Aluminum nitride sintered body, and method for manufacturing an aluminum nitride sintered body

Abstract

This aluminum nitride sintered body contains aluminum nitride as a main component and an oxide having yttrium and aluminum as constituent elements. The oxide contains 3Y2O3 · 5Al2O3, Y2O3 · Al2O3, and 2Y2O3 · Al2O3, and, in relation to the total amount of 3Y2O3 · 5Al2O3, Y2O3 · Al2O3, and 2Y2O3 · Al2O3, the ratio of 2Y2O3 · Al2O3 is 2.0% by mass or less.

Description

[Technical Field]

[0001] This disclosure relates to an aluminum nitride sintered body and a method for manufacturing an aluminum nitride sintered body. [Background technology]

[0002] In recent years, power modules for high-power control have been used in industrial equipment such as motors, and in products such as electric vehicles. Such power modules utilize circuit boards equipped with ceramic plates to efficiently dissipate heat generated from semiconductor elements and to suppress leakage current. The ceramic sintered bodies used in such ceramic plates are usually manufactured by first shaping ceramic raw material powder into a predetermined form to create a ceramic molded body, and then sintering the ceramic molded body.

[0003] Ceramic sintered bodies are known to be composed of nitrides, carbides, borides, or silicides. Among these, aluminum nitride sintered bodies have excellent thermal conductivity and electrical insulation properties. For this reason, they are used as heat sink components for electronic components such as power modules. To improve their suitability for these applications, Patent Document 1 proposes a technique to increase the thermal conductivity and mechanical strength of aluminum nitride sintered bodies by using a nitride selected from the group of Zr and Ti in terms of oxide equivalent, in the form of 3 to 20 parts by mass, as a sintering aid. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-184316 [Overview of the project] [Problems that the invention aims to solve]

[0005] Electronic components such as power modules are becoming increasingly high-performance, and consequently, the performance requirements for various products used in these electronic components are expected to rise even further. On the other hand, aluminum nitride sintered bodies exhibit greater variation in electrical insulation properties depending on their constituent components compared to, for example, silicon nitride sintered bodies. Therefore, a technology is needed that can stably improve the electrical insulation properties of aluminum nitride sintered bodies while reducing variations in thermal conductivity. Accordingly, this disclosure provides an aluminum nitride sintered body that can achieve sufficiently high electrical insulation properties while reducing variations in thermal conductivity. Furthermore, it provides a method for manufacturing such an aluminum nitride sintered body. [Means for solving the problem]

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

[0007] [1] The main component is aluminum nitride, and the oxide has yttrium and aluminum as constituent elements, The aforementioned oxides include 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3. An aluminum nitride sintered body in which the ratio of 2Y2O3·Al2O3 to the total amount of 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 is 2.0 mass% or less.

[0008] The above aluminum nitride sintered body is sufficiently densified because it contains oxides having yttrium and aluminum as constituent elements. The above oxides include 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3, and the ratio of 2Y2O3·Al2O3 to the total amount of 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 is 2.0 mass% or less, thus it has excellent electrical insulation properties and can reduce variations in thermal conductivity.

[0009] The aluminum nitride sintered body described in [1] above may be any one of the following [2] to [5].

[0010] [2] The aluminum nitride sintered body according to [1], wherein the content of Y2O3·Al2O3 relative to the total amount of aluminum nitride, 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 is 3.0% by mass or less. [3] The aluminum nitride sintered body according to [1] or [2], wherein the content of 2Y2O3·Al2O3 relative to the total amount of aluminum nitride, 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 is 0.01 to 0.1 mass%. [4] Volume resistivity at 120°C is 4.0 × 10⁻⁶ 11 An aluminum nitride sintered body having a length of Ω·cm or greater, as described in any one of [1] to [3]. [5] An aluminum nitride sintered body according to any one of [1] to [4], having a bending strength of 450 MPa or more.

[0011] The aluminum nitride sintered body described in [2] above has a content of Y2O3·Al2O3 of 3.0% by mass or less relative to the total amount of aluminum nitride, 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3. An aluminum nitride sintered body having such a composition has even better electrical insulation properties.

[0012] The aluminum nitride sintered body described in [3] above has a content of 2Y2O3·Al2O3 relative to the total amount of aluminum nitride, 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3, which is 0.01 to 0.1 mass%. An aluminum nitride sintered body having such a composition has even better electrical insulation properties.

[0013] The aluminum nitride sintered body described in [4] above has a volume resistivity of 4.0 × 10 at 120°C. 11 The electrical insulation resistance is Ω·cm or greater. Aluminum nitride sintered bodies with such electrical insulation properties have stabilized thermal resistivity and can be used more suitably as electronic components such as power modules.

[0014] The aluminum nitride sintered body described in [5] above has a flexural strength of 450 MPa or more. An aluminum nitride sintered body having such flexural strength achieves both sufficiently high mechanical strength and electrical insulation, making it even more suitable for use as an electronic component such as a power module.

[0015] One aspect of this disclosure provides the following method for manufacturing an aluminum nitride sintered body.

[0016] [6] A first heating step in which a molded body containing aluminum nitride, yttrium oxide, and aluminum oxide is heated from a temperature T0 to a soaking temperature T1 at a first heating rate V1, After the first heating step, a first soaking step is performed in which the temperature is maintained at the soaking temperature T1, Following the first soaking step, a second heating step is performed in which the temperature is raised from the soaking temperature T1 to the second soaking temperature T2 at a second heating rate V2, After the aforementioned second heating step, a second soaking step is performed in which the temperature is maintained at the soaking temperature T2, Following the second soaking step, a third heating step is performed in which the temperature is raised from the soaking temperature T2 to the maximum temperature T3 at a third heating rate V3, Following the third heating step, a third soaking step is performed to maintain the temperature at the highest attainable temperature T3, The process includes a cooling step, which follows the third soaking step, in which the temperature is lowered to at least 1600°C at a cooling rate of 10.0°C / min or less. A method for manufacturing an aluminum nitride sintered body, wherein the temperature T0 is the temperature at which heating begins, the soaking temperature T1 is 1350 to 1550°C, the second soaking temperature T2 is 1600°C or more and less than 1750°C, the maximum temperature reached T3 is 1750 to 1850°C, and the first heating rate V1, the second heating rate V2, and the third heating rate V3 satisfy the following formula (1). V1>V2>V3 (1)

[0017] The production method of the above [6] includes a first temperature raising step, a first soaking step, a second temperature raising step, a second soaking step, a third temperature raising step, a third soaking step, and a temperature lowering step. Furthermore, the first temperature raising rate V1, the second temperature raising rate V2, and the third temperature raising rate V3 satisfy V1>V2>V3, and the temperature lowering rate up to 1600°C is 10.0°C / min or less. By being a production method including such a heating step, the ratio of 2Y₂O₃·Al₂O₃ to the total amount of 3Y₂O₃·5Al₂O₃, Y₂O₃·Al₂O₃, and 2Y₂O₃·Al₂O₃ is a predetermined value below of aluminum nitride sintered body can be produced.

[0018] The method for producing the aluminum nitride sintered body of the above [6] may be the following [7].

[0019] [7] The method for producing an aluminum nitride sintered body according to [6], wherein the temperature lowering rate is 7.0°C / min or less.

[0020] In the method for producing an aluminum nitride sintered body according to the above [7], the temperature lowering rate is 7.0°C / min or less. By having such a temperature lowering rate, the electrical insulation of the obtained aluminum nitride sintered body can be further improved, and variation in thermal conductivity can be reduced. Effects of the Invention

[0021] The present disclosure provides an aluminum nitride sintered body capable of sufficiently increasing electrical insulation and reducing variation in thermal conductivity. The present disclosure also provides a method for producing such an aluminum nitride sintered body. Brief Description of the Drawings

[0022] [Figure 1] FIG. 1 is a perspective view showing an example of an aluminum nitride sintered body. [Figure 2] FIG. 2 is a perspective view showing an example of a laminate. [Figure 3] FIG. 3 is a perspective view showing an example of a circuit board. Mode for Carrying Out the Invention

[0023] Embodiments of this disclosure are described below. However, the following embodiments are illustrative for illustrating this disclosure and are not intended to limit this disclosure to the following. The upper or lower limits of numerical ranges explicitly stated herein may be replaced with any of the values ​​shown in the examples. Furthermore, the upper and lower limits described individually may be combined as desired. Unless otherwise specified, the materials or components exemplified herein may be used individually or in combination of two or more. In the description, the same reference numeral is used for elements with the same function, and redundant descriptions are omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right used in the description are based on the positional relationships shown in the drawings. In these embodiments, numerical ranges exemplified in the form "a~b" are numerical ranges that include a and b, with a as the lower limit and b as the upper limit. Numeric ranges in which the upper or lower limit is replaced with the values ​​of any of the embodiments are also included in this disclosure.

[0024] The aluminum nitride sintered body of this embodiment contains aluminum nitride as the main component and an oxide (composite oxide) dispersed in the main component, having yttrium and aluminum as constituent elements. Because the aluminum nitride sintered body contains particulate oxide having yttrium and aluminum as constituent elements, it is sufficiently densified.

[0025] Figure 1 is a perspective view showing an example of an aluminum nitride sintered body. The external shape of the aluminum nitride sintered body 100 is not particularly limited and may be, for example, plate-shaped, with sides of 50.0 to 70.0 mm. The thickness of the aluminum nitride sintered body may be 0.50 to 0.80 mm or 0.60 to 0.70 mm. Such an external shape allows for smooth joining with other components.

[0026] The content of the main component (aluminum nitride) in the aluminum nitride sintered body 100 may be 90% by mass or more, 93% by mass or more, or 95% by mass or more, from the viewpoint of increasing thermal conductivity. The content of aluminum nitride in the aluminum nitride sintered body 100 may be 99.5% by mass or less, 99% by mass or less, or 98% by mass or less, from the viewpoint of sufficiently increasing density. The content of each component in the aluminum nitride sintered body 100 can be determined, for example, by X-ray analysis. For X-ray analysis, for example, Bruker Japan Ltd.'s D8 ADVANCE (product name) can be used.

[0027] The total oxide content in the aluminum nitride sintered body 100 may be 0.5% by mass or more, 1.0% by mass or more, or 2.0% by mass or more, from the viewpoint of ensuring a sufficiently high density. The total oxide content in the aluminum nitride sintered body 100 may be 8.0% by mass or less, 7.0% by mass or less, or 5.0% by mass or less. Such an aluminum nitride sintered body can achieve both excellent electrical insulation and thermal conductivity. The total oxide content may also be determined by removing components other than oxides from the aluminum nitride sintered body 100 by hydrolysis.

[0028] The oxide contains 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3. 2Y2O3·Al2O3 is a type of Y2O3-Al2O3 compound and is also known as YAM. Hereinafter, it may be referred to as "YAM". From the viewpoint of increasing electrical insulation, the ratio of 2Y2O3·Al2O3 to the total amount of 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 is 2.0% by mass or less, may be 1.6% by mass or less, or may be 1.3% by mass or less. It is presumed that the electrical insulation properties of aluminum nitride sintered bodies can be improved by reducing the ratio of 2Y2O3·Al2O3, which has a higher yttrium content per molecule, to below a predetermined value among 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3.

[0029] The content of 2Y2O3·Al2O3 relative to the total amount of aluminum nitride, 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 may be 0.01% by mass or more, 0.03% by mass or more, or 0.05% by mass or more, from the viewpoint of further improving electrical insulation. Also, from the viewpoint of ease of firing, it may be 0.1% by mass or less, 0.08% by mass or less, or 0.07% by mass or less. Examples of YAM content are 0.01-0.1% by mass, 0.03-0.08% by mass, or 0.05-0.07% by mass. It is presumed that by lowering the YAM content in the aluminum nitride sintered body, the amount of yttrium that bonds with insulating aluminum oxide increases, and the overall electrical insulation of the aluminum nitride sintered body is further improved.

[0030] 3Y2O3·5Al2O3 is a type of Y2O3-Al2O3 compound and is also known as YAG. Hereinafter, it may be referred to as "YAG" in this disclosure. The ratio of 3Y2O3·5Al2O3 to the total amount of 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 may be 20% by mass or more, 25% by mass or more, or 30% by mass or more, from the viewpoint of further increasing electrical insulation properties. From the viewpoint of ease of firing, it may be 70% by mass or less, 60% by mass or less, or 55% by mass or less. Examples of the ratio of 3Y2O3·5Al2O3 to the total amount of 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 are 20-70% by mass or 30-55% by mass.

[0031] The content of 3Y2O3·5Al2O3 relative to the total amount of aluminum nitride, 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 may be 1.4% by mass or more, 1.6% by mass or more, or 1.8% by mass or more, from the viewpoint of further improving electrical insulation. Also, from the viewpoint of ease of firing, it may be 5.0% by mass or less, 3.0% by mass or less, or 2.5% by mass or less. Examples of 3Y2O3·5Al2O3 content are 1.4-5.0% by mass, 1.6-5.0% by mass, or 1.8-2.5% by mass.

[0032] Y2O3·Al2O3 is also a type of Y2O3-Al2O3 compound and is a component also known as YAP. Hereinafter, it may be referred to as "YAP" in this disclosure. The ratio of Y2O3·Al2O3 to the total amount of 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 may be 80% by mass or less, 70% by mass or less, or 60% by mass or less, from the viewpoint of further improving electrical insulation properties. Furthermore, from the viewpoint of ease of firing, it may be 20% by mass or more, 30% by mass or more, or 40% by mass or more. Examples of the ratio of Y2O3·Al2O3 are 20-80% by mass, 30-70% by mass, or 40-60% by mass.

[0033] The content of Y2O3·Al2O3 relative to the total amount of aluminum nitride, 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 may be 1.8% by mass or more, or 2.0% by mass or more, from the viewpoint of further improving electrical insulation. Also, from the viewpoint of ease of firing, it may be 3.0% by mass or less, or 2.7% by mass or less. Examples of the content of Y2O3·Al2O3 relative to the total amount of aluminum nitride, 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 are 1.8 to 3.0% by mass, or 2.0 to 2.7% by mass.

[0034] The aluminum nitride sintered body 100 of this embodiment may contain components other than aluminum nitride and particulate oxides having yttrium and aluminum as constituent elements. Examples of such components include oxides such as aluminum oxide and yttrium oxide, nitrides other than aluminum nitride, and silicides.

[0035] The content of oxides other than those containing yttrium and aluminum as constituent elements (primary oxide) (secondary oxide) may be small from the viewpoint of achieving sufficiently high electrical insulation and thermal conductivity. The mass ratio of secondary oxide to primary oxide may be less than 0.1 and may also be less than 0.05.

[0036] The oxygen content in the aluminum nitride sintered body 100 may be 0.3 to 3.0 mass%, or 0.5 to 2.0 mass%. Oxygen may be contained in oxides that are minor components. The oxygen content in the aluminum nitride sintered body can be determined using a commercially available oxygen / nitrogen analyzer.

[0037] The volume resistivity of aluminum nitride sintered body 100 at 120°C is 4.0 × 10⁻⁶. 11 It may be Ω·cm or larger, and 5.0 × 10 11 It may be Ω·cm or larger, and 6.0 × 10 11 It may be greater than Ω·cm. The upper limit of volume resistivity is, for example, 3.0 × 10⁻⁶. 12 Ω·cm is also acceptable.

[0038] The volume resistivity can be measured in accordance with JIS C2139. For example, a Hioki Electric ultra-insulation meter (product name: SM-8220) may be used as the measuring device. The measurement temperature may be 120 ± 1°C.

[0039] The thermal conductivity of the aluminum nitride sintered body 100 may be 100 W / (m·K) or higher, may be 120 W / (m·K) or higher, and may also be 140 W / (m·K) or higher. Such an aluminum nitride sintered body is suitable, for example, as a heat sink material for power modules and the like. However, the application thereof is not limited thereto. The upper limit of the volume resistivity may be, for example, 200 W / (m·K). When the number of measurements is 5 to 10, the standard deviation of the thermal conductivity may be 1.4 W / (m·K) or less, may be 1.3 W / (m·K) or less, and may also be 1.2 W / (m·K) or less. Such a standard deviation of thermal conductivity can suppress variation in thermal conductivity, thereby obtaining an aluminum nitride sintered body with high reliability.

[0040] The thermal conductivity can be measured by the laser flash method in accordance with JIS R1611. For the measurement device, for example, TC-7SB RT (trade name) manufactured by Advance Riko Co., Ltd. is used. The measurement temperature may be room temperature (about 25°C).

[0041] From the viewpoint of sufficiently increasing thermal conductivity, the apparent density of the aluminum nitride sintered body 100 is 3.1 g / cm 3 or higher, and may be 3.2 g / cm 3 or higher. The apparent density can be adjusted by changing the blending ratio of the sintering aid used as a raw material, molding conditions and firing conditions. The upper limit of the apparent density may be, for example, 3.4 g / cm 3 .

[0042] The flexural strength of the aluminum nitride sintered body 100 may be 450 MPa or higher, may be 460 MPa or higher, and may also be 470 MPa or higher. The flexural strength is measured by the method described in the Examples. The aluminum nitride sintered body having such high flexural strength has high electrical insulation properties, and can be suitably used as an insulating substrate for power modules. The upper limit of the flexural strength may be, for example, 800 MPa.

[0043] A method for manufacturing an aluminum nitride sintered body according to one embodiment comprises a first heating step, a first soaking step, a second heating step, a second soaking step, a third heating step, a third soaking step, and a cooling step, in which a molded body containing aluminum nitride, yttrium oxide, and aluminum oxide is produced.

[0044] The process may include a step of producing a molded body containing aluminum nitride, yttrium oxide, and aluminum oxide before the first heating step. For example, aluminum nitride, a sintering aid, and additives are used as raw materials for the molded body. 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 acid ester-based binders with excellent thermal decomposition properties. Examples of plasticizers include glycerin. Examples of dispersion media include deionized water and ethanol.

[0045] The aluminum nitride is not particularly limited, and aluminum nitride powder produced by known methods such as direct nitriding, which involves nitriding metallic aluminum under a nitrogen atmosphere, and reductive nitriding, which involves reducing aluminum oxide with carbon, can be used.

[0046] The above-mentioned sintering aid contains yttrium oxide and aluminum oxide. The sintering aid may be in granular form. For example, the mass ratio of aluminum oxide to yttrium oxide (value of aluminum oxide content / yttrium oxide content) may be less than 0.5, or 0.25 or less. This can suppress the aggregation of oxides in the aluminum nitride sintered body. The blending ratio of yttrium oxide and aluminum oxide can be adjusted within the above range, thereby adjusting the oxide composition in the aluminum nitride sintered body. During sintering, aluminum oxide and yttrium oxide form a liquid phase of composite oxide, promoting sintering. This allows the aluminum nitride sintered body to be sufficiently densified.

[0047] The content of the above-mentioned sintering aid may be, for example, 1 to 10.0 parts by mass per 100 parts by mass of aluminum nitride. By setting the content of the sintering aid within the above range, the density of the resulting aluminum nitride sintered body can be improved, and the bending strength can be further enhanced. By setting the content of the sintering aid within the above range, the thermal conductivity of the resulting aluminum nitride sintered body can be improved. The above-mentioned content of the sintering aid is a value calculated in terms of the oxide equivalent amount of the sintering aid.

[0048] Furthermore, the aluminum oxide content may be, for example, 0.1 to 5.0 parts by mass per 100 parts by mass of aluminum nitride. By setting the aluminum oxide content to 0.1 parts by mass or more, the density of the resulting sintered body can be further improved. Also, by setting the aluminum oxide content to 5.0 parts by mass or less, the relative content of aluminum nitride can be increased, and the decrease in the thermal conductivity of the resulting sintered body can be further suppressed.

[0049] Aluminum nitride, sintering aids, and additives added as needed may be blended and mixed and used as a molding raw material. The molding raw material may be formed into a sheet, for example, by a known method such as the doctor blade method. The obtained molded body may be degreased before the first heating step. 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.

[0050] Aluminum nitride sintered bodies can be obtained by firing the molded bodies described above. The firing may be carried out in an inert gas atmosphere. The inert gas may be, for example, nitrogen. The firing may be carried out under atmospheric pressure or under vacuum.

[0051] The first heating step is a step of raising the temperature from temperature T0 to the first soaking temperature T1 at a first heating rate V1. Temperature T0 is the temperature at which heating begins, meaning the temperature before firing, and may be 0 to 50°C or room temperature (25°C). The first heating rate V1 is not particularly limited and may be 5.0°C / min or more, or 10.0°C / min or more. By increasing the first heating rate V1, the firing step can be shortened. The upper limit of the first heating rate V1 may be, for example, 20.0°C / min or 15.0°C / min. The first soaking temperature T1 may be 1350 to 1550°C or 1400 to 1500°C. By setting the first soaking temperature T1 within such a temperature range, metal impurities in the raw material can be efficiently removed, and an aluminum nitride sintered body with reduced impurities can be obtained.

[0052] The first soaking step is a step of holding the material at a first soaking temperature T1. The holding time may be 15 to 60 minutes, or 20 to 40 minutes. By holding the material at the first soaking temperature T1 within this range, metal impurities in the raw material can be sufficiently removed, further improving the purity of the raw material. The first soaking temperature T1 during holding may vary, for example, within a range of ±10°C.

[0053] The second heating step is a step of heating from the first soaking temperature T1 to the second soaking temperature T2 at a second heating rate V2. The second heating rate V2 may be 0.8°C / min or more, 1.5°C / min or more, or 2.0°C / min or more. When the second heating rate V2 is within this range, the proportion of YAM in the resulting Y2O3-Al2O3 compound becomes sufficiently low, and an aluminum nitride sintered body with further improved electrical insulation properties is obtained. The upper limit of the second heating rate V2 may be, for example, 5.0°C / min or 3.0°C / min. The second soaking temperature T2 may be 1600°C or more and less than 1750°C, or it may be 1675 to 1725°C.

[0054] The second soaking step is a process of holding the material at the second soaking temperature T2. The holding time may be 90 to 150 minutes, or 100 to 130 minutes. By holding the material at the second soaking temperature T2 within this range, the sintering aid can be sufficiently dispersed in the aluminum nitride, and the aluminum nitride sintered body can be fired with high uniformity. The second soaking temperature T2 during holding may vary, for example, within a range of ±10°C.

[0055] The third heating step is to raise the temperature from the second soaking temperature T2 to the maximum temperature T3 at a third heating rate V3. The third heating rate V3 may be 0.7°C / min or higher, 0.9°C / min or higher, or 1.2°C / min or higher. When the third heating rate V3 is within this range, the proportion of YAM in the generated Y2O3-Al2O3 compound becomes sufficiently low, resulting in an aluminum nitride sintered body with further improved electrical insulation properties. The upper limit of the third heating rate V3 may be, for example, 2.0°C / min or 1.5°C / min. The maximum temperature T3 is 1750 to 1850°C. By having the maximum temperature T3 within this range, grain growth of aluminum nitride can be promoted and internal air bubbles can be sufficiently removed.

[0056] The third soaking step is a holding step at the maximum temperature T3. The holding time may be 90 to 150 minutes or 100 to 130 minutes. Holding the material at the maximum temperature T3 within this range promotes grain growth of the Y2O3-Al2O3 compound in the aluminum nitride sintered body, resulting in an aluminum nitride sintered body with further improved electrical insulation properties. The maximum temperature T3 during holding may vary, for example, within a range of ±10°C.

[0057] In the manufacturing method of the aluminum nitride sintered body according to this embodiment, the first heating rate V1, the second heating rate V2, and the third heating rate V3 satisfy the following formula (1). As shown in formula (1), by gradually reducing the heating rate until the maximum temperature T3 is reached, sufficient heating can be performed at the second soaking temperature T2 and the maximum temperature T3, and the firing of the aluminum nitride sintered body can be promoted. As a result, an aluminum nitride sintered body with high electrical insulation properties can be obtained. V1>V2>V3 (1)

[0058] The cooling process includes a step of cooling from the maximum temperature T3 to 1600°C at a cooling rate of 10.0°C / min or less. It is preferable to cool the aluminum nitride sintered body slowly during the cooling process. The cooling rate in the cooling process may be 7.0°C / min or less. The cooling rate may be, for example, 5.0°C / min or more. The cooling rate may be adjusted within the above range, for example, 5.0 to 10.0°C / min.

[0059] The process may include a step of gradually cooling the aluminum nitride sintered body from 1600°C to 1200°C at a cooling rate of 3.0 to 5.0°C / min. By including such a gradual cooling step, the firing of the aluminum nitride sintered body can be sufficiently advanced, resulting in a more dense aluminum nitride sintered body.

[0060] Rapid cooling from 1200°C to room temperature (e.g., 25°C) is permitted. The rate of rapid cooling may be, for example, 16.0°C / min or higher, 18.0°C / min or higher, or 20.0°C / min or higher. The rate of rapid cooling may also be, for example, 30.0°C / min or lower. The rate of rapid cooling may be adjusted within the above range, for example, 16.0 to 30.0°C / min.

[0061] The total time required from the first heating step to the cooling step may be 20.0 hours or less, for example, 18.0 hours or less, 16.0 hours or less, or 14.0 hours or less. By setting the total firing time within the above range, it is possible to reduce the seepage of the sintering aid on the surface layer of the molded body or aluminum nitride sintered body onto the main surface of the molded body or aluminum nitride sintered plate, and the formation of sintering aid particles. The total firing time for the above firing steps may be, for example, 6.0 hours or more, or 8.0 hours or more. By setting the total firing time within the above range, the sintering aid can be melted, the aluminum nitride particles can be sufficiently dissolved, and the aluminum nitride particles can be regrown in a more uniform environment, thereby preparing an aluminum nitride sintered body with an even more uniform particle size distribution. The firing time for the above firing steps can be adjusted within the above range, for example, 6.0 to 20.0 hours, 8.0 to 16.0 hours, or 8.0 to 14.0 hours.

[0062] The aluminum nitride sintered body obtained by the above manufacturing method may be processed into a desired shape as needed. The aluminum nitride sintered body may be processed into a plate shape having a pair of main surfaces, for example. Metal parts such as metal circuits or metal plates may be attached to the aluminum nitride sintered body to form a substrate. The substrate may be a laminate formed by joining the main surface of a plate-shaped aluminum nitride sintered body to the main surface of a metal plate such as a copper plate. Alternatively, it may be a circuit board in which a circuit pattern that forms a conductive part is formed by removing a part of the metal plate by etching or the like.

[0063] Figure 2 is a perspective view showing an example of a laminate. The laminate 200 comprises a pair of metal plates 110 arranged facing each other, and an aluminum nitride sintered body 100 between the pair of metal plates 110. Examples of metal plates 110 include copper plates. The shape and size of the aluminum nitride sintered body 100 and the metal plates 110 may be the same or different. The metal plates 110 and the aluminum nitride sintered body 100 may be joined together, for example, by a brazing material. One of the pair of metal plates 110 may be used as a heat sink, and the other may be processed into a circuit pattern. The circuit pattern may be formed by etching the metal plate 110 using a resist. This makes it possible to form a circuit board or a heat sink that can sufficiently suppress leakage current, etc.

[0064] Figure 3 is a perspective view showing an example of a circuit board. The circuit board 300 comprises an aluminum nitride sintered body 100, a plurality of conductor parts 20, and a metal plate 110. The conductor parts 20 are provided on one main surface 100A of the aluminum nitride sintered body 100, and the metal plate 110 is provided on the other side of the aluminum nitride sintered body 100. When the circuit board 300 is used in a power module, the metal plate 110 may function as a heat dissipation material.

[0065] The aluminum nitride sintered body 100 in the laminate 200 and circuit board 300 is composed of an aluminum nitride sintered body with excellent electrical insulation and thermal conductivity. Therefore, it has excellent reliability when used in various products such as power modules.

[0066] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited in any way to the above embodiments. For example, the shape and structure of the laminate and circuit board are not limited to those shown in Figures 2 and 3. For example, a circuit pattern may be formed on both main surfaces of the aluminum nitride sintered body 100. Also, the conductor portion 20 may be formed by thermal spraying and heat treatment of metal powder instead of etching the metal plate 110. Furthermore, the descriptions of the embodiments described above are applicable to each other. [Examples]

[0067] The contents of this disclosure will be described in more detail with reference to examples and comparative examples, but this disclosure is not limited to the following examples.

[0068] (Example 1) (Fabrication of aluminum nitride sintered bodies) To 100 parts by mass of aluminum nitride (AlN) powder, 3.87 parts by mass of yttrium oxide (Y2O3) powder and 0.732 parts by mass of α-aluminum oxide (Al2O3) were added as sintering aids, and the mixture was mixed using a ball mill to obtain a mixed powder. To 100 parts by mass of the mixed powder, 6 parts by mass of a cellulose ether binder (manufactured by Shin-Etsu Chemical Co., Ltd., product name: Metroze), 5 parts by mass of glycerin (manufactured by Kao Corporation, product name: Excepearl), and 10 parts by mass of ion-exchanged water were added, and the mixture was mixed for 1 minute using a Henschel mixer to obtain a molding raw material. This molding raw material was molded using a screw-type extruder to produce a sheet-like molded body (width: 80 mm, thickness: 0.8 mm), which was dried at 100°C for 1 hour and then cut to obtain molded bodies with dimensions of 60 mm (length) x 60 mm (width).

[0069] The obtained molded body was degreased by heating it in air at 570°C for 10 hours. Next, the degreased body was placed in a heating furnace and heated under reduced pressure (100 Pa) from room temperature (T0: approximately 25°C) to 1450°C at a rate of 15°C / min. After reaching 1450°C, it was held in a nitrogen gas atmosphere (atmospheric pressure) for 30 minutes, then heated to 1700°C at a rate of 1.0°C / min and held for 120 minutes. Next, it was heated to 1800°C at a rate of 0.7°C / min and held for 120 minutes. Then, it was cooled to 1600°C at a rate of 10.0°C / min, then cooled to 1200°C at a rate of 4.0°C / min, and finally cooled to 25°C at a rate of 20.0°C / min. In this way, an aluminum nitride sintered body was obtained.

[0070] (Compositional analysis of aluminum nitride sintered body) The composition of the obtained aluminum nitride sintered body was determined by X-ray analysis. A Bruker D8 ADVANCE (product name) manufactured by Bruker Japan Co., Ltd. was used for the X-ray analysis. The percentage content (%) of each component relative to the total amount of aluminum nitride (AlN), 2Y2O3·Al2O3 (YAM), 3Y2O3·5Al2O3 (YAG), and Y2O3·Al2O3 (YAP) was determined by the X-ray analysis. Furthermore, the percentage ratio (%) of each component relative to the total amount of YAM, YAG, and YAP was also determined. The results are shown in Table 1.

[0071] <Evaluation of insulating properties of aluminum nitride sintered bodies> The volume resistivity of the obtained aluminum nitride sintered body was measured. The measurement was performed using a Hioki Electric Corporation super-insulation meter (product name: SM-8220) in accordance with JIS C 2139:2008 "Solid electrical insulating materials - Method for measuring volume resistivity and surface resistivity". Specifically, the aluminum nitride sintered body was first processed to a thickness of 1.0 mm, and copper with a diameter of 10 mm was deposited on both sides of the aluminum nitride sintered plate to prepare a measurement sample (substrate). The obtained substrate was sandwiched between measurement electrodes, and a voltage of 1000 V was applied to the substrate at 125°C to allow a DC current to flow. This state was maintained for 20 seconds. After 20 seconds, the insulation resistance value was measured, and the volume resistivity was calculated using the following formula (2). The obtained results are shown in Table 1. Volume resistivity [Ω cm] = Insulation resistance value [Ω] × Copper deposition area [cm 2 ] / Thickness of aluminum nitride sintered plate [cm] (2)

[0072] <Evaluation of thermal conductivity of aluminum nitride sintered body> Thermal conductivity was measured using the laser flash method in accordance with JIS R1611:2010 "Method for measuring thermal diffusivity, specific heat capacity, and thermal conductivity of fine ceramics by flash method". The measuring device used was the TC-7SB RT (product name) manufactured by Advance Riko Co., Ltd., and the measurement temperature was set to room temperature (approximately 25°C). Eight measurements were performed, and the standard deviation σ of the obtained thermal conductivity was calculated. The results are shown in Table 1.

[0073] <Measurement of flexural strength> The three-point bending strength of an aluminum nitride sintered body at 20°C was measured using the SDT-503NB-50R1 (product name) manufactured by Imada Manufacturing Co., Ltd. The obtained results are shown in Table 1.

[0074] (Example 2) An aluminum nitride sintered body was prepared and evaluated using the same method as in Example 1, except that the heating rate from 1450°C to 1700°C was set to 2.0°C / min, and the heating rate from 1700°C to 1800°C was set to 1.0°C / min. The results obtained are shown in Table 1.

[0075] (Example 3) An aluminum nitride sintered body was prepared and evaluated using the same method as in Example 1, except that the heating rate from 1450°C to 1700°C was set to 3.0°C / min, the heating rate from 1700°C to 1800°C was set to 1.5°C / min, and the cooling rate from 1800°C to 1600°C was set to 7.0°C / min. The results obtained are shown in Table 1.

[0076] (Comparative Example 1) An aluminum nitride sintered body was prepared and evaluated using the same method as in Example 1, except that the cooling rate from 1800°C to 1600°C was set to 20.0°C / min. The results obtained are shown in Table 1.

[0077] (Comparative Example 2) An aluminum nitride sintered body was prepared and evaluated using the same method as in Example 1, except that the heating rate from 1450°C to 1700°C was 0.7°C / min, the heating rate from 1700°C to 1800°C was 0.4°C / min, and the cooling rate from 1800°C to 1600°C was 15.0°C / min. The results obtained are shown in Table 1.

[0078] [Table 1]

[0079] Comparing each comparative example with each example, it was confirmed that the greater the heating rate from 1450°C to 1700°C, and from 1700°C to 1800°C, the greater the flexural strength and volume resistivity of the aluminum nitride sintered body, and the smaller the variation in thermal conductivity. Thus, it was found that increasing the heating rate yields an aluminum nitride sintered body with excellent electrical insulation, flexural strength, and reduced variation in thermal conductivity.

[0080] It was confirmed that the flexural strength and volume resistivity of the aluminum nitride sintered body increased and the variation in thermal conductivity decreased as the cooling rate from 1800°C to 1600°C decreased. In particular, when comparing Comparative Example 1 and Example 1, which were similar processes except for the difference in cooling rates (20.0°C / min and 10.0°C / min), the aluminum nitride sintered body of Example 1, which had a lower cooling rate, exhibited superior performance compared to the aluminum nitride sintered body of Comparative Example 1.

[0081] Of all the examples and comparative examples, the aluminum nitride sintered body of Example 3, which had the highest heating rate and the lowest cooling rate, exhibited the best electrical insulation and flexural strength. Therefore, it was found that by combining a high heating rate and a low cooling rate in the firing process of the aluminum nitride sintered body, an aluminum nitride sintered body with even better electrical insulation and flexural strength, and greater reliability with less variation in thermal conductivity, can be obtained. In each example, it was confirmed that the lower the YAM content, the higher the volume resistivity, indicating that the YAM content affects the electrical insulation of the aluminum nitride sintered body. [Industrial applicability]

[0082] This disclosure provides an aluminum nitride sintered body that can achieve sufficiently high electrical insulation properties while stabilizing thermal conductivity. It also provides a method for manufacturing such an aluminum nitride sintered body. [Explanation of Symbols]

[0083] 20...Conductor part, 100...Aluminum nitride sintered body, 110...Metal plate, 200...Laminate, 300...Circuit board.

Claims

1. It contains aluminum nitride as its main component and an oxide having yttrium and aluminum as constituent elements. Said oxide comprises 3Y ２ O ３ ·5Al ２ O ３ , Y ２ O ３ ·Al ２ O ３ , and 2Y ２ O ３ ·Al ２ O ３ , and includes 3Y ２ O ３ ・5Al ２ O ３ And, Y ２ O ３ Al ２ O ３ And, 2Y ２ O ３ Al ２ O ３ 2Y for the total amount of ２ O ３ Al ２ O ３ An aluminum nitride sintered body in which the ratio of is 2.0 mass% or less.

2. The aforementioned aluminum nitride and 3Y ２ O ３ ・5Al ２ O ３ And, Y ２ O ３ Al ２ O ３ And, 2Y ２ O ３ Al ２ O ３ Y for the total amount of and ２ O ３ Al ２ O ３ The aluminum nitride sintered body according to claim 1, wherein the content of is 3.0% by mass or less.

3. The aforementioned aluminum nitride and 3Y ２ O ３ ・5Al ２ O ３ And, Y ２ O ３ Al ２ O ３ And, 2Y ２ O ３ Al ２ O ３ 2Y for the total amount of ２ O ３ Al ２ O ３ The aluminum nitride sintered body according to claim 1, wherein the content of is 0.01 to 0.1% by mass.

4. The volume resistivity at 120°C is 4.0 × 10⁻⁶ １１ An aluminum nitride sintered body according to any one of claims 1 to 3, wherein the density is Ω·cm or greater.

5. An aluminum nitride sintered body according to any one of claims 1 to 3, wherein the flexural strength is 450 MPa or more.

6. A first heating step involves heating a molded body containing aluminum nitride, yttrium oxide, and aluminum oxide from a temperature T0 to a soaking temperature T1 at a first heating rate V1. After the first heating step, a first soaking step is performed in which the temperature is maintained at the soaking temperature T1, Following the first soaking step, a second heating step is performed in which the temperature is raised from the soaking temperature T1 to the second soaking temperature T2 at a second heating rate V2, After the second heating step, a second soaking step is performed in which the temperature is maintained at the soaking temperature T2, Following the second soaking step, a third heating step is performed in which the temperature is raised from the soaking temperature T2 to the maximum temperature T3 at a third heating rate V3, After the third heating step, a third soaking step is performed to maintain the temperature at the highest temperature T3, The process includes a cooling step, which follows the third soaking step, in which the temperature is lowered to at least 1600°C at a cooling rate of 10.0°C / min or less. The temperature T0 is the temperature at which heating begins, the soaking temperature T1 is 1350 to 1550°C, the second soaking temperature T2 is 1600°C or more and less than 1750°C, the maximum temperature reached T3 is 1750 to 1850°C, and the first heating rate V1, the second heating rate V2, and the third heating rate V3 satisfy the following formula (1): A method for manufacturing an aluminum nitride sintered body, wherein the manufactured aluminum nitride sintered body comprises aluminum nitride as the main component and an oxide having yttrium and aluminum as constituent elements, wherein the oxide comprises 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3, and the ratio of 2Y2O3·Al2O3 to the total amount of 3Y2O3·5Al2O3, Y2O3·Al2O3, and 2Y2O3·Al2O3 is 2.0% by mass or less. V1>V2>V3 (1)

7. The method for producing an aluminum nitride sintered body according to claim 6, wherein the cooling rate is 7.0°C / min or less.

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