High temperature testing of nickel wire bonds for SiC devices

This paper reports our effort to study the failure mechanisms and high temperature behavior of Ni wire bonds. Ultrasonic wire bonding was used to bond 25 mu m-diameter Ni wire to 7500 Angstrom-thick Ni pads deposited on 3C-SiC substrates. A series of high temperature experiments which include electrical characterization, annealing tests, and in situ pull tests were conducted to test the reliability of the wire bonds at temperatures up to 550 degrees C. In situ pull tests were also performed on samples prepared by thermosonic wire bonding. Scanning electron microscope (SEM) was used to investigate the formation of brittle cracks on the heel of the bonds, to compare the feet of new and used wedges, and to examine the surface texture of wire bonds exposed to high temperatures.