Jim, There are many theories and proofs out there. The one thing I was interested in was that at temperatures above 450F, tin metal can alloy nickel at a small percentage. The pastes used would dictate temperature of reflow, but it is not known how these pastes would behave toward the nickel compared to tin metal. Let's say you were around 430F +/- 40F. What if the "black pads" are formed as the hot ones? A ternary or quaternary phase diagram of the metals would be useful (Sn/Pb/Au/Ni). Just speculating, Paul Wilson Plant Chemist / R&D Manager Circuit Center, Inc. 4738 Gateway Circle Dayton, OH 45440 Phone (937) 435-2131 Fax (937) 435-7698 http://www.circuitcenter.com ################################################################ 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 ################################################################