Built-in Test for Hidden Delay Faults Marginal hardware introduces severe reliability threats throughout the life cycle of a system. Although marginalities may not affect the functionality of a circuit immediately after manufacturing, they can degrade into hard failures and must be screened out during manufacturing test to prevent early life failures. Furthermore, their evolution in the field must be proactively monitored by periodic tests before actual failures occur. In recent years small delay faults have gained increasing attention as possible indicators of marginal hardware. However, small delay faults on short paths may be undetectable even with advanced timing aware ATPG. Faster-than-at-speed test (FAST) can detect such hidden delay faults, but so far FAST has mainly been restricted to manufacturing test. 38 10 1956 - 1968 1956 - 1968 IEEE