Transcript No Slide Title

10. Clean Room Application
Clean room technology -> Aerosol-free environment
Applications:
1. Pharmaceutical industry
2. Hospitals
3. Biotech industry
4. Semiconductor industry
5. Microelectronic industry
Examples
Sources of contamination
1. Aerosol -> airborne particles
2. Hydrosol, e.g., control of deionized water and
other process chemicals
3. Biological contaminants, e.g., pyrogenic and
endotoxin producing bacteria
4. Ionic and radioactive components
5. Condensation or diffusive products
6. Chemically reactive particles
Won’t be
considered!
The Principles of a Clean Room
1. The air supplied to the CR is sufficient in quantity to dilute and remove
the contamination generated in the room.
2. The air within the cleanroom moves from clean to less-clean areas and moves
in the correct direction through doorways.
3. The air supplied to the room is of sufficient quality that it will not add to the
contamination of the room.
4. The air movement in the room should insure that there are no areas in the room
of high concentration of contamination.
5. If all other principles are met then the concentration of particles should be
measured to test if the room meets the required standard.
Design
1. Room is supplied with large quantities of highly filtered air.
2. This air dilutes and removes the particles and bacteria dispersed
from personnel and machinery in the room.
3. Also this holds positive pressure and ensures that air only flows
out of the room.
4. Room is built from materials that do not generate particles and can
be easily cleaned.
Positive Isolation Schematic
A/C
3001X
Blank supplies or Terminal HEPAs
Make
Up Air
Optional
Filter Integrated
to A/C
Return
3001X
Optional
Floor
A/C
Negative Pressure (TB) Isolation Room Schematic
A/C
Exhaust
Term HEPA
Supplies
A/C
Supply
3 TOTAL
Return
Annunciator
Bathroom exhaust tied
into the exhaust ducting.
Pre filter should be
accessible from room.
Main filter housed in
module that is removed
and accessed above
ceiling.
5. Cleanroom personnel wear clothing which minimizes their dispersion
of particles
6. Two major types of cleanrooms:
Unidirectional (laminar flow) and turbulently ventilated.
7. Unidirectional uses much more air than turbulent.
8. Unidirectional CR air speed is typically about 0.4m/s.
9. Air is recirculated at a great rate, diluted with some fresh air and
some is discarded.
10. Pencils cause graphite particles!
11. 2-10% of total air supply is fresh air.
Class of clean room - U.S. standard
class
1
10
100
1,000
10,000
100,000
>0.1 m
#/ft3
35
350
-
>0.2 m
#/ft3
7.5
75
750
-
>0.3 m
#ft3
3
30
300
-
>5.0 m
#/ft3
7
70
700
Class of Filter
Filter class
H10
H11
H12
H13
H14
H15
H16
H17
Overall efficiency(%)
85
95
99.5
99.95
99.995
99.9995
99.999 95
99.999 995
1. HEPA FILTERS
High Efficiency Particulate Air filters are replaceable extended-media
dry-type filters in a rigid frame having a minimum particle collective efficiency
of
- 99.97 percent for a 0.3 micron particle (standard grade)
- 99.90 percent for a 0.3 micron particle (low grade)
- 99.99 percent for a 0.3 micron particle (high grade)
and a maximum clean filter pressure drop of 2.54 cm (1") water gauge when tested
at rated air flow capacity.
2. ULPA FILTER
Ultra Low Penetration Air filters are extended media dry filters in a rigid frame
that have a minimum particle collection efficiency of 99.999 percent for
particles greater than or equal to 0.12 micron in size
Commercial HEPA filter module.
1. Average person in poor CR garments (coats) generates about
2x106 part/min greater than 0.5 m and 300000 part/min > 5.0 m.
2. For cleanrooms of ISO class 6 (class 1000) and poorer quality, HEPA filters
are used with turbulent ventilation to meet the cleanroom classification.
3. For cleanrooms of ISO class 5 (class 100), HEPA filters are used with
unidirectional ventilation to meet the cleanroom classification.
4. For cleanrooms of ISO class 4 (class 10) or lower, ULPA filters are used with
unidirectional ventilation to meet the cleanroom classification.
5. Pressure drop across a filter is obviously dependant on the velocity of air
through the filter. The nominal air velocity is usually considered to be 0.5 m/s
(100ft/min) and pressure drop at this velocity is likely to be between 120-170 Pa.
6. When the pressure drop reaches 2.5-3 times the original pressure, its time to
replace the filters.
Filter Collection Mechanism - A Review
1. Diffusion: tiny particles which don’t have enough mass to leave the air stream on their
own move randomly in the air stream. This random motion is due to collisions with
other small dust particles and collisions with the molecules of the gas which they
are suspended. If these particles touch a fibre or previously captured particles they
will be held. (Brownian movement causes them to move randomly)
Streamlines
fiber
cross section
2. Impaction is when more massive particles leave the air stream due to their own
inertia and collide with a fibre. This will cause them to be imbedded.
Streamlines
Particle
trajectory
fiber
cross section
3. Interception is when a particle strikes a fiber as it passes (tangentially). The particle
will also be captured in this process.
Streamlines
fiber
cross section
Electrically Enhanced Filtration
Filter becomes
bactericidal!
Flow enters first
high intensity
ionizing field.
Particles and bacteria
are charged due to ion
flux in this ionizing field
- some of the bacteria
are killed here.
The charged particles
and bacteria are highly
efficiently filtered - up
to 1000 times lower
penetration than
conventional filters
with the same pressure
drop and flow rate.
Bacteria caught on
the filter are subjected
to a continuous dose
of ionizing radiation
and are thus killed.
Filter Testing
Military standard 282
1. Thermally generated particles of di-octyl phthalate (DOP) with average size of
0.3 micron. Nowadays poly-alpha olefin(PAO) or di octyl sebacate(DOS) have
replaced DOP.
2. Oil mist is produced upon heating these oils.
3. Efficiency is then measured directly.
Sodium flame test (Eurovent 4/4)
1. An aerosol of sodium chloride is sprayed into the air then sucked through the filter
2. The efficiency is tested.
Clean Room Measurements
Clean room limits: U.S. (209D) and Germany Standards (VDI 2083)
Recommended time intervals for regular particle measurements in various
clean room classes
German VDI 2083
6
US 209D
100,000
Frequency
5
10,000
4
1,000
3
100
2
10
1
1
Half- Monthly 14 days Weekly Daily Continuous
yearly
Minimize sampling loss
1. Short sampling tubes.
2. Non-conductive material for the tubings. Avoid polymeric materials.
3. Isokinetic sampling is not possible due to turbulence and it may not
be necessary.
Sampling points
1. Distributed uniformly in clean room.
2. Distance between points should not be larger than 2 m.
3. Minimum number of sampling points from US Fed Std 209D:
- Area of the entrance plane divided by 25 ft2, or
- Area of the entrance plane divided by the square root of class designation.
4. Height of the sampling should be at the working or product level.
Minimum volume per sampling in liter per minute: US Fed Std 209D
Measured particle size
Class
0.1 micron 0.2 micron 0.3 micron 0.5 micron 5 micron
1
17
85
198
566
-
10
2.83
8.5
19.8
56.6
-
100
-
2.83
2.83
5.6
-
1,000
-
-
-
2.83
85
10,000
-
-
-
2.83
8.5
100,000
-
-
-
2.83
8.5
Monotoring Systems
1. Monitor ambient air and within the equipment.
2. Sensor system is needed to give a feedback to the control system to prevent
deposition on the product.
3 Aim of clean-room monitoring
- To gain information about the process
- To determine the interdependence of different parameter
- To elucidate the cause of low product quality
- To determine the effects of any actions on product yield.
Multidrop communications clean room monitor system.
Commercial monitoring systems
Measurement Techniques
Optical Particle Counters (OPC)
Light scattering
Angular scattering for
water droplet (m = 1.33).
Spectral scattering for water
droplet (m = 1.33).
Climet OPC.
Condensation Particle Counter (CPC)
Principle of CPC
- CPC uses the principle that supersaturated vapor condenses on
small particles.
- An internal pump draws the aerosol sample into the CPC.
- A flowmeter controls the flow volumetrically.
- Upon entering the instrument, the sample passes through a
heated saturator, where butanol evaporates into the air stream
and saturates the flow.
- The aerosol sample then passes into a cooled condenser tube,where vapor supersaturates and
condenses onto the airborne particles.
- This produces larger, easily detectable aerosol droplets.
- These droplets pass through an optical detector immediately after leaving the condenser.
Particle Flux Meter
Principle of PFM
- No sample is taken. Light is introduced to measurement volume.
- Otherwise functions like an OPC.
- Three types of PFM
1. Beam expansion: Laser beam is expanded by cylindrical lenses to form a rectangular beam.
2. Multiple reflection: Light sheet is produced by multiple reflection of a laser beam between
two mirrors.
3. Scanner: Laser beam is deflected by a polygon mirror.