Diagnosis of functional failures is critical for locating manufacturing defects, increasing yield, and reducing field returns. It is important to narrow down the defective module in a failed component during board-level diagnosis. In this paper, a generic fault-diagnosis method based on an error-flow dictionary is presented to identify the root cause of functional failures on a chip or board. Error propagation mimics actual dataflow in a circuit, thus it reflects the native (functional) mode of circuit operation. In contrast to conventional fault syndromes, error flow includes the failure information in terms of circuit functionality, which significantly facilitates the diagnosis of functional failures. In the proposed diagnosis procedure, error flow is first learned from a good circuit by intentionally inserting faults, and then the root cause of a failing circuit is determined by comparing the similarity between the pre-learned error flow and the error flow observed from the failing circuit. The similarity of two error flows is evaluated based on the length of the longest common subsequence in string matching. Results for an open-source RISC SoC and an industrial communication circuit highlight the effectiveness of the proposed method.
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