Corrosion Behavior and Mechanism Analysis of Switch in ALT Environment

The ammeter was functional failed due to the poor contact of the switch used in ammeter during accelerated life test (ALT). The failure behavior and mechanism of switch in ALT environment were studied by resistance test, scanning electron microscope equipped with energy dispersive spectroscopy and focus ion beam. The results indicate that the failure site of switch is in contact surface of contact. This because the Ag plating is too thin in pits in contact surface to protect the Cu substrate, and the corrosion product of Cu substrate is high resistance, which leads to the poor contact between terminal and contact. The failure mechanism is that both the oxidation of Ag plating itself in pits and the formation of many galvanic cells on the Ag plating in ALT environment could accelerated the corrosion of Ag plating and Cu matrix especially in pits. To prevent the failure of contact in ALT, it should decrease the roughness of Cu substrate of contact and increase the Ag thickness on contact.