Aluminum nitride sintered body

Abstract

To provide an aluminum nitride sintered body having high thermal conductivity. [Solution] The aluminum nitride sintered body 50 has an area ratio of voids 30 in the cross section of 1.0% or less. The voids 30 in the cross section of the aluminum nitride sintered body 50 have an area of ​​0.15 μm 2 The above voids 30 are the subject of this study. The area ratio of the voids 30 is calculated by using image analysis software (ImageJ) to detect the voids 30 in an image taken by observing with a scanning electron microscope, and dividing the total area of ​​the voids 30 by the area of ​​the observation range.

Description

[Technical Field]

[0001] The present disclosure relates to an aluminum nitride sintered body. [Background technology]

[0002] In recent years, power modules for controlling large amounts of power have been used in industrial equipment such as motors and products such as electric vehicles. These power modules use circuit boards with ceramic plates to efficiently diffuse heat generated from semiconductor elements and suppress leakage current. These circuit boards usually use plate-shaped ceramic sintered bodies.

[0003] Known ceramic sintered bodies are those made of nitrides, carbides, borides, silicides, etc. For example, Patent Document 1 describes that a silicon nitride sintered body with improved breakdown voltage is useful for circuit boards of electronic components such as power modules. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-166445 Summary of the Invention [Problem to be solved by the invention]

[0005] Electronic components such as power modules are required to have excellent heat dissipation properties. Therefore, the present disclosure provides an aluminum nitride sintered body having high thermal conductivity. [Means for solving the problem]

[0006] One aspect of the present disclosure provides the following aluminum nitride sintered body.

[0007] [1] An aluminum nitride sintered body having a void area ratio of 1.0% or less in a cross section.

[0008] The aluminum nitride sintered body of [1] above has a sufficiently small void area ratio (void fraction) in the cross section, and has high thermal conductivity.

[0009] The aluminum nitride sintered body of the above [1] may be any one of the following [2] to [6].

[0010] [2] The aluminum nitride sintered body according to [1], wherein the average irregularity of the voids in the cross section is 0.75 or more. [3] The aluminum nitride sintered body according to [1] or [2], wherein the ratio of the number of voids having a degree of irregularity of less than 0.70 to the total number of voids contained in the cross section is 5% or less. [4] In the cross section, the average area of ​​the voids is 3.00 μm 2 The aluminum nitride sintered body according to any one of [1] to [3] below. [5] The aluminum nitride sintered body according to any one of [1] to [4], which has a thermal conductivity of 155 W / (m·K) or more. [6] The aluminum nitride sintered body according to any one of [1] to [5], which has a bending strength of 410 MPa or more.

[0011] The aluminum nitride sintered body of [2] above has a large average unevenness of voids in the cross section, and therefore has a high proportion of voids with little unevenness. This reduces the occurrence of cracks originating from the convex or concave portions of voids, and therefore increases the bending strength.

[0012] In the aluminum nitride sintered body described in [3] above, the ratio of the number of voids with a roughness of less than 0.70 in the cross section is 5% or less, so the proportion of voids with a large roughness is low. This reduces the occurrence of cracks originating from the protrusions or recesses of voids. Therefore, the bending strength can be further increased.

[0013] The aluminum nitride sintered body described above [4] has an average void area of ​​3.00 μm in cross section. 2 Such an aluminum nitride sintered body has a higher thermal conductivity.

[0014] The aluminum nitride sintered body of [5] above has sufficiently high thermal conductivity. Such an aluminum nitride sintered body has excellent heat dissipation properties and can be suitably used as a component of a circuit board, thereby improving the reliability of the circuit board.

[0015] The aluminum nitride sintered body of [6] above has sufficiently high bending strength. Such an aluminum nitride sintered body has excellent mechanical properties and can be suitably used as a component of a circuit board, thereby improving the reliability of the circuit board. [Effects of the Invention]

[0016] The present disclosure can provide an aluminum nitride sintered body having high thermal conductivity. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view showing an example of an aluminum nitride sintered body. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing a part of a cross section of an aluminum nitride sintered body. [Figure 3] FIG. 2 is a diagram illustrating the unevenness of voids in a cross section of an aluminum nitride sintered body. [Figure 4] 1 is an SEM image (magnification: 1000 times) of a cross section of an aluminum nitride sintered body in Example 1. [Figure 5] 1 is an SEM image (magnification: 1000 times) of a cross section of an aluminum nitride sintered body in Example 2. [Figure 6] 1 is an SEM image (magnification: 1000 times) of a cross section of an aluminum nitride sintered body in Example 3. [Figure 7] 1 is an SEM image (magnification: 1000 times) of a cross section of an aluminum nitride sintered body in Example 4. [Figure 8]1 is an SEM image (magnification: 1000 times) of a cross section of an aluminum nitride sintered body in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] Embodiments of the present disclosure will be described below. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. In the description, the same reference numerals will be used for identical elements or elements having the same functions, and redundant explanations will be omitted where appropriate. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships based on the orientation of the reference numerals shown in the drawings. The dimensional ratios of each element are not limited to those shown. The numerical ranges exemplified as "a to b" are numerical ranges inclusive of a and b, with a lower limit being a and an upper limit being b. The present disclosure also includes those in which the upper or lower limit of each numerical range is replaced with the numerical value of any of the examples. When multiple materials are exemplified, one of the materials may be used alone, or multiple materials may be used in combination.

[0019] [Aluminum nitride sintered body] FIG. 1 is a perspective view showing an example of an aluminum nitride sintered body. The external shape of the aluminum nitride sintered body 50 is not particularly limited, and may be, for example, a plate shape with a side length of 50.0 to 70.0 mm. The thickness of the aluminum nitride sintered body 50 may be 0.40 to 1.50 mm, or 0.50 to 1.20 mm. Such an external shape allows smooth bonding to other members. The aluminum nitride sintered body 50 may contain aluminum nitride particles and voids (closed pores).

[0020] The aluminum nitride sintered body 50 has main surfaces (a first main surface 50A and a second main surface 50B). In the present disclosure, a main surface is a surface having an area larger than that of other surfaces. Usually, two surfaces that are perpendicular to the thickness direction are the main surfaces. The areas of the first main surface 50A and the second main surface 50B of the aluminum nitride sintered body 50 are 1500 mm 2 Over 2000mm 2 or more, or 2500mm 2This allows, for example, a sufficient circuit area to be secured when the aluminum nitride sintered body 50 is made into a circuit board. The areas of the first main surface 50A and the second main surface 50B of the aluminum nitride sintered body 50 are 10,000 mm 2 The areas of the first main surface 50A and the second main surface 50B of the aluminum nitride sintered body 50 may be, for example, 1500 to 10000 mm 2 may be.

[0021] FIG. 2 is an enlarged cross-sectional view of a portion of a cross section obtained by cutting an aluminum nitride sintered body 50 along a direction X perpendicular to the first main surface 50A and the second main surface 50B. The cross section of the aluminum nitride sintered body 50 can be obtained, for example, by cutting the aluminum nitride sintered body 50 into a desired shape using a diamond pen, processing the cut surface by ion milling, and treating it with an osmium coating. The cross section thus obtained is observed with a scanning electron microscope (SEM). The observation magnification of the SEM may be, for example, 1000x. By processing the cut surface by ion milling and treating it with an osmium coating, it is possible to suppress the shedding of aluminum nitride particles during cross-section processing compared to processing by polishing. Therefore, the formation of voids 30 due to shedding during cross-section processing is suppressed, and the voids 30 formed by sintering can be observed by cross-section observation.

[0022] The area of ​​the cross-section observation range is, for example, 4000 to 30,000 μm 2 , 8000~20000μm 2 , or 10,000 to 14,000 μm 2 The area of ​​the cross section observation range may be, for example, 12096 μm 2 (length x width = 96 μm x 126 μm).

[0023] In the present disclosure, the area ratio of voids in the cross section of the aluminum nitride sintered body 50 is referred to as the "void fraction." The void fraction can be calculated, for example, by dividing the total area of ​​voids 30 detected in an SEM image by the area of ​​the observation range. The void fraction is 1.0% or less. When the void fraction is within the above range, the ratio of the total area of ​​voids 30 in the observation range becomes small. Since the voids 30 have a lower thermal conductivity than the crystal grains that make up the aluminum nitride sintered body 50, the thermal conductivity of the aluminum nitride sintered body 50 can be improved by setting the void fraction within the above range.

[0024] The voids 30 are gaps in the cross section of the aluminum nitride sintered body 50. The voids 30 appear darker in color than the aluminum nitride particles in the SEM image, and can therefore be detected by analyzing the SEM image. For example, "ImageJ" can be used as the image analysis software. The void rate, total number of voids, total area of ​​voids, average area of ​​voids, and void irregularity of the present disclosure can be determined by the settings of the image analysis software, and can be calculated by determining the number of voids with an area of ​​0.15 μm among the voids observed in the cross section shown in FIG. 2. 2 The above 30 voids are the target.

[0025] The void fraction may be 0.80% or less, or 0.50% or less, from the viewpoint of further improving the thermal conductivity of the aluminum nitride sintered body 50. The void fraction may be 0.01% or more, from the viewpoint of ease of manufacturing the aluminum nitride sintered body 50. The void fraction in the cross section may be in the range of, for example, 0.01 to 1.0%, or 0.01 to 0.50%.

[0026] From the viewpoint of further improving thermal conductivity, the total number of voids 30 in the observation range of the cross section of the aluminum nitride sintered body 50 may be 60 or less, or may be 30 or less. The total number of voids 30 can be calculated, for example, using the image analysis software "ImageJ."

[0027] In the cross section of the aluminum nitride sintered body 50, the average area of ​​the voids 30 is 3.00 μm 2The average area of ​​the voids 30 can be calculated by dividing the total area of ​​the voids 30 in the observation range by the total number of voids 30. When the average area of ​​the voids 30 is within the above range, the thermal conductivity can be further improved. From the viewpoint of further improving the thermal conductivity, the average area of ​​the voids 30 is set to 1.50 μm 2 Less than or equal to 1.00 μm 2 The average area of ​​the voids 30 may be 0.10 μm or less. 2 The average area of ​​the voids 30 may be in the range of, for example, 0.10 to 3.00 μm 2 , or 0.10 to 1.50 μm 2 may be.

[0028] The average irregularity of the voids 30 in the cross section of the aluminum nitride sintered body 50 may be 0.75 or more. The average irregularity of the voids 30 can be calculated by dividing the sum of the irregularities of each void 30 in the observation area by the total number of voids 30. When the average irregularity of the voids 30 is within the above range, the aluminum nitride sintered body 50 has many voids 30 with shapes that are less irregular. This makes it possible to reduce the occurrence of cracks originating from the convex portions 31 or concave portions 32 of the voids 30. Therefore, such an aluminum nitride sintered body 50 can have high bending strength while maintaining high thermal conductivity.

[0029] A method for calculating the irregularity of the void 30 will be described with reference to FIG. 3. The irregularity of the void 30 is calculated using the following formula (1) based on the contour and envelope of the void 30 as shown in FIG. 3. In formula (1), the area within the contour of the void 30 refers to the actual area of ​​the void 30. Furthermore, the area within the envelope of the void 30 refers to the area enclosed by the tangent lines connecting adjacent convex portions 31 of the void 30. Therefore, the area within the envelope of the void 30 is larger than the area within the contour of the void 30. The closer the irregularity of the void 30 is to 1, the more the area within the envelope of the void 30 coincides with the area within the contour, meaning that the void 30 has less irregularity. On the other hand, the smaller the irregularity of the void 30 is to 1, the more irregularity there is. The area within the envelope of the void 30 can be calculated using the image analysis software "ImageJ." Convexo-concave degree = Area within the contour of void 30 / Area within the envelope of void 30 (1)

[0030] From the viewpoint of further improving the bending strength of the aluminum nitride sintered body 50, the average unevenness of the voids 30 may be 0.80 or more, 0.85 or more, or 0.89 or more. An aluminum nitride sintered body 50 having a high unevenness of the voids 30 has high bending strength. Therefore, such an aluminum nitride sintered body 50 can achieve both high thermal conductivity and high bending strength. When such an aluminum nitride sintered body 50 is used as a component of a circuit board, the reliability of the circuit board can be further improved.

[0031] The ratio of the number of voids 30 having a degree of irregularity of less than 0.70 to the total number of voids 30 contained in the cross section of the aluminum nitride sintered body 50 may be 5% or less, 3% or less, or 1% or less. When the ratio of the number of voids 30 having a degree of irregularity of less than 0.70 is within the above range, the proportion of voids 30 with many irregularities decreases, thereby further suppressing the occurrence of cracks originating from the convex portions 31 or concave portions 32 of the voids 30. Therefore, the flexural strength of the aluminum nitride sintered body 50 can be further improved.

[0032] From the viewpoint of further improving the bending strength of the aluminum nitride sintered body 50, the ratio of the number of voids 30 having an irregularity degree of 0.90 or more to the total number of voids 30 contained in the cross section of the aluminum nitride sintered body 50 may be 40% or more, 60% or more, or 70% or more. When the ratio of the number of voids 30 having an irregularity degree of 0.90 or more is within the above range, the irregularities are reduced, and the occurrence of cracks originating from the convex portions 31 or concave portions 32 of the voids 30 can be further suppressed. Therefore, the bending strength of the aluminum nitride sintered body 50 can be further improved.

[0033] The thermal conductivity of the aluminum nitride sintered body 50 may be 155 W / (m·K) or more, 165 W / (m·K) or more, or 170 W / (m·K) or more. Such an aluminum nitride sintered body 50 has excellent heat dissipation properties and can be suitably used as a component of a circuit board, thereby improving the reliability of the circuit board. The thermal conductivity of the aluminum nitride sintered body 50 may be 200 W / (m·K) or less. The thermal conductivity of the aluminum nitride sintered body 50 may be in the range of, for example, 155 to 200 W / (m·K). The thermal conductivity of the aluminum nitride sintered body 50 can be measured, for example, in accordance with JIS R1611:2010, "Method for measuring thermal diffusivity, specific heat capacity, and thermal conductivity of fine ceramics by the flash method."

[0034] The flexural strength of the aluminum nitride sintered body 50 may be 410 MPa or more, 420 MPa or more, or 450 MPa or more. Such an aluminum nitride sintered body 50 has excellent mechanical properties and can be suitably used as a component of a circuit board, thereby improving the reliability of the circuit board. The flexural strength of the aluminum nitride sintered body 50 may be 500 MPa or less. The flexural strength of the aluminum nitride sintered body 50 may be in the range of 410 to 500 MPa, for example. The flexural strength can be measured by a three-point bending test in accordance with the description of JIS R 1601:2008 "Test method for room-temperature flexural strength of fine ceramics."

[0035] The content of the main component (aluminum nitride) in the aluminum nitride sintered body 50 may be more than 95% by mass or 96% by mass or more from the viewpoint of increasing thermal conductivity. The content of the main component in the aluminum nitride sintered body 50 may be 99% by mass or less or 98% by mass or less from the viewpoint of sufficiently increasing density. In the present disclosure, the main component is the component contained in the aluminum nitride sintered body 50 with the largest content. Components other than the main component are referred to as minor components. Minor components are components different from the main component, and examples of minor components include oxides having yttrium and aluminum as constituent elements. Granular oxides may be dispersed in the grain boundaries of granular aluminum nitride.

[0036] The oxide content in the aluminum nitride sintered body 50 may be 3% by mass or more, or 3.5% by mass or more, from the viewpoint of sufficiently increasing density. The oxide content in the aluminum nitride sintered body 50 may be less than 6% by mass or less than 5% by mass, from the viewpoint of increasing thermal conductivity. The oxide content can be determined by removing components other than oxides from the aluminum nitride sintered body 50 by hydrolysis reaction. Examples of oxides include Y2O3-Al2O3 compounds. Examples of Y2O3-Al2O3 compounds include 3Y2O3·5Al2O3, known as YAG, Y2O3·Al2O3, known as YAP, and 2Y2O3·Al2O3, known as YAM.

[0037] The aluminum nitride sintered body 50 may contain components other than aluminum nitride and oxides having yttrium and aluminum as constituent elements. Such components include oxides such as aluminum oxide and yttrium oxide, nitrides other than aluminum nitride, and silicides. The content of components other than aluminum nitride and oxides having yttrium and aluminum as constituent elements may be less than 5 mass%, less than 3 mass%, or less than 1 mass%, based on the aluminum nitride sintered body.

[0038] An example of a method for manufacturing the aluminum nitride sintered body 50 is described below. Examples of raw materials include aluminum nitride powder, a sintering aid, and, if necessary, additives. Examples of additives include binders, plasticizers, dispersion media, and mold release agents. Examples of binders include methylcellulose-based binders with plasticity or surfactant properties, and acrylic ester-based binders with excellent thermal decomposition properties. Examples of plasticizers include glycerin. Examples of dispersion media include ion-exchanged water and ethanol. The aluminum nitride powder is not particularly limited, and aluminum nitride powder manufactured by known methods such as direct nitridation, in which metallic aluminum is nitrided in a nitrogen atmosphere, and reduction nitridation, in which aluminum oxide is reduced with carbon, can be used.

[0039] The median diameter (d50) of the aluminum nitride powder may be 0.8 to 2.0 μm or 1.0 to 1.8 μm. When the d50 of the aluminum nitride powder is within the above range, the sintering aid phase easily covers the aluminum nitride particles during sintering, further suppressing the formation of voids 30 during sintering. This allows for the production of an aluminum nitride sintered body 50 with high thermal conductivity. Furthermore, the sintering aid phase is sufficiently mixed with the aluminum nitride particles, allowing sintering to proceed with high uniformity, thereby suppressing a decrease in the degree of irregularity of the voids 30. The d50 of the aluminum nitride powder can be determined, for example, by calculating the particle diameter at which the cumulative value from the smallest particle diameter reaches 50% of the total in the cumulative distribution of volumetric particle diameters measured using a particle size distribution analyzer using a laser diffraction / scattering method. An example of a particle size distribution analyzer that can be used is the "Microtrac MT3300EXII" (product name, manufactured by Nikkiso Co., Ltd.).

[0040] The d90 of the aluminum nitride powder may be 2.0 to 5.0 μm or 2.5 to 4.0 μm. When the d90 of the aluminum nitride powder is within the above range, the proportion of coarse particles is reduced, making it easier for the sintering aid phase to cover the aluminum nitride particles during sintering, thereby further suppressing the formation of voids 30 during sintering. This allows for an aluminum nitride sintered body 50 with high thermal conductivity. Furthermore, the reduced proportion of coarse particles allows for more thorough mixing of the sintering aid phase and the aluminum nitride particles. This allows for highly uniform sintering, thereby suppressing a decrease in the degree of irregularity of the voids 30. The d90 of the aluminum nitride powder can be determined, for example, by calculating the particle size at which the cumulative value from the smallest particle size reaches 90% of the total in the cumulative distribution of volumetric particle sizes measured using a particle size distribution analyzer using a laser diffraction / scattering method.

[0041] As the sintering aid, for example, yttrium oxide powder is used. The content of the yttrium oxide powder may be, for example, 2.0 to 5.0 mass % or 2.5 to 4.0 mass % with respect to the total of the aluminum nitride powder and the sintering aid. By ensuring that the content of the yttrium oxide powder is within the above range, the sintering of the aluminum nitride powder can be sufficiently promoted.

[0042] Aluminum oxide powder may be used as an oxide other than yttrium oxide powder. However, the mass ratio of aluminum oxide powder to yttrium oxide powder is preferably less than that of yttrium oxide powder. For example, the mass ratio of yttrium oxide powder to aluminum oxide powder may be 1.5 or more, or 2.0 or more.

[0043] Aluminum nitride powder, a sintering aid, and optional additives are blended and mixed to obtain a molding raw material. The molding raw material is formed into, for example, a sheet by a known method such as a doctor blade method. The obtained molded body may be degreased. The degreasing method is not particularly limited, and for example, the molded body may be heated to 300 to 700°C in air or a non-oxidizing atmosphere such as nitrogen. The heating time may be, for example, 1 to 10 hours.

[0044] The aluminum nitride sintered body 50 can be obtained by firing the above-mentioned compact. The firing can be carried out in an inert gas atmosphere under atmospheric pressure. The firing temperature may be 1700 to 1900°C, 1730 to 1870°C, or 1780 to 1860°C. The firing temperature can further promote the formation of a sintering aid phase due to the dissolution of the sintering aid. This makes it easier for the sintering aid phase to cover the aluminum nitride powder, further promoting sintering. Therefore, the formation of voids 30 in the aluminum nitride sintered body 50 can be further suppressed, resulting in an aluminum nitride sintered body 50 with even higher thermal conductivity. The holding time at the above firing temperature may be 1 to 5 hours.

[0045] The aluminum nitride sintered body 50 obtained by the above-described manufacturing method may be processed into a desired shape as necessary. A conductor such as a metal plate may be joined to the aluminum nitride sintered body 50 to form a joined body. The joined body may be produced, for example, by joining the main surface of the aluminum nitride sintered body 50 to the main surface of a metal plate such as a copper plate with a brazing material. The joined body may also be a circuit board on which a circuit pattern serving as a conductor is formed by removing a portion of the metal plate joined to the main surface of the aluminum nitride sintered body 50 by etching or the like. In this way, the joined body may be a circuit board.

[0046] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. [Example]

[0047] Example 1 (Production of sintered aluminum nitride) The particle size of the aluminum nitride powder was measured using a "Microtrac MT3300EXII" (trade name, manufactured by Nikkiso Co., Ltd.), and the median diameter (d50) of the aluminum nitride powder was 1.5 μm and the d90 was 3.2 μm. Aluminum nitride powder and yttrium oxide powder were blended in a mass ratio of 96.5:3.5 and mixed using a ball mill to obtain a mixed powder. Six parts by mass of a cellulose ether binder (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: Metrose), 5 parts by mass of glycerin (manufactured by Kao Corporation, trade name: Exepar), and 10 parts by mass of ion-exchanged water were added to 100 parts by mass of the mixed powder, and the mixture was mixed for 1 minute using a Henschel mixer to obtain a molding material. This molding material was molded using an extrusion molding machine to produce 15 sheet-like molded bodies with a thickness of 0.8 mm.

[0048] After applying boron nitride powder as a release agent to this compact, 15 compacts were stacked and heated in air at 570°C for 5 hours to obtain a degreased body. Next, the degreased body was placed in a heating furnace and heated to 1800°C in a nitrogen gas atmosphere (atmospheric pressure). After that, it was held at the firing temperature of 1800°C for 4 hours and then allowed to cool in the heating furnace. In this way, a plate-shaped aluminum nitride sintered body with a thickness of 0.635 mm (length x width x thickness = 58 mm x 49 mm x 0.64 mm) was obtained.

[0049] (Examples 2 to 4, Comparative Example 1) An aluminum nitride sintered body was produced in the same manner as in Example 1, except that at least one of the d50 of the raw material aluminum nitride powder, the content of yttrium oxide powder in the mixed powder, the firing temperature, and the thickness of the compact and the aluminum nitride sintered body was changed as shown in Table 1.

[0050] [Table 1]

[0051] (Calculation of void ratio) The aluminum nitride sintered bodies of Examples 1 to 4 and Comparative Example 1 were cut into pieces using a diamond pen to obtain cut surfaces. The cut surfaces (thickness direction cross sections) were processed by ion milling and treated with osmium coating. The cross sections after treatment were observed using a scanning electron microscope (product name: JSM-IT200, manufactured by JEOL Ltd.) at an acceleration voltage of 15 kV. An arbitrarily selected section of the cross section, length x width = 96 μm:126 μm (area: 12096 μm 2 ) was photographed (magnification: 1000 times). Cross-sectional images of Examples 1 to 4 are shown in FIGS. 4 to 7, respectively. A cross-sectional image of Comparative Example 1 is shown in FIG.

[0052] Using the image analysis software "ImageJ," voids 30 that appeared black in the photographed image were detected. By setting the image analysis software, voids with an area of ​​0.15 μm were detected. 2 Only these voids 30 were the subject of subsequent measurements. The total area of ​​the voids 30 detected in the photographed image was calculated. The total area of ​​the voids 30 was also multiplied by the area of ​​the observation range (12096 μm 2 ) to calculate the ratio of the total area of ​​voids contained in the observation range to the area of ​​the observation range (void ratio). Furthermore, the total number of voids 30 was calculated, and the average area of ​​voids 30 was calculated by dividing the total area of ​​voids 30 by the total number of voids 30. The results are shown in Table 2. Note that voids that are cut off in the image were not included. In Figure 7 of Example 4, voids 30 could not be observed with the naked eye. Furthermore, the white areas in Figures 4 to 8 indicate sintering aid phases 35.

[0053] (Calculation of void irregularity) Using ImageJ, the contour area and envelope area of ​​each void 30 in the observation area were calculated. For each void 30, the envelope area of ​​the void 30 was divided by the contour area of ​​the void 30 to calculate the irregularity of each void 30. The average irregularity was calculated by dividing the sum of the irregularities of the detected voids 30 by the total number of voids 30. The calculation results of the average irregularity are shown in Table 2. Furthermore, the number of voids in the observation area for each irregularity and the ratio of the number of voids for each irregularity were calculated. The calculated total number of voids 30, the number of voids for each irregularity, and the ratio of the number of voids for each irregularity are shown in Table 3.

[0054] (Measurement of thermal conductivity) The aluminum nitride sintered bodies of Examples 1 to 4 and Comparative Example 1 were subjected to surface treatment (carbon blackening treatment) and then their thermal conductivities were measured in accordance with JIS R 1601:2010, "Method for measuring thermal diffusivity, specific heat capacity, and thermal conductivity of fine ceramics by the flash method." A laser flash method thermal property measuring device (product name: TC-7SB RT, manufactured by ULVAC) was used to measure the thermal conductivity. The results are shown in Table 2.

[0055] (Measurement of bending strength) The three-point bending strength of the aluminum nitride sintered bodies of Examples 1 to 4 and Comparative Example 1 was measured. The measurement was performed in accordance with JIS R 1601:2008 "Room temperature bending strength test method for fine ceramics" using a commercially available bending strength tester (manufactured by Shimadzu Corporation, device name: AG-2000). The results are shown in Table 2.

[0056] [Table 2]

[0057] [Table 3]

[0058] As shown in Table 2, the aluminum nitride sintered bodies of Examples 1 to 4 had a lower void fraction and a higher thermal conductivity than the aluminum nitride sintered body of Comparative Example 1. [Industrial Applicability]

[0059] According to the present disclosure, an aluminum nitride sintered body having high thermal conductivity can be provided. [Explanation of symbols]

[0060] 50...aluminum nitride sintered body, 50A...first main surface, 50B...second main surface, X...direction, 30...void, 31...protrusion, 32...recess, 35...sintering aid phase.

Claims

1. An aluminum nitride sintered body having a void area ratio of 1.0% or less in a cross section.

2. 2. The aluminum nitride sintered body according to claim 1, wherein an average irregularity of the voids in the cross section is 0.75 or more.

3. 3. The aluminum nitride sintered body according to claim 1, wherein the ratio of the number of voids having an irregularity degree of less than 0.70 to the total number of voids contained in the cross section is 5% or less.

4. In the cross section, the average area of ​​the voids is 3.00 μm ２ 3. The aluminum nitride sintered body according to claim 1, wherein:

5. 3. The aluminum nitride sintered body according to claim 1, having a thermal conductivity of 155 W / (m·K) or more.

6. 3. The aluminum nitride sintered body according to claim 1, having a bending strength of 410 MPa or more.

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