JP2008163373A - Method for manufacturing microball of active metal, and microball - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide microballs of active metal having uniform size and its manufacturing method and further to provide the microballs stable in the air by covering the surface thereof with passivation film. <P>SOLUTION: Active metal is filled into a crucible 10 and a microball recovery bowl 19 is inserted on the underside of an orifice 17, and a gate valve 20 is closed. After an inside of the crucible 10, a space into which the recovery bowl 19 is inserted and a microball discharge chamber 22 are evacuated, inert gas is introduced. Subsequently, the active metal is melted by heating using a heating device 13, and then a piezoelectric pulse is applied to a piezoelectric actuator 11 to jet the molten active metal through the orifice 17. The jetted molten metal is formed into a microball having a size nearly the same as the bore diameter of the orifice 17 and recovered in the recovery bowl 19. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a microball made of an active metal such as aluminum, magnesium, titanium, and the like. In particular, the present invention relates to an active metal microball manufacturing method and a microball capable of manufacturing an active metal microball having a small diameter and a uniform size and capable of ultrasonic bonding.

JP 2004-317096 A JP, 2005-146370, A An ultrasonic joining technique which can be processed in a short time, keeping connection temperature low is effective in semiconductor mounting. FIG. 4 shows a schematic diagram of the ultrasonic bonding method. A bump 46 is attached to the wiring pattern 45 of the semiconductor chip 44 to be connected to the semiconductor substrate 43. Then, the semiconductor chip 44 and the semiconductor substrate 43 placed on the bonding stage 41 are accurately positioned and brought into contact with each other. Then, while being suppressed and heated with the bonding tool 42, it joins by giving an ultrasonic vibration.

However, the bumps that can be used for ultrasonic bonding are limited. Until now, extremely stable gold balls have been used. However, since gold balls are expensive and not a lot of resources, it is difficult to use them widely industrially.
An alternative metal is aluminum, which is one of the active metals. However, as described below, it is difficult to make a ball having a small diameter (particularly, a particle diameter of 20 μm or less), and a method for producing a microball having a uniform size has not been established.
As a method for producing a minute aluminum ball, there are a gas atomizing method, a uniform droplet method, and the like.

The gas atomization method is a method of manufacturing a ball of a minute size by dropping a metal in a molten state and spraying it with high pressure gas, high pressure water, or the like to powder it. Moreover, the technique which makes active metal particles, such as aluminum, combining a flotation melt | dissolution technique and a gas atomization technique is also proposed (patent document 1).
However, with these techniques, the obtained particles have a wide particle size distribution, and highly accurate particles cannot be obtained.

The uniform droplet method is described in Patent Document 2, for example.
In this method, pressure is applied to the molten metal to inject the molten metal from the tip of the lower nozzle, and at the same time, vibration is applied to the molten metal and the vibration is transmitted to the injection flow at the nozzle outlet. When the vibration is transmitted to the jet stream, the jet stream becomes constricted, and the constriction develops, so that a ball of a minute size can be formed.

  However, with this method, it is difficult to uniformly control how vibration is transmitted from resonance or the like. As a result, it is difficult for the particles to maintain a highly accurate particle size. Also, the control becomes more difficult as the diameter becomes smaller. In particular, an active metal such as aluminum is more difficult to control, so only an aluminum ball having a particle diameter of 0.5 mmφ has been proposed.

An object of this invention is to provide the manufacturing method which can manufacture the microball of the active metal of a small diameter and uniform size.
Another object of the present invention is to provide a microball that is stable in the atmosphere by covering the surface with a passive film.

The invention according to claim 1 is a step of introducing an active metal into a melting chamber made of a material whose inner surface does not generate a reaction product with the active metal.
A step of evacuating the dissolution chamber to a vacuum of 1 × 10 ⁻² Pa or less,
Replacing the dissolution chamber with an inert gas having an oxygen concentration of 0.1 ppm or less and a water concentration of 0.55 ppm or less;
Dissolving the active metal in an atmosphere of the inert gas to form a molten metal;
A step of spraying the molten metal from the orifice hole formed in the lower part of the melting chamber to form a ball by applying a pulse pressure to the molten metal,
It is a manufacturing method of the active metal microball characterized by having.
The invention according to claim 2 is a method for producing an active metal microball, wherein after the process according to claim 1, a passive film of 10 nm or less is formed on the surface.
The invention according to claim 3 is characterized in that an extraction chamber is provided in the recovery part via a gate valve, and the passive film is formed in the extraction chamber. It is a manufacturing method of a ball.
The invention according to claim 4 is characterized in that when the microball reaches a room temperature, the gate valve is closed and an oxidizing gas is introduced into the recovery part to form a passive film. Item 4. A method for producing an active metal microball according to Item 2 or 3.
The invention according to claim 5 is the method for producing an active metal microball according to claim 4, wherein the oxidizing gas is an atmospheric gas.
The invention according to claim 6 is the method for producing an active metal microball according to any one of claims 1 to 5, wherein the diameter of the microball is 40 to 200 μm.
The invention according to claim 7 is the method for producing an active metal microball according to any one of claims 1 to 6, wherein the variation in diameter is within ± 7.5%.
The invention according to claim 8 is the method for producing an active metal microball according to any one of claims 1 to 7, wherein the variation in diameter is within ± 3.5%.
The invention according to claim 9 is an aggregate of active metal microballs characterized in that the diameter is 40 μm to 200 μm and the variation in diameter is within ± 7.5%.
The invention according to claim 10 is the active metal microball according to claim 9, wherein the variation in diameter is within ± 3%.
The invention according to claim 11 is the assembly of active metal microballs according to claim 9 or 10 having a passive film of 10 nm or less on the surface.

(Claim 1)
Uniformly sized active metal microballs whose diameter is approximately the same as the orifice diameter can be produced. Therefore, it becomes possible to produce an active metal microball having a diameter of 200 μm or less, which could not be produced conventionally.
(Claim 2)
By covering the surface of the active metal microball with a passive film such as an oxide film, it is possible to produce an active metal microball that is stable at normal temperature and in the vicinity thereof. Therefore, it is possible to obtain a microball effective for ultrasonic bonding technology that can be connected at a low temperature in semiconductor mounting. Moreover, ultrasonic bonding is possible.
(Claim 3)
Since a take-out chamber is provided between the collection unit and the outside via a gate valve, it is possible to take out the ball without exposing the collection unit to the atmosphere during the take-out. For this reason, the cleanliness of the recovery unit is maintained, and there is no need to purge the recovery unit.
(Claims 4 and 5)
Since the recovery unit is lowered to room temperature and exposed to the atmosphere or an oxidizing gas while maintaining the cleanliness of the recovery unit, the thickness of the oxide film can be accurately controlled to be 10 nm or less. Note that the thickness of the oxide film can be controlled by adjusting the concentration of oxidizing components (oxygen and moisture) in the gas. The normal temperature is a temperature of 40 ° C. or lower.
(Claims 6 and 9)
An active metal microball of 200 μm or less, which did not exist conventionally, can be obtained. Therefore, it is possible to obtain a ball that substitutes for gold.
(Claims 7, 8, 10)
Since the microballs have the same diameter in a state where the molten metal is radiated from the orifice (that is, without performing an operation such as classification), it is possible to join the semiconductors without variation among products.
(Claim 11)
It is possible to provide a microball in which a pure metal portion is protected until mounting and does not cause a decrease in electrical conductivity at the joint.

Hereinafter, the meaning of each term according to the present invention will be clarified, and the best mode of the present invention will be described.
In this specification, “variation” means “100 × (average value−diameter) / average value”.

In the present invention, the aggregate of produced monodisperse particles is observed with an optical microscope. At the same time, the cross-sectional area of each particle is measured by the image analysis means provided in the optical microscope, and the diameter of each particle is calculated therefrom.
FIG. 1 shows a schematic view of an active metal microball manufacturing apparatus related to the present invention. Here, B1 is an active metal melt injection part, B2 is a passive film formation part which forms a passive film on the surface of the injected active metal.
The active metal molten metal ejection part B1 includes, for example, a melting chamber (crucible) 10, a piezoelectric actuator 11, a cylinder rod 12 connected to the piezoelectric actuator 11, and an orifice plate 16.
The melting chamber 10 is made of a material that does not generate a reaction product with the active metal. The same applies to the portion in contact with the active metal. For example, carbon, BN (boron nitride), and alumina are used. Since carbon may react with an active metal, it is preferable to use BN or alumina.
The crucible 10 is sealed with a lid 10a. A cylinder rod 12 connected to the piezoelectric actuator 11 passes through the lid 10a. The pulse pressure generated by the piezoelectric actuator 11 is transmitted to the cylinder rod 12 and the active metal melt 15 in contact with the cylinder rod 12. Further, the container 10 is provided with a gas inlet 14 for introducing an inert gas.

The lower side of the crucible 10 is a tundish 25 which is an intermediate container for holding molten metal.
An orifice 17 is provided in the orifice plate 16 below the tundish 25. One or more orifices 17 may be provided.
The passive film forming unit B2 includes, for example, a microball collection tray 19, a gate valve 20, a microball collection tray insertion rod 23, and a microball extraction chamber 22. A gas inlet 18 is also provided on the lower side of the orifice plate 16 serving as the inlet of the passive film forming part B2.

In this embodiment, by forming an oxide film on the surface of the microball, a stable microball that hardly reacts with oxygen and moisture in the atmosphere at normal temperature and in the vicinity thereof is obtained.
Next, a method for producing monodisperse particles using this apparatus will be described.
First, the lid 10a is opened, and the crucible 10 is filled with an active metal such as aluminum. Then, the lid 10a is closed and evacuated.

In the present invention, vacuuming is performed until the pressure is 1.0 × 10 ⁻² Pascal or less. That is, vacuuming is performed until the degree of vacuum becomes higher than 1.0 × 10 ⁻² Pascal. If the degree of vacuum is worse than 1.0 × 10 ⁻² Pascal, injection is hindered and the particle size becomes uneven.
From this viewpoint, 1.0 × 10 ⁻³ Pascal or less is preferable, and 1.0 × 10 ⁻⁴ Pascal or less is more preferable. Since the effect is saturated by 1.0 × 10 ⁻⁴ Pascal, considering the workability, 1.0 × 10 ⁻⁴ Pascal is preferable as the lower limit.

The present inventor has conventionally sought the cause of the difficulty in reducing and uniforming the diameter of active metal balls. As a result, we thought that the presence of oxides in the molten metal might have an effect. Then, after performing the removal of the oxide which floats in molten metal, injection was performed. However, only by removing the oxide from the molten metal, the reduction in diameter and uniformity were not achieved.
As a result of further exploration, the inventors have come up with the idea that oxides are being produced even during the injection process. Thus, although the concentration of impurity oxygen in the atmospheric gas was reduced, good results were not always obtained. The idea of whether there is an influence of moisture as well as oxygen was to reduce the moisture, and better results were obtained than when oxygen was reduced alone. However, the desired diameter reduction and uniformity were not always achieved.

As a result of further knowledge, we discovered that oxygen and moisture concentrations have critical values. That is, it has been found that when the concentration of oxygen is 0.1 ppm and the concentration of water is 0.55 ppm or less, the diameter and the uniformity are rapidly improved.
Therefore, in the present invention, after evacuation, an inert gas such as argon gas is introduced from the gas inlet 14.
At that time, an inert gas having an oxygen concentration of 0.1 ppm or less and a water concentration of 0.55 ppm or less is used. Only when the oxygen concentration is 0.1 ppm or less and the water concentration is 0.55 ppm or less, it becomes possible to produce an active metal ball having a particle diameter of 200 μm or less.
The oxygen concentration is more preferably 10 ppb or less, and further preferably 1 ppb or less. The water concentration is more preferably 200 ppb or less, and further preferably 50 ppb or less.

Next, it heats with the heating apparatus 13, and makes an active metal the active metal molten metal 15. FIG. The orifice plate 16 is provided with an orifice 17 having the same diameter as the microball to be manufactured. The number of orifices provided in the orifice plate 16 may be one or more. When a piezoelectric pulse is applied to the piezoelectric actuator 11, the cylinder rod 12 moves up and down by the tundish 25. In synchronism with the piezoelectric pulse, molten metal is ejected from the orifice 17.
At this time, the aluminum is solidified without being oxidized to form a microball.
Further, by forming the active metal ejection part B1 as described above, an aluminum microball having a particle size accuracy within ± 7.5% (or within ± 3%) with respect to the diameter of the orifice 17 is manufactured. I was able to.

When the active metal is filled in the crucible 10 of the molten metal ejection portion B1, the insertion rod 23 is operated to insert the microball collection tray 19 below the orifice 17, and the gate valve 20 is closed to shut off from the atmosphere. At the same time as evacuating the crucible 10 and introducing the inert gas, the space into which the microball collection tray 19 is inserted and the microball take-out chamber 22 are also evacuated to introduce the inert gas. The degree of vacuum during evacuation and the concentration of oxygen and moisture contained in the inert gas may be the same as those of the crucible 10. However, it is preferable to adjust the speed of the inert gas introduced from the gas introduction port 18 so that the molten active metal ejected from the orifice 17 becomes spherical.
The molten active metal ejected from the orifice 17 is solidified during the fall and collected in the microball collection tray 19.
After the ejection from the orifice 17 is finished, the gate valve 20 is opened and the operation rod 23 is operated to move the microball collection tray 19 to the microball extraction chamber 22. Then, it is allowed to cool for a while in an inert atmosphere. When it reaches room temperature, it is exposed to an oxidizing atmosphere. An air atmosphere is preferable as the oxidizing atmosphere.

What is necessary is just to adjust the leaving time in an oxidizing atmosphere suitably with heating temperature. The relationship between these conditions and the film thickness may be obtained in advance by experiments so as to be 10 nm or less.
By the treatment in the take-out chamber, an oxide film is formed on the surface of the microball, and a stable active metal microball that hardly reacts with oxygen and moisture in the atmosphere at normal temperature and in the vicinity thereof can be obtained.
Finally, the microball collection tray outlet 24 is opened, and the microball and the collection tray 19 are removed.

The results of manufacturing microballs from aluminum having a purity of 99.99% (weight%) using the apparatus shown in FIG. 1 will be described.
Experiments were conducted using several cylinder rods 12 having a diameter on the side of the dandish 25 in the range of 5 to 30 mm. The dundish 25 is substantially the same as or slightly larger than the cylinder rod 12.
While filling the crucible 10 with 99.99% purity aluminum, the microball collection tray 19 was placed below the orifice 17 and the gate valve 20 was closed. Then, after evacuating the crucible 10, the space in which the microballs 19 are arranged, and the microball take-out chamber 22 to 1.0 × 10 ⁻² Pascal or less, the oxygen concentration is 0.1 ppm and the water concentration is 0.5401 ppm. Argon gas was introduced. After the aluminum was heated by the heating device 13 and melted, a piezoelectric pulse was applied to the piezoelectric actuator 11 to eject the molten aluminum from the orifice 17. The molten aluminum ejected from the orifice 17 was solidified during the fall and deposited on the microball collection tray 19. After the ejection from the orifice 17 was finished, the operation rod 23 was operated to move the microball collection tray 19 to the microball extraction chamber 22. Cooling is allowed to stand in the argon gas for a while. Then, when it reached normal temperature, it exposed to oxygen atmosphere, and formed the oxide film on the microball surface. Finally, the microball collection tray outlet 24 was opened, and the microball and the collection tray 19 were taken out.

FIG. 2 shows an optical micrograph of the obtained microball. A microball with a uniform size and close to a true sphere was obtained.
FIG. 3 shows the particle size distribution of the microballs measured by the image analysis means provided in the optical microscope. It can be seen that microballs having a substantially uniform particle diameter are obtained.

It is the schematic of the active metal microball manufacturing apparatus which concerns on embodiment of this invention. It is an optical microscope photograph of the aluminum microball obtained in the Example of this invention. It is a graph which shows the particle size distribution of the aluminum microball obtained by the Example of this invention. It is the schematic which shows an ultrasonic bonding method.

Explanation of symbols

B1: Active metal melt injection unit B2: Passive film forming unit 10: Crucible 10a: Lid 11: Piezoelectric actuator 12: Cylinder rod 13: Heating devices 14, 18, 21: Gas inlet 15: Active metal melt 16: Orifice plate 17: Orifice 19: Microball collection tray 20: Gate valve 22: Microball removal section 23: Microball collection tray insertion rod 24: Microball collection tray removal outlet 25: Tundish 41: Bonding stage 42: Bonding tool 43: Semiconductor Substrate 44: Semiconductor chip 45: Wiring pattern 46: Bump

Claims (11)

Introducing an active metal into a melting chamber made of a material whose inner surface does not generate a reaction product with the active metal;
A step of evacuating the dissolution chamber to a vacuum of 1 × 10 ⁻² Pa or less,
Replacing the dissolution chamber with an inert gas having an oxygen concentration of 0.1 ppm or less and a water concentration of 0.55 ppm or less;
Dissolving the active metal in an atmosphere of the inert gas to form a molten metal;
A step of spraying the molten metal from the orifice hole formed in the lower part of the melting chamber to form a ball by applying a pulse pressure to the molten metal,
A method for producing an active metal microball, comprising: A method for producing an active metal microball, wherein a passive film of 10 nm or less is formed on the surface after the step according to claim 1. The method for producing an active metal microball according to claim 2, wherein an extraction chamber is provided in the recovery unit via a gate valve, and the passivation film is formed in the extraction chamber. 4. The active metal according to claim 2, wherein when the microball reaches a normal temperature, a passive film is formed by introducing an oxidizing gas into the recovery portion with the gate valve closed. A method for producing a microball. The method for producing an active metal microball according to claim 4, wherein the oxidizing gas is an atmospheric gas. 6. The method for producing an active metal microball according to claim 1, wherein the diameter of the microball is 40 to 200 [mu] m. The method for producing an active metal microball according to any one of claims 1 to 6, wherein the variation in diameter is within ± 7.5%. The method for producing an active metal microball according to any one of claims 1 to 7, wherein a variation in diameter is within ± 3%. An aggregate of active metal microballs having a diameter of 40 μm to 200 μm and a variation in diameter within ± 7.5%. The aggregate of active metal microballs according to claim 9, wherein a variation in diameter is within ± 3.5%. The aggregate of active metal microballs according to claim 9 or 10, which has a passive film of 10 nm or less on the surface.

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