WO2023162598A1 - Method for producing boron nitride powder, boron nitride powder, and resin sealing material - Google Patents

Method for producing boron nitride powder, boron nitride powder, and resin sealing material Download PDF

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Publication number
WO2023162598A1
WO2023162598A1 PCT/JP2023/003085 JP2023003085W WO2023162598A1 WO 2023162598 A1 WO2023162598 A1 WO 2023162598A1 JP 2023003085 W JP2023003085 W JP 2023003085W WO 2023162598 A1 WO2023162598 A1 WO 2023162598A1
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mass
boron nitride
acid
boron
nitride powder
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PCT/JP2023/003085
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French (fr)
Japanese (ja)
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豪 竹田
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デンカ株式会社
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B21/00—Nitrogen; Compounds thereof
    • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
    • C01B21/064—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron 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
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/38—Boron-containing compounds
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L101/00—Compositions of unspecified macromolecular compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/28—Encapsulations, e.g. encapsulating layers, coatings, e.g. for protection
    • H01L23/29—Encapsulations, e.g. encapsulating layers, coatings, e.g. for protection characterised by the material, e.g. carbon
    • 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

Definitions

  • the present disclosure relates to a method for producing boron nitride powder, boron nitride powder, and a resin sealing material.
  • Boron nitride powder which is an aggregate of boron nitride particles, has lubricating properties, high thermal conductivity, insulating properties, etc., and is widely used for applications such as solid lubricants, thermally conductive fillers, and insulating fillers. .
  • Boron nitride particles especially hexagonal boron nitride particles
  • a resin sealing material for a semiconductor memory element needs to be made of a material that hardly emits ⁇ -rays so as not to cause soft errors in the semiconductor memory element. As such a material, it is particularly desirable to use a material with a low uranium content.
  • aggregated particles as disclosed in Patent Document 1 usually contain a small amount of uranium. Also, due to its structure, the uranium trapped inside the agglomerated particles is difficult to remove. Therefore, it is difficult to reduce the uranium content in agglomerated particles after they are formed.
  • the present disclosure provides at least [1] to [9] below.
  • a preparatory step of preparing the boron carbonitride powder is further included, wherein the preparatory step is an acid treatment step of contacting the boron carbide powder with an acid solution containing hydrofluoric acid to acid-treat the boron carbide powder. and a pressurized nitriding step of firing the acid-treated boron carbide powder in a pressurized nitrogen atmosphere.
  • the treatment temperature in the acid treatment step is 60°C or higher, the treatment time in the acid treatment step is 3 hours or longer, and the acid concentration of the acid solution is 20% by mass or higher, [4] or [ 5], the method for producing a boron nitride powder.
  • a boron nitride powder containing agglomerated particles composed of agglomerated primary particles of boron nitride, having an orientation index of 15 or less and a uranium content of 20 mass ppb or less.
  • a resin sealing material for a semiconductor memory device containing the boron nitride powder according to [7] or [8].
  • a method for producing a boron nitride powder containing agglomerated particles composed of agglomerated primary particles of boron nitride and having a reduced uranium content can.
  • a boron nitride powder containing agglomerated particles composed of agglomerated primary particles of boron nitride and having a sufficiently low uranium content it is possible to provide a resin encapsulant for a semiconductor memory device containing the boron nitride powder of the aspect described above.
  • each component in the composition means the total amount of the multiple substances present in the composition unless otherwise specified when there are multiple substances corresponding to each component in the composition. .
  • a numerical range indicated using “to” indicates a range including the numerical values before and after "to” as the minimum and maximum values, respectively. Also, unless otherwise specified, the units of numerical values described before and after "-" are the same.
  • the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples. Moreover, the upper limit value and the lower limit value described individually can be combined arbitrarily.
  • a method for producing a boron nitride powder includes firing a raw material mixture containing a boron carbonitride powder, a boron source, and a carbonate to produce primary particles of boron nitride, and the primary particles are aggregated. including a decarburizing crystallization step to obtain a powder comprising aggregated particles that are structured.
  • the method for producing boron nitride powder may further include a preparation step of preparing the boron carbonitride powder used in the decarburization and crystallization step.
  • the preparatory step includes, for example, a pressurized nitriding step of firing the boron carbide powder in a pressurized nitrogen atmosphere.
  • the preparation step may further include an acid treatment step (first acid treatment step) of acid-treating the boron carbide powder by contacting the boron carbide powder with an acid solution containing hydrofluoric acid.
  • the pressurized nitriding step uses acid-treated boron carbide powder obtained through the acid treatment step.
  • the preparation step may further include an acid treatment step (second acid treatment step) of acid-treating the boron carbonitride powder by contacting the boron carbonitride powder with an acid solution containing hydrofluoric acid.
  • the boron carbonitride powder used in the second acid treatment step may be a powder obtained through a pressure nitriding step.
  • the preparation step includes the second acid treatment step, the acid-treated boron carbonitride powder obtained through the acid treatment step is used in the decarburization and crystallization step.
  • the amounts of the boron source and the carbonate used in the decarburization and crystallization step are set within the predetermined ranges, respectively, and then the first acid treatment step and/or the second acid treatment step are performed to finally obtain The uranium content in the boron nitride powder obtained in 1 can be further reduced.
  • the boron carbide powder (B 4 C powder) is brought into contact with an acid solution containing hydrofluoric acid, thereby dissolving the portions of the boron carbide particles that come into contact with the acid solution. This removes at least part of the uranium present in the boron carbide powder (in particular, uranium present near the surface of the boron carbide particles).
  • Boron carbide powder is an aggregate of boron carbide particles.
  • the purity of the boron carbide powder (content of boron carbide) is preferably, for example, 97% by mass or more.
  • As the boron carbide powder commercially available boron carbide powder may be used, or separately prepared boron carbide powder may be used.
  • Boron carbide powder for example, after mixing boric acid and acetylene black, is heated in an inert gas atmosphere at 1800 to 2400 ° C. for 1 to 10 hours to obtain a boron carbide mass;
  • a boron lump can be obtained by a method including steps of pulverizing, sieving, washing, removing impurities, drying, etc. as appropriate to prepare a boron carbide powder.
  • boron carbide powder As the boron carbide powder, it is preferable to use boron carbide powder having an average particle size of 10 ⁇ m or more (for example, 10 to 50 ⁇ m) from the viewpoint of improving the removal efficiency of uranium during acid treatment. From the same point of view, it is preferable to use boron carbide powder having a specific surface area of 1 m 2 /g or less (for example, 0.05 to 1 m 2 /g).
  • the acid solution is an aqueous solution containing hydrofluoric acid as an acid component.
  • An aqueous solution of hydrogen fluoride is sometimes referred to as hydrofluoric acid, but in this specification, among the acid components contained in the aqueous solution (acid solution), a compound represented by HF is referred to as hydrofluoric acid.
  • an acid component is defined as a substance that dissolves in water and releases hydrogen ions.
  • the concentration of hydrofluoric acid in the acid solution may be 0.1% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, or 10% by mass. % or more.
  • the concentration of hydrofluoric acid in the acid solution may be 50% by mass or less, 45% by mass or less, 40% by mass or less, or 30% by mass or less from the viewpoint of production cost and safety. From these points of view, the concentration of hydrofluoric acid in the acid solution is, for example, 0.1 to 50% by mass, 1 to 50% by mass, 2 to 45% by mass, 3 to 40% by mass, or 10 to 30% by mass.
  • the concentration of hydrofluoric acid means the content of hydrofluoric acid (HF) based on the total mass of the acid solution.
  • the acid solution may be a mixed acid that further contains an acid component other than hydrofluoric acid.
  • the ratio of hydrofluoric acid to all acid components in the acid solution may be 4% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, from the viewpoint of improving the uranium removal efficiency. It may be at least 40% by mass or at least 40% by mass.
  • the proportion of hydrofluoric acid in all acid components may be 80% by mass or less, 70% by mass or less, or 60% by mass or less from the viewpoint of production cost and safety. From these viewpoints, the proportion of hydrofluoric acid in the total acid component is, for example, 4 to 80% by mass, 10 to 70% by mass, 20 to 60% by mass, 30 to 60% by mass, or 40 to 60% by mass. It's okay.
  • Acid components other than hydrofluoric acid that can be contained in the acid solution include, for example, hydrochloric acid (HCl), nitric acid (HNO 3 ), sulfuric acid (HSO 4 ), and the like.
  • hydrochloric acid is preferably used from the viewpoint of improving the removal efficiency of uranium.
  • the concentration of hydrochloric acid in the acid solution may be 2% by mass or more, 3% by mass or more, 5% by mass or more, 7% by mass or more, 10% by mass or more, and 20% by mass. Above, it may be 30% by mass or more, or 40% by mass or more. From the viewpoint of production cost and safety, the concentration of hydrochloric acid in the acid solution may be 60% by mass or less, 50% by mass or less, 35% by mass or less, 30% by mass or less, or 25% by mass or less. good.
  • the concentration of hydrochloric acid in the acid solution is, for example, 2 to 60% by mass, 3 to 60% by mass, 5 to 60% by mass, 7 to 60% by mass, 10 to 60% by mass, 20 to 60% by mass. %, 30-60% by weight or 40-60% by weight, and may be 5-35% by weight, 7-30% by weight or 10-25% by weight.
  • the concentration of hydrochloric acid means the content of hydrochloric acid (HCl) based on the total mass of the acid solution.
  • the acid concentration of the acid solution may be 2% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more. Alternatively, it may be 40% by mass or more.
  • the acid concentration of the acid solution may be 50% by mass or less, 45% by mass or less, or 40% by mass or less from the viewpoint of production cost and safety. From these viewpoints, the acid concentration of the acid solution is, for example, 2 to 50% by mass, 3 to 45% by mass, 5 to 40% by mass, 10 to 50% by mass, 20 to 50% by mass, 30 to 50% by mass, or It may be 40 to 50% by mass.
  • the acid concentration means the content of all acid components based on the total mass of the acid solution.
  • the method of contacting the boron carbide powder with the acid solution is not particularly limited, but for example, a method of mixing the boron carbide powder and the acid solution by putting the boron carbide powder into the acid solution, or a method of mixing the boron carbide powder with the acid solution. and a method of continuously injecting.
  • the mixed liquid containing the boron carbide powder and the acid solution may be stirred from the viewpoint of improving the uranium removal efficiency. Stirring can be performed using, for example, a stirrer, magnetic stirrer, disperser, or the like.
  • the acid treatment of the boron carbide powder may be repeated multiple times. For example, a series of operations of mixing boron carbide powder and an acid solution, separating the boron carbide powder from the acid solution after a certain period of time has passed, and mixing the separated boron carbide powder again with a new acid solution is repeated.
  • the amount of the acid solution used may be, for example, 80 parts by mass or more, 500 parts by mass or less, or 80 to 500 parts by mass with respect to 100 parts by mass of the boron carbide powder.
  • the treatment temperature in the acid treatment step may be 40°C or higher, 60°C or higher, or 75°C or higher from the viewpoint of improving the uranium removal efficiency.
  • the treatment temperature in the acid treatment step may be 95° C. or lower, 92° C. or lower, or 90° C. or lower from the viewpoint of suppressing deterioration in treatment efficiency due to volatilization of hydrogen fluoride and from the viewpoint of safety. From these points of view, the treatment temperature in the acid treatment step may be, for example, 40-95°C, 60-92°C or 75-90°C.
  • the above treatment temperature indicates the temperature of the acid solution that is brought into contact with the boron carbide powder during the acid treatment. When the boron carbide powder is acid-treated by mixing the boron carbide powder and the acid solution, the treatment temperature can be said to be the temperature of the mixed liquid containing the boron carbide powder and the acid solution.
  • the treatment time in the acid treatment step may be 1 hour or more, 2 hours or more, 3 hours or more, or 5 hours or more.
  • the treatment time in the acid treatment step may be 15 hours or less, 12 hours or less, or 10 hours or less from the viewpoint of production cost and safety. From these points of view, the treatment time in the acid treatment step may be, for example, 1 to 15 hours, 2 to 12 hours, 3 to 10 hours, or 5 to 10 hours.
  • the above treatment time indicates the contact time between the boron carbide powder and the acid solution.
  • the treatment temperature in the acid treatment step is 60° C. or higher and the treatment time in the acid treatment step is 3 hours or longer, and the treatment temperature in the acid treatment step is 60° C. or higher. More preferably, the treatment time in the acid treatment step is 3 hours or more, and the acid concentration of the acid solution is 20% by mass or more.
  • the boron carbide powder is sintered in a pressurized nitrogen atmosphere to nitride the boron carbide and obtain a sintered product containing boron carbonitride.
  • the resulting fired product tends to contain hexagonal boron carbonitride with high purity.
  • the boron carbide powder include those exemplified as the boron carbide powder used in the first acid treatment step.
  • acid-treated boron carbide powder obtained through the first acid treatment step is used.
  • the firing temperature in the pressurized nitriding step is preferably higher than the firing temperature in the decarburization and crystallization step.
  • the firing temperature in the pressurized nitriding step may be, for example, 1900-2200°C, 2000-2200°C or 2100-2200°C. By setting the firing temperature within the above range, the crystallinity of the boron carbonitride can be enhanced and the proportion of hexagonal boron carbonitride can be increased.
  • the baking time in the pressurized nitriding step is not particularly limited as long as the nitriding is sufficiently progressed, and may be, for example, 6 to 30 hours, 8 to 25 hours, or 10 to 20 hours.
  • the pressure (atmospheric pressure) in the pressurized nitriding step may be, for example, 0.6 to 1 MPa, 0.7 to 1 MPa, or 0.8 to 1 MPa.
  • the pressure indicates a gauge pressure.
  • the nitrogen gas concentration of the nitrogen pressurized atmosphere in the pressurized nitriding step may be, for example, 95% by volume or more, 98% by volume or more, or 99.9% by volume or more.
  • the upper limit of the nitrogen gas concentration is 100% by volume.
  • the fired product obtained in the pressurized nitriding step may be used as it is in the decarburization and crystallization step, and may be subjected to pulverization treatment, classification treatment, washing treatment, heat treatment (for example, oxidation treatment in an atmosphere containing oxygen), etc. as appropriate. It may be used in the decarburization and crystallization step after being carried out.
  • the pulverization treatment can be performed using a general pulverizer or pulverizer such as a ball mill, vibration mill, or jet mill.
  • "pulverization" in this specification also includes "crushing".
  • Decarburization crystallization step In the decarburization and crystallization step, the boron carbonitride powder (B 4 CN 4 powder) is fired together with a boron source and a carbonate, thereby decarburizing the boron carbonitride and increasing the crystallinity of the boron nitride. . As a result, a boron nitride powder (BN powder) containing agglomerated particles in which primary particles of boron nitride are agglomerated is obtained.
  • BN powder boron nitride powder
  • the boron nitride in the boron nitride powder obtained by this method is usually hexagonal boron nitride, and contains aggregated particles in which primary particles of scale-like hexagonal boron nitride are aggregated.
  • Boron carbonitride powder is an aggregate of boron carbonitride particles.
  • the purity of the boron carbonitride powder (content of boron carbonitride) is preferably 98% by mass or more, for example.
  • a commercially available boron carbonitride powder may be used, or the powder prepared in the above preparation step may be used. From the viewpoint of increasing the ratio of hexagonal boron nitride in the obtained boron nitride powder, it is preferable to use a boron carbonitride powder having a high ratio of hexagonal boron carbonitride, and the boron carbonitride powder obtained through the above pressure nitriding step. is more preferred.
  • Boron sources include, for example, boric acid and boron oxide. These can be used individually by 1 type or in combination of 2 or more types.
  • boric acid is preferably used from the viewpoint of easily obtaining the effect of promoting the growth of primary particles and from the viewpoint of easily reducing the uranium content.
  • Carbonates include, for example, sodium carbonate, calcium carbonate, strontium carbonate, and the like. These can be used individually by 1 type or in combination of 2 or more types.
  • sodium carbonate is preferably used from the viewpoint of easily obtaining the effect of promoting the growth of primary particles and from the viewpoint of easily reducing the uranium content.
  • the amount of the boron source used may be 55% by mass or more, 57% by mass or more, or 59% by mass or more.
  • the amount of the boron source used may be 70% by mass or less, 65% by mass or less, or 60% by mass or less from the viewpoint of increasing the crushing strength of the aggregated particles.
  • the amount of boron source used may be less than 55% by weight.
  • the amount of the boron source used is 50% by mass or more, the growth of the primary particles of boronitride is likely to be promoted, and the boron nitride powder having an average particle size of 10 to 90 ⁇ m and a crushing strength of 5 MPa or more. becomes easier to obtain.
  • the amount of the boron source used is 50 to 70% by mass, 55 to 70% by mass, 57 to 70% by mass, 59 to 70% by mass, 55 to 65% by mass, 57 to 65% by mass, 59 to 65% by mass. % by weight, 55-60% by weight, 57-60% by weight or 59-60% by weight.
  • the amount used is the amount based on the total mass of the raw material mixture, but the amount used based on the total amount of the boron carbonitride powder, the boron source and the carbonate may be within the above range. .
  • the amount of carbonate used may be 4% by mass or more, 5% by mass or more, or 6% by mass or more.
  • the amount of carbonate used may be 10% by mass or less, 8% by mass or less, or 6% by mass or less from the viewpoint of increasing the crushing strength of aggregated particles.
  • the amount of carbonate used may be less than 4% by mass.
  • the amount of carbonate used is 1% by mass or more, the growth of primary particles of boron nitride is likely to be promoted, and the boron nitride powder having an average particle size of 10 to 90 ⁇ m and a crushing strength of 5 MPa or more. becomes easier to obtain.
  • the amount of carbonate used is 1 to 10% by mass, 4 to 10% by mass, 5 to 10% by mass, 6 to 10% by mass, 4 to 8% by mass, 5 to 8% by mass, 6 to 8% by mass. % by weight, 4-6% by weight or 5-6% by weight.
  • the amount used is the amount based on the total mass of the raw material mixture, but the amount used based on the total amount of the boron carbonitride powder, the boron source and the carbonate may be within the above range. .
  • materials other than the boron carbonitride powder, the boron source and the carbonate may be used, or only the boron carbonitride powder, the boron source and the carbonate may be used.
  • the firing temperature in the decarburization and crystallization step is preferably 1800°C or higher, and may be 1900°C or higher or 2000°C or higher. By setting the sintering temperature to 1800° C. or higher, the primary particles can be grown more sufficiently.
  • the firing temperature in the decarburization and crystallization step is preferably 2400° C. or lower, and may be 2200° C. or lower or 2100° C. or lower. By setting the firing temperature to 2400° C. or lower, yellowing of the boron nitride powder can be suppressed. From the above point of view, the firing temperature in the decarburization and crystallization step may be, for example, 1800-2400°C, 1900-2200°C or 2000-2100°C.
  • the said baking temperature means the holding temperature during heating (baking).
  • the heating start temperature is not particularly limited, but may be room temperature (for example, 25°C).
  • the temperature increase rate up to 1000° C. may be, for example, 1 to 10° C./min, and the temperature increase rate at 1000° C. or higher may be, for example, 0.1 to 10° C./min. It may be 5°C/min.
  • the firing time in the decarburization and crystallization step is preferably 4 hours or longer, and may be 6 hours or longer or 8 hours or longer. By setting the firing time to 4 hours or longer, the growth of the primary particles can be sufficiently advanced.
  • the firing time in the decarburization and crystallization step is preferably 40 hours or less, and may be 30 hours or less or 20 hours or less. By setting the firing time to 40 hours or less, it is possible to suppress an increase in manufacturing cost. From the above point of view, the firing time in the decarburization and crystallization step may be, for example, 4 to 40 hours, 6 to 30 hours, or 8 to 20 hours.
  • the firing time means the retention time at the firing temperature (holding temperature).
  • the uranium content can also be reduced by changing the firing conditions in the decarburization and crystallization process.
  • the firing temperature is 1800° C. or more and the firing time is 8 hours or more, or the firing temperature is 2000° C. or more and the firing time is 4 hours or more. More preferably, the firing temperature is 2000° C. or higher, and the firing time is 8 hours or longer.
  • the firing atmosphere in the decarburization and crystallization step may be, for example, air or vacuum, or may be an inert gas atmosphere such as nitrogen gas or argon gas.
  • the calcination in the decarburization and crystallization step may be performed under normal pressure (atmospheric pressure) or under atmospheric pressure or higher.
  • the pressure (atmospheric pressure) in the decarburization and crystallization step may be, for example, 10 kPa or more, 15 kPa or more, or 20 kPa or more.
  • the pressure (atmospheric pressure) in the decarburization and crystallization step may be, for example, 80 kPa or less, 60 kPa or less, or 40 kPa or less. By setting the pressure to 80 kPa or less, it is possible to further suppress the collapse of the aggregated particles during the decarburization and crystallization step.
  • the pressure (atmospheric pressure) in the decarburization and crystallization step may be 10 to 80 kPa, 10 to 60 kPa, or 20 to 40 kPa. Note that the above pressure indicates a gauge pressure.
  • the boron nitride powder after the decarburization and crystallization process may be appropriately subjected to pulverization treatment, classification treatment, washing treatment, and the like.
  • the pulverization treatment can be performed using a general pulverizer or pulverizer such as a ball mill, vibration mill, or jet mill.
  • boron nitride powder having an orientation index of 15 or less, including aggregated particles composed of agglomerated primary particles of boron nitride.
  • the amount of the boron source and the carbonate used in the decarburization and crystallization step is set to 55% by mass or more and 4% by mass or more, respectively, and an acid containing hydrofluoric acid
  • the uranium content can be reduced while forming agglomerated particles composed of agglomerated primary particles of boron nitride. It is not necessary to implement all of these means for reducing the uranium content, but by combining a plurality of means, it is possible to provide a boron nitride powder with a further reduced uranium content.
  • the orientation index of boron nitride powder means a value measured according to the following method.
  • the X-ray diffraction spectrum of the boron nitride powder is obtained, and from the X-ray diffraction spectrum, the peak intensity I (002) corresponding to the (002) plane and the (100) plane and I(100).
  • the obtained peak intensity is used to calculate the orientation index [I(002)/I(100)] of the boron nitride powder.
  • the X-ray diffractometer for example, "ULTIMA-IV" (product name) manufactured by Rigaku Corporation is used.
  • a boron nitride powder includes agglomerated particles composed of agglomerated primary particles of boron nitride, has an orientation index of 15 or less, and has a uranium content of 20 mass ppb or less.
  • the boron nitride powder may contain primary particles in addition to aggregated particles.
  • the primary particles of boron nitride may be, for example, scale-like hexagonal boron nitride particles.
  • the boron nitride powder Since the boron nitride powder has a uranium content of 20 mass ppb or less, it can be said that it is a material that hardly emits ⁇ -rays. In addition, since the boron nitride powder has an orientation index of 15 or less, according to the boron nitride powder, when at least a part of the aggregated particles collapses during kneading with the resin, and the orientation increases Even so, it is possible to suppress occurrence of large anisotropy in the heat dissipation property and the like of the resin sealing material. Therefore, the boron nitride powder is suitable for use as a resin encapsulant for semiconductor memory devices, which require heat dissipation.
  • the boron nitride powder can be obtained, for example, in the manufacturing method according to the above embodiment, by setting the amount of the boron source and the carbonate used in the decarburization and crystallization step to 55% by mass or more and 4% by mass or more, respectively. can.
  • the uranium content of the boron nitride powder may be, for example, 18 mass ppb or less, 16 mass ppb or less, 14 mass ppb or less, 12 mass ppb or less, 10 mass ppb or less, 7 mass ppb or less, or 5 mass ppb or less.
  • Boron nitride powder having such a uranium content is obtained by, for example, acid treatment, in addition to using amounts of boron source and carbonate of 55% by mass or more and 4% by mass or more, respectively, in the decarburization and crystallization step.
  • the lower limit of the uranium content may be, for example, 5 mass ppb.
  • the uranium content is, for example, 5-20 mass ppb, 5-18 mass ppb, 5-16 mass ppb, 5-14 mass ppb, 5-12 mass ppb, 5-10 mass ppb or 5-7 mass ppb. you can The above content is based on the total mass of the boron nitride powder.
  • the uranium content of boron nitride powder in this specification means a value measured according to the following method.
  • JCRS108 boron nitride powder chemical analysis method 0.5 g of a sample (boron nitride powder) is subjected to pressure acid decomposition in a mixed solution of nitric acid, sulfuric acid and hydrofluoric acid at 180° C. for 18 hours. Thereafter, the solution obtained by pressure acid decomposition is dried on a hot plate to solidify, and the obtained solid content is mixed with nitric acid to obtain a mixed solution.
  • ICP-MS inductively coupled plasma mass spectrometer
  • the orientation index may be 12 or less or 10 or less from the viewpoint of further reducing the influence of the collapse of the aggregated particles.
  • the orientation index may be 3 or higher, 4 or higher, or 6 or higher, and may be 3-15, 4-12, or 6-10.
  • the orientation index of the boron nitride powder can be adjusted, for example, by controlling the growth of primary particles when producing the boron nitride powder.
  • the purity of the boron nitride powder is preferably 98.5% by mass or higher, and may be 99% by mass or higher or 99.5% by mass or higher.
  • the upper limit of the purity of the boron nitride powder is not particularly limited, and may be 100% by mass or 99.5% by mass.
  • the purity of boron nitride powder herein means a value determined by titration, which will be described later.
  • a sample of boron nitride powder is alkali-decomposed with sodium hydroxide, ammonia is distilled from the decomposed solution by a steam distillation method, and collected in an aqueous boric acid solution. This collected liquid is titrated with a normal sulfuric acid solution.
  • the content of nitrogen atoms (N) in the sample is calculated from the titration results. From the obtained nitrogen atom content, the boron nitride content in the sample can be determined based on formula (I), and the purity of the boron nitride powder can be calculated.
  • the formula weight of boron nitride is 24.818 g/mol, and the atomic weight of nitrogen atoms is 14.006 g/mol.
  • Boron nitride content [mass%] in the sample nitrogen atom (N) content [mass%] x 1.772 (I)
  • the aggregated particles contained in the boron nitride powder preferably have a crushing strength of 5 MPa or more from the viewpoint of being difficult to collapse when kneading with the resin.
  • the crushing strength of the aggregated particles may be 8 MPa or more, or 10 MPa or more.
  • the crush strength of the agglomerated particles may be 20 MPa or less, 15 MPa or less, or 12 MPa or less.
  • the crushing strength of the aggregated particles is 20 Mpa or less, at least a part of the aggregated particles appropriately collapses during kneading with the resin, and the generation of voids is easily suppressed. As a result, the resulting resin encapsulant has higher insulation.
  • the crushing strength of the aggregated particles may be, for example, 5-20 MPa, 8-15 MPa or 10-12 MPa.
  • the crushing strength of aggregated particles can be adjusted, for example, by changing the firing conditions.
  • the crushing strength herein is a value measured in accordance with the description of JIS R 1639-5:2007 "Fine ceramics-Method for measuring (granule) properties-Part 5: Single granule crushing strength”.
  • the measurement was performed on 20 or more aggregated particles, and the value at the time when the cumulative destruction rate was 63.2% was calculated.
  • a microcompression tester can be used for the measurement.
  • As the microcompression tester for example, "MCT-W500" (product name) manufactured by Shimadzu Corporation can be used.
  • the average particle size of the boron nitride powder may be, for example, 90 ⁇ m or less, 80 ⁇ m or less, or 70 ⁇ m or less. When the average particle diameter is 90 ⁇ m or less, it becomes possible to make the sealing portion formed by the resin sealing material thinner.
  • the average particle size of the boron nitride powder may be, for example, 10 ⁇ m or more, 20 ⁇ m or more, or 30 ⁇ m or more. When the average particle diameter is 10 ⁇ m or more, the thermal conductivity of the resin sealing material can be further improved. From these points of view, the average particle size of the boron nitride powder may be, for example, 10-90 ⁇ m, 20-80 ⁇ m, or 30-70 ⁇ m.
  • the average particle diameter in this specification means the 50% cumulative diameter (median diameter) in the volume-based cumulative particle size distribution. More specifically, it means the particle diameter (D50) when the cumulative value in the volume-based cumulative particle size distribution obtained by the laser diffraction scattering method for the powder reaches 50%.
  • the laser analysis scattering method is measured according to the method described in ISO 13320:2009.
  • a laser diffraction scattering particle size distribution analyzer or the like can be used.
  • LS-13 320 product name
  • Beckman Coulter, Inc. Beckman Coulter, Inc.
  • the boron nitride powder preferably has a purity of 98.5% by mass or more, an average particle diameter of 10 to 90 ⁇ m, and a crushing strength of aggregated particles of 5 MPa or more, from the viewpoint of the insulating properties of the resin sealing material. .
  • a resin encapsulant according to one embodiment is a resin encapsulant for a semiconductor memory and contains the boron nitride powder according to the above embodiment.
  • resins used for resin sealing materials can be used.
  • resins include liquid crystal polymers, fluororesins, silicone resins, silicone rubbers, acrylic resins, polyolefins (polyethylene, etc.), epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, polyimides, polyamideimides, poly Etherimide, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, wholly aromatic polyester, polysulfone, polyethersulfone, polycarbonate, maleimide-modified resin, ABS (acrylonitrile-butadiene-styrene) resin, AAS (acrylonitrile-acrylic rubber, styrene) resins and AES (acrylonitrile ethylene propylene diene rubber-styrene) resins.
  • the resin content may be, for example, 15% by volume or more, 20% by volume or more, or 30% by volume or more based on the total volume of the resin sealing material.
  • the resin content may be, for example, 60% by volume or less, 50% by volume or less, or 40% by volume or less based on the total volume of the resin sealing material.
  • the resin content may be, for example, 15 to 60% by volume, 20 to 50% by volume, or 30 to 40% by volume based on the total volume of the resin sealing material.
  • the content of the boron nitride powder may be, for example, 30% by volume or more, 40% by volume or more, 50% by volume or more, or 60% by volume or more based on the total volume of the resin sealing material.
  • the content of the boron nitride powder may be, for example, 85% by volume or less, 80% by volume or less, or 70% by volume or less based on the total volume of the resin sealing material.
  • the content of the boron nitride powder is, for example, 30 to 85% by volume, 40 to 85% by volume, 40 to 80% by volume, 50 to 80% by volume, 50 to 70% by volume, based on the total volume of the resin sealing material. , or 60-70% by volume.
  • the resin sealing material may further contain a curing agent for curing the resin in addition to the resin and boron nitride powder.
  • the curing agent can be appropriately selected according to the type of resin.
  • examples of curing agents include phenol novolac compounds, acid anhydrides, amino compounds, imidazole compounds, and the like.
  • the content of the curing agent may be, for example, 0.5 parts by mass or more or 1 part by mass or more, and may be 15 parts by mass or less or 10 parts by mass or less with respect to 100 parts by mass of the resin. It may be up to 15 parts by weight or 1 to 10 parts by weight.
  • Example 1 [Preparation of boron carbide powder] 100 parts by mass of orthoboric acid manufactured by Shin Nippon Denko Co., Ltd. and 35 parts by mass of acetylene black (product name: HS100L) manufactured by Denka Co., Ltd. were mixed using a Henschel mixer. The resulting mixture was filled in a graphite crucible and heated in an arc furnace at 2200° C. for 6 hours under an argon atmosphere to obtain massive boron carbide (B 4 C). The resulting mass was coarsely pulverized with a jaw crusher to obtain coarse powder. The obtained coarse powder was further pulverized by a ball mill having silicon carbide balls (diameter: 10 mm) to obtain pulverized powder.
  • Pulverization by a ball mill was performed for 60 minutes at a rotation speed of 25 rpm. Thereafter, the pulverized powder was classified using a vibrating sieve with an opening of 63 ⁇ m to prepare a boron carbide powder (B 4 C powder) with an average particle size of 20 ⁇ m.
  • the boron carbide powder had a specific surface area of 0.4 m 2 /g and a purity of 98% by mass.
  • the average particle size of the boron carbide powder was measured according to ISO 13320:2009 using a Beckman Coulter laser diffraction scattering method particle size distribution analyzer (equipment name: LS-13 320).
  • the boron carbide powder was not treated with a homogenizer.
  • water was used as a solvent for dispersing the boron carbide powder, and hexametaphosphoric acid was used as a dispersant.
  • a numerical value of 1.33 was used as the refractive index of water, and a numerical value of 2.6 was used as the refractive index of the boron carbide powder.
  • the specific surface area of the boron carbide powder was calculated according to the description of JIS Z 8830:2013 "Method for measuring specific surface area of powder (solid) by gas adsorption", applying the BET single point method using nitrogen gas.
  • a specific surface area measuring device a specific surface area measuring device manufactured by Yuasa Ionics Co., Ltd. (device name: Kantersorb) was used. The measurement was performed after the boron carbide powder was dried and degassed at 300° C. for 15 minutes.
  • the purity of boron carbide powder was calculated from the sum of carbon content and boron content.
  • the amount of carbon was calculated from a combustion infrared absorption method, and the amount of boron was calculated from an ICP emission analysis.
  • the temperature was raised from room temperature to 1000°C at a temperature increase rate of 10°C/min, the temperature was raised from 1000°C to 1950°C at a temperature increase rate of 2°C/min, and held at 1950°C for 5 hours. Firing was performed.
  • the obtained powder was pulverized 20 times with a Henschel mixer, the obtained pulverized product was classified by passing it through a sieve with an opening of 75 ⁇ m, and aggregated particles composed of aggregated primary particles of hexagonal boron nitride. to obtain the boron nitride powder of Example 1.
  • the obtained boron nitride powder had a uranium content of 19 mass ppb, an orientation index of 7, a purity of 99 mass%, and an average particle size of 40 ⁇ m.
  • the strength was 12 Mpa.
  • the uranium content of boron nitride powder was determined by the following method.
  • boron nitride powder chemical analysis method 0.5 g of a sample (boron nitride powder) was subjected to pressure acid decomposition in a mixture of nitric acid, sulfuric acid and hydrofluoric acid at 180° C. for 18 hours. Thereafter, the solution obtained by the pressure acid decomposition was dried on a hot plate to solidify, and the obtained solid content was mixed with nitric acid to obtain a mixed solution.
  • ICP-MS inductively coupled plasma mass spectrometer
  • the orientation index of the boron nitride powder was determined from the measurement results by the powder X-ray diffraction method.
  • boron nitride powder was filled into the concave portion of a glass cell having a concave portion with a depth of 0.2 mm attached to an X-ray diffractometer (manufactured by Rigaku Co., Ltd., product name: ULTIMA-IV), and a powder sample molding machine ( Ameena Tech Co., Ltd., product name: PX700) was used to solidify at a set pressure M to prepare a measurement sample. When the surface of the filling solidified by the molding machine was not smooth, it was smoothed manually before measurement.
  • the peak intensity ratio between the (002) plane and the (100) plane of boron nitride is calculated, and based on this value, the orientation index [I (002 )/I(100)] was determined.
  • the purity of boron nitride powder was determined by the following method. First, boron nitride powder was alkali-decomposed with sodium hydroxide, ammonia was distilled from the decomposed solution by steam distillation, and collected in an aqueous boric acid solution. This collected liquid was subjected to titration with a normal sulfuric acid solution. The content of nitrogen atoms (N) in the boron nitride powder was calculated from the titration results. Based on the obtained nitrogen atom content, the content of boron nitride in the boron nitride powder was determined based on the formula (1), and the purity of the boron nitride powder was calculated.
  • boron nitride 24.818 g/mol, and the atomic weight of nitrogen atoms is 14.006 g/mol.
  • Boron nitride (BN) content [mass%] in the boron nitride powder Nitrogen atom (N) content [mass%] x 1.772 (1)
  • the average particle size of the boron nitride powder was measured according to ISO 13320:2009 using a Beckman Coulter laser diffraction scattering particle size distribution analyzer (device name: LS-13 320).
  • the boron nitride powder was not treated with a homogenizer.
  • water was used as a solvent for dispersing the boron nitride powder, and hexametaphosphoric acid was used as a dispersant.
  • a numerical value of 1.33 was used as the refractive index of water, and a numerical value of 1.80 was used as the refractive index of the boron nitride powder.
  • the crushing strength of agglomerated particles was measured according to the description in JIS R 1639-5:2007 "Fine ceramics-Method for measuring (granule) properties-Part 5: Single granule crushing strength”.
  • a microcompression tester manufactured by Shimadzu Corporation, product name "MCT-W500" was used.
  • the measurement was performed for 20 or more aggregated particles, and the value at the time of cumulative destruction rate of 63.2% was calculated.
  • Example 2 to 4 Boron nitride powders of Examples 2 to 4 were obtained in the same manner as in Example 1, except that the firing temperature and/or firing time in the decarburization and crystallization step were changed as shown in Table 1. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 1 shows the results.
  • Example 5 Pulverization with a ball mill in [Preparation of boron carbide powder] was performed for 100 minutes at a rotation speed of 100 rpm, and then classification was performed using a vibrating sieve with an opening of 34 ⁇ m, and crushing in [Decarburization and crystallization step].
  • a boron nitride powder of Example 5 was obtained in the same manner as in Example 1, except that the subsequent classification was performed using a sieve with an opening of 45 ⁇ m. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 1 shows the results.
  • Comparative Examples 1 and 2 Nitriding of Comparative Examples 1 and 2 was performed in the same manner as in Example 1, except that the amounts of boric acid and sodium carbonate used (based on the total mass of the raw material mixture) in the decarburization and crystallization step were changed to the values shown in Table 1. Boron powder was obtained respectively. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 1 shows the results.
  • Example 6 Boron carbide powder prepared in the same manner as in Example 1 was subjected to acid treatment. Specifically, first, boron carbide powder prepared in the same manner as in Example 1 was prepared. An acid solution was then prepared by mixing a hydrofluoric acid solution and a hydrochloric acid solution. The acid concentration of the acid solution was 40% by mass, and the mass ratio of hydrofluoric acid and hydrochloric acid in the acid solution (mass ratio of HF and HCl) was 1:1 (i.e., hydrogen fluoride in the acid solution Both the acid concentration and the hydrochloric acid concentration were set to 20% by mass.).
  • the acid solution was heated and maintained at 80° C., and boron carbide powder was added thereto and stirred at 80° C. for 5 hours.
  • the boron carbide powder and the acid solution were brought into contact with each other, and the boron carbide powder was acid-treated.
  • decantation was performed, and the operation of adding a new acid solution and performing acid treatment was repeated 15 times.
  • the slurry was then dried to obtain an acid-treated boron carbide powder.
  • the average particle size and purity of the obtained boron carbide powder were measured by the method described in Example 1, the average particle size was 20 ⁇ m and the purity was 99% by mass.
  • Example 2 shows the results.
  • Example 7 A boron nitride powder of Example 7 was obtained in the same manner as in Example 6, except that the firing temperature and firing time in the decarburization and crystallization step were changed as shown in Table 2. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 2 shows the results.
  • Example 8 Same as Example 7 except that the concentration of the acid solution, the treatment temperature (the temperature of the mixture of the boron carbide powder and the acid solution), and the treatment time (stirring time) in the acid treatment step were changed to the values shown in Table 2. Then, the boron nitride powder of Example 8 was obtained. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 2 shows the results. When analyzed in the same manner as uranium, the amount of thorium was 4 mass ppb.
  • Example 9 Except for changing the concentration of the acid solution, the composition of the acid solution, the treatment temperature (the temperature of the mixture of the boron carbide powder and the acid solution), and the treatment time (stirring time) in the acid treatment step to the values shown in Table 2, Boron nitride powder of Example 9 was obtained in the same manner as in Example 6. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 2 shows the results.

Abstract

This method for producing boron nitride powder involves a decarburization crystallization step for producing boron nitride primary particles by baking a raw material mixture including boron carbonitride powder, a boron source, and a carbonate to obtain powder including aggregated particles formed from aggregation of primary particles, wherein, in the decarburization crystallization step, the amount of the boron source used is 55% by mass or more based on the total mass of the raw material mixture, and the amount of the carbonate used is 4% by mass or more based on the total mass of the raw material mixture.

Description

窒化ホウ素粉末の製造方法、窒化ホウ素粉末及び樹脂封止材Method for producing boron nitride powder, boron nitride powder and resin sealing material
　本開示は、窒化ホウ素粉末の製造方法、窒化ホウ素粉末及び樹脂封止材に関する。 The present disclosure relates to a method for producing boron nitride powder, boron nitride powder, and a resin sealing material.
　窒化ホウ素粒子の集合体である窒化ホウ素粉末は、潤滑性、高熱伝導性、絶縁性等を有しており、固体潤滑材、熱伝導性フィラー、絶縁性フィラー等の用途に幅広く利用されている。 Boron nitride powder, which is an aggregate of boron nitride particles, has lubricating properties, high thermal conductivity, insulating properties, etc., and is widely used for applications such as solid lubricants, thermally conductive fillers, and insulating fillers. .
　窒化ホウ素粒子（特に六方晶窒化ホウ素粒子）は、熱伝導率の異方性が大きいことから、窒化ホウ素の一次粒子を凝集させて窒化ホウ素凝集粒子とすることで、一次粒子の配向による熱伝導率の異方性を抑えることが検討されている（例えば特許文献１等）。 Boron nitride particles (especially hexagonal boron nitride particles) have a large anisotropy of thermal conductivity. Suppressing the anisotropy of the modulus has been studied (for example, Patent Document 1, etc.).
特開２０１６－１３５７３１号公報JP 2016-135731 A
　熱伝導率の向上が求められる材料の一つとして、半導体メモリ素子用の樹脂封止材が挙げられる。半導体メモリ素子用の樹脂封止材には、半導体メモリ素子のソフトエラーを引き起こさないように、α線を放出し難い材料を使用する必要がある。そのような材料としては、とりわけ、ウラン含有量の少ない材料を用いることが望ましい。 One of the materials that require improved thermal conductivity is the resin encapsulant for semiconductor memory devices. A resin sealing material for a semiconductor memory element needs to be made of a material that hardly emits α-rays so as not to cause soft errors in the semiconductor memory element. As such a material, it is particularly desirable to use a material with a low uranium content.
　一方、上記特許文献１に開示されるような凝集粒子は、通常、微量のウランを含有している。また、その構造上、凝集粒子の内部に取り込まれたウランは除去され難い。そのため、凝集粒子の形成後に該粒子中のウラン含有量を低減することは難しい。 On the other hand, aggregated particles as disclosed in Patent Document 1 usually contain a small amount of uranium. Also, due to its structure, the uranium trapped inside the agglomerated particles is difficult to remove. Therefore, it is difficult to reduce the uranium content in agglomerated particles after they are formed.
　そこで、本開示の一側面は、窒化ホウ素の一次粒子が凝集して構成される凝集粒子を含む窒化ホウ素粉末であって、ウラン含有量が低減された窒化ホウ素粉末の製造方法を提供することを目的とする。また、本開示の他の一側面は、窒化ホウ素の一次粒子が凝集して構成される凝集粒子を含み、ウラン含有量が充分に低い窒化ホウ素粉末を提供することを目的とする。また、本開示の他の一側面は、上記側面の窒化ホウ素粉末を含有する半導体メモリ素子用の樹脂封止材を提供することを目的とする。 Therefore, one aspect of the present disclosure is to provide a method for producing a boron nitride powder containing agglomerated particles composed of agglomerated primary particles of boron nitride and having a reduced uranium content. aim. Another object of the present disclosure is to provide a boron nitride powder containing agglomerated particles composed of agglomerated primary particles of boron nitride and having a sufficiently low uranium content. Another object of the present disclosure is to provide a resin encapsulant for a semiconductor memory device containing the boron nitride powder of the above aspect.
　本開示は、少なくとも下記［１］～［９］を提供する。 The present disclosure provides at least [1] to [9] below.
［１］　炭窒化ホウ素粉末とホウ素源と炭酸塩とを含む原料混合物を焼成することによって、窒化ホウ素の一次粒子を生成し、前記一次粒子が凝集して構成される凝集粒子を含む粉末を得る脱炭結晶化工程を含み、前記脱炭結晶化工程において、前記ホウ素源の使用量が、前記原料混合物の全質量を基準として、５５質量％以上であり、前記炭酸塩の使用量が、前記原料混合物の全質量を基準として、４質量％以上である、窒化ホウ素粉末の製造方法。 [1] By firing a raw material mixture containing a boron carbonitride powder, a boron source, and a carbonate, primary particles of boron nitride are generated, and a powder containing aggregated particles composed of the primary particles is obtained. A decarburized crystallization step is included, and in the decarburized crystallization step, the amount of the boron source used is 55% by mass or more based on the total mass of the raw material mixture, and the amount of the carbonate used is A method for producing a boron nitride powder having a content of 4% by mass or more based on the total mass of the raw material mixture.
［２］　前記脱炭結晶化工程における焼成温度が１８００℃以上であり、焼成時間が８時間以上である、［１］に記載の窒化ホウ素粉末の製造方法。 [2] The method for producing boron nitride powder according to [1], wherein the firing temperature in the decarburization and crystallization step is 1800°C or higher and the firing time is 8 hours or longer.
［３］　前記脱炭結晶化工程における焼成温度が２０００℃以上であり、焼成時間が４時間以上である、［１］に記載の窒化ホウ素粉末の製造方法。 [3] The method for producing boron nitride powder according to [1], wherein the firing temperature in the decarburization and crystallization step is 2000°C or higher, and the firing time is 4 hours or longer.
［４］　前記炭窒化ホウ素粉末を準備する準備工程を更に含み、前記準備工程は、炭化ホウ素粉末にフッ化水素酸を含む酸溶液を接触させて、前記炭化ホウ素粉末を酸処理する酸処理工程と、酸処理された前記炭化ホウ素粉末を窒素加圧雰囲気下で焼成する加圧窒化工程と、を含む、［１］～［３］のいずれかに記載の窒化ホウ素粉末の製造方法。 [4] A preparatory step of preparing the boron carbonitride powder is further included, wherein the preparatory step is an acid treatment step of contacting the boron carbide powder with an acid solution containing hydrofluoric acid to acid-treat the boron carbide powder. and a pressurized nitriding step of firing the acid-treated boron carbide powder in a pressurized nitrogen atmosphere.
［５］　前記酸溶液が、前記フッ化水素酸を含む混酸であり、前記混酸中の全酸成分に占めるフッ化水素酸の割合が、１０質量％以上である、［４］に記載の窒化ホウ素粉末の製造方法。 [5] Nitriding according to [4], wherein the acid solution is a mixed acid containing the hydrofluoric acid, and the proportion of hydrofluoric acid in the total acid components in the mixed acid is 10% by mass or more. A method for producing boron powder.
［６］　前記酸処理工程における処理温度が６０℃以上であり、前記酸処理工程における処理時間が３時間以上であり、前記酸溶液の酸濃度が２０質量％以上である、［４］又は［５］に記載の窒化ホウ素粉末の製造方法。 [6] The treatment temperature in the acid treatment step is 60°C or higher, the treatment time in the acid treatment step is 3 hours or longer, and the acid concentration of the acid solution is 20% by mass or higher, [4] or [ 5], the method for producing a boron nitride powder.
［７］　窒化ホウ素の一次粒子が凝集して構成される凝集粒子を含み、配向性指数が１５以下であり、ウラン含有量が２０質量ｐｐｂ以下である、窒化ホウ素粉末。 [7] A boron nitride powder containing agglomerated particles composed of agglomerated primary particles of boron nitride, having an orientation index of 15 or less and a uranium content of 20 mass ppb or less.
［８］　純度が９８．５質量％以上であり、平均粒子径が１０～９０μｍであり、前記凝集粒子の圧壊強度が５ＭＰａ以上である、［７］に記載の窒化ホウ素粉末。 [8] The boron nitride powder according to [7], which has a purity of 98.5% by mass or more, an average particle size of 10 to 90 μm, and a crushing strength of the aggregated particles of 5 MPa or more.
［９］　［７］又は［８］に記載の窒化ホウ素粉末を含む、半導体メモリ素子用の樹脂封止材。 [9] A resin sealing material for a semiconductor memory device, containing the boron nitride powder according to [7] or [8].
　本開示の一側面によれば、窒化ホウ素の一次粒子が凝集して構成される凝集粒子を含む窒化ホウ素粉末であって、ウラン含有量が低減された窒化ホウ素粉末の製造方法を提供することができる。また、本開示の他の一側面によれば、窒化ホウ素の一次粒子が凝集して構成される凝集粒子を含み、ウラン含有量が充分に低い窒化ホウ素粉末を提供することができる。また、本開示の他の一側面によれば、上記側面の窒化ホウ素粉末を含有する半導体メモリ素子用の樹脂封止材を提供することができる。 According to one aspect of the present disclosure, it is possible to provide a method for producing a boron nitride powder containing agglomerated particles composed of agglomerated primary particles of boron nitride and having a reduced uranium content. can. Further, according to another aspect of the present disclosure, it is possible to provide a boron nitride powder containing agglomerated particles composed of agglomerated primary particles of boron nitride and having a sufficiently low uranium content. Further, according to another aspect of the present disclosure, it is possible to provide a resin encapsulant for a semiconductor memory device containing the boron nitride powder of the aspect described above.
　本明細書において例示する材料は、特に断らない限り、１種を単独で又は２種以上を組み合わせて用いることができる。組成物中の各成分の含有量は、組成物中の各成分に該当する物質が複数存在する場合には、特に断らない限り、組成物中に存在する当該複数の物質の合計量を意味する。本明細書中、「～」を用いて示された数値範囲は、「～」の前後に記載される数値をそれぞれ最小値及び最大値として含む範囲を示す。また、特に明示しない限り、「～」の前後に記載される数値の単位は同じである。本明細書中に記載されている数値範囲において、その数値範囲の上限値又は下限値は、実施例に示されている値に置き換えてもよい。また、個別に記載した上限値及び下限値は任意に組み合わせ可能である。 The materials exemplified in this specification can be used singly or in combination of two or more unless otherwise specified. The content of each component in the composition means the total amount of the multiple substances present in the composition unless otherwise specified when there are multiple substances corresponding to each component in the composition. . In this specification, a numerical range indicated using "to" indicates a range including the numerical values before and after "to" as the minimum and maximum values, respectively. Also, unless otherwise specified, the units of numerical values described before and after "-" are the same. In the numerical ranges described herein, the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples. Moreover, the upper limit value and the lower limit value described individually can be combined arbitrarily.
　以下、本開示の実施形態を説明する。ただし、以下の実施形態は、本開示を説明するための例示であり、本開示を以下の内容に限定する趣旨ではない。 The embodiments of the present disclosure will be described below. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents.
＜窒化ホウ素粉末の製造方法＞
　一実施形態に係る窒化ホウ素粉末の製造方法は、炭窒化ホウ素粉末とホウ素源と炭酸塩とを含む原料混合物を焼成することによって、窒化ホウ素の一次粒子を生成し、該一次粒子が凝集して構成される凝集粒子を含む粉末を得る脱炭結晶化工程を含む。 <Method for producing boron nitride powder>
A method for producing a boron nitride powder according to one embodiment includes firing a raw material mixture containing a boron carbonitride powder, a boron source, and a carbonate to produce primary particles of boron nitride, and the primary particles are aggregated. including a decarburizing crystallization step to obtain a powder comprising aggregated particles that are structured.
　本発明者らの検討の結果明らかになったことであるが、上記脱炭結晶化工程において、ホウ素源及び炭酸塩を使用するとともに、これらの使用量を所定量以上とすることで、最終的に得られる窒化ホウ素粉末中のウラン含有量を低減することができる。具体的には、ホウ素源の使用量が、原料混合物の全質量を基準として、５５質量％以上であり、上記結晶化工程での炭酸塩の使用量が、原料混合物の全質量を基準として、４質量％以上であると、ウラン含有量が低減される。 As a result of the studies of the present inventors, it has become clear that in the above decarburization and crystallization step, by using a boron source and a carbonate and setting the amount of these used to a predetermined amount or more, the final It is possible to reduce the uranium content in the boron nitride powder obtained in Specifically, the amount of the boron source used is 55% by mass or more based on the total mass of the raw material mixture, and the amount of the carbonate used in the crystallization step is, based on the total mass of the raw material mixture, When it is 4% by mass or more, the uranium content is reduced.
　一実施形態に係る窒化ホウ素粉末の製造方法は、上記脱炭結晶化工程で使用される炭窒化ホウ素粉末を準備する準備工程を更に含んでいてよい。準備工程は、例えば、炭化ホウ素粉末を窒素加圧雰囲気下で焼成する加圧窒化工程を含む。準備工程は、炭化ホウ素粉末にフッ化水素酸を含む酸溶液を接触させて炭化ホウ素粉末を酸処理する酸処理工程（第１の酸処理工程）を更に含んでいてもよい。準備工程が第１の酸処理工程を含む場合、加圧窒化工程では、酸処理工程を経て得られる酸処理された炭化ホウ素粉末を用いる。準備工程は、炭窒化ホウ素粉末にフッ化水素酸を含む酸溶液を接触させて炭窒化ホウ素粉末を酸処理する酸処理工程（第２の酸処理工程）を更に含んでいてもよい。第２の酸処理工程で使用される炭窒化ホウ素粉末は加圧窒化工程を経て得られる粉末であってよい。準備工程が第２の酸処理工程を含む場合、脱炭結晶化工程では、酸処理工程を経て得られる酸処理された炭窒化ホウ素粉末を用いる。第１の酸処理工程及び／又は第２の酸処理工程を実施することで、最終的に得られる窒化ホウ素粉末中のウラン含有量を低減することができる。したがって、上記脱炭結晶化工程におけるホウ素源及び炭酸塩の使用量をそれぞれ上記所定範囲とした上で、第１の酸処理工程及び／又は第２の酸処理工程を実施することで、最終的に得られる窒化ホウ素粉末中のウラン含有量をより一層低減することができる。 The method for producing boron nitride powder according to one embodiment may further include a preparation step of preparing the boron carbonitride powder used in the decarburization and crystallization step. The preparatory step includes, for example, a pressurized nitriding step of firing the boron carbide powder in a pressurized nitrogen atmosphere. The preparation step may further include an acid treatment step (first acid treatment step) of acid-treating the boron carbide powder by contacting the boron carbide powder with an acid solution containing hydrofluoric acid. When the preparation step includes the first acid treatment step, the pressurized nitriding step uses acid-treated boron carbide powder obtained through the acid treatment step. The preparation step may further include an acid treatment step (second acid treatment step) of acid-treating the boron carbonitride powder by contacting the boron carbonitride powder with an acid solution containing hydrofluoric acid. The boron carbonitride powder used in the second acid treatment step may be a powder obtained through a pressure nitriding step. When the preparation step includes the second acid treatment step, the acid-treated boron carbonitride powder obtained through the acid treatment step is used in the decarburization and crystallization step. By performing the first acid treatment step and/or the second acid treatment step, the uranium content in the finally obtained boron nitride powder can be reduced. Therefore, the amounts of the boron source and the carbonate used in the decarburization and crystallization step are set within the predetermined ranges, respectively, and then the first acid treatment step and/or the second acid treatment step are performed to finally obtain The uranium content in the boron nitride powder obtained in 1 can be further reduced.
　以下、窒化ホウ素粉末の製造方法における各工程を詳細に説明する。ただし、第２の酸処理工程は、炭化ホウ素粉末に代えて炭窒化ホウ素粉末を用いる点を除き、第１の酸処理工程と同様であるため、第２の酸処理工程の説明は省略する。 Each step in the method for producing boron nitride powder will be described in detail below. However, since the second acid treatment step is the same as the first acid treatment step except that boron carbonitride powder is used instead of the boron carbide powder, description of the second acid treatment step is omitted.
（準備工程）
［第１の酸処理工程］
　第１の酸処理工程では、炭化ホウ素粉末（Ｂ４Ｃ粉末）にフッ化水素酸を含む酸溶液を接触させることで、炭化ホウ素粒子における酸溶液との接触部分を溶解させる。これにより、炭化ホウ素粉末中に存在するウランの少なくとも一部（特に、炭化ホウ素粒子の表面近傍に存在するウラン）が除去される。 (Preparation process)
[First acid treatment step]
In the first acid treatment step, the boron carbide powder (B 4 C powder) is brought into contact with an acid solution containing hydrofluoric acid, thereby dissolving the portions of the boron carbide particles that come into contact with the acid solution. This removes at least part of the uranium present in the boron carbide powder (in particular, uranium present near the surface of the boron carbide particles).
　炭化ホウ素粉末は、炭化ホウ素粒子の集合体である。炭化ホウ素粉末の純度（炭化ホウ素の含有量）は、例えば、９７質量％以上であることが好ましい。炭化ホウ素粉末としては、市販の炭化ホウ素粉末を使用してよく、別途調製された炭化ホウ素粉末を使用してもよい。炭化ホウ素粉末は、例えば、ホウ酸とアセチレンブラックとを混合した後、不活性ガス雰囲気中、１８００～２４００℃にて、１～１０時間加熱し、炭化ホウ素塊を得る工程と、得られた炭化ホウ素塊を、粉砕後、篩分けし、洗浄、不純物除去、乾燥等を適宜行い、炭化ホウ素粉末を調製する工程とを含む方法によって得ることができる。炭化ホウ素粉末としては、酸処理時のウランの除去効率が向上する観点から、平均粒子径１０μｍ以上（例えば１０～５０μｍ）の炭化ホウ素粉末を用いることが好ましい。同様の観点から、比表面積１ｍ２/ｇ以下（例えば０．０５～１ｍ２/ｇ）の炭化ホウ素粉末を用いることが好ましい。 Boron carbide powder is an aggregate of boron carbide particles. The purity of the boron carbide powder (content of boron carbide) is preferably, for example, 97% by mass or more. As the boron carbide powder, commercially available boron carbide powder may be used, or separately prepared boron carbide powder may be used. Boron carbide powder, for example, after mixing boric acid and acetylene black, is heated in an inert gas atmosphere at 1800 to 2400 ° C. for 1 to 10 hours to obtain a boron carbide mass; A boron lump can be obtained by a method including steps of pulverizing, sieving, washing, removing impurities, drying, etc. as appropriate to prepare a boron carbide powder. As the boron carbide powder, it is preferable to use boron carbide powder having an average particle size of 10 μm or more (for example, 10 to 50 μm) from the viewpoint of improving the removal efficiency of uranium during acid treatment. From the same point of view, it is preferable to use boron carbide powder having a specific surface area of 1 m 2 /g or less (for example, 0.05 to 1 m 2 /g).
　酸溶液は、酸成分としてフッ化水素酸を含む水溶液である。フッ化水素の水溶液をフッ化水素酸と呼ぶことがあるが、本明細書では、水溶液（酸溶液）中に含まれる酸成分のうち、ＨＦで表される化合物をフッ化水素酸という。また、酸成分は、水に溶解して水素イオンを放出する物質と定義される。 The acid solution is an aqueous solution containing hydrofluoric acid as an acid component. An aqueous solution of hydrogen fluoride is sometimes referred to as hydrofluoric acid, but in this specification, among the acid components contained in the aqueous solution (acid solution), a compound represented by HF is referred to as hydrofluoric acid. Also, an acid component is defined as a substance that dissolves in water and releases hydrogen ions.
　酸溶液中のフッ化水素酸の濃度は、ウランの除去効率を向上させる観点から、０．１質量％以上であってよく、１質量％以上、２質量％以上、３質量％以上又は１０質量％以上であってもよい。酸溶液中のフッ化水素酸の濃度は、製造コスト及び安全性の観点から、５０質量％以下であってよく、４５質量％以下、４０質量％以下又は３０質量％以下であってもよい。これらの観点から、酸溶液中のフッ化水素酸の濃度は、例えば、０．１～５０質量％、１～５０質量％、２～４５質量％、３～４０質量％又は１０～３０質量％であってよい。なお、上記フッ化水素酸の濃度は、酸溶液の全質量を基準とする、フッ化水素酸（ＨＦ）の含有量を意味する。 From the viewpoint of improving the uranium removal efficiency, the concentration of hydrofluoric acid in the acid solution may be 0.1% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, or 10% by mass. % or more. The concentration of hydrofluoric acid in the acid solution may be 50% by mass or less, 45% by mass or less, 40% by mass or less, or 30% by mass or less from the viewpoint of production cost and safety. From these points of view, the concentration of hydrofluoric acid in the acid solution is, for example, 0.1 to 50% by mass, 1 to 50% by mass, 2 to 45% by mass, 3 to 40% by mass, or 10 to 30% by mass. can be The concentration of hydrofluoric acid means the content of hydrofluoric acid (HF) based on the total mass of the acid solution.
　酸溶液は、フッ化水素酸以外の酸成分を更に含む混酸であってもよい。この場合、酸溶液中の全酸成分に占めるフッ化水素酸の割合は、ウランの除去効率を向上させる観点から、４質量％以上であってよく、１０質量％以上、２０質量％以上、３０質量％以上又は４０質量％以上であってもよい。全酸成分に占めるフッ化水素酸の割合は、製造コスト及び安全性の観点から、８０質量％以下であってよく、７０質量％以下又は６０質量％以下であってもよい。これらの観点から、全酸成分に占めるフッ化水素酸の割合は、例えば、４～８０質量％、１０～７０質量％、２０～６０質量％、３０～６０質量％又は４０～６０質量％であってよい。 The acid solution may be a mixed acid that further contains an acid component other than hydrofluoric acid. In this case, the ratio of hydrofluoric acid to all acid components in the acid solution may be 4% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, from the viewpoint of improving the uranium removal efficiency. It may be at least 40% by mass or at least 40% by mass. The proportion of hydrofluoric acid in all acid components may be 80% by mass or less, 70% by mass or less, or 60% by mass or less from the viewpoint of production cost and safety. From these viewpoints, the proportion of hydrofluoric acid in the total acid component is, for example, 4 to 80% by mass, 10 to 70% by mass, 20 to 60% by mass, 30 to 60% by mass, or 40 to 60% by mass. It's okay.
　酸溶液に含まれ得るフッ化水素酸以外の酸成分としては、例えば、塩酸（ＨＣｌ）、硝酸（ＨＮＯ３）、硫酸（ＨＳＯ４）等が挙げられる。これらの中でも、ウランの除去効率を向上させる観点から、塩酸が好ましく用いられる。 Acid components other than hydrofluoric acid that can be contained in the acid solution include, for example, hydrochloric acid (HCl), nitric acid (HNO 3 ), sulfuric acid (HSO 4 ), and the like. Among these, hydrochloric acid is preferably used from the viewpoint of improving the removal efficiency of uranium.
　酸溶液中の塩酸の濃度は、効率的に除去を進める観点から、２質量％以上であってよく、３質量％以上、５質量％以上、７質量％以上、１０質量％以上、２０質量％以上、３０質量％以上又は４０質量％以上であってもよい。酸溶液中の塩酸の濃度は、製造コスト及び安全性の観点から、６０質量％以下であってよく、５０質量％以下、３５質量％以下、３０質量％以下又は２５質量％以下であってもよい。これらの観点から、酸溶液中の塩酸の濃度は、例えば、２～６０質量％、３～６０質量％、５～６０質量％、７～６０質量％、１０～６０質量％、２０～６０質量％、３０～６０質量％又は４０～６０質量％であってよく、５～３５質量％、７～３０質量％又は１０～２５質量％であってもよい。なお、上記塩酸の濃度は、酸溶液の全質量を基準とする、塩酸（ＨＣｌ）の含有量を意味する。 From the viewpoint of efficient removal, the concentration of hydrochloric acid in the acid solution may be 2% by mass or more, 3% by mass or more, 5% by mass or more, 7% by mass or more, 10% by mass or more, and 20% by mass. Above, it may be 30% by mass or more, or 40% by mass or more. From the viewpoint of production cost and safety, the concentration of hydrochloric acid in the acid solution may be 60% by mass or less, 50% by mass or less, 35% by mass or less, 30% by mass or less, or 25% by mass or less. good. From these points of view, the concentration of hydrochloric acid in the acid solution is, for example, 2 to 60% by mass, 3 to 60% by mass, 5 to 60% by mass, 7 to 60% by mass, 10 to 60% by mass, 20 to 60% by mass. %, 30-60% by weight or 40-60% by weight, and may be 5-35% by weight, 7-30% by weight or 10-25% by weight. The concentration of hydrochloric acid means the content of hydrochloric acid (HCl) based on the total mass of the acid solution.
　酸溶液の酸濃度は、ウランの除去効率を向上させる観点から、２質量％以上であってよく、３質量％以上、５質量％以上、１０質量％以上、２０質量％以上、３０質量％以上又は４０質量％以上であってもよい。酸溶液の酸濃度は、製造コスト及び安全性の観点から、５０質量％以下であってよく、４５質量％以下又は４０質量％以下であってもよい。これらの観点から、酸溶液の酸濃度は、例えば、２～５０質量％、３～４５質量％、５～４０質量％、１０～５０質量％、２０～５０質量％、３０～５０質量％又は４０～５０質量％であってよい。なお、上記酸濃度は、酸溶液の全質量を基準とする、全酸成分の含有量を意味する。 From the viewpoint of improving the uranium removal efficiency, the acid concentration of the acid solution may be 2% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more. Alternatively, it may be 40% by mass or more. The acid concentration of the acid solution may be 50% by mass or less, 45% by mass or less, or 40% by mass or less from the viewpoint of production cost and safety. From these viewpoints, the acid concentration of the acid solution is, for example, 2 to 50% by mass, 3 to 45% by mass, 5 to 40% by mass, 10 to 50% by mass, 20 to 50% by mass, 30 to 50% by mass, or It may be 40 to 50% by mass. The acid concentration means the content of all acid components based on the total mass of the acid solution.
　炭化ホウ素粉末に酸溶液を接触させる方法は、特に限定されないが、例えば、炭化ホウ素粉末を酸溶液中に投入すること等により炭化ホウ素粉末と酸溶液とを混合する方法、炭化ホウ素粉末に酸溶液を連続的に注液する方法などが挙げられる。炭化ホウ素粉末と酸溶液とを混合する方法では、ウランの除去効率を向上させる観点から、炭化ホウ素粉末と酸溶液とを含む混合液を撹拌してよい。攪拌は、例えば、撹拌機、マグネットスターラー、ディスパーサー等を用いて行うことができる。炭化ホウ素粉末と酸溶液とを混合する方法により炭化ホウ素粉末の酸処理を行う場合、炭化ホウ素粉末の酸処理を複数回繰り返し行ってもよい。例えば、炭化ホウ素粉末と酸溶液とを混合し、一定時間経過した後に、酸溶液から炭化ホウ素粉末を分離し、分離された炭化ホウ素粉末を再度新たな酸溶液と混合する一連の操作を繰り返し行ってもよい。酸溶液の使用量は、例えば、炭化ホウ素粉末１００質量部に対して、８０質量部以上であってよく、５００質量部以下であってよく、８０～５００質量部であってよい。 The method of contacting the boron carbide powder with the acid solution is not particularly limited, but for example, a method of mixing the boron carbide powder and the acid solution by putting the boron carbide powder into the acid solution, or a method of mixing the boron carbide powder with the acid solution. and a method of continuously injecting. In the method of mixing the boron carbide powder and the acid solution, the mixed liquid containing the boron carbide powder and the acid solution may be stirred from the viewpoint of improving the uranium removal efficiency. Stirring can be performed using, for example, a stirrer, magnetic stirrer, disperser, or the like. When the boron carbide powder is acid-treated by a method of mixing the boron carbide powder and the acid solution, the acid treatment of the boron carbide powder may be repeated multiple times. For example, a series of operations of mixing boron carbide powder and an acid solution, separating the boron carbide powder from the acid solution after a certain period of time has passed, and mixing the separated boron carbide powder again with a new acid solution is repeated. may The amount of the acid solution used may be, for example, 80 parts by mass or more, 500 parts by mass or less, or 80 to 500 parts by mass with respect to 100 parts by mass of the boron carbide powder.
　酸処理工程における処理温度は、ウランの除去効率を向上させる観点から、４０℃以上であってよく、６０℃以上又は７５℃以上であってもよい。酸処理工程における処理温度は、フッ化水素の揮発による処理効率の低下を抑制する観点及び安全性の観点から、９５℃以下であってよく、９２℃以下又は９０℃以下であってもよい。これらの観点から、酸処理工程における処理温度は、例えば、４０～９５℃、６０～９２℃又は７５～９０℃であってよい。なお、上記処理温度は、酸処理時に炭化ホウ素粉末に接触させる酸溶液の温度を示している。炭化ホウ素粉末と酸溶液とを混合する方法により炭化ホウ素粉末の酸処理を行う場合、上記処理温度は、炭化ホウ素粉末と酸溶液とを含む混合液の温度といいかえてよい。 The treatment temperature in the acid treatment step may be 40°C or higher, 60°C or higher, or 75°C or higher from the viewpoint of improving the uranium removal efficiency. The treatment temperature in the acid treatment step may be 95° C. or lower, 92° C. or lower, or 90° C. or lower from the viewpoint of suppressing deterioration in treatment efficiency due to volatilization of hydrogen fluoride and from the viewpoint of safety. From these points of view, the treatment temperature in the acid treatment step may be, for example, 40-95°C, 60-92°C or 75-90°C. The above treatment temperature indicates the temperature of the acid solution that is brought into contact with the boron carbide powder during the acid treatment. When the boron carbide powder is acid-treated by mixing the boron carbide powder and the acid solution, the treatment temperature can be said to be the temperature of the mixed liquid containing the boron carbide powder and the acid solution.
　酸処理工程における処理時間は、ウランの除去量を増加させる観点から、１時間以上であってよく、２時間以上、３時間以上又は５時間以上であってもよい。酸処理工程における処理時間は、製造コスト及び安全性の観点から、１５時間以下であってよく、１２時間以下又は１０時間以下であってもよい。これらの観点から、酸処理工程における処理時間は、例えば、１～１５時間、２～１２時間、３～１０時間又は５～１０時間であってよい。なお、上記処理時間は、炭化ホウ素粉末と酸溶液との接触時間を示している。 From the viewpoint of increasing the amount of uranium removed, the treatment time in the acid treatment step may be 1 hour or more, 2 hours or more, 3 hours or more, or 5 hours or more. The treatment time in the acid treatment step may be 15 hours or less, 12 hours or less, or 10 hours or less from the viewpoint of production cost and safety. From these points of view, the treatment time in the acid treatment step may be, for example, 1 to 15 hours, 2 to 12 hours, 3 to 10 hours, or 5 to 10 hours. The above treatment time indicates the contact time between the boron carbide powder and the acid solution.
　ウランの除去量をより一層増加させる観点では、酸処理工程における処理温度を６０℃以上とし、酸処理工程における処理時間を３時間以上とすることが好ましく、酸処理工程における処理温度を６０℃以上とし、酸処理工程における処理時間を３時間以上とし、酸溶液の酸濃度を２０質量％以上とすることがより好ましい。 From the viewpoint of further increasing the amount of uranium removed, it is preferable that the treatment temperature in the acid treatment step is 60° C. or higher and the treatment time in the acid treatment step is 3 hours or longer, and the treatment temperature in the acid treatment step is 60° C. or higher. More preferably, the treatment time in the acid treatment step is 3 hours or more, and the acid concentration of the acid solution is 20% by mass or more.
［加圧窒化工程］
　加圧窒化工程では、炭化ホウ素粉末を窒素加圧雰囲気下で焼成することで、炭化ホウ素を窒化させ、炭窒化ホウ素を含む焼成物を得る。得られる焼成物は、六方晶炭窒化ホウ素を高純度で含有する傾向がある。炭化ホウ素粉末としては、上記第１の酸処理工程で使用される炭化ホウ素粉末として例示したものと同じものが挙げられる。第１の酸処理工程を実施する場合には、第１の酸処理工程を経て得られる、酸処理された炭化ホウ素粉末が用いられる。 [Pressure nitriding step]
In the pressurized nitriding step, the boron carbide powder is sintered in a pressurized nitrogen atmosphere to nitride the boron carbide and obtain a sintered product containing boron carbonitride. The resulting fired product tends to contain hexagonal boron carbonitride with high purity. Examples of the boron carbide powder include those exemplified as the boron carbide powder used in the first acid treatment step. When carrying out the first acid treatment step, acid-treated boron carbide powder obtained through the first acid treatment step is used.
　加圧窒化工程における焼成温度は、脱炭結晶化工程における焼成温度よりも高いことが好ましい。加圧窒化工程における焼成温度は、例えば、１９００～２２００℃、２０００～２２００℃又は２１００～２２００℃であってよい。焼成温度を上記範囲内とすることで、炭窒化ホウ素の結晶性を高め、六方晶炭窒化ホウ素の割合を高めることができる。加圧窒化工程における焼成時間は、窒化が充分に進む範囲であれば特に限定されず、例えば、６～３０時間、８～２５時間又は１０～２０時間であってよい。 The firing temperature in the pressurized nitriding step is preferably higher than the firing temperature in the decarburization and crystallization step. The firing temperature in the pressurized nitriding step may be, for example, 1900-2200°C, 2000-2200°C or 2100-2200°C. By setting the firing temperature within the above range, the crystallinity of the boron carbonitride can be enhanced and the proportion of hexagonal boron carbonitride can be increased. The baking time in the pressurized nitriding step is not particularly limited as long as the nitriding is sufficiently progressed, and may be, for example, 6 to 30 hours, 8 to 25 hours, or 10 to 20 hours.
　加圧窒化工程における圧力（雰囲気圧力）は、例えば、０．６～１ＭＰａ、０．７～１ＭＰａ又は０．８～１ＭＰａであってよい。圧力を上記範囲内とすることで、製造コストを抑えつつ、炭化ホウ素の窒化を効率よく充分に進行させることができる。なお、上記圧力はゲージ圧を示している。 The pressure (atmospheric pressure) in the pressurized nitriding step may be, for example, 0.6 to 1 MPa, 0.7 to 1 MPa, or 0.8 to 1 MPa. By setting the pressure within the above range, the nitriding of boron carbide can be efficiently and sufficiently progressed while suppressing the manufacturing cost. Note that the above pressure indicates a gauge pressure.
　加圧窒化工程における窒素加圧雰囲気の窒素ガス濃度は、例えば、９５体積％以上、９８体積％以上又は９９．９体積％以上であってよい。窒素ガス濃度の上限値は１００体積％である。窒素ガス濃度を上記範囲内とすることで、炭化ホウ素の窒化をより穏和な条件で行うことができる。なお、上記窒素ガス濃度は、標準状態における体積に基づく濃度である。 The nitrogen gas concentration of the nitrogen pressurized atmosphere in the pressurized nitriding step may be, for example, 95% by volume or more, 98% by volume or more, or 99.9% by volume or more. The upper limit of the nitrogen gas concentration is 100% by volume. By setting the nitrogen gas concentration within the above range, boron carbide can be nitrided under milder conditions. The above nitrogen gas concentration is the concentration based on the volume in the standard state.
　加圧窒化工程で得られた焼成物は、そのまま脱炭結晶化工程に使用してよく、粉砕処理、分級処理、洗浄処理、加熱処理（例えば酸素を含む雰囲気下での酸化処理）等を適宜行ってから、脱炭結晶化工程に使用してもよい。粉砕処理は、ボールミル、振動ミル、ジェットミル等の一般的な粉砕機又は解砕機を用いて行うことができる。なお、本明細書における「粉砕」には「解砕」も包まれる。 The fired product obtained in the pressurized nitriding step may be used as it is in the decarburization and crystallization step, and may be subjected to pulverization treatment, classification treatment, washing treatment, heat treatment (for example, oxidation treatment in an atmosphere containing oxygen), etc. as appropriate. It may be used in the decarburization and crystallization step after being carried out. The pulverization treatment can be performed using a general pulverizer or pulverizer such as a ball mill, vibration mill, or jet mill. In addition, "pulverization" in this specification also includes "crushing".
（脱炭結晶化工程）
　脱炭結晶化工程では、炭窒化ホウ素粉末（Ｂ４ＣＮ４粉末）をホウ素源及び炭酸塩とともに焼成することで、炭窒化ホウ素を脱炭化させるとともに、窒化ホウ素の結晶化度を高めることができる。その結果、窒化ホウ素の一次粒子が凝集した凝集粒子を含む窒化ホウ素粉末（ＢＮ粉末）が得られる。この方法で得られる窒化ホウ素粉末中の窒化ホウ素は、通常、六方晶窒化ホウ素であり、鱗片状である六方晶窒化ホウ素の一次粒子が凝集した凝集粒子を含む。 (Decarburization crystallization step)
In the decarburization and crystallization step, the boron carbonitride powder (B 4 CN 4 powder) is fired together with a boron source and a carbonate, thereby decarburizing the boron carbonitride and increasing the crystallinity of the boron nitride. . As a result, a boron nitride powder (BN powder) containing agglomerated particles in which primary particles of boron nitride are agglomerated is obtained. The boron nitride in the boron nitride powder obtained by this method is usually hexagonal boron nitride, and contains aggregated particles in which primary particles of scale-like hexagonal boron nitride are aggregated.
　炭窒化ホウ素粉末は、炭窒化ホウ素粒子の集合体である。炭窒化ホウ素粉末の純度（炭窒化ホウ素の含有量）は、例えば、９８質量％以上であることが好ましい。炭窒化ホウ素粉末としては、市販の炭窒化ホウ素粉末を使用してよく、上記準備工程で準備したものを用いてもよい。得られる窒化ホウ素粉末中の六方晶窒化ホウ素の割合を高める観点では、六方晶炭窒化ホウ素の割合が高い炭窒化ホウ素粉末を用いることが好ましく、上記加圧窒化工程を経て得られる炭窒化ホウ素粉末を用いることがより好ましい。 Boron carbonitride powder is an aggregate of boron carbonitride particles. The purity of the boron carbonitride powder (content of boron carbonitride) is preferably 98% by mass or more, for example. As the boron carbonitride powder, a commercially available boron carbonitride powder may be used, or the powder prepared in the above preparation step may be used. From the viewpoint of increasing the ratio of hexagonal boron nitride in the obtained boron nitride powder, it is preferable to use a boron carbonitride powder having a high ratio of hexagonal boron carbonitride, and the boron carbonitride powder obtained through the above pressure nitriding step. is more preferred.
　ホウ素源としては、例えば、ホウ酸、酸化ホウ素等が挙げられる。これらは一種を単独で、又は、二種以上を組み合わせて使用することができる。ホウ素源としては、一次粒子の成長促進効果が得られやすい観点及びウランの含有量が低減されやすい観点から、ホウ酸が好ましく用いられる。 Boron sources include, for example, boric acid and boron oxide. These can be used individually by 1 type or in combination of 2 or more types. As the boron source, boric acid is preferably used from the viewpoint of easily obtaining the effect of promoting the growth of primary particles and from the viewpoint of easily reducing the uranium content.
　炭酸塩としては、例えば、炭酸ナトリウム、炭酸カルシウム、炭酸ストロンチウム等が挙げられる。これらは一種を単独で、又は、二種以上を組み合わせて使用することができる。炭酸塩としては、一次粒子の成長促進効果が得られやすい観点及びウランの含有量が低減されやすい観点から、炭酸ナトリウムが好ましく用いられる。 Carbonates include, for example, sodium carbonate, calcium carbonate, strontium carbonate, and the like. These can be used individually by 1 type or in combination of 2 or more types. As the carbonate, sodium carbonate is preferably used from the viewpoint of easily obtaining the effect of promoting the growth of primary particles and from the viewpoint of easily reducing the uranium content.
　ホウ素源の使用量は、ウラン含有量を低減する観点から、５５質量％以上であってよく、５７質量％以上又は５９質量％以上であってもよい。ホウ素源の使用量は、凝集粒子の圧壊強度を高める観点から、７０質量％以下、６５質量％以下又は６０質量％以下であってよい。ホウ素源の使用量は、５５質量％未満であってもよい。ただし、ホウ素源の使用量が、５０質量％以上であると、窒化ホウ素の一次粒子の成長が促進されやすくなり、平均粒子径が１０～９０μｍであり、圧壊強度が５ＭＰａ以上である窒化ホウ素粉末が得られやすくなる。上記観点から、ホウ素源の使用量は、５０～７０質量％、５５～７０質量％、５７～７０質量％、５９～７０質量％、５５～６５質量％、５７～６５質量％、５９～６５質量％、５５～６０質量％、５７～６０質量％又は５９～６０質量％であってよい。なお、上記使用量は、原料混合物の全質量を基準とする使用量であるが、炭窒化ホウ素粉末とホウ素源と炭酸塩との合計量を基準とする使用量が上記範囲であってもよい。 From the viewpoint of reducing the uranium content, the amount of the boron source used may be 55% by mass or more, 57% by mass or more, or 59% by mass or more. The amount of the boron source used may be 70% by mass or less, 65% by mass or less, or 60% by mass or less from the viewpoint of increasing the crushing strength of the aggregated particles. The amount of boron source used may be less than 55% by weight. However, when the amount of the boron source used is 50% by mass or more, the growth of the primary particles of boron nitride is likely to be promoted, and the boron nitride powder having an average particle size of 10 to 90 μm and a crushing strength of 5 MPa or more. becomes easier to obtain. From the above viewpoint, the amount of the boron source used is 50 to 70% by mass, 55 to 70% by mass, 57 to 70% by mass, 59 to 70% by mass, 55 to 65% by mass, 57 to 65% by mass, 59 to 65% by mass. % by weight, 55-60% by weight, 57-60% by weight or 59-60% by weight. The amount used is the amount based on the total mass of the raw material mixture, but the amount used based on the total amount of the boron carbonitride powder, the boron source and the carbonate may be within the above range. .
　炭酸塩の使用量は、ウラン含有量を低減する観点から、４質量％以上であってよく、５質量％以上又は６質量％以上であってもよい。炭酸塩の使用量は、凝集粒子の圧壊強度を高める観点から、１０質量％以下、８質量％以下又は６質量％以下であってよい。炭酸塩の使用量は、４質量％未満であってもよい。ただし、炭酸塩の使用量が、１質量％以上であると、窒化ホウ素の一次粒子の成長が促進されやすくなり、平均粒子径が１０～９０μｍであり、圧壊強度が５ＭＰａ以上である窒化ホウ素粉末が得られやすくなる。上記観点から、炭酸塩の使用量は、１～１０質量％、４～１０質量％、５～１０質量％、６～１０質量％、４～８質量％、５～８質量％、６～８質量％、４～６質量％又は５～６質量％であってよい。なお、上記使用量は、原料混合物の全質量を基準とする使用量であるが、炭窒化ホウ素粉末とホウ素源と炭酸塩との合計量を基準とする使用量が上記範囲であってもよい。 From the viewpoint of reducing the uranium content, the amount of carbonate used may be 4% by mass or more, 5% by mass or more, or 6% by mass or more. The amount of carbonate used may be 10% by mass or less, 8% by mass or less, or 6% by mass or less from the viewpoint of increasing the crushing strength of aggregated particles. The amount of carbonate used may be less than 4% by mass. However, when the amount of carbonate used is 1% by mass or more, the growth of primary particles of boron nitride is likely to be promoted, and the boron nitride powder having an average particle size of 10 to 90 μm and a crushing strength of 5 MPa or more. becomes easier to obtain. From the above viewpoint, the amount of carbonate used is 1 to 10% by mass, 4 to 10% by mass, 5 to 10% by mass, 6 to 10% by mass, 4 to 8% by mass, 5 to 8% by mass, 6 to 8% by mass. % by weight, 4-6% by weight or 5-6% by weight. The amount used is the amount based on the total mass of the raw material mixture, but the amount used based on the total amount of the boron carbonitride powder, the boron source and the carbonate may be within the above range. .
　脱炭結晶化工程では、炭窒化ホウ素粉末、ホウ素源及び炭酸塩以外の材料を使用してもよく、炭窒化ホウ素粉末、ホウ素源及び炭酸塩のみを用いてもよい。 In the decarburization and crystallization step, materials other than the boron carbonitride powder, the boron source and the carbonate may be used, or only the boron carbonitride powder, the boron source and the carbonate may be used.
　脱炭結晶化工程における焼成温度は、１８００℃以上であることが好ましく、１９００℃以上又は２０００℃以上であってもよい。焼成温度を１８００℃以上とすることで、一次粒子の成長をより充分に進行させることができる。脱炭結晶化工程における焼成温度は、２４００℃以下であることが好ましく、２２００℃以下又は２１００℃以下であってもよい。焼成温度を２４００℃以下とすることで、窒化ホウ素粉末の黄色化を抑制することができる。上記観点から、脱炭結晶化工程における焼成温度は、例えば、１８００～２４００℃、１９００～２２００℃又は２０００～２１００℃であってよい。なお、上記焼成温度は、加熱（焼成）中の保持温度を意味する。加熱開始温度は特に限定されないが、室温（例えば２５℃）であってよい。保持温度より低い温度から加熱を開始する場合、１０００℃までの昇温速度は、例えば、１～１０℃／分であってよく、１０００℃以上での昇温速度は、例えば、０．１～５℃／分であってよい。 The firing temperature in the decarburization and crystallization step is preferably 1800°C or higher, and may be 1900°C or higher or 2000°C or higher. By setting the sintering temperature to 1800° C. or higher, the primary particles can be grown more sufficiently. The firing temperature in the decarburization and crystallization step is preferably 2400° C. or lower, and may be 2200° C. or lower or 2100° C. or lower. By setting the firing temperature to 2400° C. or lower, yellowing of the boron nitride powder can be suppressed. From the above point of view, the firing temperature in the decarburization and crystallization step may be, for example, 1800-2400°C, 1900-2200°C or 2000-2100°C. In addition, the said baking temperature means the holding temperature during heating (baking). The heating start temperature is not particularly limited, but may be room temperature (for example, 25°C). When heating is started from a temperature lower than the holding temperature, the temperature increase rate up to 1000° C. may be, for example, 1 to 10° C./min, and the temperature increase rate at 1000° C. or higher may be, for example, 0.1 to 10° C./min. It may be 5°C/min.
　脱炭結晶化工程における焼成時間は、４時間以上であることが好ましく、６時間以上又は８時間以上であってもよい。焼成時間を４時間以上とすることで、一次粒子の成長をより充分に進行させることができる。脱炭結晶化工程における焼成時間は、４０時間以下であることが好ましく、３０時間以下又は２０時間以下であってもよい。焼成時間を４０時間以下とすることで、製造コストの上昇を抑制することができる。上記観点から、脱炭結晶化工程における焼成時間は、例えば、４～４０時間、６～３０時間又は８～２０時間であってよい。なお、上記焼成時間は、上記焼成温度（保持温度）での保持時間を意味する。 The firing time in the decarburization and crystallization step is preferably 4 hours or longer, and may be 6 hours or longer or 8 hours or longer. By setting the firing time to 4 hours or longer, the growth of the primary particles can be sufficiently advanced. The firing time in the decarburization and crystallization step is preferably 40 hours or less, and may be 30 hours or less or 20 hours or less. By setting the firing time to 40 hours or less, it is possible to suppress an increase in manufacturing cost. From the above point of view, the firing time in the decarburization and crystallization step may be, for example, 4 to 40 hours, 6 to 30 hours, or 8 to 20 hours. The firing time means the retention time at the firing temperature (holding temperature).
　本発明者らの検討によれば、脱炭結晶化工程における焼成条件を変更することでもウラン含有量を低減することができる。ウラン含有量をより低減する観点では、焼成温度が１８００℃以上であり、焼成時間が８時間以上であるか、又は、焼成温度が２０００℃以上であり、焼成時間が４時間以上であることが好ましく、焼成温度が２０００℃以上であり、焼成時間が８時間以上であることがより好ましい。 According to the studies of the present inventors, the uranium content can also be reduced by changing the firing conditions in the decarburization and crystallization process. From the viewpoint of further reducing the uranium content, the firing temperature is 1800° C. or more and the firing time is 8 hours or more, or the firing temperature is 2000° C. or more and the firing time is 4 hours or more. More preferably, the firing temperature is 2000° C. or higher, and the firing time is 8 hours or longer.
　脱炭結晶化工程の焼成雰囲気は、例えば、大気又は真空であってよく、窒素ガス、アルゴンガス等の不活性ガス雰囲気であってもよい。脱炭結晶化工程の焼成は、常圧（大気圧）下で行ってもよく、大気圧以上の圧力下で行ってもよい。脱炭結晶化工程における圧力（雰囲気圧力）は、例えば、１０ｋＰａ以上、１５ｋＰａ以上、又は２０ｋＰａ以上であってよい。上記圧力を１０ｋＰａ以上とすることで、ホウ素源、炭酸塩等の助剤が系外に除去されることを抑制し、窒化ホウ素粒子の反応場をより一層均一なものとすることができる。脱炭結晶化工程における圧力（雰囲気圧力）は、例えば、８０ｋＰａ以下、６０ｋＰａ以下、又は４０ｋＰａ以下であってよい。上記圧力を８０ｋＰａ以下とすることで、脱炭結晶化工程中に凝集粒子が崩壊することをより抑制することができる。上記観点から、脱炭結晶化工程における圧力（雰囲気圧力）は、１０～８０ｋＰａ、１０～６０ｋＰａ又は２０～４０ｋＰａであってよい。なお、上記圧力はゲージ圧を示している。 The firing atmosphere in the decarburization and crystallization step may be, for example, air or vacuum, or may be an inert gas atmosphere such as nitrogen gas or argon gas. The calcination in the decarburization and crystallization step may be performed under normal pressure (atmospheric pressure) or under atmospheric pressure or higher. The pressure (atmospheric pressure) in the decarburization and crystallization step may be, for example, 10 kPa or more, 15 kPa or more, or 20 kPa or more. By setting the pressure to 10 kPa or more, it is possible to suppress removal of the auxiliary agent such as the boron source and carbonate to the outside of the system, and to make the reaction field of the boron nitride particles even more uniform. The pressure (atmospheric pressure) in the decarburization and crystallization step may be, for example, 80 kPa or less, 60 kPa or less, or 40 kPa or less. By setting the pressure to 80 kPa or less, it is possible to further suppress the collapse of the aggregated particles during the decarburization and crystallization step. From the above viewpoint, the pressure (atmospheric pressure) in the decarburization and crystallization step may be 10 to 80 kPa, 10 to 60 kPa, or 20 to 40 kPa. Note that the above pressure indicates a gauge pressure.
　脱炭結晶化工程後の窒化ホウ素粉末に対しては、粉砕処理、分級処理、洗浄処理等を適宜行ってよい。粉砕処理は、ボールミル、振動ミル、ジェットミル等の一般的な粉砕機又は解砕機を用いて行うことができる。 The boron nitride powder after the decarburization and crystallization process may be appropriately subjected to pulverization treatment, classification treatment, washing treatment, and the like. The pulverization treatment can be performed using a general pulverizer or pulverizer such as a ball mill, vibration mill, or jet mill.
　以上説明した窒化ホウ素粉末の製造方法では、窒化ホウ素の一次粒子が凝集して構成される凝集粒子を含み、配向性指数が１５以下である窒化ホウ素粉末を得ることができる。また、以上説明した窒化ホウ素粉末の製造方法では、脱炭結晶化工程でのホウ素源及び炭酸塩の使用量をそれぞれ５５質量％以上及び４質量％以上とすること、フッ化水素酸を含む酸溶液により炭化ホウ素粉末を酸処理すること等により、窒化ホウ素の一次粒子が凝集して構成される凝集粒子を形成しつつ、ウラン含有量を低減することができる。これらのウラン含有量の低減手段は、必ずしもその全てを実施しなくてよいが、複数の手段を組み合わせることで、ウラン含有量がより一層低減された窒化ホウ素粉末を提供することができる。なお、本明細書において、窒化ホウ素粉末の配向性指数とは、以下の方法に沿って測定される値を意味する。 In the method for producing the boron nitride powder described above, it is possible to obtain a boron nitride powder having an orientation index of 15 or less, including aggregated particles composed of agglomerated primary particles of boron nitride. Further, in the method for producing boron nitride powder described above, the amount of the boron source and the carbonate used in the decarburization and crystallization step is set to 55% by mass or more and 4% by mass or more, respectively, and an acid containing hydrofluoric acid By acid-treating the boron carbide powder with a solution or the like, the uranium content can be reduced while forming agglomerated particles composed of agglomerated primary particles of boron nitride. It is not necessary to implement all of these means for reducing the uranium content, but by combining a plurality of means, it is possible to provide a boron nitride powder with a further reduced uranium content. In this specification, the orientation index of boron nitride powder means a value measured according to the following method.
　窒化ホウ素粉末に対するＸ線回折測定を行うことによって、窒化ホウ素粉末のＸ線回折スペクトルを取得し、当該Ｘ線回折スペクトルから、（００２）面及び（１００）面に対応するピーク強度Ｉ（００２）及びＩ（１００）を取得する。得られたピーク強度を用いて、窒化ホウ素粉末の配向性指数［Ｉ（００２）／Ｉ（１００）］を算出する。Ｘ線回折装置としては、例えば、株式会社リガク製の「ＵＬＴＩＭＡ－ＩＶ」（製品名）等が使用される。 By performing X-ray diffraction measurement on the boron nitride powder, the X-ray diffraction spectrum of the boron nitride powder is obtained, and from the X-ray diffraction spectrum, the peak intensity I (002) corresponding to the (002) plane and the (100) plane and I(100). The obtained peak intensity is used to calculate the orientation index [I(002)/I(100)] of the boron nitride powder. As the X-ray diffractometer, for example, "ULTIMA-IV" (product name) manufactured by Rigaku Corporation is used.
＜窒化ホウ素粉末＞
　一実施形態に係る窒化ホウ素粉末は、窒化ホウ素の一次粒子が凝集して構成される凝集粒子を含み、配向性指数が１５以下であり、ウラン含有量が２０質量ｐｐｂ以下である。窒化ホウ素粉末は、凝集粒子の他、一次粒子を含んでいてもよい。窒化ホウ素の一次粒子は、例えば、鱗片状の六方晶窒化ホウ素粒子であってよい。 <Boron nitride powder>
A boron nitride powder according to one embodiment includes agglomerated particles composed of agglomerated primary particles of boron nitride, has an orientation index of 15 or less, and has a uranium content of 20 mass ppb or less. The boron nitride powder may contain primary particles in addition to aggregated particles. The primary particles of boron nitride may be, for example, scale-like hexagonal boron nitride particles.
　上記窒化ホウ素粉末は、ウラン含有量が２０質量ｐｐｂ以下であることから、α線を放出し難い材料であるといえる。また、上記窒化ホウ素粉末は、１５以下の配向性指数を有することから、上記窒化ホウ素粉末によれば、樹脂との混練の際に凝集粒子の少なくとも一部が崩壊し、配向性が上昇した場合であっても、樹脂封止材における放熱性等に大きな異方性が生じることを抑制することができる。したがって、上記窒化ホウ素粉末は、放熱性が求められる半導体メモリ素子用の樹脂封止材に好適に用いられる。 Since the boron nitride powder has a uranium content of 20 mass ppb or less, it can be said that it is a material that hardly emits α-rays. In addition, since the boron nitride powder has an orientation index of 15 or less, according to the boron nitride powder, when at least a part of the aggregated particles collapses during kneading with the resin, and the orientation increases Even so, it is possible to suppress occurrence of large anisotropy in the heat dissipation property and the like of the resin sealing material. Therefore, the boron nitride powder is suitable for use as a resin encapsulant for semiconductor memory devices, which require heat dissipation.
　上記窒化ホウ素粉末は、例えば、上記実施形態に係る製造方法において、脱炭結晶化工程でのホウ素源及び炭酸塩の使用量をそれぞれ５５質量％以上及び４質量％以上とすることによって得ることができる。 The boron nitride powder can be obtained, for example, in the manufacturing method according to the above embodiment, by setting the amount of the boron source and the carbonate used in the decarburization and crystallization step to 55% by mass or more and 4% by mass or more, respectively. can.
　窒化ホウ素粉末のウラン含有量は、例えば、１８質量ｐｐｂ以下、１６質量ｐｐｂ以下、１４質量ｐｐｂ以下、１２質量ｐｐｂ以下、１０質量ｐｐｂ以下、７質量ｐｐｂ以下又は５質量ｐｐｂ以下であってもよい。このようなウラン含有量を有する窒化ホウ素粉末は、脱炭結晶化工程でのホウ素源及び炭酸塩の使用量をそれぞれ５５質量％以上及び４質量％以上とすることに加えて、例えば、酸処理工程（第１の酸処理工程及び／又は第２の酸処理工程）の実施、酸処理工程における酸処理条件の変更、脱炭結晶化工程における焼成条件の変更等を組み合わせることによって得ることができる。ウラン含有量の下限値は、例えば、５質量ｐｐｂであってよい。ウラン含有量は、例えば、５～２０質量ｐｐｂ、５～１８質量ｐｐｂ、５～１６質量ｐｐｂ、５～１４質量ｐｐｂ、５～１２質量ｐｐｂ、５～１０質量ｐｐｂ又は５～７質量ｐｐｂであってよい。なお、上記含有量は、窒化ホウ素粉末の全質量を基準とする含有量である。 The uranium content of the boron nitride powder may be, for example, 18 mass ppb or less, 16 mass ppb or less, 14 mass ppb or less, 12 mass ppb or less, 10 mass ppb or less, 7 mass ppb or less, or 5 mass ppb or less. . Boron nitride powder having such a uranium content is obtained by, for example, acid treatment, in addition to using amounts of boron source and carbonate of 55% by mass or more and 4% by mass or more, respectively, in the decarburization and crystallization step. It can be obtained by combining the implementation of the steps (first acid treatment step and/or second acid treatment step), change of acid treatment conditions in the acid treatment step, change of firing conditions in the decarburization and crystallization step, etc. . The lower limit of the uranium content may be, for example, 5 mass ppb. The uranium content is, for example, 5-20 mass ppb, 5-18 mass ppb, 5-16 mass ppb, 5-14 mass ppb, 5-12 mass ppb, 5-10 mass ppb or 5-7 mass ppb. you can The above content is based on the total mass of the boron nitride powder.
　本明細書における窒化ホウ素粉末のウラン含有量は、以下の方法に沿って測定される値を意味する。
　ＪＣＲＳ１０８の窒化ホウ素粉末化学分析方法に従って、試料（窒化ホウ素粉末）０．５ｇを、硝酸、硫酸及びフッ化水素酸の混合液中、１８０℃１８時間の条件で加圧酸分解する。その後、加圧酸分解により得られた溶液をホットプレート上で乾燥させることで固化させ、得られた固形分を硝酸と混合して混合液とする。次いで、得られた混合液をホットプレート上で加熱することで固形分を溶解させて硝酸溶液を得た後、該硝酸溶液中のウラン量をＩＣＰ－ＭＳ（誘導結合プラズマ質量分析装置）を用いて測定する。ＩＣＰ－ＭＳの測定条件は以下のとおりとする。
（ＩＣＰ－ＭＳ測定条件）
プラズマモード：低マトリックスモード、チューンモード：Ｈｅ、スペクトルモード　ピークパターン：１ポイント、繰り返し：３、スイープ回数：１００、積分時間：１秒 The uranium content of boron nitride powder in this specification means a value measured according to the following method.
According to JCRS108 boron nitride powder chemical analysis method, 0.5 g of a sample (boron nitride powder) is subjected to pressure acid decomposition in a mixed solution of nitric acid, sulfuric acid and hydrofluoric acid at 180° C. for 18 hours. Thereafter, the solution obtained by pressure acid decomposition is dried on a hot plate to solidify, and the obtained solid content is mixed with nitric acid to obtain a mixed solution. Next, the resulting mixed solution is heated on a hot plate to dissolve the solid content to obtain a nitric acid solution, and the amount of uranium in the nitric acid solution is measured using ICP-MS (inductively coupled plasma mass spectrometer). to measure. The measurement conditions for ICP-MS are as follows.
(ICP-MS measurement conditions)
Plasma mode: low matrix mode, tune mode: He, spectrum mode Peak pattern: 1 point, repetition: 3, number of sweeps: 100, integration time: 1 second
　配向性指数は、上記凝集粒子の崩壊による影響をより低減する観点から、１２以下又は１０以下であってもよい。配向性指数は、３以上、４以上又は６以上であってよく、３～１５、４～１２又は６～１０であってよい。なお、窒化ホウ素粉末の配向性指数は、例えば、窒化ホウ素粉末を製造する際の一次粒子の成長を制御すること等により調整することができる。 The orientation index may be 12 or less or 10 or less from the viewpoint of further reducing the influence of the collapse of the aggregated particles. The orientation index may be 3 or higher, 4 or higher, or 6 or higher, and may be 3-15, 4-12, or 6-10. The orientation index of the boron nitride powder can be adjusted, for example, by controlling the growth of primary particles when producing the boron nitride powder.
　窒化ホウ素粉末の純度は、好ましくは９８．５質量％以上であり、９９質量％以上又は９９．５質量％以上であってもよい。窒化ホウ素粉末の純度の上限値は特に制限されるものではなく、１００質量％であってよく、９９．５質量％であってもよい。 The purity of the boron nitride powder is preferably 98.5% by mass or higher, and may be 99% by mass or higher or 99.5% by mass or higher. The upper limit of the purity of the boron nitride powder is not particularly limited, and may be 100% by mass or 99.5% by mass.
　本明細書における窒化ホウ素粉末の純度は、後述する滴定によって決定される値を意味する。まず、窒化ホウ素粉末のサンプルを水酸化ナトリウムでアルカリ分解させ、水蒸気蒸留法によって分解液からアンモニアを蒸留して、ホウ酸水溶液に捕集する。この捕集液を対象として、硫酸規定液で滴定行う。滴定の結果からサンプル中の窒素原子（Ｎ）の含有量を算出する。得られた窒素原子の含有量から、式（Ｉ）に基づいて、サンプル中の窒化ホウ素の含有量を決定し、窒化ホウ素粉末の純度を算出することができる。なお、窒化ホウ素の式量は２４．８１８ｇ／ｍｏｌとし、窒素原子の原子量は１４．００６ｇ／ｍｏｌとする。
　サンプル中の窒化ホウ素の含有量［質量％］＝窒素原子（Ｎ）の含有量［質量％］×１．７７２・・・（Ｉ） The purity of boron nitride powder herein means a value determined by titration, which will be described later. First, a sample of boron nitride powder is alkali-decomposed with sodium hydroxide, ammonia is distilled from the decomposed solution by a steam distillation method, and collected in an aqueous boric acid solution. This collected liquid is titrated with a normal sulfuric acid solution. The content of nitrogen atoms (N) in the sample is calculated from the titration results. From the obtained nitrogen atom content, the boron nitride content in the sample can be determined based on formula (I), and the purity of the boron nitride powder can be calculated. The formula weight of boron nitride is 24.818 g/mol, and the atomic weight of nitrogen atoms is 14.006 g/mol.
Boron nitride content [mass%] in the sample = nitrogen atom (N) content [mass%] x 1.772 (I)
　窒化ホウ素粉末に含まれる凝集粒子は、樹脂との混練の際に崩壊し難い観点から、好ましくは５ＭＰａ以上の圧壊強度を有する。凝集粒子の圧壊強度は、８ＭＰａ以上又は１０ＭＰａ以上であってもよい。凝集粒子の圧壊強度は、２０ＭＰａ以下、１５ＭＰａ以下又は１２Ｍｐａ以下であってよい。凝集粒子の圧壊強度が２０Ｍｐａ以下であることで、樹脂との混練の際に凝集粒子の少なくとも一部が適度に崩壊し、ボイドの発生が抑制されやすくなる。その結果、得られる樹脂封止材がより高い絶縁性を有することとなる。上記観点から、凝集粒子の圧壊強度は、例えば、５～２０ＭＰａ、８～１５ＭＰａ又は１０～１２ＭＰａであってよい。なお、凝集粒子の圧壊強度は、例えば、焼成条件等を変更することにより調整することができる。 The aggregated particles contained in the boron nitride powder preferably have a crushing strength of 5 MPa or more from the viewpoint of being difficult to collapse when kneading with the resin. The crushing strength of the aggregated particles may be 8 MPa or more, or 10 MPa or more. The crush strength of the agglomerated particles may be 20 MPa or less, 15 MPa or less, or 12 MPa or less. When the crushing strength of the aggregated particles is 20 Mpa or less, at least a part of the aggregated particles appropriately collapses during kneading with the resin, and the generation of voids is easily suppressed. As a result, the resulting resin encapsulant has higher insulation. From the above point of view, the crushing strength of the aggregated particles may be, for example, 5-20 MPa, 8-15 MPa or 10-12 MPa. The crushing strength of aggregated particles can be adjusted, for example, by changing the firing conditions.
　本明細書における圧壊強度は、ＪＩＳ　Ｒ　１６３９－５：２００７「ファインセラミックス－か（顆）粒特性の測定方法－第５部：単一か粒圧壊強度」の記載に準拠して測定される値を意味する。凝集粒子１個の圧壊強度σ（単位：ＭＰａ）は、凝集粒子内の位置によって変化する無次元数α（α＝２．４８）、圧壊試験力Ｐ（単位：Ｎ）及び粒子径ｄ（単位：μｍ）の値から、σ＝α×Ｐ／（π×ｄ２）という式を用いて算出される。測定は、２０個以上の凝集粒子に対して行い、累積破壊率６３．２％時点の値を算出した。測定には、微小圧縮試験器を用いることができる。微小圧縮試験器としては、例えば、株式会社島津製作所製の「ＭＣＴ－Ｗ５００」（製品名）等を使用することができる。 The crushing strength herein is a value measured in accordance with the description of JIS R 1639-5:2007 "Fine ceramics-Method for measuring (granule) properties-Part 5: Single granule crushing strength". means The crushing strength σ (unit: MPa) of one aggregated particle is a dimensionless number α (α = 2.48) that changes depending on the position in the aggregated particle, the crushing test force P (unit: N), and the particle diameter d (unit: : μm) using the formula σ=α×P/(π×d 2 ). The measurement was performed on 20 or more aggregated particles, and the value at the time when the cumulative destruction rate was 63.2% was calculated. A microcompression tester can be used for the measurement. As the microcompression tester, for example, "MCT-W500" (product name) manufactured by Shimadzu Corporation can be used.
　窒化ホウ素粉末の平均粒子径は、例えば、９０μｍ以下、８０μｍ以下又は７０μｍ以下であってよい。平均粒子径が９０μｍ以下であることで、樹脂封止材によって形成される封止部をより薄くすることが可能となる。窒化ホウ素粉末の平均粒子径は、例えば、１０μｍ以上、２０μｍ以上又は３０μｍ以上であってよい。平均粒子径が１０μｍ以上であることで、樹脂封止材の熱伝導率をより向上させることができる。これらの観点から、窒化ホウ素粉末の平均粒子径は、例えば、１０～９０μｍ、２０～８０μｍ又は３０～７０μｍであってよい。 The average particle size of the boron nitride powder may be, for example, 90 μm or less, 80 μm or less, or 70 μm or less. When the average particle diameter is 90 μm or less, it becomes possible to make the sealing portion formed by the resin sealing material thinner. The average particle size of the boron nitride powder may be, for example, 10 μm or more, 20 μm or more, or 30 μm or more. When the average particle diameter is 10 µm or more, the thermal conductivity of the resin sealing material can be further improved. From these points of view, the average particle size of the boron nitride powder may be, for example, 10-90 μm, 20-80 μm, or 30-70 μm.
　本明細書における平均粒子径は、体積基準の累積粒度分布における５０％累積径（メディアン径）を意味する。より具体的には、粉末に対するレーザー回折散乱法で得られる体積基準の累積粒度分布における累積値が５０％となったときの粒子径（Ｄ５０）を意味する。レーザー解析散乱法は、ＩＳＯ　１３３２０：２００９に記載の方法に準拠して測定する。測定には、レーザー回折散乱法粒度分布測定装置等を使用することができる。レーザー回折散乱法粒度分布測定装置は、例えば、ベックマン・コールター社製の「ＬＳ－１３　３２０」（製品名）等を使用できる。測定の際はホモジナイザーによる処理を行わずに、凝集粒子が存在する状況で測定を行う。 The average particle diameter in this specification means the 50% cumulative diameter (median diameter) in the volume-based cumulative particle size distribution. More specifically, it means the particle diameter (D50) when the cumulative value in the volume-based cumulative particle size distribution obtained by the laser diffraction scattering method for the powder reaches 50%. The laser analysis scattering method is measured according to the method described in ISO 13320:2009. For the measurement, a laser diffraction scattering particle size distribution analyzer or the like can be used. As a laser diffraction scattering particle size distribution analyzer, for example, "LS-13 320" (product name) manufactured by Beckman Coulter, Inc. can be used. Measurement is performed in the presence of agglomerated particles without treatment with a homogenizer.
　窒化ホウ素粉末は、樹脂封止材の絶縁性の観点では、純度が９８．５質量％以上であり、平均粒子径が１０～９０μｍであり、凝集粒子の圧壊強度が５ＭＰａ以上であることが好ましい。 The boron nitride powder preferably has a purity of 98.5% by mass or more, an average particle diameter of 10 to 90 μm, and a crushing strength of aggregated particles of 5 MPa or more, from the viewpoint of the insulating properties of the resin sealing material. .
＜樹脂封止材＞
　一実施形態に係る樹脂封止材は、半導体メモリ用の樹脂封止材であり、上記実施形態に係る窒化ホウ素粉末を含有する。 <Resin sealing material>
A resin encapsulant according to one embodiment is a resin encapsulant for a semiconductor memory and contains the boron nitride powder according to the above embodiment.
　樹脂封止材に含まれる樹脂としては、樹脂封止材に使用される公知の樹脂を用いることができる。かかる樹脂としては、例えば、液晶ポリマー、フッ素樹脂、シリコーン樹脂、シリコーンゴム、アクリル樹脂、ポリオレフィン（ポリエチレン等）、エポキシ樹脂、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、ポリイミド、ポリアミドイミド、ポリエーテルイミド、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、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、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（アクリロニトリル－ブタジエン－スチレン）樹脂、ＡＡＳ（アクリロニトリル－アクリルゴム・スチレン）樹脂及び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）樹脂が挙げられる。 As the resin contained in the resin sealing material, known resins used for resin sealing materials can be used. Examples of such resins include liquid crystal polymers, fluororesins, silicone resins, silicone rubbers, acrylic resins, polyolefins (polyethylene, etc.), epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, polyimides, polyamideimides, poly Etherimide, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, wholly aromatic polyester, polysulfone, polyethersulfone, polycarbonate, maleimide-modified resin, ABS (acrylonitrile-butadiene-styrene) resin, AAS (acrylonitrile-acrylic rubber, styrene) resins and AES (acrylonitrile ethylene propylene diene rubber-styrene) resins.
　樹脂の含有量は、樹脂封止材の全体積を基準として、例えば、１５体積％以上、２０体積％以上、又は３０体積％以上であってよい。樹脂の含有量は、樹脂封止材の全体積を基準として、例えば、６０体積％以下、５０体積％以下、又は４０体積％以下であってよい。樹脂の含有量は、樹脂封止材の全体積を基準として、例えば、１５～６０体積％、２０～５０体積％、又は３０～４０体積％であってよい。 The resin content may be, for example, 15% by volume or more, 20% by volume or more, or 30% by volume or more based on the total volume of the resin sealing material. The resin content may be, for example, 60% by volume or less, 50% by volume or less, or 40% by volume or less based on the total volume of the resin sealing material. The resin content may be, for example, 15 to 60% by volume, 20 to 50% by volume, or 30 to 40% by volume based on the total volume of the resin sealing material.
　窒化ホウ素粉末の含有量は、樹脂封止材の全体積を基準として、例えば、３０体積％以上、４０体積％以上、５０体積％以上、又は６０体積％以上であってよい。窒化ホウ素粉末の含有量は、樹脂封止材の全体積を基準として、例えば、８５体積％以下、８０体積％以下、又は７０体積％以下であってよい。窒化ホウ素粉末の含有量は、樹脂封止材の全体積を基準として、例えば、３０～８５体積％、４０～８５体積％、４０～８０体積％、５０～８０体積％、５０～７０体積％、又は６０～７０体積％であってよい。 The content of the boron nitride powder may be, for example, 30% by volume or more, 40% by volume or more, 50% by volume or more, or 60% by volume or more based on the total volume of the resin sealing material. The content of the boron nitride powder may be, for example, 85% by volume or less, 80% by volume or less, or 70% by volume or less based on the total volume of the resin sealing material. The content of the boron nitride powder is, for example, 30 to 85% by volume, 40 to 85% by volume, 40 to 80% by volume, 50 to 80% by volume, 50 to 70% by volume, based on the total volume of the resin sealing material. , or 60-70% by volume.
　樹脂封止材は、樹脂及び窒化ホウ素粉末に加えて、上記樹脂を硬化させる硬化剤を更に含有してよい。硬化剤は、樹脂の種類によって適宜選択することができる。樹脂がエポキシ樹脂である場合、硬化剤としては、例えば、フェノールノボラック化合物、酸無水物、アミノ化合物、及びイミダゾール化合物等が挙げられる。硬化剤の含有量は、樹脂１００質量部に対して、例えば、０．５質量部以上又は１質量部以上であってよく、１５質量部以下又は１０質量部以下であってよく、０．５～１５質量部又は１～１０質量部であってよい。 The resin sealing material may further contain a curing agent for curing the resin in addition to the resin and boron nitride powder. The curing agent can be appropriately selected according to the type of resin. When the resin is an epoxy resin, examples of curing agents include phenol novolac compounds, acid anhydrides, amino compounds, imidazole compounds, and the like. The content of the curing agent may be, for example, 0.5 parts by mass or more or 1 part by mass or more, and may be 15 parts by mass or less or 10 parts by mass or less with respect to 100 parts by mass of the resin. It may be up to 15 parts by weight or 1 to 10 parts by weight.
　実施例及び比較例を参照して本開示の内容をより詳細に説明するが、本開示は下記の実施例に限定されるものではない。 The contents of the present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.
＜実施例１＞
［炭化ホウ素粉末の準備］
　新日本電工株式会社製のオルトホウ酸１００質量部と、デンカ株式会社製のアセチレンブラック（商品名：ＨＳ１００Ｌ）３５質量部とをヘンシェルミキサーを用いて混合した。得られた混合物を、黒鉛製のルツボ中に充填し、アーク炉にて、アルゴン雰囲気下、２２００℃で６時間加熱し、塊状の炭化ホウ素（Ｂ４Ｃ）を得た。得られた塊状物を、ジョークラッシャーで粗粉砕して粗粉を得た。得られた粗粉を、炭化珪素製のボール（直径：１０ｍｍ）を有するボールミルによって、さらに粉砕して粉砕粉を得た。ボールミルによる粉砕は、回転数２５ｒｐｍで６０分間行った。その後、目開き６３μｍの振動篩を用いて、粉砕粉を分級し、平均粒子径が２０μｍの炭化ホウ素粉末（Ｂ４Ｃ粉末）を作製した。炭化ホウ素粉末の比表面積は０．４ｍ２／ｇであり、純度は９８質量％であった。 <Example 1>
[Preparation of boron carbide powder]
100 parts by mass of orthoboric acid manufactured by Shin Nippon Denko Co., Ltd. and 35 parts by mass of acetylene black (product name: HS100L) manufactured by Denka Co., Ltd. were mixed using a Henschel mixer. The resulting mixture was filled in a graphite crucible and heated in an arc furnace at 2200° C. for 6 hours under an argon atmosphere to obtain massive boron carbide (B 4 C). The resulting mass was coarsely pulverized with a jaw crusher to obtain coarse powder. The obtained coarse powder was further pulverized by a ball mill having silicon carbide balls (diameter: 10 mm) to obtain pulverized powder. Pulverization by a ball mill was performed for 60 minutes at a rotation speed of 25 rpm. Thereafter, the pulverized powder was classified using a vibrating sieve with an opening of 63 μm to prepare a boron carbide powder (B 4 C powder) with an average particle size of 20 μm. The boron carbide powder had a specific surface area of 0.4 m 2 /g and a purity of 98% by mass.
　炭化ホウ素粉末の平均粒子径は、ＩＳＯ　１３３２０：２００９の記載に準拠し、ベックマン・コールター社製のレーザー回折散乱法粒度分布測定装置（装置名：ＬＳ－１３　３２０）を用いて測定した。なお、炭化ホウ素粉末に対するホモジナイザー処理は行わなかった。粒度分布の測定に際し、炭化ホウ素粉末を分散させる溶媒には水を用い、分散剤にはヘキサメタリン酸を用いた。この際、水の屈折率として１．３３の数値を用い、炭化ホウ素粉末の屈折率として２．６の数値を用いた。 The average particle size of the boron carbide powder was measured according to ISO 13320:2009 using a Beckman Coulter laser diffraction scattering method particle size distribution analyzer (equipment name: LS-13 320). The boron carbide powder was not treated with a homogenizer. In measuring the particle size distribution, water was used as a solvent for dispersing the boron carbide powder, and hexametaphosphoric acid was used as a dispersant. At this time, a numerical value of 1.33 was used as the refractive index of water, and a numerical value of 2.6 was used as the refractive index of the boron carbide powder.
　炭化ホウ素粉末の比表面積は、ＪＩＳ　Ｚ　８８３０：２０１３「ガス吸着による粉体（固体）の比表面積測定方法」の記載に準拠し、窒素ガスを使用したＢＥＴ一点法を適用して算出した。比表面積測定装置としては、ユアサアイオニクス株式会社製の比表面積測定装置（装置名：カンターソーブ）を用いた。なお、測定は、炭化ホウ素粉末を、３００℃で、１５分間かけて、乾燥脱気した後に行った。 The specific surface area of the boron carbide powder was calculated according to the description of JIS Z 8830:2013 "Method for measuring specific surface area of powder (solid) by gas adsorption", applying the BET single point method using nitrogen gas. As a specific surface area measuring device, a specific surface area measuring device manufactured by Yuasa Ionics Co., Ltd. (device name: Kantersorb) was used. The measurement was performed after the boron carbide powder was dried and degassed at 300° C. for 15 minutes.
　炭化ホウ素粉末の純度は、炭素量とホウ素量の和から算出した。炭素量は燃焼赤外線吸収法から算出し、ホウ素量はＩＣＰ発光分析から算出した。 The purity of boron carbide powder was calculated from the sum of carbon content and boron content. The amount of carbon was calculated from a combustion infrared absorption method, and the amount of boron was calculated from an ICP emission analysis.
［加圧窒化工程］
　調製した炭化ホウ素粉末を、カーボン式抵抗加熱炉内で１２時間焼成した。この際、焼成雰囲気は窒素ガス雰囲気とし、焼成温度は２０５０℃とし、雰囲気圧力は０．９０ＭＰａとした。このようにして炭窒化ホウ素粉末を得た。炭窒化ホウ素粉末を粉末Ｘ線回折（ＸＲＤ）法で分析し、炭化ホウ素の消失と六方晶炭窒化ホウ素の生成を確認した。 [Pressure nitriding step]
The prepared boron carbide powder was fired in a carbon resistance heating furnace for 12 hours. At this time, the firing atmosphere was a nitrogen gas atmosphere, the firing temperature was 2050° C., and the atmospheric pressure was 0.90 MPa. Thus, boron carbonitride powder was obtained. The boron carbonitride powder was analyzed by powder X-ray diffraction (XRD) to confirm the disappearance of boron carbide and the formation of hexagonal boron carbonitride.
［脱炭結晶化工程］
　上記加圧窒化工程で得られた焼成物（炭窒化ホウ素粉末）と、ホウ酸と、炭酸ナトリウムとをヘンシェルミキサーによって混合して、原料混合物を得た。ホウ酸の使用量は、原料混合物の全質量を基準として６０質量％とし、炭酸ナトリウムの使用量は、原料混合物の全質量を基準として５質量％とした。次に、得られた原料混合物を、窒化ホウ素製のルツボに充填し、抵抗加熱炉内で、窒素ガス雰囲気下、１９５０℃の焼成温度且つ大気圧の圧力条件で５時間焼成した。具体的には、室温から１０００℃まで昇温速度１０℃／分で昇温した後、１０００℃から昇温速度２℃／分で１９５０℃まで昇温し、１９５０℃で５時間保持することで焼成を行った。次いで、得られた粉末をヘンシェルミキサーで２０分解砕した後、得られた粉砕物を目開き７５μｍの篩に通すことで分級し、六方晶窒化ホウ素の一次粒子が凝集して構成される凝集粒子を含む、実施例１の窒化ホウ素粉末を得た。得られた窒化ホウ素粉末のウラン含有量は１９質量ｐｐｂであり、配向性指数は７であり、純度は９９質量％であり、平均粒子径は４０μｍであり、窒化ホウ素粉末中の凝集粒子の圧壊強度は１２Ｍｐａであった。 [Decarburization crystallization step]
The baked product (boron carbonitride powder) obtained in the above pressure nitriding step, boric acid, and sodium carbonate were mixed by a Henschel mixer to obtain a raw material mixture. The amount of boric acid used was 60% by mass based on the total mass of the raw material mixture, and the amount of sodium carbonate used was 5% by mass based on the total mass of the raw material mixture. Next, the obtained raw material mixture was filled in a crucible made of boron nitride and fired in a resistance heating furnace under nitrogen gas atmosphere at a firing temperature of 1950° C. and atmospheric pressure for 5 hours. Specifically, after the temperature was raised from room temperature to 1000°C at a temperature increase rate of 10°C/min, the temperature was raised from 1000°C to 1950°C at a temperature increase rate of 2°C/min, and held at 1950°C for 5 hours. Firing was performed. Next, after the obtained powder was pulverized 20 times with a Henschel mixer, the obtained pulverized product was classified by passing it through a sieve with an opening of 75 μm, and aggregated particles composed of aggregated primary particles of hexagonal boron nitride. to obtain the boron nitride powder of Example 1. The obtained boron nitride powder had a uranium content of 19 mass ppb, an orientation index of 7, a purity of 99 mass%, and an average particle size of 40 μm. The strength was 12 Mpa.
　窒化ホウ素粉末のウラン含有量は、以下の方法で決定した。
　ＪＣＲＳ１０８の窒化ホウ素粉末化学分析方法に従って、試料（窒化ホウ素粉末）０．５ｇを、硝酸、硫酸及びフッ化水素酸の混合液中、１８０℃１８時間の条件で加圧酸分解した。その後、加圧酸分解により得られた溶液をホットプレート上で乾燥させることで固化させ、得られた固形分を硝酸と混合して混合液とした。次いで、得られた混合液をホットプレート上で加熱することで固形分を溶解させて硝酸溶液を得た後、該硝酸溶液中のウラン量をＩＣＰ－ＭＳ（誘導結合プラズマ質量分析装置）を用いて測定した。ＩＣＰ－ＭＳの測定条件は以下のとおりとした。
（ＩＣＰ－ＭＳ測定条件）
プラズマモード：低マトリックスモード、チューンモード：Ｈｅ、スペクトルモード　ピークパターン：１ポイント、繰り返し：３、スイープ回数：１００、積分時間：１秒 The uranium content of boron nitride powder was determined by the following method.
In accordance with JCRS108 boron nitride powder chemical analysis method, 0.5 g of a sample (boron nitride powder) was subjected to pressure acid decomposition in a mixture of nitric acid, sulfuric acid and hydrofluoric acid at 180° C. for 18 hours. Thereafter, the solution obtained by the pressure acid decomposition was dried on a hot plate to solidify, and the obtained solid content was mixed with nitric acid to obtain a mixed solution. Next, the resulting mixed solution is heated on a hot plate to dissolve the solid content to obtain a nitric acid solution, and the amount of uranium in the nitric acid solution is measured using ICP-MS (inductively coupled plasma mass spectrometer). measured by The ICP-MS measurement conditions were as follows.
(ICP-MS measurement conditions)
Plasma mode: low matrix mode, tune mode: He, spectrum mode Peak pattern: 1 point, repetition: 3, number of sweeps: 100, integration time: 1 second
　窒化ホウ素粉末の配向性指数は、粉末Ｘ線回折法による測定結果から決定した。まずＸ線回折装置（株式会社リガク製、商品名：ＵＬＴＩＭＡ－ＩＶ）に付属している深さ０．２ｍｍの凹部を有するガラスセルの凹部に、窒化ホウ素粉末を充填し、粉末試料成型機（株式会社アメナテック製、商品名：ＰＸ７００）を用いて、設定圧力Ｍにて固めることで測定サンプルを調整した。上記成型機にて固めた充填物の表面が平滑になっていない場合は手動で平滑にしてから測定を行った。測定サンプルにＸ線を照射して、ベースライン補正を行った後、窒化ホウ素の（００２）面と（１００）面とのピーク強度比を算出し、この数値に基づき配向性指数［Ｉ（００２）／Ｉ（１００）］を決定した。 The orientation index of the boron nitride powder was determined from the measurement results by the powder X-ray diffraction method. First, boron nitride powder was filled into the concave portion of a glass cell having a concave portion with a depth of 0.2 mm attached to an X-ray diffractometer (manufactured by Rigaku Co., Ltd., product name: ULTIMA-IV), and a powder sample molding machine ( Ameena Tech Co., Ltd., product name: PX700) was used to solidify at a set pressure M to prepare a measurement sample. When the surface of the filling solidified by the molding machine was not smooth, it was smoothed manually before measurement. After irradiating the measurement sample with X-rays and performing baseline correction, the peak intensity ratio between the (002) plane and the (100) plane of boron nitride is calculated, and based on this value, the orientation index [I (002 )/I(100)] was determined.
　窒化ホウ素粉末の純度は以下の方法で決定した。まず、窒化ホウ素粉末を水酸化ナトリウムでアルカリ分解させ、水蒸気蒸留法によって分解液からアンモニアを蒸留して、ホウ酸水溶液に捕集した。この捕集液を対象として、硫酸規定液で滴定を行った。滴定の結果から窒化ホウ素粉末中の窒素原子（Ｎ）の含有量を算出した。得られた窒素原子の含有量から、式（１）に基づいて、窒化ホウ素粉末中の窒化ホウ素の含有量を決定し、窒化ホウ素粉末の純度を算出した。なお、窒化ホウ素の式量は２４．８１８ｇ／ｍｏｌ、窒素原子の原子量は１４．００６ｇ／ｍｏｌを用いた。
　窒化ホウ素粉末中の窒化ホウ素（ＢＮ）の含有量［質量％］＝窒素原子（Ｎ）の含有量［質量％］×１．７７２・・・（１） The purity of boron nitride powder was determined by the following method. First, boron nitride powder was alkali-decomposed with sodium hydroxide, ammonia was distilled from the decomposed solution by steam distillation, and collected in an aqueous boric acid solution. This collected liquid was subjected to titration with a normal sulfuric acid solution. The content of nitrogen atoms (N) in the boron nitride powder was calculated from the titration results. Based on the obtained nitrogen atom content, the content of boron nitride in the boron nitride powder was determined based on the formula (1), and the purity of the boron nitride powder was calculated. The formula weight of boron nitride is 24.818 g/mol, and the atomic weight of nitrogen atoms is 14.006 g/mol.
Boron nitride (BN) content [mass%] in the boron nitride powder = Nitrogen atom (N) content [mass%] x 1.772 (1)
　窒化ホウ素粉末の平均粒子径は、ＩＳＯ　１３３２０：２００９の記載に準拠し、ベックマン・コールター社製のレーザー回折散乱法粒度分布測定装置（装置名：ＬＳ－１３　３２０）を用いて測定した。なお、窒化ホウ素粉末に対するホモジナイザー処理は行わなかった。粒度分布の測定に際し、窒化ホウ素粉末を分散させる溶媒には水を用い、分散剤にはヘキサメタリン酸を用いた。この際、水の屈折率として１．３３の数値を用い、窒化ホウ素粉末の屈折率として１．８０の数値を用いた。 The average particle size of the boron nitride powder was measured according to ISO 13320:2009 using a Beckman Coulter laser diffraction scattering particle size distribution analyzer (device name: LS-13 320). The boron nitride powder was not treated with a homogenizer. In measuring the particle size distribution, water was used as a solvent for dispersing the boron nitride powder, and hexametaphosphoric acid was used as a dispersant. At this time, a numerical value of 1.33 was used as the refractive index of water, and a numerical value of 1.80 was used as the refractive index of the boron nitride powder.
　凝集粒子の圧壊強度は、ＪＩＳ　Ｒ　１６３９－５：２００７「ファインセラミックス－か（顆）粒特性の測定方法－第５部：単一か粒圧壊強さ」の記載に準拠して測定した。測定には、微小圧縮試験器（株式会社島津製作所製、製品名「ＭＣＴ－Ｗ５００」）を用いた。なお、測定は、２０個以上の凝集粒子に対して行い、累積破壊率６３．２％時点の値を算出した。 The crushing strength of agglomerated particles was measured according to the description in JIS R 1639-5:2007 "Fine ceramics-Method for measuring (granule) properties-Part 5: Single granule crushing strength". For the measurement, a microcompression tester (manufactured by Shimadzu Corporation, product name "MCT-W500") was used. In addition, the measurement was performed for 20 or more aggregated particles, and the value at the time of cumulative destruction rate of 63.2% was calculated.
＜実施例２～４＞
　脱炭結晶化工程における焼成温度及び／又は焼成時間を表１に示すように変更したこと以外は、実施例１と同様にして、実施例２～４の窒化ホウ素粉末をそれぞれ得た。また、実施例１と同様にして、窒化ホウ素粉末のウラン含有量、配向性指数、純度及び平均粒子径、並びに、窒化ホウ素粉末中の凝集粒子の圧壊強度を測定した。結果を表１に示す。 <Examples 2 to 4>
Boron nitride powders of Examples 2 to 4 were obtained in the same manner as in Example 1, except that the firing temperature and/or firing time in the decarburization and crystallization step were changed as shown in Table 1. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 1 shows the results.
＜実施例５＞
　［炭化ホウ素粉末の準備］におけるボールミルによる粉砕を、回転数１００ｒｐｍで１００分間行い、その後の分級を目開き３４μｍの振動篩を用いて行ったこと、及び、［脱炭結晶化工程］における解砕後の分級を目開き４５μｍの篩を用いて行ったこと以外は、実施例１と同様にして、実施例５の窒化ホウ素粉末を得た。また、実施例１と同様にして、窒化ホウ素粉末のウラン含有量、配向性指数、純度及び平均粒子径、並びに、窒化ホウ素粉末中の凝集粒子の圧壊強度を測定した。結果を表１に示す。 <Example 5>
Pulverization with a ball mill in [Preparation of boron carbide powder] was performed for 100 minutes at a rotation speed of 100 rpm, and then classification was performed using a vibrating sieve with an opening of 34 μm, and crushing in [Decarburization and crystallization step]. A boron nitride powder of Example 5 was obtained in the same manner as in Example 1, except that the subsequent classification was performed using a sieve with an opening of 45 μm. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 1 shows the results.
＜比較例１～２＞
　脱炭結晶化工程におけるホウ酸及び炭酸ナトリウムの使用量（原料混合物の全質量基準）を表１に示す値に変更したこと以外は、実施例１と同様にして、比較例１～２の窒化ホウ素粉末をそれぞれ得た。また、実施例１と同様にして、窒化ホウ素粉末のウラン含有量、配向性指数、純度及び平均粒子径、並びに、窒化ホウ素粉末中の凝集粒子の圧壊強度を測定した。結果を表１に示す。 <Comparative Examples 1 and 2>
Nitriding of Comparative Examples 1 and 2 was performed in the same manner as in Example 1, except that the amounts of boric acid and sodium carbonate used (based on the total mass of the raw material mixture) in the decarburization and crystallization step were changed to the values shown in Table 1. Boron powder was obtained respectively. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 1 shows the results.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
＜実施例６＞
［酸処理工程］
　実施例１と同様にして準備した炭化ホウ素粉末に対して酸処理を行った。具体的には、まず、実施例１と同様にして準備した炭化ホウ素粉末を用意した。次いで、フッ化水素酸溶液と塩酸溶液とを混合して酸溶液を準備した。酸溶液の酸濃度は４０質量％とし、酸溶液中のフッ化水素酸と塩酸との質量比（ＨＦとＨＣｌとの質量比）は１：１とした（すなわち、酸溶液中のフッ化水素酸濃度及び塩酸濃度はいずれも２０質量％とした。）。次いで、酸溶液を８０℃に加熱保持し、ここに炭化ホウ素粉末を投入して８０℃で５時間撹拌した。このようにして、炭化ホウ素粉末と酸溶液とを接触させ、炭化ホウ素粉末の酸処理を行った。撹拌後、デカンテーションを行い、新たな酸溶液を追加して酸処理を行う操作を１５回繰り返した。その後、スラリーを乾燥することによって、酸処理された炭化ホウ素粉末を得た。得られた炭化ホウ素粉末の平均粒子径及び純度を、実施例１に記載した方法により測定したところ、平均粒子径は２０μｍであり、純度は９９質量％であった。 <Example 6>
[Acid treatment process]
Boron carbide powder prepared in the same manner as in Example 1 was subjected to acid treatment. Specifically, first, boron carbide powder prepared in the same manner as in Example 1 was prepared. An acid solution was then prepared by mixing a hydrofluoric acid solution and a hydrochloric acid solution. The acid concentration of the acid solution was 40% by mass, and the mass ratio of hydrofluoric acid and hydrochloric acid in the acid solution (mass ratio of HF and HCl) was 1:1 (i.e., hydrogen fluoride in the acid solution Both the acid concentration and the hydrochloric acid concentration were set to 20% by mass.). Next, the acid solution was heated and maintained at 80° C., and boron carbide powder was added thereto and stirred at 80° C. for 5 hours. In this way, the boron carbide powder and the acid solution were brought into contact with each other, and the boron carbide powder was acid-treated. After stirring, decantation was performed, and the operation of adding a new acid solution and performing acid treatment was repeated 15 times. The slurry was then dried to obtain an acid-treated boron carbide powder. When the average particle size and purity of the obtained boron carbide powder were measured by the method described in Example 1, the average particle size was 20 μm and the purity was 99% by mass.
　次いで、炭化ホウ素粉末として上記酸処理された炭化ホウ素粉末を使用したこと以外は、実施例１と同様にして加圧窒化工程及び脱炭結晶化工程を行い、実施例６の窒化ホウ素粉末を得た。また、実施例１と同様にして、窒化ホウ素粉末のウラン含有量、配向性指数、純度及び平均粒子径、並びに、窒化ホウ素粉末中の凝集粒子の圧壊強度を測定した。結果を表２に示す。 Next, the pressurized nitriding step and the decarburization and crystallization step were performed in the same manner as in Example 1 except that the acid-treated boron carbide powder was used as the boron carbide powder to obtain the boron nitride powder of Example 6. Ta. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 2 shows the results.
＜実施例７＞
　脱炭結晶化工程における焼成温度及び焼成時間を表２に示すように変更したこと以外は、実施例６と同様にして、実施例７の窒化ホウ素粉末を得た。また、実施例１と同様にして、窒化ホウ素粉末のウラン含有量、配向性指数、純度及び平均粒子径、並びに、窒化ホウ素粉末中の凝集粒子の圧壊強度を測定した。結果を表２に示す。 <Example 7>
A boron nitride powder of Example 7 was obtained in the same manner as in Example 6, except that the firing temperature and firing time in the decarburization and crystallization step were changed as shown in Table 2. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 2 shows the results.
＜実施例８＞
　酸処理工程における酸溶液の濃度、処理温度（炭化ホウ素粉末と酸溶液との混合液の温度）及び処理時間（撹拌時間）を表２に示す値に変更したこと以外は、実施例７と同様にして、実施例８の窒化ホウ素粉末を得た。また、実施例１と同様にして、窒化ホウ素粉末のウラン含有量、配向性指数、純度及び平均粒子径、並びに、窒化ホウ素粉末中の凝集粒子の圧壊強度を測定した。結果を表２に示す。なおウランと同様に分析したところ、トリウム量は４質量ｐｐｂであった。 <Example 8>
Same as Example 7 except that the concentration of the acid solution, the treatment temperature (the temperature of the mixture of the boron carbide powder and the acid solution), and the treatment time (stirring time) in the acid treatment step were changed to the values shown in Table 2. Then, the boron nitride powder of Example 8 was obtained. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 2 shows the results. When analyzed in the same manner as uranium, the amount of thorium was 4 mass ppb.
＜実施例９＞
　酸処理工程における酸溶液の濃度、酸溶液の配合、処理温度（炭化ホウ素粉末と酸溶液との混合液の温度）及び処理時間（撹拌時間）を表２に示す値に変更したこと以外は、実施例６と同様にして、実施例９の窒化ホウ素粉末を得た。また、実施例１と同様にして、窒化ホウ素粉末のウラン含有量、配向性指数、純度及び平均粒子径、並びに、窒化ホウ素粉末中の凝集粒子の圧壊強度を測定した。結果を表２に示す。 <Example 9>
Except for changing the concentration of the acid solution, the composition of the acid solution, the treatment temperature (the temperature of the mixture of the boron carbide powder and the acid solution), and the treatment time (stirring time) in the acid treatment step to the values shown in Table 2, Boron nitride powder of Example 9 was obtained in the same manner as in Example 6. Further, in the same manner as in Example 1, the uranium content, orientation index, purity and average particle size of the boron nitride powder, and the crushing strength of aggregated particles in the boron nitride powder were measured. Table 2 shows the results.
Figure JPOXMLDOC01-appb-T000002
  
 

 
Figure JPOXMLDOC01-appb-T000002
  
 

 

Claims (9)

  1. 　炭窒化ホウ素粉末とホウ素源と炭酸塩とを含む原料混合物を焼成することによって、窒化ホウ素の一次粒子を生成し、前記一次粒子が凝集して構成される凝集粒子を含む粉末を得る脱炭結晶化工程を含み、
    　前記脱炭結晶化工程において、前記ホウ素源の使用量が、前記原料混合物の全質量を基準として、５５質量％以上であり、前記炭酸塩の使用量が、前記原料混合物の全質量を基準として、４質量％以上である、窒化ホウ素粉末の製造方法。     A decarburized crystal obtained by firing a raw material mixture containing a boron carbonitride powder, a boron source, and a carbonate to produce primary particles of boron nitride, and obtaining a powder containing aggregated particles constituted by aggregating the primary particles. including the conversion process,
    In the decarburization and crystallization step, the amount of the boron source used is 55% by mass or more based on the total mass of the raw material mixture, and the amount of the carbonate used is based on the total mass of the raw material mixture. , 4% by mass or more, a method for producing a boron nitride powder.
  2. 　前記脱炭結晶化工程における焼成温度が１８００℃以上であり、焼成時間が８時間以上である、請求項１に記載の窒化ホウ素粉末の製造方法。 The method for producing boron nitride powder according to claim 1, wherein the firing temperature in the decarburization and crystallization step is 1800°C or higher, and the firing time is 8 hours or longer.
  3. 　前記脱炭結晶化工程における焼成温度が２０００℃以上であり、焼成時間が４時間以上である、請求項１に記載の窒化ホウ素粉末の製造方法。 The method for producing boron nitride powder according to claim 1, wherein the firing temperature in the decarburization and crystallization step is 2000°C or higher, and the firing time is 4 hours or longer.
  4. 　前記炭窒化ホウ素粉末を準備する準備工程を更に含み、
    　前記準備工程は、炭化ホウ素粉末にフッ化水素酸を含む酸溶液を接触させて、前記炭化ホウ素粉末を酸処理する酸処理工程と、酸処理された前記炭化ホウ素粉末を窒素加圧雰囲気下で焼成する加圧窒化工程と、を含む、請求項１～３のいずれか一項に記載の窒化ホウ素粉末の製造方法。     further comprising a preparation step of preparing the boron carbonitride powder;
    The preparation step comprises an acid treatment step of contacting the boron carbide powder with an acid solution containing hydrofluoric acid to acid-treat the boron carbide powder; The method for producing the boron nitride powder according to any one of claims 1 to 3, comprising a pressure nitriding step of firing.
  5. 　前記酸溶液が、前記フッ化水素酸を含む混酸であり、
    　前記混酸中の全酸成分に占めるフッ化水素酸の割合が、１０質量％以上である、請求項４に記載の窒化ホウ素粉末の製造方法。     The acid solution is a mixed acid containing the hydrofluoric acid,
    5. The method for producing boron nitride powder according to claim 4, wherein the ratio of hydrofluoric acid to all acid components in said mixed acid is 10% by mass or more.
  6. 　前記酸処理工程における処理温度が６０℃以上であり、
    　前記酸処理工程における処理時間が３時間以上であり、
    　前記酸溶液の酸濃度が２０質量％以上である、請求項４に記載の窒化ホウ素粉末の製造方法。     The treatment temperature in the acid treatment step is 60° C. or higher,
    The treatment time in the acid treatment step is 3 hours or more,
    The method for producing boron nitride powder according to claim 4, wherein the acid concentration of the acid solution is 20% by mass or more.
  7. 　窒化ホウ素の一次粒子が凝集して構成される凝集粒子を含み、
    　配向性指数が１５以下であり、
    　ウラン含有量が２０質量ｐｐｂ以下である、窒化ホウ素粉末。     Containing agglomerated particles composed of agglomerated primary particles of boron nitride,
    The orientation index is 15 or less,
    A boron nitride powder having a uranium content of 20 mass ppb or less.
  8. 　純度が９８．５質量％以上であり、平均粒子径が１０～９０μｍであり、
    　前記凝集粒子の圧壊強度が５ＭＰａ以上である、請求項７に記載の窒化ホウ素粉末。     Purity is 98.5% by mass or more, average particle size is 10 to 90 μm,
    8. The boron nitride powder according to claim 7, wherein the crushing strength of said aggregated particles is 5 MPa or more.
  9. 　請求項７又は８に記載の窒化ホウ素粉末を含む、半導体メモリ素子用の樹脂封止材。 A resin encapsulant for semiconductor memory elements, containing the boron nitride powder according to claim 7 or 8.
PCT/JP2023/003085 2022-02-22 2023-01-31 Method for producing boron nitride powder, boron nitride powder, and resin sealing material WO2023162598A1 (en)

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WO2019073690A1 (en) * 2017-10-13 2019-04-18 デンカ株式会社 Boron nitride powder, method for producing same, and heat-dissipating member produced using same
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