JPS63277571A - Production of sintered aluminum nitride having high thermal conductivity - Google Patents

Abstract

PURPOSE:To produce the titled sintered article having high density and thermal conductivity, by calcining a specific molded article or sintered article in a calcination vessel made of AlN in an atmosphere or in vacuum. CONSTITUTION:AlN powder having impurity oxygen content of <=7wt.% and an average particle diameter of 0.05-5mum is mixed with 0.01-15wt.% (in terms of element) of a compound of at least one kind of element selected from group IIa, group IIIa and rare-earth elements and a binder. The mixture is granulated, graded and molded to obtain a molded article. The molded article or a sintered article containing 0.01-15wt.% of at least one kind of element selected from group IIa, group IIIa and rare earth elements, having an oxygen content of 0.01-20wt.% and containing AlN as a principal phase and a (group IIa, group IIIa or rare earth element)-Al-O compound phase and/or (group IIa, group IIIa or rare earth element)-O compound phase is put into a calcination vessel made of AlN and calcined in vacuum or in a non-oxidizing atmosphere at 1,550-2,050 deg.C for >=4hr.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for producing an aluminum nitride sintered body.

(Prior art) Aluminum nitride (Af2N) has little strength loss even at high temperatures and has excellent chemical resistance, so it is used as a heat-resistant material. It is also seen as a promising material for heat sinks in devices and insulator materials for circuit boards.

Such aluminum nitride does not have a melting point under normal pressure,
Since it decomposes at high temperatures of 2,500°C or higher, it is used as a sintered body except for applications such as thin films.

Such an aluminum nitride sintered body is usually obtained by molding and sintering aluminum nitride powder. When ultrafine AsLN powder (approximately 0.3- or less) is used alone, a dense sintered body can be obtained, but oxygen in the oxidized layer on the surface of the raw material powder forms in the A and IN lattices during sintering. solid solution, Aλ-〇-N
A compound is produced, and as a result, the thermal conductivity of the additive-free sintered body is about 1001/mK at most. Also, the particle size is 0.5. When the above-mentioned A-mon N powder is used, the sinterability is not good, so it is difficult to obtain a dense sintered body without additives other than by hot pressing. Therefore, when trying to obtain a sintered body under normal pressure, rare earth oxides are used as a sintering aid in order to increase the density of the sintered body and to prevent the impurity oxygen of the AiN raw powder from dissolving into the A4N grains. It is common practice to add alkaline earth metal oxides, etc.
0-127267, JP-A-61-10071, JP-A-60-71575, etc.), these sintering aids are AiN
It reacts with impurity oxygen in the raw material powder to produce a liquid phase and achieve densification of the sintered body, and also fixes this impurity oxygen as a grain boundary phase (oxygen trap) to achieve high thermal conductivity.

By adding a sintering aid in this way, it is true that the sintered body becomes m-densified and has high thermal conductivity, but on the other hand.

As a result, due to the amount of remaining grain boundary phase (subphase to the main phase A3.N phase) and the presence of oxygen, etc. that could not be completely trapped, the aluminum nitride sintered body has a concentration of at most 16
It was about 0 w/Il-.

Therefore, various attempts have been made to improve the thermal conductivity of aluminum nitride sintered bodies, but nothing that is fully satisfactory has yet been achieved.

(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.

However, oxygen and other impurities, especially due to the presence of grain boundary phases that form at the grain boundaries as a result of additive addition.

There was a limit to increasing the thermal conductivity of aluminum nitride sintered bodies.

The present invention has been made with one or more points in mind.

The purpose is to provide an aluminum nitride sintered body with excellent thermal conductivity.

[Structure of the invention]

(Means and effects for solving the problem) In order to achieve the above object, the present inventors have developed a sintering aid added to aluminum nitride powder, sintering conditions, sintered body composition, sintered body fine structure, etc. As a result of conducting experiments and studies on the relationship between thermal conductivity, we discovered the following new matter and completed the present invention.

That is, A! uses an yttrium compound as a sintering aid. L
When added to N powder and fired for a long time in an aluminum nitride firing vessel, grain growth occurred.

It has been discovered that an aluminum nitride sintered body having high thermal conductivity can be obtained. This effect is.

Similar findings were observed for other rare earth, IIa group, and Ha group elements.

Based on this fact, the present invention is the result of various studies on the optimal conditions for achieving high thermal conductivity. The aluminum powder and at least one of the Ua group element, IIa group element, and rare earth element are 0.0 in terms of weight.
A molded article formed after mixing with 1 to 15% by weight of a group IIa group IIa compound or a rare earth element compound, or I
Ia group, Ha group and rare earth element content is 0.01-1
5 wt%, oxygen content is 0.01 to 20 wt%, main phase is A, gN, group IIa, group Ha, and rare earth elements) -A or -0 compound phase and/or (group IIa) ,
■A sintered body containing a group A and rare earth elements)-0 compound phase.

b) Using an aluminum nitride firing vessel.

C) Non-oxidizing gas atmosphere, 1550-2050°C, 4
This is a method for producing a highly thermally conductive aluminum nitride sintered body, characterized by firing under atmospheric pressure including vacuum for a period of time or more.

Next, a method for manufacturing the highly thermally conductive aluminum nitride sintered body of the present invention will be described.

The main points of the production method of the present invention are the purity and average particle size of the aluminum nitride raw material powder, sintering aid, sintering container, firing time, and firing atmosphere.

The aluminum nitride raw material powder, which is the main component, contains oxygen at 7% by weight or less, practically 0.01 to 7% by weight, in consideration of sinterability and thermal conductivity, and has an average particle size of 0.05 to 7% by weight. 5μ
Use the one from s.

As additives, compounds of the na group, group IIIa, and rare earth elements are used. As compounds of these elements, oxides, nitrides, fluorides, oxyfluorides, oxynitrides, or substances that become these compounds upon firing are optimal. Examples of substances that become oxides upon firing include carbonates, nitrates, oxalates, and hydroxides of these elements.

The addition of Group IIa, Group IIa and rare earth element compounds.

These elements are added in an amount of 0.01 to 15% by weight in terms of weight.

In the method of the present invention, such AXN powder and na group, I
A molded body containing a mixture of Group IIa and rare earth element compounds may be sintered under the conditions described below, or a conventional method (for example, JP-A No. 61-117160) may be used to form a mixture of Group IIa and rare earth element compounds.
The content of group A and rare earth elements is 0.01 to 15% by weight, the content of oxygen is 0.01 to 20% by weight, the main phase is A or N, and the group Na, group IIa, and rare earth elements)-A ,
A sintered body comprising an I-0 compound phase and/or a (IIa group, IIa group, and rare earth element)-○ compound phase may be produced and used in place of the above molded body.

As for the firing vessel, alumina is sufficient if the purpose is simply to make the molded body a-densified.

However, high thermal conductivity cannot be obtained using this container.In the present invention, an aluminum nitride firing container is used. By using this container, grain growth occurs, resulting in (na group, IIa group and rare earth elements) -Al-
This acts to remove grain boundary phases such as zero compounds from the sintered body, and the sintered body changes into a highly thermally conductive sintered body.

Regarding the sintering time, conventionally the sintering time has been reduced to 1 to 3 hours using various auxiliaries. Although it is possible to refine the

Grain growth does not occur. In addition, when using an alumina container, 4 hours or more is required to achieve 0 grain growth, which does not occur even with long firing, although it depends on the sintering temperature and the amount of additive added. . More preferably, the time is 6 hours or more, and still more preferably 12 hours or more.

Regarding the firing temperature, 1550 to 2050°C is preferable.

If fired at a temperature lower than 1550°C, a dense sintered body will not be obtained and grain growth will not occur, although it depends on the particle size of the raw powder and the amount of oxygen, and if fired at a temperature higher than 2050°C, A! L
The vapor pressure of N itself increases, making densification difficult. The firing temperature is more preferably 1800 to 1950°C.

The firing atmosphere is preferably one or more non-oxidizing atmospheres selected from the group of vacuum, nitrogen gas, hydrogen gas, -carbon oxide, argon, etc. If firing in an oxidizing atmosphere, solid solution of oxygen and generation of different phases are preferred. Therefore, high thermal conductivity cannot be obtained, and sintering is performed in a vacuum or under reduced pressure.

It is carried out under atmospheric pressure, including pressurized and normal pressure.

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

First, a predetermined amount of a rare earth element compound as a sintering additive is added to AiN powder, and then mixed using a ball mill or the like.

The pressureless sintering method is used for sintering.

In this case, a binder is added to the mixed powder and kneaded.

After granulation and grading, it is molded. As a molding method,
Mold press, hydrostatic press, sheet molding, 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 sintered under normal pressure. As the firing vessel, an aluminum nitride firing vessel is used. The sintering temperature was 1550-2050℃, and the sintering time was 4
Set it to more than an hour. The sintered body of the present invention can be obtained by such a method.

Next, the effect of improving thermal conductivity of the aluminum nitride sintered body of the present invention will be explained. Although the exact mechanism has not been completely elucidated at present, according to the research conducted by the present inventors, the following factors are presumed to be responsible for the increase in thermal conductivity.

Particles of the sintered body grow by firing in an aluminum nitride container for a long time. This means that as A4N grains grow, the number of grain boundaries that provide thermal resistance decreases as a result.
Scattering of phonons results in small sintered bodies.

For the above reasons, a highly thermally conductive aluminum nitride sintered body can be obtained.

(Example) Ay and N powders containing 1.0% by weight of oxygen as an impurity and having an average particle size of 0.6 mm were added as additives with an average particle size of 0.6 mm.
9p of Y2O, converted to the weight of yttrium element, is 2.5
% by weight was added and mixed using a ball mill to prepare raw materials. Next, 4% by weight of an organic binder was added to this raw material and granulated, followed by press molding at a pressure of 500 kg/(!J) to form a compact of 38 x 38 x 10 cm. The binder was removed by heating to 700° C. in a gas atmosphere, and the degreased body was placed in an aluminum nitride firing container.

This container was used in a nitrogen gas atmosphere (1 atm).

Normal pressure sintering was carried out at ℃ for 24 hours. The density and particle size of the obtained AiN sintered body were measured. A disk with a diameter of 10 cm and a thickness of 3.3 cm was also ground from the sintered body.

Using this as a test piece, thermal conductivity was measured by the laser flash method (using Shinku Riko 11TC-3000).

The measured temperature is 25°C. The above sintering conditions and the properties of the obtained sintered body are shown in Table 1. AIN sintering was carried out in the same manner as in Example 1 above, with various amounts of second sintering additives added. Each body was manufactured and evaluated in the same manner.

A, IN sintered bodies were produced in the same manner as in Example 1, with various addition amounts of sintering additives and sintering temperatures, and each was evaluated in the same manner.

Lost Garden Goro A! AiN sintered bodies were produced in the same manner as in Example J above by changing the particle size of the LN raw material powder, the impurity acid IT, and the sintering temperature, and were evaluated in the same manner.

A was carried out in the same manner as in Example 1, with various changes in the amount of sintering additives, sintering temperature, sintering atmosphere, and atmospheric pressure.
, IN sintered bodies were produced, and the same evaluations were performed on each of them.

A'
RN sintered bodies were manufactured and the same evaluations were performed on each of them.

Lost Storm U AAN powder containing 1.5% by weight of oxygen as an impurity and having an average particle size of 1.5-, as an additive, an average particle size of 0.9
μs of Y, O3 is 0.0 in terms of weight of yttrium element.
It was added in an amount of 8% by weight. Using an aluminum nitride firing container,
Sintering was carried out at 1700° C. for 12 hours under pressure of nitriding gas at 10 atm. The obtained sintered body was evaluated in the same manner as in Example 1 above.

AlN sintered bodies were produced in the same manner as in Example 1, except that the sintering temperature, sintering time, and sintering atmosphere were changed.

A similar evaluation was conducted.

A was carried out in the same manner as in Example 1 above, except that the five-plate sintering temperature and the sintering atmosphere were reduced to N, +H, (5%)!
A N sintered body was manufactured and evaluated in the same way.

AJN sintered bodies were produced in the same manner as in Example 1 except that the cations of the additives were changed to various Na group, Ha group, and rare earth elements, and the same evaluations were conducted for each.

The AgN degreased body obtained by the same method as in Example 1 was set in an aluminum nitride firing container, and heated at 1800°C for 2, (r
, N, and pressureless sintering in an air stream to obtain a sintered body. The properties of these sintered bodies are shown in Table 2, and from the results of the same evaluation as in Example 1, it was found that when the sintering time was short, less than 4 hours, the effect of grain growth by using an aluminum nitride container was not sufficient. It can be seen that sintering for a long time (4 hours or more) is necessary to obtain an AQN sintered body with high thermal conductivity.

In Comparative Examples 2 and 4, Ag obtained by the same method as in Example 1 was used.
An AgN degreased body obtained by the same method as in Example 1 except that the amount of auxiliary added was changed in Comparative Example 3 and the type of auxiliary agent was changed in Comparative Example 5 was set in an alumina firing container. 2
, 3.5 is 1800°C, 2ir, 1soo in comparative example 4
℃ and 244r, both were sintered under normal pressure in a N2 stream, and the same evaluation was performed. From this result, when using the AraO1 firing vessel, an AQN sintered body having high thermal conductivity could not be obtained, and it can be seen that the aluminum nitride firing vessel is effective.

500 kg/2N powder used in Example 1
Press molded with pressure of Ci, 30 x 30 x
This green compact was put into a carbon mold and hot-press sintered in a nitrogen gas atmosphere at a temperature of 1800° C. and under a pressure of 400 kg/d for 1 hour to obtain a sintered compact. The properties of this sintered body are shown in Table 2, and the thermal conductivity was as low as 8 hl/mK.

In this way, without the addition of rare earth element compounds, Aj! The effectiveness of adding the rare earth element compound can be seen from the fact that the impurity oxygen on the surface of the N raw material powder reacts with A3N, producing an Aλ-〇- compound that impedes heat conduction.

(The following is a blank space) [Effects of the Invention] As stated above, the method for producing an aluminum nitride sintered body of the present invention provides a dense aluminum nitride sintered body having high thermal conductivity, and is suitable for industrial use. The value is extremely large.

Agent: Patent Attorney Noriyuki Chika Same as Mitsuyuki Matsuyama

Claims (3)

[Claims] (1) a) aluminum nitride powder having an impurity oxygen content of 7% by weight or less and an average particle size of 0.05 to 5 μm;
Group IIa, containing at least one of Group IIa elements, Group IIIa elements, and rare earth elements in an amount of 0.01 to 15% by weight;
A molded article formed after mixing with a compound of Group IIIa or a rare earth element, or containing at least one of Group IIa, Group IIIa, and rare earth element from 0.01 to 15% by weight, and having an oxygen content of 0.01 to 15% by weight. 20% by weight, with AlN as the main phase (group IIa, group IIIa or rare earth element) -Al
A sintered body containing an -O compound phase and/or a (IIa group, IIIa group, or rare earth element) -O compound phase is produced b) using an aluminum nitride firing container, c) in a non-oxidizing gas atmosphere at 1550 to 2050°C. , 4
A method for producing a highly thermally conductive aluminum nitride sintered body, characterized by firing under atmospheric pressure including vacuum for a period of time or more. (2) A method for producing a highly thermally conductive aluminum sintered body according to claim 1, wherein the firing time is 24 hours or more. (3) A method for producing a highly thermally conductive aluminum nitride sintered body according to claim 2, wherein the firing temperature is 1500°C or more and less than 1800°C.