What is the future of bonding wire? Will copper entirely replace gold?

Thermosonic ball bonding is a major interconnect process in microelectronics packaging and is positioned to remain one of the key process technologies available to package designers in the near future. However, the main wire material used in fine pitch (FP) and ultra-fine pitch (UFP) ball bonding is gold and with significant increases in gold price, gold ball bonding has become a more costly process that has a considerable economic effect on the assembly of packages used in consumer electronics. An alternative wire material to gold is copper, which is much cheaper and has several technical benefits including better electrical conductivity and has been widely used in discrete and power devices with wire diameters typically larger than 30 mu m in diameter for many years. However, copper wire behaves quite differently than gold due to its different physical properties, some of which are beneficial and others detrimental to bonding performance. In this article, we briefly review some of the advantages and difficulties with using copper wire advanced packaging and explain why copper cannot replace gold in many applications and why gold offers significant benefits.