Keith:

Thanks for the distinction. I'm more accustomed to thinking of the solder/surface interface
when intermetallic comes up.

Best wishes,
Jim Smith
Cambridge Management Sciences, Inc.

Keith Sweatman wrote:

> Jim,
>
> The Sn-Cu equilibrium phase diagram indicates that the two phases present at
> room temperature in the eutectic that occurs at around 0.7% Cu are beta-Sn
> and the intermetallic compound, Cu6Sn5 (that "6" and "5" should be
> subscripts).  That is the intermetallic I am referring to.   Under
> non-equilibrium conditions and if the Cu content is hypereutectic there will
> also be some primary intermetallic as well as eutectic intermetallic.
> This intermetallic is clearly visible in cross-sections of soldered joints
> and is distinct from the intermetallic layer that forms at the
> solder/substrate interface as a result of interaction between the tin in the
> solder and  the substrate metal.
>
> Regards
> Keith Sweatman
> Nihon Superior Co Ltd
>
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