Aluminum nitride sintered body, method for producing the same, and circuit substrate

Abstract

The present application provides a method for manufacturing an aluminum nitride sintered body, which has a molding step of molding a molding material containing an aluminum nitride powder, a sintering aid, and a binder; a debinding step of heating the molded body in an inert gas atmosphere or a reduced pressure atmosphere at 500 to 600°C; and a heating step of firing the molded body after debinding in a nitrogen atmosphere at 1500 to 1700°C for 7 hours or more, and then firing in a nitrogen atmosphere at 1750 to 1880°C for 3 to 5 hours. The volume resistivity of the aluminum nitride sintered body is 5.0 x 10 12 Ω·cm or more.

Description

Technical Field

[0001] This disclosure relates to aluminum nitride sintered bodies, methods for manufacturing the same, and circuit boards. Background Technology

[0002] In recent years, high-power control modules have been used in industrial equipment such as motors and products such as electric vehicles. In these power modules, circuit boards with ceramic plates are used to effectively dissipate heat generated from semiconductor elements and suppress leakage current. The ceramic sintered body used for such ceramic plates is typically manufactured by sintering a molded body shaped into a specified form.

[0003] As ceramic sintered bodies, sintered bodies composed of nitrides, carbides, borides, or silicides are known. Among them, aluminum nitride sintered bodies exhibit excellent thermal conductivity and electrical insulation. Therefore, they are used as heat dissipation components for electronic components such as power modules. To improve adaptability to these applications, Patent Document 1 proposes a technique for improving the insulation of aluminum nitride sintered bodies by using specified sintering aids.

[0004] Existing technical documents Patent documents Patent Document 1: International Publication No. 2021 / 261452 Summary of the Invention

[0005] The problem that the invention aims to solve As electronic components such as power modules achieve further performance improvements, the performance requirements for various products using these components are becoming increasingly stringent. Therefore, this disclosure provides an aluminum nitride sintered body with sufficiently high electrical insulation properties and a method for manufacturing the same. Furthermore, it provides a circuit board with excellent reliability.

[0006] Methods for solving problems One aspect of this disclosure provides aluminum nitride sintered bodies of [1] to [3].

[0007] [1] An aluminum nitride sintered body having a volume resistivity of 5.0 × 10⁻⁶. 12 Ω·cm or higher.

[0008] [2] The sintered aluminum nitride body according to [1] has an oxygen content of less than 1.80% by mass.

[0009] [3] The aluminum nitride sintered body according to [1] or [2] has a bending strength of 430 MPa or more.

[0010] The aluminum nitride sintered bodies described above [1] to [3] have sufficiently high volume resistivity. Therefore, they have sufficiently high electrical insulation properties. Such aluminum nitride sintered bodies are suitable for use as components such as insulating substrates and power modules.

[0011] One aspect of this disclosure provides a method for manufacturing aluminum nitride sintered bodies [4] to [7].

[0012] [4] A method for manufacturing an aluminum nitride sintered body, comprising: a molding step, wherein a molding raw material containing aluminum nitride powder, a sintering aid and a binder is molded to obtain a sintered body; a degreasing step, wherein the sintered body is heated in a nitrogen atmosphere or a reduced pressure atmosphere at 500~600°C; and a heating step, wherein the degreased sintered body is sintered in an inert gas atmosphere or a reduced pressure atmosphere at 1500~1700°C for more than 7 hours, and then sintered in a nitrogen atmosphere at 1750~1880°C for 3~5 hours.

[0013] [5] According to the method for manufacturing aluminum nitride sintered body described in [4], in the heating process, the shaped body is sintered in a nitrogen atmosphere at 1500~1880°C for 11~30 hours.

[0014] [6] The method for manufacturing an aluminum nitride sintered body according to [4] or [5], wherein the volume resistivity of the aluminum nitride sintered body is 5.0 × 10⁻⁶. 12 Ω·cm or higher.

[0015] [7] The method for manufacturing an aluminum nitride sintered body according to any one of [4] to [6], wherein the volume of the sintered body is 1000 to 9000 mm. 3 .

[0016] The methods for manufacturing aluminum nitride sintered bodies described above [4] to [7] involve a degreasing process performed in an inert gas atmosphere or a reduced pressure atmosphere, which significantly reduces the oxygen content in the aluminum nitride sintered body. However, when the degreasing process is performed in an inert gas atmosphere or a reduced pressure atmosphere, carbon from the binder component is more likely to remain in the aluminum nitride sintered body compared to degreasing in air. Therefore, in the above manufacturing methods, the body is sintered in a nitrogen atmosphere at 1500-1700°C for 7 hours or more. This significantly reduces the amount of carbon remaining in the aluminum nitride sintered body. Furthermore, sintering in a nitrogen atmosphere at 1750-1880°C for 3-5 hours sufficiently densifies the aluminum nitride sintered body and suppresses over-sintering. For these reasons, an aluminum nitride sintered body with sufficiently high electrical insulation can be manufactured. Such an aluminum nitride sintered body is suitable for use as a component in power modules, such as an insulating substrate.

[0017] One aspect of this disclosure provides a circuit board [8].

[0018] [8] A circuit board comprising: an insulating substrate made of aluminum nitride sintered body as described in any one of [1] to [3] above; and a metal circuit bonded to the insulating substrate.

[0019] The circuit board described above [8] has an insulating substrate made of aluminum nitride sintered body with sufficiently high electrical insulation, and therefore has excellent reliability. Such a circuit board can be used in semiconductor devices such as power modules.

[0020] Invention Effects According to this disclosure, it is possible to provide an aluminum nitride sintered body with sufficiently high electrical insulation and a method for manufacturing the same. Furthermore, it is possible to provide a circuit board with excellent reliability. Attached Figure Description

[0021] Figure 1 This is a perspective view showing an example of an aluminum nitride sintered body.

[0022] Figure 2 This is a three-dimensional view showing an example of a circuit board.

[0023] Figure 3 This is a three-dimensional diagram representing an example of a stacked body. Detailed Implementation

[0024] The following describes embodiments of this disclosure. However, these embodiments are merely illustrative and not intended to limit this disclosure to their specific content. In this disclosure, the numerical range expressed in the form of "a to b" is a numerical range including a and b, with the lower limit set to a and the upper limit set to b. Values ​​obtained by substituting the upper and / or lower limits of each numerical range with the illustrated values ​​or values ​​from any embodiment are also included in this disclosure. Furthermore, numerical ranges formed by arbitrarily combining separately described upper and lower limit values ​​are also included in this disclosure. Unless otherwise specified, the materials or components illustrated in this disclosure may be used individually or in combination of two or more. In the description, the same reference numerals are used to denote the same elements or elements having the same function, and repeated descriptions are omitted as appropriate.

[0025] Aluminum nitride sintered bodies contain aluminum nitride as the main component. The aluminum nitride content in the aluminum nitride sintered body can be 90% by mass or more. The aluminum nitride content in the aluminum nitride sintered body can be 93% by mass or more, or 95% by mass or more. From the viewpoint of maximizing density, the aluminum nitride content in the aluminum nitride sintered body can be 99.5% by mass or less, 99% by mass or less, or 98% by mass or less. An example of the aluminum nitride content in the aluminum nitride sintered body is 90% by mass to 99.5% by mass. The content of each component in the aluminum nitride sintered body can be determined, for example, by X-ray analysis. For X-ray analysis, for example, the D8 ADVANCE (trade name) manufactured by Bruker Japan Co., Ltd. can be used.

[0026] The aluminum nitride sintered body disclosed herein is a solid in which aluminum nitride particles are bonded together. The aluminum nitride sintered body may contain oxides as secondary components. The oxides may include oxides having yttrium and aluminum as constituent elements (composite oxides).

[0027] Figure 1 This is a perspective view showing an aluminum nitride sintered body according to one embodiment. The shape of the aluminum nitride sintered body 100 is not particularly limited; for example, it can be sheet-like. From the viewpoint of maximizing its usefulness as an electronic component, the volume of the aluminum nitride sintered body 100 can be 1000 mm². 3 Above, 1500mm 3 Above or 2000mm 3 That's all. From the viewpoint of sufficiently reducing the carbon content in the aluminum nitride sintered body 100, the volume of the aluminum nitride sintered body 100 can be 9000 mm². 3 Below, 5000mm 3 Below, or 3000mm 3 The volume of the aluminum nitride sintered body 100 can be 1000~9000 mm² in some cases. 3 .

[0028] The volume resistivity of the aluminum nitride sintered body 100 is 5.0 × 10⁻⁶. 12 Ω·cm and above, can be 7.0×10 12 Ω·cm or more, 8.0×10 12 Ω·cm or above, or 1.0×10 13 The volume resistivity is above Ω·cm. Aluminum nitride sintered bodies 100 with sufficiently high volume resistivity exhibit superior reliability, for example, when used as insulating substrates. The volume resistivity of the aluminum nitride sintered body 100 can, for example, be 1.0 × 10⁻⁶ Ω·cm. 14 Below Ω·cm. An example of the volume resistivity of an aluminum nitride sintered body 100 can be 5.0 × 10⁻⁶ Ω·cm. 12 ~1.0×10 14 Ω·cm.

[0029] The volume resistivity of the aluminum nitride sintered body 100 can be adjusted, for example, by changing the atmosphere in the degreasing process and the temperature profile in the heating process during the manufacture of the aluminum nitride sintered body 100. The volume resistivity can be measured according to JIS C2139:2008 "Solid electrical insulating materials—Methods for determination of volume resistivity and surface resistivity". Furthermore, the measuring device can be, for example, a super-insulator manufactured by Hioki Electric (trade name: SM-8220). The measuring temperature can be 20℃±1℃.

[0030] From the viewpoint of maximizing volume resistivity, the oxygen content in the aluminum nitride sintered body 100 can be less than 1.80% by mass, less than 1.70% by mass, or less than 1.65% by mass. From the viewpoint of maximizing density, the oxygen content in the aluminum nitride sintered body 100 can be 0.50% by mass or more, 1.00% by mass or more, or 1.30% by mass or more. An example of the oxygen content in the aluminum nitride sintered body 100 is 0.5% by mass or more and less than 1.80% by mass. Oxygen can be included in the aluminum nitride sintered body 100, for example, as the aforementioned oxide.

[0031] The oxygen content of the aluminum nitride sintered body 100 can be adjusted, for example, by changing the synthesis method and oxygen content of the aluminum nitride powder used as raw material, as well as the atmosphere in the degreasing process during the manufacture of the aluminum nitride sintered body 100. The oxygen content of the aluminum nitride sintered body 100 can be measured using a commercially available oxygen and nitrogen analyzer.

[0032] The thermal conductivity of the aluminum nitride sintered body 100 can be 120 W / m·K or higher, 140 W / m·K or higher, 150 W / m·K or higher, or 160 W / m·K or higher. The aluminum nitride sintered body 100 with sufficiently high thermal conductivity is suitable, for example, as a heat dissipation component for power modules. However, the application of the aluminum nitride sintered body 100 is not limited to this. The thermal conductivity of the aluminum nitride sintered body 100 can, for example, be 200 W / m·K or lower. An example of the thermal conductivity of the aluminum nitride sintered body 100 is 120~200 W / m·K.

[0033] The thermal conductivity of the aluminum nitride sintered body 100 can be adjusted, for example, by changing the highest temperature (temperature within the second temperature range TR2) in the heating process during the manufacture of the aluminum nitride sintered body 100. The thermal conductivity can be measured using the laser flash method according to JIS R1611:2010 "Determination of thermal diffusivity, specific heat capacity and thermal conductivity of fine ceramics by flash method". The measuring apparatus can be, for example, the TC-7SB RT (trade name) manufactured by Advance Technology Co., Ltd. The measuring temperature can be 20℃ ± 1℃.

[0034] The flexural strength of the aluminum nitride sintered body 100 can be 430 MPa or higher, 450 MPa or higher, 460 MPa or higher, or 470 MPa or higher. The aluminum nitride sintered body 100 with high flexural strength has high electrical insulation properties, making it suitable for use as an insulating substrate for power modules, etc. The flexural strength of the aluminum nitride sintered body 100 can be, for example, 800 MPa or less, 700 MPa or less, or 600 MPa or less. An example of the flexural strength of the aluminum nitride sintered body 100 is 430 MPa to 800 MPa.

[0035] The flexural strength of the aluminum nitride sintered body 100 can be adjusted, for example, by changing the atmosphere in the degreasing process or the temperature profile in the heating process during the manufacture of the aluminum nitride sintered body 100. The flexural strength can be measured using an SDT-503NB-50R1 (trade name) manufactured by Imada Manufacturing Co., Ltd. The measurement temperature can be 20℃±1℃.

[0036] From the perspective of maximizing volume resistivity, the apparent density of aluminum nitride sintered body 100 can be 3.1 g / cm³. 3 The above can also be 3.2 g / cm³. 3 The above applies. Apparent density can be adjusted by changing the proportion of sintering aids used as raw materials, molding conditions, or the temperature profile during the heating process. The upper limit of apparent density can be, for example, 3.4 g / cm³. 3 .

[0037] The aluminum nitride sintered body 100 has sufficiently high electrical insulation properties, making it suitable for use as an insulating substrate. The insulating substrate made of the aluminum nitride sintered body 100 exhibits excellent insulation reliability, making it suitable as a component in semiconductor devices such as power modules.

[0038] Figure 2 This is a perspective view showing an example of a circuit board. The circuit board 300 includes an insulating substrate 150 made of aluminum nitride sintered body 100, a metal circuit 20 bonded to one side of the insulating substrate 150, and a metal plate 110 bonded to the other side of the insulating substrate 150. The metal circuit 20 is disposed on one main surface 150A of the insulating substrate 150, and the metal plate 110 is disposed on the other main surface of the aluminum nitride sintered body 100. The metal circuit 20 can be made of aluminum or copper. The metal circuit 20 is electrically connected to other electronic components to form a circuit. The metal plate 110 can be an aluminum plate or a copper plate. When the circuit board 300 is used in a power module, the metal plate 110 can also function as a heat dissipation material.

[0039] The circuit board 300 includes an insulating substrate 150 made of an aluminum nitride sintered body 100 having sufficiently high electrical insulation properties. The insulating substrate 150 has excellent insulation reliability, therefore the circuit board 300 also has excellent reliability. Therefore, the circuit board 300 is suitable for use as a component in semiconductor devices such as power modules. The aluminum nitride sintered body 100 can be obtained, for example, by the aluminum nitride sintered body manufacturing method described below.

[0040] One embodiment of a method for manufacturing an aluminum nitride sintered body includes: a molding step, wherein a molding raw material comprising aluminum nitride powder, a sintering aid and a binder is molded to obtain a sintered body; a degreasing step, wherein the sintered body is heated in a nitrogen atmosphere or a reduced pressure atmosphere at 500-600°C; a heating step, wherein the degreased sintered body is sintered in a nitrogen atmosphere at 1500-1700°C (first temperature range TR1) for 7 hours or more, and then sintered in a nitrogen atmosphere at 1750-1880°C (second temperature range TR2) for 3-5 hours; and a cooling step, wherein heating is stopped and the aluminum nitride sintered body is cooled.

[0041] The forming raw materials can be prepared by combining aluminum nitride powder, sintering aids, binders, and additives. Aluminum nitride powder can be manufactured by the direct nitriding method. The direct nitriding method refers to the process of synthesizing aluminum nitride by heating aluminum in a nitrogen atmosphere. Compared with the reduction nitriding method using alumina, the direct nitriding method can reduce the oxygen content in aluminum nitride powder. Therefore, by using aluminum nitride powder manufactured by the direct nitriding method, sintered aluminum nitride bodies with sufficiently reduced oxygen content can be obtained.

[0042] The oxygen content of aluminum nitride powder can be 0.3~1.2% by mass, 0.5~1.0% by mass, or less than 0.6~0.9% by mass. The oxygen content can be measured using a commercially available oxygen-nitrogen analyzer. The oxygen content of aluminum nitride powder can be adjusted by changing the purity of the aluminum used in manufacturing the powder or the oxygen concentration in the firing atmosphere. By using aluminum nitride powder with such an oxygen content, the sintered aluminum nitride body can be sufficiently densified, and residual carbon can be significantly reduced.

[0043] In the cumulative distribution of the volume-based particle size distribution of aluminum nitride powder determined by laser diffraction / scattering, when the particle sizes at which the cumulative value from the smallest particle size reaches 10%, 50%, and 90% of the total are set as d10, d50, and d90, respectively, the following numerical ranges can be satisfied: d10 can be 0.1~0.6 μm or 0.3~0.5 μm; d50 can be 1.3~5.0 μm, 1.5~4.0 μm, or 2.0~3.5 μm; d90 can be 3.0~10 μm, 4.0~8.0 μm, or 4.5~7.0 μm. By using aluminum nitride powder with such a particle size distribution, aluminum nitride sintered bodies with sufficiently high volume resistivity can be obtained.

[0044] The specific surface area of ​​aluminum nitride powder can range from 1.2 to 2.5 m². 2 / g, 1.4~2.3m 2 / g or 1.5~2.2m 2 / g. The specific surface area of ​​aluminum nitride powder is a value determined by the BET single-point method. By using aluminum nitride powder with such a specific surface area, it is possible to obtain fully densified aluminum nitride sintered bodies with a highly uniform microstructure.

[0045] The sintering aid may contain yttrium oxide and alumina. The sintering aid may be in granular form. The mass ratio of alumina to yttrium oxide (alumina content / yttrium oxide content) may, for example, be 0.1 or more and less than 0.5, or 0.1 to 0.25. This suppresses the agglomeration of oxides in the aluminum nitride sintered body. The proportion of yttrium oxide and alumina can be adjusted within the above range, thereby adjusting the composition of oxides in the aluminum nitride sintered body. Alumina and yttrium oxide form a liquid phase of composite oxides during sintering, promoting sintering. This allows for sufficient densification of the aluminum nitride sintered body.

[0046] The content of the aforementioned sintering aid in the forming raw material can be, for example, 1 to 5 parts by mass relative to 100 parts by mass of aluminum nitride powder. By keeping the content of the sintering aid within the above range, the volume resistivity of the aluminum nitride sintered body can be further improved. The content of the aforementioned sintering aid can be determined by converting the composition of the sintering aid into oxides.

[0047] The alumina content in the molding raw material can be, for example, 0.1 to 2.0 parts by mass or 0.3 to 1.0 parts by mass relative to 100 parts by mass of aluminum nitride. This allows for sufficient densification of the aluminum nitride sintered body and increases the relative content of aluminum nitride. Consequently, the volume resistivity of the aluminum nitride sintered body can be significantly improved.

[0048] Examples of adhesives include methylcellulose-based adhesives with plasticity or surface-active effects, and acrylate-based adhesives with excellent thermal decomposition properties. Examples of additives include plasticizers, dispersion media, and release agents. Examples of plasticizers include glycerin. Examples of dispersion media include deionized water and ethanol.

[0049] Molding raw materials can be prepared by combining and mixing aluminum nitride, sintering aids, binders, and additives as needed. The molding raw materials can be shaped into sheets, for example, using known methods such as doctor blade molding or extrusion molding. The resulting molded body can have the shape of... Figure 1 The aluminum nitride sintered body is the same as 100.

[0050] From the perspective of maximizing the usability of the electronic component, the volume of the molded body can be 1000 mm². 3 Above, 1500mm 3 Above, or 2000m 3That's all. From the perspective of fully promoting carbon removal during the degreasing and heating processes, the volume of the molded body can be 9000 mm². 3 Below, 5000mm 3 Below, or 3000mm 3 The volume of the molded body can be, for example, 1000~9000 mm². 3 .

[0051] The degreasing process involves heating the molded body in an inert gas atmosphere or a reduced pressure atmosphere at 500~600℃. By heating the molded body in an inert gas atmosphere or a reduced pressure atmosphere, the oxidation of aluminum nitride contained in the molded body can be suppressed. As a result, an aluminum nitride sintered body with sufficiently high volume resistivity can be obtained.

[0052] The "inert gas atmosphere" in the degreasing process of this disclosure refers to an atmosphere containing an inert gas as the main component, and the inert gas content can be 95% by volume or more, 98% by volume or more, or 99% by volume or more. Examples of inert gases include nitrogen, argon, and carbon dioxide. The oxygen content in the "inert gas atmosphere" can be 5% by volume or less, 3% by volume or less, 1% by volume or less, or 0.5% by volume or less. The "reduced pressure atmosphere" in the degreasing process is an atmosphere with an absolute pressure of 5 kPa or less, and can be a vacuum atmosphere. The absolute pressure can be 1 kPa or less or 0.5 kPa or less.

[0053] In the degreasing process, the molded body is heated in an atmosphere of 500-600°C for 5-20 hours or 6-10 hours. If the degreasing process is carried out in an inert gas atmosphere or a reduced pressure atmosphere, the removal of carbon from binders, etc., is more difficult compared to the case when it is carried out in air. Therefore, sufficient carbon removal is required in the subsequent heating process.

[0054] In the heating process, the degreased molded body is heated in a nitrogen atmosphere. The "nitrogen atmosphere" in this disclosure refers to an atmosphere containing nitrogen as the main component, with a nitrogen content of 95% by volume or more, 98% by volume or more, or 99% by volume or more. The average heating rate from the initial heating temperature (e.g., 20°C) to reaching the first temperature range TR1 is 5°C / min to 30°C / min or 10°C / min to 20°C / min. The first temperature range TR1 is 1500~1700°C. Heating within this temperature range sufficiently reduces the carbon content in the molded body. The lower limit of the first temperature range TR1 is 1550°C. This further reduces the carbon content in the molded body, resulting in an aluminum nitride sintered body with an excellent appearance. The upper limit of the first temperature range TR1 is 1680°C. This suppresses over-sintering of the aluminum nitride sintered body.

[0055] The heating time in the first temperature range TR1 can be 7 hours or more, 8 hours or more, 9 hours or more, or 10 hours or more. This allows for a significant reduction in the carbon content of the molded body. The heating time in the first temperature range TR1 can be less than 20 hours, less than 18 hours, or less than 15 hours. This improves the production efficiency of aluminum nitride sintered bodies. An example of the heating time in the first temperature range TR1 is 7 to 20 hours.

[0056] The upper limit of the first temperature range TR1 can be 1650℃ or 1630℃. This significantly improves the thermal conductivity of the aluminum nitride sintered body. The lower limit of the first temperature range TR1 can be 1580℃. This further reduces the residual carbon in the aluminum nitride sintered body, resulting in an aluminum nitride sintered body with a superior appearance.

[0057] The second temperature range TR2 is 1750~1880℃. Heating within this temperature range can suppress over-sintering and ensure sufficient densification of the aluminum nitride sintered body. Since the second temperature range TR2 is higher than the first temperature range TR1 (first temperature range TR1 < second temperature range TR2), after heating for a specified time in the first temperature range TR1, the temperature inside the furnace is increased towards the second temperature range TR2. This heating can also be carried out under a nitrogen atmosphere. The time required to reach the second temperature range TR2 from the first temperature range TR1 can be 4 hours or more, 5 hours or more, or 5.5 hours or more. This sufficiently reduces residual carbon in the aluminum nitride sintered body and facilitates densification and grain growth. The time required to reach the second temperature range TR2 from the first temperature range TR1 can be less than 20 hours or less than 15 hours. This improves the production efficiency of the aluminum nitride sintered body. An example of the time required to reach the second temperature range TR2 from the first temperature range TR1 is 4 hours to 20 hours.

[0058] The heating time in the second temperature range TR2 is 3 hours or more. This effectively promotes the densification of the aluminum nitride sintered body and increases its volume resistivity. From the same perspective, the heating time in the second temperature range TR2 can be 3.5 hours or more. Alternatively, the heating time in the second temperature range TR2 can be 5 hours or less. This effectively suppresses over-sintering of the aluminum nitride sintered body and significantly improves its volume resistivity and flexural strength.

[0059] The upper limit of the second temperature range TR2 can be 1850℃, 1830℃, or 1820℃. This effectively suppresses over-sintering of the aluminum nitride sintered body, further improving volume resistivity and flexural strength. The lower limit of the second temperature range TR2 can be 1780℃ or 1800℃. This allows for sufficient densification and grain growth of the aluminum nitride sintered body.

[0060] In the heating process, the heating time in a nitrogen atmosphere within the third temperature range TR3 (1500~1880℃) can be 11 hours or more, 15 hours or more, or 20 hours or more. This significantly reduces residual carbon in the aluminum nitride sintered body, improving its appearance. Furthermore, it allows for sufficient densification and grain growth, resulting in an aluminum nitride sintered body with sufficiently high volume resistivity and flexural strength. In the heating process, the heating time in a nitrogen atmosphere within the third temperature range TR3 can be less than 30 hours or less, or less than 25 hours. This improves the productivity of the aluminum nitride sintered body.

[0061] From the viewpoint of sufficiently reducing residual carbon in the aluminum nitride sintered body, the lower limit of the third temperature range TR3 can be 1500℃ or 1580℃. From the viewpoint of suppressing over-sintering, the upper limit of the third temperature range TR3 can be 1850℃, 1830℃ or 1820℃.

[0062] After the heating process is completed, a cooling process can be performed to reduce the nitrogen atmosphere in the heating furnace from the second temperature range TR2. There are no particular limitations on the cooling rate; for example, it can be 5.0~50.0℃ / min. The cooling process can also be performed under a nitrogen atmosphere. This results in an aluminum nitride sintered body with sufficiently high electrical insulation properties. The aluminum nitride sintered body can be processed into the desired shape as needed. For example, the aluminum nitride sintered body can be processed into… Figure 1 The sheet-like shape is shown. Alternatively, sintered aluminum nitride can be used as an insulating substrate, on which metal circuits and metal plates can be mounted. Figure 2 The circuit board shown. For example, the main surface of a sheet-like aluminum nitride sintered body (aluminum nitride plate) can also be bonded to the main surface of a metal plate such as a copper plate or an aluminum plate to form a laminate.

[0063] Figure 3 This is a perspective view illustrating an example of a laminate. The laminate 200 includes a pair of metal plates 110 arranged opposite each other and an insulating substrate formed of an aluminum nitride sintered body 100 between the pair of metal plates 110. Examples of metal plates 110 include copper plates and aluminum plates. The aluminum nitride sintered body 100 and the metal plates 110 may have the same shape and different dimensions. The metal plates 110 and the insulating substrate 150 may also be joined, for example, by soldering. Alternatively, one of the pair of metal plates 110 may be used as a heat dissipation material, and the other may be processed into a circuit pattern to obtain... Figure 2 The circuit board 300 shown. The circuit pattern can also be formed by etching the metal plate 110 with a photoresist. In this way, a circuit board that can effectively suppress leakage current, etc., can be formed, or a heat sink can be formed.

[0064] The above description illustrates several embodiments of this disclosure, but this disclosure is not limited to any of the above embodiments. For example, the shape and structure of the circuit board and the laminate are not limited to... Figure 2 and Figure 3 For example, circuit patterns can also be formed on the two main surfaces of the insulating substrate 150, which is made of aluminum nitride sintered body 100. Alternatively, the metal circuit 20 can be formed by sputtering metal powder and performing heat treatment, instead of etching the metal plate 110.

[0065] Example The present disclosure is described in more detail with reference to the embodiments and comparative examples, but the present disclosure is not limited to the embodiments described below.

[0066] (Example 1) [Manufacturing and Evaluation of Aluminum Nitride Powder] Aluminum nitride powder was obtained by nitriding commercially available aluminum powder (average particle size: 20 μm–30 μm) using a direct nitriding method. The nitriding of the aluminum powder was carried out by heating to 1600–1700 °C under a nitrogen atmosphere. The volumetric particle size distribution of the obtained aluminum nitride powder was determined by laser diffraction / scattering. In the cumulative particle size distribution, the particle sizes at which the cumulative value from the smallest particle size reached 10%, 50%, and 90% of the total particle size were defined as d10, d50, and d90, respectively. The values ​​of d10, d50, and d90 are shown in Table 1.

[0067] The specific surface area of ​​aluminum nitride powder was determined by the BET single-point method. The results are shown in Table 1. The oxygen content of the aluminum nitride powder was determined using an oxygen and nitrogen analyzer (trade name: EMGA-920) manufactured by Horiba Corporation, and the result was 0.72% by mass.

[0068] [Manufacturing of aluminum nitride sintered bodies] 100 parts by weight of aluminum nitride powder obtained through the above steps were mixed with 3.87 parts by weight of yttrium oxide (Y₂O₃) powder (as a sintering aid) and 0.732 parts by weight of α-alumina (Al₂O₃) powder using a ball mill to obtain a mixed powder. 6 parts by weight of cellulose ether binder (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: Metalose), 5 parts by weight of glycerol (manufactured by Kao Corporation, trade name: EXCEPARL), and 10 parts by weight of deionized water were added to the mixed powder and mixed for 1 minute using a Henschel mixer to obtain a molding material. This molding material was shaped using a screw extruder to produce a sheet-like first molded body (thickness: 1.0 mm). After drying the first molded body at 100°C for 1 hour, it was cut to obtain a second molded body with dimensions of 90.0 mm × 90.0 mm × 1.0 mm.

[0069] The second molded body was degreased (degreasing process) by heating it in a nitrogen atmosphere at 550°C for 8 hours using an electric furnace. The resulting degreased body was removed from the furnace and cooled to room temperature. Then, the degreased body was placed in a heating furnace and heated in a nitrogen atmosphere from room temperature (T0: approximately 20°C) to temperature T1 as shown in Table 2 at an average rate of 15°C / min. The holding time at temperature T1 is shown in Table 2. Then, the temperature was increased to T2. The time required for the temperature increase from T1 to T2 is shown in the "Time Required for Temperature Increase" section of Table 2. The holding time at T2 is shown in Table 2.

[0070] Based on the aforementioned temperature rise curves, the heating times for each temperature range in the heating process—the first temperature range TR1 (1500℃~1700℃), the second temperature range TR2 (1750℃~T2), and the third temperature range TR3 (1500℃~T2)—were calculated. The results are shown in Table 3. The heating times in the first temperature range TR1 and the third temperature range TR3 both include the holding time at temperature T1. The heating times in the second temperature range TR2 and the third temperature range TR3 both include the holding time at temperature T2.

[0071] After holding at temperature T2 as shown in Table 2 for the specified time, the temperature was cooled from Tmax to 1600°C at an average cooling rate of 10.0°C / min, and then cooled from 1600°C to room temperature at an average cooling rate of 5.0°C / min (cooling process). Thus, the aluminum nitride sintered body of Example 1 was obtained.

[0072] Evaluation of aluminum nitride sintered bodies <Insulation Evaluation of Aluminum Nitride Sintered Bodies> The volume resistivity of the aluminum nitride sintered body was measured. The measurement was performed using a super-insulator (trade name: SM-8220) manufactured by Hioki Electric Co., Ltd., according to JIS C 2139:2008 "Solid electrical insulating materials - Methods for determination of volume resistivity and surface resistivity". Specifically, a sample (substrate) was prepared by depositing copper with a diameter of 10 mm on both main surfaces of the aluminum nitride sintered body. The substrate was held with the measuring electrodes, and a voltage of 1000 V was applied at 20°C, allowing a direct current to flow through the substrate. This state was maintained for 20 seconds. The insulation resistance value was measured after 20 seconds, and the volume resistivity was calculated using the following formula (1). The results are shown in Table 4.

[0073] Volume resistivity [Ω·cm] = Insulation resistance [Ω] × Copper vapor deposition area [cm] 2 ] / Thickness of substrate [cm] (1) <Evaluation of Thermal Conductivity of Aluminum Nitride Sintered Bodies> Thermal conductivity was measured using the laser flash method according to JIS R1611:2010 "Determination of thermal diffusivity, specific heat capacity and thermal conductivity of fine ceramics by flash method". The measuring apparatus used was an Advance Riko Co., Ltd. The measurement temperature was 20°C. The results are shown in Table 4.

[0074] Evaluation of the flexural strength of aluminum nitride sintered bodies The three-point flexural strength of aluminum nitride sintered bodies at 20°C was measured using SDT-503NB-50R1 (trade name) manufactured by Imada Manufacturing Co., Ltd. The results are shown in Table 4.

[0075] <Determination of oxygen content in aluminum nitride sintered bodies> The oxygen content in aluminum nitride sintered bodies was determined using an oxygen and nitrogen analyzer (trade name: EMGA-920) manufactured by Horiba Corporation, using argon gas. The results are shown in Table 4.

[0076] (Examples 2 to 7) At least one of the group consisting of T1, the holding time at T1, the time required for heating, and T2 was modified as shown in Table 2. Otherwise, aluminum nitride sintered bodies of Examples 2-7 were manufactured in the same manner as in Example 1 and evaluated. The heating times in the first temperature range TR1, the second temperature range TR2, and the third temperature range TR3 for each example are shown in Table 3. The evaluation results of the aluminum nitride sintered bodies of each example are shown in Table 4.

[0077] (Comparative Example 1) Commercially available aluminum nitride powder was prepared by reduction nitriding. d10, d50, d90, and specific surface area were determined in the same manner as in Example 1. The results are shown in Table 1. Using this aluminum nitride powder, a degreasing process was performed in an air atmosphere. The holding time at T1, the time required for heating, and T2 are shown in Table 2. Otherwise, an aluminum nitride sintered body was manufactured in the same manner as in Example 1 and evaluated. The heating times in the first temperature range TR1, the second temperature range TR2, and the third temperature range TR3 of Comparative Example 1, as well as the evaluation results of the aluminum nitride sintered body, are shown in Tables 3 and 4, respectively.

[0078] (Comparative Example 2) Except for using the aluminum nitride powder manufactured in Example 1, aluminum nitride sintered bodies were prepared in the same manner as in Comparative Example 1, and evaluation was conducted. The heating times in the first temperature range TR1, the second temperature range TR2, and the third temperature range TR3 of Comparative Example 2, as well as the evaluation results of the aluminum nitride sintered bodies, are shown in Tables 3 and 4, respectively.

[0079] (Comparative Examples 3 to 5) At least one of the group consisting of T1, the holding time at T1, the time required for heating, and T2 was modified as shown in Table 2. Otherwise, aluminum nitride sintered bodies of Comparative Examples 3-5 were manufactured in the same manner as in Example 1 and evaluated. The heating times in the first temperature range TR1, the second temperature range TR2, and the third temperature range TR3 for each comparative example are shown in Table 3. The evaluation results of the aluminum nitride sintered bodies of each comparative example are shown in Table 4.

[0080] [Table 1]

[0081] [Table 2]

[0082] [Table 3]

[0083] [Table 4]

[0084] Compared to Examples 1-7 and Comparative Examples 3-5, where the degreasing process was carried out in a nitrogen environment, Comparative Examples 1 and 2, where the degreasing process was performed in air, showed a higher oxygen content. It is believed that in Comparative Examples 1 and 2, aluminum nitride oxidation occurred during the degreasing process. The main reason for the higher oxygen content of the aluminum nitride sintered body in Comparative Example 1 compared to Comparative Example 2 is that the aluminum nitride powder prepared by the reduction nitriding method has a higher oxygen content than the aluminum nitride powder prepared by the direct nitriding method.

[0085] Compared to Examples 1 to 7, Comparative Examples 3 to 5, which had heating times exceeding 5 hours within the second temperature range TR2, exhibited lower volume resistivity and flexural strength. This was primarily attributed to excessive sintering. Conversely, the aluminum nitride sintered bodies of Examples 1 to 7 possessed sufficiently high volume resistivity and flexural strength.

[0086] The appearance of the aluminum nitride sintered bodies from Examples 1 to 7 was visually confirmed, and Example 2 showed the best appearance. This is believed to be due to the longest heating time in the third temperature range TR3, which resulted in sufficient carbon reduction.

[0087] Industrial availability This disclosure provides an aluminum nitride sintered body with sufficiently high electrical insulation and a method for manufacturing the same. Additionally, it provides a circuit board with excellent reliability.

[0088] Symbol Explanation 20…metal circuit, 100…aluminum nitride sintered body, 110…metal plate, 150…insulating substrate, 200…laminated body, 300…circuit substrate.

Claims

1. An aluminum nitride sintered body having a volume resistivity of 5.0 × 10⁻⁶. 12 Ω·cm or higher.

2. The aluminum nitride sintered body according to claim 1, wherein, The oxygen content is less than 1.80% by mass.

3. The aluminum nitride sintered body according to claim 1 or 2 has a flexural strength of 430 MPa or higher.

4. A method for manufacturing an aluminum nitride sintered body, comprising: The molding process involves molding a molding material containing aluminum nitride powder, a sintering aid, and a binder to obtain a molded body; the degreasing process involves heating the molded body in an inert gas atmosphere or a reduced pressure atmosphere at 500-600°C; and In the heating process, the degreased molded body is fired in a nitrogen atmosphere at 1500~1700℃ for more than 7 hours, and then fired in a nitrogen atmosphere at 1750~1880℃ for 3~5 hours.

5. The method for manufacturing an aluminum nitride sintered body according to claim 4, wherein, In the heating process, the molded body is fired in a nitrogen atmosphere at 1500~1880°C for 11~30 hours.

6. The method for manufacturing an aluminum nitride sintered body according to claim 4 or 5, wherein, The volume resistivity of the aluminum nitride sintered body is 5.0 × 10⁻⁶. 12 Ω·cm or higher.

7. The method for manufacturing an aluminum nitride sintered body according to claim 4 or 5, wherein, The volume of the molded body is 1000~9000 mm². 3 .

8. A circuit board comprising: an insulating substrate formed of an aluminum nitride sintered body as described in claim 1 or 2; and a metal circuit bonded to said insulating substrate.

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