Addressing the challenges in solder resistance measurement for electromigration test

In the continuous drive for smaller chips with more functionality, I/O counts and power requirements increase. This leads to a growing concern on the electromigration (EM) reliability of solder joints in the high-density flip-chip package. For solder EM tests, it is a great challenge to detect early EM failure since the 10% change in resistance is very small due to the small initial resistance of the solder. Furthermore, the small change in resistance can often be masked by the parasitic resistance in the interconnect connecting the solder daisy chain type structures commonly employed in EM tests. The Wheatstone bridge method has been reported to address the inaccuracy associated with the use of Four-probe measurement method in solder EM tests successfully. In this work, we describe the use of Kelvin double bridge configuration that can further increase the accuracy of the bump resistance measured.