I could not agree with you more, Inge, hence my original posting on this subject. However, it does NOT reduce my respect and esteem for Dr. Lydecker and the team at NASA. 

Being a process engineer in high-reliability military products, I totally empathize with them regarding their efforts to keep their spacecraft reliable, (keep the mice away) while being forced to work with an industry that was essentially blindsided by a set of uneducated and ignorant political hacks trying to shove RoHS and lead-free solder down our throats, without any sense of due diligence or qualification. That includes the hacks at solder companies that promoted lead-free solder as a component finish that "could do no harm".

Also, I am not sure of the source of the original news bulletin that Tom Gervascio posted, but I question whether it was directly quoted from NASA. I recommend we know the source of the publication before we allow this to tarnish NASA's image.

And even if it was, I still cannot fault NASA because I know it is very, very difficult to control everything that goes into any company's CCAs.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
Sent: Wednesday, March 21, 2012 4:41 PM
To: [log in to unmask]
Subject: Re: [TN] Out of the world tin whiskers

Wow, that's a fraudulent anticipation..

 It is believed that these or additional tin whiskers that may grow on
Cassini cannot carry enough current to cause problems, but will burn out on
their own like a lightweight fuse.

....because

a. singel crystal metals can carry more current

b. some signal paths may measure nanoamps or even picoamps

c. they can start arcing

d. a typical long whisker can carry 10 mA before burning

e. a short one can carry 50 mA

f. dozens of whiskers can be in parallel, thus carrying even more current

g. burnt whiskers can come back if the 'root' is intact

So, to think 'they will just burn away' is not a philosophy when building
radar and other sensors (from where I came).  I have been involved in
Galileo as well. If we found just a few whiskers, it took just a few days
and a whole delegation went to ESA.

I think I will lower my admiration of NASA a little bit. But not Jay....

Inge

On 20 March 2012 18:08, Gervascio, Thomas L <[log in to unmask]>wrote:

> Tin whiskers at Saturn
>
> PASADENA, Calif. -- The Cassini plasma spectrometer instrument (CAPS)
> aboard NASA's Cassini spacecraft at Saturn has resumed operations. Mission
> managers received confirmation on Friday, March 16, that it was turned on.
> They plan to monitor the instrument for any unusual behavior.
> Last June, short circuits in the instrument led to unexpected voltage
> shifts on the spacecraft. As a precaution, mission managers turned off the
> CAPS instrument while engineers investigated the issue. The investigation
> led to the conclusion that tin plating on electronics components had grown
> "whiskers." The whiskers were very small, less than the diameter of a human
> hair, but they were big enough to contact another conducting surface and
> carry electrical current. Researchers are still trying to understand why
> whiskers grow on tin and other metals, but they know now that whiskers can
> grow in space and on Earth. It is believed that these or additional tin
> whiskers that may grow on Cassini cannot carry enough current to cause
> problems, but will burn out on their own like a lightweight fuse.
>
>
>
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