A total standard WIP estimation method for wafer fabrication

The standard work-in-process (WIP) level in a wafer fabrication factory is an important parameter which can be properly used to trigger the decision of when to release specific wafer lots. There are many WIP-based release control policies which have been proven to be effective for wafer fabrication manufacturing, few methods have been proposed to find the suitable WIP-level as a parameter for these release policies. This paper proposes a queueing network-based algorithm to determine the total standard WIP level so that the Fixed-WIP release algorithm to determine the total standard WIP level so that the Fixed-WIP release control policy can apply. A numerical example is provided to elaborate the algorithm. A simulation model of a real-world wafer fabrication factory in Taiwan is built and analyzed. Results of simulation experiment indicate that under the Fixed-WIP control policy, the total standard WIP level estimated from this study achieves a target throughput rate while keeping the corresponding cycle time relatively low. Results also demonstrate that the queueing network-based algorithm is a very useful method to determine the standard WIP level efficiently.