JPS6121977A - Manufacture of aluminum nitride sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an aluminum nitride sintered body having high purity, high density, and particularly excellent thermal conductivity.

Sintered aluminum nitride is a well-known substance that has recently attracted much attention as an insulator that has excellent physical properties such as heat resistance, corrosion resistance, and sink strength, as well as high thermal conductivity.

However, conventionally, aluminum nitride powder, which is used as a raw material for manufacturing aluminum nitride sintered bodies, inevitably contains various impurities and varies in particle size and particle size distribution, depending on the manufacturing method. As it was not sufficient, it was difficult to provide a highly pure and dense sintered body, and even if a large amount of sintering aid was used, the sinterability was insufficient during normal pressure sintering. It has been difficult to fully utilize aluminum nitride's inherent excellent properties such as thermal conductivity.

As a result of extensive research into aluminum nitride powder and sintered bodies thereof, the present inventors have already proposed a novel aluminum nitride powder that is a uniformly fine powder of unprecedented purity and has excellent sinterability. As a result of continued research, it was discovered that the sintering properties of aluminum nitride powder and the properties of the sintered body are greatly affected by the sintering aid used, and the present invention was completed and proposed.

That is, the present invention relates to the production of an aluminum nitride sintered body by adding a sintering aid to aluminum nitride powder or a mixed powder of aluminum nitride powder and boron nitride and/or silicon nitride. This is a method for producing an aluminum nitride sintered body, characterized in that at least one compound selected from the group consisting of calcium chloride, barium halide, and strontium halide is used.

The aluminum nitride powder used in the present invention is not particularly limited, and any known aluminum nitride powder can be used. Particularly effective aluminum nitride powder has an average particle size of 2 μm or less and 6 μm.
Contains particles of 70% by volume or more, the oxygen content is 3% by weight or less, and the cationic impurity content is 0.
It is a powder containing 5% by weight or less. The average particle size referred to here is not the average value of the particle size of primary particles calculated from a scanning electron microscope photo of powder, but the average value of the particle size of secondary agglomerated particles as actually measured by a sedimentation type particle size distribution analyzer. Mean size. No matter how fine the secondary particles are, if they agglomerate, especially if they are larger than 2 μm, densification will not proceed sufficiently during sintering, and as a result, a product with high thermal conductivity may not be obtained. Furthermore, when aluminum nitride powder containing 3% by weight or more of oxygen and 0.5% by weight or more of cationic impurities is used as a raw material, these impurities form a second phase at the grain boundaries of the sintered body. May significantly reduce thermal conductivity. Typical methods for producing the aluminum nitride powder preferably used in the practice of the present invention are as follows.

(1) Purity 99.0% by weight, preferably 99.5% by weight
In the above, aluminum oxide fine powder containing particles with an average particle size of 2 μm or less and 3 μm or less in a ratio of 70% by volume or more, and an ash content of 0.2% by weight at most and an average particle size of 1 μm.
m or less fine carbon powder is intimately mixed in a liquid dispersion medium, and the weight ratio of the fine aluminum oxide powder to the fine carbon powder is 1:0.36 to 1:1; The resulting intimate mixture is suitably dried and calcined at a temperature of 1400-1700°C under an atmosphere of nitrogen or ammonia; (3) the resulting fine powder is then heated under an oxygen-containing atmosphere for 6
It can be obtained by heating at a temperature of 00 to 900°C to remove unreacted carbon.

In the present invention, one of the other components that can be mixed with the aluminum nitride powder and used as a composite raw material is boron nitride powder. The boron nitride powder is a well-known layered crystal compound. The boron nitride powder used in the present invention is not particularly limited, and any known powder can be used. The boron nitride powder commonly used is one in which the purity of boron nitride is 97.0% by weight or more, preferably 99.0% by weight or more, and the average particle size is 5 μm or less. Furthermore, the method for producing the boron nitride powder is not limited to specific circumstances, and any known method can be employed.

For example, (1) H3BO5 or Na2B4 in the presence of urea
A method of manufacturing by heating O7 at 500 to 950°C in an NH atmosphere, (2) A method of manufacturing by reacting BCIs and NH, (3) A method of manufacturing Be-B alloy at a temperature of 500 to 1400°C. A method of heating and then dissolving and removing Fe with, for example, an acid can be adopted.

In addition, in the present invention, one of the other components that can be mixed with the aluminum nitride powder and used as a composite raw material is silicon nitride. The silicon nitride powder is also a well-known compound, and in the present invention, any of these known compounds can be used without particular limitation. Generally, purity of 95% by weight or more, preferably 97% by weight or more is suitable.

Furthermore, when mixed powder is used as the raw material, it is generally preferable that the mixing ratio of aluminum nitride powder is 50% or more, more preferably 60% or more.

The most important feature of the present invention is the use of calcium, barium or strontium halide as a sintering aid. Halides include fluorides, chlorides, bromides and iodides. Specific examples of the sintering aids used in the present invention include calcium fluoride and barium fluoride.

Strontium fluoride, calcium oxalide.

Barium oxalide, strontium oxalide.

Examples include calcium iodide, barium iodide, strontium iodide, and the like. In particular, fluorinated substances can be preferably used in the present invention because the resulting aluminum nitride sintered body or composite sintered body has better thermal conductivity. When the aluminum nitride powder or the mixed powder containing the aluminum nitride powder is sintered, what effect does the calcium, barium or strontium halide have on improving the sinterability of the sintered body and improving the sintered body? At present, the effect of vines on properties such as high thermal conductivity, which can be significantly improved, is still unclear. The present inventors presume that the halides are stable at high temperatures and exist in liquid form, so that they can be uniformly dispersed by aluminum nitride powder or a mixed powder containing aluminum nitride and exhibit the above effects. are doing.

The amount of the sintering aid used in the present invention varies depending on the properties required of the sintered body and cannot be absolutely limited, but generally, the amount of the sintering aid used in the mixed powder containing aluminum nitride, ram powder, or aluminum nitride powder is 0. It is preferable to select from the range of .01 to 5% by weight.

The mixing of the aluminum nitride powder or the mixed powder containing the aluminum nitride powder and the sintering aid in the present invention is not particularly limited, and may be dry mixing or wet mixing.

A particularly preferred embodiment is wet mixing, ie mixing in the wet state using a liquid dispersion medium.

The liquid dispersion medium is not particularly limited, and commonly used water, alcohols, hydrocarbons, or mixtures thereof are preferably used. In particular, lower alcohols having 4 or less carbon atoms, such as methanol, ethanol, and butanol, are most preferably employed industrially.

Further, the wet mixing device used for mixing the raw materials is not particularly limited and any known device may be used, but it is preferable to select one that does not generate impurity components due to the materials.

For example, the material may be aluminum nitride itself, a plastic material such as polyethylene, polyurethane, nylon, or a material coated with these materials.

The mixture uniformly mixed in the liquid dispersion medium may be suitably dried and then hot-pressed or sintered under normal pressure to form an aluminum nitride sintered body or a composite sintered body. In the case of hot pressing, a known method can be used as is, for example, the mixture is filled into a mold made of graphite, etc.
To? 1600℃ in a nitrogen stream while applying a pressure of /cr&
It is preferable to produce a sintered body by heating to ~2100°C. In addition, in the case of the above-mentioned pressureless sintering, the mixture may be used as it is or may be made of known materials such as paraffin or polyvinyl butyral.
/(It is common to add an inder, mold it into a desired shape using a method such as a rubber press, and then bake it. Alternatively, a binder is added to the mixture.

A method may also be suitably employed in which a plasticizer, a peptizer, and an organic solvent are added to form a slurry, which is formed into a sheet-like product using a doctor blade molding machine, and then fired. As conditions for the pressureless sintering, it is preferable to sinter at a temperature of 1600 to 2000° C. in a general nitrogen atmosphere.

The aluminum nitride sintered body and the composite sintered body of aluminum nitride and boron nitride and/or silicon nitride obtained by the method of the present invention are heat resistant.

It is a ceramic that exhibits the excellent characteristics inherent to aluminum nitride, such as excellent corrosion resistance, low dielectric loss, and high thermal conductivity, and has extremely high industrial value as a material for various substrates, heat dissipation materials, and insulating materials.

It is not necessary to add a sintering aid in the present invention (it does not need to be added to the mixed powder containing aluminum oxide powder or aluminum nitride powder, and it is not necessary to add it to the mixed powder containing aluminum oxide powder or aluminum nitride powder, and it is necessary to add it in advance at the time of manufacturing these powders).
At least one member selected from the group consisting of calcium halogenide, barium halide, and strontium halogenide.
Aluminum nitride powder obtained by mixing a seed compound into the raw material for producing the powder or the above-mentioned mixed powder may be used.

EXAMPLES In order to explain the present invention more specifically, the present invention will be described below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Average particle diameter is 1.31 μm, 90% by volume is 3 μm or less
1.0% calcium fluoride powder with an average particle size of 4.5 μm was added to aluminum nitride powder with the composition shown in Table 1.
vrt% was added and mixed uniformly. This mixed powder 21 was rubber-pressed at a pressure of 1500 Ke/cdO, and a disk-shaped compact was placed in a graphite crucible coated with boron nitride and sintered under normal pressure at 1900° C. for 6 hours in a nitrogen gas flow of 1 atm. The obtained sintered body had a density of 3.22 f/ctl and was translucent.

The thermal conductivity of the 2-5 m thick sintered body was measured by a laser flash method and was found to be 115 W/mK.

Further, when the in-line transmittance of a sample of this sintered body was ground and polished to a thickness of 0.5 μm for light having a wavelength of 5.5 μm was measured, it was 42%.

For comparison, a rubber press molded sample of the aluminum nitride powder without adding calcium fluoride was sintered under the same conditions, and the resulting sintered body had a density of 2.9Of/
CD is white and opaque, and the thermal conductivity value is 62W.
/mK.

Example 2 The same aluminum nitride powder as used in Example 1 was mixed with the sintering aids shown in Table 2 and subjected to pressureless sintering or hot press sintering. Table 2 shows the burned fruit.

Table I AtN powder analysis value AtN content 97.8% Element Content Mg<5 (PPM) Cr 21(') 8i 125(') Zn 9(') Fe 20(') Cu <5(') Mn
5(') Ni 27(') Ti <5(#)Co
<5 (') At64.8 (wtX) N 3? ), 4 (#) o 1.1. (') C0,11 (#) Example 3 Same aluminum nitride powder as used in Example 1 80
1 part by weight of calcium fluoride powder with an average particle size of 4.5 μm was mixed with 20 parts by weight of hexagonal boron nitride powder with an average particle size of 2.5 μm and a purity of 99.5%.
．． 0 wt% was added and mixed uniformly. 12 tons of this mixed powder
was filled into a graphite mold whose inner wall was coated with boron nitride powder, and pressure sintered at 2000° C. for 3 hours under a pressure of 200 Kf/cd in nitrogen gas at 1 atm. The obtained sintered body had a density of 2.98 f/cd, was white in color, and had workability that allowed it to be easily machined with a tungsten carbide cutting tool. Furthermore, when the six-point bending strength and thermal conductivity of this sintered body were measured, they were found to be 56.
Kl/wJ was 85 W/mK.

Example 4 Instead of the boron nitride powder in Example 6, an average particle size of 2.
The same procedure as in Example 3 was carried out except that silicon nitride powder having a diameter of 2 μm and a purity of 99.2% was used. As a result, the obtained sintered body had a density of 6.92 t/aA and a six-point bending strength of 31 Kt/a.
-, the thermal conductivity was 48 w/mK.

Claims (2)

[Claims] (1) When producing an aluminum nitride sintered body by adding a sintering aid to aluminum nitride powder or a mixed powder of aluminum nitride powder and boron nitride and/or silicon nitride, calcium halide is used as the sintering aid. A method for producing an aluminum nitride sintered body, characterized in that at least one compound selected from the group consisting of barium halide and strontium halide is used. (2) Claims (1) in which the amount of the sintering aid added is in the range of 0.01 to 5% by weight based on the aluminum nitride powder or the mixed powder of aluminum nitride powder and boron nitride and/or silicon nitride. ) A method for producing an aluminum nitride sintered body.