Cleanrooms and cleanroom technology – Global differences in standards

Controlled environments such as cleanrooms are essential to maintaining product quality, safety and standards in many industries. In semiconductor manufacturing, for example, even the smallest particles can damage the sensitive surfaces or lead to undesirable chemical reactions. But what defines a cleanroom? What conditions must be met and what classes are there? And what cleanroom technology can be used to implement cleanrooms? The following article introduces the concept of cleanroom in more detail, including addressing these questions and standards worldwide.

What is a cleanroom?

Cleanrooms are highly-controlled rooms in which the concentration of airborne particles is kept as low as possible. They are set up for the production of particularly sensitive components. Particles present in normal ambient air would already be sufficient cause defects, e.g. in semiconductor production, optics or laser technology. Such airborne particles can for example be:

• Dust
• Skin particles
• Hair
• Germs
• Chemicals

Cleanrooms are also used when sterility requirements cause products to become unusable due to the smallest contamination. Their size varies from small facilities to large machine parks.

Cleanrooms must be distinguished from so-called sterile rooms. The term describes a spatially segregated area whose air purity is better than in the surrounding areas, but that does not necessarily meet cleanroom standards. Sterile rooms primarily filter out coarser particles from the air.

Cleanroom Classes

Cleanrooms are available with low and high purity requirements. These are based on the purity requirements for the different manufacturing processes. In this context, ISO 14644 specifies various cleanroom classes, ISO 1 to ISO 9. The nine cleanroom ISO classes each define maximum allowable limits for airborne particle concentration. The lower the number, the higher the cleanroom requirements. For example, the semiconductor industry requires a very high purity level of ISO 1 to ISO 5. The range from ISO 1 to ISO 3 is also referred to as ultra-sterile rooms.

The classes define the permissible airborne particle concentration, as measured in particles per cubic meter of air. Each cleanroom class has a maximum value for particle concentration. Different maximum concentrations per class apply for different particle sizes. For example, for cleanroom ISO class 1, for each cubic meter of air:

• particles ≥ 0.3 μm may not occur at all,
• particles ≥ 0.2 μm may occur a maximum of 2x,
• particles ≥ 0.1 μm may occur a maximum of 10x,

The higher the ISO class, the larger the permitted particle sizes and their permitted number.

Particle measurement

The cleanliness of a cleanroom is defined by the number of airborne particles. The naked eye cannot detect when the limit is exceeded. It is therefore precisely defined how the number of airborne particles can be measured. Measurement methods are therefore defined in various standards. There are three types of cleanliness standards: FS 209E-1992, JIS B 9920-1989 and ISO 14644-1.

However, not only the measurement of particles, but also other parameters such as pressure control and humidity in the cleanroom are relevant. The measuring instruments used for this are, for example:

• Particle counter or sensor measures the concentration of airborne particles
• Hygrometer determines relative humidity
• Thermometer measures temperature
• Pressure gauge measures air pressure difference

Learn more about quality control through measurement in this blog.

Cleanroom design

The number of airborne particles in the cleanroom must be limited. For this purpose, the access areas to cleanrooms are generally closely monitored and the particle concentration, temperature, air pressure and humidity must also be continuously monitored. This is the only way to ensure that specified values are observed. The room design as well as the operating equipment used are subject to special criteria. The work environment is typically arranged so that people have to move as little as possible while working. Humans represent the greatest risk of particulate carryover.

Measurement specifications and the appropriate cleanroom technology

Measurement specifications, such as the number of measuring points per room, are regulated by ISO 14644. To keep the values comparable over a long period of time, other parameters such as temperature, pressure and humidity must be kept constant.

In general, consideration must be given to:

• How can contaminants (e.g. by special surfaces) be kept away?
• What conditions must apply to people entering the room from outside? This also applies to items brought into the cleanroom.
• And as a last point, consideration must be given how to avoid accumulations of contaminants, e.g. through straight surfaces, air circulation, etc.

For this purpose, there are various cleanroom products, such as adhesive mats, laminar flow benches or filters. A few examples are presented below.

Cleanroom Filters

Air conditioning for clean air supply is located in each cleanroom.

The use of filters plays an important role in this context. HEPA filters, for example, are capable of collecting particles up to 0.3 microns from the air. The HEPA H14 class guarantees almost complete removal of particles. ULPA filters, as a special type of HEPA filter, can even capture particles of 0.12 microns.

Cleanroom greases

Machinery must invariably be lubricated for good functionality. To this end, there are specially designed greases, such as those used for lubricating ball screws that ensure particle absence and chemical stability. At the same time, the functionality of the machines is not impaired. For example, class G grease is a particle-reduced grease used in cleanrooms. Silicone-free and low-viscosity lubricants also often release fewer particles than many conventional greases.

A suitable test procedure is required to demonstrate a reduced particle rate for components.

The test setup used here in the example of a low particle emission rate filled roller bearing was as follows:

• Bearing: 6205 open
• Load: 5 to 10% of dynamic load rating
• Speed: 450 rpm
• Environment: In air, in pure cell (class 10)
• Temperature: Room temperature

The special, particle-reduced lubricant showed a significantly low particle emission:

The following table provides a particle incidence comparison of the MISUMI ball bearings according to lubrication performance and working environment:

Design-based approaches

In addition to using specialty grease, there are also many design-based solutions, such as particle-reduced bearings, threaded drives and linear drives or single axis robots, which are suited for use in particle-reduced environments. In linear units with cover, for example, the particle emission is largely minimized by using a cover. The cover is mounted over the guide and carriage and extends over the entire length of the linear unit. Bearings can also be sealed or provided with special abrasion-minimizing coatings. MISUMI has various grooved ball bearings with reduced particle emission rate, for example:

• single row grooved ball bearing
• single-row grooved ball bearing with flange

Since humans are often the largest source of contaminants in the cleanroom, the use of robots in the cleanroom is also worthwhile. For this purpose, electric actuators, also known as single-axis robots, are suited for use in particle-reduced environments.

In certain cleanroom classes, pneumatic systems and circuitry are also used to further reduce particle concentration. Learn more about pneumatic circuits in this blog.

MISUMI also allows you to specifically look for solutions with reduced particle emission rates.

Various cleanroom standards

As mentioned earlier, there are several cleanroom standards. The following is an overview of the standards, their applicability, special features, and differences:

Internationally applicable standards

The ISO 14644 series of standards is considered standard in many countries. It contains 15 individual standards, including:

• ISO 14644-1 addresses the classification of air purity in cleanrooms and sterile areas based on particle concentration.
• ISO 14644-3 describes test procedures for cleanrooms and associated cleanroom areas.
• ISO 14644-4 describes planning, execution and initial commissioning
• ISO 14644-5 describes the operation of cleanrooms and associated cleanroom areas.

ISO 14644-14 and ISO 14644-15 both provide methodologies for assessing the usability of equipment for cleanroom use, such as measuring instruments, tools, process equipment, etc. ISO 14644-14 assesses this by determining the concentration of airborne particles according to ISO 14644-1. ISO 14644-15 defines usability based on the concentration of airborne chemicals. They are closely linked to the requirements for chemical purity classes according to ISO 14644-8.

The following table provides an overview of the purity classes according to DIN EN ISO 14644-1:2015:

European Standards

In addition to the recognized ISO 14644, the EU GMP guidelines also apply in Europe in the medical field. They are binding for drug manufacturers in the European Union. The guidelines define four different cleanroom classes, describe measures to avoid contamination and provide clear regulations on cleanroom operation, personnel air locks and hygiene measures. In general, GMP guidelines and ISO 14644 are complementary, but GMP guidelines focus primarily on product protection, while the ISO 14644 approach is more comprehensive and also regulates the classification and monitoring of air purity. In Germany, there is another standard that addresses the cleanroom topic: VDI 2083. It provides an overview of planning, monitoring and operation.

The following table provides an overview of the purity classes according to EU GMP Annex 1:

US standards

ISO 14644 also applies in the USA. Until the 1990s, however, there was also the Federal Standard 209E, which is still relevant today in industries such as the semiconductor industry. However, the biggest difference is merely the specification of the particle concentration in particles per cubic foot instead of cubic meters. USP 797 also applies for sterile pharmaceuticals.

The following table provides an overview of the purity classes according to US FED 209E:

Japanese standards

In Japan, JIS B 9920 applies to the classification and monitoring of cleanrooms. However, it is strongly based on ISO 14644 and contains essentially similar requirements. They are largely compatible, thus facilitating international collaboration. JIS B 9920 for example also defines the cleanroom classes based on the particle concentration in the air. However, the described test procedures are adapted to the requirements of local industries.

Differences in standards

Overall, the standards address the same content and only have different regional and industry-related applications. The classification of cleanroom classes differs depending on the standard:

ISO 14644, JIS B 9920, VDI 2083 are based on cleanroom ISO classes 1 to 9. USP 797 also uses the ISO classes, but only that of 5.7 and 8. The EU GMP guidelines define their own classes (A to D) based on particle and microbiological limits.

Monitoring focuses on particle measurement and air cleanliness in ISO 14644 and JIS B 9920. The EU GMP and USP 797 have stricter requirements and therefore stricter microbiological monitoring methods.

VDI 2083 focuses on technical validation and structural inspection. In general, it can be said that ISO 14644 is a generally valid standard for cleanroom applications, but special requirements may require referencing other standards.

The following table provides an overview of the various standards and their applications: