Hi LK & others, You asked for a rebuttal—here it goes. Just throwing [[[[[[THERMAL STRESS]]]]]] around is neither elegant nor simple—simplistic, maybe. And referring to evidence without stating what the evidence is, what it represents, and under what circumstances it was obtained proves nothing and only serves to obfuscate. One always needs to precisely define what one is talking about and the original statement did not confine itself to HASL, but included all soldering processes the way I read it anyway. My statement addressed multiple reflow passes. (1) I certainly agree that if one HASL pass shows poor wetting, multiple passes will not improve things as far as solderability is concerned. (2) The quality and shelf life of a HASL'ed surface will depend on the thickness of the solder layer above the IMC layers and the storage conditions. (3) If a second HASL pass is necessary, because too much solder remains and forms too much of a meniscus for component placement, a second pass will result in a somewhat thicker IMC layer. But that has no impact on quality and reliability as long as the solder layer above the IMC is thick enough (~2-3 micro-meter plus) to avoid that the layer above the IMC is not mostly lead- rich phase (higher Liquidus temperature) or to prevent the IMC growing through the solder layer (no solderability). (4) Reflow soldering passes, even multiple ones, will not degrade either the quality or long-term reliability of solder joints if adequate wetting has taken place, because the slightly thicker Cu6Sn5 IMC layer has no impact on long-term reliability of the solder joints (these IMCs are much stronger than solder); I have seen many solder joint failures because of inadequate wetting, but never one because of excessive IMC layer growth in a finished well-wetted solder joint. The reflow temperatures are typically low enough (certainly lower than the HASL temperature) not to affect the PCB. (5) I agree that manual soldering operations—single or multiple ones—can result in a significant degradation of pad and inner laminar bond strength; in fact, it is the manual soldering operations, where frequently soldering irons with no temperature limits are used, where most damage due to PTH barrel cracking, post separation, pad lifting, etc., occurs. None of the examples of degradation/deficient quality that were cited, are caused by multiple solder process passes, but result from other problems (oxidation, contamination, cranking up the solder temperature, slowing down the conveyor, boards and processes defective, etc.). Most of the horror stories that I have seen over the years result from inadequate designs and bad incoming materials/components; processing errors, while they can occur to fix some problem, are a relatively small part of the picture. The problems can be inadequate solderability, lack of information of what materials are being soldered (BeCu, Alloy 42, Ni, Pd, Sn/Pb plating, solder coating, etc.), inadequate protection of components/PCBs during shipping, etc. 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'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 ################################################################