JP3537241B2 - Method for producing silicon nitride sintered body - Google Patents

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 more particularly to a method of producing a silicon nitride sintered body having a high thermal conductivity and excellent heat dissipation in addition to the inherent 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.

2. Description of the Related Art 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 more, and has excellent thermal shock resistance due to a low coefficient of thermal expansion. Therefore, application to various high-strength heat-resistant parts such as gas turbine parts, engine parts, and steelmaking machine parts has been attempted as a high-temperature structural material replacing conventional heat-resistant superalloys. In addition, because of its excellent corrosion resistance to metals, application of molten metal as a melting-resistant material has been attempted, and because of its excellent wear resistance, it has been put to practical use in sliding members such as bearings and cutting tools. ing.

[0003]

2. Description of the Related Art Conventionally, silicon nitride sintered bodies include silicon nitride-rare earth element oxide (such as yttrium oxide) -aluminum oxide, silicon nitride-rare earth element oxide-aluminum oxide-aluminum nitride, silicon nitride. A system mainly using a rare earth element oxide and aluminum oxide as a sintering aid, such as a rare earth element oxide-aluminum oxide-titanium or zirconium oxide system, is mainly used.

[0004] Oxides of rare earth elements such as yttrium oxide (Y ₂ O ₃ ) are added to enhance the sinterability and to densify and increase the strength of the sintered body, and aluminum oxide is used as a high-temperature structural material. Is added to increase the durability of the steel.

However, in the above-mentioned silicon nitride sintered body, electrical characteristics such as withstand voltage are similar to those of aluminum nitride, so that there is no problem. Is aluminum nitride (AlN)
Since the sintered body, beryllium oxide (BeO) sintered body, silicon carbide (SiC) sintered body and the like are remarkably low, there has been a problem in applying to a circuit board for a semiconductor that requires heat radiation. .

On the other hand, an aluminum nitride sintered body has a higher thermal conductivity and a lower coefficient of thermal expansion as compared with other ceramic sintered bodies. Although it is widely used as a circuit board material or a package material for a semiconductor chip, its mechanical strength is not sufficient.

Therefore, the emergence of a ceramic sintered body having high strength and high thermal conductivity has been desired. In order to meet these demands, the conversion of rare earth elements to oxides is 2.0 to
7.5% by weight, not more than 2.0% by weight of at least one of aluminum nitride and alumina, and other Li, Na, K,
Fe, Ca, Mg, Sr, Ba, Mn, B, etc., containing 0.3% by weight or less of impurity cation elements, comprising β-phase silicon nitride crystal and grain boundary phase, and a crystalline 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-point or more and a three-point bending strength of 80 kg / mm ² or more at room temperature has been proposed (Japanese Patent Laid-Open No. 6-1).
35771).

[0008] The production method, oxygen content 1.
7% by weight or less, preferably 0.5 to 1.5% by weight, the total amount of the impurity cation element is 0.3% by weight or less, preferably 0.2% by weight or less, α phase 90% by weight or more, preferably 9%
A molded body is molded using 3% by weight or more of α-type silicon nitride powder, degreased, and then subjected to atmospheric pressure sintering at a temperature of 1800 to 2000 ° C., and then formed of the rare earth element oxide from the sintering temperature. The temperature until the liquid phase solidifies is 10
It is disclosed that cooling is performed at a cooling rate of 0 ° C. or less.

In other words, this method requires an aluminum component as a sintering aid, crystallizes a grain boundary phase (sintering aid phase) by a special method of slow cooling, and further comprises Li, N
High thermal conductivity is achieved by defining cation elements such as a, K, Fe, Ca, Mg, Sr, Ba, Mn, and B as impurities having an adverse effect.

[0010]

However, in this method, since the sintering temperature is very high at 1900 ° C., not only is the burden on the sintering furnace large, but also the cooling rate is set as low as 100 ° C./hour or less. There is a problem that productivity is significantly reduced.

The present invention solves such problems and manufactures a silicon nitride sintered body having excellent mechanical properties and thermal conductivity, particularly a silicon nitride sintered body suitable for a circuit board, with increased productivity. It is intended to do so.

[0012]

That is, the present invention is a method for producing a silicon nitride sintered body having the following gist. (Claim 1) A molded body containing a silicon nitride powder, a sintering aid and an organic binder is degreased and sintered, and the Al component is 0.25% by weight or less in terms of metal, and the Fe component is 0.3% or less in terms of metal.
In a method for producing a silicon nitride sintered body of not more than
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 method for producing a silicon nitride sintered body, which is 0.5 to 7.0 parts by weight per 100 parts by weight of the total of the compound and oxides. (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 of the total of the silicon nitride powder and the rare earth element compound in terms of oxide. 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, the number of grain boundaries observed on the polished surface of the silicon nitride sintered body is 7 per 10 μm when a straight line is drawn in an arbitrary cross section.
A method for producing a silicon nitride sintered body for manufacturing a circuit board, wherein the number is less than 60 pieces and the thermal conductivity is 60 W / m · K or more.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

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 Al is 0.25% by weight or less, preferably 0.15% by weight in terms of metal.
Hereinafter, Fe is 0.3% by weight or less, preferably 0.2% by weight or less in terms of metal. Further, in consideration of a decrease in thermal conductivity and a decrease in weather resistance, Li, Be, Na,
Preferably, the content of impurity cation elements such as K, Mn, and Ga is suppressed to a total of 0.3% by weight or less, particularly 0.2% by weight or less. These impurity cation elements are unlikely to be mixed in a general method for producing silicon nitride powder.

The amount of oxygen in the silicon nitride powder may be not more than 2.0% by weight, especially about 0.5 to 1.5% by weight, which is usually contained in a commercially available silicon nitride raw material powder for a structural material. .

The average particle diameter of the silicon nitride powder is preferably 3 μm or less, particularly preferably 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
g and / or Ca compounds. Examples thereof include MgO, CaO, forsterite (Mg ₂
SiO ₄ ), steatite (MgSiO ₃ ), Mg (O
H) ₂ , oxides such as Ca (OH) ₂ , hydroxides, silicides, nitrides, and basic carbonates, nitrates, formates, acetates and various alkoxides of Mg and / or Ca. is there.

The higher the purity of the sintering aid, the better.
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% by weight in terms of metal.
Hereinafter, since the Fe component is 0.3% by weight or less in terms of metal, the Al component and the Fe component in the sintering aid are desirably as small as possible. The average particle size of the sintering aid is
3 μm or less, especially 2 μm, from the viewpoint of mixing 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 of the total of the oxides of the compound of Mg and / or Ca (MgO and / or CaO) and the silicon nitride powder.
Parts by weight. If the amount is less than 0.5 part by weight, the sintered body is not densified and has low strength and low thermal conductivity. If the amount exceeds 7.0 parts by weight, an excessive amount of grain boundary phase is generated, and the thermal conductivity is reduced.
Preferably it is 2 to 5 parts by weight.

In the present invention, the above Mg and / or Ca compound and a rare earth element compound can be used in combination as a sintering aid. As an example of a rare earth element compound,
Y, La, Sc, Pr, Ce, Nd, Sm, Dy, H
It is an oxide such as o or Gd or a precursor that becomes such an oxide in a sintering process. These rare earth element compounds react with the silicon nitride raw material powder to form 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 proportion of the rare earth element compound is preferably 15 parts by weight or less, more preferably 2 to 10 parts by weight, and even more preferably 3 to 6 parts by weight, per 100 parts by weight of the total of the oxide equivalent of the rare earth element compound and the silicon nitride powder. If the amount exceeds 15 parts by weight, an excessive amount of grain boundary phase is generated, which causes 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, methylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, ethylcellulose, ethylhydroxyethylcellulose, hydroxypropylcellulose, various waxes and acrylics. Base resin (polyacrylate, polymethacrylate, etc.), urethane resin and the like. These are usually used in an amount of 0.1 to 20 parts by weight based on a total of 100 parts by weight of the silicon nitride and the sintering aid, although they vary depending on the forming means of the formed body.

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

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

In the present invention, the size of the silicon nitride crystal grains of the sintered body can be 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 used. 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 shows m · K or more, it is particularly suitable for manufacturing a circuit board.

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

Further, the strength and fracture toughness of the silicon nitride sintered body are appropriately selected depending on the application, based on a balance between the three factors including thermal conductivity, but generally, the three-point bending strength at room temperature is 600 MPa or more. , A room temperature fracture toughness value of 5 MPa√m or more. These adjustments can be made 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]

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 a sintering aid (Mg and / or Ca compound, rare earth element compound, silica powder) at the ratios shown in Table 1 and ethyl alcohol as a medium The mixture was wet-mixed by a ball mill using silicon nitride balls for 20 hours, and then dried to prepare a raw material powder mixture. The amounts of the sintering aids shown in Table 1 are parts by weight of the oxides of the respective compounds with respect to 100 parts by weight of the total of the oxides of the respective compounds and the silicon nitride powder.

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

After adding 8% by weight of a 5% by weight aqueous solution of polyvinyl alcohol to the obtained raw material powder mixture and uniformly mixing the mixture, CIP molding was performed at a molding pressure of 2000 kg / cm ² to obtain a length of 50 mm × width of 50 mm × thickness. A molded body having a thickness of 5 mm was formed, heat-treated in air at a temperature of 500 ° C. for 2 hours, degreased, 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.)
The three-point bending strength and the fracture toughness at room temperature were measured. Table 1 shows the results.

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

[0033]

[Table 1]

As is clear from Table 1, the example is a silicon nitride sintered body having higher thermal conductivity and higher strength than the comparative example.

[0035]

According to the present invention, a silicon nitride sintered body having a high thermal conductivity and a high strength, which is particularly suitable for manufacturing a circuit board, can be specially sintered at a relatively low sintering temperature and gradually cooled. Without performing, it can be manufactured with increased productivity.

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

Continuation of the front page (56) References JP-A-4-212441 (JP, A) JP-A-1-145380 (JP, A) JP-A-9-30866 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) C04B 35/584-35/596

Claims (3)

(57) [Claims] 1. A molded body containing a silicon nitride powder, a sintering aid and an organic binder is degreased and sintered, and the Al component is 0.25% by weight or less in terms of metal, and the Fe component is 0.25% by weight or less in terms of metal.
In a 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. Wherein the proportion 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 of the compound. Manufacturing method. 2. A rare earth element compound is further contained as a sintering aid, and the ratio of the rare earth element compound is 15 parts by weight or less per 100 parts by weight of the total of the silicon nitride powder and the oxide of the rare earth element compound in terms of oxide. 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, and a method for producing a silicon nitride sintered body for producing a circuit board.