Environmental effects on the electrical performance of silver contact-substrate systems

In this work, commercial silver metal contacts welded on top of brass or silver plated copper substrates have been exposed to air rich in SO/sub 2/ and air rich in NaCl. Scanning Electron Microscopy (SEM) and Energy Dispersive Analysis (EDA) of the exposed contact surfaces were performed to identify the corrosion byproducts on top of the silver contacts, substrates, and welding materials. Surface corrosion products were mainly found to consist of small spherules of Cu-Zn or Ag-Cu compounds which cover the surface of the contact proper with low adhesion properties. They mainly originate from under the plating of the substrate or from the welding materials. Electrical characterization of the contacting materials was based upon DC temperature overheat tests, current switching cycle tests, and energy storage during AC current excitation. The experimental results show that the operating environment is indeed a very significant parameter determining the overall performance of the electrical contacts. New design rules as well as material selection properties may have to be systematically considered to allow for electrochemical induced degradation in heavy pollutant operating environments.