Dispatching Rules

Dispatching rules is the decision logic that determines which waiting lot a tool processes next under competing priorities and constraints - rule quality directly affects throughput, cycle time, and due-date performance.

What Is Dispatching rules?

• Definition: Scheduling heuristics or algorithms applied at each resource release event.
• Rule Families: FIFO, shortest processing time, critical ratio, due-date based, and weighted score approaches.
• Decision Inputs: Lot priority, queue age, processing time, setup state, and downstream constraints.
• Execution Scope: Applied in MES and dispatch engines across tool groups and route segments.

Why Dispatching rules Matters

• Throughput Performance: Dispatch choice determines bottleneck utilization and queue accumulation.
• Cycle-Time Control: Good rules reduce average and tail waiting times.
• Delivery Reliability: Priority-sensitive rules improve due-date adherence.
• Quality Protection: Rules can enforce queue-time and hold-risk constraints.
• Operational Stability: Consistent dispatch logic lowers ad hoc manual intervention.

How It Is Used in Practice

• Rule Selection: Match rule behavior to business objective and process constraint profile.
• Simulation Testing: Validate candidate rules against historical and projected fab scenarios.
• Continuous Tuning: Adjust rule parameters as demand mix, bottlenecks, and risk patterns change.

Dispatching rules is a central lever in fab operations optimization - disciplined next-lot decision logic is essential for balancing speed, utilization, and quality risk in high-complexity manufacturing.