Scan Slice Encoding for Test-time and Test-volume Reduction

1. Scan Slice Encoding for Test-time and Test-volume Reduction Z. Wang and K. Chakrabarty, ITC 2005, Paper 24.3

2. Motivation High test-data volume increases test time and may exceed limited memory depth of ATE Multiple ATE reloads time consuming May take minutes to hours! Test application time can be reduced by multiple scan chains but limited by device pins and ATE constraints.

3. Proposed Solution Based on lossless encoding of test-data for compression Exploits preponderance of X-bits in ATPG vectors without random fill. Test pattern broken up into N-bit slices, where N is the number of scan channels. Before encoding, X-bits in a slice are set to the majority care-bit value. Each slice is encoded into one or more c-bit groups, where c = K+2 and K = ceiling(log2(N+1))

4. Test Application Schematic

5. Encoding Procedure

6. Slice Encoding Example

7. Encoding Example

8. Decoder Schematic

9. STG of Decoder

10. Industrial Circuit Characteristics Eight circuits 50K to 1.4 M gates Test sets generated by commercial ATPG tools Dynamic compaction but no random fill Care bits: 1% to 4% Results not reported on ISCAS-89 benchmarks: Too small, not representative of current designs Too many care bits due to large circuit depth

11. Industrial Circuits and Test Sets

12. Compression Results

14. Cf. Dictionary Based [21]

15. Extension In an extension of this work, the X-bits are set is different ways to reduce switching activity during scan shifting: 0-filling 1-filling Adjacent or Minimum-transition filling: set to the value of the last encountered care bit. Reference: Badereddine et al. J. Electron Test (August 2008) 24: 353-364.