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

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 (>10³) 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 10⁴ 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 10⁴ 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.