Effect of mold compound components on moisture-induced degradation of gold-aluminium bonds in epoxy encapsulated devices

Abstract

Degradation of the intermetallic region of the gold wire-aluminium bonding pad interface of several types of IC devices in plastic packages is accelerated by moisture at relatively low temperatures (121-135 degrees C), leading to near-complete loss of strength after 300-400 h of autoclave testing. Measurement of bonding strength as a function of steam-autoclave time in a designed experiment shows that one common component of semiconductor molding compounds (Sb/sub 2/O/sub 3/) is the overriding factor in causing ball-lift. In support of this conclusion, a variety of brominated flame retardants, including those that claimed to be more stable to Br release, were tested in similar formulations and all were found to give ball-bond degradation, to about the same degree, when Sb/sub 2/O/sub 3/ was present. Cross sections of the bonds that show the Sb/sub 2/O/sub 3/-induced degradation and elemental analysis of the pulled ball-bonds suggest that the degradative reaction starts at the interface of the gold-rich intermetallic and the gold ball. Antimony trioxide appears to be associated with the Al portion of the Au-Al ball-bond intermetallics, and to be participating in the reactions or affecting the reactivity of Al in a high-moisture environment. These results contrast with several previous reports that Sb/sub 2/O/sub 3/ improves wire bond reliability in a dry environment.<>