Degradation Mechanisms in Tin- and Gold-Plated Connector Contacts

Degradation mechanisms in tin-plated contacts (Sn contacts) and gold-plated contacts (Au contacts) are clarified. Contact resistance and corrosion characteristics for both types of contacts are investigated and compared. Contact resistance is more stable for Sn contacts than for Au contacts in a SO2+ NO2+ C12atmosphere. This is because relatively few corrosion products are formed on Sn contacts. Also, the surface films formed on Sn contacts shatters more easily upon plastic deformation. Corrosion experiments in atmospheres containing different combinations of SO2, NO2, and Cl2demonstrate that two types of corrosion processes take place in plated contacts. One is surface corrosion which occurs when the surface finish is severely attacked by a corrosive atmosphere. The other is pore corrosion which occurs when the underplating materials are attacked to a greater extent than surface corrosion. Both processes occur in Sn contacts and the former is dominant in atmospheres containing Ci2. On the other hand, only pore corrosion occurs in Au contacts. Furthermore, galvanic corrosion either enhances or inhibits the formation of outcroppings in the pore corrosion process, depending on the electrode potential of the surface finish and underplating materials.