STRATEGIC ENVIRONMENTAL RESEARCH AND DEVELOPMENT PROGRAM (SERDP) LAYERED NANOPARTICLE ENHANCED CONFORMAL COATING FOR WHISKER MITIGATION

摘要

Lead-free electronics using tin-based solders and pure tin have a significant risk of tin whisker growth that can result in electrical short circuits in systems expected to operate for at least 20 years. In an effort to mitigate tin whisker induced failures, conformal coatings are increasingly being used to block tin whisker growth and prevent shorts. A Strategic Environmental Research and Development Program (SERDP) project seeks to develop a polyurethane (PU) conformal coating with enhanced properties and coverage to provide improved whisker short circuit mitigation for aerospace and defense systems. In order for a coating to provide whisker mitigation, it must have adequate coverage at a minimum thickness. Using the previously developed functionalized nanosilica particle enhanced PU coating, a combination of dipping and spraying was performed to obtain a multilayer build-up. Lead-free soldered electronic assemblies were evaluated for coating coverage and thickness with particular emphasis on areas susceptible to thinning like corners and vertical surfaces. Scanning electron microscopy, metallurgical cross-sectioning and microtome cross-sectioning was used for the evaluation. High temperature/high humidity 85°C/85%RH environmental exposure was used to evaluate corrosion and whisker mitigation effectiveness on Sn-3.0wt%Ag-0.5wt%Cu (SAC305) soldered assemblies.