of primary particles without forming aggregates, or aggregated particles that are once formed but fall off from the aggregated particles in subsequent processing. Since particles such as boron nitride primary particles are classified by 1 Bar air flow dispersion, the circularity is measured by performing image analysis. The measurement of the circularity by Morpholog is to measure and calculate the perimeter of the particle and the perimeter of a circle having an area equal to the area of the particle, using the former as the denominator and the latter as the numerator. 10000 pieces were measured, and the average value thereof was regarded as the circularity. In addition, since the measurement in Filler 1 was not carried out, it was described as "-" in Table 1.

[Physical properties of aggregated particles (sheet ash content)] (particle inner pore volume A ₂ , particle interstitial volume B ₂ , A ₂ /A ₁ and B ₂ /B ₁ ) Residual ash content when a thermally conductive resin sheet is heated to 700°C Intraparticle pore volume A ₂ (mL/g) and particle interstitial volume B ₂ (mL/g) measured by mercury porosimetry of the boron nitride agglomerated particles included in , were measured in the following manner. First, the following thermally conductive resin layer with a thickness of 150 μm prepared for the moisture absorption reflow test was laminated with a copper plate to form a composition consisting of "metal plate for heat dissipation (copper plate, thickness 2 mm) / thermally conductive resin sheet ( Thickness: 0.15 mm)/copper plate for conductive circuit formation (thickness: 0.5 mm)”, the copper plate was completely removed from the laminated heat sink by etching, and only the resin sheet was isolated as a sample. Take 400 mg of the sample (the area of the resin sheet is about 3.6 cm×3.6 cm), and heat it in a heating furnace at 700°C for 5 hours under the atmosphere to decompose and remove the resin part, and make heating ash. Weighed the ash content of the sheet before heating and after heating, respectively, and confirmed that the mass of the ash content was approximately the same as the calculated value of the mass of the prepared boron nitride aggregated particles. Then, using the AutoPore IV manufactured by Micromeritics as a mercury porosimeter, 200 mg of the sample was filled into the measurement cell, and the pore size distribution curve was prepared in the same way as the measurement of _A1 and _B1 above, and the ash content of the sheet was calculated. Particle interstitial volume B ₂ (ml/g) and interparticle pore volume A ₂ (ml/g) of boron nitride aggregated particles. Intra-particle pore volume A 1 , inter-particle interstitial volume B ₁ , intra-particle pore volume A _{2 and} inter-particle interstitial volume B in the ashes of the thermally conductive resin sheet of the fillers used in Examples 1-3 and Comparative Examples 1-4 respectively _2. Obtain the survival rate A ₂ /A ₁ and B ₂ /B ₁ .

(peak height and peak diameter) From the pore size distribution curve in the ash content of the sheet obtained above, the first peak top height, first peak top diameter, second peak top height, and second peak top diameter were obtained.

(circularity) About Examples 2-3 and Comparative Examples 1-3, the circularity of the ash content of a thermally conductive resin sheet was measured using the particle|grain image analysis apparatus (Malvern company make, Morpholog G3S). Furthermore, for any sheet ash, it is considered that there are the following particles: boron nitride particles that do not form aggregates but remain in the state of primary particles, or although aggregated particles are once formed, but are added to the subsequent processing or sheet forming In the pressing step, particles falling from the aggregated particles to become boron nitride primary particles, etc., were classified by 1 Bar air flow dispersion, and then image analysis was performed to measure the circularity. The measurement of the circularity by Morpholog is to measure and calculate the perimeter of the particle and the perimeter of a circle having an area equal to the area of the particle, using the former as the denominator and the latter as the numerator. 10000 pieces were measured, and the average value thereof was regarded as the circularity. In addition, since the measurement in the thermally conductive resin sheet of Example 1 was not performed, it was described as "-" in Table 1. Since the aggregated particles of the thermally conductive resin sheet of Comparative Example 3 were disintegrated, the circularity could not be measured.

[Thermal conductivity at 25°C] Using a measurement sample with a size of 10 mm square cut out from the thermally conductive resin sheet (sample) with a thickness of 500 μm obtained in Examples 1 to 3 and Comparative Examples 1 to 4, Spray for laser light absorption ("Black Guard Spray FC-153" manufactured by Fine Chemical Japan Co., Ltd.) was thinly applied to both sides of the measurement sample, and after drying, the thermal conductivity analyzer (NETZSCH "LFA447・NanoFlash300" manufactured by the company is measured by the laser flash method, and the thermal diffusivity a (mm ² /sec) in the thickness direction of the resin sheet is measured at a measurement temperature of 25°C. The measurement was performed at 5 points cut out from the same sheet, and the arithmetic mean thereof was obtained.

Then, according to JIS K6268, the density ρ (g/m ³ ) of the resin sheet was determined by the Archimedes method using a specific gravity measuring machine (manufactured by A&D Corporation). In addition, the specific heat capacity c (J/(g·K)) at 25° C. was measured using a DSC measuring device (ThermoPlusEvo DSC8230, manufactured by RIGAKU Co., Ltd.) in accordance with JIS K7123. Based on these respective measured values, the thermal conductivity in the thickness direction of the sheet at 25° C. was determined as “H=a×ρ×c”.

Furthermore, regarding the above-mentioned thermal diffusivity a (mm ² /sec), since there is no JIS standard on the thermal diffusivity and thermal conductivity of resin-based materials, refer to JIS R1611-2010 (Measurement of thermal conductivity of fine ceramics by the flash method) diffusivity, specific heat capacity, and thermal conductivity method), in the same specification, there is a requirement that "the thickness of the sample should be 0.5 mm to 5 mm", so the thickness of the sample used only for thermal conductivity measurement is adjusted to 0.5 mm. To measure.

[Dielectric breakdown voltage (BDV) before moisture absorption reflow test] (Production of circuit boards for heat dissipation) The thermally conductive resin sheet with a thickness of 150 μm produced in Examples 1 to 3 and Comparative Examples 1 to 4 was cut into a size of 40 mm×80 mm, and this was used as a thermally conductive resin sheet for circuit boards. On the other hand, for one thermally conductive resin sheet for a circuit board, a copper plate with a size of 40 mm x 80 mm and a thickness of 2000 μm as a metal plate for heat dissipation and a copper plate with a size of 40 mm x 80 mm for forming a conductive circuit were prepared. 1 copper plate of 80 mm and 500 μm thick. Roughen the surface by grinding one side of a copper plate with a thickness of 2000 μm and a copper plate with a thickness of 500 μm with #100 sandpaper in advance. The above-mentioned thermally conductive resin sheet for circuit boards was clamped in such a way that the thermally conductive resin sheets for substrates faced each other, and pressurized for 10 minutes at a pressurization temperature of 390°C and a pressure surface pressure of 13 MPa to obtain the Form material (copper plate) / thermally conductive resin sheet / copper plate for conductive circuit formation” laminated heat sink.

On the other hand, regarding Comparative Example 4, which is a thermally conductive resin sheet containing a thermosetting resin, the unhardened or only slightly The hardened epoxy resin sheet molded body with a thickness of 150 μm was vacuum pressed at a press temperature of 175°C and a pressure surface pressure of 10 MPa for 30 minutes to complete the hardening reaction of the thermosetting resin. Laminated heat sink including "metal plate for heat dissipation (copper plate) / thermally conductive resin sheet / copper plate for conductive circuit formation".

25 mm之圓狀圖案之導電電路用銅板。 Furthermore, the said copper plate for conductive circuit formation of each laminated heat sink was etched and patterned, and the heat dissipation circuit board was obtained. The pattern is to leave two places on the 40mm×80mm thermally conductive resin sheet

25mm copper plate for conductive circuit with circular pattern.

25 mm之銅板上載置

25 mm之電極，施加0.5 kV電壓，每隔60秒增加0.5 kV，逐步升壓來實施測定直至達到絕緣破壞。測定係於頻率60 Hz、升壓速度1000 V/sec下實施。 (Measurement of Dielectric Breakdown Voltage (BDV)) The heat-dissipating circuit boards produced by using the thermally conductive resin sheets obtained in Examples 1-3 and Comparative Examples 1-4 by the above-mentioned method were immersed in Fluorinert FC-40 (3M Company Manufacturing), using ultra-high voltage withstand voltage tester 7470 (manufactured by Measurement Technology Research Institute Co., Ltd.), patterning the above-mentioned heat-dissipating circuit board by etching

Mounted on 25 mm copper board

Apply a voltage of 0.5 kV to a 25 mm electrode, increase the voltage by 0.5 kV every 60 seconds, and gradually increase the voltage to carry out the measurement until the insulation breakdown is reached. The measurement was carried out at a frequency of 60 Hz and a boost rate of 1000 V/sec.

When the dielectric breakdown voltage is 60 kV/mm or more per unit thickness (conversion value when the thickness is 1 mm), it is recorded as "〇 (excellent)", and it is 40 kV/mm or more and less than 60 In the case of kV/mm, it is recorded as "△ (poor)", and in the case of less than 40 kV/mm, it is recorded as "× (poor)". These measurement results are shown in Table 1. The evaluation of the dielectric breakdown voltage (BDV) before the moisture absorption reflow test can be used as the evaluation of the withstand voltage performance.

25 mm之銅板上載置

25 mm之電極，施加0.5 kV電壓，每隔60秒增加0.5 kV，逐步升壓來實施測定直至達到絕緣破壞。測定係於頻率60 Hz、升壓速度1000 V/sec下實施。 [Dielectric breakdown voltage (BDV) after moisture absorption reflow test] (Measurement of dielectric breakdown voltage (BDV)) Using a constant temperature and humidity machine SH-221 (manufactured by ESPEC), the samples 1 to 3 and The heat-conducting resin sheet obtained in Comparative Examples 1-4 and the heat-dissipating circuit board prepared by the same method as the above [dielectric breakdown voltage (BDV) before the moisture absorption reflow test] were placed at 85°C and 85%RH. After being stored in the environment for 3 days, within 30 minutes, the temperature was raised from room temperature to 290°C in a nitrogen atmosphere for 12 minutes, kept at 290°C for 10 minutes, and then cooled to room temperature (moisture absorption reflow test). Thereafter, the heat-dissipating circuit board was dipped in Fluorinert FC-40 (manufactured by 3M Co., Ltd.), and the above-mentioned heat-dissipating circuit board was etched using an ultra-high voltage withstand voltage tester 7470 (manufactured by Measurement Technology Research Institute Co., Ltd.). patterned

Mounted on 25 mm copper board

Apply a voltage of 0.5 kV to a 25 mm electrode, increase the voltage by 0.5 kV every 60 seconds, and gradually increase the voltage to carry out the measurement until the insulation breakdown is reached. The measurement was carried out at a frequency of 60 Hz and a boost rate of 1000 V/sec.

When the dielectric breakdown voltage is 60 kV/mm or more per unit thickness (conversion value when the thickness is 1 mm), it is recorded as "〇 (excellent)", and it is 40 kV/mm or more and less than 60 In the case of kV/mm, it is recorded as "△ (poor)", and in the case of less than 40 kV/mm, it is recorded as "× (poor)". These measurement results are shown in Table 1. The evaluation of the dielectric breakdown voltage (BDV) after the moisture absorption reflow test can be used as the evaluation of the resistance to moisture absorption reflow.

25 mm之銅電極與導熱性樹脂片之界面。測定時使用頻率50 MHz之探針，設為增益30 dB、間距0.2 mm，將試樣置於水中實施。將未觀察到界面產生剝離或鼓起、孔隙之情況者記為「○(優)」，將觀察到界面產生剝離或鼓起、孔隙之情況者記為「×(劣)」。將該評估結果亦示於表1。 吸濕回焊試驗後界面剝離之評估可作為將導熱性樹脂片與金屬板積層進行回焊步驟時，是否易發生由熱膨脹及熱收縮引起之界面剝離及由導熱性樹脂片之發泡所導致之變形之評估。 [Observation of the state of the sample after the moisture absorption reflow test] In the same manner as above, the heat dissipation circuit boards produced in Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to the moisture absorption reflow test, and the ultrasonic imaging device was used. FinSAT (FS300III) (manufactured by Hitachi Power Solutions), observing the above-mentioned patterning by etching

The interface between the 25 mm copper electrode and the thermally conductive resin sheet. During the measurement, a probe with a frequency of 50 MHz was used, with a gain of 30 dB and a spacing of 0.2 mm, and the sample was placed in water for implementation. The case where no peeling, bulging, or voids were observed at the interface was marked as "○ (excellent)", and the case where peeling, bulging, or voids were observed at the interface was marked as "X (poor)". The evaluation results are also shown in Table 1. The evaluation of interfacial peeling after the moisture absorption reflow test can be used as the reflow step of laminating the thermally conductive resin sheet and the metal plate, whether it is prone to interface peeling caused by thermal expansion and shrinkage and caused by foaming of the thermally conductive resin sheet The evaluation of the deformation.

[Table 1] Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 resin Thermoplastic resin 1 (PEEK) [wt%] 28.5 28.5 28.5 28.5 28.5 28.5 - Thermosetting resin 1 (epoxy system) [wt%] - - - - - - 28.5 Boron Nitride Agglomerated Particles filler 1 [wt%] 71.5 - - - - - 71.5 filler 2 [wt%] - 71.5 - - - - - filler 3 [wt%] - - 71.5 - - - - filler 4 [wt%] - - - 71.5 - - - filler 5 [wt%] - - - - 71.5 - - Filler 6 [wt%] - - - - - 71.5 - Physical properties of aggregated particles (raw material powder) Volume average particle size (D50) [μm] 35 35 35 34 40 25 35 The form of aggregated particles house of cards house of cards house of cards house of cards house of cards kale house of cards Particle internal pore volume A ₁ [mL/g] 0.446 0.448 0.379 0.410 0.515 1.28 0.446 Particle interstitial volume B ₁ [mL/g] 0.882 0.877 0.699 0.437 0.645 1.01 0.882 Total pore volume A ₁ + B ₁ [mL/g] 1.328 1.325 1.078 0.847 1.160 2.290 1.328 Particle interstitial volume/total pore volume B ₁ /(A ₁ +B ₁ ) - 0.664 0.662 0.648 0.516 0.556 0.441 0.664 Circularity - - 0.966 0.965 0.939 0.961 - - Physical properties of aggregated particles (ash content of sheet) Particle internal pore volume A ₂ [mL/g] 0.348 0.386 0.314 0.383 0.368 0.407 0.425 Particle internal pore volume residual ratio A ₂ /A ₁ - 0.780 0.862 0.828 0.934 0.715 0.318 0.953 Particle interstitial volume B ₂ [mL/g] 0.568 0.406 0.556 0.427 0.570 0.437 0.850 Particle interstitial volume residual ratio B ₂ /B ₁ - 0.644 0.463 0.795 0.978 0.884 0.433 0.964 1st peak diameter [μm] 0.31 0.37 0.31 0.45 0.54 0.45 - 1st Peak Height [mL/g] 0.55 0.57 0.47 0.45 0.76 0.56 - 2nd peak diameter [μm] 20.0 17.6 16.6 7.2 14.4 7.2 - 2nd Peak Height [mL/g] 1.71 1.61 1.95 0.84 1.74 0.49 - Circularity - - 0.954 0.961 0.934 0.945 particle destruction - Thermal conductivity (25℃) [W/m・K] 20.7 21.3 18.8 14.4 15.7 9.1 16.8 Dielectric breakdown voltage Before moisture absorption reflow test 〇 〇 〇 〇 〇 〇 x After moisture absorption reflow test 〇 〇 〇 〇 〇 〇 x Interface observation (after moisture absorption reflow test) 〇 〇 〇 〇 〇 〇 x

Comparing Examples 1 to 3 with Comparative Examples 1 to 3, it can be seen that by using boron nitride aggregated particles with B ₁ /(A ₁ + B ₁ ) of 0.60 or more, heat dissipation with significantly higher thermal conductivity can be obtained. piece. In addition, it can be seen that by making the second peak height and the second peak diameter in the ash of the sheet fall within the range of the present invention, it is also possible to obtain a heat sink having significantly higher thermal conductivity. Also, in Examples 1 to 3, A ₂ /A ₁ before and after sheet forming is 0.70 or more, B ₂ /B ₁ is 0.85 or less, and the first peak, second peak, and round shape in the ash content of the sheet It is considered that, in the boron nitride aggregated particles used in these, by maintaining the internal structure of the aggregated particles themselves even after sheet molding, the high thermal conductivity inside the aggregated particles is maintained, and by making the adjacent The moderate deformation of the surface of the contact part of the particles will also suppress the thermal resistance between the particles to be low. From the SEM photograph of boron nitride aggregated particles contained in the ashes of the thermally conductive resin sheet of Example 2 shown in FIG. 9, it can also be confirmed that the internal structure of the aggregated particles is maintained and the contact between adjacent particles is confirmed. Part of the surface is moderately deformed. In addition, regarding the value of the dielectric breakdown voltage before and after the moisture absorption reflow test, if Examples 1 to 3 are compared with Comparative Example 4, it can be seen that by using a thermoplastic resin having a melting point of 300° C. or higher as the matrix resin, the resistance Voltage performance and moisture absorption reflow resistance become good. Furthermore, in Examples 1 to 3, it can be seen that by making the production method include a mixing step of mixing powder containing a thermoplastic resin and boron nitride aggregated particles, and pressurizing the mixture, it can be molded into a sheet The pressure forming step of the material will not damage the original characteristics of the boron nitride agglomerated particles with high thermal conductivity, and it will also suppress the pores remaining in the sheet during forming, so that the withstand voltage performance and thermal conductivity can be balanced. In Comparative Example 4, an epoxy resin and boron nitride aggregated particles of Example 1 were used to form a sheet by the conventional wet coating method. It is presumed that the particle interstitial volume of boron nitride aggregated particles is too large when used in the wet coating method. It is considered that the withstand voltage performance is reduced due to the occurrence of streaks during coating and film formation and the large number of bubbles contained in the sheet. Affected by air bubbles in the sheet, the thermal conductivity was also poorer than that of Example 1 in which the same amount of the same boron nitride aggregated particles was prepared.

Furthermore, the present invention may also adopt the following configurations. [1] A thermally conductive resin composition comprising a thermoplastic resin and aggregated boron nitride particles, wherein the volume of pores in the particles of the aggregated boron nitride particles measured by mercury intrusion porosimetry is set to When A ₁ and the particle interstitial volume are defined as B ₁ , B ₁ /(A ₁ +B ₁ ) is 0.60 or more. [2] The resin composition according to the above [1], wherein the main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher. [3] The resin composition according to the above [2], wherein the crystalline thermoplastic resin having a melting point of 300° C. or higher is a polyetherketone resin. [4] The resin composition according to the above [3], wherein the polyetherketone-based resin is polyetheretherketone. [5] The resin composition according to any one of the above [1] to [4], wherein the boron nitride aggregated particles have a house of cards structure. [6] The resin composition according to any one of [1] to [5] above, wherein the boron nitride aggregated particles have a volume-based average particle diameter D50 of 10 μm or more and 200 μm or less. [7] The resin composition according to any one of the above-mentioned [1] to [6], wherein the above-mentioned thermoplastic resin is contained in an amount of 15% by mass to 40% by mass in 100% by mass of the above-mentioned resin composition, and contains 60% by mass or more and 85% by mass or less of the above boron nitride aggregated particles. [8] A thermally conductive resin sheet comprising the resin composition as described in any one of [1] to [7] above. [9] The thermally conductive resin sheet as described in [8] above, wherein the boron nitride aggregated particles contained in the residual ash when the thermally conductive resin sheet is heated at 700° C. for 5 hours are obtained by When the particle internal pore volume measured by mercury intrusion porosimetry is set as A ₂ , and the particle interstitial volume is set as B ₂ , A ₂ /A ₁ is above 0.70, and B ₂ /B ₁ is below 0.85. [10] The thermally conductive resin sheet as described in [8] or [9] above, wherein the boron nitride aggregated particles contained in the residual ash after heating the thermally conductive resin sheet at 700°C for 5 hours are circular The degree is 0.85 or more. [11] The thermally conductive resin sheet according to any one of [8] to [10] above, which has a thickness of not less than 50 μm and not more than 300 μm. [12] The thermally conductive resin sheet according to any one of [8] to [11] above, which has a thermal conductivity in the thickness direction at 25°C of 16 W/m·K or more. [13] A laminated heat sink having a structure in which a metal layer for heat dissipation is laminated on one surface of the thermally conductive resin sheet as described in any one of [8] to [12]. [14] A heat dissipating circuit board having the laminated heat sink as described in the above [13]. [15] The heat-dissipating circuit board as described in [14] above, which has a configuration in which a conductive circuit is formed on the other surface of the above-mentioned heat-conductive resin sheet. [16] A power semiconductor device comprising the heat-dissipating circuit board according to the above [14] or [15]. [17] A method for producing a thermally conductive resin sheet, comprising: a mixing step of obtaining a mixture of a thermoplastic resin powder and boron nitride aggregated particles; and a press molding step of heating the mixture and Forming it into a sheet by applying pressure; When the pore volume in the particle of the above-mentioned boron nitride aggregated particle raw material measured by mercury porosimetry is A ₁ , and the particle interstitial volume is B ₁ , B ₁ /(A ₁ +B ₁ ) is 0.60 or more. [18] A thermally conductive resin sheet comprising a resin composition comprising a thermoplastic resin and boron nitride aggregated particles, when the thermally conductive resin sheet is heated at 700° C. for 5 hours by mercury porosimetry In the pore size distribution curve obtained by measuring the residual ash, the peak with the maximum value in the range of pore diameters less than 5 μm is set as the first peak, and the peak with the maximum value in the range of pore diameters above 5 μm is set as the second peak When peaking, the height of the second peak top is 1.0 mL/g or more, and the diameter of the second peak top is 15 μm or more. [19] The thermally conductive resin sheet according to the above [18], wherein the main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher. [20] The thermally conductive resin sheet as described in [19] above, wherein the crystalline thermoplastic resin having a melting point of 300° C. or higher is a polyetherketone resin. [21] The thermally conductive resin sheet according to the above [20], wherein the polyetherketone-based resin is polyetheretherketone. [22] The thermally conductive resin sheet according to any one of [18] to [21] above, wherein the boron nitride aggregated particles have a house of cards structure. [23] The thermally conductive resin sheet according to any one of [18] to [22] above, wherein the volume-based average particle diameter D50 of the boron nitride aggregated particles is not less than 10 μm and not more than 200 μm. [24] The thermally conductive resin sheet according to any one of [18] to [23], wherein the thermoplastic resin is contained in an amount of 15% by mass to 40% by mass in 100% by mass of the resin composition, and Contains not less than 60% by mass and not more than 85% by mass of the boron nitride aggregated particles described above. [25] The thermally conductive resin sheet according to any one of [18] to [24] above, wherein the first peak top diameter is 0.4 μm or less. [26] The thermally conductive resin sheet according to any one of [18] to [25] above, wherein the first peak top height is not less than 0.25 mL/g and not more than 0.7 mL/g. [27] The thermally conductive resin sheet according to any one of [18] to [26] above, wherein boron nitride contained in the residual ash after heating the thermally conductive resin sheet at 700° C. for 5 hours is aggregated The circularity of the particles exceeds 0.945. [28] The thermally conductive resin sheet according to any one of [18] to [27] above, which has a thickness of not less than 50 μm and not more than 300 μm. [29] The thermally conductive resin sheet according to any one of [18] to [28] above, which has a thermal conductivity in the thickness direction at 25°C of 18 W/m·K or more. [30] A laminated heat sink having a structure in which a metal layer for heat dissipation is laminated on one surface of the thermally conductive resin sheet as described in any one of [18] to [29]. [31] A heat dissipating circuit board having the laminated heat sink as described in the above [30]. [32] The heat-dissipating circuit board as described in [31] above, which has a configuration in which a conductive circuit is formed on the other surface of the heat-conductive resin sheet. [33] A power semiconductor device comprising the heat-dissipating circuit board as described in [31] or [32]. [34] A method for producing a thermally conductive resin sheet, comprising: a mixing step of obtaining a mixture of powder containing a thermoplastic resin and boron nitride aggregated particles; and a press molding step of heating the mixture and Form it into a sheet by applying pressure; in the pore size distribution curve obtained by measuring the residual ash when the above sheet was heated at 700°C for 5 hours by mercury intrusion porosimetry, the pore size will be less than 5 μm When the peak with the maximum value in the range is set as the first peak, and the peak with the maximum value in the range with a pore diameter of 5 μm or more is set as the second peak, the height of the second peak is more than 1.0 mL/g, and the second peak The diameter is more than 15 μm. [35] A thermally conductive resin sheet comprising a resin composition comprising a thermoplastic resin and boron nitride aggregated particles, when the thermally conductive resin sheet is heated at 700° C. for 5 hours by mercury porosimetry In the pore size distribution curve obtained by measuring the residual ash, the peak with the maximum value in the range of pore diameters less than 5 μm is set as the first peak, and the peak with the maximum value in the range of pore diameters above 5 μm is set as the second peak When peaking, the first peak top diameter is 0.4 μm or less, and the second peak top diameter is 15 μm or more. [36] The thermally conductive resin sheet as described in [35] above, wherein the main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher. [37] The thermally conductive resin sheet according to the above [36], wherein the crystalline thermoplastic resin having a melting point of 300° C. or higher is a polyetherketone resin. [38] The thermally conductive resin sheet according to the above [37], wherein the polyetherketone-based resin is polyetheretherketone. [39] The thermally conductive resin sheet according to any one of the above [35] to [38], wherein the boron nitride aggregated particles have a house of cards structure. [40] The thermally conductive resin sheet according to any one of [35] to [39] above, wherein the volume-based average particle diameter D50 of the boron nitride aggregated particles is not less than 10 μm and not more than 200 μm. [41] The thermally conductive resin sheet according to any one of [35] to [40] above, wherein the above-mentioned thermoplastic resin is contained in an amount of 15% by mass to 40% by mass in 100% by mass of the above-mentioned resin composition, and Contains not less than 60% by mass and not more than 85% by mass of the boron nitride aggregated particles described above. [42] The thermally conductive resin sheet according to any one of [35] to [41] above, wherein the second peak height is 1.0 mL/g or more. [43] The thermally conductive resin sheet according to any one of [35] to [42] above, wherein the first peak height is 0.25 mL/g to 0.7 mL/g. [44] The thermally conductive resin sheet according to any one of [35] to [43] above, wherein boron nitride contained in the residual ash after heating the thermally conductive resin sheet at 700° C. for 5 hours is aggregated The circularity of the particles exceeds 0.945. [45] The thermally conductive resin sheet according to any one of [35] to [44] above, which has a thickness of not less than 50 μm and not more than 300 μm. [46] The thermally conductive resin sheet according to any one of [35] to [45] above, which has a thermal conductivity in the thickness direction at 25°C of 18 W/m·K or more. [47] A laminated heat sink having a structure in which a metal layer for heat dissipation is laminated on one surface of the thermally conductive resin sheet described in any one of [35] to [46] above. [48] A heat dissipating circuit board having the laminated heat sink as described in the above [47]. [49] The heat-dissipating circuit board as described in [48] above, which has a configuration in which a conductive circuit is formed on the other surface of the heat-conductive resin sheet. [50] A power semiconductor device comprising the heat-dissipating circuit board as described in [48] or [49] above. [51] A method for producing a thermally conductive resin sheet, comprising: a mixing step of obtaining a mixture of powder containing a thermoplastic resin and boron nitride aggregated particles; and a press molding step of heating the mixture and Form it into a sheet by applying pressure; in the pore size distribution curve obtained by measuring the residual ash when the above sheet was heated at 700°C for 5 hours by mercury intrusion porosimetry, the pore size will be less than 5 μm When the peak with the maximum value in the range is set as the first peak, and the peak with the maximum value in the range with a pore diameter of 5 μm or more is set as the second peak, the diameter of the first peak top is 0.4 μm or less, and the diameter of the second peak top is 15 μm or more.

Fig. 1 is a diagram showing the principle of measuring the intra-particle pore volume, particle interstitial volume, peak diameter and peak height of boron nitride aggregated particles by mercury intrusion porosimetry. Fig. 2 is a conceptual diagram of the pore volume in particles. Fig. 3 is a conceptual diagram of particle interstitial volume. Fig. 4 is a conceptual diagram of a particle cross-sectional view of an example of boron nitride agglomerated particles having a small particle interstitial volume. Fig. 5 is an SEM (Scanning Electron Microscope, scanning electron microscope) photo of the particle surface of an example of boron nitride aggregated particles with a small particle interstitial volume (picture instead of a drawing). Fig. 6 is a conceptual diagram of a particle cross-sectional view of an example of boron nitride agglomerated particles having a large particle interstitial volume. Fig. 7 is an SEM photo of the particle surface of an example of boron nitride agglomerated particles with a large particle interstitial volume (picture instead of a diagram). Figure 8 is a model diagram of the structure of the house of cards. FIG. 9 shows an example of a SEM photograph of boron nitride aggregated particles contained in residual ash when the thermally conductive resin sheet of Example 2 was heated at 700° C. for 5 hours.

Claims (29)

A thermally conductive resin composition, which is a resin composition comprising a thermoplastic resin and boron nitride aggregated particles, where the volume of pores in the particles of the above-mentioned boron nitride aggregated particles measured by mercury intrusion porosimetry is A ₁ , When the particle interstitial volume is defined as B ₁ , B ₁ /(A ₁ +B ₁ ) is 0.60 or more. The resin composition according to claim 1, wherein the main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher. The resin composition according to claim 2, wherein the above-mentioned crystalline thermoplastic resin having a melting point above 300° C. is a polyetherketone resin. The resin composition according to claim 3, wherein the polyetherketone-based resin is polyetheretherketone. The resin composition according to any one of claims 1 to 4, wherein the boron nitride aggregated particles have a card house structure. The resin composition according to any one of claims 1 to 5, wherein the volume-based average particle diameter D50 of the boron nitride aggregated particles is not less than 10 μm and not more than 200 μm. The resin composition according to any one of claims 1 to 6, wherein in 100% by mass of the above-mentioned resin composition, the above-mentioned thermoplastic resin is contained in an amount of 15% by mass to 40% by mass, and in an amount of 60% by mass to 85% by mass The above boron nitride aggregated particles. A thermally conductive resin sheet comprising the resin composition according to any one of claims 1 to 7. The thermally conductive resin sheet according to claim 8, wherein the aggregated particles of boron nitride contained in the residual ash when the thermally conductive resin sheet is heated at 700° C. for 5 hours will be measured by mercury intrusion porosimetry When the pore volume in the particle is A ₂ and the particle interstitial volume is B ₂ , A ₂ /A ₁ is 0.70 or more, and B ₂ /B ₁ is 0.85 or less. The thermally conductive resin sheet according to claim 8 or 9, wherein the circularity of boron nitride aggregated particles contained in the residual ash after heating the thermally conductive resin sheet at 700° C. for 5 hours is 0.85 or more. A thermally conductive resin sheet comprising a resin composition comprising a thermoplastic resin and boron nitride aggregated particles, In the pore size distribution curve obtained by measuring the residual ash content of the above-mentioned thermally conductive resin sheet heated at 700°C for 5 hours by mercury porosimetry, a peak with a maximum value in the range of pore size less than 5 μm was set. is the first peak, and when the peak with the maximum value in the range of pore diameter of 5 μm or more is set as the second peak, The height of the second peak top is 1.0 mL/g or more, and the diameter of the second peak top is 15 μm or more. The thermally conductive resin sheet according to claim 11, wherein the main component of the thermoplastic resin is a crystalline thermoplastic resin having a melting point of 300°C or higher. The thermally conductive resin sheet according to claim 12, wherein the crystalline thermoplastic resin having a melting point of 300° C. or higher is a polyetherketone resin. The thermally conductive resin sheet according to claim 13, wherein the polyetherketone-based resin is polyetheretherketone. The thermally conductive resin sheet according to any one of claims 11 to 14, wherein the boron nitride aggregated particles have a house of cards structure. The thermally conductive resin sheet according to any one of claims 11 to 15, wherein the volume-based average particle diameter D50 of the boron nitride aggregated particles is not less than 10 μm and not more than 200 μm. The thermally conductive resin sheet according to any one of claims 11 to 16, wherein in 100% by mass of the above-mentioned resin composition, the above-mentioned thermoplastic resin is contained in an amount of 15% by mass to 40% by mass, and 60% by mass to 85% by mass The above-mentioned boron nitride aggregated particles are as follows. The thermally conductive resin sheet according to any one of claims 11 to 17, wherein the diameter of the first peak top is 0.4 μm or less. The thermally conductive resin sheet according to any one of claims 11 to 18, wherein the first peak height is not less than 0.25 mL/g and not more than 0.7 mL/g. The thermally conductive resin sheet according to any one of claims 11 to 19, wherein the circularity of boron nitride aggregated particles contained in the residual ash after heating the thermally conductive resin sheet at 700° C. for 5 hours exceeds 0.945. The thermally conductive resin sheet according to any one of claims 8 to 20, which has a thickness of not less than 50 μm and not more than 300 μm. The thermally conductive resin sheet according to any one of Claims 8 to 21, wherein the thermal conductivity in the thickness direction at 25°C is 16 W/m·K or more. The thermally conductive resin sheet according to any one of Claims 8 to 21, wherein the thermal conductivity in the thickness direction at 25°C is 18 W/m·K or more. A laminated heat sink, which has a structure in which a metal layer for heat dissipation is laminated on one surface of the thermally conductive resin sheet according to any one of claims 8 to 23. A heat-dissipating circuit substrate, which has a laminated heat sink as claimed in claim 24. According to claim 25, the heat-dissipating circuit board has a structure in which a conductive circuit is formed on the other surface of the above-mentioned thermally conductive resin sheet. A power semiconductor device having the heat dissipation circuit substrate as claimed in claim 25 or 26. A method for producing a thermally conductive resin sheet, comprising: a mixing step of obtaining a mixture of a thermoplastic resin powder and boron nitride aggregated particles; and a pressure molding step of heating and pressurizing the mixture to form Forming it into a sheet; When the particle pore volume of the above-mentioned boron nitride aggregated particle raw material measured by mercury porosimetry is set as A ₁ , and the particle interstitial volume is set as B ₁ , B ₁ /(A ₁ + B ₁ ) is 0.60 or more. A method of manufacturing a thermally conductive resin sheet, comprising: a mixing step of obtaining a mixture of a powder comprising a thermoplastic resin and boron nitride aggregated particles; and A pressure forming step, which is to heat and press the above-mentioned mixture to form it into a sheet; In the pore size distribution curve obtained by measuring the residual ash when the above-mentioned sheet was heated at 700°C for 5 hours by mercury intrusion porosimetry, the peak with the maximum value in the range of pore size less than 5 μm was set as the second 1 peak, when the peak with the maximum value in the range of pore diameter less than 5 μm is set as the 2nd peak, The height of the second peak top is 1.0 mL/g or more, and the diameter of the second peak top is 15 μm or more.

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