JPH108113A - Production of metallic ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce nearly spherical metallic balls having a desired diameter with high dimensional accuracy by embedding a prescribed weight of metallic pieces into powder contg. a specific amt. of graphite powder and heating these metallic pieces together with the powder to melt the metallic powders and to spheroidize the metallic pieces by surface tension, then cooling the metallic balls. SOLUTION: Metallic materials, such as bar materials and plate materials, consisting of base metals or noble metals contg. gold or their alloys, are weighed and cut to form the prescribed weight of the metallic pieces. The metallic pieces are embedded into the powder contg. 30>=vol.%, more preferably about 50 to 100% graphite powder and others, such as ceramic powder, etc., stable at a high temp. The metallic pieces are then melted together with the powder by heating to the m.p. thereof or above. After the molten metal is spherodized by the surface tension, the molten metal is cooled. The metallic balls formed to the desired diameter are sieved and are taken out of the powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simple method for producing a metal sphere having a desired diameter, and more particularly, to a true sphere for use as a decorative material, a semiconductor brazing material, a wiring electrode material and the like. The present invention relates to a method for efficiently producing close metal balls with high dimensional accuracy.

[0002]

2. Description of the Related Art Conventionally, metal balls having desired dimensions and weight for use as decorative materials, brazing materials for semiconductors, electrode materials for wiring, and the like have been produced by methods such as a rotating electrode method and an atomizing method. .

[0003]

However, since the metal balls obtained by any of the above methods have a large spherical variation,
A step of classifying metal balls by sieving was required, and the distribution of the ball diameters was wide, so that the yield of balls having a desired diameter was not good. In addition, when the size exceeds a certain size, the sphere does not become a true sphere due to the action of gravity, and only a distorted metal sphere is obtained.

A method of manufacturing a metal ball by filling a metal powder in a concave portion of a carbon or ceramic jig having a large number of concave portions and fusing the metal powder has been proposed (Japanese Patent Publication No. Hei 7-91561). Publication), it takes time and cost to manufacture and weigh metal powder, and a special jig must be required.

Accordingly, the present invention provides a simple metal ball manufacturing method for manufacturing a metal ball close to a true sphere of a desired diameter with high dimensional accuracy and efficiency without requiring a special jig. The purpose is to do.

[0006]

In order to solve the above-mentioned problems, a method for manufacturing a metal sphere according to the present invention comprises weighing a base metal, a noble metal containing gold alone, or a metal material made of an alloy thereof. A metal piece having a predetermined weight is embedded in a powder containing 30% by volume or more of graphite powder, and the metal piece is heated together with the powder to a temperature equal to or higher than its melting point to melt the metal piece. It is characterized in that it is formed into a metal sphere having a desired diameter by cooling after spheroidizing by the surface tension.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, it is considered that a base material or a simple substance of a noble metal of gold, silver, or a platinum group element, or a metal material made of an alloy thereof, generates a surface tension at an interface thereof when melted. To use. Therefore, the material is not particularly limited as long as it is a melting metal. However, in order to keep the surface clean, a material that does not react with graphite at a high temperature is desirable.

In order to weigh a metal material to obtain a metal piece having a predetermined weight, the metal piece may be weighed, but a wire made of a metal material having a constant diameter, a constant thickness, and a constant cross-sectional area may be used.
It is efficient to cut a bar, a plate, a strip, or the like into a metal piece having a uniform weight by cutting it into a fixed length or a fixed area. In this way, a metal piece having a constant weight can be obtained extremely easily and accurately as compared with the conventional method of weighing powder. Known shears, scissors, punching, and the like can be used for cutting the metal material.

Since the metal piece becomes spherical due to surface tension at the time of melting, the metal piece may have a large aspect ratio. However, it is more preferable if a cylindrical metal piece having a diameter close to a desired diameter can be produced.

The purpose of embedding the metal pieces in a powder containing 30% by volume or more of graphite powder is to hold the metal pieces at the time of heating and to function as a support that suppresses deformation of the molten metal by its own weight as much as possible at the time of heating. . In addition, the powder creates a non-oxidizing atmosphere around the metal piece at the time of heating, which is also to prevent oxidation.

The reason why graphite powder is used is that graphite has a low wettability to metals such as gold and has an effect of retaining the shape of metal spheres. The reason why the graphite powder in the powder is 30% by volume or more is that
If the amount is less than this, the shape holding effect is reduced, and the obtained metal sphere tends to have an incorrect shape. More preferably, a powder containing 50% by volume or more and 100% or less of graphite powder is used.

In order to enhance the workability during handling, the powder may contain a powder other than graphite powder, such as ceramic powder such as alumina or magnesia, within the above conditions. The material of the powder other than the graphite powder is not particularly limited as long as it does not react with a metal material or graphite at the melting temperature, or liquefy, solidify, or evaporate. Although the particle size is not particularly limited, it is preferable that the particle size is approximately the same as that of the graphite powder to be used because uniform mixing can be achieved.

In order to embed the metal pieces in the powder, the powder is laid in a heat-resistant container made of graphite or ceramic or the like, and the prepared metal pieces are placed on top of the powder. The metal piece may be embedded in the powder by a method such as covering the body. At this time, depending on the properties of the powder, the packing density of the powder may be increased by squeezing or applying pressure from above.

The metal pieces may be arranged in the powder as long as the metal pieces do not contact each other after melting. It may be planar, but may be arranged three-dimensionally, or may be arranged in a tray-like container two-dimensionally in several layers.

The metal piece is heated to a temperature equal to or higher than the melting point of the metal while the metal piece is buried in the powder containing the graphite powder. In order to heat the metal piece together with the powder to a temperature equal to or higher than its melting point, a known heat treatment furnace can be used. Even when heated in an oxidizing atmosphere such as in the air, graphite burns to form a CO atmosphere and metal oxidation is prevented. However, graphite powder is quickly consumed in the air, so it is heated in a non-oxidizing atmosphere. Is more preferred.

When the temperature of the metal piece reaches a temperature equal to or higher than the melting point, the metal piece is melted, and each metal piece becomes spherical due to its surface tension. At this time, the graphite powder does not hinder the spheroidization of the metal, so that a molten metal sphere having a good shape is formed. By cooling this, a metal sphere having a desired diameter can be obtained. After cooling, the metal spheres are buried in the powder,
The metal spheres and the powder can be very easily separated by sieving.

Since the size of the metal sphere is determined by the weight of the metal piece before heating, a plurality of jigs are required depending on the size of the metal sphere, as in the case of heating metal powder in a conventional jig having a concave portion. There is no need to prepare.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for producing a metal sphere according to the present invention will be described with reference to typical examples. Example 1 In order to form a metal sphere having a sphere diameter of 0.5 mm, a 0.3 mm wire of Au-10% Cu alloy was used for 0.1 mm each.
500 pieces were cut out to a length of 93 mm to obtain metal pieces. Next, a graphite powder having a primary particle size of 50 nm was placed in a graphite container for 10 m.
m, and a large number of the metal pieces are arranged on the graphite powder so that they do not touch each other.
The same graphite powder as described above was covered with a thickness of 0 mm to fill the metal pieces. This graphite container was placed in an electric furnace, and kept at 1100 ° C. for 15 minutes in a nitrogen gas atmosphere to melt the metal pieces, to make the molten metal spheroidized by surface tension, to cool and solidify in the same atmosphere, A metal ball was obtained.

As a result of classifying 500 obtained metal spheres with a sieve, 99% of the spheres having a diameter of 0.45 to 0.55 mm had a diameter of 0.45 to 0.55 mm.
1% exceeded 55 mm (number basis; the same applies hereinafter).

Example 2 In order to form a metal ball having a ball diameter of 0.7 mm, the same wire rod as in Example 1 was used for 2.54 mm.
A metal sphere was produced in the same manner as in Example 1 except that 500 pieces were cut out into lengths to obtain metal pieces. The obtained metal sphere 5
As a result of classifying 00 pieces with a sieve, a sphere diameter of 0.65 to 0.75 m
m is 98%, 0.7% more than 1 mm is 1%,
1% was less than 0.65 mm.

Example 3... Table 1 with a sphere diameter of 1.5 mm
Example 1 was repeated except that 500 pieces of 1 mm wire of each pure metal (each having a purity of 99.99% by weight) were cut out to a length of 2.2 mm to make metal spheres of the materials shown in FIG.
A metal sphere was produced in the same manner as in Example 1. As a result of classifying the obtained metal balls with a sieve, the results are as shown in Table 1.

[0022]

[Table 1] Spherical diameter (unit: mm) Material Less than 1.0 1.0 to 2.0 Greater than 2.0----------------- -------- Gold 2% 93% 5% Silver 1% 95% 4% Copper 2% 94% 4%

Example 4 In order to produce metal spheres of the materials shown in Table 2 having a sphere diameter of 2 mm, each pure metal (purity 99.99) was prepared.
Weight%) or 1-10 mm thick gold-10% copper alloy
A metal ball was produced in the same manner as in Example 1, except that the plate material was punched out to a metal piece of 0.23 mm in diameter. As a result of classifying the obtained metal spheres with a sieve, the results are as shown in Table 2.

[0024]

[Table 2] Sphere diameter (unit: mm) Material Less than 1.5 1.5 to 2.5 Greater than 2.5 ------------------------------------ ------ Gold 2% 92% 6% Silver 4% 90% 6% Copper 3% 91% 6% Gold-10wt% Copper 2% 90% 8%

Example 5 A metal piece of 0.93 mm length as in Example 1 was buried in a powder obtained by mixing graphite powder and alumina powder in a volume ratio of 40% / 60%. Heated to produce a metal sphere. As a result of classifying each of the obtained 500 metal spheres with a sieve, 92 to 0.45 to 0.55 mm were obtained.
%, Those exceeding 0.55 mm were 8%.

Comparative Example 1 A metal sphere was prepared in the same manner as in Example 5 except that graphite powder and alumina powder were mixed in a volume ratio of 20% / 80%. 50 obtained metal spheres
As a result of classifying 0 pieces with a sieve, 34% of the pieces having a size of 0.45 to 0.55 mm, 23% of those having a size of less than 0.45 mm, 0.5%
The yield was remarkably reduced to 43% of those exceeding 5 mm. Further, since the amount of graphite powder was smaller than that of Example 5, the graphite powder burned during the heat treatment and was largely consumed, and an oxide was generated on the surface of the obtained metal sphere, resulting in an irregular shape. Was.

[0027]

According to the method for producing metal spheres of the present invention, metal spheres close to true spheres having a desired diameter can be produced with good dimensional accuracy and efficiency by a simple method.

Claims (3)

[Claims] 1. A metal material is weighed to obtain a metal piece having a predetermined weight, the metal piece is buried in a powder containing 30% by volume or more of graphite powder, and the metal piece is heated together with the powder to a melting point or more. And melting the metal piece by spheroidizing the molten metal by surface tension thereof, followed by cooling to obtain a metal sphere having a desired diameter. 2. The method according to claim 1, wherein the metal material is a noble metal or an alloy thereof. 3. The method according to claim 1, wherein the metal material is gold or a gold alloy.