A unified test compression technique for scan stimulus and unknown masking data with no test loss

This paper presents a unified test compression technique for scan stimulus and unknown masking data with seamless integration of test generation, test compression and all unknown response masking for high quality manufacturing test cost reduction. Unlike prior test compression methods, the proposed approach considers the unknown responses during test pattern generation procedure, and then selectively encodes the less specified bits (either Is or Os) in each scan slice for compression while at the same time masks the unknown responses before sending them to the response compactor. The proposed test scheme could dramatically reduce test data volume as well as the number of required test channels by using only c tester channels to drive N internal scan chains, where c = [10g₂ N + 2- In addition, because all the unknown responses could be exactly masked before entering into the response compactor, test loss due to unknown responses would be eliminated. Experimental results on both benchmark circuits and larger designs indicated the effectiveness of the proposed technique.