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High temperature and element alloying influences on Kirkendall voiding in Au ball bond interconnects on Al chip metallization

: Schneider-Ramelow, M.; Schuch, B.; Lang, K.-D.; Reichl, H.

International Microelectronics and Packaging Society -IMAPS-:
International Symposium on Microelectronics 2007. Proceedings : November 11- 15, 2007, San Jose Convention Center, San Jose, California, USA
Washington, DC: IMAPS, 2007
ISBN: 0-930815-82-3
International Symposium on Microelectronics <40, 2007, San Jose/Calif.>
Conference Paper
Fraunhofer IZM ()
Metallisierung; Packungsdichte; Kirkendall-Effekt; Altern (Werkstoff); Gold; Aluminium; intermetallische Phase; Mikrosystemtechnik

The presentation addresses the reliability of Au ball bond interconnects on Al chip metallizations of different thicknesses and compositions. Interfacial reactions, intermetallic phase (IP) and Kirkendall void growing are discussed. The results contribute to a better understanding of failure mechanisms caused by interdiffusion and Kirkendall voiding. The mentioned failure mechanism is influenced by numerous factors, such as curing temperature and time, Au wire and Al metallization composition and ratio of mixture as well as the real area of interconnect formation under the ball. These influences are mainly responsible for ball lift offs under load. It was discovered that numerous lift offs already occur with Al metallization thicknesses more than 1 micron and temperatures in the range of 175 deg C, while temperatures of 150 deg C or 200 deg C are less critical. Therefore interpolation or extrapolation of aging temperature results without considering certain bonding conditions is no longer expedient. Investigations include mechanical tests of Au wires as well as microstructure observations of the contacts in correlation to material composition, aging temperature and Al metallization thickness. Au/Al intermetallic phase thicknesses below the Au contacts on Al metallization are typically a few hundred nanometers thick directly after the bonding process, depending on bonding conditions like process parameters and material combination. These phases grow under temperature influence and Kirkendall voiding can occur. A most significant result in this context is that pull and shear lift offs occur if the chip metallization consists of pure Al (not Si and Cu alloyed) and clearly thicker than 1 micron and the temperature is in the range of 175 deg C.