Strategic Environmental Research and Development Program (SERDP) Nanoparticle Enhanced Conformal Coating for Whisker Mitigation
Authors: S. Meschter, J. Cho, S. Maganty, D. Starkey, M. Gomez, D. Edwards, A. Ekin, K. Elsken, J. Keeping, P. Snugovsky, Eva Kosiba, Zohreh Bagheri, and J. Kennedy Company: BAE Systems, Binghamton University (SUNY), Henkel Electronic Materials LLC, Bayer Materia lScience LLC, Celestica Inc. Date Published: 9/28/2014
Abstract: Lead-free electronics using tin-based solders and pure tin have a significant risk of tin whisker growth that can result in electrical failure in systems expected to operate for at least 20 years. In an effort to mitigate tin whisker induced short circuit failures, conformal coatings are used to provide an efficient means of blocking the tin whisker growth. A Strategic Environmental Research and Development Program (SERDP) project seeks to develop a polyurethane (PU) conformal coating with enhanced properties and coating coverage to provide improved whisker short circuit mitigation for aerospace and defense systems. To successfully prevent whisker penetration, the coating should possess optimum mechanical properties by providing sufficient strength, modulus, and hardness while maintaining good ductility and toughness. Typical PU films, however, often do not possess all these required properties, so incorporation of nanoparticles from silica or alumina is being evaluated to improve its whisker mitigation effectiveness. With the introduction of nanoparticles, agglomeration, non-uniform distribution, and void-defects need to be avoided. In the present work, nanoparticles were functionalized to bind them to the PU structure. Selection of the optimum concentration of nanoparticles was determined by establishing microstructure-property relations. Structural features at different length scales were characterized by various instruments including atomic force microscope (AFM), scanning electron microscope (SEM) and transmission electron microscope (TEM) while mechanical properties were evaluated via macroscopic testing as well as nanoindentation. This work compares coating mechanical properties, microstructure and coverage thickness to mitigation effectiveness testing on whisker prone substrates and assemblies.
Tin Whiskers, Lead Free, Assembly, Testing, Conformal coating