Multi-Objective Parallel Batch Scheduling In Wafer Fabs With Job Timelink Constraints

We consider multi-objective batch scheduling in the complex flexible job shop problem applied to semi-conductor wafer fabs. Batches have different operating costs and consecutive steps of a job are constrained with timelinks. We also consider several other process aspects that arise in semiconductor wafer fabrication facilities such as flexible machine downtime, incompatible job families, different job sizes and parallel machines. The aim is to minimize the total weighted batching cost, queuing time, and the number of violations of timelink constraints. We present a hybrid two-stage solution strategy, combining Mixed Integer Linear Programming (MILP) models and heuristics. At a high level, the proposed approach can be broken down into “constructive” and “improvement” steps. The comparison of Flexciton schedules evaluated under uncertainty against factory schedules when solving large industrial instances shows the significant improvements that our solution can bring.