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44 The PCB Magazine • February 2015 ments for the final finish is the driving force for this article. It is also the intention of this article to highlight the superiority of the direct palladium processes in achieving the expected requirements of the future. Generic Technical Requirements Regardless of the surface finish, there exist perceived and accepted minimum requirements for total functionality. The established stan- dards will inevitably be augmented and many technology sectors will adopt their own perfor- mance criteria and expectations as the future era of high-frequency and fine-line applications become more necessary. It is also apparent that the new requirements will also include more economic wire bonding materials. Despite being vital, solderability satisfies only part of the surface finish requirements. The surface finish must also provide adequate protection of the underlying copper circuitry from the time of substrate fabrication until packaging and assembly (copper corrosion on fine-line technology has the potential to impact significantly on signal integrity). The surface finish should not add to solder joint reliability concerns by contributing to the formation of undesirable intermetallic compounds (IMCs) or adversely affecting their growth. In other words, the bondability must be ensured. Whilst negating all responsibility for look- ing into the future, some trends can be predict- ed as a result of integration trends. Circuit fea- tures continue to shrink and maintaining sig- THE FUTURE OF NICKEL IN NICKEL/PALLADIUM/GOLD FINAL FINISHES continues feature Figure 1: the generic capabilities of ni, Pd and Au final finishes. note: Electroless palladium/immersion gold (EPIG) has not been included due to the process's copper corrosion and poor wire bonding attributes.

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