[ RadSafe ] RE: Lead

[Jaro]

Actually, the ban on lead in electronics isn't funny at all....

http://www.nrc.gov/reading-rm/doc-collections/commission/speeches/2005/s-05-
019.html
U.S. Nuclear Regulatory Commission
OFFICE OF PUBLIC AFFAIRS
IMPROVEMENTS TO THE UNITED STATES NUCLEAR REGULATORY COMMISSION’S OPERATING
EXPERIENCE PROGRAM
Peter B. Lyons, Commissioner, U. S. Nuclear Regulatory Commission
before the International Conference on Operational Safety Performance,
International Atomic Energy Agency
Vienna, Austria, November 30, 2005

<SNIP>

The Millstone 3 PWR plant experienced a reactor trip as a result of "tin
whiskers," which are fine threads of soft metal that grow on electronic
circuit boards and can cause short circuits. The staff first performed an
internal Operating Experience Briefing to inform NRC management and to
facilitate evaluation of the issue. The staff subsequently issued an
Information Notice to inform industry of the cause of this event and related
operating experience from international and non-nuclear industry sources.
The NRC’s Office of Nuclear Regulatory Research is currently evaluating
whether tin whiskers should be identified as a new Generic Safety Issue.
Although the staff acted quickly and forcefully to this latter event, I
should note my personal view that this is an issue that might well have been
anticipated much sooner within the nuclear industry, before revealing itself
in a plant trip. These phenomena were well known outside of the nuclear
industry. We clearly must continue to make progress in our efforts to gather
relevant information and must continue to improve our ability to look beyond
our own industry for useful lessons.
<SNIP>


http://www.aviationnow.com/publication/awst/loggedin/AvnowStoryDisplay.do?pu
bKey=awst&issueDate=2005-10-03&story=xml/awst_xml/2005/10/03/AW_10_03_2005_p
58-01.xml&headline=Lead-Free+Movement+Troubles+Aircraft+Industry
Lead Astray
Lead-Free Movement Troubles Aircraft Industry
Aviation Week & Space Technology, 10/03/2005, page 58
Robert Wall, Paris

Regulations banning some metals in electronics raise concern throughout
aerospace industry

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.

Tin whiskers can grow up to 10 mm. in length and have been known to cause
aerospace components to fail, according to NASA.Credit: NASA

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.

THE PROBLEM OF SUPPLY ACCESS isn't just limited to equipment manufacturers.
One of the questions is how maintenance organizations will in a few years
fix equipment that was fielded with lead-solder. An industrial working group
addressing the lead-free electronics issue is trying to come up with
practices to ease the in-service support. For instance, techniques must be
devised to avoid lead-free items being contaminated with lead components
during repair processes. "In order to properly manage equipment, users must
be able to distinguish lead-free units from units containing lead without
resorting to detailed research," according to an Arinc-prepared paper on
lead-free soldering, repair and rework processes.

New materials will call for new processes. The Arinc group is trying to
devise standardized ways to ensure the air-worthiness of components, while
at the same time guarding against component makers "over-specifying
soldering, repair and rework requirements." Arinc notes that airframe and
engine suppliers have the responsibility to keep airlines notified of
developments.
NASA believes some tin-plating has already crept into systems without
consumer knowledge. Although military specifications bar pure-tin plating,
NASA says there have been cases where the material was introduced by third-
or fourth-tier suppliers, nonetheless.






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