JPH05186207A - Aluminum nitride powder - Google Patents

Abstract

PURPOSE:To provide aluminum nitride powder so as to be smaller in the variation of the thickness in its sheet molding process. CONSTITUTION:The objective aluminum nitride powder satisfies the relationship: of Ax/Ay<3.0X10<-3> where Ax is the sum of the maximum absorbance for the absorption peak at a wave number of 3000 to 3450cm<-1> and that for the peak at a wave number of 3500 to 3800cm<-1> in its diffuse reflectance infrared absorption spectrum and Ay is the maximum absorbance for the absorption peak at a wave number of 900 to 1100cm<-1>.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an aluminum nitride powder having a specific surface condition.

[0002]

2. Description of the Related Art Recently, aluminum nitride powder has a high thermal conductivity and is in the spotlight as a raw material for an aluminum nitride sintered body which is extremely useful as an electronic material.
The aluminum nitride powder is, for example, disclosed in JP-A-59-500.
It is known from Japanese Patent Publication No. 08-08. The aluminum nitride powder described in the above publication is highly pure and fine particles, and is used as a raw material for an aluminum nitride sintered body having excellent properties such as high thermal conductivity and translucency. That is, the above publication discloses that the powder has an average particle size of 2 μm or less, an oxygen content of 1.5% by weight or less, and an aluminum nitride composition of A
0.3% by weight of cation impurities contained when 1N
The following aluminum nitride powder is shown.

[0003]

The above-mentioned aluminum nitride powder is a raw material of an aluminum nitride sintered body having excellent properties because it is highly pure and fine particles. However, it was difficult to make the above-mentioned aluminum nitride powder into a sufficiently stable slurry at the time of preparing the slurry for forming into a sheet or the like. For this reason, it is difficult to obtain a sintered body having a large thickness variation during sheet molding and having a high thickness accuracy in a sintered state without surface polishing.

[0004]

Therefore, the present inventors have
Research has been conducted for the purpose of obtaining an aluminum nitride powder that reduces variations in thickness during sheet forming. As a result, they have found that an aluminum nitride powder having a specific surface state achieves the above object, and completed the present invention.

That is, according to the present invention, in the infrared absorption spectrum by the diffuse reflection method, the wave number is 3000 to 3450 cm ^-1.
Absorbance of Absorption Peak and Wavenumber 3500-3800c
Let Ax be the sum of the maximum absorbances of the absorption peak at m ⁻¹ , and let the maximum absorbance of the absorption peak at the wave number of 900 to 1100 cm ^{−1 be} Ax.
When y, the aluminum nitride powder is characterized by satisfying the following formula Ax / Ay <3.0 × 10 ⁻³ .

The infrared absorption spectrum of the aluminum nitride powder of the present invention is measured by the diffuse reflection method. As an infrared absorption spectrum measuring device, for example,
An FTS-7 type infrared spectrophotometer manufactured by Nippon Bio Rat Laboratories can be used.

FIG. 1 is an infrared absorption spectrum of the aluminum nitride powder of the present invention obtained in Example 1 described later. In FIG. 1, the absorption peak appearing in the wave number range of 900 to 1100 cm ⁻¹ is estimated to be due to the vibration of Al—O. On the other hand, in FIG. 1, wave numbers 3000 to 3800
No visible absorption peak was observed in the cm ⁻¹ range, but it was measured using the above-mentioned infrared absorption spectrum measuring device.
The absorption peak can be confirmed by scanning 56 times and obtaining the integrated value. Wave number 3000 to 0 to 3
Absorption peak of 450 cm ^-1 and 3500～3800Cm ^-1 can be estimated to be due to vibration of O-H and N-H.

In the present invention, the wave numbers 3000 to 345
Maximum absorbance at 0 cm ^-1 absorption peak and wave number 3500-3
When the total of the maximum absorbance of the absorption peak at 800 cm ^-1 is Ax and the maximum absorbance of the absorption peak appearing in the wave number range of 900 to 1100 cm ^-1 is Ay, the following formula Ax / Ay <3.0 × 10 ^-3 I have to be satisfied. Ax / Ay is 3.0 × 10 ^-3
The above-mentioned aluminum nitride powder has unstable slurry characteristics, and particularly the thixotropy of the slurry increases, so that the thickness variation of the sheet molded body becomes large, and a sintered body having a highly accurate thickness cannot be obtained. To obtain better thickness accuracy, the above Ax / Ay is 2.0 x 1
It is preferably in the range of 0 ^-3 or less. Regarding FIG. 1, Ax / Ay is 0.15 × 10 ⁻³ .

From the above, it can be said that the aluminum nitride powder of the present invention is a powder having an extremely small amount of hydrophilic groups on the surface.

The aluminum nitride powder of the present invention should satisfy the above conditions, but in order to further improve the dimensional accuracy due to the dimensional shrinkage during sintering, the average particle size (D ₁ ) And the average particle diameter (D ₂ ) measured by the sedimentation method are both aluminum nitride powders satisfying the following formula 0.2 μm ≦ D ₁ ≦ 1.5 μm D ₂ / D ₁ <2.00. Here, the specific surface area of the aluminum nitride powder is B
It was obtained by nitrogen gas adsorption by the ET method. From this specific surface area, the particle diameter (D ₁ ) can be obtained by converting into a true sphere. The particle size (D ₁ ) obtained by this method represents the primary particle size of the aluminum nitride powder. On the other hand, sedimentation method, for example, automatic particle size distribution analyzer CAPA-500 manufactured by Horiba Ltd.
The average particle diameter (D ₂ ) measured by means of represents the average particle diameter of aggregated particles formed by aggregating primary particles.

Further, in order to obtain an aluminum nitride sintered body having further excellent thermal conductivity, it is preferable that the oxygen content and the cation impurities are small. That is, when AlN has an aluminum nitride composition, an aluminum nitride powder having an oxygen content of 1.5% by weight or less and a cation impurity of 0.3% by weight or less is preferable. Furthermore, an aluminum nitride powder having an oxygen content of 0.4 to 1.3% by weight and a cationic 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 the Al-N bond is replaced with the Al-O bond, but this bonded Al is not regarded as a cation impurity. Therefore, Al-N, Al
Metallic aluminum without the -O bond is a cationic impurity.

The aluminum nitride powder in the present invention may be obtained by any method.

Generally, it can be preferably produced by the following method. That is, the powder obtained by mixing alumina and carbon was treated with 1300 in a non-oxidizing atmosphere.
˜1700 ° C. and further 650 to 750 ° C. in an oxygen-containing atmosphere of oxygen of 25 mol% or more, or 650 to 750 ° C. twice or more in an oxygen-containing atmosphere of oxygen of less than 25 mol%. It is a method of baking.

Here, in order to reduce shrinkage of the obtained aluminum nitride powder during sintering, it is preferable that the raw material carbon has a specific sulfur content. That is, the sulfur content is 500 ppm to 7000 pp
m, preferably 1000 to 5000 ppm, more preferably 2000 to 5000 ppm.

Further, the carbon as a raw material in the present invention preferably has a specific specific surface area and a specific oil absorption amount. That is, the specific surface area is 60 m ² / g or more, preferably 1
0 to 300 m ² / g, and the oil absorption is 80 c
c / 100 g or more, preferably 100 to 200 cc /
It is preferably 100 g.

Alumina, which is one of the starting materials, is represented by Al ₂ O ₃ without any limitation. It may be an alumina compound obtained by firing an aluminum compound that can be converted to alumina by firing described later, for example, aluminum chloride, aluminum sulfate, aluminum nitrate, alum, aluminum hydroxide or the like. That is, a method of mixing an aluminum compound capable of forming alumina by firing and carbon, firing the mixture under the conditions described below to decompose the aluminum compound into alumina, and further firing the nitriding reaction is also adopted in the present invention. You can

As for the particle size of alumina, the particle size (D ₃ ) calculated from the specific surface area and the average particle size (D ₄ ) measured by the sedimentation method are
Those satisfying the following expressions 0.1 μm ≦ D ₃ ≦ 1.0 μm D ₄ / D ₃ ≦ 8.00 are preferably used. The particle diameter (D ₃ ) is preferably in the range of 0.1 μm ≦ D ₃ ≦ 0.8 μm. Further, D ₄ / D ₃ is preferably 6.00 or less, and more preferably 5.00 or less from the viewpoint of suppressing agglomeration of the produced aluminum nitride powder.

Most of the impurities contained in the above-mentioned raw materials carbon and alumina remain in the aluminum nitride powder to become impurities. Therefore, in order to obtain high-purity aluminum nitride powder, the ash content of carbon is 0.3
Wt% or less, preferably 0.2 wt% or less, and the purity of alumina is 99.0 wt% or more, preferably 99.5.
It is preferably at least wt%.

The mixing ratio of alumina and carbon is 1: 1.5.
It is preferably in the range of 1: 4 to 1: 4 for the purpose of obtaining an AlN powder having a very small degree of aggregation.
More preferably, it is in the range of 5.

The mixing of alumina and carbon may be either dry type or wet type, but in general, wet mixing is preferable in order to achieve sufficient mixing. Usually, mixing by a ball mill is suitable as the mixing means, but it is preferable that the containers, balls, etc. used at this time are made of high-purity alumina or plastic and the like to prevent contamination of impurities as much as possible. Examples of the ball mill include known ones such as a rotary ball mill and a vibro ball mill. Also,
Mixing with an attritor may also be employed. Further, in order to increase the reaction rate and minimize the amount of unreacted alumina, it is preferable to perform sufficiently uniform mixing. The mixed powder is put in a baking furnace 13
The aluminum nitride powder of the present invention can be obtained by firing at a temperature of 00 to 1700 ° C, preferably 1450 to 1650 ° C for usually 3 to 10 hours. If the firing temperature is lower than the above lower limit temperature, the nitriding reaction does not proceed sufficiently and the desired aluminum nitride powder may not be obtained, which is not preferable. Further, although the nitriding reaction sufficiently proceeds at a high temperature where the firing temperature exceeds the above-mentioned upper limit temperature, the particle size of the aluminum nitride powder that is often produced becomes large or the agglomeration becomes remarkable, and the fine powder of the present invention is obtained. It may not be possible, which is not preferable.

During the firing, it is preferable to consider the materials of the furnace material of the firing furnace and the boat so as not to cause impurities. Further, the firing atmosphere is preferably an atmosphere containing nitrogen, usually high-purity nitrogen gas or a gas obtained by adding ammonia gas or the like thereto, and usually these reaction gases are continuously added in an amount sufficient for the nitriding reaction to proceed. Alternatively, it may be fired while being intermittently supplied.

Since the mixture after firing contains unreacted carbon in addition to the aluminum nitride powder, the mixture is generally fired at a temperature of 650 to 750 ° C. in an oxygen-containing atmosphere to remove carbon. At this time, in the present invention, firing is performed in an oxygen-containing atmosphere in which oxygen content is 25 mol% or more, or oxygen content is 25 mol%.
In order to obtain the aluminum nitride powder of the present invention, firing twice or more in an oxygen-containing atmosphere of less than is essential.

The oxygen-containing atmosphere is preferably a mixed gas containing nitrogen and oxygen as main components. The composition of the mixed gas containing oxygen is nitrogen / oxygen = 10 mol.
% / 90 mol% to 75 mol% / 25 mol% is preferable. In this case, if the oxidation temperature is too high or the nitrogen / oxygen ratio is too small, the surface of the aluminum nitride powder is excessively oxidized, and it is difficult to obtain the target powder. In order to obtain a highly pure aluminum nitride powder having the desired surface characteristics, it is preferable to use a gas in the above composition range and further select an appropriate oxidation temperature and time. In addition, an oxygen-containing atmosphere in which oxygen is less than 25 mol%,
For example, even in the case of firing in the air, the aluminum nitride powder having the desired surface characteristics can be obtained by performing the oxidation treatment twice or more. At this time, the aluminum nitride powder of the present invention cannot be obtained even if the oxidation treatment is performed once and the treatment time is prolonged, and it is necessary to perform the oxidation treatment twice or more. The time of one oxidation treatment is within a range where carbon can be sufficiently removed, for example,
It may be selected from 4 to 20 hours.

[0025]

The aluminum nitride powder of the present invention has a specific surface state based on the type and amount of surface functional groups. Therefore, when the aluminum nitride powder of the present invention is used for molding, an extremely stable slurry can be obtained, and as a result, a sheet having extremely high thickness accuracy can be obtained particularly in a sheet molded body. Therefore, the sintered body of the sheet thus obtained has a process capability index (C
p) can be 1.0 or more. Further, when a specific raw material is used, it is possible to obtain an aluminum nitride powder in which the degree of aggregation of primary particles is extremely small. Therefore, when the aluminum nitride powder of the present invention is used for sintering, the linear shrinkage can be 14% or less. As described above, the aluminum nitride powder of the present invention has good dimensional stability during sintering in both thickness and surface direction, and can significantly increase the process capability index.

Therefore, the aluminum nitride powder of the present invention is suitable for use in the simultaneous firing method in which a paste of a refractory metal is printed on the surface and fired, because the difference in shrinkage with the metal can be reduced. To be done. In particular, it is preferably used for an aluminum nitride laminated package substrate which requires high accuracy in sheet thickness and shrinkage rate one by one.

Further, when aluminum nitride powder having a low oxygen content and a small amount of cationic impurities is used as a raw material, in addition to the above effects, an aluminum nitride sintered body having high thermal conductivity and translucency is obtained. Obtainable.

[0028]

EXAMPLES The following examples and comparative examples are given in order to explain the present invention more specifically, 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) Carbon ash content: JIS K-62
According to 21-1970, it was determined from the weight after ashing at 750 ° C.

2) Carbon oil absorption: JIS K-62
According to 21-1970, it was determined from the amount of dibutyl phthalate added dropwise.

3) Specific surface area: determined by the BET method by N ₂ adsorption. (Shimadzu (manufactured) "Flowsorb 2300"
4) Average primary particle size of powder (D ₁ , D ₃ ) Average primary particle size (μm) = 6 / (S × ρ) S: Specific surface area of powder (m ² / g) ρ: Apparent density of powder 6 : constant 5) average agglomerated particle size of the powder (D _2, D _4): was determined by centrifugal sedimentation. (Using "CAPA500" manufactured by HORIBA, Ltd.) 6) Impurity amount in powder Cation impurity amount: The powder was alkali-melted, neutralized with acid, and quantified by ICP emission spectroscopic analysis of the solution. (Shimadzu Corporation [ICPS-1000] is used) Impurity carbon amount: C generated by burning powder in an oxygen stream
It quantified from the amount of O and CO ₂ gas. (Using "EMIA-110" manufactured by HORIBA, Ltd.) Impurity oxygen amount: determined from the amount of CO gas generated by the high temperature thermal decomposition method of the powder in the graphite crucible. (Using "EMGA 2800" manufactured by Horiba Ltd.) 7) Sulfur content: Automatic combustion type sulfur content tester (titration method) (manufactured by Yoshida Scientific Co., Ltd.) is used.

8) Apparent density: Determined by the helium substitution type pressure comparison method. (Using an auto pycnometer 1320 manufactured by Shimadzu Corp.) 9) Density (d (g)) of sheet molded body: AlN powder and a dispersant are dispersed in an organic solvent to form a slurry, which is prepared by a doctor blade method. The green density was calculated from the size and weight of the molded product obtained by molding, and the molding density of only the AlN powder was calculated from this value.

D (g) = (green density of compact) × (weight of AlN in slurry) / {(weight of slurry) − (weight of organic solvent)} 10) density of sintered AlN (d (S)): Archimedes Obtained by law. ("Toyo Seiki Co., Ltd.""high-precision specific gravity meter D-
H ”) 11) AlN sintered body thermal conductivity: Measured by a two-dimensional method by a laser flash method. (Using "Thermal constant measurement device TC-7000" manufactured by Vacuum Riko Co., Ltd.) 12) Shrinkage rate during sintering: Determined by dimensional measurement before and after sintering.

Shrinkage = (1-dimension of sintered body / dimension of compact before sintering) × 100 13) Surface characteristics of powder Pretreatment of sample 2 g of aluminum nitride powder at 150 ° C.
It was treated under a reduced pressure of 30 mmHg for 3 hours.

Diffuse Reflectance FT-IR Measurement-Japan Biorat Laboratories FTS-7 type infrared spectrophotometer was used.

Scanning was performed 256 times at a resolution of 8 cm ^-1 and the value was calculated from the integrated value.

For background correction, KBr powder was used, and then automatic correction was performed.

Kubelk for the purpose of further increasing the quantitativeness
The a-Munk conversion process was performed.

Absorbance Ax is wave number 3000 to 3450c
Maximum absorbance at m ^-1 absorption peak and wave number 3500-380
The maximum absorbances of the absorption peaks at 0 cm ^-1 were summed, and the absorbance Ay was determined from the maximum absorption peak at 900 to 1100 cm ^-1 .

14) Process capability index (Cp) Cp = standard width / 6S (S: standard deviation) Here, the tolerance of thickness is set to ± 5%, and the standard width is defined by the following formula: Standard width = thickness average value It was determined by × 0.05 × 2.

Example 1 Purity 99.9%, average particle size (D ₄ ) measured by sedimentation method 0.95 μm, specific surface area 8.0 m ² / g, particle size calculated from specific surface area (D ₃ ) 0. 19 μm, D ₄ / D ₃ =
15 kg of 2.00 Al ₂ O ₃ powder and 0.06 ash
% By weight, sulfur content 2510 ppm, specific surface area 120
m ² / g, oil absorption 115 cc / 100 g of carbon 35
kg was mixed using a nylon lined pot and a nylon coated ball. Put the mixed powder in a high-purity graphite dish,
Heat treatment was carried out at 1550 ° C. for 6 hours under N ₂ gas flow. Then, decarburization treatment was performed in the atmosphere at 650 ° C. for 10 hours. This treatment in air was performed twice in total to obtain aluminum nitride powder.

The X-ray diffraction pattern of the obtained powder is AlN
Only the peak of is shown. The infrared absorption spectrum is shown in Fig. 1.
And Ax / Ay = 0.15 × 10 ⁻³ . Other properties are shown in No. 2 of Table 2. It is as shown in 1.

Next, 10 kg of the obtained AlN powder and Y ₂ O ₃
375 g, 100 g of sorbitan trioleate, 3.3 kg of toluene, and 2.7 kg of ethanol were placed in a nylon-lined pot having an internal volume of 50 l and mixed using a nylon-coated ball for 24 hours.

Polyvinyl butyral 70 was added to the mixed slurry.
0 g, 700 g of benzyl butyl phthalate, 1.1 kg of toluene, and 900 g of ethanol were added and further mixed for 24 hours. The resulting slurry has a viscosity of 25000 cps
Vacuum degassing was performed until the temperature reached (at 25 ° C.).

The defoamed slurry was molded by a doctor blade sheet molding method to obtain a molded body having a thickness of 1.01 mm.
150 sheets of this molded body were punched out with a mold having a 59 mm opening to obtain a sample for a sintering test. Sheet compact density (d
(G)) was 2.11 (g / cm ³ ).

The punched molded body was degreased in air at 600 ° C. for 3 hours in a muffle furnace. Then, this molded body was put in a baking tray made of BN and a sintering test was performed. Sintering was performed in a N ₂ stream at a temperature rising rate from room temperature to 1800 ° C. of 5 ° C./min, at 1800 ° C. for 7 hours, and after natural cooling. The obtained sintered body was subjected to measurement of thickness, size and thermal conductivity.

The density of the obtained sintered body is 3.328 g on average.
/ Cm ³ , standard deviation 0.003 g / cm ³ , size averages 5
The average thickness was 1.071 mm, the standard deviation was 0.075 mm, the thickness was 0.871 mm, and the standard deviation was 0.009 mm. When the thickness tolerance was set to ± 5%, the process capability index regarding the thickness of the sintered body of this sheet was Cp = 1.61.

Example 2 The alumina powder shown in Table 1 and carbon were mixed in various weight ratios, heat-treated in a nitrogen stream in the same manner as in Example 1, and then decarburized by various methods. Did. The X-ray diffraction pattern of the obtained powder was all AlN single phase. Next, molding and firing were performed in the same manner as in Example 1, and the dimensions, thickness and physical properties of the sintered body were measured. The results are shown in Table 2. No. 5 in Tables 1 and 2 is a comparative example.

[0050]

[Table 1]

[0051]

[Table 2]

[Brief description of drawings]

FIG. 1 is an infrared absorption spectrum of the aluminum nitride powder of the present invention.

Claims (1)

[Claims] 1. A infrared absorption spectrum by diffusion reflection method, the sum of the maximum absorbance of the absorption peak of maximum absorbance and the wave number 3500～3800Cm ^-1 of the absorption peak at a wavenumber 3000～3450Cm ^-1 and Ax, wave number 900-110
When the maximum absorbance of the absorption peak at 0 cm ^-1 is Ay,
An aluminum nitride powder characterized by satisfying the following formula: Ax / Ay <3.0 × 10 ⁻³ .