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9 Cleanroom Testing and Monitoring

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									9. Cleanroom Testing
    and Monitoring
        Purposes for initial test:
• Fulfill the design
   – working correctly and achieving the contamination
• Bench-mark:
   – establish the initial performance of the room to
     compare the results of routine check or contamination
     problem in the future.
• Training the staff: (most important)
   – initial testing is to familiarize and train the staff.
   – Only opportunity to understand how their cleanroom
     works and learn the methods used to test.
                 initial test
• Time
  – been built/ going to hand over/ reopen
• Tested standards
  – ISO 14644-1.
• Monitoring
  – to regularly check the room at the time
   intervals set by ISO 14644-2
Principles of Cleanroom Testing
• Quantity:
   – Turbulently: dilute--air volume (supply and extract)
   – Unidirectional: remove –air velocity
• Direction (flow direction):
   – from clean area  less-clean areas to minimise the
     movement of contaminated air.
• Quality:
   – the air will not add significantly to the contamination
     within the room
• Distribution inside cleanroom
   – the air movement has no areas with high
     concentrations of contamination.
Cleanroom Tests
• Air supply and extract quantities
  – turbulently ventilated cleanrooms the air
    supply and extract volumes
  – unidirectional airflow  air velocity.
• Air movement control between areas:
  – The pressure differences between areas are
  – The air direction through doorways, hatches,
    etc. is from clean to less-clean.
• Filter installation leak test
  – a damaged filter
  – between the filter and its housing or
  – any other part of the filter installation.
• Containment leak testing
  – Contamination is not entering the cleanroom
    through its construction materials.
• Air movement control within the room
  – turbulently ventilated : check that there are no
    areas within the room with insufficient air
  – unidirectional airflow : check that the air
    velocity and direction throughout the room is
    that specified in the design.
• Airborne particles and microbial
  – final measurements of the concentration of
    particles and micro-organisms
• Additional tests
  – temperature
  – relative humidity
  – heating and cooling capabilities of the room
  – sound levels
  – lighting levels
  – vibration levels.
• Guides provided by
  – the American Society Heating Refrigeration
    and Airconditioning Engineers (ASHRAE) in
    the USA, and
  – the Chartered Institute of Building Services
    Engineers (CIBSE) in the UK.
 Testing in Relation to Room Type
       and Occupation State
• The type of tests to be carried out in a
  cleanroom depends on whether the room
  is unidirectional, turbulent or mixed airflow:
  – ‘as-built’ ---in the empty room,
  – ‘at rest’ --- the room fitted with machinery but
    no personnel present or
  – ‘fully operational’---these occupancy states
    are discussed more fully in Section 3.4 of this
        Re-testing to Demonstrate
• The cleanroom
  intervals, these
  intervals being
  more frequent
  in higher
  rooms: ISO
     Monitoring of Cleanrooms
• Use risk assessment to decide what monitoring
  tests should be done and how often. The
  variables that are most likely to be monitored
  – air pressure difference
     • This might be necessary in high quality cleanrooms such as
       ISO Class 4, and better.
  – airborne particle count
     • This might be necessary in high quality cleanrooms such as
       ISO Class 4, and better.
  – where appropriate, microbiological counts.
10. Measurement of Air
Quantities and Pressure
• A cleanroom must have sufficient clean air
  supplied to dilute and remove the airborne
  contamination generated within the room.
• Air Cleanliness:
  – Turbulently ventilated cleanroom
     • air supply; the more air supplied in a given time, the cleaner
       the room.
  – unidirectional cleanroom
     • air supply velocity
• Test:
  – Initial testing of the design
  – Regular intervals check
                 Air Quantities
• Instruments:
  – Hoods: air supply
  – Anemometers: air
• Turbulently ventilated
  – measured within the
    air conditioning
    ducts Pitot-static
  Measuring air quantities from
      within a cleanroom
• Air air filter (no diffuser) anemometer at the
  filter face average velocity  air volume
  – Difficulty: the non-uniformity of the air velocity
    inaccurate measurement
• Air air diffusers unevenness of air
  velocities incorrect air volume
• Hood: air supply volume average velocity
  measured at the exit of the hood air volume
• Anemometers: away from the filter of
  about 30cm (12 inches)
• Vane Anemometer
  – Principle: Air supply  turning a vane 
    frequency  velocity
  – Accuracy: velocity is less than about 0.2 m/s
    (40 ft/min), the mechanical friction affects the
    turning of the vane
Vane Anemometer
      Thermal Anemometers
• Principle: Air passing
  through the head of
  the instrument
  cooling effect  the
  air velocity: Fig.10.3 :
  a bead thermistor (有
• Low velocities can be
  measured with this
  type of apparatus
    Differential Pressure Tests
• The units:
  – Pascals, inch water gauge are used (12Pa =
    0.05 inch water gauge).
• Pressure difference: 10 or 15 Pa between
  clean areas
  – 15 Pa is commonly used between a
    cleanroom and an unclassified room,
  – 10 Pa between two cleanrooms.
• Large openings:
  – problems can occur when trying to achieve a
   pressure difference between areas connected
   by large openings, such as a supply tunnel.
   To achieve the suggested pressure drop :
    • Very large air quantities through the tunnel
    • To accept a lower pressure difference
     Apparatus for measuring
      pressure differences
• Manometer:
  – range of pressure
    difference of 0-60 Pa
    (0-0.25 inch water)
  – inclined manometer;
    magnehelic gauge;
    electronic manometer
             Inclined manometer
• works by pressure
  pushing a liquid up an
  inclined tube.
   – small pressure
     changes in the inclined
     tube up to a pressure
     of about 60 Pa.
   – After that pressure, the
     tube moves round to
     the vertical measuring
     pressure differences
     can be in the 100 to
     500 Pa range.
  Methods of checking pressure
• pressure differences between areas
   – adjusting the pressure differences :
       • extract be reduced to increase the pressure, and increased to
         decrease it.
• If manometers are not permanently installed, a tube from
  a pressure gauge is passed under the door, or through
  an open by-pass grille or damper into the adjacent area.
• In some ventilation systems, the pressures within rooms
  are measured with respect to one reference point. When
  this type of system is being checked, the pressure
  difference across a doorway can be calculated by
  subtracting the two readings of the adjoining spaces.
11. Air Movement Control
   Between and Within
• To show that a cleanroom is working
  correctly, it is necessary to demonstrate
  that no contamination infiltrates into the
  cleanroom from dirtier adjacent areas.
• Cleanroom Containment Leak Testing
  – Airborne contamination: doors and hatches,
    holes and cracks in the walls, ceilings and
    other parts of the cleanroom fabric
    Contamination can be pushed into
           the cleanroom at
•   ceiling-to-wall interface
•   filter and lighting housings-to-ceiling interfaces
•   ceiling-to-column interface
•   the cladding of the ceiling support pillars
•   Service plenums and the entry of services into
    the cleanroom: electrical sockets and switches,
    and other types of services providers.
    Particularly difficult to foresee and control in a
    negatively pressurized containment room.
 Methods of checking infiltration

• Smoke test (dust test)
  – flow direction: open door, or through the
    cracks around a closed door, cracks at the
    walls, ceiling, floor and filter housings, service
    ducts or conduits.
• Difficulty
  – where the containment originates from may
   be unknown, and it is often difficult to find the
   places to release test smoke.
     Containment leak testing
• Timing
  – handing it over to the user
  – major reconstruction work has been carried
  – ISO 14644-2 lists the ‘containment leak’ test
    as an ‘optional’ test and suggest a re-testing
    interval of two years
    Air Movement Control within a
• sufficient air movement
   – dilute, or remove airborne contamination prevent a build-up of
• turbulently ventilated cleanroom:
   – good mixing, critical areas: where the product is exposed to the
     risk of contamination
• unidirectional flow cleanroom
   – critical areas should be supplied with air coming directly from
     the high efficiency filters. However, problems may be
     encountered because of:
       • heat rising from the machinery and disrupting the airflow
       • obstructions preventing the supply air getting to the critical area
       • obstructions, or the machinery shape, turning the unidirectional flow
         into turbulent flow
       • contamination being entrained into the clean air.
  Air movement visualization
• Objective: sufficient clean air gets to the critical
  areas qualitative methods
• Visualization:
   – Streamers
   – smoke or particle streams
• Streamers (threads or tapes):
   – high surface-area-to-weight ratio, ex. recording tapes
   – A horizontal flow: 0.5 m/s (100 ft/min) streamer 45°
     to the horizontal
• about 1m/s (200 ft/min) almost horizontal.
 smoke or particle streams
–oil smoke 
–Water vapour :
 from solid C02
 (dry ice) or by
      putter and smoke tube':
• Titanium tetrachloride
  acid  corrodes some
  surfaces harmful to
  sensitive machinery or
  harm the operator's
     Air Movement in turbulently
          ventilated rooms
• working well: quickly dispersed
• not working well Areas: not disperse
  quickly contamination build up 
  improved by adjusting the air supply
  diffuser blades, removing an obstruction,
  moving a machine.
Air Movement in unidirectional flow
• air moves in lines
  – Visualisation
    techniques: smoke
  – Still picture
      Air velocity and Direction
• A permanent record: velocity and direction
      Recovery Test Method
• A quantitative approach
• A burst of test particles introduced into
  the area to be tested mixed with their
  surroundingsthe airborne particle count
  should be measured,
• A useful endpoint is one-hundredth of the
  original concentration, and the time taken
  to reach there can be used as an index of
         Ch. 12
Filter Installation Leak
                   HEPA test
• Manufacturer's factory and packed OK
• Unpacked and fitted into the filter housings
  maybe damage
• Leakage problems
   – casing
   – housing
• Testing : artificial test aerosol
 Leakage areas in a HEPA filter

A - filter paper-to-case cement area         C- gasket
D - frame joints.     B - filter paper (often at the paper fold)
 Gasket leaks from filters     Gasket and casing leaks from
inserted down from ceiling   filter inserted up from cleanroom
Figure 12.4 Filter-housing gel seal method
 Artificial Smoke and Particle Test

• Cold-generated oils
  – Di-octyl phthalate (DOP)鄰苯二甲酸二辛酯
    • oily liquid, potentially toxic effects, no longer used
  – Di-octylsebacate (DOS)葵二酸二辛酯
    • 常用
  – poly alpha olefin (PAO)聚烯茎油
    • 常用
       Cold-generated oil Test

air               Laskin nozzle   Air+
(high pressure)                   oil particle
                                    0.5 mm

      Air pump        oil
     Hot generated smokes

inert gas:
                                      oil smoke

   oil                          condense

                                      0.3 mm
Hot oil smoke generator
 Semiconductor manufacturing
• 'outgassing'
• chemical products harmful to filter
• 使用Polystyrene Latex Spheres (PLSs)
  聚苯乙烯乳膠球(0.1 ~ 1mm)
 Apparatus for Measuring Smoke
• Photometer光度計
 – 28 1/min (1 ft3/min) of
   airborne particles
 – particles refract the light
 – electrical signal
 – concentration: between
   0.0001 μg/1 and 100 μg/1.
• Single particle
  – sample a volume of
    air and this is
    collected in a set time
    Methods of Testing Filters and
          Filter Housings
• Scanning methods
  – a probe with a photometer, or single particle
  – Scan speed : not more than 5cm/s
  – leaks : media, filter case, its housing
  – The most common leaks:
     • around the periphery of the filter
     • the casing-to-housing seal,
     • the casing joints
              Repair of leaks
• Filter media leak
  – at the fold of the paper
  – repaired on site with
• replaced
         Ch. 13
Airborne Particle Counts
          Cleanroom test
• air supply volume,
• pressure differences,
• air movement within and between
• filter integrity
• airborne particle concentration
           Particle counter
• Particle counter : both counts
  and sizes
• Photometer : mass of particles
principle of Particle Counter
Particle Counter
Airborne particle counter:
flow rate: 28 1/min (1 ft3/min) of air
size range: regular 0.3 μm or 0.5 μm
high-sensitivity: 0.1 μm but with a smaller air

Continuous Monitoring Apparatus
      for Airborne Particles
      • sequential
      • simultaneous
Sequential monitoring system
Simultaneous monitoring system
               best but most expensive
   Particle Counting in Different
        Occupancy States
• Occupancy state: as built, at rest,
• cleanroom contractor: 'as built'
• ‘rule of thumb: ‘as built’ room will be
  about one class of cleanliness cleaner
  than when ‘operational’.
     Measurement of Particle
   Concentrations (ISO 14644-1)
• Principles: The number of sampling
  locations must reflect the size of the room
  and its cleanliness.
• The methods: (a) number of sampling
  locations and (b) the minimum air volume
   Sample locations and number
      (ISO standard 14644-1)
• Minimum number of locations:
  – Where NL rounded up to a whole

                                        NL  A
  – A is the area of the cleanroom,
    or clean air controlled space, in
    m 2.
• evenly distributed and height
  Airborne sampling volume
• Minimum volume at each location: the air
  volume should be large enough to count
  20 particles of the largest particle size
• V= 20/C x 1000
  – where V is the minimum single sample
    volume per location, expressed in litres.
  – C is the class limit (number of particles/m3)
• One or more samples : at each location
• The volume sampled at each location: at
  least two liters
• The minimum sample time : at least one
 Acceptance criteria( ISO 14644-
• the average particle concentration at each of
  the particle measuring locations falls below
  the class limit
• when the total number of locations sampled is
  less than 10, the calculated 95% Upper
  Confidence Limit (UCL) of the particle
  concentrations is below the class limit.
• 4m x 5m size. ISO Class 3 in the 'as built'
  condition at a particle size of >= 0.1 μm.
• Number of locations
  – A= 4m x 5m.  N = √4x5 = 4.475
  – The minimum number of locations is 5
• Minimum air sampling volume
  – V= 20/C x 1000
  – C: ISO Class 3 room is 1000/m3.
  – ∴Minimum volume = 20/1000 x 1000= 20 litres
• particle counter flow rate of 28.3 liter/min,
           i.e. 20liter, time = 42 s
• ISO 14644-1 requires a minimum sample time
  of 1 minute
•  1 minute
• first part of the ISO requirement is
  therefore satisfied(<1000).OK
• As less than nine samples were taken
  95% UCL does not exceeded the class
  limit. ???
       Calculation of 95%UCL
• the 'means of averages': M
  M = (580+612+706+530+553)/5 = 596
• Standard deviation (s.d).
                                               (Xi  M )   2

• Standard deviation s.d.=69   s.d     i 1
                                               N 1

• 95﹪UCL = M+[UCL factor x (s.d/√n)]
• As number of locations is 5, the t-factor is 2.1.
• ∴ 95﹪ UCL for particles > 0.1 μm = 596 + [ 2.1 x
  69/√5 ]= 661<1000
• The cleanroom is therefore within the
  required class limit.

• The way to avoid any 95% UCL problems
  is to always test more than nine points in
  the room
Ch.14 Microbial Counts
• People are normally the only source of
  micro-organisms in a cleanroom
• as built/ at rest  little value
• Operational: micro-organisms are
  continually dispersed from people in the
Microbial Sampling of the Air

  • Volumetric air sampler
  • Settle plate sampling
  Volumetric' air samplers

• a given volume of air is sampled; also
  known as 'active' sampling.
• impact micro-organisms onto agar
• remove micro-organisms by membrane
• Agar: jelly-type material with nutrients
  added to support microbial growth.
• Micro-organisms landing 
  temperature, time colony (millimetres
        Settle plate sampling
• where micro-organisms are deposited,
  mainly by gravity, onto an agar plate.
• Impaction onto agar:
  – inertial impaction
  – centrifugal forces.
• Time and Temperature to grow
• Bacteria : 48 hours at 30° C to 35° C;
• Fungi: 72 hours at 20° C to 25° C
  Inertial impaction samplers
• Flow rate: 30 to 180 litres/min (1 ft3/min to 6
  ft3/min) of air
• Air Inertial impactors  slit or hole 
  accelerate (20~30m/s)
     Centrifugal air samplers
• Air rotating vane centrifugal force  agar
• The impaction surface is in the form of a
  plastic strip with rectangular recesses into
  which agar is dispensed
        Membrane filtration
• A membrane filter is mounted in a
  holder vacuum draw air  microbe-
  carrying will be filtered out by membrane
   The membrane placed an agar plate
• A membrane filter with a grid printed on
  the surface will assist in counting the
Membrane holder with filter
Microbial Deposition onto Surfaces

• Indirect measurementvolumetric
• direct method settle plate sampling
      Settle plate sampling
• micro-organisms skin particles 10 to
  30μm by gravity onto surfaces at an
  average rate of about 1 cm/s
• Settle plate sampling: Petri dishes
  (diameter:90mm) containing agar medium
   opened and exposed  time (4~5
  hours) particles to deposit Petri dishes
Calculation of the likely airborne

   Contaminat ion rate
    Settle plate count
              area of product
              area of petri dish
                time product exposed
              time settle plates exposed
Microbial Surface Sampling

  • contact sampling
  • swabbing
   Contact surface sampling
• surface (flat) RODAC
  (Replicate Organisms
  Detection and Counting)
  dishes Fig 14.5 are
  usedThe agar is rolled
  over the cleanroom
  surface Micro-
  organisms stick to the
  agar incubated time
  and temperature micro-
  organisms grow &
Contact Slides
• uneven surfaces: bud
  swab rubbed surface
  and then rubbed over
  an agar plate.
Copan Swab Rinse Kits
          Personnel sampling
• Personnel are the primary source of micro-
  organisms in a cleanroom.
• The methods commonly used are:
  – Finger dabs.
         – The person's fingers tips, or their gloved hand, is pressed or wiped
           on an agar plate and the number of micro-organisms ascertained.
  – Contact plates or strips.
         – The person's garments are sampled by pressing the plate or strip
           onto their clothing. This is best done as they come out of the
  – Body box.
         – If a person wearing normal indoor clothing exercises within a body
           box their dispersion rate of airborne micro-organisms can be
Dip   Slide
Operating a Cleanroom:
Contamination Control
• considering the sources and routes of
  contamination within a cleanroom and how
  to control these.
       Control contamination
• assessing risk during manufacturing: such
  as Fault Tree Analysis (FTA) and Failure
  Mode and Effect Analysis (FMEA).
  (Electrical and mechanical systems)
   Hazard Analysis and Critical
  Control Point (HACCP) system.

• HACCP has a seven-step approach:
  – Identify the sources of contamination in the
  – Assess the importance of these sources
  – Identify methods that can be used to control these
  – Determine valid sampling methods to monitor
    either the hazards, or their control methods, or
– Establish a monitoring schedule with 'alert' and
  'action' levels
– Establish a monitoring schedule with 'alert' and
  'action' levels
– Verify that the contamination control system is
  working effectively by reviewing the product rejection
  rate, sampling results and control methods and,
  where appropriate, modifying them.
– Establish and maintain appropriate documentation.
– Train the staff.
      Identification of Sources and
        Routes of Contamination
• Sources of contamination
  –   dirty areas adjacent to the cleanroom;
  –   unfiltered air supply;
  –   room air;
  –   surfaces;
  –   people;
  –   machines, as they work;
  –   raw materials;
  –   containers;
  –   packaging.
Airborne and contact routes of
– The two main routes of transfer are airborne
  and contact.
– Airbone: particles are small; fibres, chips or
  cuttings fall directly on to the product.
– Contact: machines, containers, packaging,
  raw materials, gloves, clothes, etc.
 Construction of a risk diagram

• Risk diagram: possible sources of
  contamination; their main routes of
  transfer; methods of controlling this
• Figure 15.1 is an example of a risk
  diagram; the manufacturing process has
  been shown
Sources and routes of particle and microbial contamination in a
        cleanroom along with preventative measures
Sources and routes of control associated with process machinery.
 Assessment of the Importance of
• Possible sources of contamination routes of
  transmission risk assessment
• Risk factors:
  – risk factor A: the amount of contamination on, or in,
    the source that is available for transfer
  – risk factor B: the ease by which the contamination is
    dispersed or transferred
  – risk factor C: the proximity of the source to the critical
    point where the product is exposed
  – risk factor D: how easily the contamination can pass
    through the control method
Risk factors for assessing hazards

                 • Risk rating = A x B x C
                 • Low: a risk rating of
                   less than 4
                 • Medium: between 4
                   and 12
                 • High: higher than 12
Identification of Methods to Control
• Identify the contamination hazards their
  degree of risk assessed methods
  available to control them.
• Figures 15.1 and 15.2 show methods that can be used to
  control the routes of spread of contamination. These are:
   – HEPA or ULPA air filters  supply air
   – Airborne contamination from areas outside the cleanroom air
     moves from the cleanroom outward
   – The contamination from the floors, walls and ceiling  cleaning
   – People’s mouth, hair, clothing and skin Cleanroom garments
     and gloves
   – Contamination from machines  design of the machine, the use
     of exhaust air systems to draw the contamination away.
     Cleaning  dirt on the machine.
   – Raw materials, containers and packaging  made from
     materials that do not generate contamination; manufactured in
     an environment have minimal concentrations of contamination;
     correctly wrapped to ensure that they are not contaminated
     during delivery
   Sampling Methods to Monitor
   Hazards and Control Methods
• Monitoring:
  – collection efficiency of sampling instruments;
  – calibration of the instruments;
  – determination that the hazard is of sufficient
    importance to need to be monitored;
  – determination that the sampling method used
    is the best available for directly measuring the
    hazard, or its control method.
Establishing a Monitoring Schedule
   with Alert and Action Levels
• 'alert' and 'action' conditions; 'warning' and
  'alarm' levels.
• The 'alert' level should be set to indicate that the
  contamination concentrations are higher than
  might be expected, but are still under control.
• The 'action' level should be set such that when it
  is exceeded there should be an investigation.
• Analysing the monitoring results and setting
  'alert' and 'action' levels is quite a complicated
  subject if a statistical approach is used.
  Knowledge of statistical techniques, especially
  the use of trend analysis.
Verification and Reappraisal of the
• The method is correctly implemented 
  rejection rate of the product; measurement of the
  particle, or microbial, levels in samples of the
  final product. We can now reassess the
  – the relative importance of the hazards
  – the necessity and the methods for controlling the
  – the effectiveness of the control methods
  – the correctness of the monitoring schedule
  – whether the 'action' and 'alert' levels should be
    lowered or raised.
• An effective contamination control system will
• (1) the methods described in the preceding
  steps of this chapter,
• (2) the monitoring procedures, and
• (3) results from the monitoring.
• Regular reports should be issued of an analysis
  of the monitoring results and any deviations from
  the expected results.
             Staff Training
• They first arrive at the cleanroom
• Train at regular intervals throughout their
16. Cleanroom Disciplines

• source of contamination
  – micro-organisms
  – particles and fibres
 People Allowed into Cleanrooms

• Walking:
  – produce 1,000,000 particles >= 0.5 mm
  – several thousand microbe-carrying particles
    per minute
• Suggestions contain criteria that can discriminate
  against some personnel
  – Skin conditions: skin cells, dermatitis, sunburn or bad
  – Respiratory conditions: coughing, sneezing
  – Biocleanroom:
     • allergic conditions, which cause sneezing, itching, scratching,
       or a running nose
     • allergic to materials used in the cleanroom, (a) garments
       (polyester) (b) plastic or latex gloves, (c) chemicals: acids,
       solvents, cleaning agents and disinfectants, and (d) products
       manufactured in the room, e.g. antibiotics and hormones.
  Personal Items Not Allowed into
         the Cleanroom
• General rule: nothing should be allowed
  into the cleanroom that is not required for
  production within the room.
       Prohibited items:
• food, drink, sweets and chewing gum
• cans or bottles, smoking materials
• radios, CD players, Walkmans, cell phones,
  pagers, etc.
• newspapers, magazines, books and paper
• pencils and erasers
• wallets, purses and other similar items.
 Disciplines within the Cleanroom
• Within a cleanroom: rules-of-conduct:
  written procedures; 'does and don'ts'
  posted in the change or production area
• Air transfer:
  – come in and out through change areas: buffer
    zone; not use emergency exit
  – Doors: not be left open; not be opened or
    closed quickly: open inwards into the
    production room
    Personnel behaviour
• No Silly behaviour: The generation of
  contamination is proportional to activity.
   – motionless: 100,000 particles >=0.5 μm/min
   – head, arms and body moving: 1,000,000 particles >= 0.5
   – walking: 5,000,000 particles >= 0.5 μm/min
        Personnel product

• position themselves correctly
• not lean over the product;
• working in unidirectional air: not between
  the product and the source of the clean
  air, i.e. the air filter.
• 'No-touch' techniques should be devised:
  from gloved hand onto the product.
• Oil and skin particles would contaminate
  the wafer with catastrophic results.
• not support material against their body
• No personal handkerchiefs
• Washing, or disinfection when required, of
  gloves during use should be considered.
         Handling materials
• The movement of materials between the
  inside and outside of a cleanroom should
  be minimized.
• Waste material: collected frequently into
  easily identified containers and removed
  frequently from the cleanroom.
       Maintenance and Service
• Enter a cleanroom with permission.
• Maintenance be trained  cleanroom
  techniques, or closely supervised when they are
  within the cleanroom.
• Wear the same cleanroom clothing as
  cleanroom personnel
• Technicians should ensure they remove dirty
  boiler suits, etc. and wash their hands before
  changing into cleanroom clothing.
• Tools  cleaned and sterilized; stored for sole used
  within the cleanroom; Tool’s materials  not corrode.
  Only the tools or instruments needed within the room
  should be selected, decontaminated, and put into a
  cleanroom compatible bag or container.
• instructions or drawings can be photocopied onto
  cleanroom paper, or laminated within plastic sheets, or
  placed in sealed plastic bags.
• Particle generating operations such as drilling holes, or
  repairing ceilings and floors should be isolated from the
  rest of the area. A localized extract or vacuum can also
  be used to remove any dust generated.
17. Entry and Exit of
• Skin and clothing: millions of particles and
  thousands of microbe-carrying particles
• Features of cleanroom clothing:
  – not break up and lint: disperse the minimum
    of fibres and particles
  – filter: against particles dispersed from the
    person's skin and their clothing.
• The type of cleanroom clothing
  – contamination control is very important: a
    coverall, hood, facemask, knee-length boots
    and gloves
  – contamination is not as important: less
    enveloping clothing such as a smock, cap and
    shoe covers
 Prior to Arriving at the Cleanroom
• Frequency of bathe or shower:
      • remove the natural skin oils;
      • dispersion of skin and skin bacteria;
      • dry skin may wish to use a skin lotion
• What clothing is best worn below cleanroom garments?
      • Artificial fibres: polyester are better than those made from wool and
      • Close-woven fabrics: more effective in filtering and controlling the
        particles and microbe-carrying particles
• Cosmetics, hair spray, nail varnish removed rings,
  watches and valuables removed and stored
      Changing into Cleanroom
• The best method of changing into
  cleanroom garments is one that minimises
  contamination getting onto the outside of
  the garments.
• The design of clothing change areas is
  divided into zones:
  – Pre-change zone
  – Changing zone
  – Cleanroom entrance zone.
Approaching the pre-change zone

• blow nose, go to the
• shoe cleaner
  – Sticky cleanroom mats
    or flooring: two general
            Pre-change zone

• street or factory clothes removed
• Watches and rings removed. Items such as cigarettes and
  lighters, wallets and other valuables should be securely stored.
• Remove cosmetics and apply a suitable skin moisturizer (no
  chemicals used in the formulation cause contamination
  problems in the product being manufactured)
• Put on a pair of disposable footwear coverings, or change into
  dedicated cleanroom shoes.
• wash the hands, dry them and apply a suitable hand lotion.
• Cross over from the pre-entry area into the change zone.
              Changing zone
• The garments to be worn are
• A facemask and hood (or cap) is
  put on
• Temporary gloves known as
  'donning gloves' are sometimes
• The coverall (or gown) should be
  removed from its packaging and
  unfolded without touching the floor.
    Cleanroom entrance zone
• rossover bench: allows
  cleanroom footwear
  (overshoes or overboots)
  to be correctly put on.
• Protective goggle can be
  put on. These are used
  not only for safety
  reasons but to prevent
  eyelashes and eyebrow
  hair falling onto the
• The garments should be checked in a full-length
  mirror to see that they are worn correctly.
• If donning gloves have been used they can be
  dispensed with now. They can, however, be kept
  on and a pair of clean working gloves put on top.
  Two pairs of gloves can be used as a precaution
  against punctures, although sensitivity of touch
  is lost.
• Low particle (and if required, sterile)
  working gloves should now be put on. In
  some cleanrooms this task is left until the
  personnel is within the production
    Exit Changing Procedures
•       When leaving a cleanroom, personnel will either
•       discard all their garments and on reentry use a new
        set of garments (this is normally only employed in an
        aseptic pharmaceutical cleanroom)
•       discard their disposable items, such as masks and
        gloves, but reuse their coverall, smock, etc. on re-
    –     clothing  rolled up; footwear  pigeon holes;
    –     The hood (or cap) can be attached to the outside of the
          coverall (or gown)  hung up, preferably in a cabinet.
    –     Garment bags can be used.
18. Materials、Equipment
     and Machinery
    Materials used in a cleanroom
• For manufacturing
• Packaging for the product
• Process machinery and equipment
• Tools used for the maintenance,
  calibration or repair of equipment and
• Clothing for personnel, such as suits,
  gloves and masks;
– Materials for cleaning, such as wipers and
– Disposable items such as writing materials,
  labels and swabs.
Materials used in a cleanroom for

• pharmaceutical manufacturing:
  containers and ingredients
• microelectronics industry: silicon wafers
  and process chemicals;
Contamination on materials can be:
 – particles
 – micro-organisms
 – chemicals
 – electrostatic charge
 – molecular outgassing.
       Prohibited material:
– abrasives or powders;
– aerosol-producing cans or bottles;
– items made from wood, rubber, paper,
  leather, wool, cotton and other naturally
  occurring materials that break up easily;
– items made from mild steel, or other materials
  that rust, corrode or oxidise;
– items that cause problems when machined or
  processed, e.g. they may smoke or break up;
– paper not manufactured for use in
– pencils and erasers;
– paper correcting fluid;
– personal items listed in Section 16.2 should
  not be brought in by cleanroom personnel;
– disposable items such as swabs, tapes and
  labels that are not cleanroom compatible.
Transfer of Items and Small Pieces
 of Equipment through an Airlock
 – Transfer area with a
    • door (uncontrolled area)
      opened and the person
      enters The package
      should be placed on the
      'wrapped receiving' or
      'dirtier' part of the pass-
      over bench
• The wrapping is then
  cleaned and removed
• The outer packaging
  is now removed and
  deposited into a
  suitable container.
  The item is then be
  placed on the
  'wrapping removed' or
  'clean' part of the
• The person leave. The
  airlock may be left for a
  few minutes to allow the
  airborne contamination to
  come down to a
  concentration. Cleanroom
  personnel now enter the
  cleanroom and pick up
  items that have been left
  (Figure 18.6).
       Entry of Machinery
– Machines, and other heavy and large bulky
  items of equipment, are occasionally taken in
  or out of a cleanroom.
– The best solution to the movement of bulky
  items is to design the materials airlock to be
  large enough to allow the entry and exit of
  every piece of machine to be brought in or out
  of the room.
19. Cleanroom Clothing
• Contamination source: people  clothing
   product
• Cleanroom clothing: originated from
• Function: reducing inert particles and
  microbe-carrying particles.
    Sources and Routes of Inert
        Particle Dispersion
• More activity  more particles disperse
  Dispersion is dependent on the clothing
  worn, but can be in the range of 106 to 107
  per minute for particles >= 0.5 μm, i.e. up
  to 1010 per day.
• People may disperse particles from:
     • Skin;     clothing they wear under cleanroom
       garments; cleanroom clothing
     • mouth and nose.
      Sources of particles and
      mechanisms of release
• Skin: People shed approximately 109 skin cells
  per day. Skin cells are approximately 33μm x 44
• Skin cells:
  – released onto clothing and laundered away;
  – others are washed away in the bathtub or shower.
  – a large number are dispersed into the air.
Sources and routes of particles and microbe containing particles from people
Skin surface showing skin cells and beads of sweat
     Clothing under cleanroom
• natural fabrics: such as a cotton shirt,
  cotton jeans and woollen jerseylarge
  quantities of particles. natural materials
  have fibres that are both short and break
  up easily.
• synthetic fabric: the particle challenge can
  be reduced by 90% or more.
Cotton fabric photographed through a microscope. Magnification about 100 times
        Cleanroom clothing
• synthetic plastic materials: such as
  polyester or nylon.
Routes of transfer of particles
• Pores: between 80μm and 100μm The
  particles generated from the skin and the inner
  clothing therefore pass through easily.
• Personnel move: particles be pumped out of
  closures at the neck, ankles, wrists and zips.
  Secure closures tight
• tears or holes, particles can easily pass through.
Microcolony of bacteria on surface of skin
 Routes of microbial dispersion
• The routes of transfer the same as with inert
     •   the pores in the fabric
     •   poor closures at the neck, sleeves and ankles
     •   damage to the fabric, i.e. tears and holes.
     •   expelled from the mouth: speaking, coughing and sneezing.
• When males wear ordinary indoor clothing, the
  average rate being closer to 200 per minute.
  Females will generally disperse less.
  Types of Cleanroom Clothing
• Clothing designs
  – The most effective type:
     • completely envelopes a person;
     • be made from a fabric that has effective filtration properties
     • have secure closures at the wrist, neck and ankle.
  – The choice of clothing will depend on what is being
    produced in the cleanroom. A poorer standard of
    cleanroom may use a cap, zip-up coat (smock) and
    shoe covers
• In a higher standard
  of cleanroom a one-
  piece zip-up coverall,
  knee-high overboots
  and a hood that tucks
  under the neck of the
  garment will be typical
                 Cleanroom fabrics
•   The most popular type of clothing is
    made from woven synthetic fabrics.
•   Non-woven fabrics, such as Tyvek, are
    used as single, or limited reuse,
    garments. They are popular for visitors
    and are used by builders when
    constructing the room. They are also
    popular in pharmaceutical
    manufacturing facilities in the USA.
    Membrane barrier fabrics, such as
    GoreTex, which use a breathable
    membrane sandwiched onto, or
    between, synthetic woven fabrics, are
    very efficient; they are expensive, and
    hence are used in the higher standard
      Garment construction
• To prevent the raw edges
• To minimise shedding, the zippers,
  fasteners and shoe soles should not chip,
  break up or corrode.
• Choice of garments
  – IEST Recommended Practice RP-CC-003.2.
            R = recommended            NR == not recommended
AS = application specific (NR*) = not recommended in nonunidirectional flow
 Table 19.2 Garment systems for aseptic cleanrooms (IEST RP CC-003.2)
   Processing of Cleanroom
Garments and Change Frequency
• Processing
  – to be reused cleanroom laundry antistatic
    treatment and disinfection or sterilisation
• Frequency of change
    • semiconductor industry ( the highest specification),
      changed once or twice a week.
    • fresh garments are put on every time personnel
      move into an aseptic pharmaceutical production
Body box: a, metronome; b, bacterial and particle sampler
  Comparison of clothing made
     from different fabrics
• Bacterial dispersion (counts/min) in
  relation to fabrics
Particle dispersion rate per minute
         in relation to fabric
20. Cleanroom Masks and
  Dispersion from the month
• sneezing, coughing and talking; these droplets
  contain salts and bacteria.
• Saliva particles and droplets : about 1 to
  2000μm; 95% of them lie being between 2 and
  100μm, with an average size of about 50μm;
  bacteria in saliva is normally over 107 bacteria
  per ml.
• A 100μm particle will drop 1 metre in about 3
  seconds, but a 10μm particle takes about 5
• Drying time: Particles of water 1000μm in
  diameter will take about 3 minutes to
  evaporate, a 200μm particle will take 7
  seconds, a 100μm particle about 1.6
  seconds and a 50 μm particle about 0.4
• Efficiencies of over 95% for particles
  expelled from the mouth are usually
  obtained by most masks. A loss in
  efficiency is caused by particles passing
  round the side of the mask, and much of
  this is due to small particles (reported to
  be < 3μm in the dry state).
Number of inert and microbe-carrying
   particles emitted by a person
 Particles emitted when
pronouncing the letter `f’
               Face masks
• surgical-style with
  straps and loops:
  disposable surgical-
• Consideration: pressure drop across the mask
  fabric; masks  high filtration efficiency against
  small particles give a high-pressure drop
  across the mask that causes the generated
  particles to be forced round the outside of the
  mask.  'veil' or 'yashmak' type, one of these
  types being exposed to show its shape in Figure
  20.4. The normal way it is worn is shown in
  Figure 20.5.
  Powered exhaust headgear
• These provide a barrier to
  contamination coming
  from the head, as well as
  the mouth. The exhaust
  from the helmet and face-
  shield is provided with a
  filtered exhaust system
  so that contamination
  does not escape into the
  cleanroom. An example is
  shown in Figure 20.6.
         Cleanroom Gloves
• Hand contamination and gloves
  – There are two types of gloves associated with
    • Knitted or woven gloves are used for lower
      classes, i.e. ISO Class 7 (Class 10,000) and
      poorer areas, as well as undergloves. The knit or
      weave should be tight and a number of loose
      threads minimised.
    • Barrier gloves, which have a continuous thin
      membrane covering the whole hand are used in
      the majority of cleanrooms.
• Cleanroom gloves are not usually manufactured in a
  cleanroom; they therefore require cleaning before being
• Gloves may be required in some cleanrooms to prevent
  dangerous chemicals, usually acids or solvents,
  attacking the operator's hands.
• Some operator's skin is allergic to the materials that
  gloves are made from.
• Other glove properties: chemical resistance and
  compatibility, electrostatic discharge properties, surface
  ion contribution when wet, contact transfer, barrier
  integrity, permeability to liquids, heat resistance and
Glove manufacturing process
• Gloves are generally manufactured by dipping a 'former'
  (porcelain or stainless steel), shape of a hand, molten
  or liquid glove material removed from the molten or
  liquid material a layer of material stripped by release
  agent Release agents are a problem in cleanrooms 
  Release agents kept to a minimum.
• When stripped from the formers, latex gloves are 'sticky'.
  To correct this, latex gloves are washed in a chlorine
  bath. The free chlorine combines chemically with the
  latex chemical bonds and lead to a 'case-hardening' of
  the surface of the glove, which prevents them sticking to
  each other. This washing also helps to clean to the
          Types of gloves

• Polyvinyl chloride (PVC) gloves
• Latex Gloves
• Other Polymer Gloves
 Polyvinyl chloride (PVC) gloves
• These plastic gloves are also known as vinyl
  gloves and are popular in electronic cleanrooms;
  can not sterilised, not used in bioclean rooms.
• They are available in normal and long-sleeve
  length. Consideration should be made of the fact
  that plasticisers make up almost 50% of a vinyl
  glove. Plasdcisers come from the same group of
  chemicals used to test the integrity of air filters,
  i.e. phthalates, antistatic properties, outgassing
                    Latex Gloves
• This is the type used by surgeons, and the 'particle-free' type is now
  used in cleanrooms. Latex gloves can be produced 'powder-free',
  and those gloves that are washed further by use of filtered,
  deionised water are often used in ISO Class 4 (Class 10) or ISO
  Class 3 (Class 1) cleanrooms.
• They have good chemical resistance, giving protection against most
  weak acids and bases, and alcohols, as well as having a fairly good
  resistance against aldehydes and ketones.
• They are slightly more expensive to buy than the PVC type, but
  cheaper than any other polymer. They can be sterilised. Because of
  their elasticity, the glove can securely incorporate the cuff of a
  garment under the sleeve.
             Other Polymer Gloves
•   Polythene gloves
     –   are used in cleanrooms and have the advantage of being free of oils and additives, as well
         as resistant to puncturing. They are not resistant to aliphatic solvents. The main drawback of
         this glove type is that they are constructed from float sheets and the seams are welded.
         Manual dexterity is reduced with these gloves.
•   Neoprene and nitrile gloves
     –   are chemically similar to latex gloves, but have the advantage of having a better resistance to
         solvents than latex gloves. They are slightly more expensive than latex.
•   Polyurethane gloves
     –   are strong, very thin, quite inflexible, and expensive. They may be manufactured with
         microporous material for better comfort, or with carbon in the formulation which makes them
•   PVA gloves
     –   are resistant to strong acids and solvents, but not water in which they are soluble. They are
•   Gore-Tex gloves
     –   have welded seams and are hypoallergenic. They are breathable because of their porous
         membrane. They are expensive.
21. Cleaning a Cleanroom
       Why a Cleanroom Must be
• Particles:
   – cleanroom clothing, over 100,000 particles >= 0.5 μm and over
     10,000 particles >= 5.0μm.
   – Machines also disperse millions of particles.
• Microbe-carrying particles: People can also disperse
  hundreds, or thousands, of microbe-carrying particles
  per minute. Because these micro-organisms are carried
  on skin cells, or fragments of skin cells, their average
  equivalent diameter is between 10 μm and 20 μm.
• Transfer: Cleanrooms surfaces get dirty be transferred
  by personnel touching a cleanroom surface and then the
Cleaning Methods and the Physics
      of Cleaning Surfaces
• Forces hold particles to cleanroom
  – The main force : the London-van der WaaP’s
    force, this being an inter-molecular force.
  – Electrostatic forces can also attract particles
    to a surface.
  – A third force can arise after wet cleaning.
    Particles that are left behind will dry on the
    surface, and may adhere to it
• The methods that are generally used for
  cleaning a cleanroom, are:
  – Vacuuming (wet or dry): immersing the particle in a
    liquid, as occurs in wet pick-up vacuuming
  – Wet wiping (mopping or damp wiping): an aqueous-
    based detergent is used then the London-van der
    WaaFs force and electrostatic forces can be reduced
    or eliminated. The particle can then be pushed or
    drawn off from a surface by wiping, mopping or
  – Picking-up with a tacky roller.

• Dry vacuuming :
   – depends on a jet of air moving towards the vacuum
     nozzle and overcoming the adhesion forces of
     particles to the surface
   – Figure 21.1 : efficiency of dry vacuuming against
     different sizes of sand particles on a glass surface.
• Wet vacuum: Water and solvents have much
  higher viscosity than air, so that the drag forces
  exerted by liquids on a surface particle are very
  much greater.
Efficiency of dry vacuuming
• Wet -wiping
  – Wet wiping, with wipers or mops, can
    efficiently clean cleanroom surfaces. The
    liquid used allows some of the particle-to-
    surface bonds to be broken and particles to
    float off.
• Tacky rollers
  – The particle removal efficiency of 'tacky'
    rollers is dependent on the strength of the
    adhesive force of the roller's surface.
• dry brush should never be used to sweep
  a cleanroom. they can produce over 50
  million particles >= 0.5 μm per minute.
• String mops are not much better, as they
  can produce almost 20 million particles >=
  0.5 μm per minute.
• Dry vacuuming: popular method
  – relatively inexpensive
  – no cleaning liquids are needed
  – Note: unfiltered exhaust-air must not pass into
    the cleanroom. This is achieved by using
    either an external central-vacuum source, or
    providing a portable vacuum's exhaust air with
    a HEPA or ULPA filter.
• Wet vacuum or 'pick-up' system: is more
  efficient than dry vacuum
  – more efficient than a mopping method,
  – less liquid left to dry on the floor
  – floor will also dry quicker.
  – Wet pick-up systems are used on
    conventionally ventilated cleanroom floors,
    but may not be suitable for the pass-though
    type of floor used in the vertical unidirectional
• Mopping systems
  – mops for cleanroom:
     • materials that do not
       easily break up: PVA or
       polyurethane open-pore
       foam, or a fabric such as
     • The compatibility of the
       material to sterilization,
       disinfectants and solvents
       should be checked
     • Buckets should be made
       from plastic or stainless
Two and three bucket systems
How to use a three-bucket mopping system
• Wipers
   – Purpose: wipe surfaces and remove contamination; to
     wipe contamination from products produced; used dry
     to mop-up liquids that may have been spilled.
   – Sorbency
      • Sorbency is an important property of wipers. Wipers are often
        used to mop up a spillage and other similar tasks.
• wiper's sorbency: both its capacity (the amount
  of liquid it can sorb) and its rate (how fast it can
  sorb liqu
• Tacky rollers
  – Tacky rollers are
    similar in size and
    shape to paint rollers
    used in the home, but
    they have a tacky
    material around the
    outside of the roller.
    An example of a tacky
    roller is shown in
    Figure 21.7.

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