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CuAl Intermetallic

We are qualifying bare Cu leadframe for our transistor package and we are using Al wire for wirebond. Problem is, brittle CuAl intermetallic system occurs at high temps (150 C)thus creating a poor bond integrity between the Al wire and the Cu leadframe. Any solution to this? Does doping the Al wire with another metal (e.g Ni) do any good. Any other suggestion to this? How could I prevent the brittle CuAl intermetallic from occurring (without plating the leadframe)?

Thanks.

Aniceto Idjao
Semiconductors - Quezon City, Manila, Philippines
2003

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Hmm. Bare copper has proven unsuccessful for busbar, unsuccessful for soldering irons, unsuccessful for circuit board tabs, unsuccessful for wire wrap terminals, unsuccessful for contacts; in all cases the fix was to plate it. So now it is used on lead frames, and success is expected when aluminum is wirebonded to it. I hope these packages prove successful in the long run but I guess it doesn't surprise me that difficulties are encountered when we try to leave out the plating.

I don't know if the following page will still be on line when readers see this page in the future, but a thesis at www.sjsu.edu/faculty/selvaduray/page/papers/mate234/yingzheng.pdf is very enlightening on this subject of bare copper leadframes and aluminum wirebonding.

Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey