Standards
Before selecting standards it is import to determine what is important. Which contaminants are important, how critical are these contaminants and what activities should be performed; setting up a cleanroom or running a cleanroom. When providing services or products it is important to understand what the potential client needs.
All standards deal with subjects related to ‘Clean rooms and associated controlled environments’. For any such room or environment Part 1: Classification of air cleanliness by particle concentration (ISO 14644-1) applies. Additional to particles in air other cleanliness attributes can be applicable: viable micro-organisms, macroparticles, chemicals or nano-particles. These can be found in ISO 14644-8 (chemicals) ISO 14644-12, (nanoscale particles), ISO 14644-17 (macro-particles) and the ISO 14698- series of standards on micro-organisms. Besides contaminants in air also contaminants on surfaces are recognized. ISO only refers to classification for ‘cleanliness by particle concentration in air’. All other cleanliness attributes and surface cleanliness are considered to be monitored and not classified.
All standards deal with subjects related to ‘Clean rooms and associated controlled environments’. For any such room or environment Part 1: Classification of air cleanliness by particle concentration (ISO 14644-1) applies. Additional to particles in air other cleanliness attributes can be applicable: viable micro-organisms, macroparticles, chemicals or nano-particles. These can be found in ISO 14644-8 (chemicals) ISO 14644-12, (nanoscale particles), ISO 14644-17 (macro-particles) and the ISO 14698- series of standards on micro-organisms. Besides contaminants in air also contaminants on surfaces are recognized. ISO only refers to classification for ‘cleanliness by particle concentration in air’. All other cleanliness attributes and surface cleanliness are considered to be monitored and not classified.
All standards deal with subjects related to ‘Clean rooms and associated controlled environments’. For any such room or environment Part 1: Classification of air cleanliness by particle concentration (ISO 14644-1) applies.
Additional to particles in air other cleanliness attributes can be applicable: viable micro-organisms, chemicals or nano-particles. These can be found in ISO 14644-8 (chemicals) ISO 14644-12 (nanoscale particles) and the ISO 14698- series of standards on micro-organisms. Besides contaminants in air also contaminants on surfaces are recognized. ISO only refers to classification for ‘cleanliness by particle concentration in air’. All other cleanliness attributes and surface cleanliness are considered to be monitored and not classified.
Additional to particles in air other cleanliness attributes can be applicable: viable micro-organisms, chemicals or nano-particles. These can be found in ISO 14644-8 (chemicals) ISO 14644-12 (nanoscale particles) and the ISO 14698- series of standards on micro-organisms. Besides contaminants in air also contaminants on surfaces are recognized. ISO only refers to classification for ‘cleanliness by particle concentration in air’. All other cleanliness attributes and surface cleanliness are considered to be monitored and not classified.
There are many factors in contamination control. This is described in several standards. The first 2 parts of ISO 14644 deal with particles. Then there are 4 parts on measurement methods, design and construction, operations and separative devices. Next to air cleanliness surface cleanliness is important. Then other types of contamination like micro-organisms, nanoscale particles, chemicals and macroparticles are important. This lead to 6 parts. When setting up a cleanroom energy management and cleanroom suitability of equipment, tools and materials are important. This leads to 3 additional parts.
More knowledge and new applications will lead to more specialistic parts.
More knowledge and new applications will lead to more specialistic parts.
Each country has a national standards body. This organisation decides which standards will be adopted as national standards. Some countries make their own translations. In Cleanrooms the Technical Committee 209 of the International Standard Organisation (ISO) develops standards that can be adapted by national standards organisations. ISO TC209 cooperates with the Technical Committee 243European standards organisation CEN and the Vienna Agreement they can adopt each other’s standards. CEN standards are adopted by all European member countries.
When the publication year of a standard is mentioned, that particular standard should be used. If only the standard number is mentioned the latest published version should be used.
For example if ISO 14644-1:1999 is mentioned, this particular standard should be used. If ISO 14644-1 is stated, the latest version, which is ISO 14644-1:2015, should be applied.
For example if ISO 14644-1:1999 is mentioned, this particular standard should be used. If ISO 14644-1 is stated, the latest version, which is ISO 14644-1:2015, should be applied.
Cleanroom
Next to books on cleanroom technology and contamination control the ISO 14644-1 is a good start, Then parts 2, 3, 4, 5 and 7 should be read. In case micro-organisms are important ISO 14698 should be read. The other standards offer information on chemicals and nanoscale particles, surface cleanliness, cleaning, cleanroom suitability and energy management.
The emission of contamination (particles and/or chemicals) should be within the acceptable limit. The acceptable limit is determined by the required air cleanliness and the effective ventilation (air supply times ventilation effectiveness). See ISO 14644-16 and ISO DIS 14644-4. The determination of the emission of particle is describe in ISO 14644-14 and of chemicals in ISO 14644-15.
Many design guidelines have stated certain air change rates per hour for certain cleanliness classes. Although a quite straight forward method this does not account for the actual ‘particle load’ the cleanroom has to counter. Currently there is more information about particle and viable emission rates of personnel, equipment and materials. More guidance can be found in the ISO standards ISO 14644-4, ISO 14644-13, ISO 14644-14, ISO 14644-16.
For non unidiractional airflow (Non-UDAF) systems, where HEPA filters (EN 1822 / ISO 29463) or better are used, the equation:
Q = S/(C*ε).
Where
Q is supply air volume flow rate to the cleanroom (m3·s−1);
S is rate of particle emission in cleanroom air (source strength) (number·s−1);
C is particle concentration limit in the cleanroom (number·m−3);
ε is ventilation effectiveness (dimensionless)
As the energy consumption for ventilation is corelated to the flow rate to the third power, designing for sufficient air flow and not over designing, is very important for sustainability.
For non unidiractional airflow (Non-UDAF) systems, where HEPA filters (EN 1822 / ISO 29463) or better are used, the equation:
Q = S/(C*ε).
Where
Q is supply air volume flow rate to the cleanroom (m3·s−1);
S is rate of particle emission in cleanroom air (source strength) (number·s−1);
C is particle concentration limit in the cleanroom (number·m−3);
ε is ventilation effectiveness (dimensionless)
As the energy consumption for ventilation is corelated to the flow rate to the third power, designing for sufficient air flow and not over designing, is very important for sustainability.
A cleanroom is a separated space that is required to be able to control unwanted contamination of products and processes from the environment. A cleanroom is made to keep potential contamination from the environment outside the room. The airborne contamination generated during the activities in the cleanroom are diluted and removed by ventilation with high volumes of very clean filtered air. Surface contamination is frequently removed by cleanroom cleaning methods. The performance of the cleanroom is monitored by measuring air cleanliness, deposition rates, surface cleanliness and other environmental parameters.
The number of particles that’s can contaminate critical surfaces is controlled by the use of a cleanroom and a set of operational procedures. First the introduction of particles by air, surfaces or particle generating sources is limited. Secondly the emission of particles is limited by shielding and by only allowing cleaned low emitting materials, tools and equipment. Thirdly by an effective clean air ventilation system that dilutes and removes the airborne particle concentration. Fourth by removing all surface particles by frequent cleaning. Fifth by monitoring the effectiveness of the control activities by measuring air and surface cleanliness and particle deposition rate.
A separative device is a relative small cleanroom where no people can enter and can only be accessed by hands, fixed gloves and/or manipulators. Often inside a separative devices there is a uni-directional airflow. There open and closed separative devices. Materials can enter a closed separative device by a load lock. A separative device can be classified. A separative device can be place in a cleanroom with lesser class.
There are cleanrooms of different classes (at rest or operational) from clean (ISO 8) to extreme clean (ISO 1). The layout of a cleanroom is determined by the type of application, for example: semiconductor, electronics, space industry, pharmaceutical, medical, health care and food.
Next to scientific research various industries make use of cleanrooms to perform contamination control. Examples are: semiconductor, electronics, space industry, automotive, displays, batteries, life sciences, pharmaceutical, medical, health care and food.
The first step is a risk assessment. Determine what, how much, and where contamination can have a negative impact on a product, process or patient. The second step is to make a process lay out. In this lay out the selection of cleaning steps is important. Then determine the required cleanliness levels in air and on surfaces. Determine where and how much cleanroom is required.
This information is used to write a functional program requirements. This document is used to make a basic design. This process can lead to modification of the program of requirements. Via a concept design a detailed design is made, which covers all the functional requirements. The detailed design is the base for the construction, verification and start up. During construction and start up personnel must be trained to be to achieve the required cleanliness levels. All these activities are described in ISO DIS 14644-4:2021.
This information is used to write a functional program requirements. This document is used to make a basic design. This process can lead to modification of the program of requirements. Via a concept design a detailed design is made, which covers all the functional requirements. The detailed design is the base for the construction, verification and start up. During construction and start up personnel must be trained to be to achieve the required cleanliness levels. All these activities are described in ISO DIS 14644-4:2021.
Moisture and gasses are treated as chemical contamination. In the ISO cleanroom standard any cleanroom is classified by particles. If chemical of molecular contamination are of concern ISO 14644-8 can be used for air cleanliness and ISO 14644-10 for surface cleanliness. In ISO 14644-15 the determination of emission of chemicals by materials is described.
First the air cleanliness of this space should be specified, then the cleanability should be determined. After that the impact of the environment should be considered. This could lead to requirement for the classification and operation of the immediate environment. Finally the way to operate the controlled space should be determined and described.
In a risk assessment the functions of a product or process are determined. In a multidisciplinary team the potential treats of these function by contamination are determined. When the unwanted contamination is known the quantity that is accepted before the function are affected in a negative way. To determine contamination risk the consequences and the exposure (surface area times the time of exposure) are determined. This information can be used to determine the required air cleanliness and deposition rate limit.
The particle deposition rate determines the likelihood of surface contamination during exposure. The local particle deposition rate is determined by the ventilation system that must realise the air cleanliness and the operations that are described in the operational procedures.
Particles < 5 µm are removed by airflow, but locally gravitation, electrostatic, viscous or aerodynamic, thermophoresis and/or diffusion forces can cause deposition. Since this is only a small fraction it can be controlled by the air cleanliness level. To minimize electrostatic attraction materials with a low surface charge should be used.
Particles ≥ 5 µm are deposited by gravitational forces. The removal of macroparticles by airflow decreases with increasing particle size. Operational procedures determine the amount of large particles in a cleanroom. Turbulent airflow can cause surface particles to become airborne.
In ISO 14644-17 the particle deposition rate applications are described. These can be used as requirements or as monitoring limits.
Particles < 5 µm are removed by airflow, but locally gravitation, electrostatic, viscous or aerodynamic, thermophoresis and/or diffusion forces can cause deposition. Since this is only a small fraction it can be controlled by the air cleanliness level. To minimize electrostatic attraction materials with a low surface charge should be used.
Particles ≥ 5 µm are deposited by gravitational forces. The removal of macroparticles by airflow decreases with increasing particle size. Operational procedures determine the amount of large particles in a cleanroom. Turbulent airflow can cause surface particles to become airborne.
In ISO 14644-17 the particle deposition rate applications are described. These can be used as requirements or as monitoring limits.
Probably this is a question about the environmental air cleanliness. To determine how clean this should be the information in ISO 14644-17 can be used. From a product analysis the maximum acceptable particle deposition rate for the smallest critical particle should be determined. In many applications in cleanrooms with personnel this is for particles ≥ 5 µm. In cleanrooms without personnel and in separative devices this is mostly for particle < 5 µm.
Particles are counted and sized within known particle size bins ‘≥ d1 µm and < d2 µm’, ‘≥ d2 µm and < d3 µm’, etc. This gives a differential distribution. In cumulative all particles in bins above particle size di are counted. This way the air cleanliness can be given by one number.
A High Efficiency Particle Air filter removes particles from an air flow. To extend the life time the air is prefiltered to remove most particles > 1-5 µm. The filter efficiency is determined for the most penetrating particle size (MPPS). Particles smaller and particles larger than the MPPS are filtered with a better efficiency. HEPA filters are mostly used as a point of entry filter of the supplied air.
Cleanroom installations can consist of multiple zones and/or rooms with different requirements for contamination control. This is the case where rooms have different classifications or where the purpose of the room includes substances (contaminants, vapors, odors e.g.) that require segregation. More guidance can be found in the ISO standard ISO 14644-4 Design, construction and start-up (Annex B Guidance on design)
For the transition of materials into or out of a clean room or zone PTB’s are widely utilized. They commonly are at the perimeter of area’s with one or possibly two ISO classes difference. They can be flushed by filtered air by active ventilation within the PTB or by active filtered air from the cleanest room they lead to. When the relative pressure differential between both rooms is sufficient and stable, a designed air flow can be established via specific openings in both doors/sides of a PTB. The flow over such a PTB will increase by 40% when one of the doors is opened by Bernoulli’s law. As PTB's usually have limited internal volume, the needed amount of airflow is low in relation to the supply air of associated cleanrooms. For those PTB's, operated by the airflow resulting from diffential pressure between the connected rooms, the cleanliness (particles in air) in at rest state (closed doors and no transfer activity) the claenliness (particle concentration in air) will be the same as the actual cleanliness of the room with the highest pressure.
In practice, such PTB's will achieve 100:1 recovery times below 3-5 minutes.
PTB doors should always be interlocked.
In practice, such PTB's will achieve 100:1 recovery times below 3-5 minutes.
PTB doors should always be interlocked.
Classification
ISO 14644-4 (currently under revision) gives guidance on the steps to be taken during the design. The series of ISO standards on cleanrooms do not prescribe any required level nor an exact method to determine the ISO 14644-1 class. Professional experts can assist to help any organisation in establishing the appropriate requirements.
Although this still seems to be common practice ISO 14644-1 clearly determines three elements that are required for the proper classification: The ISO-number (1 till 9), the applicable particle size range (≥0,1 µm, ≥0,2 µm, ≥0,3 µm, ≥0,5 µm, ≥1 µm, ≥5 µm, and the occupancy state referred to (As built, At rest, Operational)
Cleanroom classes show the capability of a cleanroom. The cleanroom class for a given state occupancy and cumulative particle size is determined by the location with the highest average particle concentration. The classification of a cleanroom is a snapshot. Mostly in a classification process a proof should be made that the air cleanliness is within a specified class limit.
First the state of occupancy and relevant particle size should be determined. Then the area of the cleanroom is determined. The ventilation lay out should be the same throughout the considered cleanroom. ISO 14644-1:2015 has a table that gives the minimal number of sampling locations.
Divide the floor in equal sections so that per section one representative sample location can be chosen. Measure sufficient air volume so that during 1 minute or longer at least 20 particles ≥ the considered particle size can be counted. The location with the highest average particle concentration should be within the concentration limit of the classification table.
In monitoring a critical location in a cleanroom is selected and the particle concentration is measured at regular time intervals. The measured values should be within the class limit.
First the state of occupancy and relevant particle size should be determined. Then the area of the cleanroom is determined. The ventilation lay out should be the same throughout the considered cleanroom. ISO 14644-1:2015 has a table that gives the minimal number of sampling locations.
Divide the floor in equal sections so that per section one representative sample location can be chosen. Measure sufficient air volume so that during 1 minute or longer at least 20 particles ≥ the considered particle size can be counted. The location with the highest average particle concentration should be within the concentration limit of the classification table.
In monitoring a critical location in a cleanroom is selected and the particle concentration is measured at regular time intervals. The measured values should be within the class limit.
Although Classification by ISO 14644-1 is not requiring any formal other form of testing it is a common good practice to commission a cleanroom installation first. Depending on the requirements a couple of tests from part 3 test methods (currently under revision) are advised such as airflow tests, installed filter system leakage tests and room pressure tests. Defects on these aspects could cause a failure to meet the required cleanliness during classification according to ISO14644-1
Depending on the nature of the operational usage during use a type of monitoring can be applied. Typically ISO 14644-2 ‘Monitoring to provide evidence of cleanroom performance related to air cleanliness by particle concentration’ gives guidance in the process to establish a suitable monitoring program using the risk based approach.
Monitoring
In ISO 14644-1 cleanrooms are classified by particle concentrations determined by light scattering airborne particle counters (LSAPC). These particle counters take an air sample with a specific velocity. The lower the velocity the cheaper the particle counter, but the longer the sample time at low concentrations. A LSAPC counts and determines the particle size bin of each counted particle. The particle size depends on the optical appearance and is compared with the diameter of known spherical particles and thus gives an equivalent diameter. When measuring particles ≥ 5 µm sampling tubes can trap and release trapped particles on the tube wall especially in bends. These phenomena can decrease the correctness of the measurement. An ISO TR 14644 is in preparation to provide more guidance on particle counting.
For counting macro particles alternative methods are described in ISO 14644-1. Also Here sampling can disturb the measurement result.
Surface particles can be measured directly by a microscopic system (see ISO 14644-9). This determine the silhouette of a particle which is used to determine the particle size according to an agreed method, for example the Feret diameter.
In case a direct method can not be executed particles can be removed by air flow, liquid or tacky surface. Then an adequate particle measurement method can be used to determine the collected particles. These are referred to the original surface to calculate the particle concentration. The correctness is determined by the removal efficiency and the accuracy of the measuring device.
Measurement of the particle deposition rate is executed by measuring the change of surface cleanliness of a witness plate or test surface at subsequent times.
For counting macro particles alternative methods are described in ISO 14644-1. Also Here sampling can disturb the measurement result.
Surface particles can be measured directly by a microscopic system (see ISO 14644-9). This determine the silhouette of a particle which is used to determine the particle size according to an agreed method, for example the Feret diameter.
In case a direct method can not be executed particles can be removed by air flow, liquid or tacky surface. Then an adequate particle measurement method can be used to determine the collected particles. These are referred to the original surface to calculate the particle concentration. The correctness is determined by the removal efficiency and the accuracy of the measuring device.
Measurement of the particle deposition rate is executed by measuring the change of surface cleanliness of a witness plate or test surface at subsequent times.
Operation
The emission of a person in normal street clothes varies from 1 to 10 million particles ≥ 0,5 µm per minute depending on the activity and personal condition. This a very high air supply is required to reduce the surrounding particle concentration. Cleanroom clothing shield the emission of a person from the environment. Depending on the type of garment the emission can be reduced with a factor 10 to 100. However cleanroom clothing and changing procedure will increase surface contamination which will also contribute to the particle emission. These contributions can reduce the shielding efficiency with a factor 1 to 5.
The smaller the number of people in a cleanroom and the better the shielding efficiency the less air supply is required to achieve a good air cleanliness. However in general ISO 4 are better can not be achieved with continued presence of personnel in the cleanroom.
The smaller the number of people in a cleanroom and the better the shielding efficiency the less air supply is required to achieve a good air cleanliness. However in general ISO 4 are better can not be achieved with continued presence of personnel in the cleanroom.
Garments and gloves have a shielding function. A wiper is used to clean a surface. Beside the quality of their function, these consumables can emit particles and chemicals. This emission will impact the local air cleanliness and surface cleanliness.
In ISO CD 14644-18 guidance is given on the cleanroom suitability of these consumables.
In ISO CD 14644-18 guidance is given on the cleanroom suitability of these consumables.