JPH0920564A - Aluminum nitride green sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sintered aluminum nitride(AlN) having low warpage and free from micropores in the sintered material by adjusting the sheet density (d1 ) of an AlN green sheet and the ratio (R) of organic material in the void to respective specific levels. SOLUTION: This AlN green sheet consists of an inorganic component composed mainly of AlN and an organic component composed mainly of a binder. The value R calculated by the formula, R=1- (1-d1 /d2 )/(1-d3 /d4 )} is 0.3-0.75 and the sheet density d is 2-2.8g/cm<3> . In the formula, d1 is sheet density calculated from the measured weight and volume of the green sheet, d2 is sheet density calculated from the real specific gravities of the organic component and the inorganic component, d3 is sheet density calculated from the measured values of the weight and volume of the inorganic component and d4 is sheet density calculated from the real specific gravity of the inorganic component. Preferably, the impurity of the AlN powder has an oxygen content of <=1.5wt.% and a cationic impurity content of <=0.3wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride green sheet suitable for producing an aluminum nitride sintered body having a small warpage and no micropores in the sintered body.

[0002]

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

On the other hand, aluminum nitride powder has a high thermal conductivity and a high insulating property, and is in the spotlight as a raw material of an aluminum nitride sintered body which is extremely useful as an electronic material such as a package material. As a method for obtaining an aluminum nitride sintered body, after granulating aluminum nitride powder into granules, a press molded body is obtained by molding by dry pressing, and a method for firing or wet molding aluminum nitride powder to obtain a green sheet, There is a method of firing this. For the production of the green sheet in the latter case, a method of mixing a surface active agent, a binder, an organic solvent and the like with aluminum nitride powder and molding by a doctor blade method or the like is generally adopted.

However, when an aluminum nitride sintered body is manufactured by using the above-mentioned aluminum nitride green sheet, it is difficult to obtain an aluminum nitride sintered body having a small warp and no micropores in the sintered body. there were.

[0005]

[Means for Solving the Problems] The present inventors have conducted extensive studies to solve the above problems. As a result, in the aluminum nitride green sheet, the ratio of the organic component having the binder as the main component occupies the void formed by the inorganic component having aluminum nitride as the main component, that is, the aluminum nitride green sheet of the above formula. It was found that the occupancy ratio R of organic matter in the voids affects the residual form of carbon in the aluminum nitride compact after degreasing, which in turn leads to warpage of the aluminum nitride sintered body obtained and generation of micropores.

As a result of further research, an aluminum nitride green sheet having the sheet density d _{1 of} the aluminum nitride green sheet and the organic substance occupancy R in the voids of the aluminum nitride green sheet adjusted to a specific range has been obtained. The inventors have found that the above can be achieved and have proposed the present invention.

That is, the present invention relates to an aluminum nitride green sheet comprising an inorganic component containing aluminum nitride as a main component and an organic component containing a binder as a main component, and the measured values of the weight and volume of the green sheet are used. The calculated sheet density is d ₁ , and the sheet density obtained by calculating from the true specific gravity of the organic component and the inorganic component forming the green sheet is d ₁ .
₂ , when the sheet density calculated from the measured values of the weight and volume of the inorganic components of the green sheet is d ₃ , and the sheet density calculated from the true specific gravity of the inorganic components constituting the green sheet is d _4. , The following formula R = 1-{(1-d ₁ / d ₂ ) / (1-d ₃ / d ₄ )}, the organic matter occupancy (R) in the void is 0.3 to 0.
The aluminum nitride green sheet has a weight ratio of 75 and a d _{1 in} the range of 2 to 2.8 g / cm ³ .

The sheet density d ₁ of the aluminum nitride green sheet of the present invention is a density obtained by measuring the size and weight of a sheet molded product punched from the green sheet into a predetermined shape. The sheet density d ₂ is a density calculated from the true specific gravities of all the raw materials forming the aluminum nitride green sheet excluding the organic solvent, assuming that no pores are contained. In addition, the sheet density d ₃ is determined by measuring the size and weight (inorganic content) after removing the organic component by firing the above-mentioned sheet molded body under conditions where the sheet molded body does not substantially expand or contract, that is, at 600 ° C. for 5 hours. It is the density obtained by measuring the weight of the components). The sheet density d ₄ is a density obtained by calculation from the true specific gravity of the inorganic component forming the aluminum nitride green sheet, assuming that no pores are contained.

The inorganic component constituting the aluminum nitride green sheet of the present invention may be one having aluminum nitride as a main component. Generally, the inorganic component is aluminum nitride alone, or aluminum nitride and a sintering aid 0.1.
~ 10% by weight. Alumina may be added in a proportion of 5% by weight or less, if necessary.

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 that the oxygen content and the amount of cationic impurities be small. That is, when AlN has an aluminum nitride composition, the oxygen content as impurities is 1.5 wt% or less, and the cation impurities are
Aluminum nitride powder with 0.3 wt% or less is preferred. Furthermore, an aluminum nitride powder having an oxygen content of 0.4 to 1.3% by weight and a cation impurity of 0.2% by weight or less is more preferable. The aluminum nitride in the present invention is a 1: 1 compound of aluminum and nitrogen, and all other compounds are treated as impurities. However, the surface of the aluminum nitride powder is inevitably oxidized in air, and Al-
The N bond is replaced with an Al-O bond, but this bond A
l is not considered a cationic impurity.

Accordingly, metallic aluminum having no Al-N or Al-O bond is a cation impurity.

The particles of the aluminum nitride powder used in the present invention are preferably those having a small particle size. For example, the average particle size (centrifugal particle size distribution measuring device, for example, the average particle size of the agglomerated particles measured by CAPA500 manufactured by Horiba Ltd.) is 5 μm or less, and further 3 μm.
It is preferably m or less.

As a sintering aid which is one of the inorganic components other than the above-mentioned aluminum nitride powder, known sintering aids, for example, alkaline earth metal oxides such as calcium oxide and strontium oxide; yttrium oxide, and oxidation Rare earth oxides such as lanthanum; complex oxides such as calcium aluminate are generally used.

As the organic component constituting the aluminum nitride green sheet of the present invention, a surface active agent, a binder and a plasticizer are usually used.

When producing a green sheet, a surfactant is generally used in order to enhance the dispersibility of sludge. As the surface-active agent, known ones are employed without any limitation, and particularly, those having a hydrophilic-lipophilic balance (hereinafter, abbreviated as HLB) of 4.5 to 18, and more preferably 6.0 to 10.0 are nitrided. It is preferably used because the molding density of the aluminum compact increases. Note that HLB in the present invention is a value calculated by the Davis formula.

Specific examples of the surface active agent that can be preferably used in the present invention include carboxylated trioxyethylene tridecyl ether, diglycerin monooleate, diglycerin monostearate, carboxylated heptaoxyethylene tridecyl ether, Examples thereof include tetraglycerin monooleate, hexaglycerin monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate and the like. The surfactant in the present invention may be used as a mixture of two or more kinds, and the HLB at that time can be calculated by the arithmetic mean of the HLB of each surfactant.

As the binder that can be used in the present invention, known binders generally used for molding ceramic powder can be used without any limitation. For example, polyvinyl butyral, polymethylmethacrylate, polyethylmethacrylate, poly-2-ethylhexylmethacrylate, polybutylmethacrylate, polyacrylate, cellulose acetate butyrate, nitrocellulose, methylcellulose, hydroxymethylcellulose, polyvinyl alcohol, polyoxyethylene oxide and polypropylene oxide. Oxygen-containing organic polymer; hydrocarbon-based synthetic resin such as petroleum resin, polyethylene, polypropylene, polystyrene; polyvinyl chloride; organic polymer such as wax and emulsion thereof, or a mixture of two or more thereof is used. It The molecular weight of the organic polymer used as the binder is not particularly limited, but generally 3,000 to 1,000,000, preferably 5,000 to 300,000 is suitable for obtaining a green sheet having high strength and flexibility. is there.

Further, when the aluminum nitride green sheet of the present invention is processed into a specific shape,
It is preferable to use a plasticizer for the purpose of imparting more flexibility. For the above purpose, known materials used for molding general ceramic powder can be used without particular limitation. Specific examples of those preferably used as plasticizers are polyethylene glycol and its derivatives; phthalates such as dimethyl phthalate, dibutyl phthalate, butylbenzyl phthalate and dioctyl phthalate; stearic acid such as butyl stearate. Esters; Tricresol phosphate; Tri-
N-butyl phosphate; glycerin and the like.

In the aluminum nitride green sheet of the present invention, the mixing ratio of the organic component such as the binder, the surface active agent and the plasticizer constituting the green sheet and the inorganic component containing aluminum nitride powder as the main component is the surface active agent, It is generally suitable that the ratio of the organic component is in the range of 5 to 30 parts by weight with respect to 100 parts by weight of the inorganic component, although it is somewhat different depending on the types of binder and plasticizer.

In the present invention, one of the important requirements is that the occupancy ratio (R) of organic substances in the voids is in the range of 0.3 to 0.75. That is, the organic matter occupancy rate (R) in the above-mentioned void is 0.
If it is less than 3, the green sheet has insufficient strength and cracks occur during sheet forming.
If it is larger than the above range, the warp is large and micropores are generated, which is not preferable. In order to obtain a good aluminum nitride green sheet, an aluminum nitride sintered body having a small warp and no micropores, it is more preferable that the organic substance occupancy ratio R in the void be in the range of 0.35 to 0.7.

Further, it is important that the sheet density d ₁ is 2.0 to 2.8 g / cm ³ . That is, the sheet density d ₁ is 2.0 g / cm ³
If it is lower, the shrinkage ratio due to sintering is relatively large, so that the warpage becomes large and the effect of the present invention cannot be obtained, which is not preferable. Further, when the sheet density d ₁ is higher than 2.8 g / cm ³ , a crack-free green sheet cannot be obtained when the above-mentioned organic matter occupancy ratio (R) in the void is adjusted to 0.30 to 0.75. Sheet density d ₁ may be in the range of above but beyond 2.3 g / cm ^3, further preferably 2.7 g / cm ³ or less.

In producing the aluminum nitride green sheet of the present invention, an organic solvent is generally used in mixing. However, since the organic solvent does not substantially exist after forming the green sheet, it is excluded from the organic components.

Examples of organic solvents preferably used are 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. Or one or a mixture of two or more halogenated hydrocarbons such as trichloroethylene, tetrachloroethylene and bromochloromethane. The amount of organic solvent used is selected from the range of 25 to 200 parts by weight.

The above-mentioned respective components are generally mixed in two batches in order to sufficiently mix and disperse the inorganic components such as the aluminum nitride powder and the sintering aid. The first time, the surface active agent and the solvent are added to the inorganic components such as aluminum nitride and the sintering aid and mixed, and the second time, the binder, the plasticizer and the remaining solvent are added and mixed to the first time mixture. It Thus, a viscous slurry generally called mud is produced. Then, it is formed into a sheet using a sheet forming machine such as a doctor blade method. Then, the sheet-shaped molded product is dried at a temperature between room temperature and the boiling point of the solvent to form an aluminum nitride green sheet.

In the aluminum nitride green sheet of the present invention, the sheet density d ₁ which is a constituent factor can be adjusted mainly by the amount of the solvent used for the first mixing in the above manufacturing method. Here, as the amount of solvent,
It is preferably selected from the range of 25 to 60 parts by weight, more preferably 28 to 55 parts by weight, based on 100 parts by weight of the aluminum nitride powder.

The occupancy ratio (R) of the organic matter in the voids, which is a constituent feature of the present invention, is mainly adjusted by the sheet density d ₁ and the sheet densities d ₂ , d ₃ , d _{4 in} the above manufacturing method, Specifically, it can be adjusted mainly by the amount of the solvent used for the first mixing and the ratio of the total organic component excluding the solvent to the inorganic component containing aluminum nitride as the main component.

The aluminum nitride green sheet thus obtained is degreased and fired by a known method. The above degreasing is generally carried out in an air or nitrogen atmosphere, and the degreasing temperature is set to 300 depending on the type of binder and the atmosphere.
It is arbitrarily selected from the range of up to 1000 ° C. The aluminum nitride molded body after degreasing is generally 1700-
It is fired at any temperature selected from the range of 1950 ° C.

In this way, it is possible to obtain an aluminum nitride sintered body having a small warpage and no micropores in the sintered body.

[0029]

When an aluminum nitride sintered body is manufactured using the aluminum nitride green sheet of the present invention, it is possible to obtain an aluminum nitride sintered body having a small warpage and no micropores in the sintered body. Therefore, there is no need for post-processes for warping correction such as warping back and surface processing, and it is possible to efficiently and inexpensively manufacture industrial materials such as substrates that are highly reliable thermally, electrically and mechanically. It will be possible.
Also, a co-fired substrate with a refractory metal such as tungsten,
It is preferably used as an electronic material such as 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 of the present invention is
The material is industrially extremely useful for the electronic materials and the like that require high reliability.

[0031]

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.

Various physical properties in the following examples and comparative examples were measured by the following methods.

1) Specific surface area Using a "Flowsorb 2300" manufactured by Shimadzu Corporation, N ₂
It was determined by the BET method by adsorption.

2) Average Aggregate Particle Size It was measured by a centrifugal sedimentation method using "CAPA 500" manufactured by Horiba Ltd.

3) Amount of Impurities As for the cationic impurities, aluminum nitride powder was alkali-melted, neutralized with an acid, and then "ICPS-100" manufactured by Shimadzu Corporation.
The solution was quantified by ICP emission spectroscopy using "0". The amount of impurity carbon is "EMIA-110" manufactured by Horiba, Ltd. by burning aluminum nitride powder in an oxygen stream.
Was used to quantify the amount of generated CO and CO ₂ gas. The amount of impurity oxygen was determined from the amount of CO gas generated by a high temperature thermal decomposition method in a graphite crucible using aluminum nitride powder "EMGA-2800" manufactured by Horiba Ltd.

4) Sheet Density (d ₁ , d ₂ , d ₃ , d ₄ ) The sheet density d ₁ was obtained by measuring the dimensions and weight of a sheet molded product punched from a green sheet into a predetermined shape.
The sheet density d ₂ was calculated from the true specific gravities of all the raw materials constituting the aluminum nitride green sheet excluding the organic solvent, assuming that no pores were contained, and calculated. Sheet density d
₃ was obtained by firing the above-mentioned sheet molded body at 600 ° C. for 5 hours to remove organic components, and then measuring the dimensions and weight. The sheet density d ₄ was calculated from the true specific gravities of all the inorganic substances containing aluminum nitride as a main component that compose the aluminum nitride green sheet, assuming that no pores were included.

5) Sintered body density The density was determined by the Archimedes method using "High-precision specific gravity meter DH" manufactured by Toyo Seiki.

6) Sintered body warp The slits having a width obtained by adding 60 μm to the thickness of the sintered body were passed through the sintered body, and the passing rate was shown.

7) Sintered Micropores Photomicrographs were made at a magnification of 40 using a stereomicroscope. 1
Micropores of 20 μm or more per square cm were counted and determined as the micropore density. The average value of 3 samples was used as the measured value.

Example 1 Nylon balls with an iron core were placed in a nylon pot having an internal volume of 10 L, and then aluminum nitride powder 10 shown in Table 1 was used.
After adding 0 parts by weight, tetraglycerin monooleate as a surface active agent 0.5 part by weight, yttrium oxide 4.0 parts by weight, and toluene as a solvent in the amounts shown in Table 2, after sufficiently performing the first ball mill mixing, To this mixture was added 2.5 to 12.0 parts by weight of the binder shown in Table 2, 1.0 to 5.5 parts by weight of dibutyl phthalate as a plasticizer, 30 parts by weight of toluene, and 30 parts by weight of ethanol, and the mixture was further ball-milled for the second time to give a white mixture. Got the mud

The sludge thus obtained is desolvated, the viscosity is adjusted to 10,000 to 20000 cps, and the sheet is formed by the doctor blade method, and dried at room temperature for 1 hour, 60 ° C. for 2 hours, and 100 ° C. for 1 hour. Then, a green sheet having a width of 20 cm and a thickness of 0.6 to 0.7 mm was produced. 60 green sheets obtained
Punching was performed with a die of × 40 mm to obtain a sheet molded body, and the sheet density d ₁ and the organic matter occupancy R in the voids of the green sheet were determined. Then, after applying boron nitride as a release agent to the sheet molded body, 5 layers are stacked, baked in air at 600 ° C. for 5 hours, then, while stacked in 5 layers, carbon coated with boron nitride on the inner surface 18 in a nitrogen atmosphere
It was baked at 00 ° C for 5 hours. The density, warpage, and micropore density of the obtained sintered body were measured. The results are shown in Table 2.

[0042]

[Table 1]

[0043]

[Table 2]

Claims (1)

[Claims] 1. An aluminum nitride green sheet comprising an inorganic component containing aluminum nitride as a main component and an organic component containing a binder as a main component, the sheet density being calculated from an actual measurement value of the weight and volume of the green sheet. Where d _{1 is} the sheet density calculated from the true specific gravity of the organic and inorganic components that make up the green sheet, and d _{2 is} the sheet density calculated from the measured values of the weight and volume of the inorganic components of the green sheet. when d _3, and a sheet density was calculated from the true specific gravity of the inorganic component constituting the green sheet was d _4, the following equation R = 1 - {(1- d 1 / d 2) / (1- d ₃ / d ₄ )}, the organic matter occupancy (R) in the void is 0.3 to 0.
An aluminum nitride green sheet having a weight ratio of 75 and d _{1 in} the range of 2 to 2.8 g / cm ³ .