US20120240727A1

US20120240727A1 - Method of manufacturing solder powder having diameter of sub-micrometers or several micrometers

Info

Publication number: US20120240727A1
Application number: US13/364,347
Authority: US
Inventors: Yong Sung Eom; Jong Tae Moon; Kwang Seong Choi
Original assignee: Electronics and Telecommunications Research Institute ETRI
Current assignee: Electronics and Telecommunications Research Institute ETRI
Priority date: 2011-03-24
Filing date: 2012-02-02
Publication date: 2012-09-27
Also published as: KR20120108500A

Abstract

Disclosed is a method of manufacturing a solder powder having a diameter of sub-micrometers or several micrometers, the method including: mixing solder powder having a diameter of 10 to 1000 micrometers with a polymer resin to obtain a mixture; heating the mixture to a temperature higher than a melting point of the solder powder in the mixture; applying ultrasonic waves to the heated mixture so that the diameter of the solder powder becomes 0.1 to 10 micrometers; and cooling the mixture to the room temperature without exposing the solder powder of 0.1 to 10 micrometers to the air.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority from Korean Patent Application No. 10-2011-0026431, filed on Mar. 24, 2011, with the Korean Intellectual Property Office, the present disclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present invention relates to a method of manufacturing a solder powder having a diameter of sub-micrometers or several micrometers.

BACKGROUND

Due to a trend of reducing the size of mobile communication devices, studies on fineness and integration of chips themselves are being actively made.
A fine pitch patterned substrate is used for integration of a chip. Conventionally, a semiconductor process using photolithography or a process of screen-printing and reflow-soldering a solder paste on a substrate has been used to form a solder bump on a metal pad located on a fine pitch patterned substrate. However, the semiconductor process requires high costs, and the screen-printing process has a difficulty in forming a solder bump with a pitch of below approximately 150 micrometers.
A solder bump is generally formed on a metal pad on a substrate. Then, a diameter of solder powder should be sub-micrometers or several micrometers. It is because the metal pad on which the solder bump is formed has a size of several micrometers. Although it has been known that ultrasonic waves may be used to manufacture solder powder having a diameter of sub-micrometers or several micrometers, the solder powder (increased surface area, see FIG. 1) manufactured to have a diameter of sub-micrometers or several micrometers are exposed to the atmosphere (air), resulting in an increase in an oxide film on surfaces of the solder powder. When the oxide film increases, soldering performance is lowered.

SUMMARY

Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an aspect of the present invention provides a method of manufacturing a solder powder having a diameter of sub-micrometers or several micrometers without increasing an oxide film in the solder powder.
In accordance with an aspect of the present invention, there is provided a method of manufacturing a solder powder having a diameter of sub-micrometers or several micrometers, the method including: mixing solder powder having a diameter of 10 to 1000 micrometers with a polymer resin to obtain a mixture; heating the mixture to a temperature higher than a melting point of the solder powder in the mixture; applying ultrasonic waves to the heated mixture so that the diameter of the solder powder becomes 0.1 to 10 micrometers; and cooling the mixture to the room temperature without exposing the solder powder of 0.1 to 10 micrometers to the air.
Accordingly, in the method of manufacturing a solder powder having a diameter of sub-micrometers or several micrometers according to the present invention, a small-sized solder powder can be manufactured without increasing an oxide film, and a flux solvent may not be used to form a solder bump, making it possible to reduce manufacturing costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating changes in a surface area of a solder powder according to changes in a diameter of the solder powder in a unit volume.

FIG. 2 is a view illustrating that solder powder having a diameter of 10 to 1000 micrometers is mixed with a polymer resin and is contained in a vessel.

FIG. 3 is a view illustrating that solder powders having a diameter of 0.1 to 10 micrometers which has undergone the ultrasonic wave applying process is mixed with a liquid polymer resin and is contained in a vessel.

DETAILED DESCRIPTION

The present invention provides a method of manufacturing a solder powder having a diameter of sub-micrometers or several micrometers, which comprises: a mixing process of mixing solder powder having a diameter of 10 to 1000 micrometers with a polymer resin to manufacture a mixture; a melting process of heating the mixture to a temperature higher than a melting point of the solder powder in the mixture; an ultrasonic wave applying process of applying ultrasonic waves to the heated mixture (mixture solution) so that the diameter of the solder powder becomes 0.1 to 10 micrometers; and a cooling process of cooling the mixture to the room temperature without exposing the solder powder of 0.1 to 10 micrometers to the air.
The polymer resin (one-component polymer resin) has a property of not reacting with a change in temperature. It is preferable that the polymer resin does not react at the room temperature or at a temperature around the melting point of the solder powder (at the melting point plus 100° C.). Examples of the polymer resin include an epoxy resin and oils. In more detail, examples of the epoxy resin include a resin including DGEBA (Diglycidyl ether of bisphenol-A), TGDDM (Tetraglycidyl-4,4-diaminodiphenylmethane), TriGDDM (Diglycidyl ether of para-aminophenol), and Isocyanate, and a Bismaleimide resin. Examples of the oil include an epoxy modified silicon oil, an amine modified silicon oil, a carboxyl modified silocon oil, and a polyol resin.
A reducing agent may be added to remove a solder oxide film. The epoxy resin is apt to react with a reducing agent and is advantageous in the removal of the solder oxide film, so it is more desirable for the polymer material.
Prior to the ultrasonic wave applying process, the diameter of the solder powder is 10 to 1000 micrometers. The solder powder is made of an alloy of Sn, Bi, Ag, Cu, In, Pb, etc., such as 60Sn/40Bi, 52In/48Sn, 97In/3Ag, 57Bi/42Sn/1Ag, 58Bi/42Sn, 52Bi/32Pb/16Sn, and 96.5Sn/3Ag/0.5Cu. The melting point of the solder powder is preferably 80 to 250° C. The solder powder is preferably mixed with the polymer resin at a volume ratio of 1 to 60 with respect to 100 volume of the polymer resin. If the volume ratio of the solder powder is less than 1, a problem may be caused in a dispersion degree of the solder powder. On the other hand, if the volume ratio of the solder powder is more than 60, the viscosity may excessively increase, making it difficult to produce the solder powder having a uniform size.
Hereinafter, an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.
1. Mixing Process
FIG. 2 illustrates that a solder powder 1 having a diameter of 10 to 1000 micrometers is mixed with a polymer resin 2 and is contained in a vessel 3. Since the solid solder powder 1 is impregnated in the liquid polymer resin 2 and is isolated from the atmosphere (air), an increase in oxide film does not occur. The vessel 3 is preferably made of a material which can endure a temperature higher than the melting point of the solder powder while not being decomposed or corroded. The shape of the vessel 3 is not limited specifically. The vessel 3 may include a propeller type agitator and an ultrasonic wave generator. That is, the propeller type agitator and the ultrasonic wave generator may be attached to the vessel 3. A heating wire may be installed in the vessel 3 to generate heat by itself without using any external heat source. A thermometer also may be installed within the vessel 3. Further, an apparatus for flowing a cooling medium may be installed outside the vessel 3.
2. Melting Process
Although not illustrated in the drawings, the solder powder is melted by applying heat at a temperature higher than the melting point of the solder powder. The method of applying heat is not specifically limited. The vessel 3 may be heated by using an external heat source such as a hot plate. Further, the vessel 3 may be heated by itself without using any external heat source by using its own heat source such as a heating wire installed inside the vessel 3.
3. Ultrasonic Wave Applying Process
Although not illustrated in the drawings, solder powder having a diameter of 0.1 to 10 micrometers is manufactured by applying an ultrasonic wave to a mixture solution where the solder powder is melted. An external apparatus such as a vibrator may be immersed in the mixture solution to apply an ultrasonic wave. The ultrasonic wave may be applied by using an apparatus (ultrasonic wave generator) installed inside the vessel 3. The shape and material of the ultrasonic wave generator such as a vibrator may not be specifically limited. The ultrasonic wave preferably has a frequency of 28 KHz or more.
4. Cooling Process
FIG. 3 illustrates that the solder powder 4 having a diameter of 0.1 to 10 micrometers which has undergone the ultrasonic wave applying process is mixed with the liquid polymer resin and is contained in the vessel 3. The mixture solution is preferably cooled to the room temperature while being contained in the vessel 3. If the solder powder is exposed to the atmosphere (air) during the cooling process, an oxide film may increase. The method of cooling the mixture solution to the room temperature while the mixture solution is contained in the vessel 3 is not specifically limited. The mixture solution may be cooled by an apparatus for flowing a cooling medium installed outside the vessel 3, or may be cooled by leaving it in the air.
Solid solder powder having a diameter of 0.1 to 10 micrometers may be obtained by removing a polymer resin removed from the mixture which has undergone the mixing process, the melting process, the ultrasonic wave applying process, and the cooling process, and then drying the mixture.
If necessary, one or more compounds selected from the group consisting of a reducing agent, a hardener, and a catalyst may be added. The time when the additive compounds are added is not specifically limited. Examples of the reducing agent include glutamic acid, malic acid, azelaic acid, abietic acid, adipic acid, ascorbic acid, acrylic acid, and citric acid. Examples of the hardener include amine-based components (MPDA, DDM, DDS, etc.) and anhydride-based components (MNA, DDSA, MA, SA, MTHPA, HHPA, THPA, PMDA, etc.). Examples of the catalyst include BDMA, BF3-MEA, DMP-30, DMBA, and MI.
Hereinafter, the present invention will be described in detail through the exemplary embodiment of the invention, in order to explain the invention in more detail. Here, the scope of the present invention is not limited by the exemplary embodiment.

EXEMPLARY EMBODIMENT

1. Mixing Process
15 grams of 42Sn/58Bi solder powder having a diameter of 40 to 50 micrometers, 5 grams of DGEBA (YD-128, Gukdo Chemicals Inc.), and 1 gram of malic acid which is a reducing agent are mixed and the mixture is introduced into a cylindrical metal vessel which may be heated or vibrated with ultrasonic waves.
2. Melting Process
The vessel in which the mixture is contained is placed on a hot plate and is heated from the room temperature to 180° C. at a rate of 100° C./min (A melting point of 42Sn/58Bi solder powder is 138° C.)
3. Ultrasonic Wave Applying Process
After the temperature of the vessel reaches 180° C., which is higher than the melting point of the solder powder, a cylindrical vibrator is immersed in a mixture solution. Thereafter, ultrasonic waves having an oscillation frequency of approximately 28 KHz are applied to the mixture solution by using a US-50 ultrasonic oscillator of Nussei (Japanese company) so that a diameter of the solder powder becomes 0.1 to 10 micrometers.
4. Cooling Process
The solder powder is left in the air while being contained in the vessel to be cooled to the room temperature.
According to SEM (Scanning Electron Microscope) image, it was found that the solder power of the diameter 0.1 to 10 micrometers was forming in the DGEBA.
Although the present invention has been described with reference to the limited example and drawings, the present invention is not limited thereto and those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A method of manufacturing a solder powder having a diameter of sub-micrometers or several micrometers, the method comprising:

mixing solder powder having a diameter of 10 to 1000 micrometers with a polymer resin to obtain a mixture;

heating the mixture to a temperature higher than a melting point of the solder powder in the mixture;

applying ultrasonic waves to the heated mixture so that the diameter of the solder powder becomes 0.1 to 10 micrometers; and

cooling the mixture to the room temperature without exposing the solder powder of 0.1 to 10 micrometers to the air.

2. The method of claim 1, wherein the polymer resin is an epoxy resin or oils.

3. The method of claim 1, wherein the melting point of the solder powder is 80° C. to 250° C.

4. The method of claim 1, further comprising removing the polymer resin and performing a drying operation.

5. The method of claim 1, further comprising adding at least one compound selected from the group consisting of a reducing agent, a hardener, and a catalyst.