New final finish stack including a custom nano-crystalline silver alloy for mobile connector systems with high cycling wear and powered environmental exposure requirements

摘要

Electronic interconnections frequently employ a combination of electroplated nickel or nickel alloy as a barrier layer to the substrate and electroplated gold as a topcoat. However, under extended mating cycles (>10) and potential bias in wet environments, these gold on nickel stacks often fail due to wear through and/or corrosion of the connector base substrate. This paper reports on a new custom-engineered, electroplated, nano-crystalline silver alloy (NCSA) material stack that differentiates itself from both traditional hard gold and other silver technologies by offering improved wear durability up to and beyond 10 mating cycles, as well as improved corrosion protection for immersion environmental exposures. Voltage-biased immersion tests involving common liquids such as perspiration and saline solutions as well as high cycling wear beyond 10 mating cycles have been conducted on a gold-on-nickel stack as well as two embodiments of the new NCSA final finish stack: 1) with the NCSA plated onto a nano-crystalline nickel-tungsten alloy (NCNA) as a barrier layer and 2) with the NCSA plated directly on the substrate with no nickel-based barrier layer. Both embodiments of the NCSA stack exhibited at least equivalent performance, and in some cases outperformed a standard gold-on-nickel stack in both wear durability and biased corrosion resistance.