Characterization of a wire bonding process with the added challenges from palladium-coated copper wires

In this study, we experimented with palladium-coated copper (PdCu) wires of different diameters (0.6 mil, 0.7 mil and 0.8 mil) and from different manufactures. It was seen that wire diameters that varied within the manufacturing tolerances show an effect on bonding responses. The effect was especially prominent in the production environment, for example, when electric-flame-off (EFO) time remained fixed and free air ball (FAB) and subsequent bonded ball size varied according to the variation in wire diameter. The effect of Pd thickness control in PdCu wire was also studied and its implication to bonding responses is presented. Aside from the variations from the wires, bonding parameters such as EFO conditions, cover gas types, and gas flow rates were also found to affect wire bonding responses by varying degrees for wires from different suppliers. All of these observations suggest the added complications and considerations necessary when dealing with PdCu wire. Therefore, ensuring an understanding of the wire characteristics, especially pertaining to the Pd coating and their relations to wire bonding responses, is critical in overcoming these additional challenges.