The role of nodules in the growth of Zn whiskers from alkaline cyanide-free Zn electrodeposits

Electroplated zinc finishes have been widely used in the packaging of electronic products for many years as a result of their excellent corrosion resistance and relatively low cost. However, the spontaneous formation of whiskers on zinc electroplated components, which are capable of resulting in electrical shorting or other damaging effects, can be highly problematic for the reliability of long life electrical and electronic equipment. The current work investigated whisker growth from commercial alkaline cyanide-free zinc electrodeposits on mild steel substrates. The presence of nodules on the deposit surface significantly reduced the incubation time for whisker growth in comparison with that from planar regions of the deposit. The nodules were probably formed due to the built-in residual stress within the electrodeposit during deposition. The nodules were eliminated by grinding the surface of the steel prior to Zn deposition. However, in the absence of the nodules the incubation time for whisker growth was reduced compared with that from the as-received surface.