WO2022149434A1 - 放熱シート及び放熱シートの製造方法 - Google Patents
放熱シート及び放熱シートの製造方法 Download PDFInfo
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- WO2022149434A1 WO2022149434A1 PCT/JP2021/046743 JP2021046743W WO2022149434A1 WO 2022149434 A1 WO2022149434 A1 WO 2022149434A1 JP 2021046743 W JP2021046743 W JP 2021046743W WO 2022149434 A1 WO2022149434 A1 WO 2022149434A1
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- Prior art keywords
- boron nitride
- particle size
- maximum point
- nitride powder
- heat dissipation
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
- C09K5/08—Materials not undergoing a change of physical state when used
- C09K5/14—Solid materials, e.g. powdery or granular
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/38—Boron-containing compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
- H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
- H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
- H01L23/3737—Organic materials with or without a thermoconductive filler
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/38—Boron-containing compounds
- C08K2003/382—Boron-containing compounds and nitrogen
- C08K2003/385—Binary compounds of nitrogen with boron
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K2201/00—Specific properties of additives
- C08K2201/001—Conductive additives
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K2201/00—Specific properties of additives
- C08K2201/002—Physical properties
- C08K2201/005—Additives being defined by their particle size in general
Definitions
- the present invention is a heat-dissipating sheet obtained by molding a heat-conductive resin composition containing a resin and a boron nitride powder containing at least aggregated boron nitride particles formed by aggregating hexagonal boron nitride primary particles, and a method for manufacturing the heat-dissipating sheet. Regarding.
- heat-generating electronic components such as power devices, transistors, thyristors, and CPUs
- heat-generating electronic components such as power devices, transistors, thyristors, and CPUs
- (1) the insulating layer of the printed wiring board on which the heat-generating electronic component is mounted is made highly thermally conductive
- the heat-generating electronic component or the printed wiring on which the heat-generating electronic component is mounted is mounted.
- a silicone resin or an epoxy resin filled with ceramic powder is used as the insulating layer and thermal interface material of the printed wiring board.
- Patent Document 1 describes a boron nitride powder in which primary particles of boron nitride are aggregated, and has a peak A existing in a region of 5 ⁇ m or more and less than 30 ⁇ m and a peak A of 50 ⁇ m or more and less than 100 ⁇ m in a volume-based particle size distribution.
- a boron nitride powder having a peak B present in the region is disclosed.
- an object of the present invention is to provide a heat radiating sheet having excellent thermal conductivity and insulating properties, and a method for manufacturing a heat radiating sheet having excellent thermal conductivity and insulating properties.
- a heat-dissipating sheet obtained by molding a heat-conducting resin composition containing a resin and a boron nitride powder containing at least aggregated boron nitride particles formed by aggregating hexagonal boron nitride primary particles.
- the particle size distribution of the boron nitride powder is a first maximum point, a second maximum point having a larger particle size than the first maximum point, and a second maximum particle size larger than the second maximum point. It has at least 3 maximum points, the particle size of the first maximum point is 0.4 ⁇ m or more and less than 10 ⁇ m, and the particle size of the second maximum point is 10 ⁇ m or more and less than 40 ⁇ m.
- thermo conductivity and insulating properties it is possible to provide a heat radiating sheet having excellent thermal conductivity and insulating properties and a method for manufacturing a heat radiating sheet having excellent thermal conductivity and insulating properties.
- FIG. 1 is a conceptual diagram of the particle size distribution of the boron nitride powder contained in the heat conductive resin composition for the heat dissipation sheet of the present invention.
- the heat dissipation sheet of the present invention is formed by molding a heat conductive resin composition containing a resin and a boron nitride powder containing at least agglomerated boron nitride particles formed by aggregating hexagonal boron nitride primary particles.
- the partial discharge start voltage of the heat dissipation sheet of the present invention is 2800 to 5000 kV / mm.
- the partial discharge means a discharge partially generated in the insulator between the electrodes when a voltage is applied, and is not a discharge that completely bridges the electrodes.
- the insulating property of the heat radiating sheet deteriorates. It is considered that this is because when the partial discharge start voltage of the heat radiation sheet is less than 2800 kV / mm, excessive voids are present in the heat radiation sheet. If there is a void in the discharge sheet, an electric field is concentrated on that portion, and a weak discharge (partial discharge) is generated.
- the partial discharge start voltage of the heat radiating sheet is larger than 5000 kV / mm, the insulating property of the heat radiating sheet is improved, but the thermal conductivity is deteriorated.
- the partial discharge starting voltage of the heat dissipation sheet of the present invention is preferably 2900 to 4700 kV / mm, more preferably 3000 to 4500 kV / mm.
- the partial discharge start voltage of the heat dissipation sheet can be measured by the method described in Examples described later. Further, the partial discharge start voltage of the heat radiating sheet is adjusted, for example, in the method of manufacturing the heat radiating sheet described later, the pressure at which the heat conductive resin composition sheet is pressurized according to the strength of the aggregated boron nitride particles and the like. Can be controlled with.
- the particle size distribution of the boron nitride powder contained in the heat conductive resin composition for the heat dissipation sheet of the present invention is such that the particle size is 0.4 ⁇ m or more and less than 10 ⁇ m at the first maximum point and the particle size is 10 ⁇ m or more and less than 40 ⁇ m. It is preferable to have at least one maximum point of a second maximum point and a third maximum point having a particle size of 40 ⁇ m or more and 110 ⁇ m or less.
- the filling property of the boron nitride powder in the heat radiating sheet is enhanced, so that the partial discharge start voltage of the heat radiating sheet is set to 2800 by adjusting the pressure when the heat conductive resin composition sheet is pressed in the method for manufacturing the heat radiating sheet described later. It is even easier to adjust within the range of ⁇ 5000 kV / mm.
- the particle size distribution of the boron nitride powder contained in the heat conductive resin composition for the heat radiating sheet of the present invention is the above-mentioned first maximum point, the above-mentioned second maximum point, and the above-mentioned third maximum point. It is more preferable to have at least points.
- FIG. 1 is a conceptual diagram showing a particle size distribution of boron nitride powder contained in the heat conductive resin composition for the heat dissipation sheet of the present invention.
- the vertical axis of the particle size distribution shown in FIG. 1 is linear, and the horizontal axis is logarithmic.
- the particle size distribution of the boron nitride powder shown in FIG. 1 is merely a conceptual diagram, and does not limit the boron nitride powder contained in the heat conductive resin composition for the heat dissipation sheet of the present invention.
- the boron nitride powder contained in the heat conductive resin composition for the heat dissipation sheet of the present invention is a boron nitride powder containing at least agglomerated boron nitride particles formed by aggregating hexagonal boron nitride primary particles.
- reference numeral MAX1 indicates a first maximum point (MAX1)
- reference numeral MAX2 indicates a second maximum point
- reference numeral MAX3 indicates a third maximum point.
- the particle size of the first maximum point (MAX1) is 0.4 ⁇ m or more and less than 10 ⁇ m
- the particle size of the second maximum point (MAX2) is 10 ⁇ m or more and less than 40 ⁇ m
- the third maximum point (MAX3) is preferably 40 ⁇ m or more and 110 ⁇ m or less.
- the filling property of the boron nitride powder in the heat radiating sheet is enhanced, so that the thermal conductivity of the heat radiating sheet can be further improved.
- the particle size distribution of the boron nitride powder can be measured by the method of Examples described later.
- the particle size of the first maximum point (MAX1) is preferably 0.4 ⁇ m or more and less than 10 ⁇ m.
- the particle size of the first maximum point (MAX1) is 0.4 ⁇ m or more and less than 10 ⁇ m, the filling property of the boron nitride powder in the heat radiating sheet is enhanced, which makes it easier to control the partial discharge start voltage of the heat radiating sheet.
- the thermal conductivity of the heat dissipation sheet is further improved. From this point of view, the particle size of the first maximum point (MAX1) is more preferably 1.0 to 8.0 ⁇ m, and even more preferably 3.0 to 6.0 ⁇ m.
- the particle size of the second maximum point (MAX2) is preferably 10 ⁇ m or more and less than 40 ⁇ m.
- the particle size of the second maximum point (MAX2) is 10 ⁇ m or more and less than 40 ⁇ m, the filling property of the boron nitride powder in the heat radiating sheet is improved, which makes it easier to control the partial discharge start voltage of the heat radiating sheet.
- the thermal conductivity of the heat dissipation sheet is further improved. From this point of view, the particle size of the second maximum point (MAX2) is more preferably 15 to 35 ⁇ m, still more preferably 18 to 30 ⁇ m.
- the particle size of the third maximum point (MAX3) is preferably 40 ⁇ m or more and 110 ⁇ m or less.
- the particle size of the third maximum point (MAX3) is 40 ⁇ m or more and 110 ⁇ m or less, the filling property of the boron nitride powder in the heat radiating sheet is enhanced, which further facilitates the control of the partial discharge start voltage of the heat radiating sheet.
- the thermal conductivity of the heat dissipation sheet is further improved.
- the particle size of the third maximum point (MAX3) is more preferably 55 to 95 ⁇ m, still more preferably 65 to 90 ⁇ m.
- the maximum point adjacent to the first maximum point (MAX1) is the second maximum point (MAX2)
- the maximum point adjacent to the second maximum point (MAX2) is the third maximum point (MAX3).
- the absolute value of the difference from the particle size of the second local minimum point (MIN2) between them is preferably 15 to 60 ⁇ m.
- the absolute value of the difference between the particle size of the first minimum point (MIN1) and the particle size of the second minimum point (MIN2) is 15 to 60 ⁇ m, the filling property of the boron nitride powder in the heat dissipation sheet is enhanced. This makes it easier to control the partial discharge start voltage of the heat radiating sheet, and further improves the thermal conductivity of the heat radiating sheet.
- the absolute value of the difference between the particle size of the first minimum point (MIN1) and the particle size of the second minimum point (MIN2) is more preferably 21 to 43 ⁇ m, still more preferably 25. It is ⁇ 35 ⁇ m.
- the half width of the peak having the third maximum point (MAX3) is preferably 20 to 60 ⁇ m.
- the filling property of the boron nitride powder in the heat radiating sheet is enhanced, which makes it easier to control the partial discharge start voltage of the heat radiating sheet.
- the thermal conductivity of the heat dissipation sheet is further improved.
- the half width of the peak having the third maximum point (MAX3) is more preferably 28 to 53 ⁇ m, still more preferably 40 to 50 ⁇ m.
- the half-value width of the peak having the third maximum point (MAX3) is the width of the peak at half the frequency of the third maximum point (MAX3).
- the absolute value of the difference from the particle size is preferably 3 to 30 ⁇ m.
- the reference numeral D10 indicates the particle size at which the integrated amount of frequency is 10%, and the maximum point of the particle size distribution of the boron nitride powder having the smallest particle size is the first.
- the maximum point (MAX1) the maximum point having the second smallest particle size in the particle size distribution of the boron nitride powder, is the second maximum point (MAX2), and the maximum point having the smallest particle size and the second smallest particle size.
- the minimum point between the small maximum points is the first minimum point (MIN1).
- the absolute value of the difference in particle size is 3 to 30 ⁇ m, the filling property of the boron nitride powder in the heat radiating sheet is enhanced, which makes it easier to control the partial discharge start voltage of the heat radiating sheet and the heat radiating sheet.
- the thermal conductivity of is further improved. From this point of view, the absolute value of the difference in particle size is more preferably 4 to 17 ⁇ m, still more preferably 6 to 15 ⁇ m.
- the integrated amount (V1) of the frequency between the peak start and the peak end at the peak having the first maximum point (MAX1) is preferably 2 to 25% by volume.
- the integrated amount (V1) is 2 to 25% by volume, the filling property of the boron nitride powder in the heat radiating sheet is enhanced, which makes it easier to control the partial discharge start voltage of the heat radiating sheet and the heat radiating sheet.
- the thermal conductivity of is further improved. From such a viewpoint, the integrated amount (V1) is more preferably 5 to 20% by volume.
- the peak start at the peak having the first maximum point (MAX1) is the minimum point on the side where the particle size is smaller than the first maximum point (MAX1).
- the peak start is the end (DS) on the side where the particle size of the particle size distribution is small.
- the peak end at the peak having the first maximum point (MAX1) is the minimum point (MIN1) on the side where the particle size is larger than the first maximum point (MAX1).
- the integrated amount of frequency (V1) is the grain size of the minimum point on the side where the particle size is smaller than the first maximum point (MAX1) or the grain at the end (DS) on the side where the particle size of the particle size distribution is small.
- the particle size is relative to the first maximum point (MAX1). Is a value obtained by subtracting the frequency of the particle size of the minimum point (MIN1) on the larger side.
- the frequency of the particle size of the minimum point (MIN1) on the side where the particle size is larger than the first maximum point (MAX1) is subtracted from the peak start at the peak having the first maximum point (MAX1).
- the first maximum point (MAX1) in both the integrated amount of frequency between the peak and the peak end and the integrated amount of the frequency between the peak start and the peak end at the peak having the second maximum point (MAX2). This is to prevent the frequency of the particle size of the minimum point (MIN1) on the side having the larger particle size from being added.
- the integrated amount (V2) of the frequency between the peak start and the peak end at the peak having the second maximum point (MAX2) is preferably 15 to 50% by volume.
- the integrated amount (V2) is 15 to 50% by volume, the filling property of the boron nitride powder in the heat radiating sheet is improved, which makes it easier to control the partial discharge start voltage of the heat radiating sheet.
- the thermal conductivity of the heat dissipation sheet is further improved. From such a viewpoint, the integrated amount (V2) is more preferably 20 to 45% by volume.
- the peak start at the peak having the second maximum point (MAX2) is the minimum point (MIN1) on the side where the particle size is smaller than the second maximum point (MAX2).
- the peak end at the peak having the second maximum point (MAX2) is the minimum point (MIN2) on the side where the particle size is larger than the second maximum point (MAX2).
- the integrated amount of frequency (V2) is determined from the particle size of the minimum point (MIN1) on the side where the particle size is smaller than the second maximum point (MAX2) to the second maximum point (MAX2). From the integrated amount of frequency to the particle size of the minimum point (MIN2) on the side with a large particle size, the particle size of the minimum point (MIN2) on the side with a large particle size with respect to the second maximum point (MAX2) It is the value obtained by subtracting the frequency.
- the frequency of the particle size of the minimum point (MIN2) on the side where the particle size is larger than the second maximum point (MAX2) is subtracted from the peak start at the peak having the second maximum point (MAX2).
- the second maximum point (MAX2) in both the integrated amount of frequency between the peak and the peak end and the integrated amount of the frequency between the peak start and the peak end at the peak having the third maximum point (MAX3). This is to prevent the frequency of the particle size of the minimum point (MIN2) on the side having the larger particle size from being added.
- the integrated amount (V3) of the frequency between the peak start and the peak end at the peak having the third maximum point (MAX3) is preferably 30 to 80% by volume.
- the integrated amount (V3) is 30 to 80% by volume, the filling property of the boron nitride powder in the heat radiating sheet is improved, which makes it easier to control the partial discharge start voltage of the heat radiating sheet.
- the thermal conductivity of the heat dissipation sheet is further improved. From such a viewpoint, the integrated amount (V3) is more preferably 45 to 75% by volume.
- the peak start at the peak having the third maximum point (MAX3) is the minimum point (MIN2) on the side where the particle size is smaller than the third maximum point (MAX3).
- the peak end at the peak having the third maximum point (MAX3) is the minimum point on the side where the particle size is larger than the third maximum point (MAX3).
- the peak end is the end (DE) on the side where the particle size is large in the particle size distribution.
- the integrated amount of frequency (V3) is determined from the particle size of the minimum point (MIN2) on the side where the particle size is smaller than the third maximum point (MAX3) to the third maximum point (MAX3).
- the frequency of the particle size of the minimum point on the side where the particle size is larger than the third maximum point (MAX3) is subtracted from the peak start to the peak end at the peak having the third maximum point (MAX3).
- the crushing strength of the aggregated boron nitride particles in the boron nitride powder contained in the heat conductive resin composition for the heat dissipation sheet of the present invention is preferably 5 to 18 MPa.
- the crushing strength of the aggregated boron nitride particles is 5 MPa or more, it is possible to suppress the destruction of the aggregated boron nitride particles during the production of the heat dissipation sheet.
- the crushing strength of the aggregated boron nitride particles is 18 MPa or less, the resin can sufficiently penetrate into the aggregated boron nitride particles in the heat radiating sheet, and air remains in the aggregated boron nitride particles in the heat radiating sheet. Can be suppressed.
- the crushing strength of the aggregated boron nitride particles in the boron nitride powder of the present invention is more preferably 6 to 15 MPa, still more preferably 7 to 13 MPa.
- the crushing strength of the aggregated boron nitride particles can be measured by the method described in Examples described later.
- the boron nitride powder of the present invention is provided as long as the filling property of the boron nitride powder in the heat radiating sheet is improved, which makes it easier to control the partial discharge start voltage of the heat radiating sheet and improves the thermal conductivity of the heat radiating sheet.
- the particle size distribution of may have other maximum points.
- the boron nitride powder contained in the heat conductive resin composition for the heat dissipation sheet of the present invention is, for example, the first boron nitride powder having the first maximum particle size distribution and the second maximum particle size distribution.
- the second and third boron nitride powders are preferably boron nitride powders containing at least aggregated boron nitride particles formed by agglomerating hexagonal boron nitride primary particles, respectively.
- the first boron nitride powder may be aggregated boron nitride particles, but is preferably hexagonal boron nitride primary particles.
- the maximum point of each of the first to third boron nitride powders means the apex of the peak in the particle size distribution of each of the first to third boron nitride powders.
- the particle size distribution of the first to third boron nitride powders is measured in the same manner as the particle size distribution of the boron nitride powder described above.
- the volume ratio of the third boron nitride powder is larger than the volume ratio of the second boron nitride powder, and the volume ratio of the second boron nitride powder is larger than the volume ratio of the first boron nitride powder.
- the first to third boron nitride powders may be mixed so as to increase the amount. As a result, the filling property of the boron nitride powder in the heat radiating sheet is improved, the control of the partial discharge start voltage of the heat radiating sheet becomes easier, and the thermal conductivity of the heat radiating sheet is improved.
- the volume ratio of the third boron nitride powder is determined with respect to a total of 100 parts by volume of the first to third boron nitride powders from the viewpoint of controlling the partial discharge start voltage of the heat radiating sheet and the thermal conductivity of the heat radiating sheet. It is preferably 30 to 80 parts by volume, more preferably 45 to 75 parts by volume, and even more preferably 50 to 70 parts by volume.
- the volume ratio of the second boron nitride powder is determined with respect to a total of 100 parts by volume of the first to third boron nitride powders from the viewpoint of controlling the partial discharge start voltage of the heat radiation sheet and the thermal conductivity of the heat radiation sheet.
- the volume ratio of the first boron nitride powder is determined with respect to a total of 100 parts by volume of the first to third boron nitride powders from the viewpoint of controlling the partial discharge start voltage of the heat radiating sheet and the thermal conductivity of the heat radiating sheet. It is preferably 2 to 25 parts by volume, more preferably 5 to 20 parts by volume, and even more preferably 8 to 15 parts by volume.
- Each of the first to third boron nitride powders has, for example, a crushing step of crushing massive boron carbide, a nitriding step of nitriding the crushed boron carbide to obtain boron nitride, and decarburizing the boron nitride. It can be manufactured by a manufacturing method including a decarburization step.
- lumpy boron carbide (boron carbide lump) is crushed using a general crusher or crusher.
- a boron carbide powder having a desired maximum point can be obtained.
- the maximum point of the boron carbide powder can be measured in the same manner as the maximum point of the boron nitride powder described above.
- the first to third boron nitride powder having the above-mentioned maximum point can be obtained.
- boron carbide is obtained by firing the boron carbide powder in an atmosphere where the nitriding reaction proceeds and under pressure conditions.
- the atmosphere in the nitriding step is an atmosphere in which the nitriding reaction proceeds, and may be, for example, nitrogen gas, ammonia gas, or the like, and may be one kind alone or a combination of two or more kinds thereof.
- the atmosphere is preferably nitrogen gas from the viewpoint of ease of nitriding and cost.
- the content of nitrogen gas in the atmosphere is preferably 95% by volume or more, more preferably 99.9% by volume or more.
- the pressure in the nitriding step is preferably 0.6 MPa or more, more preferably 0.7 MPa or more, preferably 1.0 MPa or less, and more preferably 0.9 MPa or less.
- the pressure is more preferably 0.7 to 1.0 MPa.
- the firing temperature in the nitriding step is preferably 1800 ° C. or higher, more preferably 1900 ° C. or higher, preferably 2400 ° C. or lower, and more preferably 2200 ° C. or lower.
- the firing temperature is more preferably 1800 to 2200 ° C.
- the pressure conditions and the calcination temperature are preferably 1800 ° C. or higher and 0.7 to 1.0 MPa because the nitriding of boron carbide proceeds more preferably and the conditions are industrially appropriate.
- the firing time in the nitriding step is appropriately selected within a range in which nitriding proceeds sufficiently, and may be preferably 6 hours or more, more preferably 8 hours or more, preferably 30 hours or less, and more preferably 20 hours or less.
- the boron nitride obtained in the nitriding step is heat-treated to be held at a predetermined holding temperature for a certain period of time in an atmosphere of normal pressure or higher. This makes it possible to obtain aggregated boron nitride particles formed by agglomerating decarburized and crystallized hexagonal boron nitride primary particles.
- the atmosphere in the decarburization process is a normal pressure (atmospheric pressure) atmosphere or a pressurized atmosphere.
- the pressure may be, for example, 0.5 MPa or less, preferably 0.3 MPa or less.
- the temperature is raised to a predetermined temperature (a temperature at which decarburization can be started), and then the temperature is further raised to the holding temperature at a predetermined temperature rise rate.
- the predetermined temperature temperature at which decarburization can be started
- the rate of raising the temperature from a predetermined temperature (temperature at which decarburization can be started) to the holding temperature may be, for example, 5 ° C./min or less, preferably 4 ° C./min or less, 3 ° C./min or less, or 2 ° C. It may be less than / minute.
- the holding temperature is preferably 1800 ° C. or higher, more preferably 2000 ° C. or higher, from the viewpoint that grain growth is likely to occur well and the thermal conductivity of the obtained boron nitride powder can be further improved.
- the holding temperature may be preferably 2200 ° C. or lower, more preferably 2100 ° C. or lower.
- the holding time at the holding temperature is appropriately selected within a range in which crystallization proceeds sufficiently, for example, it may be more than 0.5 hours, and from the viewpoint that grain growth is likely to occur well, it is preferably 1 hour or more, more preferably. It is 3 hours or more, more preferably 5 hours or more, and particularly preferably 10 hours or more.
- the holding time at the holding temperature may be, for example, less than 40 hours, which can reduce the decrease in particle strength due to excessive grain growth, and is preferably 30 hours or less, more preferably 20 hours or less from the viewpoint of cost reduction. It's less than an hour.
- a boron source in addition to the boron nitride obtained in the nitriding step as a raw material, a boron source may be mixed to perform decarburization and crystallization.
- Boron sources include boric acid, boron oxide, or mixtures thereof. In this case, other additives used in the art may be further used, if necessary.
- the mixing ratio of boron nitride and the boron source is appropriately selected.
- the ratio of boric acid or boron oxide may be, for example, 100 parts by mass or more, preferably 150 parts by mass or more, based on 100 parts by mass of boron carbide. Further, for example, it may be 300 parts by mass or less, preferably 250 parts by mass or less.
- the boron nitride powder obtained as described above may be classified by a sieve so that the boron nitride powder having a desired particle size distribution can be obtained (classification step). As a result, the first to third boron nitride powders having a desired maximum point can be more preferably obtained.
- the obtained first to third boron nitride powders can be mixed to obtain the boron nitride powder contained in the heat conductive resin composition for the heat dissipation sheet of the present invention.
- the mixing method is not particularly limited as long as the first to third boron nitride powders can be uniformly mixed.
- the first to third boron nitride powders may be mixed using a container rotary type mixing device, or the first to third boron nitride powders may be mixed using a container fixed type mixing device.
- the first to third boron nitride powders may be mixed using a fluid motion type mixing device.
- Examples of the resin contained in the heat conductive resin composition for the heat dissipation sheet of the present invention include epoxy resin, silicone resin (including silicone rubber), acrylic resin, phenol resin, melamine resin, urea resin, and unsaturated polyester. , Fluorine resin, polyamide (eg, polyimide, polyamideimide, polyetherimide, etc.), polyester (eg, polybutylene terephthalate, polyethylene terephthalate, etc.), polyphenylene ether, polyphenylene sulfide, total aromatic polyester, polysulfone, liquid crystal polymer, polyether.
- epoxy resin silicone resin (including silicone rubber), acrylic resin, phenol resin, melamine resin, urea resin, and unsaturated polyester.
- Fluorine resin eg, polyamide (eg, polyimide, polyamideimide, polyetherimide, etc.), polyester (eg, polybutylene terephthalate, polyethylene terephthalate, etc.), polyphenylene ether, polyphenylene
- silicone resin is preferable from the viewpoint of heat resistance, flexibility, and adhesion to a heat sink or the like.
- the silicone resin is preferably one that is vulcanized with an organic peroxide and cured.
- the viscosity of the heat conductive resin composition at 25 ° C. is, for example, 100,000 cp or less from the viewpoint of improving the flexibility of the sheet-shaped molded product.
- the content of the boron nitride powder with respect to the total 100% by volume of the boron nitride powder and the resin is preferably 30 to 85% by volume, more preferably 40 to 80% by volume. preferable.
- the content of the boron nitride powder is 30% by volume or more, the thermal conductivity is improved and sufficient heat dissipation performance can be easily obtained.
- the content of the boron nitride powder is 85% by volume or less, it is possible to reduce the tendency for voids to occur during molding, and it is possible to suppress the deterioration of the insulating property and the mechanical strength.
- the content of the resin component with respect to the total 100% by volume of the boron nitride powder and the resin is preferably 15 to 70% by volume, more preferably 20 to 60% by volume.
- the thermally conductive resin composition may further contain a solvent.
- the solvent is not particularly limited as long as it can dissolve the resin and is easily removed from the applied heat conductive resin composition after the heat conductive resin composition is applied.
- examples of the solvent include toluene, xylene, chlorine-based hydrocarbons and the like. Toluene is preferred among these solvents from the viewpoint of easy removal.
- the content of the solvent can be appropriately selected depending on the desired viscosity of the thermally conductive resin composition.
- the content of the solvent is, for example, 40 to 200 parts by mass with respect to 100 parts by mass of the components other than the solvent of the heat conductive resin composition.
- the thermally conductive resin composition may contain components other than the boron nitride powder, the resin component and the solvent.
- the other components are inorganic fillers, additives, impurities, etc. other than the boron nitride powder, and the content of the other components is preferably 5 parts by mass or less with respect to 100 parts by mass in total of the boron nitride powder and the resin. Yes, more preferably 3 parts by mass or less, still more preferably 1 part by mass or less.
- the thickness of the heat dissipation sheet of the present invention is preferably 100 to 1200 ⁇ m.
- the thickness of the heat radiating sheet is 100 ⁇ m or more, the heat radiating sheet can be reliably brought into close contact with the heat-generating electronic component.
- the thickness of the heat radiating sheet is 1200 ⁇ m or less, the heat radiating property of the heat radiating sheet can be further improved.
- the thickness of the heat dissipation sheet of the present invention is more preferably 150 to 800 ⁇ m, still more preferably 200 to 600 ⁇ m.
- the method for producing a heat-dissipating sheet of the present invention is a step of blending a boron nitride powder containing at least aggregated boron nitride particles formed by agglomerating hexagonal boron nitride primary particles and a resin to prepare a thermally conductive resin composition (A). ), The step (B) of forming the heat conductive resin composition into a sheet to prepare the heat conductive resin composition sheet, and the step (C) of heating and pressurizing the heat conductive resin composition sheet under vacuum. )including.
- a thermally conductive resin composition is prepared by blending a boron nitride powder containing at least agglomerated boron nitride particles formed by aggregating hexagonal boron nitride primary particles and a resin.
- the boron nitride powder used in the step (A) is preferably the boron nitride powder contained in the heat conductive resin composition for the heat dissipation sheet of the present invention. Since the boron nitride powder and the resin used in the step (A) have already been described, the description thereof will be omitted.
- the heat conductive resin composition is formed into a sheet to prepare a heat conductive resin composition sheet.
- the thermally conductive resin composition can be formed into a sheet by the doctor blade method or calendar processing.
- the thermally conductive resin composition passes through the calendar roll, the aggregated boron nitride particles in the thermally conductive resin composition may be broken. Therefore, it is preferable to mold the thermally conductive resin composition into a sheet by the doctor blade method.
- the heat conductive resin composition sheet is heated and pressurized under vacuum.
- the partial discharge start voltage of the heat dissipation sheet can be controlled. For example, if the pressure when the heat conductive resin composition sheet is pressurized is increased, the partial discharge start voltage of the heat radiation sheet becomes large. However, if the pressure when the heat conductive resin composition sheet is pressed is too high, the agglomeration of the agglomerated boron nitride particles in the heat conductive resin composition sheet may be broken.
- the pressure at this time of pressurizing the heat conductive resin composition sheet is reduced, the partial discharge start voltage of the heat radiation sheet becomes smaller. Further, by heating and pressurizing the heat conductive resin composition sheet under vacuum, the microvoids in the heat radiation sheet can be further reduced, so that the heat conductivity of the heat radiation sheet can be improved and the insulation property of the heat radiation sheet is also improved. can do. Further, by heating and pressurizing the heat conductive resin composition sheet under vacuum, even if the pressure at this time of pressurizing the heat conductive resin composition sheet is small, the microvoids in the heat radiation sheet can be reduced. It is possible to prevent the agglomeration of the agglomerated boron nitride particles in the heat conductive resin composition sheet from breaking.
- the pressure in the vacuum environment when heating and pressurizing the heat conductive resin composition sheet is preferably 0.1 to 5 kPa, more preferably 0.1 to 3 kPa.
- the heating temperature of the heat conductive resin composition sheet is preferably 120 to 200 ° C, more preferably 130 to 180 ° C.
- the pressure at the time of pressurizing the heat conductive resin composition sheet is preferably 80 to 250 kg / cm 2 , and more preferably 100 to 200 kg / cm 2 .
- the particle size distribution of the boron nitride powder was measured using a laser diffraction / scattering method particle size distribution measuring device (LS-13 320) manufactured by Beckman Coulter Co., Ltd. Then, from the obtained particle size distribution, the frequency between the peak start and the peak end at the peak having the first to third maximum points (the first to third maximum values) and the first to third maximum points. (1st to 3rd frequency integration amount), the minimum point between the particle size where the frequency integration amount is 10%, the maximum point with the smallest particle size, and the maximum point with the second smallest particle size.
- the crushing strength of the aggregated boron nitride particles was measured according to JIS R1639-5: 2007. Specifically, after spraying the aggregated boron nitride particles on a sample table of a microcompression tester (“MCT-W500” manufactured by Shimadzu Corporation), five aggregated boron nitride particles were selected and a compression test was performed one by one. ..
- the crushing strengths of the five inorganic filler components were weibull plotted according to JIS R1625: 2010, and the crushing strength at which the cumulative fracture rate was 63.2% was defined as the crushing strength of the aggregated boron nitride particles.
- the dielectric breakdown voltage of the heat dissipation sheet was evaluated based on the values measured in a short-time fracture test (room temperature 23 ° C.) according to the method described in JIS C2110-1: 2016. The results are shown in Table 1.
- the evaluation criteria for insulation are as follows. ⁇ : Dielectric breakdown voltage is 10 kV or more ⁇ : Dielectric breakdown voltage is 5 kV or more and less than 10 kV ⁇ : Dielectric breakdown voltage is less than 5 kV
- Thermal conductivity The thermal resistance of the heat dissipation sheet was evaluated according to the method described in ASTM D5470: 2017 and based on the measured values. The results are shown in Table 1. The evaluation criteria for thermal conductivity are as follows. ⁇ : Thermal conductivity is 5 W / (m ⁇ K) or more ⁇ : Thermal conductivity is 3 W / (m ⁇ K) or more and less than 5 W / (m ⁇ K) ⁇ : Thermal conductivity is 3 W / (m ⁇ K) Less than
- Boron nitride powders A to I having one maximum point were prepared as raw materials for the boron nitride powder having a plurality of maximum points as follows.
- Boron nitride powder A was produced by boron carbide synthesis, pressure nitriding step, and decarburization crystallization step as described below.
- Boric acid orthoboric acid
- HS100 acetylene black
- the synthesized boron carbide mass is pulverized with a ball mill for 1 hour, sieved to a particle size of 75 ⁇ m or less using a sieve net, washed with an aqueous nitrate solution to remove impurities such as iron, and then filtered and dried to have an average particle size of 4 ⁇ m.
- a boron carbide powder was prepared.
- Boron nitride (B 4 ) is obtained by filling the synthesized boron carbide into a crucible nitride and then heating it in a nitrogen gas atmosphere at 2000 ° C. and 9 atm (0.8 MPa) for 10 hours using a resistance heating furnace. CN 4 ) was obtained.
- the synthesized aggregated boron nitride particles were decomposed and crushed by 15 with a Henschel mixer, and then classified with a nylon sieve having a sieve mesh of 150 ⁇ m using a sieve net. Boron nitride powder A was obtained by crushing and classifying the fired product.
- the average particle size (D50) of the obtained boron nitride powder A measured by the laser scattering method was 4.5 ⁇ m.
- the obtained boron nitride powder A was scaly particles.
- Boron nitride powder B was prepared in the same manner as boron nitride powder A, except that boron carbide powder having an average particle diameter of 6 ⁇ m was used.
- the average particle size (D50) of the obtained boron nitride powder B measured by the laser scattering method was 8.0 ⁇ m.
- the obtained boron nitride powder B was scaly particles.
- Boron nitride powder C was prepared in the same manner as boron nitride powder A, except that boron carbide powder having an average particle diameter of 1 ⁇ m was used.
- the average particle size (D50) of the obtained boron nitride powder C measured by the laser scattering method was 1.0 ⁇ m.
- the obtained boron nitride powder C was scaly particles.
- Boron nitride powder D was prepared in the same manner as boron nitride powder A, except that boron carbide powder having an average particle diameter of 15 ⁇ m was used.
- the average particle size (D50) of the obtained boron nitride powder D measured by the laser scattering method was 23 ⁇ m.
- the obtained boron nitride powder D was agglomerated particles formed by agglomerating primary particles.
- Boron nitride powder E was prepared in the same manner as boron nitride powder A, except that boron carbide powder having an average particle diameter of 25 ⁇ m was used.
- the average particle size (D50) of the obtained boron nitride powder E measured by the laser scattering method was 35 ⁇ m.
- the obtained boron nitride powder E was agglomerated particles formed by agglomerating primary particles.
- Boron nitride powder F was prepared in the same manner as boron nitride powder A, except that boron carbide powder having an average particle diameter of 10 ⁇ m was used.
- the average particle size (D50) of the obtained boron nitride powder F measured by the laser scattering method was 15 ⁇ m.
- the obtained boron nitride powder F was agglomerated particles formed by agglomerating primary particles.
- Boron nitride powder G was prepared in the same manner as boron nitride powder A, except that boron carbide powder having an average particle diameter of 12 ⁇ m was used.
- the average particle size (D50) of the obtained boron nitride powder G measured by the laser scattering method was 18 ⁇ m.
- the obtained boron nitride powder L was agglomerated particles formed by agglomerating primary particles.
- Boron nitride powder H was prepared in the same manner as boron nitride powder A, except that boron carbide powder having an average particle diameter of 55 ⁇ m was used.
- the average particle size (D50) of the obtained boron nitride powder H measured by the laser scattering method was 78 ⁇ m.
- the obtained boron nitride powder H was agglomerated particles formed by agglomerating primary particles.
- the half width of the peak of the particle size distribution of the boron nitride powder H was 46 ⁇ m.
- Boron nitride powder I was prepared in the same manner as boron nitride powder A, except that boron carbide powder having an average particle diameter of 70 ⁇ m was used.
- the average particle size (D50) of the obtained boron nitride powder I measured by the laser scattering method was 95 ⁇ m.
- the obtained boron nitride powder I was agglomerated particles formed by agglomerating primary particles.
- the half width of the peak of the particle size distribution of the boron nitride powder I was 53 ⁇ m.
- Boron nitride powder J was prepared in the same manner as boron nitride powder A, except that boron carbide powder having an average particle diameter of 40 ⁇ m was used.
- the average particle size (D50) of the obtained boron nitride powder J measured by the laser scattering method was 55 ⁇ m.
- the obtained boron nitride powder J was agglomerated particles formed by agglomerating primary particles.
- the half width of the peak of the particle size distribution of the boron nitride powder J was 28 ⁇ m.
- Boron nitride powder K was prepared in the same manner as boron nitride powder A, except that boron carbide powder having an average particle diameter of 65 ⁇ m was used.
- the average particle size (D50) of the obtained boron nitride powder K measured by the laser scattering method was 82 ⁇ m.
- the obtained boron nitride powder K was agglomerated particles formed by agglomerating primary particles.
- the half width of the peak of the particle size distribution of the boron nitride powder K was 45 ⁇ m.
- Boron nitride powder L was prepared in the same manner as boron nitride powder A, except that boron carbide powder having an average particle diameter of 50 ⁇ m was used.
- the average particle size (D50) of the obtained boron nitride powder L measured by the laser scattering method was 73 ⁇ m.
- the obtained boron nitride powder L was agglomerated particles formed by agglomerating primary particles.
- the half width of the peak of the particle size distribution of the boron nitride powder K was 48 ⁇ m.
- Boron nitride powders A to L were mixed at the blending ratios shown in Table 1 to prepare boron nitride powders 1 to 5.
- % Silicone resin 1, 1 part by volume of curing agent (2,5-dimethyl-2,5-bis (t-butylperoxy) hexane, manufactured by Chemical Nurion Co., Ltd., trade name " Trigonox 101 "), 0.5 parts by volume of silane coupling agent with respect to 100 parts by volume of boron nitride powder (dimethyldimethoxysilane, manufactured by Dow Toray Co., Ltd., trade name” DOWNSIL Z-6329 Silane ", 25 ° C.
- a pet film having a thickness of 0.05 mm was laminated on the surface of the heat conductive resin composition of the obtained sheet-shaped molded product to prepare a laminated body.
- the layer structure of this laminate was a pet film / a heat conductive resin composition / a pet film.
- the obtained laminate was heated and pressed under vacuum (pressure 3.5 kPa) at a temperature of 150 ° C. at the pressure shown in Table 2 for 30 minutes, and the pet films on both sides were peeled off to form a sheet. And said. Then, it was subjected to secondary heating at normal pressure and 150 ° C. for 4 hours to obtain a heat dissipation sheet.
- Table 2 shows the evaluation results of the obtained boron nitride powder and heat dissipation sheet.
- the thermal conductivity and the insulating property of the heat radiating sheet were improved.
- the particle size distribution is the first maximum point having a particle size of 0.4 ⁇ m or more and less than 10 ⁇ m, the second maximum point having a particle size of 10 ⁇ m or more and less than 40 ⁇ m, and the third maximum point having a particle size of 40 ⁇ m or more and 110 ⁇ m or less. It was found that the thermal conductivity and the insulating property of the heat dissipation sheet were further improved by using the boron nitride powder having at least the maximum point.
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Abstract
Description
そこで、本発明は、熱伝導性及び絶縁性が優れた放熱シート並びに熱伝導性及び絶縁性が優れた放熱シートの製造方法を提供することを目的とする。
本発明は、上記の知見に基づくものであり、以下を要旨とする。
[1]六方晶窒化ホウ素一次粒子が凝集してなる凝集窒化ホウ素粒子を少なくとも含む窒化ホウ素粉末と樹脂とを含む熱伝導性樹脂組成物を成形してなる放熱シートであって、
部分放電開始電圧が2800~5000kV/mmである放熱シート。
[2]前記窒化ホウ素粉末の粒度分布が、第1の極大点、前記第1の極大点よりも粒径が大きい第2の極大点、及び前記第2の極大点よりも粒径が大きい第3の極大点を少なくとも有し、前記第1の極大点の粒径が0.4μm以上10μm未満であり、前記第2の極大点の粒径が10μm以上40μm未満であり、
前記第3の極大点の粒径が40μm以上110μm以下である上記[1]に記載の放熱シート。
[3]前記窒化ホウ素粉末の粒度分布における頻度の積算量が10%となる粒径と、前記窒化ホウ素粉末の粒度分布の最も粒径が小さい極大点及び2番目に粒径が小さい極大点の間の極小点の粒径との差の絶対値が3~30μmである上記[2]に記載の放熱シート。
[4]前記第1の極大点に隣接する極大点が前記第2の極大点であり、前記第2の極大点に隣接する極大点が前記第3の極大点であり、前記第1の極大点及び前記第2の極大点の間の第1の極小点の粒径と前記第2の極大点及び前記第3の極大点の間の第2の極小点の粒径との差の絶対値が15~60μmである上記[2]又は[3]に記載の放熱シート。
[5]前記第3の極大点を有するピークの半値幅が20~60μmである上記[2]~[4]のいずれか1つに記載の放熱シート。
[6]前記凝集窒化ホウ素粒子の圧壊強度が5~18MPaである上記[1]~[5]いずれか1つに記載の放熱シート。
[7]六方晶窒化ホウ素一次粒子が凝集してなる凝集窒化ホウ素粒子を少なくとも含む窒化ホウ素粉末と樹脂とを配合して熱伝導性樹脂組成物を作製する工程、前記熱伝導性樹脂組成物をシート状に成形して、熱伝導性樹脂組成物シートを作製する工程、及び前記熱伝導性樹脂組成物シートを真空下で加熱及び加圧する工程を含む上記[1]~[6]のいずれか1つに記載の放熱シートの製造方法。
本発明の放熱シートは、六方晶窒化ホウ素一次粒子が凝集してなる凝集窒化ホウ素粒子を少なくとも含む窒化ホウ素粉末と樹脂とを含む熱伝導性樹脂組成物を成形してなるものである。そして、本発明の放熱シートの部分放電開始電圧が2800~5000kV/mmである。なお、部分放電とは、電極間に電圧を加えたとき、その間の絶縁物中で部分的に発生する放電をいい、電極間を完全に橋絡する放電ではない。放熱シートの部分放電開始電圧が2800kV/mm未満であると、放熱シートの絶縁性が悪くなる。これは、放熱シートの部分放電開始電圧が2800kV/mm未満である場合、放熱シート中に過度のボイドが存在するためであると考えられる。なお、放電シート内にボイドがあると、その部分に電界が集中し、微弱な放電(部分放電)が発生する。放熱シートの部分放電開始電圧が5000kV/mmよりも大きいと、放熱シートの絶縁性は改善するが、熱伝導性は悪くなる。これは、放熱シートの電開始電圧が5000kV/mmよりも大きい場合、放熱シート中に存在するボイドは減少するものの、放熱シート中のボイドを減少させるために放熱シートの製造で実施した加圧により、放熱シート中の凝集窒化ホウ素粒子の凝集が壊れたためであると考えられる。このような観点から、本発明の放熱シートの部分放電開始電圧は、好ましくは2900~4700kV/mmであり、より好ましくは3000~4500kV/mmである。なお、放熱シートの部分放電開始電圧は、後述の実施例に記載の方法により測定することができる。また、放熱シートの部分放電開始電圧は、例えば、後述の放熱シートの製造方法において、凝集窒化ホウ素粒子の強度等に応じて、熱伝導性樹脂組成物シートを加圧するときの圧力を調整することで制御することができる。
本発明の放熱シートのための熱伝導性樹脂組成物に含まれる窒化ホウ素粉末の粒度分布は、粒径が0.4μm以上10μm未満である第1の極大点及び粒径が10μm以上40μm未満である第2の極大点の少なくとも1つの極大点と、粒径が40μm以上110μm以下である第3の極大点とを少なくとも有することが好ましい。これにより、放熱シート中の窒化ホウ素粉末の充填性が高まるので、後述の放熱シートの製造方法における熱伝導性樹脂組成物シートを加圧するときの圧力の調整による放熱シートの部分放電開始電圧を2800~5000kV/mmの範囲内に調整することが、さらに容易になる。このような観点から、本発明の放熱シートのための熱伝導性樹脂組成物に含まれる窒化ホウ素粉末の粒度分布は、上記第1の極大点、上記第2の極大点及び上記第3の極大点を少なくとも有することがより好ましい。
本発明の放熱シートのための熱伝導性樹脂組成物に含まれる窒化ホウ素粉末の製造方法の一例を以下説明する。
本発明の放熱シートのための熱伝導性樹脂組成物に含まれる窒化ホウ素粉末は、例えば、粒度分布が上記第1の極大点を有する第1の窒化ホウ素粉末、粒度分布が上記第2の極大点を有する第2の窒化ホウ素粉末、及び粒度分布が上記第3の極大点を有する第3の窒化ホウ素粉末をそれぞれ作製し、作製した第1~3の窒化ホウ素粉末を混合することにより、製造することができる。
本発明の放熱シートのための熱伝導性樹脂組成物に含まれる樹脂には、例えば、エポキシ樹脂、シリコーン樹脂(シリコーンゴムを含む)、アクリル樹脂、フェノール樹脂、メラミン樹脂、ユリア樹脂、不飽和ポリエステル、フッ素樹脂、ポリアミド(例えば、ポリイミド、ポリアミドイミド、ポリエーテルイミド等)、ポリエステル(例えば、ポリブチレンテレフタレート、ポリエチレンテレフタレート等)、ポリフェニレンエーテル、ポリフェニレンスルフィド、全芳香族ポリエステル、ポリスルホン、液晶ポリマー、ポリエーテルスルホン、ポリカーボネート、マレイミド変性樹脂、ABS樹脂、AAS(アクリロニトリル-アクリルゴム・スチレン)樹脂、AES(アクリロニトリル・エチレン・プロピレン・ジエンゴム-スチレン)樹脂などが挙げられる。これらの中で、耐熱性、柔軟性及びヒートシンク等への密着性の観点から、シリコーン樹脂が好ましい。シリコーン樹脂は有機過酸化物による加硫して硬化するものが好ましい。また、熱伝導性樹脂組成物の25℃における粘度は、シート状の成形体の柔軟性を改善する観点から、例えば、100,000cp以下である。
熱伝導性樹脂組成物の粘度を調節するために、熱伝導性樹脂組成物は溶媒をさらに含んでもよい。溶媒は、樹脂を溶解でき、熱伝導性樹脂組成物を塗布したのち、塗布した熱伝導性樹脂組成物から容易に除去されるものであれば特に限定されない。樹脂がシリコーン樹脂である場合、溶媒には、例えば、トルエン、キシレン、塩素系炭化水素などが挙げられる。除去が容易であるという観点から、これらの溶媒の中でトルエンが好ましい。溶媒の含有量は、熱伝導性樹脂組成物の目的とする粘度により適宜選択することができる。溶媒の含有量は、例えば、熱伝導性樹脂組成物の溶媒以外の成分100質量部に対して40~200質量部である。
本発明の放熱シートの厚さは、好ましくは100~1200μmである。放熱シートの厚さが100μm以上であると、放熱シートを発熱性電子部品により確実に密着させることができる。放熱シートの厚さが1200μm以下であると、放熱シートの放熱性をさらに良好にすることができる。そのような観点から、本発明の放熱シートの厚さは、より好ましくは150~800μmであり、さらに好ましくは200~600μmである。
本発明の放熱シートの製造方法は、六方晶窒化ホウ素一次粒子が凝集してなる凝集窒化ホウ素粒子を少なくとも含む窒化ホウ素粉末と樹脂とを配合して熱伝導性樹脂組成物を作製する工程(A)、熱伝導性樹脂組成物をシート状に成形して、熱伝導性樹脂組成物シートを作製する工程(B)、及び熱伝導性樹脂組成物シートを真空下で加熱及び加圧する工程(C)を含む。
工程(A)では、六方晶窒化ホウ素一次粒子が凝集してなる凝集窒化ホウ素粒子を少なくとも含む窒化ホウ素粉末と樹脂とを配合して熱伝導性樹脂組成物を作製する。工程(A)で使用する窒化ホウ素粉末は、好ましくは、本発明の放熱シートのための熱伝導性樹脂組成物に含まれる窒化ホウ素粉末である。工程(A)で使用する窒化ホウ素粉末及び樹脂については、既に説明したので、説明を省略する。
工程(B)では、熱伝導性樹脂組成物をシート状に成形して、熱伝導性樹脂組成物シートを作製する。例えば、ドクターブレード法またはカレンダー加工によって熱伝導性樹脂組成物をシート状に成形することができる。しかし、熱伝導性樹脂組成物がカレンダーロールを通過する際、熱伝導性樹脂組成物中の凝集窒化ホウ素粒子が壊れるおそれがある。したがって、ドクターブレード法により熱伝導性樹脂組成物をシート状に成形することが好ましい。
工程(C)では、熱伝導性樹脂組成物シートを真空下で加熱及び加圧する。熱伝導性樹脂組成物シートを加圧するときの圧力を調節することにより、放熱シートの部分放電開始電圧を制御することができる。例えば、熱伝導性樹脂組成物シートを加圧するときの圧力を大きくすると、放熱シートの部分放電開始電圧は大きくなる。しかし、熱伝導性樹脂組成物シートを加圧するときの圧力を大きくしすぎると、熱伝導性樹脂組成物シート中の凝集窒化ホウ素粒子の凝集が壊れる場合がある。一方、熱伝導性樹脂組成物シートを加圧するこのときの圧力を小さくすると、放熱シートの部分放電開始電圧は小さくなる。また、熱伝導性樹脂組成物シートを真空下で加熱及び加圧することにより、放熱シート中のマイクロボイドをさらに低減できるので、放熱シートの熱伝導性を改善できるとともに、放熱シートの絶縁性も改善することができる。さらに、熱伝導性樹脂組成物シートを真空下で加熱及び加圧することにより、熱伝導性樹脂組成物シートを加圧するこのときの圧力が小さくても、放熱シート中のマイクロボイドを低減できるので、熱伝導性樹脂組成物シート中の凝集窒化ホウ素粒子の凝集が壊れることを抑制できる。このような観点から、熱伝導性樹脂組成物シートを加熱及び加圧する際の真空環境の圧力は、好ましくは0.1~5kPaであり、より好ましくは0.1~3kPaである。また、熱伝導性樹脂組成物シートの加熱温度は、好ましくは120~200℃であり、より好ましくは130~180℃である。さらに、熱伝導性樹脂組成物シートの加圧する際の圧力は、好ましくは80~250kg/cm2であり、より好ましくは100~200kg/cm2である。
JEC-0401-1990(部分放電測定)に準拠して、下記の条件にて、放熱シートの部分放電開始電圧を測定した。
試験装置:同調式コロナ測定器(株式会社日本計測器製造所製、商品名「CD-6形部分放電測定器」)
検出電荷:10pc
窒化ホウ素粉末の粒度分布をベックマン・コールター株式会社製レーザー回折散乱法粒度分布測定装置、(LS-13 320)を用いて測定した。そして、得られた粒度分布から、第1~3の極大点の粒径(第1~3の極大値)、第1~3の極大点を有するピークにおけるピークスタートからピークエンドまでの間の頻度の積算量(第1~3の頻度の積算量)、頻度の積算量が10%となる粒径と、最も粒径が小さい極大点及び2番目に粒径が小さい極大点の間の極小点の粒径との差の絶対値(D10と最初の極小値間距離)、第1の極小点の粒径と第2の極小点の粒径との差の絶対値(極小値間距離)、第3の極大点を有するピークの半値幅(極大値3の半値幅)を求めた。
凝集窒化ホウ素粒子の圧壊強度は、JIS R1639-5:2007に準拠して測定した。具体的には、凝集窒化ホウ素粒子を微小圧縮試験器(「MCT-W500」株式会社島津製作所製)の試料台に散布後、凝集窒化ホウ素粒子を5個選び出し、1粒ずつ圧縮試験を行った。そして、圧壊強度(σ:MPa)は、粒子内の位置によって変化する無次元数(α=2.48)と圧壊試験力(P:N)と粒径(d:μm)からσ=α×P/(π×d2)の式を用いて算出した。JIS R1625:2010に準拠して5個の無機フィラー成分の圧壊強度をワイブルプロットし、累積破壊率が63.2%となる圧壊強度を凝集窒化ホウ素粒子の圧壊強度とした。
(絶縁性)
放熱シートの絶縁破壊電圧を、JIS C2110-1:2016に記載の方法に準拠し、短時間破壊試験(室温23℃)にて測定した値に基づき、評価した。結果を表1に示す。
絶縁性の評価基準は厚さ以下の通りである。
◎:絶縁破壊電圧が10kV以上
○:絶縁破壊電圧が5kV以上、10kV未満
×:絶縁破壊電圧が5kV未満
放熱シートの熱抵抗を、ASTM D5470:2017に記載の方法に準拠し、測定した値に基づき、評価した。結果を表1に示す。
熱伝導性の評価基準は以下の通りである。
◎:熱伝導率が5W/(m・K)以上
○:熱伝導率が3W/(m・K)以上、5W/(m・K)未満
×:熱伝導率が3W/(m・K)未満
以下のように、炭化ホウ素合成、加圧窒化工程、脱炭結晶化工程にて、窒化ホウ素粉末Aを作製した。
新日本電工株式会社製オルトホウ酸(以下ホウ酸)100質量部と、デンカ株式会社製アセチレンブラック(HS100)35質量部とをヘンシェルミキサーを用いて混合したのち、黒鉛ルツボ中に充填し、アーク炉にて、アルゴン雰囲気で、2200℃にて5時間加熱し炭化ホウ素(B4C)を合成した。合成した炭化ホウ素塊をボールミルで1時間粉砕し、篩網を用いて粒径75μm以下に篩分け、さらに硝酸水溶液で洗浄して鉄分等不純物を除去後、濾過・乾燥して平均粒子径4μmの炭化ホウ素粉末を作製した。
合成した炭化ホウ素を窒化ホウ素ルツボに充填した後、抵抗加熱炉を用い、窒素ガスの雰囲気で、2000℃、9気圧(0.8MPa)の条件で10時間加熱することにより炭窒化ホウ素(B4CN4)を得た。
合成した炭窒化ホウ素100質量部と、ホウ酸90質量部とをヘンシェルミキサーを用いて混合したのち、窒化ホウ素ルツボに充填し、抵抗加熱炉を用い0.2MPaの圧力条件で、窒素ガスの雰囲気で、室温から1000℃までの昇温速度を10℃/min、1000℃からの昇温速度を2℃/minで昇温し、焼成温度2020℃、保持時間10時間で加熱することにより、一次粒子が凝集して塊状になった凝集窒化ホウ素粒子を合成した。合成した凝集窒化ホウ素粒子をヘンシェルミキサーにより15分解砕をおこなった後、篩網を用いて、篩目150μmのナイロン篩にて分級を行った。焼成物を解砕及び分級することより、窒化ホウ素粉末Aを得た。
平均粒子径6μmの炭化ホウ素粉末を用いた点を除いて、窒化ホウ素粉末Aと同様な方法で窒化ホウ素粉末Bを作製した。なお、得られた窒化ホウ素粉末Bのレーザー散乱法により測定した平均粒子径(D50)は8.0μmであった。SEM観察の結果、得られた窒化ホウ素粉末Bは鱗片状の粒子であった。
平均粒子径1μmの炭化ホウ素粉末を用いた点を除いて、窒化ホウ素粉末Aと同様な方法で窒化ホウ素粉末Cを作製した。なお、得られた窒化ホウ素粉末Cのレーザー散乱法により測定した平均粒子径(D50)は1.0μmであった。SEM観察の結果、得られた窒化ホウ素粉末Cは鱗片状の粒子であった。
平均粒子径15μmの炭化ホウ素粉末を用いた点を除いて、窒化ホウ素粉末Aと同様な方法で窒化ホウ素粉末Dを作製した。なお、得られた窒化ホウ素粉末Dのレーザー散乱法により測定した平均粒子径(D50)は23μmであった。SEM観察の結果、得られた窒化ホウ素粉末Dは、一次粒子が凝集してなる凝集粒子であった。
平均粒子径25μmの炭化ホウ素粉末を用いた点を除いて、窒化ホウ素粉末Aと同様な方法で窒化ホウ素粉末Eを作製した。なお、得られた窒化ホウ素粉末Eのレーザー散乱法により測定した平均粒子径(D50)は35μmであった。SEM観察の結果、得られた窒化ホウ素粉末Eは、一次粒子が凝集してなる凝集粒子であった。
平均粒子径10μmの炭化ホウ素粉末を用いた点を除いて、窒化ホウ素粉末Aと同様な方法で窒化ホウ素粉末Fを作製した。なお、得られた窒化ホウ素粉末Fのレーザー散乱法により測定した平均粒子径(D50)は15μmであった。SEM観察の結果、得られた窒化ホウ素粉末Fは、一次粒子が凝集してなる凝集粒子であった。
平均粒子径12μmの炭化ホウ素粉末を用いた点を除いて、窒化ホウ素粉末Aと同様な方法で窒化ホウ素粉末Gを作製した。なお、得られた窒化ホウ素粉末Gのレーザー散乱法により測定した平均粒子径(D50)は18μmであった。SEM観察の結果、得られた窒化ホウ素粉末Lは、一次粒子が凝集してなる凝集粒子であった。
平均粒子径55μmの炭化ホウ素粉末を用いた点を除いて、窒化ホウ素粉末Aと同様な方法で窒化ホウ素粉末Hを作製した。なお、得られた窒化ホウ素粉末Hのレーザー散乱法により測定した平均粒子径(D50)は78μmであった。SEM観察の結果、得られた窒化ホウ素粉末Hは、一次粒子が凝集してなる凝集粒子であった。また、窒化ホウ素粉末Hの粒度分布のピークの半値幅は46μmであった。
平均粒子径70μmの炭化ホウ素粉末を用いた点を除いて、窒化ホウ素粉末Aと同様な方法で窒化ホウ素粉末Iを作製した。なお、得られた窒化ホウ素粉末Iのレーザー散乱法により測定した平均粒子径(D50)は95μmであった。SEM観察の結果、得られた窒化ホウ素粉末Iは、一次粒子が凝集してなる凝集粒子であった。また、窒化ホウ素粉末Iの粒度分布のピークの半値幅は53μmであった。
平均粒子径40μmの炭化ホウ素粉末を用いた点を除いて、窒化ホウ素粉末Aと同様な方法で窒化ホウ素粉末Jを作製した。なお、得られた窒化ホウ素粉末Jのレーザー散乱法により測定した平均粒子径(D50)は55μmであった。SEM観察の結果、得られた窒化ホウ素粉末Jは、一次粒子が凝集してなる凝集粒子であった。また、窒化ホウ素粉末Jの粒度分布のピークの半値幅は28μmであった。
平均粒子径65μmの炭化ホウ素粉末を用いたを除いて、窒化ホウ素粉末Aと同様な方法で窒化ホウ素粉末Kを作製した。なお、得られた窒化ホウ素粉末Kのレーザー散乱法により測定した平均粒子径(D50)は82μmであった。SEM観察の結果、得られた窒化ホウ素粉末Kは、一次粒子が凝集してなる凝集粒子であった。また、窒化ホウ素粉末Kの粒度分布のピークの半値幅は45μmであった。
平均粒子径50μmの炭化ホウ素粉末を用いた点を除いて、窒化ホウ素粉末Aと同様な方法で窒化ホウ素粉末Lを作製した。なお、得られた窒化ホウ素粉末Lのレーザー散乱法により測定した平均粒子径(D50)は73μmであった。SEM観察の結果、得られた窒化ホウ素粉末Lは、一次粒子が凝集してなる凝集粒子であった。また、窒化ホウ素粉末Kの粒度分布のピークの半値幅は48μmであった。
得られた窒化ホウ素粉末及び液状シリコーン樹脂(メチルビニルポリシロキサン、ダウ・東レ株式会社製、商品名「CF-3110」)の合計100体積%に対して、60体積%の窒化ホウ素粉末及び40体積%のシリコーン樹脂1、シリコーン樹脂100質量部に対して1質量部の硬化剤(2,5-ジメチルー2,5-ビス(t-ブチルパーオキシ)ヘキサン、化薬ヌーリオン株式会社製、商品名「トリゴノックス101」)、窒化ホウ素粉末の合計100質量部に対して0.5質量部のシランカップリング剤(ジメチルジメトキシシラン、ダウ・東レ株式会社製、商品名「DOWSIL Z-6329 Silane」、25℃における粘度:1cp)、シランカップリング剤100質量部に対して15質量部の水、並びに上述の原料の合計100質量部に対して110質量部のトルエンを攪拌機(HEIDON社製、商品名「スリーワンモーター」)に投入し、タービン型撹拌翼を用いて15時間混合して熱伝導性樹脂組成物のスラリーを作製した。
そして、ドクターブレード法により、上記スラリーを厚さ0.05mmのペットフィルム(キャリアフィルム)上に厚さ1.0mmで塗工し、75℃で5分乾燥させて、ペットフィルム付きのシート状成形体を作製した。得られたシート状成形体の熱伝導性樹脂組成物面に厚さ0.05mmのペットフィルムを積層して、積層体を作製した。なお、この積層体の層構造はペットフィルム/熱伝導性樹脂組成物/ペットフィルムであった。次いで、得られた積層体に対して、真空下(圧力3.5kPa)、温度150℃の条件で、表2に示す圧力で30分間の加熱プレスを行い、両面のペットフィルムを剥離してシートとした。次いで、それを常圧、150℃で4時間の2次加熱を行い、放熱シートとした。
Claims (7)
- 六方晶窒化ホウ素一次粒子が凝集してなる凝集窒化ホウ素粒子を少なくとも含む窒化ホウ素粉末と樹脂とを含む熱伝導性樹脂組成物を成形してなる放熱シートであって、
部分放電開始電圧が2800~5000kV/mmである放熱シート。 - 前記窒化ホウ素粉末の粒度分布が、第1の極大点、前記第1の極大点よりも粒径が大きい第2の極大点、及び前記第2の極大点よりも粒径が大きい第3の極大点を少なくとも有し、
前記第1の極大点の粒径が0.4μm以上10μm未満であり、
前記第2の極大点の粒径が10μm以上40μm未満であり、
前記第3の極大点の粒径が40μm以上110μm以下である請求項1に記載の放熱シート。 - 前記窒化ホウ素粉末の粒度分布における頻度の積算量が10%となる粒径と、前記窒化ホウ素粉末の粒度分布の最も粒径が小さい極大点及び2番目に粒径が小さい極大点の間の極小点の粒径との差の絶対値が3~30μmである請求項2に記載の放熱シート。
- 前記第1の極大点に隣接する極大点が前記第2の極大点であり、
前記第2の極大点に隣接する極大点が前記第3の極大点であり、
前記第1の極大点及び前記第2の極大点の間の第1の極小点の粒径と前記第2の極大点及び前記第3の極大点の間の第2の極小点の粒径との差の絶対値が15~60μmである請求項2又は3に記載の放熱シート。 - 前記第3の極大点を有するピークの半値幅が20~60μmである請求項2~4のいずれか1項に記載の放熱シート。
- 前記凝集窒化ホウ素粒子の圧壊強度が5~18MPaである請求項1~5のいずれか1項に記載の放熱シート。
- 六方晶窒化ホウ素一次粒子が凝集してなる凝集窒化ホウ素粒子を少なくとも含む窒化ホウ素粉末と樹脂とを配合して熱伝導性樹脂組成物を作製する工程、
前記熱伝導性樹脂組成物をシート状に成形して、熱伝導性樹脂組成物シートを作製する工程、及び
前記熱伝導性樹脂組成物シートを真空下で加熱及び加圧する工程を含む請求項1~6のいずれか1項に記載の放熱シートの製造方法。
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