Tin Whiskers: The Next Y2K Problem?
Engineers are racing to avert what could become a plague of short circuits
in electrical and electronic devices.
Wednesday, December 29, 2004
By Ivan Amato

In the cold vacuum of space, on a gleaming metal surface inside the Galaxy 4
communications satellite, tiny whiskers of tin grew in perfect stealth‹until
May 19, 1998, that is. That's when at least one of those whiskers bridged a
pair of metal contacts in the satellite's control processor. The short
circuit killed the satellite. Some 40 million pagers stopped working all
over the country. Millions of dollars' worth of ATM and credit card
transactions were interrupted. The $250 million satellite became, in the
words of NASA engineer Henning Leidecker, "a doorstop in space."

The loss of Galaxy 4 was just one of the more visible consequences of a
little-understood problem with catastrophic potential for electronic and
electrical systems: metal that grows whiskers. An F-15's radar system,
pacemakers, fuse switches in air-to-air missiles, electronic relays in a
nuclear power plant, and global positioning system receivers‹not to mention
many other satellites‹all have fallen victim to the problem. One group of
University of Maryland theorists has estimated that tin whiskers have caused
losses of billions of dollars to date.

And the problem suddenly could be poised to get worse. The march of
miniaturization means that ever smaller metal whiskers can short out the
ever smaller distances between leads, solder bumps, and other jam-packed
conductive surfaces in electronic systems. Furthermore, the European Union
has ordered that by the middle of next year, electronic and electrical
products sold in its vast market must be free of lead‹and it is lead that
best checks the growth of whiskers. "We are more vulnerable now than we used
to be," says Ron Gedney, director-turned-consultant for the National
Electronic Manufacturing Initiative (NEMI) in Herndon, Va.

The phrase "tin whiskers" is pretty darned descriptive. Under just the right
lighting, if you look at a metal surface with whiskers, it sparkles. No one
can tell you the specific conditions under which whiskers may or may not
grow, but it usually has something to do with surface tension. Just as you
might move to the less crowded outside wall of a room packed with people,
metal atoms move around and reform into whiskers as a way of easing
tension‹even the pressing of a bracket or screw.

Until the new millennium the tin-whisker problem actually seemed like a
plague of the past. The metallurgical bug first became apparent in the late
1940s to telecommunications engineers who were investigating why relays in
telephone switching systems were failing. The research community came up
with a whisker-quashing solution: Add 2% to 3% lead to the tin plating used
in electronic assemblies, particularly on wires and leads to make them
solderable. Lead-tin alloys became standards for the industry, and their use
relegated tin whiskers, at least for most of us, to nuisance status.

As often happens, the solution became a problem: Lead became a material non
grata and for good reason. It does a nasty number on neural circuitry,
especially if you're a kid. To reduce human exposure to lead, governments
have regulated it out of paint, gasoline, plumbing, and other sources. The
relatively small amount of lead in electronic and electrical systems‹about
0.2 gram in an Intel processor and about two to three grams in a
motherboard‹hadn't attracted much attention, but that changed as the volume
of electronic waste showing up in landfills began ballooning.

Although some companies had been anticipating an era of lead-free
electronics for more than a decade and already are shipping lead-free
products, the get-the-lead-out clock started ticking in earnest for the
entire electronics industry in 2002 when the European Union enacted the
Restriction of Hazardous Substances (RoHS) and the Waste Electrical and
Electronic Equipment (WEEE) directives. Among other things, the directives
mandate that by July 1, 2006, only lead-free electronic and electrical
products will be legally salable in member countries. Unfortunately, no one
knows for sure whether there is a no-lead substitute that will be immune to
whisker growth. And that means tin whiskers and the failures they can foment
could become as familiar in electronic products as flat tires are in cars.

To those who make electronic products, the no-lead restriction is akin to
phasing salt out of food. Lead is a trace ingredient in these products, but
its whisker-stopping and other traits have a technical taste that's hard to
do without. Even though some companies are claiming to have developed
reliable substitutes to lead-tin alloys, a fundamental metallurgical
ignorance about why whiskers form on metals‹including cadmium, zinc, and
silver in addition to tin‹means that there is no rock-solid basis for
expecting success through any particular fix. That's why military systems
are, for the moment, exempt from the lead-free requirements. But because
military procurement has relied more and more on off-the-shelf consumer
products, even military systems in coming years could end up with more
vulnerable components.

"When you have something like lead-tin, and you have 50 years of experience
with it, you hate having to change it," says NEMI's Gedney. What's too bad,
he and others in the industry argue, is that going after lead in electronics
is not a good way of getting a lot of environmental bang for the buck,
especially when it includes the risk of bringing down more satellites. Even
so, says Gedney, "no company wants to be against progress on the
environmental front; every company knows it has to have a solution to this."

Some companies, such as Texas Instruments, developed lead-free technologies
even a decade ago, well before the heavy metal made it to the top of
regulators' to-do lists. By the late 1990s the likelihood that lead would be
excised from the diet of electronics makers and suppliers became more
apparent, and in 2002 the European Union made it official. Japan, China, and
several American states, including California and New Jersey, also are in
various stages of outlawing lead. Denial is not an option.

Almost as out of sight to most people as the tin whiskers themselves is a
worldwide network of detail-minded engineers, metallurgists, technology
managers, chip manufacturers, government officials, and others who are
racing against the clock to make sure that the get-the-lead-out movement
does not awaken the tin-whisker dragon. They have until about right now to
come up with a solution if they want to make sure that the products that
ship in the coming months and years do not collectively harbor a Y2K of
sorts‹the wide distribution of everything from microwave ovens to missiles
that are more prone to whisker-induced failure than most electronic products
have been for the past half-century.

"You don't want to go out and buy a brand-new HDTV, only for it to fail
before you've finished your payments," says Gedney. Researchers have come up
with a variety of potential solutions. Semiconductor maker Agere Systems,
for example, announced in September that it will undercoat the leads on the
components it uses with nickel before it puts pure tin on top. Engineers
also have developed a tin-silver-copper alloy that appears to limit whiskers
to a mostly manageable fact of metallic life.

However promising those lead-free solutions might look in laboratory and
beta tests, however, the real assessment of their long-term ability to keep
whiskering at bay will be taking place over the next few years in the wild
as lead-free electronic systems are made and sold throughout the world. It's
a done deal for any electronics industry player that wants to remain in the
game, but all are moving forward with the nagging anxiety that they might be
setting trillions of individual stages for the quiet, stealthy growth of
metal whiskers that can do no good. 

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