Environazis threaten Aviation Safety - Banning Lead in new Aircraft

Cardinal

Of The Kremlin
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Lead-Free Movement Troubles Aircraft Industry
10/02/2005 09:07:56 PM
By Robert Wall
LEAD ASTRAY

Aerospace companies and some of their customers are struggling to deal with a movement to phase out lead and other dangerous metals from electronics products. And they are worried the trend could have a significant impact on their systems' performance.
Europe is leading the charge on trying to eliminate dangerous metals, with a European Union mandate in place stipulating that electronic products introduced after July 1, 2006, can no longer feature lead or certain other metals. Industry officials expect others to follow, noting that China and some U.S. states at the local level are pursuing similar policies.
Aerospace suppliers have managed to obtain an exclusion from the EU rule after lobbying from Airbus, Rockwell Collins and others, and with the backing of the European Aviation Safety Agency and FAA. But that hasn't completely eased the predicament. Many suppliers to avionics and other component makers generate most of their revenue through business in the commercial electronics world, so they are phasing out proscribed materials nevertheless.
ONE EXAMPLE IS LEAD-SOLDER, which is on the list of items the commercial electronics industry will have to do without to remain in compliance with EU rules. As a result, the aerospace industry is not only faced with a dwindling supply of these components made with familiar processes, but also the possibility of needing to recertify systems to comply with the offered alternatives--and soon. "Our ability to buy lead-plated components is diminishing rapidly," notes Roger Southgate, director of avionics certification at Rockwell Collins.
The lead-free solder drive represents a particular concern. "There are many unanswered questions regarding lead-free solder in aerospace applications," according to a letter Boeing has sent to suppliers. The aerospace giant has instructed suppliers to "notify Boeing of any plans to transition to lead-free electronics, even where required to accommodate obsolescence situations." Airbus may soon issue its own guidance, mandating compliance with lead-free electronics rules, according to industry officials.
Coming into vogue as a replacement substance as a result of the anti-hazardous material campaign is the application of pure-tin plating in switches and other components. Pure tin is deemed a cost-effective alternative for the current tin-lead material.
But pure tin has a nefarious and poorly understood side effect, warn industry and NASA officials. The material can create "tin whiskers," which are electrically conductive hair-like structures that can grow to 10 mm., come loose and short-circuit electronics. Studies at NASA Goddard Space Flight Center have concluded that "tin whiskers pose a serious reliability risk to electronic assemblies." In fact, the agency attributes at least three on-orbit commercial satellite failures to the phenomenon. Growth rates of the whiskers range from 0.03-0.09mm. per year.
Although the appearance of whiskers on pure tin has been known for some time, the cause is still poorly understood. Whisker growth has been observed in sealed boxes, so even those types of protected avionics components are susceptible. One of the simplest ways to suppress whisker growth is "poisoning" the pure tin, but that would involve use of one of the banned substances and, therefore, is not deemed an option. Tin-lead plating can also grow whiskers, NASA notes, but because they aren't nearly as long as those for pure-tin plating, are seen as less of a concern.
Lead-free solder could pose other hazards too, suggests Southgate. Soldering temperatures have to be higher and it isn't necessarily clear what effect that may have on the reliability of components such as resistors or integrated circuits.
 

PeteCO

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I have dealt personally with those whiskers in a raised floor computer facility. I assure you they are very real, and will randomly destroy computer equipment.

We took electron micrographs of the destroyed equipment, and sure enough, it looked like someone sprinkled metal sawdust all over the boards. Nasty, insidious stuff. You can't even epoxy-coat the offending metal, as the whickers will "grow" right through it.
 
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