The Traffic Cop - Consequences and Corrections

If no corrective action is taken, the extreme downtime in the 5xStep tool group leads to increased operation-level cycle times over the next several shifts. The 95th percentile cycle times are particularly large. Even after four days, the cycle times are still significantly higher than they were before the downtime problem, and exceed the goal for the tool group. 

One possible corrective measure which the Traffic Cop can take is to try to slow the rate of arrivals into the 5xStep tool group. As illustrated below, even if no corrective action is taken, the arrival rate into the 5xStep tool group will be less than normal for several days, due to the reentrant nature of the fab (if lots are sitting in queue for the 5xStepper, then they are not able to return for the next layer of processing). 

Other potential corrective measures that the Traffic Cop might undertake or recommend, include:

Temporarily reduce starts into the fab, to give the bottleneck a chance to catch up.

Check dedication policies on the tools in the 5xStep group (to understand why one tool in the group showed idle time).

Temporarily increase the number of operators assigned to the 5xStep tool group (so that no additional time is lost due to operator delays).

Conclusions

This example illustrated the FabTime cycle time management style known as “The Traffic Cop.” The idea is to monitor bottleneck utilization and factory starts to manage utilization, and thus keep cycle times from becoming a problem. Because a fab is a dynamic environment, sometimes the Traffic Cop can only react (e.g. to downtime problems). WIP turns provide a good early warning system regarding new problems, provided sufficient data is available to track down the problem location (or locations) in the fab.   

(Go back to Cycle Time Management Styles page)