Resistance drift in aluminum to gold ultrasonic wire bonds

When the potential of aluminum wire to gold bond technology was evaluated, reliability problems were experienced, and so some fundamental studies were initiated. The system of interest consisted of a 0.002 in diameter Al-1% Si wire ultrasonically bonded to Ni-Au electroplated copper printed circuit pads. The reliability problems observed manifested themselves as resistance drifting associated with thermal aging of the sample. It was found that plating thickness, plating current density, and bath agitation strongly influenced the resistance drift phenomenon. A simple four-wire resistance test to monitor for out-of-control gold plating was developed