5 O’clock Shadow on your Electronic Assemblies and Printed Circuits?

Zinc & Metal Whiskers
Coastal Technical Services is actively involved in the study of the effects of Zinc and other metal whisker phenomena concerning electronic assemblies and printed circuits. Moreover, Coastal Technical Services has been instrumental in assisting original equipment manufacturers in addressing field failure problems as well as developing remediation efforts associated with metal whisker exposure events.

What are Zinc Whiskers? Zinc whiskers are electrically conductive, crystalline structures of Zinc that sometimes grow from surfaces where Zinc is used as a final finish. Zinc whiskers have been observed to grow to lengths of several millimeters (mm) and in rare instances to lengths in excess of 10 mm. Numerous electronic system failures have been attributed to short circuits caused by Zinc whiskers that bridge closely-spaced circuit elements maintained at different electrical potentials.

Zinc is only one of several metals that is known to be capable of growing whiskers. Other metals that may form whiskers include some cadmium, indium, antimony, silver, tin and tin alloys.

Differences between Whiskers and Dendrites
People sometimes confuse the term "whiskers" with a more familiar phenomenon known as "dendrites" commonly formed by electrochemical migration processes. Therefore, it is important to note here that whiskers and dendrites are two very different phenomena. A "Whisker" generally has the shape of a very thin, single filament or hair-like protrusion that emerges outward (z-axis) from a surface. "Dendrites", on the other hand, form in fern-like or snowflake-like patterns growing along a surface (x-y plane) rather than outward from it. The growth mechanism for dendrites is well-understood. While the precise mechanism for whisker formation remains unknown, it is known that whisker formation does not require either dissolution of the metal nor the presence of an electromagnetic field. 

For more information concerning metal whisker phenomena visit the following NASA Government website: 
http://nepp.nasa.gov/WHISKER/