Turning Copper into Gold

The adage that the only constant is change always holds true in electronics. In some areas, like wire bonding inside chip packages, change doesn’t occur too quickly, but it inevitably comes.

Many chipmakers and packaging companies have used gold wire bonds for decades. But some are moving away from the precious metal.

Freescale is “aggressively moving” its automotive portfolio to copper, Glenn Daves, director, Packaging Solutions Development at Freescale, told me recently. That’s because the intermetallic bond between gold wires and the aluminum pads on chips isn’t very stable at high temperatures.

Other semiconductor companies have moved to copper, but automakers rarely want to be at the leading edge of emerging technologies. The high reliability requirements of the automotive market are a key driving factor behind Freescale’s move.

Making this aggressive shift isn’t without challenges. Copper is harder than gold, making it a bit tougher to work with. Also, it oxidizes and corrodes more readily, which isn’t the best thing in a car where chips are expected to last a decade or more. Apparently, those challenges are easier to solve than the task of resolving the CTE mismatch between gold and aluminum.

Using copper wires changes the cost model, which can impact other decisions in packaging. For example, some system designers may opt for package-on-package configurations which have been costly because users pay for two packages.

Any move that improves reliability while lowering cost is destined to see widespread usage. That’s one thing that isn’t going to change.



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