Definition
A tin whisker is a thin, electrically conductive single-crystal filament that grows spontaneously from pure or tin-rich metal surfaces. Whiskers are needle-like, can grow straight or kinked, and have been observed to reach lengths of up to roughly one inch. Because they are conductive, a whisker that bridges two adjacent conductors can cause leakage current or a hard short, producing failures that are notoriously intermittent and hard to diagnose.
Why lead-free solder made this worse
Adding lead to tin finishes historically suppressed whisker growth. The shift to lead-free (RoHS) solders and pure-tin platings removed that mitigation, and internal compressive stress in the tin layer is widely understood to be the driving force behind whisker formation. Stress sources include intermetallic compound growth at the tin-copper interface, thermal cycling, and externally applied mechanical pressure.
Standards and mitigation
JEDEC and IPC publish test and acceptance standards for whisker susceptibility (for example JESD201 and JESD22A121). Mitigation strategies used in industry include alloying the tin (such as adding a small amount of another metal), using an underplate, annealing to relieve stress, and applying a conformal barrier coat. For mining hardware that runs for years in warm, vibration-prone environments, whiskering is a slow, latent risk on tin-finished pins and connectors.
See also our entries on dendrite growth and conformal coating, which addresses several whisker and migration risks at once.
In Simple Terms
A tin whisker is a thin, electrically conductive single-crystal filament that grows spontaneously from pure or tin-rich metal surfaces. Whiskers are needle-like, can grow straight…