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 INTERNETALLIC 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 RESISTIVITY OXIDE METAL LAYER (40) IS PREFERABLY SILVER OR A SILVER-BASE ALLOY.