On the frequency and location of set point adjustments in sequential tolerance control

Sequential tolerance control (STC) is an approach that uses real-time measurement information at the completion of a stage to exploit the available space inside a dynamic feasible zone and reposition the set points for the remaining operations. STC has been shown to produce significantly higher yields than conventional tolerance control given constant equipment precision. STC was developed under the premise that a measurement and set point adjustment would follow each operation. However, measuring after each operation may not be practical under certain conditions. This study develops techniques for determining when measurements and set point adjustments should take place so that the benefits of STC are realized without interrupting the process after every operation.