Test Generation for Defect-Based Faults of Scan Flip-Flops

When testing scan flip-flops (SFFs), chain test is first applied to ensure the functionality of scan chains and to detect the majority of stuck-at (SA) and transition delay (TD) faults along scan paths. However, there still exist some defects inside scan cells that cannot be effectively detected by chain test or conventional SA and TD patterns. This paper presents five cell-aware (CA) fault models to explicitly target the defects inside scan flip-flops. The proposed static shift (SS) and dynamic shift (DS) faults identify the defects detectable by chain test. For the defects escaping chain test, static single-capture (SSC) faults target the defects detectable when SFFs are in one-cycle capture mode, while static double-capture (SDC) and dynamic double-capture (DDC) faults target those detectable when SFFs are in two-cycle capture mode. The identified CA faults of SFFs are output in a format compatible with a commercial ATPG tool for pattern generation. Experimental results on large IWLS05 benchmarks demonstrate that our proposed faults cannot be fully covered by conventional SA and TD patterns and hence require dedicated test patterns to detect.