A modified Kanban system in a semiconductor manufacturing environment

The author discusses a modified Kanban WIP (work in process) control system successfully implemented in a CMOS fabrication facility. The fundamental problem this system was designed to prevent uneven line loading resulting from various operational problems. Even after a problem had been resolved, the residual impact on production due to disrupted WIP flow could last for weeks. Thus, poor line loading led directly to increased cycletimes, poor predictability, and more manufacturing mistakes. The goal of the Kanban system was to minimize queue time by delivering WIP to each operation only when the operation was ready to process it. Unfortunately, a conceptually pure Kanban system will not work in a semiconductor fabrication area due to the nature of the manufacturing process. Thus, if the Kanban concept was to be effective in a fab environment it had to be modified to take these factors into account. These modifications and the system used to control the line are discussed in detail