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.
