Increasing the Fault Coverage of a Truncated Test Set

Abstract

Defect-aware, cell-aware, and gate-exhaustive faults are described by input patterns of subcircuits or cells that are expected to activate defects. Even with single-cycle faults, an \( n \) -input subcircuit can have up to \( 2^n \) faults with unique fault detection conditions, resulting in a large test set. Such a test set may have to be truncated to fit in the tester memory or satisfy constraints on test application time. In this case, a loss of fault coverage is inevitable. This article considers the test set denoted by \( T_1 \) obtained after truncating a larger test set denoted by \( T_0 \) . Suppose that the truncation reduces the set of detected faults from the set denoted by \( D_0 \) to the set denoted by \( D_1 \) . The procedure described in this article modifies the tests in \( T_1 \) to gain the detection of faults from \( D_0 \) \( \setminus \) \( D_1 \) , even at the cost of losing the detection of faults from \( D_1 \) . The goal is to reduce the fault coverage loss by computing a test set denoted by \( T_2 \) that detects a set of faults denoted by \( D_2 \) such that \( |T_2| = |T_1| \) and \( |D_2| \gt |D_1| \) . Experimental results for benchmark circuits demonstrate the ability of the procedure to increase the coverage of gate-exhaustive faults over several iterations.