Tin whiskers are absolutely not "ironed out" and there still is not a good answer besides alloying with either lead, or antimony, both of which are toxic. But

Tin whiskers are absolutely not "ironed out" and there still is not a good answer besides alloying with either lead, or antimony, both of which are toxic. But it's a tradeoff, because without the lead or the antimony, tin whiskers will eventually form. There is no known way to stop them, on a long enough timescale they will 100% certainly grow whiskers and eventually that will cause a failure. Conformal coatings can reduce the rate of growth, but they don't stop it, and the conformal coating can itself cause failure as the tin whisker still grows and will exert mechanical pressure as it does.