Why do Integrated Circuits contain gold?

Gold is used in ICs for interfacing to the package. Copper can cause corrosion in the packagins. There are two solutions to avoid this, aluminium plating on copper pads or nickel/gold packaging. Gold plating is somehow found to be cheaper because it eliminates costs associated with the thin film sputter, photo lithography and metal etch. Gold also offers thermal stability for the package.

With much advances in technology, Copper interconnects are being used instead. Conventional problems associated with copper are being eliminated and hence can reuse the tooling already available instead of designing a special tool for the specific usecase of using gold or copper.

However, many ICs which need fast processing still use Gold. These type of ICs mostly include ASIC and speed-critical applications.