Meaning
Specialized interface used to facilitate electrical communication between automated test equipment and individual semiconductor dice while they are still in wafer form. A probe card contains a dense array of contact elements that align precisely with the bond pads on the surface of a radio integrated circuit. It enables the verification of chip functionality before the wafer is diced into separate units.
Mechanical Alignment
High precision is required to ensure the probe tips touch the correct areas without damaging the underlying silicon structure. If the vertical force is too high, the needles can penetrate the metal layers and create a permanent defect. Operators use microscopes to calibrate the position of the card relative to the wafer chuck.
Signal Integrity
Transmission of high frequency signals requires the internal wiring of the card to maintain a specific impedance. Small capacitors are often mounted directly onto the probe card to stabilize the power supply during the bursts of activity typical in cellular modem testing. This localized decoupling prevents noise from corrupting the measurement of sensitive receiver circuits.
Operational Maintenance
Repeated contact with metal pads causes the tips to accumulate debris. Abrasive cleaning sheets are used inside the probing machine to restore the surface of the contacts. A card that is not maintained will eventually show high contact resistance and cause functional chips to fail the test.
