Effects of corrosion on the electrical properties of conducted finishes for EMI shielding

A variety of combinations of fingerstock materials both before and after exposure to an accelerated atmospheric corrosion environment was tested. The following materials/finishes were tested during this study: 304 stainless steel, passivated, MIL STD QQ-P-35B; 1010 steel, electroplated bright tin, 0.0003 in. nominal coating thickness, ASTM B545; 1010 steel, electroplated nickel 0.0005 in. nominal coating thickness, ASTMB689; 1010 steel, electroless nickel, 0.0005 in. coating thickness; 1010 steel, zinc-plated, 0.0005 in. plating thickness with yellow chromate conversion coating; 1010 steel, zinc-plated, 0.0002 in. minimum zinc thickness, with blue-bright chromate conversion coating; electrogalvanized steel, 0.0007 in. zinc thickness, with yellow chromate conversion coating; steel with hot-dipped aluminum-zinc (55:45) coating, 0.0008 in. coating thickness; 5052 aluminum, with yellow chromate conversion coating; and 5052 aluminum, with clear chromate conversion coating, ASTM B449, class 3. Metal panels were mated with beryllium copper fingerstock to make the joints typical of computer enclosure doors and panels. The finishes on the beryllium copper were: electroplated bright tin; electroplated bright nickel; electroplated tin-lead (60:40); and bright dip (a thin chromated conversion coating). The transfer impedance of the joint was used to measure the electrical performance and then the corrosion resistance of the conductive finishes