High temperature resistant galvanically deposited gold layers for switching contacts

Due to new environmental requirements, all electronic components must be able to withstand peak soldering temperatures up to 265 °C. In the worst case scenario, this temperature is applied 3 times. In order to make electromechanical relays resistant to the soldering heat during manufacture, the products are pre-aged by applying the same peak temperature, but usually for a longer duration. This temperature stress results in a high risk of oxidation of gold alloys, e.g. when they are galvanically deposited, as only a limited number of alloys can be deposited using galvanic processes, and a gold-gold combination is not suitable for switching contacts due to a high tendency towards cold welding. A method of protecting galvanically deposited gold alloys from oxidation has been developed. In order to prevent the formation of nickel- or cobalt-oxides, the gold layers were protected by a very thin layer of palladium (0.075μm). In addition, a further improvement can be achieved by adding an even thinner layer of pure gold (0.005μm). These layers make AuNi and AuCo alloys resistant to temperatures of 265 °C, so no significant changes in contact resistance were observed any more, even during prolonged storage at high temperatures. Due to the minimum thickness no significant precious metal costs are involved. Adding a thin Pd layer hardens the pure gold layer and efficiently prevents from cold welding. The performance during service life at temperatures up to 110 °C was not affected by the additional layers.