It's not just structures within silicon you need to worry about. Lead-free solder is susceptible to growing tin whiskers [0], which can cause short circuits. Often you can't even see the growth of these whiskers as they're under a BGA or on a microscopic level.
IIRC, NASA still requires all space hardware to be manufactured with leaded solder to avoid having a multi-million/billion dollar mission ruined by some tin whiskers.