Test Structure for Evaluation of Pad Size for Wafer Probing

A new, cage-like structure is presented and is shown to be able to electrically identify a probe needle that has fallen slightly off its probe pad, even when the standard probe resistance structure (pads shorted together) reports “good” probe resistance. Using both structures together enables a more accurate evaluation of a probe system’s capabilities. Both test structures were used to compare three types of probe cards, reporting the smallest probe pad size that provides 100& probe yield.