Resistance drift in aluminum to gold ultrasonic wire bonds

It is noted that the literature contains many instances of reliability problems associated with the aluminum wire to gold bond system. The authors, in evaluating the potentials of this technology, experienced similar problems and initiated some fundamental studies to enhance their knowledge base. The system of interest consisted of 0.002-in. diameter Al-1% wire ultrasonically bonded to Ni-Au electroplated Cu 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 was developed to monitor for out-of-control gold plating