dispatching

Dispatching is the **decision logic** that determines which waiting lot a tool should process next. Good dispatching rules maximize throughput and on-time delivery while respecting critical queue-time limits. **Common Dispatching Rules** **FIFO (First In, First Out)** processes lots in arrival order—simple and fair, but it ignores priorities. **Priority-based** dispatching processes hot lots and engineering lots first regardless of arrival time. **Critical Ratio** calculates priority as (time remaining until due date) / (remaining process time)—when the ratio drops below **1.0**, the lot is behind schedule. **Shortest Queue Next** sends lots to the tool group with the shortest queue. **Advanced Dispatching** Modern systems use **Q-time aware** dispatching that automatically escalates lots approaching queue-time limits to prevent scrap. **Setup minimization** groups lots requiring the same recipe to reduce tool changeover time. **Bottleneck starvation avoidance** prioritizes lots heading to bottleneck tools so the constraint never sits idle. **Implementation** The **MES (Manufacturing Execution System)** enforces dispatching rules automatically. Dispatch lists update in real-time as lots move and tool status changes. Operators follow the dispatch list unless overridden by engineering for special circumstances.