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August 2004

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Subject:
From:
"Ingemar Hernefjord (KC/EMW)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Ingemar Hernefjord (KC/EMW)
Date:
Mon, 2 Aug 2004 13:20:03 +0200
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August 2, 2004

We have reported to NASA a unique tin whisker growth in Ku-band waveguide's entrance flanges (tubes for leading electromagnetic waves, all are not familiar with microwave things of cause). The US maker had occasionally plated inside of tube entrance with pure Tin instead of the usual chromate (our spec wasn't quite readible either)and after just a few weeks in stock, the entrance of the waveguides had a 'curtain' or 'beard' of up to 5 mms long whiskers. The number of babywhiskers were thousands. The manufacturer makes new waveguides, no problem, but we had a need for several pcs immideately, so we did the following: dipped the outermost part, the mounting flange,  in an acidous solution with U/S agitation for just a few seconds, hopefully enough to reorganise and eliminate the built-in stress in the tin flakes, some fraction of a micron to one micron deep. All whiskers vanished instantly, even the short and chubby babywhiskers. Then we cleaned thoroughfully in Vigon and dist!
 illed water.

Telling you this as a curiosa, bet no others have seen such whiskers in a waveguide. Don't copy our recipe, designed more on guessing than on science! But it worked...

Ingemar Hernefjord
Ericsson Microwave Systems



-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of - Bogert
Sent: den 31 juli 2004 17:14
To: [log in to unmask]
Subject: Re: [TN] Tin Whiskers


July 31, 2004

We had a military application wherein a tin plated box with electronics included therein had numerous tin whiskers growing therein.  Since we had numerous fielded equipment we did not want to scrap, we repaired it by cleaning off the tin whiskers and then conformal coating with Type UR. Since that was done we had no further tin whisker problems.  However, that does not necessarily mean that conformal coating prevents tin whisker growth.  It could have been that once the tin whiskers were removed, the initial whisker growth removed the internal stress, and therefore, once the whiskers were cleaned off, no further whisker growth was noted, independent of whether or not we conformal coated the box.
  ----- Original Message -----
  From: David Douthit<mailto:[log in to unmask]>
  To: [log in to unmask]<mailto:[log in to unmask]>
  Sent: Monday, July 26, 2004 10:46 AM
  Subject: Re: [TN] Tin Whiskers


  Edwin,

  NASA did some experiments and have pictures on their web site
  (   http://nepp.nasa.gov/whisker/index.html<http://nepp.nasa.gov/whisker/index.html>  )  of whiskers "punching"
  through
  coatings. I don't know if the coating "inhibited" growth (time, length,
  or amount).

  David A. Douthit
  Manager
  LoCan LLC

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