[tinwhiskers] Should suppliers lead the transition to pure tin?
- From: "Bob Landman" <rlandman@xxxxxxxxxxxxxxxxx>
- To: "tinwhiskers@xxxxxxxxxxxxx" <tinwhiskers@xxxxxxxxxxxxx>
- Date: Sun, 6 Apr 2008 14:56:37 -0400
Lead-Free Zone Blog
Hi, this is Design News contributing editor, Rob Spiegel. Welcome to my
Lead-Free Zone blog. This is your opportunity (and mine) to discuss RoHS and
other environmental issues. Green regulations have produced waves of industry
confusion, and I do not expect things to clear up quickly. So use this blog to
inform us of your opinions, to instruct us all on what you're doing about this
initiative, or just to blow off some steam.
http://www.designnews.com/blog/710000071/post/750022675.html?
Friday, February 29, 2008
Should suppliers lead the transition to pure tin?
Feb 29 2008 6:23AM | Permalink | Email this | Comments (0) |
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Design Chain Associates, a company that helps manufacturers cope with
environmental compliance has released an article from its partner DfR Solutions
that looks at the state of pure tin in the electronics industry.
Here's the opening to the article:
One of the greatest concerns during this transition to Pb-free electronics, and
therefore Pb-free components, has been the supposed rapid and widespread
adoption of pure tin plating as the solderability plating of choice. A number
of questionable surveys have driven this belief, with some promoting that
'pure' tin has captured 75% or more of the market.
The response to this wave of tin-whisker susceptible components has been
impressive. Numerous organizations have sprung up to either analyze (iNEMI,
E4), inform (ELFNET, GEIA), or fight (NASA Tin Whisker Group) this potential
reliability threat. Millions have been spent on testing, analysis, report
writing, and, most importantly, material identification (have you bought stock
in XRF companies?).
Why all this time, money, and effort? Because, supposedly, the electronics
supply chain is backwards. Suppliers call the shots and the OEMs, especially
those in Hi-Rel (telecom, industrial, military, avionics, medical, etc.), have
no control over what goes in their product and out to the customer. Could we be
more wrong? For more of the article, click here:
http://www.designchainassociates.com/pdf/dfr_tm.pdf
=============
I just returned from NASA Goddard Space Flight Center where in their Tin
Whiskers group, thanks to Henning Leidecker, Jay Brusse and esp. Lyudmyla
Panashchenko's time lapse 3D photos of growing tin whiskers in a SEM, I saw for
the first time "live" tin whiskers and zinc whiskers.
Until you actually see them, unfortunately, most of you will relegate them to
UFO status. Seeing is believing, sad to say.
I just read the above article from DfR. It's an interesting argument but it
lacks completeness as it does not mention passive components such as L/C/R
parts, tin connectors and other mechanical parts such as shields - all of which
can grow whiskers and which can come loose and short circuitry or grow to 25mm
length and short to adjacent components.
Conformal coatings can mitigate the whiskers that do grow but the problem is
that the sharp edges on IC leads do not coat well with conformal coatings, so
I'm advised by NASA, unless the coatings are thickened with, for example,
cabosil. This is why NASA insists on 3% lead in solder as a minimum and
expensive XRF testing. I saw a $40K benchtop tester mfg by Fischer that did an
excellent job of analyzing coatings at their lab as well as a $500K Nikon
SEM-EDX instrument. It is very unlikely industrial companies will buy SEM-EDX
instruments.
Bob Landman
H&L Instruments,LLC
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