JPS621807A - Manufacture of metallic powder - Google Patents

Abstract

PURPOSE:To manufacture spherical metallic powder useful to form a thick paste film having a smooth surface by atomizing a metallic salt soln. to form drops of the soln. and by heating the drops at a temp. satisfying specified conditions. CONSTITUTION:A metallic salt soln. A contg. one or more kinds of metallic salts is sent from a tank 1 to a double tube type atomizer 2 and atomized with compressed air B to form drops of the soln. in a ceramic pipe 4. The drops are heated to a temp. above the decomposition temp. of the metallic salt and below the m.p. of the metal with an electric furnace 3. When the metal forms oxide at a temp. below the m.p. of the metal, the drops are heated to a temp. above the decomposition temp. of the oxide. Metallic powder produced by thermal decomposition is collected in a cyclone 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing metal powders, particularly metal powders useful for thick film pastes.

In the electronics field, thick film pastes such as conductor pastes and resistor pastes are used to manufacture components such as electronic circuits, resistors, capacitors, and IC packages. This is a paste made by uniformly mixing and dispersing metal, alloy, or metal oxide powders in an organic vehicle along with a glassy binder and other additives as needed, and then applying it onto a substrate. A conductive film or a resistive film is formed by baking at an invasive temperature or heating and drying at a relatively low temperature.

Such metal powder for thick film paste is desired to have the following properties.

■It must be well dispersed in the paint to form a dense and uniform film.

■Less impurities.

A large amount of impurities will adversely affect ohmic contact with semiconductors, corrosion resistance, environmental resistance, and other electrical properties, so it is necessary to keep the level as low as possible.

■Have good crystallinity.

In particular, with high-temperature firing type pastes, if the crystallinity is not good, the metal powder will sinter too quickly during the firing process, and the molten glassy binder will not transfer to the substrate side, resulting in poor adhesion or glass sticking to the film surface. Floating leads to problems such as conductivity and inhibiting soldering. Therefore, it is desirable that the crystallinity is good and the directions of the crystals are aligned.

The particle size should be in the range of approximately 0.1 to 10^1 and the particle shape should be uniform.

(Metal powders used in thick film pastes have conventionally been produced by wet reduction methods in which a reducing agent is applied to a solution of metal compounds, by atomizing molten metals, or by atomizing metals in a vacuum or in a vacuum. A method of pulverization by evaporation in an active gas is known.

Problems to be Solved by the Invention Although the wet reduction method has the advantage of being able to easily produce metal powders of various shapes and particle sizes by controlling the type and concentration of the starting salt and reducing agent, as well as the reaction conditions, it has problems with dispersibility. In order to obtain a good powder, a large amount of deflocculant is usually used, which makes solid-liquid separation from the reaction solution difficult and increases the amount of impurities. Furthermore, in order to improve crystallinity, the reaction rate must be extremely slow, resulting in poor productivity.

In the atomization method, the particle size of the powder produced is large and it is difficult to pulverize it. Furthermore, high melting point metals such as palladium and platinum have the disadvantage of high equipment costs.

In the evaporation method, on the other hand, the particle size is too small and particles with good dispersibility cannot be obtained. Furthermore, this method is expensive and cannot be mass-produced.

Therefore, with these methods, there is a limit to the ability to obtain metal powders with appropriate particle size, good dispersibility and crystallinity in paints, and high purity.

The object of the present invention is to easily and at low cost produce a metal powder having the above-mentioned desirable properties for use in thick film pastes.

Another method for solving the problem is that a solution containing one or more metal salts is sprayed into droplets, and the droplets are formed at a temperature higher than the decomposition temperature of the metal salt and at a temperature higher than the melting point of the metal. This method of producing metal powder is characterized by heating at a higher temperature, and in the case where the metal forms an oxide at a temperature below the melting point of the metal, heating is performed at a temperature higher than the decomposition temperature of the oxide. Note that the metal powder as used in the present invention includes not only a single metal but also an alloy powder.

As the working metal salt, the target metal, such as noble metals such as gold, silver, platinum, and palladium, and base metals such as copper, nickel, cobalt, iron, aluminum, molybdenum, and tungsten, or oxides thereof, is precipitated by thermal decomposition. Any of these metals may be used - for example, nitrates, sulfates, chlorides, ammonium salts, phosphates,
Examples include carboxylates, metal alcoholades, resinates, and the like. A plurality of different salts of a single metal can also be used together. A mixture of salts of two or more metals may be used, or a double salt or a complex salt may be used.

A metal salt solution is prepared by dissolving one or more of these metal salts in water, an organic solvent such as alcohol, acetone, or ether, or a mixed solvent thereof. Pure metal powder can be obtained by using a salt solution of a single metal, but alloy powder can be produced by using a solution in which two or more metals forming an alloy are dissolved. A mixed powder may be obtained if the two or more metals to be mixed do not form an alloy.

The metal salt solution is atomized into droplets by an atomizer, and then at a temperature higher than the decomposition temperature of the metal salt and higher than the melting point of the metal, but below the melting point of the metal, when the metal forms an oxide. By heating at a temperature higher than the decomposition temperature of the oxide, a spherical metal powder with a smooth surface is produced. The obtained powder has very good crystallinity and also has good dispersibility when made into a paint. If the decomposition temperature is lower than the melting point of the metal, spherical powder will not be formed and the density will be low, making it undesirable for use in pastes. Therefore, it is necessary to heat at least at a temperature higher than the melting point. Preferably, the heating is performed at a temperature 100° C. or more higher than the melting point of the target metal. In addition, for metals that form oxides at temperatures lower than the melting point of the metal when or after the metal salt decomposes, it is necessary to heat the metal to at least the temperature at which the oxide decomposes.

In addition, when forming two or more types of metal salts forming an alloy, the heating temperature may be a temperature higher than the decomposition temperature of the salt and higher than the melting point of the alloy containing the metal as a constituent component.

In water droplets, the atmosphere during heating is appropriately selected from oxidizing, reducing, and inert atmospheres depending on the type of metal, heating temperature, and the like.

The particle size of the metal powder depends on the concentration of the metal salt, the type and mixing ratio of the solvent, the spray speed, the size of the spray droplets, and the heating temperature, so it can be easily controlled by appropriately setting these conditions. Can be done. In particular, the size of the sprayed droplets, which seems to be directly related to the particle size, can be reduced by further colliding the sprayed liquid with a solid obstacle or rotating body. Furthermore, if the boiling point of the solvent is low, droplets are likely to break up due to boiling during heating, and the droplets become finer, which is thought to reduce the particle size of the produced metal powder.

The method for producing metal powder of the present invention will be explained based on the drawings. FIG. 1 shows an example of a metal salt solution spraying and pyrolysis apparatus, in which metal salt solution A is sent from a tank 1 to a double pipe sprayer 2, and is passed through a ceramic pipe heated in an electric furnace 3. 4 using compressed air B and pyrolyzed. The generated metal powder is collected in the cyclone 5.

EXAMPLES Next, the present invention will be specifically explained with reference to Examples and Comparative Examples.

Example I AQ NO3 crystals were dissolved in an ethanol-water mixed solvent containing 80% ethanol to prepare a solution of 0.511101/λ. This solution is flowed out from the inner cylinder of the two-fluid nozzle using a double pipe sprayer at a flow rate of 2.0 x 1 min, and at the same time compressed air is flowed through the outer cylinder at a flow rate of 10 x 7 min, and heated to 1100°C in an electric furnace. The solution was sprayed into a ceramic tube. At this time, 20
Flow the air at a rate of 7 minutes to ensure that the atomized droplets are well directed to the heating zone. The droplets were thermally decomposed through a heating zone and collected with a cyclone and glass filter. The obtained powder has a maximum particle size of 1.7. Ml,
Minimum particle size 0.5. It was a perfectly spherical Ag powder with a size of Mll, very good crystallinity, and a smooth surface.

Comparative Example 1 Example 1 except that the heating temperature was 500°C and 900°C
AIJ powder was produced in the same manner as above. In all cases, spherical particles were not obtained, but were irregularly shaped, with a maximum particle size of 10 Al and a minimum particle size of 1.

Comparative Test Example 1 and Comparative Example 1 (heating temperature 900°C) A (+ powder and maximum particle size 1.5 made by wet reduction method,
A conductive paste was prepared using Ag powder with a minimum particle size of 0.5 s and the following formulation.

A(I powder 100g Glass frit 5g Bi2O58g Organic vehicle 30Q These three pastes were printed on an alumina substrate, fired at 800℃, and tested using the usual evaluation method for thick film conductors. Table 1 shows the results. show.

Table 1 *Adhesive strength was evaluated using a 1.5 hardness pattern.

The aging strength is the value after being left at 150°C for 24 hours.

As is clear from Table 1, Ag obtained by the present invention
The powder exhibits excellent properties as a thick film paste powder. That is, the paste example above has ideal viscosity characteristics for screen printing and has good printability. In addition, it has been known that solder wettability and adhesive strength are contradictory properties, but these results show that solder wettability and adhesive strength are better than when using powder produced by the conventional wet reduction method. It can be seen that both adhesive strength is excellent.

This is because the AO powder made according to the present invention has no agglomeration and has excellent dispersibility in the paste, making it possible to form a dense film.In addition, the individual particles have good crystallinity, so they are sintered during the paste firing process. This is thought to be due to the fact that the transition from glass to substrate was smooth as a result.

Example 2 AIJNO3 and Pd(NO3)2 were mixed with methanol 50
Dissolved in methanol-water mixed solvent containing 0.5 mo
A solution of l/β was made. However, AClNO3 and Pd(NO
3) The mixing ratio of 2 was such that the weight ratio of A(l and Pd) was 8:2.This solution was prepared in the same manner as in Example 1,
It was sprayed into a ceramic tube heated to 1200°C in an electric furnace and collected. The obtained powder is a spherical Ag/P with a maximum particle size of 2.5 μm and a minimum particle size of 1.5 μm and a smooth surface with good crystallinity.
d alloy powder.

Example 3 HAu Cl 4 crystals were dissolved in ethanol and 0°5m
A solution of ol/β was prepared. This solution was subjected to spray pyrolysis in the same manner as in Example 2, with a maximum particle size of 1.0 and a minimum particle size of 0.
．． 5 g of spherical AU powder with good crystallinity was obtained.

As is clear from the effect examples, according to the production method of the present invention, metal powder that is spherical, has good crystallinity, and is highly dispersible can be produced. Moreover, unlike the wet reduction method, there is no need for solid-liquid separation, making it easy to manufacture.Also, since there is no need to use additives that affect purity, a highly pure powder containing almost no impurities can be obtained, and the particle size It is also easy to adjust. Therefore, the metal powder obtained by the present invention can be particularly suitably used for thick film pastes.

Furthermore, this method has the advantage that it can be carried out using simple equipment, has low manufacturing costs, and can be mass-produced.

Although only the application for thick film paste has been described, the metal powder produced by water droplets can be effectively used not only for thick film paste but also for decoration, catalyst use, and other applications.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an apparatus used for producing metal powder by the method of the present invention.

Claims (1)

[Claims] 1. A solution containing one or more metal salts is sprayed into droplets, and the droplets are heated to a temperature higher than the decomposition temperature of the metal salt and higher than the melting point of the metal. , and furthermore, when the metal forms an oxide at a temperature below the melting point of the metal, heating is carried out at a temperature higher than the decomposition temperature of the oxide. 2. The method for producing metal powder according to claim 1, wherein the salts of two or more metals are salts of metals forming an alloy. 3 Claim 1 in which the melting point of the metal is the melting point of the alloy
A method for producing metal powder according to item 1 or 2.