Whisker Prevention Using Hard Metal Cap Layers

Application of conformal coatings has shown promise as a practical scheme for preventing whisker growth in electronic assemblies. Coatings have been proposed utilizing elastomeric, ceramic, and metallic materials. The ability to prevent whiskers is particularly important in assemblies containing Pb-free materials and finishes. Further, many otherwise desirable COTS (commercial off the shelf) electronic components and assemblies are available only with Pb-free tin as the termination finish or Pb-free SAC solder balls under BGAs. In this work we have investigated a variety of proposed whisker-impenetrable hard metal caps through use of Auger electron spectroscopy (AES) and Rutherford backscattering spectroscopy (RBS) and discuss plausible reasons why only certain metals are effective in blocking Sn whiskers.