Anecdote #7: Tin Whiskers on RF Shield/Bracket

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Anecdote #8:  Tin Whiskers Detaching from RF Shield (Bracket) and Producing Electrical Short Circuits Found at End-Of-Line Testing

The images and video below describe failures found during end-of-line testing caused by tin whiskers detaching from tin-plated RF shields (brackets). The whiskers are electrically conductive and some bridged across exposed conductors within the assembly producing electrical short circuit anomalies detected at end-of-line testing.

Video Describing This Tin Whisker Experience

bracket-overall.jpg (838117 bytes)
Tin-Plated Steel RF Shield/Bracket (copper underlayer)
tin-whisker-bracket.jpg (140362 bytes)
Tin Whisker Found on Bracket
tin-whisker-shorting-connector.jpg (162337 bytes)
Tin Whisker Detached from RF Shield/Bracket which then bridged exposed conductor pins of connector within the module covered the shield.
Connector Pitch is 100 mils.

During end-of-production-line testing of electronics assemblies, multiple functional test failures (electrical short circuit / low resistance) were identified.

Investigation found that tin whiskers growing from RF shields/brackets became dislodged during the electronics assembly process.  The loose whiskers were scattered onto un-insulated pins of a nearby connector producing undesirable short circuits

The RF shield was tin-plated steel with an intermediate copper barrier layer between the tin and steel. The user of this RF shield had specified that a nickel barrier be used instead of copper; however, the product was not built to specification.

Within 5 to 6 months of plating these RF shields, thousands of tin whiskers had formed with many of them extending as long as 2.5 millimeters or more.

During the assembly process where these shields were being installed over the electronics module, the assemblers were unaware of the presence of tin whiskers on the shields. This is not surprising since tin whiskers can be extremely difficult to see with the unaided eye due to their extremely narrow cross sections (typically only a few microns or less across).

Failure analyses of modules that failed end-of-production-line testing identified detached tin whiskers had bridged exposed conductors in the assembly producing the observed electrical faults. In one example, a tin whisker bridged adjacent connector pins whose pitch was 100 mils.  As a result of the failures, a careful inspection of the module was performed at which point  the extensive tin whisker growth on the RF shields as well as loose tin whisker debris scattered within the module were identified as the root cause of the problems observed.

Source: Anonymous

Responsible NASA Officials:

   Michael Sampson/NASA GSFC Code 306
   Dr. Henning Leidecker/NASA GSFC Code 562
Additional Researchers: 

   Jay Brusse/Perot Systems
Jong Kim/Orbital Sciences Corp.

Last Updated:

August 3, 2009

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