Broadside and Skewed-Load Tests Under Primary Input Constraints

Tester limitations may impose certain constraints on the primary input vectors applicable as part of a two-pattern test for delay faults. Under these constraints, the primary input vectors may be held constant, or the second primary input vector of a test may be obtained by a single shift of a scan chain relative to the first. The goal of this brief is to study the differences in achievable transition fault coverage between various primary input constraints that are similar to the commonly used ones of holding or shifting primary input vectors. This brief also studies the possibility of combining the constraints in order to increase the transition fault coverage. The combination requires a fixed and circuit-independent hardware structure similar to the case where shifting of primary input vectors is used. This study is done using test sets that consist of both broadside and skewed-load tests in order to maximize the transition fault coverage.