Thermomigration in Eutectic Two-Phase Structures

When an inhomogeneous binary solid solution (or alloy) is aimealed at constant temperature, it tends to become homogenous. On the contrary, if a homogeneous binary solid solution is annealed in a temperature gradient, the opposite happens 

We discuss here thermomigration in eutectic two-phase structures, such as the SnPb solder. It is very different from the Soret effect. The change in concentration in the two-phase structure under a fixed temperature does not mean any change of 

However, when the composite solder joints were subjected to thermomigration, a substantial segregation of Sn and Pb occurred in the joint A temperature gradient of about 1000 K cm , or a 10 °C difference across a flip-chip solder 

When an electron microprobe was used to measure composition distribution across a polished cross section of the flip-chip sample after thermomigration, a 

Distance from the copper line on chip side (pm) 

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