JPH05105524A - Highly heat conductive ceramics and their production - Google Patents

Abstract

PURPOSE:To provide heat conductive and dense ceramics, having high heat conductivity and sinterable more readily than conventional ones and a simple method for producing the ceramics. CONSTITUTION:Highly heat conductive ceramics of this invention are characterized by adding a group Ia element of the periodic table or its compound and at least one element of groups IIIa and IIa or its compound to aluminum nitride powder, molding and sintering the resultant mixture and forming the ceramics. The content of the group Ia element of the periodic table contained in the mixture is preferably set at 0.05-3wt.% expressed in terms of the element. On the other hand, the content of at least one element of groups IIIa and IIa is preferably set at 0.5-7wt.% expressed in terms of the element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high thermal conductivity ceramic and a method for producing the same, and particularly to a high thermal conductivity ceramic composed of a sintered body containing aluminum nitride as a main component, which is suitable as a substrate material for electronic circuits, and the ceramic. And a simple and efficient manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, due to rapid technological innovation in the semiconductor industry, high integration and high output of large-scale integrated circuits incorporated in electronic devices have advanced, and the amount of heat generated per unit area of semiconductor elements has significantly increased. ing. Then, in order to prevent the malfunction of the semiconductor element due to the increased heat generation, a ceramic substrate material excellent in thermal conductivity and insulation is required.

As a substrate material having the above characteristics, a sintered body such as alumina (Al ₂ O ₃ ), beryllia (BeO), silicon carbide (SiC) or aluminum nitride (AlN) is known. In particular, an aluminum nitride (AlN) sintered body having excellent properties such as thermal conductivity, electrical insulation (withstand voltage property), coefficient of thermal expansion, and mechanical strength has been widely used.

[0004]

However, aluminum nitride has a strong covalent bond property and is a material that is difficult to sinter and cannot be densified by sintering only AlN powder. Therefore, in order to obtain dense and dense AlN ceramics having high conductivity, compounds of Group IIIa elements of the periodic table such as yttria (Y ₂ O ₃ ) and oxides of rare earth elements and calcia (CaO) are used. It was necessary to add a compound of the group IIa element such as), etc. as a sintering aid to the raw material AlN powder, and to fire the molded body formed of the obtained mixture at a high temperature of about 1800 ° C.

Therefore, a heating furnace having a large heat capacity is required as a heating furnace for sintering, and there is a drawback that operating cost increases. Also, as a sintering aid that has been used conventionally,
When only the compound of the group IIIa and / or the group IIa is added, there is a problem that it is still difficult to sinter, the production cost is increased and the production efficiency is lowered, and mass production is difficult. It was

The present invention has been made in order to solve the above problems, and has a high thermal conductivity, a dense and high strength, and a high thermal conductivity ceramic which is easier to sinter than before, and its simple structure. It aims at providing a simple manufacturing method.

[0007]

Means and Actions for Solving the Problems In order to improve the sinterability of aluminum nitride powder, the present inventors have used various sintering aids in combination with conventionally used sintering aids. It was added to the raw material aluminum nitride powder, and the quality of its sinterability was confirmed by experiments.

As a result, the conventionally used No. III
In addition to the sintering aid containing at least one element of the group a element and the group IIa element, when a compound containing the group Ia element is added to the raw material aluminum nitride powder and fired, the aluminum nitride powder The liquid phase sintering action was further improved, the sintering operation was facilitated, and ceramics with high thermal conductivity were obtained.

The present invention has been completed based on the above findings.

That is, the high thermal conductive ceramics according to the present invention is characterized by the periodic table Ia of the aluminum nitride powder.
It is characterized in that a mixture obtained by adding a group element or a compound thereof and at least one element of a group IIIa or a group IIa or a compound thereof is formed by sintering and formed.

The content of the group Ia element of the periodic table contained in the mixture is set to 0.05 to 3% by weight in terms of the element, and the group IIIa element and the group IIIa element of the periodic table contained in the mixture.
The content of at least one of the Group IIa elements may be set to 0.5 to 7% by weight in terms of element.

The aluminum nitride powder used in the present invention is synthesized by a reduction nitriding method of alumina, a direct nitriding method of aluminum, a CVD method using aluminum halide and nitrogen or ammonia, and has an average particle size of Al of 0.05 to 10 μm, preferably 3 μm or less
N powder is used.

Further, the group Ia element of the periodic table or a compound thereof used in the present invention promotes the generation of a liquid phase at a low temperature and facilitates the sintering action by 0.1 to 3 in terms of elements. Wt% is added. That is, the periodic table Ia
Group elements and their compounds are generally strongly alkaline,
The melting point is not higher than that of other endless compounds. When such a compound of the group Ia element is added together with a compound of the group IIIa element and / or a compound of the group IIa, the melting power due to the strong alkalinity peculiar to the group Ia element causes the aluminum nitride powder and the group as a sintering additive to be added. The liquid phase of the compound of the group IIIa element and the group IIa element is promoted at a low temperature, and the sintering action can be facilitated. That is, it is possible to form a sufficiently dense sintered body even at a lower sintering temperature than before.

Specific examples of the group Ia element and its compound include Li ₂ PO ₄ , NaF, Na ₂ CO ₃ and Na _{2.
B 4 O 7, Li 2 CO} 3, LiF , and the like. When the content of these Group Ia element and its compound is less than 0.05% by weight in terms of element, the effect of promoting the liquid phase during sintering is not sufficient, while the content exceeds 3% by weight. In addition, the thermal conductivity of the AlN sintered body decreases, the amount of liquid phase produced becomes excessive, and the surface roughness of ceramics increases, making it unsuitable as a substrate material. Therefore, Ia
Addition amount of group element and its compound is 0.05-3% by weight
It is set to the range of.

The elements of Group IIa and Group IIIa of the periodic table and their compounds are conventional sintering aids mainly composed of alkaline earth metal oxides and rare earth oxides, respectively.
These sintering aids react with the impurity oxygen of the AlN raw material powder to generate a liquid phase, achieve densification of the sintered body, and fix the impurity oxygen as a grain boundary phase (oxygen trap). It also achieves high thermal conductivity.

Specific examples of the compound containing a Group IIa element include CaO, SrO, BaO, Ca ₃ (P
O ₄ ) ₂ , Ca ₂ B ₆ O ₁₁ , CaB ₂ O ₄ , CaCO ₃
If the content of the Group IIIa element is less than 1% by weight, the densification of the AlN sintered body does not proceed sufficiently, while if the content exceeds 7% by weight, Due to an increase in oxygen that has not been trapped, the thermal conductivity of the AlN sintered body is lowered, and the original heat dissipation characteristics cannot be exhibited. Therefore, the content of at least one of the Group IIa and Group IIIa elements is set in the range of 0.5 to 7% by weight.

The high thermal conductivity ceramics which is the object of the present invention contains 0.05 to 3% by weight of the group Ia element of the periodic table, the group IIIa element and the group IIIa element with respect to the aluminum nitride powder.
Produced by a method in which 1 to 7% by weight of at least one element of the IIa group elements is added and uniformly mixed to form a molded body, and the molded body is fired at a temperature of 1600 to 1750 ° C. in a non-oxidizing atmosphere. To be done.

Here, the aluminum nitride powder and the No. Ia
The mixing operation with Group IIIa, Group IIa, Group IIIa elements or compounds thereof is carried out using a ball mill, an attritor, a V-type mixer, etc., in which case alcohol, benzene,
Wet mixing using a solvent such as acetone is preferable because a uniform mixture can be obtained.

In the molding step, the obtained mixture is formed into a molded body by using a doctor blade method, a casting method, a rubber pressing method, a die pressing method or the like.

Furthermore, according to the method of the present invention, 16
It is fired in a temperature range of 00 to 1750 ° C. That is, in the conventional method, it was necessary to heat to a high temperature of about 1800 ° C. or higher, but according to the method of the present invention, in addition to the conventional sintering aid, a Group Ia element that promotes liquefaction is added. Is added as a sintering aid, a sufficiently dense sintered body can be formed even at a low sintering temperature. Therefore, the sintering temperature is low, the heat capacity of the heating furnace can be reduced, and the operation cost is reduced and the manufacturing efficiency is significantly improved.

When the heating temperature at the time of sintering is as low as less than 1600 ° C., the liquid phase is insufficiently produced, and it is difficult to produce a dense sintered body. On the other hand, the heating temperature is 17
If the temperature exceeds 50 ° C, the heat load of the heating furnace increases and the operating cost rises. In particular, if the temperature exceeds 2000 ° C, the crystal grains of the sintered body tend to become coarse.

In order to exhibit the high thermal conductivity which is the object of the present invention, the molded body is made of, for example, argon, helium,
It is important to fire in an atmosphere of an inert gas such as nitrogen or hydrogen or a non-oxidizing gas or in vacuum. For this firing, either a normal pressure sintering method or a pressure sintering method may be adopted.

The aluminum nitride ceramics produced by the method of the present invention has a density of 3.1 g / cm ³ or more and a thermal conductivity of 100 to 190 w / m · k at room temperature.
It is most suitable as a substrate for electric circuits that requires high heat dissipation.

[0024]

EXAMPLES Next, the present invention will be described more specifically based on the following examples and comparative examples.

Examples 1 to 4 In Examples 1 and 2, aluminum nitride powder having an average particle size of 2 μm produced by the aluminum oxide reduction method was used, and yttrium oxide (Y) as a group IIIa element compound was used.
₂ O ₃ ) was added as a sintering aid in an amount of 5% by weight (3.9% by weight in terms of Y element), and 1% by weight of anhydrous sodium borate (Na ₂ B ₄ O ₇ ) which is a Group Ia element compound. % (N
0.23% by weight in terms of element a) was added, and a mixed solvent of ethanol and n-butanol was further added, and mixed by a ball mill for 24 hours to obtain a slurry-like mixture. An acrylic binder was added to the slurry mixture, and the mixture was further mixed for 24 hours, dried, sieved and press-molded to form a substrate molded body. Further, the obtained substrate compact was degreased in a nitrogen stream at a temperature of 500 ° C. for 1 hour and then fired at 1650 ° C. and 1750 ° C. for 5 hours in a nitrogen atmosphere at atmospheric pressure to obtain an aluminum nitride sintered body. The AlN sintered bodies according to 1-2 were prepared.

In Examples 3 to 4, 0.4% by weight of sodium borate anhydrous (Na ₂ B ₄ O ₇ ) which is a Group Ia element compound was added to the aluminum nitride powder used in Example 1. 0.09% by weight (calculated as Na element) is added, and calcium oxide (Ca
After adding 2% by weight (O) as a sintering aid (1.4% by weight in terms of Ca element), the mixture was mixed and molded under the same conditions as in Example 1 to prepare a large number of compacts of the same size. Then, the obtained molded body was degreased under the same conditions as in Example 1, and further fired at a temperature of 1650 ° C. and 1750 ° C. for 5 hours to prepare AlN sintered bodies according to Examples 3 to 4.

Comparative Examples 1 to 4 On the other hand, with respect to the aluminum nitride powder used in Example 1 as Comparative Examples 1 to _3, only 5.0% by weight of the group IIIa element compound Y ₂ O ₃ (Y element) was used. 3.9 in conversion
%) As a sintering aid was mixed under the same conditions as in Example 1, molded and degreased, and the resulting molded bodies were divided into three groups, 1650 ° C. and 1750 ° C., respectively.
The AlN sintered bodies of Comparative Examples 1 to 3 were prepared by firing for 5 hours under three temperature conditions of 1800 ° C. Further, as Comparative Example 4, only 2.0% by weight of CaO was added and fired at a temperature of 1650 ° C. to similarly prepare an AlN sintered body.

In order to evaluate the sinterability and heat dissipation characteristics of the AlN sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 4 thus prepared, the density and the thermal conductivity of the sintered bodies were measured, The results shown in Table 1 below were obtained.

[0029]

[Table 1]

As is clear from the results shown in Table 1, according to the AlN sintered bodies of Examples 1 to 4, the conventional AlN powders of the group IIIa element compound or the group IIa element compound of the conventional AlN powder were used. In addition to the sintering aid, since the Group Ia element compound that promotes liquid phase is added, the density is sufficiently increased even when firing at a lower sintering temperature than before,
Moreover, an AlN sintered body having a significantly improved thermal conductivity was obtained.

On the other hand, in the sintered bodies which were fired at a lower temperature than the conventional one without adding the group Ia element like Comparative Examples 1 to 2 and 4, the densification did not proceed sufficiently and the thermal conductivity was relatively high. Will fall to.

[0032]

As described above, according to the high thermal conductivity ceramics and the method for producing the same according to the present invention, the group IIa element and / or the group IIIa element or the compound thereof is added to the aluminum nitride raw material powder. With
Since the Group Ia element that promotes liquefaction is added, it is possible to obtain a high thermal conductive ceramics having a high density and a significantly improved thermal conductivity even when fired at a lower sintering temperature than before. ..

Therefore, the manufacturing process is simple and easy, and the manufacturing cost can be reduced.
It is possible to inexpensively provide a ceramic circuit board or the like having excellent heat dissipation characteristics.

Claims (4)

[Claims] 1. An aluminum nitride powder, a group Ia element of the periodic table or a compound thereof, a group IIIa group and a group IIIa group thereof.
A high thermal conductive ceramics characterized by being formed by sintering a mixture to which at least one element of Group IIa or its compound is added. 2. The high thermal conductive ceramics according to claim 1, wherein the content of the Group Ia element of the periodic table contained in the mixture is 0.05 to 3% by weight in terms of element. 3. The content of at least one of Group IIIa element and Group IIa element of the periodic table contained in the mixture is 0.5 to 7% by weight in terms of element. The high thermal conductive ceramics described in 1. 4. An aluminum nitride powder containing 0.05 to 3% by weight of a Group Ia element of the periodic table and 0.5 to at least one of a Group IIIa element and a Group IIa element.
After adding 7% by weight and mixing uniformly, a molded body is formed,
This molded body is heated at a temperature of 1600 to 175 in a non-oxidizing atmosphere.
A method for producing a high thermal conductive ceramics, which comprises firing at 0 ° C.