High Temperature Resistant Gold Alloys for Switching Signal Relay Contacts

Abstract

Most telecom/signal relays are of the surface-mounted type nowadays. Since the introduction of lead-free soldering processes, the temperature exceeds 260degC during the soldering process. In a growing share of applications, these relays are additionally used in high-temperature environments such as motor compartments. Regardless of the high ambient temperatures of up to 125degC at which the relays are operated, there are unchanged requirements of the stability of the contact resistance, with target values of less than 10 mOmega deviation during the entire lifetime. In order to achieve low and stable contact resistance, the type of gold alloy and the way the gold layers are processed are of major importance. Sputtered and diffused gold layers showed better performance at high temperatures than rolled gold layers as well as gold alloys with no or very low concentration of non- precious metals. But not only the top layer has an impact; the base material too has a major impact on the contact resistance stability. PdRulO as base material resulted in much better contact resistance stability than AgNi20. When these contact materials are used in telecom/signal relays even at high ambient temperatures, extremely low and stable contact resistance values can be achieved for a long period of time.