Thermomigration

Thermomigration, also called the Sorét effect, is the diffusion of materials due to a thermal gradient. For example, impurity ions may move from the cold side of a semiconductor wafer towards the hot side, since the higher temperature makes the transition structure required for atomic jumps more achievable. The diffusive flux may occur in either direction (either up or down the temperature gradient), dependent on the materials involved.

See also Mohd Foad Abdul Hamid "Thermomigration: An Experimental Damage Mechanics Study on Nanoelectronics Lead Free Solder Alloys", Ph.D. Disseration submitted to the State University of New York at Buffalo, 2008