KR0173041B1 - Method of producing fine metal balls - Google Patents

Abstract

A method of efficiently and accurately manufacturing fine metal balls such as solder is provided. A liquid is poured into a vertically extending cylindrical vessel, heated from the top to the middle of the liquid to a temperature above the melting point of the metal, and the bottom is kept below the melting point of the metal. Each volume of metal balls is introduced into the container. The metal pieces are heated and melted while passing through the high temperature region, and due to their surface tension they become substantially spherical in shape. However, when these balls reach the low temperature region, they cool and harden to become substantially complete metal balls. Since this process can be carried out continuously, many fine low melting point metal balls with high dimensional accuracy can be efficiently manufactured by combining this process with a high precision wire cutter.

Description

Fine metal ball manufacturing method

1 is a schematic view showing one embodiment of the present invention.

2 is a schematic view of an apparatus for continuously pulling out a metal ball.

* Explanation of symbols for main parts of the drawings

1, 1 ': container 2: silicone oil

3: electric resistance heater

4: metal piece 5: high temperature zone

6: low temperature area 7: metal ball

8: glass cock 9: sliding contact connection

The present invention relates to a method of manufacturing fine metal balls such as very small solder balls used for electrically connecting an integrated circuit (ICS).

Regarding conventional methods for producing fine metal balls having a low melting point, there are an atomization method and a method of dipping a piece of metal into a heated liquid. Japanese Patent Application Laid-open No. 50-102558 proposes a method for producing fine metal balls, which prints a paste containing a low melting point metal powder onto a metal plate through a porous plate. Dividing the paste into predetermined amounts and then heating them.

The atomization method is suitable for producing a large amount of particles, but is not suitable for forming the particles into a ball shape or making particles of the same size. In addition, the method of immersing the metal piece in the heated liquid can make substantially spherical particles and improve the ball size accuracy by using the same size metal pieces prepared in advance, Due to this, it can be regarded as unsuitable for mass production because it is necessary to maintain large spaces between the metal particles so that the molten particles do not stick or bond together when they contact each other in the liquid, This is because the metal particles need a period of time to cool the liquid to a temperature below the melting point of the metal so that it can solidify while retaining in the form of a ball.

On the other hand, the method disclosed in Japanese Patent Application Laid-open No. 50-102558 is suitable for mass production, but it is difficult to provide a ball of the correct size because the ball is flatly distorted when the ball diameter is large, and the printing process Since it is difficult to precisely divide the metal of the low melting point, and because of the nonuniform mixing of the metal particles, it is difficult to obtain a constant size of the fine ball. For this reason, there is a disadvantage that the diameter of the ball is limited to 0.1 to 1.0 mm.

The prior art has the following requirements: controllability to provide a metal ball of uniform diameter, controllability to provide a complete ball shape; It does not satisfy the controllability to increase the ball size as much as possible.

It is an object of the present invention to utilize a significantly improved means of immersing a piece of metal in a heated liquid, thereby producing a wide range of ball sizes that can be produced and having a substantially complete ball shape, which enables efficient mass production of metal balls of the correct size. By providing a fine metal ball manufacturing method for eliminating the drawbacks of the prior art.

According to the first aspect of the present invention, a metal piece of a predetermined volume (or weight) is prepared, the metal piece is introduced into a liquid maintained at a temperature higher than the melting point of the metal, and the respective metal pieces are heated and melted. Because of its surface tension, it is formed into a ball shape (i.e., spherical), and the lower area of the liquid is kept at a lower temperature than the melting point of the metal, so that the molten metal balls are moved to a lower temperature area due to gravity There is provided a method of making a fine metal ball consisting of the steps of forming a hardened ball when descending.

It is preferable to use a liquid having an oxide layer removal effect formed on the surface of the metal.

In addition, it is preferable that another liquid having an oxide film removing effect formed on the surface of the metal is placed in the upper region of the original liquid, and then melted by heating after pieces of metal pass through the oxide layer removing liquid.

In the present invention, a metal ball is obtained by putting a piece of metal in a liquid maintained at a temperature higher than the melting point of metal, and when the metal pieces are heated and melted, they may become spherical due to their own surface tension. The liquid is contained in a vertically extending cylindrical vessel in which the liquid is heated to a temperature above the melting point of the metal piece in the range from the top to the middle of the vessel and maintained at a temperature below the melting point of the metal in the lower region. .

By injecting metal pieces into the container, the metal pieces are heated and melted through the hot zone and become substantially spherical due to their surface tension. Then, when the balls pass through the low temperature region, they cool and harden to become a substantially complete metal ball. Balls of a certain size (or weight) can be obtained by using metal pieces of the same size, for example, by cutting a wire of a certain diameter (or cross section) or a ribbon of a certain width and thickness by a certain length of operation To prepare a piece of metal.

Several methods can be used to inject metal pieces into the liquid. That is, a method of using a parts feeder to separate pieces of metal cut so that the pieces of metal do not stick to each other and into the liquid, and a wire cutter is used to continuously cut the wire to a certain length and to put the liquid into the liquid. There is a way.

In the present invention, the metal pieces are melted while descending into the liquid to become ball-shaped droplets and then harden. In this case, many metal balls can be produced in a short time because the metal pieces descend at substantially the same speed, and even if metal pieces fall into the liquid continuously, disadvantages such as mutual contact or bonding of metal pieces or droplets are eliminated. Because it becomes. This feature is shown in the method of claim 1.

The liquid used in the present invention should have a boiling point sufficiently higher than the melting point of the metal and should not adversely affect chemically and physically the metal. Liquids with low water vapor pressure at high temperatures are more easily handled. The greater the specific gravity and viscosity of the liquid, the smaller the rate at which the metal pieces and molten droplets pass through the liquid, so that the time necessary for the metal pieces to melt and become spherical can be sufficiently maintained. Silicone oils or fluorine oils can be used as liquids meeting these requirements.

It is not difficult to keep the liquid portion of the intermediate portion from the top at a high temperature while keeping the lower portion of the liquid received into the vertically extending cylindrical container at a lower temperature. When silicone oil enters a cylindrical container of heat resistant glass having an inner diameter of 50 mm and a length of 500 mm, the middle part of the container is wrapped with an electrothermal ribbon. And, if the silicone oil is heated to maintain the upper half of the liquid at 200 DEG C or more, the liquid temperature near the bottom does not exceed 50 DEG C even after 5 hours from the start of heating, and the lower half of the silicone oil There is no need to cool them.

The type of metal used to obtain fine balls is limited by the nature of the liquid. In particular, metals with melting points above the boiling point of the liquid cannot be used, and the manufacture of fine balls is limited to metals with low melting points, including alloys such as solder. The temperature of the heated liquid should be at least 10 ° C. above the melting point or melting temperature of the metal, preferably at least 50 ° C. above the melting point of the metal. The time required for the passage of metal fragments and droplets to maintain the liquid at this high temperature should be at least 0.5 seconds, preferably at least 2 seconds to achieve a stable spherical shape.

The surface of the metal, such as solder, is sometimes covered with a thin layer of oxide, which prevents the metal from becoming ball form even when the metal is heated to a melting point or higher. When a 0.05 × 2.0 mm solder ribbon containing 50% tin (Sn) and 50% lead (Pb) is cut into 5 mm pieces and dropped into the fluorine oil heated to 300 ° C without pretreatment. , 80% or more of these pieces are not in ball form. Although this problem can be solved by immersing the metal pieces in solution or adding the solvent to the metal pieces in advance, this can increase the number of processes. In addition, solder wires containing a solvent in the core are commercially available and applicable to this process. However, it is difficult to obtain wires of small diameter, and it is also difficult to precisely manufacture fine balls using such wires. A method for solving this problem is disclosed in claims 2 and 3.

As a liquid for melting the metal pieces, substantially true spherical droplets can be formed by heating and melting the metal pieces while simultaneously removing the oxide films using a liquid (liquid solvent) having an oxide film layer removing effect.

When a liquid (liquid solvent) having an oxide layer removal effect of a metal piece is placed on a heated liquid, first, when the separated metal pieces are heated to a melting point or higher while passing through the liquid and passing through the heated liquid, Covered with As a result, the oxide film on the metal surface is removed by the action of the solvent, and the metal droplets become substantially spherical. To keep the liquid at a temperature above the break point of the solvent, place another liquid between the heated liquid and the solvent, which has not only a high boiling point but also a smaller specific gravity than the heated liquid and a greater specific gravity than the solvent, so that the liquid forms an intermediate layer. It is necessary to cool the nearby vessel wall to prevent the solvent temperature from reaching its break point.

Example 1

As shown in FIG. 1, a cylindrical container 1 made of heat-resistant glass was prepared, which was 50 mm in diameter and 500 mm in length, and filled with silicone oil 2. The upper region of the silicone oil at the top of the vessel was heated with an electric resistance heater 3 provided at the top of the vessel, thereby heating the upper portion (high temperature region) of the silicone oil to 220 ° C. The temperature of the bottom of the silicone oil at the bottom of the container 1 was about 25 ° C. while the temperature of the high temperature region of the silicone oil was maintained at 220 ° C. On the other hand, a metal wire having a composition of 63 approximately% tin-37 wt% lead having a diameter of 0.1 mm and whose outer circumference was covered with a solvent was prepared. This metal wire was cut into metal pieces 4 having a length of 1.0 mm, and at the same time, the cut metal pieces 4 were introduced into the silicone oil. Each piece of metal passed through the high temperature region of the silicone oil for about 2 seconds, during which it became molten and became a metal ball (7) due to its surface tension.

The metal balls 7 were further hardened through the low temperature region 6 of the silicone oil, and these hardened metal balls were stacked at the bottom of the container 1. The fabrication conditions in Example 1 and the evaluation of the metal balls produced are shown in the horizontal column of the sample (NO.1) in Table 1. Regarding the evaluation of the metal balls in Table 1, the mark (◎) indicates that the number of excellent metal balls in the degree of true spherical is 99% or more of the total metal balls. A good metal ball in terms of true spherical shape is defined as the difference between the long and short diameters of the metal ball as much as 10% or less of the average diameter of the entire metal ball.

In the manufacture of other metal balls, instead of the container 1, a container 1 'having a lower part as shown in FIG. 2 was used, and in this lower part, a small diameter having an opening and closing glass cock 8 was provided. There is a part, at the end of which part a sliding contact connection 9 with one opening is provided. A small container 10 for discharging and storing metal balls is mounted on the connection 9. In the initial stage of manufacturing the metal balls, the glass cock 8 was opened and the metal balls were dropped through the glass cock and stored in the small container 10. When a small number of metal balls are filled in this small container, the glass cock is closed, and the container is dropped from the sliding contact connecting portion 9 so that the metal balls are discharged. Another small container was mounted at the connection and the glass cock was opened so that the metal balls produced continuously were stored in the other small container. In this way, metal ball production could be carried out continuously.

Regarding the manufactured metal balls (Nos. 2, 4 to 9, 11 to 15), the manufacturing conditions such as the type of metal, the type of liquid, the temperature of the high and low temperatures of the liquid, and the evaluation of these metal balls Is shown in Table 1. In the evaluation, the mark (○) indicates that the number of balls superior in true spherical degree is at least 90% of the total balls, the mark (△) indicates that such balls are at least 80%, and the mark (×) indicates such Indicates that the balls are 80% or less.

Example 2

Using the same container 1 'as in Example 1, the metal balls (Nos. 3, 10) in Table 1 were prepared using one solvent layer and two liquid layers to be described later. In other words, a heated liquid solvent layer for removing oxide film on the metal pieces and a layer of heated silicone oil higher than the break point of the solvent layer were placed on top of the vessel (the solvent layer and the silicone oil layer were Formed to constitute a high temperature region), and a fluoro oil, which is a low temperature region, was placed under the silicone oil layer. Specific manufacturing conditions and evaluations are shown in Table 1.

Example 3

In this example, another liquid was still contained in the same vessel 1 'as in Example 1, which was mixed with fluoro oil at a ratio of 10 g of solvent per 1000 ml of fluorine oil. It consists of a solvent which can be used. Metal pieces of a silver-tin (Ag-Sn) eutectic alloy having a diameter of 35 µm and a length of 0.1 mm were introduced into a high temperature region of a liquid maintained at a temperature of 260 to 280 ° C. Micrometer metal balls were prepared. When the cut pieces were put into the liquid, the pieces of metal were first made into a mixture in which about 5000 pieces of metal were mixed with 5 ml of fluoro oil and dispersed in the fluorine oil, the mixture being in positive Substantially each was divided into ten identical portions, each separated portion being introduced into the liquid ten times at predetermined intervals. The resulting metal balls were rated by ◎ for their true spherical accuracy.

Example 4

In this example, peanut oil liquid was used in the same container 1 'as in Example 1, and the peanut oil was heated so that the temperature of the high temperature region was 280-320 degreeC. About 5000 pieces of metal were mixed with 5 ml of peanut oil and dispersed in the peanut oil. Each piece of metal with a diameter of 50 µm and 0.2 mm in length was mixed with peanut oil and dispersed in the peanut oil. The mixture was divided into ten portions, each substantially equal in quantity, and each portion was introduced into the hot zone in such a way that each separated portion was introduced ten times into the solution at predetermined intervals. The resulting metal balls were rated by ◎ for their true spherical accuracy.

According to the invention, the metal pieces are melted into ball-shaped droplets because of their surface tension, and also because the cooling and curing process is completed while the droplets descend through the liquid, the shape of the balls does not become distorted, Substantially spherical metal balls can be obtained. According to the present invention, a plurality of low melting point metal balls having high dimensional accuracy and sphericity can be efficiently manufactured. Advantageously, the present invention also prevents the surface of the metal balls from being oxidized since the metal balls are produced in a liquid shielded from air, thereby providing metal balls with excellent surface properties.

Claims (6)

In the method of producing a fine metal ball, by preparing metal pieces of a predetermined volume or weight, by heating the metal pieces into the liquid maintained at a temperature higher than the melting point of the metal, by heating and melting the respective pieces of metal, Formed in the form of a ball due to their own surface tension, and maintaining the lower region of the solution at a temperature below the melting point of the metal balls, so that the molten metal balls formed in the upper high temperature region of the solution When falling, the method of producing a fine metal ball, characterized in that consisting of the step of forming a hardened metal ball. The method of claim 1, wherein the liquid is a liquid having an effect of removing an oxide layer from a metal surface. 2. The second liquid layer according to claim 1, wherein a second liquid having an effect of removing the oxide layer on the metal surface is disposed on the upper region of the first liquid, thereby removing the oxide layer from the metal piece surface. The method of producing a fine metal ball, characterized in that it further comprises the step of heating and melting the metal pieces after the metal pieces pass. A fine metal ball manufacturing method comprising: preparing metal pieces of a predetermined volume or weight; Preparing a first liquid having a solvent effect to remove the oxide layer from each metal piece surface in a container, wherein the solvent effect of the first liquid is lower than that of the solvent alone; The liquid is maintained at a temperature above the melting point of the metal in this liquid upper region; Preparing a mixture of a second liquid having the same composition as the first liquid and the metal pieces or another mixture of the metal pieces and a third liquid dissolved in the first liquid; By injecting metal pieces mixed with the second or third liquid into the first liquid, the respective metal balls are heated and melted to form balls due to their own surface tension; And maintaining the lower region of the first liquid at a temperature lower than the melting point of the metal ball so that when the molten metal balls formed in the upper high temperature region of the first liquid descend through the low temperature region due to gravity, the hardened metal Fine metal ball manufacturing method comprising the step of forming the ball. 3. A method according to claim 2, wherein the liquid is an oil which has the effect of removing the oxide film, i.e. contains a flux component. 5. A method according to claim 4, wherein the first liquid is an oil which has the effect of removing the oxide film, i.e. contains a flux component.