JP2684728B2 - Manufacturing method of aluminum nitride sintered body - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an aluminum nitride sintered body, and more particularly to a conventional aluminum nitride sintered body having a high density and good thermal conductivity. The present invention relates to a method capable of sintering at a lower temperature than that.

[Problems to be Solved by Conventional Techniques and Inventions] Alumina has been used for IC packages and substrate materials for the past, but heat generation from chips has increased with higher integration, higher speed, and higher output of LSIs. There is a growing need for efficient release to the outside of the system, and there is a demand for a material that has better thermal conductivity than alumina and excellent heat dissipation.

Aluminum nitride has high thermal conductivity and excellent electrical properties such as insulation resistance, withstand voltage, dielectric constant and mechanical properties such as strength.
It is a material that has attracted attention as a substrate material.

In order to obtain an aluminum nitride sintered body having excellent thermal conductivity, it is necessary to mold the aluminum nitride powder and sinter it densely.

Since aluminum nitride is difficult to sinter under normal pressure by itself, conventional oxides such as CaO and Y ₂ O ₃ are added as sintering aids in the atmospheric pressure sintering method. _The method of densification utilizing the reaction with ₂ O ₃ has been adopted.

For example, JP-B-47-18655 discloses a method of densifying by adding Y ₂ O ₃ and sintering, JP-B-58-49510.
The publication discloses a method of obtaining a dense aluminum nitride sintered body having a relative density of 98.5% or more by adding CaO, BaO, SrO or the like and sintering.

However, in order to obtain a dense sintered body with high thermal conductivity by pressureless sintering, a high temperature of 1800 ° C or higher is required when Y ₂ O ₃ is added, and usually 1700 ° C or higher even when CaO is added. High temperature sintering is required.

Alumina, which is currently used for IC packages and substrate materials, is usually sintered and densified at a temperature of 1500 to 1600 ° C.

When an aluminum nitride sintered body is obtained by adding a sintering aid as described above compared to this temperature, the sintering temperature is considerably high, which is the reason why the cost of the aluminum nitride sintered body cannot be reduced. It is one.

Therefore, JP-A-61-209959 proposes a method capable of densification at 1600 ° C. by adding a rare earth oxide or fluoride and an alkaline earth oxide or fluoride. The conductivity is about 100 W / mK.

The present invention is intended to solve the problem of low temperature sintering of aluminum nitride powder, which could not be achieved by conventional sintering aids, and the object is to densify by sintering at a lower temperature than before. It is an object of the present invention to provide a method for producing an aluminum nitride sintered body having high thermal conductivity.

[Means for solving the problem]

That is, in the present invention, a compound of calcium and copper as a sintering aid in aluminum nitride powder is converted into CaO and CuO with respect to aluminum nitride, respectively, in the range of 0.01 to 3% by weight, and a molar ratio in terms of CuO / CaO of 1 or less. And yttrium compound Y ₂
Provided is a method for producing an aluminum nitride sintered body, which comprises adding in the range of 0.1 to 10% by weight in terms of O ₃ , mixing and molding, and then firing in a non-oxidizing atmosphere.

According to the present invention, it is possible to obtain an aluminum nitride sintered body having a density of 3.15 g / cm ³ or more and high thermal conductivity even at a lower sintering temperature than conventional ones.

In the present invention, the reason why the aluminum nitride sintered body is densified from a low temperature and exhibits high heat conduction has not been fully clarified yet, but in the present situation, it can be considered as follows.

That is, it is considered that the normal pressure sintering of aluminum nitride progresses the densification through the liquid phase. Therefore, if a substance that forms a liquid phase at a lower temperature is added as a sintering aid,
It is considered that the densification of aluminum nitride proceeds from a lower temperature.

When a compound of calcium and copper is mixed and a compound of yttrium is further added thereto, it becomes easier to react with Al ₂ O _{3 in} the surface oxide layer of the aluminum nitride powder, and Ca-C
It is considered that the u-Y-Al-O system liquid phase is generated and the densification proceeds from a low temperature.

 Hereinafter, the present invention will be described in detail.

The manufacturing method of the aluminum nitride powder used in the present invention is not particularly limited, but fine powder having high purity is preferable.

Regarding the particle size of the powder, it is preferable to use a powder having a central particle size of 4.0 μm or less.

In particular, in order to densify from a low temperature of 1600 ° C. or less, it is preferable to use fine powder having a central particle diameter of 2.0 μm or less if possible.

As the calcium and copper compounds used as a sintering aid, oxides, hydroxides, carbonates, sulfates, nitrates, acetates, oxalates, halides, sulfides, higher fatty acid salts and the like can be used. .

As the yttrium compound, oxides, nitrates, oxalates, halides and the like can be used.

Further, a composite compound containing any two or more elements of calcium, copper and yttrium and a composite compound of these and aluminum can be used.

Calcium, copper and yttrium may be any compounds as long as they are compounds, but compounds containing no water of crystallization are preferable.

For _{example, CaO, Ca (OH) 2} , CaCO 3, CaSO 4 · 2H 2 O, Ca
(NO ₃ ) ₂ , 4H ₂ O, Ca (CH ₃ COO) ₂ , Ca (COO) ₂・ H
₂ O, CaF ₂ , CaS, Ca (CH ₃ (CH ₂ ) ₁₆ COO) ₂ , CuO, Cu
₂ O, Cu (OH) ₂ , CuCO ₃ · Cu (CH) ₂ · H ₂ O, CuSO ₄ , Cu
_{(NO 3) 2 · 3H 2} O, Cu (CH 3 COO) 2 · H 2 O, Cu (CO
O) ₂ , CuF ₂ , CuS, Cu (CH ₃ (CH ₂ ) ₁₆ COO) ₂ , Y ₂ O ₃ ,
_{Y (NO 3) 2 · 9H} 2 O, Y (COO) 3 · H 2 O, YF 3 · 0.5H 2 O,
CuO · 2CaO, Ca ₂ AlO ₄ , CaYAlO _4, etc. are used.

In addition, the finer the particle size of these compounds, the more preferable, especially when using a compound that does not dissolve or is difficult to dissolve in the solvent used when mixing with the aluminum nitride powder, usually the central particle size is 5.0 μm or less. It is preferable to use fine powder.

The addition amount of these compounds is 0.01 to 3% by weight in terms of CaO and CuO in terms of calcium and copper compounds, respectively, based on aluminum nitride powder, and the range of CuO / CaO conversion molar ratio is 1 or less. It is preferably in the range of 0.1 to 10% by weight in terms of ₂ O ₃ .

If the amount of each additive deviates from this range, it is difficult to obtain a dense sintered body by pressureless sintering, and even if a dense sintered body is obtained, sufficiently high thermal conductivity cannot be obtained.

More preferable addition amount is aluminum nitride, calcium, copper compounds are each converted to CaO, CuO 0.05 ~
2% by weight, the CuO / CaO conversion molar ratio is in the range of 1 or less, and the yttrium compound is 0.5 to 5% by weight in terms of Y ₂ O ₃ .

The aluminum nitride powder and the calcium, copper and yttrium compound powder can be mixed by dry mixing or wet mixing using a non-aqueous solvent such as alcohol, but usually, a wet mixing using a non-aqueous solvent is performed. It is preferable to use.

During wet mixing, to facilitate the next molding step,
Known binders such as polyvinyl butyral, polyvinyl alcohol, and polyacrylic acid ester are usually added.

In addition to the binder, various dispersants, plasticizers and wetting agents are usually added. These additives and the addition amounts are appropriately selected and used according to the molding method described below.

As the mixing device, a ball mill, a kneader, or the like which is normally used can be used. Further, the mixture is prepared in the form of dried, granulated granules, clay or slurry depending on the molding method.

As a molding method, known methods such as a dry method such as a uniaxial press and a rubber press, a wet method such as a doctor blade method, an extrusion method and the like can be used.

Further, there is no problem even if a hot pressing method in which molding and sintering are simultaneously performed is used.

The obtained molded body is usually housed in a container called a bowl and sintered. Its material is graphite, boron nitride,
Aluminum nitride, alumina, or the like can be used, but it is preferable to use a casket made of graphite, boron nitride, or aluminum nitride by sintering at a high temperature of 1700 ° C. or higher. Alternatively, a powder bed method in which a compact is embedded in a powder containing aluminum nitride as a main component and then sintered can be used.

Sintering needs to be performed in a non-oxidizing atmosphere in order to prevent oxidation of aluminum nitride during sintering.

As the non-oxidizing atmosphere, nitrogen, argon, a mixed gas atmosphere of nitrogen and hydrogen, a mixed gas atmosphere of nitrogen and argon and the like can be used, but a nitrogen gas atmosphere is most preferable from the viewpoint of manufacturing cost, handling of the apparatus and the like.

The sintering temperature can be applied in the range of 1500 to 2000 ° C, but in practice, the range of 1550 to 1850 ° C is applied.

 The heating rate is usually in the range of 1 to 5 ° C / min.

The holding time at the sintering temperature is within the range of 2 to 20 hours,
The holding time is selected so that the density of the aluminum nitride sintered body becomes 3.15 g / cm ³ or more, but the range of 2 to 8 hours is preferable.

The density of the obtained aluminum nitride sintered body was 3.15 g / cm ³
It is preferable that it is above.

Even if the density of the sintered body is 3.15 g / cm ³ or less, it appears to be densified in appearance, but the sintered body contains many pores, and as a result, it does not become a sintered body with high thermal conductivity.

〔Example〕

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

 The various properties were measured by the following methods and devices.

(Oxygen content) Impulse heating-infrared absorption method Device: LECO TC-436 type (Metallic impurities) ICP emission spectroscopy device: Shimadzu Corporation Cantlet GQM-75 (particle size distribution) Sedigraph device: Micromeritics SediGraph 5000ET (Sintered body density) Archimedes method Device: Shimadzu Corporation Fixed specific gravity measuring device (Thermal conductivity) Laser flash method Device: Vacuum Riko Co., Ltd. TC-7000 type Example 1 Aluminum nitride (AlN) powder of alumina A powder having an oxygen content of 1.3%, iron, silicon and titanium contents of 10, 60 and 16 ppm and a central particle size of 1.4 μm, which was obtained by the reduction nitriding method, was used.

Calcium carbonate (CaCO ₃ ) as a calcium compound
(Calcium shiraishi: Shirakanka CCR), cupric oxide (CuO) as a copper compound (Hanai Chemical: GR grade reagent), yttrium oxide (manufactured by Shin-Etsu Chemical Co., Ltd.) was used as an yttrium compound.

AlN powder 18.9g, CaCO ₃ powder 0.36g and CuO powder 0.1
4g, Y ₂ O ₃ takes a powder 0.6g into 250ml polyethylene pot n- butanol 25 g, acrylic binder (Sanyo Chemical:
CB-1) 4.0 g and dispersant (Daiichi Kogyo Chemical: Ceramo D-
18) 1.0 g was added and a nylon ball coated with a 15 mmφ iron core was used to perform a wet ball mill at a rotation speed of 60 rpm for 4 hours.

After the obtained slurry was dried, it was lightly crushed in an agate mortar to prepare a powder for sintering.

This sintering powder was put into a molding die, uniaxially pressed at 300 kg / cm ² , and then rubber press molded at 1500 kg / cm ² , to obtain a molded body having a diameter of 13 mm and a thickness of 10 mm.

This molded body was placed in a graphite container, embedded in a mixed powder of aluminum nitride and boron nitride, and placed in a nitrogen atmosphere.
Sintering was carried out at a temperature of 1550, 1600, 1700 and 1800 ° C for 5 hours under atmospheric pressure.

Table 1 shows the sintered body density and thermal conductivity of the obtained sintered body.

Table-1 Sintering temperature Sintered body density Thermal conductivity 1550 ° C. 3.16 g / cm ³ 118 W / mK 1600 3.28 142 1700 3.28 163 1800 3.28 198 Example 2 Aluminum nitride powder, calcium carbonate, and oxide similar to Example 1 Using dicopper and yttrium oxide powder,
A powder for sintering was prepared by treating in the same manner as in Example 1 except that the addition amount of each was changed as shown in Table 2.

These sintering powders were molded in the same manner as in Example 1, and then sintered under normal pressure at 1600 ° C. for 5 hours.

Table 2 shows the sintered body density and thermal conductivity of the obtained sintered body.

Comparative Example A sintering powder obtained by adding 3% by weight of only the Y ₂ O ₃ powder used in Example 1 to the same AlN powder as in Example 1 was processed into a sintered body in the same manner as in Example 1. Created.

 Table 3 shows the density and thermal conductivity of the sintered body.

Table-3 Sintering temperature Sintered body density Thermal conductivity 1550 ° C. 2.43 g / cm ³ 38 W / mK 1600 2.87 68 1700 2.97 87 1800 3.28 190 [Effect of the invention] According to the present invention, compounds of calcium, copper and yttrium When used as a sintering aid, the aluminum nitride powder can be densified to 3.15 g / cm ³ or more at temperatures up to 1600 ° C., and an aluminum nitride sintered body having high density and excellent thermal conductivity can be obtained. This is intended to allow the sintering of refractory aluminum nitride at a temperature comparable to that of alumina, and it is expected that the manufacturing cost of the sintered body will be greatly reduced.
It has a very important industrial effect.

Claims (1)

(57) [Claims] 1. A compound of calcium and copper as a sintering aid in aluminum nitride powder, to aluminum nitride, respectively.
0.01 to 3 wt% in terms of CaO and CuO, a range of 1 or less in terms of CuO / CaO conversion, and a yttrium compound in the range of 0.1 to 10 wt% in terms of Y ₂ O ₃ , and mixed, After molding,
A method for manufacturing an aluminum nitride sintered body, which comprises firing in a non-oxidizing atmosphere.