JPS6077176A - Manufacture of aluminum nitride sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention is directed to an improvement in a method for producing an aluminum nitride sintered body by pressureless sintering.

[Technical background of the invention and its problems]

Aluminum nitride is useful as a heat-resistant material because of its stability, high strength at room and high temperatures, and excellent chemical resistance.
It is a promising material as a heat sink for the electronic industry due to its high electrical insulation properties.

Such aluminum nitride typically has no melting point.

Since it decomposes at high temperatures of 2200° C. or higher, it is often used as a sintered body, except in cases such as thin film production.

Incidentally, as a method for producing an aluminum nitride sintered body, conventionally, a reaction sintering method, an atmospheric pressure sintering method, a hot press method, etc. have been adopted.

In the reactive sintering method, the obtained sintered body is not porous, and depending on the shape, unreacted metal may remain inside. In order to obtain a dense aluminum crabide sintered body (for C, the normal pressure sintering method or the hot press method is mainly adopted. In the normal pressure sintering method, in order to achieve high density It is necessary to add a sintering aid, and compounds of alkaline earth metals or rare earth metals are usually used.In the hot-breathing method, the raw material is aluminum nitride powder alone or aluminum nitride powder with an additive added. Use.

However, the hot-breath method has the drawbacks of low productivity and high costs. On the other hand, although pressureless sintering can easily cause embrittlement and can reduce costs, it has the following drawbacks.

That is, the sintering aid used in the pressureless sintering method generally has a relatively low vapor pressure at high temperatures, and the sintering aid near the surface of the powder compact evaporates and scatters during sintering. As a result, the sintered body has the disadvantage that the vicinity of the surface thereof is no longer densified, or that the sintered body is significantly deformed depending on the shape of the product. This tendency is particularly remarkable when an alkaline earth metal compound is used as a sintering aid, and the larger the surface area/volume ratio is, as in the case where the sintered body is flat, the more remarkable it is. The evaporation of the sintering aid near the surface was confirmed by XMA (X-ray microanalyzer) and EDX (fluorescent X-ray analysis). For these reasons, there is a demand for the development of a method for obtaining a high-density, non-deformable aluminum nitride sintered body by pressureless sintering.

[Purpose of the invention]

The present invention aims to provide a method for manufacturing a high-density aluminum nitride sintered body without deformation by suppressing the evaporation and scattering of a sintering aid near the surface mJ of a molded body in the pressureless sintering method. It is.

[Summary of the invention]

The present invention will be explained in detail below.

First, an easily evaporable sintering aid is added to aluminum nitride powder, and the mixture is sufficiently mixed using a ball mill or the like. A binder is then added to the mixture, and the mixture is granulated and sized. The aluminum nitride powder used here preferably has an average particle size of several μm or less, preferably 1 μm or less. Examples of the easily evaporable sintering aid include MgO.

CaO, SrO, BaO* MgC03r CaCO3
, SrCO3゜B aCO3 and other alkali metal compounds,
Y2O3 or La2O3, CeO2, Pr02,
Rare earth element compounds such as Nd'205 and Sm2O3 can be used, and any sintering aid can be used as long as its evaporation at low and high temperatures is a problem.

Next, the granulated powder is molded by a molding method, an isostatic pressing method, another sheet molding method, etc., and then heated to about 700°C in a nitrogen gas stream to degrease (remove the binder).
Do the following.

Next, pressureless sintering is performed with the partial pressure of the sintering aid near the surface of the degreased compact being increased by the sintering aid evaporated from the outside. Specifically, the molded body is pressureless sintered by the following method.

■ The degreased molded body is embedded in a container filled with powder of the same composition as the molded body or with an excess composition of sintering aid, and after being sealed with a lid, it is heated at about 1700 to 1820°C under normal pressure in an N2 atmosphere. Perform sintering.

The aluminum nitride powder in the above-mentioned filling powder may be large particles of about several tens of micrometers, or it may be particles as fine as the aluminum nitride powder that is the starting material for the compact.

It is necessary that the amount of fleas of the sintering aid in the above-mentioned filling powder be the same as that of the molded article, or be slightly excessive. If the amount of sintering aid in the filling powder is less than that in the compact, the partial pressure of the sintering aid near the surface of the compact cannot be sufficiently increased, and the evaporation and scattering of the sintering aid may be prevented. Cannot be prevented. On the other hand, if the amount of sintering aid in the filling powder is too large, the partial pressure of the sintering aid near the surface of the compact will increase, but the partial pressure of the sintering aid near the surface of the compact will be <7i. :! ll, non-uniform sintering occurs. Moreover, in the method of using a sintering aid for the filling powder as a generation source, if the composition of the compact and the filling powder differs widely, the density will change between the contact area and the non-contact area between the compact and the filling powder. This causes local non-uniformity and causes deformation of the sintered body.

For this reason, the amount of sintering aid in the filling powder is
It is desirable to make the range 1 to 10 times that in the molded body. Specifically, when the composition of the compact is aluminum nitride (AzN) powder with 1% by weight of CaCO3 added, 1 to 51% of CaCO3 is added to AtN powder.
It is preferable to use a filler powder that has been added with a certain amount.

Regarding the selection of the particle size of the above-mentioned filling powder, there are no general restrictions, but if the shape of the compact is relatively complex or if it is desired to suppress deformation during sintering as much as possible, a relatively fine particle size (
For example, it is desirable to set the number of layers to 0.1 μm]. however,
If it is too fine, the filling powder itself may firmly adhere to each other and the sintered body, which is not preferable.

On the other hand, when the shape of the molded body is simple, by using coarse particles, it is possible to prevent the filling powder itself from sintering or from sticking to the sintered body.

■Also, in the case of a mixed system of easy-to-form sintering aids.

Even if there is a difference in susceptibility, evaporation and scattering can be prevented in the partially compressed powder in the mixed filling powder. Specifically, the composition of the molded body was as follows: AtN powder, 1% by weight of CaCO3, 5rCO
In the case of a mixed system containing 1% by weight of CaCO3,5r in the filling powder, the amount added in the filling powder is the same as in (2) above, but since CaO is more easily formed than SrO, the amount of CaCO3,5r in the filling powder is
The addition ratio of CO is desirably CaC0≧S r Cos. In the case of such a mixed system, a uniform sintered body with little deformation during sintering can be obtained.

According to the present invention, the aluminum nitride compact is sintered under normal pressure with the partial pressure of the sintering aid near the surface increased by the sintering aid evaporated from the outside. Since evaporation and scattering of the sintering aid from near the surface can be suppressed, it is possible to obtain an aluminum nitride sintered body whose entire surface including the surface is uniformly densified and which is free from deformation and has high dimensional accuracy.

[Embodiments of the invention]

Next, one aspect of the present invention will be explained in detail.

Example 1 Example of AtN powder with average particle size of 0.9 μm Commercially available high purity CaC
Add 1% by weight of O3 reagent to prepare 200g of mixed powder,
Paraffin was added in an amount of 7% by weight and granulated. Subsequently, this granulated powder was cold-formed under a pressure condition of 300 kg/'crn2 to produce a plate-shaped compact of 37 x 37 x 6 tm. Subsequently, this molded body was coated with At having a particle size of 1.2 μm.
It was embedded in N powder and heated to 200° C. in a nitrogen gas atmosphere, held as such for 12 hours, and then heated to 600° C. to remove paraffin (degreasing).

Next, the degreased molded body is mixed with AtN powder and high-purity CaC.
After embedding it in a graphite container filled with powder with an average particle size of 1.2 μm to which 1 t% of O5 was added, the container was sealed with a lid and incubated at 1780°C in nitrogen gas at normal pressure for 2 hours. Sintering was performed to produce an AtN sintered body.

Comparative Example 1 A degreased molded body was placed on a bed of AtN powder, and pressureless sintering was performed in the same manner as in Example 1 to produce an AtN sintered body.

Comparative Example 2 After embedding the degreased molded body in a graphite container filled with AtN powder and sealing the inside of the container using a lid, Example 1
An AtN sintered body was produced by pressureless sintering in the same manner as in the above.

Therefore, the At obtained in Example 1 and Comparative Examples 1 and 2
The relative density, degree of deformation, and properties of the N sintered body were investigated. The results are shown in the table below. In addition, the degree of deformation is specifically claimed to be determined by measuring the maximum value of the diagonal between the central part and the peripheral part with reference to the diagonal line of the sintered body.

As is clear from the above table, the AtN f obtained in Comparative Example J
JF: The lower surface of the viscous material has extreme Ke, shrinks and deforms to a large degree, and has a low density. Also, Comparative Example 2 Busyoshi obtained A
Although the tN sintered body has a relatively low degree of deformation, it cannot be sufficiently densified due to the evaporation of CaO from near the surface.
Moreover, the cross section is sintered uniformly in layers on the surface and inside.

On the other hand, the AtN sintered body obtained in Example 1 has less deformation, higher density, and less sintering unevenness observed in cross section.

Examples 2 and 3 Degreased molded bodies produced in the same manner as in Example 1 were treated with AtN
Powder 1c Added 1% by weight of Cocos, average particle size 1.
After embedding the powder in a graphite container filled with 2 μm powder, the container was sealed using a lid and sintered under normal pressure in the same manner as in the example.
A tN sintered body was manufactured.

Example 3 AAN-Ca COs powder with the same composition as Example 2 was
After heat-treating at 0°C, it was ground to about 10 to 50 μm in a mortar and filled into a graphite container. Next, a degreased molded body similar to that in Example 1 was embedded in this container, the container was sealed using a lid, and then pressureless sintered in the same manner as in Example 1.
A tN sintered body was manufactured.

The degree of deformation of the sintered bodies obtained in Examples 2 and 3 was then examined. As a result, the degree of deformation of the sintered body of Example 2 was 0.2~
The degree of deformation of the sintered body of Example 3 was small at about 0.01 to 0.2. On the other hand, regarding other properties of each sintered body, they are all homogeneous and have a strength of 40 to 50.
kg/III++2.

Example 4 5% by weight of paraffin was added to a mixed powder of 99.5% by weight of AtN powder with an average particle size of 1.5 μm and 0.5% by weight of CaO powder with an average particle size of 1.8 μm and kneaded. Subsequently, this kneaded product was molded at a molding pressure of 2 ton A" to produce a plate-shaped molded product of 30 x 30 x 5 tmm. Next, after removing the i4 rough-in from this molded product in a N2 gas flow, it was placed in a graphite container. It was placed together with the same type of powder as the mixed powder and sealed with a lid.

Thereafter, sintering was performed at 1800° C. for 60 minutes in a nitrogen stream.

Comparative Example 3 The same method as in Example 4 was carried out except that only the plate-shaped molded body was placed in a graphite container, sealed with a lid, and sintered.
A tN sintered body was manufactured.

Therefore, when the CaO concentration near the surface of the molded body during the sintering process of Example 4 and Comparative Example 3 was measured, the characteristic diagram shown in the figure was obtained. In FIG. 1, A indicates the density characteristic line of Example 4, and B indicates the density characteristic line of Comparative Example 3. As is clear from this figure, in the method of Comparative Example 3, in which sintering was performed without externally vaporizing 90aO, the CaO concentration between the surface and the inside was significantly different. On the other hand,
A method in which the compact is placed in a graphite container together with powder of the same type as the mixed powder, and sintered.This method involves sintering by increasing the partial pressure near the surface of the compact using vaporized CaO from outside the container. In the method of Example 4, the C between the surface of the compact and its inner part is
It can be seen that there is almost no aO concentration.

In fact, the A/=N sintered body of Example 4 has a deformation degree of 01 to 0.
It was as small as 2, had a relative density of 98 cm to the theoretical density, and was homogeneous and day-dense.

Example 5 5% by weight of paraffin was added to a mixed powder of 99% AtN powder with an average particle diameter of 1.2 μm and 1% by weight Y2O3 powder with an average particle size of 0.8 μm, and the mixture was kneaded. This mixed wire material was molded in the same manner as in Example 4 to produce a plate-shaped molded body. Subsequently, after removing the mother rough-in from this molded body in a N2 gas flow, it was placed in a graphite container together with a powder of the same type as the mixed powder, and the container was sealed with a lid. After this, N
Sintering was performed at 1800° C. for 60 minutes in two air streams.

The obtained AtN sintered body of Example 5 had a deformation degree of 0.1 to 0.
．． 2, had a relative density of 98.4% of the theoretical density, and was homogeneous and highly dense.

Example 6 99% by weight of AtN powder with an average particle size of 1.2 μm, 0.5% by weight of S r Co 3 powder with an average particle size of 0.7 μm,
A mixed powder was prepared by blending Ca C03 powder with an average particle size of 0.9 μm in an amount of 0.5 M, and this was used to conduct Example 4.
When sintered under the same conditions as , the degree of deformation was extremely small.
A homogeneous and highly dense AtN sintered body could be obtained.

〔Effect of the invention〕

As detailed above, according to the present invention, during the pressureless sintering method,
It is possible to provide a method that can extremely easily produce a homogeneous, high-density aluminum nitride sintered body that is free from deformation and has high dimensional accuracy by suppressing evaporation and scattering of the sintering aid near the surface of the molded body.

[Brief explanation of drawings]

The drawing is a characteristic diagram 1 showing the CaO concentration distribution near the surface of the compact during the sintering process of Example 4 and Comparative Example 3. Applicant's agent Patent attorney Takeshi Suzue Hikotoko Hasugi (
Surface Z・ra0 distance angle good

Claims (2)

[Claims] (1) A step of adding an easily evaporable sintering aid to aluminum nitride powder and then forming it, and reducing the partial pressure of the sintering aid near the surface of the compact to the evaporated sintering aid with an external force of 1. A method for producing an aluminum nitride sintered body, comprising the step of performing pressureless sintering in a state where a chemical agent is elevated. (2) Claim 1, characterized in that the easily evaporable sintering aid is one or a mixture of two or more selected from alkaline earth metals, rare earth metals, and compounds thereof.
A method for manufacturing a nitrided aluminum sintered body as described in 2.