Investigation of tin whiskers formation

After many studies and analysis the Tin Whisker Group of iNEMI recommended three tests to evaluate the whisker growth propensity of plating finishes: storage at ambient office condition, storage in climatic chamber and temperature cycling. In the paper results of investigation of whisker formation on the PWB immersion tin coatings as well as on the electroplated Sn on leads and terminations of components according these testes are presented. The tested immersion tin coatings of PWB were deposited from solution without additives which can minimize whisker formation and from solution with additives reducing tin whisker formation. Another investigated tin layer was deposited on copper which was ennobles and passivated by application of the ultra-thin layer (0.08 μm) of special organic compound. The results of the study indicate that whisker formation is a very long process and isothermal storage especially with high humidity is more effective in inducing whisker growth, than temperature cycle method.