The Microstructure of Ball Bond Corrosion Failures

A scanning electron microscope (SEM) and transmission electron microscope (TEM) both with energy dispersive x-ray spectrometers (EDS), have been used to Investigate wire bond failures due to corrosion and oxidation. We have found that the bond strength is reduced by the oxidation of the intermetallic compounds Au4Al and Au5Al2. This results in a cellular and porous microstructure consisting of Au rich cell walls and an amorphous Al rich cell Interior. The decomposition reaction is accelerated when the bonds are aged in the presence of epoxy molding compounds at temperatures of 175°C to 200°C. An analysis of the outdiffusing products from the epoxy links the bond degradation with the presence of halogen-containing flame retardants.