IEEE Transactions on Very Large Scale Integration (VLSI) Systems
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The size of a diagnostic test set is significantly larger than the size of a fault detection test set. As a result, fault detection test sets may be used for initial defect diagnosis, and diagnostic tests may be added only when needed to narrow down a set of candidate defect sites. Between a fault detection test set and a full diagnostic test set there is a large range of test sets that can be used for improved (initial) diagnosis. We describe a diagnostic test generation process that produces such a range of test sets. As part of the process we rank the indistinguished fault pairs of the fault detection test set according to the importance of distinguishing them, and perform diagnostic test generation based on the ranked list. The ranking of fault pairs is based on the structural distance between the two faults of a pair. This allows failure analysis to explore fewer and more localized areas of the circuit as the size of the diagnostic test set is increased. Diagnostic test generation can stop with a test set of any size between a fault detection and a full diagnostic test set, having targeted the fault pairs that are most important to distinguish.