Quantitative measurement of the degradation of EMI shielding and mating flange materials after environmental exposure

A test program that demonstrated that the electrical degradation of a conductive elastomer-aluminum flange joint could be determined using shielding effectiveness measurements is described. Two tests were developed. One measures the degradation of shielding effectiveness of a simulated gasketed enclosure seam (test set). Shielding effectiveness measurements are made at frequencies up to 10 GHz. The second test method yields a quantitative scale of conductive elastomer corrosivity (galvanic compatibility) and a quantitative measure of DC electrical degradation of the conductive elastomer. The tests demonstrated that a Ag-Al gasket/aluminum flange joint was more stable than a nickel-coated graphite gasket/aluminum flange joint after 192 h of sulfur dioxide salt fog exposure. This result reflects the greater stability of the Ag-Al gasket and the better galvanic compatibility of the Ag-Al gasket with the aluminum flange.<
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