JPS63185868A - 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 [Industrial Field of Application] The present invention relates to a method for producing an aluminum nitride sintered body by pressureless sintering.

[Conventional technology]

In recent years, as integrated circuits such as ICs and LSIs have become more highly integrated and have higher outputs, problems with heat dissipation from silicon elements have arisen. In line with this current situation, we have developed an aluminum nitride sintered body that has even higher thermal conductivity, high electrical insulation, and excellent thermal expansion compatibility with silicon, instead of the conventional insulating substrate made of alumina sintered body. The development of substrates consisting of

By the way, aluminum nitride sintered bodies produced by the pressureless sintering method contain yttrium compounds such as yttrium as sintering aids,
Or add calcium compounds such as calcia,
It is manufactured by firing at a high temperature of 700°C to 2000°C in a nitrogen-7s'# atmosphere (for example, as disclosed in Japanese Patent Application Laid-Open No.
-207883).

[Problem that the invention seeks to solve]

However, at such high temperatures, since the vapor pressure of the yttrium compound and calcium compound is relatively high, the sintering aid near the surface of the powder compact tends to evaporate and scatter during sintering. The thermal conductivity of the aluminum nitride sintered body depends on the amount of sintering aid added, for example, 3 to 5% by weight of ittria.
Since the thermal conductivity decreases by about 20% with respect to the added amount of 1% by weight, scattering of the sintering aid as described above is preferable for imparting high thermal conductivity to the aluminum nitride sintered body. do not have.

Conventionally, to solve this problem, the powder compact is coated with powder of the same composition and then sintered, but in the case of aluminum nitride, the powder compact and filling powder are coated during sintering. reacts and sticks.

It cannot be used as a coating powder.

For this reason, there is a demand for the development of a method for producing a sintered body in which the sintering aid does not scatter during firing in the pressureless sintering method of aluminum nitride.

This invention provides a method for producing an aluminum nitride sintered body that prevents evaporation and scattering of a sintering aid from a molded body in the pressureless sintering method, and that can produce an aluminum nitride sintered body that has high thermal conductivity. The purpose is to provide

[Means for solving problems]

The method for producing an aluminum nitride sintered body of the present invention includes adding a sintering aid to aluminum nitride powder, mixing and shaping the mixture,
In this method, the obtained compact is coated with boron nitride powder containing a sintering aid of the same kind as the above-mentioned sintering aid, and then sintered under normal pressure.

This invention will be specifically explained below.

First, a sintering aid such as an yttrium compound or a calcium compound is added to aluminum nitride powder and thoroughly mixed using a ball mill or the like.

A binder is added to this mixture, granulated and sized, and molded using a molding method, isostatic pressing method, etc., or a dispersant and a binder are added to the above mixture and mixed in a medium. It is made into a slurry and formed into sheets using a doctor blade method.

On the other hand, high-purity boron nitride powder mixed with the same sintering aid as the above molded body is filled into a container free of components that melt and decompose even at the sintering temperature, and the aluminum nitride molded body is placed in the powder. After degreasing (a step to remove the dispersant and binder added during molding), pressureless sintering is performed. In order to prevent impurities from entering the molded body during sintering, the boron nitride powder used for the coating should contain less than the amount of impurities, preferably 99.5% or more high purity boron nitride powder. use. Further, the amount of the sintering aid in the coated powder is approximately the same as the amount added to the compact or slightly in excess. If the amount of sintering aid is less than the amount added to the compact, evaporation and scattering of the sintering aid cannot be prevented, and if the amount of sintering aid is too large, the sintering aid on the surface of the sintered compact may be prevented. The concentration of the agent becomes high, and a sintered body with homogeneous properties cannot be obtained.

Specifically, for an aluminum nitride molded body to which 3% by weight of yttria is added, it is desirable that the amount of yttria added to the coating powder is 3 to 7% by weight.

Regarding the timing of embedding the molded body in the coating powder, the molded body may be placed outside the container or on a container spread with the coating powder, degreased by heating, and then embedded in the powder. In this case, the efficiency of the degreasing process However, the molded product after degreasing is brittle and must be handled with care.

After degreasing the molded body, 1700 to 200 in N and gas atmosphere.
Sintering is performed at 0° C. under normal pressure to obtain an aluminum nitride sintered body.

At this time, since the surface of the aluminum nitride compact is coated with boron nitride powder to which the same sintering aid has been added, evaporation and scattering of the sintering aid from near the surface of the sintered compact is suppressed, and the resulting aluminum nitride The sintered body is homogeneous and has high thermal conductivity.

〔Example〕

Examples of the present invention will be described below.

Example 1 3% by weight of high-purity ittria powder was added to aluminum nitride powder with an average particle size of 0.5 μm, a binder and a plasticizer were added, the mixture was mixed in a medium to form a slurry, and a sheet was formed using a doctor blade method. It was made into a shaped molded body. On the other hand, 3% by weight of ittria was added to high-purity boron nitride powder and mixed, and this mixed powder was made into a coated powder and filled into a heat-resistant container.
The molded body was embedded in the powder and degreased in air at 500°C. After degreasing, 1800 min in nitrogen gas
'C.

Pressureless sintering was performed for 2 hours to produce an aluminum nitride sintered body.

Comparative Example 1 The same molded body as in Example 1 was embedded in a container filled with boron nitride powder to which no sintering aid was added, and after degreasing, pressureless sintering was performed under the same conditions as in Example 1. An aluminum nitride sintered body was produced.

Comparative example 2 The same molded body as in Example 1 was placed in an empty container.

After degreasing, pressureless sintering was performed under the same conditions as in Example 1 to produce an aluminum nitride sintered body.

Table 1 shows the thermal conductivity at room temperature of the sintered bodies obtained in Example 1 and Comparative Examples 1 and 2, determined by a laser flash method.

Table 1 As is clear from Table 1, the aluminum nitride sintered body of Example 1 coated with boron nitride powder to which a sintering aid was added and sintered was coated with boron nitride powder to which no sintering aid was added. It has higher thermal conductivity than Comparative Example 1, which was coated with boron nitride powder and sintered, or Comparative Example 2, which was sintered without being coated with boron nitride powder.

Example 2 A sheet-shaped molded body was obtained in the same manner as in Example 1 by adding 2% by weight of high-purity calcium carbonate powder to aluminum nitride powder having an average particle size of 0.5 μm. On the other hand, 2% by weight of calcium carbonate is added to high-purity boron nitride powder and mixed, and this mixed powder is filled into a heat-resistant container as a coated powder.
The compact was embedded in the powder, and after degreasing, pressureless sintering was performed under the same conditions as in Example 1 to produce an aluminum nitride sintered body.

Comparative Example 3 The same compact as in Example 2 was embedded in a container filled with boron nitride powder to which no sintering aid was added, and after degreasing, pressureless sintering was performed under the same conditions as in Example 1. An aluminum nitride sintered body was produced.

Comparative Example 4 The same molded body as in Example 2 was placed in an empty container, and after completion of degreasing, pressureless sintering was performed under the same conditions as in Example 1 to produce an aluminum nitride sintered body.

Table 2 shows the thermal conductivity at room temperature of the sintered bodies obtained in Example 2 and Comparative Examples 3 and 4, determined by the laser flash method.

Table 2 As is clear from Table 2, the aluminum nitride sintered body of Example 2 coated with boron nitride powder to which a sintering aid was added and sintered was coated with boron nitride powder to which no sintering aid was added. It has higher thermal conductivity than Comparative Example 3, which was coated with boron nitride powder and sintered, or Comparative Example 4, which was sintered without being coated with boron nitride powder.

〔Effect of the invention〕

According to this invention, an aluminum nitride molded body is coated with boron nitride powder added with the same sintering aid as the molded body,
By sintering, evaporation and scattering of the sintering aid from near the surface of the sintered body can be suppressed, which has the effect of obtaining a homogeneous aluminum nitride sintered body with high thermal conductivity.

Claims (2)

[Claims] (1) A sintering aid is added to aluminum nitride powder, mixed and molded, and the resulting molded body is coated with boron nitride powder containing the same kind of sintering aid as the above-mentioned sintering aid, and then under normal pressure. A method for producing an aluminum nitride sintered body, the method comprising sintering the aluminum nitride sintered body. (2) The method for producing an aluminum nitride sintered body according to claim 1, wherein the sintering aid is one or a mixture of two or more selected from calcium compounds and yttrium compounds.