Interesting Behavior in Sn During Electromigration Testing
IBM T.J. Watson Research Center
Yorktown Heights NY 10598
The resistance of thick film (2 mm) Sn conductors deposited on Ni and Cr underlays was found to decrease several percent during electromigration stressing. Sn deposited directly onto SiO2 did not always exhibit this behavior. The observed resistance decrease was not purely thermally induced. The application of DC was necessary to initiate the resistance decrease. Equivalent AC current (RMS values equal) did not produce the effect. A model where the electromigration induced stress gradient and the anisotropic electrical and mechanical properties of Sn are responsible for the observations is presented.