A coated electrically conductive substrate has particular utility where
there are multiple closely spaced leads and tin whiskers constitute a
potential short circuit. This electrically conductive substrate has a
plurality of leads separated by a distance capable of bridging by a tin
whisker, a silver or silver-base alloy layer coating at least one surface
of at least one of the plurality of leads, and a fine grain tin or
tin-base alloy layer directly coating said silver layer. An alternative
coated electrically conductive substrate has utility where debris from
fretting wear may increase electrical resistivity. This electrically
conductive substrate has a barrier layer deposited on the substrate that
is effective to inhibit diffusion of the substrate into a subsequently
deposited layers, which include a sacrificial layer deposited on the
barrier layer that is effective to form intermetallic compounds with tin,
and a low resistivity oxide metal layer deposited on the sacrificial
layer.An alternative coated electrically conductive substrate has
particular utility where debris from fretting wear may oxidize and
increase electrical resistivity, such an in a connector assembly. This
electrically conductive substrate has a barrier layer deposited on the
substrate that is effective to inhibit diffusion of constituents the
substrate into a plurality of subsequently deposited layers. The
subsequently deposited layers include a sacrificial layer deposited on
the barrier layer that is effective to form intermetallic compounds with
tin, a low resistivity oxide metal layer deposited on said sacrificial
layer, and an outermost layer of tin or a tin-base alloy directly
deposited on the low resistivity oxide metal layer.In this alternative
embodiment, the barrier layer is preferably nickel or a nickel-base alloy
and the low resisitivity oxide metal layer is preferably silver or a
silver-base alloy.When heated, the coated substrate of this second
embodiment forms a unique structure having a copper or copper-base alloy
substrate, an intervening layer formed from a mixture or metals including
copper and tin, and an outermost layer which is a mixture of a copper-tin
intermetallic containing phase and a silver-rich phase. It is believed
that this silver-rich phase is particularly beneficial to reduce an
increase in resistivity due to oxidation of fretting wear debris.