Introducing the virtual time based flow principle in a high-mix low-volume wafer test facility and exploring the behavior of its key performance indicators

In modern semiconductor manufacturing and primarily in high-mix-low-volume facilities it is increasingly important to ensure throughput and machine utilization requirements are met while satisfying tight goals in object tardiness at the same time. This is especially a challenge for the field of wafer test with its natural fluctuations and uncertainties of test times. A further important objective is the lowering of the work in process (WIP) for the purposes of minimizing costs held in the system and improving production predictability. For this, the Virtual Time Based Flow Principle (VTBFP) - a partly synchronized control strategy - is investigated in this paper. Tests are performed on a complex system, which is close to reality. As a result it is shown the benefits but also the limitations of the VTBFP approach.