High Performance Compaction for Test Responses with Many Unknowns

We present a new compactor architecture for extreme compaction of test responses with a high percentage of x-values. The test response data is compacted into a single, 1-bit wide bit stream. A major contribution of this work is a new technique to efficiently load x-masking data into a masking logic. A method eliminating the need for explicit mask control signals using ATE timing flexibility is also introduced. The proposed compactor can efficiently be employed in multi-chip testing. Experiments with industrial designs show that the proposed compactor enables compaction ratios exceeding 200x.