JPH0672770A - Sheetlike aluminum nitride compact - Google Patents

Abstract

PURPOSE:To provide a sheetlike aluminum nitride compact hardly causing cracking even in the case of a large thickness and capable of compacting in one body with general-purpose AlN powder as starting material having wide particle size distribution. CONSTITUTION:This sheetlike aluminum nitride compact consists of aluminum nitride powder as starting material contg. >=70vol.% particles having <5mum particle diameter and >=2vol.% particles having >=5mum particle diameter and an org. binder having average mol.wt. added by >=1wt.% of the amt. of the aluminum nitride powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet-shaped molded product made of aluminum nitride, and particularly when forming a thick product,
The present invention relates to an aluminum nitride sheet-shaped compact capable of producing a high-quality aluminum nitride sintered body with little cracking and high yield.

[0002]

2. Description of the Related Art Ceramics prepared by molding raw material powders of nitrides, carbides, borides, suicides, etc., into predetermined shapes and then sintering, generally have hardness, insulation, wear resistance, heat resistance and corrosion resistance. Since various properties such as properties are superior to conventional metal materials, they have been put to practical use in a wide field in recent years.

For example, as an insulating substrate material for semiconductors and integrated circuits, conventionally, a sintered body made of alumina (Al ₂ O ₃ ) is used.
Was commonly used. However, in the substrate made of an alumina sintered body, the thermal conductivity is low and the thermal expansion coefficient is larger than that of silicon, so that the adhesion of the large silicon chip to the substrate is poor, and the silicon chip is easily peeled off. There was a drawback that the heat dissipation property was also low.

Therefore, an aluminum nitride (AlN) sintered body, which has remarkably high thermal conductivity and electrical insulation and has a thermal expansion coefficient similar to that of silicon, is regarded as a promising material for electronic circuit boards.

Conventionally, flat plate-shaped AlN used for substrates and the like
The sintered body is composed of fine AlN raw material powder, a sintering aid, a dispersant,
A binder, a plasticizer, and a solvent are added to prepare a uniform slurry, and the obtained slurry is molded into a predetermined sheet shape by using a roll molding method or a doctor blade method to obtain a sheet-shaped AlN molded body, Obtained sheet A
It is manufactured by heat-sintering a 1N molded body in a temperature range of 1600 to 2000 ° C.

By the way, since the AlN powder does not have a good sinterability, the finest possible raw material powder is used and
Yttrium oxide (Y ₂ O ₃ ) and calcium oxide (Ca
O), alkaline earths, metal oxides, etc. are added as sintering aids. As a result, an aluminum nitride sintered body that is relatively dense and has high strength under normal pressure can be obtained.

[0007]

However, if a fine AlN raw material powder having a uniform fineness distribution is used in order to improve the sinterability, it may be difficult to increase the density of the sheet-shaped compact. With such a low-density compact, the shrinkage rate during sintering becomes large, and it is difficult to obtain an AlN substrate sintered compact having high dimensional accuracy.

On the other hand, when an attempt is made to form a thick sheet-like compact having a thickness of 0.6 mm or more by a sheet forming method such as a doctor blade method using a general-purpose raw material powder having a wide particle size distribution, the raw material particles are Sedimentation and accumulation of fine particles are generated on the upper surface layer of the sheet molded product, and a coating film is formed on the upper surface layer part of the sheet molding. There is a problem that the density decreases.

In particular, the coating film formed on the surface layer of the upper surface of the sheet-shaped molded product impedes the drying of the entire molded product, causes a non-uniform drying rate in the thickness direction, and stress concentration during drying causes the surface layer to be concentrated on the surface layer. There is a problem that cracks are generated and the product yield is significantly reduced. This tendency becomes more remarkable as the thickness of the sheet-shaped compact increases, and it has been difficult to integrally form a sheet-shaped compact having a thickness of 0.6 mm or more with a high yield.

Therefore, the conventional copper plate direct bonding substrate (DBC)
In order to manufacture a sheet-shaped compact having a thickness of about 1 mm used for a substrate, etc., a sheet-shaped compact having a thickness of 0.5 mm is used.
A method of stacking one sheet on another was adopted. However, in a substrate manufacturing process involving a laminating step, problems such as delamination of each sheet-shaped molded body, inclusion of foreign matter, and increase in man-hours are likely to occur, and in particular, the laminating step is extremely difficult to automate, resulting in product yield and There is a problem that the reduction in manufacturing efficiency becomes remarkable.

The present invention has been made in order to solve the above-mentioned problems, and uses a general-purpose AlN raw material powder having a wide particle size distribution, and it is possible to perform integral molding with little cracking even if it is thick. It is an object of the present invention to provide a sheet-shaped molded product made of aluminum nitride that can be used.

[0012]

Means for Solving the Problems The inventors of the present invention have made earnest experiments to find out the cause of cracks in the case of forming a thick sheet-like molded product by using AlN raw material powder having a wide particle size distribution. For the first time, I obtained such knowledge. That is,
When fine particles having a particle size of 1.5 μm or less are selectively gathered on the upper surface layer of the sheet-shaped molded product, a film is easily formed, and this film hinders drying, resulting in many cracks and product yield. Lower. Then, when a linear organic polymer compound having a weight average molecular weight of 100,000 or more is added to the raw material powder as an organic binder, and the fine raw material powder is aggregated to form coarse secondary particles having a predetermined average particle diameter, A thick sheet-like molded product with few cracks was obtained.

Even when using an AlN raw material powder having a wide particle size distribution, by using the AlN raw material powder in which fine particles of a predetermined ratio or more and coarse particles of a predetermined ratio or more are mixed, sheet-shaped molding It has been found that the sinterability is improved as the body density is increased, and a plate-shaped sintered body with good dimensional accuracy can be obtained.

The present invention has been completed based on the above findings. That is, in the aluminum nitride sheet-shaped molded product according to the present invention, particles having a particle size of less than 5 μm account for 70% or more and less than 98% of the total volume ratio, and particles having a particle size of 5 μm or more account for 2% or more. It is characterized by comprising an aluminum nitride raw material powder of less than 30% and an organic binder having a weight average molecular weight of 100,000 or more added to the aluminum nitride raw material powder in a proportion of 1% by weight or more.

It is preferable that particles having a particle diameter of 1.5 μm or less occupy 20% or more of the entire aluminum nitride raw material powder by volume ratio.

Further, the density after drying is 1.7 to 2.
Set within the range of 1 g / cm ³ .

Further, it can be applied to a thick product having a thickness after drying of 0.6 mm or more.

Further, it is preferable to use a linear polymer compound as the organic binder.

Further, in an aluminum nitride sheet-shaped compact formed from secondary particles formed by adding an organic binder to the aluminum nitride raw powder to agglomerate the aluminum nitride raw powder, one of the surface portions of the sheet-shaped compact is The average particle diameter of the secondary particles is 3 μm or more, and the average particle diameter of the secondary particles on the other surface portion is not more than twice the average particle diameter of the secondary particles on the one surface portion.

The aluminum nitride sheet-shaped molded product according to the present invention is obtained by adding a predetermined amount of a high molecular weight organic binder to an AlN raw material powder having a wide particle size distribution in which fine particles and coarse particles are appropriately mixed. It consists of secondary particles formed by agglomerating raw material powder.

The mixing ratio of fine particles and coarse particles has a great influence on the density, sinterability of the molded body and the dimensional accuracy of the sintered product as the final product, and the volume ratio of fine particles having a particle diameter of less than 5 μm. If it is less than 70%, the proportion of fine particles agglomerated around the coarse particles is small, resulting in a molded article having large voids and low density and sinterability. On the other hand, if the proportion of coarse particles having a particle size of 5 μm or more is less than 2%, fine particles are likely to migrate to the upper surface portion of the molded product, and a dense coating film may be formed on the surface portion to easily cause cracking. .

On the other hand, among particles having a particle size of 5 μm or less, particularly fine particles having a particle size of 1.5 μm or less fill the voids formed between coarse particles and enhance the sinterability of the molded body. In order to function, 20% by volume or more of the entire raw material powder is contained. When the content is less than 20% by volume,
The molded body has many voids, and the strength and heat transfer characteristics of the AlN sintered body deteriorate.

The organic binder agglomerates fine raw material particles to form coarse secondary particles, which easily causes pores on the surface of the sheet-shaped molded product to prevent the formation of a coating film and cracks, and the raw material powders 1% by weight or more with respect to the AlN raw material powder in order to maintain a certain shape of the molded body by bonding with each other and to improve the handleability and the shape accuracy.

When the amount of the organic binder added is less than 1% by weight, the aggregating action and shape retention are not sufficiently exhibited, while when the amount added exceeds 25% by weight, degreasing after molding is insufficient. Or the degreasing time becomes long, and the sinterability and the thermal conductivity peculiar to AlN decrease. Therefore, the addition amount of the organic binder is set in the range of 1 to 25% by weight, preferably 5 to 15% by weight.

Specific examples of the organic binder include polyacrylic resin, polyvinyl butyral (PVB), polyvinyl alcohol (PVA), polyvinyl acetate (PVA).
There are organic polymer compounds such as c).

The magnitude of the weight average molecular weight of the organic binder has a great influence on the dispersibility of a slurry system using an organic solvent as a solvent and the cohesiveness of particles. That is, when the molecular weight is less than 100,000, the powder particles are less entangled with each other, and so-called steric hindrance is less formed.
The dispersibility of particles tends to decrease. On the other hand, the molecular weight is 300,000.
When an excessively large organic polymer binder is exceeded, the molecular ends are entangled with other particles, causing so-called cross-linking agglomeration, and the density of the sheet-shaped molded article tends to decrease, and the sinterability and Dimensional accuracy decreases. Therefore, the weight average molecular weight of the organic binder is 100,000 to 3
It is set in the range of 00000, more preferably 15
It is in the range of 0000 to 250,000. In particular, it is desirable to use a linear polymer compound as an organic binder in order to express the cohesiveness of particles with a smaller addition amount.

The above-mentioned aluminum nitride sheet-like molded product was obtained by adding a proper amount of a solvent, a dispersant, an organic binder and a plasticizer to the prepared raw material powder and mixing them by a ball mill to prepare a uniform slurry. After molding the slurry to a predetermined thickness using the roll molding method or doctor blade method,
It is manufactured by subjecting the obtained molded body to a drying treatment by infrared heating or air drying.

In the above manufacturing process, particularly by adding a linear organic polymer compound having a weight average molecular weight of 100,000 or more as a binder, fine AlN particles are aggregated to have an average particle diameter of several μm to several tens of μm. Coarse secondary particles are formed, and these coarse secondary particles are deposited on the front surface portion, the central portion, and the rear surface portion in the thickness direction of the sheet-shaped molded body, respectively. At this time, the average particle diameter of the secondary particles on one surface portion (upper surface side) of the sheet-shaped molded product is 3 μm or more, and the average particle diameter of the secondary particles on the surface portion (lower surface side) of the other method is It is set to not more than twice the average particle diameter on the upper surface side.

As described above, since the surface portion, the central portion and the back surface portion of the sheet-shaped molded product are formed by the coarse secondary particles as described above, pores are easily generated on the surface of the sheet-shaped molded product and the sheet-shaped molded product is dense. It is possible to prevent the formation of various coatings. Therefore, cracks are less likely to occur in the compact, and high-quality sintered compacts can be produced with high yield.

Since the entire sheet-shaped compact is formed of coarse secondary particles, the density of the compact after drying is 1.
It is about 7 to 2.1 g / cm ^3, which tends to be slightly lower than the density (2.0 to 2.3 g / cm ³ ) of the conventional sheet-shaped molded product. However, even with the above-described low-density molded body, it is possible to secure the same sintered density as that of the conventional one by firing at a sintering temperature which is higher by about 10 ° C. than the conventional one.

Since the entire sheet-shaped compact is made up of the coarse secondary particles as described above, even when a thick compact having a thickness of 0.6 mm or more is integrally formed, the surface portion is A dense film is not formed on the
The product yield of the plate-shaped sintered body can be significantly increased.

[0032]

According to the aluminum nitride sheet-shaped molded product having the above-mentioned structure, the entire molded product is composed of coarse secondary particles obtained by adding an organic binder having a weight average molecular weight of 100,000 or more to agglomerate fine AlN raw material particles. As a result, the pores are likely to be formed on the surface of the sheet-shaped molded product, and a dense coating as in the conventional case is rarely formed. Therefore, even if it is a thick molded product, a sheet-shaped molded product with less cracking can be obtained,
High-quality plate-shaped AlN sintered bodies can be manufactured with high yield.

[0033]

EXAMPLES The present invention will now be specifically described based on the following examples.

Examples 1 to 5 Centrifugal sedimentation type automatic particle size distribution analyzer (CAPA-500,
5 μm as shown in the left column of Table 1 using HORIBA, Ltd.)
AlN powder having a particle size of less than 70-90 vol% and 5μ
Triene and ethanol as a solvent were added at a ratio of 7: 3 (volume ratio) to an AlN raw powder consisting of 10 to 30 vol% of AlN powder having a particle size of m or more, and a surfactant (PE-220A).・ 0.5 from Toho Chemical Co., Ltd.
wt% was added, and the mixture was rotationally crushed for 3 hours at 60 rpm with a pot roller using Al ₂ O ₃ balls as a crushing medium.

Next, as shown in the middle column of Table 1, PVB or PVA having a weight average molecular weight of 180 to 210,000 as an organic binder is added to each raw material mixture at a ratio of 10 to 15% by weight, and a plasticizer. Dibutyl phthalate (D
BP) was added in a proportion of 6% by weight. Then, each raw material mixture is rotatively mixed for 24 hours by the pot roller (rotation speed: 60 rpm) to sufficiently mix and dissolve the organic binder, and
Different types of slurries were prepared. Each slurry was defoamed with a vacuum defoaming device and adjusted to have a viscosity of 30 Pa · s.

Next, using each slurry, the gap of the dritter blade was set so that the thickness of the molded body after drying was 1 mm, and the defoamed slurry was extruded from the gap between the conveyor belt and the doctor blade. Then, it was dried to produce a sheet-shaped AlN molded body having a thickness of 1 mm according to Examples 1 to 5.

The temperature of the low temperature part of the drying chamber is 70 ° C.
The temperature of the high temperature part was 120 ° C., and the molding speed (belt speed) was 6 cm / min. Also obtained sheet-like AlN
The molded body was punched into an area of 7.14 cm ² , the density of each punched sample was measured, and the cut samples were cut at intervals of 30 cm, and the thickness was measured with a micrometer at three points in the widthwise center, left end and right end. The measurement was performed, and the rate of occurrence of defects such as cracks was calculated for each sample lot. Further, the texture and microstructure of the surface and cross section of each thick molded article were observed with a scanning electron microscope (SEM), and the average particle diameter of secondary particles was measured for the upper surface and lower surface of each sample.

Comparative Examples 1 to 3 On the other hand, as Comparative Example 1, except that polyvinyl butyral having a weight average molecular weight of 50,000 was used, the same treatments as those in Examples were carried out to prepare a large number of sheet-shaped AlN compacts having the same size. Each property of the molded body was measured in the same manner.

As Comparative Example 2, Comparative Example 1 was used except that the thickness of the dried molded body was set to be 0.5 mm.
Using the same raw material as above, raw materials were mixed and doctor blade molding was carried out to prepare a large number of thin sheet-shaped AlN molded bodies, and the respective characteristics were measured in the same manner.

Further, as Comparative Example 3, the treatment was performed under the same conditions as Comparative Example 1 except that the proportion of fine particles having a particle size of less than 5 μm was set to 65 vol% and the proportion of coarse particles of 5 μm or more was set to 35 vol%. A large number of sheet-shaped molded articles made of AlN were prepared, and each property was measured in the same manner.

The measurement results in Examples and Comparative Examples are summarized in Table 1 below.

[0042]

[Table 1]

As is clear from the results shown in Table 1, an organic binder having a weight average molecular weight of 100,000 or more was added to the AlN raw material powder in which fine AlN particles and coarse AlN particles were mixed to aggregate the raw material particles. In the sheet-shaped molded products according to Examples 1 to 5, although the molded product density is slightly lower than that of the conventional example, the occurrence of defects such as cracks during molding is small, and a thick sheet-shaped molded product has a high yield. Could be integrally molded with. Moreover, the peelability from the carrier film was good.

On the other hand, as shown in Comparative Example 1, in the case of the conventional sheet-like molded article using the low molecular weight organic binder, the raw material particles are less likely to aggregate and the difference in particle diameter between the upper surface portion and the lower surface portion of the molded article is small. 2 times or more, and in particular, a dense coating film is formed on the upper surface portion and the drying operation is hindered, so that the occurrence rate of defects such as cracks becomes high.

Therefore, the thickness of the sheet-shaped molded body is 0.5 mm.
When it was reduced to the following, as apparent from the results of Comparative Example 2, the occurrence of cracks sharply decreased. Therefore, it has been confirmed that the limit value of the thickness is 0.5 mm when a sound sheet-like molded product is produced with a high yield by the conventional method.

In the case of a sheet-shaped compact having a relatively large amount of coarse particles contained in the AlN raw material powder as in Comparative Example 3, the compact density is slightly lowered and fine particles are formed on the surface (upper surface side). It was easy to migrate and form a film, and cracks were generated relatively frequently.

Next, the particle size distribution of the AlN raw material powder used in Example 1 and the particle size distribution of the secondary particles in the slurry prepared by adding the organic binder to the AlN raw material powder are shown in FIG. As is clear from the results shown in FIG. 1, AlN having a grain size of 7.5 μm or less is all used in the raw material powder stage.
When the high molecular weight organic binder was added, the fine particles aggregated with each other, but the ratio of coarse secondary aggregated particles of about 20 to 15 μm increased, and the particle size distribution widened and particles less than 5 μm decreased. You can see that

Further, the scanning electron microscope (SE) of the surface and the surface layer section of the sheet-shaped AlN molded body according to Example 1 was used.
M) Photos are shown in FIGS. 2 and 3, respectively. That is, in the molded body of Example 1, as is clear from FIG. 2, it was confirmed that the surface of the molded body had relatively large pores (dark areas), and densification by fine particles did not proceed. did it. Further, as is clear from FIG. 3, the surface layer portion of the molded body also agglomerates and densification is avoided. It is considered that the stress concentration during drying is alleviated due to the progress of the agglomeration, and the occurrence of cracks during molding is eliminated.

On the other hand, scanning electron micrographs of the cross section of the surface and the surface layer portion (upper surface side) of the sheet-shaped molded product according to Comparative Example 1 are shown in FIGS. 4 and 5, respectively. That is, in the molded body of Comparative Example 1, the surface is densified as is clear from FIG. 4, and the surface layer cross section is densely formed as is clear from FIG. 5, both of which are the primary powders. It was clear that the entire compact was formed in a state close to the particles.

The sheet-shaped AlN compacts according to the above-mentioned Examples and Comparative Examples were degreased in air and then calcined at a temperature in the range of 1750 to 1770 ° C. for 2 hours, and the density of the resulting sintered body was measured by Archimedes. It was measured by the method. There was no particular problem regarding degreasing property in Examples and Comparative Examples, and the degreased body was not damaged by air degreasing.

In the case of the molded body of the embodiment, the density of the molded body is slightly lower than that of the conventional molded body, but by sintering at a temperature 10 ° C. higher than the conventional sintering temperature of 1750 ° C. The sinterability of the molded body sample was good, and the sintered body density was 3.31 to 3.33 g / cm ^3, which was about the same level as the conventional one.

[0052]

As described above, the aluminum nitride sheet-shaped molded product according to the present invention is a coarse secondary particle obtained by aggregating fine AlN raw material particles by adding an organic binder having a weight average molecular weight of 100,000 or more. Since the entire molded body is constituted by, pores are easily generated on the surface of the sheet-shaped molded body, and a dense coating as in the conventional case is rarely formed. Therefore, a sheet-shaped molded body with less cracking can be obtained even with a thick molded body, and a high-quality plate-shaped AlN sintered body can be manufactured with a high yield.

[Brief description of drawings]

FIG. 1 is a graph showing a cumulative particle size distribution of an AlN raw material powder used in Example 1 and a cumulative particle size distribution of secondary particles in a slurry.

2 is an electron micrograph showing the particle structure on the surface of the sheet-shaped molded product according to Example 1. FIG.

FIG. 3 is an electron micrograph showing the particle structure of the surface layer section of the sheet-shaped molded product according to Example 1.

FIG. 4 is an electron micrograph showing a particle structure on the surface of a sheet-shaped molded body according to Comparative Example 2.

5 is an electron micrograph showing a particle structure of a cross section of a surface layer portion of a sheet-shaped molded product according to Comparative Example 2. FIG.

Claims (6)

[Claims] 1. An aluminum nitride raw material powder having 70% or more by volume of particles having a particle diameter of less than 5 μm and 2% or more of particles having a particle diameter of 5 μm or more, and the aluminum nitride raw material powder. A sheet-shaped molded product made of aluminum nitride, which is composed of an organic binder having a weight average molecular weight of 100,000 or more added in a proportion of 1% by weight or more. 2. A sheet-shaped molded article made of aluminum nitride according to claim 1, wherein particles having a particle diameter of 1.5 μm or less account for 20% or more of the entire aluminum nitride raw material powder in volume ratio. 3. The density after drying is 1.7 to 2.1 g.
The sheet-shaped molded product made of aluminum nitride according to claim 1, wherein the molded product is in the range of / cm ³ . 4. The aluminum nitride sheet-shaped molded product according to claim 1, which has a thickness after drying of 0.6 mm or more. 5. The aluminum nitride sheet-shaped molded product according to claim 1, wherein the organic binder is a linear polymer compound. 6. A sheet-shaped molded article made of aluminum nitride, which comprises secondary particles formed by adding an organic binder to the aluminum nitride raw material powder to agglomerate the aluminum nitride raw material powder. Nitriding, characterized in that the average particle size of the secondary particles is 3 μm or more, and the average particle size of the secondary particles on the other surface part is not more than twice the average particle size of the secondary particles on the one surface part. Sheet-shaped molded product made of aluminum.