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.        *
***************************************************************************