Timing-based delay test for screening small delay defects

The delay fault test pattern set generated by timing unaware com-mercial ATPG tools mostly affects very short paths, thereby in-creasing the escape chance of smaller delay defects. These small delay defects might be activated on longer paths during functional operation and cause a timing failure. This paper presents an im-proved pattern generation technique for transition fault model, which provides a higher coverage of small delay defect that lie along the long paths, using a commercial no-timing ATPG tool. The pro-posed technique pre-processes the scan flip-flops based on their least slack path and the detectable delay defect size. A new delay defect size metric based on the affected path length and required increase in test frequency is developed. We then perform pattern generation and apply a novel pattern selection technique to screen test patterns affecting longer paths. Using this technique will pro-vide the opportunity of using existing timing unaware ATPG tools as slack based ATPG. The resulting pattern set improves the defect screening capability of small delay defects