With the move to lead-free components upon the electronics
industry, many companies are haunted with worry about tin whiskers
produced by pure tin plating in solder.
The warnings are coming primarily from the engineering community
- particularly those in aerospace and military organisations. In
the world of commercial electronics, there’s less concern
with tin whiskers and more concern with complying new environmental
laws that ban lead and other hazardous materials.
Two very real fears have gripped the electronic industry. One is
the fate Sony suffered when The Netherlands held back 1.3 million
of its PlayStation game consoles last December because there was
cadmium in its cables. The Netherlands government, which has strict
laws against products with cadmium, was tipped by a Sony
competitor. And two is the fate of the $250m Galaxy 4
communications satellite that shut down in its cold, empty space
orbit. Engineers believe the cause was tin whiskers growing under
the extreme pressures of space. When the whisker grows long enough,
it can break off and create a short circuit.
Commercial electronics manufacturers are most fearful of
Sony’s fate - losing sales in markets that enforce
Restriction of Hazardous Materials (RoHS) standards. Military,
aerospace and hi-rel manufacturers are most concerned about the
fate of Galaxy 4 - potential equipment failure due to pure tin
soldering growing tin whiskers that break off and short out the
product.
The RoHS, passed by the European Union in 2002, bans the sale of
products containing lead and other hazardous materials and goes
into effect on July 1, 2006. But in order to make that deadline,
the electronics industry is moving now to products that use tin
soldering, which doesn’t contain the two per cent or three
per cent lead that has proved over the last 50 years to dampen the
whiskering phenomenon. RoHS applies to all electronic products,
exempt those produced by the military and portions of the
telecommunications industry.
Industry scratches head on tin whiskers
No definitive explanation has been given for the whiskering,
though it is known to be mitigated by the presence of some lead,
gold, antimony or indium. Gold has been cited as the most
successful additive besides lead in controlling whiskering, but it
adds to the cost of the component and has not been used widely. For
the most part, RoHS-compliant components use pure tin. Some in the
components industry say that only electroplated tin will grow
electrically conductive tin whiskers. Yet many engineers insist
that any form of pure tin will grow whiskers.
Engineers have found that pure tin grows whiskers mostly in
high-stress environments. “I have some parts that are pure
tin and they are 12 to 15 years old, and there are no tin
whiskers,” said a Lockheed Martin engineer who was willing to
speak with Electronic News anonymously. “Whisker
growth requires mechanical stress, a torque force, pressure on the
metal itself.”
The military has been exempted from RoHS regulations so they can
avoid potential failure due to the use of pure tin. But the
Lockheed Martin engineer points out that the military has
increasingly turned to commercial-grade components for the cost
savings, and those components will quickly shift to lead-free
versions. He also noted that commercial jets and life-support
medical equipment will be vulnerable to tin-whisker malfunctions
because these products are not exempt from RoHS rules.
Over at component producer Actel, executives note they will
continue to produce commercial leaded components for customers in
the military and telecommunications industries. “The military
and aerospace do buy commercial products, but we will still offer
components containing lead for exempt customers,” Cindy
Newell, Actel’s tactical marketing manager, said.
Newell notes that Actel has switched much of its shipment to
lead-free components and there has not been a rise in returns due
to tin whiskering. “We’ve been shipping lead-free
product for over a year and we have not had a customer come back
and say we have an issue with whiskers,” she said.
Meanwhile, the Lockheed Martin engineer contends that you often
can’t easily identify whiskering as the source of a failed
product. The whisker often vaporises when it shorts out a system,
so when engineers open the product to see why it failed,
there’s no whisker apparent. He also noted that when a $49
cell phone fails, there is typically not an investigation into the
source of the failure and thus tin whiskering may be causing
difficulties in commercial products without being identified as the
culprit. Newell countered that Actel has not seen an increase in
reported product failures for any reason since it started shipping
lead-free components.
At component producer Integrated Device Technology (IDT),
executives acknowledge that pure tin can produce whiskers, but they
insist the whiskers are harmless. “We do believe that given
the right conditions, tin whiskers will grow,” Anne Katz,
IDT’s v-p of worldwide assembly and test operations, said.
“What we disagree with is the likelihood of the product
shorting out.”
Katz said IDT tested lead-free versions of its components
extensively and adopted a manufacturing process that produces
lead-free parts that are unlikely to have whiskering problems.
“We have developed a proprietary process that mitigates
whisker growth. We spent thousands of hours testing our components.
Some have spent over a years under stress, and there’s no
whisker growth.”
Jerry Czerwonka, director of quality assurance for Avnet EM in
the Americas, the components business at Phoenix-based Avnet, noted
that most of the worry over tin whiskers comes from engineers in
the military and aerospace. “When you talk to the military
and aerospace people, they say whiskers are very real, but when you
talk to the commercial commodity folks, they say, ‘Hey,
it’s no problem'.”
Czerwonka believes that the phenomenon of smacking a
malfunctioning electronics product to make it work again is likely
a tin whisker problem. You hit the product and the malfunction goes
away because you’ve dislodged a whisker that was shorting out
the system. “That’s not a big deal if you have an
inexpensive commercial product,” Czerwonka said. “But
let’s say you have a satellite that cost billions. You
can’t get a Martian to thump it on its head and make it work
again.”
Like the Lockheed Martin engineer, Czerwonka believes that most
vulnerable area for lead-free products comes from the
commercial-grade components that are designed into military and
aerospace systems. “The military went to commercial best
practices, and now the commercial products are going to lead-free
components,” he said, adding that the military can’t
simply redesign products to switch to leaded military-grade
components. “When you’re talking about a missile, you
can’t just redesign it.”
Like Actel, some component suppliers say that’s not a
problem because they intend to continue producing components with
lead content, as well as lead-free parts. But military engineers
question how long suppliers will continue to produce leaded parts
if the market shrinks to the small portion of the electronics
market this is exempt from RoHS.
According to Ken O’Neill, Actel’s director of
military and aerospace product marketing, any phase out of leaded
components would come under the company’s normal phase-out
procedures. “If we had a leaded product phase out, it would
be under our usual 18 month cycle, so there would be plenty of
warning.”