Noble platings are characterized exclusively by the pure gold or gold alloy used as the final
plating in the system. By their nature, gold plating systems reign supreme for signal applications
since noble materials do not corrode or oxidize and, therefore, maintain very low resistance
interfaces. Pure gold, being very soft, is seldom used alone and is typically alloyed with cobalt or
palladium to increase the hardness of the surface. Contact interface normal forces can be very
light with gold (50 grams or less) making it very desirable for high-pin count connector systems,
where the combined mating and unmating forces can be quite significant.
Since gold plating is costly, gold plating on contacts is very thin and, in a number of instances,
very selectively placed on the contact interface. Figure 3 shows some strategies in plating. As
gold prices escalated, plating the entire contact (a) became prohibitive. Selective plating (b),
where gold is applied only in the areas where it will benefit the electrical performance, is
increasingly common. Another approach is dual plating (c), where gold is applied at the
separable interface and tin is used for permanent soldered or press fit connections, further
reducing the use of gold without decreasing performance.
Figure 3. Approaches to plating to reduce gold without decreasing performance.
Gold plating is almost always applied over some type of barrier plating, most often nickel, to
minimize pore corrosion (Figure 4). While the gold itself does not corrode, pore corrosion results
