JPH03242379A - Production of sintered body of aluminum nitride and granulated powder of aluminum nitride - Google Patents

Abstract

PURPOSE:To readily obtain a sintered body of AlN having excellent strength, precision, etc., by blending AlN powder with a specific binder, solvent and surfactant, granulating, molding by press molding while removing defect parts such as depression formed in the granulated product and sintering the molding under heating. CONSTITUTION:(A) Raw material powder of aluminum nitride is blended with (B) <=10 pts.wt. based on 100 pts.wt. component A of wax-containing acrylic binder, (C) a solvent and (D) a surfactant (e.g. phosphoric ester compound). Then the mixed slurry is granulated by a spray dryer, etc., the granulated powder is packed into a mold of press molding machine and molded by press molding while removing defect parts such as depression formed on the granulat ed product. Then the molding is sintered be heating to give a sintered body of aluminum nitride.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for producing an aluminum nitride sintered body and an aluminum nitride granulated powder, and in particular to a dense and high-strength aluminum nitride sintered body. The present invention relates to a method for producing an aluminum nitride sintered body that enables easy production of aluminum nitride sintered bodies, and a granulated aluminum nitride powder used in the production method.

(Prior art) Ceramics prepared by sintering nitrides, carbides, halides, and silicides generally have properties such as hardness, insulation, abrasion resistance, heat resistance, and corrosion resistance that are superior to those of conventional metals. Because it is superior to other materials, it has been put into practical use in a wide range of fields in recent years.

For example, a sintered body of alumina (Al2203) has conventionally been generally used as an insulating substrate material for integrated circuits. However, since the substrate made of alumina sintered body has low thermal conductivity and a high coefficient of thermal expansion compared to silicon, the adhesion of large silicon chips to the substrate is poor, and the silicon chips are easy to peel off. It also had the disadvantage of poor heat dissipation characteristics.

Therefore, aluminum nitride (AI), which has extremely high thermal conductivity and electrical insulation, and has a coefficient of thermal expansion close to that of silicon,
N) Sintered bodies are seen as promising as insulator materials for circuit boards. However, in order to take advantage of these characteristics, A
The IN sintered body itself is required to be dense, have high strength, and have a low oxygen content. However, even if an attempt is made to sinter AIN powder with a low oxygen content alone, it is difficult to obtain a dense sintered body because the sinterability is not good. Therefore, when trying to obtain a sintered body that is dense, has high thermal conductivity, and has high strength, it is necessary to use oxide oxide (Y2O2), calcium oxide (CaQ), or alkaline earth metal oxide as a sintering aid. It is common practice to add substances, etc.

A7! The N sintered body is formed by uniformly mixing the AIN raw material powder and the sintering aid, molding it into a predetermined shape, and then sintering the resulting molded product. Molding methods include the doctor blade method, in which a kneaded material obtained by uniformly mixing raw material powder and a sintering aid, etc., is extruded into a flat plate from the tip of a blade, and the doctor blade method, in which raw material powder, etc. is placed in a solvent. There is a slip casting method in which a uniform slurry (slip) is prepared by dispersing the slurry, and the slurry is filled into a mold of a predetermined shape and hardened by dehydration. A press forming method, etc. in which a plasticizer, etc. is uniformly mixed and then granulated to form a nodule-shaped granulated powder having a particle size larger than that of the raw material powder, and then the obtained granulated powder is press-molded, etc. There is. This press molding method uses granulated powder obtained by granulating fine raw material powder, which improves the handling of raw materials and enables uniform dispersion of raw materials within the mold, resulting in excellent quality. A molded body can be obtained.

Generally, when manufacturing circuit boards, the above-mentioned doctor blade method is employed. However, the doctor blade method has the disadvantage that it is difficult to form a thick plate material or a molded body with a large internal thickness, and that the yield of the material is low and the economical efficiency is low.

On the other hand, the press molding method has the advantage that the thickness of the molded body can be easily adjusted and the material yield is higher than that of the doctor blade method, so its use is being advanced.

(Problems to be Solved by the Invention) By the way, in order to form a high-quality molded body and obtain a good sintered body in the press molding method, the characteristics of the raw material powder to be filled into the mold are important. Therefore, when using granulated powder as a raw material, the granulation conditions are a key point.

In other words, the raw material powder used as the raw material for the sintered body is required to have a shape that can be easily packed as densely as possible, that is, to have high sphericity, a sharp particle size distribution, and little variation in particle size.

However, in the past, a spray drying method that can efficiently produce granulated powder was used, in which a solution of raw material powder mixed with a solvent, a binder, etc. was rapidly sprayed from a sprayer, and dried instantly. The granulated powder formed by this method had a drawback of having a high proportion of depressions formed on the surface and low sphericity.

The proportion of the granulated powder in which this depression is formed varies depending on the granulation conditions, but usually ranges from 20 to 80%.

Granulated powder having depressions has poor fluidity in the mold, which causes deterioration in moldability. Further, the depressed portions do not disappear easily even by pressure forming, and remain as bores when formed into a sintered body, degrading the quality of the AIIN sintered body.

Therefore, granulated powder with significant depressions cannot be used as a raw material, resulting in a low yield of raw materials for sintered products, which is uneconomical.

Further, in order to prevent the granulated powder from caving, a wax-based binder or a PVB (polyvinyl butyral)-based binder may be added to form the granulated powder.

However, when a wax-based binder is added, the amount of cavities that occur decreases and the sphericity of the granulated powder increases, but the strength of the molded product decreases, handling becomes poor, and the molded product is easily deformed and chipped. There is a drawback that an AIN sintered body with high dimensional accuracy cannot be obtained.

On the other hand, PVB (polybutyral) binders have good solubility in solvents and relatively good moldability as raw materials, or the PVB component is difficult to volatilize and has poor degreasing properties, so even after degreasing, the amount of carbon remaining in the molded product is small. In many cases, cracks may occur in the molded product.

There was a problem in that a high quality AIN sintered body could not be obtained in the end.

The present invention was made to solve the above-mentioned problems, and AI! has excellent moldability and degreasing properties. An object of the present invention is to provide a method for producing an aluminum nitride sintered body that can easily produce a N sintered body, and an aluminum nitride granulated powder used in the production method.

[Structure of the invention]

(Means and effects for solving the problem) In order to achieve the above object, the inventors of the present application have developed a method for granulating powder by changing various kinds of binders, solvents, and surfactants used when producing granulated powder. Experiments were repeated to compare and investigate the shape of the powder, the strength characteristics and moldability of the compact, and the strength characteristics of the AIN sintered body obtained by sintering the compact.

As a result, even when the wax content in the A[N raw material powder is suppressed to a small amount of 1% or less, the use of an acrylic compound as a binder results in the formation of granulated powder with a high incidence of depression. However, we have found that the strength characteristics of the molded body are rarely impaired, and that when it is finally made into a sintered body, a dense and high-strength sintered body can be manufactured. The present invention was completed based on the above findings.

That is, in the method for producing an aluminum nitride sintered body according to the present invention, an acrylic binder containing 10 parts by weight or less of wax, a solvent, and a surfactant are added to the aluminum nitride raw material, based on 100 parts by weight of the aluminum nitride raw material powder. By press-molding the granulated powder obtained by adding it to the powder and granulating it to prepare a compact, defects such as depressions that have occurred in the granulated powder are removed, and then the above-mentioned compact is heated and sintered. It is characterized by

Further, it is preferable to use ethanol as a solvent and a phosphoric acid ester compound as a surfactant.

Furthermore, the aluminum nitride granulated powder according to the present invention is characterized by comprising an acrylic binder whose content is adjusted to be 10 parts by weight or less with respect to 100 parts by weight of the aluminum nitride raw material powder, and an aluminum nitride raw material powder. shall be.

The aluminum nitride granulated powder according to the present invention has an average particle size of 0.
An acrylic binder, ethanol as a solvent, a phosphoric acid ester compound as a surfactant, a sintering aid, a plasticizer, etc. are added to crushed aluminum nitride raw material powder of approximately 7 to 8 μm and mixed uniformly. It is formed by spray drying the mixed solution.

Here, the wax content contained in the acrylic binder is set to 10% by weight or less based on the aluminum nitride raw material powder. If the content exceeds 10% by weight, the strength of the molded body formed from the granulated powder will decrease, and the handleability of the molded body will be significantly reduced, and the molded body will be easily deformed, making it difficult to obtain a sintered body of a predetermined shape. This is because it becomes difficult.

In addition, since an acrylic compound is added as a binder, many depressions occur in the granulated powder, and the sphericity decreases significantly, but the depressions disappear by the pressure forming operation described later, and the sintered body has holes. There are very few remaining as such.

On the other hand, the aluminum nitride sintered body according to the present invention is produced by press-forming the granulated powder using, for example, a press molding machine, thereby crushing and eliminating the depressions generated in the granulated powder. After degreasing the molded body, it was heated for 17 hours in a reducing atmosphere.
It is obtained by heating and sintering at 00 to 2000°C.

The acrylic compound used as a binder has an excellent effect on increasing the strength of the formed body, unlike a binder containing a wax component, and unlike a conventional PVB binder, it evaporates easily and has good degreasing properties. Therefore, it becomes possible to improve the handleability of the molded body, and finally it is possible to form a high quality aluminum nitride sintered body with excellent dimensional accuracy.

The amount of the acrylic compound added is 2 to 10% by weight, preferably 5 to 7% by weight based on the weight of the aluminum nitride raw material powder.
Good to add. As a surfactant, 0.1 to 3% by weight of a phosphoric acid ester compound having good dispersibility is added.

On the other hand, when an acrylic compound is used as a binder, compared to the case where a wax-based binder or PVB-based binder is used, are there any drawbacks such as an increase in the rate of formation of depressions on the surface of the granulated powder? By using ethanol as a binder and a phosphoric acid ester compound as a surfactant, the heli of the granulated powder during molding is improved, and the above depressions are effectively crushed by normal molding pressure. , a high-density molded body is obtained.

Therefore, granulated powder with a large proportion of depressions formed can also be used as a raw material for sintered bodies, the range of raw material shape selection is greatly expanded, and the yield of raw material powder relative to the amount of products is greatly improved. . By the way, the incidence of cave-ins is 80.
Even when using a granulated powder exceeding .about.90, a molded body with sufficiently high density can be obtained with little influence of depression, and a high-quality aluminum nitride sintered body with excellent strength properties can be manufactured.

(Example) Next, an example of the present invention will be described in more detail. As Example 1, an attritor was prepared by adding 70 M parts of ethanol as a solvent and 0.25 parts by weight of a phosphate ester compound as a surfactant to 100 parts by weight of aluminum nitride raw material powder with an average particle size of 2 μm. to prepare a slurry, and then to the obtained slurry, 5 parts by weight of an acrylic binder and 10 parts by weight of a plasticizer were added per 100 parts by weight of aluminum nitride raw material powder, and mixed in a polypot. The obtained mixture slurry was then granulated using a spray dryer to form granulated powder having an average particle size of about 100 μm as shown in FIG. The surface of the obtained granulated powder was observed under a microscope to determine the occurrence rate of depressions, which was approximately 80%.

Next, the obtained granulated powder is filled into the mold of a press molding machine,
Pressure molded with pressure cuff 50kg/cffl to length and width 20-1
A number of molded bodies each having a thickness of 5 cm were formed. In order to evaluate the moldability of the granulated powder, each molded body was observed under a microscope with a magnification of 400 times, and the crushed state of the granulated powder on the surface and inside of the molded body, and the presence or absence of bores and grain boundaries were investigated.

In addition to measuring the density and yield of the molded bodies, each molded body was degreased in air at a temperature of 550°C for 2 hours to evaluate the degreasability of the molded bodies, and the amount of residual carbon in each molded body was measured. The degreasing ratio was determined. This degreasing ratio was calculated as the ratio of the carbon weight reduced by degreasing to the weight of the added binder. The yield of molded products was expressed as a percentage of the total number of samples, excluding those with cracks or chips after degreasing.

Further, each degreased molded body was sintered at a temperature of 1900° C. for 3 hours in a nitrogen gas atmosphere, and the density, thermal conductivity, and bending strength (flexural strength) of the obtained aluminum nitride sintered body were measured.

On the other hand, as Comparative Example 1, 5 parts by weight of a wax-based binder (wax content 50% by weight) and 1 part by weight of a dispersant were added to the slurry prepared by crushing with an attritor in Example 1, per 100 parts by weight of aluminum nitride raw material powder. parts by weight were added and mixed in a polypot, and the resulting mixture slurry was granulated in a spray dryer to form granulated powder with an average particle size of 100 μm as shown in FIG. The resulting granulated powder was examined under a microscope to investigate the occurrence of depressions, but almost no depressions were observed, and a granulated powder with extremely high sphericity was obtained.

Next, this granulated powder was used to form a molded body under the same molding conditions as in Example 1, and was degreased and sintered to form an aluminum nitride sintered body.

In addition, as Comparative Example 2, AIN raw material powder 100
5 parts by weight of PVB binder and 1 part by weight of plasticizer
When 0 part by weight was added and mixed in a polypot, the resulting mixture slurry was granulated with a spray dryer to prepare granulated powder as shown in Figure 3, the proportion of granulated powder with depressions was 10%. It was about. Then, this granulated powder was used in Example 1.
After press forming under the same conditions as above, degreasing and sintering were performed to form an aluminum nitride sintered body, and each characteristic value was measured and evaluated in the same manner as in Example 1.

The measurement evaluation results are shown in Table 1 below.

Margin below C] As is clear from the results shown in Table 1, the AIN granulated powder according to this example has a high density and high strength with few cracks, despite the high occurrence of caving. A molded body is obtained. Further, when the molded body was observed under a microscope, the granulated powder was effectively crushed both on the surface and inside of the molded body, and no bores or grain boundaries were observed.

Furthermore, the strength of the molded product was excellent, and the proportion of cracks and chips that occurred during the molding and degreasing process was extremely low compared to Comparative Example 1. In addition, Comparative Example 2 had a large amount of residual binder,
Due to the low strength of the molded product, it was found to be unsuitable for mass production.

Furthermore, the density, thermal conductivity, bending strength, etc. of the aluminum nitride sintered body of Example 1 are superior to those of Comparative Examples 1 and 2, and these characteristic values are higher than those of the sintered body produced by the doctor blade method. It almost matched the characteristic values of the body.

On the other hand, in Comparative Example 1, a granulated powder with high sphericity is obtained, but the strength of the compact is reduced due to the wax content in the binder, and the wax content is less volatilized and the degreasing performance is poor. It is not practical as it often cracks and chips.

Also for Comparative Example 2, PV added as a binder
B increases the shape accuracy of the granulated powder, but it lowers the strength of the molded body and further reduces the degreasing properties, so it is clear that the characteristic values of the sintered body tend to decrease overall.

〔Effect of the invention〕

As explained above, according to the method for producing an aluminum nitride sintered body and the aluminum nitride granulated powder according to the present invention, since an acrylic binder is used, the strength of the molded body is excellent, the handleability is excellent, and the aluminum nitride granulated powder has excellent strength. Precision sintered bodies can be manufactured. In addition, the moldability is good even without the addition of a wax-based binder, and the depressions that occur in the granulated powder can be effectively eliminated by pressure molding, and there is no risk that the depressions will remain as bores in the sintered body. It is possible to easily produce an aluminum nitride sintered body with excellent strength properties.

In particular, it is possible to obtain a dense compact regardless of the amount of depression that occurs on the surface of the granulated powder, and it also has excellent degreasing properties, so it is possible to significantly improve the raw material yield of the sintered compact. , a high quality aluminum nitride sintered body can be obtained.

[Brief explanation of drawings]

1 to 3 are micrographs showing the particle structure of aluminum nitride granulated powder prepared in Example 1, Comparative Example 1, and Comparative Example 2, respectively.

Claims (3)

[Claims] 1. An acrylic binder containing 10 parts by weight or less of wax per 100 parts by weight of aluminum nitride raw material powder, a solvent, and a surfactant are added to aluminum nitride raw material powder and granulated, and then the granulated powder is pressurized. 1. A method for producing an aluminum nitride sintered body, the method comprising: preparing a compact by molding, removing defects such as depressions caused in the granulated powder, and then heating and sintering the compact. 2. The method for producing an aluminum nitride sintered body according to claim 1, characterized in that ethanol is used as a solvent and a phosphoric acid ester compound is used as a surfactant. 3. A granulated aluminum nitride powder comprising an acrylic binder whose content is adjusted to 10 parts by weight or less based on 100 parts by weight of the aluminum nitride raw material powder, and an aluminum nitride raw material powder.