FIELD OF INVENTION This invention relates to a system of producing granulated solder. More particularly, the present invention relates to a system and a method of producing granulated solder using the concept of microencapsulation; whereby the granulated solder can be used in manufacturing of solder paste for the use in semiconductor industry. BACKGROUND OF INVENTION

Solder paste is typically used in the screen-printing process for manufacturing of printed circuit board (PCB). Properties of solder paste are very important in making a good PCB. Solder paste must not only able to form solder joints on PCB, the solder paste must also have sufficient tackiness to hold the components on PCB throughout the manufacturing process. However, the tackiness of solder paste is not only depends on the flux medium, the properties of granulated solder or solder balls are in fact more important.

Basically, a solder ball is spherical in shape to reduce surface oxidation and to ensure formation of good solder joints. Spherical solder ball has lower surface area which can minimize oxidation and prevent clogging of the stencil, hence, less printing defects. To produce a quality solder joint, it is important that the solder ball must also have a regular size and shape as well as low level of oxidation. Another important property of a solder ball is its particle roundness and smoothness. A smoother solder ball will have lower viscosity and tendency to shear thin when printing at high speed. Thus, it can prevent slumping and smearing which may result in solder bridging and solder balling. Due to the technology boom recently, the demand for granulated solder for making of solder paste is increasing. A traditional method of producing granulated solder is by continuous cutting of solder wire until it is sufficiently small, followed by cleaning and fabricating the small solder wire into ball-shaped. This process involves a large number of steps and is not practical for continuous industrial process. The solder ball produced is also irregular in shape and size. More research effort has been done to improve the properties of granulated solder. Recent research is focusing on a method comprising the steps of melting solder alloy, forming molten solder droplets and subsequently cooling to form granules. There are few patented technologies over the prior art relating to systems for producing granulated solder. However, there is a wide variation in the system designs and qualities as well as the method of operating the system. Basically, the main difference between the prior arts is the method of atomising the solder alloy and cooling to obtain granulated solder.

One of the inventions relates to ultrasonic atomisation of solder alloy is Chinese Patent No. 101332513 (A). This method comprises the steps of flowing pre-melted solder alloy at a predetermined flow rate to an atomising disk which vibrates at ultrasonic frequency and with a predetermined rotary speed; atomising the solder melt by force of high frequency; cooling and solidifying the molten solder droplets into granules in an environment of limited oxygen content. The solder granules are sieved to obtain granules of certain particle size. However, the granulated solder produced has a large particle size distribution.

Another invention which relates to centrifugal atomisation is Chinese Patent No. 102248173 (A). This prior art discloses a method of producing solder powder comprising the steps of mixing, heating, and melting the raw material of solder alloy; instilling the material on an atomising disk rotating at high speed in an atomisation chamber with cooling water circulation; condensing the atomised solder alloy into spherical powder due to the surface tension. The powder is then sieved to obtain powder of certain particle size. However, the hardware of system is easily damaged due to the high speed rotation of the atomising disk.

There is also patented technology utilising gas atomisation. In U. S. Patent No. 20120325051 (Al), it discloses a method of producing atomised powder of glassy aluminium alloy comprising the steps of providing a positive pressure of inert gas in a atomisation chamber; melting aluminium alloy in a crucible and delivering molten aluminium alloy out of the crucible to the chamber; crushing the aluminium alloy and cooling to form powder alloy with stream of pressurised inert gas in the chamber, which is maintained at a predetermined dew temperature. Frequent cleaning of the chamber is needed with this invention as the molten solder droplets are easily stuck to the wall of the chamber due to the turbulent flow of gas.

To overcome the drawbacks of the prior art, it is desirable for the invention to develop an improved system as well as systematic operating method which are able to produce granulated powder with regular shape and size, high sphericity, and low level of oxidation.

SUMMARY OF INVENTION

One of the objects of the invention is to provide an improved system of producing granulated solder.

Another object of the invention is to provide a method of operating a system for producing granulated solder.

Still another object of the invention is to develop a system of producing granulated solder in which the granulated solder produced has regular shape and size as well as high level of sphericity, at the same time, has low level of oxidation.

Yet another object of the invention is to develop a system of producing granulated solder in which the system can be customised to produce granulated solder of different sizes.

Again another object of the invention is to provide a system of producing granulated solder which is well-equipped with safety features.

Also another object of the invention is to develop a system of producing granulated solder whereby the granulated solder produced can be used to manufacture solder paste, which will be used in screen-printing process in the semiconductor industry. At least one of the preceding aspects is met, in whole or in part, by the present invention, in which the embodiment of the present invention describes a system of producing granulated solder comprising a tank for storing molten solder; a drying chamber having a covered top and a bottom outlet for collecting granulated solder, in which the covered top is fabricated with apertures of predetermined number and size around the circumferential edge of the top; an atomiser attached to the top cover of the drying chamber, draining the molten solder to the drying chamber and produce molten solder droplets; an annealing apparatus having a first gas inlet connected to the drying chamber substantially adjacent to the top cover, injecting heated inert gas to the drying chamber to anneal the molten solder droplets; and a second gas inlet provided onto the drying chamber directing inert gas at ambient temperature at a portion relatively lower than the first inert gas inlet to quench and solidify the molten solder droplets, wherein the tank is being connected to the atomiser with a heated piping system. In a preferred embodiment of the invention, the system of producing granulated solder further comprises a compressed gas inlet attached to the atomiser.

In another preferred embodiment of the invention, the system of producing granulated solder further comprises a pumping device for channeling the molten solder from the tank to the atomiser.

Still in another preferred embodiment of the invention, the system of producing granulated solder further comprises at least a container for collecting granulated solder produced in the drying chamber.

A further embodiment of the invention is a method of producing granulated solder comprising the steps of melting solder in a tank; producing molten solder droplets by the atomiser at presence of inert gas flowing into a drying chamber through a first and a second gas inlet; and collecting granulated solder produced in the drying chamber in at least one container, wherein each step is carried out at predetermined temperature, pressure, and duration. In another further embodiment of the invention, the method of producing granulated solder further comprises the step of supplying compressed gas to the atomiser through a compressed gas inlet. The preferred embodiment of the invention consists of novel features and a combination of parts hereinafter fully described and illustrated in the accompanying drawings and particularly pointed out in the appended claims; it being understood that various changes in the details may be effected by those skilled in the arts but without departing from the scope of the invention or sacrificing any of the advantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawing the preferred embodiments from an inspection of which when considered in connection with the following description, the invention, its construction and operation and many of its advantages would be readily understood and appreciated.

FIGURE 1 is a schematic diagram of the system of producing granulated solder as embodied by one of the preferred embodiments of the invention.

FIGURE 2 is a top view diagram of the drying chamber showing the position of apertures as embodied by one of the preferred embodiments of the invention.

DETAILED DESCRD7TION OF THE INVENTION

This invention relates to a system of producing granulated solder. More particularly, the present invention relates to a system and a method of producing granulated solder using the concept of microencapsulation; whereby the granulated solder can be used in manufacture of solder paste for the use in semiconductor industry. Hereinafter, the invention shall be described according to the preferred embodiments of the present invention and by referring to the accompanying description and drawings. However, it is to be understood that limiting the description to the preferred embodiments of the invention and to the drawings is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications without departing from the scope of the appended claim.

The invention discloses a system of producing granulated solder comprising a tank (101) for storing molten solder; a drying chamber (102) having a covered top and a bottom outlet for collecting granulated solder, in which the covered top is fabricated with apertures (110) of predetermined number and size around the circumferential edge of the top; an atomiser (103) attached to the top cover of the drying chamber(102) , draining the molten solder to the drying chamber (102) and produce molten solder droplets; an annealing apparatus (104) having a first gas inlet (105) connected to the drying chamber (102) substantially adjacent to the top cover, injecting heated inert gas to the drying chamber (102) to anneal the molten solder droplets; and a second gas inlet (106) provided onto the drying chamber (102) directing inert gas at ambient temperature at a portion relatively lower than the first gas inlet (105) to quench and solidify the molten solder droplets, wherein the tank (101) is being connected to the atomiser with a heated piping system.

As illustrated in FIGURE 1, the system of the invention comprises a tank (101) for storing of molten solder, a drying chamber (102) with an annealing apparatus (104) and gas inlets (105, 106) attached to it, and an atomiser (103) attached to the top cover of the drying chamber (102) being connected to the tank (101) with a heated piping system.

According to the preferred embodiment of the invention, the tank (101), with a predetermined size to store molten solder, is equipped with a heating element to melt and maintain the temperature of molten solder. The tank (101) may have a closed top and bottom to prevent molten solder from spilling. Preferably, the heating element can be heated up to a temperature of 1000 °C. To ensure complete melting of the solder, the temperature of the heating element is recommended to be at least 10% higher than the melting temperature of the solder. The entire melting system which comprises the tank (101) and the heating element can be controlled by a temperature controller. The melting system can be equipped with a closed door chamber sensor for safety reasons. The system of producing granulated solder will not be operating if the tank ( 101 ) is not closed.

Accordingly, the drying chamber (102) with predetermined dimension and shape has a closed top cover and a bottom outlet configured to collect granulated solder. The dimension of the drying chamber (102) is recommended to be 2.5 m in height and 2 m in top diameter. The upper portion of the drying chamber (102) is substantially a cylinder and the bottom portion of the drying chamber (102) is substantially a cone. Preferably, the drying chamber (102) may be made of stainless steel and is able to withstand a temperature of at least 600 °C. The height of the drying chamber (102) is preferred to be sufficiently high to allow complete annealing and solidification process to be carried out.

As illustrated in FIGURE 2, apertures (110) of predetermined number and size are arranged around the circumferential edge of the top cover of the drying chamber (102). The apertures (110) are configured to create pressure difference in the drying chamber (102), so as to force the gas which is injected from the first gas inlet (105) of the annealing apparatus (104) to flow around the wall of the drying chamber (102), creating an air curtain around the wall of the drying chamber (102) to prevent sticking of the molten solder droplets to the wall of the drying chamber (102).

As part of the safety features of the system, the drying chamber (102) can be enclosed inside a cabinet substantially made of Perspex glass to prevent accidental in contact with the heated drying chamber (102). The drying chamber (102) can be insulated with a heat proof element to minimise heat loss.

As described by the preferred embodiment of the invention, an atomiser (103) is attached to the top cover of the drying chamber (102) and is connected to the tank (101) with a heated piping system to drain the molten solder to the drying chamber (102). Preferably, the atomiser (103) comprises a heater to maintain the heating environment around the atomiser (103) and prevent clogging of the atomiser (103) due to solidification of solder. The size of tip opening of the atomiser (103) can be customised to a size of 0.25 mm, 0.5 mm, and 0.75 mm. The size of the molten solder droplet produced may be customised through customising the size of the atomiser (103) tip opening.

In accordance with the preferred embodiment of the invention, a compressed gas inlet (107) is connected to the atomiser (103) to allow mixing of gas and molten solder at the atomiser (103). An air regulator can be installed on the atomiser (103) to control the amount of compressed gas from entering the atomiser (103). The compressed gas is preferred to be nitrogen gas with at least pressure of 12 bar.

In the system disclosed in the invention, a pumping device (108) is connected to the tank (101) and the atomiser (103) with the heated piping system. The pumping device (108) is configured to pump the molten solder from the tank (101) to the atomiser (108) once the solder has reached a predetermined melting temperature. Preferably, a positive displacement pump is used as the pumping device (108) and is selected from the group consisting of gear pump, screw pump, and rotary vane pump. Preferably, the heated piping system comprises a piping system being insulated with a heater to maintain temperature and liquid state of molten solder.

In another preferred embodiment of the invention, an annealing apparatus (104) has a first gas inlet (105) connected to the drying chamber (102) substantially adjacent to the top cover, in which the level of the annealing apparatus (104) is higher than the tip of the atomiser (103) to prevent direct injection of gas onto the molten solder droplets. Preferably, the gas supplied to the first inlet is nitrogen gas with at least pressure of 8 bar.

The inert gas is heated to a temperature higher than the critical temperature of a selected type of solder and is injecting to the drying chamber (102) through the first gas inlet (105). The first gas inlet (105) is configured to inject air in downward direction. The annealed temperature is preferred to be 5% to 10% higher than the critical temperature of the selected type of solder. However, an extreme high annealing temperature may be avoided to minimise oxidation of solder. The heater is preferred to deliver a temperature of between 60 °C to 500 °C. Still in another preferred embodiment of the invention, a second gas inlet (106) is attached to the lower portion of the drying chamber (102) wall. The gas supplied to the second gas inlet (106) is preferred to be nitrogen gas at ambient temperature with at least pressure of 8 bar. The inert gas injected to the drying chamber (102) is used to quench and solidify the molten solder droplets into granulated solder.

The annealing apparatus (103) and the second gas inlet (106) are configured to improve properties of the solder. Upon atomisation, the molten solder droplets are encountering with the heated inert gas having a temperature higher than the critical temperature of the solder at the upper portion of the drying chamber (102). The kinetic energy of the atoms in solder increases due to higher temperature. The atoms vibrate and diffuse more frequently within the solder material, causing the material progresses towards its equilibrium state by redistributing and destroying the dislocations in solder.

The molten solder droplets eventually decent to the lower portion of the drying chamber (102) by force of gravity. The molten solder droplets are encountering with the inert gas at ambient temperature. Rapid heat exchange occurs between the molten solder droplets and the surrounding environment. The molten solder droplets with a more stable structure solidify, forming a stable granulated solder. With the process of annealing and quenching, the granulated solder produced may have lower hardness and higher ductility.

Again in another preferred embodiment of the invention, at least a container (109) is placed at the bottom outlet of the drying chamber (102) to collect the granulated solder produced. Preferably, the container (109) is made of steel. As part of the safety features of the system, over temperature cut off sensors are installed in the tank (101) and the annealing apparatus (104) to prevent overheating. The system will be shut down automatically once the temperature of the tank (101) exceeded 1000°C and 600°C for annealing apparatus (104).

A further embodiment of the invention is a method of producing granulated solder comprising the steps of melting solder in a tank (101); channeling the molten solder from the tank (101) to a atomiser (103) by a pumping device (108); producing molten solder droplets by the atomiser (108) at presence of inert gas flowing into a drying chamber (102) through a first (105) and a second gas inlet (106); and collecting granulated solder produced in the drying chamber (102) in at least one container (109), wherein each step is carried out at predetermined temperature, pressure, and duration.

In another further embodiment of the invention, the tank (101) is charged with predetermined amount of source of solder. The heating element is turn on to melt the solder in the tank (101). Once the temperature of the solder has reached a predetermined melting temperature, the pumping device (108) is turned on, pumping a predetermined amount of molten solder to the atomiser (103).

Preferably, dry compressed nitrogen gas of at least a pressure of 12 bar is supplied to the atomiser (103) through the compressed gas inlet (107) before pumping of molten solder.

Still in another further embodiment of the invention, the molten solder is mixed with the dry compressed gas at the atomiser (103). The atomiser (103) with a predetermined size of tip opening atomises the molten solder into molten solder droplets. The molten solder droplets are annealed and quenched at the upper portion and the lower portion of the drying chamber (103) respectively. At the bottom outlet of the drying chamber (103), granulated solder are collected in at least one container (109).

The granulated solder produced in combination with a flux can be used to produce solder paste which can be used in screen-printing process in manufacturing of printed circuit board (PCB). The processed gas leaving the drying chamber (102) can be channeled to a dry scrubbing system to remove hazardous particulates present in the processed gas before releasing to the environment as effluent. Although the invention has been described and illustrated in detail, it is to be understood that the same is by the way of illustration and example, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.

EXAMPLE

The temperature of tank and annealing apparatus according to different types of solder selected is shown in Table 1.

Table 1

Component Sn-3.5Ag Sn-0.7Cu

Tank 242 °C 250 °C

Annealing Apparatus 275 °C 281 °C