FabTime Cycle Time Management
Newsletter Abstracts - Volume 11 (5 Issues)
In this final newsletter issue of the year, we have
community announcements about Future Fab International’s
new email publication, and the Fab Owners Association upcoming
member meetings. Our FabTime user tip of the month is about
adding complex logic within standard filters, using the new
in-filter WHERE clause. We have subscriber discussion related
to early lot delivery times, OEE, and the number of columns
in the PDF newsletter.
In our main article this month, we discuss the application
of “reverse dispatch” in the presence of time
constraints between process steps. Where there are time
windows between steps, lots are usually held at the upstream
step, and only released when needed by the downstream step.
This poses an implementation issue for dispatch systems,
which usually look at one tool at a time. What FabTime has
been working on is a system called “reverse dispatch”, by
which the person running the downstream tool can look back
at all of the WIP queued at the upstream tool, and then make
the best dispatching decision for both steps.
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In this issue, we have a community announcement about a
new position for Professor Scott Mason. Our FabTime User Tip
of the Month is about using the Quick Jump feature to navigate
within FabTime. We have several subscriber discussion topics,
ranging from a couple of changes requested in the newsletter
format to responses to the topics raised in the last issue
(OEE and capacity planning). We welcome your feedback.
Our main article this month sprang from a subscriber
discussion comment about the importance of tracking lots
that are early. In most fabs that we’ve observed, lots that
are late garner a lot of attention, while lots that are
early exit without fanfare. It turns out, however, that
early lots can be a symptom of an underlying problem,
such as too wide a distribution of cycle times, or
inaccurate planning models. In this article, we discuss
both the underlying fab behavior that contributes to
early lots (including a brief mention of hot lots), and
list a few potential consequences of having lots be
significantly early.
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In this issue, we have three community announcements:
the results of the raffle for a complete set of past FabTime
newsletters; a notice about the upcoming Fab Owners Association
meeting; and a conference announcement for the ISMI's Manufacturing
Week. Our FabTime user tip of the month is about setting goals
for Pareto charts. We also have one subscriber discussion question
about data structures for capacity models.
In our main article this month we discuss some of the
computation issues that go along with using OEE (overall
equipment effectiveness) as a metric. At its simplest,
OEE measures the actual good units produced on a tool relative
to the most units that could have been produced on that tool
if everything went perfectly (no scrap, no rework, no
downtime, no wasted time). Much of the value of OEE lies
not so much in the actual OEE values, but in analyzing the
underlying components, and understanding why a particular
tool is not performing as expected. We last wrote about OEE
in the newsletter in detail back 2002. In this article, we
revisit the basics of OEE, with emphasis on calculating OEE
values from fab performance data. We also specifically address
the issues of calculating OEE for batch tools and estimating planned OEE.
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This is our 100th issue of the newsletter. Issue number
1.01 was sent out on April 14th, 2000, to 33 subscribers
from 17 different companies and universities (plus several
consultants). Some of those initial companies don’t even
exist anymore, while others have merged and split and
changed almost beyond recognition. It’s hard to keep
track. But we’re happy to still number some of those
initial subscribers among our current 2731 newsletter
recipients. And, given the year that the semiconductor
industry went through last year, we’re happy to still
be here. For our main article this month, we’ll be
revisiting the 10 years of newsletter issues, in a
bit of a 100th issue celebration.
In this issue, we also have a call for papers for
the 6th International MASM Conference and links to
several recent news articles that we thought that our
subscribers would find of interest. Our FabTime user
tip of the month is about using customized text in
email alerts.
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In this issue, we have two community announcements, and
one response to a previously introduced subscriber
discussion topic. Our FabTime user tip of the month
is about using the new Forecast Arrivals Charts to
predict future arrivals to a particular tool or step.
In our main article this month we return to a topic
first discussed five years ago, the effect of product
mix on fab cycle time. Our return to this topic was
triggered by a question raised in discussion with a
friend: Is it inevitable that cycle time increases as
you add technology mix to an existing fab (because you
have more dedication, smaller tool groups, tools at
higher utilization, more setups, smaller batches, etc.)?
In light of this question, we have revised and expanded
our previous thoughts on product mix and cycle time, and
added some new suggestions for mitigating the negative
effects.
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