Palladium-coated copper wire has emerged as another low-cost wire option in addition to bare copper wire. Most of the major bonding wire suppliers now offer Pd-coated Cu wire (Pd-Cu wire) in their portfolio and multiple device manufacturers are already using it in fine-pitch applications. Relative to Cu wire, it offers the advantages of a) a substantially more robust 2nd bond process with associated greater ease of dialing in a bonding process and higher mean-time-between-assist rates and b) alternative to use nitrogen instead of forming gas during free-air ball formation. This latter advantage is the main topic of this paper. The disadvantages are a) two to three times greater material cost and b) greater ball hardness and propensity toward pad damage. Balancing these pros and cons, subcons, with their great product mix, often favor Pd-Cu wire for its ease of implementation while still gaining substantial cost savings relative to gold wire. In contrast, IDM's chose bare Cu wire in the vast majority of applications, since their smaller product portfolio allows them to more thoroughly optimize each individual process.
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