Highly reliable Au-Sn eutectic bonding with background GaAs LSI chips

The authors investigate the reliability of mechanically ground chips through die-shear and thermal shock tests. The bonded chips, which were ground to 450 mu m thickness by an original technology, were proved to be as reliable as polished chips through 1000 cycles of thermal shock between -65 degrees C and +150 degrees C. No chip fracture occurred and no induced void was observed with scanning acoustic microscopy. The shear strength of the chips after thermal shocks remained at more than 10 kg, passing the MIL-STD-883C test. Surface flaws due to backgrinding, which would cause chip fracture, were eliminated by the slight chemical etching after backgrinding. Scrubbing action has been confirmed to be necessary to obtain void-free bondings consistently in low-cost production. The Sn in the Au-Sn preform easily forms on oxide film at the surface, which tends to prevent wetting at the bonding interface. This tin oxide film (300-400 AA) was observed through Auger electron spectroscopy (AES) to be broken down by scrubbing action.<
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