Dave Hillman is absolutely right-- the appropriate phase diagrams show that the real eutectic Sn/Pb solder is 61.9%Sn/38.1%Pb (mass percent) (MP=183C), just as 62.5%Sn/36.1%Pb/1.4%Ag (MP=179C) is one of the true eutectic mixtures of this ternary alloy system. However, 63Sn/37Pb (Solidus=183, Liquidus~185 to 186C) and 62Sn/36Pb/2Ag (S=177C, L=189C) have become the 'nominal' industry eutectics. In both cases the difference between solidus and liquidus may be small enough, that for practical purposes the existence of a pasty temperature range may be negligible. However, 62Sn/36Pb/2Ag a 177C solidus--189C liquidus difference is not exactly small and could make the difference between adequately wetted and inadequately wetted solder joints. Werner Engelmaier Engelmaier Associates, Inc. Electronic Packaging, Interconnection and Reliability Consulting 23 Gunther Street Mendham, NJ 07945 USA Phone & Fax: 201-543-2747 E-Mail: [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************