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Solder Phase Equilibrium


Solder Phase Equilibrium | 24 August, 2000

At room temperature, how long does it take for the phases of a common tin (Sn) / lead (Pb) solder, say 60/40, to reach equilibrium?

While the materials are diffusing toward equilibrium do the material properties of the solder change significantly?

How is the phase equilibium time for a indium (In) / tin (Sn) solder different?

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Dr. Ning-Cheng Lee


Re: Solder Phase Equilibrium | 24 August, 2000

Depending on the stress condition experienced by the solder joints. For joints under a greater stress, the time to reach equilibrium can be shorter. Of course, the change is also more significant in phase structure. For low stress conditions, it may take several years. For high stress conditions, it can be less than several months.

Yes, the material properties do change significantly. Usually, the change is toward a larger grain size, hence a joint more prone to fail.

For In/Sn solder, the solder exhibits superplastic behavior in creep, and has a longer isothermal fatigue life than non-superplastic materials. There is no microstructure change like coarsening and recrystallization that occur in Sn63.

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