X-compact: an efficient response compaction technique for test cost reduction

We present a technique for compacting test response data using combinational logic circuits. Our compaction technique enables up to an exponential reduction in the number of pins required to collect test response from a chip. The combinational circuits require negligible area, do not add any extra delay during normal operation, guarantee detection of defective chips even in the presence of sources of unknown logic values (often referred to as Xs) and preserve diagnosis capabilities for all practical scenarios. The technique has minimum impact on current design and test flows, and can be used to reduce test time, test data volume, test-I/O pins and tester channels, and also to improve test quality.