Interfacial degradation mechanism of Au-Al bonding in quad flat package

We have studied the interfacial degradation mechanism of Au-Al bonding in epoxy encapsulated quad flat package (QFP) induced by the high temperature storage (HTS) test conditions. In a way of root cause analysis to elucidate the degradation mechanism, atomic force microscope (AFM), SEM-EDX (energy disperse X-ray) and Auger electron spectrometry (AES) are used. It is found that the bonding strength of the wire pull and ball shear decreases with increasing depth profile of preexisting contamination layer and surface roughness. The plasma cleaning on the Al pad prior to an epoxy molding, however, enhances initial wire pull and ball shear strength. We firstly report the appearance of Sb on Auger spectrum from the fractured surface of Au-Al bonding. In the case of alloy-Al bonding, Pd retards the growth of intermetallics. The life time of Au-Al ball encapsulated with BP resin is much longer than that of OCN under the HST conditioned at 150 and 170°C. It is also found that lessening in the wire pull and ball shear strength is correlated to the interfacial degradation coupled with the material of wire and EMC.