JPH0651593B2 - Method for manufacturing aluminum nitride sintered body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an aluminum nitride sintered body used for a ceramic substrate used for electronic materials.

[Prior Art] Conventionally, a method industrially used for sintering aluminum nitride is called a Serpek method, and aluminum nitride is heated by heating a mixed powder of alumina and carbon in nitrogen or ammonia. It is a worm. This reaction is represented by the following equation.

Al ₂ O ₃ + 3C + N ₂ → 2AlN + 3CO (1) In this reaction process, aluminum nitride (AlN) is synthesized using aluminum oxycarbide produced by the solid-state reaction of alumina and carbon as an intermediate phase. In order to allow the reaction to proceed sufficiently, a large excess of carbon is actually mixed with the carbon equivalent of the formula (1). Therefore, after completion of the reaction, excess carbon is removed when passing through a temperature range below the AlN decomposition temperature in air.

In order to obtain a sintered body from the AlN powder obtained in this way, the following steps are required.

(1) Grinding AlN powder with a ball mill, etc. (2) Forming with a press, etc. (3) Firing in nitrogen In the conventional technology, the above-mentioned complicated steps are required to obtain an AlN sintered body. .

[Problems to be Solved by the Invention] An object of the present invention is not to separately perform the aluminum nitride powder manufacturing step and the sintered body manufacturing step as described above,
Another object of the present invention is to provide a simple method for producing an aluminum nitride sintered body which does not require removal of excess carbon.

[Means for Solving Problems] The present invention provides an aluminum nitride sintered body by a forming step of adding an organic binder to boehmite sol to form a sheet, and a firing step of firing the obtained green sheet in a nitrogen stream. Is a method of manufacturing. The boehmite sol may be a sol obtained by using an aluminum alkoxide and an acid peptizer, and the organic binder may be an organic binder having a carbon content of 50 to 80% by weight.

According to the present invention, boehmite sol is used as a starting material, mixed with an organic binder, and directly molded into a substrate-shaped sheet to form a green sheet composed of boehmite and an organic binder, and the green sheet is fired in a nitrogen atmosphere. As a result, the organic binder is decomposed and carbonized, and the boehmite sol is directly reduced to synthesize aluminum nitride, and at the same time, a sintering reaction is caused to directly obtain a sintered aluminum nitride body.

At this time, the amount of the organic binder is naturally required to be equal to or more than the amount required for sheet formation, and is the amount of carbon required for producing aluminum nitride after the organic binder is decomposed. That is, more than the amount for reducing the boehmite sol is required.

In the production method of the present invention, the amount of residual carbon after decomposition varies depending on the type of the organic binder, but in order to obtain the amount of carbon necessary for producing aluminum nitride, the carbon content is 50 to 80% by weight. Is desirable.

In addition, it is desirable to use boehmite sol peptized with an acid because the carbonization of the organic binder is promoted.

As a starting material, an acid-deflocculated boehmite sol is used, but it is preferable to colloid (deflocculate) an organoaluminum such as an aluminum alkoxide with a peptizer of an acid such as acetic acid, hydrochloric acid or nitric acid. The obtained boehmite sol is used. Such a boehmite sol is
It is very suitable for the reducing action by the organic binder.

As the organic binder, those having a carbon content as described above are suitable, but the following can be selected.

That is, polyvinyl alcohol (PVA), methyl cellulose
(MC), ethyl cellulose, ethylene oxide polymer, polyvinylpyrrolidone, acrylic resin, wax,
Alternatively, it is selected from polyvinyl butyral, polyvinyl chloride and the like.

The sintered body obtained according to the present invention is a single phase of AlN as shown in FIG. 1 of the X-ray diffraction spectrum of the one sintered at 1800 ° C. Then, looking at FIG. 2 of the X-ray diffraction spectrum in the case of sintering at 1400 ° C., it can be seen that the Al ₂ O ₃ phase remains. 1500 ° C as shown in the following examples
It is clearly understood that a substrate having a phase of aluminum nitride alone can be obtained by the above firing. The sintering density of aluminum nitride alone is 2.9 g / 1800 ° C.
Can be obtained in cm ³ . When yttrium oxide was used as the additive when the present invention was carried out with the additive added, it was 3.1 g / cm ³ at 1800 ° C.

Next, a method for manufacturing an aluminum nitride sintered body according to the present invention will be described with reference to the following examples.
It is not limited to the following examples.

Example 1 204 g of aluminum isopropoxide was added at 90 ° C. for 3 hours.
In distilled water, hydrolyze, then 24 ml of acetic acid
Was added, and the mixture was left for 1 hour while heating and stirring. The boehmite sol thus obtained was used as a starting material.

The carbon content was 55% with respect to 60 g of boehmite sol in the boehmite sol so that the amount of carbon was 3 times the molar amount of the calculated amount of alumina generated from the boehmite sol.
Add 33 g of polyvinyl alcohol (PVA) of weight%,
Mix. The slurry obtained in this way is clay-adjusted sufficiently and formed into a sheet by the doctor blade method.
Created a green sheet.

The obtained green sheet is 1400 in a nitrogen stream.
℃, 1500 ℃, 1600 ℃, 1700 ℃, 1800 ℃
Was fired at each temperature.

Each of them was measured by X-ray diffraction. The result is 140
It was found that the one fired at 0 ° C was AlN + Al ₂ O _{3 and} the one fired at 1500 ° C or higher was a single phase of AlN. Sintered density is 1800g, 2.9g
It was / cm ³ .

[Example 2] An aluminum nitride sintered body was prepared by substantially the same operation as in Example 1.

A calculated amount of 0.5% by weight of aluminum nitride to yttrium oxide was added to the boehmite sol, and to 60 g of boehmite, 28 g of methylcellulose (MC) having a carbon content of 65% by weight was added, and a green sheet was added. It was created and fired in a nitrogen stream.

After firing each obtained sintered sheet was examined by X-ray diffraction. The one burned at 1400 ° C is AlN + Al ₂ O ₃ ,
Only AlN was detected in the samples fired at 500 ° C or higher.
The peak of Y ₃ Al ₅ O ₁₂ should be detected because there is 0.5 wt% Y ₂ O _3, but it could not be confirmed by X-ray diffraction because the first diffraction peak and the diffraction peak of AlN overlap. .

The sintered density was 3.1 g / cm ^{3 when} burned at 1800 ° C.

Further, in the above example, the case of the casting molding method using a doctor blade was described, but in addition to this, an extrusion molding method or the like can be used to manufacture the aluminum nitride sintered body according to the present invention.

[Advantages of the Invention] The method for producing an aluminum nitride sintered body according to the present invention is, firstly, that a complicated treatment step for separately performing a conventional aluminum nitride powder producing step and a sintered body producing step is not required, and is directly performed. To obtain an aluminum nitride sintered body, secondly, there is no fear of excessive carbon deposition due to direct reduction, and thirdly, a substrate having a good sinterability by a simple treatment method compared with the conventional one. Fourthly, technical effects such as a sheet can be obtained, and fourthly, a direct substrate sheet can be obtained, so that a thermally efficient and therefore economically advantageous manufacturing method can be provided.

[Brief description of drawings]

FIG. 1 shows an X-ray diffraction spectrum graph of the product obtained by firing at 1800 ° C. by the manufacturing method of the present invention. FIG. 2 shows an X-ray diffraction spectrum graph of the product obtained by firing at 1400 ° C. by the manufacturing method of the present invention.

Claims (4)

[Claims] 1. An organic binder is added to boehmite sol,
A method for producing an aluminum nitride sintered body, comprising: a forming step of forming a sheet; and a baking step of baking the obtained green sheet in a nitrogen atmosphere. 2. The method for producing an aluminum nitride sintered body according to claim 1, wherein the boehmite sol is a sol obtained by using an aluminum alkoxide and an acid peptizer. 3. The method for producing an aluminum nitride sintered body according to claim 1, wherein the organic binder has a carbon content of 50 to 80% by weight. 4. The method for producing an aluminum nitride sintered body according to claim 1, wherein the firing temperature in a nitrogen atmosphere is 1500 ° C. or higher.