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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:

  1. Stable short circuits in low voltage, high impedance circuits.
  2. Transient short circuits
  3. Metal Vapor Arc
  4. Debris/Contamination

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.

Download Our Guide on Urethane Resins

Sources:

http://nepp.nasa.gov/WHISKER/reference/tech_papers/2010-Panashchenko-IPC-Tin-Whisker.pdf

http://nepp.nasa.gov/whisker/background/index.htm

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