Sources and Types of Contamination

• Contamination happens when materials or surfaces become soiled.

Broad Categories of Surface Contaminants:

• Film type
• Particulates
• Film contaminants can drastically reduce coating adhesion on wafers or chips, even at small sizes (10 nm).
• Aim of a cleanroom environment is to prevent contaminants from entering production areas.

Basic Sources of Contamination:

• Facilities
• People
• Tools
• Fluids
• Product

Sources within Facilities:

• Walls, floors, ceilings
• Paint and coatings
• Construction material-dust
• Air conditioning debris
• Room air and vapors
• Spills and leaks

Sources from People:

• Skin flakes and oil
• Cosmetics and perfume
• Spittle
• Clothing debris (lint, fibers etc.)
• Hair

Tool-Generated Sources:

• Friction and wear particles
• Lubricants and emissions
• Vibrations
• Brooms, mops and dusters

Sources from Fluids:

• Particulates floating in air
• Bacteria, organics and moisture
• Floor finishes or coatings
• Cleaning chemicals
• Plasticizers (outgasses)
• Deionized water

Product-Generated Sources:

• Consumables and disposables
• Cleanroom debris
• Aluminum particles

Key Elements of Contamination Control:

• HEPA filters remove particles as small as 0.3 microns with 99.97% efficiency.

Cleanroom Architecture:

• Designs strive for laminar airflow, where air moves uniformly along parallel flow lines.
• Laminar flow is desired because turbulence can cause particle movement.

Filtration:

• Essential
• Includes HEPA filters and other filtration mechanisms

Cleaning:

• Essential element of contamination control.
• Uses SOPs/WIs

Cleanroom Garments:

• Gloves, face masks, and head covers are standard attire.

Humans in Cleanrooms:

• Fast motion and horseplay increase contamination.

Ways people produce contamination:

• Body regenerative processes (skin flakes, oils, perspiration, hair)
• Behavior (rate of movement, sneezing, coughing)
• Attitude (work habits and communication between workers)
• People are a major contamination source in cleanrooms.

Particle Generation by Activity:

• Motionless (Standing or Seated): 100,000 particles/minute (0.3 microns and larger)
• Walking about 2 mph: 5,000,000 particles/minute
• Walking about 3.5 mph: 7,000,000 particles/minute
• Walking about 5 mph: 10,000,000 particles/minute
• Horseplay: 100,000,000 particles/minute

Contamination from Commodities:

• Wipers, cleanroom paper, pencils, and other supplies

Contamination concerns with Cosmetics:

• Many contain sodium, magnesium, silicon, calcium, potassium, or iron, which create damaging particles.

Measurements & Instrumentation:

• Particle count, air flow & velocity, humidity, temperature and surface cleanliness are related to contamination control.

Electrostatic Discharge (ESD):

• Occurs when two surfaces rub together and create an electrical charge.
• Moving air, people touching surfaces, or walking across the floor can create a charge.

Cleanroom Environment Control:

• Controlled environment where products are manufactured
• Air particle concentration controlled to specified limits
• Contaminants come from people, processes, facilities, and equipment.
• Air must be continually cleaned
• Removal level of particles depends on standards required.
• Federal Standard 209E establishes air cleanliness classes for airborne particulate levels in cleanrooms and clean zones.
• Controlling the total environment controls contamination.
• Air flow rates/direction, pressurization, temperature, humidity and specialized filtration must be controlled.
• Environment control is required for electronics, pharmaceutical, biopharmaceutical, and medical device industries.

Particle Levels:

• Office building air contains 500,000 to 1,000,000 particles (0.5 microns or larger) per cubic foot.
• Class 100 cleanroom contains 100 particles (0.5 microns or larger) per cubic foot.
• Class 1000 and Class 10,000 cleanrooms -to 1000 and 10,000, respectively.
• A small particle (0.5 micron), much smaller than a human hair (75-100 microns in diameter), causes major disaster in a cleanroom.
• Neglecting contamination can lead to equipment failure
• NASA Hubble Space Telescope damaged because of particles of 0.5 microns.
• Cleanrooms must be maintained and cleaned regularly.

U.S. Federal Standard 209E Cleanroom Standard Examples (Particles/ft³):

• Class 1: - ≥0.1 μm = 35 - ≥0.2 μm = 7 - ≥0.3 μm = 3 - ≥0.5 μm = 1 - ISO Equivalent: ISO 3
• Class 10: - ≥0.1 μm = 350 - ≥0.2 μm = 75 - ≥0.3 μm = 30 - ≥0.5 μm = 10 - ISO Equivalent: ISO 4
• Class 100: - ≥0.2 μm = 750 - ≥0.3 μm = 300 - ≥0.5 μm = 100 - ISO Equivalent: ISO 5
• Class 1,000: - ≥0.5 μm = 1,000 - ≥5 μm = 7 - ISO Equivalent: ISO 6
• Class 10,000: - ≥0.5 μm = 10,000 - ≥5 μm = 70 - ISO Equivalent: ISO 7
• Class 100,000: - ≥0.5 μm = 100,000 - ≥5 μm = 700 - ISO Equivalent: ISO 8

Biosafety Levels:

• Define levels of containment required for handling various biological hazards.
• There are four levels of containment specified by the CDC in the US.

Biosafety Level 1 (BSL-1):

• Basic level of protection for agents not known to cause disease in healthy humans.

Biosafety Level 2 (BSL-2):

• Protection level is used for handling moderate-risk agents that cause human disease, varying in severity by ingestion/mucous membrane.

Biosafety Level 3 (BSL-3):

• Protection level for agents of indigenous/exotic origin with aerosol transmission potential, serious/lethal infections from inhalation.

Biosafety Level 4 (BSL-4):

• High level of protection for exotic agents posing life-threatening disease risk from infectious aerosols, for which no treatment is available.

Air Changes:

• Air changes per hour (ACPH/ACH) or air change rate measures the air volume added to or removed from a space divided by the space's air volume.

Air Changes per Hour (European Standard):

• Grade A 480-600
• Grade B 35-70
• Grade C 20
• Grade D 20

Calculating Air Changes:

• Determine air changes per hour through the fan's capacity and volume
• Step 1: Determine the approximate cubic feet of air
• Step 2: Find CFM (cubic feet per minute) capacity of the fan
• Step 3: Multiply fan's CFM by 60 to get cubic feet per hour.
• Step 4: Divide the figure by the volume of the room to determine the number of air changes per hour .

Air Handling Units (AHU):

• Condition and distribute air within a building.
• Take fresh ambient air from outside, clean it, heat it or cool it, humidify it perhaps and then force it through ductwork.
• Most units have an additional duct run to pull dirty air to the AHU for discharge or recirculation.
• AHU controls: Temperature, humidity, air movement, air cleanliness

AHU Components:

• Blower
• Heating elements
• Cooling elements
• Filter racks or chambers
• Sound attenuators
• Dampers

Types of Air Handling Units:

• Draw-Through
• Blow-Through

Draw-Through AHU type:

• The fan pulls air through components (mixing box, filters etc) before discharging.
• The fan is located downstream of the filter, creating an area of negative pressure.

Blow-Through AHU type:

• The fan blows the air through the mixing box, filters and cooling coil before discharging.
• The fan is located upstream of the filter, creating an area of positive pressure.

Air Handling Unit Common Components:

• Fans
• Filters
• Cooling/Heating Coils
• Heat recovery systems
• Humidifiers
• Dehumidifiers
• Ultraviolet UV disinfection lamps
• Photocatalytic oxidation (PCO) air cleaners
• Sound attenuators
• Mist/Droplet eliminators
• Dampers

Housing

• Metal, some are painted to prevent corrosion
• 1 to 2 inches of polyurethane foam -insulate them to prevent the condensation on the panel
• Drain pan also used as a precaution in the event of condensation of water

Fan:

• Centrifugal fan is used to circulate the air to the various parts.
• Typical types of fan available are Backward Inclined, Backward Curved, Forward Curved

Variable Air Volume:

• When load is high, fan speed will be higher and when load is low, speed of fan will be lower.

Cooling Coil:

• Used to cool and dehumidify the air.

Filters:

• Remove particles and contaminants of various sizes from the air.
• Used varies widely by filtration system.
• Panel Filter: - Flat, rectangular - Provides minimum / low efficiency filtration
• HEPA Filter: - Very efficient - Achieves efficiencies of up to 99.97% - Removes minute particles and airborne bacteria

Humidifiers:

• During winter, humidity level of the air is low and causes discomfort to occupants so air is increased via humidifiers.

Mixing Box:

• Air inlets attached to dampers
• Place where outside and return air is mixed and correct proportion of air is distributed

Dampers:

• Located at the fresh air housing inlet and the return air housing discharge.
• Multiple sheets of metal that can rotate.
• Close to prevent air entry/exit
• Can be adjusted vary position somewhere in between to restrict the amount of air.

Filter Function:

• Catches the dirt and dust entering AHU and the building
• Is fitted to each bank of filters and contains a pressure sensor to measure how dirty filters are
• As filters pickup dirt, the pressure of air that can flow through is restricted and this causes a pressure drop across the filters.
• Panel filters/pre-filters are used to catch the larger dust particles. Then some bag filters are used to catch the smaller dust particles.

Cooling and Heating Coils:

• Used to heat/cool the air.
• The supply air temperature is measured as it leaves the AHU and enters the ductwork so people are comfortable and the designed temp is called the set point temp.
• If the air temp is below this value, the heating coil will inject heat to bring it up to setpoint.
• If the air temp is too hot, the cooling coil will remove heat to lower and hit setpoint.

Fan Function:

• Pulls the air from the outside then through the dampers, filters and coils then pushes this air out into the ductwork.
• The centrifugal fans can be retro fitted for enhanced energy efficiency.
• Pressure sensor senses if the fan is running by a notable pressure difference,

Return AHU

• Has a fan and damper
• The fan pulls the air from around the building and then pushes it outwards..
• The damper is located at the exit of the AHU housing and will close when AHU turns off.

Winter Precautions:

• When winter-air gets to freezing, a pre-heater is needed at the fresh air inlet to protect components from frost.
• If frost prevention is not put in place then heating and cooling coils could freeze burst.

Humidity Control Measures:

• Humidity sensor located at the supply AHU outlet measures the moisture in the supply air and this has setpoint.
• If the air's moisture content is below this value, a humidifier is introduced
• The device used will add steam or spray a water mist into the air.
• If the air is too humid, this can be reduced through the cooling coil: - The cool surfaces condense the moisture that drains with the use of a drain pan.,

Exhaust/Fresh Air Mixing Ducts:

• Connect the exhaust and the fresh air intake.
• The air can be recirculated back into the fresh air intake to off set the heating/cooling demand.

Co2 levels:

• If the CO2 level is too high, the air cannot be re-used, the mixing damper will close and discard return air.
• Important: the inlet/outlet dampers do not fully close to ensure there is still a minimum amount of fresh air.

General Cleanroom Regulations:

• Store all personal items (keys, accessories, etc.) outside the gowning room.
• Approved garments worn should be used in the cleanroom.
• Never remove wallet or items from beneath the cleanroom garments.
• No eating, smoking, or gum chewing is ever to occur in the cleanroom.
• Approved garments worn should be used in the cleanroom.
• No cosmetics (rouge, lipstick, eye shadow etc) including heavy use of aerosols or aftershaves are to be worn in the cleanroom.
• Only use approved cleanroom paper and ball point pens.
• Use of paper/fabric towels is prohibited
• The use of hand dryers equipped with HEPA filters are encouraged.
• Prevent gloves or finger cots from touching any item/surface.
• Only apply gloves, finger cots, pliers, tweezers and handle the items with these.
• Prevent solvent contact with you bare skin.
• Sometimes Approved skin lotions/soaps are allowed.
• Sterilize or clean all tools, containers and fixtures as cleanroom surfaces.
• The tool should rest on a cleanroom wiper, not a bench or surface.
• Subject equipment, materials and containers to stringent sterilization before facility entrance.
• Individuals with illness (especially respiratory/stomach orders) in a sterile room is prohibited.

Actions Prohibited in Cleanrooms:

• Fast motions such as running, walking fast, or horseplay
• Sitting/leaning on equipment or work surfaces
• Writing on equipment or garments
• Removal of items from beneath cleanroom garments
• Wearing cleanroom garments outside the cleanroom
• Wearing torn or soiled garments

Key Aspects of Cleaning Procedures:

• cleaning schedule is prepared
• defined cleaning schedule
• daily cleaning
• Not selecting the correct cleaning solution can affect
• Proper cleaning products selected
• Strict vendor enforcement.

Equipment and Supplies:

• Cleaning and disinfecting solutions
• Cleanroom mops
• Vacuum cleaner (if allowed)
• Cleanroom mops and wipers.

Cleaning Tasks:

• The main job is cleaning all work surface and empty waste in the controlled environment.
• Following this, vacuum if needed
• Cleaning room and mop it.

Biosafety Cabinet:

• Microbiological safety cabinet used to safely handle materials requiring a defined biosafety level.
• Primarily to protect laboratory worker and surrounding environment from pathogens.
• All exhaust air is HEPA-filtered, removing harmful bacteria and viruses.

Contrast with Laminar Flow:

• Unlike Laminar Flow clean benches, it is unsafe to work with pathogenic agents.

Fume Hood:

• Is not safe for use.
• A fume hood fails to provide the HEPA filtration of biosafety.

Biosafety Cabinet Classes:

• Most classes of BSCs have maintain sterility of materials.

Classification of Biosafety Cabinets:

• Class I
• Class II
• Class III

Class I Cabinets:

• Provide personnel and environmental protection, but no product protection.
• The inward airflow of air results in contamination samples.
• BSCs of this class are either: ducted (connected to the building exhaust system) or unducted and recirculate the filtered exhaust back into the laboratory.

Class II Cabinets:

• Provides full protection with HEPA-filtration since makeup air is also HEPA-filtered.
• There are five types: Type A1 (formerly A), Type A2 (formerly A/B3), Type B1, Type B2 and Type C1.
• Utilize motor driven blowers to draw directional air flow around a user into the air grille.
• It is then drawn downwards from the work surface and into the cabinet where it bypasses through the HEPA filters.

Class III Cabinets:

• Primarily for handling for pathogens and provides the maximum protection.
• Enclosure is gas-tight.
• Materials enter and exit a dunk tank or a double-door autoclave.
• Integrated gloves at the front to prevent contact with hazardous materials.
• These often use custom-built equipment that are installed inside.

Ultraviolet Lamps in BSCs:

• CDC does not recommend
• The American Biological Safety Association (ABSA) does not support the CDC
• UV lamps is less effective because of safety risk, penetration, high relative humidity and requirement to change the bulb.
• UV lamps should not used as a primary surface as surface decontamination.
• Need to replace the bulbs should not be required because clean room has very clear air

For those in support of the lamps:

• Clean air and humidity eliminate UV's lack of effectiveness
• Is effective for germicide and virucide and inhibiting DNA contamination from PCR
• Relative safety/risks depends with the disinfection techniques used(risks should be considered)
• Biological Safety Cabinets (BSCs) must meet country or region-specific standards

Field Test Requirements:

• Are required for all class II BSC.
• Include measurements like Air Velocity, Air Barrier, Filter Integrity, Particle Counting, Gas Tightness, Illuminance, UV Light Effectiveness and Sound Level,

Quality Assurance (QA) vs Quality Control (QC):

• QA focuses on providing assurance that requested quality is achieved, aiming to prevent defects whereas QC focuses on fulfilling the quality requested and aims to identify and fix defects.
• QA is Verification as method is to manage quality
• QC is Validation as the method is verify quality
• QA is a preventive, proactive technique.
• QC is a corrective, reactive technique.
• In order to meet the customer requirements, quality definitions are defined.
• If the customer requirements are met, the QA defines standards and methodologies so standards are followed while working on a product. QA is performed first before QC and involves statistical process control (SPC), whereas QC relies on testing and involves statistical quality control (SQC).