A pattern set with 100% stuck-at fault coverage consists of tests to detect every possible stuck-at fault in a circuit. 100% stuck-at fault coverage does not necessarily guarantee high quality, since faults of many other kinds -- such as bridging faults, opens faults, and transition (aka delay) faults -- often occur.
== Sequential ATPG ==
Sequential-circuit ATPG searches for a sequence of vectors to detect a particular fault through the [[State space|space of all possible vector sequences]]. Various search strategies and heuristics have been devised to find a shorter sequence and/or to find a sequence faster. However, according to reported results, no single strategy/heuristic out-performs others for all applications/circuits. This observation implies that a test generator should include a comprehensive set of heuristics.
Even a simple stuck-at fault requires a sequence of vectors for detection in a sequential circuit. Also, due to the presence of memory elements, the [[controllability]] and [[observability]] of the internal signals in a sequential circuit are in general much more difficult than those in a combinational circuit. These factors make the complexity of sequential ATPG much higher than that of combinational ATPG.
Due to the high complexity of the sequential ATPG, it remains a challenging task for large, highly sequential circuits that do not incorporate any [[Design For Test]]ability (DFT) scheme. However, these test generators, combined with low-overhead DFT techniques such as [[partial scan]], have shown a certain degree of success in testing large designs. For designs that are sensitive to area and/or performance overhead, the solution of using sequential-circuit ATPG and partial scan offers an attractive alternative to the popular full-scan solution, which is based on combinational-circuit ATPG.
