Whiskers are single crystals in the shape of needles, which grow out oft in layers. Their diameter is a few micrometers, whereas their length can be up to a few hundred micrometers. Because of the growth of whiskers, electronic assemblies that are in use for years already may fail because of short circuits. Lead or other alloyed components prevent the growth, as do surfaces with a nickel-gold, OSP or silver coating. Particularly dangerous are layers of pure tin which have not been remelted.