Contact Finish Considerations for High-Frequency Ground Connections

Fundamental literature and electromagnetic simulations show DC contact resistance values on ground connections of up to several ohms can be tolerated with little impact on signal transmission. This indicates traditional DC contact resistance failure criterion on the order of milliohms may be overly conservative for high-speed ground contacts, enabling consideration of lower cost electroplated contact finishes. Electromagnetic simulations at the connector level validated that signal integrity is intact with ground contact resistance values up to 1 ohm and beyond. Gold and a non-noble tin-nickel alloy exhibiting higher, yet stable electrical contact resistance as compared to typical contact finishes were evaluated using industry standard accelerated testing. Results indicate that with a relaxed DC contact resistance failure criterion, the lower cost ground tin-nickel alloy finish can deliver reliable signal integrity performance over the lifetime of a typical high-speed connector product.