JP2913060B2 - Aluminum nitride ceramic firing powder and firing method using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for firing aluminum nitride ceramics, and more particularly to a powder used for firing.

[Prior Art] Aluminum nitride ceramics have high thermal conductivity and high electrical insulation and are therefore used for circuit boards for mounting semiconductor elements.

When firing this aluminum nitride ceramics,
Generally, each compact was stacked and fired with a bedding powder made of ceramic powder interposed between plate-like aluminum nitride compacts (Japanese Patent Application Laid-Open No. 61-117161,
See JP-A-1-108169).

[Problems of the prior art]

The examples of the above-mentioned JP-A-61-117161 have an average particle diameter of 3 μm.
A method is disclosed in which a lint powder made of boron nitride having a thickness of 15 m is formed to a thickness of 15 μm, and an aluminum nitride molded body is supported and fired.

However, in the case of such small bedding powder, the bedding powder enters the aluminum nitride ceramics during firing,
There is a problem that the surface roughness is increased by sticking to the surface. Therefore, when used as a circuit board for mounting a semiconductor element, there is a disadvantage that barrel polishing or the like must be performed after firing.

In addition, in the above method, the thickness of the powder layer tends to be non-uniform, and the aluminum nitride sintered body may be warped or distorted. In addition, when boron nitride or aluminum oxide is used as the powder, the aluminum nitride fired body has a spot or uneven color tone.

On the other hand, according to JP-A-1-108169, the average particle size is
A method of using calcined aluminum nitride powder of 100 to 250 mesh (61 to 152 μm) as a bedding powder is disclosed. However, calcining must be performed to prevent sticking of the bedding powder. It took something.

[Object of the invention]

The present invention has been made to solve the above problems. In other words, it eliminates the reaction and sticking of the powder to aluminum nitride ceramics, maintains the smoothness and flatness of the surface well, reduces the warpage and distortion of the aluminum nitride ceramics, and eliminates spots and uneven color tone. The purpose is to:

[Means for solving the problem]

In view of the above, the present invention supports a molded product containing aluminum nitride as a main component, using aluminum nitride powder having an oxygen content of 10% by weight or less as a spreading powder, in a non-oxidizing atmosphere of 1600 to
It is baked at 1900 ° C.

According to the present invention, it has been found that in order to eliminate the sticking of the litter, the oxygen content of the aluminum nitride powder used as the litter should be 10% by weight or less. When the oxygen content of the aluminum nitride powder exceeds 10% by weight, the adhesion of the litter powder to the sintered body increases and the surface of the sintered body becomes rough. The lower the oxygen content of the aluminum nitride powder, the better, but it is extremely difficult to reduce the oxygen content to less than 0.4% by weight. That is, aluminum nitride powder is produced by a method of reducing alumina or a method of directly nitriding metallic aluminum. In any case, in order to reduce the oxygen content to less than 0.4% by weight, the synthesis time is extremely long. This is because it is long or the synthesis temperature becomes extremely high.

The oxygen content of the aluminum nitride powder refers to the amount of oxygen contained in an oxide such as boehmite or α-alumina present on the surface of the powder or an oxygen-substituted product of aluminum nitride solid-dissolved inside the aluminum nitride particles. The oxygen content in the present invention is measured by LECO, TC
A -136 type oxygen and nitrogen simultaneous analyzer was used.

The size of the aluminum nitride powder used as the bedding powder in the present invention has an average particle size of 10 to 300 μm, and has a narrow particle size distribution, and preferably does not contain fine powder having a particle size of 10 μm or less. If the average particle size of the bedding powder is smaller than 10 μm, it tends to stick to the sintered body, while the average particle size is 300 μm
If it is larger, warping tends to occur on the sintered body. Furthermore, it is desirable that the ratio of the major axis to the minor axis is close to 1, that is, the spherical powder is used as the litter, and that the litter is desirably arranged in a single layer so as not to overlap with each other to form a litter layer.

The firing conditions of the present invention are as follows: firing is performed at a temperature of 1600 to 1900 ° C. in a non-oxidizing atmosphere of N ₂ gas having a purity of 99.9% or more, and a mixed gas of N ₂ gas and H ₂ gas having a purity of 99.9% or more. A normal pressure sintering method or a gas pressure sintering method is used.

Further, as a support plate on which the aluminum nitride molded body is placed during firing, a carbon plate having a boron nitride layer formed thereon, an aluminum nitride ceramics plate, a boron nitride layer formed thereon, or a metal tungsten plate is used.

Further, the aluminum nitride molded body may not contain a sintering aid, but when using a sintering aid, at least one metal selected from the group consisting of yttrium, a lanthanum group metal and an alkaline earth metal is used. An oxygen-containing compound is blended in a proportion of 15% by weight or less.

〔Example〕

 Hereinafter, embodiments of the present invention will be described.

First, six kinds of powder shown in Table 1 were prepared as bedding powder. In Table 1, the bedding powder 1 was obtained by agglomerating primary particles and was non-spherical, whereas the bedding powders 2 to 6 were obtained by granulating primary particles with a spray dryer or the like, and were substantially spherical. doing.

Next, the following three types were prepared as compacts mainly containing aluminum nitride.

A binder and methanol are added to an aluminum nitride powder having an average particle size of 1.6 μm, a BET (specific surface area) of 3.2 m ² / g, an oxygen content of 1.2% by weight, and a cation impurity content of 500 ppm or less, and then mixed by spray drying. Granular powder was prepared, and the granulated powder was formed into a size of 120 × 120 × 2 mm by a dry press molding method. [Aluminum nitride compact a] 5% by weight of ytterbium oxide was added to aluminum nitride powder having an average particle size of 1.8 μm, a BET (specific surface area) of 2.8 m ² / g, an oxygen content of 0.9% by weight, and a cation impurity content of 500 ppm or less. After adding and mixing a binder and methanol, the mixture was molded into a size of 60 × 60 × 2 mm in the same manner as described above. [Aluminum nitride compact b] Aluminum nitride powder having an average particle size of 2.8 μm, a BET (specific surface area) of 2.8 m ² / g, an oxygen content of 1.0% by weight, and a cation impurity content of 500 ppm or less, 3% by weight of erbium oxide and calcium oxide After adding 0.5% by weight and adding and mixing the binder and methanol, 33 × 33 × 1.
It was formed into a size of 5 mm. [Aluminum nitride compact c] Next, as a firing method of these aluminum nitride compacts, three types of stacked bodies were prepared as described below.

Spreading powder was spread on the surface of the carbon plate, and four aluminum nitride compacts were placed thereon, and the powder was spread between the aluminum nitride compacts. [Stack I] A boron nitride layer is formed on the surface of a carbon plate, an aluminum nitride ceramic plate having a purity of 95% or more is placed thereon, and powder is spread on the aluminum nitride ceramic plate. Place the aluminum nitride compacts, spread the powder between each aluminum nitride compact,
An aluminum nitride ceramics container was covered so as to cover them. [Stacked body II] An aluminum nitride ceramics plate was placed on a metal tungsten plate, and powder was spread on this surface. Four aluminum nitride compacts were placed thereon, powder was spread between the aluminum nitride compacts, and a metal tungsten container was covered so as to cover them. (Stack II
I] In each of the above-mentioned stacked bodies, the bedding powder was spread so as to be substantially one layer, depending on the particle size.

Aluminum nitride compacts a, b, c and stack shown above
Seven types of conditions 1 to 7 were set as shown in Table 2 by combining I, II, and III.

In each condition, the aluminum nitride molded body was degreased and then fired. In Table 2, N ₂ has a purity of 99.9.
% Or more of gas and normal pressure indicates 1.0 to 1.4 atm.

Under these conditions, an experiment was carried out under the conditions 1 to 7, using the six types of bedding powders 1 to 6 shown in Table 1 as the respective bedding powders.

For each of the obtained sintered bodies, the presence or absence of fixation between the sintered bodies, the presence or absence of fixation between the sintered body and the bedding powder, and the like were examined. The results are as shown in Tables 3 to 9.

In Tables 3 to 9, the reaction between the sintered bodies and the presence / absence of the adhesion means that the sintered bodies react with each other and adhere, or the powder powder and the sintered body react and the sintered bodies come together. Those that were fixed were represented by x, and those where the sintered bodies were not fixed were represented by Δ.

The presence or absence of infiltration and fixation of the bedding powder into the sintered body means that the bedding powder is fixed to the sintered body and the center line average roughness (Ra) of the surface is 4%.
Those having a diameter of not less than μm are indicated by x, and those having a center line average roughness (Ra) of the sintered body surface of 0.2 to 4 μm are indicated by Δ.

Further, the warpage value of the sintered body is an average deformation value in the thickness direction of the sintered body.

The thermal conductivity was obtained by polishing the surface of the sintered body by a laser flash method, measuring the thermal diffusivity, and calculating from the equation: thermal conductivity = thermal diffusivity × specific heat × sintered body density.

From the above results, the bedding powder 6 made of boron nitride was likely to be fixed to the sintered body, and the color tone of the sintered body was poor. Further, since the amount of oxygen of the bedding powder 5 was as large as 20% by weight, sticking to the sintered body was large. Furthermore, the bedding powder 1 has an average particle size of 1.28 μm.
Therefore, the sintered body was frequently fixed.

On the other hand, in the powders 2 to 4, the amount of oxygen was 10% by weight or less, and thus the adhesion to the sintered body was small.

However, the bedding powder 4 had a large warp value of the sintered body because the average particle size was as large as 830 μm. As a result of further experiments, it was found that the average particle size was
The thickness should be 300 μm or less. However, if the average particle size of the bedding powder is less than 10 μm, the adhesion to the sintered body increases, and therefore, those having an average particle size of 10 to 300 μm were excellent.

Further, in the conditions 1 to 7, the thermal conductivity is
20-50W / m ・ K, Condition 2 is 160-170W / m ・ K, Condition 3 is 17
5 to 190 W / mK, condition 4 is 95 to 110 W / mK, condition 5 is 120
~ 140W / m ・ K, Condition 6 is 135 ~ 150W / m ・ K, Condition 7 is 170
180180 W / m · K, and under the same conditions, there was little correlation depending on the type of bedding powder.

〔The invention's effect〕

As described above, according to the present invention, the oxygen content is 10% by weight.
The following aluminum nitride powder is used as a spreading powder to support a molded body containing aluminum nitride as a main component.
By firing at 1600 to 1900 ° C, the reaction and sticking of the powder to the aluminum nitride sintered body is eliminated,
It is possible to maintain the smoothness and flatness of the surface of the sintered body satisfactorily, reduce warpage and distortion of the sintered body, and eliminate stains and uneven color tone.

Thereby, the application of electronic components such as a substrate for mounting a semiconductor element made of aluminum nitride ceramic can be promoted, and the mass productivity can be improved.

Claims (2)

(57) [Claims] (1) an average particle diameter of 10 to 300 μm and an oxygen content of 1
Powder for baking aluminum nitride ceramics, characterized in that the powder comprises 0% by weight or less of aluminum nitride powder. 2. A molded product containing aluminum nitride as a main component, having an average particle size of 10 to 300 μm and an oxygen content of 10% by weight.
A method for firing aluminum nitride ceramics, comprising: supporting a powder of aluminum nitride powder as follows; and firing at 1600 to 1900 ° C. in a non-oxidizing atmosphere.