Paul and any other TechNetters are no doubt wondering how in the world (um, I mean the known universe) NASA could make such a bu-bu (sp?)...

I've had some experience with govt purchasing. I'm not terribly impressed with their competence.  Paper pushers.  

Henning has told me is that the knowledge of tin whiskers has to keep resurfacing again and again as people retire and specs are not consistently calling out the need for a tin/lead alloy.  
 
I'm 68 years and counting.  Mea culpa... I have to admit that until the RoHS issue surfaced, I had no awareness of the problem of tin whiskers whatsoever.  I took material science in college (1973).  It was never mentioned in the textbook, in fact its in none of the textbooks or any other technical book on my shelves (and I've got quite a collection).

My colleague John Barnes has cataloged over 17,000 papers on the subject, by the way..  http://www.dbicorporation.com/whiskbib.htm 

The history of the problem includes tin whisker problems at Bell Telephone/Western Electric and IBM in the 1960s yet the problem goes back to the 1940s.  Its an elusive animal.  What I cannot begin to understand is how clueless (and I'm being kind here) the EU could be to go to a lead-free solder dictate!  What kind of %$#@! are running that asylum?  

Moreover, I wondered, how could the rest of the world just sit back and let it happen?  As soon as I read about the proposed ban I read articles and saw Henning's name on a paper.  He was one of my physics professors at American U so I tracked him down at NASA and we renewed our relationship (we hadn't talked in 35+ years).  
 
My incredulity led me to read everything I could find on the subject and ultimately to form a company to come up with a way to prevent (instead of mitigate (a word I have no use for whatsoever) the growth of whiskers from pure tin finishes (the patent pending LDF Coatings electroless nickel process).
 
This is what Michael Sampson at NASA Goddard wrote in the paper "Developing a NASA Lead-Free policy":

"5. NASA'S CURRENT SITUATION

There is currently no NASA-wide policy or position on the Pb-free issue. There are some existing requirements but they are not universally implemented. The NASA workmanship standards for soldering NASA-STD-8739.3 [I41 and NASA-STD-8739.2 [I51 both contain requirements to use SN60 or SN63 (Sn/Pb) solders except a tin silver alloy is an option for high melting point applications. While these standards are mandated by NASA policy document NPD 8730.5 [16], some NASA Centers continue to use their own documentation and individual project contracts may allow the contractor to use their own standards that may not specify the use of Pbed solders. The wording in the standards, combined with the well established use of Pbed solders in the industry does provide considerable confidence that NASA is unlikely to encounter Pb-free substitutions for Pbed solders for the foreseeable future.

The protections against exposure to pure tin and the whisker and pest threats are not as strong. There is no NASA-level document that currently restricts the use of pure tin finishes or that requires mitigation of pure tin finishes against the risk of whisker growth. NASA makes extensive use of US Military (MIL) specified parts and since 1994, most of the US MIL specifications have restricted the use of pure tin finishes."

================== 
And then there's the paper "Lessons learned" by Ray Perez at JPL
 
"4.0 Tin Whiskers Cause Electrical Shorts

During the period May-July 1998, one or more of the redundant spacecraft control processors (SCPs) failed in each of three commercial communications satellites. This resulted in one of the satellites being removed from service. Three SCP failures were attributed to intermittent or continuous short circuits caused by the growth of conductive filaments, known as "tin whiskers," from the tin-plated surface of an electronic assembly or its cover..."

To err is human so its said ...
 
Bob



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards
Sent: Monday, March 26, 2012 12:53 PM
To: [log in to unmask]
Subject: Re: [TN] More Information on Casini Tin Whisker Investigation

Thanks Bob...

This puts the meat on the bones...

Paul

Paul Edwards
Process/Quality Engineering
Surface Art Engineering


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
Sent: Sunday, March 25, 2012 8:57 AM
To: [log in to unmask]
Subject: [TN] More Information on Casini Tin Whisker Investigation

> From: Leidecker, Henning W. (GSFC-5600)
> Sent: Friday, March 23, 2012 7:55 PM
> 
> Subject: RE: Any Information on Casini Tin Whisker Investigation?
> 
> The group that did this investigation met today to assign tasks for 
> the writing of the final report.  So, the final report is "in 
> progress" but it is not yet released.  (I am one of this group.)
> 
> Each of the three radio-isotope generators has a high-rail at V+ and a low-rail at V-, with a resistor bridge that establishes a connection to ground, held between V+ and V-.  One of the three radio-isotope generators has shown a sequence of soft-shorts: it is still able to deliver its power, but it is shifting its off-set from ground -- this has not been a problem, yet.  This behavior has been seen on a few other radio-isotope generators: it is probably not of direct interest to most industries.
> 
> The CAPS instrument has show a sequence of soft-shorts in distinct locations.  Each has 'cleared' after various durations of elapsed times.  Another has just appeared after the recent turn-on.  The instrument is still working, and the shorts do not draw so much current as to cause harm.  But no one likes these, and folks wonder whether one of these will jump to a "hard short".  The specific concern is that such a hard short might harm the power system and thus kill the other instrument.
> 
> We never found an explanation for these radio-isotope events, or for the soft shorts in CAPS, that had the sweep smell of "Yes!  That has to be the reason!"  We have found tin whiskers growing from tin-plated transformer cans of the precise type used in the CAPS, when we inspected similar items still on the ground, and we showed that the shorting/clearing behavior of these whiskers were consistent with the observed "soft shorts" and also the time-dynamics of the coming/going of these soft shorts.  So, we supposed that tin whiskers were a possible cause.  While we considered many alternatives, some of which were also plausible, it was the whiskers that seems the least objectionable.
> 
> See the "tin whiskers (and other metal whiskers)" web site run by 
> GSFC: http://nepp.nasa.gov/WHISKER/ This site illustrates many many horrors that have been rigorously established to be caused by metal whiskers.
> 

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