Hi David,

You asked about the stabilised Sn-0.7Cu eutectic to which I referred in an
earlier contribution to the forum.

As most people have found, the problem with the straight Sn-0.7Cu eutectic in
wave soldering is the high incidence of bridges (shorts) and sometimes rough
and cracked joints.   There is some evidence that these problems are
associated with the growth of the Cu6Sn5 intermetallic under the
non-equilibrium conditions obtaining in the exit area of the wave in a way
which interferes with the drainage of solder from the joint.   As you know it
is inadequate drainage of solder in the exit area that results in shorts.   A
way has been found of controlling the nucleation and growth of the
intermetallic so that it does not so detrimentally affect the drainage
process.   The resulting joints are also smoother and brighter than those
produced under comparable conditions with the straight eutectic.

A paper on this alloy will be presented by Nihon Superior's Executive
Director, Tetsuro Nishimura, at a conference in Hawaii later this year and I
am sure he will be happy to send you a copy after that conference.

Regards
Keith Sweatman
Nihon Superior Co Ltd

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