JP2001010865A - Silicon nitride sintered compact and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a silicon nitride sintered compact having sufficient mechanical characteristics and thermal conductivity as a circuit substrate and capable of preventing malfunction of a semiconductor element with electromagnetic waves, etc., and to provide a method for producing the silicon nitride sintered compact. SOLUTION: This silicon nitride sintered compact comprises silicon nitride crystal grains, microcrystal grains comprising a metal simple substance and/or a compound of at least one kind of element selected from W and Mo and a grain boundary phase. The microcrystal grains are dispersed in the sintered compact. Further, the sintered compact is produced by including a rare earth element in an amount of 1.0-10 wt.% expressed in terms of an oxide, Mg in an amount of 0.3-5 wt.% expressed in terms of an oxide and W and/or Mo in an amount of 0.001-5.0 wt.% expressed in terms of a carbide and making >=5 silicon nitride grains having >=30 μm major axis length exist in an optional region of 200×150 μm size in the sintered compact.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride sintered body having excellent mechanical properties such as mechanical strength and fracture toughness, high thermal conductivity, and low brightness, and a method for producing the same.

[0002]

2. Description of the Related Art A silicon nitride sintered body has mechanical properties such as mechanical strength and fracture toughness, as well as wear resistance, oxidation resistance, and the like.
Because it is excellent in various properties such as electrical insulation, it is widely used as a structural material for heat engines such as diesel and gas turbines, but has a higher thermal conductivity than sintered bodies such as BeO, AlN, and SiC. Therefore, it has not been used for a member (for example, a circuit board) requiring heat radiation.

However, the present applicant considers that a silicon nitride sintered body can be suitably used as a circuit board and the like if the heat conduction property can be improved while utilizing the excellent mechanical properties and electrical insulation properties. And various improvements have been made. For example, by controlling the size of the crystal grains of the silicon nitride polycrystal and the content of Al as an impurity, a silicon nitride sintered body having both excellent mechanical properties and good heat conduction properties can be obtained. (Japanese Unexamined Patent Publication No. Hei 3-2189)
No. 75 gazette).

Further, recently, the crystal grains of the silicon nitride polycrystal are formed into a composite structure of coarse grains and fine grains, and by controlling the ratio of the coarse grains, satisfactory mechanical properties are satisfied and high thermal conductivity is obtained. It is disclosed that a silicon nitride sintered body having the following can be obtained (JP-A-9-30866).

Further, it is composed of a silicon nitride crystal and a grain boundary phase.
oxides, carbides, nitrides, silicides, borides of elements such as i, Zr, Mo, W, etc.
A highly thermally conductive silicon nitride sintered body containing 3% by weight is also disclosed (JP-A-7-48174).

Further, the crystal grains of the silicon nitride polycrystal are formed into a composite structure of coarse grains and fine grains, the average grain size and the average aspect ratio of the entire crystal grains are specified, and an arbitrary 30
By setting the number of coarse particles having a major axis length of 20 μm or more in a region of 0 × 300 μm to 5 or more, a silicon nitride sintered body having both good mechanical properties and high thermal conductivity can be obtained. It is disclosed (JP-A-11-100276).

[0007]

Problems to be Solved by the Invention Since silicon nitride is also excellent in electrical insulation, a silicon nitride sintered body having excellent heat conduction characteristics as described above quickly dissipates heat generated from the element, and furthermore, heats and cools the substrate. Further, it can be suitably used as a circuit board required to reliably insulate between wirings on the board. For example, a semiconductor module in which a metal circuit is provided on the silicon nitride sintered body and a semiconductor element is further mounted has been studied.

However, even if the above-mentioned silicon nitride sintered body is used, it cannot be used as a circuit board due to insufficient densification of the sintered body. Mechanical properties and thermal conductivity may be insufficient,
Further, there has been a problem that malfunctions due to electromagnetic waves or the like occur depending on the type of semiconductor element mounted on the substrate. In addition, in a defect inspection of a circuit board using an automatic inspection machine, mere color unevenness of a sintered body and black spots that constantly occur on the sintered body are frequently detected as defects, which causes a problem in manufacturing. Was pointed out.

The present invention has been made in view of such problems of the prior art, and has as its object to provide a circuit board with sufficient mechanical properties and thermal conductivity, and to provide an electromagnetic wave It is an object of the present invention to provide a silicon nitride sintered body capable of preventing a malfunction of a semiconductor element due to the above and the like, and a method for manufacturing the same.

[0010]

That is, according to the present invention, silicon nitride crystal grains, fine crystal grains composed of a simple metal and / or a compound of at least one element selected from W and Mo, and grain boundaries A silicon nitride sintered body composed of a phase, wherein the fine crystal grains are dispersed in a sintered body, wherein 1.0 to 10% by weight of a rare earth element in terms of oxide;
-5% by weight of Mg, and 0.001-5.
0% by weight of W and / or Mo, and a major axis length of 30 μm in an arbitrary area of 200 μm × 150 μm of the sintered body.
A silicon nitride sintered body characterized in that five or more silicon nitride grains are present. In the silicon nitride sintered body of the present invention, it is preferable that five or more silicon nitride grains having a major axis length of 40 μm or more exist in an arbitrary region of 200 μm × 150 μm of the sintered body.

Further, in the silicon nitride sintered body of the present invention, 0.001 microcrystalline grains composed of a simple metal and / or a compound of at least one element selected from W and Mo are used.
The fine crystal grains made of a substance other than silicon nitride are preferably made of W and / or Mo carbide.

Further, in the silicon nitride sintered body of the present invention, the rare earth element contained in the sintered body is preferably Y, and preferably contains 0.1 to 10% by weight of Zr in terms of oxide. Preferably, 0 to 0.5% by weight of Al in terms of oxide
It is preferable to include In the above-described silicon nitride sintered body of the present invention, the thermal conductivity (JIS R1611) is set to 80 (W / m).
K), the fracture toughness value K _IC (JIS R1607) is set to 8 (MPa).
m ^1/2 ) or more, and the brightness (JIS Z8721) can be N6 or less. Further, according to the present invention, there is provided a circuit board comprising the above-described silicon nitride sintered body of the present invention.

Further, according to the present invention, a silicon nitride powder having an impurity oxygen content of 1.4% by weight or less, a rare earth element compound, a Mg compound, and at least one element selected from W and Mo A method for producing a silicon nitride sintered body, comprising forming a forming raw material containing a metal simple substance and / or a compound, and firing the formed body in a nitrogen atmosphere. The molding raw material is prepared so as to contain 0.3% to 5% by weight of Mg, 0.3 to 5% by weight in terms of oxides, and 0.001 to 5.0% by weight of at least one element selected from W and Mo in terms of carbides. And pressing the compact under a nitrogen gas pressure of 1 to 11 atm.
A method for producing a silicon nitride sintered body characterized in that it is fired for 2 hours or more in a temperature range of 0 ° C.

The silicon nitride powder used as a forming raw material in the production method of the present invention is preferably an α-type silicon nitride powder having a β conversion of 5% by weight or less, and a content of impurity Al of 0.01% by weight or less. It is preferred that

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The silicon nitride sintered body of the present invention comprises a predetermined amount of a rare earth element, Mg, and a metal simple substance and / or compound of at least one element selected from W and Mo as essential components. And 5 or more coarse particles of silicon nitride having a major axis length of 30 μm or more are present in the sintered body.

Such a silicon nitride sintered body is excellent in mechanical properties such as mechanical strength and fracture toughness and has a high thermal conductivity, and thus can be suitably used as a circuit board used for a semiconductor element, for example. In addition, since the brightness (JIS Z 8721) is low, it is possible to prevent malfunction of the semiconductor element due to electromagnetic waves or the like. Hereinafter, the silicon nitride sintered body of the present invention will be described in detail.

Generally, a silicon nitride sintered body has a particle size of 0.1
A sintered body having a grain boundary phase composed of an oxide, an oxynitride, or the like in a gap between silicon nitride crystal grains of about 100 μm;
Usually, the relative density is about 97 to 100%, and the number of grain boundaries per 10 μm is usually about 5 to 30.
The silicon nitride sintered body of the present invention additionally has the following features.

(1) Fine crystal grains The silicon nitride sintered body of the present invention is composed of a single metal and / or a compound of at least one element selected from W and Mo dispersed in the sintered body. Contains fine crystal grains. The microcrystal grains are dispersed in the grain boundary phase of the sintered body or in the silicon nitride crystal grains, thereby improving the mechanical strength of the sintered body. The fine crystal grains have a higher effect of improving the mechanical strength as the particle diameter is smaller. Therefore, it is necessary that the average particle diameter is at least 2 μm or less, and spherical particles having an average particle diameter of 1 μm or less are preferable. .

[0019] Furthermore, the sintered body containing the fine crystal grains is preferable in that it can block an electromagnetic wave having a low brightness and a wavelength near a visible light, thereby preventing a malfunction of a semiconductor element. In addition, in a defect inspection of a circuit board by an automatic inspection machine, mere color unevenness of a sintered body or black spots that occur regularly may be detected as defective. Such a problem can be prevented.

The fine crystal grains are preferably carbides such as WC and Mo ₂ C from the viewpoint that they are easily available. However, W and Mo such as simple metals of W and Mo or oxides are preferable.
It may be a compound of o, or may be present in a state of silicide reacted with silicon nitride.

The simple substance metal and / or compound of at least one element selected from W and Mo is contained in the sintered body in the range of 0.001 to 5.0% by weight in terms of carbide. It is necessary to be. 0.00% content
A sintered body of less than 1% by weight has a low mechanical strength and a high lightness, while a sintered body with a content of more than 5.0% by weight has a low lightness but is inferior in mechanical strength and thermal conductivity. Because it is enough.
Among the above ranges, a sintered body having a content of 0.001 to 0.2% by weight is preferable in terms of high thermal conductivity.

(2) Rare earth element The silicon nitride sintered body of the present invention is 0.1 to 10 in terms of oxide.
It contains a rare earth element by weight as an essential component. A sintered body having a rare earth element content in the above range is preferable in terms of high mechanical strength. A sintered body containing a rare earth element such as Yb or Nd may be used, but a sintered body containing Y is particularly preferable in terms of high mechanical strength.

(3) Mg The silicon nitride sintered body of the present invention has an oxide equivalent of 0.3 to 10
It contains Mg as an essential component by weight. A sintered body having a Mg content in the above range is preferable in terms of high mechanical strength and thermal conductivity.

(4) Coarse Grains The silicon nitride sintered body of the present invention has an arbitrary size of 200 μm.
In the region of × 150 μm, five or more silicon nitride particles having a major axis length of 30 μm or more, preferably 40 μm or more are present. That is, most of the silicon nitride crystal grains are columnar β-type crystals, and only some of the crystal grains have a long axis length of 30 μm or 4 μm.
It is a coarse particle of 0 μm or more.

The phonon that transfers heat is well transmitted in a portion where the crystal lattice in the sintered body is well-ordered, but is scattered and transmitted in a grain boundary phase in which the crystal lattice is disordered or in an interface between the crystal grains and the grain boundary phase. Therefore, if the crystal grains are made larger, the interface between the crystal grains and the grain boundary phase is reduced, and the thermal conductivity of the sintered body is improved. On the other hand, it is known that the mechanical strength of the sintered body decreases when the crystal grains become too large as a whole.

A sintered body in which coarse particles having an extremely long major axis length are present at a predetermined ratio as described above is preferable in that thermal conductivity and mechanical strength are balanced at a high level.
In addition, even if the sintered body contains coarse grains, those having a major axis length of less than 30 μm are not preferable in that the thermal conductivity is low. In addition, when coarse particles having an extremely long major axis length are present at a predetermined ratio, the coarse particles are three-dimensionally entangled with each other and cracks are difficult to progress, so that the fracture toughness value of the sintered body can be improved. It is also preferable in that it is possible.

(5) Zr In the silicon nitride sintered body of the present invention, Zr is 0.1% in terms of oxide.
It is preferable to contain 10 to 10% by weight. This is because a sintered body having a Zr content in the above range has high mechanical strength.

(6) Impurity Al The silicon nitride sintered body of the present invention preferably has an impurity Al content of 0.5% by weight or less in terms of oxide. This is because a sintered body having an Al content of more than 0.5% by weight has a low thermal conductivity.

The above-described silicon nitride sintered body of the present invention has a high thermal conductivity (JIS R1611) of 80 (W / mK) or more,
It has excellent mechanical properties such as room temperature strength (JIS R1601) of 650 (MPa) or more and fracture toughness value K _IC (JIS R1607) of 8 (MPam ^1/2 ) or more. Therefore, it is suitable as a circuit board used for a semiconductor element, for example. Can be used. Further, since the brightness (JIS Z8721) is as low as N6 or less, it is possible to prevent malfunction of the semiconductor element due to electromagnetic waves or the like.

The silicon nitride sintered body of the present invention is obtained by forming a forming raw material comprising silicon nitride powder and a sintering aid such as Y ₂ O ₃ as in a conventional manufacturing method, and forming the formed body with nitrogen. Although it cannot be obtained only by firing in an atmosphere or an inert gas atmosphere, rare earth element compounds, Mg compounds, W, Mo
A simple metal of at least one element selected from the group consisting of:
Alternatively, the compound can be produced by allowing the compound to be contained in the molding raw material at a predetermined ratio and firing under predetermined firing conditions. Hereinafter, the production method of the present invention will be described in detail.

In the production method of the present invention, first, a molding raw material is molded to produce a molded body. The forming raw material used in the present invention is a metal of at least one element selected from the group consisting of a silicon nitride powder having an impurity oxygen content of at most 1.4% by weight, a rare earth element compound, a Mg compound, and W and Mo. It contains a simple substance and / or a compound.

Since silicon nitride is a hardly sinterable ceramic, the silicon nitride powder constituting the forming raw material has a particle size of 2 μm.
It is preferable to use fine particles of m or less. This is because by reducing the particle size, the surface tension increases and sintering becomes easy. Silicon nitride has an α-phase and a β-phase as a crystal structure, but it is preferable that the silicon nitride powder used as a forming material is an α-type silicon nitride powder having a β conversion of 5% or less. β
If the conversion ratio exceeds 5%, the sinterability deteriorates and the mechanical strength of the sintered body decreases. In addition, when coarse β powder is added as a seed crystal, care must be taken because the mechanical strength of the sintered body is significantly reduced.

Further, the content of oxygen existing as an impurity in the silicon nitride powder needs to be 1.4% by weight or less. Although the reason is not clear, if the oxygen content exceeds 1.4% by weight, the thermal conductivity tends to decrease when the sintered body is formed, and the desired thermal conductivity cannot be obtained. .

Further, the silicon nitride powder preferably has an impurity Al content of 0.01% by weight or less. Al
This is because the solid solution dissolves in silicon nitride crystal grains and scatters phonons that transfer heat, thereby lowering the thermal conductivity of the sintered body. For the same reason, the content of impurity Al in the entire forming raw material needs to be 0.5% by weight or less in terms of oxide.

In the production method of the present invention, a rare earth element compound such as an oxide, a nitrate, or a carbonate of a rare earth element is contained in the forming raw material. The rare earth element compound is uniformly distributed at the interface of the silicon nitride crystal grains and combines with the impurity SiO ₂ or other sintering aid such as MgO to form a liquid phase or crystal having a high melting point. This is because it has the effect of densifying the body and increasing the mechanical properties.

In order to obtain the above-mentioned effects, it is necessary to contain at least 0.1% by weight or more of a rare earth element compound in terms of oxide. It may be formed and the thermal conductivity may decrease. Therefore, the content needs to be at most 10% by weight or less.

Further, in the production method of the present invention, a Mg compound such as MgO is contained in the forming raw material. Rare earth element compound (especially Y ₂ O ₃ ) and Mg compound (especially Mg
When O) is used in combination, a liquid phase having a high melting point is formed during sintering, so that the sintered body can be densified even if the sintering aids such as Y ₂ O ₃ and MgO are reduced. It becomes possible. That is, when the Mg compound is used as an essential component of the forming raw material, the grain boundary phase in the sintered body can be reduced, so that the mechanical strength and thermal conductivity of the sintered body can be improved. preferable.

However, in the range of the present invention in which the rare earth element compound in the forming raw material is 0.1 to 10% by weight in terms of oxide, 0.3% by weight or more of Mg in terms of oxide is used.
If the compound is not contained, the above effects cannot be obtained. On the other hand, when the Mg compound is excessively contained, there is a possibility that a problem that the sintered body is not densified may occur. Therefore, the content needs to be at most 10% by weight in terms of oxide.

Furthermore, in the production method of the present invention, a simple substance and / or a compound of at least one element selected from W and Mo in the forming raw material (hereinafter referred to as “W-based auxiliary”,
It is called "Mo-based auxiliary agent". ). W-based auxiliaries,
By adding Mo-based auxiliaries as fine crystal grains having an average particle size of 2 μm or less, not only the effect of improving mechanical strength and lowering of lightness can be obtained, but also rare earth element compounds (particularly, Y ₂
The combined use of O ₃ ) and a Mg compound (particularly MgO) is preferable in that the densification of the sintered body can be further promoted. This is presumably because the W-based auxiliary agent and the Mo-based auxiliary agent contribute to the liquid phase forming process during sintering.

Examples of the W-based auxiliary agent and the Mo-based auxiliary agent include WC,
It is preferable to use a carbide such as Mo ₂ C,
It may be a single metal of W or Mo, or a compound of W or Mo other than a carbide such as an oxide. When the W-based and Mo-based auxiliaries are added as fine crystal grains to the forming raw material, they usually remain in the sintered body as they are, but react with the silicon nitride during firing to form silicides. It may be converted. In any case, at least one element selected from W and Mo is 0.001-5.
If the forming raw material is prepared so as to contain 0% by weight, the effect of the present invention can be obtained.

In the past, SiC, TiC, TiN and the like were sometimes included in the forming raw material as auxiliary agents for lowering the brightness of the sintered body, but these auxiliary agents were W-based auxiliary agents and Mo-based auxiliary agents. Unlike the auxiliary, there is no effect of improving the mechanical strength, and white spots or tea spots may be generated on the sintered body. Therefore, in order to obtain the effects of the present invention, it is essential to use a W-based auxiliary agent and / or a Mo-based auxiliary agent.

The forming raw material of the present invention includes silicon nitride powder, rare earth element compound, Mg compound, W, Mo
A simple metal of at least one element selected from the group consisting of:
Alternatively, another substance may be added as long as the compound and the compound are contained in the above-mentioned predetermined ratio. For example, it is also preferable to include ZrO ₂ as a sintering aid. 0.1 ~
By incorporating ZrO ₂ in the range of 10% by weight, it is possible to increase the mechanical strength while preventing a decrease in thermal conductivity.

The content of components other than silicon nitride crystal grains (hereinafter referred to as “sintering aids, etc.”) with respect to the entire forming raw material is not particularly limited, but is preferably 1 to 10% by weight. Sintering does not proceed if there is too little sintering aid, etc.,
If the amount is too large, a large amount of glass phase is formed between the silicon nitride particles, and the thermal conductivity of the sintered body decreases.

The above-mentioned molding raw material can be formed into a molded body by a conventionally known molding method. For example, water is added to the above molding material, and the mixture is mixed and pulverized with a stirring tank type stirring mill (trade name: Attritor (Mitsui Miike Kakoki Co., Ltd.) or the like) to form a slurry. After adding a binder, the slurry is added to a spray dryer. After granulating and drying, the granulated powder is put into a molding die, and subjected to uniaxial molding, followed by isostatic pressing.
Such a molding method is preferable in that aggregation at the molding material interface is prevented, uniform dispersion is possible, and fluidity can be imparted to the molding material.

Further, the addition of the binder is preferable in that the frictional resistance between the primary particles is reduced and the granulated powder is easily crushed, so that the generated defects can be reduced. The type of the binder is not particularly limited, and examples thereof include organic materials such as polyvinyl alcohol and polyethylene glycol.

The above compact is fired in a nitrogen atmosphere to form a sintered body in order to prevent decomposition and oxidation of silicon nitride, but it is preferable to perform firing under a nitrogen gas pressure of 1 to 11 atm. If the pressure is not at least 1 atm, silicon nitride will sublime or decompose, while if it is at most 11 atm, the firing furnace does not need to have a special pressure-resistant structure, so that it can be easily manufactured and the manufacturing cost can be reduced. In addition, 1
When sintering is performed under nitrogen gas pressure of about 11 atm, the sintering temperature needs to be 1800 to 2000 ° C. in order to obtain a high-density sintered body while preventing decomposition of silicon nitride.

Further, when firing in a temperature range of 1800 to 2000 ° C., firing must be performed for 2 hours or more. If the firing time is short, crystal grains do not grow due to dissolution and precipitation of silicon nitride crystal grains, and coarse grains having a major axis length of 30 μm or more are not formed, so that the thermal conductivity of the sintered body does not improve.

As described above, according to the manufacturing method of the present invention, for example, heat can be suitably used as a circuit board used for a semiconductor element, and malfunction of the semiconductor element due to electromagnetic waves or the like can be prevented. Conductivity (JIS R1611)
Is 80 (W / mK) or more and room temperature strength (JIS R1601) is 6
50 (MPa) or more, fracture toughness value K _IC (JISR1607) is 8
(MPam ^1/2 ) or more, and the brightness (JIS Z8721) is N6
The following silicon nitride sintered body can be easily manufactured.

[0049]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to these examples. The silicon nitride powder, the sintering aid, and the fine crystal grains used in the following Examples and Comparative Examples all had an impurity Al content of 0.01% by weight or less.

(Evaluation Method of Sintered Body) The manufactured silicon nitride sintered body was evaluated by the following evaluation methods for relative density, thermal conductivity, major axis length of silicon nitride crystal grains, and average grain size of fine crystal grains. ,
The content of rare earth elements and the like, lightness, β conversion, room temperature strength, fracture toughness, and impurity oxygen content were measured and evaluated.

(1) Relative density: Measured by the Archimedes method of an aqueous solvent. The theoretical density in each auxiliary composition was calculated by weighted average based on the compounding weight of the density of silicon nitride and each auxiliary alone. (2) Thermal conductivity: A sintered body processed into a cylindrical shape having a diameter of 10 mm and a thickness of 3 mm was used as a sample and measured by a laser flash method in accordance with the method described in JIS R1611.

(3) Length of silicon nitride crystal grains: After cutting the sintered body, the mirror-finished surface is etched with weak hydrofluoric acid to emphasize silicon nitride grain boundaries, Made it easier to see. Next, using a scanning electron microscope (SEM), an area of 200 μm × 150 μm was observed at five arbitrary positions at a magnification of 500 × and photographed.
After enlargement of the photograph four times, the number of silicon nitride grains having a major axis length of 30 μm or more and 40 μm or more present in the area was counted, and the average was calculated.

(4) Average grain size of fine crystal grains: After cutting the sintered body, it was mirror-finished. Next, using a SEM / EDS, a region of 20 μm × 15 μm at a magnification of 5000 ×
Observation was made at any one place, and a reflected electron image was taken.
The average particle size of the dispersed particles that glow brightly in the photograph was determined. Since W and Mo are heavy elements, they are brightly lit and observed when a reflected electron image is taken. W, Mo for dispersed particles
Was confirmed by EDS.

(5) Rare earth elements, Mg, Zr, Al,
W, Mo content: The sintered body was decomposed under pressure and calculated by ICP wet analysis. (6) Brightness: Based on the method described in JIS Z8721, the sintered body and the color of the standard color chart were compared to determine the brightness to the first decimal place. However, the first place of the decimal point was only 0 or 5. As the standard color chart, "Standard color sample book for paint 1995 T edition, pocket edition: Japan Paint Industry Association" was used.

The lightness is an index of the magnitude of the reflectance of the surface of the object. The ideal lightness of black is N0 and the ideal lightness of white is N10. The color is divided into ten so as to be displayed. (7) β conversion: X-ray diffraction revealed that (21) of α-Si ₃ N ₄
0), (201) diffraction intensity α (210), α (20)
1) and the diffraction intensity β (101) and β (210) of the (101) and (210) planes of β-Si ₃ N ₄ were determined by the following equation.

[0056]

(Equation 1)

(8) Room temperature strength: A sintered body processed into a rod having a length of 4 mm × a width of 3 mm × a length of 40 mm was used as a sample,
The four-point bending strength was measured according to the method described in SR1601. However, the sintered body of Example 4-1 and Comparative Example 4-1 (4
0 × 50 × 0.6 mm flat plate)
The three-point bending strength of 0 mm was measured.

(9) Fracture toughness: Measured by the SEPB method according to the method described in JIS R1607. (10) Impurity oxygen content of raw silicon nitride powder: measured by combustion gas analysis.

Example 1 In Example 1, the effects of the composition of the forming raw material and the manufacturing conditions were examined.

A commercially available silicon nitride powder having a β conversion ratio and an impurity oxygen amount shown in Table 1 having a specific surface area of 11 m ² / g, Mo ₂ C or WC as fine crystal grains, and Mg as a sintering aid
ZrO ₂ was further added as a sintering aid to the forming raw material consisting of O and Y ₂ O _3, and the mixture was prepared at the ratio shown in Table 1. In Table 1, the contents of MgO and Y ₂ O ₃ are shown in the forming raw material, and the contents of Mo ₂ C or WC and ZrO ₂ are shown in the addition ratio to the forming raw material.

Water is added to the above molding material, and a stirring tank type stirring mill (trade name: Attritor (Mitsui Miike Kakoki Co., Ltd.))
) To form a slurry,
(Polyvinyl alcohol) and PEG (polyethylene glycol) are added as binders, and then granulated and dried by a spray dryer.
After the uniaxial molding, a molded product of 60 × 60 × 6 mm was produced by isostatic pressing at 690 MPa.

After the binder was removed from the obtained molded body, the molded body was fired at 1900 ° C. in an N ₂ atmosphere.
-1 to 1-9 and Comparative Examples 1-1 to 1-4 were obtained.
Table 1 shows the raw material composition and production conditions, and Table 2 shows the sintered body characteristics.
Table 3 shows the microstructure and characteristics of the sintered body. Comparative Example 1-3 was the same as Example 1-3 except that the firing time was 1 hour.
In Comparative Example 1-4, a sintered body was produced in the same manner as in Example 1-3 except that a forming raw material was prepared using silicon nitride powder having an impurity oxygen content of 1.6% by weight.

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

[Table 3]

(Results) As long as the composition of the forming raw material was within the range of the present invention, a sintered body having good thermal conductivity, room temperature strength and lightness could be obtained. The type of rare earth oxide is Y ₂
As O ₃ limited not examples 1-5 can obtain the same effect even Yb ₂ O _3, as can be seen from the comparison between Examples 1-3 and 1-4, with the addition of ZrO ₂ Room temperature strength increased.

On the other hand, as shown in Comparative Examples 1-1 and 1-2, when the rare earth oxide or MgO was not added or was out of the range of the present invention, coarse particles having a major axis of 30 μm or more were reduced, Conductivity and fracture toughness values decrease. When the firing time was short as in Comparative Example 1-3, the silicon nitride crystal grains could not grow, so that coarse grains were not formed and the thermal conductivity and the fracture toughness decreased. Furthermore, when silicon nitride powder having a large amount of impurity oxygen is used as in Comparative Examples 1-4, coarse particles are formed within the scope of the present invention, but the required thermal conductivity cannot be obtained. Was.

Example 2 In Example 2, the effect of adding fine crystal grains was verified. In the same manner as in Example 1-3,
Sintered bodies were manufactured by adjusting only the amount of Mo ₂ C added as fine crystal grains, and Examples 2-1 and 2-2 and Comparative Examples 2-1 and 2-1 were performed.
A sintered body 2-2 was obtained. Table 4 shows raw material composition and manufacturing conditions.
Table 5 shows the characteristics of the sintered body, and Table 6 shows the microstructure of the sintered body and the characteristics of the sintered body.

[0069]

[Table 4]

[0070]

[Table 5]

[0071]

[Table 6]

(Results) As long as the added amount of the fine crystal grains was within the range of the present invention, a sintered body having good thermal conductivity, room temperature strength and lightness could be obtained. On the other hand, as in Comparative Example 2-1, M
When o ₂ C was not added, the thermal conductivity was high but the brightness was high, and when Mo ₂ C was excessively added as in Comparative Example 2-2, the thermal conductivity sharply decreased.

Example 3 In Example 3, the effect of the type of the substance constituting the fine crystal grains was verified. In the same manner as in Example 1-5, a sintered body was similarly manufactured by changing the type of the material constituting the fine crystal grains, and
A sintered body of 3-4 was obtained. Table 4 shows raw material composition and manufacturing conditions.
Table 5 shows the characteristics of the sintered body, and Table 6 shows the microstructure of the sintered body and the characteristics of the sintered body.

(Results) The type of the substance constituting the fine crystal grains is not limited to Mo ₂ C, and the same effect can be obtained with Mo alone, MoSi ₂ , WC or a mixture thereof.

(Example 4) Example 1-3, Comparative example 2-1
By molding a molding raw material having the same composition as in Example 1 at 150 MPa, a molded body of 50 × 60 × 1 mm was obtained.
-3, baking was performed under the same conditions as in Comparative Example 2-1, and finally, grinding was performed to produce 100 plate-shaped sintered bodies each having a size of 40 × 50 × 0.6 mm (each of which was Example 4). −
1, referred to as the sintered body of Comparative Example 4-1. ).

(Results) The average values of the thermal conductivity and the room temperature strength (three-point bending strength) of each of the three sintered bodies of Example 4-1 and Comparative Example 4-1 were determined as in Example 4--1. The sintered body of No. 1 was good at 85 W / mK, 730 MPa, and the sintered body of Comparative Example 4-1 was good at 86 W / mK, 650 MPa.

However, the sintered body of Example 4-1 had a uniform gray-black color and a low brightness of N5.5, whereas the sintered body of Comparative Example 4-1 had a light cream color. The brightness was also high at N7.5. Further, color unevenness and black spots having an outer diameter of 1 mm or less were observed on the surface of the sintered body of Comparative Example 4-1.

Further, for each of the above-mentioned 100 sintered bodies, an image of the sintered body surface is imaged with a CCD camera, and the color shading is recognized. As a result of the inspection, it was determined that all of the 100 sintered bodies of Example 4-1 had no black spots and no color unevenness, but 53 of the 100 sintered bodies of Comparative Example 4-1 had black spots. Or a defective product having color unevenness.

Example 5 Example 4-1 and Comparative Example 4-1
, A commercially available Ag-Cu-Ti wax was applied to each
screen printing on both sides except for the m width, and a copper plate having a thickness of 0.3 mm stuck on both sides.
By performing a heat treatment for a minute, a silicon nitride / copper composite joined body was obtained.

Next, a circuit forming resist was printed on one surface of the composite joined body, cured, and then etched with an aqueous ferric chloride solution to form a circuit pattern. Further, in order to remove the brazing material between the circuits, the circuit boards were washed with an aqueous solution of acidic ammonium fluoride, and then washed several times with water to produce circuit boards (each of which was the circuit board of Example 5-1 and Comparative Example 5-1). ).

The circuit boards of Example 5-1 and Comparative Example 5-1 showed no difference in the wetting of the brazing material, the bonding state of copper, and the like.
All of them had high thermal conductivity and could withstand use as an insulated circuit board. However, since the circuit board of Comparative Example 5-1 has high brightness, there is a concern that malfunction of the semiconductor element due to electromagnetic waves having a wavelength near visible light or the like may occur.

[0082]

As described above, the silicon nitride sintered body of the present invention has a thermal conductivity (JIS R1611) of 80 (W / m).
K) or higher and room temperature strength (JIS R1601) of 650 (M
Pa) and a fracture toughness value K _IC (JIS R1607) of 8 (MP
am ^1/2 ) or more, which is excellent in mechanical properties, and thus can be suitably used as a circuit board used for a semiconductor element, for example. Further, since the lightness (JIS Z8721) is as low as N6 or less, it is possible to prevent malfunction of the semiconductor element due to electromagnetic waves or the like.

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Claims (14)

[Claims] The present invention comprises a silicon nitride crystal grain, a microcrystal grain composed of a simple substance and / or a compound of at least one element selected from W and Mo, and a grain boundary phase, wherein the microcrystal grain is a sintered body. A silicon nitride sintered body dispersed therein, comprising 1.0 to 10% by weight of a rare earth element in terms of oxide, 0.3 to 5% by weight of Mg in terms of oxide, and 0.1% in terms of oxide;
It is characterized in that five or more silicon nitride grains containing 001 to 5.0% by weight of W and / or Mo and having a major axis length of 30 μm or more are present in an arbitrary area of 200 μm × 150 μm of the sintered body. Silicon nitride sintered body. 2. An arbitrary 200 μm × 150 μm of a sintered body
2. The silicon nitride sintered body according to claim 1, wherein five or more silicon nitride grains having a major axis length of 40 μm or more are present in the region. 3. The silicon nitride according to claim 1, which contains 0.001 to 0.2% by weight of fine crystal grains made of a metal simple substance and / or a compound of at least one element selected from W and Mo. Sintered body. 4. The silicon nitride sintered body according to claim 1, wherein the fine crystal grains dispersed in the sintered body are made of a carbide of W and / or Mo. 5. The silicon nitride sintered body according to claim 1, wherein the rare earth element contained in the sintered body is Y. 6. Zr of 0.1 to 10% by weight in terms of oxide
The silicon nitride sintered body according to any one of claims 1 to 5, comprising: 7. The silicon nitride sintered body according to claim 1, comprising 0 to 0.5% by weight of Al in terms of oxide. 8. The thermal conductivity of the sintered body (JIS R1611) is 80.
(W / mK) or more, The silicon nitride sintered body according to any one of claims 1 to 7. 9. The silicon nitride sintered body according to claim 1, wherein the brightness (JIS Z8721) of the sintered body is N6 or less. 10. The fracture toughness value K _IC of a sintered body (JIS R160
The silicon nitride sintered body according to any one of claims 1 to 9, wherein 7) is 8 (MPam ^1/2 ) or more. 11. A circuit board comprising the silicon nitride sintered body according to claim 1. 12. A silicon nitride powder having an impurity oxygen content of 1.4% by weight or less, a rare earth element compound, a Mg compound, and a simple metal and / or compound of at least one element selected from W and Mo. A method for producing a silicon nitride sintered body, comprising: forming a forming raw material containing: and sintering the formed body in a nitrogen atmosphere, wherein the rare earth element is 1.0 to 10% by weight in terms of oxide and Mg is oxidized. 0.3 to 5% by weight in terms of material, 0.001 to 0.001 in terms of carbide in at least one element selected from W and Mo
The molding raw material is prepared so as to contain 5.0% by weight, and the molded body is subjected to 1800 to 11,000 atmospheres of nitrogen gas pressure.
A method for producing a silicon nitride sintered body, comprising firing at a temperature of 2000 ° C. for 2 hours or more. 13. An α-type silicon nitride powder having a β conversion ratio of 5% or less in a silicon nitride powder used as a forming raw material.
3. The method for producing a silicon nitride sintered body according to item 1. 14. The method for producing a silicon nitride sintered body according to claim 12, wherein the content of the impurity Al in the silicon nitride powder used as a forming raw material is 0.01% by weight or less.