Meaning
A rapid testing procedure determines the long-term reliability of metal traces before the whole substrate is diced into individual pieces. Executing wafer level electromigration identifies weak batches in days instead of months. Probes apply intense heat and current directly to test structures on the flat surface.
This technique saves time but uses higher stress levels that must be carefully related to actual service conditions.
Probing Sequence
Automated arms lower tiny needles onto designated pads to start the electrical flow. During wafer level electromigration, testers cycle through hundreds of sites across the round disk. Data from each pad are recorded in a central database to show the uniformity of the metal quality.
Thermal Stress
Heating elements under the platform keep the entire substrate at a constant elevated temperature. The speed of wafer level electromigration depends on this heat to move the metal atoms into visible configurations of damage. Technicians check the voltage drop across these spots every few minutes.
Acceleration Factor
Models translate the results of these short tests into an expected failure rate over ten years of low-intensity use. Reliability for wafer level electromigration is valid only if the failure looks the same as it would in a real package. If the test melts the metal instead of migrating it, the data is rejected as invalid.
