Arrhenius Life Consumption Modeling for Elevated Temperature and Bias Stress Screening
Arrhenius life consumption modeling quantifies wear out from bias screening, preventing overstress while proving infant mortality removal.
Electromigration
Transport Mechanism
A physical process involves the transport of atoms in a metallic conductor driven by the momentum transfer between conducting electrons and the metal lattice. This atomic drift, known as electromigration, leads to the accumulation of material in some regions and voids in others. It occurs primarily under high current densities in sub-micron lines of semiconductor devices and fine-pitch solder bumps.
Solder Joint Degradation
High current density forces metal ions to migrate along the direction of electron flow, creating a flux divergence that damages the conductor. At the anode, the piling up of metal atoms creates hillocks and whiskers that can bridge adjacent circuits to cause short circuits. At the cathode, the depletion of atoms creates voids that reduce the cross-sectional area of the conductor, thereby increasing localized electrical resistance and heating.
This localized heating further accelerates the void growth in a self-reinforcing failure loop. In fine-pitch ball grid arrays, the phenomenon rapidly degrades the copper-tin intermetallic compound layer, resulting in premature mechanical separation of the joint.
Mitigation Strategy
Operating current limits and trace geometries must be designed to keep current densities below the threshold that initiates atomic drift. Copper traces on circuit boards are rarely affected due to their relatively large cross-sections, but solder joints in modern chip-scale packages are highly susceptible. Design guidelines restrict the maximum current allowed through individual microvias and solder bumps to ensure a lifetime of fifteen years or more.