Dear David
In principle you are right. But sometimes it will be possible to solder
also below the liquidus temperature. Indeed the amount of solid phase of
SnCu2 at 235°C will be only in the range of 2% in the melt. You can
calculate that by the lever rule with the phase diagram for different
temperatures and compositions. From experience I can confirm, that we
have soldered successful with a SnCu3 alloy at 240°C. But I like to
concede, that this must not work for all assemblies.
sincerely
Mathias Nowottnick
Group Manager Joining Technology
Fraunhofer Institute IZM
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