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Old 23rd Sep 2005, 7:38 pm   #9
Paul Stenning
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Default Re: Whiskers in germanium transistors etc

Quote:
Originally Posted by darren-uk
Must now find out if AF117 etc transistor cases are tin or zinc plated on the inside.
I emailed the contact address on the website with brief details plus a copy of the email and photos from Chris Walter, and received the following reply:
Quote:
Dear Paul,

We are pleased that our metal whisker www site has been useful to you and hopefully your colleagues as well once you've made them aware of it's location.

Would you and your colleagues be interested in having an "anecdote" of your observations posted within the NASA www site? I would simply use your note below as the foundation along with the 2 images you provided.

For examples of other whisker anecdotes we've posted, see:
http://nepp.nasa.gov/whisker/anecdote/index.html

Also, if any of the subject transistors could be provided to me, I could easily have a materials analysis performed to determine if these are tin, zinc, cadmium or other form of metal whiskers. If so, I could provide you with mailing information, etc. We'd gladly share any info we produce from such specimens with your club.

Sincerely,
Jay

P.S.-- I'm a little delayed in posting links (or anecdotes) I've heard from a few other "radio" enthusiasts related to their whisker experiences. Their interests are in 2-way (HAM) type radio applications in which they've noted whiskers (zinc and possibly tin) have impacted the performance of older models.

See for example -- http://www.repeater-builder.com/ge/mastrIIcasting.html
While the note on the above page identifies these as TIN whiskers, I have subsequently acquired info that leads me to believe this is misidentified and that they are really ZINC whiskers in this case.
Later I received a further email from another member of the team:
Quote:
Dear Paul,

The two images you provided show a fine set of whiskers. I second Jay's remark that we could carry out an assay to determine the kind of metal; this is non-destructive to the part (but we might need to remove a whisker), and we would return the part to you along with a copy of the analysis.

The analysis instrument of choice is a Scanning Electron Microscope
(SEM) for imaging at powers up to ~10,000X, although mostly we would work at ~1,000X and even lower. This SEM has an EDAX attachment: the electrons in the scanned beam have sufficient energy that they drive inner-shell electrons out of the atoms at the surface of the object being examined. As other electrons flood back to fill the just-created vacancy, x-rays are emitted. The energy of these x-rays is uniquely related to the specific element, so we can read off the abundance of elements present on the surface of the specimen, with a spacial resolution of micrometers. (This does not make the specimen radioactive, or harm it.)

But the goo visible inside these transistor packages might outgas fast enough when placed into the SEM's vacuum chamber to interfere with the beam --- hard to tell from these images. If so, then we would extract a single whisker and examine it.

Best,
Henning Leidecker
I have several NOS AF115s here so I will take them up on their offer and send them a couple for analysis. I am not bothered whether they are returned or what state they are in.

I suspect the team at NASA are interested in getting hold of any samples they can to help with their research, which is why they are so keen to investigate this for us. Otherwise why would NASA be remotely interested in helping a group of vintage radio collectors?

I will also take them up on the offer of an "anecdote" on their website, if this is appropriate once we have further information on the material used.
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