Hi Paul & John, The original question had to do with soldering only, when one looks at what is important for edge connectors other considerations become more important. I agree with most of John's response of 4/23. Au is not a good coating over Cu to preserve solderability and the primary reason is Au porosity and the oxydation of the underlying metal. That explains the time-dependent reduction in solderability as well as the increasing resistivity. But Au does not create a good "intermetallic bond between the solder, Au, and Ni"; this bond is brittle and weak and is the reason for gold embrittlement. In fact, proper reflow soldering with Au present should keep the solder liquid long enough that the AuSn intermetallics are as evenly distributed throughout the solder joint as possible to avoid the concentrations leading to gold embrittlement. Our problem is that we are trying to have one surface preparation do multiple functions—that typically means that one or all of these functions are performed less than optimally as compared to a single-function surface. But, we do live in the real world, where what is best is frequently too expensive. Werner Engelmaier Engelmaier Associates, L.C. Electronic Packaging, Interconnection and Reliability Consulting 7 Jasmine Run Ormond Beach, FL 32174 USA Phone: 904-437-8747, Fax: 904-437-8737 E-mail: [log in to unmask] ################################################################ 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 web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################