Effect of Electromigration on Micro Tensile Test Mechanical Properties and Micro Structure of Pure Copper

Copper as the fine pitch circuit line material of advanced electronic packaging substrate will experience tensile stress during manufacturing as well as electronic application. Electromigration will induce electromigration force and Joule heat to the circuit line during electronic application. It is imaginable that electromigration will have impact on the mechanical properties and microstructure of the copper circuit. In this study, we investigated the effect of electromigration on the micro tensile mechanical property of pure copper, and the mechanism was explored by incorporating the microstructure evolutions. The pure copper specimens were pre-annealed at 678°C for 12 hours to reduce the residual stress generated during fabrication. The subsequent current stressing treatments at different current densities (2 3× 10⁴ A/cm²) were found to enhance the yield strength up to 89%, Young's modulus 96.2%, and ultimate tensile strength 6.5%, whereas degrade elongation by 5.5%. The electron backscatter diffraction analysis showed that non-deformation recrystallization occurred which induced grain refining and twin formation of Cu. The influence of dislocation, twin fraction, and grain orientation on the mechanical properties were investigated and discussed in the study. The athermal electron wind force effect was found predominated over the thermal Joule heat on governing the microstructure variation and the mechanical properties.