Gold-tin interconnections will degrade at Class I environmental levels (Class I as described by the Battelle Environmental Study Group (BESG)) as a result of corrosion (i.e. fretting corrosion). Gold-tin interconnections are more susceptible to corrosion than tin-tin interfaces. Gold plating, as a noble finish, is free of surface films. (This is true as long as the application (i.e. plating) of the noble metal is continuous and thick enough to prevent diffusion of the base metal to the surface (this includes diffusion through an underplate, such as nickel, as well).) Tin and tin-lead plating, non noble finishes, will always have some amount of surface film (oxide) present. (This is true if no lubricants are present.) Tin, being softer than gold, will transfer to the gold surface during the mating/unmating cycle and the ever present surface oxides on the tin will transfer as well. The mating/unmating cycles will continue this build up of oxides until it becomes an insulator. In the case where the "spring" half of the interconnection is gold plated, the contact normal force is normally specified (or designed) for mating to another gold plated surface. If this gold plated "spring" member is now mating to a tin plated surface, the normal force (and wiping action) may not be enough to "break through" this oxide film. Martha Rupert AMP Incorporated ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################