Self-Assembled Monolayers For Reduced Temperature Direct Metal Thermocompression Bonding

A reduction in the bonding temperature required for direct gold-gold (Au-Au) thermocompression bonding is observed by coating a monolayer of dodecanethiol on gold surfaces prior to bonding. The results show that Au-Au bonded joints of 26.9 g per bump strength can be achieved at a temperature as low as 160 degrees C. The temperature drop becomes more apparent when both coated and blank gold samples are exposed in air over some time before bonding. The authors propose that self-assembled monolayers passivate metal surface by obviating the adsorption of surface contaminants, in particular, carbon and oxygen but get desorbed just before bonding takes place.