Orbital validation for tin whisker suppression by conformal coating

To investigate the use of lead-free tin-based parts for satellites, the effectiveness of using a conformal coating for suppressing the growth of tin whiskers in Earth orbit was validated. An exposed handrail attachment mechanism on Kibo, the outboard platform of the International Space Station, was used in the experiments in the study. Experimental samples were exposed in orbit for up to four years, and the ability of parylene and polyurethane coatings to suppress whisker growth was investigated. Numerous thin, long, and straight whiskers grew in orbit on the uncoated samples, but the whiskers did not penetrate the parylene- and polyurethane-coated samples. In addition, no whiskers were generated from tin plating under these coatings. Parylene exhibited hardness, which completely suppressed the growth of whiskers and nodules. Polyurethane, being a softer material, showed some nodules under the coating, but no whiskers were observed. Furthermore, there was no difference between the whisker suppression effect in the orbital and ground test samples for both coatings. There was also no significant degradation in the hardness or Young's modulus of the coatings. These results demonstrate that lead-free parts coated with parylene or polyurethane can be used in satellites operating in this orbit for four years. To our knowledge, this is the first study to report and clarify the effects of a conformal coating on whisker suppression in Earth orbit.