FRETTING AND WHISKER RESISTANT COATING SYSTEM AND METHOD

摘要

A coated electrically conductive substrate (26) where there are multiple closely spaced leads (10) and tin whiskers constitute a potential short circuit. Such substrates (26) include leadframes, terminal pins and circuit traces. This electrically conductive substrate (26) has a plurality of leads (16) separated by a distance (14) capable of bridging by a tin whisker, a silver or silver-base alloy layer (28) coating at least one surface, and a fine grain tin or tin-base alloy layer (30) directly coating said silver layer. An alternative coated electrically conductive substrate (26) has particular utility where debris from fretting wear may oxidize and increase electrical resistivity, such as in a connector assembly. This electrically conductive substrate (26) has a barrier layer (32) deposited on the substrate (26). Subsequently deposited layers include a sacrificial layer (34) deposited on the barrier layer (32)that is effective to form intermetallic compounds with tin, a low resistivity oxide metal layer (40) and an outermost layer (36) of tin or a tin-base alloy. The barrier layer (32) is preferably nickel or a nickel-base alloy and the low resisitivity oxide metal layer (40) is preferably silver or a silver-base alloy.