JP2642184B2 - Method for producing aluminum nitride-hexagonal boron nitride sintered body - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high thermal conductivity in a specific plane, which can be used as a material for an IC substrate, a material for an IC package, or an electrically insulating heat radiation material. The present invention relates to a method for manufacturing an aluminum nitride-hexagonal boron nitride-based sintered body, which is an insulator.

2. Description of the Related Art Aluminum nitride-hexagonal boron nitride-based composite sintered body is a machinable ceramic with high thermal conductivity, and is considered to be widely applied as a ceramic for electronic materials and structural materials, and many patent applications have been filed. .

For example, Japanese Patent Application Laid-Open No. Sho 60-195059 discloses that aluminum nitride, boron nitride, and a group IIa metal and a group IIIa metal compound are filled with aluminum nitride particles having a polygonal fracture surface and a part of the grain boundary. Alternatively, there is a description about a sintered body in which a thin layer of boron nitride is interposed. The feature of this sintered body is that it is a so-called machineable ceramic composite sintered body that can be cut at high speed with ordinary tools.

Japanese Patent Application Laid-Open No. Sho 60-195060 describes the particle size and purity of aluminum nitride powder used for producing this composite sintered body.
61-63572 discloses the range of the heating rate during sintering.

JP-A-61-31360 discloses a method for producing a composite sintered body under nitrogen gas pressure.

Further, Japanese Patent Application No. 62-329626, which is an invention of the present inventors, includes 40 to 95 parts by weight of boron nitride, 5 to 60 parts by weight of a total amount of aluminum nitride and aluminum oxynitride, and calcium compound and yttrium compound. There is a description of a composite sintered body comprising at least one of 0.01 to 5 parts by weight and a method for producing the same by a pressurized heating method. The characteristics of the sintered body include thermal conductivity, electrical insulation, low coefficient of thermal expansion,
It has low dielectric constant and excellent machinability.
A value of about 40 to 135 W / m · K is reported as the thermal conductivity of these sintered bodies.

On the other hand, as an example of improving the thermal conductivity in a specific plane of the sintered body, Japanese Patent Application No. 63-135562 by the present inventors
There is. In the specification, 20 to 80 parts by weight of hexagonal boron nitride, 80 to 20 parts by weight of aluminum nitride, and a sintering aid 0.
2 to 5 parts by weight, having an anisotropy of thermal conductivity of 2 or more, and an anisotropic sintered body having a higher value of thermal conductivity of 150 W / m · K or more; 2200 ° C, 5-50MP
There is a description of a method for producing the sintered body by hot pressing in a.

As for the value of thermal conductivity, the higher one is 153 to 258 W / mK,
The lower one reports 16 to 80 W / m · K, and as another feature, it shows good machinability. However, when considering use for IC substrates and IC packages,
Needless to say, a material having a higher thermal conductivity is required in order to increase the heat radiation efficiency from the semiconductor chip.

Problems to be Solved by the Invention In view of these problems, an object of the present invention is to provide a method for producing an aluminum nitride-boron nitride-based composite sintered body having a higher thermal conductivity within a specific plane.

Means for Solving the Problems That is, the present invention provides (1) aluminum nitride 95-5
Parts by weight, a mixed powder consisting of 5 to 95 parts by weight of hexagonal boron nitride and 0.2 to 5 parts by weight of a sintering aid is uniaxially compacted at a pressure of 5 MPa or more. The present invention relates to a method for producing an aluminum nitride-hexagonal boron nitride-based sintered body, characterized in that a compact is filled in a die so as to coincide with the pressing axial direction of the sintering and hot-pressed. The present invention also relates to (2) a method for producing the aluminum nitride-hexagonal boron nitride-based sintered body, wherein the hexagonal boron nitride powder used as a raw material has an average particle diameter of 1 μm or more.

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

According to the production method of the present invention, after the raw material mixed powder is uniaxially molded at a pressure of 5 MPa or more, the mixture is filled into a die such that the pressing axial direction of the uniaxial molding matches the pressing axial direction of hot press sintering, Hot press sintering is performed.

As a pre-process of hot press sintering, by performing uniaxial molding at a pressure of 5 MPa or more, orientation and lamination of boron nitride particles can be caused during this uniaxial molding, and thereafter, the pressure of the uniaxial molding is increased. The uniaxial compact is filled in a graphite die so that the axial direction matches the pressing axial direction of hot press sintering, and hot press sintering is performed, and the orientation and lamination of boron nitride particles that occur during uniaxial compaction Can be encouraged.

As a result, the powder is directly filled in a graphite die, or uniaxially formed under a pressure of less than 5 MPa, and then becomes a sintered body with greater anisotropy as compared to the case of hot press sintering. The thermal conductivity in the direction perpendicular to the pressure axis (the pressure axis of uniaxial molding) is significantly improved. On the other hand, the thermal conductivity in the direction parallel to the hot press pressure axis (the pressure axis for uniaxial molding) slightly decreases, but hardly changes.

The molding pressure for uniaxial molding is preferably 5 MPa or more. If the pressure is less than 5 MPa, orientation and lamination of the boron nitride particles during uniaxial molding hardly occur, and the effect of increasing the thermal conductivity due to the uniaxial molding is hardly recognized. In addition, the higher the molding pressure, the more preferable the orientation and lamination of the boron nitride particles become remarkable, but above a certain pressure, the degree of orientation and lamination of the boron nitride particles with the increase in the pressure becomes insignificant, It is not advisable to use a higher pressure than necessary. The diameter of the boron nitride particles is about 1 μm, and about 100 MPa is one measure of the upper limit of the molding pressure.

The raw material mixed powder contains 95 to 5 parts by weight of aluminum nitride, 5 to 95 parts by weight of hexagonal boron nitride, and 0.2 to 5 parts by weight of a sintering aid.
Consists of 5 parts by weight.

In a composition where aluminum nitride is around 95 parts by weight,
Although the effect of improving the thermal conductivity by the orientation and lamination of boron nitride is not so large, a sintered body having relatively large bending strength, Vickers hardness, etc., and a relatively large thermal expansion coefficient can be obtained.

When the composition of aluminum nitride is in the vicinity of 5 parts by weight, a remarkable effect of improving thermal conductivity by orientation and lamination of boron nitride is recognized.

Also, with this composition, a sintered body having extremely good machinability, although the bending strength is not so large, can be obtained.

If the blending ratio of the raw material powder exceeds these ranges and the aluminum nitride content exceeds 95 parts by weight, the effect of the orientation and lamination of the boron nitride particles cannot be expected because the content of hexagonal boron nitride is small. . When the content of aluminum nitride is less than 5 parts by weight, although the thermal conductivity is improved by the orientation and lamination of the boron nitride particles, a large amount of sintering is promoted to obtain a dense sintered body. Therefore, it is difficult to obtain a sintered body with high thermal conductivity,
It is not suitable for use as a substrate or package material.

The particle diameter of the boron nitride particles used as a raw material is preferably 1 μm or more. When powder having a particle size of less than 1 μm is used,
The orientation and lamination of the boron nitride particles during uniaxial molding and hot-press sintering do not significantly occur, and the sintered body becomes more isotropic. In particular, the effect of orientation and lamination of boron nitride particles by uniaxial molding of the present invention is hardly exhibited. In addition, the particle size of the boron nitride particles described here is
The size in the plane direction of the flaky boron nitride particles is not the size in the thickness direction.

The raw material mixed powder contains 0.2 to 5 parts by weight of a sintering aid in addition to aluminum nitride and boron nitride.

When the amount is less than 0.2 part by weight, the effect as a sintering aid cannot be expected. When the amount is more than 5 parts by weight, the thermal conductivity of the sintered body is undesirably reduced. Also, since the thermal conductivity, especially the higher value, is sensitive to the amount of the sintering aid added, when manufacturing a sintered body having a high thermal conductivity, the amount to be added is carefully determined. There is a need to.

Known sintering aids such as calcium oxide, calcium carbide, calcium cyanamide, yttrium oxide, and yttrium carbide can be used. However, when considering the orientation and lamination of boron nitride particles, it reacts with oxides inevitably generated on the surface of aluminum nitride powder or boron nitride powder and generates a liquid phase at lower temperatures. It can be said that a calcium-based compound is more preferable in view of the possibility.

For mixing these powders, dry mixing and wet mixing by a known method such as a ball mill can be used, but wet mixing is preferable. The dispersion medium used in the wet mixing is not particularly limited, and alcohols, hydrocarbons, and ketones are preferably used. Since water may react with the nitride powder to generate ammonia, it is better not to use water unless it is particularly necessary.

The raw material mixed powder is uniaxially molded as described above, and then filled in a graphite die so that the pressing axial direction of the uniaxial molding coincides with the pressing axial direction of the hot press firing, followed by hot press firing. . Hot press sintering is a well-known method for producing a boron nitride-aluminum nitride based sintered body at 1700 to 2200 ° C.
This is performed under the condition of about 5 to 50 MPa.

If the temperature is lower than 1700 ° C., a sintered body having desired physical properties, particularly high thermal conductivity cannot be obtained, and if it exceeds 2200 ° C., it is not economical. On the other hand, if the pressure is less than 5 MPa, the sinter may be insufficient to densify the sintered body or cause the orientation of boron nitride particles. If the pressure exceeds 50 MPa, dies that can be used in hot pressing are limited. The holding time at the highest temperature can be selected up to 4 hours. When the holding time is longer than 4 hours, the properties of the sintered body are not significantly affected but are not economical.

The atmosphere during sintering is preferably an inert gas such as nitrogen gas in order to prevent oxidation of the nitride.
However, when a specific sintering aid is used, sintering is performed in a vacuum so that these sintering aids or reaction products of the sintering aids and other components can be relatively quickly formed. It may be released to the outside, and as a result, the thermal conductivity of the sintered body may be improved. In such a case, sintering in a vacuum is preferable.

 Hereinafter, the present invention will be described using examples.

Example 1 Hexagonal boron nitride powder having an average particle diameter of 6 μm, aluminum nitride powder having an average particle diameter of 1.8 μm or less, and calcium carbide as a sintering aid were mixed in the proportions shown in Table 1 and the mixture was mixed in a ball mill. For 24 hours with acetone as a solvent.

After drying the obtained powder, uniaxial molding was performed under the conditions shown in Table 1, and a graphite die was filled so that the pressing axial direction of the uniaxial molding coincided with the pressing axial direction of the hot press. Hot press burning was carried out at 1800 ° C. for 2 hours at a pressure of 40 MPa in a nitrogen stream for 2 minutes. The cooling rate was 10 ° C./min.

The bulk density and the thermal conductivity of the obtained sintered body were measured.
Since the sintered body has anisotropy, the thermal conductivity
The values in the vertical and parallel directions to the hot press pressure axis are also shown. The bulk density was measured by the Archimedes method using water, and the thermal conductivity was measured by the laser flash method. In the table, for comparison, the values of the sintered body when uniaxial molding was performed at a low pressure and when the uniaxial molding was not performed are also described.

The results are shown in Table 1. As can be seen from Table 1, in any composition in which the content of aluminum nitride is 95 to 5 parts by weight, in the sintered body which was uniaxially molded at a pressure of 5 MPa or more, the uniaxial molding was not performed or less than 5 MPa. The value of the thermal conductivity in the direction perpendicular to the pressure axis of the hot press (the higher value) is 5 to 50 W / m compared to the sintered body that was uniaxially molded in
・ It can be seen that K has been improved. On the other hand, the value (lower value) in the direction parallel to the pressure axis of the hot press may slightly decrease, but hardly changes. In addition, there was almost no difference between the values of the bulk density.

Example 2 A hexagonal boron nitride raw material was formed into a powder having an average particle size of 10 μm,
Further, yttrium oxide was added as a sintering aid, and hot press sintering was performed in the same manner as in Example 1.

The measurement results of the bulk density and thermal conductivity of the obtained sintered body
It is shown in the table. In any composition, at a pressure of 5 MPa or more, uniaxially formed sintered body and other sintered body,
Almost the same results as in the example were obtained, and the higher value of the thermal conductivity was improved by about 20 to 35 W / m · K.

Effect of the Invention As described above, the method for manufacturing an aluminum nitride-boron nitride-based composite ceramics sintered body of the present invention is used as a preceding step when a sintered body is manufactured by a hot press method.
After uniaxially molding at a pressure of 5 MPa or more, the compact is filled into a die so that the pressure axis during molding matches the pressure axis of hot press sintering, and hot press sintering is performed. The thermal conductivity in the direction perpendicular to the pressure axis can be improved.

Therefore, it is suitable as a method for producing an aluminum nitride-boron nitride-based composite sintered body having a high thermal conductivity which can be used as a material for IC substrates and IC packages, and is extremely useful in industry.

Claims (2)

(57) [Claims] A mixed powder comprising 95 to 5 parts by weight of aluminum nitride, 5 to 95 parts by weight of hexagonal boron nitride, and 0.2 to 5 parts by weight of a sintering aid is uniaxially formed at a pressure of 5 MPa or more. The aluminum nitride-hexagonal boron nitride sintering is characterized in that the compact is filled into a die so that the pressure axis direction of the uniaxial molding coincides with the pressure axis direction of the hot press sintering, and hot press sintering is performed. The method of manufacturing the aggregate. 2. The method for producing an aluminum nitride-hexagonal boron nitride-based sintered body according to claim 1, wherein the average particle diameter of the hexagonal boron nitride powder used as a raw material is 1 μm or more.