Novel Whisker Mitigating Composite Conformal Coat Assessment

European Union RoHS compliant commercial lead-free electronics use in DoD electronics have an increased failure risk due to tin whisker short circuits unless properly mitigated by design. The current project focused on enhancing liquid coating conformal materials and processes for tin whisker mitigation on coupons and assemblies. The project evaluated increasing strength by adding functionalized nanoparticles to rigid polyurethane coatings and improving coverage with sequential dip and spray layer processing. Coating microstructure and properties evaluations in combination with coverage assessments, environmental whisker tests, and finite element analysis were used. Successful coating rework was also demonstrated. Thicker and higher strength coating improved mitigation, but where thickness was excessive, coating cracking was observed and, solder joint thermal cycling reliability could be reduced. In addition to the new coating development, the samples from the WP1753 project were in exposed to additional simulated power cycling thermal cycling from 50 to 85C for 6,000 cycles and the polyurethane acrylate coating developed some cracks, but still had significantly better whisker mitigation than the uncoated samples.