JP7346366B2 - Aluminum nitride sintered body and its manufacturing method - Google Patents

Description

The present invention relates to an aluminum nitride sintered body and a method for manufacturing the aluminum nitride sintered body.

Aluminum nitride (AlN) sintered bodies have excellent thermal conductivity, thermal radiation (heat dissipation), thermal shock resistance, and electrical insulation, and have a coefficient of thermal expansion close to that of silicon semiconductor elements, so they are used as heat dissipation substrates for semiconductor packaging. Used in parts of semiconductor manufacturing equipment.

When an aluminum nitride sintered body is used as a heat dissipation substrate, a metallized layer is formed on the surface. Cracks may occur at the ends of the metallized layer due to the difference in thermal expansion coefficient between the substrate and the metallized layer. In order to suppress this cracking, it is effective to improve the fracture toughness of the substrate.

Improvement in fracture toughness is also required when aluminum nitride sintered bodies are used for parts of semiconductor manufacturing equipment. Parts of semiconductor manufacturing equipment are required to be used for a long period of time, and this is to ensure the reliability of the parts.

In addition, heat dissipation boards for LEDs, LDs, etc., which are designed to achieve high output, are required to be made thinner in order to lower thermal resistance. It is necessary to increase the strength of the objective.

Therefore, many attempts have been made to improve the fracture toughness of aluminum nitride. For example, Japanese Patent Application Laid-Open No. 62-078160 (Patent Document 1) discloses that SiC whiskers are present in an amount of 5 to 50% by weight for the purpose of providing a composite reinforced sintered body having high hardness for use in cutting tools, etc. A composite reinforced sintered body consisting of 0.5 to 10% by weight of a sintering aid and the balance AlN is described, and depending on the composition, the strength ranges from 6.0 MPa・m ^1/2 to a maximum of 7.9 MPa・m ^1/ A fracture toughness of ² was obtained.

JP-A-3-174365 (Patent Document 2) describes an aluminum nitride sintered body in which silicon nitride whiskers are distributed in the aluminum nitride grain boundaries, and the maximum fracture strength is 4.7 MPa・m ^1/2 . Toughness has been obtained.

JP-A No. 2001-122671 (Patent Document 3) discloses that aluminate is added to the surface of fibrous aluminum nitride in a sintered matrix mainly composed of aluminum nitride particles in order to improve strength and toughness. An aluminum nitride sintered body in which existing coarse particles are dispersed is described, and a maximum fracture toughness of 5.2 MPa·m ^1/2 is obtained.

Japanese Unexamined Patent Publication No. 2009-76649 (Patent Document 4) discloses a plate-shaped aluminum nitride substrate for the purpose of providing a power module substrate that suppresses the propagation of cracks during thermal cycles and improves durability. A ceramic sintered body comprising aluminum nitride particles having aluminum nitride particles, fibrous aluminum nitride particles, and spherical aluminum nitride particles is described.

Japanese Unexamined Patent Publication No. 61-84036 (Patent Document 5) discloses that an aluminum nitride polytype having a chemical structure of Al-Si-O-N is used for the purpose of increasing thermal conductivity for mounting on a semiconductor. An aluminum nitride ceramic substrate is described in which the precipitated portion of acicular crystals is within ⅓ of the thickness of the substrate.

JP-A-7-82047 (Patent Document 6) discloses a ceramic composite sintered body in which spherical particles of silicon carbide or spherical particles of silicon nitride are added to an aluminum nitride matrix for the purpose of improving fracture toughness and the like. The fracture toughness is 8 MPa・m ^1/2 when silicon carbide spherical particles are added to the matrix, and 8.3 MPa・m ^1/2 when silicon nitride spherical particles are added to the matrix. fracture toughness has been obtained.

Japanese Unexamined Patent Publication No. 62-078160 Japanese Patent Application Publication No. 3-174365 Japanese Patent Application Publication No. 2001-122671 Japanese Patent Application Publication No. 2009-76649 Japanese Unexamined Patent Publication No. 61-84036 Japanese Patent Application Publication No. 7-82047

In order to ensure the reliability of a heat dissipation board for use in a vehicle, the fracture toughness is preferably 5.0 MPa·m ^1/2 or more, more preferably 6.0 MPa·m ^1/2 or more.

In the composite reinforced sintered body described in Patent Document 1, the thermal conductivity is 0.17 cal/cm・s・℃ (71W/mK) at the composition that provides the maximum fracture toughness of 7.9 MPa・m ^1/2 . Therefore, it cannot be used for a heat dissipation board that requires high thermal conductivity.

In addition, in the aluminum nitride sintered body described in Patent Document 2, a thermal conductivity of 235 W/mK is obtained with a composition that provides the maximum fracture toughness of 4.7 MPa・m ^1/2 , but Toughness is not achieved.

The aluminum nitride sintered body described in Patent Document 3 has a maximum fracture toughness of 5.2 MPa·m ^1/2 , but its thermal conductivity at that time is only 87 W/mK.

Patent Document 4 does not describe specific fracture toughness or thermal conductivity of the power module substrate.

The thermally conductive AlN ceramic substrate described in Patent Document 5 has a thermal conductivity of 80 to 100 W/mK, but the fracture toughness is not described.

The ceramic composite sintered body described in Patent Document 6 has a fracture toughness of 8 MPa·m ^1/2 when silicon carbide whiskers are added, and a fracture toughness of 8.3 MPa·m ^1/2 when silicon nitride whiskers are added. is obtained, but thermal conductivity is not taken into consideration.

As described above, conventionally, increasing fracture toughness lowers thermal conductivity, making it impossible to achieve both fracture toughness and thermal conductivity.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an aluminum nitride sintered body that can improve fracture toughness while maintaining the high thermal conductivity of aluminum nitride, and a method for manufacturing the same.

As a result of intensive research, the present inventors focused on the relationship between the oxygen content of aluminum nitride whiskers, which are needle-shaped single crystals, and fracture toughness and thermal conductivity. It has been found that fracture toughness can be improved while obtaining high thermal conductivity by adding so that the content of single crystal aluminum nitride whiskers in the body has a specific relationship. Based on the above findings of the present inventors, the present invention is constructed as follows.

The aluminum nitride sintered body according to the present invention is obtained by sintering a molded body mainly composed of aluminum nitride powder, which is mainly composed of polycrystalline aluminum nitride grains and includes at least aluminum nitride powder and single-crystal aluminum nitride whiskers. It is a sintered aluminum nitride body. The molded body contains 1% by weight or more of single crystal aluminum nitride whiskers based on 100% by weight of aluminum nitride powder. In the molded body, the product of the oxygen concentration (wt%) of the single-crystal aluminum nitride whiskers and the content (wt%) of the single-crystal aluminum nitride whiskers relative to 100 wt% of the aluminum nitride powder is 1 or more and 40 or less. be.

In the molded body, the product of the oxygen concentration (wt%) of the single crystal aluminum nitride whiskers and the content (wt%) of the single crystal aluminum nitride whiskers relative to 100 wt% of the aluminum nitride powder is 1 or more and 40 or less. In other words, the oxygen concentration of the total amount of single crystal aluminum nitride whiskers is 0.01% by weight or more and 0.40% by weight or less with respect to 100% by weight of aluminum nitride powder in the molded body.

By doing so, it is possible to provide an aluminum nitride sintered body that can achieve both high thermal conductivity and high fracture toughness.

In the aluminum nitride sintered body according to the present invention, the single crystal aluminum nitride whisker preferably has an oxygen concentration of 3% by weight or less.

By doing so, higher thermal conductivity can be obtained.

In the aluminum nitride sintered body according to the present invention, the single crystal aluminum nitride whisker preferably has a length (L50) of 20 μm or less.

By doing so, it is possible to prevent the single crystal aluminum nitride whiskers from becoming strongly entangled with each other, thereby preventing sintering inhibition.

The aluminum nitride sintered body according to the present invention preferably has a bulk density of 3.25 g/cm ³ or more.

The method for manufacturing the above-mentioned aluminum nitride sintered body according to the present invention includes adding a sintering aid and single crystal aluminum nitride whiskers to aluminum nitride powder in an amount of 1% by weight or more, mixing the mixture, molding, and then heating the mixture to 1900°C or higher. The method includes the step of obtaining a sintered body fired at a temperature of .

The method for producing an aluminum nitride sintered body according to the present invention includes the step of reducing the oxygen concentration of single-crystal aluminum nitride whiskers to 3% by weight or less by subjecting the single-crystal aluminum nitride whiskers to a reduction treatment.

The method for manufacturing the above-described aluminum nitride sintered body according to the present invention includes a step of degreasing in nitrogen after molding.

The aluminum nitride molded body according to the present invention contains at least aluminum nitride powder and single-crystal aluminum nitride whiskers, and is mainly composed of aluminum nitride powder, with 1 weight of single-crystal aluminum nitride whiskers per 100 weight % of aluminum nitride powder. Contains more than %. The product of the oxygen concentration (weight %) of the single crystal aluminum nitride whiskers and the content (weight %) of the single crystal aluminum nitride whiskers relative to 100 weight % of the aluminum nitride powder is 1 or more and 40 or less.

In the aluminum nitride molded body according to the present invention, the single crystal aluminum nitride whisker preferably has an oxygen concentration of 3% by weight or less.

In the aluminum nitride molded body according to the present invention, the single crystal aluminum nitride whisker preferably has a length (L50) of 20 μm or less.

By doing so, it is possible to provide aluminum nitride and its manufacturing method that can achieve both high thermal conductivity and high fracture toughness.

This is a SEM image of aluminum nitride whiskers, which are needle-like single crystals. This is an electron diffraction image showing that the aluminum nitride whisker is a single crystal. This is a SEM image showing that the aluminum nitride whiskers are tangled and form a lump after being pulverized. This is a SEM image showing that aluminum nitride whiskers remain in the sintered body in a lumpy state.

The aluminum nitride sintered body according to the present invention is obtained by sintering a molded body mainly composed of aluminum nitride powder, which is mainly composed of polycrystalline aluminum nitride grains and includes at least aluminum nitride powder and single-crystal aluminum nitride whiskers. It is a sintered aluminum nitride body. The molded body contains 1% by weight or more of single crystal aluminum nitride whiskers based on 100% by weight of aluminum nitride powder. In the molded body, the product of the oxygen concentration (wt%) of the single-crystal aluminum nitride whiskers and the content (wt%) of the single-crystal aluminum nitride whiskers relative to 100 wt% of the aluminum nitride powder is 1 or more and 40 or less. be.

In the molded body, the product of the oxygen concentration (wt%) of the single-crystal aluminum nitride whisker and the content (wt%) of the single-crystal aluminum nitride whisker relative to 100 wt% of the aluminum nitride powder is 1 or more and 40 or less. In other words, in the molded body, the oxygen concentration of the entire amount of single crystal aluminum nitride whiskers is 0.01% by weight or more and 0.40% by weight or less with respect to 100% by weight of the aluminum nitride powder.

First, each component of the molded body for manufacturing the aluminum nitride sintered body according to the present invention will be explained. The content and oxygen concentration of each component below are the content in the molded body unless otherwise specified.

The aluminum nitride powder in the molded body used for producing the aluminum nitride sintered body according to the present invention preferably has an average particle size of 0.8 to 2.5 μm, and preferably 0.8 to 1.4 μm. It is more preferable. The oxygen concentration is preferably 0.7 to 0.9% by weight. The specific surface area is preferably 2.3 to 2.9 m ² /g.

The single-crystal aluminum nitride whisker in the molded body used for manufacturing the aluminum nitride sintered body of the present invention is synthesized by using aluminum as a raw material and reacting it with nitrogen gas at high temperature. As shown in FIG. 1, the obtained single crystal aluminum nitride is a needle-shaped single crystal. As shown in Figure 2, regular diffraction spots can be seen in the electron diffraction image of single crystal aluminum nitride obtained in this way, so it is necessary to confirm that the aluminum nitride whisker is a single crystal by looking at the electron diffraction image. Can be done.

The single crystal aluminum nitride whiskers in the molded body have a distribution in diameter (short axis diameter) and length (long axis diameter). The diameter distribution (D10, D50, D90) and length distribution (L10, L50, L90) of single-crystal aluminum nitride whiskers are measured, for example, by an image analysis method. Specifically, single-crystal aluminum nitride whiskers well-dispersed in a liquid are photographed, and the diameter and length of each single-crystal aluminum nitride whisker are measured from the photographed image to determine their distribution. Alternatively, single crystal aluminum nitride whiskers well dispersed on a glass plate may be photographed and the distribution may be determined from the photographed image. The diameter and length distribution of single crystal aluminum nitride whiskers may be determined by other methods.

The diameter (D10) of the single crystal aluminum nitride whisker in the molded body is preferably 0.8 to 1.5 μm, more preferably 1.0 to 1.5 μm. By setting the diameter (D10) of the single crystal aluminum nitride whisker within the range of 1.0 to 1.5 μm, it is possible to prevent the single crystal aluminum nitride whisker from disappearing during firing, and the single crystal nitride that remains after firing can be prevented. Fracture toughness can be improved by aluminum whiskers.

Specifically, the diameter (D50) of the single crystal aluminum nitride whisker in the molded body is preferably 1 μm or more, more preferably 1.5 to 2.5 μm. By having the diameter (D50) of the single crystal aluminum nitride whiskers within the range of 1.5 to 2.5 μm, it is possible to prevent the single crystal aluminum nitride whiskers from disappearing during firing, and the single crystal aluminum nitride whiskers remaining after firing can be prevented from disappearing. Fracture toughness can be improved by aluminum whiskers.

The diameter (D90) of the single crystal aluminum nitride whisker in the molded body is preferably 3.5 to 5.0 μm, more preferably 3.5 to 4.0 μm. By having the diameter (D90) of the single crystal aluminum nitride whisker within the range of 3.5 to 4.0 μm, it is possible to prevent sintering inhibition during firing and a decrease in the density of the aluminum nitride sintered body, A dense sintered body can be obtained. Furthermore, it is possible to prevent single crystal aluminum nitride whiskers themselves from acting as defects and reducing strength.

The length (L10) of the single crystal aluminum nitride whisker in the molded body is preferably 5 to 10 μm, more preferably 7 to 10 μm. By setting the length (L10) of the single crystal aluminum nitride whisker within the range of 7 to 10 μm, it is possible to prevent the single crystal aluminum nitride whisker from disappearing during firing, and the single crystal aluminum nitride whisker remaining after firing can prevent the single crystal aluminum nitride whisker from disappearing. Fracture toughness can be improved.

The length (L50) of single crystal aluminum nitride whiskers in the molded body is preferably 5 to 20 μm, more preferably 10 to 15 μm. The single crystal aluminum nitride whiskers immediately after synthesis are in a state where the single crystal aluminum nitride whiskers are independent from each other, as shown in FIG. When single-crystal aluminum nitride whiskers as shown in FIG. 1 are pulverized, they tend to become lumpy as shown in FIG. 3. At this time, if the length (L50) of the single crystal aluminum nitride whiskers is 20 μm or less, it is possible to prevent the single crystal aluminum nitride whiskers from becoming strongly entangled with each other, and the lumped single crystal aluminum nitride whiskers are It can be prevented from becoming difficult to be dispersed in polycrystalline grains. As shown in FIG. 4, the strongly entangled lump-like single-crystal aluminum nitride whiskers remain in the sintered body in a lump-like state and may cause sintering inhibition. When sintering inhibition occurs, the density of the sintered body decreases, and the decrease in density can cause a decrease in thermal conductivity and fracture toughness. Therefore, the length (L50) of single-crystal aluminum nitride whiskers is preferably 20 μm or less so that even if they are crushed, they are unlikely to get entangled strongly.

The length (L90) of single crystal aluminum nitride whiskers in the molded body is preferably 25 to 50 μm, more preferably 30 to 40 μm. By setting the length (L90) of the single crystal aluminum nitride whisker within the range of 30 to 40 μm, even if the single crystal aluminum nitride whisker becomes lumpy, it is easily dispersed in the aluminum nitride polycrystalline grains, thereby inhibiting sintering. This can prevent the aluminum nitride sintered body from decreasing in density.

If the length of single crystal aluminum nitride whiskers does not have an appropriate distribution, the distribution can be adjusted by classification treatment, sedimentation treatment, or mechanical crushing. As the pulverization method, any known method such as a ball mill, jet mill, disk shearing, etc. may be used.

The oxygen concentration of the single crystal aluminum nitride whiskers in the molded body is preferably 12% by weight or less, more preferably 3% by weight or less. When the oxygen concentration of the single crystal aluminum nitride whisker is 3% by weight or less, the thermal conductivity of the obtained aluminum nitride sintered body can be further increased. By lowering the oxygen concentration of the single crystal aluminum nitride whiskers, it is possible to prevent the formation of an aluminum oxide layer with poor thermal conductivity within the aluminum nitride sintered body, thereby preventing the thermal conductivity from decreasing.

The oxygen content of single crystal aluminum nitride whiskers in the molded body is measured by a combustion method, fluorescent X-ray analysis, or other known methods. The carbon monoxide generated by melting in an inert gas is measured by infrared absorption method.

When the oxygen concentration of single crystal aluminum nitride whiskers is high, the oxygen concentration can be reduced by, for example, treating in vacuum or in a hydrogen flow at a temperature of 800 to 1200° C. for 1 to 20 hours. Furthermore, the oxygen concentration can be reduced by adding carbon and treating in a nitrogen atmosphere at 1,600 to 1,700° C. for 1 to 20 hours in the same manner as the method for synthesizing aluminum nitride powder. In addition, oxygen concentration can be reduced by the method of synthesizing single crystal aluminum nitride whiskers, and the atmosphere when crushing single crystal aluminum nitride whiskers can be made into a nitrogen atmosphere, and after crushing single crystal aluminum nitride whiskers, vacuum, nitrogen, Alternatively, the oxygen concentration can be reduced by heat treatment in hydrogen.

The content of single crystal aluminum nitride whiskers in the molded body is 1% by weight or more, preferably 1 to 10% by weight, more preferably 3 to 10% by weight. When the content of single-crystal aluminum nitride whiskers is less than 1% by weight, there are few single-crystal aluminum nitride whiskers that contribute to improving fracture toughness, and it may be difficult to obtain the effect of improving fracture toughness. On the other hand, if the content of single crystal aluminum nitride whiskers exceeds 15% by weight, sintering may be inhibited and the density of the aluminum nitride sintered body may be reduced.

In the molded body, the product of the oxygen concentration (wt%) of single-crystal aluminum nitride whiskers and the content (wt%) of single-crystal aluminum nitride whiskers relative to 100 wt% of aluminum nitride powder is 1 or more and 40 or less. It is. In other words, in the molded body, the oxygen concentration of the total amount of single crystal aluminum nitride whiskers is 0.01% by weight or more and 0.40% by weight or less with respect to 100% by weight of the aluminum nitride powder.

As the sintering aid, rare earth element oxides, alkaline earth element oxides, carbonates, oxalates, nitrates, etc. are used. More specifically, it is preferable to use oxides of rare earth elements. The sintering aid is preferably contained in an amount of 1 to 5% by weight in terms of oxide based on 100% by weight of the aluminum nitride powder.

Next, a method for manufacturing an aluminum nitride sintered body according to the present invention will be described.

First, a single-crystal aluminum nitride whisker with an adjusted oxygen concentration, a sintering aid, a binder, an organic solvent, or a water dispersion medium are added to aluminum nitride powder, and the mixture is mixed in a ball mill to prepare a slurry. Furthermore, if the molding method is press molding, granulation is performed using a spray dryer or the like. The particle size of the resulting granules is preferably 50 to 60 μm.

The resulting mixed slurry or powder granules are shaped. Molding can be performed by a molding method suitable for the shape required depending on the purpose and size, such as die press, rubber press, cast molding, and sheet molding. The obtained molded body is, for example, block-shaped and has a size of, for example, 50 mm x 50 mm x 8 mm. A molded body of an appropriate size can be obtained by appropriately selecting a device or a jig. When molding is performed using a mold press, the single-crystal aluminum nitride whiskers are oriented by uniaxial pressure. On the other hand, when molding is performed using a rubber press, the single-crystal aluminum nitride whiskers are not oriented because pressure is applied at a constant pressure.

Next, the molded body is degreased and fired to obtain an aluminum nitride sintered body. Degreasing and firing are performed by known methods. Preferably, degreasing is carried out under nitrogen. The degreasing temperature is preferably 500 to 1000°C, more preferably 500 to 800°C. The time for degreasing is preferably 1 to 20 hours. The firing temperature is preferably 1700 to 1950°C. More preferably, the temperature is 1900°C or higher. The firing time is preferably 1 to 20 hours, more preferably 2 to 12 hours. Appropriate firing conditions are selected depending on the size and thickness of the molded body. Firing is performed in nitrogen, and either normal pressure firing or pressure firing may be used, but it is preferable to perform normal pressure firing for economic efficiency and for producing a large sintered body.

In the obtained aluminum nitride sintered body, single crystal aluminum nitride whiskers and fibrous particles derived from the single crystal aluminum nitride whiskers are present. The presence of fibrous particles can be confirmed by observing the fractured or polished surface with an optical microscope or an electron microscope.

As described above, the single crystal aluminum nitride whiskers in the aluminum nitride sintered body are oriented by the molding method. Oriented single crystal aluminum nitride whiskers may form an oriented texture. The orientation during molding is maintained even after firing. The orientation of single-crystal aluminum nitride whiskers in the aluminum nitride sintered body can be confirmed, for example, by X-ray diffraction. The orientation is determined by the peak intensity ratio I(100)/I(002) from the (100) plane parallel to the length direction of the single crystal aluminum nitride whisker and the (002) plane perpendicular to it. According to the I(f) value in the X-ray diffraction database JCPDS-25-1133, I(100)/I(002) is 1.67 in an isotropic sintered body, but the stronger the orientation, the more , I(100)/I(002) increases. When single crystal aluminum nitride whiskers are required to be oriented, the value of I(100)/I(002) is 2 or more, and when stronger orientation is required, I( 100)/I(002) is preferably 3 or more.

By controlling the orientation of single crystal aluminum nitride whiskers, the properties of the sintered body can be controlled. For example, fracture toughness increases when cracks propagate along a direction perpendicular to the direction of orientation of single-crystal aluminum nitride whiskers. Therefore, by arranging single crystal aluminum nitride whiskers preferentially along a direction perpendicular to the direction in which crack propagation is desired to be inhibited when the sintered body is used, fracture toughness can be improved.

The effect of suppressing crack growth due to such orientation can be confirmed, for example, by measuring the length of Vickers cracks. The indenter is driven so that the apex of the square pyramid of the Vickers indenter is located along the direction perpendicular to and parallel to the orientation direction, and the length of the crack is measured. Depending on the orientation, a difference occurs between the crack length in the vertical direction (Lt) and the crack length in the parallel direction (Lp). The direction in which the crack is short is the direction in which the effect of suppressing the growth is high. When a growth suppressing effect is required, it is preferable that the value of Lp/Lt is 1.1 or more.

In this way, an aluminum nitride sintered body having a bulk density of 3.25 g/cm ³ or more, a thermal conductivity of 170 W/mK or more, and a fracture toughness of 5.0 MPa・m ^1/2 or more can be obtained. The aluminum nitride sintered body preferably has a bulk density of 3.25 g/cm ³ or more. Moreover, it is preferable that the aluminum nitride sintered body has a relative density of 97.5% or more.

The thermal conductivity of a sintered body can be measured, for example, by a laser flash method, a hot wire method, etc., and in the present invention, the thermal conductivity is measured by a laser flash method.

The fracture toughness of a sintered body can be measured, for example, by an indentation method that does not introduce a pre-crack, a notch processing method, or a method that introduces a pre-crack (SEPB method). In the specification, fracture toughness is measured by the SEPB method.

The present invention will be explained in more detail by Examples and Test Examples, but the present invention is not limited thereto.

[Preparation of single crystal aluminum nitride whiskers]
Single-crystal aluminum nitride whiskers were synthesized by a known method, and the resulting cotton-like single-crystal aluminum nitride whiskers were placed in an organic solvent and classified into two levels: those that had settled and those that had been dispersed in the organic solvent. In each Example and Comparative Example, single crystal aluminum nitride whiskers classified as shown in Table 1 were used. The classified single-crystal aluminum nitride whiskers were ground with a ball mill to adjust the length. Furthermore, in Examples 1 to 5, the crushed single crystal aluminum nitride whiskers were treated at 1000° C. for 5 hours in a hydrogen flow to reduce the oxygen concentration. Table 1 shows the classification, length (L50), and oxygen concentration (wt%) of the single crystal aluminum nitride whiskers of each example and comparative example. Note that single crystal aluminum nitride whiskers were not added to the sintered bodies of Comparative Examples 1 and 2. The oxygen concentration of single crystal aluminum nitride whiskers was determined by melting the single crystal aluminum nitride whiskers in an inert gas according to JIS Z2613, and measuring the generated carbon monoxide by an infrared absorption method.

[Preparation of aluminum nitride sintered body]
[Preparation of slurry]
5% by weight of yttrium oxide was added to 100% by weight of aluminum nitride powder, appropriate amounts of pure water, a dispersant, and an antifoaming agent were added, and the mixture was mixed for a predetermined time using an alumina ball mill. In Examples 1 to 6 and Comparative Examples 3 to 7, only single crystal aluminum nitride whiskers were added at the content shown in Table 2 to 100% by weight of aluminum nitride powder mixed previously in a separate container, and purified water, Appropriate amounts of a dispersant and an antifoaming agent were added, and the mixture was mixed for a predetermined time using a nylon ball mill so as not to shorten the single crystal aluminum nitride whiskers. As shown in FIG. 2, single-crystal aluminum nitride whiskers after pulverization tend to form lumps. It was observed that the longer the single-crystal aluminum nitride whiskers, the more difficult it was to disperse the single-crystal aluminum nitride whiskers, and the more difficult it was to form a slurry. Thereafter, the slurry containing the previously mixed aluminum nitride powder was put into the container in which the single crystal aluminum nitride whiskers were mixed, and then mixed in a nylon ball mill for a predetermined period of time. After that, a binder was added and the mixture was subjected to nylon ball milling again to prepare a slurry. In Comparative Examples 1 and 2, after mixing for a predetermined time without adding single crystal aluminum nitride whiskers, a binder was added to the raw material powder container, and mixing was performed again for a predetermined time to prepare a slurry.

[Molding]
In Examples 1 to 5 and Comparative Examples 1 to 7, the prepared slurry was granulated using a spray dryer. The particle diameter D50 of the obtained granules was in the range of 50 to 60 μm. The granules were press-molded by uniaxial pressure using a die press to produce a molded body of 50 x 50 x 8 mm. In Example 6, a sheet with a thickness of 300 μm was produced using the slurry by a sheet molding method. The sheets were cut out to a size of 55 x 40 mm, laminated, and then crimped at 150°C to produce a molded body of 55 x 40 x 6 mm.

[Degreasing and firing]
Degreasing was carried out at 600° C. for 3 hours in the air (Example 1, Comparative Examples 1 and 3 to 6) or in nitrogen (Examples 2 to 6 and Comparative Examples 2 and 7). Firing was carried out in nitrogen atmosphere by normal pressure firing, increasing the temperature at 1.5° C./min, holding at 1900° C. for 2 hours, and decreasing the temperature at 0.5° C./min.

The bulk density, relative density, thermal conductivity, and fracture toughness of the obtained aluminum nitride sintered body were measured. The results are shown in Table 2. In Table 2, "whisker oxygen concentration" is the oxygen concentration (wt%) of single-crystal aluminum nitride whiskers, "whisker content" is the content (wt%) of single-crystal aluminum nitride whiskers relative to 100 wt% of aluminum nitride powder, " Oxygen amount Relative density, thermal conductivity, and fracture toughness are the bulk density of the sintered body (g/cm ³ ), the relative density of the sintered body (%), and the thermal conductivity of the sintered body (W/mK), respectively. , means the fracture toughness (MPa·m ^1/2 ) of the sintered body.

The bulk density of the sintered body was measured by the Archimedes method after processing the obtained sintered body into a size of 8 mm x 30 mm x 4 mm.

The relative density was calculated taking into account the amount of yttrium oxide added and assuming a theoretical bulk density of 3.33 g/cm ³ .

The thermal conductivity was measured by processing the obtained sintered body into a size of 8 mm x 8 mm x 4 mm using a laser flash method.

Fracture toughness was measured using the SEPB method after processing the sample into a size of 3 x 4 x 40 mm.

As shown in Table 2, the product of the oxygen concentration (wt%) of single-crystal aluminum nitride whiskers and the content (wt%) of single-crystal aluminum nitride whiskers relative to 100 wt% of aluminum nitride powder is 1 or more. 40 or less, in other words, in Examples 1 to 6, the oxygen concentration of the total amount of single crystal aluminum nitride whiskers is 0.01% by weight or more and 0.40% by weight or less with respect to 100% by weight of aluminum nitride powder, 170W/ A fracture toughness exceeding 5.0 MPa·m ^1/2 was obtained while maintaining a thermal conductivity of mK or higher.

Further, as shown in Table 2, from Comparative Examples 1 and 2, it was found that the thermal conductivity of nitrogen degreasing was higher than that in the air in a state where single crystal aluminum nitride whiskers were not added. Further, from Examples 1 and 2, it was found that even if single-crystal aluminum nitride whiskers were added, the thermal conductivity was higher in nitrogen degreasing than in the air, and the fracture toughness remained almost unchanged.

In addition, the single crystal aluminum nitride whisker of Comparative Example 7 has an oxygen concentration of 2.8% by weight, the same as in Example 4, but the content is as high as 15% by weight, and the single crystal aluminum nitride whisker is The product of the whisker content (weight %) exceeds 40. The aluminum nitride sintered body of Comparative Example 7 had a low bulk density and a low relative density, making it impossible to obtain a dense sintered body, which is considered to have caused a decrease in thermal conductivity and fracture toughness. The aluminum nitride sintered body preferably has a bulk density of 3.25 g/cm ³ or more. Moreover, it is preferable that the aluminum nitride sintered body has a relative density of 97.5% or more.

The orientation of the aluminum nitride sintered body of Example 6 was measured by X-ray diffraction on the laminated sheet surface. In diffraction from the laminated sheet surface, I(100)/I(002) was 39.5.

Regarding the aluminum nitride sintered body of Example 6, a Vickers crack was introduced into the side surface of the laminated sheet, and the length was measured, and Lp/Lt was 1.3.

The embodiments and examples disclosed above should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and includes meanings equivalent to the claims and all modifications within the scope.

Claims (14)

An aluminum nitride sintered body made by sintering a molded body mainly composed of aluminum nitride powder, which is mainly composed of polycrystalline aluminum nitride grains and contains at least aluminum nitride powder and single-crystal aluminum nitride whiskers,
It has a thermal conductivity of 170 W/mK or more and a fracture toughness of more than 5.0 MPa m ^1/2 ,
The molded body contains 1% by weight or more and 10% by weight or less of single crystal aluminum nitride whiskers based on 100% by weight of the aluminum nitride powder,
The product of the oxygen concentration (wt%) of the single crystal aluminum nitride whisker and the content (wt%) of the single crystal aluminum nitride whisker relative to 100 wt% of the aluminum nitride powder is 1 or more and 40 or less. , aluminum nitride sintered body. The aluminum nitride sintered body according to claim 1 , wherein the single crystal aluminum nitride whisker has a length (L50) of 20 μm or less. The aluminum nitride sintered body according to claim 1 or 2, wherein the single crystal aluminum nitride whisker has a length (L90) of 30 μm or more and 40 μm or less. The aluminum nitride sintered body according to any one of claims 1 to 3, having a bulk density of 3.25 g/cm ³ or more. The product of the oxygen concentration (wt%) of the single crystal aluminum nitride whisker and the content (wt%) of the single crystal aluminum nitride whisker relative to 100 wt% of the aluminum nitride powder is 27 or more and 40 or less. , The aluminum nitride sintered body according to any one of claims 1 to 4. The aluminum nitride sintered body according to any one of claims 1 to 5, wherein the molded body is sintered under normal pressure. Includes the step of adding a sintering aid and single crystal aluminum nitride whiskers to aluminum nitride powder in an amount of 1% by weight or more and 10% by weight or less , mixing, shaping, and then obtaining a sintered body by firing at a temperature of 1900°C or higher. , A method for producing an aluminum nitride sintered body according to any one of claims 1 to 6 . 8. The manufacturing method according to claim 7 , comprising the step of reducing the oxygen concentration of the single crystal aluminum nitride whisker to 3% by weight or less by subjecting the single crystal aluminum nitride whisker to a reduction treatment. The manufacturing method according to claim 7 or 8 , further comprising a step of degreasing in nitrogen after the molding. The manufacturing method according to any one of claims 7 to 9, wherein the firing is performed at normal pressure. Mainly composed of aluminum nitride powder,
Containing 1% by weight or more and 10% by weight or less of single crystal aluminum nitride whiskers based on 100% by weight of the aluminum nitride powder,
The product of the oxygen concentration (wt%) of the single crystal aluminum nitride whisker and the content (wt%) of the single crystal aluminum nitride whisker relative to 100 wt% of the aluminum nitride powder is 1 or more and 40 or less. the law of nature,
The single crystal aluminum nitride whisker is an aluminum nitride molded body having a length (L50) of 20 μm or less . Mainly composed of aluminum nitride powder,
Containing 1% by weight or more and 10% by weight or less of single crystal aluminum nitride whiskers based on 100% by weight of the aluminum nitride powder,
The product of the oxygen concentration (wt%) of the single-crystal aluminum nitride whisker and the content (wt%) of the single-crystal aluminum nitride whisker relative to 100 wt% of the aluminum nitride powder is 1 or more and 40 or less. ,
The single crystal aluminum nitride whisker is an aluminum nitride molded body whose length (L90) is 30 μm or more and 40 μm or less. Mainly composed of aluminum nitride powder,
Containing 1% by weight or more and 10% by weight or less of single crystal aluminum nitride whiskers based on 100% by weight of the aluminum nitride powder,
The product of the oxygen concentration (wt%) of the single-crystal aluminum nitride whisker and the content (wt%) of the single-crystal aluminum nitride whisker relative to 100 wt% of the aluminum nitride powder is 1 or more and 40 or less. ,
The single crystal aluminum nitride whisker has a length (L50) of 20 μm or less, and a length (L90) of 30 μm or more and 40 μm or less. The product of the oxygen concentration (wt%) of the single crystal aluminum nitride whisker and the content (wt%) of the single crystal aluminum nitride whisker relative to 100 wt% of the aluminum nitride powder is 27 or more and 40 or less. , The aluminum nitride molded body according to any one of claims 11 to 13.