Electrostatic Mechanism of Nucleation and Growth of Metal Whiskers


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Abstract

Metal whiskers can grow across leads of electric equipment causing short circuits, arcing, and raising significant reliability issues. The nature of metal whiskers remains a mystery after several decades of research. Here, their existence is attributed to the energy gain due to electrostatic polarization of metal filaments in the electric field induced by a metal surface.

The field is induced by surface imperfections: contaminations, oxide states, grain boundaries, etc. This theory provides closed form expressions and quantitative estimates for the whisker nucleation and growth rates, explains whisker and Growth of Metal Whiskers parameters and predicts statistical distribution of their lengths. The details of the underlying mathematical treatments have been presented in a recent publication. Here, the emphasis is on a more intuitive level, and the references are omitted.

Metal whiskers are hair-like protrusions observed at surfaces of some metals; tin and zinc examples are illustrated in Figure 1. In spite of being omnipresent and leading to multiple failure modes in the electronics industry, the mechanism behind metal whiskers remains unknown after more than 60 years of research.

While not formally proclaimed, some consensus, at a rather qualitative level, is that whiskers can represent a stress relief phenomenon. However, that never led to any quantitative description including order-of-magnitude estimates of whisker parameters.

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Editor’s Note: This article originally appeared in the February 2015 issue of SMT Magazine.

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