Tin whiskers aren't the result of lead free solder. They are a result of the tin coating on component leads. If you take a close look at that nasa page you'll see that every photo is of just a component lead/termination.

Tin plating has largely been replaced by tin alloys at this point which has more or less solved the whisker issue at a large scale.

More info here: https://www.indium.com/blog/pb-free-solders-are-not-the-caus...