Oct 06 2008
What do you know about tin whiskers?
On today’s menu is another real something that has tremendous potential in the plot of a book (particularly science fiction, though any contemporary book could use it): tin whiskers.
Never heard of them, you say? Well, get some popcorn and sit back. Tin whiskers are cool, they’re scary, and we might be hearing much more about these before you know it. See, two years ago, I had never heard of them either. Last year, I wrote a paper on them (You can also find the presentation). The subject is fascinating.
See, certain metals and alloys, particularly when used as a plating, will start to grow slim little hairs of metal. One of them is tin. Most never get more than a few mm long, but others have grown cm long under the right circumstances. Here’s a great picture of some we found in avionics boxes used to control reaction jets and aerosurfaces on the Orbiter (see page 5). If they bridge a gap with some power, but not too much, they just fuse and evaporate. If it’s a data connection, they can change a control, turn something on that shouldn’t be, for instance. But, if it has power and the conditions are right, you can get something call metal vapor arcing that will make a big unholy mess. I have some pictures in my linked presentation and paper, but there are other examples at the source for all things metal whiskery: Goddard’s Tin Whisker Website. For the science minded, this is a treasure trove of data, stories, pictures, videos, pointers, etc. of all kinds of metal whiskers, well worth wandering through.
Tin whiskers are not a new phenomena. We discovered them the hard way in the 50’s. However, it was discovered early that adding as little as 3%lead to the mix mitigated the whisker problem. But, tin plating is quick, simple, cheap, environmentally friendly and there’s no lead waste to worry over, so tin plated components began working their way into critical circuits. Tin whiskers have been blamed for losing several satellites and the redundant string for others, tripping a nuclear reactor, issues and a major recall on pacemakers, and several ugly accidents with metal vapor arcing. Really, check out those anecdotes.
Tin isn’t the only metal. Zinc and cadmium are also prone to whiskering. Zinc whiskering is becoming a serious concern in computer server facilities. Zinc whisker grows from the galvanized metal shielding on the underside of floor tiles in these facilities. When they go to upgrade or do work below, the floor tiles are lifted up and often shoved over the other floor tiles, shearing the unseen whiskers off and letting them drop into the crawlspace below. When they restart the system, the ventilation, which often flows underneath the floor, picks these whiskers up and sends them right into the computers. Huge, highly redundant server systems have been disabled this way. Really, read about it here or you can just stumble over many resources at the Goddard Tin Whisker Website. They’ve even found lead whiskers, gold whiskers and silver whiskers (though the latter is a different mechanism that grows silver whiskers like mad in a suphur rich environment. See this.
No one’s entirely sure what causes metal whiskers or what factors slow or speed the process. Whiskers may not grow for years and then grow very fast. Others might grow quickly from the beginning.
OK, so this is all cool in a geeky kind of way. So, how is this useful for fiction? Well, whiskers are an effective way to screw up all kinds of redundancy, which is frequently used to mitigate risk for space craft, with one mechanism. It’s one reason why NASA has severe restrictions on the use of pure tin plating. But, it’s not necessarily on the minds of regular people either, so this may not even be on the radar for commercial electronics. That makes it a potential factor in electric cars or planes or, in fact, anything that has critical functions that is governed by electronics. And remember, though we may come up with some way of beating this time, a generation from now, we might forget about them all over again and have to learn it all over.
I don’t know that I’ll ever have occasion to use this…but it was a very interesting read anyway.
Would have never guessed that I would be interested in such things!
this is fascinating
Like flit, I’m not sure if I’d have the opportunity to work this into any future tale I’d craft, but I’ll keep it in mind. Cheers!
Whoa, nifty… Pity I never work in modern settings, or I’d be all over that.
flit, I first “heard about them” when we found some 23 cm long in some Shuttle hardware. What really amazed me was that, though I took classes in electrical engineering and knew many electrical engineers, no one had ever mentioned this before. MOST electrical engineers don’t know about this, or didn’t before the new laws in the European Union precluding the use of lead. When I found out how old a phenomena this was, it floored me again because that means we’re doing a poor job of carrying our information forward so we have to relearn our lessons.
Interestingly enough, the reason I became really immersed in this for a year or so was because, since electronics were pressurized, it was assumed they couldn’t cause metal vapor arcing at 28 VDC. That seemed like a heck of an assumption and I couldn’t find anything that made that so. I asked and they said “the expert told us.” So I asked the expert and he said, “Well, we really don’t know. We could get metal vapor arcing (MVA) at 28VDC in a vacuum but probably not in 1 atm.” Probably sounded too much like speculation to me.
I work for a really cool company that does research and support for the Air Force, NASA and several other space-related organization and, doing research, I’d stumbled upon two scientists who were exploring the minimum voltage level at vacuum for MVA. I called them and asked what the minimum was for 1 atm and they said, “No one knows.” I asked if it could be 28 VDC and they said, “You know, my research money would cover a test, if you wanted.” I wanted.
Not ten minutes later, they scientist call me back and said, “That was great!” Guess what will MVA at 28 VDC? Spectacularly. (I think their papers on are the Goddard Whisker website, too.)
It turns out that the circuits in question weren’t susceptible to MVA because current was clamped down with inductors. They could never pull enough into the system to sustain it. But we never would have found that out without checking.
This is important, though, because many thing MVA is not an issue here on the ground and normal circuit protection is not sufficient to preclude it.
Damn, I’m such a geek.
Thank you *Lynne*, always a pleasure to see a new face.
ravyn, welcome!
Something else that can be used in fiction, past, present and future is “tin pest.” Pure tin, when it gets cold, can change from it’s lovely and useful metallic form into a brittle powdery form of tin that no longer is ductile or conducts electricity the same. Cold, in this case, is 13.2 Deg C. And it grows. It’s also called “tin leprosy” or “tin disease.”
Of course, in the past, we didn’t have electronics, but we did have tin utensils and objets d’art. It has corrupted pipe organs.
Check out Wikipedia on this topic for some useful info and examples. It’s fun to learn!
Interesting. Never heard of that phenomenon before. “Tin whiskers” sounds like something a certain character in The Wizard of Oz would have the day after he lost his razor…
What… you expected an astute and relevant technical response?
Any comment from you, Gumby, is welcome.
very interesting, never heard of this before. didn’t have the same idea for a post this time. LOL.
Stephanieebarr, you have a good point about the way we fail to carry some of our knowledge forward. Another example is cold solder joints. Several pilots lost their lives when control circuitry failed before we realized that cold solder joints don’t bond as stably as hot ones, even though every electronics hobbyist learns that you’re supposed to “heat the joint, not the solder”.
It frightens me sometime, The_Yeti, how much useful information is thoughtlessly tossed. I see programs where, as soon as the funding’s cut, all the records are zapped from disc drives and tossed into dumpsters. Since I work in spaceflight, I can’t help but be appalled at the notion that we do work over and over because we haven’t tossed away our expertise.
It’s bigger than the space program, of course, but I worry about what else we don’t know that we should know.
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