Hi Michael! Turkeyday in Iowa was only 70F but we didn't' complain! The
answer to your question is pretty simple: you will get a solder alloy which
lies somewhere between the two alloy compositions you start with. The tin
content will be in  the 63% - 90% range and you Pb content will be in the
10%-37% range provided the soldering operation allows for the normal
diffusion/mixing mechanisms to take place. Some folks consider this a
problem because finding or understanding the reliability characteristics of
this "new" solder alloy can be difficult. Other folks just evaluate the two
alloys (the Sn63 and Sn90) for their reliability characteristics/merits and
if both alloy data sets fit their use environment then they assume the
"new" alloy won't cause them any issues. The use/combination of different
solder alloys for solder joints can be a pretty involved topic - I don't
know of a lot of published information on the subject. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]





"Alderete, Michael" <[log in to unmask]> on 11/25/98 04:55:05 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to "Alderete, Michael" <[log in to unmask]>

To:   [log in to unmask]
cc:
Subject:  [TN] ASSY:mixing of high and low-temp PbSn alloys




Dave Hillman, et al...
1st, Happy Thanksgiving to all on TechNet.

QUESTION: at "normal" soldering iron temperatures, what happens when you
melt a eutectic solder preform (p/o clip lead) together with hi-temp, 90
to 94% Sn (bal=Pb) solder?
Will the two solders alloy, or just form a mixture? Please provide as
metallurgically correct an answer as possible.

Thanks in advance

Michael Alderete
Aerojet, Azusa (So.) CA

...it's going to be about 80F here tomorrow. Hope you'll still answer
this question on solder mixtures.

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