A Comprehensive Partial Scan Chain Assignment and Test Generation

Current approaches to partial scan may not necessarily cover all faults, in particular the faults introduced by the partial scan chain (or the test machine) itself. Typically, the user does not have complete control on the fault coverage achieved by the partial scan. In this paper, we introduce a new partial scan assignment algorithm that not only ensures user-specified coverage of all target faults in the object machine but also effectively addresses the complete coverage of faults in the test (or partial scan) machine. The algorithm allows a trade-off of increased test application time to reduce scan chain size, while maintaining a user-specified level of fault coverage. For a given scan chain, a single application of a test sequence may not detect a particular fault. We raise the probability of detecting the fault by repeating the test sequence. Experimental results on large sequential benchmark circuits demonstrate that the model we use predicts this trade-off consistently and accu..