Polyurethane Conformal Coatings Filled with Hard Nanoparticles for Tin Whisker Mitigation

ABSTRACT Lead – free electronics using tin-based solders and pure tin are susceptible to tin whisker growth that can result in electrical failure. In an effort to prevent the whisker short circuits, we have developed polyurethane (PU) – based conformal coatings filled with the nanoparticles (nanosilica, nanoalumina). In particular, surface functionalization of those nanoparticles were explored to effectively bind them to the PU structure, as well as to prevent agglomeration. As the performance of the conformal coatings is strongly influenced by nano- and microstructural features, the structural and chemical variations due to the nanoparticle addition were examined by a wide range of characterization methods. The corresponding mechanical properties were also evaluated via ‘macroscopic’ tensile testing as well as ‘localized’ nanoindentation. Based upon mechanical properties and microstructure observations, this work identifies optimum concentration of the nanoparticles in PU. Some preliminary results on the effectiveness of nanoparticle-filled PU coatings for the tin whisker mitigation is also discussed in this paper.