Void free bonding of large silicon dice using gold-tin alloys

The successful bonding of large (6 mm*10 mm) silicon dice on alumina substrates with Au-Sn eutectic using a particular bonding technique is described. The bonding quality was examined by a scanning acoustic microscope having a resolution of 25 mu m and it was found that nearly perfect bondings have been achieved. Use of Au-Sn alloy rather than Au-Si resulted in not only lower processing temperature but also lower stress on the dice. This is confirmed by simple stress analysis. The die-bonded specimens endured 40 cycles of thermal shock between -196 degrees C (liquid nitrogen) and +160 degrees C (boiling cyclohexanol) without cracking or bond degradation despite the significant mismatch of thermal expansion coefficients between silicon and alumina. Storage tests at -196 and 250 degrees C also do not induce cracking or bond degradation. Pull test results indicate that the bondings are stronger than the silicon dice themselves.<
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