JPH02296707A - Production of aluminum nitride powder - Google Patents

Abstract

PURPOSE:To obtain aluminum nitride powder having a sharp distribution of particle size with little coase particle or aggregation by using a mixture of alumina and alumina sol with a specified proportion in the production process of aluminum nitride powder by a nitridation reduction method. CONSTITUTION:Alumina powder, carbon powder and alumina sol are mixed with to satisfy the relation of (alumina in the alumina sol)/(alumina in the alumina sol + alumina powder)X100(wt.%)=40 to 60(wt.%). Then the mixture is made to react in nitrogen-containing atmosphere by heating to reduce alumina.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention improves the dispersion and mixing of raw material alumina powder and carbon powder when water is used as a dispersion medium in a reaction system. The present invention relates to a method for producing aluminum nitride powder, which has a sharp particle size distribution almost equivalent to that of alumina powder and has fewer coarse particles and agglomerated particles.

[Conventional technology]

Alumina, which has traditionally been used as a material for IC packages and semiconductor substrates, has low thermal conductivity and is no longer able to keep up with the increase in heat dissipation from chips that has accompanied the recent increase in the integration and speed of semiconductors. It has higher thermal conductivity than alumina (requires a material with excellent heat dissipation).

Aluminum nitride has a thermal conductivity that is an order of magnitude higher than that of alumina and a coefficient of thermal expansion that is close to that of silicon.Aluminum nitride has excellent mechanical properties as well as electrical properties such as insulation resistance, dielectric strength, and dielectric constant. It is expected to be an alternative IC substrate material.

The main manufacturing methods for aluminum nitride include: ■ Direct nitriding method, in which totally bent aluminum is heated in a nitrogen atmosphere to nitride it, ■
There are three types of methods: a gas phase reaction method in which a halide or hydride of aluminum is reacted with NH in a gaseous state, and (2) a reduction nitridation method in which a mixture of alumina and carbon is heated in a nitrogen atmosphere to reduce alumina. Process (2) is simple, but it is difficult to nitridate the inside of the raw metal aluminum, and because it involves a pulverization step after firing to adjust the particle size of the powder, contamination with impurities cannot be avoided, making it difficult to achieve high purity. The powder obtained in step (2) is amorphous and cannot be used as a raw material for sintering ceramics, so a crystallization step is required. On the other hand, the reductive nitriding method described in (2) depends to some extent on the purity of the raw materials alumina and carbon, but in the current situation where high-purity products are readily available as raw materials, it is easier to produce high-purity products than the direct nitriding method. Therefore, the reduction nitriding method is considered to be a promising method for obtaining high-purity aluminum nitride powder, which is a raw material for highly thermally conductive substrates.

[Problem that the invention seeks to solve]

When aluminum nitride powder is produced by the reductive nitriding method described in (2) above, the particle size distribution and cohesiveness of the obtained aluminum nitride powder can be improved to some extent by selecting the raw material alumina, but at 1400°C where the nitriding reaction occurs. At temperatures below, alumina powders undergo initial sintering and form a neck, so compared to the raw material powder, there are more agglomerated particles (secondary particles), and only those with a wide particle size distribution can be obtained. When such powder is used as a raw material for sintering, only a low-density sintered body with many pores is obtained, and no improvement in thermal conductivity can be expected. Therefore, in order to obtain aluminum nitride powder with high thermal conductivity, powder with few agglomerated particles and a sharp particle size distribution is required.

When alumina powder and carbon powder as raw materials are wet-mixed, it is necessary to uniformly disperse and mix them. Originally, alumina powder has a hydrophilic surface, while carbon powder has a hydrophobic surface. Uniformly dispersing and mixing these two powders with contradictory surface characteristics in the same dispersion medium is extremely difficult.

If the mixing and dispersion conditions are poor, the fired aluminum nitride powder will have a wide particle size distribution with many agglomerated particles.

Although the dispersibility is improved when an organic solvent such as acetone is used as the dispersion medium, it is preferable to use wood in consideration of the simplicity and economic efficiency of post-processes such as drying and granulation. but,
When water is used as a dispersion medium, uniform dispersion is difficult;
Suitable dispersants and wetting agents need to be considered.

Conventional wet mixing methods attempt to disperse and mix powders with contradictory surface characteristics in a single operation, which inevitably results in insufficient dispersion of each powder, resulting in the formation of coarse particles and agglomerated particles after firing. I couldn't control it. In addition, as a means to obtain aluminum nitride powder with a fine and uniform particle size, water is added to a mixture of aluminum alkoxide and carbon powder to perform hydrolysis, or an alkali is added to a mixture of water-soluble aluminum salt and carbon powder. A method of performing neutralization precipitation has also been proposed. However, when water or alkali is added dropwise for hydrolysis or neutralization precipitation, localized precipitation is produced and flocculation occurs immediately.

However, it is difficult to improve the cohesiveness of the resulting powder.

Therefore, the present inventors reexamined the mixing method of the raw material powder and found that dispersibility could be improved by using water as a dispersion medium and further adding alumina sol to this. Therefore, an object of the present invention is to improve the dispersion and mixing of raw alumina powder and carbon powder when water is used as a dispersion medium, thereby reducing coarse particles and aggregated particles to the same extent as the raw material high-purity alumina powder. The object of the present invention is to provide a method for producing aluminum nitride powder with a sharp particle size distribution.

[Means for solving problems]

As mentioned above, the purity, particle size and particle size distribution of the aluminum nitride powder obtained by the nitriding reduction method depend to some extent on that of the raw material alumina powder. Therefore, as a necessary condition for obtaining high-purity aluminum nitride powder, it is preferable to use high-purity alumina as a raw material.
Examples include those containing a small amount of metal impurities such as e, Si, and Ca. The raw material carbon is also highly pure and fine powder (average particle size 0.5μ).
Acetylene black, furnace black, channel black, carbon black, etc. are known, but carbon blank is preferable in terms of high purity.

The problem is that it is important to uniformly disperse these two powders in water and mix them thoroughly, but uniform dispersion is difficult because they have contradictory dispersibility in water.

Normally, when alumina powder and carbon powder are mixed using water as a dispersion medium, a water-soluble polymeric surfactant is added, but in the present invention, instead of that, alumina sol with a small amount of metal impurities is used as part of the raw material alumina. Alumina powder and carbon powder were added to this sol to make a mixed slurry, an appropriate amount of water was added to adjust the viscosity, and the slurry was mixed in using a ball mill. As a result, aluminum nitride powder having a primary particle size that is almost the same as the primary particle size of the raw material alumina can be obtained.

Examples of alumina sol include the product names "Alumina Sol-100J" and "R Alumina Sol 200J" manufactured by Yasan Kagaku Kogyo Co., Ltd.
Examples include "Alumina Sol-520".

The slurry thus obtained can be dried using a spray dryer, a rotary evaporator, or the like, and a granulation process can be added depending on the case.

The obtained mixture (powder, granules) is heated in an atmosphere containing nitrogen such as nitrogen, ammonia, or a mixture thereof.
A reductive nitriding reaction is caused by heat treatment at 450 to 1700°C for 2 to 6 hours. If the temperature exceeds 1,700°C, grain growth will proceed too much, resulting in a large number of coarse particles, and if the temperature is less than 1,450°C, nitriding will take a long time, which is not preferable. moreover,
After the nitriding reaction, heat treatment is performed at 600 to 700° C. for 1 to 3 hours in an oxidizing atmosphere to remove remaining carbon to obtain aluminum nitride powder.

Hereinafter, the present invention will be explained in more detail with reference to examples and conventional examples.

Purity 99.99%, BBT with raw material mixing ratio shown in Table 1
Specific surface area 9.7d, average particle size 1.5μI11.1μm or less 90%, total amount of metal impurities (Fe+Ca, Si) 110
High purity alumina powder of 0pp or less, carbon blank with ash content of 0.05%, and metal impurities (Fe, Ca, S
t) Total ffi 480ppm, alumina content 10.2
Disperse 8% alumina sol (manufactured by Yasan Kagaku Kogyo Co., Ltd., "Alumina Sol-100J") in ion-exchanged water, and
400 im and high purity alumina balls each with a diameter of 15 mm
Put it in a polyethylene container of 21 with g and 40 rpm.
The slurry obtained was dried and granulated using a spray dryer, and then the obtained powder was formed into pellets weighing approximately 5 g each.
3ry in an electric furnace? /h of nitrogen flow, 1660
℃ for 4 hours to perform a reductive nitriding reaction. The reaction product was heated in air at 700° C. for 1 hour to remove residual carbon and obtain aluminum nitride powder.

In addition, in the conventional example that does not use alumina sol, humic acid 1.
A sample was prepared by dispersing alumina and carbon blank in ion-exchanged water using 4.0 g of 5g5 PVA-based binder.

Table 1 shows the BET specific surface area, average particle size, and elemental analysis values of the aluminum nitride powder obtained.

In addition, the particle size distribution curve of the obtained aluminum nitride powder by microtrack is shown in FIG. 1. However, Example 7
-9 have many parts that overlap with the curves of Example 6 and Example 10, making the diagram difficult to see (so the illustration is omitted),
Figure 2 shows the alumina sol mixing ratio and the average particle size of the obtained aluminum nitride powder. Indicates the relationship between

As can be seen from the results in Table 1 and Figures 1 and 2, when alumina sol is added to alumina, the specific surface area of the produced aluminum nitride powder becomes larger than that of the conventional example using only alumina, and the average particle size increases. The diameter becomes smaller.

In addition, in Example 10 where only alumina sol was used, the specific surface area of the aluminum nitride powder was large (and the average particle size was small. Generally, the content of alumina in alumina sol varies depending on the product, but is approximately 10%). Therefore, when producing aluminum nitride powder using only alumina sol as in Example 10, the alumina content only accounts for about 1/10 of the total amount of alumina sol.

Therefore, if you want to obtain the same amount of aluminum nitride powder as when producing aluminum nitride powder only from alumina, considering the amount of water used in addition to the alumina sol, the amount of raw material slurry in the latter case is the same as in the former case. The time required for drying and granulation becomes significantly longer. Moreover, the particle size of the alumina component in the alumina sol is 0.01 to 0.
Since it is extremely small at 0.05 μm, drying and granulation processes are not easy.

On the other hand, if the mixing ratio of alumina and alumina sol is 40% by weight or more calculated using the formula: alumina content in alumina sol/(alumina molecule in alumina sol) Aluminum nitride powder can be obtained which has approximately the same ET specific surface area and average particle size as aluminum powder, but if the mixing ratio of alumina sol is 40 to 60% by weight, the amount of raw material slurry will not increase so much, and drying and Since granulation becomes easier, the content is preferably 40 to 60% by weight.

In addition, the present inventor confirmed only the diffraction peak of aluminum nitride by X-ray diffraction with respect to the aluminum nitride obtained in each example.

Furthermore, according to observation using a scanning electron microscope, coarse particles,
The presence of agglomerated particles (secondary particles) was small, and the aluminum nitride powder obtained in the examples was a collection of primary particles with uniform particle size.

〔Effect of the invention〕

According to the present invention, by adding alumina sol to raw alumina powder, the average particle size of the resulting aluminum nitride powder can be reduced (and the number of agglomerated particles can also be reduced).

Moreover, aluminum nitride powder having a particle size distribution comparable to that of the raw material alumina powder can be obtained without using all raw materials as expensive alumina sol. In addition, the aluminum nitride powder obtained in the present invention has a cohesiveness and particle size distribution comparable to that of the raw material alumina powder, has few coarse particles and agglomerated particles (and has a sharp particle size distribution), and can be used for appropriate sintering. By sintering under these conditions, a highly thermally conductive sintered body with few pores can be obtained.

[Brief explanation of drawings]

Figure 1 shows the particle size distribution curves of aluminum nitride powder obtained in the conventional example, Examples 1 to 6, and Example 10 by microtrack, and Figure 2 shows the amount of alumina sol added and the obtained alumina sol in the conventional example and each example. Average particle size of aluminum nitride powder. Indicates the relationship between

Claims (4)

[Claims] (1) A mixture of alumina powder, carbon powder, and alumina sol is used in a method for producing aluminum nitride powder by a reductive nitriding method in which a mixture of alumina powder and carbon powder is heated and reacted in an atmosphere containing nitrogen to reduce alumina. A method for producing aluminum nitride powder, characterized by: (2) The aluminum nitride according to claim 1, wherein the mixing ratio of alumina and alumina sol is 40% by weight or more calculated from the formula: alumina content in alumina sol/(alumina molecule in alumina sol) x 100 (weight%) Method of manufacturing powder. (3) The proportion of alumina in the alumina sol of the mixture of alumina and alumina sol is 40 to 60% by weight, calculated by the formula: alumina content in alumina sol/(alumina content in alumina sol + alumina) x 100 (weight%). A method for producing aluminum nitride powder according to claim 1. (4) The method for producing aluminum nitride powder according to any one of claims 1 to 3, wherein the nitrogen-containing atmosphere is nitrogen, ammonia, or a mixture thereof.