JPH0450106A - Production of readily sinterable aluminum nitride powder - Google Patents

Abstract

PURPOSE:To obtain the title powder little in agglomerated granules and sharp in particle size distribution by mixing in an aqueous dispersion medium of a specified pH value alumina powder, carbon powder and a nonionic surfactant followed by reaction under heating in a nitrogen-contg. atmosphere. CONSTITUTION:The objective aluminum nitride powder can be obtained by mixing in an aqueous dispersion medium with a pH of 2.0-6.0 (A) alumina powder, (B) carbon powder and (C) 5-20 pts.wt. based on 100 pts.wt. of the carbon powder, of a nonionic surfactant followed by reaction under heating in a nitrogen-contg. atmosphere. Using the present aluminum nitride powder, high- density sintered compacts of excellent thermal conductivity virtually free from pores can be easily obtained, therefore, the present aluminum nitride powder is useful as stock powder for producing such sintered compacts.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing easily sinterable aluminum nitride powder. The present invention relates to a method for obtaining aluminum nitride powder with few particles and a sharp particle size distribution.

[Conventional technology]

Alumina has traditionally been widely used in highly reliable IC substrates or package materials. High integration of LSI etc.
As speed increases and power increases, the amount of heat generated from semiconductor chips increases, and the need to efficiently dissipate heat outside the system increases. It is requested.

Aluminum nitride has high thermal conductivity and excellent electrical properties such as insulation resistance, dielectric strength, and dielectric constant, and mechanical properties such as strength, and is attracting attention as an IC substrate and package material with excellent heat dissipation properties.

Methods for producing aluminum nitride powder include direct nitriding, in which metal aluminum powder is heated in a nitrogen-containing atmosphere to nitride it, and a mixture of alumina or alumina hydrate and carbon is heated in a nitrogen-containing atmosphere to nitride it. There are two typical methods known in the past: the reduction nitridation method.

The former method usually uses high-purity aluminum powder or foil as a raw material, but an oxide film exists on the surface of these and is contained in aluminum nitride as an oxygen impurity after the nitriding reaction. Furthermore, due to the exothermic reaction, lumpy products are likely to be formed due to aluminum welding, and it is necessary to adjust the particle size by crushing the product after the nitriding reaction.

For this reason, impurities are likely to be mixed in, making it difficult to obtain highly pure aluminum nitride powder. Therefore, as a method for obtaining high purity aluminum nitride powder to obtain high thermal conductivity,
The latter reductive nitriding method is seen as promising.

[Problem to be solved by the invention]

It is already known that this reductive nitriding method uses high-purity fine powder alumina as a raw material to obtain high-purity aluminum nitride powder that retains the characteristics of the raw material.

However, sintering of alumina occurs during the nitriding reaction process, and as a result, only aluminum nitride powder with a broad particle size distribution containing more coarse or agglomerated particles than the raw material alumina powder is currently available.

When sintering is performed using a powder with a broad particle size distribution including many coarse particles or agglomerated particles, sinterability is generally poor and a sintered body containing many pores is likely to be obtained. In the case of aluminum nitride, pores in particular cause a decrease in thermal conductivity, so a raw material powder with few coarse or aggregated particles and a sharp particle size distribution is desired.

In the production of aluminum nitride powder by the alumina reduction nitriding method, it is necessary to sufficiently mix and disperse raw materials alumina powder and carbon powder. By nature, alumina powder has a hydrophilic surface, while carbon powder has a lipophilic surface. It is very difficult to uniformly mix and disperse powders having these contradictory surface characteristics in a dispersion medium.

Generally, in an aqueous dispersion medium, alumina powder is highly dispersed in an acidic region, while carbon powder is highly dispersed in an alkaline region, so the dispersibility of alumina powder is usually prioritized and manufactured in an acidic region. .

Therefore, there is a problem in that the aluminum nitride powder obtained by this method contains a large amount of coarse particles or agglomerated particles. In order to improve this point, Japanese Patent Application Laid-Open No. 60-60910
A method using an organic solvent as a dispersion medium as disclosed in the above publication has also been proposed, but this method was not always satisfactory.

[Means for solving problems]

In view of these circumstances, the present inventors have conducted extensive studies and found that by using a nonionic surfactant when the aqueous dispersion medium is acidic, sintering of alumina with each other during the nitriding reaction process can be prevented, and coarse particles can be reduced. Alternatively, the inventors discovered a method for producing easily sinterable aluminum nitride powder with few agglomerated particles and a sharp particle size distribution, leading to the completion of the present invention.

That is, the present invention provides a method for producing aluminum nitride powder by mixing alumina powder and carbon powder in an aqueous dispersion medium and causing a heating reaction in an atmosphere containing nitrogen. 5 to 20 parts by weight to adjust the pH of the aqueous dispersion medium to 2.6 to 6.
The present invention provides a method for producing easily sinterable aluminum nitride powder, which is characterized in that the sinterability of the aluminum nitride powder is within the range of 0.

The present invention will be explained in detail below.

The purity and particle size of the aluminum nitride powder obtained in the present invention approximately correspond to the purity and particle size of the alumina powder used as the raw material. Therefore, the purity and particle size of the raw material alumina powder can be appropriately selected in consideration of the intended purity and particle size of the aluminum nitride powder.

However, when a large alumina powder with a center particle size of 10 μm or more is used as a raw material, heating at a high temperature for a long time is required to allow the nitriding reaction to proceed sufficiently. In addition, when using alumina powder containing coarse particles or aggregated particles as a raw material, it is inevitable that coarse particles or aggregated particles will be mixed in the aluminum nitride powder produced even if the raw materials are thoroughly mixed and dispersed. .

In addition, metal impurities such as iron, magnesium, silicon, and titanium are known to have a negative effect on the thermal conductivity of sintered bodies, so in order to obtain aluminum nitride powder with excellent sinterability, it is necessary to The diameter is 10 μm or less, preferably 5
It is preferable to select as the raw material an alumina powder having a particle size of 1100 pp or less and metal impurities such as iron, magnesium, silicon, and titanium.

Such alumina powders include low soda alumina,
Commercially available high-purity alumina and easily sinterable alumina can be used. Further, as the carbon powder, a highly purified and fine grade carbon powder can be used. -Powder having a secondary particle size of 1 μm or less and an ash content of 0.3% by weight or less is preferable. As such carbon powder, acetylene black, furnace black, channel black, thermal black, etc. are known, and among these, acetylene black is preferable in terms of higher purity. Furthermore, for ease of handling and dispersion, it is advantageous to use granular products granulated to a size of 0.3 to 5 mm or press-compressed powder particles.

Polyethylene glycol type surfactants are used as nonionic surfactants, such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene olein ether, polyoxyethylene lauryl ether, etc. Polyoxyethylene alkylphenyl ether or polyoxyethylene alkyl ether is known.

The amount added is 5 to 100 parts by weight of carbon powder.
A range of 20 parts by weight is suitable. If it is less than 5 parts by weight, the dispersibility of the carbon powder will be insufficient, and only aluminum nitride powder with many aggregated particles will be obtained.

On the other hand, if it exceeds 20 parts by weight, the dispersibility of the carbon powder becomes saturated, and the cost also increases, which is not preferable.

The above nonionic surfactant is added when alumina powder and carbon powder are mixed and dispersed in an aqueous dispersion medium. The amount of water added is in a weight ratio of 0.5 to 6, preferably 1 to 5, based on the solid components of alumina powder and carbon powder.

Further, the pH of the aqueous dispersion medium needs to be adjusted to a range of 2.0 to 6.0, and the pH is adjusted using nitric acid, an aqueous aluminum nitrate solution, or the like as appropriate. If the pH of the aqueous dispersion medium is less than 2.0 or more than 6.0, the nonionic surfactant will not function sufficiently and the dispersibility of the carbon powder will be insufficient, which is not preferable.

By adjusting the pH of the aqueous dispersion medium to a range of 2.0 to 6.0, the alumina powder is highly dispersed, and the carbon powder is similarly highly dispersed due to the action of the nonionic surfactant.
As a result, alumina powder and carbon powder are uniformly mixed and dispersed, and sintering of the alumina powders is suppressed in the subsequent nitriding reaction step, and aluminum nitride powder containing no aggregated particles or coarse particles is obtained.

The mixing ratio of alumina powder and carbon powder is preferably in the range of 3 to 10 in carbon/alumina molar ratio. When the molar ratio is less than 3, unreacted alumina remains;
If it exceeds 10, a large amount of unreacted carbon remains, making it difficult to remove and increasing the cost, which is not preferable.

Mixing and dispersion methods include general methods such as ball mills and ultrasonic dispersion machines, particle granulators,
Although it is possible to use various types of mixers such as a Unilunar mixer, it is preferable to use a device whose parts that come into direct contact are made of a material that does not contain metal impurities.

As such a mixer, it is desirable to use one made of synthetic resin such as polyethylene, nylon, urethane, natural or synthetic rubber, alumina or aluminum nitride, or one lined or coated with these materials.

Normal industrial methods can be used to dry the mixture, but if the viscosity of the slurry during mixing is low and there is a risk of separation of alumina powder and carbon powder during drying, spray drying or freeze drying may be used. It is preferable to use a method such as a rotary evaporator method or the like.

In addition, if necessary, we can also mix and dry 20 μm to 3 mm.
Since it can be granulated into particles of a certain size, granulation has the advantage that subsequent handling becomes easier.

The powder or granulated mixture thus obtained is heat-treated in an atmosphere containing nitrogen to perform a reductive nitriding reaction.The atmosphere includes nitrogen, ammonia, nitrogen-ammonia mixed gas, nitrogen- Hydrogen mixed gas, nitrogen-argon mixed gas, etc. can be used.

The heat treatment temperature is usually in the range of 1450 to 1700°C,
Preferably it is in the range of 1ff00 to 1600°C. 14
If it is less than 50°C, it will take a long time for the reduction-nitridation reaction to proceed sufficiently, and if it is more than 1700°C, coarse particles will be produced in large quantities, which is not preferable. 150 as an economical range
It is most appropriate to hold the temperature at 0 to 1600°C for 2 to 6 hours.

Furthermore, heat treatment is performed in an oxidizing atmosphere for the purpose of removing excess carbon remaining after the reductive nitriding reaction.
The treatment temperature is suitably 600-750°C for 1-4 hours.

For the heat treatment, commonly used equipment such as an oven-type box type or a rotary kiln-type rotary furnace can be used.

〔Effect of the invention〕

The aluminum nitride powder obtained in the present invention is an easily sinterable aluminum nitride powder with few coarse grains or agglomerated grains and a soaring particle size distribution. It is possible to easily obtain a sintered body with excellent properties, and it is useful as a raw material powder for producing an aluminum nitride sintered body with excellent thermal conductivity.

〔Example〕

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

The particle size distribution described in the examples was measured using Sedigraph 5000ET manufactured by Shimadzu Corporation. The thermal conductivity was measured using a thermal conductivity measurement device TC-7000 by Vacuum Riko (immediately made using the laser flash method).

Example 1 255 g of low soda alumina powder with a purity of 99.9% and a center particle size of 0.7 μm and 80% of 1 μm or less with an ash content of 0.00
5% acetylene black (Denki Kagaku Kogyo (ready made 100
% pressed product) 120g, polyethylene glycol (#1000 manufactured by Wako Pure Chemical Industries, Ltd.) as a viscosity modifier.
8g, 14.4g (12 parts by weight) of polyoxyethylene alkylphenyl ether as a nonionic surfactant.
Then, 1100 g of ion-exchanged water was added as a dispersion medium, placed in a polyethylene pot of 51 along with 200 urethane balls with a diameter of 2 smtn, and 1.9 g of aluminum nitrate and 28 g of IN nitric acid were added to adjust the pH of the aqueous dispersion medium to 3.5. was prepared, and time mixing was performed at lθ at a rotational speed of 40 rpm.

After drying the mixed slurry thus obtained in a dryer, 300 g of it was filled into a graphite tray and heated at 1550°C for 8 hours using an electric furnace while flowing nitrogen gas at 201/min. , a reductive nitriding reaction was performed. Next, this reaction product was heated in dry air for 700 min.
After heating at ℃ for 3 hours, 135 g of aluminum nitride powder was obtained.

The particle size distribution curve of this aluminum nitride powder according to a Sedigraph is shown in FIG. 1 (1).

The central particle size is 1.5 μm, with 193% of the particles being 3 μm or less.
The powder had a sharp particle size distribution with almost no coarse particles or agglomerated particles.

To this powder, 3% by weight of Y2O3 (Nippon Yttrium Co., Ltd.) was added as a sintering aid, and the green molded body obtained by press molding at 1500 kg/cm was buried in a mixed powder of aluminum nitride and boron nitride. 180 in nitrogen atmosphere
Sintering was carried out at normal pressure at 0°C and 1850°C for 5 hours.

Table 1 shows the sintered density and thermal conductivity of the obtained sintered body.

Table-1 Sintering temperature Sintering density Thermal conductivity 1800°C3
,15g/am2186W/mK1850°C3,26
g/am2207W/mK Comparative Example 1 Aluminum nitride powder was obtained in the same manner as in Example 1 except that 3.6 g (3 parts by weight) of polyoxyethylene alkylphenyl ether was used as the nonionic surfactant.

The particle size distribution curve of the obtained powder by Sedigraph is
This is shown in Figure (2).

The center particle size is 1.9 μm, and 80% of the particles are 3 μm or less.
It was a powder with many aggregated particles.

This powder was sintered in the same manner as in Example 1, and the sintered density and thermal conductivity of the obtained sintered body are shown in Table 2.

Table-2 Sintering temperature Sintering density Thermal conductivity 1800°C3
,06g/cm' 164W/mK1850°C3
, 23g/cm' 193W/mK Comparative Example 2 Instead of using aluminum nitrate and nitric acid, 0.5g of concentrated ammonia water was added to the aqueous dispersion medium, and the pH of the aqueous dispersion medium was adjusted to 1.
Aluminum nitride powder was obtained in the same manner as in Example 1 except that the powder was adjusted to 0.8.

The particle size distribution curve of the obtained powder by Sedigraph is
It is shown in Figure (3).

The central particle size is 2.2 μm, with 169% of the particles being 3 μm or less.
It was a powder with many agglomerated particles.

This powder was sintered in the same manner as in Example 1, and the sintered density and thermal conductivity of the obtained sintered body are shown in Table 3.

Table-3 Sintering temperature Sintering density Thermal conductivity 1800°C2
,95g/cm' 149W/mK1850°C3
,24g/cm' 195W/mK

[Brief explanation of the drawing]

FIG. 1 is a graph showing particle size distribution curves of aluminum nitride powders obtained in Examples and Comparative Examples measured using a Sedigraph, and shows the relationship between cumulative weight and particle size. Agent: Patent attorney Koretsu Moroishi (and 1 other person) Cumulative type H1 (
%) Procedural amendment (voluntary)

Claims (1)

[Claims] Mixing alumina powder and carbon powder in an aqueous dispersion medium,
In a method for producing aluminum nitride powder by heating reaction in an atmosphere containing nitrogen, 5 to 20 parts by weight of a nonionic surfactant is added to 100 parts by weight of carbon powder, and the pH of the aqueous dispersion medium is adjusted to 2. A method for producing easily sinterable aluminum nitride powder, characterized in that the particle diameter is within the range of 0 to 6.0.