Thermosonic Gold Wire Bonding to Copper Conductors

The use of thick film copper conductors in hybrid microcircuitry requires that wire bonding to their surfaces be demonstrated as a feasible and reliable interconnection technique. Previous work has shown that acceptable and reliable ultrasonic aluminum wire bonds can be made to copper. The conditions necessary to make successful thermosonic gold wire bonds to copper are described. Items covered are the types of tool to use, the influence of stage temperature, the maximum dwell time for the parts on the stage, and the bonding window that yields the best results. In addition, information is provided on the reliability of the bonds following aging at temperatures in the range 150° to 350°C, in high temperature-humidity conditions such as 40°C, 90 percent RH, and 85°C, 85 percent RH and after 100 thermal cycles between -55°C and 150°C.