Keith:

Your posting is very interesting. I'm not certain I understand which Cu6Sn5 intermetallic you
mean. I'd be grateful for clarification.

Jim Smith
Cambridge Management Sciences, Inc.
St. Petersburg, Florida

Keith Sweatman wrote:

> 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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