Wafer map
Beginner
A picture of a wafer with each chip colored by whether it passed the test.
Novice
Test results (pass, fail, or which grade) plotted at each chip’s position on the wafer. Patterns such as a ring of failures at the edge, a cluster, or a line along a scratch point to a cause in manufacturing.
Expert
Stacking maps from many wafers separates random loss from loss tied to a position. Grouping neighboring dies into pairs, triples and so on (the windowing technique) turns one product’s maps into an estimate of defect density and of the loss that doesn’t depend on die size.