Accelerated Testing Methods for Electromigration-Based Failure in Solder Joints

Abstract

Rapid and aggressive advancements in the electronics and packaging industry have led to the emergence of electromigration as a failure mode of concern. As electronic footprints have decreased, current densities have increased, placing electromigration-based degradation well within the functional lifetimes of interconnects in modern electronics. Thus, the demand for novel materials resilient to electromigration has increased. This work presents the development and demonstration of experimental platforms and a testing methodology for rapid reliability testing of interconnect materials. The testing methodology emphasizes optimizing measurement sensitivity versus experimental simplicity. This work then shows a comparison between dissimilar interconnect materials. The methodology is then compared to established standards of electromigration testing – such as JESD202 and Arrhenius plotting – used by consortia and regulatory bodies. Two types of specimens were electrically stressed to yield resistance over time datasets: SAC305 solder paste specimens with an approximate paste volume of 0.0187 mm3 deposited onto 450 μm diameter ENIG pads, and initial as-reflowed resistance between 0.187 mΩ and 0.298 mΩ, and aluminum wire on gold metallization wedge-wedge wire bond contact pad specimens: A custom printed circuit board (PCB) was designed to enable simultaneous electrical stressing and low-level voltage measurements of the screen-printed solder paste specimens. Solder specimens were heated in a convection oven to 70 ℃ and stressed with 8 A current, yielding an approximate current density of 4020 A/cm2. The PCB hosts a serpentine resistive copper element for additional and localized on-board heating. The testing platform allowed detection of the micrometer-level resistance changes indicative of material degradation. Additionally, the wire bond specimens were tested with a 3.653 x 10-5 cm2 apparent contact area at various stress currents, with estimated current densities between 20800 A/cm2 and 49700 A/cm2. Both datasets were compared against each other using Arrhenius plotting and against existing datasets collected for SAC305 solder paste, revealing that the wire bond contact interface degraded notably faster than SAC305 solder paste. Also, the SAC305 solder paste in this work was comparably robust to resistance changes as the same material as reported in literature, validating the testing platform and methodology. In parallel, a simple and reproducible mixing method was developed to homogeneously incorporate 15 – 53 μm high entropy alloy (HEA) particles into SAC305 solder paste using a glass slide mixing technique, offering a low-complexity alternative to conventional mixing approaches in the microelectronics industry. Experimental results indicate that 2%wt HEA powder reinforcement yields inconclusive impacts on plain SAC305 solder’s electromigration resiliency under the conditions tested, but increases the as-prepared temperature coefficient of resistance by approximately 22% for the one specimen tested. These findings suggest that the testing methodology developed in this work can assess how HEA additions impact electrical properties, but any reliability performance differences could be too fine to resolve without leveraging the statistical approaches currently employed in industry and academia. The developed testing methodology enables rapid and flexible comparison of interconnect materials, as demonstrated between wire bonds and solder joints. By analyzing observable resistance evolution under electrical stress and leveraging existing datasets, conservative lifetime estimations can be made. The approach significantly reduces experimental complexity and may provide sufficiently informative insights for testers during the early stages of material evaluation, potentially accelerating development cycles in the electronics and packaging industries.