JPH0250961B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing micro metal spheres. Generally, metal balls are manufactured by: (1) Cutting a metal wire, molding it into a shape similar to a sphere using a mold, and then finishing it by polishing. (2) A method in which molten metal is dispersed in a spray form and then solidified. (3) A method of solidifying molten metal by dropping it into a liquid. etc. are known and used. However, although method (1) is good for objects with large diameters, it has its limitations because it is difficult to process microspheres into molds, and it is extremely difficult to process microspheres with a diameter of 0.5 mm or less, which slows down the processing speed. It's also slow. In addition, methods (2) and (3) tend to cause variations in the size of the metal balls, easily distort the shape, and have a poor yield. The present invention was made in view of the above circumstances, and has a spherical shape with little distortion, a uniform spherical diameter, and a diameter of 0.5.
It is an object of the present invention to provide a method for producing microscopic metal spheres that can reliably and easily produce microspheres that are approximately true spheres of mm or less. The method for manufacturing micro metal spheres according to the present invention involves placing metal grains or pieces on a flat plate, heating and melting them in a non-oxidizing atmosphere while applying vibrations, making them spheroidal due to surface tension, and then cooling and solidifying them. It is characterized in that it is made into microscopic metal spheres. Describing specific embodiments of the present invention,
A pure Ag wire with a diameter of 0.185 mm was cut into a length of 0.3 mm to obtain Ag grains 1 as shown in FIG. 1A. This Ag grain 1
After 174 pieces were arranged at appropriate intervals on a carbon flat plate 2 as shown in Fig. 1b, they were melted by applying minute vibrations while heating to 1100° C. in a heating furnace in an N ₂ gas atmosphere. Thereafter, the molten Ag particles were cooled and solidified to obtain approximately perfect spherical minute Ag particles 1' as shown in FIG. 1c.
When the sphere diameters of the micro Ag spheres 1' were measured, the sphere diameter distribution was as shown below. In addition, this minute Ag sphere 1'
As a result of passing through a sieve with a hole diameter of 0.27 mm, the ball diameter is 0.23 to 0.27.
An approximately perfect sphere of mm was obtained.

[Table] Micro Ag spheres 1' with sphere diameters of 0.31 mm and 0.32 mm are 2
Two heat-molten Ag pieces 1 are brought into contact and solidified into one Ag sphere. Next, a comparative example will be explained. 0.4mm diameter Ag-Cu alloy wire with 28% weight
The Ag wax grains were obtained by cutting them into lengths. After distributing and placing the Ag wax grains on a carbon flat plate,
When the pieces were heated and melted at 810°C in a heating furnace with a stream of N ₂ gas, and then cooled to room temperature in an N ₂ gas atmosphere, many pieces were distorted in shape. That is, there were those that were solidified into approximately perfect spheres and those that were flattened at the portions that were in contact with the carbon flat plate. The ratio was 60% for those with almost perfect spheres and 40% for those with flattened parts. Therefore, the Ag--Cu28 weight% alloy wire with a diameter of 0.4 mm was cut again into a length of 0.4 mm, and the Ag shown in Figure 2 a was obtained.
The solder grains 3 are arranged one by one in a vertical barrel shape on the carbon flat plate 2, and the Ag solder grains 3 are arranged one by one in a horizontal barrel shape on the carbon flat plate 2 as shown in Fig. 2b. Figure 3a shows the case in which the Ag solder grains were placed in a vertical barrel shape by heating and melting them separately at 810°C in a heating furnace with an _N2 gas atmosphere, and then cooling them as they were in a _N2 gas atmosphere to room temperature. As shown in Figure 3b, all of the Ag solder balls 4 had flat parts, whereas those with Ag solder grains placed in a horizontal barrel shape all became almost perfect spheres 5, as shown in Figure 3b. . As is clear from this comparative example, in order to obtain a nearly perfectly spherical minute metal sphere, it is preferable that the shape of the metal grains or pieces used as the material be in the shape of a wire cut rather than a flat plate; It is preferable to contact the upper surface of No. 2 at a point or a line so that when heated and melted, it becomes spherical due to surface tension. Therefore, if the metal grain is barrel-shaped, if the diameter is larger than the length,
It tends to stay in the shape of a barrel when placed naturally, and therefore its fixed surface tends to become flat when it is heated and melted, but if the diameter is smaller than the length l, it will form a horizontal barrel shape when placed naturally, resulting in line contact. Therefore, when heated and melted, the surface tension causes no flattened portions to form and the material becomes a substantially perfect sphere. Furthermore, as is clear from the above example, when a metal grain or piece is in a molten state, vibration is applied from the outside and the metal grain moves even slightly, causing the flat part to disappear due to surface tension and becoming a nearly perfect sphere. I understand that. As detailed above, the method for manufacturing micro metal spheres of the present invention involves heating and melting metal grains or pieces in a non-oxidizing atmosphere and turning them into spheres by surface tension, that is, applying micro vibrations to the heated and melted metal particles. The molten metal particles or pieces are heated and melted by placing them in point or line contact before being heated and melted, and the surface tension of the molten metal particles turns them into spheres, which are then cooled and solidified, so there is little distortion of the spherical shape. The ball diameter is also approximately uniform, and it has the excellent effect of being able to reliably and easily obtain even a substantially true minute metal ball of 0.5 mm or less.

[Brief explanation of the drawing]

FIGS. 1a to 1c are diagrams showing the steps of an embodiment of the method for manufacturing micro metal spheres of the present invention, and FIGS. 2a and 2b are perspective views showing the fixed state of barrel-shaped metal particles during heating and melting, respectively. FIGS. 3a and 3b are perspective views showing minute metal spheres obtained by heating and melting the metal grains shown in FIGS. 2a and 2b, and then cooling and solidifying them. 1...Ag grain, 1'...Ag sphere, 2...Carbon flat plate, 3...Ag solder grain, 4...Ag solder ball with a flat part, 5...Almost perfect Ag solder ball.

Claims (1)

[Claims] 1 Metal grains or pieces are placed on a flat plate, heated and melted in a non-oxidizing atmosphere while being vibrated to form a sphere due to surface tension, and then cooled and solidified to form fine metal particles. A method for manufacturing microscopic metal balls characterized by forming them into spheres. 2. The method for producing minute metal spheres according to claim 1, wherein the metal particles are obtained by cutting a thin metal wire into a size that is equal to or somewhat longer than the diameter of the metal wire.