Plastic article or earthenware shaping or treating: apparatus – Means making particulate material directly from liquid or...
Reexamination Certificate
2000-11-17
2003-05-20
Silbaugh, Jan H. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means making particulate material directly from liquid or...
C425SDIG002, C264S009000, C264S012000
Reexamination Certificate
active
06565342
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods of making metal spheres. In particular, the present invention relates to making metal spheres from molten metal, such that the solid metal spheres achieve a very close tolerance for sphericity and size. Such metal spheres, particularly precision miniature metal spheres, have many industrial applications. For example, such spheres may be used to form Ball Grid Array (BGA) and Flip Chip (FC) arrangements in high-density integrated circuit packaging, and are also used as writing tips of ball pens.
BACKGROUND OF THE INVENTION
Conventionally, small precision metal spheres are made using a mechanical process by which a number of small metal particles are cut or punched out from fine wire or sheets. Those particles are then dropped into a tank of hot oil having a temperature that is higher than that of the melting point of the particles. In this hot oil bath, all the metal particles are melted, forming small round droplets due to surface tension of the molten metal. As the temperature of the oil cools down to below the melting point of the metal droplets, the droplets solidify into spheres. This mechanical method has intrinsic limitations that result in coarse dimensional tolerances, because each mechanical operation adds a certain amount of deviation to the size and uniformity of the particles, which together produce an unacceptable cumulative effect. Therefore, spheres are not precisely made according to this process. Further, the resulting spheres must undergo a sophisticated washing process to get rid of the oil and other surface contaminants.
Over the past two decades, many methods have been developed for generating precision molten droplets to improve the dimensional tolerances of the spheres. These new methods commonly utilize a crucible in which to melt the metal, and then cause the molten metal to flow out of the crucible through a small nozzle. Droplets are formed by shaking either the crucible or the nozzle, or by oscillating inlet gas to affect the pressure on the molten metal in the crucible. These types of vibratory disturbances that are used to generate the droplets are typically controlled by some electronic means. Due to the surface tension of the molten metal droplets, they automatically form a spherical shape while passing through a cooling medium after passing through the nozzle. However, the parameters of those processes and the environmental conditions of the electronic droplet generators are critical to the uniformity of the output. In many cases, these processes can only reach a quasi-steady-state, which limits the production throughput as well as the quality of the resulting spheres.
There is therefore a need for a process for forming metal spheres by which tolerances on the size and shape of the spheres can be kept small. Such a process must allow for a reasonable throughput, and processing of the spheres such as by washing and other finishing actions should be kept to a minimum. In order to be truly useful, such a process must relatively simple, requiring few controls of parameters of the process.
SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide a process by which precision metal spheres may be formed.
It is a further objective of the present invention to provide a process by which the degree of deviation from a perfect spherical shape of the metal spheres can be minimized.
It is an additional objective of the present invention to provide a process by which the size of the metal spheres can be determined within a small tolerance.
It is also an objective of the present invention to provide a process by which metal spheres are formed such that the metal spheres require less post-formation cleaning than do conventionally-produced metal spheres.
It is another objective of the present invention to provide a process by which fewer parameters must be controlled than when utilizing conventional processes.
It is a further objective of the present invention to provide a process by which throughput of the metal spheres is not hampered by the precision achieved in the finished product.
It is also an objective of the present invention to provide an apparatus that facilitates the process of the present invention.
The present invention is a method of forming metal spheres from molten metal in which precisely-sized droplets of the molten metal are separated from a metal mass to form the metal spheres. The droplets of the molten metal are first projected in an upward direction and buffered prior to descending through a cooling medium. Through the use of inlet gas and liquid, the cooling medium is controlled for precision solidification of the metal spheres. The solid spheres enter a liquid bath in a collection receptacle at the end of the cooling process, where they are automatically collected and separated from the liquid, which is returned to the collection receptacle for reuse.
Instead of disturbing the steady flow of the molten metal stream to create droplets, the method of the present invention utilizes a fast vibratory piston to strike each individual droplet out through a nozzle. Driven in this manner, the droplets can be shot initially upward through a cooling medium and spend more time passing through the medium before solidification of each droplet begins. Thus, a shorter cooling tower can be used, thereby saving costs related to the height of the manufacturing room, as well as reducing the amount of coolant required during the solidification process. As the piston slams a stopper or withdraws its direction of motion quickly, the resulting sudden impact transfers the energy at the piston to the molten metal and creates a droplet that shoots out through the nozzle. Control of the striking force of the piston against the stopper, and knowledge of the size of the aperture in the nozzle, allow droplets of molten metal having precisely-controlled volumes to be separated from the molten metal mass and propelled through the cooling medium, allowing for the formation of spheres of uniform size.
The structure of the apparatus of the present invention includes a buffering chamber that is designed to provide the cooling droplets with enough time to allow the internal energy to settle down before final formation and solidification. The kinetic energy within a molten droplet is usually higher than its surface tension energy right after the droplet changes dynamically in this fashion, and therefore the droplet does not acquire a spherical shape until a large percentage of this internal kinetic energy is released. When the surface tension of a droplet dominates the internal kinetic energy as the molten metal cools, the shape of the droplet becomes spherical automatically. As previously stated, the molten metal droplets are first propelled in an upward direction in the chamber, before being overcome by gravity and allowed to fall back downward. This buffering chamber has a heating system that controls the temperature of the gas inside the chamber to prevent the droplets from solidifying before the shape of the sphere is mature. The gas used is preferably an inert gas such as nitrogen, or a mixture of nitrogen and hydrogen. The temperature inside the chamber is determined empirically, depending on certain properties of the molten droplets. Typically, this temperature falls in the range between 0° C. and 100° C., depending on the size and material of the droplets.
A gas screen gate is disposed beneath the buffering chamber. This gate is a large hollow disc with two openings, one each at the centers of both top and bottom faces of the circular disc. One or more fans are disposed inside the disc along the edge of the disc wall. The fan blows in a direction tangential to the circular wall, causing the gas within the disc to flow in a circular direction within the hollow interior of the disc. This movement creates a gas barrier that slows down the heat exchange rate between the buffer chamber and the top end of the cooling tower, so that the droplets do not experience quick cooling
Accurus Scientific Co. Ltd.
Del Sole Joseph S
IP Strategies P.C.
Silbaugh Jan H.
LandOfFree
Apparatus for making precision metal spheres does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for making precision metal spheres, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for making precision metal spheres will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3085620