The improvement of automated material handling system traffic control

AMHS (automatic material handling system) is gaining more importance in wafer fabs as the demands to automation and WIP management efficiency getting tougher, also as wafers become larger and heavier. Aggressive fab managers have always been trying every effort to drive the fab production over its limit; however, once installed, an AMHS generally has little room for improvement (if any). This paper demonstrates how we tried to improve the existing AMHS at one of Winbond´s DRAM fabs under the pressure of extra traffic that was required by an increased production volume that went over its original design capacity. We were able to improve the efficiency a bit by modifying the traffic control logic. The vehicle transportation time was reduced 4.4%, and the average daily waiting time for total transportations was reduced 37.35 hours under the original transportation load. Consequently, the overall AMHS transportation capacity was increased and was able to accommodate the heavy traffic.