JPH01198404A - Inorganic sintering body and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an inorganic sintered body having excellent heat conductivity and electrical insulating property by mixing alumina-coated Al powder and low melting point glass powder at the specific ratio, compacting and sintering. CONSTITUTION:The low melting point glass powder having about 1-10mum particle size and 200-600 deg.C softening point of PbO series, B2O3 series, ZnO series, PbO-B2O3 series, etc., is mixed to 50-97wt.% the Al powder having <=30mum median of size for 50% particles forming coated layer of Al2O3, which the surface is oxidized by chemically oxidize-treating the Al powder, at 50-3wt.%. Then, binder of stearic acid, polyvinyl alcohol, etc., diapersant of surface active agent, etc., and organic solvent of acetone, lower alcohol, etc., are added to the above mixed material, to make slurry state. After drying this paste at 80 deg.C, it is cold-pressed and successively, by sintering at for example 500 deg.C, the inorganic sintered body having excellent heat conductivity and electrical insulating property is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an inorganic sintered body and a method for producing the same. The inorganic sintered body of the present invention has excellent thermal conductivity and insulation properties, so it can be used as a circuit board for electronic components, a heat sink, etc.
Useful.

BACKGROUND ART Conventionally, resins and ceramics have been used as circuit board materials for electronic components. However, resin circuit boards have problems such as low thermal conductivity and corrosion of wiring due to moisture permeability.

Further, known ceramic circuit boards have low thermal conductivity (and high sintering temperatures, making it difficult to co-fire with base metal pastes having low melting points).

Means for Solving the Problems In view of the current state of the prior art as described above, the present inventor has conducted various studies and has developed a method in which a mixture of alumina-coated aluminum powder and low-melting glass is molded and sintered. It has been found that the problems of the prior art can be greatly alleviated.

That is, the present invention provides the following inorganic sintered body and its manufacturing method: ■ An inorganic sintered body consisting of 50 to 97% by weight of alumina-coated aluminum powder and 50 to 3% by weight of low melting glass. and (2) a method for producing an inorganic sintered body, which comprises molding a mixture of 50 to 97% by weight of alumina-coated aluminum powder and 50 to 3% by weight of low-melting point glass, and then sintering the mixture.

The alumina-coated aluminum powder used in the present invention can be produced by any method. Typically, the particle size has a 50% median particle size of 30 μm or less, more preferably 20 μm or less, and an oxygen content of 1.5 to 20 μm.
About % by weight (hereinafter all % means % by weight) is used, more preferably about 3 to 10%.

The particle size of the alumina-coated aluminum powder is preferably as small as possible in order to improve the smoothness of the surface of the circuit board. If the median 50% particle size exceeds 30 μm, the smoothness of the circuit board surface will be significantly impaired.

Further, if the oxygen content exceeds 20%, the thermal conductivity decreases, whereas if the oxygen content exceeds 1.5%, the insulation property decreases.

The alumina-coated aluminum powder as described above is, for example,
Raw material aluminum powder may be subjected to chemical oxidation treatment to form a hydrated oxide film on its surface, and then heat treatment may be performed to convert the film into an alumina layer. The composition of the raw material aluminum powder is not particularly limited, and high-purity aluminum powder, high-silicon aluminum alloy powder, etc. are used. Further, the form of the raw aluminum powder is not particularly limited, and examples thereof include spherical to teardrop-shaped powder obtained by an atomizing method. Chemical oxidation treatment of raw aluminum powder includes, for example, immersion in water at room temperature for a long time; immersion in aqueous solutions such as chromate, phosphoric acid-chromate, and phosphoric acid-alcohol; various alkalis. Methods include immersion in aqueous solutions of (sodium hydroxide, ammonia, amines, alcohol amines, etc.); methods of immersion in solutions of various acids (sulfuric acid, nitric acid, boric acid, etc.); methods of contact with pressurized steam or high-temperature water, etc. Can be mentioned. Among these methods, the method of contact treatment with pressurized steam or high-temperature water is preferable because it forms a dense boehmite film or pseudo-boehmite containing payerite on the surface of the aluminum powder.

The aluminum powder with a hydrated oxide film formed on its surface in this way is dried, and then dried for 350 minutes under reduced pressure or in the atmosphere.
A heat treatment at a temperature of about ˜600° C. converts the hydrated oxide film into an alumina film to obtain the desired alumina-coated aluminum powder. If the heat treatment temperature is less than 350°C, a non-negligible amount of crystal water may remain, while if it exceeds 600°C, aluminum powder may fuse together.

As the low melting point glass used in the present invention, known low melting point glasses for sealing electronic components can be used, and specifically, pbo type, B2O3 type, ZnO type, PbOB2O3 type, Pb0-B2O3-8i02 type. , ZnOA (2203
Examples include systems. Low melting point glass usually has a softening point of 100
-about 660℃, more preferably softening point 200-600
Use a temperature around ℃. If the softening point of the glass is less than 100°C, the heat resistance of the sintered body will be insufficient;
If the temperature exceeds 60°C, it is necessary to increase the sintering temperature, so that the alumina-coated aluminum powder starts to melt and flow during the production of the sintered body. The particle size and shape of the low melting point glass are not particularly limited, but from the viewpoint of ease of handling and uniform mixability with alumina-coated aluminum powder, it is preferable to use it in the form of a powder with a particle size of about 1 to 10 μm. preferable.

The mixing ratio of the alumina-coated aluminum powder and the low melting point glass is usually in the range of 50 to 97:50 to 3, more preferably in the range of 80 to 95:20 to 5 by weight.

The amount of alumina coated aluminum powder in the mixture is 50%
If it is less than 97%, the thermal conductivity of the sintered body decreases, whereas if it exceeds 97%, it becomes difficult or impossible to sinter the molded product.

The inorganic sintered body of the present invention is prepared by adding a small amount of a binder, a dispersant, an organic solvent, etc. to 100 parts by weight of a mixed powder of alumina-coated aluminum powder and low-melting glass according to a conventional method, and kneading the mixture to form a slurry. After forming into a predetermined shape, the temperature is 100 to 660°C depending on the softening point of the low melting point glass used.
Sintering is performed at a temperature within the range of 1 to 10 hours. All known materials can be used other than the alumina-coated aluminum powder and the low-melting glass. For example, the binder may be stearic acid, polyvinyl alcohol, etc. The dispersant may be a surfactant, etc. 1. Organic solvent Examples include acetone, methyl ethyl ketone, and lower alcohols.

In the present invention, since the temperature during firing of the compact is low, if necessary, the base metal conductive paste layer for circuit formation can be fired at the same time to form a circuit.

Effects of the Invention According to the present invention, the following remarkable effects are achieved.

(1) The inorganic sintered body of the present invention has excellent thermal conductivity due to the presence of aluminum, so its heat dissipation as a substrate for electronic components is significantly improved.

(2) Since low temperature firing is possible when forming the substrate, a base metal conductive paste layer with low electrical resistance can be sintered at the same time.

(3) As a result, it is possible to obtain a co-fired substrate with a lower calorific value than when a circuit made of a conductive paste layer of Mo, W, etc. is formed by high-temperature co-firing with the substrate material.

(4) Since the individual particles of the alumina-coated aluminum powder used are insulated by the alumina coating, short circuits will not occur between the through holes of the laminated substrate.

EXAMPLES Examples will be shown below to further clarify the features of the present invention. In the following, "%" and "parts" mean "% by weight" and "parts by weight", respectively.

Example 1 Atomized aluminum powder (oxygen content 0.30%)
was immersed in deionized water at 70°C for 50 minutes to form a hydrated aluminum film on its surface, filtered and dried, and then heat-treated at 500°C for 3 hours in an electric furnace communicating with the atmosphere to form alumina. Coated aluminum powder (50% median particle size 2
0 μm) was obtained. The oxygen content of the alumina-coated aluminum powder obtained was 5.2%. The oxygen content was measured using an EMGA-2800 oxygen measuring device manufactured by Horiba, Ltd.

The alumina-coated aluminum powder (referred to as aluminum powder) obtained as described above and the low-melting point glass powder for semiconductor sealing (PbO
-B203-3i02 system: Nigarasu powder with a softening point of 397°C and a median particle size of 50% of 4.7 μm) was used to obtain mixtures Nos. 1 to 8 with the blending ratios shown in Table 1.

Table 1 Next, 10 parts of stearic acid, 1 part of nonionic surfactant and 40 parts of acetone were added to 100 parts of each of Mixture Nos. 1 to 8, and the mixture was heated in a polyethylene-lined ball mill using alumina balls for 24 hours. Knead for an hour,
It turned into slurry.

The obtained slurry was dried at 80°C for 3 hours, formed into a pellet with a diameter of 10 m + a x height of 2.5 mm by cold pressing, and fired at 500°C for 3 hours to form a sintered body No.

1 to 8 were obtained.

The thermal conductivity of the obtained sintered body was measured by a laser flash method, and the volume resistivity was determined.

The results are shown in Table 2.

Table 2 Sintered body Thermal conductivity Volume resistivity No.
(W/mk) (Ω・cm)1 (
Note 1) (Note 1) 2 195 7.5xlO1132007,8
xlO" 4 170 8.5x10115 155
3.2x10126 105 8.9x
lO127654, 2xlO' 8 30 7, 4xlO13 (Note 1): Unmeasurable due to insufficient sintering of the compact Example 2 The 50% median particle size of the alumina-coated aluminum powder was 5 μm (No. 9) and 30 μm (No. , lO)
A sintered body was obtained in the same manner as in Example 1 except that.

Table 3 shows the thermal conductivity and volume resistivity of the obtained sintered body. Table 3 also shows the results for sintered bodies No. 3 of Example 1, in which the 50% median particle size of the alumina-coated aluminum powder used was 20 μm.

Table 3 Sintered body Thermal conductivity Volume resistivity No.
(W/mk) (Ω・Cm)9
195 6.9X10113 200 7
．． 8xlO" 10 205 7, 0xb Example 3 To 100 parts of a mixture having the same composition as each of Mixture No., 3.4. and 5 of Example 1, 10 parts of polyvinyl butyral (number average molecule ff 155000) and 4 parts of dibutyl phthalate were added.
1 part, 2 parts of nonionic surfactant, 3 parts of methyl ethyl ketone
2 parts of methanol, 22 parts of methanol, and 8 parts of n-butanol were added to form a slurry in the same manner as in Example 1, and the slurry viscosity was adjusted to 15,000 CpS. The obtained slurry was formed into a 1 mm thick sheet using a doctor blade type forming machine, and baked at 500° C. for 3 hours.

Table 4 shows the thermal conductivity and volumetric surface a resistance of the obtained sintered bodies NQ, 11112 and 13.

Sintered body thermal conductivity No, (W/mk)

Claims (1)

[Claims] [1] Alumina-coated aluminum powder 50 to 97% by weight
and 50 to 3% by weight of low melting point glass. [2] Alumina-coated aluminum powder 50-97% by weight
1. A method for producing an inorganic sintered body, which comprises molding a mixture of and 50 to 3% by weight of low melting point glass and then sintering the mixture.