An algorithmic technique for diagnosis of faulty scan chains

This paper presents an algorithmic scan-chain-fault diagnosis procedure. The diagnosis for a single scan-chain fault is performed in three steps. The first step uses special chain test patterns to determine both the faulty chain and the fault type in the faulty chain. The second step uses a novel procedure to identify the suspect scan cell within a range of scan cells. The final step further improves the diagnostic resolution by ranking the suspect scan cells inside this range. The proposed technique handles both stuck-at and timing failures (transition faults and hold-time faults). The application of the procedure in a production test flow is discussed. Simulation and silicon results from several products show the effectiveness of the proposed method.