Stress-Induced Tin Whisker Initiation Under Contact Loading

Abstract

As electronic components become smaller, tin whiskers have an increasingly adverse effect on the assessment of the reliability of the components. In particular, the contact between components brings about whisker initiation near the contact area. Although a number of spontaneous tin whisker models have been proposed, a model of tin whisker initiation by contact loading has not yet been established. In this paper, the behavior of stress-induced tin whiskering by contact load was examined in a tin plating based on multiaxial creep theory. Creep properties were measured using a nanoindentation creep technique. The creep rate of Sn-10Pb is higher than that of Sn and affects the generation of compressive stresses after stress relaxation. Nonlinear finite-element analysis (FEA) reveals that the multiaxial compressive stress state appears after stress relaxation. The axial compressive stress increases even though the contact stress decreases. When multiaxial stresses are applied, not only axial stress but also the difference between stresses, affects the behavior of whisker formation. The axial compressive stress depends on the structures of the contact bodies, and the contact stress depends on the creep properties of the plating