FabTime Cycle Time Management
Newsletter Abstracts - Volume 12 (6 Issues)
In this issue, we have an announcement about a change
to our Tip of the Month email list (a separate subscription
from the newsletter, for customers). Our FabTime Tip of the
Month is about identifying top causes of equipment downtime.
In our subscriber discussion forum we have two responses to
last month’s question
about capacity planning for cascading tools.
In our main article this month, we focus on metrics
for fab variability. This article was inspired by informal
discussions with several people at the November Fab Owner’s
Association meeting in Austin, Texas. These discussions
encouraged us to consider whether we are providing the best
toolkit that we can in FabTime in terms of fab variability
metrics. We review the sources of variability in fabs, and
our current approach for tracking fab variability, and propose
a brief variability sources snapshot report. We seek our
subscribers’ feedback regarding other metrics that
should be added to this fab variability toolkit.
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In this issue, we have community announcements about
the upcoming Fab Owners Association meeting at Spansion,
and a call for editors for the International Journal of
Production Research. Our FabTime software tip of the month
is about setting default filters for charts. This month’s
subscriber discussion forum includes several responses
sparked by the main topic of the last issue, PM Scheduling.
We also have a new question about capacity analysis for cascading tools.
Our main article this month is about using OEE to
enhance fab performance. Recently, in response to a
suggestion from one of our customer sites, FabTime
changed the method by we calculate OEE (Overall Equipment
Effectiveness) Loss Factors. Several of our customers were
interested in the details of not only the equations used;
but also the methodology of using OEE to improve operations.
In this article we discuss the definition and calculation
of OEE, introduce FabTime’s current methodology for
calculating OEE Loss Metrics, and review how to properly
use the information provided by OEE to continuously
improve an organization’s manufacturing capacity.
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We have a community announcement about two new FabTime
employees in this issue. Our FabTime user tip of the month
is about setting a default home page tab for login. In our
subscriber discussion forum we have two responses to last
month’s article about queueing models for wafer
fabs, as well as a new question about measuring coefficient
of variation for effective process times.
Our main article this month is about PM scheduling.
Equipment downtime in general is one of the top contributors
to fab cycle time. Scheduled downtime, and more specifically
preventive maintenance, contributes to fab variability, but
is somewhat controllable. It’s possible to take the cycle
time impact into account when deciding whether or not to
group maintenance events, and thus minimize the impact of
the scheduled maintenance. In this article, we discuss
ways to do that.
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In this issue, we begin with a call for papers for
the ISMI Symposium on Manufacturing Effectiveness. Our
FabTime user tip of the month is about using a PowerPoint
add-in to display live FabTime charts (mixed with other content)
on monitors. In our subscriber discussion forum we have inputs
on analyzing staffing productivity, embracing the downturn,
and scheduling in the lithography area.
In our main article this month we discuss the application
of queueing models to wafer fabs. We begin by outlining the
benefits and drawbacks of queueing models (as compared with
static models and with simulation). We then discuss toolgroup-level
models, as implemented in FabTime's operating curve spreadsheet,
as well as different approaches for constructing fab-level models.
We conclude by discussing the simplified approach of using
aggregated fab-level inputs in a simple G/G/c queueing model,
and where this approach might, and might not, be useful. If
any readers would care to share their experiences in applying
queueing models to fab planning or operations, we will post
those in a followup article. We welcome your feedback.
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In this issue we also have two calls for papers for
conferences. Our FabTime user tip of the month is about
ways to export full chart datasets to Excel. In our
subscriber discussion forum we have two responses to
last month’s question about managing in the presence
of multiple constraints, and a follow-up from Bob
Kotcher to last month’s main article about confidence
intervals vs. prediction intervals.
In our main article this month, we have provided a
forum for re-introducing a number of previously raised
subscriber discussion topics. Our hope is that some of
you will find that you have something to say on one or
more of these topics, so that we can all learn from one
another as a community. We welcome your feedback
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In this issue we have three announcements, one about
a survey from WWK, another with a call for papers, and
the third about staying in touch with FabTime via my
LinkedIn profile. Our software tip of the month is about
using the new lot line yield charts in FabTime. We only
have one subscriber discussion question, but it is quite
detailed (about fab management in a multi-constraint
environment).
In our main article this month, we address the
difference between confidence intervals and prediction
intervals. Both can be applied to simulated or actual
recorded data, anything where you have repeated, variable
observations (cycle times, WIP, etc.). Confidence intervals
are used to estimate an underlying value that can’t be
directly observed, like the “true” mean cycle time for
a product line. Prediction intervals, instead, are used
to establish a range in which it is likely that a future
observation will occur, given a series of past observations.
So, for example, you might use a prediction interval to
predict the upper and lower bound of expected fab throughput
next week. We hope that you’ll find this discussion useful.
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