(chuckle) I'm thinking I really should comment on this...but wow...what more
can I add that's not already been repetitively conveyed...
Franklin
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Thursday, September 21, 2006 3:42 PM
To: [log in to unmask]
Subject: [TN] LF
Mike Martel, a man with a positive attitude.
Ramon
Jun 26, 2006 (See Comments Below)
Editorial
Managing the Naughty Child
Mike Martel, Editor, Circuitnet
I've been listening to voices on both sides of the RoHS issue and the more I
hear, the more foreboding the tone becomes. Despite what some writers have
suggested to me, i.e., don't fight it, get with the program
- I think the electronics manufacturing industry has a real mess on its
hands that will only grow in complexity as new lead-free assemblies age in
the field. The ultimate outcome, as one friend commented the other day at
lunch, will probably be the granting of so many exemptions - necessary ones
- that the whole experiment in going lead-free will have proven to be a
many-headed hydra, a RoHarce farce that will ultimately spawn more problems
than its short-sighted authors could ever have hoped to solve. Somehow I
recall the old proverb that the Road to Hell is paved with Good Intentions.
The implications of the impending RoHS-inspired process and reliability
quagmire came to me in hints and whispers - actually, whiskers, the tin kind
- a year ago when I was looking into efforts and studies that iNEMI was
involved in regarding mitigating tin whisker growth.
Tin Whiskers. Source: Circuits Assembly Magazine Tin is a problematic,
spooky metal, and I suppose that the electronics industry would be glad to
get rid of it if only there were a suitable or economically feasible
replacement. It does strange things - such as turn to powder at very cold
temperatures, grow whiskers, etc., and while I am neither metallurgist nor
scientist in any qualification, I do understand that tin, like a naughty
child, can be governed when paired with its strict nanny, lead. Right now I
hear that the most popular tin/lead replacement alloys, SAC-alloys,
unfortunately have problems with tin whiskering, but even worse than that,
they are prone to serious voiding problems that may compromise the integrity
of the soldered connections.
One solder paste supplier, Cobar BV, appears to have addressed the voiding
problem with one specific SAC alloy. Since we recognize that voids don't
come from the alloy itself but must be related to the flux, Cobar, which has
been working for a long time in the development of high heat tolerant
synthetic fluxes, focused on the purity of the synthetic materials and
claims to have a void-free formula that is currently producing millions of
joints in consumer electronic products for a major European maker.
That being said, we still must look to the tin whisker issue. Being the
neophyte that I am, I recently queried Harvey Miller, who appears to have
(vociferously) taken up the standard of the Anti-RoHS Rebels, is the use of
conformal coating might, in some cases, particular with the tougher
coatings, prevent the growth of tin whiskers. Thinking myself a little
clever to have asked, I was nonetheless horrified to receive a response
through Harvey from a colleague of his, a Mr. John Burke:
"It is proven that conformal coating does nothing to stop tin whiskers.
It will push through the coating and will be deflected by the next coating
it comes to, so it is kind of OK in that respect unless you have a whisker
coming from the other direction. It does nothing for whiskers under the
coating, since they will propagate regardless."
Like little hypodermics, yes? I would not have expected it, so I suspect
that as whiskers grow, they grow, like an asparagus, from the base, pushing
upward and away. Harvey writes further:
"When I asked Carol Handwerker if silver could stop tin whisker formation,
she replied "only lead". (Carol Handwerker is Professor of Materials
Engineering at Purdue University, and the former chief of the Metallurgy
Division at NIST and moderator of the first iNEMI Tin Whisker Workshop). I'm
sure the process can be ameliorated one way or other but not reliably
stopped. Kirkendall voids are more insidious because copper will diffuse
into tin w/o lead, leaving voids behind. Drop your cell phone and open
circuits result. We could go on."
"The present Environmental Commissioner at the EU Parliament is Stavros
Dimas from Greece. I suspect he would like to get rid of the lead ban.
He wrote someone that he is aware of how much additional energy it will
waste because of higher temperatures. But reversing is not that easy when so
many egos and so much money have been invested in lead-free. So it will take
some time, but it will be reversed."
Now that's optimism. Let's see how it plays out.
Mike Martel, Editor
Circuitnet
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