JP2003034522A - Method for manufacturing coated magnesium oxide powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnesia powder having superior durability, moisture resistance, and dispersability into resins. SOLUTION: The manufacturing method is characterized in that, by mixing an aluminum salt aqueous solution and magnesium oxide powders, filtering solid components, washing it with water, drying it, and firing it, the surface of magnesium oxide powder is coated with a coating layer containing aluminum magnesium composite oxide.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the production of a heat conductive filler, and more particularly to the production of a heat conductive filler having improved hydration resistance of magnesium oxide powder and excellent in heat dissipation characteristics.

[0002]

2. Description of the Related Art Conventionally, silicon dioxide (hereinafter referred to as silica) powder or the like has been used as a material for a filler such as a resin for semiconductor encapsulation. 2. Description of the Related Art In recent years, the amount of heat generated by semiconductor elements has increased with the high integration and high power consumption of semiconductor elements. Therefore, the thermal conductivity efficiency of silica is not sufficient to dissipate heat, which causes a problem in stable operation of semiconductors.

Therefore, instead of silica, magnesium oxide (hereinafter referred to as magnesia) having a heat conductivity higher by one digit is used as a material for a resin filler for semiconductor encapsulation.
However, magnesia powder has greater hygroscopicity than silica powder. Therefore, when magnesia powder is used as the resin filler for sealing the semiconductor, the absorbed water and magnesia are hydrated, and cracks occur due to volume expansion of the filler, which causes problems such as reduced thermal conductivity. Was there.
Thus, imparting moisture resistance to the magnesia powder used as the resin filler for semiconductor encapsulation has been a major problem in ensuring long-term stable operation of the semiconductor.

As a method for improving the moisture resistance of magnesia powder, it has been disclosed to perform surface treatment with an inorganic coupling agent such as silane. However, during the kneading process with the resin, the surface-treated treatment agent was easily peeled off from the surface of the magnesia powder, resulting in lack of mechanical strength. for that reason,
Moisture resistance was not sufficient, and the magnesia powder as a filler raw material was hydrated to change to magnesium hydroxide Mg (OH) ₂ and a whitening phenomenon occurred, which was not at a practical level.

Further, a method of coating magnesia particles with a chemically stable compound by an alkoxide method, a uniform precipitation method or the like has been studied. In the alkoxide method,
The particles to be coated (core particles) are dispersed and mixed in a solution in which an alkoxide is dissolved in alcohol, and then distilled water is added to hydrolyze the alkoxide to coat the core particles with the produced metal hydroxide. To process. However, when distilled water was added, the hydrolysis reaction of the alkoxide did not proceed uniformly in the solution, so it was difficult to form a uniform metal hydroxide coating layer on the surface of the core particles.

In the homogeneous precipitation method, a precipitating agent is usually added to the solution in advance to control the pH of the solution to control the rate of metal hydroxide formation. For this reason,
Unlike the alkoxide method, the metal hydroxide can be uniformly deposited. However, in the case of magnesia particles, since the pH of the solution changes with the hydration of magnesia, the pH of the solution cannot be controlled even if a precipitant is added,
Uncontrolled formation of metal hydroxides. Therefore, it is difficult to selectively deposit another metal hydroxide only on the surface of the magnesia particles.

In Japanese Patent Laid-Open No. 3-8714, a solution of a metal salt is gradually added dropwise to a dispersion of magnesia powder under heating and stirring under reflux to precipitate a metal hydroxide, which is then filtered and washed. , A method of producing a metal oxide-coated magnesia powder which is dried and subjected to heat dehydration treatment is disclosed. In this method, a solvent such as alcohol is used, and it is necessary to drop the metal compound solution while heating and stirring under reflux, so that the steps are complicated and costly.

As described above, in the conventional technique, the mechanical strength of the coating layer and the coating of the magnesia powder surface are not perfect,
Moisture resistance sufficient as a filler for a resin for semiconductor encapsulation has not been obtained.

Further, the magnesia powder to be the core particles also has strong cohesiveness when obtained by thermal decomposition of various magnesium compounds such as magnesium hydroxide and basic magnesium carbonate, and the dispersibility is not sufficient for kneading with the resin. There is a problem.

[0010]

In view of the above problems, an object of the present invention is to provide a magnesia powder excellent in durability and moisture resistance and dispersibility in a resin, particularly a filler such as a resin for semiconductor encapsulation. Is to provide a magnesia powder that can be used as.

[0011]

The inventor has found the present invention as a result of various studies in order to achieve the above object. That is, by coating the surface of the magnesia powder with a double oxide of aluminum (Al) and magnesium (Mg), the mechanical strength of the coating layer can be easily maintained at low cost while maintaining hydration resistance (moisture resistance). Further, they have found a method for producing a magnesia powder having excellent electrical insulating properties and thermal conductivity, which further improves dispersibility in a resin.

According to the method of the present invention, an aqueous solution of an aluminum salt is mixed with magnesium oxide powder, and a solid content is separated by filtration.
The present invention relates to a method for producing a coated magnesium oxide powder, which comprises coating the surface of the magnesium oxide powder with a coating layer containing a double oxide of aluminum and magnesium by washing with water, drying and firing.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the "aluminum-magnesium composite oxide" is a metal oxide containing aluminum, magnesium and oxygen, and includes spinel and the like. Further, “composite of MgO and Al ₂ O ₃ ” has the same meaning. In the present invention, the “coating layer” is a layer containing a double oxide of aluminum and magnesium and contains spinel. Further, the boundary with the magnesium oxide particles, which are the core particles, may be discontinuous. In the present invention, the “crystallite size” is a value calculated by the Scherrer equation using the X-ray diffraction method. In general, one particle is a polycrystal composed of a plurality of single crystals, and the crystallite diameter indicates the average value of the sizes of the single crystals in the polycrystal. The "particle diameter" is a volume average diameter measured by a laser diffraction method. In general,
This is the size of the particles. In the present invention, “spinel” is phenocrite, which is an equiaxed substance having the composition formula Al ₂ MgO ₄ . In the present invention, "baking" means
The firing temperature is set below the melting temperature of the coating material. Here, the coating material does not dissolve.

According to the method of the present invention, when an aluminum salt solution such as an aluminum nitrate solution is mixed with magnesia, aluminum hydroxide is produced by the following reaction (see FIG. 1 (A)).

2Al (NO ₃ ) ₃ + 3MgO + 3H ₂ O → 2
_{Al (OH) 3 + 3Mg (} NO 3) 2

According to the method of the present invention, it is preferable to mix the aluminum salt and magnesia by a wet method in order to uniformly form a composite of MgO and Al ₂ O _{3 on} the surface of the magnesia powder when mixing. Considering the addition amount and the mass increase rate, the mixing ratio of the aluminum salt converted to Al ₂ O ₃ is 1 to the magnesium oxide powder.
It is preferably from 35 to 35 mass%, more preferably from 5 to 25 mass%.

According to the method of the present invention, an aqueous solution of an aluminum salt is mixed with magnesium oxide, and the solid content is separated by filtration or the like. Washing the collected solids with water
In order to prevent water-soluble magnesium nitrate from remaining on the outside of Al (OH) ₃ adsorbed on magnesia, it is preferable to perform it sufficiently. This is to prevent the residual magnesium nitrate from forming MgO on the outside of the hydration resistant / moisture resistant coating layer upon firing, thereby inhibiting the performance of the coated magnesia obtained by the method of the present invention. Is. It is preferable to dry and crush the solid content washed with water. A mill can be used for crushing.

The crushed solid is calcined to obtain coated magnesia (see FIG. 1 (B)). Here, considering the BET specific surface area and the mass increase rate, it is preferable to perform the firing at a temperature of 1473 to 2073 K which is equal to or lower than the melting point of the coating material,
1673-1873K is more preferable.

Further, according to the method of the present invention, it is not necessary to use an organic solvent such as alcohol, nor is heating or dropping necessary. Therefore, it is possible to easily manufacture the magnesia powder having excellent hydration resistance at low cost.
In addition, by going through a firing step for converting aluminum hydroxide into spinel, the particle size distribution becomes sharp, and when kneaded with a resin, magnesia powder having excellent dispersibility can be produced.

The aluminum salt used in the present invention is preferably one salt selected from the group consisting of aluminum nitrate, aluminum sulfate and aluminum chloride.
The purity of the aluminum salt is preferably 98% or more. Also, a hydrate can be used.

The magnesia powder used in the present invention has a crystallite diameter of 50 × 10 ^-9 m or more. The purity is not limited, but a purity of 95% or more is preferable for the insulating properties of electronic parts.

The crystallite size of magnesia used in the present invention is
It is preferably 50 × 10 ⁻⁹ m or more. This is because aluminum hydroxide can be deposited only on the surface of the magnesia particles by using magnesia having a crystallite diameter of 50 × 10 ⁻⁹ m or more in order to improve hydration resistance. Magnesia having a crystal particle size of 50 × 10 ⁻⁹ m or more has low reactivity as compared with a finer powder. Therefore, as a result of the above reaction proceeding only on the magnesia surface, aluminum hydroxide can be uniformly deposited on the surface of the magnesia particles. The average particle size of magnesia is preferably 5 × 10 ^{−6 to} 500 × 10 ⁻⁶ m, and 10
× 10 ^{−6 to} 100 × 10 ⁻⁶ m is more preferable. The average particle size affects the efficiency and amount of coating on magnesia, and the mechanical and electrical properties. According to the method of the present invention, the component that coats magnesia is a complex oxide formed by the reaction of Al and Mg, and does not deteriorate the high thermal conductivity and high electrical insulation of magnesia.

According to the present invention, magnesia having the characteristics of the present invention can be formed using known methods. For example, it can be formed using an electrofusion method, a sintering method, or the like.

In the coated magnesium oxide according to the present invention, the average particle size is preferably 5 × 10 ^{−6 to} 500 × 10 ⁻⁶ m, more preferably 10 × 10 ^{−6 to} 100 × 10 ⁻⁶ m. The BET specific surface area is preferably 1.0 × 10 ³ m ² / kg or less, more preferably 0.5 × 10 ³ m ² / kg or less.

[0025]

EXAMPLES The present invention will be specifically described with reference to Examples.
The present invention is not limited to the examples below.

Example 1 (a) Magnesium oxide having a crystallite size of 58.3 × 10 ⁻⁹ m (KMAO-H manufactured by Tateho Chemical Industry Co., Ltd.) was used with an alumina ball mill to have a particle size of 45 × 10 ^{−. It} was crushed to ⁶ m or less. 4% aluminum nitrate aqueous solution [Al (NO ₃ ) ₃ ·
9H ₂ O] (special grade reagent manufactured by Kanto Chemical Co., Inc.) was converted to Al ₂ O ₃ and added so that the mixing ratio was 11 mass% with respect to magnesium oxide, and 400 to 500 rp was added.
The mixture was stirred and mixed at 600 m for 600 s. (b) After stirring and mixing, the mixture was filtered, and when a cake was formed, it was thoroughly washed with distilled water to remove residual aluminum nitrate. The cake washed with water was dehydrated.
The cake was dried overnight at 383K using a dryer. The dried cake was crushed for 60 s with a mill to adjust the particle size to the same level as the raw material magnesium oxide powder. (c) 40 × 10 ⁻³ kg of the powder of the above step (b) is added to 1 × 10 ⁻⁴
It was put in an alumina crucible having a volume of m ^{3 and} fired in air at 1673 K for 3600 s. After the firing, the crucible was taken out from the furnace after being left to cool to 1223 K in the furnace, and rapidly cooled at room temperature to obtain a heat conductive filler sample. The BET specific surface area, average particle size and moisture resistance of the sample were measured. The results are shown in Table 1.

BET Specific Surface Area: The specific surface area of the powder sample was measured by a gas adsorption method using Flowsorb II2300 manufactured by Shimadzu Corporation. Average particle size: The volume average particle size of the powder sample was measured using a particle size distribution measuring device (Microtrac HRA) by a laser diffraction / scattering method. Moisture resistance test: 10 x 10 ^-3 kg of the obtained sample was measured at a temperature of 3
It was stored in a thermo-hygrostat set at 33 K and humidity of 90% for 8 days, and the mass increase rate was measured to evaluate the humidity resistance.

Example 2 Epoxysilane was added to the sample prepared in Example 1 at 1.0 ma.
Add ss%, stir and mix for 60 s for surface treatment, then 4
It was dried at 22K for 7200s. 231 parts by weight of the obtained sample was used as an orthocresol novolac type epoxy resin 5
Using 1.8 parts by weight, 46.2 parts by weight of novolac type phenol resin, 1 part by weight of triphenylphosphine and 2 parts by weight of carnauba wax, 600 s were mixed and pulverized using a disintegrator. Then, the mixture is 373 using a two-roll.
The mixture was kneaded for 300 s at K, and then this kneaded material was further pulverized to 10 mesh or less to produce pellets of φ38 × t15 mm. The pellets were pressure molded at 7 MPa and 448 K for 180 s, and then post-cured at 453 K for 18 × 10 ³ s to obtain a molded body of φ50 × t3 mm. This molded product was subjected to a weather resistance test, and changes in appearance were observed. The results are shown in Table 2.

Weather resistance test: The obtained molded body was subjected to a temperature of 33
It was stored in a thermo-hygrostat set at 3K and a humidity of 90% for 8 days, and the appearance was observed to evaluate the moisture resistance after kneading with the resin.

Comparative Example 1 Magnesium oxide (KMAO-manufactured by Tateho Chemical Industry Co., Ltd.)
H) with an alumina ball mill having a particle size of 45 × 10
The sample of Comparative Example 1 was obtained by crushing to ^-6 m or less. A sample of Comparative Example 1 was obtained without further treatment. Samples were tested as in Example 1. The results are shown in Table 1.

Comparative Example 2 Magnesium oxide (KMAO-manufactured by Tateho Chemical Industry Co., Ltd.)
H) with an alumina ball mill having a particle size of 45 × 10
Crushed to less than ^-6 m and then added epoxy silane to 1.0 ma
ss% was added, and the mixture was stirred and mixed for 60 seconds for surface treatment. Then, it was dried at 423 K for 7200 s to obtain a sample of Comparative Example 2. Samples were tested as in Example 1. Table 1
The results are shown in.

Comparative Example 3 A molded body was prepared in the same manner as in Example 2 except that the sample of Comparative Example 2 was used. The molded body thus obtained was subjected to a weather resistance test, and changes in appearance were observed. The results are shown in Table 2.

[0033]

[Table 1]

As is clear from Table 1, in Example 1 according to the method of the present invention, Al was wet-added, washed with water, and then calcined at 1673 K to form a composite of Al _{2 on the} surface of Mg _2. Since MgO ₄ was formed uniformly, it was possible to suppress an increase in mass due to water adsorption, and it was excellent in moisture resistance.

The heat conductive filler (Al-added 1673K fired product) according to Example 1 of the present invention was superior in moisture resistance to Comparative Example 1 which was not coated at all. In addition, Example 1 has hydration resistance equal to or higher than that of Comparative Example 2.

[0036]

[Table 2]

In Example 2 of the present invention, the weather resistance was maintained even after kneading with the resin. However, the whitening phenomenon was observed in Comparative Example 3 surface-treated with epoxysilane, and there was almost no weather resistance after kneading with the resin.

[0038]

EFFECTS OF THE INVENTION According to the method of the present invention, since the magnesia powder having excellent electric insulating properties and thermal conductivity is used as a filler such as a resin for semiconductor encapsulation, hydration resistance (moisture resistance), coating layer The mechanical strength of, and further dispersibility in resin,
It can be easily applied at low cost.

[Brief description of drawings]

FIG. 1 is a manufacturing process flow of a method of the present invention.

[Explanation of symbols]

1 core particle, magnesium oxide, MgO 2 aluminum hydroxide, Al (OH) ₃ 3 coating layer, coating material, spinel, Al ₂ MgO ₄

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yutaka Hirats             974 Kato, Kariya, Ako City, Hyogo Vertical             Ho Chemical Industry Co., Ltd. F-term (reference) 4G076 AA02 AB02 BF05 CA02 CA26                       CA28 DA20

Claims (7)

[Claims] 1. An aqueous solution of an aluminum salt and magnesium oxide powder are mixed, solids are separated by filtration, washed with water, dried and calcined, whereby the surface of the magnesium oxide powder is mixed with aluminum and magnesium. A method for producing a coated magnesium oxide powder, which comprises coating with a coating layer containing an oxide. 2. The method of claim 1, wherein the aluminum salt is one salt selected from the group consisting of aluminum nitrate, aluminum sulfate and aluminum chloride. 3. The crystallite size of the magnesium oxide particles is
The method according to claim 1 or 2, which has a size of 50 × 10 ^-9 m or more. 4. The coated magnesium oxide powder according to claim 1, wherein the composition ratio of the aluminum and magnesium double oxides is 5 to 50 mass% with respect to the coated magnesium oxide. Method. 5. The mixing ratio of the aluminum salt converted to Al ₂ O ₃ is 1 to 35 ma based on the magnesium oxide powder.
The method according to claim 1, wherein the method is ss%. 6. A firing temperature 1473 to below the melting point of the coating material.
The method according to any one of claims 1 to 5, which is fired at 2073K. 7. The coated magnesium oxide having an average particle diameter of 5 × 10 ^{−6 to} 500 × 10 ⁻⁶ m, and BET
2. The specific surface area is 1.0 × 10 ³ m ² / kg or less.
7. The method according to any one of 6 to 6.