Mitigation of Long Whisker Growth Based upon the Dynamic Recrystallization Mechanism

Microstructural Analysis of Cadmium Whiskers on Long-Term-Used Hardware

“…The Sn literature has shown that the nucleation of either a nodule or whisker is dependent on the microstructural features present in the plating; a whisker can form only if the plating grain boundaries are constrained from horizontal movement, otherwise a nodule or hillock is proposed to form. [15,23] If this Sn literature findings are applied to Cd, the large quantity of nodules observed here suggests that the cap screw plating grain boundaries are not pinned, resulting in a microstructure more conducive to nodule formation than whisker formation. However, nodule formation…”

“…Hillocks are reported to form instead of whiskers when plating grain boundaries are not pinned and are able to move laterally, spanning multiple grains. [15,23] The low aspect ratio features here will be referred to as nodules, because they appear to be very irregular and large; it is unclear if they share the same formation mechanism as hillocks studied in the Sn whisker system. Nodules and whiskers were found to grow together in agglomerates on the hardware, as Figure 2(c) shows.…”

“…Numerous studies of Sn whiskers have agreed that stress relief is the primary driving force for whisker growth. [11] Whisker inducing stresses can originate from anisotropic thermal expansion during thermal cycling, [12] interdiffusion and phase formation (the Cu 6 Sn 5 intermetallic often associated with Sn whiskers), [13][14][15] mechanical loading, [16][17][18] etc. To relieve this stress, atoms at high stress locations within the plating diffuse to low stress locations, [16] including oblique grain boundaries at the base of a whisker; this results in outward whisker growth and stress relief within the plating.…”