Extremely reliable bonding of large silicon dice using gold-tin alloy

Large silicon dice have been bonded on alumina substrates with Au-Sn eutectic using a novel bonding technique. The bonding quality was examined by a scanning acoustic microscope (SAM) having a resolution of 20 μm. Nearly perfect bondings have been achieved. Au-Sn alloy was chosen rather than the commonly used Au-Si alloy because the lower eutectic point of the Au-Sn system would result not only in lower processing temperature but also lower stress on the dice. The die-bonded specimens endured 40 cycles of thermal shock between -196°C and +160°C without cracking or bond degradation despite the significant mismatch of thermal expansion coefficients between silicon and alumina. Storage tests at -196°C and +250°C also do not induce cracking or bond degradation. Pull-test results indicate that the bondings are stronger than the silicon dice themselves