problems with an open mind, as in the following
In one case, an inspection of the product showed
particle contamination of some of the wafers. The
suspected source was a contaminated tool; however,
during troubleshooting, SSOE engineers discovered
that an ionization emitter had failed, which created
a charge on the wafers and emitted particles that
were attaching to them. When the emitter rods were
replaced, the problem was solved.
In another case, a particle source was reported
to be a light station, but the actual source was found
at a point 15 feet further down the bay. Engineers
discovered that the installation of the laminar flow
hoods in the space was not parallel, which affected
airflow and caused the particles to travel down the
side of the wall and fall out at the light station.
Use CFD modeling to help identify the source of a
problem. A good Computational fluid
dynamics (CFD) model creates a visual
representation of what is occurring in
the facility but which cannot be seen. It
also lets engineers compare the results
of various facility solutions during the
design phase, thus avoiding additional construction costs to correct the
problem. Unfortunately, many CFD
models are generated based on incomplete data. As a result, the modeler may
make assumptions that are not based on
field-gathered information. For example,
the design documents may not show a
wall of conduit that acts as a barrier in a
certain area of the facility, so the model
shows free airflow through that area.
To ensure that the data are complete, a
modeler must ask the right questions—
what objects may be obstructing flow or
altering the pattern?
Take field measurements to complete the data required to develop a
valid model. They also know that the
entire facility affects the 10-square-foot
process area they have been engaged
to model; therefore, they factor in the
appropriate variables in a wider area.
They also interface with the many
facility experts who have access to all of
the information, including the facility’s
air-balancing team, as well as engineers
and other contractors with experience in the facility.
In fact, these experts’ involvement in the process of
CFD modeling and the completion of its information
is a vital step in the integrity of that model.
It is now universally recognized that SPC can be
applied to any process where output of a product
meeting specifications—conforming product—can
be measured. At its full potential, the process is an
enormous aid to cost effectiveness because it can
make as much conforming product as possible with
a minimum amount of rework or scrap.
Dewayne Galyon is a technical specialist and associate at SSOE Group. With nearly 30 years of experience,
Dewayne leads, performs, and participates in reviews
of multi-discipline projects, critical investigation boards,
operational readiness reviews, facility turnover and start-up, environmental compliance assessments, and time and
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