Aggressive Exclusion of Scan Flip-Flops from Compression Architecture for Better Coverage and Reduced TDV: A Hybrid Approach

Abstract

Scan-based structural testing methods have seen numerous inventions in scan compression techniques to reduce TDV (test data volume) and TAT (test application time). Compression techniques lead to test coverage (TC) loss and test patterns count (TPC) inflation when higher compression ratio is targeted. This happens because of the correlation issues introduced by these techniques. To overcome this issue, we propose a new hybrid scan compression technique, the aggressive exclusion (AE) of scan cells from compression for increasing overall TC and reduce TPC. This is achieved by excluding scan cells which contribute to 12% to 43% of overall care bits from compression architecture, placing them in multiple scan chains with dedicated scan-data-in and scan-data-out ports. The selection of scan cells to be excluded from the compression technique is done based on a detailed analysis of the last 95% of the patterns from a pattern set to reduce correlations. Results show improvements in TC of up to 1.33%, and reductions in TPC of up to 77.13%.