Hi Bill - Please email me the photos but I have a couple of questions: 1) If gold is truely on the solder joint surface then it had to come from somewhere - what surfaces are in the vicinity of the diode during soldering that are gold coated? 2) When does this "gold" surface coating appear? After solder processes (reflow) or after ??????? Sorry for the obvious questions but having gold on the surface of a solder joint as the result of a reflow process is pretty tough to accomplish. Gold has a very fast diffusion rate in solder so if the solder joint had a gold coating to start with or was in contact with a gold finish then the gold would go directly into the solder joint itself rather than "deposit" on the solder joint surface. Getting gold (or other metals) to migrate onto a solder joint surface would take an electrochemical reaction - some reasonable temperature(s) (but not molten!) coupled with moisture (e.g. humidity). You gave one clue to what you might have - the use of a low residue material in a no-clean process mode. It has been documented that flux residues can give a solder joint a "golden" appearance (many of the old RMA fluxes if not removed properly could give this appearance). I recommend getting a scanning electron microscopy xray analysis of the solder joint - it will tell you definitavely if you truely have a "gold" coating or if you have an flux residue coating. Good Luck. Dave Hillman Rockwell Collins [log in to unmask] Bill Fabry <[log in to unmask]> on 06/23/98 02:00:16 PM Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to [log in to unmask] To: [log in to unmask] cc: (bcc: David D Hillman/CedarRapids/Collins/Rockwell) Subject: [TN] Gold Coated Solder Deat "Techies": I have a "GOLDEN" opportunity for the experts to shine. I have in my possession some SMT assemblies built on gold flash fabs that exhibit gold residing on the surface of the fillet, rather than being dissolved in the solder. The fillet is fully formed with no graininess or other visual anomilies. The phenomenon occurs on ONE end of a MELF diode, not on both ends. To answer the obvious question, it is NOT dependant on the diode polarity; it happens on either end but on one end only. I have digitally captured a couple of photos of the phenomenon. If you need pictorial representation, please e-mail me directly and I can attach it to a return e-mail. As you will see, the gold remains on the surface of the fillet, rather than being dissolved in the fillet. A slight scraping of the fillet surface will uncover the base solder with NO visual evidence of gold inside. Other terminations on other components do NOT exhibit this phenomenon. The assembly subcontractor is using standard NO-CLEAN solder paste (OMG Americas 500ADV NO-CLEAN 63SN). Unsoldered parts show a tin/lead termination, indicating that the gold has possibly migrated over the entire termination. My question: What mechanism is at work to keep the gold from totally dissolving into the Sn/Pb paste after it leaves the fab during reflow? Thanks for the help. Bill Fabry, Sr. Manufacturing Engineer Plantronics, Inc. 345 Encinal Street Santa Cruz, Ca. 95060 (408) 458-7555 [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 technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################ ################################################################ 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 technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################