A coated
electrically conductive substrate has particular utility where there are multiple closely spaced leads and
tin whiskers constitute a potential
short circuit. Such substrates include leadframes, terminal pins and circuit traces such as on printed circuit boards and
flexible circuits. 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 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.