Functional Screen
An electrical testing procedure evaluates individual integrated circuits or sensors directly on the silicon wafer before they are diced and packaged. Through wafer probe testing, a probe card with microscopic needles is aligned with the contact pads of each die to measure electrical signals and functionality. This in-line screening identifies defective dies early, which prevents the waste of packaging materials and labor on non-functional parts.
Probe Card Contact
A precision wafer prober automatically positions the wafer under the probe card, bringing the contact pads into contact with the probe tips. A small overtravel force is applied to ensure that the tips break through the native oxide layer on the contact pads to establish low-resistance connections. Automated test equipment then executes a suite of test patterns to measure leakage currents, threshold voltages, and operational frequencies.
The results are logged into a wafer map file that directs the subsequent dicing and assembly tools.
Parametric Evaluation
This testing process is also used to perform parametric measurements on test structures located in the wafer scribe lines. These test structures provide critical feedback on the performance of individual manufacturing steps such as lithography and ion implantation. Any systematic deviations from the design rules can be detected and corrected before the rest of the batch is completed.
Mechanical Damage
The physical contact of the probe tips can cause mechanical damage such as scratching or deformation of the bond pads. To prevent this, the probe force and tip shape must be carefully managed to avoid compromising subsequent wire bonding or solder bumping.
