Keith,
Do they see difference between various additives?

Regards
Ofer Cohen
Seabridge - a Siemens company 

> -----Original Message-----
> From: Leadfree [mailto:[log in to unmask]] On Behalf Of 
> [log in to unmask]
> Sent: Saturday, August 13, 2005 06:58
> To: [log in to unmask]
> Subject: Re: [LF] 96.5% Tin / 3.5% Silver vs. SAC305
> 
> 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.
> 
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