I have a positive attitude, but do to all the negatives associated with
all the other finishes, I can no longer stay neutral on this subject.
Nickel Palladium Gold is the only finish I would choose right now.
IMHO
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Thursday, September 21, 2006 7:23 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG Problem...

 

        Mike Martel, some one 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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