Tin whiskers is a major problem of RoHS Lead-free design, whose components are having pure Tin or Matte Tin. Tin is only one of several metals that is known to be highly capable of growing whiskers. A “Whisker” generally has the shape of a very thin, single filament or hair-like protrusion that emerges outward (z-axis) from a surface. The vast disparity in the observations reported by different experimenters is evidence of the complications associated with understanding and controlling tin whiskers. The following list is intended to provide a very basic overview of some of the observed characteristics of tin whiskers.

Tin Whiskers Growth Characteristics

  • Shapes: Whiskers may be straight, kinked, hooked or forked. Their outer surfaces are often grooved. Some growths may form as nodules or pyramidal structures.
  • Incubation (Dormancy) Period: Experimenters report the incubation period may range from days to years. This attribute of whisker growth is particularly concerning because meaningful experiments to determine the propensity for a particular process to form whiskers may need to span very long periods of time.
  • Growth Rate: Growth rates from 0.03 to 9 mm/yr have been reported. Growth is highly variable and is likely to be determined by a complex relationship of factors including plating chemistry, plating thickness, substrate materials, grain structure and environmental storage conditions.
  • Whisker Length: Whiskers as long as a few millimeters are not uncommon with some experimenters observing whiskers in excess of 10 mm (400 mils) in length. Only a few researchers have measured the distribution of whisker lengths for specific specimens. Invariably, these researchers report the length distribution fits a lognormal distribution.
  • Whisker Diameter: Typical diameters are a few microns with some reports in excess of 10 um and rarely less than 100 nm.