Method of manufacturing solder balls

A method of manufacturing solder balls, comprising the steps of:

• maintaining a level of molten metal in a tundish constant by using a molten metal level regulating means, said tundish having a bottom with at least one orifice formed therein;
• dividing the molten metal into metal droplets of a uniform size by applying vibrations to a stream of the molten metal passing through said at least one orifice;
• providing a chamber containing inert gas beneath said tundish and in communication with said at least one orifice;
• providing a movable molten metal receiving tray, said tray being movably disposed in said chamber and, during an initial start-up operation, being disposed beneath said at least one orifice to collect and remove unregulated free size molten droplets separated from the at least one orifice;
• following the initial start-up operation, moving said molten metal receiving tray from beneath said at least one orifice and thereby permitting said uniform-sized metal droplets to fall through the chamber containing inert gas;
• sphering the droplets by dropping the uniform-sized metal droplets into a cooling liquid tank containing a cooling liquid, said cooling liquid having a temperature gradient ranging from a temperature higher than a melting point of the metal at an upper portion of the cooling liquid tank to a gradually decreasing temperature at middle portions of the cooling liquid tank and then to a normal temperature at lower portions of the cooling liquid tank;
• maintaining a level of cooling liquid in said cooling liquid tank constant by letting excess cooling liquid, which is caused by accumulation of completed solder balls at a bottom of the tank, to overflow through a cooling liquid discharge conduit disposed at the upper portion of the cooling liquid tank.