Exploring linear structures of critical path delay faults to reduce test efforts

It has been shown that the delay of a target path can be composed linearly of other path delays. If the later paths are robustly testable (with known delay values), the target path can then be validated through simple calculation. Yet, no decomposition process is available to find paths that satisfy the above property. In this paper, given a set of target critical paths, we propose a two-stage method to find a set of robust-testable paths (with smaller number than the original set). The first stage constructs a necessary subset for critical robust paths, and the second stage identifies remaining functional sensitizable segments and their corresponding composing robust paths. The experiments show that a large percentage (several benchmarks close to 100%, 75% on average) of critical paths can be covered for most circuits. All paths and coverage are verified to match the best possible results. The data also indicate that the remaining hard-to-test (functional sensitizable) paths actually result from only a few tens of segments in the circuit (except for one circuit, s35932). DfT technique can then be applied to these uncovered segments for full testability with small overheads.