JP2501786B2 - Aluminum nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an aluminum nitride sintered body having high purity, high density, and particularly excellent thermal conductivity.

[Problems to be Solved by Prior Art and Invention]

The aluminum nitride sintered body is a known material, and is a material that has recently attracted particular attention as an insulator having high thermal conductivity in addition to its excellent physical properties such as heat resistance, corrosion resistance, and strength.

The aluminum nitride sintered body is usually obtained by firing a mixed powder of an aluminum nitride powder and a sintering aid when pressure-sintered. However, the aluminum nitride sintered body thus obtained contains a few percent of impurities derived from the sintering aid. Therefore,
Due to the influence of these impurities, it was difficult to obtain an aluminum nitride sintered body having excellent original properties of the aluminum nitride sintered body, for example, high thermal conductivity.

[Means for solving problems]

In view of the above problems, the present inventors have conducted earnest studies for the purpose of obtaining an aluminum nitride sintered body having excellent properties inherent to the aluminum nitride sintered body, particularly high thermal conductivity. As a result, even if the aluminum nitride powder is sintered using a relatively large amount of a sintering aid necessary for sintering the aluminum nitride powder, the sintering can be performed under specific conditions. It was found that the amount of the sintering aid contained in was extremely small. Then, since the residual amount of the sintering aid is extremely small, an aluminum nitride sintered body having excellent characteristics of the aluminum nitride sintered body, particularly high thermal conductivity, was found, and the present invention was completed. It was

That is, the present invention is: (i) 95% by weight or more of aluminum nitride (ii) 0.0005% by weight or more and less than 0.02% by weight in terms of oxide of a sintering aid composed of a compound of an alkaline earth metal (iii) silicon, The content of iron, chromium, nickel, cobalt, copper and titanium compounds is 0.1 wt% or less as metal (iv) Oxidation content is 0.3 wt% or less (v) Density is 3.0 g / cm ³ or more Thermal conductivity 120 W It is an aluminum nitride sintered body of / mk or more.

The sintering aid contained in the aluminum nitride sintered body of the present invention comprises an alkaline earth metal compound. Beryllium, magnesium, calcium, barium, and strontium are used as the alkaline earth metal. As these alkaline earth metal compounds, known compounds are used without any limitation, and suitable compounds in the present invention include, for example, oxides, nitrates, nitrites, carbonates, halides and the like. it can. Further, it is composed of the above-mentioned oxide of alkaline earth metal and alumina, and has the following general formula (I) mMO.Al ₂ O ₃ .nH ₂ O (I) (where M is an alkaline earth metal and m Is an integer of 1 or more, and n is an integer of 0 or more.) An aluminate compound of an alkaline earth metal represented by the formula is also preferably used in the present invention.

Among the above alkaline earth metals, calcium, barium, and strontium are preferably used in order to improve the thermal conductivity of the obtained aluminum nitride sintered body.

Examples of sintering aids that are particularly preferably used in the present invention are as follows. For example, calcium oxide, barium oxide, strontium oxide, calcium nitrate, barium nitrate, strontium nitrate, calcium fluoride,
Barium fluoride, strontium fluoride, calcium oxalate, barium oxalate, strontium oxalate,
Calcium iodide, barium iodide, compounds of alkaline earth metals such as strontium iodide; and _{3CaO · Al 2 O 3, 12CaO} · 7Al 2 O 3, 5CaO · 3Al 2 O 3, CaO · A
Examples thereof include aluminate compounds of oxides of alkaline earth metals such as l ₂ O ₃ , 3BaO · Al ₂ O ₃ and 3SrO · Al ₂ O _{3 and} hydrates thereof.

The above-mentioned alkaline earth metal compound is 0.0005% by weight or more in terms of oxide in the aluminum nitride sintered body of the present invention.
It is contained in the range of less than 0.02% by weight. The smaller the amount of alkaline earth metal, the better the properties such as thermal conductivity of the obtained aluminum nitride sintered body. Therefore, it is preferable that the amount of alkaline earth metal compound is small, 0.015% by weight.
It is preferably 0.012% by weight or less.

Next, it is preferable that the amount of cation (metal) impurities unavoidably mixed in the aluminum nitride sintered body of the present invention is small. In particular, the sum of the compounds of silicon, iron, chromium, nickel, cobalt, copper and titanium is 0.1% by weight or less as a metal in order to impart high thermal conductivity to the sintered body and, in some cases, translucency. is necessary.

The aluminum nitride sintered body of the present invention is a sintered body having a sintered density of 3.0 g / cm ³ or more. Especially the sintered density is 3.2g / c
The m ³ sintered body is preferable because the sintered body has more excellent thermal conductivity and also becomes a translucent sintered body.

The smaller the oxygen content in the aluminum nitride sintered body of the present invention, the more excellent the thermal conductivity and the translucency can be obtained. Therefore, the oxygen content in the aluminum nitride sintered body is preferably 0.3% by weight or less.

Various kinds of cation impurities are inevitably mixed. For example, unreacted alumina and carbon remaining in the aluminum nitride powder, which is the raw material of the aluminum nitride sintered body, is one of them, and it is mixed with the solvent, the mixer, the pipe, etc. during the manufacturing process of the aluminum nitride powder. Impurity components and the like. Therefore, the cation impurities that are inevitably mixed in the present invention are considered to be the cations of compounds other than the compound resulting from AlN in the obtained aluminum nitride sintered body and the sintering additive positively added. You can also AlN in the aluminum nitride sintered body obtained in the present invention based on the oxygen content in the aluminum nitride sintered body
The content is generally 95% by weight or more, and particularly preferably 98% by weight or more when high heat conductivity and translucency are required.

Further, the cation impurities that are inevitably mixed are magnesium, chromium, silicon, zinc, iron, copper, manganese,
Nickel, titanium, cobalt, etc., which are contained as unreacted alumina and carbon remaining after the synthesis of the aluminum nitride powder. Furthermore, metallic aluminum is also a cationic impurity. Among these unavoidable cation impurities, unreacted alumina, carbon, metallic aluminum, or aluminum nitride powder whose surface is oxidized and changed to alumina is extremely sintered aluminum nitride of the present invention. Although it does not deteriorate the physical properties of the body, it is extremely preferable that the content ratio of these is low considering the preparation of the high thermal conductive sintered body. That is, in order to impart high thermal conductivity to the sintered body, it is preferable to control the content of the above-mentioned cationic impurities such as aluminum metal, alumina and carbon to 0.5% by weight or less, preferably 0.3% by weight or less. Further, in particular, since each component of silicon, iron, chromium, nickel, cobalt, copper and titanium adversely affects the thermal conductivity of the aluminum nitride sintered body, it is preferable to reduce the mixing of these components as much as possible. Therefore, the amount of the cation impurities unavoidably mixed in the present invention should be controlled to 0.5% by weight or less, preferably 0.3% by weight or less.
In order to provide the aluminum nitride sintered body with sufficient thermal conductivity, the total content of silicon, iron, chromium, nickel, cobalt, copper, and titanium among the cation impurities inevitably mixed is 0.1% by weight. It should be controlled not to exceed%.

Since the aluminum nitride sintered body of the present invention is greatly improved in purity and density as compared with conventionally known sintered bodies, it has excellent performance in thermal properties and mechanical properties. Furthermore, an aluminum nitride sintered body having a remarkably high translucency to visible light to infrared light can also be used.

Among the above-described aluminum nitride sintered bodies of the present invention, the following sintered bodies are particularly excellent in thermal conductivity and also have translucency. That is, (i) aluminum nitride is 98% by weight or more, (ii) a compound of an alkaline earth metal as a sintering aid is converted to an oxide and is 0.0005% by weight or more and less than 0.02% by weight (iii) oxygen content is 0.3 Weight% or less, (iv) content of a metal compound selected from the group consisting of silicon, iron, chromium, nickel, cobalt, copper and titanium is 0.1 weight% or less as a metal, and (v) unavoidable except for the above (iv) This is an aluminum nitride sintered body in which the metal compound mixed in as a metal is 0.3% by weight or less and the density is 3.20 g / cm ³ or more.

The above aluminum nitride sintered body usually has a thermal conductivity of
It has a very high thermal conductivity of 120 w / m · k or more, preferably 140 w / m · k or more. Further, in the following Lambert Beer's equation, the absorption coefficient for light having a wavelength of 6 μm is 60 cm ⁻¹ or less, which is excellent in light transmittance.

The aluminum nitride sintered body of the present invention is not particularly limited as long as it satisfies the above requirements regardless of the manufacturing method. The following is an example of a typical manufacturing method that is generally suitably used.

That is, the mixed powder of aluminum nitride powder and a sintering aid composed of a compound of an alkaline earth metal is at least 1300-
Average temperature rise time in the temperature range of 1700 ℃ is 1-40 ℃ / min
Is a method of firing. According to this method, although the amount necessary for sintering the aluminum nitride powder, that is, several percent by weight of the sintering aid is added, only 0.0005% by weight is contained in the sintered aluminum nitride body. % Or more 0.02% by weight
The surprising result is that less than less than the sintering aid is included.

It is considered that this is because the sintering aid is volatilized by firing, but more surprisingly, a phenomenon was found that oxygen atoms are reduced as the sintering aid is volatilized. Therefore, not only the amount of the sintering aid in the aluminum nitride sintered body obtained according to the above method but also the amount of oxygen atoms is extremely smaller than the amount before firing.

The mixed powder of the raw material aluminum nitride powder and the sintering aid composed of a compound of an alkaline earth metal contains (i) 90% by weight or more of aluminum nitride, and (ii) an alkaline earth metal compound as an oxide. Converted to 0.02
~ 5.0 wt%, (iii) contains 4.5 wt% or less oxygen atoms, and (iv) inevitably contains cation impurities as a metal.
Aluminum nitride powder containing 0.3% by weight or less and having an average particle diameter of 3 μm or less is preferably used.

The production method of such aluminum nitride powder is not particularly limited, and known methods can be adopted without any limitation.

The amount of the sintering aid used in the present invention varies depending on the properties required for the sintered body and cannot be unconditionally limited, but generally the amount contained in the mixture of the aluminum nitride powder and the sintering aid is 0.02. It is preferable to select it so as to be in the range of 5% by weight.

The mixing of the aluminum nitride powder and the sintering aid in the present invention is not particularly limited, and may be dry mixing or wet mixing. A particularly preferred embodiment is wet mixing, that is, wet mixing using a liquid dispersion medium.
The liquid dispersion medium is not particularly limited, and commonly used water, alcohols, hydrocarbons, or a mixture thereof is preferably used. Particularly, industrially most preferably employed are lower alcohols having 4 or less carbon atoms such as methanol, ethanol and butanol.

The wet mixing device used for mixing the raw materials is not particularly limited and a known device is used, but it is preferable to select a device that does not generate an impurity component due to the material. For example, as the material, aluminum nitride itself, a plastic material such as polyethylene, polyurethane, or nylon, or a material coated with these may be selected.

As a specific embodiment of the firing in the present invention, a mixed powder obtained by adding a sintering aid to the aluminum nitride powder is appropriately formed by a molding method such as a dry pressing method, a rubber pressing method, an extrusion method, an injection method, or a doctor blade sheet molding. After forming it into the desired shape by a method, etc., place it on a suitable crucible, sheath material, etc. and under a vacuum or atmospheric pressure non-oxidizing atmosphere, for example, under an atmosphere of nitrogen gas, helium gas, argon gas, etc. Alternatively, there may be mentioned a method of firing at a high temperature under a nitrogen gas pressure of about 2 to 100 atm. Alternatively, a method of firing the mixed powder directly at a high temperature under a non-oxidizing atmosphere of vacuum or atmospheric pressure or nitrogen gas pressure of about 2-100 atm while applying a mechanical pressure of about 20-500 kg / cm ² is adopted. To be done. The firing temperature is preferably 1700 to 2100 ° C in the case of a non-oxidizing atmosphere of vacuum or atmospheric pressure, preferably a temperature of 1750 to 2050 ° C is suitably adopted, and 1700 to 2400 ° C under a nitrogen gas pressure of 2 to 100 atm. A temperature of 1750 to 2300 ° C is preferably adopted. The temperature in the present invention is a value obtained by measuring the surface of the graphite crucible containing the mixed powder with a radiation thermometer and compensating for the gas temperature in the graphite crucible.

The most important firing condition in the firing is the heating rate, and it is extremely important to set the average heating rate in the temperature range of 1300 to 1700 ° C to 1 ° C / min to 40 ° C / min. Is. Average heating rate in the temperature range of 1300 to 1700 ℃ is 1 ℃ / m
If it is smaller than in, the densification of the aluminum nitride powder is remarkably slowed down, and it becomes impossible to obtain a sintered body having a high density and a high thermal conductivity.

Further, when the average heating rate is faster than 40 ° C / min, the rate between the rate at which pores escape through grain boundaries during grain growth during sintering and the rate at which pores are confined within grains due to grain growth However, it is difficult to obtain a dense and uniform sintered body. In addition, when the temperature is rapidly raised, even if the density is increased, warpage often occurs in the sintered body, which is not preferable. Further, an oxide added as a sintering aid may remain in the sintered body more than necessary, which may impede the thermal conductivity and the translucency of the sintered body.

The above-mentioned average heating rate has an optimum range depending on the type and amount of the sintering additive to be added, and therefore may be appropriately determined according to the sintering additive. For example, when the alkaline earth metal aluminate compound represented by the general formula (I) is used as a sintering aid, the temperature rising rate is generally set in consideration of the density and thermal conductivity of the obtained sintered body. 1 to 25 ℃ / m
and more preferably 5 to 20 ° C./min.

Further, when a compound of an alkaline earth metal other than the above is used as the sintering aid, it is preferably 10 to 40 ° C / min, more preferably 15 to 25 ° C / min.

In determining the temperature raising rate, it is important to set the temperature raising conditions such that the sintering additive added during the temperature raising does not excessively evaporate and the sintering additive component does not remain after sintering as much as possible. It is to choose. As a method of raising the temperature, it is industrially preferable to set a single temperature raising rate in the range of 1300 to 1700 ° C, but other than that, a temperature raising program having a two-step or three-step speed gradient is selected. It is also possible.

The heating rate until reaching 1300 ° C. and the heating temperature when it is necessary to raise the temperature from 1700 ° C. to the firing temperature are not particularly limited, and any heating rate may be used. However, considering the density and thermal conductivity of the obtained sintered body,
Even in the temperature range of 00 ° C., it is preferable that the average heating rate is maintained. Further, industrially, it is preferable to have a single average heating rate over the entire temperature range up to the firing temperature.

After the temperature is raised in this manner, it is preferably 17
It is fired at a firing temperature of 00 to 2400 ° C. The firing time varies depending on the firing temperature, the type and amount of the sintering aid, and the average heating rate, but is usually selected from the range of 10 minutes to 20 hours. At a firing holding temperature of 1700 ° C or higher, the alkaline earth metal compound added as a sintering aid is melted and acts as a densification aid, and is eventually burned with evaporation according to its vapor pressure. The amount of auxiliary agent remaining in the body is less than 10% of the initial amount added.

Further, among the above-mentioned manufacturing methods, in a non-oxidizing atmosphere of vacuum or atmospheric pressure, for example, a method of firing at a high temperature under an atmosphere of nitrogen gas, helium gas, argon gas or the like or under a nitrogen gas pressure of about 2-100 atm. When adopted, the X-ray diffraction pattern of the obtained aluminum nitride sintered body is AlN single phase, and [002] plane (2θ = 36.2 °) / [100] plane (2θ = 33.2
The peak intensity ratio of () is 0.5 to 0.7.

Moreover, while directly applying a mechanical pressure of about ²⁰ to 500 kg / cm ^{2 in} a non-oxidizing atmosphere of vacuum or atmospheric pressure or 2 to 100
When a method of firing at a high temperature under a nitrogen gas pressure of about atmospheric pressure is adopted, the X-ray diffraction pattern of the obtained aluminum nitride sintered body is an AlN single phase, and the [002] plane (2θ =
The peak intensity ratio of (36.2 °) / [100] plane (2θ = 33.2 °) is 0.7 to 1.0.

〔effect〕

In the aluminum nitride sintered body of the present invention, the amount of the sintering aid contained after the sintering is the same as the addition amount of the sintering aid required for the sintering of the aluminum nitride powder. It is a remarkably small amount of 10% or less. Moreover, the oxygen content in the sintered body is smaller than that before firing.

Therefore, it is possible to obtain a high-purity aluminum nitride sintered body, that is, an aluminum nitride sintered body having a sintering aid content of less than 200 ppm in terms of oxide, and more preferably 150 ppm or less. Since these aluminum nitride sintered bodies have high purity, they have very good thermal conductivity. Thermal conductivity is usually
More than 120w / m ・ k can be obtained, preferably 140w / m ・ k
A sintered body having the above high thermal conductivity can be obtained. Moreover, an aluminum nitride sintered body having excellent translucency can be obtained.

Therefore, the aluminum nitride sintered body of the present invention is an industrially extremely useful material as a heat dissipation substrate for electronic equipment, an electronic circuit board, a heat dissipation material, and an insulating material.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 100 g of AlN powder having the composition shown in Table 1 containing 82% by volume of particles having an average particle size of 1.51 μm and 3 μm or less was used,
2.0 g of a single phase 3CaO.Al ₂ O ₃ powder was added by X-ray diffraction at 1.2 μm and mixed uniformly. About 1 g of the mixture was molded with a die having an inner diameter of 15 mmφ at a pressure of 200 kg / cm ² and then rubber pressed at a pressure of 1500 kg / cm ² to obtain a disc-shaped molded body. This molded body was placed in a graphite crucible whose inner wall was coated with boron nitride powder, heated to 1000 ° C in 40 minutes, heated from 1000 ° C to 1800 ° C at a heating rate of 15 ° C / min, and heated to 1800 ° C. It was kept at 10 ° C for 10 hours and then cooled. The obtained sintered body was a light-transmitting body having a brown color, and had a density of 3.26 g / cm ² . This sintered body was used for non-contact measurement of the thermal conductivity of a sample ground to a thickness of 3.0 mm using an infrared detector using an InSb semiconductor using a laser flash method thermal constant measuring device (PS-7) manufactured by Rigaku Denki. It was 155 W / m · k when measured by the method.

This aluminum nitride sintered body was placed in a platinum crucible and melted with alkali, and calcium was analyzed by inductively coupled plasma optical emission spectroscopy.
It was pm. In addition, Mg, Cr, S in the sintered body can be
When the contents of i, Zn, Fe, Cu, Mu, Ni, Ti and Co were measured, it was converted to the concentration in the sintered body and Hg <5ppm, Cr <10pp
m, Si = 83ppm, Zn <10ppm, Fe <10ppm, Cu <10ppm, Mu
<5ppm, Ni <20ppm, Ti = 20ppm, Co <10ppm.

On the other hand, the mixture of AlN and 3CaO ・ Al ₂ O ₃ is about 30 mm × 30 mm ×
A 2 mm ^t- shaped plate was sintered under the same conditions as above to obtain a sintered body having a density of 3.26 g / cm ³ . The oxygen content of this sample was measured by activation analysis and found to be 0.19 wt%. Further, the sintered body was ground to a thickness of 0.5 mm, and its both surfaces were mirror-polished, and the light transmittance was measured. As a result, a linear transmittance of 45% was obtained at a wavelength of 5.5 μm.

Example 2 The same method as in Example 1 was performed by using 100 g of AlN powder having the composition shown in Table 1 and containing 82% by volume of particles having an average particle size of 1.51 μm and 3 μm or less, using the sintering aid shown in Table 2. A molded body was created with. This molded body was placed in a graphite crucible whose inner wall was coated with boron nitride powder, heated to 1000 ° C. for 40 minutes, and fired at a firing temperature of 1000 ° C. or higher as shown in Table 2 to burn aluminum nitride. I got a union.

 The results are shown in Table 2.

The thermal conductivity was measured under the same conditions as in Example 1 for a sintered body ground to a thickness of 3 mm.

Example 3 To 100 g of AlN powder having a composition shown in Table 1 containing 82% by volume of particles having an average particle diameter of 1.51 μm and 3 μm or less, 1 to 5% by weight of various sintering aids shown in Table 3 was added, A molded body was prepared in the same manner as in Example 1. Place this compact in a graphite crucible with an inner wall coated with boron nitride powder,
The temperature was raised to 00 ° C. or higher for 40 minutes, and firing was performed under the firing temperature conditions of 1000 ° C. or higher shown in Table 3 to produce a sintered body. Table 3 shows the results. The thermal conductivity was measured in Example 1,
It measured by the method similar to 2.

Example 4 A molded body molded by the same method as in Example 1 was placed in a graphite crucible whose inner wall was coated with boron nitride powder.
Table 4 shows the results of manufacturing five types of aluminum nitride sintered bodies by heating the temperature to 00 ° C. for 40 minutes, changing the temperature rising rate from 1000 ° C. to 1800 ° C. variously, and firing at 1800 ° C. for 40 minutes. The thermal conductivity of the sintered body ground to 3 mm thickness was obtained in Examples 1 and 2.
It measured on the same conditions as. No. 4 and No. 5 are comparative examples.

Claims (1)

(57) [Claims] 1. (i) 95% by weight or more of aluminum nitride (ii) 0.0005% by weight or more and less than 0.02% by weight in terms of oxide of a sintering aid composed of a compound of an alkaline earth metal (iii) silicon, iron The content of compounds of chromium, chromium, nickel, cobalt, copper and titanium is 0.1 wt% or less as metal (iv) Oxidation content is 0.3 wt% or less (v) Density is 3.0 g / cm ³ or more Thermal conductivity 120 W / Aluminum nitride sintered body of mk or more