This is a very late response but Iver Anderson's team at Iowa State
University are doing very interesting work that includes study of the effect of
quaternary additions on the solidification and the subsequent stability in the solid
state of the Sn-Ag-Cu eutectic.    These modifications do affect the
sensitivity of the microstructure to cooling rate.    The non-equilibrium
microstructures that develop during solidification largely arise because of the difficulty
of nucleating one of the phases predicted by the thermodynamics.   It is
usually the intermetallics that are difficult to nucleate which is why a
theoretically eutectic composition ends up with a microstructure dominated by primary
tin dendrites (with consequent grainy finish and shrinkage cracks).   Amongst
other things the quaternary additions seem to lower the free energy of
nucleation of those intermetallics so the alloy can freeze more like the eutectic it is
supposed to be.

Keith Sweatman
Nihon Superior Co., Ltd.

-------------------------------------------------------------------------------Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL)
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-------------------------------------------------------------------------------