Copper Wire Bonding On Pure Palladium Surface Finishes – Eliminating The Gold Cost From The Electronic PackageAuthors: Mustafa Özkök, Hugh Roberts, and Horst Clauberg
Company: Atotech and Kulicke and Soffa Industries, Inc.
Date Published: 1/18/2011 Conference: Pan Pacific Symposium
Although some technical challenges remain, many years of research have now resolved most of the problems associated with copper wire bonding and attention is beginning to shift from merely ensuring reliable manufacturing processes to optimizing processes for efficiency and throughput. The most advanced wire bonders now have pre-configured processes specifically designed for copper. In addition to throughput optimization, further cost reductions are being sought. Among these is the desire to eliminate the high-cost gold not just from the wire, but also from the substrate.
On the substrate side the electronics packaging industry still works with electrolytic nickel / electrolytic (soft) gold (Ni/Au) for copper wire bond applications. This surface finish works with copper wire bonding but includes some disadvantages, such as: -Thick expensive Au layers of 0.1 to 0.4µm -Electrically connected pads (bussing for the plating) which require added space on the substrate. -Pd-coated copper wire often delivers better results on gold covered finishes, but is two to three times more expensive as pure copper wire.
Furthermore electrolytic Ni/Au was not chosen as a result of in-depth investigations for the most effective surface finish. The selection was made because it was the surface finish with the highest distribution in the market for wire bond packages.
This paper is offering the results of a two company joint work regarding an alternative copper wire bondable surface finish for substrates mainly with palladium as the final copper wire bondable layer. This offers further cost reduction possibilities. Furthermore, copper palladium intermetallics are regarded as very reliable.
Key words: ENEPIG, ENEP, wire bonding, gold wire bonding, copper wire bonding
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