Gold has long been the favorite for the all-important bonding wire in semiconductor chips, but copper is fast replacing the precious metal as gold prices soar and semiconductor making equipment improves.
Five years ago, 80% of all bonding wire used in semiconductor fabrication was made of gold. This has shrunk to below 40%, while the amount of copper wire in use has jumped from 10% to 60% over the same period.
Bonding wire links an integrated circuit chip with the leadframe. A single wire measures about 20 micrometers in diameter, or about one-third the thickness of a human hair.
Increased use of copper reflects the high price of gold and advances in semiconductor manufacturing equipment. The shift from gold to copper has progressed “at an explosive pace,” according to a spokesperson at Tanaka Denshi Kogyo, a subsidiary of Japan’s Tanaka Holdings and the world’s largest manufacturer of bonding wire.
Gold is softer than copper, making it unlikely to scratch the delicate circuits during fabrication. According to Semiconductor Equipment and Materials International, a technology association, 16 billion meters of bonding wire was shipped in 2007, of which 98% was made of gold.
But as gold prices began to climb after 2005, the metal began to fall out of favor. Benchmark gold futures on the New York market rose above $1,900 per troy ounce to their all-time high in September 2011. The figure has since fallen to around $1,200 but still remains nearly twice the level of 10 years ago.
Gold bonding wire can represent as much as 10% of the cost of a semiconductor chip, prompting manufacturers to seek cheaper alternatives in regular copper wire and high-performance palladium-coated copper wire.
Copper is significantly cheaper than gold but comes with added processing costs. Still, even with the increased costs, copper wire is cheaper than the gold version.
New semiconductor manufacturing equipment has also driven use of copper wire, which is more difficult to handle in the chip fabrication process due to its hardness.
Shinkawa, a Tokyo-based manufacturer of semiconductor equipment, said orders for optional parts that allow standard chipmaking equipment to handle copper wire have increased since 2011. The company started offering copper wire-compatible semiconductor manufacturing equipment in 2013. These products now represent about half of overall sales, a company source said.