"Tin whiskers" sound harmless, don’t they?

I got a cold chill as I read this article yesterday on the Metro crash investigation:

“In the aftermath of the crash on the Red Line between the Takoma and Fort Totten stations, Metro officials analyzed track circuit data and found that one circuit in the crash area intermittently lost its ability to detect a train. The circuit would report the presence of a train one moment, then a few seconds later the train would “disappear,” only to return again.”

It sounded to me like the same problems that have been encountered on the Space Shuttle, nuclear power plants, and various military systems. And that problem is tin whiskers.

The backstory:  When people first started building electric circuits, they used tin metal to solder the interconnections between the copper bits.  It wasn’t long before they noticed the tin would get “furry”, growing spiky whiskers as the part was used.  These spikes could grow long enough to short out the circuits, and then were so weak that they would break off right after doing so.  A smart metallurgist figured out that adding a small amount of lead to the tin alloy stopped this behavior.  And so the electronics industry grew, and electronic circuits got so small and fast and reliable that they ended up in nearly every control system — with a bit of solder in every one of them.

In the early 2000’s two things happened:  Europe passed legislation that prohibited lead in consumer products, and at the same time, the production of interconnection technologies went global.  So even though only European markets mandated this change, producers all over the world had to comply.  And that means that consumers all over the world were getting lead-free electronics, many times without knowing it.  Many times the same part number started showing up with lead-free solder, making this trend very hard to track.

So yesterday, I dropped a note to one of my expert friends, who agreed with me that the circuitry in the Metro replacement part, more likely than not, contained lead-free solder.  And then, he pointed out the likelihood that the latest Airbus crashes had lead-free solder components in their flight controls.

Hence the cold chills.

Yes, it’s a bad thing to have lead where kids might put it in their mouths (especially drinking water).  Yet the activists admit that the amount of lead in electronics isn’t at dangerous levels; they say their ultimate goal is to shut down lead production entirely.   (In the interest of full disclosure, I facilitated a study back in 2005 that predicted this, and only now is the military starting to address those findings.) 

Hey, guys, maybe technology might need to trump politics for once?

1 Comment so far

  1. threedonia.com » Fall of the Machines (pingback) on July 10th, 2009 @ 8:13 pm

    [...] here’s a follow-up post. which links to this interesting post at Metblogs on a thing called “tin whiskers”. In it he comments on a Washington Post article on why the train computer systems failed. From [...]



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