Ceramic sintered body, method for producing same, bonded body, and power supply module

Abstract

Provided is a ceramic sintered body which contains ceramic particles, has an average number of coarse pores having a size of 10 [mu] m or more of less than 1 / mm2 in a cross section thereof, has an average number of fine pores having a size of 0.05 [mu] m or more and less than 10 [mu] m of less than 400 / mm2, and has a flexural strength of 640 MPa or more.

Description

Technical Field

[0001] The present invention relates to a ceramic sintered body, a method for manufacturing the same, a joined body, and a power module. Background Art

[0002] In recent years, power modules for high-power control have been used in industrial equipment such as engines and products such as electric vehicles. In such a power module, a circuit board having a ceramic plate is used in order to effectively dissipate heat generated by a semiconductor element and suppress leakage current (for example, refer to Patent Document 1). The ceramic sintered body used in such a ceramic plate is usually manufactured by molding a ceramic raw material powder into a predetermined shape to form a ceramic green body and then firing the ceramic green body.

[0003] As the ceramic sintered body, those composed of nitrides, carbides, borides, silicides, etc. are known. When manufacturing such a ceramic sintered body, a sintering aid is used in order to promote sintering. For example, Patent Document 2 proposes using Si powder, MgO powder, and Y2O3 powder when manufacturing a silicon nitride sintered substrate.

[0004] Prior Art

[0005] Patent Document 1: International Publication No. 2019 / 022133

[0006] Patent Document 2: International Publication No. 2017 / 170247 Summary of the Invention

[0007] Electronic components such as power modules are achieving high performance, miniaturization, and thinning. Along with this, it is considered that the level of reliability requirements for various products used in electronic components is also increasing day by day. The present invention provides a ceramic sintered body having excellent heat cycle resistance and excellent insulation reliability at high temperatures, a method for manufacturing the same, and a joined body. The present invention provides a power module having excellent reliability due to including such a ceramic sintered body.

[0008] One embodiment of the present invention provides the following ceramic sintered body.

[0009] [1] A ceramic sintered body including ceramic particles, in a cross section thereof, the average number of coarse pores having a size of 10 μm or more is less than 1 per mm 2 , the average number of fine pores having a size of less than 10 μm is less than 400 per mm 2 , and its flexural strength is 640 MPa or more.

[0010] The above-mentioned ceramic sintered body has a sufficiently small number of both large pores and small pores in its cross-section and has a high flexural strength. When such a ceramic sintered body is joined to a material of a different type such as a metal plate, internal stress is generated during temperature changes, which can cause dielectric breakdown. The above-mentioned ceramic sintered body not only has a high flexural strength but also sufficiently reduces the number of large pores and small pores. Therefore, when internal stress is generated due to temperature changes, the generation and development of cracks can be sufficiently suppressed. Therefore, it has excellent heat cycle resistance and excellent insulation reliability at high temperatures.

[0011] The ceramic sintered body of [1] above may also be the following [2] or [3].

[0012] [2] The ceramic sintered body as described in [1], wherein the maximum value of the pore size in the above cross-section is 6 μm or less.

[0013] [3] The ceramic sintered body as described in [1] or [2], wherein the average value of the size of the above small pores is 1.0 μm or less and the standard deviation is 0.6 μm or less.

[0014] In the ceramic sintered body of [2] above, since the maximum value of the pore size is 6 μm or less, cracks generated due to temperature changes can be sufficiently suppressed. Therefore, the insulation reliability is more excellent. The ceramic sintered body of [3] above can sufficiently improve the durability in a thermal cycle environment.

[0015] One embodiment of the present invention provides a method for manufacturing the following ceramic sintered body.

[0016] [4] A method for manufacturing a ceramic sintered body, which includes:

[0017] A step of pulverizing a sintering aid raw material with a pulverizer to obtain a sintering aid powder having a median particle size of 0.5 to 1.0 μm; and

[0018] A step of preparing a mixed raw material containing ceramic powder and the above sintering aid powder; and

[0019] A step of firing the molded body of the above mixed raw material to obtain a ceramic sintered body having a flexural strength of 640 MPa or more.

[0020] The above manufacturing method includes a step of pulverizing a sintering aid raw material with a pulverizer to obtain a sintering aid powder having a median particle size of 0.5 to 1.0 μm. Such a sintering aid powder has a sufficiently small particle size and can sufficiently suppress aggregation. 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 with sufficiently reduced pores and high flexural strength can be obtained. When such a ceramic sintered body generates internal stress with temperature change, the generation and development of cracks can be sufficiently suppressed. Therefore, it has excellent heat cycle resistance and excellent insulation reliability at high temperatures.

[0021] The manufacturing method of the ceramic sintered body in the above [4] may also be the following [5].

[0022] [5] In the cross-section of the above ceramic sintered body, the average number of coarse pores with a size of 10 μm or more may be less than 1 / mm 2 , and the average number of fine pores with a size less than 10 μm may be less than 400 / mm 2 . Such a ceramic sintered body has more excellent insulation reliability.

[0023] One embodiment of the present invention provides the following joined body.

[0024] [6] A joined body, which includes the plate-shaped ceramic sintered body described in any one of the above [1] to [3], a metal plate, and a brazing material layer that joins the main surface of the ceramic sintered body and the main surface of the metal plate.

[0025] The above joined body includes the above ceramic sintered body. When this ceramic sintered body generates internal stress with temperature change, the generation and development of cracks can be sufficiently suppressed. Therefore, the above joined body has excellent heat cycle resistance and excellent insulation reliability at high temperatures.

[0026] The joined body in the above [6] may also be the following [7] or [8].

[0027] [7] The joined body as described in [6], wherein the thickness of the above metal plate is 0.8 mm or less.

[0028] [8] The joined body as described in [6] or [7], wherein the above 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.

[0029] One embodiment of the present invention provides the following power module.

[0030] [9] A power module, which includes:

[0031] A joined body, which has the plate-shaped ceramic sintered body described in any one of [1] to [3] above, a metal plate, and a brazing material layer that joins the main surface of the ceramic sintered body and the main surface of the metal plate; and

[0032] A semiconductor element, which is electrically connected to the metal plate of the joined body.

[0033] The power supply module includes the ceramic sintered body, which serves as an insulator of the joined body through which heat generated by the semiconductor element is conducted. The ceramic sintered body has excellent heat cycle resistance and excellent insulation reliability at high temperatures. Therefore, the power supply module has excellent reliability.

[0034] The present invention can provide a ceramic sintered body having excellent heat cycle resistance and excellent insulation reliability at high temperatures, a manufacturing method thereof, and a joined body. By including such a ceramic sintered body, the present invention can provide a power supply module having excellent reliability. Description of the Drawings

[0035] Figure 1 It is an enlarged cross-sectional view schematically showing a part of the cross-section of the ceramic sintered body.

[0036] Figure 2 It is a cross-sectional view along the thickness direction of the joined body.

[0037] Figure 3 It is a cross-sectional view of the power supply module.

[0038] Figure 4 It is a diagram showing an example of the volume-based particle size distribution of the sintering aid powder obtained by the laser diffraction scattering method.

[0039] Figure 5 It is a diagram showing an example of an image of grain growth during sintering in an example of the manufacturing method.

[0040] Figure 6 It is a photograph (200 times) showing an example of the cross-section obtained by a scanning electron microscope.

[0041] Figure 7 It is a photograph (1000 times) showing an example of the cross-section obtained by a scanning electron microscope.

[0042] Figure 8 It is a diagram schematically showing an example of an inspection device for checking dielectric breakdown.

[0043] Figure 9 It is a diagram showing an image of grain growth during sintering in a conventional manufacturing method.

[0044] Figure 10It is a photograph showing a cross-section (200 times magnification) of a conventional formed body (green ceramic sheet) obtained by a scanning electron microscope, and an aggregate of sintering aid powder contained in the cross-section.

[0045] Figure 11 It is a photograph (200 times magnification) showing a cross-section of a conventional ceramic sintered body obtained by a scanning electron microscope.

[0046] Figure 12 It is a graph showing an example of the particle size distribution of a conventional sintering aid powder obtained by the laser diffraction scattering method.

[0047] Figure 13 It is a photograph (200 times magnification) showing an example of a conventional cross-section obtained by a scanning electron microscope.

[0048] Figure 14 It is a photograph (1000 times magnification) showing an example of a conventional cross-section obtained by a scanning electron microscope. Detailed Embodiments

[0049] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings as appropriate. However, the following embodiments are illustrative of the present invention, and the gist thereof is not to limit the present invention to the following content. In addition, the numerical range indicated by the symbol "~" includes the lower limit value and the upper limit value. That is, the numerical range indicated by "A~B" means A or more and B or less. A numerical range formed by combining a numerical range having only an upper limit value and a numerical range having only a lower limit value is also included in the present invention. The upper limit or the lower limit of each numerical range can be replaced with the numerical value of any one of the embodiments, and it is also included in the present invention. When illustrating a plurality of materials, any one of them can be used alone, or a plurality of them can be used in combination.

[0050] A ceramic sintered body according to one embodiment contains ceramic particles. The ceramic sintered body may also contain pores. The number and size of the pores contained in the ceramic sintered body affect the heat cycle resistance and insulation reliability at high temperatures of the ceramic sintered body. The pores include large pores and fine pores. The sizes of the large pores and the fine pores are different from each other, and the size of the pores is measured by the following method.

[0051] Figure 1 It is a graph schematically showing an example of an image when observing a part of the cross-section of a ceramic sintered body with a scanning electron microscope. Figure 1 The cross-section 10C of the shown ceramic sintered body contains ceramic particles and pores 20. Figure 1 In, the pores 20 are schematically magnified and shown. In addition, although the cross-section 10C contains a large number of ceramic particles, Figure 1 the display of the ceramic particles is omitted for convenience in.

[0052] In the present invention, the size of the air hole 20 is the length of the line segment L formed by connecting two points selected in such a way that the interval at the outer edge of the air hole 20 is maximized. Then, according to the length of this line segment L, it is classified into "coarse air holes", "tiny air holes", and other air holes. If Figure 1 the length of the line segment L of the air hole 20 shown is 0.05 μm or more and less than 10 μm, it is classified as a "tiny air hole". On the other hand, an air hole with the length of the line segment L measured in the same way being 10 μm or more is classified as a "coarse air hole". The length of the line segment L of other air holes is less than 0.05 μm.

[0053] The flexural strength of the ceramic sintered body varies significantly according to the average number of coarse air holes and the average number of tiny air holes. The average number P1 of coarse air holes in the ceramic sintered body of the present embodiment is less than 1 per mm 2 . The average number P1 of coarse air holes is obtained by observing the cross-section (magnification: 200 times) obtained by a scanning electron microscope in 5 or more fields of view, and according to the total number obtained by adding up the coarse air holes contained in each field of view, using the following formula.

[0054] Average number P1 of coarse air holes = Total number of coarse air holes / Number of fields of view / Area per field of view

[0055] From the viewpoint of sufficiently improving the heat cycle resistance and insulation reliability at high temperatures of the ceramic sintered body, the average number P1 of coarse air holes can also be less than 0.8 per mm 2 , can also be less than 0.6 per mm 2 , can also be less than 0.5 per mm 2 , can also be less than 0.1 per mm 2 . The lower limit value of the average number P1 of coarse air holes can also be 0 per mm 2 . The average number P1 of coarse air holes can be adjusted, for example, by changing the particle size or degree of aggregation of the sintering aid powder.

[0056] The average number P2 of tiny air holes in the ceramic sintered body of the present embodiment is less than 400 per mm 2 . The average number P2 of tiny air holes is obtained by observing the cross-section (magnification: 1000 times) obtained by a scanning electron microscope in 5 or more fields of view, and according to the total number obtained by adding up the tiny air holes contained in each field of view, using the following formula. In addition, the size and number of tiny air holes can be calculated using image processing software such as ImageJ.

[0057] Average number P2 of tiny air holes = Total number of tiny air holes / Number of fields of view / Area per field of view

[0058] From the viewpoint of sufficiently improving the thermal cycle resistance and insulation reliability at high temperatures of the ceramic sintered body, the average number P2 of minute pores can be less than 350 pores / mm 2 , can be less than 320 pores / mm 2 , can be less than 290 pores / mm 2 , can also be less than 210 pores / mm 2 . The average number P2 of minute pores can also be 10 pores / mm 2 or more, can also be 50 pores / mm 2 or more, can also be 100 pores / mm 2 or more. The average number P2 of minute pores can be adjusted, for example, by changing the particle diameter or degree of aggregation of the sintering aid powder.

[0059] The average number P1 of large pores can be 0 pores / mm 2 , the maximum value of the size of the pores contained in the cross-section of the ceramic sintered body can be 6 μm or less, can be 5 μm or less, or can also be 3 μm or less. Thereby, the flexural strength of the ceramic sintered body can be further improved. The maximum value of the size of the pores contained in the cross-section of the ceramic sintered body can be 0.5 μm or more, can be 1.0 μm or more, or can also be 1.2 μm or more. The maximum value of the pore size is obtained from the measured values of the sizes of all the pores detected when observing the cross-section (magnification: 200 times) obtained by a scanning electron microscope in 5 or more fields of view.

[0060] From the viewpoint of being able to further enhance the thermal cycle resistance and insulation reliability at high temperatures, the average value of the sizes of the minute pores contained in the cross-section of the ceramic sintered body is 1.0 μm or less, and the standard deviation of this size can be 0.6 μm or less. In several examples, the average value of the sizes of the minute pores contained in the cross-section of the ceramic sintered body can be 0.7 μm or less, and the standard deviation of this size can be 0.5 μm or less. In several other examples, the average value of the sizes of the minute pores contained in the cross-section of the ceramic sintered body can be 0.6 μm or less, and the standard deviation of this size can be 0.47 μm or less. The average value of the sizes of the minute pores contained in the cross-section of the ceramic sintered body can be 0.1 μm or more. The average value of the pore sizes is obtained by the same method as when obtaining the above-mentioned average number P2. That is, it is the arithmetic mean of the sizes of the minute pores contained in 5 or more fields of view. The standard deviation of the pore sizes is also obtained based on the standard deviation of the sizes of the minute pores contained in 5 or more fields of view.

[0061] In cross-section 10C, in addition to pores 20 and ceramic particles, a sintering aid phase may also be included. The average value of the area ratio of the ceramic particles (ceramic phase) in cross-section 10C may be 70 to 90%, or may be 75 to 85%. The average value of the area ratio of the sintering aid phase in cross-section 10C may be 10 to 25%, or may be 14 to 22%. The ceramic sintered body having cross-section 10C containing ceramic particles and a sintering aid phase in such area ratios has a sufficiently high thermal conductivity and flexural strength.

[0062] Preferably, the number of ceramic particles having a major axis of 20 μm or more included in the cross-section of the ceramic sintered body is large. Thus, flexural strength and thermal conductivity can be both achieved at a high level. The measurement of the number of ceramic particles having a major axis length of 20 μm or more is performed using an image (field area: 0.02 mm 2 ) displayed by a scanning electron microscope magnified 1000 times. The major axis length of the ceramic particles can be measured in the same manner as the size of the pores 20. That is, the major axis length of the ceramic particles is the length of the line segment (major axis) connecting two points selected at the maximum interval on the outer edge of the ceramic particles.

[0063] The measurement is carried out in 5 or more fields of view, and the average value of the number of ceramic particles having a major axis length of 20 μm or more in each field of view is taken as the average number. The average number of ceramic particles having a major axis of 20 μm or more can be 10 or more, can be 15 or more, or can be 17 or more. The average number of ceramic particles having a major axis of 20 μm or more can be 50 or less, can be 45 or less, or can be 40 or less. The standard deviation of the number of ceramic particles having a major axis of 20 μm or more can be less than 0.6 μm, or can be less than 0.5 μm. The standard deviation of the number of ceramic particles having a major axis of 20 μm or more can be 0.1 μm or more, or can be 0.15 μm or more. Such a ceramic sintered body has a fine structure with high uniformity. Therefore, its reliability is excellent.

[0064] The aspect ratio of the ceramic particles having a major axis (size) of 20 μm or more can be 3 or more, or can be 4 or more. The number of ceramic particles having such a shape and size can be increased by facilitating grain growth during sintering. The aspect ratio is the ratio of the major axis length to the minor axis length. The minor axis is the line segment connecting two points selected at the maximum interval on the outer edge of the ceramic particles in a direction orthogonal to the major axis.

[0065] The ceramic particles constituting the ceramic sintered body may also contain at least one selected from the group consisting of silicon nitride particles, aluminum nitride particles, and alumina particles.

[0066] Examples of the ceramic sintered body include: a silicon nitride sintered body containing silicon nitride particles as a main component, an aluminum nitride sintered body containing aluminum nitride particles as a main component, and an alumina sintered body containing alumina particles as a main component. Additionally, it may also be a composite sintered body containing multiple ceramic particles.

[0067] 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. The ceramic sintered body with such a high flexural strength has high insulation. In addition to having such a flexural strength, the average number of large pores and small pores is sufficiently small, so its heat cycle resistance is excellent and its insulation reliability at high temperatures is excellent. Such a ceramic sintered body is, for example, suitable for use 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. Additionally, the use of the ceramic sintered body is not limited to this.

[0068] A 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 the main surface of the ceramic sintered body to the main surface of the metal plate. The ceramic plate may be the ceramic sintered body of the above embodiment. When internal stress is generated due to temperature change in this ceramic sintered body, the generation and development of cracks can be sufficiently suppressed. Therefore, the heat cycle resistance of the above bonded body is excellent, and its insulation reliability at high temperatures is also excellent.

[0069] Figure 2 It shows an example of the bonded body of the present embodiment, which is a cross-sectional view along the thickness direction. However, the description content of this example is not limited to this example and also applies to other examples of the bonded body. Figure 2 The bonded body 100 includes a ceramic plate 10, a metal plate 41 bonded to one main surface 10A of the ceramic plate 10 through a brazing material layer 51, and a metal plate 42 bonded to the other main surface 10B of the ceramic plate 10 through a brazing material layer 52. A pattern is formed on the metal plate 41, which, for example, functions as a circuit. In this specification, such a metal plate with a pattern formed on it is also referred to as a metal plate. No pattern is formed on the metal plate 42, which, for example, functions as a heat sink. The ceramic plate 10 is composed of the above ceramic sintered body.

[0070] The metal plates 41 and 42 may be, for example, copper plates. From the viewpoints of improving heat dissipation performance and electrical conductivity, the thickness of the metal plates 41 and 42 may be 0.3 mm or more, and may also be 0.4 mm or more. From the viewpoint of reducing the internal stress generated in the ceramic plate 10 due to temperature change, the thickness of the metal plates 41 and 42 may be 0.8 mm or less, and may also be 0.7 mm or less. An example of the thickness range of the metal plates 41 and 42 is 0.3 - 0.8 mm.

[0071] The thickness of the ceramic plate 10 can be 0.2 mm or more, or can be 0.3 mm or more, from the viewpoint of improving insulation. The thickness of the ceramic plate 10 can be 0.8 mm or less, or can be 0.6 mm or less, from the viewpoint of thinning the joined body 100.

[0072] The brazing material layers 51 and 52 are layers that join the ceramic plate 10 to the metal plates 41 and 42, and contain a brazing material component. The brazing material layer may contain, for example, silver derived from the brazing material, or silver and copper. The brazing material layers 51 and 52 may further contain tin derived from the brazing material and one or more metals selected from the group consisting of reactive metals. In the brazing material layers 51 and 52, two or more metals may form an alloy. The reactive metal may also contain one or more selected from the group consisting of titanium, hafnium, zirconium, and niobium. The silver and copper contained in the brazing material layers 51 and 52 may be contained therein, for example, as an alloy such as an Ag-Cu eutectic alloy. The silver content in the brazing material layers 51 and 52, in terms of Ag conversion, can be 45 to 95 mass%, or can be 50 to 95 mass%. The total content of silver and copper in the brazing material layers 51 and 52, converted to Ag and Cu respectively, can be 65 to 100 mass%, can be 70 to 99 mass%, or can be 90 to 98 mass%. The thickness and composition of the brazing material layers 51 and 52 may be the same as each other or may be different from each other.

[0073] In a modified example of the joined body, each metal plate joined to the two main surfaces of the ceramic plate may have the same shape. For example, it may be a joined body before forming a circuit pattern. In another modified example, there may be a plurality of metal plates joined to one main surface of the ceramic plate. There may be metal plates joined only on one main surface of the ceramic plate.

[0074] A power module according to one embodiment includes a joined body (circuit board) and a semiconductor element electrically connected to the metal plate of the joined body. The joined body may also be the above-mentioned joined body 100 or a modified example thereof. The description related to the ceramic sintered body, the joined body, and modified examples thereof is applicable to the power module of this embodiment. Such a power module includes a joined body having a ceramic plate with excellent thermal cycle resistance and excellent insulation reliability at high temperatures. Therefore, even when used in an environment with large temperature variations, high performance can be maintained. Thus, the above-mentioned power module has excellent reliability.

[0075] Figure 3 It 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 the power module. Figure 3The power supply module 200 includes a base plate 90 and a bonding body 100, which is bonded to one surface of the base plate 90 by solder 82. A metal plate 42 (heat sink) on one surface side of the bonding body 100 is bonded to the base plate 90 by solder 82.

[0076] On the other metal plate 41 (circuit pattern) on the other surface side of the bonding body 100, a semiconductor element 80 is mounted by solder 81. The semiconductor element 80 is connected to a specified position of the metal plate 41 by a metal wire 84 such as an aluminum wire (aluminum wire). In this way, the semiconductor element 80 is electrically connected to the metal plate 41. In order to electrically connect the outside of the housing 86 to the metal plate 41, a metal plate 41a of the metal plate 41 is connected to an electrode 83 provided through the housing 86 by solder 85.

[0077] A housing 86 is disposed on one main surface of the base plate 90 and is integrated with the main surface for housing the bonding body 100. A resin 95 is filled in the housing space formed by one main surface of the base plate 90 and the housing 86. The resin 95 seals the bonding body 100 and the semiconductor element 80. The resin may be, for example, a thermosetting resin or a photocuring resin.

[0078] On the other main surface of the base plate 90, a cooling fin 92 as a heat dissipation member is bonded by a grease 94. A screw 93 is installed at an end of the base plate 90 to fix the cooling fin 92 to the base plate 90. The base plate 90 and the cooling fin 92 may also be made of aluminum. The base plate 90 and the cooling fin 92 function well as a heat dissipation part because they have a high thermal conductivity.

[0079] The metal plate 41 and the metal plate 42 are electrically insulated by a ceramic plate 10 (plate-shaped ceramic sintered body). The metal plate 41 (41a) may constitute an electronic circuit. The metal plate 41 and the metal plate 42 are respectively bonded 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. Since the power supply module 200 includes the bonding body 100, the reliability is excellent.

[0080] A manufacturing method of a ceramic sintered body in one embodiment includes the following steps: a pulverizing step of pulverizing a sintering aid raw material with a pulverizer to obtain a sintering aid powder having a D50 (median particle size) of 0.5 to 1.0 μm; a mixing step of preparing a mixed raw material containing a ceramic powder and a sintering aid powder; and a firing step of firing a molded body of the mixed raw material.

[0081] 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, silicon dioxide, and alumina. The sintering aid powder may contain at least three selected from the group.

[0082] Alkaline earth metal oxides have alkaline earth metals and oxygen as constituent elements. The alkaline earth metal oxides may include at least one selected from the group consisting of magnesium oxide, calcium oxide, and strontium oxide. Rare earth oxides have rare earth elements and oxygen as constituent elements. The rare earth oxides may include, for example, at least one selected from the group consisting of yttrium oxide and cerium oxide. Transition metal oxides different from the rare earth oxides have transition metals different from rare earths and oxygen as constituent elements. Such transition metal oxides may include, for example, iron oxide.

[0083] An example of the sintering aid powder includes magnesium oxide, rare earth oxide, and silica. In this case, when the total amount of the sintering aid powder is set to 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. At this time, the content of magnesium oxide may be 5 to 40 parts by mass, or may be 10 to 30 parts by mass. At this time, the content of silica may be 5 to 40 parts by mass, or may be 10 to 30 parts by mass.

[0084] The D50 (median particle size) of the sintering aid powder in the pulverization process can be adjusted, for example, by pulverizing the sintering aid raw material using a pulverizer. As the pulverizer, a bead mill type pulverizer can be used. The particle size distribution of the sintering aid powder can be adjusted by changing at least one condition selected from the bead diameter, peripheral speed, and pulverization time of the bead mill type pulverizer. The bead diameter may be 0.1 to 0.3 mm. The peripheral speed of the rotor may also be 8 to 12 m / second. The pulverization time may be 5 to 20 minutes. Examples of pulverizers other than the bead mill type pulverizer include: ball mills, vibration mills, and pot mills.

[0085] When the D50 of the sintering aid powder exceeds 1.0 μm, the number and size of pores increase, resulting in a decrease in the flexural strength. When the D50 of the sintering aid powder is less than 0.5 μm, due to the relationship between the input energy applied by the pulverizer to the sintering aid raw material and the pulverization ratio, the pulverized particles tend to aggregate. The main reason is considered to be that as pulverization progresses, the frequency of contact between the pulverized particles increases, and the potential energy becomes a state where the gravitational force is stronger.

[0086] The D50 of the sintering aid powder is obtained based on the volume-based particle size distribution measured by a device for measuring the particle size distribution by laser diffraction scattering method. By making the D50 of the sintering aid powder within the above range, the particles contained in the sintering aid powder are small enough, and aggregation of the particles can be suppressed. Thus, when manufacturing a ceramic sintered body, the generation of pores due to the particles and aggregates of the sintering aid powder can be suppressed. In addition, the grain growth of ceramic particles can be carried out with a high degree of uniformity.

[0087] Figure 4 and Figure 12This is a diagram showing an example of the volume-based particle size distribution of a sintering aid powder obtained by the laser diffraction scattering method. The horizontal axis represents the particle size [μm] on a logarithmic scale, and the vertical axis represents the frequency [%]. The particle size distribution in the present invention is measured according to the method described in JIS Z8825:2013 "Particle Size Analysis - Laser Diffraction Scattering Method". The particle size distribution can be measured using LS-13 320 (trade name) manufactured by Beckman Coulter, Inc. As the measurement conditions, the refractive index of the particles is set to 2.2, and the refractive index of the solvent is set to 1.33.

[0088] As shown in the sintering aid powder Figure 4 The peak in the particle size distribution (frequency %) can be only one. Such a sintering aid powder can sufficiently suppress aggregation compared to Figure 12 the sintering aid powder having multiple peaks as shown. Therefore, the pore size and number in the ceramic sintered body can be sufficiently reduced. The peak in the particle size distribution can be sharp. For example, D100 of the sintering aid powder can be less than 5.5 μm, or can be less than 5 μm. For example, the ratio of D100 to D50 can also 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.

[0089] In the mixing process, the obtained sintering aid powder, ceramic powder, and additives compounded as required are mixed, for example, using a ball mill or the like. Thus, a mixed raw material containing the sintering aid powder and the ceramic powder is prepared. As additives, binders, plasticizers, dispersion media, and mold release agents can be cited. As binders, for example, methyl cellulose-based binders having a plasticizing or surface-active effect, and acrylate-based binders having excellent thermal decomposability can be cited. As plasticizers, for example, glycerol can be cited. As dispersion media, ion-exchanged water and ethanol can be cited.

[0090] As the ceramic powder, for example, silicon nitride powder, aluminum nitride powder, or alumina powder can be used. The D50 (median particle size) of the ceramic powder can be 0.1 to 6 μm, or can be 0.5 to 4 μm. Thereby, a sufficiently densified ceramic sintered body can 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 can be one.

[0091] The mixing ratio of the sintering aid powder based on the mass of the ceramic powder can be 0.03 to 0.12, or can be 0.05 to 0.1. Thereby, the ceramic sintered body becomes easily densified, and the flexural strength can be sufficiently improved.

[0092] The mixed raw materials obtained in the mixing process are coated on a release film with a specified thickness by a doctor blade method, a calendering method, an extrusion method, etc., and then dried and formed to obtain a formed body. The forming pressure can be 3 to 30 MPa. The formed body can also be produced by uniaxial pressing or by CIP. In addition, it can also be sintered while being formed by a hot pressing method. For example, after producing a green ceramic sheet substrate by the above methods such as the doctor blade method, a formed body can be obtained by stamping the green ceramic sheet substrate using a mold equipped with a die and a punch.

[0093] When stamping with a mold, the content of the solid component of the green ceramic sheet substrate can be 65 to 85% by mass, or can also be 75 to 85% by mass. Before stamping with a mold, a drying process of drying the green ceramic sheet substrate can also be performed to adjust the content of the solid component.

[0094] Before sintering the formed body in the sintering process, debinding of the formed body can also be performed. The debinding method is not particularly limited. For example, the formed body can be heated to 300 to 700 °C in air or a non-oxidizing environment such as nitrogen. The heating time can be, for example, 1 to 10 hours.

[0095] The ceramic sintered body can be obtained by sintering the formed body. The atmosphere, temperature, time, etc. during sintering can be appropriately set according to the type of the ceramic sintered body. In the case of manufacturing a silicon nitride sintered body as the ceramic sintered body, it can be carried out in an inert gas atmosphere such as nitrogen or argon. The pressure during sintering can be 0.7 to 1 MPa. The sintering temperature can be 1800 to 2100 °C, 1800 to 2000 °C, or 1800 to 1900 °C. The sintering time at this sintering temperature can be 3 to 20 hours, or can also be 4 to 16 hours.

[0096] When manufacturing an aluminum nitride sintered body as the ceramic sintered body, the sintering temperature can be, for example, 1760 to 1840 °C. The holding time in the temperature range of 1760 to 1840 °C can be, for example, 1 to 10 hours. The sintering can be carried out at atmospheric pressure. When manufacturing a ceramic sintered body other than a silicon nitride sintered body and an aluminum nitride sintered body (for example, an alumina sintered body), as long as the sintering conditions that can sufficiently densify the sintered body are appropriately set.

[0097] Figure 5 It is a figure showing an image of grain growth during sintering in an example of the manufacturing method of the present embodiment. In this example, as Figure 5 (a) shows, in the formed body, fine sintering aid powders 32 are highly uniformly dispersed in the ceramic particles 12. When such a formed body is sintered, as Figure 5 (b) shows, the liquefied sintering aid phase 32a diffuses to the grain boundaries due to capillary action. When the sintering aid phase 32a diffuses, the formed body (ceramic sintered body) gradually shrinks, as Figure 5As shown in (c), the air holes 22 disappear. When continuously heated, the ceramic particles 12 dissolve in the sintering aid phase 32a, generating Figure 5 the columnar ceramic particles 14 shown in (d). Thus, during liquid-phase sintering, as the grain growth of the ceramic particles proceeds smoothly and the air holes 22 disappear sufficiently, the air holes contained in the ceramic sintered body can be sufficiently reduced. A part of the sintering aid phase 32a may also remain in the ceramic sintered body.

[0098] Figure 9 is a diagram showing an image of grain growth during sintering in the conventional manufacturing method. In the conventional manufacturing method, as Figure 9 shown in (a), in the green compact, the agglomerates 132 of the sintering aid powder are contained in the ceramic particles 112. A cross-sectional photograph of such a conventional green compact is shown in Figure 10 . When such a green compact is fired, as Figure 9 shown in (b), the liquefied sintering aid phase 132a diffuses to the grain boundaries due to capillary action starting from the agglomerates 132. When the diffusion caused by capillary action continues, since the size of the agglomerates 132 is large, air holes 122 are generated in the part of the agglomerates 132. Because the air holes 122 have a large size, they will not disappear even if the green compact shrinks. As Figure 9 shown in (c), the air holes 122 will remain in the ceramic sintered body. Thus, the number of large-sized air holes contained in the ceramic sintered body increases. Figure 11 shows the cross-section 110C of the conventional ceramic sintered body obtained in this way. The cross-section 110C contains the air holes 122 derived from the agglomerates 132.

[0099] Compared with the conventional manufacturing method, 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. Therefore, the air holes remaining as traces of the sintering aid powder can be reduced. Thereby, the number of air holes generated during the sintering process can be reduced, and the size of the air holes can be reduced. The number of air holes in the ceramic sintered body obtained in this way is sufficiently reduced, and the size of the air holes is sufficiently small. In addition, this ceramic sintered body has a high flexural strength of 640 MPa or more. The flexural strength of the ceramic sintered body, as described above, can also be 670 MPa or more, 690 MPa or more, or 720 MPa or more. The average numbers P1 and P2 of the coarse air holes and the fine air holes contained in the ceramic sintered body are also as described above. Such a ceramic sintered body can sufficiently suppress the generation and development of cracks when internal stress is generated due to temperature change. Therefore, its thermal cycle resistance is excellent, and its insulation reliability at high temperatures is excellent.

[0100] Figure 8It is a diagram schematically showing an example of an inspection device for checking dielectric breakdown by measuring the leakage current of a bonded body (circuit board). The inspection device 400 includes an AC power supply 60 and a withstand voltage tester 50 connected to the AC power supply 60. One terminal of the withstand voltage tester 50 is electrically connected to the conductive support member 72a, and the conductive support member 72a contacts the metal plate 41 bonded to the ceramic plate 10. The other terminal of the withstand voltage tester 50 is electrically connected to the conductive support member 72b in contact with the metal plate 42 through the electrode 70 disposed in the storage tank 77 storing the insulating oil 76.

[0101] The electrode 70 is disposed along the bottom surface and one side surface of the storage tank 77. As shown in Figure 8 , when observed in a vertical cross-section, the electrode 70 has an L-shaped configuration. Two insulating support members 74 are provided on the electrode 70, which are adjacent to the conductive support member 72b. The two insulating support members 74 respectively contact the metal plate 42 and support the bonded body 100 in the insulating oil 76.

[0102] As the electrode 70 and the conductive support members 72a, 72b, for example, oxygen-free copper can be used. As the insulating oil 76, for example, a fluorine-based inert liquid can be used. As the withstand voltage tester 50, a commercially available product can be used. In such an inspection device 400, a voltage of about 10 to 15 kV is applied between the metal plates 41, 42 sandwiching the ceramic plate 10, and the withstand voltage tester 50 measures the presence or absence of leakage current. By heating the insulating oil 76, for example, the insulation performance of the ceramic plate 10 in the bonded body 100 at a high temperature of 100 °C or higher can be evaluated.

[0103] The inspection device is not limited to the Figure 8 configuration. For example, as long as it is an inspection device that can measure the leakage current when a voltage is applied between the metal plates 41, 42 at a temperature of 100 °C or higher, there is no particular limitation and any such device can be used.

[0104] The above describes the embodiments of the present invention, but the present invention is not limited by the above embodiments. The description related to the embodiments of the ceramic sintered body also applies to the bonded body, the power module, and the manufacturing method of the ceramic sintered body. The description related to the embodiments of the manufacturing method of the ceramic sintered body also applies to the ceramic sintered body.

[0105] The numerical ranges obtained by arbitrarily combining the upper limit values and the lower limit values of the numerical ranges specifically described in the above embodiments are also included in the present invention. In addition, those obtained by substituting the values of the examples described below for the upper limit value and / or the lower limit value of the numerical range are also included in the present invention.

[0106] Examples

[0107] The content of the present invention will be described in more detail with reference to the examples and comparative examples, but the present invention is not limited to the following specific examples.

[0108] [Preparation of Sintering Aid Powder]

[0109] (Comparative Examples 1-5, Examples 1-3)

[0110] Commercially available yttrium oxide powder, magnesium oxide powder, and silicon dioxide powder were prepared as raw materials for the sintering aid powder. These raw materials 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 (manufactured by Ashizawa Finetech Co., Ltd., device name: Star Mill LMZ) to obtain a sintering aid powder. According to the pulverization conditions (bead diameter, peripheral speed of the rotor, and pulverization time) shown in Table 1 and Table 2, a variety of sintering aid powders with different pulverization conditions were prepared.

[0111] An apparatus for measuring the particle size distribution by laser diffraction scattering method (manufactured by Nikkiso Co., Ltd., device name: Particle Size Distribution Analyzer MT3000II) was used to measure the volume-based particle size distribution of each sintering aid powder. Based on the measurement results of these particle size distributions, D50 (median particle size) and D100 (maximum particle size) were obtained. The results are shown in Table 1 and Table 2. The ratio of D100 to D50 is also shown in Table 1 and Table 2. The particle size distributions (frequency %) of Examples 1-3 are as Figure 4 shown, and all have only one peak.

[0112] Table 1

[0113]

[0114] Table 2

[0115]

[0116] From the results of Comparative Examples 1-3 in Table 1, it was confirmed that by reducing the bead diameter, D50 and D100 of the sintering aid could be made smaller. In addition, from the results of Comparative Examples 3, 4, and Example 1, it was confirmed that by increasing the peripheral speed of the rotor, D50 and / or D100 could be made smaller. From the results of Examples 1 and 2, it was confirmed that when the pulverization time was extended, D50 and D100 could be made smaller. On the other hand, from the results of Examples 2, 3, and Comparative Example 5, it was confirmed that when the pulverization time was extended excessively, D50 and D100 became larger. This is considered to be due to the aggregation of the pulverized powder.

[0117] [Fabrication of Silicon Nitride Plate]

[0118] (Example 4)

[0119] A commercially available silicon nitride powder (D50: 0.7 μm), the sintering aid powder of Example 2, and an additive (a solvent-based binder) were placed in a bead mill and mixed to prepare a raw material slurry. The mixing ratio of the silicon nitride powder to the sintering aid powder was silicon nitride powder: sintering aid powder = 91:9. Subsequently, the above-mentioned raw material slurry was coated on a release film by a doctor blade method to produce a green sheet. The produced ceramic green sheet was cut into a size of longitudinal × transverse = 250 mm × 180 mm, and 70 sheets were laminated 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 for debinding.

[0120] The debound compact was placed in a firing furnace, the pressure in the firing furnace was reduced to 100 Pa or less, and the temperature was raised to 900 °C. Thereafter, nitrogen was introduced into the firing furnace, and the temperature was raised to 1500 °C under a pressure of about 0.9 MPa and held for 4 hours. After holding, the temperature was raised to 1830 °C and held at 1830 °C for 5 hours. Thus, a silicon nitride plate with a thickness of 3 mm was obtained.

[0121] (Example 5)

[0122] The sintering aid powder of Example 1 was used instead of the sintering aid powder of Example 2, and otherwise, the same operations as in Example 4 were carried out to obtain a silicon nitride sintered body.

[0123] (Example 6)

[0124] The sintering aid powder of Example 3 was used instead of the sintering aid powder of Example 2, and otherwise, the same operations as in Example 4 were carried out to obtain a silicon nitride sintered body.

[0125] (Comparative Example 6)

[0126] A commercially available yttrium oxide powder, magnesium oxide powder, and silicon dioxide powder were mixed in the same mass ratio as in Example 1 to obtain a mixed powder. This mixed powder was not pulverized by a bead mill and was used as a sintering aid powder and mixed with the silicon nitride powder and additive used in Example 4. These were mixed using a ball mill to prepare a raw material slurry. Using this raw material slurry, otherwise, the same operations as in Example 4 were carried out to obtain a silicon nitride sintered body. Using the particle size distribution measuring device used in Example 1, the particle size distribution of the mixed powder (sintering aid powder) before being put into the ball mill was measured. From the measurement results of this particle size distribution, D50 (median particle 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 was the same as Figure 12 and had two peaks. The presence of these two peaks was due to the inclusion of aggregates of particles in the sintering aid powder.

[0127] [Evaluation of Silicon Nitride Sintered Body]

[0128] [Measurement of Density]

[0129] Measure the density of the plate-shaped silicon nitride sintered bodies obtained in each of the examples and comparative examples. Specifically, arbitrarily select 5 silicon nitride sintered bodies obtained in each of the examples and comparative examples, and measure the density by the Archimedes method. The results are shown in Table 3. As shown in Table 3, the densities of the silicon nitride sintered bodies in each of the examples and comparative examples are the same. Therefore, it is considered difficult to estimate the average number of large pores and fine pores based on the density.

[0130] Table 3

[0131]

[0132]

[0133] [Measurement of Large Pores]

[0134] Cut the silicon nitride sintered bodies obtained in each of the examples and comparative examples along the thickness direction, and grind each cut surface. Using a scanning electron microscope (SEM), observe the cut surface after magnifying it 200 times. In Figure 6 and Figure 13 In each of the cut surfaces shown, observe 24 fields of view (area of each field of view: 0.74 mm 2 ), and measure the size and total number of large pores. As described above, pores with a length of 10 μm or more of the line segment connecting two points selected at the maximum interval on the outer edge of a single pore are defined as large pores. Based on these measurement results, calculate the average number P1 of large pores. The results are shown in Table 4.

[0135] Table 4

[0136]

[0137] [Measurement of Fine Pores]

[0138] Magnify each cut surface of the above-mentioned silicon nitride plate 1000 times and observe it. Use image processing software (ImageJ) to measure Figure 7 and Figure 14 the size and number of fine pores included in the SEM images shown. Similar to the measurement of large pores, in each cut surface, in 24 fields of view (area of each field of view: 0.02 mm 2)The size and total number of the micropores are measured. As described above, the length of the line segment connecting two points selected in the outermost edge of a pore at the maximum interval is 0.05 μm or more and less than 10 μm, which is defined as a micropore. Based on the measurement results, the average number P2 of the micropores, the maximum value, average value, minimum value, and standard deviation of the size (the line segment) of the micropores are obtained. The results are shown in Table 5.

[0139] <Measurement of silicon nitride particles>

[0140] In the SEM images (1000 times magnification) of the cross-sections (area per field of view: 0.02 mm 2 ) of each of the examples and comparative examples, the number of silicon nitride particles in which the length of the line segment (major axis) connecting two points selected in the outermost edge at the maximum interval is 20 μm or more is calculated. The results are shown in the column of "Particle number" in Table 5.

[0141] Table 5

[0142]

[0143] As shown in Table 5, the average value of the size of the micropores does not vary significantly among each of the examples and Comparative Example 6. On the other hand, regarding the degree of non-uniformity of the size of the micropores, it is smaller in each of the examples than in Comparative Example 6. In addition, it is also confirmed that the grain growth of the silicon nitride particles in each of the examples proceeds more sufficiently than in the comparative examples. The silicon nitride particles in the silicon nitride plates of each of the examples, in which the length of the above-mentioned line segment is 20 μm or more, all have an aspect ratio of 4 or more. The "Particle number" in Table 5 is the measurement result in one field of view. The same measurement is performed in 10 fields of view. As a result, in Examples 4 to 6, the number of silicon nitride particles with a major axis length of 20 μm or more in each field of view is 15 or more.

[0144] <Measurement of flexural strength (before thermal cycle test)>

[0145] The flexural strength of three-point bending of the silicon nitride plates of each of the examples and Comparative Example 6 is measured. The measurement is carried out in accordance with JIS R1601:2008, using a commercially available flexural strength meter (manufactured by Shimadzu Corporation, device name: AG-2000). In each of the examples and Comparative Example 6, 20 measurement specimens are fabricated and measured respectively (N = 20). The average value, maximum value, and minimum value of the measured values are shown in Table 6.

[0146] Table 6

[0147]

[0148]

[0149] As shown in Table 6, the silicon nitride sintered bodies of the examples have higher flexural strength compared to Comparative Example 6.

[0150] <Measurement of Flexural Strength (After Thermal Cycling Test)>

[0151] Prepare a brazing material of a total of 100 parts by mass relative to 89.5 parts by mass of Ag powder (manufactured by Fukuda Metal Foil & Powder Co., Ltd., product name: Ag-HWQ, average particle size D50: 2.5 μm, specific surface area 0.4 m 2 / g), 9.5 parts by mass of Cu powder (manufactured by Fukuda Metal Foil & Powder Co., Ltd., product name: Cu-HWQ, average particle size D50: 3.0 μm, specific surface area: 0.4 m 2 / g), and 1.0 part by mass of Sn powder (manufactured by Fukuda Metal Foil & Powder Co., Ltd.: Sn-HPN, average particle size D50: 3 μm, specific surface area 0.1 m 2 / g), containing 3.5 parts by mass of titanium hydride powder (manufactured by TOHO TECHNICAL SERVICE Co., Ltd., product name: TCH-100). This brazing material was applied to both main surfaces of Examples 4, 5, 6 and Comparative Example 6 by screen printing so that the coating amount became 8 mg / cm 2 .

[0152] A copper plate for circuit formation was overlapped on the brazing material layer on one main surface of the plate-shaped silicon nitride sintered body (silicon nitride plate), and a copper plate for heat sink formation (both are C1020 oxygen-free copper plates with a thickness of 0.8 mm and a purity of 99.60% by mass) was overlapped on the brazing material layer on the other main surface to obtain a laminate. In a vacuum of 1.0×10 -3 Pa or less, the laminate was heated at 830 °C for 30 minutes to obtain a joined body. An etching resist was printed on the joined copper plate for circuit formation, and the copper plate for circuit formation was etched with a ferric chloride solution to form a circuit pattern. Then, the excess brazing material layer was removed with an ammonium fluoride / hydrogen peroxide solution. Thus, a circuit board was fabricated.

[0153] A thermal cycling test of repeating 2500 cycles was performed on the fabricated circuit board with -55 °C for 15 minutes, 25 °C for 15 minutes, 175 °C for 15 minutes, and 25 °C for 15 minutes as one cycle. After the thermal cycling test, etching was performed using a ferric chloride solution and an ammonium fluoride / hydrogen peroxide solution to remove the circuit pattern and the copper plate for heat sink formation, obtaining a silicon nitride plate. The three-point bending flexural strength of the obtained silicon nitride plate was measured. The measurement method and the number of measurement samples were the same as those before the thermal cycling test. The average value, maximum value, and minimum value of the measurement results are shown in Table 7.

[0154] Table 7

[0155]

[0156] Even after the thermal cycling test, the silicon nitride plates of Examples 4 to 6 had higher flexural strength than the silicon nitride plate of Comparative Example 6. By comparing the values in Table 6 and Table 7, it can be seen that, in terms of the degree of reduction in flexural strength caused by the thermal cycling test, the degree of reduction in Examples 4 to 6 was less than that in Comparative Example 6. This indicates that the silicon nitride plates of Examples 4 to 6 have excellent heat cycle resistance. The reason is considered to be that the number of large pores and fine pores in Examples 4 to 6 is less than that in Comparative Example 6, thus suppressing the generation and development of cracks caused by internal stress accompanying thermal expansion and thermal contraction.

[0157] <Evaluation of High-Temperature Insulation>

[0158] Using the same procedure as when measuring the flexural strength, circuit boards were fabricated using the silicon nitride sintered bodies of Examples 4 to 6 and Comparative Example 6. As shown in Figure 8 the inspection device was used to perform a withstand voltage inspection (N = 3) on each circuit board in accordance with JIS C2110-1:2010. This inspection was carried out using an AC 20 kV withstand voltage tester (model: 7473) manufactured by Measurement Technology Research Institute Co., Ltd. The insulating oil used was perfluorocarbon (manufactured by 3M Japan Ltd., trade name: Fluorinert, model: FC-3283). As the storage tank 77, electrodes 70, conductive support members 72a, 72b, and insulating support member 74, an inspection jig manufactured by Onishi Electronics Co., Ltd. was used. The electrode 70 was made of oxygen-free copper, and the conductive support members 72a, 72b were made of rhodium-plated carbon tool steel (SK material).

[0159] The insulating oil of the inspection device was heated to 120 °C, and the circuit board was placed in this insulating oil. The voltage was increased to 9 kV at a rate of 0.1 kV / second and maintained for 60 seconds. Then, the voltage was increased at a rate of 0.1 kV / second. In this way, repeating the process of maintaining for 60 seconds at each 1 kV and increasing the voltage at a rate of 0.1 kV / second, and increasing the voltage to 15 kV. The case where the current flowing until reaching 15 kV was above the threshold value of the current interruption current was determined as dielectric breakdown. The threshold value was 9.99 mA. The results are shown in Table 8.

[0160] Table 8

[0161]

[0162] In Example 4, dielectric breakdown did not occur even when the voltage reached 15 kV. Thus, it was confirmed that the circuit board of Example 4 had the most excellent insulation reliability at high temperatures. It was also confirmed that the circuit boards of Examples 5 and 6 had better insulation reliability at high temperatures than the circuit board of Comparative Example 6.

[0163] Industrial applicability

[0164] According to the present invention, there is provided a ceramic sintered body having excellent heat cycle resistance and excellent insulation reliability at high temperatures, a method for manufacturing the same, and a joined body. The present invention provides a power module having excellent reliability by including such a ceramic sintered body.

[0165] Symbol description

[0166] 10A, 10B: Main surface

[0167] 10C, 110C: Cross section

[0168] 10: Ceramic plate

[0169] 12, 14, 112: Ceramic particles

[0170] 20, 22, 122: Air holes

[0171] 32: Sintering aid powder

[0172] 32a, 132a: Sintering aid phase

[0173] 41, 41a, 42: Metal plate

[0174] 50: Dielectric strength tester

[0175] 51, 52: Brazing material layer

[0176] 60: AC power supply

[0177] 70: Electrode

[0178] 72a, 72b: Conductive support member

[0179] 74: Insulating support member

[0180] 76: Insulating oil

[0181] 77: Storage tank

[0182] 80: Semiconductor element

[0183] 81, 82, 85: Solder

[0184] 83: Electrode

[0185] 84: Metal wire

[0186] 86: Housing

[0187] 90: Bottom plate

[0188] 92: Cooling fin

[0189] 93: Screw

[0190] 94: Grease

[0191] 95: Resin

[0192] 100: Bonded body

[0193] 132: Aggregate

[0194] 200: Power supply module

[0195] 400: Inspection device

Claims

1. A ceramic sintered body comprising ceramic particles, wherein, In its cross-section, the average number of large pores with a size of 10 μm or more is less than 1 per mm 2 , and the average number of small pores with a size of 0.05 μm or more and less than 10 μm is less than 400 per mm 2 ; its flexural strength is 640 MPa or more.

2. The ceramic sintered body according to claim 1, wherein, The maximum value of the size of pores in the cross section is 6 μm or less.

3. The ceramic sintered body according to claim 1, wherein, The average value of the size of the fine pores is 1.0 μm or less, and the standard deviation is 0.6 μm or less.

4. A method for manufacturing a ceramic sintered body, comprising: a pulverization step of pulverizing a sintering aid raw material with a pulverizer to obtain a sintering aid powder having a median particle size of 0.5 to 1.0 μm; and a mixing step of preparing a mixed raw material containing ceramic powder and the sintering aid powder; and a firing step of firing a molded body of the mixed raw material to obtain a ceramic sintered body having a flexural strength of 640 MPa or more.

5. The manufacturing method of the ceramic sintered body according to claim 4, wherein, In the cross-section of the ceramic sintered body, the average number of large pores with a size of 10 μm or more is less than 1 per mm 2 , and the average number of small pores with a size less than 10 μm is less than 400 per mm 2 .

6. A joined body comprising the plate-shaped ceramic sintered body according to any one of claims 1 to 3, a metal plate, and a brazing material layer joining the main surface of the ceramic sintered body and the main surface of the metal plate.

7. The bonded body according to claim 6, wherein, The thickness of the metal plate is 0.8 mm or less.

8. The bonded body according to claim 6, 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.

9. A power module comprising: a joined body comprising the plate-shaped ceramic sintered body according to any one of claims 1 to 3, a metal plate, and a brazing material layer joining the main surface of the ceramic sintered body and the main surface of the metal plate; and a semiconductor element electrically connected to the metal plate of the joined body.

Images