Comparing four lower confidence limits for process yield index Spk

Abstract

Process yield has long been a standard criterion used in the manufacturing industry as a common measure on process performance. Boyles considered a yield index Spk for normal processes. The measurement Spk establishes the relationship between the manufacturing specifications and the actual process performance, which provides an exact measure on the process yield. In this paper, the natural estimator of Spk is considered using the bootstrap simulation technique to find four approximate lower confidence limits. The four bootstrap methods including the standard bootstrap (SB), the percentile bootstrap (PB), the biased corrected percentile bootstrap (BCPB), and the bias-corrected and accelerated (BCa) bootstrap methods are compared based on the coverage fraction. The simulation results show that the SB method significantly outperforms PB, BCPB and BCa, and therefore is recommended for use in assessing process performance Spk based on the yield.