Other Abstracts

FabTime Cycle Time Management Newsletter Abstracts - Volume 9 (5 Issues - In Progress)

Paper vs. Electronic Lot Travelers (Issue 9.05)

In this issue we have a community announcement about the third issue of Fab Engineering & Operations Magazine (a publication that’s not affiliated with ours, but that we think our readers will enjoy). Our FabTime user tip of the month is about using FabTime’s software to generate a list of lots ahead of or behind schedule, according to planned cycle times at future operations.

We have one new subscriber discussion question in this issue, about the use of short-term simulation. We also received several detailed responses to last month’s question about the transition between paper and electronic lot travelers. In fact, these responses are so thorough, and varied, that we’ve decided to convert them into this month’s main issue. This is a slightly unusual approach to our main article, but one that we think will prove useful to anyone facing this paper to electronic traveler transition. The strength of these responses also shows what a valuable resource this subscriber community can be. We are very grateful to the subscribers who took time to respond to this topic and to all of you who have helped us with prior discussions. We welcome further feedback on paper vs. electronic lot travelers.

Dynamic X-Factor and Shipped Lot X-Factor (Issue 9.04)

In this issue we have a brief summary of upcoming industry conferences in our community announcements section. Our FabTime software user tip of the month is about using the home page chart alert functionality. We have one subscriber discussion question, about the transition from paper to electronic travelers, for which we could use your input. Our main article this month is about the comparison between dynamic x-factor (a point estimate measured as total WIP divided by WIP running on tools) and shipped lot cycle time x-factor. We show that although in the long run, DXF can be used to predict x-factor, various issues sometimes make it difficult to draw exact comparisons between this week’s DXF and some future week’s shipped lot x-factor value.

Batch Loading Policies for Wafer Fabs (Issue 9.03)

In this issue, we have community announcements about the second issue of Fab Engineering and Operations Magazine and a milestone reached by the Fab Owners Association. Our software user tip of the month describes how to use FabTime's new Queue Limit Lot List chart, which shows the non-held lots in queue that have exceeded, or are in danger of exceeding, a user-specified threshold.

We have one subscriber discussion question this month, about batch loading rules. In responding to this question, we realized that it has been more than five years since we last discussed batching in detail in the newsletter. Therefore, we decided to discuss batching in our main article this month. Specifically, we review the cycle time benefits of a greedy vs. a full batch policy, with examples, and also provide a simple rule of thumb for using look-ahead information in the batch formation decision. We welcome subscriber feedback, especially about experiences with greedy vs. full batch policies and incorporating look-ahead information into the batch loading decision.

Manual Lot Transfer in Wafer Fabs (Issue 9.02)

In our main article, we discuss lot transfer between operations for non-automated fabs. Although material handling in automated fabs has gained considerable attention in the literature, we believe that lot transfer is also having a significant impact on cycle time in less automated fabs, and that this topic is relevant for many of our newsletter subscribers. Behaviors such as the use of carts for lot transfer and the use of performance incentives for operators that do not reward the movement of material between areas can lead to higher than anticipated cycle times. For those fabs that are experiencing delays due to lot transfer, we recommend working towards reducing transfer batch sizes between steps, either by physically purchasing smaller carts, or by changing the way that operators are assigned or measured. If a full-scale change in carts or operating practices is not possible, we recommend identifying the specific areas in which material movement issues are causing cycle time, and implementing changes in those areas first. We discuss these potential solutions in detail, and welcome feedback. We also have one community announcement - a call for papers for the 2008 MASM conference. Our software user tip of the month is about showing and hiding data table columns in FabTime. We have no subscriber discussion this month.

Our Top Recommendation for Cycle Time Improvement: Tackle Single Path Operations (Issue 9.01)

We have one brief community announcement this month, about the winter Fab Owners Association meeting. Our FabTime software user tip of the month is about eliminating time spent with particular hold codes or owner codes from Operation Cycle Time Trend and Pareto charts. We also have a subscriber discussion response from Dov Kotlar of Tower Semiconductor (one of our software customers) to some previous questions that we raised about cycle time benchmarking.

In our main article this month we return to a topic that we have discussed before, but that continues to pose challenges for people who manage wafer fabs: single path operations. We review the different types of single path operations, and focus on those that stem from tool dedication. We present a rule of thumb for estimating the potential impact of going from single path to dual path for a given operation, and discuss two particularly insidious forms of tool dedication: soft dedication due to operator preferences; and process restrictions for new operations. In both cases, we recommend strategies for identifying and eliminating the single path operations. We believe that this is one of the highest benefit low-cost changes that an existing fab can make to improve cycle time.