JP2683528B2 - Method for firing aluminum nitride substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for manufacturing an aluminum nitride substrate, and more particularly to a method for firing a laminate formed by a green sheet method using aluminum nitride raw material powder. Aluminum nitride green sheet with Ca compound added as a sintering aid for the purpose of providing a firing method for obtaining a dense and high thermal conductivity AlN substrate without warping or waviness without embedding. An aluminum nitride substrate obtained by punching the green sheet into a predetermined shape, laminating and pressing the punched green sheets to form an aluminum nitride laminate, and firing the aluminum nitride laminate to obtain an aluminum nitride substrate. in the process of firing, when firing the sintering aid as a Ca compound added aluminum nitride laminate, or Al ₂ O ₃ and CaO Composite sintered body consisting (CaxAl _y O _z: X is 1 to 12, y is 1 to 14, O is 1-33)
Is simultaneously fired under normal pressure or reduced pressure.

[Industrial applications]

The present invention relates to a method for manufacturing an aluminum nitride substrate, and more particularly to a method for firing a laminate formed by a green sheet method using aluminum nitride raw material powder.

The aluminum nitride sintered body produced according to the present invention is made of high-purity alumina (Al ₂ O ₃ ) as a starting material, and is produced from the aluminum nitride raw material powder obtained by the reduction nitriding method, and is dense and excellent in translucency, It has a high thermal conductivity.

[Conventional technology]

A circuit board having excellent thermal conductivity is required for high-density mounting of elements such as IC and LSI. For such substrate materials, Be has a limited range of use due to toxicity.
There is O, but most of them use alumina.

Therefore, aluminum nitride (AlN), which has a high thermal conductivity and strength equivalent to that of alumina, has come to be used as a substrate material replacing BeO and alumina.

Aluminum nitride is difficult to sinter, and it is difficult to sinter by itself. For this reason, a sintering aid is often added in a normal atmospheric pressure sintering method using a tunnel furnace.

Further, as a method of sintering without using a sintering aid, there is a hot pressing method. However, it has drawbacks such as poor mass productivity and difficulty in manufacturing complicated shapes. Furthermore, it is impossible to sinter a circuit board having three-dimensional wiring inside.

Compounds of Y and Ca are known to be effective as the above-mentioned sintering aid (JP-A-59-207814, JP-A-60).
-60910, JP-A-60-71575).

The thermal conductivity of a sintered body obtained by a normal pressure sintering method using a tunnel furnace using the sintering aid of the above Y or Ca compound is 140 to 180 W / mK and a theoretical value of 320 W / mK. It is only about 1/2.

This is because the removal of oxygen impurities, which is the largest factor that reduces the thermal conductivity of AlN, is incomplete. When fired in a special atmosphere (reducing atmosphere such as N ₂ containing H ₂ or CO gas), it may exceed 200 W / mK.

In addition, in order to perform firing without impairing the high thermal conductivity, which is the greatest feature of AlN, not only optimization of sintering aids and firing conditions but also how to set the article to be fired in the firing furnace Is known to be an important issue.
-100479).

Normally, it is stored in a graphite container and baked, but in this case, it is possible to see a device such as applying AlN or BN powder to the inside of the graphite container. Also, the product to be fired is AlN
The method of embedding in powder is generally used.

In any case, the method of alternately stacking BN setters and AlN laminates provided by JP-A-62-100479 and firing in a BN container, even in obtaining a dense AlN sintered body, warps and waviness It is very effective in eliminating it.

However, adhesion of BN can be seen on the surface of the AlN sintered body,
There is a problem that there is a large variation in the shrinkage ratio within the substrate (particularly at the corners). With such a problem, a complicated sintered body, such as providing internal wiring or forming a via, cannot be obtained in the laminated body.

[Problems to be solved by the invention]

In the conventional firing method, in order to obtain a dense, high thermal conductivity, flat AlN substrate without warping or waviness, a method of applying a load with a BN setter or embedding it in AlN powder is often used. However, this method has a problem in that it is inferior in mass productivity, and it is still impossible to control the shrinkage ratio and form the surface wiring layer and the via in the same substrate.

Further, there are problems that impurities are unavoidable and the evaporation components such as the sintering aid are not sufficiently removed, so that the thermal conductivity is about 1/2 of the theoretical value of 320 W / mK.

The present invention is a dense and high thermal conductivity AlN powder without warping or waviness without being loaded or embedded in AlN powder.
It is an object to provide a firing method for obtaining a substrate.

[Means for solving the problem]

According to the present invention, the above object is to form an aluminum nitride green sheet to which a Ca compound is added as a sintering aid, punch the green sheet into a predetermined shape, and laminate and press the punched green sheets. In the method for firing an aluminum nitride substrate, the body is formed to obtain an aluminum nitride substrate obtained by firing the aluminum nitride laminate. In firing the aluminum nitride laminate to which a Ca compound is added as the sintering aid, Al ₂ O ₃ a composite sintered body consisting of CaO (CaxAl _y O _z: X is 1 to 12, y is 1 to 14, O is 1-33)
Is solved at the same time under normal pressure or under reduced pressure, which is solved by a method for baking an aluminum nitride substrate.

The x, y, limitation of z is required to control the solid → liquid → vapor temperature of CaxAl _y O _x. The reason for the pressure condition at the time of firing and normal pressure or reduced pressure is for promoting evaporation of CaxAl _y O _z.

(Operation)

In the present invention, Al ₂ O ₃ and C
By evaporating the composite sintered body (Al _x Ca _y O _z ) composed of aO, it has almost the same composition as calcium aluminate formed by the reaction between Al ₂ O ₃ in the AlN raw material powder and the sintering aid CaCO ₃ . By supplying an equal atmosphere, the evaporation of calcium aluminate from the product to be fired is moderated in a wide temperature range during firing (during heating and holding of the maximum temperature). It is possible to make the phase diffusion uniform.

As a result, it is possible to obtain an AlN substrate which is free from warpage and undulation, and is dense and has high thermal conductivity.

In the method for firing AlN according to the present invention, when firing an AlN laminated body, a composite sintered body made of Al ₂ O ₃ and CaO is fired at the same time, but a corrugated shape made of BN (or having a large number of protrusions)
It is preferable to use a setter to support the article to be fired by the tips of the protrusions and to install the composite sintered body in the recessed portion.

In the composition of the composite sintered body to be used in the present invention (CaxAl _y O _z) is
When x: y is in the range of 1:12 to 3: 2, the evaporation of calcium aluminate from the product to be fired can be more gradual. This CaxAl _y O _z sintered body was CaCO ₃ measured in CaO conversion.
And α-Al ₂ O ₃ as starting materials, and can be obtained by firing in air at 1200 to 1800 ° C, preferably 1400 to 1800 ° C.

The composition of the product to be fired is 0.5 to 10 parts by weight, preferably 1 to 4 parts by weight of Ca compound as a sintering aid with respect to 100 parts by weight of AlN.
The inclusion of parts by weight is more effective for promoting the sintering reaction. As the Ca compound, CaO, CaCO ₃ , Ca (NO ₃ ) ₂ , CaTiO
One or more of ₃ Ca ₃ (PO ₄ ) ₂ and halides can be used.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

For 100 parts by weight of aluminum nitride (AlN) powder, 3 parts by weight of sintering aid CaCO ₃ is weighed. 400 g of this powder was milled for 50 hours in a resin pot together with 260 g of ethanol using a ball in which a net ball was coated with resin.

Subsequently, 25 g of PVB (polyvinyl butyral) and 35 g of plasticizer DBP (dibutyl phthalate) were added as organic binders, and milling was continued for another 50 hours.

The slurry thus obtained was subjected to vacuum defoaming to adjust its viscosity and defoam, and was made into a green sheet by the doctor blade method. Doctor blade gap is 40
The feed rate of the carrier film was 0 μm and 2.2 m / min.

The obtained green sheet had a thickness of 250 μm, and 10 sheets were laminated to form a laminated body at a laminating pressure of 45 MPa.

The laminate was fired in a wet nitrogen atmosphere at 600 ° C. for 10 hours to remove organic components such as a binder and a plasticizer.

The laminated body from which the organic components were removed was set in a container as shown in FIG. In FIG. 1, 1 is a graphite container, and 2 and 3 are a boron nitride BN spacer and a setter, respectively. Reference numeral 4 is a composite sintered body (Al _x Ca _y O _z ) composed of Al ₂ O ₃ and CaO, and 5 is an AlN laminated body which is a product to be fired. Further, 6 is AlN powder, and the firing atmosphere is under reduced pressure,
Alternatively, it is provided under atmospheric pressure in an atmosphere such as Ar or He. At this time, the filling degree of the AlN powder is about 20 to 40%. AlN powder 6
As shown in the figure, the product 5 is placed in a container made of the same material as the product to be baked without coming into contact with the product 5.

The composite sintered body (Al _x Ca _y O _z ) composed of Al ₂ O ₃ and CaO is Al ₂ O.
200 g of the mixed powder was weighed so that the molar ratio of ₃ and CaCO ₃ in terms of CaO was 2: 1 and mixed using a V-type mixer. The obtained mixed powder was made into a cylindrical green compact of about 20 g using a mold. Next, the green compact was fired at 1500 ° C. in the air to obtain a sintered body.

The sample set as shown in FIG. 1 was fired in a batch furnace. Maximum temperature is 1800 ℃, 1800 ℃ holding time is 9 hours, 18
The heating time to 00 ° C. was 2 hours. The atmosphere in the furnace is
Replace the gas sufficiently at room temperature and fill it with 1.1 atm of N ₂ gas,
During the firing, the N ₂ gas flow state was 10 / min. The target AlN substrate was obtained by this firing.

After cooling the obtained AlN substrate to room temperature, warpage and density and thermal conductivity were measured. Example 1
Are shown in Table 1.

As for the warp, as shown in FIGS. 2A and 2B, the warp hμm at a length of l mm was measured and shown as h / l.

Next, for comparison, under the same firing conditions as those of the example,
The same measurement as above was performed for the composite fired body (Al _x Ca _y O _z ) which was not fired at the same time. The results are shown in Comparative Example 1
Are shown in Table 2.

Under the firing conditions of Example 1, the maximum firing temperature was 19
The case where the temperature is 50 ° C is set as the second embodiment, and the maximum temperature is 1950 ° C.
Table 2 shows the respective results as Comparative Example 2 in which the composite fired body was not fired at the same time.

Similarly, under the firing conditions of Example 1 above, the maximum temperature of 1800
The results are shown in Example 3 when the pressure during firing at 0.5 ° C. is 0.5 atm (10 / min), and as Comparative Example 3 when the composite sintered body is not simultaneously fired at a pressure of 0.5 atm. Is shown in Table 3.

[Effects of the Invention] According to the present invention as described above, without applying a load using a BN setter, or embedding a body to be fired in an AlN powder, there is no warp, a dense and transparent property. It is possible to obtain an AlN sintered body having excellent heat conductivity and high thermal conductivity.

[Brief description of the drawings]

1A and 1B are a schematic vertical sectional view showing a set state of an article to be fired at the time of firing according to the present invention and a sectional view taken along line I-I of FIG. 1A. 1 ... Graphite container, 2 ... BN (boron nitride) spacer, 3 ... BN (hydrogen nitride) setter, 4 ... Composite sintered body, 5 ... Laminated body (baked product), 6 ... AlN Powder. 2A and 2B are schematic diagrams showing a method for measuring the warpage of a fired product (AlN substrate).

Claims (1)

(57) [Claims] 1. An aluminum nitride green sheet to which a Ca compound is added as a sintering aid is formed, the green sheet is punched into a predetermined shape, and the punched green sheets are laminated and pressed to form an aluminum nitride laminate. Then, in the method for firing an aluminum nitride substrate to obtain an aluminum nitride substrate obtained by firing the aluminum nitride laminate, when firing the aluminum nitride laminate to which a Ca compound is added as the sintering aid, Al ₂ O ₃ and CaO composite sintered body consisting of (CaxAl _y O _z: X is 1 to 12, y is 1 to 14, O is 1-33) sintering of the aluminum nitride substrate and firing under the same time normal pressure or reduced pressure Method.