NASA Goddard Space Flight Center
Experiment 7: Matte Tin Plated IC Leadframe Examination

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Experiment #7: Ongoing

Examination of Tin Whiskers on Matte Tin Finished Leadframes

Purpose:
Several researchers and component manufacturers claim that "matte" (as opposed to "bright") tin plating on components effectively reduces (if not prevents) tin whisker growth. The rationale provided is that most matte tin plating processes produce a lower residual stress in the tin layer and larger sized tin grains when compared to typical bright finishes which are considered most prone to whisker formation.  While both of these attributes tend to reduce whisker propensity, NASA-GSFC has seen previous reports of tin whisker formation on "matte" tin plated components including reports of field failures attributable to whiskers from matte tin plated components. For this experiment, one IC manufacturer offered to donate samples of their current "matte" tin plated products to NASA-GSFC for ongoing examination.

Set-up:
Samples of three different surface mount package styles of "matte tin plated" Plastic Encapsulated Microcircuits (PEMs) were supplied to NASA-GSFC by one IC manufacturer for tin whisker evaluation (circa May 2001).  The exact date code and history of these components was not provided, but the manufacturer provided these samples to be representative of their current production processes.  Initial observations (as received) of the leadframes were made in June 2001 using both optical and scanning electron microscopy.  Subsequently, the samples were stored in a room ambient environment (~22 C, ~30%RH:  not rigorously controlled) for long term storage.  Repeat visual  inspections have been performed at approximately two month intervals.

Overall View of the Three "Matte" Tin Plated Plastic Encapsulated Microcircuits
Package Type #1 Package Type #2 Package Type #3

Results To Date (experiment is ongoing):

Initial inspection (June 2001) did not reveal any evidence of whisker formation for the 3 package types.
Parts stored in ambient environment (~22C, ~30% RH) for the entire experiment
Whisker Growth was observed on one of three package types (type #3) only on the heat-sink pads 6 months after the initial inspection.  The other two package types remain whisker free to date (April 2002).
SEM Photos of Heat Sink from Package Type #3 after ~6 Months of Ambient Storage

 
Responsible NASA Officials:

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

   Jong Kadesch/Orbital Sciences Corp.
   Jay Brusse/QSS Group, Inc.

Last Updated:

April 20, 2005

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