Investigations of failure mechanisms of TAB-bonded chips during thermal aging

Eutectic soldering and thermocompression bonding were investigated with regard to thermal aging mechanisms. These methods require two different metallurgies: Cu-Sn-Au and Cu-Au. Effects like pore formation due to the Kirkendall effect and the formation of ternary phases were investigated. The influence of the lead roughness and of copper recrystallization is shown by the use of ED (electrodeposited) copper and RA (rolled-annealed) copper. The influence of these parameters on long-term reliability is summarized. The formation of pores for eutectic soldering can be avoided by a tape with reduced roughness, which minimizes the accumulation of tin during the bonding process. No pore formation was observed for thermocompression-bonded chips. The increase in Al-Au interdiffusion due to the cracks induced in the Ti:W layer during the bonding process had no notable influence on the failure mechanisms in a pull test. The shear test appears to be a more appropriate method for the investigation of degradation mechanisms at this interface. Compared with other contact methods for chips. TAB (tape automated bonding) technology shows a high reliability with very low degradations even after very severe thermal aging at 200°C