JPH0774105B2 - Manufacturing method of aluminum nitride-based green sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an aluminum nitride green sheet for obtaining a highly heat-conductive, high-density aluminum nitride sheet-like sintered body.

[Background technology]

With the development of LSIs in recent years, a substrate material having high thermal conductivity is required for mounting high heat generation type semiconductors such as highly integrated circuits, power transistors, and laser diodes.

As such a ceramic having high thermal conductivity, an aluminum nitride substrate material has been attracting attention. Among them, in the case of forming a conductor pattern such as a thick film circuit on the surface of such a substrate by a printing technique, screen printing is performed on the surface of the green sheet, the printed sheet is block-formed by punching and laminated and then fired. The molding and firing methods such as are inexpensive and suitable for mass production, and therefore a manufacturing method for obtaining a good green sheet is being studied.

[Prior art]

Recently, a method for producing an aluminum nitride green sheet using an aluminum nitride raw material powder by an oxide reduction method has been proposed. (For example, JP-A-60-171270, JP-A-60-180954 and JP-A-60-180964) [Problems to be solved by the invention] However, the oxides currently obtained The aluminum nitride powder obtained by the reduction method (1) has a uniform particle shape and a substantially spherical shape as shown in the electron micrograph of FIG.
When the particle size distribution of such powder is examined, the maximum particle size is up to about 5 μm as shown in FIG. 4, the particle size of 3 μm or more is about 10% by volume or less, and the particle size of less than 3 μm is about 90% by volume or more. Is large. Since the aluminum nitride powder having such a particle size distribution has a good filling property of particles in the green sheet compact, that is, the particles are easily clogged with each other, the solvent between these particles is easily formed in the drying step during the production of the green sheet. It does not volatilize and the decomposing of the thermally decomposed binder is difficult even during debinding. Therefore, when creating a green sheet by the doctor blade method, cracks are likely to occur, and even if a product with few cracks is obtained, the crease resistance is poor, and therefore cracks tend to occur even after binder removal. .

[Means for solving problems]

As a result of earnest research for solving the above-mentioned drawbacks, the present inventor obtained a green sheet molded product having a good filling property by using aluminum nitride powder having a relatively large number of particles having a particle size of 3 μm or more as a starting material. I found out that.

In the present invention, the particles of the aluminum nitride powder have good filling properties with each other, so that cracks are less likely to occur during the production of the green sheet, and they are excellent in bending resistance, and therefore cracking is less likely to occur even after binder removal. An excellent method of making an aluminum nitride based green sheet is provided.

According to the present invention, Y ₂ O ₃ is added as a sintering aid to an aluminum nitride raw material powder having a particle size distribution of 22 to 45% by volume for a particle size of 3 μm or more and 55 to 78% by volume for a particle size of less than 3 μm. Then, after mixing and pulverizing, a slurry obtained by mixing an appropriate organic binder is formed into a tape, and a method for producing an aluminum nitride green sheet is provided.

That is, as a means for obtaining a good green sheet, it is essential to use the aluminum nitride raw material powder having an appropriate particle packing property. As the aluminum nitride raw material powder having such a particle packing property, one having the above particle size distribution is most suitable. Many of the commercially available raw materials having such a particle size distribution can be obtained by the direct nitriding method of metallic aluminum. Therefore, an electron micrograph of an aluminum nitride raw material powder obtained by the direct nitriding method of commercially available metallic aluminum is shown in FIG. Unlike the raw material powder shown in FIG. 3, such a powder contains an aggregate of primary particles of irregular polygonal shape (large particle size) and non-aggregated particles (small particle size). Examining the particle size distribution of this powder, as shown in FIG. 2, the maximum particle size is about 7 to 9 μm, the particle size of 3 μm or more is about 22 to 45% by volume, and the particle size of less than 3 μm is about 55 to 78% by volume. is there. Compared to the raw material powder obtained by the oxide reduction method shown in FIG. 3, the maximum particle size is large and the proportion of particles having a particle size of 3 μm or more is relatively large.

When a suitable sintering aid is added to such an aluminum nitride raw material powder and mixed and pulverized, an organic binder is added and mixed, and the resulting slurry is tape-formed, the filling property of the particles is maintained in an appropriate state. The solvent can be easily volatilized between the aluminum nitride particles in the drying step during the production of the green sheet, and the thermally decomposed binder can be easily degassed during debinding.

Therefore, when producing the green sheet, the number of cracks is small, the folding resistance is good, and the cracks that easily occur during binder removal can be suppressed.

Less than 22% by volume for particle size 3 μm or more and 78 for particle size less than 3 μm
When the content exceeds the volume%, the raw material becomes closer to the raw material shown in FIGS. 3 and 4 and the packing property of the particles becomes too good, cracks are likely to occur, and the bending resistance is poor.

If the particle size of 3 μm or more is more than 45% by volume and the particle size of less than 3 μm is less than 55% by volume, on the contrary, the filling property of the particles is deteriorated, cracks are likely to occur, and the folding resistance is inferior.

Preferably, the particle size of 3 μm or more is 23 to 38% by volume, and the particle size is 3 μm.
Less than 62-77% by volume.

More preferably, the particle size of 1.5 μm or less is 30 to 54% by volume, and the particle size of 2 μm or less (including the particle size of 1.5 μm or less) is 40 to 6
6% by volume, particle size 4μm or less (including particle size 3μm or less) is 6
4-86% by volume, particle size 5 μm or less (including particle size 4 μm or less) 64-86% by volume, particle size 6 μm or less (including particle size 5 μm or less) 75-98% by volume, particle size exceeding 6 μm Is 2
It is desired to be -24% by volume.

Further, as the sintering aid, Group IIa group, IIIa group, I
Va group, IIIb group, simple substance of IVb group element, compounds such as oxides, carbides, nitrides, borides are used, and among them, Y ₂ O ₃ or CaO is particularly preferable, but in the present invention, high thermal conductivity is obtained. In view of the above, Y ₂ O ₃ is contained as an essential component.

Further, organic binders that can be used in the present invention include polyvinyl butyral (PVB), polyisobutyl methacrylate (PIBMA), polybutyl methacrylate (PBM).
A), butyral type or acrylic type such as methyl methacrylate (MMA) and ethyl acrylate (EA) and copolymers thereof are used.

[Examples 1 to 9] Yttria (Y ₂ O ₃ ) as a sintering aid and a binder to a raw material powder of aluminum nitride obtained by a direct nitriding method of aluminum metal having a particle size distribution shown in FIGS. 2A and 2B. Polyvinyl butyral (PVB), polyisobutyl methacrylate (PIBMA), polybutyl methacrylate (PBMA) and copolymer of methyl methacrylate (MMA) and ethyl acrylate (EA) were added at the ratio shown in Table 1. Then, using toluene as a solvent, these were mixed in a ball mill for 17 hours to prepare a slurry having a predetermined viscosity. These slurries were made into green sheets by the doctor blade method. The tape molding state of the obtained green sheet (crack and wrinkle generation state), tape molding thickness, green density, tape formation state after debinding (crack generation state), crease resistance and raw density after debinding The evaluation was shown in Table 1.

The binder removal rate for Examples 1 to 5 was 50 in the atmosphere.
° C. / time holding 600 ° C. × 1 hour, for Example 6-9 was carried out by holding 1000 ° C. × 1 hour with N ₂ NakaNoboru raising rate of 50 ° C. / hour. The bending resistance was evaluated by pressing the obtained green sheet against a plate having a side with a semicircular cross section with a diameter of 3 mm and bending it to evaluate the occurrence of cracks.

[Comparative Examples 1 to 4] Yttria (Y ₂ O ₃ ) as a sintering aid and polyvinyl as a binder were added to aluminum nitride raw material powders obtained by the reduction method of aluminum oxide having a particle size distribution shown in FIGS. 4C and 4D. Butyral (PVB), Polyisobutylmethacrylate (PIBMA), Polybutylmethacrylate (PBM)
A) and were added at a ratio shown in Table 1, and toluene was used as a solvent and mixed in a ball mill for 17 hours to prepare a slurry having a predetermined viscosity. These slurries were made into green sheets by the doctor blade method. The tape molding state of the obtained green sheet (crack and wrinkle generation state), tape molding thickness, green density, tape molding state after debinding (crack generation state), fold resistance and raw density after debinding Evaluation was carried out in the same manner as in the above-mentioned examples.

The binder was held in the atmosphere at a temperature rising rate of 50 ° C / hour for 600 ° C x 1 hour.

As understood from the above Examples 1 to 9 and Comparative Examples 1 to 4, the particle size of 3 μm or more is 22 to 45% by volume and the particle size of less than 3 μm is 55.
In Examples 1 to 9 of the present invention using the aluminum nitride raw material powder having a particle size distribution of ˜78% by volume, the green sheet has a green density of about 2.08 to 2.20 g / cm ³ The green sheet has no or little cracking in the tape molding state,
In addition, no cracks were observed in the tape molding state after the binder removal and the bending resistance evaluation, which is good. Furthermore, the green density after binder removal is appropriate at about 1.78 to 1.87 g / cm ³ , and good green sheets are obtained.

On the other hand, Comparative Examples 1 to 4 using the aluminum nitride raw material powder having a particle size distribution of 3 μm or more and about 10% by volume or less and less than 3 μm and about 90% or more by volume produce green sheets. The density is 2.29 to 2.34 g / cm ^3, which is too close to the closest packing property as compared with those of Examples 1 to 9 of the present invention, and the crack generation rate is high in the tape molding state. In addition, cracks are more likely to occur in the fold resistance evaluation, and the green density after binder removal shows a high value of 1.97 to 2.01 as compared with the examples of the present invention, and cracks are likely to occur.

[Advantages of the Invention] As described above, in the present invention, the particle size of 3 μm or more is 22 to 45 μm.
Since the aluminum nitride raw material powder having a particle size distribution of 55 to 78 volume% with a particle size of less than 3 μm in volume% is tape-formed, it is necessary to keep the filling property of the particles in the formed tape in an appropriate state. In addition, cracks and wrinkles are less likely to occur during tape molding, folding resistance is good, and cracks that tend to occur after binder removal can be suppressed, and a good green sheet can be provided.

[Brief description of drawings]

FIG. 1 shows a typical aluminum nitride raw material powder particle structure (a particle form in which primary particles and secondary particles are mixed) obtained by a direct nitriding method of metallic aluminum used in Examples of the present invention. Electron micrograph, FIG. 2 is a particle size integral distribution chart of the aluminum nitride raw material powder of the present invention (Horiba Seisakusho)
CAPA500-by precipitation method), FIG. 3 is a raw material powder of a comparative example, and a typical aluminum nitride raw material powder particle structure (primary particles and secondary particles are obtained by the oxide reduction method currently provided). Electron micrograph of mixed particle morphology), and FIG. 4 is a particle size integral distribution diagram (based on CAPA500-precipitation method of Horiba, Ltd.) of the aluminum nitride raw material powder of the comparative example.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area C04B 35/00 G

Claims (1)

[Claims] 1. A particle size of 3 μm or more is 22 to 45% by volume, and a particle size of 3
After less than μm is added Y ₂ O ₃ as a sintering aid to an aluminum nitride raw material powder having a particle size distribution of 55 to 78 vol% mixed and ground, to tape casting a slurry obtained by mixing an organic binder A method for producing an aluminum nitride-based green sheet characterized by: