28L Mems Probe Card

What Is a Probe Card?

A probe card or DUT board is a printed circuit board (PCB), and is the interface between the integrated circuit and a test head, which in turn attaches to automatic test equipment (ATE) (or “tester”).Typically, the probe card is mechanically docked to a Wafer testing prober and electrically connected to the ATE . Its purpose is to provide an electrical path between the test system and the circuits on the wafer, thereby permitting the testing and validation of the circuits at the wafer level, usually before they are diced and packaged. It normally comprises a PCB and some form of contact elements, usually metallic.

A semiconductor manufacturer will typically require a new probe card for each new device wafer and for device shrinks (when the manufacturer reduces the size of the device while keeping its functionality) because the probe card is effectively a custom connector that takes the universal pattern of a given tester and translates the signals to connect to electrical pads on the wafer. For testing of Dynamic random-access memory (DRAM) and Flash memory (FLASH) devices, these pads are typically made of aluminum and are 40–90 um per side. Other devices may have flat pads, or raised bumps or pillars made of copper, copper alloys or many types of solders such as lead-tin, tin-silver and others.

The probe card must make good electrical contact to these pads or bumps during the testing of the device. When the testing of the device is complete, the prober will index the wafer to the next device to be tested.

Normally a probe card is inserted into a wafer prober, inside which the position of the wafer to be tested will be adjusted to ensure a precise contact between the probe card and wafer. Once the probe card and the wafer are loaded, a camera in the prober will optically locate several tips on the probe card and several marks or pads on the wafer, and using this information it will align the pads on the device under test (DUT) to the probe card contacts.

Representative types of probe cards

Probe cards can be classified according to their structure including the probe alignment and probe fixation. Two representative probe cards and their characteristics are shown below.

Vertical (advanced) probe card

A vertical (advanced) probe card consists of a PCB and an attached block to which perpendicular probes are affixed. With this type, probes can be aligned flexibly such as in a grid or aligned to measure multiple chips. Maintenance is easy because probes can be replaced individually. Also, dents can be minimised, causing no damage to solders. However, the manufacturing costs are relatively high, which is not really suitable for aluminium electrode pads (Al pads) on wafers.

Cantilever probe card

A cantilever probe card has needles made from tungsten and similar materials. These needles are directly fixed on a PCB.
This type can be manufactured at costs lower than the vertical type. Its probes can also be aligned at smaller pitches, supporting Al pads. When compared to the vertical type, the cantilever type has greater restriction on pin alignment and generates larger dents. This type also requires operators to spend time and effort for periodic maintenance such as repair and adjustment (such as height adjustment).

Evolving Technologies Pushing the Boundaries:

As semiconductor technology continues to advance, so do the techniques employed in MEMS Probe Card Manufacturing. Microfabrication technologies, borrowed from the semiconductor industry itself, enable the creation of smaller, more densely packed probes. This allows for testing the ever-shrinking components of modern semiconductor devices with unparalleled precision.

Microelectromechanical systems (MEMS) technology has also found its way into MEMS Probe Card Manufacturing. MEMS-based probes, with their tiny movable structures, offer enhanced flexibility and contact accuracy. They can adapt to the varying heights of the ICs on a wafer, ensuring reliable contact during testing. This integration of MEMS technology represents a leap forward in the quest for higher testing accuracy and efficiency.

The choice of materials for MEMS Probe Cards continues to evolve. Researchers are exploring new materials with superior electrical properties, enhanced durability, and thermal stability. Nanomaterials, with their unique properties at the nanoscale, are under consideration for MEMS Probe Card designs, promising even higher performance and reliability.

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