This research focuses on scheduling problem in a leadframe manufacturing system with the objective of minimizing mean tardiness of orders. The leadframe manufacturing system is the flowshop with several special characteristics: parallel machines at each production stage, sequence-dependent setup times and multiple products with different process plans. We suggest two heuristic methods to determine schedules of production lots at each stage. One is a method based on lot sizing and dispatching rule and the other is a method based on the idea of Optimized Production Technology (OPT). To evaluate performance of the suggested methods, a simulation model of a real leadframe manufacturing system is developed and computational experiments are performed on randomly generated problems. Results of the tests show that the suggested methods perform better than existing methods.