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Classifications-
Cleanrooms are classified according to the
amount and size of particulate contamination which exists in the work area. Air
cleanliness classes are determined by Federal Standard no. 209E. Briefly stated,
they are as follows.
Class 10 -- particle count not to
exceed a total of 10 particles per cubic foot of a size 0.5 microns and
larger, and zero particles of 5.0 microns and larger.
Class 100 -- particle count not to
exceed a total of 100 particles per cubic foot of a size 0.5 microns and
larger, and zero particles of 5.0 microns and larger.
Class 1000 -- particle count not to
exceed a total of 1000 particles per cubic foot of a size 0.5 microns and
larger, or 6.5 particles per cubic foot of a size 5.0 microns and larger.
Class 10,000 -- particle count not
to exceed a total of 10,000 particles per cubic foot of a size 0.5 microns and
larger, or 65 particles per cubic foot of a size 5.0 microns and larger.
Class 100,000 -- particle count not
to exceed a total of 100,000 particles per cubic foot of a size 0.5 microns
and larger, or 700 particles per cubic foot of a size 5.0 microns and larger.
ESD standards
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About Cleanrooms
A cleanroom is a controlled environment where products are
manufactured. It is a room in which the concentration of airborne particles is
controlled to specified limits. Eliminating sub-micron airborne contamination is
really a process of control. These contaminants are generated by people,
process, facilities and equipment. They must be continually removed from the
air. The level to which these particles need to be removed depends upon the
standards required. The most frequently used standard is the Federal Standard
209E. The 209E is a document that establishes standard classes of air
cleanliness for airborne particulate levels in cleanrooms and clean zones.
Strict rules and procedures are followed to prevent contamination of the
product.
The only way to
control contamination is to control the total environment. Air flow rates and
direction, pressurization, temperature, humidity and specialized filtration all
need to be tightly controlled. And the sources of these particles need to
controlled or eliminated whenever possible. There is more to a clean room than
air filters. Cleanrooms are planned and manufactured using
strict protocol and methods. They are frequently found in electronics,
pharmaceutical, biopharmaceutical, medical device industries and other critical
manufacturing environments.
It only takes a quick monitor of the air in a cleanroom
compared to a typical office building to see the difference. Typical office
building air contains from 500,000 to 1,000,000 particles (0.5 microns or
larger) per cubic foot of air. A Class 100 cleanroom is designed to never allow
more than 100 particles (0.5 microns or larger) per cubic foot of air. Class
1000 and Class 10,000 cleanrooms are designed to limit particles to 1000 and
10,000 respectively.
A human hair is about 75-100 microns in diameter. A particle
200 times smaller (0.5 micron) than the human hair can cause major disaster in a
cleanroom. Contamination can lead to expensive downtime and increased production
costs. In fact, the billion dollar NASA Hubble Space Telescope was damaged and
did not perform as designed because of a particle smaller than 0.5 microns.
Once a cleanroom is built it must be maintained and cleaned
to the same high standards. This handbook has been prepared to give professional
cleaning staff information about how to clean the cleanroom.
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What
is Contamination?
Contamination is a process or act that causes materials or
surfaces to be soiled with contaminating substances. There are two broad
categories of surface contaminants: film type and particulates. These
contaminants can produce a “killer defect” in a miniature circuit.
Film contaminants of only 10 nm (nanometers) can drastically reduce
coating adhesion on a wafer or chip. It is widely accepted that particles of 0.5
microns or larger are the target. However, some industries are now targeting
smaller particles.
A partial list of contaminants is found below. Any of these
can be the source for killing a circuit. Preventing these contaminants from
entering the cleanroom environment is the objective. It requires a commitment by
everyone entering the cleanroom to make it happen. Professional cleaning
personnel need to be aware of the importance of controlling contaminants. Strict
procedures should be followed whenever entering or cleaning a cleanroom.
Compromise is not acceptable when cleaning in a cleanroom.
Sources of Contamination
This is a partial list of some of the commonly known contaminants
that can cause problems in some cleanroom environments. It has been found that
many of these contaminants are generated from five basic sources. The
facilities, people, tools, fluids and the product being manufactured can all
contribute to contamination. Review this list to gain a better understanding of
where contamination originates.
1.
Facilities
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Walls, floors and ceilings
Paint
and coatings
Construction material (sheet rock, saw dust etc.)
Air
conditioning debris
Room
air and vapors
Spills and leaks
2.
People
Skin
flakes and oil
Cosmetics and perfume
Spittle
Clothing debris (lint, fibers etc.)
Hair
3.
Tool Generated
Friction and wear particles
Lubricants and emissions
Vibrations
Brooms, mops and dusters
4.
Fluids
Particulates floating in air
Bacteria, organics and moisture
Floor
finishes or coatings
Cleaning chemicals
Plasticizers (outgasses)
Deionized water
5.
Product generated
Silicon chips
Quartz flakes
Cleanroom debris
Aluminum particles
Key Elements of Contamination Control
We will look at several areas of concern to get a better idea of the
overall picture of contamination control. These are the things that need to be
considered when providing an effective contamination control program.
HEPA (High Efficiency Particulate Air Filter) - These filters are
extremely important for maintaining contamination control. They filter particles
as small as 0.3 microns with a 99.97% minimum particle-collective efficiency.
CLEANROOM ARCHITECTURE - Cleanrooms are designed to achieve and
maintain a airflow in which essentially the entire body of air within a confined
area moves with uniform velocity along parellel flow lines. This air flow is
called laminar flow. The more restriction of air flow the more turbulence.
Turbulence can cause particle movement.
FILTRATION - In addition to the HEPA filters commonly used in
cleanrooms, there are a number of other filtration mechanisms used to remove
particles from gases and liquids. These filters are essential for providing
effective contamination control.
CLEANING - Cleaning is an essential element of contamination control.
Decisions need to made about the details of cleanroom maintenance and cleaning.
Applications and procedures need to be written and agreed upon by cleanroom
management and contractors (if used). There are many problems associated with
cleaning. Managers need to answer the following questions before proceeding with
any cleanroom cleaning program:
1.
What is clean?
2.
How is clean measured?
3.
What cleaning materials can be used in the cleanroom?
4.
When can the cleanroom be cleaned?
5.
How frequent does it need to be cleaned?
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CLEANROOM GARMENTS - The requirements for cleanroom garments will
vary from location to location. It is important to know the local garment
requirements of the cleanroom management. Gloves, face masks and head covers are
standard in nearly every cleanroom environment. Smocks are being used more and
more. Jump suits are required in very clean environments.
HUMANS IN CLEANROOMS - There are both physical and psychological
concerns when humans are present in cleanrooms. Physical behavior like fast
motion and horseplay can increase contamination. Psychological concerns like
room temperature, humidity, claustrophobia, odors and workplace attitude are
important. Below are several ways people produce contamination:
1.
Body Regenerative Processes-- Skin flakes, oils, perspiration and hair.
2.
Behavior-- Rate of movement, sneezing and coughing.
3.
Attitude-- Work habits and communciation between workers.
People are a major source of contamination in the cleanroom. Look at the people
activies listed below. Notice the number of particles produced per minute during
these activities.
|
PEOPLE ACTIVITY |
PARTICLES/MINUTE
(0.3 microns and larger) |
|
Motionless
(Standing or Seated) |
100,000 |
|
Walking about 2 mph |
5,000,000 |
|
Walking about 3.5
mph |
7,000,000 |
|
Walking about 5 mph |
10,000,000 |
|
Horseplay |
100,000,000 |
COMMODITIES - Care is taken when selecting and using commodity items
in cleanrooms. Wipers, cleanroom paper and pencils and other supplies that
service the cleanroom should be carefully screened and selected. Review of the
local cleanroom requirements for approving and taking these items into the
cleanroom are essential. In fact, many cleanroom managers will have approval
lists of these types of items.
COSMETICS - Many cosmetics contain sodium, magnesium, silicon,
calcium, potassium or iron. These chemicals can create damaging particles.
Cleanroom managers may ban or restrict cosmetics in the cleanroom. This is
usually dependent upon the threat to the product being made in the cleanroom. A
recent mirror on a space telescope was fogged up from the cologne that was
present in the cleanroom.
MEASUREMENT AND INSTRUMENTATION - Some important measurements
related to contamination control are particle count, air flow & velocity,
humidity, temperature and surface cleanliness. Cleanroom managers usually have
specific standards and/or instruments to measure these factors.
ELECTROSTATIC DISCHARGE (ESD) - When two surfaces rub together an
electrical charge can be created. Moving air creates a charge. People touching
surfaces or walking across the floor can create a triboelectric charge. Special
care is taken to use ESD protective materials to prevent damage from ESD.
Cleaning managers should work with their personnel to understand where these
conditions may be present and how to prevent them.
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Cleaning Procedures for Clean Rooms
What
follows are some recommended procedures for cleaning cleanrooms. It is important
to emphasize that these procedures are guidelines and not standards or rules.
The procedures listed here are routine cleaning tasks. Local cleanroom cleaning
procedures may supercede the ones listed here. It is important for cleaning
managers to review all cleaning procedures to be used in a cleanroom with the
cleanroom management. A detailed cleaning schedule should be prepared for every
cleanroom. Here are some procedures to be completed when cleaning a Class 10,000
cleanroom:
Cleaning Procedures for a Class 10,000 Cleanroom
Housekeeping maintenance of the cleanroom and restricted areas is essential to
assure quality. Cleaning of a cleanroom should be performed on a daily basis.
Improper cleaning of the cleanroom can lead to contamination and a loss in end
user product quality. Proper selection of equipment and materials is important
for proper cleaning. Only products that have proven cleanroom performance
records should be considered for use in cleanrooms. These products should be
listed and all vendors should be informed about the strict policies of how
products are qualified. All procedures should be strictly enforced. Below are
some examples of how to organize the cleaning to be done in a cleanroom. These
are NOT schedules or exact procedures. They are guidelines for preparing work
procedures and schedules. Local requirements must be included in any cleaning
program.
List of Some of Equipment and Supplies Needed to Clean the Cleanroom
(All
supplies must meet the Class 10,000 minimum requirements)
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Cleaning and disinfecting solutions
-
Cleanroom mops
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Cleanroom
vacuum cleaner (if allowed)
-
Cleanroom
wipers
-
Cleanroom
mop bucket and wringer
List of Cleaning Tasks to be Completed in the Cleanroom
(Frequency
may vary depending upon local requirements)
-
Cleaning of all work surfaces in the controlled environment.
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Vacuuming (if allowed) of the floors and work surfaces.
-
Emptying of appropriate trash and waste.
-
Cleaning of the doors, door frames and lockers in the pre-staging area and
gowning areas using the approved cleaning solution.
-
Mop
gowning and cleanroom floors.
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Cleaning Procedures for a Class 1000 Cleanroom
Below
is a sample of a cleaning program in a Class 1000 Cleanroom. This is only a
sample of a program. Local standards and requirements must be followed.
|
Area |
Description of Work |
Frequency |
|
101 |
Change tacky mats |
Every 2 hours |
|
102 |
Wet mop with
approved mop, cleaner & DI water |
2 times per shift |
|
103 |
Dust mop (if
allowed) |
2 times per shift |
|
104 |
Remove trash,
sweep, mop with appropriate cleaner wipe down tables and coffee area, clean
walls and recycle cans |
1 time per shift |
|
105 |
Vacuum entry mats,
sweep and mop floors |
1 time per shift |
|
106 |
Mop floor with
pre-burnish cleaner and tap water |
1 time per shift |
|
107 |
Remove trash. Always wear gloves. Never take waste containers inside
cleanrooms. |
1 time per shift |
|
108 |
Wet mop floors |
1 time per shift |
|
109 |
Remove acid and
solvent trash |
1 time per shift |
|
110 |
Clean and replenish
dispenser in all restrooms |
3 times per week |
|
111 |
Vacuum floor (if
allowed) |
2 times per week |
|
112 |
Clean stainless steel pass throughs with s/s cleaner and appropriate wipes |
1 time per week |
The
list above is a sample of some of the common tasks that need to be performed in
a Class 1000 cleanroom. The list is not exhaustive. But gives some ideas of how
to prepare work schedules and procedures. An assessment of the cleanroom in
conjunction with cleanroom management will help define these tasks and
frequencies.
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Cleaning Procedures for a Class 100 Cleanroom
|
Zone |
Procedure |
Frequency |
|
Zone 1a |
Trash removal |
Once daily |
|
|
Mop walkways |
Once a week |
|
|
Wipe down
horizontal surfaces |
Once monthly |
|
Zone 1b |
Pull tacky mats |
Every 2 hours |
|
Zone 1c |
Mop and trash
removal |
Once daily |
|
|
Wipe down walls and
trim |
Once a week |
|
Zone 1d |
Mop and trash
removal |
Once daily |
|
|
Wipe walls and trim |
Once a week |
|
Zone 2a |
Mop |
Twice a shift |
|
|
Wipe walls and trim |
Once a week |
|
|
Vacuum
|
Once monthly |
|
Zone 2b |
Mop and trash
removal |
Once per shift |
|
Zone 2c |
Wipe down walls,
windows, doors, trim, showers, passthroughs and fire extinguishers. |
Once a week |
The
list above is a sample of some of the common tasks that need to be performed in
a Class 100 cleanroom. The list is not exhaustive. But gives some ideas of how
to prepare work schedules and procedures. An assessment of the cleanroom in
conjunction with cleanroom management will help define these tasks and
frequencies.
General
Cleanroom Regulations
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Below is a list of
general regulations recommended as a minimum for the successful
operation of a cleanroom. All professional cleaning personnel should be aware
and follow these regulations at all times.
-
1. All personal
items such as keys, watches, rings, matches, lighters and cigarettes should be
stored in the personal locker outside the gowning room.
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2. Valuable
personal Items such as wallets may be permitted in the cleanroom provided they
are NEVER removed from beneath the cleanroom garments.
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3. NO eating,
smoking or gum chewing allowed inside the cleanroom.
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4. Only garments
approved for the cleanroom should be worn when entering.
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5. NO cosmetics
shall be worn in the cleanrooms. This includes: rouge, lipstick, eye shadow,
eyebrow pencil, mascara, eye liner, false eye lashes, fingernail polish, hair
spray, mousse, or the heavy use of aerosols, after shaves and perfumes.
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6. Only approved
cleanroom paper shall be allowed in the cleanroom.
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7. Approved ball
point pens shall be the only writing tool used.
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8. Use of paper
or fabric towels are prohibited. Use of hand dryers equipped with HEPA filters
are suggested.
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9. Gloves or
finger cots should not be allowed to touch any item or surface that has not
been thoroughly cleaned.
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10. Only approved
gloves, finger cots (powder-free), pliers, tweezers should be used to
handle product. Finger prints can be a major source of contamination on some
products.
-
11. Solvent
contact with the bare skin should be avoided. They can remove skin oils and
increase skin flaking.
-
12. Approved skin
lotions or lanolin based soaps are sometimes allowed. These can reduce skin
flaking.
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13. All tools,
containers and fixtures used in the cleaning process should be cleaned to the
same degree as the cleanroom surfaces. All of these items are a source of
contamination.
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14. NO tool should
be allowed to rest on the surface of a bench or table. It should be place on a
cleanroom wiper.
-
15. Only cleanroom
approved wipers are allowed to be used. The wipers must be approved for the
Class of cleanroom being cleaned.
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16. ALL equipment,
materials and containers introduced into a sterile facility must be subjected
to stringent sterilization prior to entrance.
-
17. NO ONE who is
physically ill, especially with respiratory or stomach disorders, may enter a
sterile room. This is a good practice in any cleanroom environment.
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