JP2021172556A - Aluminum nitride sintered compact and manufacturing method thereof - Google Patents

Abstract

To provide an aluminum nitride sintered compact having high thermal conductivity and excellent mechanical strength.SOLUTION: An aluminum nitride sintered compact includes aluminum nitride crystal grains and compound oxide crystal grains containing a rare earth element and aluminum. In the aluminum nitride sintered compact, the median diameter of the aluminum nitride crystal grains is 3.0 μm or less. A value obtained by dividing the difference between the cumulative value 90% particle diameter of the particle size distribution based on the number of the aluminum nitride crystal grains and the cumulative value 10% particle diameter of the particle size distribution based on the number of the aluminum nitride crystal grains by the median diameter of the aluminum nitride crystal grains is 0.80-1.00. A value obtained by dividing the median diameter of the compound oxide crystal grains by the median diameter of the aluminum nitride crystal grains is 0.50 or more and less than 1.00.SELECTED DRAWING: None

Description

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

Conventionally, the miniaturization of circuit boards and the increase in output of power modules have been progressing. As a circuit board used for a power module or the like, a circuit board in which a metal circuit layer is bonded to the surface of a ceramic sintered body with a brazing material and a semiconductor element is mounted at a predetermined position of the metal circuit layer is widely used.

In order for a power module to operate with high reliability, a circuit board with excellent heat dissipation (thermal conductivity) and mechanical strength is required. If the heat dissipation (thermal conductivity) is good, the heat generated by the circuit is efficiently released, and overheating of the semiconductor element is suppressed. If the mechanical strength is excellent, the circuit board can withstand the thermal stress caused by the difference in the coefficient of thermal expansion from the metal circuit layer. As a circuit board that meets such demands, a ceramics insulating substrate using an aluminum nitride sintered body having high electrical insulation and high thermal conductivity has been applied.

In recent years, the amount of heat generated by a semiconductor element has increased as the performance of the power module has improved, and cracks are likely to occur in the circuit board material due to the heat cycle associated with the operation of the semiconductor element. Therefore, the application of a silicon nitride substrate having further excellent mechanical strength, which can cope with an increase in the amount of heat in recent years, is being studied. However, the silicon nitride substrate has a low thermal conductivity, and only a silicon nitride substrate having a maximum thermal conductivity of about 100 W / mK has been obtained (see, for example, Patent Document 1).

Further, it is derived from the aluminum nitride substrate in which the particle size distribution of the aluminum nitride crystal particles in the sintered body is controlled (see, for example, Patent Document 2), the particle size of the aluminum nitride crystal particles in the sintered body, and the sintering aid. An aluminum nitride substrate having a controlled particle size of composite oxide crystal grains (see, for example, Patent Document 3) has also been studied.

JP-A-2002-029849 Japanese Unexamined Patent Publication No. 2005-200287 Japanese Unexamined Patent Publication No. 2010-215465

However, Patent Document 2 has a problem that the range of the particle size distribution of the aluminum nitride crystal particles in the sintered body is too wide and the degree of improvement in mechanical strength is poor. Further, in Patent Document 3, although the mechanical strength is improved by reducing the particle size of the aluminum nitride crystal grains and the composite oxide crystal grains in the sintered body, the mechanical strength exceeds 600 MPa. No aluminum substrate has been obtained.

From the above, it has been strongly desired to obtain an aluminum nitride sintered body having high thermal conductivity and excellent mechanical strength.

The present invention has been made to solve such a technical problem, and an object of the present invention is to provide an aluminum nitride sintered body having high thermal conductivity and excellent mechanical strength and a method for producing the same. ..

In the present invention, (i) the median diameter of the aluminum nitride crystal grains, (ii) the cumulative value of the particle size distribution based on the number of aluminum nitride crystal grains 90%, and the cumulative value of the particle size distribution based on the number of aluminum nitride crystal grains 10 The value obtained by dividing the difference from the% particle size by the median diameter of the aluminum nitride crystal grains and the value obtained by dividing the median diameter of the (iii) composite oxide crystal grains by the median diameter of the aluminum nitride crystal grains are specified. This is based on the finding that an aluminum nitride sintered body having better mechanical strength than the conventional one can be obtained while maintaining high thermal conductivity.
Further, in the present invention, the above (i), (ii) and (iii) are the volume average particle diameters of the aluminum nitride powder and the sintering aid powder in the (iv) primary mixing step in the method for producing an aluminum nitride sintered body. , (V) The content of the sintering aid powder in the primary mixing step, and (vi) the firing conditions in the sintering step, etc., are found to be adjustable. ..

That is, the present invention provides the following [1] to [6].
[1] An aluminum nitride sintered body containing aluminum nitride crystal grains and composite oxide crystal grains containing rare earth elements and aluminum elements, wherein the aluminum nitride crystal grains have a median diameter of 3.0 μm or less, and the above. The difference between the cumulative value of 90% particle size of the particle size distribution based on the number of aluminum nitride crystal grains and the cumulative value of 10% particle size of the particle size distribution based on the number of aluminum nitride crystal grains is determined by the median diameter of the aluminum nitride crystal grains. The value obtained by dividing is 0.80 to 1.00, and the value obtained by dividing the median diameter of the composite oxide crystal grain by the median diameter of the aluminum nitride crystal grain is 0.50 or more and less than 1.00. Aluminum sintered body.
[2] The aluminum nitride sintered body according to the above [1], wherein the rare earth element contains at least one selected from the group consisting of yttrium elements and lanthanoid-based rare earth elements.
[3] The aluminum nitride sintered body according to the above [1] or [2], which has a thermal conductivity of 130 W / m · K or more and a bending strength of 700 MPa or more.
[4] The above [1] to [3], wherein the total content of the composite oxide crystal grains in X-ray diffraction measurement in terms of mass is 8 to 16% by mass in 100% by mass of the aluminum nitride sintered body. The aluminum nitride sintered body according to any one of.
[5] The method for producing an aluminum nitride sintered body according to any one of the above [1] to [4], which comprises an aluminum nitride powder and a raw material powder containing a sintering aid powder containing a rare earth element. , A primary mixing step of mixing with an organic solvent to obtain a raw material slurry, a molding step of molding an aluminum nitride molded body using the raw material slurry, and degreasing the aluminum nitride molded body with an oxidizing gas. The aluminum nitride sintered body is obtained by firing the aluminum nitride degreased body in an inert gas atmosphere under the conditions of a firing temperature of 1800 ° C. or lower and a firing time of 24 hours or less. In the primary mixing step, the volume average particle size of the aluminum nitride powder is 0.50 to 0.85 μm, and the volume average particle size of the sintering aid powder is 0.40. A method for producing an aluminum nitride sintered body, which is ~ 0.90 μm and the content of the sintering aid powder is 5 to 14% by mass in 100% by mass of the raw material powder.
[6] The method for producing an aluminum nitride sintered body according to the above [5], wherein the inert gas is nitrogen gas.

According to the present invention, it is possible to provide an aluminum nitride sintered body having high thermal conductivity and excellent mechanical strength.
Further, according to the production method of the present invention, an aluminum nitride sintered body having high thermal conductivity and excellent mechanical strength can be preferably obtained.

It is a scanning electron microscope (hereinafter, abbreviated as "SEM") observation image (magnification 1000 times) of the cross section of the aluminum nitride sintered body of Example 2. In FIG. 1, the dark part is the aluminum nitride crystal grain and the bright part is the composite oxide crystal grain. It is an SEM observation image (magnification 5000 times) of the cross section of the aluminum nitride sintered body of Example 2. In FIG. 2, the length A of one of the arrows (dark part) is the longest diameter of the aluminum nitride crystal grains, and the length B of the other (bright part) of the arrow is the longest diameter of the composite oxide crystal grain size. .. It is an SEM observation image (magnification 1000 times) of the cross section of the aluminum nitride sintered body of Comparative Example 1. It is an SEM observation image (magnification 5000 times) of the cross section of the aluminum nitride sintered body of Comparative Example 1.

Hereinafter, the aluminum nitride sintered body of the present embodiment and a method for producing the same will be described in detail.
In the present specification, the preferred provisions can be arbitrarily selected, and it can be said that the combination of the preferred provisions is more preferable.
In the present specification, the description of "XX to YY" means "XX or more and YY or less".
In the present specification, the lower limit value and the upper limit value described stepwise for a preferable numerical range (for example, a range such as content) can be independently combined. For example, from the description of "preferably 10 to 90, more preferably 30 to 60", the "preferable lower limit value (10)" and the "more preferable upper limit value (60)" are combined to obtain "10 to 60". You can also do it.

[Aluminum nitride sintered body]
The aluminum nitride sintered body of the present embodiment is defined as aluminum nitride (hereinafter, also referred to as “AlN”) crystal grains and composite oxide crystal grains containing rare earth elements and aluminum elements (simply referred to as “composite oxide crystal grains”). There is also) and.
Here, the AlN sintered body is preferably a polycrystalline body containing AlN crystal grains as a main component, and preferably a composite oxide crystal grain as a sub component.
Further, in the present specification, the "main component" means a component whose content exceeds 50% by mass.
The content of AlN crystal grains in the AlN sintered body is not particularly limited, but from the viewpoint of mechanical strength and heat dissipation (thermal conductivity) of the AlN sintered body, in 100% by mass of the aluminum nitride sintered body, It is preferably 84 to 92% by mass, more preferably 85 to 89% by mass, and even more preferably 86 to 88% by mass.
The total content of the composite oxide crystal grains in the AlN sintered body is not particularly limited, but the sinterability in the production of the AlN sintered body, the mechanical strength of the AlN sintered body, and the heat dissipation (thermal conductivity). From this point of view, it is preferably 8 to 16% by mass, more preferably 11 to 15% by mass, still more preferably 12 to 14% by mass, and particularly preferably 11 to 14% by mass in 100% by mass of the aluminum nitride sintered body. ..
The contents of the AlN crystal grains and the composite oxide crystal grains are determined by the method shown in the column of "Measurement of the content of AlN crystal grains and the composite oxide crystal grains by X-ray diffraction measurement (XRD measurement)" in the example. It is the content rate in terms of measured mass.
Further, the AlN sintered body includes the AlN sintered body because there is a high possibility that the thermal conductivity of the AlN sintered body is lowered when the AlN sintered body contains the AlN crystal grains and the crystal grains other than the composite oxide crystal grains. The crystal grains preferably consist only of AlN crystal grains and composite oxide crystal grains.
The crystal phases of AlN crystal grains and composite oxide crystal grains can be identified by X-ray diffraction measurement (XRD measurement), and these identifications can be made by analysis software HighScore Plus (Spectris Co., Ltd.) in X-ray diffraction measurement (XRD measurement). It can be done by using (manufactured by).
For example, as shown in FIG. 1, when the AlN crystal grains and the composite oxide crystal grains are observed in the SEM image of the cross section of the AlN sintered body, the particles (dark portion) appear relatively dark (for example, the figure described later). P) in 2 is an AlN crystal grain, and a particle (bright part) that looks relatively bright (for example, X in FIG. 2 described later) is a composite oxide crystal grain described later.
The distinction between AlN crystal grains and composite oxide crystal grains can also be confirmed by the difference in the elements contained in the crystal grains using the energy dispersive X-ray spectroscopy (EDS) analyzer attached to the SEM device (this). The method may be hereinafter referred to as "SEM-EDS analysis").

(AlN crystal grains)
The AlN crystal grains preferably contain AlN and contain AlN as a main component, and more preferably a pure substance consisting only of AlN.
The content of AlN in the AlN crystal grains is not particularly limited, but is preferably 95% by mass or more, more preferably 99% by mass or more, and further preferably 100% by mass.

<Median diameter of AlN crystal grains>
In this specification, the size of AlN crystal grains is defined by the median diameter. In the present specification, the "median diameter" is a value corresponding to a cumulative value of 50% particle size of a number-based particle size distribution measured by a scanning electron microscope (SEM).
The median diameter of the AlN crystal grains is not particularly limited as long as it is 3.0 μm or less, but from the viewpoint of the mechanical strength of the AlN sintered body, it is preferably 2.5 μm or less, more preferably 2.0 μm or less. From the viewpoint of densification of the AlN sintered body, it is preferably 1.0 μm or more, more preferably 1.5 μm or more.
When the median diameter of the AlN crystal grains is 3.0 μm or less, the mechanical strength can be exhibited, and when it is within the above preferable range, the mechanical strength can be sufficiently exhibited.
The detailed measurement method of the median diameter of AlN crystal grains will be described below.
For the median diameter of AlN crystal grains, a diamond pen (D point pen manufactured by AS ONE) was used to break the AlN sintered body to prepare a cross section of the AlN sintered body, and the cross section was subjected to a scanning electron microscope (SEM). Observe at a magnification of 1000 times or more (for example, 1000 times, 3000 times, 5000 times, etc.). The particle size of at least 500 AlN crystal grains in an arbitrary 100 μm square region is measured and determined using a caliper. More specifically, it is obtained by the method described in Examples described later. Since the AlN crystal grains are not completely spherical, the longest diameter is defined as the particle size of the AlN crystal grains. As described above, for example, in the SEM image shown in FIG. 2, the particles (dark portion) P that appear to be relatively dark are AlN crystal grains.

<Particle size distribution of AlN crystal grains>
The particle size distribution of AlN crystal grains is defined by the difference between the cumulative 90% particle diameter and the cumulative 10% particle diameter obtained by the same method as the above-mentioned measurement of the median diameter, divided by the median diameter.
The particle size distribution of the AlN crystal grains is not particularly limited as long as it is 0.80 to 1.00, but is preferably 0.85 to 1.00, and more preferably 0.99 to 1.00.
When the particle size distribution of the AlN crystal grains is 0.80 or more, the mechanical strength can be exhibited, and when it is 0.85 or more, the mechanical strength can be more sufficiently exhibited.

(Composite oxide crystal grains)
The composite oxide crystal grain is a crystal grain of a composite oxide containing a rare earth element and an aluminum element, and preferably contains a rare earth element and an aluminum element, and preferably contains only a rare earth element and an aluminum element. The composite oxide crystal grains are usually present at the grain boundaries of AlN crystal grains.
The content of the rare earth element in the composite oxide crystal grains is not particularly limited, but from the viewpoint of heat dissipation (thermal conductivity), it is preferably 45% by mass or more, more preferably 54% by mass or more, still more preferably 60. It is mass% or more.
The content of the aluminum element in the composite oxide crystal grains is not particularly limited, but from the viewpoint of heat dissipation (thermal conductivity), it is preferably 23% by mass or less, more preferably 16% by mass or less, still more preferably 13. It is less than mass%.
The crystal phase of the composite oxide crystal grains includes a monoclinic structure (RE ₄ Al ₂ O ₉ ) crystal phase, an oblique perovskite structure (REALO ₃ ) crystal phase, and a cubic garnet structure (RE _3). Examples include the crystal phase of _{Al 5} O _12). Here, "RE (sometimes referred to as" RE element ")" represents at least one selected from the group consisting of yttrium element and lanthanoid rare earth element.
The composite oxide crystal grains preferably contain an RE element and an aluminum element (that is, the rare earth element preferably contains at least one selected from the group consisting of the yttrium element and the lanthanoid-based rare earth element). It is more preferable to include at least one crystal phase selected from the group consisting of RE ₄ Al ₂ O ₉ , REAlO ₃ , and RE ₃ Al ₅ O _12. However, it is preferable not to include the one consisting of the crystal phase of _{RE 3} Al ₅ O _{12 alone.}
As the lanthanoid rare earth element, samarium (Sm) is preferable.

<Median diameter of composite oxide crystal grains>
The median diameter of the composite oxide crystal grains is not particularly limited, but from the viewpoint of the mechanical strength of the AlN sintered body, it is preferably 2.5 μm or less, more preferably 2.0 μm or less, and the AlN sintered body. From the viewpoint of densification, the thickness is preferably 1.0 μm or more, more preferably 1.2 μm or more.
In the present specification, the size of the composite oxide crystal grains is defined by the median diameter as in the case of the AlN crystal grains described above. The median diameter of the composite oxide crystal grains is determined by breaking the AlN sintered body with a diamond pen (D point pen manufactured by AS ONE) to prepare a cross section of the AlN sintered body, and scanning the cross section with a scanning electron microscope (SEM). For observation at a magnification of 1000 times or more (for example, 1000 times, 3000 times, 5000 times, etc.). The particle size of at least 200 composite oxide crystal grains in an arbitrary 100 μm square region is measured and determined using a caliper. More specifically, it is obtained by the method described in Examples described later. Since the composite oxide crystal grains are not completely spherical, the longest diameter is defined as the particle size of the composite oxide crystal grains. As described above, for example, in the SEM image shown in FIG. 2, the particles (bright portions) X that appear relatively bright are composite oxide crystal grains.

<Ratio of "Median diameter of AlN crystal grains" and "Median diameter of composite oxide crystal grains">
Generally, the smaller the median diameter of the composite oxide crystal grains, the higher the mechanical strength of the AlN sintered body. However, in the AlN sintered body of the present embodiment, the AlN crystal grains contained in the AlN sintered body The median diameter and the median diameter of the composite oxide crystal grains are adjusted to have a specific ratio.
The value obtained by dividing the median diameter of the composite oxide crystal grains by the median diameter of the AlN crystal grains is not particularly limited as long as it is 0.50 or more and less than 1.00, but is preferably 0.60 or more and 0.99 or less. It is more preferably 0.70 or more and 0.97 or less, and further preferably 0.70 or more and 0.95 or less.
In the AlN sintered body of the present embodiment, the value obtained by dividing the median diameter of the composite oxide crystal grains by the median diameter of the AlN crystal grains is 0.50 or more, so that the stress dispersion is made uniform and mechanical. On the other hand, when the strength is less than 1.00, the composite oxide crystal grains themselves can be suppressed from becoming the starting point of fracture, and the mechanical strength can be improved.

As described above, AlN firing containing AlN crystal grains and composite oxide crystal grains, and adjusting the median diameter of the AlN crystal grains, the particle size distribution of the AlN crystal grains, and the median diameter of the composite oxide crystal grains, respectively. The body is excellent in thermal conductivity and mechanical strength.
Therefore, the AlN sintered body of the present embodiment is highly expected to be used for applications that require high heat dissipation, thermal conductivity, and mechanical strength, as typified by circuit boards of power modules.

(Thermal conductivity of AlN sintered body)
The thermal conductivity of the AlN sintered body is not particularly limited, but is preferably 130 W / m · K or more, more preferably 140 W / m · K or more, and further preferably 150 W / m · K or more.
The "thermal conductivity" is measured by the method described in Examples.

(Bending strength of AlN sintered body)
The bending strength of the AlN sintered body is not particularly limited, but is preferably 700 MPa or more, more preferably 730 MPa or more, and further preferably 750 MPa or more.
The "bending strength (three-point bending strength)" is measured by the method described in the examples.

(Density and relative density of AlN sintered body)
The absolute value of the density of the AlN sintered body, the content ratio of yttrium (charged amount of Y ₂ O _3, the addition amount of the sintering aid powder), the type of oxide in the AlN sintered body, depending on the variation Therefore, although it cannot be defined unconditionally, in the present specification, the density of the AlN sintered body is determined by the method described in Examples described later.
The relative density of the AlN sintered body, the total charge amount of AlN and Y ₂ O ₃ (total content ratio) was defined as 100% by mass, which is used for relative evaluation is not particularly limited, From the viewpoint of mechanical strength and heat dissipation (thermal conductivity) of the AlN sintered body, it is preferably 98.0 to 99.9% by mass, more preferably 99.0 to 99.9% by mass, and further preferably 99. It is 5 to 99.9% by mass. The relative density of the AlN sintered body is determined by the method described in Examples described later.

[Manufacturing method of AlN sintered body]
The method for producing the AlN sintered body of the present embodiment includes (1) a primary mixing step of mixing a raw material powder containing AlN powder and a sintering aid powder with an organic solvent to obtain a raw material slurry, and (2) a binder. A binder solution preparation step of obtaining a binder solution by dissolving the above in an organic solvent, (3) a secondary mixing step of mixing a raw material slurry and a binder solution to obtain a mixed slurry, and (4) molding a mixed slurry to form AlN. A molding step of obtaining a molded body, (5) a degreasing step of degreasing an AlN molded body with an oxidizing gas to obtain an AlN degreased body, and (6) a predetermined AlN degreased body in an inert gas atmosphere. It is preferable to include a sintering step of firing under the conditions to obtain an AlN sintered body. Of these steps, (1) and (4) to (6) are essential steps. The steps (2) and (3) may be omitted to obtain a mixed slurry in which the binder is directly dissolved in the step (1).
Each step will be described in detail below.

((1) Primary mixing step)
The primary mixing step is a step of mixing a raw material powder containing AlN powder and a sintering aid powder with an organic solvent to obtain a raw material slurry. Here, the raw material powder preferably consists of only AlN powder and sintering aid powder.
The mixing method in the primary mixing step is not particularly limited, and examples thereof include mixing each component (raw material powder, organic solvent) using a normal stirrer. For the AlN powder and the sintering aid powder, it is preferable that the respective raw materials are pulverized (primary pulverization) to adjust the particle size to a predetermined value. The mixing in the primary mixing step is usually carried out under the condition that the particle size of the AlN powder particles does not change. Further, in the step after the primary mixing step (secondary mixing step), stirring, filtration, etc. are performed under the condition that the particle sizes of the AlN powder particles and the sintering aid powder do not change. Therefore, in the AlN powder and the sintering aid powder, the particle size adjusted by crushing (primary pulverizing) each raw material is usually the particle size in the molding step and the degreasing step described later.

<AlN powder>
For the AlN powder, it is preferable to pulverize (primary pulverize) the AlN raw material so that the volume average diameter is within a predetermined range.
Here, as the primary pulverization of the AlN raw material, for example, a mixing container having a pulverizing function such as a ball mill, a vibration mill, or an attritor can be used. Among these, a ball mill is preferable from the viewpoint of productivity.
The material of the mixing container used for the primary pulverization is not particularly limited, but a resin or high-purity alumina is preferable from the viewpoint of suppressing contamination of impurities such as transition metal elements.
The material of the crushed balls used in the ball mill is not particularly limited, but high-purity alumina is preferable, and high-purity alumina having a purity of 99.9% by mass or more is more preferable.

As the AlN raw material to be pulverized (primary pulverized) to obtain the AlN powder, a commercially available material having a particle size of about 1 μm can be used. The AlN raw material may be produced by either a direct nitriding method or a reduction nitriding method. The oxygen atom content in the AlN raw material is not particularly limited, but is preferably 0.5 to 3 mass from the viewpoint of setting the oxygen atom content in the AlN degreased body obtained in the degreasing step described later in a suitable range. %, More preferably 0.7 to 2% by mass, still more preferably 0.8 to 1% by mass. The oxygen atom content is determined by the method described in Examples described later.

The volume average diameter of the AlN powder used in the primary mixing step (for example, "volume average diameter after primary pulverization (AlN powder)" in Tables 1 and 2 described later) is as long as 0.50 to 0.85 μm. Although there is no particular limitation, it is preferably 0.50 to 0.80 μm, more preferably 0.60 to 0.78 μm, and further preferably 0.70 to 0.75 μm. When the volume average diameter of the AlN powder is 0.50 μm or more, it is possible to suppress a significant increase in the viscosity of the raw material slurry, improve the handleability, and improve the productivity. On the other hand, when the volume average diameter of the AlN powder is 0.85 μm or less, it is possible to suppress the coarseness of the AlN crystal grains in the AlN sintered body and improve the mechanical strength. In the step after the primary mixing step (secondary mixing step), stirring, filtration, etc. are performed under the condition that the particle size of the AlN powder particles does not change.
Here, the volume average diameter of the AlN powder is determined by drying the slurry after the primary pulverization, dispersing it in water, adding a 0.2% by mass solution of sodium hexametaphosphate, and using the particle size distribution measuring device “MICROTRAC MT3000II”. It is determined by laser diffraction method.

The content of the AlN powder is not particularly limited, but is preferably 86 to 95% by mass, more preferably 88 to 94% by mass, and further, in 100% by mass of the raw material powder containing the AlN powder and the sintering aid powder. It is preferably 90 to 92% by mass. When the content of the AlN powder is 95% by mass or less, the AlN sintered body is effectively densified in the sintering step described later, and the impurity oxygen in the AlN crystal particles is efficiently removed and obtained. The thermal conductivity of the AlN sintered body can be improved, and if it is 86% by mass or more, the mechanical strength of the obtained AlN sintered body can be improved.

<Sintering aid powder>
The sintering aid powder is preferably pulverized (primary pulverization) of the sintering aid raw material so that the volume average diameter is within a predetermined range.
Here, as the primary pulverization of the sintering aid raw material, for example, a mixing container having a pulverizing function such as a ball mill, a vibration mill, or an attritor can be used. Among these, a ball mill is preferable from the viewpoint of productivity.
The material of the mixing container used for the primary pulverization is not particularly limited, but a resin or high-purity alumina is preferable from the viewpoint of suppressing contamination of impurities such as transition metal elements.
The material of the crushed balls used in the ball mill is not particularly limited, but high-purity alumina is preferable, and high-purity alumina having a purity of 99.9% by mass or more is more preferable.

As the raw material for the sintering aid that is pulverized (primarily pulverized) to obtain the sintering aid powder, a commercially available material having a particle size of about 1 μm can be used.
The sintering aid raw material (sintering aid powder) is not particularly limited as long as it contains a rare earth element and can be used as a raw material for composite oxide crystal grains. For example, aluminum oxide (Al ₂ O ₃ ). Aluminum element oxides such as yttrium element oxides, rare earth element oxides such as lanthanoid-based rare earth element oxides; and the like. One of these may be used alone, or two or more thereof may be used in combination.
Among these, yttrium oxide (Y ₂ O ₃ ) is preferable.
The sintering aid raw material (sintering aid powder) may be obtained by heating the precursor.

The volume average diameter of the sintering aid powder used in the primary mixing step (for example, "volume average diameter after primary pulverization (Y ₂ O ₃ powder)" in Tables 1 and 2 described later) is 0.40 to 0. As long as it is .90 μm, there is no particular limitation, but it is preferably 0.40 to 0.60 μm, more preferably 0.45 to 0.58 μm, and further preferably 0.50 to 0.56 μm. The sintering aid raw materials are pulverized and mixed to obtain a sintering aid powder so that the volume average diameter of the sintering aid powder is within the above range in the primary mixing step. When the volume average diameter of the sintering aid powder is 0.40 μm or more, it is possible to suppress a significant increase in the viscosity of the raw material slurry, improve the handleability, and improve the productivity. On the other hand, when the volume average diameter of the sintering aid powder is 0.90 μm or less, it is possible to suppress the coarseness of the composite oxide crystal grains in the AlN sintered body and improve the mechanical strength. .. In the step after the primary mixing step (secondary mixing step), stirring, filtration, etc. are performed under the condition that the particle size of the sintering aid powder does not change.
The volume average diameter of the sintering aid powder is determined by drying the slurry after the primary pulverization, dispersing it in water, adding a 0.2% by mass solution of sodium hexametaphosphate, and adding a particle size distribution measuring device "MICROTRAC MT3000II". Is obtained by the laser diffraction method.

The content of the sintering aid powder with respect to 100% by mass of the raw material powder containing the AlN powder and the sintering aid powder is not particularly limited as long as it is 5 to 14% by mass, but is preferably 6 to 12% by mass. , More preferably 8 to 10% by mass. When the content of the sintering aid powder is 5% by mass or more, the AlN sintered body is effectively densified in the sintering step described later, and the impurity oxygen in the AlN crystal grains is efficiently removed. The amount of the composite oxide crystal grains is appropriate, the thermal conductivity of the obtained AlN sintered body can be improved, and if it is 14% by mass or less, the composite oxide crystal grains maintain a spherical morphology. It is possible to improve the mechanical strength of the obtained AlN sintered body.

<Organic solvent>
The organic solvent is not particularly limited, and examples thereof include methanol, 1-butanol, 2-butanone, methyl ethyl ketone (MEK), xylene, and the like. One of these may be used alone, or two or more thereof may be used in combination.
Among these, 1-butanol and 2-butanol are preferable, and 1-butanol and 2-butanol are more preferably mixed and used.
The content of the organic solvent in the raw material slurry is not particularly limited, but is preferably 10 to 50% by mass, more preferably 15 to 40% by mass, and further preferably 20 to 35% by mass from the viewpoint of productivity. ..

<Other ingredients>
In addition, the raw material slurry contains polyethylene glycol-based nonionic dispersants such as polyoxyethylene lauryl ether; plasticizers such as dibutyl phthalate and butyl phthalyl butyl glycolate; and the like as other components other than the raw material powder and the organic solvent. It may be further contained.

The method for producing the AlN sintered body of the present embodiment may further include (2) a binder solution preparation step and (3) a secondary mixing step.

((2) Binder solution preparation step)
The binder solution preparation step is an arbitrary step of dissolving the binder in an organic solvent to obtain a binder solution.

<Binder solution>
The binder solution can be obtained by dissolving the binder in an organic solvent.
The binder is not particularly limited, and examples thereof include organic compounds such as polyvinyl butyral, paraffin wax, ethyl cellulose, and acrylic resin. One of these may be used alone, or two or more thereof may be used in combination. Among these, polyvinyl butyral is preferable.
Examples of the organic solvent include the same ones as those used for producing the raw material slurry in the above-mentioned primary mixing step, and the same ones are preferable. When a plurality of types of organic solvents are mixed and used, the mixing ratio can be appropriately changed according to the characteristics of the binder as a solute.
The method for obtaining the binder solution can be carried out in the same manner as the method for obtaining the mixed slurry in the secondary mixing step described later. For example, filtration can remove lumps of insoluble binder components. The holding particle size of the filter medium used in the binder solution preparation step is not particularly limited, but from the viewpoint of removing coarse insoluble binder component lumps, increasing the density of the sheet in the molding step, and densifying the sintered body. , It is preferable that the diameter of the filter medium used in the secondary mixing step is at least twice the retained particle size and not more than twice the retained particle size.

((3) Secondary mixing step)
The secondary mixing step is an arbitrary step of mixing the raw material slurry obtained in the primary mixing step with the binder solution to obtain a mixed slurry. As described above, by mixing the raw material slurry and the binder solution instead of adding the binder to the raw material slurry, it is possible to suppress the generation of insoluble lumps of the binder.
In the secondary mixing step, a mixing method in which the particle size does not change is used. Mixing can be performed, for example, with a normal stirrer having no pulverizing ability. That is, in the secondary mixing step, stirring is performed under the condition that the particle sizes of the AlN powder particles and the sintering aid powder do not change.
The mixing time (secondary mixing time) in the secondary mixing step is not particularly limited, but is preferably 1 to 50 hours, more preferably 4 to 40 hours, and further preferably 6 to 6 to 50 hours from the viewpoint of material homogenization. 30 hours.

Further, the mixed slurry obtained in the secondary mixing step may further contain a polyethylene glycol-based nonionic dispersant such as polyoxyethylene lauryl ether; a plasticizer such as dibutyl phthalate or butyl phthalyl butyl glycolate; good.

The content of the binder in the mixed slurry obtained in the secondary mixing step is not particularly limited, but is preferably 3 to 15 parts by mass, more preferably 4 to 13 parts by mass, and further, with respect to 100 parts by mass of the raw material powder. It is preferably 4 to 10 parts by mass.

It is desirable to remove foreign substances and agglomerates from the mixed slurry. Examples of such a removal method include filtration, decantation, and the like. One of these may be used alone, or two or more thereof may be used in combination. Of these, filtration is preferred.
Examples of the filtration include natural filtration, pressure filtration, vacuum filtration, and the like. One of these may be used alone, or two or more thereof may be used in combination.
Among these, pressure filtration is preferable from the viewpoint of suppressing the components in the mixed slurry from settling and becoming unbalanced and shortening the time. Here, when the pressure filtration is performed, compressed air can be used as the pressure gas, but from the viewpoint of suppressing unnecessary oxidation of the AlN powder in the mixed slurry, the pressure is applied with an inert gas such as nitrogen gas. Is preferable. The pressure in pressurization is not particularly limited, and the amount and viscosity of the mixed slurry and the pressurization filter device to be used (for example, versatile disc filter holder: manufactured by ADVANTEC Co., Ltd., model number: KST-142-UH)). It is appropriately prepared according to the characteristics of.

The filter medium used for filtration is selected according to the particle size of the powder contained in the mixed slurry to be filtered, and is selected, for example, by the holding particle size of the filter medium.
The holding particle size of the filter medium is not particularly limited, but is preferably 1.0 to 10.0 μm, more preferably 2.0 to 8.0 μm, and even more preferably 2.0 to 6.0 μm.
The type of the filter medium is not particularly limited, and examples thereof include a filter paper made of PTFE resin. By filtering using such a filter medium, insoluble lumps (lumps larger than the holding particle size of the filter medium) generated during the primary mixing step and the secondary mixing step can be removed.
Further, it is preferable to perform a defoaming treatment on the obtained mixed slurry, if necessary. For the defoaming treatment of the mixed slurry, for example, a commercially available vacuum pump can be used.
In the above-mentioned secondary mixing step, filtration is performed under the condition that the particle sizes of the AlN powder particles and the sintering aid powder do not change.

((4) Molding process)
The molding step is a step of molding the mixed slurry obtained in the secondary mixing step to obtain an AlN molded product. For example, a sheet-shaped AlN molded product can be produced by pouring the mixed slurry into a predetermined mold, casting it on a base sheet, and then removing the solvent by air drying or the like. The AlN molded product which is not in the form of a sheet can be obtained in the form of a cake by pouring the mixed slurry into a desired frame and then subjecting it to solvent pressing, filtration, drying or the like. The obtained AlN molded product can be cut into an appropriate size and shape, if necessary.
Examples of the molding method include a method using a dry press machine; a method using a rubber press machine; an extrusion method; an injection method; a doctor blade method; and the like. One of these may be used alone, or two or more thereof may be used in combination.
Examples of the method for producing an AlN sintered substrate as an AlN molded product include a doctor blade method; a method of drying and granulating a mixed slurry and molding it by a mold molding method. One of these may be used alone, or two or more thereof may be used in combination.

((5) Solventing process)
The degreasing step is a step of degreasing the AlN molded body with an oxidizing gas to obtain an AlN degreased body. For example, it is a step of obtaining an AlN degreased body by heating to 600 ° C. or lower in an oxidizing gas atmosphere. In the degreasing step, organic components such as a binder component and a residual solvent contained in the AlN molded product are oxidized, decomposed, gasified and removed.
Examples of the oxidizing gas include gases that oxidize organic substances such as oxygen, carbon dioxide, and water vapor. One of these may be used alone, or two or more thereof may be used in combination. Among these, an oxygen mixed gas mixed with oxygen is preferable, and atmospheric gas (air) is more preferable.
The oxygen content of the oxidizing gas is not particularly limited, but from the viewpoint of reactivity, it is preferably 5 to 20% by volume, more preferably 10 to 20% by volume, and further preferably 15 to 20% by volume. be.
The heating temperature in degreasing (that is, "defatting temperature") is not particularly limited, but from the viewpoint of suppressing oxidation of the raw material AlN powder, it is preferably 600 ° C. or lower, more preferably 400 to 600 ° C., still more preferably 450 to. It is 550 ° C.
The heating time in degreasing (that is, "defatting time") is not particularly limited, but is preferably 1 to 24 hours, more preferably 1 to 1 from the viewpoint of degradability of the binder component and suppression of oxidation of the raw material AlN powder. It is 5 hours, more preferably 1 to 3 hours.
As the degreasing furnace used for degreasing, a commercially available one can be used, and it is preferable that the degreasing furnace is provided with a wax trap mechanism for trapping the removal component gas removed from the AlN molded product.
The content of the impurity carbon atom in the AlN degreased body obtained in the degreasing step is not particularly limited, but from the viewpoint of stabilizing the circuit board characteristics, it is preferably 0.1% by mass or less, more preferably 0.05% by mass. % Or less, more preferably 0.03% by mass or less. The content of the impurity carbon atom is determined by a carbon sulfur analyzer (HORIBA EMIA-920V).
The oxygen atom content in the AlN degreased body obtained in the degreasing step is not particularly limited, but is preferably 3 to 10% by mass, more preferably 4 to 4 to 10% by mass from the viewpoint of heat dissipation (thermal conductivity). It is 8% by mass, more preferably 5 to 7% by mass. The oxygen atom content is determined by the method described in Examples described later.

((6) Sintering process)
The sintering step is a step of calcining the AlN degreased body under predetermined conditions in an inert gas atmosphere to obtain an AlN sintered body.
The firing temperature is not particularly limited as long as it is 1800 ° C. or lower, but is preferably 1400 to 1800 ° C., more preferably 1600 to 1800 ° C., and even more preferably 1700 to 1800 ° C.
When the firing temperature is 1800 ° C. or lower, the composite oxide crystal grains can maintain a substantially spherical shape, and sufficient mechanical strength can be obtained. On the other hand, if the firing temperature is 1400 ° C. or higher, it can be sufficiently densified.
The firing time is adjusted according to the firing temperature and is not particularly limited as long as it is 24 hours or less, but is preferably 20 minutes to 18 hours, more preferably 30 minutes to 12 hours, and further preferably 30 minutes to 6 hours. It's time.
If the firing time is 20 minutes or more, it can be sufficiently densified. Further, when the firing time is 18 hours or less, the median diameter of the AlN crystal grains can be easily adjusted to 3.0 μm or less, and an AlN sintered body having sufficient mechanical strength can be obtained.
Examples of the inert gas include nitrogen gas and argon gas. One of these may be used alone, or two or more thereof may be used in combination.
Among these, nitrogen gas is preferable from the viewpoint of economy.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

[Evaluation measurement]
AlN sintered body density and relative density, volume average diameter of AlN powder and sintering aid powder, median diameter and cumulative value of 10% grain size and cumulative value of 90% grain size of AlN crystal grains, composite oxide crystal grains The median diameter, the content of AlN crystal grains and composite oxide crystal grains by X-ray diffraction measurement (XRD measurement), the three-point bending strength, and the thermal conductivity were measured by the methods described below, respectively.

(Density and relative density of AlN sintered body)
The density of the AlN sintered body was determined by the Archimedes method using "Specific gravity measurement kid AD-1653" manufactured by AS ONE, and the relative value with the theoretical sintered body density was taken as the relative density. The results of density and relative density are shown in Tables 1 and 2. Incidentally, the density of the AlN density of 3.26 g ^/ cm _3, Y 2 _{O 3} and 5.03 g / cm ^3, the total charge amount of AlN and _Y 2 _{O 3} (the total content ratio) was defined as 100 mass% The theoretical sintered body density was calculated. The theoretical sintered density, for example, charge amount of AlN (content ratio): 92 _wt%, the charged amount of Y 2 _{O 3} (content ratio): 8 If mass%, "3.26 × 0. 92 + 5.03 x 0.08 ".

(Volume average diameter of AlN powder and sintering aid powder)
The volume average diameter of the AlN powder is determined by drying the raw material slurry after the primary pulverization, dispersing it in water, adding a 0.2% by mass solution of sodium hexametaphosphate, and using the particle size distribution measuring device "MICROTRAC MT3000II". , The average diameter on a volume basis was determined by the laser diffraction method. Further, the volume average diameter of the sintering aid powder was also determined in the same manner as the volume average diameter of the AlN powder. The results are shown in Tables 1 and 2.

(Median diameter and cumulative value of 10% particle size and cumulative value of 90% particle size of AlN crystal grains)
A diamond pen (D point pen manufactured by AS ONE) is used to break the AlN sintered body to prepare a cross section of the AlN sintered body, and the cross section is subjected to a scanning electron microscope (SEM) (JSM-7900 (manufactured by JEOL Ltd.)). ), Acceleration voltage 15.0 kV) was observed at a magnification of 1000 times, and the longest diameter of the AlN crystal grains was measured to obtain the particle size of the AlN crystal grains. The particle size of 500 AlN crystal grains in an arbitrary 100 μm square region was measured using a caliper to determine the median diameter, cumulative value of 10% particle size, and cumulative value of 90% particle size of the AlN crystal grains. Tables 1 and 2 show the measurement results and the calculation results using the measurement results (ratio of the particle size distribution based on the number of AlN crystal grains to the median diameter of the AlN crystal grains).

(Median diameter of composite oxide crystal grains)
A diamond pen (D point pen manufactured by AS ONE) is used to break the AlN sintered body to prepare a cross section of the AlN sintered body, and the cross section is subjected to a scanning electron microscope (SEM) (JSM-7900 (manufactured by JEOL Ltd.)). ), Acceleration voltage 15.0 kV) was observed at a magnification of 1000 times, and the longest diameter of the composite oxide crystal grains was measured to obtain the particle size of the composite oxide crystal grains. The particle size of 200 composite oxide crystal grains was measured using a caliper in an arbitrary 100 μm square region, and the median diameter of the composite oxide crystal grains was determined. Tables 1 and 2 show the measurement results and the calculation results using the measurement results (ratio of the median diameter of the AlN crystal grains to the median diameter of the composite oxide crystal grains).

(Measurement of AlN crystal grains and composite oxide crystal grains by X-ray diffraction measurement (XRD measurement))
The X-ray diffraction measurement (XRD measurement) of the AlN sintered body was performed using the powder X-ray diffraction measuring device PANalytical MPD (manufactured by Spectris Co., Ltd.). As the measurement conditions, Cu-Kα ray (output 45 kV, 40 mA) is used, scanning axis: θ / 2θ, measurement range (2θ): 10 to 120 °, measurement mode: Continuous, reading width: 0.006565 °, Sampling time: 37.995 seconds, DS, SS, RS: 2 °, 2 °, 5 mm, 0.04 ° solar slits on the incident side and 0.04 ° on the light receiving side, respectively. With respect to the obtained X-ray diffraction pattern, the crystal phases of AlN crystal grains and composite oxide crystal grains were identified using analysis software HighScore Plus (manufactured by Spectris Co., Ltd.) and quantified by the RIR method.
Further, the content of AlN crystal grains and composite oxide crystal grains (Y ₃ Al ₅ O ₁₂ , YAlO ₃ , Y ₄ Al ₂ O ₉ ) obtained by the above X-ray diffraction measurement (XRD measurement) in terms of mass ( The content (% by mass) in 100% by mass of the aluminum nitride sintered body is shown in Tables 1 and 2.

(3-point bending strength)
From 10 AlN sintered sheets, a rectangular shape having a size of 40 mm × 4 mm × thickness 0.82 mm was cut out using a diamond cutter. Further, the surface was polished to a surface roughness Ra of 0.5 μm or less to prepare 100 test pieces having a surface roughness of 40 mm × 4 mm × thickness of 0.635 mm. The obtained test piece is subjected to a precision universal testing machine (manufactured by Shimadzu Corporation, model number: AG-X) and a commercially available test piece according to the JIS standard room temperature 3-point bending strength measurement method (JIS-R-1601: 2008). Using a 3-point bending test tool, the 3-point bending strength was measured at room temperature (23 ° C.) under the conditions of a distance between external fulcrums of 30 mm and a crosshead speed of 0.5 mm / min. The arithmetic mean value of the obtained 3-point bending strength of 100 points was calculated. The results are shown in Tables 1 and 2.

(Thermal conductivity)
Ten test pieces of 40 mm × 40 mm × 0.82 mm in thickness were cut out from 10 sheets of AlN sintered body, and the thermal conductivity of the AlN sintered body was determined by Bethel Hudson Laboratory Co., Ltd. for the obtained test pieces. It was measured by the periodic heating radiation temperature measurement method using a measuring device (model number: Thermowave Analyzer TA35), and the average value of thermal conductivity was calculated from the sintered body density and the specific heat. The specific heat was 710 J / K. The results are shown in Tables 1 and 2.

(Example 1)
<Primary mixing process>
100 parts by mass of a commercially available AlN raw material (manufactured by Toyo Aluminum Co., Ltd., model number: JC, volume average diameter: 1.20 μm) manufactured by the Al direct nitride method, 10 parts by mass of polyoxyethylene lauryl ether as a dispersant, as a solvent. 30 parts by mass of 1-butanol and 28 parts by mass of 2-butanone were added, and primary pulverization (AlN raw material) was carried out for 110 hours in a nylon ball mill pot using high-purity alumina balls having a diameter of 5 mm to obtain an AlN raw material slurry. The volume average diameter of the AlN powder in the AlN raw material slurry after the primary pulverization was 0.73 μm.
Yttrium oxide (Y ₂ O ₃ ) raw material as a sintering aid (manufactured by Shinetsu Chemical Industry Co., Ltd., model number: RU-P (volume average diameter 1.00 μm)) 100 parts by mass, polyoxyethylene lauryl as a dispersant ether 20 parts by weight, as the 1-butanol 52 parts by mass 2-butanone 48 weight parts were added solvent, primary crushing of 46 hours a nylon ball mill pot using high purity alumina balls having a diameter of 5mm (Y ₂ O ₃ raw material ) to _obtain a Y 2 _{O 3} slurry. The volume average diameter of the Y ₂ O _{3 powder in the Y 2} O ₃ raw material slurry after the primary grinding was 0.53 μm.
These slurries to obtain a mixed slurry (primary mixing) to the raw material slurry so that 92 wt% AlN powder and Y ₂ O ₃ powder 8% by weight. Incidentally, AlN powder and _Y 2 _{O 3} powder were mixed so that 100% by weight in total.

<Binder solution preparation process>
5 parts by mass of polyvinyl butyral (manufactured by Kuraray Co., Ltd., Mobile B60H) as a binder component, 5 parts by mass of dibutylphthalate as a plasticizer, and 27 parts by mass of 1-butanol and 23 parts by mass of 2-butanone as a solvent are mixed to retain particle diameter. Pressurization condition of nitrogen gas 0.3 MPa using a versatile disc filter holder (manufactured by ADVANTEC Co., Ltd., model number: KST-142-UH) set with 1 μm filter paper (manufactured by ADVANTEC Co., Ltd., model number: No. 5C). The mixture was filtered with a binder solution.

<Secondary mixing process>
The AlN raw material slurry obtained in the primary mixing step and the Y ₂ O ₃ raw material slurry are combined, and the binder solution obtained in the binder solution preparation step is added to a total of 100 parts by mass _{of the AlN powder and the Y 2} O _{3 powder.} On the other hand, polyvinyl butyral was added so as to be 5 parts by mass. After that, it was mixed for 24 hours with a stirrer (manufactured by Inoue Seisakusho Co., Ltd., trade name "Planetary Mixer"), and a versatile disc filter holder (PF050 manufactured by ADVANTEC Co., Ltd.) set with a filter paper having a holding particle diameter of 5 μm ( Using ADVANTEC Co., Ltd., model number: KST-142-UH), a mixed slurry was obtained by filtering under a pressurized condition of nitrogen gas of 0.3 MPa. Further, the mixed slurry was defoamed by pulling it with a vacuum pump while stirring.
Table 1 shows the content of AlN powder and Y ₂ O ₃ powder in the mixed slurry obtained in the second mixing step. The content of components other than the above in the mixed slurry obtained in the secondary mixing step, to the AlN powder and Y ₂ O ₃ powder per 100 parts by weight, respectively, 11 parts by weight of polyoxyethylene lauryl ether, polyvinyl butyral It was 5 parts by mass, 5 parts by mass of dibutyl phthalate, 59 parts by mass of 1-butanol, and 53 parts by mass of 2-butanone.

<Molding process>
The mixed slurry obtained in the secondary mixing step was sheet-molded by the doctor blade method and air-dried for 8 hours to remove the solvent to obtain a 1 mm-thick sheet made of an AlN molded product. Further, this sheet was punched into a square shape having a size of 70 mm × 70 mm to obtain an AlN molded product.

<Solvent degreasing process>
Boron nitride fine powder (manufactured by Showa Denko KK, model number: UHP-1K) was applied to both sides of the sheet of the AlN molded product obtained in the molding step as a spreading powder for preventing adhesion. Ten of these sheets were stacked and stored in a boron nitride container, and the sheet was held in an atmospheric pressure air stream at 500 ° C. for 2 hours for degreasing to obtain an AlN degreased body. As the degreasing furnace, a stainless steel core tube equipped with a wax trap mechanism and an externally heated tubular furnace having a heating element using a cantal wire were used. Here, the oxygen atom content contained in the AlN degreased body was 6% by mass. The oxygen atom content was measured by encapsulating the sample in a nickel capsule and using the Infrared gas melting-infrared absorption method (oxygen nitrogen analyzer LECO TC-600).

<Sintering process>
The AlN degreased material obtained in the degreasing step is placed in a boron nitride container, and an internal heating type sintering furnace (manufactured by Fuji Denpa Kogyo Co., Ltd., Hi-Multi 5000) having a graphite heating element is used to create an atmospheric nitrogen gas stream. Under the conditions of a firing temperature of 1780 ° C. and a firing time of 0.5 hours, an AlN sintered body (10 sheets of AlN sintered body sheets stacked, 57 mm × 57 mm × thickness 0.82 mm) was obtained. ..

(Examples 2 to 5)
AlN powder content, sintering aid powder (Y ₂ O ₃ powder) weight, baking time, except that the firing temperature was changed as shown in Table 1, in the same manner as in Example 1, respectively, AlN sintered body Was produced. Table 1 shows the evaluation results obtained in the same manner as in Example 1.

As shown in Table 1, in each of Examples 1 to 5, the arithmetic mean value of the three-point bending strength was 700 MPa or more, and the thermal conductivity was 130 W / mK or more.

(Comparative Examples 1 to 7)
AlN powder amount, sintering aid powder (Y ₂ O ₃ powder) amount, AlN powder primary grinding time, sintering aid powder (Y ₂ O ₃ powder) primary grinding time, firing time, firing temperature, degreasing conditions Each AlN sintered body was prepared in the same manner as in Example 1 except that the above was changed as shown in Table 2. Table 2 shows the evaluation results obtained in the same manner as in Example 1. Incidentally, in Comparative Example 4, yttrium oxide and sintering aid powder _(Y 2 _{O 3)} powder: Change in (Shin-Etsu Chemical Co., Ltd., model number RU-P (volume-average diameter 1.00 .mu.m)), compare In Example 6, nitrogen was used instead of air in the degreasing step.

As shown in Table 2, in each of Comparative Examples 1 and 3 to 7, the arithmetic mean value of the three-point bending strength was less than 700 MPa. Further, in Comparative Examples 6 and 7, the thermal conductivity was less than 130 W / mK.
In Comparative Example 2, the mixed slurry obtained in the secondary mixing step became highly viscous, and a sheet could not be produced. Further, in Comparative Example 7, the composite oxide was present at the grain boundaries of the AlN crystal grains in a non-spherical shape.

Since the aluminum nitride sintered body of the present invention has high thermal conductivity and excellent mechanical strength, it can be suitably used for a circuit board, for example, a circuit board for a power module.

P; Particles that look relatively dark (dark areas)
X: Particles that look relatively bright (bright part)

Claims (6)

An aluminum nitride sintered body containing aluminum nitride crystal grains and composite oxide crystal grains containing rare earth elements and aluminum elements.
The median diameter of the aluminum nitride crystal grains is 3.0 μm or less, and the aluminum nitride crystal grains have a median diameter of 3.0 μm or less.
The difference between the cumulative value of 90% particle size of the particle size distribution based on the number of aluminum nitride crystal grains and the cumulative value of 10% particle size of the particle size distribution based on the number of aluminum nitride crystal grains is the median diameter of the aluminum nitride crystal grains. The value divided by is 0.80 to 1.00.
An aluminum nitride sintered body in which the value obtained by dividing the median diameter of the composite oxide crystal grains by the median diameter of the aluminum nitride crystal grains is 0.50 or more and less than 1.00. The aluminum nitride sintered body according to claim 1, wherein the rare earth element contains at least one selected from the group consisting of yttrium elements and lanthanoid-based rare earth elements. The aluminum nitride sintered body according to claim 1 or 2, wherein the thermal conductivity is 130 W / m · K or more and the bending strength is 700 MPa or more. According to any one of claims 1 to 3, the total content of the composite oxide crystal grains in X-ray diffraction measurement in terms of mass is 8 to 16% by mass in 100% by mass of the aluminum nitride sintered body. The aluminum nitride sintered body according to the description. The method for producing an aluminum nitride sintered body according to any one of claims 1 to 4.
A primary mixing step of mixing a raw material powder containing aluminum nitride powder and a sintering aid powder containing a rare earth element with an organic solvent to obtain a raw material slurry.
A molding step of molding an aluminum nitride molded product using the raw material slurry, and
A degreasing step of degreasing the aluminum nitride molded body with an oxidizing gas to obtain an aluminum nitride degreased body,
A sintering step of obtaining the aluminum nitride sintered body by firing the aluminum nitride degreased body under the conditions of a firing temperature of 1800 ° C. or lower and a firing time of 24 hours or less in an inert gas atmosphere.
In the primary mixing step, the volume average particle size of the aluminum nitride powder is 0.50 to 0.85 μm, and the volume average particle size of the sintering aid powder is 0.40 to 0.90 μm.
A method for producing an aluminum nitride sintered body, wherein the content of the sintering aid powder is 5 to 14% by mass in 100% by mass of the raw material powder. The method for producing an aluminum nitride sintered body according to claim 5, wherein the inert gas is nitrogen gas.

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