Aging Aware Steepening of the Fault Coverage Curve of a Scan Based Transition Fault Test Set

Chip aging may result in hardware defects whose likelihood of occurrence depends on the layout and functional workload at the defect site. In-field testing is important for the detection of defects that occur because of aging. In-field test periods have different durations, and it is important to utilize every test period for the detection of the defects that are the most likely to occur with aging. This article considers this problem for the first time in the context where a stored deterministic scan-based test set is used for in-field test application. The article formulates the problem as that of steepening the fault coverage curve of the test set by introducing an aging aware steepening metric. Using the suggested metric, the procedure described in this article reorders and modifies a given test set to ensure that every additional test would detect as many additional faults as possible out of the faults that are the most susceptible to aging. The procedure is implemented in an academic simulation environment and applied to benchmark circuits. The results demonstrate its effectiveness in ensuring that each test period would be utilized for detecting the faults that are the most likely to occur with aging.