The relationship between yield and flow time in a production system under inspection

Abstract

This work studies the relationship between Yield and Flow Time (FT) in a production system monitored by in-line inspection. It originates in the known semiconductors Yield vs. FT trade-off premise, but can be adapted to other industries. We challenge the common premise, and suggest an alternate analytical model to demonstrate this relationship. The model relies on a simplified production system that represents a repetitive segment in a production line. It illustrates that rising inspection rate increases both Yield and FT while exhibiting a trade-off. However with further growing inspection rate the Yield reaches a maximum and then starts to decline, while FT continues to increase. The Yield decline is explained by longer delay of inspection results which trigger the repair of an out-of-control machine. Clearly, lower Yield performance and higher FT are undesired. Our work defines this relationship with the analytical model and validates it with simulation. The model can be embedded in a decision support tool to pre-determine the inspection policy, while simultaneously considering Yield and FT.

Keywords:

• inspection
• queueing systems
• scheduling
• semiconductors manufacture
• flow time
• yield