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Interduffision and Kirkendall Voiding in the Contact System Au Ball Bond on Al Chip Metallization

: Schneider-Ramelow, M.; Schmitz, S.; Schuch, B.; Grübl, W.

Michel, B.; Lang, K.-D.:
Smart Systems Integration and Reliability. Honorary Volume on the Occasion of Herbert Reichl's 65th Birthday
Dresden: ddp Goldenbogen, 2010
ISBN: 978-3-932434-77-8
Aufsatz in Buch
Fraunhofer IZM ()

The presentation addresses the reliability of Au ball bonds of fifferent Au wire qualities on Al chip metallizations of different thickness and compositions at temperature storage up to 200 °C. In this context the interfacial reactions, the intermetallic phase (IP) and Kirkendall void growing are discussed. Aim was fo find boundary conditions under which critical Kirkendall void growth can be avoided.
The mentioned failure mechanism is influenced by numerous factors, such as aging temperature and time, Au wire and Al metallization composition and ratio of mixture as well as the percental area of interconnection formation under the ball [1-6]. These influences are mainly responsible for ball lift offs under operating conditions. In many cases lift offs already occur at Al metallization thicknesses > 1 µm and temperatures in the range of 175 °C, while temperatures up to 150 °C or at 200 °C are less critical.
Investigations include mechanical tests of Au loops and ball contacts as wess as microstructure observations of the contacts in correlation to material composition, aging temperature and Al metallization thickness as well as intermatallic coverage under the ball directly afer bonding. The Au/Al intermatallic phase thicknesses below the Au contacts on Al metallization are typically a few hundres nunometers thick directly after the bondin process, depending on bonding conditions like process parameters and material combination [7, 8]. These phases grow under temperature influence and Kirkendall voiding ca occur. A most significant result in this context is that pull and shear lift offs occur if the chip metallization is clearly thicker than 1µm and intermatallic phase coverage (after bonding) isn't optimized. these results will considerably contribute to a better understanding of Kirkendall voiding failure mechanisms.