The effect on quality of non-uniform fault coverage and fault probability

This paper addresses problems associated with the production and interpretation of traditional fault coverage numbers. The first part addresses the issue of non-uniform distribution of detected faults. It is shown that there is a large difference in final quality between covering the chip all over and leaving parts relatively untested, even if the coverage is the same in both cases. The second part deals with the use of weighted, rather than unweighted fault coverages and investigates the use of readily-available extracted capacitance information to produce a weighted fault coverage which is more useful for producing quality estimates, without having to perform a full defect analysis. Results show significant differences in weighted versus unweighted coverages, and also that these differences can be in either direction.