Test Sequences for Faults in the Scan Logic

Abstract

Functional test sequences are used as manufacturing tests to complement scan-based tests. Functional test sequences target defects in the functional logic of the circuit. However, they may fail because of defects in the scan logic that prevent the circuit from operating correctly in functional mode. It is advantageous to detect such defects by dedicated test sequences before attempting to apply functional test sequences. The computation of dedicated test sequences for faults in the scan logic is the topic of this brief. The procedure described in this brief accepts a pool of functional test sequences. It identifies subsequences from the pool that are effective for detecting faults in the scan logic while balancing their lengths. It then compacts the sequences to reduce their total length further. Experimental results for benchmark circuits demonstrate large variations among different circuits in the total length of the sequences and significant reductions in the total length for all the circuits considered.