The equivalent diameter of copper wire and gold wire based on the sweep stiffness evaluation in semiconductor packaging

As gold content accounts for the majority of bonding wire expense, wire diameter reduction is an effective way to reduce cost. However, it had been proved by authors' previous studies that the smaller the wire diameter is used, the smaller the sweep stiffness of wire bond will is. The lower sweep stiffness of the wire bond will always cause higher risk of wire sweep. To reduce cost, copper wire is an alterative way to replace gold wire. The advantages of using Cu instead of Au wire are the lower price, the higher electrical conductivity and the high resistance to wire sweep during plastic encapsulation, although, the oxidation problem of copper wire during bonding process needs to be overcome in the future. From the material property point of view, Cu is harder than Au, which represents the possible smaller diameter of wire can be used. Moreover, the introduction of Cu wire will lead to the further development of smaller pitch devices. In this paper, the corresponding diameters of gold wire and copper wire will be presented by the evaluation of sweep stiffness of wire bonds. Based on the results of sweep stiffness, the listed tables for the appropriate choice of gold wire diameter versus copper wire diameter can be proposed to reduce cost and, furthermore, provide smaller allowance standard of fine pitch in a chip.