JPH0466602A - Production of fine metal ball - Google Patents

Abstract

PURPOSE:To form metal wire chips into fine balls by heating metal wire chips conveyed by a conveyance means up to a temp. not lower than the melting point of the above metal wire chips by a heating means and carrying out melting. CONSTITUTION:Metal wire chips 10 are placed on a rotary table 2. The metal wire chips 10 are turned together with the rotary table 2, and, on entering a heating furnace 4, the temp. begins to rise rapidly and the metal wire chips are melted when the temp. becomes higher than the melting point of the metal. Since molten metal is usually increased in surface tension, the metal is changed into ball shape by itself in molten state. Accordingly, although this molten metal is changed into ball shape in the course of passing through the heating furnace 4, the temp. is sharply reduced on leaving the heating furnace 4 and this metal begins to solidify. Finally, the resulting metal balls are dropped by means of a guide 8 into a recovery vessel 6, by which fine metal balls 20 can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for manufacturing fine metal balls used as a joining member when joining between an electrode of an IC chip and a lead of a TAB tape, etc. It is about the method.

[Conventional technology]

Various methods are used to connect the electrodes of the IC chip and external leads.

There is a method of connecting using ultra-thin wiring wire (bonding wire), but a method of thermocompression bonding by sandwiching a metal protrusion called a bump between the chip electrode and the lead is also becoming widely used.

T A B (Tape Auto+wated Bo
The nding) method is a technique that is attracting attention as a representative of the latter. In this method, a bump is formed in advance on either the electrode part of the IC chip or the lead tip part on the TAB tape, and then the IC chip electrode part and the TAB tape having the lead are stacked with the bump interposed therebetween. The two are then joined together. In addition to the TAB method, bumps are also used in the flip chip method.

Up until now, the method of making bamboo provided for such uses has mainly been the method of making bamboo sticks. In other words, the force is applied by directly plating the metal (mainly high-purity gold) that will become the bump on the electrode part of the IC chip, or by applying the force to form the bump once formed by plating on the glass substrate etc. to the lead tip on the TAB tape side. The mainstream method is transcription.

However, the method using plating has the disadvantage that the equipment becomes bulky and there are also restrictions on the composition of the metal used as the bump. Further, particularly when forming bumps by directly plating the electrode portions of IC chips, there is a problem that the IC chips themselves have to go through the plating process, which deteriorates the yield of the IC chips.

As a way to overcome these drawbacks, bump forming methods that do not involve plating have come to be considered. An application was filed for a method of obtaining spherical bumps by cutting them to a fixed length and then melting and solidifying them at intervals, utilizing surface tension (Patent Application No. 1-32029).
No. 6), the spherical bump made by this method is used by thermocompression bonding to the tip of the lead, etc. (Japanese Patent Application No. 1-2349)
No. 17).

The new method of melting any piece of metal wire to form a bump greatly expands the possibility of using any metal that has properties suitable for a joining member as a bump. In other words, in addition to gold, copper, silver, and various alloys based on these can now be easily formed into bumps.

[Problem to be solved by the invention]

In a conventional method for manufacturing fine metal balls, pieces of metal wire cut to a predetermined length are placed in a crucible at regular intervals and then melted. This is because if the metal wire pieces enter the melting process while being in contact with each other or placed too close to each other, these metal wire pieces may coalesce during melting.

In this method, if all the metal wire pieces had a certain length, fine metal spheres of uniform size could be formed. However, this metal wire piece is 2 to 3 meters long at most.
Since the particles are as small as m, there is a problem in that arranging the metal wire pieces and collecting the fine metal balls takes time and effort.

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a method for manufacturing fine metal balls that can improve work efficiency and mass productivity.

C) Means for Solving the Problem) The method for manufacturing fine metal balls according to the present invention for achieving the above object includes using a metal wire piece conveyed by a conveying means on the metal wire piece by a heating means. The method is characterized in that the metal wire piece is spheroidized by heating and melting the metal wire to a temperature higher than the melting point of the metal.

[Effect]

According to the present invention, the metal wire piece is conveyed by the conveying means, and during the conveyance, the metal wire piece is heated and melted by the heating means to a temperature equal to or higher than the melting point of the metal. Since molten metal has a large surface tension and spheroidizes itself, the metal wire piece is deformed into a spherical shape during transportation and becomes a fine metal sphere.

[Example] A first example of the present invention will be described below with reference to FIG. FIG. 1 is a schematic diagram of an apparatus used in the method for producing fine metal balls according to the first embodiment of the present invention. In this embodiment, a piece of gold wire (25 μm in wire diameter and 0.55 mm in length)
A gold ball (fine metal ball) with a diameter of 80 μm is produced using a metal wire piece).

The apparatus shown in FIG. 1 includes a heat-resistant rotary table 2 for conveying a metal wire piece 10, a driving motor (not shown) for the rotary table 2, and a U-shaped heating device for melting the metal wire piece 10. Furnace 4 and recovery container 6 for recovering formed fine metal spheres 20
and a guide 8 for dropping the fine metal balls 20 on the rotary table 2 into the collection container 6. The rotary table 2 is made of ceramic and has a circular shape, and its diameter is approximately 200 mm.
It is mm. The maximum temperature in the heating furnace 4 is the melting point of gold (106
The temperature is set at 1200°C, which is slightly higher than 0°C.

The metal wire piece 10 cut by a fine metal wire cutting device (not shown) is placed on the rotary table 2 .

The metal wire piece IO rotates together with the rotary table 2, and the heating furnace 4
Once inside, the temperature begins to rise rapidly. The piece of metal wire then melts when the temperature rises above the melting point of the metal. Generally, molten metal has a large surface tension, so it changes into a spherical shape by itself in the molten state. Therefore, this molten metal changes into a spherical shape while passing through the heating furnace 4.
Once the metal leaves, the temperature drops rapidly and the metal begins to solidify.

Finally, the metal ball is dropped into the collection container 6 by the guide 8,
Fine metal spheres 20 are obtained.

In addition, in order to reliably melt the metal wire piece, it is necessary to change the speed of the rotary table depending on the heating capacity of the heating furnace.

When the present inventors actually conducted tests using the above-mentioned apparatus and metal wire pieces, they were able to obtain fine metal spheres with a uniform and beautiful spherical shape.

In this way, in the method for manufacturing fine metal balls of this example, the process of collecting fine metal balls can be performed automatically by simply placing the metal wire piece on the rotary table, which improves work efficiency and facilitates mass production. It is possible to improve sexual performance. Furthermore, by providing the apparatus of this embodiment with a device for cutting fine metal wires one by one at regular intervals on the top of the rotary table of this embodiment, the cutting process of the fine metal wires, the cut metal The step of spheroidizing the wire piece and the step of recovering fine metal can be performed continuously.

Furthermore, the method of this embodiment can be applied to metals and alloys that have not been considered in the past, so that fine metal spheres having an appropriate composition for bumps can be easily and efficiently produced.

Next, a second embodiment of the present invention will be described using FIG. 2.

FIG. 2 is a schematic diagram of an apparatus used in a method for manufacturing fine metal spheres, which is a second embodiment of the present invention. The material and size of the metal wire pieces used are the same as those in the first embodiment.

The apparatus shown in FIG. 2 includes a belt conveyor 3 that conveys the metal wire piece 10, a driving motor (not shown) for the belt conveyor 3, and a tunnel-type heating furnace 4 that melts the metal wire piece 10.
a, and a collection container 6a for collecting the formed fine metal spheres 20.
It consists of Because the belt conveyor 3 passes through the heating furnace 4a, it is necessary to ensure heat resistance, so in this embodiment, a belt made of heat-resistant steel chains is attached with many small plates made of ceramics. I am using it.

The metal wire piece 10 cut by a fine metal wire cutting device (not shown) is gently dropped from above the belt conveyor 3, for example. When the metal wire piece 10 is conveyed by the belt conveyor 3 and enters the heating furnace 4a, its temperature begins to rise rapidly. Then, when the temperature of the metal wire piece 10 becomes higher than the melting point of the metal, the metal wire piece 10 melts and changes into a spherical shape. Heating furnace 4
Upon leaving a, the temperature drops rapidly and the metal begins to solidify. Finally, the metal spheres fall from the belt conveyor 3 and are collected in the collection container 6 to obtain fine metal spheres 20.

When the present inventors conducted actual tests using the apparatus of this embodiment, they were able to obtain uniform and beautiful spherical fine metal spheres in the same way as when using the apparatus of the first embodiment. Ta. Other functions and effects are the same as in the first embodiment.

In the first and second embodiments described above, a case was explained in which a gold ball was manufactured using a piece of gold wire, but the present invention is not limited to this, and other metals suitable for bumps may be used. However, since the melting point differs depending on the metal, it is necessary to set the maximum temperature of the heating furnace and change the material and speed of the rotary table and belt conveyor accordingly. Furthermore, depending on the metal, it may be necessary to replace the inside of the heating furnace 4 with a specific gas atmosphere so that a chemical reaction does not occur in the high-temperature heating furnace 4.

〔Effect of the invention〕

As explained above, according to the present invention, fine metal balls can be easily manufactured by melting the metal wire pieces conveyed by the conveying means using the heating means and utilizing the large surface tension of the molten metal. Therefore, it is possible to provide a method for manufacturing fine metal balls that can improve work efficiency and mass productivity.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus used in a method for manufacturing fine metal balls, which is a first embodiment of the present invention, and FIG. 2 is a schematic diagram of an apparatus used in a method for manufacturing fine metal balls, which is a second embodiment of the present invention. FIG. 2... Rotary table, 3... Belt conveyor, 4.
4a... Heating furnace, 6, 6a... Collection container, 8...
Guide, 10...Metal wire piece, 0... Fine metal ball.

Claims (1)

[Claims] The metal wire piece conveyed by the conveying means is heated and melted by the heating means to a temperature higher than the melting point of the metal used for the metal wire piece, thereby making the metal wire piece spherical. Method for manufacturing fine metal balls.