JPH09157030A - Production of silicon nitride sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a sintered compact having high heat conductivity as well as high strength peculiar to silicon nitride, excellent in heat radiating property and especially fit to produce a circuit board. SOLUTION: A compact consisting of silicon nitride powder, a sintering aid and an org. binder is dewaxed and sintered to produce the objective silicon nitride sintered compact contg. <=0.25wt.% (expressed in terms of metal) Al component and <=0.3wt.% (expressed in terms of metal) Fe component. The silicon nitride powder has 15-40wt.% β-phase content, the sintering aid contains a compd. of Mg and/or Ca and the amt. of the compd. is 0.5-7.0 pts.wt. (expressed in terms of oxide) per 100 pts.wt., in total, of the silicon nitride powder and the compd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon nitride sintered body having a high thermal conductivity, and in particular, it has a high thermal conductivity and a high heat dissipation characteristic in addition to the original high strength characteristics of silicon nitride. The present invention relates to a method for manufacturing a silicon nitride sintered body suitable for manufacturing a substrate.

A ceramic sintered body containing silicon nitride as a main component has excellent heat resistance even in a high temperature environment of 1000 ° C. or higher, and also has excellent thermal shock resistance due to its low coefficient of thermal expansion. Therefore, it has been attempted to be applied to various high-strength heat-resistant parts such as gas turbine parts, engine parts, and steel-making machine parts as high-temperature structural materials replacing conventional heat-resistant superalloys. In addition, since it has excellent corrosion resistance to metals, it has been tried to apply it as a melt-resistant material of molten metal, and because it has excellent wear resistance, it can be put to practical use in sliding members such as bearings and cutting tools. ing.

[0003]

2. Description of the Related Art Conventionally, a silicon nitride sintered body is a silicon nitride-oxide of rare earth element (yttrium oxide or the like) -aluminum oxide, silicon nitride-oxide of rare earth element-aluminum oxide-aluminum nitride, silicon nitride. A system in which an oxide of a rare earth element and aluminum oxide are used together as a sintering aid is the mainstream, such as an oxide of a rare earth element, an aluminum oxide, an oxide of titanium or zirconium.

Oxides of rare earth elements such as yttrium oxide (Y ₂ O ₃ ) are added in order to enhance the sinterability and make the sintered body dense and strong, and aluminum oxide is a high temperature structural material. Is added to increase the durability of the.

However, in the above-mentioned silicon nitride sintered body, the electrical characteristics such as withstand voltage are about the same as aluminum nitride and there is no problem, and the mechanical strength such as the toughness value is excellent, but the thermal conductivity characteristics. Is aluminum nitride (AlN)
Compared with sintered bodies, beryllium oxide (BeO) sintered bodies, silicon carbide (SiC) sintered bodies, etc., they are extremely low, so there was a difficulty in applying them to circuit boards for semiconductors, which particularly require heat dissipation. .

On the other hand, the aluminum nitride sintered body has a higher thermal conductivity and a lower thermal expansion coefficient than other ceramics sintered bodies, so that higher speed, higher output, multi-functionality and larger size can be achieved. It is widely used as a circuit board material and a package material for semiconductor chips, but its mechanical strength is not sufficient.

Therefore, the advent of a ceramic sintered body having high strength and high thermal conductivity has been earnestly desired. In order to meet these demands, the rare earth elements are converted into oxides of 2.0 to
7.5% by weight, 2.0% by weight or less of at least one of aluminum nitride and alumina, other Li, Na, K,
Fe, Ca, Mg, Sr, Ba, Mn, B, etc., containing 0.3 wt% or less of an impurity cation element, consisting of a β phase type silicon nitride crystal and a grain boundary phase, and a crystal compound in the grain boundary phase. The area ratio of the phase to the whole grain boundary phase is set to 20% or more, the porosity is 1.5% or less, and the thermal conductivity is 60 W / m.
A silicon nitride sintered body having a K or more and a three-point bending strength of 80 kg / mm ² or more at room temperature is proposed (Japanese Patent Laid-Open No. 6-1).
35771).

Regarding its manufacturing method, the oxygen content is 1.
7% by weight or less, preferably 0.5 to 1.5% by weight, the total amount of the above impurity cation elements is 0.3% by weight or less, preferably 0.2% by weight or less, and α phase 90% by weight or more, preferably 9%.
A compact is molded using 3% by weight or more of α-type silicon nitride powder, and after degreasing, pressure-sintered in atmosphere at a temperature of 1800 to 2000 ° C., and then formed from the oxide of the rare earth element at the sintering temperature. The temperature until the liquid phase solidifies 10
It is disclosed to cool at a cooling rate of 0 ° C. or less.

That is, in this method, an aluminum component is essential as a sintering aid, and the grain boundary phase (sintering aid phase) is crystallized by a special method called slow cooling, and further Li, N is added.
High thermal conductivity is achieved by defining a cation element such as a, K, Fe, Ca, Mg, Sr, Ba, Mn, or B as an impurity having an adverse effect.

[0010]

However, in this method, since the sintering temperature is as high as 1900 ° C., not only is the burden on the firing furnace large, but the cooling rate is set to a small value of 100 ° C. or less per hour. There is a problem that productivity is significantly reduced.

The present invention solves these problems and produces a silicon nitride sintered body having excellent mechanical properties and thermal conductivity, particularly a silicon nitride sintered body suitable for a circuit board, with high productivity. The purpose is to do.

[0012]

That is, the present invention is a method for manufacturing a silicon nitride sintered body, which is summarized below. (Claim 1) A compact containing a silicon nitride powder, a sintering aid and an organic binder is degreased and then sintered to have an Al component of 0.25 wt% or less in terms of metal and an Fe component of 0.3 in terms of metal.
In the method for producing a silicon nitride sintered body of less than or equal to wt%,
The silicon nitride powder has a β phase content of 15 to 40% by weight, and the sintering aid contains a compound of Mg and / or Ca, and the ratio of the compound is the same as that of the silicon nitride powder. A method for producing a silicon nitride sintered body, characterized in that the total amount is 0.5 to 7.0 parts by weight per 100 parts by weight in terms of oxide of the compound. (Claim 2) The sintering aid further contains a rare earth element compound, and the ratio of the rare earth element compound is 15 parts by weight or less per 100 parts by weight in total of the silicon nitride powder and the oxide conversion of the rare earth element compound. The method for producing a silicon nitride sintered body according to claim 1, wherein. (Claim 3) In the silicon nitride sintered body according to claim 1 or 2, when the number of grain boundaries observed on the polished surface of the silicon nitride sintered body is a straight line in an arbitrary section, 7 per 10 µm.
A method for producing a silicon nitride sintered body for producing a circuit board, characterized in that the number is less than the number and the thermal conductivity is 60 W / m · K or more.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below.

The silicon nitride powder used in the present invention has a β phase content of 15 to 4 in consideration of sinterability, strength and thermal conductivity.
0% by weight, preferably 20 to 35% by weight, and 0.25% by weight or less of Al in terms of metal, preferably 0.15% by weight
Hereinafter, Fe is 0.3 wt% or less, preferably 0.2 wt% or less in terms of metal. Also, considering the decrease in thermal conductivity and the decrease in weather resistance, Li, Be, Na,
It is preferable that the total content of impurity cation elements such as K, Mn, and Ga is suppressed to 0.3% by weight or less, particularly 0.2% by weight or less. These impurity cation elements are unlikely to be mixed in in a general method for producing silicon nitride powder.

Regarding the amount of oxygen in the silicon nitride powder, the amount of oxygen normally contained in commercially available silicon nitride raw material powders for structural materials is 2.0% by weight or less, particularly about 0.5 to 1.5% by weight. .

The average particle size of the silicon nitride powder is preferably 3 μm or less, particularly 2 μm or less, from the viewpoint of producing a dense and high-strength silicon nitride sintered body. 50 μm for silicon nitride powder
It is important not to include the above coarse particles.

On the other hand, the sintering aid used in the present invention is M
It contains a compound of g and / or Ca, and examples thereof include MgO, CaO, and forsterite (Mg ₂
SiO ₄ ), steatite (MgSiO ₃ ), Mg (O
H) ₂ , Ca (OH) _2, etc. oxides, hydroxides, silicides, nitrides, and also basic carbonates, nitrates, formates, acetates and various alkoxides of Mg and / or Ca. is there.

Higher purity sintering aids are more suitable,
Particularly, in the present invention, for the purpose of producing a silicon nitride sintered body having high thermal conductivity, the Al component is 0.25 wt% in terms of metal.
In the following, since the Fe component is 0.3 wt% or less in terms of metal, it is desirable that the Al component and the Fe component in the sintering aid be as small as possible. The average particle size of the sintering aid is
3 μm or less, especially 2 μm from the viewpoint of compatibility with silicon nitride powder
The following is preferred.

The proportion of the sintering aid is 0.5 to 7.0 per 100 parts by weight in total of the oxide (MgO and / or CaO) equivalent of the compound of Mg and / or Ca and the silicon nitride powder.
Parts by weight. If it is less than 0.5 parts by weight, it will not be densified and will be a low-strength and low thermal conductivity sintered body, and if it exceeds 7.0 parts by weight, an excessive amount of grain boundary phase will be generated and the thermal conductivity will decrease.
Preferably it is 2 to 5 parts by weight.

In the present invention, the compound of Mg and / or Ca and the rare earth element compound may be used in combination as a sintering aid. Exemplifying rare earth element compounds,
Y, La, Sc, Pr, Ce, Nd, Sm, Dy, H
Oxides such as o and Gd, or precursors that become those oxides during the sintering process. These rare earth element compounds react with the silicon nitride raw material powder to generate a liquid phase and function as a sintering accelerator. Among them, yttrium oxide (Y ₂ O
₃ ) or cerium oxide (CeO ₂ ) is preferred. The ratio of the rare earth element compound is preferably 15 parts by weight or less, and particularly preferably 2 to 10 parts by weight, further preferably 3 to 6 parts by weight, per 100 parts by weight of the total of the oxide conversion value of the rare earth element compound and the silicon nitride powder. If it exceeds 15 parts by weight, an excessive amount of grain boundary phase is generated, resulting in a decrease in thermal conductivity and a decrease in strength.

Examples of the organic binder used in the present invention include polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, polyethylene oxide, methyl cellulose, hydroxypropylmethyl cellulose, carboxymethyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, hydroxypropyl cellulose, various waxes, and acrylic. Examples include resin (polyacrylate, polymethacrylate, etc.) and urethane resin. These are usually used in an amount of 0.1 to 20 parts by weight per 100 parts by weight of the total of silicon nitride and a sintering aid, although it varies depending on the forming means of the formed body.

In the present invention, the above silicon nitride powder, the sintering aid and the organic binder are mixed, and further, a medium such as water, ethyl alcohol, benzene, or toluene is mixed according to the molding method to mold into a predetermined shape. Shape the body. As a forming method, a die pressing method, a doctor blade method, a sheet forming method such as an extrusion forming method, or the like can be adopted.

The molded body is then heated at a temperature of 300 to 800 ° C. to remove the organic binder and degrease it. The degreasing atmosphere is an oxidizing atmosphere or a non-oxidizing atmosphere, although it depends on the type of organic binder. The degreased compact is sintered at a temperature of 1600 to 2000 ° C. for a predetermined time in an atmosphere of an inert gas such as nitrogen gas or argon gas.
The sintering temperature varies depending on the sinterability of the silicon nitride raw material powder used, the type and amount of the sintering aid, and the desired sintered body structure. When sintering is performed at normal pressure without applying pressure such as nitrogen gas, the sintering is performed at a temperature of about 1600 to 1800 ° C.

In the present invention, the size of the silicon nitride crystal particles in the sintered body is increased to a specific value or more by changing the β phase content and particle size of the silicon nitride powder and the type and amount of the sintering aid. can do. For example, the number of grain boundaries observed on the polished surface of the silicon nitride sintered body can be less than 7 per 10 μm when a straight line is drawn in an arbitrary cross section. The thermal conductivity of such a silicon nitride sintered body is 60 W /
Since it exhibits m · K or more, it is particularly suitable for producing a circuit board.

Since the porosity of the silicon nitride sintered body affects the thermal conductivity and strength, it is 2.0% or less, especially 1.5%.
The following is preferred. If the porosity exceeds 2.0%, the thermal conductivity and the strength of the silicon nitride sintered body decrease. The porosity can be adjusted by changing the particle size of the silicon nitride powder, the type and amount of the sintering aid used, and the sintering conditions.

Further, the strength and fracture toughness of the silicon nitride sintered body are appropriately selected according to the balance of the three factors including the thermal conductivity depending on the application, but generally, room temperature three-point bending strength is 600 MPa or more. The room temperature fracture toughness value is 5 MPa√m or more. These adjustments can be performed by changing the β phase content and particle size of the silicon nitride powder, the type and amount of the sintering aid, and the sintering conditions.

[0027]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Examples 1 to 25 Comparative Examples 1 to 6 Silicon nitride powder and sintering aid (compound of Mg and / or Ca, rare earth element compound, silica powder) were used in the ratios shown in Table 1, and ethyl alcohol was used as a medium. After wet-mixing with a ball mill using silicon nitride balls for 20 hours, it was dried to prepare a raw material powder mixture. The amounts of the sintering aids shown in Table 1 are parts by weight of the oxide conversion value of each compound with respect to the total of 100 parts by weight of the oxide conversion value of each compound and the silicon nitride powder.

Al and Fe in the raw material powder of silicon nitride
Other impurities such as Li, Be, Na, K, Mn, and Ga were below the detection limit, and were at most 0.01% by weight. The average particle size of the sintering aid is 0.8 to 1.5 μm.
m, the impurities such as Li, Be, Na, K, Mn, and Ga were below the detection limit, and the total impurities including Al and Fe were at most 0.01% by weight.

To the obtained raw material powder mixture, 8% by weight of a 5% by weight aqueous solution of polyvinyl alcohol was added and uniformly mixed, and then CIP molding was carried out at a molding pressure of 2000 kg / cm ² to obtain a length 50 mm × width 50 mm × thickness. A molded body having a size of 5 mm was molded, heat-treated in air at a temperature of 500 ° C. for 2 hours to degrease, and then sintered under the conditions shown in Table 1.

Regarding the obtained silicon nitride sintered body, the number of grain boundaries per 10 μm, thermal conductivity (25 ° C.), and
Three-point bending strength and fracture toughness at room temperature were measured. Table 1 shows the results.

(1) Number of Grain Boundaries After polishing the polished surface of the silicon nitride sintered body by alkali etching so that the grain boundaries can be identified, a grain boundary on an arbitrary straight line having a total length of 500 μm is obtained by a scanning electron microscope. Was measured and calculated as the number of grain boundaries per 10 μm. (2) Thermal conductivity (25 ° C.) Measured by the laser flash method. (3) Three-point bending strength at room temperature It was measured according to JIS-R1601. (4) Room temperature fracture toughness value Measured according to JIS-R1607 (IF method). The elastic modulus used to calculate the fracture toughness value is JIS-R16.
02 (Static elastic modulus test method).

[0033]

[Table 1]

As is clear from Table 1, the examples are silicon nitride sintered bodies having higher thermal conductivity and higher strength than the comparative examples.

[0035]

According to the present invention, a silicon nitride sintered body having high thermal conductivity and high strength, which is particularly suitable for producing a circuit board, is subjected to special sintering such as gradual cooling at a relatively low sintering temperature. It can be manufactured with high productivity without performing.

The silicon nitride sintered body produced according to the present invention can be used for electronic members such as semiconductor substrates, circuit substrates, metallized substrates, various heat sinks, and various structural members.

Claims (3)

[Claims] 1. A molded body containing silicon nitride powder, a sintering aid and an organic binder is degreased and then sintered to have an Al component of 0.25% by weight or less in terms of metal and an Fe component of 0.
In the method for producing a silicon nitride sintered body of 3% by weight or less, the silicon nitride powder has a β phase content of 15 to 40% by weight, and the sintering aid contains a compound of Mg and / or Ca. A silicon nitride sintered body containing the compound, wherein the ratio of the compound is 0.5 to 7.0 parts by weight per 100 parts by weight of the total of the silicon nitride powder and the oxide conversion of the compound. Manufacturing method. 2. The sintering aid further contains a rare earth element compound, and the ratio of the rare earth element compound is 15 parts by weight or less per 100 parts by weight in total of the silicon nitride powder and the oxide conversion of the rare earth element compound. The method for producing a silicon nitride sintered body according to claim 1, wherein. 3. The silicon nitride sintered body according to claim 1, wherein the number of grain boundaries observed on the polished surface of the silicon nitride sintered body is less than 7 per 10 μm when a straight line is drawn in an arbitrary cross section. And a thermal conductivity of 60 W / m · K or more, the method for producing a silicon nitride sintered body for producing a circuit board.