JPH0442862A - Preparation of aln sintered product - Google Patents

Abstract

PURPOSE:To prepare an AlN sintered product having high thermal conductivity and free from color irregularity by adding a sintering auxiliary and an organic binder to AlN fine powder, molding the mixture, defatting the molded product and subsequently sintering the molded product containing remaining carbon under specific conditions. CONSTITUTION:AlN fine powder for sintering is mixed with a sintering auxiliary (e.g. Y2O3) and an organic binder (e.g. ethyl cellulose), molded and defatting. The defatting molded product containing remained carbon is sintered in an non-oxidative atmosphere and subsequently treated at 1400-1700 deg.C in vacuum atmosphere at least one time to prepare the objective AlN sintered product. The vacuum treatment thereby permits to accelerate the removal of oxygen from the AlN, achieve high thermal conductivity, remove excessive carbon and prevent the generation of color irregularity, deformation, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing an AlN sintered body having a small amount of impurity oxygen and having high thermal conductivity.

Conventional technology Recent advances in LSI have led to improvements in the degree of integration and
As the chip size has improved, the amount of heat generated per package has increased accordingly.

For this reason, the heat dissipation properties of substrate materials are considered important, and beryllia substrates with high thermal conductivity are used as an alternative to alumina substrates. However, beryllia has the disadvantage of being highly toxic and difficult to handle, and in recent years ApN substrates have been is being actively developed.

Since Al)N is inherently difficult to sinter, sintering aids such as calcia and ittria are used in pressureless sintering for boat fishing; It is also known that it has the effect of preventing the impurity oxygen contained in the AlN raw material from forming a solid solution in the A9N sintered body and improving the thermal conductivity of the sintered body.

However, even if a sintering aid was used to prevent impurity oxygen from forming a solid solution, a sintered body with a thermal conductivity of only about 160 W/m 2 K could only be obtained.

Furthermore, in recent years, firing has been carried out in a non-oxidizing (gas) atmosphere in a container that creates a carbon gas atmosphere (Japanese Patent Application Laid-Open No. 1986-1999).
182280), by leaving carbon in the AIN molded body (Japanese Patent Application Laid-open No. 1-172272),
A product with a thermal conductivity of about 220 W/m- has been obtained.

Problems to be Solved by the Invention Although it is possible to increase the thermal conductivity by reducing the amount of impurity oxygen in the Aj2N sintered body by using a reducing atmosphere, as in the above-mentioned Japanese Patent Application Laid-Open No. 63-182260, There are problems in that the sintering agent, such as ittria, turns into carbides or nitrides, causing coloring of the AlN sintered body, uneven coloring, and even deformation of the sintered body.

In addition, as in the above-mentioned Japanese Patent Application Laid-Open No. 1-172272, residual carbon in the molded body may be used to sufficiently reduce the amount of impurity oxygen in the Aj7N sintered body, resulting in high thermal conductivity.
Perhaps because of the difficulty in mixing the fine powders, it is necessary to leave an excess of carbon in the compact relative to the amount of impurity oxygen in the raw AlN powder. Perhaps for this reason, even after the sintered body is densified, carbon remains and stabilizes the AI of the high thermal conductivity product.
It is difficult to obtain an IN sintered body, and in some cases, the sintered body may have low thermal conductivity, low insulation properties, etc. Furthermore, there is also the problem that discoloration, color unevenness, and deformation are likely to occur due to excessive residual carbon.

Not only the AIIN sintered body having such inferior properties, but also the coloration, color unevenness, and deformation of the sintered body lead to a decrease in the yield in the production of the AjllN sintered body.

Therefore, the present invention aims to maintain high thermal conductivity, eliminate the above-mentioned coloring, uneven color, and deformation of the sintered body, and produce a highly thermally conductive A11IN sintered body in a stable and high yield. purpose.

Means for Solving the Problems In order to solve the above-mentioned problems, the inventor of the present invention investigated various sintering conditions, etc., and found that after adding a sintering aid and an organic binder to AfiN fine powder for sintering and shaping it. , a method for manufacturing an A, QN sintered body by sintering a degreased molded body in which carbon remains after degreasing in a non-oxidizing atmosphere,
We have discovered a method for producing an AlN sintered body, which is characterized by reducing the pressure of the atmosphere at least once in a temperature range of 1700°C.

Next, the present invention will be explained in detail.

The main raw material, AIN fine powder, has a purity of 95% or more, an average particle size of 20m or less, preferably 5- or less, and a metal impurity amount of 500pI)ffl or less. is preferably 2 wt% or less.

As the sintering aid, rare earth oxides, halides, etc., alkaline earth metal oxides, halides, nitrates, carbonates, etc. can be used. In particular, when using yttrium compounds such as yttria, sintering Since the solid body is markedly colored and unevenly colored, the sintering method of the present invention is an effective means. Further, the average particle diameter of the sintering aid powder used is preferably 2 trm or less, and the amount added is 1 to 10 wt%, preferably 2 to 5 vt%, based on AfIN.

The AIN fine powder and the sintering aid are mixed by dry mixing or wet mixing using an organic solvent, but the latter wet mixing is preferred.

Furthermore, an organic binder such as paraffin wax, polyvinyl butyral, ethyl cellulose, etc. is added to the mixed powder in an amount of 3 to 15 νt%, preferably 5 to IOνt%.
It is then molded into a predetermined shape by a suitable molding method, such as a dry press method, a rubber press method, an extrusion method, an injection method, a doctor blade sheet molding method, etc.

In the present invention, in order to increase the thermal conductivity of the A, QN sintered body to a high level, it is necessary to reduce the oxygen content in the sintered body.
Therefore, carbon remains in the degreased molded body that has been degreased after molding.

In the present invention, this residual carbon amount represents the total amount of carbon contained in the degreased molded product after it is heated at 1300°C in a non-oxidizing atmosphere or vacuum atmosphere. .

The appropriate amount of residual carbon varies depending on the purity of the A and QN raw material powders used. For example, when using IN raw materials with a purity of 98% or more, it is recommended to set it at 0.2 to 2.5 vt%. preferable. This is because if the amount of residual carbon exceeds 2.5 wt%, carbon tends to remain even after the sintered body is densified, making it difficult to obtain a sintered body with stable high thermal conductivity. If it is less than that, the deoxidizing effect of A and QN will be insufficient and the thermal conductivity cannot be increased.

Note that this residual carbon may be a residue resulting from thermal decomposition of the added organic binder, may be based on a carbon source such as carbon black, or may be a mixture of both.

When the amount of residual carbon is in the range of 0.2 to 0.5 wt%, A
The 11N sintered body is sometimes colored, unevenly colored, and sometimes deformed, sometimes not, but the reasons for this are not well understood. In the case of residual carbon content in this range, it is better to stably obtain a high-quality A11N sintered body by performing the depressurization operation according to the present invention, rather than reducing the yield of a high-quality AlN sintered body due to coloring, etc. can.

When the amount of residual carbon is 0.5 to 2.5 vt%, the AlN sintered body almost always becomes discolored, uneven in color, and deformed, and the present invention is an effective means for preventing this.

In the present invention, the above-mentioned appropriate amounts of Al)N fine powder, a sintering aid, an organic inder, and, if necessary, a carbon source such as carbon black are mixed, molded, and then the molded body is degreased. The degreasing conditions depend on the type of organic binder, but it is generally held at 400 to 1000°C for 0 to 12 hours, and the temperature increase rate is 50 to 50°C.AlN is easily oxidized in the atmosphere during degreasing. Therefore, it is preferable to conduct the process in vacuum or in a non-oxidizing atmosphere such as N 2 or Ar gas.

Next, the degreased molded body containing residual carbon was heated with N2
In a method of sintering in a non-oxidizing atmosphere such as , Ar gas, etc., the present invention is characterized in that sintering is carried out at least once in a temperature range of 1400 to 1700° C. while reducing the pressure of the atmosphere. The pressure may be maintained at a reduced pressure in the range of 1400 to 1700° C., or the pressure may be reduced once and then non-oxidizing gas may be poured in again to return the inside of the sintering furnace to normal pressure. Further, the pressure reduction operation may be performed while maintaining the temperature in the range of 1400 to 1700°C, or may be performed while continuing to raise the temperature.

The reason why the temperature range for the depressurization operation was set to 1400 to 1700°C is that below 1400°C, the deoxidizing effect of AIIN due to residual carbon in the compact is small, and the amount of impurity oxygen in A11H cannot be sufficiently reduced. This is because it is difficult to obtain a stable high thermal conductivity of the sintered body. On the contrary, 1700℃
If the depressurization operation is carried out in excess of This also leads to instability of the conductivity, and it becomes difficult to improve or reduce coloration and color unevenness of the sintered body.

In addition, the degree of pressure reduction in the pressure reduction operation in the range of 1400 to 1700°C depends on the amount of residual carbon in the degreased body, but basically it is to the extent that no carbon remains in the sintered body and AlN does not decompose. The pressure inside the sintering furnace should be 160 to t6.
It is desirable to set the amount to about 0 iml 1 g.

After depressurization, the final temperature was 1750 in a non-oxidizing atmosphere.
Sintering treatment is performed at ~1950°C for about 2 to 10 hours.

The present invention is not limited to the furnace material of the sintering furnace. That is,
If the heater or furnace material is made of carbon, problems such as coloring and uneven coloring may occur in the sintered body, but in such cases, hBN, l! It may be sintered by placing it in a container made of N or the like. If the heater is W and the furnace material is W and/or Mo, there is no need to put it in the container as described above.

AIN is generally sintered in a non-oxidizing atmosphere such as N2, Ar gas, etc.
As exemplified in Example 15, when sintered in a vacuum (reduced pressure) atmosphere, the thermal conductivity of the A, QN sintered body is 13.
Usually, it is a low value of only 5 W/m-K.

Example The present invention will be explained in detail below using examples.

Example 1 Specific surface area 4.0rd/g, average particle diameter 1.5g, content impurity oxygen amount (impulse furnace extraction method (Leco equipment)
)■, 5νt%, AJN fine powder for sintering with metal impurities of 200 ppm or less, a specific surface area of 15 rrr/g,
2vt% of Y2O3 fine powder with an average particle size of 0.4" and a purity of 99.9wt% was added, and further, 100% of these mixed powders were added.
7 parts of polyvinyl butyral and 6 parts of di-n-butyl phthalate (plasticizer) were added to the part as external cutting, and the slurry concentration was made to 72vt% with an organic solvent of a 2:1 mixture of butanol and xylene, and the thickness of the green sheet was adjusted. It was formed into a sheet and dried at 25°C for 2 days.

Thereafter, degreasing was performed at 600° C. for 10 hours at a temperature increase of 100° C./hr in N2. The amount of residual carbon in this degreased body is o, svt% as measured at 1300°C in a N2 atmosphere.
Met.

Place this degreased body in a hexagonal BN container that can maintain airtightness.
In a sintering furnace where the heater and furnace material are carbon materials,
The temperature was raised at a rate of 100°C/hr in a N2 atmosphere, and when it reached 1600°C, while holding it, the pressure inside the sintering furnace was reduced to 2EiOmaHg using a vacuum pump, and when the degree of pressure reduction reached 260 parts mHg, N2 gas was introduced. , return the inside of the furnace to normal pressure,
Subsequently, the temperature was raised to 1800''C, and the temperature was maintained for 10 hours to perform sintering.

As a result, there is no coloring, uneven color, or deformation, and the thermal conductivity is 224.
An AlN sintered body with excellent W/m- was obtained. These and other characteristic values are shown in Table 1.

The thermal conductivity, oxygen content, and amount of residual carbon of the obtained Al)N sintered body were determined by the laser flash method (TC-7000 type device manufactured by Shinku Riko Co., Ltd.), the impulse furnace extraction method (device manufactured by Leco Co., Ltd.), and the and measured by combustion in oxygen stream-infrared absorption method. Note that these measurements were performed after the surface of the sintered body was ground.

Examples 2 and 3 AlN of Examples 2 and 3 was prepared under the same conditions as Example 1 except that the amount of Y2O3 fine powder added was 3 and 5 wt%.
A sintered body was obtained. Both in N2 atmosphere in degreased body 130
The amount of residual carbon, which was measured at 0° C., was also the same value as in Example 1, which was 0.8 vt%.

Both of the obtained AlN sintered bodies had no coloration, uneven color, or deformation, and had excellent thermal conductivity as shown in Table 1.

Example 4 Specific surface area4. Ord/g, average particle size 1.5, impurity oxygen content 1,5 wt%, metal impurities 200 ppm or less A, QN fine powder for sintering, specific surface area 15 rrf/g
, average particle size 0.4 mm, purity 99.9 wt% Y20
Add 5vt% of a fine powder, and further add 5 parts of polyvinyl butyral and 5 parts of di-n-butyl phthalate as external cuttings to 100 parts of these mixed powders, and make a mixture of butanol:xylene-2:1. Slurry concentration 7 with organic solvent
At 2vt%, the raw sheet was molded into a sheet with a thickness of 25%.
It was dried at ℃ for 2 days.

Thereafter, degreasing was performed at 600° C. for 10 hours at a temperature increase of 100° C./hr in N2. The amount of residual carbon in this degreased body is 0.5νt% when measured at 1300°C in a N2 atmosphere.
Met.

Place this degreased body in a hexagonal BN container that can maintain airtightness.
In a sintering furnace where the heater and furnace material are carbon materials,
The temperature was increased at 100°C/hr in a N2 atmosphere, and when the temperature reached 1400°C, the pressure inside the sintering furnace was reduced to 360 tsHg using a vacuum pump. When the degree of pressure reduction reached 3BOsmHg, N2 gas was introduced. , return the inside of the furnace to normal pressure,
Subsequently, the temperature was raised to 1800° C. I7, and sintering was carried out by holding at that temperature for 6 hours.

As a result, there is no coloration, uneven color, or deformation, and the thermal conductivity is 171.
Excellent W/m-. A JN sintered body was obtained. These and other characteristic values are shown in Table 1.

Note that the method for measuring the physical property values of the AlN sintered body, etc. is as described in Example 1.
It is similar to

Examples 5 to 7 Decompression operation temperature is 1500°C instead of 1400°C, 1
AlN sintered bodies of Examples 5 to 7 were obtained under the same conditions as Example 4 except that the temperatures were 600°C and 1700°C.

Note that the degree of pressure reduction was 360+un+Hg, which is the same as in Example 4.

The obtained AlN sintered body has no coloring, uneven color, or deformation,
The sintered body also had excellent thermal conductivity as shown in Table 1.

Example 8 Specific surface area4. Ord/g, average particle size 1.5 particles, amount of impurity oxygen contained 2. 5vt% of Y2O3 fine powder with a specific surface area of L5rd/g, average particle size of 0.4, and purity of 99.9vt% was added to AIN fine powder for sintering with Ovt% and metal impurities of 200 ppa+, and further, these were mixed. To 100 parts of powder, 7 parts of polyvinyl butyral, 6 parts of di-n-butyl phthalate, and 7 parts of carbon black (Denka Black manufactured by Denki Kagaku Co., Ltd.) were added as external polishing, and butanol:
Slurry concentration 72w with xylene-2:1 mixed organic solvent
As t%, the raw sheet is formed into a sheet with a thickness of 1, and heated at 25°C.
It was dried for 2 days.

Thereafter, degreasing was performed in N2 at a temperature increase of 100° C./hr to 600° C. for 10 hours. The amount of residual carbon in this degreased body is 2.5vt% as measured at 1300°C in a N2 atmosphere.
Met.

Thereafter, this degreased body was treated under the same conditions as in Example 1.

However, the holding time at the sintering temperature of 1800°C was 6 hours.

As a result, an A11N sintered body as shown in Table 1 was obtained without coloring, color unevenness, or deformation.

Comparative Example 1 An IN sintered body was obtained by processing under the same conditions as in Example 1 except that the pressure reduction operation was not performed.

This A47N sintered body had coloration and color unevenness, which was thought to be caused by residual carbon, and was also greatly deformed, and as shown in Table 1, the thermal conductivity was as low as 153 W/m-.

Comparative Example 2 The same raw materials as in Example 3, such as p, IN, Y2O3, etc., were blended under the same conditions, formed into a sheet, and then similarly heated to 600 ml.
It was degreased at ℃ for 10 hours.

Place this degreased body in a hexagonal BN container that can maintain airtightness.
In a sintering furnace where the heater and furnace material are carbon materials,
The temperature was raised at a rate of 100°C/hr in a N2 atmosphere, and when it reached 1300°C, while holding it, the pressure inside the sintering furnace was reduced to 280a+a+Hg using a vacuum pump, and the temperature was 260+++ mHg.
When the degree of pressure reduction reached , N2 gas was introduced to return the inside of the furnace to normal pressure, and as in Example 1, the temperature was subsequently raised to 1800°C and held at that temperature for 10 hours to perform sintering.

In this case, the amount of residual carbon in the molded body after the vacuum treatment at 1300°C was 0.15 wt%.

Although the obtained AlN sintered body had no coloration, uneven color, or deformation, the thermal conductivity was 147 W/m as shown in Table 1.
It was very low.

Comparative Example 3 An Al)N sintered body was obtained under the same conditions as Comparative Example 2 except that the pressure reduction operation was performed at 1750°C instead of 1300°C. The sintered body was discolored, uneven in color, and deformed. We cut out a good part and determined its physical properties, but the thermal conductivity was also low.

Comparative example 4 Specific surface area 4. Ord/g, average particle diameter 1.5, impurity oxygen content 1.5vt%, metal impurity 200ppI11
The following ApN fine powder for sintering has a specific surface area of 15rd/lr.
, average particle size 0.4'', purity 99.9wt% Y2O3
5 wt% of fine powder was added, and 10% of these mixed powders were added.
7 parts of polyvinyl butyral as 40% of 0 parts, 6
1 part of di-n-butyl phthalate and 2.2 parts of the same carbon black as in Example 8 were added, slurried with an organic solvent in the same manner as in Example 1, formed into a sheet, dried, and degreased.

The amount of residual carbon in this degreased body is 1300℃ in N2 atmosphere.
It was measured at 3.0 wt%.

This degreased body was placed in an hBN container in the same manner as in Example 1,
In the same sintering furnace, the temperature was raised to 1600℃ and 260a.
Perform a pressure reduction operation to +mHg, return to normal pressure with N2 gas,
Subsequently, the temperature was raised to 1800° C. and sintered by holding at that temperature for 6 hours.

The obtained Aj7N sintered body had severe coloration and color unevenness, large deformation (and low thermal conductivity).

Effects of the Invention According to the present invention, deoxidation of AIH is promoted by depressurizing the degreased body in which carbon remains, and
By removing excess carbon, it is possible to obtain A and QN sintered bodies that stably have high thermal conductivity and are free from coloration and color unevenness.

Claims (1)

[Claims] After adding a sintering aid and an organic binder to AlN fine powder for sintering and molding, the degreased molded body with residual carbon is sintered in a non-oxidizing atmosphere to produce an AlN sintered body. A method characterized in that the atmosphere is reduced in pressure at least once in a temperature range of 1400 to 1700°C.
Method for manufacturing an IN sintered body.