A control scheme for high-yield correlated production under group inspection

Abstract

For some high-yield processes with very low defect parts-per-million (dppm), inspection is carried out in groups. Very often, within each group, the output characteristic is correlated. In this paper, we propose a control scheme that is effective in detecting changes in fraction nonconforming for high-yield processes with correlation within each inspection group. A Markov model is used to analyze the characteristics of the proposed scheme from which the average run length (ARL) and average time to signal (ATS) are obtained. The performance of the proposed scheme in terms of ATS is presented along with the comparison with the traditional cumulative conformance count (CCC) chart. Moreover, the effects of correlation and group size are also investigated. Finally, a numerical example and simulation studies are presented to reaffirm the performance of the proposed scheme in comparison with that of the conventional CCC chart.