On the Probability of Fault Occurrence

INTRODUCTION: In this paper we introduce the probability of fault occurrence. For a modeled fault (e.g., a stuck fault) this is the probability with which the fault will occur on a chip. The occurrence of a fault is only observable as fault indication by a test capable of detecting it. We determine the probability of fault occurrence from chip test data. No attempt is made to find these probabilities for individual faults but they are determined only as a distribution for all faults. Combined with detection probabilities (related to the conventional fault coverage), fault occurrence probabilities provide a revised coverage requirement versus chip quality relation.