Study of Void Formation Mechanism in Electroplated SnAg Solder Bump

Abstract SnAg electroplating method is widely used in the formation of LF solder bump for flip chip connection. While electroplating is able to form void free solder bump in a suitable operating condition, void may occur suddenly when used in mass production. This study aims at understanding the gas source in the void of electroplated SnAg solder bumps and determining the manufacturing process factors which affect the void formation. There are various types of void formation mode. One mode is H2 gas generation on cathode surface during electroplating. Both the cross-sections of solder bumps, as well as an analysis data of the gas in the void taken by the TDS (Thermal Desorption Spectrometry) were evaluated. The cross-section of the solder bump which contains void due to the reflow process revealed the existence of several tens of nm to several μm size pits in the solder bump before reflow. TDS analysis indicates that the pits consisted of mainly H2O, H2 and the decomposition of organics. A possible void f...