A capture-safety checking metric based on transition-time-relation for at-speed scan testing

Test power has become a critical issue, especially for lowpower devices with deeply optimized functional power profiles. Particularly, excessive capture power in at-speed scan testing may cause timing failures that result in test-induced yield loss. This has made capturesafety checking mandatory for test vectors. However, previous capturesafety checking metrics suffer from inadequate accuracy since they ignore the time relations among different transitions caused by a test vector in a circuit. This paper presents a novel metric called the Transition-Time-Relation-based (TTR) metric which takes transition time relations into consideration in capture-safety checking. Detailed analysis done on an industrial circuit has demonstrated the advantages of the TTR metric. Capturesafety checking with the TTR metric greatly improves the accuracy of test vector sign-off and low-capture-power test generation.