Method for producing ceramic sintered body

Abstract

To provide a method for producing a ceramic sintered compact by which the surface waviness of the ceramic sintered compact can highly be prevented.SOLUTION: A method for producing a ceramic sintered body, comprising: a coating step of dry-coating at least one surface of a green body containing a ceramic powder with a charged boron nitride powder to obtain a green body having a boron nitride layer; a laminating step of laminating a plurality of the green bodies having a boron nitride layer; and a firing step of firing the laminate to produce a laminate of a ceramic sintered body.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a ceramic sintered body. [Background technology]

[0002] In recent years, ceramic sintered bodies have been widely used as substrates for semiconductor modules and structural components. For example, substrates for power element modules that mount high-power, high-heat-generating semiconductor elements are required to have high mechanical strength, high thermal conductivity, and high electrical insulation. Ceramic sintered bodies excel in these properties, and in recent years, ceramic sintered bodies have come to be widely used as substrates for power element modules.

[0003] Ceramic sintered bodies are produced by firing green bodies whose main component is ceramic powder. The green bodies are fired using an electric furnace or the like, but to reduce production costs, multiple green bodies are stacked and fired simultaneously. When firing multiple stacked green bodies, it is common to coat the surfaces of the green bodies with a separating material to facilitate separation of the sintered ceramic bodies after firing.

[0004] For example, Patent Document 1 describes a method for producing a ceramic sintered body in which ceramic powder is molded to produce green bodies, a slurry containing a separating material made of boron nitride (BN) is applied to the green bodies, the green bodies coated with the slurry are stacked, and the stacked green bodies are fired, thereby simultaneously firing a plurality of green bodies. Patent Document 2 also describes a method in which a slurry containing boron nitride powder, a dispersion medium, and a dispersant is applied to one side of a green body to form a separating material layer, and then the green bodies are stacked and fired, thereby simultaneously firing a plurality of green bodies. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-216577 [Patent Document 2] Japanese Patent Application Publication No. 2023-173138 Summary of the Invention [Problem to be solved by the invention]

[0006] When applying a separation material to a green body, wet application is generally used, in which a slurry of the separation material is applied to the green body, as described in Patent Document 1 and Patent Document 2. However, according to the investigations conducted by the present inventors, it was thought that wet application was the cause of the surface waviness of the green body.

[0007] When wet coating is performed, the green body absorbs the solvent and swells. When the solvent is then removed by drying, localized differences in drying speed are unavoidable, and it is thought that the difference in drying shrinkage causes surface waviness.

[0008] If the green body has surface waviness, the surface waviness of the resulting ceramic sintered body will increase, causing a decrease in adhesion when a metal layer is formed on the ceramic sintered body by various metallization methods, etc. Therefore, an object of the present invention is to provide a manufacturing method that can highly prevent surface waviness of ceramic sintered bodies. [Means for solving the problem]

[0009] In order to solve the above problems, the inventors conducted extensive research. Specifically, they considered using a dry coating method without using a solvent to prevent surface waviness caused by drying shrinkage. However, it was difficult to uniformly coat the surface of the green body with boron nitride simply by dry coating, and surface waviness could not be sufficiently prevented. After further investigation into this issue, they found that coating the green body with charged boron nitride could suppress surface waviness during dry coating, leading to the completion of the present invention.

[0010] That is, the present invention is a method for producing a ceramic sintered body, comprising: a coating step of dry-coating electrically charged boron nitride powder onto at least one surface of a green body containing ceramic powder to obtain a green body having a boron nitride layer; a lamination step of stacking a plurality of green bodies having the boron nitride layer; and a firing step of firing the laminate to produce a laminate of ceramic sintered bodies.

[0011] In the green body having the boron nitride layer, the amount of boron nitride in the boron nitride layer is 0.01 mg / cm 2 ~0.60mg / cm 2 Preferably, the boron nitride powder has an average particle size D50 of 3 to 25 μm. Preferably, the ceramic is silicon nitride. [Effects of the Invention]

[0012] According to the present invention, a ceramic sintered body having highly suppressed surface waviness can be easily obtained. DETAILED DESCRIPTION OF THE INVENTION

[0013] The method for producing a ceramic sintered body of the present invention includes a coating step of dry-coating charged boron nitride powder onto at least one surface of a green body containing ceramic powder to obtain a green body having a boron nitride layer.

[0014] Boron nitride powder generally contains aggregates of boron nitride primary particles. In particular, in wet coating, the boron nitride particles move during the time it takes for the solvent to evaporate after application, resulting in a uniform surface. However, in dry coating, the applied state is maintained, making the presence of aggregates problematic. Controlling the size of these aggregates is difficult, resulting in uneven coatings during standard dry coating. On the other hand, when boron nitride powder is electrically charged, the electrical repulsion between the boron nitride primary particles makes it difficult for aggregates to form. This allows the powder to be applied to the green body as single particles, presumably facilitating uniform dry coating.

[0015] The method for charging the boron nitride powder is not particularly limited, and can be carried out by a known method. A simple method includes, for example, charging by friction between powders or between a powder and a device. The boron nitride powder can be charged by placing it on a sieve and rubbing it with another object, or by rubbing the boron nitride powder against a stainless steel plate, aluminum plate, or the like after incorporating it into something that can hold the powder, such as a sponge. The powder may also be rubbed against the mesh part of a sieve or the side of the container over the sieve. The rubbing time is not particularly limited, and may be, for example, from 3 to 100 seconds.

[0016] The boron nitride powder may be positively or negatively charged. The absolute value of the charged potential of the boron nitride immediately before application is 0.30 kV or more, preferably 0.50 kV or more. There is no particular upper limit to the absolute value of the charged potential, but if it is too high, handling becomes difficult, so it is preferable to set it to 5.0 kV or less, particularly 3.0 kV or less.

[0017] The charge potential can be measured using a surface electrometer. The charged hexagonal boron nitride powder on the sieve can be directly measured. When charging the boron nitride powder by rubbing it against a sponge or the like, the charge amounts of the boron nitride powder on the sieve and the sponge are approximately the same immediately after rubbing, so it is acceptable to measure the boron nitride powder attached to the sponge or the like.

[0018] The method for applying the charged boron nitride powder is not particularly limited, and examples thereof include a method in which the charged boron nitride powder is applied using a sieve, a method in which the boron nitride powder is attracted to and adhered to the green body by static electricity, etc. Among these, the method of applying using a sieve is preferred when emphasis is placed on simplicity of the equipment and work, and a method in which the boron nitride powder is attracted to and adhered to the green body by static electricity when emphasis is placed on uniformity of application.

[0019] In the method of applying the powder using a sieve, for example, the charged boron nitride powder may be placed on a sieve and applied by vibrating the sieve. The opening size of the sieve may be determined depending on the particle size of the boron nitride powder used, and from the viewpoints of efficiency and operability, the opening size is preferably 3 to 300 times, more preferably 5 to 100 times, and even more preferably 10 to 70 times the average particle size of the boron nitride powder.

[0020] A method for electrostatically attracting and adhering boron nitride powder to a green body can be, for example, electrostatic screen printing. In electrostatic screen printing, a voltage is applied between an electrostatic screen plate (sieve) and the green body to generate an electrostatic field. Charged boron nitride powder is then released through the holes in the electrostatic screen into the electrostatic field, and the boron nitride powder is attracted to the green body by electrostatic force and applied to its surface. The direction of the voltage between the electrostatic screen plate and the green body is not particularly limited; the green body side can be positive or negative, and the direction is determined depending on whether the boron nitride powder is positively or negatively charged. The magnitude of the voltage is also not particularly limited; it can be determined appropriately depending on the charge of the boron nitride powder; for example, it can be 0.1 to 20 kV, particularly 1 to 10 kV. Application by such an electrostatic screen method can be performed using commercially available equipment such as an electrostatic screen printer. An example of such an equipment is an electrostatic screen printing device (Berg Industrial Co., Ltd.).

[0021] In the manufacturing method of the present invention, the application of boron nitride powder is carried out by dry application. The application of a separating material (boron nitride powder) to a green body is generally carried out by wet application using a slurry in which boron nitride powder is dispersed in a solvent, but in dry application, the boron nitride powder is used without being dispersed in a solvent. Since dry application does not require a large amount of solvent, it is advantageous in terms of environmental impact and working environment.

[0022] Although cubic boron nitride powder is also available as boron nitride powder, it is preferable to use hexagonal boron nitride powder because of the ease of separating the sintered body.

[0023] The physical properties of the boron nitride powder used are not particularly limited, and known boron nitride powders can be used. The average particle size D50 of the boron nitride powder is preferably 0.5 to 50 μm, more preferably 3 to 25 μm, and particularly preferably 4 to 20 μm. By setting the particle size within the above range, handleability is improved and the occurrence of surface waviness is easily prevented. The average particle size D50 of the boron nitride powder can be measured by a wet laser diffraction / scattering method. The average aspect ratio of the boron nitride powder is preferably 5 or more, more preferably 7 or more. There is no particular upper limit to the average aspect ratio of the boron nitride powder, but it can be, for example, 30 or less, particularly 20 or less. The average aspect ratio of boron nitride powder can be determined by randomly selecting 100 different primary particles of boron nitride from a scanning electron microscope image observed at 1000x magnification, measuring the length and thickness of the major axis of the primary particles of boron nitride, calculating the aspect ratio of each (major axis length / thickness length), and taking the average value.

[0024] In the manufacturing method of the present invention, the amount of boron nitride powder to be applied to the green body is not particularly limited, but the amount of boron nitride in the boron nitride layer is preferably 0.01 mg / cm. 2 ~1.0mg / cm 2 It is preferable to set the density to 0.05 mg / cm 2 ~0.7mg / cm 2 More preferably, it is 0.1 mg / cm 2 ~0.6mg / cm 2 It is more preferable that the boron nitride layer has a too small amount of boron nitride, which limits its effectiveness as a separator. If the boron nitride layer has a too large amount of boron nitride, a large amount of boron nitride powder will remain on the sintered body obtained by firing the green body. If a large amount of boron nitride powder remains, it may adversely affect the bondability with copper and the heat cycle characteristics when the sintered body is used as a heat dissipation substrate or the like.

[0025] In the manufacturing method of the present invention, the boron nitride powder may be applied to only one side of the green body or to both sides of the green body. When boron nitride powder is applied to both sides of the green body, only one side may satisfy the above-mentioned coating method, but it is preferable that both sides satisfy the above-mentioned coating method.

[0026] The ceramic powder used in the green body of the present invention is not particularly limited as long as it is a ceramic powder used as a raw material for a ceramic sintered body, and examples thereof include silicon nitride, aluminum nitride, titanium nitride, aluminum oxide, titanium oxide, and zirconium oxide. These ceramic powders can be used alone or in combination of two or more. From the viewpoint of obtaining a ceramic sintered body having excellent insulating properties and high thermal conductivity and being used in applications where it is particularly important to suppress surface waviness, the ceramic powder is preferably silicon nitride powder, aluminum nitride powder, aluminum oxide powder, or a mixed powder of aluminum oxide and zirconium oxide, and more preferably silicon nitride powder.

[0027] From the viewpoint of sinterability, the specific surface area of ​​the ceramic powder is preferably 1 m 2 / g or more, especially 2m 2 / g or more, especially 5m 2 / g or more, especially 7m 2 / g or more, and the upper limit is preferably 20m 2 / g or less, especially 15m 2 The specific surface area of ​​the ceramic powder is the BET specific surface area measured by the BET single-point method using nitrogen gas adsorption.

[0028] The green body may contain, in addition to the ceramic powder, a sintering aid, a binder resin, and the like.

[0029] The sintering aid can be any sintering aid commonly used for sintering ceramic powders, and examples include yttria, magnesia, ceria, silica, and calcia. In particular, when the ceramic powder contains silicon nitride powder, carbonitride compounds such as Y2Si4N6C, Yb2Si4N6C, Ce2Si4N6C, and MgSi4N6C, and nitride compounds such as MgSiN2 may be used as sintering aids. The amount of sintering aid in the green body is preferably 1 to 20 parts by mass, and more preferably 3 to 10 parts by mass, per 100 parts by mass of the ceramic powder.

[0030] The binder resin is not particularly limited, but examples thereof include polyvinyl alcohol, polyvinyl butyral, methyl cellulose, alginic acid, polyethylene glycol, carboxymethyl cellulose, ethyl cellulose, acrylic resin, etc. The content of the binder resin in the green body is preferably 1 to 40 parts by mass, more preferably 5 to 30 parts by mass, per 100 parts by mass of the ceramic powder.

[0031] The method for producing the green body is not particularly limited, and the green body may be produced by press molding using a powder obtained by dry mixing the constituent components of the green body, or by wet mixing the constituent components of the green body to produce a slurry for granule production, which is then dried using a spray dryer or the like to produce granules.

[0032] Alternatively, the green body may be produced by wet-mixing the constituent components to prepare a green body molding slurry, and then molding the green body molding slurry into a sheet. The green body molding slurry may be prepared, for example, by weighing out the components in predetermined amounts and stirring and mixing them so that the ceramic powder is dispersed in the dispersion medium. Examples of dispersion devices used for stirring and mixing include ultrasonic dispersion devices, bead mills, ball mills, roll mills, homomixers, ultramixers, disperser mixers, homomixers, through-type high-pressure dispersion devices, collision-type high-pressure dispersion devices, porous high-pressure dispersion devices, clump-removal type high-pressure dispersion devices, (collision + through-type) high-pressure dispersion devices, and ultra-high-pressure homogenizers. After stirring and mixing, the green body slurry may be filtered, if necessary, to remove clumps.

[0033] The method for producing a green body from the green body molding slurry is not particularly limited, and known molding methods can be used, but molding by a doctor blade method is preferred from the viewpoint of good sheet thickness uniformity, etc. The obtained green body can be processed into an appropriate size and any shape. For example, it is generally processed into a roughly rectangular parallelepiped shape with a side length of 100 mm to 2000 mm and a thickness of 0.3 mm to 1.2 mm. Note that after molding into a size larger than that used for firing, cutting can be performed to obtain the desired shape. Cutting can be performed before or after drying, which will be described later.

[0034] When obtaining a green body from the green body molding slurry, it is preferable to carry out a drying step as necessary. The drying step is a step of further removing the dispersion medium from the green body, which makes it easier to subsequently sinter the green body. For example, when the dispersion medium is water, the drying step can be carried out by leaving the green body at a temperature of about 30°C to 150°C, and it is preferable to dry the green body so that the water content is 10% or less.

[0035] When preparing the green body molding slurry, it is preferable to use water as a dispersion medium. Organic solvents are often used as solvents when wet-mixing ceramics (particularly silicon nitride). However, in recent years, there has been a demand for reducing environmental impact, and the use of water, which has a lower environmental impact, is becoming more common. However, according to the inventors' investigations, using water as a dispersion medium during wet mixing has a greater adverse effect on waviness during wet application than using an organic solvent. Therefore, in the present invention, the use of a green body obtained by sheet-molding using a green body molding slurry containing water as a solvent is particularly effective and is a preferred embodiment.

[0036] In the lamination process, multiple green bodies are stacked to form a laminate with a boron nitride layer between adjacent green bodies. The number of stacked green bodies can be any number, ranging from several to several tens of green bodies.

[0037] When the green bodies contain organic components such as binders, it is preferable to degrease the green body laminate prior to firing. The degreasing temperature for degreasing the green body laminate is preferably 300°C to 1200°C, more preferably 400°C to 1000°C. The degreasing of the green body laminate is typically carried out in an atmosphere of an oxidizing gas such as oxygen or air, a reducing gas such as hydrogen, an inert gas such as argon or nitrogen, carbon dioxide, or a mixture of these, or in a humidified gas atmosphere containing a mixture of these gases and water vapor. The degreasing time at the above degreasing temperature can be appropriately selected depending on the type and amount of organic components such as binders used in the green bodies, and the degreasing atmosphere, but is typically 30 minutes to 12 hours, preferably 2 hours to 10 hours.

[0038] In the firing step, the laminate is fired to produce a laminate of sintered ceramic bodies. The firing conditions are not particularly limited, and the firing may be carried out under known firing conditions for obtaining sintered ceramic bodies.

[0039] For example, when the ceramic of the ceramic powder is silicon nitride or aluminum nitride, firing is preferably carried out in an inert gas atmosphere. An inert gas atmosphere refers to, for example, a nitrogen atmosphere or an argon atmosphere. The firing pressure is not particularly limited, but because high pressures increase the cost of equipment, for example, firing is carried out at a pressure of 10 MPa·G or less, more preferably 3 MPa·G or less, and even more preferably 1 MPa·G or less. Furthermore, when the ceramic of the ceramic powder is silicon nitride, low pressures may cause silicon nitride to decompose during firing, so a firing pressure of 0 MPa·G or more is preferred. The firing temperature is not particularly limited as long as the desired sintering reaction proceeds. For example, when the ceramic of the ceramic powder is silicon nitride, it can be, for example, 1200°C to 2000°C, more preferably 1500°C to 1900°C. The firing time is not particularly limited as long as the desired sintering reaction proceeds, but for example, when the ceramic of the ceramic powder is silicon nitride, it is generally about 3 to 20 hours.

[0040] After the firing step, the ceramic sintered body is separated from the stack of ceramic sintered bodies to obtain a ceramic sintered body. In the stack of ceramic sintered bodies, a boron nitride layer is provided between adjacent ceramic sintered bodies, so that the ceramic sintered body can be easily separated from the stack of ceramic sintered bodies.

[0041] Boron nitride powder may remain on the surface of the ceramic sintered body separated from the laminate. Therefore, it is preferable to remove the boron nitride powder remaining on the surface of the ceramic sintered body after separating it from the laminate. For example, it is preferable to subject the ceramic sintered body separated from the laminate to honing using free abrasive grains. In this case, it is preferable to use alumina abrasive grains with an average particle size of 10 to 100 μm as the free abrasive grains. Furthermore, after honing, the ceramic sintered body may be ultrasonically cleaned or washed with a spray of water to remove the alumina abrasive grains and boron nitride powder. It is preferable that no boron nitride particles are observed on the surface of the ceramic sintered body when observed with a scanning electron microscope. Polishing may or may not be performed after honing.

[0042] The ceramic sintered body separated from the laminate is cut mechanically or by laser, as required, to obtain a ceramic sintered body of a desired size and shape.

[0043] The manufacturing method of the present invention makes it possible to obtain a ceramic sintered body with highly suppressed surface waviness. Specifically, it is possible to obtain a silicon nitride sintered body with an arithmetic mean waviness Wa of 0.20 μm or less.

[0044] The ceramic sintered body obtained by the manufacturing method of the present invention can be used for any purpose, including, but not limited to, substrates that require a high degree of suppression of surface waviness. Specific examples include various heat dissipation substrates, power module substrates (for automobiles, electric railways, and high-power semiconductors), high-frequency circuit boards, LED packages, and optical pickup submounts (for DVDs and CDs). [Example]

[0045] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to the following examples. The measurements of the various items in the examples and comparative examples were performed by the following methods.

[0046] (1) Evaluation of waviness of silicon nitride substrate The surface waviness of the ceramic sintered body was measured using a surface roughness meter to measure the filtered centerline waviness, and the arithmetic mean waviness Wa, i.e., the arithmetic mean of the absolute values ​​of deviations from the average surface height, was calculated. The measurement conditions were an evaluation length of 4 mm, a measurement speed of 0.3 mm / s, and a cutoff value of 0.8 mm.

[0047] (2) Average particle size of boron nitride powder Boron nitride powder was dispersed in pure water and dispersed for 30 seconds using an ultrasonic homogenizer (Nippon Seiki Seisakusho: US-600T). The suspension was then subjected to wet measurement using a particle size distribution analyzer (Microtrac: MT3300EXII) equipped with a standard sample circulator (Microtrac: SDC). D50 was calculated from the volume-based particle size distribution obtained, and this was used as the average particle size.

[0048] (3) Measurement of the charging potential of boron nitride powder Measurements were carried out using a surface potential meter (IZH10 manufactured by SMC Corporation). Specifically, a sponge soaked in boron nitride powder was rubbed against a SUS plate for at least 10 seconds to obtain charged hexagonal boron nitride powder, which was then placed on a sieve and the potential of the sponge surface was measured. The potential of the sponge surface before use, which had been measured in advance, was subtracted from this result to measure the amount of charged potential of the hexagonal boron nitride powder remaining on the sponge surface. The hexagonal boron nitride powder remaining on the sponge surface is equivalent to the powder placed on the sieve, and the amount of charged potential of the hexagonal boron nitride powder obtained in this measurement can be said to be the amount of charged potential of the hexagonal boron nitride powder applied to the green body.

[0049] The silicon nitride substrate was manufactured using the following raw materials containing silicon nitride powder and a sintering aid. <Silicon nitride powder> ·Betaization rate: 99% ·Average particle size D50: 0.9μm <Sintering aid> Yttria (manufactured by Shin-Etsu Chemical Co., Ltd.) Magnesia (manufactured by Ube Materials Co., Ltd.) <Binders and dispersants> Binder resin: Acrylic resin (manufactured by Fujikura Kasei Co., Ltd.) Dispersant: Cerna D735 (manufactured by Chukyo Yushi Co., Ltd.)

[0050] Example 1 (Preparation of green bodies) 100 parts by weight of silicon nitride powder, 5 parts by weight of yttria, 3 parts by weight of magnesia, 0.5 parts by weight of dispersant, and 22 parts by weight of binder were weighed and mixed in a ball mill using water as a solvent and a resin pot and silicon nitride balls for 48 hours. Next, a vacuum defoamer (manufactured by Sayama Riken Co., Ltd.) was used to defoam and adjust the viscosity to produce a raw material slurry. The raw material slurry was then molded into a sheet with a width of 750 mm and a thickness of 420 μm using a doctor blade method. The resulting molded body was dried in air at 40°C to evaporate the solvent, and then cut to a size of 200 mm x 268 mm on the main surface to obtain a green body (green sheet). (Coating process) A sponge was soaked in commercially available hexagonal boron nitride powder (average particle size 1 μm: manufactured by Sanwa Materials), and the sponge was rubbed against a SUS plate for more than 10 seconds to obtain hexagonal boron nitride powder charged to 0.85 kV by electrostatic friction. Next, the charged hexagonal boron nitride powder was placed on a sieve with 200 μm openings, and the sieve was vibrated to coat the charged hexagonal boron nitride powder on the green body placed on the table, thereby obtaining a green body having a boron nitride layer. The amount of the charged hexagonal boron nitride powder coated was 0.2 mg / cm. 2 In the same manner, a total of 10 green bodies were coated on one side with charged hexagonal boron nitride powder. (Lamination process) Ten green bodies having the boron nitride layer were stacked together so that the surface of one green body having the boron nitride layer was in contact with the surface of another green body not having the boron nitride layer, to produce a stack with a separator layer provided between adjacent green bodies. (Firing process) The laminate was degreased by holding it in an air atmosphere at 400°C for 5 hours. It was then fired in a nitrogen atmosphere at 1830°C for 9 hours under a pressure of 0.8 MPa·G. After firing, the laminate was removed and 10 silicon nitride sintered bodies were separated from the laminate. The silicon nitride sintered bodies were easily separated. (evaluation) All 10 of the resulting silicon nitride sintered compacts were evaluated for waviness. The evaluation results for the ceramic sintered compact with the largest Wa value are shown in Table 1. Note that the separability in Table 1 indicates whether or not the 10 silicon nitride sintered compacts could be easily separated from the sintered compact after the firing process.

[0051] <Examples 2 to 9> Silicon nitride sintered bodies were obtained in the same manner as in Example 1, except that the average particle size and coating amount of the boron nitride powder were changed as shown in Table 1, and evaluations were carried out.

[0052] Example 10 A silicon nitride sintered body was obtained and evaluated in the same manner as in Example 1, except that the coating step was carried out by the electrostatic screen printing method described below. (Coating process) A sponge was soaked in commercially available hexagonal boron nitride powder (average particle size 1 μm: manufactured by Sanwa Materials), and the sponge was rubbed against a SUS plate for more than 10 seconds to obtain hexagonal boron nitride powder charged to 0.85 kV by electrostatic friction. The charged boron nitride powder was loaded onto the electrostatic screen plate of a T-1 type tabletop electrostatic screen printing machine (manufactured by Berg Kogyo Co., Ltd.), and a voltage of 3 kV was applied between the electrostatic screen plate and the green body to generate an electrostatic field. The boron nitride powder was then released into the electrostatic field and applied to the green body, yielding a green body with a boron nitride layer. The amount of charged hexagonal boron nitride powder applied was 0.2 mg / cm. 2 Similarly, charged hexagonal boron nitride powder was applied to one side of 10 green bodies.

[0053] <Comparative Example 1> A silicon nitride sintered body was obtained and evaluated in the same manner as in Example 3, except that the boron nitride powder was used without being charged. Note that, since the boron nitride powder was not charged in this comparative example, the amount of charge potential of the boron nitride powder was not measured.

[0054] <Comparative Example 2> A silicon nitride sintered body was obtained and evaluated in the same manner as in Example 3, except that the coating step was carried out in a wet manner as described below. Note that in this comparative example, the boron nitride powder was not charged, and therefore the charged potential of the boron nitride powder was not measured. (Coating process) 100 g of boron nitride powder, 100 g of binder (acrylamide polymer solution), 10 g of dispersant (glycerol monostearate), and 2000 g of water were mixed and stirred for 48 hours to obtain a slurry of boron nitride powder. The boron nitride powder slurry was applied to one side of the green body using a spray coater, and then dried at 120°C for 180 minutes to remove the dispersant from the applied boron nitride powder slurry, yielding a green body having a boron nitride layer.

[0055] [Table 1]

Claims

1. a coating step of dry-coating charged boron nitride powder onto at least one surface of a green body containing ceramic powder to obtain a green body having a boron nitride layer; a lamination step of laminating a plurality of green bodies each having a boron nitride layer; a firing step of firing the laminate to produce a laminate of ceramic sintered bodies; A method for producing a ceramic sintered body, comprising:

2. In the green body having the boron nitride layer, the amount of boron nitride in the boron nitride layer is 0.01 mg / cm ２ ~0.60mg / cm ２ 2. The method for producing a ceramic powder according to claim 1, wherein

3. 3. The method for producing a ceramic powder according to claim 1, wherein the boron nitride powder has an average particle size of 3 to 25 μm.

4. 3. The method for producing a ceramic sintered body according to claim 1, wherein the ceramic is silicon nitride.

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