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Dendrite and whisker growth in solder plating

I am studying different leadframe copper alloy commonly used in the microelectronic packaging. One of the desirable properties is solderability. During plating, some alloys are prone to grow dendrite because of the differential etching. How do I evaluate this tendency? Do I just have to look at the composition and reject them? If zirconium and zinc are so well known alloy which cause the dendrite problem in the solder plating of copper, why are they widely used even in new products?

After plating, high purity tin plating are susceptible to whisker growth. How do I evaluate the growth? Is the growth rate warrant our attention since most of the products which utilize this i/c has very short cycle life?

sean siow
- singapore
2000

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2000

Tin whiskers are a phenomenon that has been known for years and there are numerous papers on the subject. To oversimplify, they are believed to be a stress reducing mechanism. To counteract whiskers, lead was used in the solder for many years, and even a little bit will help.

Today, bismuth is used as an alloying material to discourage whiskers. Stress relieving the substrate and the deposit via reflowing can be helpful. See our FAQs for some other letters on the subject.

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