Semiconductor system with multiple closed-loops constrains

In semiconductor assembly and test factory, the carts which are used as transports and fixtures are always cycling in the system and they are enablers for the semiconductor production. The limited cart resource, especially when the several different kinds of carts are needed to perform the operation, affect the system performance quite significantly. In this paper, a production line with three machines and two WIP buffers, two types of carts, two loop and two cart buffers are addressed, all the processing times by these machines are assumed to be exponential. Markov models for this two-loop closed line with finite buffers were derived to explore the relationship between the system performance and system structure and parameters, such as the cart numbers. Based on numerical examples, some valuable insights on how to management these systems effectively were proposed.