A method for forming solder balls that have larger spacings between them and electronic devices containing such solder balls are disclosed. In the method, an additional layer of a leachable metal such as gold or silver is used between an under bump metallurgy layer and a solder bump subsequently formed. This allows the formation of the under bump metallurgy layer prior to the deposition of the solder material into a window formed in a photoresist layer. The present invention allows the underfill of a solder window, instead of an overfill which is normally required in a conventional method.

A method for forming solder balls that have improved height on an electronic substrate such as a silicon wafer and devices formed are disclosed. In the method, after solder bumps are deposited by a conventional method such as evaporation, electroplating, electroless plating or solder paste screen printing, the solder bumps are reflown on the substrate in an upside down position such that the gravity of the solder material pulls down the solder ball and thereby increasing its height after the reflow process is completed. It has been found that a minimum of 5%, and preferably about 10% height increase has been achieved. Another benefit achieved by the present invention novel method which is associated with the increase in the solder ball height is a corresponding increase in the pitch distance between the solder balls by at least 5%.