Electromigration Stress

Physical Consequence

Material degradation under continuous electrical loading leads to the formation of microstructural voids at the electron entry point. When electromigration stress becomes elevated in lead-free solder joints, these voids coalesce into large cracks that restrict current flow and raise electrical resistance. Simultaneously, the accumulated atoms at the anode side create compressive stresses that can generate extrusion structures or whiskers.

These structural alterations threaten the physical integrity of the electronic packaging.

Failure Mechanism

Diffusion pathways along grain boundaries or phase interfaces accelerate the movement of metal atoms under the influence of the electron wind. In microbump arrays, the electromigration stress is further compounded by the temperature gradient across the joint, a phenomenon known as thermomigration. This synergistic effect leads to the rapid dissolution of the under-bump metallization layer.

Once the metallization layer is consumed, the mechanical strength of the solder joint is compromised, causing rapid failure under external vibration.

Audit Verification

Reliability certification in outsourced packaging facilities relies on high-temperature operating life tests and highly accelerated stress tests to evaluate the susceptibility of interconnects to electrical wear. Factory compliance audits analyze the test results to verify that the under-bump metallization can withstand the specified current density. When qualifying new designs, the customer requires detailed logs of electromigration stress simulation and physical test data to confirm the expected operating lifetime of the product.

These steps help prevent field failures in high-power applications where current densities are elevated.