One more time! Increasing fault detection with scan shift capture

More stringent defect detection requirements have led to the creation of new fault models, such as the cell-aware fault model, that attempt to model defects that might be missed by traditional test sets. Unfortunately, the resulting test sets can be long, and thus we have explored a DFT-based approach to reduce test time by harnessing scan shift cycles for defect detection. However, even advanced fault models may still miss some defects (for example, defects between standard cells). The n-detect test approach attempts to detect such defects fortuitously by increasing the number of times that simpler faults (e.g. stuck-at faults) are detected. In this paper, we investigate the ability of our DFT circuitry to provide multiple stuck-at fault detections of the hardest to detect stuck-at faults during scan shift. We will show that significant additional fault detections are possible in the circuits studied, even when only a subset of all scan chain flops are used for scan shift capture.