A critical assessment of the Sn-Ag-Cu phase diagram is available in the
following paper:

Experimental and thermodynamic assessment of Sn-Ag-Cu solder alloys
Moon KW, Boettinger WJ, Kattner UR, Biancaniello FS, Handwerker CA
JOURNAL OF ELECTRONIC MATERIALS 29: (10) 1122-1136 OCT 2000

If you would like an electronic version, please email [log in to unmask]

One important point to remember is that over very broad composition ranges,
many Sn-Ag-Cu alloys
contain less than 1% intermetallic phases above 217 degC.  It is not
expected that <1% solid phase will dominate wetting and spreading during
reflow, if the other 99+% of the solder is molten.  The issue then becomes
the ability of the paste system to wet under the reflow conditions of,
among other things, temperature profile and atmosphere (air vs. nitrogen).

The NEMI final report will give a detailed analysis of the effect of
composition on the pasty range and reflow.  Check the NEMI website for
further details of the project plan.
http://www.nemi.org/PbFreePUBLIC/index.html


**************************************
Carol A. Handwerker
Chief, Metallurgy Division
NIST
100 Bureau Drive Stop 8550
Gaithersburg MD 20899-8550
Office:(301) 975-6158
Fax:(301) 975-4553
e-mail:[log in to unmask]

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