Tin Whisker Mitigation and Conformal Coating
Posted by Sean Horn
Tuesday, April 10, 2012 9:35
@ 9:35 AM
WHAT ARE TIN WHISKERS
Tin whiskers are electrically conductive, crystalline structures of tin that sometimes grow from surfaces where tin (especially electroplated tin) is used as a final finish. Tin whiskers typically grow from lengths of 1-2 millimeters (mm) but have been observed to lengths in excess of 10 mm. Electronic system failures have been attributed to short circuits caused by tin whiskers that bridge closely-spaced circuit elements maintained at different electrical potentials.
ARE TIN WHISKERS AN ISSUE?
There are four main risks with tin whiskers:
- Stable short circuits in low voltage, high impedance circuits.
- Transient short circuits
- Metal Vapor Arc
Of these, a metal vapor arc is often the most destructive. A metal vapor arc occurs when a tin whisker initiates a short in an environment possessing high levels of current and voltage.
HOW CAN I STOP TIN WHISKER GROWTH?
Unfortunately, there is no known way to eliminate tin whisker growth, only the use of mitigation strategies to limit their affect on product.
IS CONFORMAL COATING A VIABLE TIN WHISKER MITIGATION STRATEGY?
As a result of an eleven year NASA study, conformal coating was proven to be a viable tin whisker mitigation strategy. While thinner coats of conformal coating were unsuccessful at preventing tin whisker penetration, Arathane 5750 (a urethane resin) applied at 2 mils thick was strong enough to prevent tin whiskers from penetrating the coating and causing any potential issues.