Electromigration induced resistance decrease in Sn conductors

The behavior of Sn conductors for Pb-free solder applications was investigated. Thick film Sn conductors were deposited onto a Ni/Cr underlay and studied under electromigration testing conditions. The calculated driving force was found to be very low. The results suggests that the observed behavior is due to an electromigration induced change in the orientation of the Sn microstructure that reduces the resistivity with time in the direction of electron flow.