A Method for Power Rating Contacts using Voltage Drop

A method of using accelerated testing and change in voltage drop (or resistance) after aging is proposed in rating the performance of power contacts. It was shown in previous papers that change in voltage drop exhibits a threshold for stability for various materials. This feature is employed in a method that monitors voltage drop (or resistance) through life testing. Moreover, a statistical model for the end-of-life change in voltage drop is recommended to establish reliability. The steps necessary to achieve this are laid out in terms of material ratings, operating temperatures, accelerated tests, voltage drop measurements and failure criteria. The present paper expands on previous work by extending the analysis of the existing data base. In this case, samples were exposed to thermal aging and current cycling which produced degradation at various current levels. Processes such as stress relaxation, diffusion, electro- migration and oxidation are believed to be accelerated under the conditions used. In this work, several current levels were used to accelerate the progression of degradation at different rates. In addition, these results were analyzed using basic contact theory in conjunction with statistical modeling. Moreover, current density and contact voltage (or contact resistance) are discussed as basic physical parameters that provide links to aging and failure criteria. It was shown how current density can be related to design features and material properties to provide a method to determine change in resistance failure criteria for various designs. It is believed this methodology can be applied to various contact materials to quantify the rating of power contacts.