Boron nitride sintered body, composite, and methods for manufacturing the same, and heat dissipation member

Abstract

Provided is a sheet-like boron nitride sintered body that includes boron nitride particles and pores and that has a thickness of less than 2 mm. Also provided is a manufacturing method for said boron nitride sintered body, the manufacturing method including a sintering step for heating and molding a compound containing boron carbonitride powder and a sintering assistant to obtain a sheet-like boron nitride sintered body that includes boron nitride particles and pores. The thickness of the boron nitride sintered body obtained in the sintering step is less than 2 mm.

Description

[Technical Field]

[0001] This disclosure relates to boron nitride sintered bodies, composites, methods for manufacturing the same, and heat dissipation members. [Background technology]

[0002] Power devices, transistors, thyristors, CPUs, and other components require efficient heat dissipation during use. To address this need, conventional methods have included increasing the thermal conductivity of the insulating layer of printed circuit boards on which electronic components are mounted, or attaching electronic components or printed circuit boards to heat sinks via electrically insulating thermal interface materials. Such insulating layers and thermal interface materials utilize composite materials (heat dissipation components) composed of resin and ceramics such as boron nitride.

[0003] As such a composite material, the use of a composite in which a resin is impregnated into a porous ceramic molded body is being considered. Since boron nitride has lubricating properties, high thermal conductivity, and insulating properties, the use of ceramics containing boron nitride as a heat dissipation member is being considered. Patent Document 1 proposes a technique to reduce the anisotropy of thermal conductivity while maintaining excellent thermal conductivity by setting the degree of orientation and graphitization index within a predetermined range. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2014-162697 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] With the increasing integration of circuits within electronic components in recent years, there is a growing demand for heat dissipation materials that possess both excellent electrical insulation and thermal conductivity. While there is a need for high performance in various materials, the space available for mounting electronic components is usually limited, so it is also considered necessary to establish technologies for miniaturizing the materials mounted on electronic components.

[0006] Therefore, this disclosure provides thin boron nitride sintered bodies and composites suitable as components for electronic components, and methods for manufacturing the same. Furthermore, this disclosure provides heat dissipation members suitable as components for electronic components. [Means for solving the problem]

[0007] In one aspect, this disclosure provides a boron nitride sintered body containing boron nitride particles and pores, which is in sheet form and has a thickness of less than 2 mm. Such a boron nitride sintered body has excellent electrical insulation and thermal conductivity because it contains boron nitride particles. Furthermore, because it is thin, it can be used as a component for electronic components, etc., and can be used to miniaturize electronic components, etc. Therefore, it is suitable as a component for electronic components, etc. In addition, because it is thin and contains pores, it can be made lightweight, and the pores can be smoothly filled with resin to form a composite.

[0008] The orientation index of the above boron nitride sintered body may be 40 or less. When boron nitride particles are formed into a sheet, they usually orient in a direction perpendicular to the thickness direction, and tend to have low thermal conductivity in the thickness direction. However, this tendency can be reduced by decreasing the orientation index. Therefore, the anisotropy of thermal conductivity can be sufficiently reduced, and the thermal conductivity in the thickness direction can be sufficiently increased.

[0009] The porosity of the boron nitride sintered body described above may be 30-65% by volume. The bulk density may be 800-1500 kg / m³. 3This is acceptable. By having at least one of the porosity and bulk density within this range, it is possible to achieve a sufficiently high thermal conductivity while reducing weight. Furthermore, such a boron nitride sintered body can form a composite that achieves both excellent thermal conductivity and high electrical insulation properties.

[0010] The average pore size of the boron nitride sintered body described above may be less than 4.0 μm. By reducing the pore size in this way, the contact area between the primary boron nitride particles can be sufficiently increased. Therefore, the thermal conductivity can be sufficiently high.

[0011] The boron nitride sintered body described above does not need to have a cut surface. Such a boron nitride sintered body does not have the fine cracks that can occur when it is cut. Therefore, its reliability as a component can be further improved.

[0012] In one aspect, this disclosure provides a composite comprising any of the boron nitride sintered bodies described above and a resin filling at least a portion of the pores of the boron nitride sintered body. Because this composite comprises the boron nitride sintered body and the resin, it possesses both excellent thermal conductivity and excellent electrical insulation properties. Furthermore, because it is thin and lightweight, it can be used as a component in electronic components and the like to achieve miniaturization and weight reduction. Therefore, it is suitable as a component in electronic components and the like.

[0013] This disclosure provides, in one aspect, a heat dissipation member having the aforementioned composite material. Because this heat dissipation member has the aforementioned composite material, it possesses both excellent thermal conductivity and excellent electrical insulation properties. Furthermore, because it is thin and lightweight, it can be miniaturized and lightened when used as a heat dissipation member for electronic components, etc. Therefore, it is suitable as a component for electronic components, etc.

[0014] In one aspect, the present disclosure provides a method for manufacturing a composite having a boron nitride sintered body and a resin filled in at least a part of pores of the boron nitride sintered body, the method including an impregnation step of impregnating the boron nitride sintered body described in any of the above with a resin composition. In this manufacturing method, since a sheet-like boron nitride sintered body having a thickness of less than 2 mm is used, the impregnation of the resin composition proceeds smoothly. As a result, a composite having a high resin filling rate and excellent electrical insulation can be easily obtained. Further, since the above-described boron nitride sintered body is used, it has excellent electrical insulation and thermal conductivity. Also, since it can be made thin and lightweight, miniaturization and weight reduction can be achieved when used as a member such as an electronic component. Therefore, it is suitable as a member such as an electronic component.

[0015] In one aspect, the present disclosure provides a method for manufacturing a boron nitride sintered body, the method including a sintering step of molding and heating a formulation containing boron carbonitride powder and a sintering aid to obtain a boron nitride sintered body containing boron nitride particles and pores, wherein the thickness of the boron nitride sintered body obtained in the sintering step is less than 2 mm.

[0016] In one aspect, the present disclosure provides a method for manufacturing a boron nitride sintered body, the method including a nitriding step of firing boron carbide powder in a nitrogen atmosphere to obtain a fired product containing boron carbonitride, and a sintering step of molding and heating a formulation containing the fired product and a sintering aid to obtain a boron nitride sintered body containing boron nitride particles and pores, wherein the thickness of the boron nitride sintered body obtained in the sintering step is less than 2 mm.

[0017] The boron nitride sintered body obtained by these production methods contains boron nitride particles, and thus is excellent in electrical insulation and thermal conductivity. Further, since the thickness is less than 2 mm, it is thin, and when used as a member of a circuit, miniaturization of the circuit can be achieved. Further, since it is thin and contains pores, weight reduction can be achieved, and the pores can be smoothly filled with resin to form a composite. Further, since a fired product containing boron carbonitride is used, the anisotropy of the thermal conductivity of the sheet-like boron nitride sintered body can be sufficiently reduced, and the thermal conductivity in the thickness direction can be made sufficiently high. Therefore, it is suitable as a member for electronic components and the like.

[0018] In one aspect, the present disclosure provides a method for producing a composite including an impregnation step of impregnating a boron nitride sintered body obtained by any of the above production methods with a resin composition, the composite including the boron nitride sintered body and resin filled in at least a part of the pores of the boron nitride sintered body. The composite obtained by such a production method includes the above-described boron nitride sintered body and resin, and thus has both excellent thermal conductivity and excellent electrical insulation. Further, since it is thin and lightweight, miniaturization and weight reduction can be achieved when used as a member for electronic components and the like. Therefore, it is suitable as a member for electronic components and the like.

Advantages of the Invention

[0019] According to the present disclosure, it is possible to provide a thin boron nitride sintered body and composite suitable as a member for electronic components and the like, and production methods thereof. Further, in the present disclosure, it is possible to provide a heat dissipation member suitable as a member for electronic components and the like.

Brief Description of the Drawings

[0020] [Figure 1] FIG. 1 is a perspective view showing an example of a boron nitride sintered body. [Figure 2] FIG. 2 is a photograph showing an example of a molded body for producing a boron nitride sintered body.

Embodiments for Carrying Out the Invention

[0021] The embodiments of this disclosure will be described below, with reference to the drawings as appropriate. However, the embodiments described below are illustrative examples for illustrating this disclosure and are not intended to limit this disclosure to the following.

[0022] Boron nitride sintered bodies are in sheet form (thin plate shape). Boron nitride sintered bodies are porous and have a thickness of less than 2 mm. Boron nitride sintered bodies contain boron nitride particles formed by the sintering of primary boron nitride particles and pores (they contain portions where primary boron nitride particles have been sintered together and pores formed by the sintered primary particles). Because boron nitride sintered bodies contain boron nitride particles (because they are formed by the sintering of primary boron nitride particles), they have excellent electrical insulation and thermal conductivity. Boron nitride sintered bodies may be composed of boron nitride particles.

[0023] Boron nitride sintered bodies are thin, with a thickness of less than 2 mm, and can be used as components for electronic parts, etc., to enable miniaturization of such parts. Furthermore, their thinness and pore structure allow for weight reduction, and the pores can be smoothly filled with resin to form composites. (Note that sintering of primary particles includes sintering of primary particles within secondary particles.)

[0024] From the viewpoint of further miniaturization and weight reduction, the thickness of the boron nitride sintered body may be less than 1 mm, or less than 0.5 mm. From the viewpoint of ease of molded body fabrication, the thickness of the boron nitride sintered body may be 0.1 mm or more, or 0.2 mm or more.

[0025] Figure 1 is a perspective view showing an example of a boron nitride sintered body. The boron nitride sintered body 10 has a thickness t. The thickness t is less than 2 mm. The boron nitride sintered body 10 may be manufactured by uniaxial pressing along the thickness direction. The area of ​​the main surface 10a is 25 mm². 2 The above is sufficient, and 100mm 2 The above is sufficient, and 800mm 2 The above is sufficient, and 1000mm 2 That's fine too.

[0026] Because the boron nitride sintered body 10 has a small thickness t, impregnation with the resin composition can be carried out smoothly. As a result, the pores of the boron nitride sintered body are sufficiently filled with resin, and a composite material with excellent electrical insulation properties can be obtained.

[0027] The shape of the boron nitride sintered body is not limited to a rectangular prism shape as shown in Figure 1; for example, it may be cylindrical, or it may be a C-shape with a curved main surface 10a. The boron nitride sintered body does not need to have a cross-section. For example, it may be obtained by sintering a sheet-like molded body as shown in Figure 1.

[0028] Boron nitride sintered bodies obtained through a cutting process have fine cracks or fine irregularities (striped patterns) on the cut surface. On the other hand, boron nitride sintered bodies obtained without a cutting process do not have a cut surface, so fine cracks and irregularities (striped patterns) on the surface can be sufficiently reduced. Therefore, boron nitride sintered bodies obtained without a cutting process can further improve thermal conductivity while maintaining sufficiently high strength. In other words, they have superior reliability as components for electronic parts, etc. Furthermore, material loss occurs when processing such as cutting. Therefore, boron nitride sintered bodies without a cut surface can reduce material loss. This can improve the yield of boron nitride sintered bodies.

[0029] In the modified example, it is sufficient that both of the pair of main surfaces 10a and 10b of the boron nitride sintered body 10 in Figure 1 are not cut surfaces. That is, the side surfaces of the boron nitride sintered body 10 may be cut surfaces. In this case as well, it is possible to sufficiently reduce the fine cracks that may occur due to cutting on both of the pair of main surfaces 10a and 10b. Therefore, it is possible to maintain sufficiently high thermal conductivity. In addition, material loss can be reduced compared to the case where both of the pair of main surfaces 10a and 10b are cut surfaces. The surface of the boron nitride sintered body may be shaped by polishing or the like. The main surfaces may have an area of ​​more than twice the area of ​​the side surfaces, and may have an area of ​​more than four times the area.

[0030] The orientation index of the boron nitride crystals in the boron nitride sintered body may be 40 or less, 30 or less, 15 or less, or 10 or less. This allows for a sufficient reduction in the anisotropy of thermal conductivity. Therefore, the thermal conductivity along the thickness direction of the sheet-like boron nitride sintered body can be made sufficiently high.

[0031] The orientation index of the boron nitride sintered body may be 2.0 or higher, 3.0 or higher, or 4.0 or higher. The orientation index in this disclosure is an index for quantifying the degree of orientation of boron nitride crystals. The orientation index can be calculated as the peak intensity ratio of the (002) plane and the (100) plane of boron nitride measured by an X-ray diffractometer [I(002) / I(100)].

[0032] The average pore size of the pores in the boron nitride sintered body may be less than 4.0 μm. By reducing the size of the pores, the contact area between primary boron nitride particles can be sufficiently increased. Therefore, the thermal conductivity can be further increased. From the viewpoint of further increasing the thermal conductivity, the average pore size of the pores may be less than 3.8 μm, less than 3 μm, or less than 2 μm. From the viewpoint of facilitating the impregnation of the resin composition into the boron nitride sintered body, the average pore size of the pores may be 0.1 μm or more, or 0.2 μm or more.

[0033] The average pore diameter is determined using a mercury porosimeter, based on the pore diameter distribution as the pressure is increased from 0.0042 MPa to 206.8 MPa. When the horizontal axis represents pore diameter and the vertical axis represents cumulative pore volume, the average pore diameter is the pore diameter at which the cumulative pore volume reaches 50% of the total pore volume. A mercury porosimeter manufactured by Shimadzu Corporation can be used.

[0034] The porosity of the boron nitride sintered body, that is, the volume ratio of pores in the boron nitride sintered body, may be 30 to 65% by volume, may be 30 to 60% by volume, or may be 35 to 55% by volume. If the porosity becomes too large, the strength of the boron nitride sintered body tends to decrease. On the other hand, if the porosity becomes too small, the mass tends to increase. Also, when manufacturing the composite, the resin content decreases and the electrical insulation tends to deteriorate.

[0035] The porosity can be calculated from the volume and mass of the boron nitride sintered body to obtain the bulk density [B (kg / m 3 )], and from this bulk density and the theoretical density of boron nitride [2280 (kg / m 3 )], it can be determined by the following formula (1). Porosity (volume %) = [1 - (B / 2280)] × 100 (1)

[0036] The bulk density B may be 800 to 1500 kg / m 3 and may be 850 to 1400 kg / m 3 and may even be 900 to 1300 kg / m 3 If the bulk density B becomes too large, the mass of the boron nitride sintered body tends to increase. Also, the resin filling amount decreases and the electrical insulation of the composite tends to deteriorate. On the other hand, if the bulk density B becomes too small, the strength of the boron nitride sintered body tends to decrease.

[0037] The thermal conductivity of the boron nitride sintered body may be 20 W / mK or more, may be 30 W / mK or more, may be 35 W / mK or more, or may be 40 W / mK or more. By using a boron nitride sintered body with a high thermal conductivity, a heat radiating member with sufficiently excellent heat radiating performance can be obtained. The thermal conductivity (H) can be determined by the following calculation formula (2). H = A × B × C (2)

[0038] In formula (2), H is the thermal conductivity (W / (m·K)), A is the thermal diffusivity (m 2 / sec), B is the bulk density (kg / m 3), and C represent the specific heat capacity (J / (kg·K)). The thermal diffusivity A can be measured by the laser flash method. The bulk density B can be determined from the volume and mass of the boron nitride sintered body. The specific heat capacity C can be measured using a differential scanning calorimeter. The boron nitride sintered body may have the above-mentioned thermal conductivity in the thickness direction.

[0039] One embodiment of the composite is a composite of a boron nitride sintered body and a resin, comprising the boron nitride sintered body and a resin filling at least a portion of the pores of the boron nitride sintered body. Examples of resins that can be used include epoxy resin, silicone resin, cyanate resin, silicone rubber, acrylic resin, phenolic resin, melamine resin, urea resin, bismaleimide resin, unsaturated polyester, fluororesin, polyimide, polyamideimide, polyetherimide, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, fully aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide resin, maleimide-modified resin, ABS (acrylonitrile-butadiene-styrene) resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin, polyglycolic acid resin, polyphthalamide, polyacetal, etc. This may include one of these types alone, or two or more types in combination.

[0040] When the composite is used as an insulating layer for printed circuit boards, the resin may contain epoxy resin from the viewpoint of improving heat resistance and adhesion strength to circuits. When the composite is used as a thermal interface material, the resin may contain silicone resin from the viewpoint of improving heat resistance, flexibility, and adhesion to heat sinks, etc. The resin may be a cured product or a semi-cured product (B-stage state).

[0041] Figure 1 is a perspective view showing an example of a composite. The composite 20 has a thickness t. The thickness t is less than 2 mm. The area of ​​the main surfaces 20a and 20b is 25 mm². 2The above is sufficient, and 100mm 2 The above is sufficient, and 800mm 2 The above is sufficient, and 1000mm 2 That's fine too.

[0042] Because the composite 20 has a small thickness t, the resin is sufficiently filled into the pores of the boron nitride sintered body 10. Therefore, it exhibits excellent electrical insulation properties. The thickness t of the composite 20 does not have to be the same as the thickness of the boron nitride sintered body 10. For example, the boron nitride sintered body 10 may have a resin layer on its surface.

[0043] The shape of the composite is not limited to a rectangular prism shape as shown in Figure 1; for example, it may be cylindrical, or a C-shape with curved main surfaces 20a and 20b. The composite does not need to have a cut surface. A composite obtained without a cutting process does not have the fine cracks that can occur as a result of cutting. Therefore, it is possible to further improve thermal conductivity while maintaining sufficiently high strength. In other words, it has excellent reliability as a component for electronic parts, etc. Also, material loss occurs when processing such as cutting is performed. For this reason, a composite without a cut surface can reduce material loss. This can improve the yield of the composite.

[0044] The content of boron nitride particles in the composite may be 40-70% by volume, or 45-65% by volume, based on the total volume of the composite. The content of resin in the composite may be 30-60% by volume, or 35-55% by volume, based on the total volume of the composite. A composite containing boron nitride particles and resin in such proportions can achieve both high electrical insulation and high thermal conductivity at a high level. From the viewpoint of further improving these properties, the porosity of the composite may be 10% by volume or less, 5% by volume or less, or 3% by volume or less. This porosity can be determined, for example, from the bulk density B1 (kg / m³) calculated from the volume and mass of the composite. 3 ) and the theoretical density B2 (kg / m³) when the resin composition is impregnated into all the pores of the boron nitride sintered body. 3 It can be calculated from ).

[0045] The composite may further contain other components in addition to the boron nitride sintered body and the resin filling its pores. These other components include curing agents, inorganic fillers, silane coupling agents, defoaming agents, surface modifiers, and wetting dispersants. The inorganic filler may contain one or more selected from the group consisting of aluminum oxide, silicon oxide, zinc oxide, silicon nitride, aluminum nitride, and aluminum hydroxide. This further improves the thermal conductivity of the composite.

[0046] The composite of this embodiment, comprising the boron nitride sintered body described above and the resin filled in its pores, possesses both excellent thermal conductivity and excellent electrical insulation properties. Furthermore, because it is thin and lightweight, it can contribute to the miniaturization and weight reduction of electronic components when used as a component in such devices. Due to these characteristics, the composite can be suitably used as a heat dissipation member. The heat dissipation member may be composed of the composite described above, or it may be composed of the composite in combination with other materials (for example, a metal plate such as aluminum).

[0047] An example of a method for manufacturing boron nitride sintered bodies, composites, and heat dissipation members is described below. The method for manufacturing the boron nitride sintered body in this example comprises a nitriding step of firing boron carbide powder under a nitrogen pressurized atmosphere to obtain a fired product containing boron carbonitride, and a sintering step of molding and heating a compound containing the fired product and a sintering aid to obtain a boron nitride sintered body containing boron nitride particles and pores.

[0048] Boron carbide powder can be prepared, for example, by the following procedure: After mixing boric acid and acetylene black, the mixture is heated in an inert gas atmosphere at 1800-2400°C for 1-10 hours to obtain boron carbide lumps. These boron carbide lumps can then be prepared by grinding, washing, removing impurities, and drying.

[0049] In the nitriding process, boron carbide powder is calcined under a nitrogen atmosphere to obtain a calcined product containing boron carbonitride (B4CN4). The calcination temperature in the nitriding process may be 1800°C or higher, or 1900°C or higher. Alternatively, the calcination temperature may be 2400°C or lower, or 2200°C or lower. For example, the calcination temperature may be between 1800°C and 2400°C.

[0050] The pressure in the nitriding process may be 0.6 MPa or higher, or 0.7 MPa or higher. It may also be 1.0 MPa or lower, or 0.9 MPa or lower. For example, the pressure may be between 0.6 and 1.0 MPa. If the pressure is too low, the nitriding of boron carbide tends to be difficult to proceed. On the other hand, if the pressure is too high, manufacturing costs tend to increase. Note that the pressure in this disclosure is absolute pressure.

[0051] The nitrogen gas concentration in the nitrogen atmosphere during the nitriding process may be 95% by volume or higher, or 99.9% by volume or higher. The partial pressure of nitrogen may be within the pressure range described above. The firing time during the nitriding process is not particularly limited as long as sufficient nitriding is carried out, and may be, for example, 6 to 30 hours, or 8 to 20 hours.

[0052] In the sintering process, a compound may be obtained by blending a calcined product containing boron carbonitride particles obtained in the nitriding process with a sintering aid. The sintering aid may contain boron compounds and calcium compounds. The compound may contain a total of 1 to 30 parts by mass of boron compounds and calcium compounds per 100 parts by mass of the calcined product. By using such a content, excessive grain growth of primary particles is suppressed while allowing for moderate grain growth to promote sintering, and the primary boron nitride particles are tightly and firmly bonded together over a wide area.

[0053] From the viewpoint of sufficiently binding the primary particles of boron nitride, the compound may contain, for example, 1 to 30 parts by mass, 5 to 25 parts by mass, or 8 to 20 parts by mass of boron compounds and calcium compounds in total per 100 parts by mass of the calcined product.

[0054] The compound may contain 0.5 to 40 atomic percent of calcium, or 0.7 to 30 atomic percent, of the boron compound relative to 100 atomic percent of boron. By including boron and calcium in such ratios, homogeneous grain growth of primary particles can be promoted, further increasing the thermal conductivity of the boron nitride sintered body.

[0055] Examples of boron compounds include boric acid, boron oxide, and borax. Examples of calcium compounds include calcium carbonate and calcium oxide. The sintering aid may contain components other than boric acid and calcium carbonate. Examples of such components include alkali metal carbonates such as lithium carbonate and sodium carbonate. In addition, a binder may be added to the mixture to improve moldability. Examples of binders include acrylic compounds.

[0056] When blending the calcined material with the sintering aid, the calcined material may be crushed using a general-purpose pulverizer or crusher. For example, a ball mill, Henschel mixer, vibratory mill, jet mill, etc., can be used. In this disclosure, "crushing" also includes "decomposition." The sintering aid may be blended after crushing the calcined material, or crushing and mixing may be performed simultaneously after blending the calcined material and the sintering aid.

[0057] The compound may be molded into a molded body by powder pressing or die molding, or into a sheet-like molded body by the doctor blade method or extrusion method. The molding pressure may be, for example, 5 to 350 MPa. The molded body may be, for example, a sheet with a thickness of less than 2 mm. By manufacturing a boron nitride sintered body using a sheet-like molded body, it is possible to manufacture a boron nitride sintered body without cut surfaces. Furthermore, compared to cutting block-shaped boron nitride sintered bodies and composites into sheets, material loss due to processing can be reduced by forming the molded body into a sheet from the molding stage. Therefore, sheet-like boron nitride sintered bodies and composites can be manufactured with a high yield.

[0058] The molded body obtained in this way is fired, for example, in an electric furnace. The heating temperature may be, for example, 1800°C or higher, or 1900°C or higher. The heating temperature may be, for example, 2200°C or lower, or 2100°C or lower. If the heating temperature is too low, grain growth tends not to proceed sufficiently. The heating time may be 0.5 hours or more, or 1 hour or more, 3 hours or more, 5 hours or more, or 10 hours or more. The heating time may be 40 hours or less, 30 hours or less, or 20 hours or less. The heating time may be, for example, 0.5 to 40 hours, or 1 to 30 hours. If the heating time is too short, grain growth tends not to proceed sufficiently. On the other hand, if the heating time is too long, it tends to be industrially disadvantageous. The heating atmosphere may be, for example, an inert gas atmosphere such as nitrogen, helium, or argon. When a binder is added to the compound, the compound may be degreased by pre-calcination at a temperature and atmosphere that causes the binder to decompose before the above-mentioned heating.

[0059] Through the above process, a sheet-like boron nitride sintered body containing boron nitride particles and pores, with a thickness of less than 2 mm, can be obtained. In this example, since boron carbonitride is used, the orientation of the boron nitride particles perpendicular to the thickness direction can be suppressed. Therefore, the anisotropy of thermal conductivity can be reduced, and the thickness direction A boron nitride sintered body with excellent thermal conductivity along the direction can be manufactured. The range of orientation index of the boron nitride sintered body is as described above. Furthermore, the above manufacturing method allows for the production of a boron nitride sintered body without a cutting step. This makes it possible to manufacture a highly reliable boron nitride sintered body without cut surfaces with a high yield.

[0060] Although one example of a method for producing a boron nitride sintered body has been described, the method is not limited to this. For example, in the sintering step described above, commercially available boron carbonitride powder may be used instead of the calcined product containing boron carbonitride particles obtained in the nitriding step to obtain a boron nitride sintered body. Alternatively, for example, a boron nitride sintered body may be obtained by drying a water slurry containing flake-shaped and / or amorphous boron nitride powder, a sintering aid, a binder, and water, forming the granules obtained, and then sintering them. By adjusting the thickness during forming, a sheet-like boron nitride sintered body with a thickness of less than 2 mm can be obtained.

[0061] One example of a method for producing the composite involves an impregnation step in which a resin composition is impregnated into a boron nitride sintered body. The boron nitride sintered body may be produced by any of the methods described above. The resin composition may contain resin components, a curing agent, and a solvent from the viewpoint of improving fluidity and handling. In addition, it may also contain inorganic fillers, silane coupling agents, defoaming agents, surface modifiers, wetting and dispersing agents, etc.

[0062] As the resin component, for example, a resin that becomes the resin described above in the description of the composite after curing or semi-curing reaction can be used. As the solvent, for example, aliphatic alcohols such as ethanol and isopropanol, ether alcohols such as 2-methoxyethanol, 1-methoxyethanol, 2-ethoxyethanol, 1-ethoxy-2-propanol, 2-butoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, and 2-(2-butoxyethoxy)ethanol, glycol ethers such as ethylene glycol monomethyl ether and ethylene glycol monobutyl ether, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone, and hydrocarbons such as toluene and xylene. One of these may be included alone, or two or more may be included in combination.

[0063] Impregnation is performed by adhering a resin composition to a boron nitride sintered body. For example, the boron nitride sintered body may be immersed in the resin composition. The process may also be carried out under pressurized or depressurized conditions while immersed. In this way, the pores of the boron nitride sintered body can be filled with resin. Since the boron nitride sintered body is in sheet form and has a thickness of less than 2 mm, the resin can be smoothly filled into the pores. Therefore, the resin filling rate can be made sufficiently high. Consequently, composites with excellent electrical insulation properties can be smoothly manufactured.

[0064] The impregnation process may be carried out using an impregnation apparatus equipped with a sealed container. For example, impregnation may be performed under reduced pressure conditions in the impregnation apparatus, and then the pressure inside the impregnation apparatus may be increased to a level higher than atmospheric pressure for impregnation under pressurized conditions. By performing both reduced pressure and pressurized conditions in this way, the pores of the boron nitride sintered body can be sufficiently filled with resin. The reduced pressure and pressurized conditions may be repeated multiple times. The impregnation process may also be carried out while heating. The resin composition impregnated into the pores of the boron nitride sintered body becomes a resin (cured or semi-cured product) after curing or semi-curing progresses or the solvent evaporates. In this way, a composite having a boron nitride sintered body and the resin that fills its pores is obtained. It is not necessary for all of the pores of the boron nitride sintered body to be filled with resin; some pores may not be filled with resin. The boron nitride sintered body and the composite may contain both closed pores and open pores.

[0065] The impregnation process may include a curing process to harden the resin that has filled the pores. In the curing process, for example, the composite filled with resin (resin composition) is removed from the impregnation device, and the resin is hardened or partially hardened by heating and / or light irradiation, depending on the type of resin (or hardening agent added as needed).

[0066] The composite obtained in this way is in sheet form and has a thin thickness. Therefore, it is thin and lightweight, and when used as a component in electronic components, it can contribute to the miniaturization and weight reduction of electronic components. Furthermore, since the pores of the boron nitride sintered body are sufficiently filled with resin, it also has excellent electrical insulation properties. Moreover, the above manufacturing method does not require a process of cutting the boron nitride sintered body and the composite. Therefore, a highly reliable composite can be manufactured with a high yield. The composite may be used as a heat dissipation member as is, or it may be processed by polishing or other methods to become a heat dissipation member.

[0067] Although several embodiments have been described above, this disclosure is not limited in any way to the embodiments described above. For example, in the sintering process, a boron nitride sintered body may be obtained by hot pressing, which performs molding and sintering simultaneously. [Examples]

[0068] The contents of this disclosure will be described in more detail with reference to the examples below, but this disclosure is not limited to the following examples.

[0069] [Boron nitride sintered body] (Example 1) <Fabrication of boron nitride sintered bodies> 100 parts by mass of orthoboric acid manufactured by Shin-Nippon Denko Co., Ltd. and 35 parts by mass of acetylene black (product name: HS100) manufactured by Denka Co., Ltd. were mixed using a Henschel mixer. The resulting mixture was packed into a graphite crucible and heated in an arc furnace under an argon atmosphere at 2200°C for 5 hours to obtain a lump of boron carbide (B4C). The obtained lump was coarsely ground in a jaw crusher to obtain a coarse powder. This coarse powder was further ground in a ball mill with silicon carbide balls (φ10 mm) to obtain a fine powder. The carbon content of the obtained boron carbide powder was 19.9% ​​by mass. The carbon content was measured using a carbon / sulfur simultaneous analyzer.

[0070] The prepared boron carbide powder was packed into a boron nitride crucible. Then, using a resistance heating furnace, it was heated under nitrogen gas atmosphere at 2000°C and 0.85 MPa for 10 hours. In this way, a calcined product containing boron carbonitride (B4CN4) was obtained.

[0071] A sintering aid was prepared by combining powdered boric acid and powdered calcium carbonate. For this preparation, 1.9 parts by mass of calcium carbonate was added to 100 parts by mass of boric acid. The atomic ratio of boron to calcium at this time was 1.2 atomic percent of calcium to 100 atomic percent of boron. 19 parts by mass of the sintering aid was added to 100 parts by mass of the calcined material and mixed using a Henschel mixer to obtain a powdered compound.

[0072] 0.67 g of the compound was pressed at 150 MPa for 30 seconds using a powder press to obtain a sheet-like molded body (length × width × thickness = 49 mm × 25 mm × 0.38 mm) as shown in Figure 2 (A). The molded body was placed in a boron nitride container and introduced into a batch-type high-frequency furnace. In the batch-type high-frequency furnace, it was heated for 5 hours under atmospheric pressure, nitrogen flow rate of 5 L / min, and 2000°C. After that, the sintered body was removed from the boron nitride container. This sintered body was a porous sintered body (boron nitride sintered body) containing boron nitride particles and pores. In this way, a sheet-like (flat plate-shaped) boron nitride sintered body was obtained. The thickness t of the boron nitride sintered body was 0.40 mm.

[0073] <Measuring Thickness> The thickness of the boron nitride sintered body was measured using a micrometer. The results are shown in Table 1.

[0074] <Measurement of thermal conductivity> The thermal conductivity (H) in the thickness direction of the boron nitride sintered body was determined using the following formula (3). H = A × B × C (3)

[0075] In equation (3), H is the thermal conductivity (W / (m·K)) and A is the thermal diffusivity (m 2 B is bulk density (kg / m³) ( / sec), B is bulk density (kg / m³) 3), and C represent the specific heat capacity (J / (kg·K)). The thermal diffusivity A was measured using a laser flash method with a boron nitride sintered body processed to a predetermined size (length × width = 10 mm × 10 mm). The measuring instrument used was a xenon flash analyzer (NETZSCH, product name: LFA447NanoFlash). The bulk density B was calculated from the volume and mass of the boron nitride sintered body. The results for thermal conductivity H and bulk density B are shown in Table 1. The specific heat capacity C was set to 0.79 (J / (kg·K)).

[0076] <Measurement of average pore diameter> The pore volume distribution of the obtained boron nitride sintered body was measured using a mercury porosimeter (device name: Autopore IV9500) manufactured by Shimadzu Corporation, while increasing the pressure from 0.0042 MPa to 206.8 MPa. In the cumulative pore volume distribution, the pore diameter at which the cumulative pore volume reached 50% of the total pore volume was defined as the "average pore diameter." The results are shown in Table 1.

[0077] <Measurement of porosity> As described above, the bulk density B and the theoretical density of boron nitride (2280 kg / m³) are used. 3 The porosity was calculated using the following formula (4) from the above. The results are shown in Table 1. Porosity (volume %) = [1 - (B / 2280)] × 100 (4)

[0078] <Measurement of Orientation Index> The orientation index [I(002) / I(100)] of a boron nitride sintered body was determined using an X-ray diffractometer (manufactured by Rigaku Corporation, product name: ULTIMA-IV). The sample (boron nitride sintered body) was placed in the sample holder of the X-ray diffractometer and irradiated with X-rays to perform baseline correction. Then, the peak intensity ratio of the (002) and (100) planes of boron nitride was calculated. This was defined as the orientation index [I(002) / I(100)]. The results are shown in Table 1.

[0079] (Example 2) Amorphous boron nitride powder with an oxygen content of 1.7% by mass and an average particle size of 3.4 μm, and hexagonal boron nitride powder with an oxygen content of 0.1% by mass and an average particle size of 16.0 μm were prepared. 10.7 parts by mass of amorphous boron nitride powder, 7.1 parts by mass of hexagonal boron nitride powder, 0.9 parts by mass of calcium carbonate (manufactured by Shiraishi Kogyo Co., Ltd., product name: PC-700), and 1.6 parts by mass of boric acid were mixed using a Henschel mixer to obtain a mixture. Then, 380 parts by mass of water were added to 100 parts by mass of the mixture and ground in a ball mill for 5 hours to obtain an aqueous slurry. Polyvinyl alcohol (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name: Gosenol) was added to this aqueous slurry to a concentration of 3.0% by mass, and the mixture was heated and stirred at 50°C until dissolved. Then, granulation treatment was performed in a spray dryer at a drying temperature of 200°C to obtain granules. A rotary atomizer was used as the spheroidizing device for the spray dryer.

[0080] 0.58 g of granules obtained by the spheroidization process was pressurized at 25 MPa for 30 seconds using a powder press to obtain a sheet-like molded body (length × width × thickness = 49 mm × 25 mm × 0.38 mm) as shown in Figure 2 (B). The molded body was placed in a boron nitride container and introduced into a batch-type high-frequency furnace. In the batch-type high-frequency furnace, it was heated for 10 hours under atmospheric pressure, nitrogen flow rate of 5 L / min, and 2050°C. After that, the sintered body was removed from the boron nitride container. This sintered body was a porous sintered body (boron nitride sintered body) containing boron nitride particles and pores. In this way, a sheet-like (flat plate-shaped) boron nitride sintered body was obtained. The thickness t of the boron nitride sintered body was 0.40 mm.

[0081] The boron nitride sintered body obtained in this manner was subjected to various measurements in the same manner as in Example 1. The measurement results are shown in Table 1.

[0082] (Example 3) A sheet-like molded body (diameter × thickness = 30 mm × 0.38 mm) was obtained using the same procedure as in Example 2, as shown in Figure 2(C). A sheet-like (disk-shaped) boron nitride sintered body was obtained in the same manner as in Example 2, except that this molded body was used. The thickness t of the boron nitride sintered body was 0.40 mm. The boron nitride sintered body obtained in this way was measured in the same manner as in Example 1. The measurement results are shown in Table 1.

[0083] (Example 4) Except for using 0.97g of the compound when molding with a powder press, the procedure was the same as in Example 1 to obtain a sheet-like molded body (length × width × thickness = 49mm × 25mm × 0.55mm) as shown in Figure 2(B). Except for using this molded body, a sheet-like (flat plate shape) boron nitride sintered body was obtained in the same manner as in Example 1. The thickness t of the boron nitride sintered body was 0.58mm. The measurements of the boron nitride sintered body obtained in this way were performed in the same manner as in Example 1. The measurement results are shown in Table 1.

[0084] (Example 5) Except for using 0.47 g of the compound when molding with a powder press, the procedure was the same as in Example 3 to obtain a sheet-like molded body (length × width × thickness = 49 mm × 25 mm × 0.27 mm) as shown in Figure 2(B). Except for using this molded body, a sheet-like (flat plate shape) boron nitride sintered body was obtained in the same manner as in Example 3. The thickness t of the boron nitride sintered body was 0.28 mm. The boron nitride sintered body obtained in this way was measured in the same manner as in Example 1. The measurement results are shown in Table 1.

[0085] (Example 6) Except for setting the pressurizing pressure of the powder press machine to 300 MPa, the procedure was the same as in Example 1 to obtain a sheet-like molded body (length × width × thickness = 49 mm × 25 mm × 0.35 mm) as shown in Figure 2(B). Except for using this molded body, a sheet-like (flat plate shape) boron nitride sintered body was obtained in the same manner as in Example 1. The thickness t of the boron nitride sintered body was 0.37 mm. The measurements of the boron nitride sintered body obtained in this way were performed in the same manner as in Example 1. The measurement results are shown in Table 1.

[0086] (Example 7) Except for setting the pressurizing pressure of the powder press machine to 15 MPa, the procedure was the same as in Example 1 to obtain a sheet-like molded body (length × width × thickness = 49 mm × 25 mm × 0.48 mm) as shown in Figure 2(B). Except for using this molded body, a sheet-like (flat plate shape) boron nitride sintered body was obtained in the same manner as in Example 1. The thickness t of the boron nitride sintered body was 0.51 mm. The measurements of the boron nitride sintered body obtained in this way were performed in the same manner as in Example 1. The measurement results are shown in Table 1.

[0087] [Table 1]

[0088] [complex] <Fabrication of the composite> A resin composition containing epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: Epicote 807) and a curing agent (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name: Acmex H-84B) was applied to the boron nitride sintered bodies of Examples 1 to 7 using a bar coater under atmospheric pressure, thereby impregnating each boron nitride sintered body with the resin composition. After impregnation, the resin was cured by heating at 120°C for 120 minutes under atmospheric pressure to obtain the composites of Examples 1 to 7. All of these composites had thickness and thermal conductivity equivalent to that of the boron nitride sintered bodies. Therefore, they are useful as heat dissipation members for electronic components.

[0089] <Measuring Thickness> The thickness of the composite was measured using a micrometer.

[0090] <Measurement of thermal conductivity> The thermal conductivity (H) in the thickness direction of the composite was calculated using the following formula (4). H = A × B1 × C (4)

[0091] In equation (4), H is the thermal conductivity (W / (m·K)) and A is the thermal diffusivity (m 2 B1 is bulk density (kg / m³) 3 ), and C represent the specific heat capacity (J / (kg·K)). The thermal diffusivity A was measured using a sample of the composite material processed to a size of length × width × thickness = 10 mm × 10 mm, and measured by the laser flash method. The measuring instrument used was a xenon flash analyzer (NETZSCH, product name: LFA447NanoFlash). The bulk density B1 was calculated from the volume and mass of the composite material. The specific heat capacity C was set to 0.97 (J / (kg·K)).

[0092] <Measurement of porosity> The porosity of the composite is determined by the bulk density B1 (kg / m³) which is calculated from the volume and mass of the composite. 3 ) and the theoretical density B2 (kg / m³) when the above resin composition is impregnated into all the pores of the boron nitride sintered body. 3 ) was calculated based on the following formula (5). Porosity of the composite (volume %) = [1 - (B1 / B2)] × 100 ... (5) Furthermore, the theoretical density B2 (kg / m³) when the above resin composition is impregnated into all the pores of the boron nitride sintered body is... 3 ) is the bulk density B (kg / m³) of the boron nitride sintered body. 3 ), the porosity P (volume %) of the boron nitride sintered body, and the theoretical density (1240 kg / m³) of the resin composition. 3 ) was calculated based on the following formula (6). Theoretical density B2 (kg / m 3 ) = B + P / 100 × 1240 (6)

[0093] <Measurement of dielectric breakdown voltage> The dielectric breakdown voltage of the composite material obtained as described above was evaluated. Specifically, two conductive tapes were attached to both sides of the composite material to prepare a measurement sample. The dielectric breakdown voltage of the obtained measurement sample was measured using a withstand voltage tester (manufactured by Kikusui Electronics Co., Ltd., device name: TOS-8700) in accordance with JIS C2110-1:2016. The results for the thickness, thermal conductivity, bulk density, porosity, and dielectric breakdown voltage of the composite material are shown in Table 2.

[0094] [Table 2]

[0095] The dielectric breakdown voltage of the composites in each embodiment was sufficiently high. This confirmed that they possessed excellent electrical insulation properties. [Industrial applicability]

[0096] This disclosure provides thin boron nitride sintered bodies and composites suitable as components for electronic components, as well as methods for manufacturing them. It also provides heat dissipation members suitable as components for electronic components. [Explanation of Symbols]

[0097] 10... Boron nitride sintered body, 20... Composite.

Claims

1. A boron nitride sintered body containing boron nitride particles and pores, in sheet form, with a thickness of less than 2 mm and a bulk density of 900 to 1230 kg / m³. ３ A boron nitride sintered body that does not have a cross-section.

2. The boron nitride sintered body according to claim 1, wherein the orientation index is 40 or less.

3. A boron nitride sintered body according to claim 1 or 2, wherein the porosity is 30 to 65 volume percent.

4. A boron nitride sintered body according to any one of claims 1 to 3, wherein the average pore diameter of the pores is less than 4.0 μm.

5. A composite comprising a boron nitride sintered body according to any one of claims 1 to 4, and a resin filling at least a portion of the pores of the boron nitride sintered body.

6. The composite according to claim 5, wherein the resin is filled only in a portion of the pores of the boron nitride sintered body, and the porosity is 10 volume percent or less.

7. A heat dissipation member having the composite material described in claim 6.

8. A method for producing a composite comprising a boron nitride sintered body and a resin filling at least a portion of the pores of the boron nitride sintered body, comprising an impregnation step of impregnating the boron nitride sintered body according to any one of claims 1 to 4 with a resin composition.

9. A compound containing boron carbonitride powder and a sintering aid is molded and heated to produce a material containing boron nitride particles and pores, with a thickness of less than 2 mm and a bulk density of 900 to 1230 kg / m³. ３ A method for producing a boron nitride sintered body, comprising a sintering step to obtain a sheet-like boron nitride sintered body that does not have a cut surface.

10. A nitriding process is performed to obtain a calcined product containing boron carbonitride by calcining boron carbide powder under a nitrogen atmosphere. A mixture containing the aforementioned fired product and a sintering aid is molded and heated to produce a product containing boron nitride particles and pores, with a thickness of less than 2 mm and a bulk density of 900 to 1230 kg / m³. ３ A method for producing a boron nitride sintered body, comprising a sintering step of obtaining a sheet-like boron nitride sintered body that does not have a cut surface.

11. A method for producing a composite comprising a boron nitride sintered body obtained by the manufacturing method described in claim 9 or 10, comprising an impregnation step of impregnating the boron nitride sintered body with a resin composition, the composite comprising a boron nitride sintered body and a resin filling at least a portion of the pores of the boron nitride sintered body.

12. The method for manufacturing the composite according to claim 8 or 11, wherein the composite is made in which the resin fills only a portion of the pores of the boron nitride sintered body, and the porosity is 10 volume percent or less.

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