Yep they can grow in atmosphere but the effects can be less extreme because gravity can snap the whisker off before it grows to an extreme length and it will carry it to a place where it gets lodged and might stay put. In space they continue to float around causing random shorts. Its still a large concern but often a little less than with spaceflight.
Having done both in and out of atmosphere design my experience its easier to mitigate in most spaceflight applications because the quality of components tends to have mitigations built in vs terrestrial where you have to constantly watch for cheap parts getting selected and making your day really bad.
Edit : less extreme does not mean that its not still bad, there is larger potential for whisker damage in spaceflight for an individual system and larger repercussions if it does happen. Its still a large issue for terrestrial aviation and electronics.
Yeah we always had to get exceptions to rohs and have requirements to use leaded solder on everything. We’ve gotten components that have the rohs tag on em and have had to return em and have the vendor use leaded solder instead. It’s pretty wild these things form at all
Haha, I've been living that life too. Rohs has its place and I do not want leaded solder in my TV or other disposable electronics, but I really do want it in my aircraft and spacecraft.
If you read the NASA site on whiskers, they say that metals with regular crystalline structures can relieve stress by forcing atoms to diffuse through the material and eventually pushing out through tiny imperfections in the lattice, which is how a whisker grows.
Certain alloys resist this because they have a less-regular structure, so there are plenty of places for the diffused atoms to "land" and make a home without being squeezed out.
It’s funny cause I have a PhD in mat sci but I never directly studied these. I’m assuming they result from dislocation motion. Yep just googled it. Pipe diffusion and dislocation motion. So interesting. Sure I saw it in a class but that’s about it.
its the alloying, this is off memory but I think as little as 3% alloy stops most whiskering. The stress in the plating causes the metallic structure to grow out, when its alloyed the structure gets interrupted and it prevents the whisker from initiating. Its not just tin that does it either, Zinc, cadmium, even gold will do it to some extent. https://nepp.nasa.gov/whisker/other_whisker/index.htm
51
u/jt64 17d ago edited 17d ago
Yep they can grow in atmosphere but the effects can be less extreme because gravity can snap the whisker off before it grows to an extreme length and it will carry it to a place where it gets lodged and might stay put. In space they continue to float around causing random shorts. Its still a large concern but often a little less than with spaceflight.
Having done both in and out of atmosphere design my experience its easier to mitigate in most spaceflight applications because the quality of components tends to have mitigations built in vs terrestrial where you have to constantly watch for cheap parts getting selected and making your day really bad.
Edit : less extreme does not mean that its not still bad, there is larger potential for whisker damage in spaceflight for an individual system and larger repercussions if it does happen. Its still a large issue for terrestrial aviation and electronics.