JPH03279264A - Production of sintered aluminum nitride having high thermal conductivity - Google Patents

Abstract

PURPOSE:To obtain a sintered aluminum nitride having dense texture and high thermal conductivity by sintering formed aluminum nitride powder without using an assistant and baking the sintered product in reducing atmosphere under reduced pressure. CONSTITUTION:The objective sintered material can be produced by forming aluminum nitride powder, sintering without using an assistant and baking the sintered product in reducing atmosphere under reduced pressure, thereby decreasing the oxygen content in the aluminum nitride crystal particles. A sintered product having high purity and strength and resistant to deformation even at a high temperature can be produced by this process. Since the product lacks grain boundary phase, it has uniform color tone and is producible in improved yield and remarkably increased productivity. The sintered product is preferable to be used e.g. as a bottom plate for the baking of an aluminum nitride product.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention relates to a method for manufacturing an aluminum nitride sintered body,
More specifically, the present invention relates to a method for producing a dense aluminum nitride sintered body having high thermal conductivity.

(Conventional technology) Aluminum nitride (IN) has little strength loss at high temperatures;
Due to its excellent chemical resistance, it is used as a heat-resistant material, while its excellent thermal conductivity and coefficient of thermal expansion are close to that of Si, making it a promising material for heat sinks in semiconductor devices and insulating materials for circuit boards. being watched.

Such aluminum nitride sintered bodies are usually made of AQN 6 ultrafine powder (approximately 0.3 m or less) obtained by molding aluminum nitride powder and sintering it alone or by adding a sintering aid.
When AQN powder is used alone, a nearly dense sintered body can be obtained, but when AQN powder with a particle size of 0.5- or more is used, the sinterability is not good, so it is difficult to obtain a sintered body other than by hot pressing. It is difficult to obtain a dense sintered body without additives. However, in additive-free sintered bodies produced by the hot press method, oxygen in the oxidized layer on the surface of the raw material powder forms AQN during sintering.
It forms a solid solution in the lattice or forms a ρ-〇-N compound, and as a result, the thermal conductivity of the additive-free sintered body is at most 100ν/++4.
That's about it. However, the aluminum nitride sintered body produced by the hot pressing method has the advantage of being higher in strength than the sintered body sintered under pressure. In recent years, the purity of aluminum nitride raw material powder has progressed, and the thermal conductivity of sintered bodies without the addition of sintering aids has improved, but a fully satisfactory product has not yet been obtained.

(Problems to be Solved by the Invention) Currently, materials having higher thermal conductivity are desired for circuit boards for mounting semiconductors, heat dissipation boards, etc.

Further, certain types of heat dissipating substrates are required to be made of materials with high strength and high thermal conductivity. Additionally, an additive-free aluminum nitride sintered body with high thermal conductivity is desired.

The present invention has been made in consideration of the above points, and an object of the present invention is to provide an aluminum nitride sintered body that has excellent thermal conductivity and is free of sintering aids.

[Structure of the invention]

(Means and operations for solving problem W) Research has already been conducted on increasing the thermal conductivity of aluminum nitride sintered bodies (Japanese Patent Laid-Open Publication No. 303863/1983, etc.). When a sintering aid is added to AQN powder and fired for a sufficiently long time in a reducing firing atmosphere containing nitrogen, AQN is virtually free of subphases.
The fact that aluminum nitride sintered bodies consisting of a single phase and having a very high thermal conductivity for a polycrystalline body can be obtained is well known. This method of manufacturing a highly thermally conductive aluminum nitride sintered body is based on the following mechanism. The sintering aid reacts with impurity oxygen in the AQN raw material powder to generate a liquid phase and achieve densification of the sintered body.The surrounding atmosphere sinters the grain boundary phase of (rare earth element)-1-0 ternary compounds The aluminum nitride sintered body has the effect of removing it from the body, and the AQN
It becomes a single phase and transforms into a highly thermally conductive sintered body.

As a result of conducting experiments and studies on additive-free aluminum nitride in which no grain boundary phase exists, the present inventors discovered the following new matter and completed the present invention.

That is, when an additive-free aluminum nitride sintered body was fired for a long time in a reducing atmosphere, oxygen solidly dissolved in the grains was diffused and reduced on the surface of the sintered body, improving thermal conductivity. This effect was observed in aluminum nitride sintered bodies in which the amount of oxygen in the sintered bodies before firing in a reducing atmosphere was 2% by weight or less.

In addition, the raw material powder used to create the additive-free aluminum nitride sintered body contains metal impurities (Fe, Si, etc.) of 0.1% by weight or more, the amount of impurity oxygen is 7% by weight or less, and the average particle size is A sintered body obtained by molding aluminum nitride powder with a thickness of 0.05 to 5 um and sintering it without adding any auxiliary agent (this sintered body has an oxygen content of 2% by weight or less and contains Fe.

It is desirable that the content of metal impurities such as Si is 0.1% by weight or less. ) in a reducing atmosphere, e.g. 1500-20
By firing at 50°C for 4 hours or more in an atmosphere including reduced pressure, W! reduce the amount of
This is a manufacturing method for obtaining a highly thermally conductive aluminum nitride sintered body.

Next, an example of the method for manufacturing the aluminum nitride sintered body of the present invention will be described below.

First, a binder is added to AQN powder, and the mixture is mixed, granulated, and sized, and then molded. As the molding method, a mold press, a hydrostatic press, etc. can be applied.

Subsequently, the molded body is heated in a non-oxidizing atmosphere, for example in a nitrogen gas stream to remove the binder, and then hot press sintered. The hot pressing conditions are, for example, 1600 to 1900°C and 400k so that the molded product is sufficiently densified.
g/(d). The additive-free aluminum nitride sintered body thus produced is sintered under normal pressure using, for example, a carbon container that creates a carbon gas atmosphere during firing.The firing temperature is 1550~ It is preferable to set the firing temperature to 2050°C and the firing time to 4 hours or more.By such a method, AρN is 99% or more and the thermal conductivity is 10100.
It is possible to obtain a fired body of W"・K-1 or higher. In addition to using solid carbon evaporated at high temperature as the reducing gas source, hydrocarbons etc. may also be used.6 As explained above, this method According to the invention, a highly thermally conductive aluminum nitride sintered body can be produced without additives.

According to this method, a sintered body with high purity and high strength, which does not easily deform even at high temperatures, can be obtained.

Since there is no grain boundary phase, there is no color unevenness in the sintered body, which improves yield and greatly improves productivity.

It is good to use it as a flooring board used when firing aluminum nitride products.

(Example) Examples of the present invention will be described in detail below.

Example 1 The content of oxygen as an impurity is 0.1% by weight.

After adding 5% by weight of an organic binder to AffiN powder with a specific surface area of 5.3+m2/g and granulating it, 15g of this granulated powder was molded by uniaxial pressure of 500 kg/d to about 30 x 30 x 15011. It was made into a green compact. This green compact was heated to 700° C. in a nitrogen gas atmosphere to remove the binder.

This green compact was sintered in a hot press at 1800° C. in a nitrogen gas atmosphere (1 atm) for 4 hours under a −axial pressure of 400 kg/cd. Next, this sintered body! Set the broom in a Tamashii carbon container and place it in a nitrogen gas atmosphere (
An AεN sintered body was produced by firing in a carbon heater furnace at 1900° C. for 96 hours. The density and grain size of the obtained An sintered body were measured. In addition, a disk with a diameter of 10 mm and a thickness of 3.3 mm was ground from the sintered body.
This was used as a test piece and the thermal conductivity was measured by the laser flash method. The measurement temperature is 25°C. Furthermore, the amount of impurity oxygen in this sintered body was analyzed by fast neutron activation analysis. Also.

The sintered body was subjected to X-ray diffraction. The results obtained are shown in Table 1.

AQN sintered bodies were produced in the same manner as in Example 1, with various firing temperatures during normal pressure firing, and the same evaluations were conducted for each.

Example 4 A4N was produced in the same manner as in Example 1, except that the particle size of the A4N raw material powder, the coulometric amount of impurities, and the sintering temperature during pressureless sintering were changed.
Sintered bodies were manufactured and the same evaluation was performed on each.

〇〇N The same procedure as in Example 1 was carried out by changing the particle size of the raw powder, the amount of impurity oxygen, the firing temperature and time during hot press sintering, and the firing temperature during pressureless sintering. AQN sintered bodies were manufactured using the same method, and the same evaluations were performed on each of them.

AQN sintered bodies were produced in the same manner as in Example 1 above, with various firing times during pressureless sintering, and the same evaluations were conducted for each.

(The following is a blank space) [Effects of the Invention] As detailed above, the aluminum nitride sintered body of the present invention is additive-free, AQN single phase, has high purity, and has excellent properties showing high thermal conductivity. be. Af with a thermal conductivity of 1701m-1 or more without using an auxiliary agent
The fiN sintered body can be manufactured with high yield, and its industrial value is extremely large.

Claims (1)

[Claims] A sintered body formed by molding aluminum nitride powder and sintering without adding any auxiliary agent is fired under atmospheric pressure including reduced pressure in a reducing atmosphere to reduce the amount of oxygen in aluminum nitride crystal grains. A method for producing a highly thermally conductive aluminum nitride sintered body.