Flip–flop selection for partial enhance scan chain using DTESFF for high transition delay fault coverage

Abstract

In nanometric technologies, testing of delay faults in the integrated circuits is becoming mandatory during manufacturing test. Delay fault testing involves two test vectors. Scan based designs is used for delay fault testing with architectural limitations of traditional scan limits the two pattern delay tests that can be applied to a design which results in degraded delay test coverage. Transition delay fault (TDF) coverage improves appreciably by the use of enhanced scan design as it solves the problem by supporting arbitrary delay test vector pairs at the cost of high area overhead. It also needs fast hold signal which is analogous to scan enable signal as in case of LOS testing. Delay testable enhanced scan flip–flop (DTESFF) has been proposed as a low cost DFT technique to achieve high TDF coverage using enhanced scan design without the need of fast hold signal. In this work, a partial DTESFF scheme augments few scan flip–flops with the DTESFF design by choosing scan flip–flops carefully. It attains most of the TDF coverage advantages of a full DTESFF design with reduced area overhead. Significant improvement in TDF coverage for partial enhance scan using DTESFF has been seen on ISCAS’ 89 benchmark circuits.