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%.

No abstract

The test data volume (TDV) increases with increased target compression in scan compression and adds to the test cost. Increased TDV is the result of a dependency across scan flip‐flops (SFFs) that resulted from compression architecture, which is absent in scan mode. The SFFs have uncompressible values logic‐0 and logic‐1 in many or most of the patterns contribute to the TDV. In the proposed new scan compression (NSC) architecture, SFFs are analysed from Automatic Test Pattern Generation (ATPG) patterns generated in a scan mode. The identification of SFFs to be moved out of the compression architecture is carried out based on the NSC. The method includes a ranking of SFFs based on the specified values present in the test patterns. The SFFs having higher specified values are moved out of the compression architecture and placed in the outside scan chain. The NSC is the combination of scan compression and scan mode. This method decides the percentage (%) of SFFs to be moved out of compression architecture and is less than 0.5% of the total SFFs present in the design to achieve a better result. The NSC reduces dependencies across the SFFs present in the test compression architecture. It reduces the TDV and test application time. The results show a significant reduction in the TDV up to 78.14% for the same test coverage.