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Degradation and failure mechanisms in thermally exposed Au–Al ball bonds

Published online by Cambridge University Press:  03 March 2011

Naren J. Noolu ,
Nikhil M. Murdeshwar ,
Kevin J. Ely ,
John C. Lippold  and
William A. Baeslack
Naren J. Noolu*
Affiliation:
Edison Joining Technology Center, The Ohio State University, Columbus, Ohio 43221
Nikhil M. Murdeshwar
Affiliation:
Kulicke & Soffa Industries, Willow Grove, Pennsylvania 19090
Kevin J. Ely
Affiliation:
Edison Welding Institute, Columbus, Ohio 43221
John C. Lippold
Affiliation:
Edison Joining Technology Center, The Ohio State University, Columbus, Ohio 43221
William A. Baeslack
Affiliation:
Renssealer Polytechnic Institute, Troy, New York 12180
*
a)Address all correspondence to this author. Present address: Center for Advanced Materials Joining, University of Waterloo, Waterloo, ON N2L 3G1, Canada. e-mail: nnoolu@mecheng1.uwaterloo.ca
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Abstract

During the manufacturing and the service life of Au–Al wire bonded electronic packages, the ball bonds experience elevated temperatures and hence accelerated interdiffusion reactions that promote the transformation of the Au–Al phases and the growth of creep cavities. In the current study, these service conditions were simulated by thermally exposing Au–Al ball bonds at 175 and 250 °C for up to 1000 h. The Au–Al phase transformations and the growth of cavities were characterized by scanning electron microscopy. The volume changes associated with the transformation of the intermetallic phases were theoretically calculated, and the effect of the phase transformations on the growth of cavities was studied. The as-bonded microstructure of a Au–Al ball bond typically consisted of an alloyed zone and a line of discontinuous voids (void line) between the Au bump and the bonded Al metallization. Thermal exposure resulted in the nucleation, growth, and the transformation of the Au–Al phases and the growth of cavities along the void line. Theoretical analysis showed that the phase transformations across and lateral to the ball bond result in significant volumetric shrinkage. The volumetric shrinkage results in tensile stresses and promotes the growth of creep cavities at the void line. Cavity growth is higher at the crack front due to stress concentration, which was initially at the edge of the void line. The crack propagation occurs laterally by the coalescence of sufficiently grown cavities at the void line resulting in the failure of the Au–Al ball bonds.

Keywords

FracturePackagingIntermetallic alloys
Type
Articles
Information
Journal of Materials Research , Volume 19 , Issue 5 , May 2004 , pp. 1374 - 1386
Copyright
Copyright © Materials Research Society 2004

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