JPH05229872A - Production of ceramic sintered compact - Google Patents

Abstract

PURPOSE:To efficiently provide a high-strength, high-thermal conductivity ceramic sintered compact excellent in heat-releasing characteristics and little in the development of deformation and color unevenness. CONSTITUTION:Plural ceramic forms 4 consisting mainly of aluminum nitride are laminatedly arranged in tiers through spread powder 5, 5a comprising (A) one or both of aluminum nitride powder and boron nitride powder as the major component and (B) a noncrystalline carbon as the minor component, and the resulting laminated ceramic forms are simultaneously sintered in a nonoxidative atmosphere, thus obtaining the objective ceramic sintered compact. It is recommended that the noncrystalline carbon content of the spread powder be set at 5-20wt%.

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 ceramics sintered body, which contains aluminum nitride as a main component, is free from deformation and color unevenness, has high strength, high thermal conductivity and excellent heat dissipation characteristics. The present invention relates to a method for manufacturing a ceramic sintered body.

[0002]

2. Description of the Related Art Sintered ceramics, which are superior in properties such as strength, heat resistance, corrosion resistance, wear resistance, and lightness to conventional metal materials, are used in semiconductors, electronic equipment materials, engine parts, high speed It is widely used as a material for cutting tools, nozzles, bearings, and other mechanical parts, structural materials, and ornamental materials used under severe temperature, stress, and wear conditions that conventional metal materials do not have.

Particularly, an aluminum nitride (AlN) sintered body is an insulator having a high thermal conductivity and has a coefficient of thermal expansion close to that of silicon (Si), so that it is used as a heat sink or a substrate of a highly integrated semiconductor device. Expanding applications.

Conventionally, the above-mentioned ceramics sintered body is generally mass-produced by the following manufacturing method. That is, when using aluminum nitride as a ceramic raw material, first, a sintering aid, an organic binder, and if necessary, various additives, solvents, and dispersants are added to the aluminum nitride powder to form a raw material mixture. The raw material mixture thus prepared is molded by a doctor blade method to obtain a thin plate-shaped or sheet-shaped molded body, or the raw material mixture is press-molded to form a thick plate-shaped or large-sized molded body. Next, the obtained molded product is heated and degreased in an air or nitrogen gas atmosphere to remove and degrease the carbon and hydrogen components used as the organic binder from the molded product. The degreased compact is heated to a high temperature in a nitrogen gas atmosphere or the like and densified and sintered to form an aluminum nitride sintered compact.

In the above sintering operation, generally, a plate-shaped firing jig (setter) 3 is placed on a hearth 2 of a firing furnace 1 as shown in FIG. 2, and degreasing is performed on the firing jig 3. It is carried out by heating a plurality of ceramic compacts 4 in a multi-layered manner with a spread powder (laying powder) 5 at a high temperature.

The firing jig 3 and the hearth 2 which come into contact with the above-mentioned ceramic molded body 4 are formed with a molded body in order to prevent the characteristics of the sintered body from being deteriorated by reacting with the molded body during high temperature sintering. It is formed of an aluminum nitride (AlN) sintered body or a boron nitride (BN) sintered body which are the same material.

[0007] In addition, in order to prevent the ceramic powder compacts 4 from being welded to each other or the ceramic powder compact 4 and the firing jig 3 at their contact points during the firing process, the contact powders 5 contact each other. Is interposed and filled. As the powdered powder 5, aluminum nitride powder or boron nitride (BN) powder that rarely reacts with the molded body 4 is used.

By interposing the above-mentioned powdery powder 5, it is possible to effectively prevent the adjoining compacts 4 from being weld-bonded to each other even in the high temperature firing step, and even after the firing is completed, each ceramic product is Can be easily removed,
It is possible to prevent a reduction in product yield due to welding.

In the above manufacturing method, when an ultrafine raw material powder having an average particle diameter of about 0.3 μm or less is used as the raw material AlN powder, a considerably dense sintered body can be obtained by using the AlN powder alone. However, a large amount of impurities such as oxygen adhering to the surface of the raw material powder form a solid solution in the AlN crystal lattice at the time of sintering, or Al-O- which hinders the propagation of lattice vibration.
As a result of producing a complex oxide such as an N compound, the thermal conductivity of the AlN sintered body that did not use a sintering aid was relatively low.

On the other hand, when an AlN powder having an average particle size of 0.5 μm or more is used as the raw material powder, the raw material powder alone does not have good sinterability, so that a dense firing without an auxiliary agent other than the hot pressing method is performed. It was difficult to obtain a bound body, and there was a drawback that mass productivity was low. Therefore, in order to efficiently produce a sintered body by the atmospheric pressure sintering method, in order to prevent the densification of the sintered body and the impurity oxygen in the AlN raw material powder from forming a solid solution in the AlN crystal grains. In addition, rare earth oxides such as yttrium oxide (Y ₂ O ₃ ) and alkaline earth metal oxides such as calcium oxide are generally added as sintering aids.

These sintering aids react with the impurity oxygen contained in the AlN raw material powder to form a liquid phase, achieve densification of the sintered body, and fix this impurity oxygen as a grain boundary phase. It is believed that high thermal conductivity will also be achieved.

[0012]

However, in the conventional manufacturing method, it is extremely difficult to quantitatively control various impurities, resulting in a large variation in the sinterability (density) of each molded body and a large amount of deformation. Therefore, there is a problem in that the product yield and the thermal conductivity decrease. For example, when a large number of ceramic compacts are collectively degreased in a heating furnace, the amount of carbon and oxygen remaining in the compacts will vary depending on the number of compacts charged in the heating furnace in one degreasing operation. ,
Further, the residual carbon amount is different between the molded body arranged above the heating furnace and the molded body arranged below the heating furnace, which makes uniform degreasing operation difficult. The appearance quality often deteriorates due to changes in the color tone of the sintered body or uneven color due to the retention of impurities such as carbon, and the yield further decreases especially when the sintered body is used as a decorative material. There was a drawback to In particular, oxygen contained in the raw material powder as an impurity or mixed in the manufacturing process substitutes for nitrogen in the AlN crystal lattice during solidification to form a solid solution, so the high thermal conductivity, which is the maximum utilization characteristic of AlN, decreases. It was often done.

The present invention has been made to solve the above problems, and efficiently manufactures a sintered body having high strength, high thermal conductivity, excellent heat dissipation characteristics, and little deformation or color unevenness. It is an object of the present invention to provide a method for manufacturing a ceramics sintered body that can be manufactured.

[0014]

In order to achieve the above-mentioned object, the inventors of the present invention, in order to achieve the above-mentioned object, the types of sintering aids and additives to be added to the raw material aluminum nitride powder, the residual amount of impurities, the composition of powder, and the sintering The composition of the body was changed variously, and the effects and relations of the effects on the properties of the sintered body were studied experimentally, and the findings were obtained as shown below.

That is, the present inventors have found that the amount of residual carbon in the green body before sintering, that is, the degreased body has a great influence on the quality characteristics of the finally produced sintered body. FIG. 1 is a graph showing changes in the thermal conductivity, sinterability, amount of deformation, and degree of color unevenness of the sintered body with respect to the amount of residual carbon in the degreased body.

As shown in FIG. 1, by reducing the amount of residual carbon in the degreased body as much as possible, the sinterability of the molded body, that is, the density of the sintered body is improved, and the amount of deformation and color unevenness are eliminated. To be done. On the other hand, it has been found that a certain amount of residual carbon is necessary to maintain high thermal conductivity. A small amount of residual carbon has a function of reducing oxygen adhering to the surface of the raw material powder and oxygen existing as an oxide to remove it as CO or CO _{2 out} of the system. However, an excessive amount of residual carbon forms carbides that impede heat conduction like other impurities, and inhibits the formation of a liquid phase required during sintering to reduce sinterability, resulting in low compactness and low density. Form a strong sintered body.

Therefore, it is understood that by adjusting the amount of residual carbon in the degreased body to an appropriate range as described above, it is possible to obtain a sintered body having high density and high thermal conductivity with little deformation and color unevenness. However, in the conventional manufacturing method, it was extremely difficult to set the residual carbon amount within an appropriate range. For example, when a raw material mixture to which an organic binder is added is molded to form a sheet-shaped molded body and the molded body is degreased in air at a temperature of about 400 ° C.,
While the amount of carbon remaining in the degreased body is extremely small, about 0.01% by weight, it becomes difficult to release impurities in a large-sized molded body, and on the contrary, the amount of residual carbon becomes too large. Was difficult.

Therefore, by adding a predetermined amount of a substance serving as a carbon source in advance to the powder used during sintering, the amount of carbon acting on the compact during sintering can be kept within a predetermined range, and It was confirmed that reducing and removing impurities such as oxygen during sintering by the reducing action is very effective in improving the characteristics of the sintered body.

That is, by adding a predetermined amount of amorphous carbon to the powder beforehand and setting the amount of carbon acting on the compact during sintering to a predetermined range, the impurity oxygen in the compact and the sintered body is It was found that the amount of the sintered body can be significantly reduced, and a sintered body having high strength and less deformation and color unevenness can be obtained.

The present invention has been completed based on the above findings. That is, the method for producing a ceramics sintered body according to the present invention, a plurality of ceramics molded body containing aluminum nitride as a main component, at least one of aluminum nitride powder and boron nitride powder as a main component and amorphous carbon as a secondary component. The present invention is characterized in that a plurality of stacked ceramics compacts are simultaneously sintered in a non-oxidizing atmosphere by stacking and arranging them in multiple stages through the contained powder.

Further, the content of amorphous carbon in the sushi flour should be 5 to 5.
It may be set to 20% by weight.

Further, the sashimi powder containing amorphous carbon is
It is advisable to use a granulated product having a particle size of 20 to 150 μm and pre-sintered.

The aluminum nitride (AlN) powder used in the method of the present invention, which is the main component of the sintered body, has an impurity oxygen content suppressed to 3% by weight or less in consideration of sinterability and thermal conductivity. The average particle size is about 0.05 to 5 μm,
It is preferably 3 μm or less.

As a sintering aid, rare earth elements (Y, Sc,
Ce, Dy, etc.) oxides, nitrides, alkaline earth metal (Ca) oxides, or substances that become these compounds by a sintering operation are used, particularly yttrium oxide (Y
₂ O ₃ ) and calcium oxide (CaO) are preferred. The addition amount of the sintering aid is adjusted in the range of 0.5 to 7.5% by weight. If the addition amount is less than 0.5% by weight, the effect of improving the sinterability is not sufficiently exerted, the sintered body is not densified and a low-strength sintered body is formed, or oxygen is not contained in the AlN crystal. However, it cannot form a sintered body having a high thermal conductivity. On the other hand, if the added amount exceeds 7.5 wt%, the grain boundary phase remains in the sintered body, or the volume of the grain boundary phase removed by the heat treatment is large, so that voids remain in the sintered body. As a result, the shrinkage rate increases and deformation is likely to occur.

AlN is a powder used for sintering.
It is prepared by using at least one of aluminum nitride (AlN) powder and boron nitride (BN) powder that do not react with the compact as a main component, and further adding a predetermined amount of amorphous carbon as a secondary component.

Amorphous carbon is added to the powder in a range of 5 to 20% by weight in order to remove impurities such as oxygen remaining in the compact by reducing during sintering and removing it from the system. It When the addition amount is too small, less than 5% by weight, the amount of carbon vapor acting on the compact during sintering is small, and the deoxidizing effect of the amorphous carbon during sintering is insufficient, resulting in a high thermal conductivity sintered body. On the other hand, when the addition amount exceeds 20% by weight, the amount of carbon vapor adhering to the molded body increases and deformation and color unevenness of the sintered body tend to occur. The thermal conductivity also decreases. More preferably, the amount of carbon vapor acting on the compact during sintering should be in the range of 0.15 to 0.3 wt% with respect to the total weight of the compact, and the amorphous carbon content in the flour should be controlled. By setting, it is possible to obtain a high-quality sintered body in which various characteristics such as deformation, color unevenness, sinterability, and thermal conductivity are balanced.

Since graphite, which is a typical example of crystalline carbon, does not decompose and evaporate even when treated at a high sintering temperature and adheres to the surface of a sintered body to form an impurity oxide or the like, Not preferable.

Further, it is effective for improving the deoxidation efficiency to use the above-mentioned non-crystalline carbon-containing powder which is previously granulated so as to have a particle size of 20 to 150 μm and pre-sintered. Is. That is, in the case where fine powder having a particle size of less than 20 μm is interstitially filled between the adjacent molded bodies, the adjacent molded bodies adhere to each other in an airtight manner, and the carbon vapor does not sufficiently flow into the gap, and The reductive nitriding reaction on the surface may not proceed smoothly. Further, carbon (CO, CO ₂ ) combined with oxygen on the surface portion of the molded body is not efficiently released from the gap portion, and the deoxidizing efficiency is reduced. on the other hand,
When a coarse granulated powder having a particle size of more than 150 μm is used, the carbon powder does not act uniformly on the surface of each molded product and the deoxidizing efficiency decreases, so the particle size of the powder is within the above range. Is set to.

Further, in order to prevent deterioration of heat transfer characteristics of the sintered body due to ash generated by combustion of amorphous carbon during high temperature sintering, an amorphous carbon powder having an ash content of 1% by weight or less is used. Good to use. Specific examples include carbon black R-30 (manufactured by Mitsubishi Kasei Co., Ltd.).

As a molding method, a general-purpose die pressing method, a hydrostatic pressing method, or a sheet forming method such as a doctor blade method can be applied.

Subsequent to the above molding operation, the molded body is heated in a non-oxidizing atmosphere, for example, in a nitrogen gas atmosphere at a temperature of 375 to 375.
By heating to 450 ° C., the previously added organic binder is sufficiently removed.

Next, as shown in FIG. 2, the degreased compacts are laminated in multiple stages in the firing furnace 1 through the non-crystalline carbon-containing powder 5a, and a plurality of compacts are formed in this arrangement. The body 4 is collectively sintered at a predetermined temperature. For the sintering operation, the molded body is heated to a temperature of 17 in a non-oxidizing atmosphere such as nitrogen gas.
It is carried out by heating to 00 to 2000 ° C. for about 2 to 10 hours. The sintering atmosphere is nitrogen gas or a reducing atmosphere containing nitrogen gas. H ₂ gas, C as reducing gas
O gas may be used. The sintering may be performed in an atmosphere including vacuum (including a slight reducing atmosphere), reduced pressure, increased pressure and normal pressure. When firing at a low sintering temperature of less than 1700 ° C, it is difficult to obtain a dense sintered body although it depends on the particle size of the raw material powder and the amount of oxygen contained. Since the vapor pressure of AlN itself becomes high and densification may become difficult, the sintering temperature is set within the above range.

In order to obtain a dense sintered body in the above-mentioned sintering operation and to improve the thermal conductivity of the sintered body, it is necessary to add a certain amount of sintering aid. However, the sintering aid reacts with AlN and impurity oxygen to cause Al ₅
Oxides such as Y ₃ O ₁₂ , AlYO ₃ and Al ₂ Y ₄ O ₉ are formed and precipitated in the grain boundary phase. It has been confirmed that these oxides in the grain boundary phase have a function of hindering heat conduction.

However, by incorporating a predetermined amount of amorphous carbon into the powder as in the method of the present invention, the above-mentioned impurity oxygen is reduced by the carbon vapor generated from the amorphous carbon during high temperature sintering, and CO And is discharged and removed to the outside of the molded body. Further, the carbon vapor is reduced and nitrided together with nitrogen to the above oxide to form AlN and yttrium nitride (YN). This YN is formed as a film on the surface of the AlN sintered body, and this YN film can be easily removed from the surface of the sintered body by hydrolysis. It is considered that the above reduction nitriding reaction mainly proceeds on the surface of the sintered body, but as the material diffusion in the sintered body progresses, the grain boundary phase is gradually removed from the entire sintered body, and AlN ceramics sintering with a small thermal resistance. The body is obtained.

The aluminum nitride sintered body produced by the above-mentioned production method has a very high polycrystal weight of 200 w / m ·
It has a thermal conductivity of k (25 ° C.) or higher, high strength, and little deformation or color unevenness.

[0036]

According to the method for manufacturing a ceramics sintered body having the above structure, a predetermined amount of amorphous carbon is contained in the powder that prevents the ceramic compacts from being welded to each other. During high-temperature sintering, the compact is deoxidized by combining with the impurity oxygen existing on the surface of the compact and its vicinity, while the oxide formed in the grain boundary phase is reduced by the amorphous carbon and the grains are removed from the sintered body. The phase is reduced and removed. Therefore, it is possible to obtain a ceramics sintered body having a high thermal conductivity with less generation or residual of oxides which hinder the heat conduction in the sintered body.

Further, the amount of carbon required for deoxidation and oxide reduction of the above-mentioned molded body can be easily controlled by adjusting the content of amorphous carbon in the sawdust, which is different from the conventional case. In addition, there are problems such as deformation of the sintered body due to excessive residual carbon, occurrence of color unevenness, decrease in sinterability and thermal thermal conductivity, and poor thermal conductivity due to insufficient deoxidation due to excessive residual carbon. As a result, a high quality ceramic sintered body can be obtained.

[0038]

EXAMPLES The effects of the method for producing a ceramics sintered body according to the present invention will be described more specifically with reference to the following examples.

Examples 1 to 4 Oxygen was added as an impurity in an amount of 1.0% by weight, and the average particle size was 1.
5% by weight of Y ₂ O ₃ (yttrium oxide) as a sintering aid was added to 5 μm of aluminum nitride powder,
A raw material powder mixture was prepared by wet-mixing in ethyl alcohol for 30 hours and then drying. Next, the raw material powder mixture obtained by drying is filled in a molding die of a press molding machine and
A large number of disk-shaped radiator plate molded bodies were prepared by compression molding under a pressure of 00 kg / cm ² , and subsequently each molded body was heated in air at a temperature of 375 ° C. for 2 hours for degreasing treatment.

On the other hand, as shown in the left column of Table 1, AlN granular powder having an average particle size of 75 μm or B having an average particle size of 1 μm.
N powder, non-crystalline carbon with an average particle size of 0.3 μm (carbon black: R30, ash content 0.01 wt% or less) C
Respectively in the range of 5 to 20% by weight,
Four kinds of powdered powder 5a for forming the sintered bodies of Examples 1 to 4 were prepared.

Next, as shown in FIG. 2, the degreased compacts were put together in groups of 5, and were stacked in multiple stages in a firing furnace filled with N ₂ gas. The same kind of powdered powder 5a was interposed between the adjacent molded bodies 4 and 4 and between the firing jig 3 and the molded body 4 for each sintering batch process. Then, the temperature in the firing furnace 1 was maintained at 1815 ° C. for 4 hours to perform densification sintering, and the AlN ceramics sintering according to Examples 1 to 4 having a diameter of 120 mm and a thickness of 3.0 mm, respectively. Five bodies were prepared.

Comparative Example 1 On the other hand, sintering treatment was performed under the same conditions as in Example 1 except that amorphous carbon was not added to the powder and powder containing only AlN powder was used. A according to Comparative Example 1
An IN ceramics sintered body was prepared.

Comparative Example 2 Further, a comparison was made in which sintering was performed under the same conditions as in Example 4 except that amorphous carbon was not added to the powder and powder containing only BN powder was used. AlN according to Example 2
A ceramic sintered body was prepared.

Comparative Example 3 Further, Al was added with an excessive amount of 30% by weight of amorphous carbon.
A ceramic sintered body according to Comparative Example 3 having the same dimensions was prepared by treating under the same conditions as in Example 3 except that N powder-based powder was used.

Then, in order to evaluate the characteristics of each of the obtained AlN ceramics sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 3, the amount of deformation thereof, the presence or absence of color unevenness, the sintering density and the heat were evaluated. The conductivity was measured, and the results shown in the right column of Table 1 below were obtained.

[0046]

[Table 1]

As is clear from the results shown in Table 1, in the ceramic sintered bodies according to Examples 1 to 4, an appropriate amount of amorphous carbon was added to the powder as compared with Comparative Examples 1 and 2. This amorphous carbon exerts a reducing action during high-temperature sintering to promote the deoxidizing action that effectively removes oxygen and oxide impurities on the surface of the degreased body, resulting in deformation and uneven coloring. In addition, a sintered body having high heat dissipation, high density (high strength) and high thermal conductivity was obtained.

On the other hand, when the amorphous carbon is not added to the sawdust as in Comparative Examples 1 and 2, deformation and color unevenness are less likely to occur, but the deoxidizing action of the molded article by carbon is sufficient. Therefore, the impurity oxygen in the compact formed an oxide phase at the crystal grain boundary, and the thermal conductivity decreased.

When the amount of the amorphous carbon added to the powder is set excessively as in Comparative Example 3, excessive carbon content is likely to remain on the surface of the sintered body, resulting in deformation of the sintered body. Color unevenness became remarkable, sinterability was lowered, and strength and thermal conductivity were also lowered.

In the examples described above, in order to improve the mass productivity of the sintered body, an example is shown in which a plurality of molded bodies are stacked in a multi-layered state and sintered together. In the case of a large molded body, one molded body is placed in the firing furnace, and a powder containing amorphous carbon is placed between the molded body and the furnace floor of the firing furnace or the firing jig. The same effect can be obtained by interposing and sintering.

However, in the method of the present invention, the reduction and removal reaction of the impurity oxygen and oxides by the amorphous carbon mainly proceeds on the surface of the compact, and when the substance diffusion is slow, the reaction proceeds slowly, so that a large compact is obtained. In this case, the deoxidizing / reducing action may not proceed sufficiently to the central portion. Therefore, the method of the present invention is extremely effective especially as a method for producing a flat plate-shaped so-called thin sintered body having a small thickness.

[0052]

As described above, according to the method for producing a ceramics sintered body of the present invention, a predetermined amount of amorphous carbon is contained in the swarf that prevents the mutual welding of the ceramics compacts, This amorphous carbon is combined with impurity oxygen existing on and near the surface of the compact during high temperature sintering to deoxidize the compact, while the oxide formed in the grain boundary phase is And the grain boundary phase is reduced and removed from the sintered body. Therefore, it is possible to obtain a ceramics sintered body having a high thermal conductivity with less generation or residual of oxides which hinder the heat conduction in the sintered body.

Further, the amount of carbon required for deoxidation and oxide reduction of the above-mentioned molded article can be easily controlled by adjusting the content of amorphous carbon in the sawdust, which is different from the conventional method. In addition, there are problems such as deformation of the sintered body due to excessive residual carbon, occurrence of color unevenness, decrease in sinterability and thermal thermal conductivity, and poor thermal conductivity due to insufficient deoxidation due to excessive residual carbon. As a result, a high quality ceramic sintered body can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing changes in thermal conductivity, sinterability, amount of deformation, and degree of color unevenness of a sintered body with respect to the amount of residual carbon in the degreased body.

FIG. 2 is a cross-sectional view showing a state in which a plurality of molded bodies are simultaneously fired using a firing furnace.

[Explanation of symbols]

 1 Baking Furnace 2 Hearth 3 Baking Jig (Setter) 4 Molded Body 5, 5a Skim Flour (Flour)

Claims (4)

[Claims] 1. A plurality of ceramic compacts containing aluminum nitride as a main component are laminated in a multi-step manner with a swarf containing at least one of aluminum nitride and boron nitride as a main component and amorphous carbon as a minor component. Then, a method for producing a ceramics sintered body, comprising simultaneously sintering a plurality of stacked ceramics formed bodies in a non-oxidizing atmosphere. 2. The content of amorphous carbon in the sushi flour is 5 to 2
The method for producing a ceramics sintered body according to claim 1, wherein the amount is set to 0% by weight. 3. The ceramic sintered product according to claim 1, wherein the powdered powder containing amorphous carbon is formed by pre-granulating so as to have a particle size of 20 to 150 μm and pre-sintering. Body manufacturing method. 4. A powder for sintering aluminum nitride, comprising at least one of aluminum nitride and boron nitride as a main component and amorphous carbon as a secondary component.