X-tolerant test response compaction

Larger, denser designs lead to more defects; higher quality requirements and new test methods lead to an explosion in test data volume. Test compression technique attempt to do more testing with fewer bits. This article summarizes one such method, X compact which addresses how unknowns the bane of compression and logic BIST techniques are eliminated. DFT engineers must spend serious effort to minimize Xs in future designs. It is impossible to eliminate all Xs. X-tolerant response compactors are necessary for tolerating residual Xs to enable massive compaction with practically no impact on test quality. X-compactors are mainly useful for test compression purposes and provide up to 80 times the test response compaction of traditional scan. X-tolerant signature analyzers extend the X-compact concept to incorporate time compaction, thereby tolerating thousands of Xs and reducing test response data volume by 50 to 2,000 times relative to traditional scan. These signature analyzers are extremely beneficial for BIST because Xs can easily corrupt traditional MISR-based BIST signature analyzers. X-tolerant response compactors also enable efficient diagnosis essential to fast yield-learning.