Factors Governing Tin Whisker Growth

Electrostatic Theory of Metal Whiskers

“…Electric bias was reported to exponentially increase whisker growth rate, 8,12,13 which was attributed to the effects of electric current (a possible role of the electric field was not analyzed), although the opposite statements have been made recently.…”

Effect of Environmental Conditions on Tin (Sn) Whisker Growth

“…Growth rate portrays the end-to-end span of a whisker changing over a certain time. Tin whiskers are reported to be single crystalline [7] [8] pure tin protrusions, a few micron diameters [9]. Tin whiskers have been found to grow on electroplated matte tin on a brass-alloy substrate when exposed to a condensation induced corrosive environment [10].…”

“…These are based on internal residual stresses, externally applied stresses [14], stored energy, surface energy effects [15], formation of intermetallics [8], thermal expansion mismatch, corrosion, and electromigration [16]. There are also other processing variables that can affect whisker growth such as film thickness and plating conditions [3], grain size [7], microstructure and composition [17].…”

“…Tensile stress is thought to slow the growth, whereas compressive stress to expedite whisker formation [7], although tin whisker protrusion on tensile regions of a tin finish was observed [9]. It is rationalized that bent tin coated substrates tend to form more whiskers at a faster rate, on the inner-curved area rather than on the flat area [18].…”

“…IMC generation leads to molar volume difference from either the tin or the substrate material. For example, brass substrate forms a common IMC-Cu 6 Sn 5 with tin at room temperature [7]. The growth of the IMC becomes even faster at elevated temperatures forming another IMC Cu 3 Sn from Cu 6 Sn 5 above 100˚C [6].…”