Comments on: Moral railroads (update) http://www.foresight.org/nanodot/?p=3175 examining transformative technology Fri, 07 Jun 2013 18:02:02 +0000 hourly 1 http://wordpress.org/?v=3.0.4 By: SteveA http://www.foresight.org/nanodot/?p=3175#comment-859518 SteveA Sat, 11 Jul 2009 06:40:39 +0000 http://www.foresight.org/nanodot/?p=3175#comment-859518 Ummm, no. Solder was always 40% lead, because that gives it the lowest meltimg point. The tin-whisker problem was noticed on other things, like "tin" cans, which (in olden times) were steel plated with basically pure tin so it wouldn't rust. Tin whiskers became a problem in the early days of spacecraft, because they could grow long enough in zero-G to short things out, as mentioned. In normal gravity, with vibration, they tend to break off before getting long enough to do harm. The Euro-crats mandated lead-free solder in most electronics starting in 2006. Google "RoHS" for details. Current lead-free solder is mostly tin, with a bit of copper (and some other things) added specifically to prevent tin-whiskering (and bring the melting point down a bit). That part of the Metro system was built decades ago. Unless the Metro signaling system was replaced after mid-2006, it was not built with lead-free solder. Ummm, no. Solder was always 40% lead, because that gives it the lowest meltimg point. The tin-whisker problem was noticed on other things, like “tin” cans, which (in olden times) were steel plated with basically pure tin so it wouldn’t rust.

Tin whiskers became a problem in the early days of spacecraft, because they could grow long enough in zero-G to short things out, as mentioned. In normal gravity, with vibration, they tend to break off before getting long enough to do harm.

The Euro-crats mandated lead-free solder in most electronics starting in 2006. Google “RoHS” for details. Current lead-free solder is mostly tin, with a bit of copper (and some other things) added specifically to prevent tin-whiskering (and bring the melting point down a bit).

That part of the Metro system was built decades ago. Unless the Metro signaling system was replaced after mid-2006, it was not built with lead-free solder.

]]> By: Agribusinessman http://www.foresight.org/nanodot/?p=3175#comment-859516 Agribusinessman Sat, 11 Jul 2009 02:49:04 +0000 http://www.foresight.org/nanodot/?p=3175#comment-859516 The effect was noted about 30 years ago on circuit boards that were thermally cycled with power on. The thermal cycling would cause condensation on the boards from the cold part of the thermal cycle. In the presence of moisture, dendritic growth (tin is prone to electromigration) occurs between adjacent soldered joints and traces at different electrical potential (primarily between power and ground). The growth of "dendrites" eventually causes shorts at these points. Normally circuit boards used in harsh environments are conformal coated to prevent this. The effect was noted about 30 years ago on circuit boards that were thermally cycled with power on. The thermal cycling would cause condensation on the boards from the cold part of the thermal cycle. In the presence of moisture, dendritic growth (tin is prone to electromigration) occurs between adjacent soldered joints and traces at different electrical potential (primarily between power and ground). The growth of “dendrites” eventually causes shorts at these points. Normally circuit boards used in harsh environments are conformal coated to prevent this.

]]> By: threedonia.com » Fall of the Machines http://www.foresight.org/nanodot/?p=3175#comment-859514 threedonia.com » Fall of the Machines Sat, 11 Jul 2009 00:13:38 +0000 http://www.foresight.org/nanodot/?p=3175#comment-859514 [...] And 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 Metblogs: 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. [...] [...] And 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 Metblogs: 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. [...]

]]>