Probe card

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A probe card is an interface between an electronic test system and a semiconductor wafer. 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 consists, normally, of a printed circuit board (PCB) and some form of contact elements, usually metallic, but possibly of other materials as well. Probe cards are broadly classified into needle type, vertical type, and MEMS(Micro Electro-Mechanical System) type depending on shape and forms of contact elements. MEMS type is the most advanced technology currently available. The most advanced type of probe card currently can test an entire 12" wafer with one touchdown.

Normally a probe card is inserted into an equipment called a Wafer prober, inside which position of the wafer to be tested will be manipulated so that there should be a precise contact between the probe card and wafer.

Probe card efficiency is affected by debris that accumulates on the tips of the probe needles. Normally these are made of tungsten or a tungsten/rhenium alloy although modern probe cards often have contact tips manufactured by MEMS technologies.

Irrespective of the probe tip material, contamination builds up on the tips as a result of successive touch down events (where the probe tips make physical contact with the bond pads of the die). Accumulation of debris has an adverse effect on the critical measurement of contact resistance. To return a used probe card to a contact resistance that is acceptable the probe tips need to be thoroughly cleaned. Cleaning can be done offline using an NWR style laser to reclaim the tips by selectively removing the contamination. Online cleaning can be used during testing to optimize the testing results within the wafer or within wafer lots.