WO2024111483A1 - Ceramic sintered body, method for producing same, bonded body, and power module - Google Patents

Abstract

Provided is a ceramic sintered body comprising ceramic particles, wherein the cross-section has an average number of less than 1 per mm2 of coarse voids having a size of 10 μm or larger and an average number of less than 400 per mm2 of fine voids having a size of at least 0.05 μm but less than 10 μm, and the flexural strength is at least 640 MPa.

Description

Ceramic sintered body, manufacturing method thereof, bonded body, and power module

This disclosure relates to a ceramic sintered body and its manufacturing method, a bonded body, and a power module.

In recent years, power modules for controlling large amounts of power have been used in industrial equipment such as motors, and in products such as electric vehicles. In these power modules, circuit boards equipped with ceramic plates are used to efficiently diffuse heat generated by semiconductor elements and suppress leakage current (see, for example, Patent Document 1). The ceramic sintered bodies used in these ceramic plates are usually manufactured by forming ceramic raw material powder into a predetermined shape to form a ceramic compact, and then firing the ceramic compact.

Known ceramic sintered bodies are composed of nitrides, carbides, borides, silicides, etc. When producing such ceramic sintered bodies, sintering aids are used to promote sintering. For example, Patent Document 2 proposes using Si powder, MgO powder, and Y ₂ O ₃ powder when producing a silicon nitride sintered substrate.

International Publication No. 2019/022133 International Publication No. 2017/170247

Electronic components such as power modules are becoming smaller and thinner while improving their performance. As a result, it is expected that the level of reliability required for various products used in electronic components will continue to increase. This disclosure provides a ceramic sintered body that has excellent heat cycle resistance and excellent insulation reliability at high temperatures, a manufacturing method thereof, and a joined body. This disclosure provides a power module that has excellent reliability by including such a ceramic sintered body.

One aspect of the present disclosure provides the following ceramic sintered body:

[1] A ceramic sintered body containing ceramic particles, in which in a cross section, the average number of coarse pores having a size of 10 μm or more is less than 1 pore/ ^mm2 , and the average number of micropores having a size of less than 10 μm is less than 400 pores/ ^mm2 , and the flexural strength is 640 MPa or more.

The above-mentioned ceramic sintered body has a sufficiently small number of both coarse pores and micropores in the cross section, and has high flexural strength. When such a ceramic sintered body is joined to a different material such as a metal plate, internal stress occurs when there is a temperature change, which causes insulation breakdown. The above-mentioned ceramic sintered body has high flexural strength, and the number of coarse pores and micropores is sufficiently reduced. Therefore, when internal stress occurs due to a temperature change, the occurrence and progression of cracks can be sufficiently suppressed. Therefore, it has excellent heat cycle resistance and excellent insulation reliability at high temperatures.

The ceramic sintered body of [1] above may be the following [2] or [3].

[2] The ceramic sintered body according to [1], wherein the maximum pore size in the cross section is 6 μm or less.
[3] The ceramic sintered body according to [1] or [2], wherein the average size of the micropores is 1.0 μm or less and the standard deviation is 0.6 μm or less.

The ceramic sintered body of [2] above has a maximum pore size of 6 μm or less, which sufficiently suppresses the occurrence of cracks due to temperature changes. This results in even better insulation reliability. The ceramic sintered body of [3] above can be made to have sufficiently high durability in a heat cycle environment.

One aspect of the present disclosure provides the following method for producing a ceramic sintered body.

[4] A step of pulverizing the sintering aid raw material with a pulverizer to obtain a sintering aid powder having a median diameter of 0.5 to 1.0 μm;
preparing a mixed raw material containing a ceramic powder and the sintering aid powder;
and firing the compact of the mixed raw material to obtain a ceramic sintered body having a flexural strength of 640 MPa or more.

The above manufacturing method includes a step of pulverizing the sintering aid raw material with a pulverizer to obtain a sintering aid powder with a median diameter of 0.5 to 1.0 μm. Such sintering aid powder has a sufficiently small particle diameter and agglomeration is sufficiently suppressed. By using a mixed raw material containing such a sintering aid, the grain growth of the ceramic powder proceeds uniformly and smoothly, and a ceramic sintered body having a sufficiently reduced number of pores and high flexural strength can be obtained. Such a ceramic sintered body can sufficiently suppress the occurrence and progression of cracks when internal stress occurs with temperature changes. This results in excellent heat cycle resistance and excellent insulation reliability at high temperatures.

The method for producing the ceramic sintered body described above in [4] may be the following [5].

[5] In a cross section of the ceramic sintered body, the average number of coarse pores having a size of 10 μm or more may be less than 1 pore/ ^mm2 , and the average number of micropores having a size of less than 10 μm may be less than 400 pores/ ^mm2 . Such a ceramic sintered body has even better insulation reliability.

One aspect of the present disclosure provides the following conjugate:

[6] A joint comprising the plate-shaped ceramic sintered body described in any one of [1] to [3] above, a metal plate, and a brazing layer joining the main surface of the ceramic sintered body to the main surface of the metal plate.

The bonded body includes the ceramic sintered body. This ceramic sintered body can sufficiently suppress the occurrence and progression of cracks when internal stress occurs due to temperature changes. Therefore, the bonded body has excellent heat cycle resistance and also excellent insulation reliability at high temperatures.

The joint of [6] above may be the joint of [7] or [8] below.

[7] The joined body according to [6], wherein the metal plate has a thickness of 0.8 mm or less.
[8] The joined body according to [6] or [7], wherein the brazing material layer contains silver, copper, tin, and an active metal, and the active metal contains one or more selected from the group consisting of titanium, hafnium, zirconium, and niobium.

One aspect of the present disclosure provides the following power module:

[9] A joined body including the plate-shaped ceramic sintered body according to any one of [1] to [3] above, a metal plate, and a brazing material layer joining a main surface of the ceramic sintered body and a main surface of the metal plate;
a semiconductor element electrically connected to the metal plate of the joint body.

The power module includes the ceramic sintered body as an insulator for the joint through which heat generated by the semiconductor element is transferred. The ceramic sintered body has excellent heat cycle resistance and excellent insulation reliability at high temperatures. Therefore, the power module has excellent reliability.

The present disclosure can provide a ceramic sintered body that has excellent heat cycle resistance and excellent insulation reliability at high temperatures, a manufacturing method thereof, and a bonded body. The present disclosure can provide a power module that has excellent reliability by including such a ceramic sintered body.

FIG. 1 is an enlarged cross-sectional view showing a schematic view of a part of a cross section of a ceramic sintered body. FIG. 2 is a cross-sectional view of the bonded body taken along the thickness direction. FIG. 3 is a cross-sectional view of the power module. FIG. 4 is a diagram showing an example of a volume-based particle size distribution of a sintering additive powder obtained by a laser diffraction/scattering method. FIG. 5 is a diagram showing an example of an image of grain growth as sintering progresses in one example of a manufacturing method. FIG. 6 is a photograph (200x) showing an example of a cross section taken by a scanning electron microscope. FIG. 7 is a photograph (1000x) showing an example of a cross section taken by a scanning electron microscope. FIG. 8 is a diagram showing a schematic diagram of an example of an inspection device for inspecting for dielectric breakdown. FIG. 9 is a diagram showing an image of grain growth as sintering progresses in a conventional manufacturing method. FIG. 10 is a photograph (magnification: 200) taken by a scanning electron microscope of a cross section of a conventional molded body (ceramic green sheet) and an agglomerate of sintering additive powder contained in the cross section. FIG. 11 is a scanning electron microscope photograph (200x) of a cross section of a conventional ceramic sintered body. FIG. 12 is a diagram showing an example of a particle size distribution of a conventional sintering additive powder by a laser diffraction/scattering method. FIG. 13 is a photograph (200x) showing an example of a conventional cross section taken by a scanning electron microscope. FIG. 14 is a photograph (1000x) showing an example of a conventional cross section taken by a scanning electron microscope.

Below, embodiments of the present disclosure will be described, with reference to the drawings where necessary. However, the following embodiments are merely examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following content. Note that the numerical ranges indicated with the symbol "to" include the lower limit and the upper limit. In other words, the numerical range indicated by "A to B" means A or more and B or less. This disclosure also includes numerical ranges that combine a numerical range having only an upper limit with a numerical range having only a lower limit. This disclosure also includes numerical ranges in which the upper or lower limit of each numerical range is replaced with the numerical value of any of the examples. When multiple materials are exemplified, one of the materials may be used alone, or multiple materials may be used in combination.

The ceramic sintered body according to one embodiment includes ceramic particles. The ceramic sintered body may include pores. The number and size of the pores included in the ceramic sintered body affect the heat cycle resistance and insulating reliability at high temperatures of the ceramic sintered body. The pores include coarse pores and micropores. The coarse pores and micropores have different sizes, and the pore size is measured as follows.

FIG. 1 is a diagram that shows a schematic example of an image of a portion of a cross section of a ceramic sintered body observed with a scanning electron microscope. As shown in FIG. 1, cross section 10C of the ceramic sintered body contains ceramic particles and pores 20. In FIG. 1, pores 20 are shown enlarged and schematic. Note that cross section 10C contains a large number of ceramic particles, but for convenience, the ceramic particles are not shown in FIG. 1.

In this disclosure, the size of a pore 20 is the length of the line segment L connecting two points selected to maximize the distance between them on the outer edge of the pore 20. Pores are classified as "coarse pores", "micropores", and other pores according to the length of this line segment L. If the length of the line segment L of the pore 20 shown in FIG. 1 is 0.05 μm or more and less than 10 μm, it is classified as a "micropore". On the other hand, pores whose length of the line segment L measured in a similar manner is 10 μm or more are classified as "coarse pores". The length of the line segment L of other pores is less than 0.05 μm.

The bending strength of a ceramic sintered body varies greatly depending on the average number of coarse pores and the average number of micropores. The average number of coarse pores _P1 of the ceramic sintered body of this embodiment is less than 1 pore/ ^mm2 . The average number of coarse pores _P1 is calculated by the following formula based on the total number of coarse pores included in each field of view obtained by observing the cross section (magnification: 200 times) in five or more fields of view using a scanning electron microscope.
Average number of coarse pores P ₁ =Total number of coarse pores/Number of fields/Area per field

From the viewpoint of sufficiently increasing the heat cycle resistance and the insulation reliability at high temperatures of the ceramic sintered body, the average number _P1 of coarse pores may be less than 0.8 pores/ ^mm2 , less than 0.6 pores/ ^mm2 , less than 0.5 pores/ ^mm2 , or less than 0.1 pores/ ^mm2 . The lower limit of the average number _P1 of coarse pores may be 0 pores/ ^mm2 . The average number _P1 of coarse pores can be adjusted, for example, by changing the particle size or degree of aggregation of the sintering aid powder.

The average number _P2 of micropores in the ceramic sintered body of this embodiment is less than 400 pores/ ^mm2 . The average number _P2 of micropores is calculated by observing the cross section (magnification: 1000 times) in five or more visual fields using a scanning electron microscope, and adding up the total number of micropores contained in each visual field, using the following calculation formula. The size and number of micropores can be counted using image processing software such as ImageJ.
Average number of micropores _P2 = Total number of micropores/Number of fields/Area per field

From the viewpoint of sufficiently increasing the heat cycle resistance and the insulating reliability at high temperatures of the ceramic sintered body, the average number _P2 of micropores may be less than 350 pcs/ ^mm2 , less than 320 pcs/ ^mm2 , less than 290 pcs/ ^mm2 , or less than 210 pcs/ ^mm2 . The average number _P2 of micropores may be 10 pcs/ ^mm2 or more, 50 pcs/ ^mm2 or more, or 100 pcs/ ^mm2 or more. The average number _P2 of micropores can be adjusted, for example, by changing the particle size or degree of aggregation of the sintering aid powder.

The average number _P1 of coarse pores may be 0/ ^mm2 , and the maximum size of the pores contained in the cross section of the ceramic sintered body may be 6 μm or less, 5 μm or less, or 3 μm or less. This can further increase the bending strength of the ceramic sintered body. The maximum size of the pores contained in the cross section of the ceramic sintered body may be 0.5 μm or more, 1.0 μm or more, or 1.2 μm or more. The maximum size of the pores is determined from the measured value of the size of all pores detected when observing the cross section (magnification: 200 times) in five or more visual fields using a scanning electron microscope.

From the viewpoint of further improving the heat cycle resistance and the insulation reliability at high temperatures, the average size of the micropores contained in the cross section of the ceramic sintered body may be 1.0 μm or less, and the standard deviation of the size may be 0.6 μm or less. In some examples, the average size of the micropores contained in the cross section of the ceramic sintered body may be 0.7 μm or less, and the standard deviation of the size may be 0.5 μm or less. In other examples, the average size of the micropores contained in the cross section of the ceramic sintered body may be 0.6 μm or less, and the standard deviation of the size may be 0.47 μm or less. The average size of the micropores contained in the cross section of the ceramic sintered body may be 0.1 μm or more. The average size of the micropores is obtained in the same manner as when obtaining the average number _P2 described above. That is, it is obtained as the arithmetic average of the sizes of the micropores contained in five or more visual fields. The standard deviation of the sizes of the micropores is also obtained as the standard deviation of the sizes of the micropores contained in five or more visual fields.

In addition to the pores 20 and ceramic particles, the cross section 10C may contain a sintering aid phase. The average area ratio of the ceramic particles (ceramic phase) in the cross section 10C may be 70-90%, or 75-85%. The average area ratio of the sintering aid phase in the cross section 10C may be 10-25%, or 14-22%. A ceramic sintered body having a cross section 10C containing ceramic particles and a sintering aid phase in such an area ratio has sufficiently high thermal conductivity and flexural strength.

It is preferable that the number of ceramic particles having a major axis of 20 μm or more contained in the cross section of the ceramic sintered body is large. This allows both flexural strength and thermal conductivity to be achieved at a high level. The number of ceramic particles having a major axis length of 20 μm or more is measured using an image (field area: 0.02 mm ² ) magnified 1000 times using a scanning electron microscope. The length of the major axis of the ceramic particle can be measured in the same manner as the size of the pores 20. In other words, the length of the major axis of the ceramic particle is the length of the line segment (major axis) connecting two points selected so that the distance between them is the largest on the outer edge of the ceramic particle.

The measurements are performed in five or more visual fields, and the average number is the average number of ceramic particles whose major axis length is 20 μm or more in each visual field. The average number of ceramic particles having a major axis of 20 μm or more may be 10 or more, 15 or more, or 17 or more. The average number of ceramic particles having a major axis of 20 μm or more may be 50 or less, 45 or less, or 40 or less. The standard deviation of the number of ceramic particles having a major axis of 20 μm or more may be less than 0.6 μm or less than 0.5 μm. The standard deviation of the number of ceramic particles having a major axis of 20 μm or more may be 0.1 μm or more, or 0.15 μm or more. Such a ceramic sintered body has a highly uniform microstructure. This makes it highly reliable.

The aspect ratio of ceramic particles having a major axis (size) of 20 μm or more may be 3 or more, or may be 4 or more. The number of ceramic particles having such shapes and sizes can be increased by smooth grain growth during sintering. The aspect ratio is the ratio of the length of the major axis to the length of the minor axis. The minor axis is the line segment connecting two points selected to have the greatest spacing at the outer edge of the ceramic particle in a direction perpendicular to the major axis.

The ceramic particles constituting the ceramic sintered body may contain at least one selected from the group consisting of silicon nitride particles, aluminum nitride particles, and alumina particles.

Examples of ceramic sintered bodies include silicon nitride sintered bodies containing silicon nitride particles as the main component, aluminum nitride sintered bodies containing aluminum nitride particles as the main component, and alumina sintered bodies containing alumina particles as the main component. In addition, composite sintered bodies containing multiple types of ceramic particles may also be used.

The flexural strength of the ceramic sintered body is 640 MPa or more. Such a ceramic sintered body has excellent reliability. The flexural strength of the ceramic sintered body may be 670 MPa or more, 690 MPa or more, or 720 MPa or more. This flexural strength is measured by the method described in the Examples. A ceramic sintered body having such a high flexural strength has high insulation properties. In addition to such flexural strength, the average number of coarse pores and micropores is sufficiently small, so that the ceramic sintered body has excellent heat cycle resistance and excellent insulation reliability at high temperatures. Such a ceramic sintered body can be suitably used, for example, as an insulating substrate for a power module. The upper limit of the flexural strength of the ceramic sintered body may be, for example, 950 MPa. Note that the uses of the ceramic sintered body are not limited to this.

The bonded body according to one embodiment includes a plate-shaped ceramic sintered body (ceramic plate), a metal plate, and a brazing material layer that bonds a main surface of the ceramic sintered body to a main surface of the metal plate. The ceramic plate may be the ceramic sintered body according to the above embodiment. This ceramic sintered body can sufficiently suppress the occurrence and progression of cracks when internal stress occurs due to temperature change. Therefore, the bonded body has excellent heat cycle resistance and also excellent insulation reliability at high temperatures.

FIG. 2 is a cross-sectional view along the thickness direction showing an example of the bonded body of this embodiment. However, the description of this example is not limited to this example, and is also applicable to other examples of the bonded body. The bonded body 100 of FIG. 2 includes a ceramic plate 10, a metal plate 41 bonded to one main surface 10A of the ceramic plate 10 via a brazing material layer 51, and a metal plate 42 bonded to the other main surface 10B of the ceramic plate 10 via a brazing material layer 51. The metal plate 41 is patterned and functions, for example, as a circuit. In this specification, such a patterned object is also referred to as a metal plate. The metal plate 42 is not patterned and functions, for example, as a heat sink. The ceramic plate 10 is composed of the above-mentioned ceramic sintered body.

The metal plates 41, 42 may be, for example, copper plates. From the viewpoint of improving heat dissipation performance and electrical conductivity, the thickness of the metal plates 41, 42 may be 0.3 mm or more, or 0.4 mm or more. From the viewpoint of reducing internal stress generated in the ceramic plate 10 due to temperature changes, the thickness of the metal plates 41, 42 may be 0.8 mm or less, or 0.7 mm or less. An example of the thickness range of the metal plates 41, 42 is 0.3 to 0.8 mm.

The thickness of the ceramic plate 10 may be 0.2 mm or more, or may be 0.3 mm or more, from the viewpoint of improving insulation. The thickness of the ceramic plate 10 may be 0.8 mm or less, or may be 0.6 mm or less, from the viewpoint of making the joined body 100 thinner.

The brazing material layers 51, 52 are layers that join the ceramic plate 10 and the metal plates 41, 42, and contain brazing material components. The brazing material layers may contain, for example, silver derived from the brazing material, or silver and copper. The brazing material layers 51, 52 may further contain one or more metals selected from the group consisting of tin and active metals derived from the brazing material. In the brazing material layers 51, 52, the two or more metals may be alloyed. The active metal may contain one or more metals selected from the group consisting of titanium, hafnium, zirconium, and niobium. The silver and copper contained in the brazing material layers 51, 52 may be contained as an alloy, such as an Ag-Cu eutectic alloy. The silver content in the brazing material layers 51, 52 may be 45 to 95 mass% in Ag equivalent, or may be 50 to 95 mass%. The total content of silver and copper in the brazing layers 51 and 52 may be 65 to 100 mass%, 70 to 99 mass%, or 90 to 98 mass% converted to Ag and Cu, respectively. The thickness and composition of the brazing layers 51 and 52 may be the same as or different from each other.

In a modified version of the bonded assembly, the metal plates bonded to both main surfaces of the ceramic plate may be of the same shape. For example, the bonded assembly may be one in which the circuit pattern has not yet been formed. In another modified version, multiple metal plates may be bonded to one main surface of the ceramic plate. Metal plates may be bonded to only one main surface of the ceramic plate.

The power module according to one embodiment includes a joint (circuit board) and a semiconductor element electrically connected to the metal plate of the joint. The joint may be the joint 100 described above or a modified version thereof. The descriptions regarding the ceramic sintered body, the joint, and their modified versions apply to the power module of this embodiment. Such a power module includes a joint having a ceramic plate that has excellent heat cycle resistance and also excellent insulation reliability at high temperatures. Therefore, high performance can be maintained even when used in an environment where the temperature fluctuates greatly. In this way, the power module has excellent reliability.

FIG. 3 is a cross-sectional view showing an example of a power module. The description of this example is not limited to this example, and is also applicable to other examples of power modules. The power module 200 in FIG. 3 includes a base plate 90 and a joint body 100 that is joined to one side of the base plate 90 via solder 82. A metal plate 42 (heat sink) on one side of the joint body 100 is joined to the base plate 90 via solder 82.

A semiconductor element 80 is attached to the metal plate 41 (circuit pattern) on the other side of the joint body 100 via solder 81. The semiconductor element 80 is connected to a predetermined location of the metal plate 41 with a metal wire 84 such as an aluminum wire. In this way, the semiconductor element 80 and the metal plate 41 are electrically connected. To electrically connect the outside of the housing 86 to the metal plate 41, one of the metal plates 41, metal plate 41a, is connected to an electrode 83 that penetrates the housing 86 via solder 85.

A housing 86 is disposed on one of the main surfaces of the base plate 90, and is integrated with the main surface to house the joint body 100. The housing space formed by the one of the main surfaces of the base plate 90 and the housing 86 is filled with resin 95. The resin 95 seals the joint body 100 and the semiconductor element 80. The resin may be, for example, a thermosetting resin or a photocurable resin.

A cooling fin 92, which serves as a heat dissipation member, is joined to the other main surface of the base plate 90 via grease 94. Screws 93 are attached to the ends of the base plate 90 to secure the cooling fin 92 to the base plate 90. The base plate 90 and the cooling fin 92 may be made of aluminum. The base plate 90 and the cooling fin 92 function well as heat dissipation parts due to their high thermal conductivity.

The metal plates 41 and 42 are electrically insulated by the ceramic plate 10 (plate-shaped ceramic sintered body). The metal plate 41 (41a) may form an electric circuit. The metal plates 41 and 42 are respectively joined to the main surface 10A and the main surface 10B of the ceramic plate 10 by a brazing material layer (not shown) containing a brazing material component. The power module 200 has excellent reliability because it includes the joint 100.

The method for producing a ceramic sintered body according to one embodiment includes a grinding process in which a sintering aid raw material is ground in a grinder to obtain a sintering aid powder having a D50 (median diameter) of 0.5 to 1.0 μm, a mixing process in which a mixed raw material containing ceramic powder and sintering aid powder is prepared, and a firing process in which a compact of the mixed raw material is fired.

The sintering aid powder contains at least two selected from the group consisting of alkaline earth metal oxides, rare earth oxides, transition metal oxides different from the rare earth oxides, silica, and alumina. The sintering aid powder may contain at least three selected from the group.

The alkaline earth metal oxide has an alkaline earth metal and oxygen as constituent elements. The alkaline earth metal oxide may include at least one selected from the group consisting of magnesium oxide, calcium oxide, and strontium oxide. The rare earth oxide has a rare earth element and oxygen as constituent elements. The rare earth oxide may include, for example, at least one selected from the group consisting of yttrium oxide and cerium oxide. The transition metal oxide different from the rare earth oxide has a transition metal different from the rare earth and oxygen as constituent elements. Such a transition metal oxide may include, for example, iron oxide.

An example of a sintering aid powder includes magnesium oxide, rare earth oxide, and silica. In this case, when the total amount of the sintering aid powder is 100 parts by mass, the content of the rare earth oxide may be 30 to 80 parts by mass, or may be 40 to 70 parts by mass. In this case, the content of the magnesium oxide may be 5 to 40 parts by mass, or may be 10 to 30 parts by mass. In this case, the content of the silica may be 5 to 40 parts by mass, or may be 10 to 30 parts by mass.

The D50 (median diameter) of the sintering aid powder in the grinding process may be prepared, for example, by grinding the sintering aid raw material with a grinder. A bead mill type grinder may be used as the grinder. The particle size distribution of the sintering aid powder may be adjusted by changing at least one condition selected from the group consisting of the diameter of the beads of the bead mill type grinder, the peripheral speed, and the grinding time. The diameter of the beads may be 0.1 to 0.3 mm. The peripheral speed of the rotor may be 8 to 12 m/sec. The grinding time may be 5 to 20 minutes. Examples of grinders other than the bead mill type grinder include a ball mill, a vibration mill, and a pot mill.

If the D50 of the sintering aid powder exceeds 1.0 μm, the number and size of pores will increase, and the flexural strength will decrease. If the D50 of the sintering aid powder is less than 0.5 μm, the crushed particles will tend to aggregate due to the relationship between the input energy applied to the sintering aid raw material from the crusher and the crushing ratio. This is thought to be due to the fact that the frequency of contact between crushed particles increases as crushing progresses, and that the potential energy becomes more attractive.

The D50 of the sintering aid powder is determined based on the volumetric particle size distribution measured by a particle size distribution measuring device using the laser diffraction/scattering method. By having the D50 of the sintering aid powder within the above range, the particles contained in the sintering aid powder are sufficiently small, and the particles can be prevented from agglomerating together. This makes it possible to prevent the occurrence of pores caused by the particles and agglomerates of the sintering aid powder when producing a ceramic sintered body. In addition, the grain growth of the ceramic particles can proceed with high uniformity.

Figures 4 and 12 are diagrams showing examples of volumetric particle size distribution of sintering aid powders by laser diffraction and scattering. The horizontal axis is particle size [μm] in logarithmic scale, and the vertical axis is frequency [volume %]. The particle size distribution in this disclosure is measured in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - laser diffraction and scattering method". For particle size distribution measurement, LS-13 320 (product name) manufactured by Beckman Coulter can be used. The measurement conditions are a particle refractive index of 2.2 and a solvent refractive index of 1.33.

The sintering aid powder may have only one peak in the particle size distribution (frequency %) as shown in FIG. 4. Such sintering aid powder has more suppressed aggregation than powders with multiple peaks as shown in FIG. 12. This allows the size and number of pores in the ceramic sintered body to be sufficiently reduced. The peak in the particle size distribution may be sharp. For example, the D100 of the sintering aid powder may be less than 5.5 μm, or may be less than 5 μm. For example, the ratio of D100 to D50 may be 5 or less. An example of the lower limit of D100 is 2 μm. An example of the lower limit of the ratio of D100 to D50 is 2.

In the mixing process, the sintering aid powder obtained by pulverization is mixed with the ceramic powder and, if necessary, additives, and mixed using, for example, a ball mill. In this way, a mixed raw material containing the sintering aid powder and the ceramic powder is prepared. Examples of additives include binders, plasticizers, dispersion media, and release agents. Examples of binders include methylcellulose-based binders that have plasticity or surface activity, and acrylic ester-based binders that have excellent thermal decomposition properties. Examples of plasticizers include glycerin. Examples of dispersion media include ion-exchanged water and ethanol.

As the ceramic powder, for example, silicon nitride powder, aluminum nitride powder, or aluminum oxide powder can be used. The D50 (median diameter) of the ceramic powder may be 0.1 to 6 μm, or may be 0.5 to 4 μm. This allows a sufficiently densified ceramic sintered body to be obtained. The D50 of the ceramic powder is determined in the same manner as the D50 of the sintering aid powder. The number of peaks in the particle size distribution (frequency %) of the ceramic powder may also be one.

The mass ratio of the sintering aid powder to the ceramic powder may be 0.03 to 0.12, or may be 0.05 to 0.1. This makes it easier to densify the ceramic sintered body, and allows the flexural strength to be sufficiently high.

The mixed raw material obtained in the mixing step is applied to a release film at a specified thickness by a doctor blade method, a calendar method, an extrusion method, or the like, and then dried and molded to obtain a molded body. The molding pressure may be 3 to 30 MPa. The molded body may be produced by uniaxial pressing or by CIP. It may also be fired while being molded by hot pressing. For example, after producing a ceramic green sheet substrate by the above-mentioned methods such as the doctor blade method, the ceramic green sheet substrate may be punched out using a mold equipped with a die and a punch to obtain a molded body.

The solid content of the ceramic green sheet substrate when punched with a die may be 65 to 85% by mass, or 75 to 85% by mass. The solid content may be adjusted by carrying out a drying process to dry the ceramic green sheet substrate before punching with a die.

The molded body may be degreased before being sintered in the sintering step. The degreasing method is not particularly limited, and may be performed, for example, by heating the molded body 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.

The ceramic sintered body can be obtained by firing the molded body. The atmosphere, temperature, time, etc. during firing can be set appropriately depending on the type of ceramic sintered body. When producing a silicon nitride sintered body as the ceramic sintered body, it may be performed in an inert gas atmosphere such as nitrogen gas or argon gas. The pressure during firing may be 0.7 to 1 MPa. The firing temperature may be 1800 to 2100°C, 1800 to 2000°C, or 1800 to 1900°C. The firing time at the firing temperature may be 3 to 20 hours, or 4 to 16 hours.

When producing an aluminum nitride sintered body as the ceramic sintered body, the firing temperature may be, for example, 1760 to 1840°C. The holding time in the temperature range of 1760 to 1840°C may be, for example, 1 to 10 hours. Firing may be carried out under atmospheric pressure. When producing a ceramic sintered body other than a silicon nitride sintered body or an aluminum nitride sintered body (for example, and an aluminum oxide sintered body), the sintering conditions may be appropriately set so that the sintered body is sufficiently densified.

5 is a diagram showing an image of grain growth as sintering progresses in an example of the manufacturing method of this embodiment. In this example, as shown in FIG. 5(a), fine sintering aid powder 32 is dispersed with high uniformity in ceramic particles 12 in the molded body. When such a molded body is fired, the liquefied sintering aid phase 32a diffuses to the grain boundaries by capillary action as shown in FIG. 5(b). When the sintering aid phase 32a diffuses, the shrinkage of the molded body (ceramic sintered body) progresses, and the pores 22 disappear as shown in FIG. 5(c). When heating is continued, the ceramic particles 12 melt into the sintering aid phase 32a, and columnar ceramic particles 14 are generated as shown in FIG. 5(d). In this way, as liquid phase sintering progresses, the pores 22 disappear sufficiently with the smooth grain growth of the ceramic particles, so that the pores contained in the ceramic sintered body can be sufficiently reduced. A part of the sintering aid phase 32a may remain in the ceramic sintered body.

9 is a diagram showing an image of grain growth as sintering progresses in a conventional manufacturing method. In the conventional manufacturing method, as shown in FIG. 9(a), in the molded body, aggregates 132 of sintering aid powder are contained in ceramic particles 112. A cross-sectional photograph of such a conventional molded body is shown in FIG. 10. When such a molded body is fired, as shown in FIG. 9(b), the liquefied sintering aid phase 132a diffuses from the aggregates 132 to the grain boundaries by capillary action starting from the aggregates 132. As diffusion by capillary action progresses, pores 122 are formed in the aggregates 132 because of the large size of the aggregates 132. Since the pores 122 are large in size, they do not disappear even when the molded body shrinks, and the pores 122 remain in the ceramic sintered body as shown in FIG. 9(c). In this way, the number of large pores contained in the ceramic sintered body increases. FIG. 11 shows a cross section 110C of the conventional ceramic sintered body obtained in this way. The cross section 110C contains pores 122 originating from the aggregates 132.

In the manufacturing method of the present embodiment, the particles of the sintering aid powder are sufficiently fine, and the aggregation of the particles is suppressed, compared to the conventional manufacturing method. Therefore, the pores remaining as traces of the sintering aid powder can be reduced. This reduces the number of pores generated during the sintering process and reduces the size of the pores. The number of pores in the ceramic sintered body obtained in this manner is sufficiently reduced, and the size of the pores is sufficiently reduced. In addition, this ceramic sintered body has a high flexural strength of 640 MPa or more. As described above, the flexural strength of the ceramic sintered body may be 670 MPa or more, 690 MPa or more, or 720 MPa or more. The average numbers P ₁ and P ₂ of the coarse pores and micropores contained in the ceramic sintered body are also as described above. Such a ceramic sintered body can sufficiently suppress the occurrence and progression of cracks when internal stress occurs with a change in temperature. Therefore, it has excellent heat cycle resistance and excellent insulation reliability at high temperatures.

FIG. 8 is a schematic diagram showing an example of an inspection device that measures the leakage current of a joint (circuit board) to inspect for dielectric breakdown. The inspection device 400 includes an AC power source 60 and a voltage resistance tester 50 connected to the AC power source 60. One terminal of the voltage resistance tester 50 is electrically connected to a conductive support part 72a that contacts the metal plate 41 joined to the ceramic plate 10. The other terminal of the voltage resistance tester 50 is electrically connected to a conductive support part 72b that contacts the metal plate 42 via an electrode 70 that is disposed in a storage tank 77 that stores insulating oil 76.

The electrode 70 is arranged along the bottom surface and one side surface of the storage tank 77. As shown in FIG. 8, the electrode 70 has an L-shape when viewed in vertical cross section. Two insulating support parts 74 are provided on the electrode 70 adjacent to the conductive support part 72b. The two insulating support parts 74 each contact the metal plate 42, and support the assembly 100 in the insulating oil 76.

The electrode 70 and the conductive support parts 72a, 72b may be made of, for example, oxygen-free copper. The insulating oil 76 may be, for example, a fluorine-based inert liquid. The voltage resistance tester 50 may be a commercially available product. In this inspection device 400, a voltage of, for example, about 10 to 15 kV is applied between the metal plates 41, 42 that sandwich the ceramic plate 10, and the voltage resistance tester 50 measures the presence or absence of leakage current. By heating the insulating oil 76, the insulating performance of the ceramic plate 10 in the bonded body 100 at high temperatures, for example, above 100°C, may be evaluated.

The inspection device is not limited to the configuration shown in FIG. 8, and can be used without any particular restrictions as long as it is an inspection device that can measure leakage current when a voltage is applied between metal plates 41 and 42 at a temperature of, for example, 100°C or higher.

Although the embodiments of the present disclosure have been described above, the present disclosure is in no way limited to the above-described embodiments. The contents of the description regarding the embodiments of the ceramic sintered body also apply to the bonded body, the power module, and the manufacturing method of the ceramic sintered body. The contents of the description regarding the embodiments of the manufacturing method of the ceramic sintered body also apply to the ceramic sintered body.

　Numerical ranges that combine the upper and lower limit values of the numerical ranges specifically described in each of the above embodiments are also included in the present disclosure. In addition, numerical ranges in which the upper and/or lower limit values are replaced with the values of the examples described below are also included in the present disclosure.

The contents of this disclosure will be explained in more detail with reference to examples and comparative examples, but this disclosure is not limited to the specific examples below.

[Preparation of sintering aid powder]
(Comparative Examples 1 to 5, Examples 1 to 3)
As raw materials for the sintering aid powder, commercially available _yttrium oxide powder, magnesium oxide powder, and silica powder were prepared. These were mixed in a mass ratio of _Y2O3 :MgO: _SiO2 = 5:2:2 to obtain a mixed powder. The mixed powder was pulverized using a bead mill type pulverizer (manufactured by Ashizawa Finetech Co., Ltd., device name: Star Mill LMZ) to obtain a sintering aid powder. The pulverization conditions (bead diameter, rotor circumferential speed, and pulverization time) of the bead mill type pulverizer were changed as shown in Tables 1 and 2 to prepare multiple types of sintering aid powders with different pulverization conditions.

The volumetric particle size distribution of each sintering aid powder was measured using a particle size distribution measuring device using the laser diffraction/scattering method (manufactured by Nikkiso Co., Ltd., device name: particle size distribution measuring device MT3000II). From the particle size distribution measurement results, D50 (median size) and D100 (maximum particle size) were calculated. The results are shown in Tables 1 and 2. Tables 1 and 2 also show the ratio of D100 to D50. The particle size distributions (frequency %) of Examples 1 to 3 all had only one peak, as shown in Figure 4.

The results of Comparative Examples 1 to 3 in Table 1 confirm that the D50 and D100 of the sintering aid can be reduced by reducing the diameter of the beads. Furthermore, the results of Comparative Examples 3 and 4 and Example 1 confirm that the D50 and/or D100 can be reduced by increasing the circumferential speed of the rotor. The results of Examples 1 and 2 confirm that the D50 and D100 can be reduced by extending the grinding time. On the other hand, the results of Examples 2 and 3 and Comparative Example 5 confirm that the D50 and D100 increase when the grinding time is too long. This is thought to be due to the aggregation of the ground powder.

[Preparation of silicon nitride plate]
Example 4
Commercially available silicon nitride powder (D50: 0.7 μm), the sintering aid powder of Example 2, and an additive (solvent-based binder) were mixed in a bead mill to prepare a raw material slurry. The compounding ratio of the silicon nitride powder and the sintering aid powder was silicon nitride powder: sintering aid powder = 91:9. Next, the above-mentioned raw material slurry was applied to a release film by a doctor blade method to prepare a green sheet. The prepared ceramic green sheet was cut to a length x width = 250 mm x 180 mm, and 70 sheets were stacked to obtain a laminate. The above laminate was placed in an electric furnace equipped with a carbon heater and heated in air at 500 ° C for 20 hours to degrease.

The degreased molded body was placed in a sintering furnace, the pressure in the furnace was reduced to less than 100 Pa, and the temperature was raised to 900°C. Nitrogen gas was then introduced into the furnace, and the temperature was raised to 1500°C under a pressure of approximately 0.9 MPa and held at that temperature for 4 hours. After that, the temperature was raised to 1830°C and held at 1830°C for 5 hours. In this way, a silicon nitride plate with a thickness of 3 mm was obtained.

Example 5
A silicon nitride sintered body was obtained in the same manner as in Example 4, except that the sintering aid powder of Example 1 was used instead of the sintering aid powder of Example 2.

Example 6
A silicon nitride sintered body was obtained in the same manner as in Example 4, except that the sintering aid powder of Example 3 was used instead of the sintering aid powder of Example 2.

(Comparative Example 6)
Commercially available yttrium oxide powder, magnesium oxide powder and silica powder were blended in the same mass ratio as in Example 1 to obtain a mixed powder. This mixed powder was blended with the silicon nitride powder and additives used in Example 4 as a sintering aid powder without being pulverized in a bead mill type pulverizer. These were mixed using a ball mill to prepare a raw material slurry. A silicon nitride sintered body was obtained in the same manner as in Example 4, except that this raw material slurry was used. The particle size distribution of the mixed powder (sintering aid powder) before being put into the ball mill was measured using the particle size distribution measuring device used in Example 1. From the measurement results of this particle size distribution, D50 (median size) and D100 (maximum particle size) were obtained. As a result, D50 was 3.171 μm and D100 was 497.7 μm. In addition, the particle size distribution of the sintering aid powder used in Comparative Example 6 had two peaks as in FIG. 12. The presence of two peaks is due to the presence of particle aggregates in the sintering aid powder.

[Evaluation of silicon nitride sintered body]
<Density measurement>
The density of the plate-shaped silicon nitride sintered body obtained in each Example and Comparative Example was measured. Specifically, five silicon nitride sintered bodies obtained in each Example and Comparative Example were randomly selected, and the density was measured by Archimedes' method. The results were as shown in Table 3. As shown in Table 3, the density of the silicon nitride sintered bodies in each Example and Comparative Example was the same. From this, it is considered difficult to estimate the average number of coarse pores and micropores based on the density.

<Measurement of coarse pores>
The silicon nitride sintered body obtained in each Example and Comparative Example was cut along the thickness direction, and each cut surface was polished. The cut surface was observed at 200 times magnification using a scanning electron microscope (SEM). In each cut surface as shown in Figures 6 and 13, 24 fields of view (area per field: 0.74 ^mm2 ) were observed to measure the size and total number of coarse pores. As described above, a line segment connecting two points selected so that the interval between them is the largest on the outer edge of one pore and has a length of 10 μm or more was defined as a coarse pore. Based on these measurement results, the average number _P1 of coarse pores was determined. The results are shown in Table 4.

<Measurement of Micropores>
Each cut surface of the silicon nitride plate was observed at a magnification of 1000 times. The size and number of micropores contained in the SEM photographs shown in Figures 7 and 14 were measured using image processing software (ImageJ). As in the measurement of coarse pores, the size and total number of micropores were measured in 24 fields of view (area per field: 0.02 mm ² ) in each cut surface. As described above, a line segment connecting two points selected so that the distance between them is the largest on the outer edge of one pore was defined as a micropore having a length of 0.05 μm or more and less than 10 μm. Based on the measurement results, the average number P ₂ of micropores, the maximum value, average value, minimum value and standard deviation of the size of the micropores (the line segment) were obtained. The results were as shown in Table 5.

<Measurement of Silicon Nitride Particles>
Among the silicon nitride particles contained in SEM photographs (1000x) of the cross sections (area per field of view: 0.02 ^mm2 ) of each Example and Comparative Example, the number of silicon nitride particles whose length of the line segment (major axis) connecting two points selected so that the distance between them is the greatest on their outer edges was 20 μm or more was counted. The results are shown in the "Number of particles" column in Table 5.

As shown in Table 5, there was no significant difference in the average size of the micropores between each Example and Comparative Example 6. On the other hand, the variation in the size of the micropores was smaller in each Example than in Comparative Example 6. It was also confirmed that the grain growth of the silicon nitride particles had progressed more sufficiently in each Example than in the Comparative Example. All of the silicon nitride particles in the silicon nitride plates of each Example, in which the length of the line segment was 20 μm or more, had an aspect ratio of 4 or more. The "number of particles" in Table 5 is the result of measurement in one visual field, but when a similar measurement was performed in 10 visual fields, the number of silicon nitride particles in each visual field with a major axis length of 20 μm or more was 15 or more in all cases in Examples 4 to 6.

<Measurement of bending strength (before heat cycle test)>
The three-point bending flexural strength of the silicon nitride plates of each Example and Comparative Example 6 was measured. The measurement was performed in accordance with JIS R 1601:2008 using a commercially available flexural strength meter (manufactured by Shimadzu Corporation, device name: AG-2000). For each Example and Comparative Example 6, 20 measurement samples were prepared and measured (N=20). The average, maximum and minimum values of the measured values were as shown in Table 6.

As shown in Table 6, the silicon nitride sintered bodies of each Example had higher flexural strength than Comparative Example 6.

<Measurement of bending strength (after heat cycle test)>
A brazing filler metal was prepared containing 89.5 parts by mass of Ag powder (manufactured by Fukuda Metal Foil & Powder Co., Ltd., product name: Ag-HWQ, average particle diameter D50: 2.5 μm, specific surface area: 0.4 ^m2 /g), 9.5 parts by mass of Cu powder (manufactured by Fukuda Metal Foil & Powder Co., Ltd., product name: Cu-HWQ, average particle diameter D50: 3.0 μm, specific surface area: 0.4 m2/g), and 1.0 part by mass of Sn powder (manufactured by Fukuda Metal Foil & Powder Co., Ltd.: Sn-HPN, average particle diameter D50: ³ μm, specific surface area: 0.1 m2/g) for a total of 100 parts by mass, and 3.5 parts by mass of titanium hydride powder (manufactured by Toho Tech Co., Ltd., product name: TCH-100). This brazing filler metal was applied by screen printing to both main surfaces of Examples 4, 5, and 6 and Comparative Example 6 to a coating amount of 8 mg/ ^cm2 .

A copper plate for forming a circuit was placed on the brazing material layer on one main surface of a plate-shaped silicon nitride sintered body (silicon nitride plate), and a copper plate for forming a heat sink (C1020 oxygen-free copper plate with a thickness of 0.8 mm and a purity of 99.60% by mass) was placed on the brazing material layer on the other main surface to obtain a laminate. This laminate was heated under conditions of 830° C. and 30 minutes in a vacuum of 1.0×10 ⁻³ Pa or less to obtain a bonded body. An etching resist was printed on the bonded copper plate for forming a circuit, and the copper plate for forming a circuit was etched with a ferric chloride solution to form a circuit pattern. Furthermore, an excess brazing material layer was removed with an ammonium fluoride/hydrogen peroxide solution. In this way, a circuit board was produced.

The fabricated circuit board was subjected to a heat cycle test in which 2,500 cycles were repeated, with one cycle consisting of 15 minutes at -55°C, 15 minutes at 25°C, 15 minutes at 175°C, and 15 minutes at 25°C. After the heat cycle test, the circuit pattern and the copper plate used to form the heat sink were removed by etching using a ferric chloride solution and an ammonium fluoride/hydrogen peroxide solution to obtain a silicon nitride plate. The three-point bending strength of the silicon nitride plate thus obtained was measured. The measurement method and number of measurement samples were the same as those used before the heat cycle test. The average, maximum, and minimum measured values were as shown in Table 7.

Even after the heat cycle test, the silicon nitride plates of Examples 4 to 6 had higher flexural strength than the silicon nitride plate of Comparative Example 6. Comparing the values in Tables 6 and 7, the degree of decrease in flexural strength due to the heat cycle test was smaller in Examples 4 to 6 than in Comparative Example 6. This shows that the silicon nitride plates of Examples 4 to 6 have excellent heat cycle resistance. The reason for this is thought to be that the number of coarse pores and micropores is smaller in Examples 4 to 6 than in Comparative Example 6, which suppresses the occurrence and progression of cracks due to internal stresses caused by thermal expansion and contraction.

<Evaluation of high temperature insulation>
Circuit boards were produced using the silicon nitride sintered bodies of Examples 4 to 6 and Comparative Example 6 in the same procedure as that for measuring the flexural strength. Using an inspection device as shown in FIG. 8, a voltage resistance test was performed on each circuit board in accordance with JIS C2110-1:2010 (N=3). For this test, an AC 20 kV voltage resistance tester (model: 7473) manufactured by Keisoku Gijutsu Kenkyusho Co., Ltd. was used. Perfluorocarbon (manufactured by 3M Japan Ltd., product name: Fluorinert, model number: FC-3283) was used as the insulating oil. An inspection tool manufactured by Onishi Electronics Co., Ltd. was used as the reservoir 77, the electrode 70, the conductive support parts 72a, 72b, and the insulating support part 74. The electrode 70 was made of oxygen-free copper, and the conductive support parts 72a, 72b were made of carbon tool steel (SK material) plated with rhodium.

The insulating oil in the testing device was heated to 120°C, and the circuit board was placed in the insulating oil. The voltage was increased to 9 kV at a rate of 0.1 kV/sec and held there for 60 seconds. Thereafter, the voltage was increased at a rate of 0.1 kV/sec. In this manner, the voltage was increased up to 15 kV by repeatedly holding at 1 kV for 60 seconds and increasing at 0.1 kV/sec. Before reaching 15 kV, if a current flowed that was equal to or greater than the threshold for the current interruption current amount, it was judged to be insulation breakdown. The threshold was set to 9.99 mA. The results are shown in Table 8.

In Example 4, no insulation breakdown occurred even when the voltage reached 15 kV. This confirmed that the circuit board of Example 4 has the best insulation reliability at high temperatures. It was also confirmed that the circuit boards of Examples 5 and 6 have better insulation reliability at high temperatures than the circuit board of Comparative Example 6.

The present disclosure provides a ceramic sintered body that has excellent heat cycle resistance and excellent insulation reliability at high temperatures, a method for producing the same, and a bonded body. The present disclosure provides a power module that has excellent reliability by including such a ceramic sintered body.

10A, 10B...Main surface, 10C, 110C...Cross section, 10...Ceramic plate, 12, 14, 112...Ceramic particles, 20, 22, 122...Pores, 32...Sintering aid powder, 32a, 132a...Sintering aid phase, 41, 41a, 42...Metal plate, 50...Voltage resistance tester, 51, 52...Brazing layer, 60...AC power source, 70...Electrode, 72a, 72b...Conductive support portion, 74...Insulating support portion, 76...Insulating oil, 77...Storage tank, 80...Semiconductor element, 81, 82, 85...Solder, 83...Electrode, 84...Metal wire, 86...Housing, 90...Base plate, 92...Cooling fin, 93...Screw, 94...Grease, 95...Resin, 100...Joint, 132...Aggregate, 200...Power module, 400...Inspection device.

Claims (9)

1. A ceramic sintered body comprising ceramic particles,
   In a cross section, the average number of coarse pores having a size of 10 μm or more is less than 1 pore/ ^mm2 , and the average number of micropores having a size of 0.05 μm or more and less than 10 μm is less than 400 pores/ ^mm2 ;
   A ceramic sintered body having a flexural strength of 640 MPa or more.
2. The ceramic sintered body according to claim 1, wherein the maximum pore size in the cross section is 6 μm or less.
3. The ceramic sintered body according to claim 1, wherein the average size of the micropores is 1.0 μm or less and the standard deviation is 0.6 μm or less.
4. A step of pulverizing the sintering aid raw material with a pulverizer to obtain a sintering aid powder having a median diameter of 0.5 to 1.0 μm;
   preparing a mixed raw material containing a ceramic powder and the sintering aid powder;
   and firing the compact of the mixed raw material to obtain a ceramic sintered body having a flexural strength of 640 MPa or more.
5. 5. The method for producing a ceramic sintered body according to claim 4, wherein in a cross section of the ceramic sintered body, the average number of coarse pores having a size of 10 μm or more is less than 1 pore/ ^mm2 , and the average number of micropores having a size of less than 10 μm is less than 400 pores/ ^mm2 .
6. A joint comprising the plate-shaped ceramic sintered body according to any one of claims 1 to 3, a metal plate, and a brazing layer that joins a main surface of the ceramic sintered body to a main surface of the metal plate.
7. The joint body according to claim 6, wherein the thickness of the metal plate is 0.8 mm or less.
8. the braze layer includes silver, copper, tin, and an active metal;
   7. The joined body according to claim 6, wherein the active metal comprises one or more metals selected from the group consisting of titanium, hafnium, zirconium, and niobium.
9. A joint body including the plate-shaped ceramic sintered body according to any one of claims 1 to 3, a metal plate, and a brazing material layer joining a main surface of the ceramic sintered body and a main surface of the metal plate;
   a semiconductor element electrically connected to the metal plate of the joint body.
   
   

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