Phase transformations in thermally exposed Au-Al ball bonds |
| |
Authors: | Naren Noolu Nikhil Murdeshwar Kevin Ely John Lippold III" target="_blank">William BaeslackIII |
| |
Affiliation: | (1) Edison Joining Technology Center, The Ohio State University, 43221 Columbus, OH;(2) Present address: the Center for Advanced Materials Joining, University of Waterloo, N2L 3G1 Waterloo, ON, Canada;(3) Kulicke & Soffa Industries, 19090 Willow Grove, PA;(4) Edison Welding Institute, 43221 Columbus, OH;(5) Renssealer Polytechnic Institute, 12180 Troy, NY |
| |
Abstract: | Gold-aluminum ball bonds were thermally exposed at constant elevated temperatures, and the resultant phase transformations
studied in detail. The as-bonded microstructure of a Au-Al ball bond essentially consisted of a reaction zone (termed “alloyed
zone” (AZ) in the as-bonded condition) between the Au bump and the bonded Al metallization. It is the growth of the reaction
zone between the Au bump and the bonded Al metallization and also the nonbonded Al metallization during thermal exposure that
gave rise to the various phase transformations. Au4Al, Au8Al3, and Au2Al are the predominant phases that grew across the ball bond until the bonded Al metallization is available to take part in
the interdiffusion reactions. After the complete consumption of the bonded Al metallization, the Au-Al phases reverse transformed
resulting in the formation of the Au4Al phase in the entire reaction zone across the ball bond (RZ-A). The lateral interdiffusion reactions resulted in the nucleation
and the growth of all of the Au-Al phases given by the phase diagram. Kidson’s analysis and Tu et al.’s treatment were extended
to a five-phase binary system to explain the phase transformations in thermally exposed Au-Al ball bonds. It is possible for
all of the Au-Al phases to grow across a ball bond uninhibited as long as the bonded metallization is available. However,
the supply limitation of the bonded metallization gives rise to reverse transformations where Al-rich phases transform to
Au-rich phases and eventually result in the formation of the Au4Al phase in the entire RZ-A. If infinite time is allowed, Au4Al would dissolve; the extent of which is dependent on the solubility of Al in Au. No supply of Au lateral to the bond causes
the reverse transformation of the Au4Al phase, giving rise to the lateral growth of the remaining Au-Al phases. If infinite time is allowed, the lateral phase
transformations would result in the formation of a phase that is dependant on the relative proportion of Au and Al present
in the nonbonded metallization (NBM) and Au4Al below the void line. Hence, the presence of a phase in a particular location of a ball bond is dependent on the time and
temperature of thermal exposure. |
| |
Keywords: | Phase transformations Au-Al ball bonds interdiffusion reactions intermetallics thermal exposure |
本文献已被 SpringerLink 等数据库收录! |
|