A Synthetic Chart to Monitor The Defect Rate for High-Yield Processes

Kusukawa and Ohta presented the CSCQ-r chart to monitor the process defect rate lambda in high-yield processes that is derived from the count of defects. The CSCQ-r chart is more sensitive to monitor lambda than the CQ (Cumulative Quantity) chart proposed by Chan et al.. As a more superior chart in high-yield processes, we propose a Synthetic chart that is the integration of the CQ-r chart and the CSCQ-r chart. The quality characteristic of both charts is the number of units y required to observe r (>= 2) defects. It is assumed that this quantity is an Erlang random variable from the property that the quality characteristic of the CQ chart follows the exponential distribution. In use of the proposed Synthetic chart, the process is initially judged as either in-control or out-of-control by using the CSCQ-r chart. If the process was not judged as in-control by the CSCQ-r chart, the process is successively judged by using the CQ-r chart to confirm the judgment of the CSCQ-r chart. Through comparisons of ARL (Average Run Length), the proposed Synthetic chart is more superior to monitor the process defect rate in high-yield processes to the stand-alone CSCQ-r chart.