JP2000264736A - Production of aluminum nitride green sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a obtain a green sheet which is free of micropores and with which a sintered compact having a high heat transfer property and high strength may be obtained by wet mixing aluminum nitride and a binder by using aluminous balls having a Vickers hardness of a specific value or above, then molding and drying the mixture. SOLUTION: The particle size of the aluminum nitride powder having small and uniform grain size is preferable. The molecular weight of an organic high- polymer material used as the binder is adequately 3000 to 1000000 and the binder is, for example, polyvinyl butyral. The compounding ratio is 4 to 30 pts.wt. per 100 pts.wt. aluminum nitride powder. The Vickers hardness of the balls for mixing is >=1100. The average particle size of the aluminum nitride particles after the mixing is 0.7 to 2.0 μm. The mixture contains 80 vol.% particles of <=3 μm. The ball diameter is adequately 5 to 30 mm. The amount. of the balls to be used is 1.5 to 6.2 times that of the aluminum nitride. The number of revolutions of a ball mill is 0.2 to 0.7 times the critical number of revolutions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum nitride green sheet suitable for producing a highly reliable and highly heat-conductive aluminum nitride sintered body having no micropores in the sintered body.

[0002]

2. Description of the Related Art Due to the recent increase in the degree of integration of LSIs, the amount of heat generated by IC chips has increased, and alumina used conventionally has insufficient thermal characteristics, and heat dissipation is reaching its limit.

On the other hand, aluminum nitride sintered bodies are:
It has high thermal conductivity and high insulation properties, and has been spotlighted as a very useful material as an electronic material such as a package material. In particular, for high power module substrates, aluminum nitride sintered body with high thermal conductivity has attracted attention instead of conventional alumina, and after joining a metal plate such as copper or aluminum plate to the surface of the sintered body, forming a circuit, It is being adopted for substrates on which semiconductor elements are mounted.

[0004] As a method of obtaining an aluminum nitride sintered body, a method of granulating aluminum nitride powder into granules, forming the pressed body by dry pressing to obtain a pressed body, and firing the green body by wet-forming the aluminum nitride powder. And baking it. For the production of the latter green sheet, a method is generally employed in which a surfactant, a binder, an organic solvent, and the like are wet-mixed with an aluminum nitride powder by a mixer such as a ball mill, and molded by a doctor blade method or the like.

However, when an aluminum nitride sintered body is manufactured using the above aluminum nitride green sheet, micropores are easily generated in the sintered body, so that the sintered body strength and dielectric breakdown voltage are low, It was difficult to obtain a highly reliable aluminum nitride sintered body.

As a countermeasure, Japanese Patent Application Laid-Open No. 7-97265 discloses a technology of a low void sintered body using zirconia balls, and Japanese Patent Application No. 7-167469 discloses an organic material occupation ratio in a void. And a green sheet technology in which the sheet density is in a specific range.

[0007]

However, in the above-mentioned method, ceramic balls such as ceramic balls, for example, are formed by contamination due to wear of the mixing balls used for wet mixing.
When alumina or silicon nitride balls are used, there is a problem that the thermal conductivity of the sintered body is reduced. When zirconia balls are used, the sintered body is blackened. Alternatively, when a metal ball coated with an organic resin, for example, a nylon resin is used, 20 μm is used.
There is a problem that there are many micropores smaller than m.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies with the aim of obtaining an aluminum nitride green sheet suitable for producing a highly reliable, highly thermally conductive aluminum nitride sintered body without micropores. Have been. as a result,
Wet-mixing using alumina balls of specific hardness excellent in abrasion resistance, molding, and using a green sheet obtained by drying, it was found that the above object was achieved, and the present invention was proposed. Reached.

That is, the present invention is a method for producing an aluminum nitride green sheet, which comprises wet-mixing aluminum nitride powder and a binder with alumina balls having a Vickers hardness of 1100 or more, forming and drying.

[0010]

DETAILED DESCRIPTION OF THE INVENTION As the aluminum nitride powder used in the present invention, known powders can be used without any limitation. Generally, in order to obtain an aluminum nitride sintered body having excellent thermal conductivity, it is preferable to use aluminum nitride powder having a small oxygen content and a small amount of cationic impurities. That is,
Aluminum nitride powder having an oxygen content of 1.5% by weight or less and a cationic impurity of 0.3% by weight or less is preferable, and an oxygen content of 0.4 to 1.3 is more preferable.
Aluminum nitride powder containing 0.2% by weight or less of cationic impurities is more preferable.

Note that aluminum nitride is a 1: 1 compound of aluminum and nitrogen, and all other substances are treated as impurities in the present invention. However, on the surface of the aluminum nitride powder, there is a portion where the Al—N bond is inevitably oxidized in the air and the Al—N bond is replaced by an Al—O bond. Not considered as ionic impurities. Therefore, aluminum existing other than the Al—N bond and the Al—O bond on the surface of the aluminum nitride powder is treated as a cationic impurity.

The particles of the aluminum nitride powder used in the present invention preferably have a small particle size and a uniform particle size. For example, the average particle size (in the present invention, the average particle size of the aggregated particles measured with a laser diffraction type particle size distribution analyzer) is 5 μm or less, and further 3 μm.
m or less.

As the binder used in the present invention, known binders generally used for molding ceramic powders can be used without any limitation. However, those having a decomposition temperature of 1400 ° C. or lower according to a thermogravimetric analysis method are preferable. More specifically, binders preferably used in the present invention include, for example, polyvinyl butyral, polymethyl methacrylate, polyethyl methacrylate, poly 2-ethylhexyl methacrylate, polybutyl methacrylate, polyacrylate, cellulose acetate butyrate, nitro Oxygen-containing organic polymers such as cellulose, methylcellulose, hydroxymethylcellulose, polyvinyl alcohol, polyoxyethylene oxide and polypropylene oxide; petroleum resins; polyethylene, polypropylene,
One or a mixture of two or more kinds of organic polymers such as hydrocarbon polymers such as polystyrene; polyvinyl chloride; wax and emulsions thereof. Among them,
It is particularly preferable to use the oxygen-containing organic polymer as a binder because it exhibits a strong bonding force based on excellent chemical affinity with the aluminum nitride powder.

Although the molecular weight of the organic polymer used as the binder is not particularly limited, it is generally 3,000 to 1,0.
00,000, preferably 5,000-300,00
It is preferred to use 0 because the green sheet is flexible and rich in toughness and can be easily handled in various processes.

The mixing ratio of the aluminum nitride powder and the binder depends on the type of the binder, the type of the organic solvent described later,
In addition, although it depends on applications such as the thickness and lamination of the green sheet, from the viewpoint of degreasing and productivity of the green sheet, generally, 4 to 30 parts by weight of a binder is added to 100 parts by weight of aluminum nitride powder, Preferably, it may be selected from the range of 5 to 20 parts by weight.

If the amount of binder is less than 4 parts by weight,
Since the sheet strength is reduced, cracks are generated in the molded body during sheet molding, and if it is more than 30 parts by weight, the degreasing property of the green sheet is reduced, and the physical properties of the sintered body obtained by firing this are reduced. It is not preferable because it decreases.

In the present invention, the method of mixing the aluminum nitride powder and the binder is as follows:
In consideration of obtaining a high thermal conductive aluminum nitride sintered body without micropores, mixing by a ball mill is necessary.

In the present invention, an important point is that the mixing balls used in the mixing by the ball mill are:
It is necessary that the alumina ball has a Vickers hardness of 1100 or more, and preferably 1200 or more.

Further, in consideration of the effect of the present invention, it is preferable that the alumina ball has the following properties.

The density of the alumina ball is 3.4 g.
/ Cm ³ or more, and the fracture toughness of the alumina ball is preferably 3.4 MPam ^1/2 or more.

Also, in the present invention, considering that a good green sheet is obtained and a high thermal conductive aluminum nitride sintered body without micropores is obtained, the average particle diameter of the aluminum nitride particles after mixing by the ball mill is 0.1. 7
It is preferable that particles having a size of from 2.0 μm to 3 μm are in a range of 80% by volume or more. That is, when the average particle diameter is smaller than 0.7 μm, the voids of the green sheet from which many fine particles are obtained become large, and the sinterability is poor, which is not preferable. On the other hand, when the average particle diameter is larger than 2.0 μm, the voids of the green sheet from which many coarse particles are obtained become large, and the sinterability is poor. Further, the average particle diameter of the mixed aluminum nitride particles is more preferably 0.75 to 1.7 μm.

On the other hand, when the particles having a size of 3 μm or more are smaller than 80% by volume, the ratio of the fine particles agglomerated around the coarse particles is small, the voids of the obtained green sheet become large, and the sinterability is poor. .

In the present invention, as a method for adjusting the average particle diameter of the aluminum nitride particles after mixing using the above-mentioned alumina balls to 0.7 to 2.0 μm and the particles of 3 μm or less to 80% by volume or more, May be adopted by a known method, but can be suitably achieved by the following method.

The diameter of the alumina ball in the present invention is preferably 5 to 30 mm in consideration of facilitating the control of the particle size of the aluminum nitride particles after mixing.
Further, it is preferably 8 to 25 mm.

The material of the mixer in the present invention may be any material having excellent abrasion resistance, and the above-mentioned abrasion-resistant alumina material or abrasion-resistant organic resin is suitably employed. Further, the size of the mixer is not particularly limited.

On the other hand, the total weight of the alumina balls charged into the mixer is preferably 1.5 to 6.2 times the weight of the aluminum nitride powder. If the total weight of the alumina balls is smaller than 1.5 times the weight of the aluminum nitride powder, the mixing becomes insufficient and cracks occur in the green sheet, which is not preferable. When the weight of the alumina ball is larger than 6.2 times the weight of the aluminum nitride powder,
It is not preferable because it becomes difficult to control the particle size of the aluminum nitride particles after mixing.

Further, it is more preferable to use the alumina balls having a weight of 2.0 to 5.3 times the weight of the aluminum nitride powder, because the particle size of the aluminum nitride particles after mixing can be easily controlled.

The rotation speed of the ball mill may be any condition that is generally employed.
The mill rotation speed is 0.2 to 0.7 times the critical rotation speed.

The mixing time in the ball mill is not particularly limited as long as it is a generally employed condition.
Preferably, it is longer than an hour.

In the present invention, a mixing method using a ball mill and a mixing method other than a ball mill may be combined.

The aluminum nitride green sheet according to the present invention has the following features as long as the effects of the present invention are not significantly impaired.
Known additives usually used, for example, a surfactant, a plasticizer, an organic solvent and the like may be added.

Known surfactants can be used without any limitation. Among them, nonionic surfactants are preferable, and specific examples thereof include carboxylated trioxyethylene tridecyl ether, diglycerin monooleate, diglycerin monostearate, carboxylated heptaoxyethylene tridecyl ether, Tetraglycerin monooleate, hexaglycerin monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, propylene glycol monostearate, glycerin monostearate, glycerin tristearate, glycerin monooleate, glycerin triolate, sorbitan Triolate, sorbitan monooleate and the like may be mentioned, and these may be used alone or in combination of two or more.

The surfactant is added in an amount of 0.01 to 100 parts by weight of the aluminum nitride powder.
10 parts by weight is suitable, and more preferably 0.02 to
4.0 parts by weight. When the amount of the surfactant is less than 0.01, the dispersion of the aluminum nitride particles is insufficient, and when the amount is more than 10 parts by weight, the strength of the green sheet is reduced and cracks occur in the sheet molded body. It is not preferable because it may occur.

Further, when the aluminum nitride green sheet of the present invention is processed into a specific shape, a plasticizer is used as needed for the purpose of imparting more flexibility to the green sheet.

As the plasticizer, known plasticizers used for molding general ceramic powders for the above purpose can be used without any particular limitation. Specific examples of plasticizers preferably used include polyethylene glycol and derivatives thereof; phthalic esters such as dimethyl phthalate, dibutyl phthalate, benzyl butyl phthalate and dioctyl phthalate; stearic esters such as butyl stearate; Tricresol phosphate; tri-N-butyl phosphate; glycerin and the like.

The amount of the plasticizer to be added depends on the properties of the aluminum nitride powder, the type of the binder, the type of the solvent and the amount used, and cannot be limited unconditionally. It may be appropriately selected and used from the range of 0.4 parts by weight or less, preferably 0.4 to 15 parts by weight.

Examples of the organic solvent include ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; alcohols such as ethanol, propanol and butanol; aromatic hydrocarbons such as benzene, toluene and xylene; ethyl acetate and acetic acid Esters such as butyl; and one or a mixture of two or more halogenated hydrocarbons such as trichloroethylene, tetrachloroethylene and bromochloromethane. The amount of the organic solvent is selected from the range of 20 to 200 parts by weight based on 100 parts by weight of the aluminum nitride powder.

Further, in addition to the above-mentioned additives, sintering aids known to be used for sintering aluminum nitride, for example, alkaline earth metal oxides such as calcium oxide and strontium oxide; yttrium oxide, Rare earth oxides such as lanthanum; composite oxides such as calcium aluminate and the like may be used in the range of 0.1 to 10% by weight based on the total amount with the aluminum nitride powder.

The order in which the above components are mixed is not particularly limited. However, in view of the effects of the present invention, the components are preferably mixed in the following order.

When a sintering aid is added among the above-described components, it is preferable to mix the aluminum nitride powder and the sintering aid in two portions in order to sufficiently disperse the sintering aid. That is, the first mixing, aluminum nitride powder, a sintering aid and, if necessary, a surfactant and a predetermined amount of a solvent are mixed by a ball mill, the second mixing with the first mixture,
A method in which a binder, and if necessary, a plasticizer and the remaining solvent are mixed by a ball mill is suitably employed.

The mixing conditions are not particularly limited.
The first and second mixing times are each preferably 10 hours or more. If the mixing time of the first and second times is shorter than 10 hours, the dispersion of the aluminum nitride powder and the binder becomes insufficient, and the resulting green sheet is undesirably cracked.

The method for producing the aluminum nitride green sheet of the present invention is not particularly limited, and a known method may be employed.

Usually, a viscous slurry generally called slurry obtained by mixing with the ball mill is
Filter with a filter if necessary, and then remove the bubbles with a device called a defoaming tank as necessary and remove the solvent if necessary to adjust the viscosity to a predetermined value. It is formed into a sheet using a forming machine.

Next, the sheet-like molded product is dried at a temperature from room temperature to the boiling point of the solvent to obtain an aluminum nitride green sheet.

In the present invention, the sheet density of the obtained aluminum nitride green sheet is preferably 2.0 to 2.8 g / cm ³ from the viewpoint of sinterability and degreasing.

The sheet density is determined by the method according to the above method.
It can be adjusted mainly by the amount of the solvent used for the first mixing. Here, the amount of the solvent is preferably selected from a range of 25 to 70 parts by weight, more preferably from a range of 28 to 60 parts by weight, based on 100 parts by weight of the aluminum nitride powder.

The aluminum nitride green sheet obtained by the above method is punched into a predetermined shape by using a mold to form an aluminum nitride sheet molded body.

The aluminum nitride green sheet thus obtained is degreased and fired by a known method. The above degreasing is generally performed in an atmosphere of air or nitrogen, and the degreasing temperature is set at 30 ° C. depending on the type of the binder and the atmosphere.
It is arbitrarily selected from the range of 0 to 1000 ° C. The aluminum nitride molded body after degreasing is generally used in a non-oxidizing atmosphere,
It is fired at any temperature in the range of 1700-1950 ° C. In this way, a highly thermally conductive aluminum nitride sintered body having no micropores in the sintered body can be obtained.

[0049]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

In the following Examples and Comparative Examples, various physical properties were measured by the following methods.

1) Average particle size "MICROTRAC-I" manufactured by LEED & NORTHRP
It was determined by the laser diffraction method using "I". The measurement was performed by dispersing the raw material aluminum nitride powder in water. Also, the aluminum nitride particles after wet mixing,
The measurement was performed by dispersing in ethanol.

2) Amount of Impurities Cation impurities are obtained by melting aluminum nitride powder with an alkali and neutralizing with an acid.
The solution was quantified by ICP emission spectroscopy using "0".

The amount of carbon impurities was determined by burning aluminum nitride powder in an oxygen stream and using “EMIA-
Using “110”, the amount was determined from the amount of generated CO and CO ₂ gas.

The amount of impurity oxygen was determined by using aluminum nitride powder produced by a high-temperature pyrolysis method in a graphite crucible using “EMGA-2800” manufactured by Horiba, Ltd.
It was determined from the amount of O gas.

3) Density of molded sheet The green density was determined from the size and weight of the molded sheet.

4) Density of Sintered Body The density was determined by Archimedes' method using "High-precision specific gravity meter DH" manufactured by Toyo Seiki.

5) Thermal Conductivity of Sintered Body “Thermal constant measuring device LF / TCM-FA” manufactured by Rigaku Corporation
8510B "using a two-dimensional method. Thickness correction was performed using a calibration curve.

6) Flexural strength of sintered body The three-point flexural strength was measured according to JIS R-1601.

7) Sintered body micropore density The sintered body whose surface was mirror-polished was
Photographic measurements were taken at 0x magnification. 10 to 2 per square cm
Micropores of 0 μm and micropores of 20 μm or more were counted and determined as a micropore density. The average value of the three samples was taken as the measured value.

Example 1 A Vickers hardness of 12 was placed in a nylon pot having an inner volume of 10 L.
7.2 kg of alumina balls with a ball diameter of 10 mm at 00
Then, the aluminum nitride powder shown in Table 1 was added to 2.
200 kg, yttrium oxide 0.110 kg, sorbitan triolate 0.044 kg as a surfactant, toluene 0.462 kg as a solvent, ethanol 0.27
After adding 0 kg and butanol 0.039 kg, and performing the first ball mill mixing at a mill rotation speed of 52 rpm (0.6 times the critical rotation speed) for 20 hours, 0.176 kg of polyvinyl butyral as a binder was added to the mixture. 0.077 kg of dibutyl phthalate as a plasticizer, 0.594 kg of toluene as a solvent, 0.347 kg of ethanol,
After adding 0.050 kg of butanol, the second ball mill mixing was performed at the same mill rotation speed of 52 rpm as in the first mixing.
After an hour, white mud was obtained. The obtained slurry was filtered through a sieve having an opening of 40 μm, and the particle size of the mixed aluminum nitride was measured by a particle size distribution measuring device.

The slurry obtained in this way is further
After removing the solvent and adjusting the viscosity to 10,000 to 20,000 cps, a sheet is formed by a doctor blade method,
The green sheet was dried at room temperature for 1 hour, at 60 ° C. for 2 hours, and at 100 ° C. for 1 hour to produce a green sheet having a width of 20 cm and a thickness of 0.75 mm, and the density of the formed sheet was measured.

Thereafter, the green sheet was punched out with a 34 mm square mold, baked in air at 600 ° C. for 5 hours, and then placed in a carbon crucible coated with boron nitride on the inner surface, and placed in a nitrogen atmosphere at 1800 ° C. For 5 hours. The color tone, sintered body density, thermal conductivity, bending strength, and micropore density of the obtained sintered body were measured. Table 2 shows the results.
It was shown to.

Example 2 An aluminum nitride green sheet was obtained and an aluminum nitride sintered body was obtained in the same manner as in Example 1 except that the weight of the alumina balls to be charged was 4.5 kg. The results are shown in Table 2.

Example 3 In Example 1, the diameter of the alumina ball to be charged was 20
An aluminum nitride green sheet was obtained in the same manner as in Example 1 except that the thickness was changed to mm, and an aluminum nitride sintered body was obtained. The results are shown in Table 2.

Example 4 An aluminum nitride green sheet was obtained and an aluminum nitride sintered body was obtained in the same manner as in Example 1 except that the one-stage mixing time was changed to 12 hours. The results are shown in Table 2.

Example 5 In Example 1, the solvent of the first mixture was toluene 0.
An aluminum nitride green sheet was obtained in the same manner as in Example 1 except that 594 kg, ethanol 0.347 kg, and butanol 0.050 kg were used, and an aluminum nitride sintered body was obtained. The results are shown in Table 2.

Comparative Example 1 An aluminum nitride green sheet was obtained and an aluminum nitride sintered body was obtained in the same manner as in Example 1 except that the ball material was changed to nylon. The obtained sintered body had many micropores. Other results are shown in Table 2.

Comparative Example 2 Example 1 except that the ball material was changed to zirconia.
In the same manner as in the above, an aluminum nitride green sheet was obtained, and an aluminum nitride sintered body was obtained. The color tone of the obtained sintered body was black-gray, and there was no translucency. Table 2 shows other results.
It was shown to.

Comparative Example 3 Example 1 except that the ball material was changed to silicon nitride
In the same manner as in the above, an aluminum nitride green sheet was obtained, and an aluminum nitride sintered body was obtained. The obtained sintered body had a low thermal conductivity. Other results are shown in Table 2.

Comparative Example 4 An aluminum nitride green sheet was obtained in the same manner as in Example 1 except that the ball material was changed to alumina having a Vickers hardness of 1000, and an aluminum nitride sintered body was obtained.
The obtained sintered body had many micropores.
Other results are shown in Table 2.

[0071]

[Table 1]

[0072]

[Table 2]

[0073]

When an aluminum nitride sintered body is manufactured using the aluminum nitride green sheet manufactured by the manufacturing method of the present invention, an aluminum nitride sintered body having no micropores in the sintered body is obtained. In addition, since it is possible to provide both high thermal conductivity and high strength, it is possible to manufacture industrial materials such as substrates having high thermal, electrical and mechanical reliability at low cost.

Further, it is preferably used as an electronic material such as a substrate co-fired with a high melting point metal such as tungsten, a metal bonded substrate, and a substrate having a metallized surface such as a fine pattern.

Therefore, the aluminum nitride sintered body obtained by using the aluminum nitride green sheet manufactured by the manufacturing method of the present invention is industrially extremely suitable for the above-mentioned electronic materials and the like which require high reliability. It becomes a useful material.

Claims (2)

[Claims] 1. A method for producing an aluminum nitride green sheet, comprising wet-mixing aluminum nitride powder and a binder using alumina balls having a Vickers hardness of 1100 or more, forming and drying. 2. An aluminum nitride sintered body obtained by firing the aluminum nitride green sheet obtained by the method according to claim 1.