study from pms
CPC TECHNOLOGY
COMPARISON STUDY
The NPC10 works by growing nanometer-sized particles in the
aerosol sample into micrometer-sized particles by passing them
through a super-saturated vapor of working fluid and creating
conditions promoting the condensation of the fluid on the
particle surface.
Consider the original particle serving as a nucleation site for
the condensation process. The condensate causes the particles
to grow sufficiently in size so that they can be detected and
counted using traditional optical light scattering approaches.
The benefit of the CPC is the ability to detect very small particles
with the trade-off being that the condensation process lacks
size resolution in the growth process. As a result, instruments
based on this technique currently provide only a single channel
measurement result.
A study was conducted to compare the counting performance
of the new, high-flow 10nm instrument with a traditional 0.1µm
optical particle counter when monitoring ISO Class 1 to ISO Class
4 environments.
Experimental and field data demonstrate that ISO Class 1 and 2
environments, which have very low concentrations of particles
greater than 100nm, can possess much higher concentrations
of nanoparticles.
This suggests that the current ISO classification system may be
insufficient to properly describe the cleanliness of the high purity
environments required for advanced electronics manufacturing.
NANOPARTICLE MONITORING IN ULTRA-CLEAN
MANUFACTURING ENVIRONMENTS
DISCUSSION
The NPC10 counted more particles than
the Lasair III 110 in each of the ISO Class
environment experiments due to its
10nm sensitivity. The ratio was the
largest for the Class 1 test (37 times
more) and decreased for Class 2 through
Class 4 (17x,10x and 4x, respectively).
In the ISO Class 1 test, there were a
significant number of particles present
below 0.1µm and very few particles
present above 0.1µm. The data shows
there were a considerable number
of nanoparticles present throughout
the testing. Although it is difficult
to pinpoint the exact source of these
particles, it is likely the two sources
during this experiment are the
preferential diffusion of nanoparticles
from the outside ambient air and
low-level particle generation from the
instruments themselves.
The agreement or “matching” between
the two NPC10 instruments was within
20% for all ISO environments tested,
which meets industry expectations.
A reasonable argument can be made that multiple channels are
not necessary for monitoring ultra-clean manufacturing processes
because contamination trends and excursions can be easily identified
above background levels using only a single channel of data.
SETUP
The experiment compared the Lasair® III
110, a traditional 0.1µm particle counter
with six fixed-size channels sampling at 28.3
LPM (1 CFM), to two NPC10 NanoParticle
Counters, which counts all particles >10nm
in size and samples at 2.8 LPM.
Testing was conducted using a laminar
flow hood as a proxy for a manufacturing
process or mini-environment. The hood
provided high velocity air flow and a
variable speed fan that allowed the
cleanliness of the environment to be
controlled to the desired cleanroom class.
Additional isolation was used around the
sample collection point within the hood
to generate the Class 1 environment.
The setup allowed small volumes of
ambient room air to be introduced on a
controlled basis to create the ISO Class 2,
3, and 4 environments.
The test instruments were placed inside
the environment and sample inlet tubes
of 1 meter and 0.5 meter were attached
to the OPC and CPCs, respectively. The
inlet end of all three sample tubes were
bundled together and attached to a fixed
post inside the flow hood. The OPC was
first used to determine the class of the
environment per ISO 14644.
RESULTS CONCLUSION
Table 1 shows the normalized counts for each of the three instruments under test in each of the ISO environments, and the counting
performance of the 10nm and the 0.1µm instruments in ISO Class 1 through 4. With its 10nm sensitivity, the NPC10 NanoParticle Counter bridges the gap between
conventional aerosol optical particle counting at 0.1µm (100nm) and sub-nm scale
airborne molecular contamination. The experimental results provided two key findings:
1. The 10nm instrument provides
higher counts than a less-
sensitive instrument, indicating
that nanoparticles can be
present in very clean areas –
likely caused by sources within
the operational environment
(chemical, thermal, etc.).
2. CPC technology has
agreement between like
instruments across a wide
spectrum of contamination
challenges – ISO Class 1
through ISO Class 4.
The test results indicate that a particle
monitoring strategy for very clean
manufacturing processes can be improved
by adding a high-sensitivity CPC instrument.
While a traditional optical counter
providing 0.1µm sensitivity is needed for
certification of the ISO class as given in
ISO 14644-1, the CPC counter is a
complementary instrument that can detect
contamination excursions and be used to
identify changes in contamination trends
that have been previously undetectable to
0.1µm sensitivity instruments.
Find out about PMS at: pmeasuring.com
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