Elucidating electromigration-induced void failures in Ni/SnAg/Ni solder microbumps using 3D X-ray laminographic inspections

This study manifests that high-resolution (0.4 μm) 3D X-ray microscopy can be leveraged for characterizing electromigration-induced (EM-induced) voids in Ni/ SnAg/Ni microbumps non-destructively and effectively. The results of 3D X-ray observations were comparable to those obtained by common destructive approaches. Inspected by consecutive laminographic observations, the voids were likely to shape irregularly and locate randomly. To evaluate the degrees of voiding failures, three levels including slight, medium, and severe were defined based on 3D X-ray observations. Voided microbumps were constantly detected (71 % ∼ 75 %) under high current density as 8× 10⁴ A/cm², whereas they were seldomly observed (33 %) at low current density as 1.6 × 10⁴ A/cm². Moreover, the dependencies of voiding failures on Sn α angles were explicated. The non-voided microbumps had intact Sn in high α angles, while the voided microbumps had residual Sn grains with lower α angles and could vary with different voiding levels. © 2025 Elsevier Inc.