JP2654108B2 - Manufacturing method of aluminum nitride sintered body - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a highly thermally conductive aluminum nitride sintered body containing aluminum nitride as a main component.

[Conventional technology]

Aluminum nitride has a theoretical thermal conductivity of 320 w / m · k
In recent years, its use as an insulating heat radiating plate has attracted attention because of its high mechanical strength, excellent electrical strength, and electrical properties comparable to alumina.

However, the thermal conductivity of the conventionally developed aluminum nitride sintered body is lower than its theoretical value and is about half, and the inherent high thermal conductivity cannot be sufficiently exhibited.

Although the thermal conductivity of the aluminum nitride sintered body depends on the purity of the sintered body, the oxygen content is particularly effective. The location of oxygen in the sintered body is determined by: (i) the triple point of aluminum nitride crystal particles or the ridge of the particles (in the form of a reaction product with a sintering aid); or (ii) the aluminum nitride crystal particles. However, especially when it is located at the position (ii), the thermal conductivity is significantly impaired.

Normally, when producing an aluminum nitride sintered body, the aluminum nitride powder as a raw material contains at least 0.8% by weight or more of oxygen, and most of this oxygen exists on the particle surface. Firing without dissolving oxygen existing on the surface as much as possible in the inside of the particles is the basis for obtaining a sintered body having more excellent thermal conductivity, and the following method has conventionally been used.

(A) As a sintering aid, a compound containing a rare earth element and / or an alkaline earth element is added to promote densification and to react with oxygen present on the surface,
These oxygens are fixed. (JP-A-60-127267) (B) By further purifying ordinary raw material powder,
Produce low oxygen content powder. In Japanese Patent Application Laid-Open No. Sho 61-201668, considerable results have been obtained particularly by adding yttrium oxide. In this method, however, the thermal conductivity of this method is less than the theoretical value. It is drowning greatly. The causes are as follows.

(1) Even when Y ₂ O ₃ is added, a small amount of oxygen diffuses and forms a solid solution in the aluminum nitride particles while Y ₂ O ₃ reacts with oxygen on the surface.

(2) To make oxygen fixation by Y ₂ O ₃ more effective, a large amount of addition is required. As a result, the diffusion of oxygen into the AlN particles can be reduced, but the amount of yttrium aluminate, which is a reaction product, increases, so that the improvement in thermal conductivity reaches a plateau.

As another problem, when a large amount of Y ₂ O ₃ is added, there is a disadvantage that color unevenness is easily generated in the sintered body, and it is difficult to obtain a homogeneous sintered body.

In the case of (B), it is possible to obtain a powder having an oxygen content of half or less as compared with a commercially available product by sufficiently controlling the production process of the AlN powder, but oxygen is adsorbed on the surface by handling or the like. Therefore, there is a limit as a powder that can be used more widely.

As described above, the aluminum nitride sintered body has a problem that the original high thermal conductivity cannot be sufficiently exhibited because the oxygen impurities cannot be sufficiently controlled.

[Problems to be solved by the invention]

An object of the present invention is to produce an aluminum nitride sintered body having a high thermal conductivity which cannot be achieved by such a conventional method, and which is uniform and has almost no color unevenness.

[Means for solving the problem]

The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that when firing a formed article containing aluminum nitride powder, yttrium oxide powder, and free carbon and / or a thermal decomposition product of an organic polymer, By strictly controlling the sintering conditions, a homogeneous sintered body with high thermal conductivity and almost no color unevenness can be obtained despite the extremely low Y ₂ O ₃ content compared to the past. The present invention has been completed.

That is, the present invention comprises aluminum nitride powder, yttrium oxide powder and pyrolysis products of free carbon and / or an organic polymer, and the content of yttrium oxide powder is 0.30 to 100 parts by weight of aluminum nitride powder. When firing the molded body of 0.92 parts by weight in a non-oxidizing atmosphere,
A method for producing an aluminum nitride sintered body, characterized in that the residence time at a temperature of 1300 ° C. to 1750 ° C. is set to 2 hours or more, followed by firing at a temperature exceeding 1750 ° C.

 Hereinafter, the present invention will be described in more detail.

As the aluminum nitride powder used in the present invention, those produced by a metal aluminum direct nitridation method, an alumina reduction nitridation method or the like are usually used, but the production history and the like are not problematic. weight%
It is preferable to use those having a content of 2% by weight or less.

In the conventional single addition of Y ₂ O ₃ , the addition amount has been changed according to the amount of oxygen contained in the raw aluminum nitride powder. For example, when using aluminum nitride powder containing 1.2% by weight of oxygen, the amount of Y ₂ O ₃ added has been set to at least 5% by weight or more to reach a value exceeding half the theoretical value. Furthermore, shall apply to the raw material powder having a high oxygen concentration than the above, which have been made to further maintain the thermal conductivity by increasing the Y ₂ O ₃ amount, however, these Y ₂ O ₃
In a single system, a large amount of Y ₂ O ₃ must be added,
The number of constituent phases other than N increased, and as a result, the amount of the impurity phase increased, so that the improvement in thermal conductivity was naturally limited. In addition, since the amount of constituent phases other than AlN to be generated is large, color unevenness due to bleeding, aggregation, and the like is likely to occur.

One feature of the present invention, even if, Yotsute also Y ₂ O ₃ amount with the use of oxygen content is more aluminum nitride raw material powder to the low addition of 0.30 to 0.92 parts by weight to the aluminum nitride powder 100 parts by weight Another object of the present invention is to produce a sintered body having a high thermal conductivity exceeding 200 W / m · K and hardly causing color unevenness and the like.

The reason why such a sintered body having high thermal conductivity can be obtained is that the surface oxygen reducing action by a carbon source such as free carbon or a thermal decomposition product of an organic polymer contained in the molded article of the present invention is given. Can be (A) Surface oxygen is sufficiently reduced and removed by a carbon source added in a temperature range of 1300 ° C. to 1750 ° C. in a non-oxidizing atmosphere. Thereby, even if oxygen diffuses into the AlN particles during sintering, the amount is suppressed to an extremely low amount.

(B) In the above temperature range (a), the diffusion rate of oxygen into AlN grains is low.

(C) The amount of Y ₂ O ₃ serving as a surface oxygen fixing agent and a sintering aid can be reduced by an amount corresponding to a small amount of surface oxygen.

In the present invention, the reason for limiting the residence time at a temperature of 1300 ° C. to 1750 ° C. to 2 hours or more is the above (a) to
This is because it is necessary to promote the effect of (c) more smoothly. In other words, when the residence time is extremely short, the effect of removing oxygen is not sufficiently achieved, and the amount of Y ₂ O ₃ as the oxygen fixing agent is also small, so that the solid solution of oxygen in the AlN particles is prevented. Uncontrollable, and carbon will remain, as a result, the liquid phase is hindered in the subsequent densification stage, resulting in insufficient densification, it is not possible to achieve high thermal conductivity by adding low Y ₂ O ₃ of the present invention It is.

In the present invention, the residence time refers to a time that exists in the above-mentioned limited temperature range, and includes all operations such as heating and holding in that temperature range. The preferred residence operation is at a temperature of 1450 ° C to 1650 ° C for 3 hours or more. After the dwell operation, a temperature exceeding 1750 ° C., preferably 18 ° C.
Baking at a temperature of 00C to 1950C. Densification is insufficient when firing at 1750 ° C or lower. The residence operation and firing were performed using N ₂ , H ₂ , NH
_3. Performed in a non-oxidizing atmosphere such as Ar, He, Co, or vacuum.

In the present invention, free carbon means carbon black, acetylene black and the like. The thermal decomposition products of organic polymers are, for example, those obtained by heating granular or powdery organic polymers such as vinyl chloride resin, polyvinyl alcohol, and vinyl acetate resin in an inert atmosphere. It is preferably a solid having a shape, in which the weight ratio (C / H) of carbon atoms to hydrogen atoms is controlled to 10 to 25. Regardless of the type of organic polymer, these pyrolysis products are usually produced by heat treatment at a temperature of 200 ° C. to 500 ° C. in Ar or N ₂ .

The carbon source used in the present invention is at least one of the organic carbon and the thermal decomposition product of the organic polymer.
These carbon sources are blended in an appropriate amount according to the oxygen content of aluminum nitride. The amount is (amount of carbon source)
/ (Aluminum nitride-containing oxygen content) weight ratio (hereinafter P / O
When the ratio is set to 0.08 to 2.5, particularly 0.9 to 1.5, the effect is remarkably increased.

In the present invention, by using a carbon source, the amount of Y ₂ O ₃ serving as an oxygen fixing agent can be reduced, and the sintered body can be highly purified. When the present inventors examined,
From the viewpoint of thermal conductivity, densification, color unevenness, etc., an appropriate amount of Y ₂ O ₃ is 0.30 to 0.92 parts by weight, preferably 0.1 to 100 parts by weight of AlN.
50 to 0.92 parts by weight. If it is added in excess of 0.92 parts by weight, color unevenness is likely to occur, and if it is less than 0.30 parts by weight, it becomes difficult to densify the sintered body.

In the present invention, any method can be selected as a method for producing a molded body, and a sintered body having excellent thermal conductivity can be obtained by any method. Normally, a press molding method or a sheet molding method is employed, but it is desirable that both are sufficiently mixed in the mixing step to uniformly disperse the carbon source.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 Acetylene black was mixed with 100 parts by weight of aluminum nitride powder having an oxygen content of 1.2% by weight so that the P / O ratio became 0.95, and 0.5 or 0.9 part by weight of Y ₂ O ₃ was further added. I got This mixture was put into an alumina pot together with toluene, mixed well by a ball mill, dried, and then subjected to pressure molding at 400 kg / cm ² to obtain a powder mixture.
A 5 mm × 5 t disk-shaped compact was obtained.

These compacts were fired at 1900 ° C. for 2 hours at a rate of temperature rise of 20 ° C./min in N ₂ and 1 atm to produce sintered bodies. The obtained sintered body is ground to 10φmm x 3t mm and after measuring the density,
The thermal conductivity was measured by a laser flash method.

 Table 1 shows the results.

Comparative Example 1 A molded article having the same composition as in Example 1 was prepared, except that the holding time at 1500 ° C. was changed to 0.5 hour or 1 hour.
A sintered body was obtained in the same manner as described above. Table 1 shows the results.

Example 2 Aluminum nitride powder 100 having an oxygen content of 1.5% by weight
The weight ratio of carbon atoms to hydrogen atoms (C / H) is 1
The thermal decomposition product of the vinyl chloride resin of No. ₂ was blended so that the P / O ratio became 0.6, and 0.4 or 0.8 parts by weight of Y ₂ O ₃ was added to obtain a mixture. This mixture was put in an alumina pot together with trichlene, thoroughly mixed by a ball mill, dried, and then press-molded at 350 kg / cm ² to obtain a 25 mm × 5 mm disc-shaped compact. Was.

The temperature of these molded bodies was raised at a rate of 25 ° C./min in N ₂ at 1 atm.
C. for 6 hours to produce a sintered body. Table 2 shows the measurement results of the density and thermal conductivity of the obtained sintered body.

Comparative Example 2 A sintered body was produced in the same manner as in Example 2, except that the intermediate holding time was changed to 0.5 hour or 1 hour. Table 2 shows the results.

Example 3 Aluminum nitride powder 100 having an oxygen content of 2.0% by weight
The parts, those C / H is 25 by thermal decomposition product of a vinyl chloride resin formulated as P / O ratio is 1.2, further Y ₂ O ₃
Was added in an amount of 0.3, 0.5 or 0.92 parts by weight to obtain a mixture. Using these mixtures, a molded article was produced in the same manner as in Example 1.

These molded bodies were heated at a heating rate of 25 ° C./min in N ₂ at 1 atm and kept at 1400 ° C. for 5 hours on the way.
It was fired at 1850 ° C. for 4 hours to produce a sintered body. About the obtained sintered body, the color unevenness was visually observed and the density and the thermal conductivity were measured. Table 3 shows the results.

Comparative Example 3 A sintered body was produced in the same manner as in Example 3 except that the addition amount of Y ₂ O ₃ was changed to 0.2, 1.0 or 2.0 parts by weight. Table 3 shows the results.

[Effects of the Invention] According to the present invention, it is possible to produce a uniform aluminum nitride sintered body that has high thermal conductivity and does not cause color unevenness even with a very small amount of yttrium oxide used.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-277573 (JP, A) JP-A-1-115875 (JP, A) JP-A-63-166765 (JP, A) JP-A-63-166765 129075 (JP, A)

Claims (1)

(57) [Claims] An aluminum nitride powder, an yttrium oxide powder and a pyrolysis product of free carbon and / or an organic polymer, and the content of the yttrium oxide powder is from 0.30 to 0.92 per 100 parts by weight of the aluminum nitride powder. When sintering a molded part which is part by weight in a non-oxidizing atmosphere,
After setting the residence time at 2 ° C to 1750 ° C for 2 hours or more, 1750
A method for producing an aluminum nitride sintered body, characterized by firing at a temperature exceeding ℃.