An eutectic bonding technology at a temperature below the eutectic point

The authors report a technique which needs only 240°C to produce nearly eutectic Au-Sn bonding. After bonding, the device can take a postprocessing temperature of 250°C without bonding degradation. The bonding medium consists of Au-Sn multilayer composite deposited directly on the object to be bonded. This technology also eliminates the preforms, reduces tin oxidation, and provides good control of bonding layer thickness. Results of bonding 2 mm×3 mm GaAs dice show that high-quality bondings are obtained, as evaluated by a scanning acoustic microscope. The specimens underwent 40 cycles of thermal shock test between -196°C and 160°C without bonding degradation and die cracking. Scanning electron microscopy and energy-dispersive X-ray studies reveal interesting characteristics of the bonding process. Melting point tests confirm that the bonding layer indeed has a melting temperature of 280°C, higher than the 240°C process temperature