**14. Whiskers**

Whiskers are electrically conductive and relatively mechanically resistant crystals growing on the surface of some metals. They may grow on the surface of the solder alloys with a high tin content (majority of lead-free solder alloys). It most

**Figure 24.** *Photos of whiskers.*

often concerns surfaces where tin (mainly galvanic) was used as a final finish [28, 29]. Whiskers can be straight, curved or kinked. Photos of whiskers are given in **Figure 24**.

Whiskers represent a very serious threat to the proper function and reliability of electronic equipment, mainly from the perspective of creating a short circuit (permanent, short-term or possible arcing). Therefore, materials with the potential risk of the growth of whiskers are not used in those industrial sectors that have higher demands on reliability and where they could cause large-scale damage or pose a threat to human life.

Whisker diameters range from 1 to 10 μm. Their length is typically in the order of micrometres, but in extreme cases they can reach lengths of up to 1 cm. The rate of whisker growth is determined by many factors; the literature [11] gives the approximate growth rate of whiskers in the range of 5 mm/year up to 1 cm/year. The following factors affect the whiskers' growth:


Due to their size and growth on shiny surfaces, whiskers are very difficult to detect by classical optical methods. The experimental results of whisker growth are unpredictable and unrepeatable, and so far the exact mechanism of their growth is not known.
