Meaning
Gradual increase in the electrical resistance across a closed contact interface occurs over time under thermal or environmental stress. This change, known as contact resistance drift, typically arises from oxidation or micro-motion at the mating surfaces. It causes localized heating and signal attenuation in RF coaxial connections.
Thermal Instability
Accelerated chemical reactions at the mating interface drive the progressive degradation of electrical joints. While noble metal platings resist direct oxidation, diffusion of underlying base metal through the thin protective layer establishes a non-conductive oxide film at the contact points. This surface film restricts current flow to a smaller number of microscopic contact spots, which increases local current density and causes localized heating.
Standard environmental tests use elevated thermal exposure to simulate this behavior over a ten-year operating life in telecommunication equipment.
Degradation Metric
Measurement of this phenomenon requires high-precision micro-ohmmeters operating under dry circuit conditions. Testing must limit the voltage to twenty millivolts to avoid puncturing the thin oxide films that cause contact resistance drift. Acceptable drift limits are defined in product specifications as a maximum percentage increase from the initial value.
Mitigation Strategy
Plating with diffusion barriers like nickel suppresses the migration of base metal atoms to the contact surface. This barrier extends the operating life of high-reliability connector assemblies in industrial environments. Adequate contact force must also be maintained to disrupt minor surface films mechanically.
