Model to determine a general X-factor contribution and apply to cycle time improvement for wafer fabrication

Abstract

Shortening cycle time and maximising output are the major concerns of highly competitive industry. In this paper, an Adjusted X-Factor Contribution (AXFC) measurement is developed, which considers batching process, un-batching process and machine failure. A general model is established to determine the X-factor contribution for all types of machines. In this model, GI/G/m queuing theory is applied to estimate the aggregated cycle time. The machine downtime variability, lot arrival variability, batching and un-batching processing are considered. Finally, the effects of system performances by improving the workstations with high utilisation and high AXFC are explored. The results showed that the cycle time and cycle time variability of products could be affected by the relative locations of high utilisation and high AXFC workstations. Furthermore, the results also revealed that reducing failure frequency of high AXFC workstation will perform as good as high utilisation workstation on cycle time improving.