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The FabTime Cycle Time Management newsletter is a forum for introducing and discussing best practices in wafer fab cycle time management.
In this installment we have an announcement about a new issue of Future Fab International. Our FabTime software tip of the month is about setting time windows for individual alerts. We have no new subscriber discussion topics. However, our main article this month was written by long-time newsletter subscriber Mike Hillis from Spansion. Mike’s article is a detailed response to the topic of reentrant flow introduced in Issue 13.3. Mike discusses the way that variation in the fab makes it difficult to achieve planned output at reentrant tools (particularly nested reentrant tools, and particularly for fabs using critical ratio dispatching). He shares a solution that has worked for his company to keep WIP flowing linearly through the fab.
In this issue of the newsletter, we have an announcement about a new member of the Fab Owners Association. Our FabTime tip of the month is about understanding how actual and planned XFactor values are used in FabTime. We have two subscriber discussion submissions; a follow-on to the main article in the last issue about choosing the appropriate level of capacity planning: and a new question about downtime reason codes.
In our main article this month, we take a look at the reasons that reentrant flow makes managing cycle time and WIP in wafer fabs challenging. We first focus on the fundamentals - the ways that multiple visits to the same tool affect utilization, number of tools, and variability. We then explore some of the ways that reentrant flow affects capacity planning and dispatching.
In this issue, we have a community announcement about the new issue of Future Fab International (and an article within it about cycle time and variability by one of our newsletter subscribers). We also have a call for papers for the e-Manufacturing & Design Collaboration Symposium 2012. Our FabTime user tip of the month is about using the new average WIP lines on the Moves Trend and Pareto charts. We have subscriber discussion related to the economic benefits of cycle time improvement, the impact of engineers on cycle time, and the reasons that reentrant flow in fabs contributes to high cycle time and WIP.
Our main article this month is a guest article by Bob Kotcher of Simitar, Inc. Bob writes about choosing the appropriate level of capacity planning (from a simple static model to a highly detailed dynamic model) for each fab. He discusses investment in additional capacity for cycle time improvement in general, and highlights the need to focus on the question that the capacity model is being asked to solve. He concludes that "Millions of dollars can be left on the table by building models that are too basic. On the other hand, even the most detailed model is useless if it’s unfinished or resources are not available to keep it accurate." We hope you find this article of interest.
In this issue we have a link to a news story from the Wall Street Journal that references Little’s Law (one of the fundamental drivers of fab behavior), a call for papers for the MASM 2012 conference (to be held in Berlin in December), and an announcement about recent and upcoming Fab Owners Association meetings. Our FabTime user tip of the month is about using new stacked WIP and Moves charts. We have an extensive amount of subscriber discussion in this issue. Apparently, December's topic of metrics for fab variability was of particular interest.
In our main article this month, we share six potential variability-related metrics, inspired by subscriber and customer suggestions. These range from tracking first pass success rate for preventive maintenance events to aggregating lot slack times across tools or areas in the fab. It is clear from the broad response to this topic that many of us are working on finding new metrics to reduce variability in the fab. It is our hope that, together, through discussions like the ones shared below, we can work to find better solutions. We are grateful to all of the people who took time to share their thoughts on this topic, and welcome additional feedback.
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