Cleanroom vs. Controlled Environment
Although the two are very similar, a cleanroom and a controlled environment are not the same. In a controlled environment, certain parameters must be carefully controlled, such as temperature, pressure, humidity, and physical separation from non-controlled environments. However, unlike a cleanroom, a controlled environment generally doesn’t have to meet any specific particle contamination standards.
Therefore, it could be said that a cleanroom is a controlled environment that must meet far stricter criteria. A cleanroom also requires a specific temperature, pressure, and humidity, along with separation from outside environments and careful management of airborne particulates. All of these factors must be closely monitored and controlled to maintain specific standards and conditions.
What Class of Cleanroom Do I Need?
An important factor in selecting the cleanroom you need is the class, or classification, required. Key considerations when determining the correct class of cleanroom for your application include:
- What are the sources of contamination in my location?
- How small are smallest particles I need to remove from the air?
- How much air do I need to circulate to remove contaminants?
ISO 14644-1 Modular Clean Room Classifications
Cleanrooms By United provides ISO Class 5 (Class 100) through ISO Class 9 (ambient) cleanrooms. Particle count is measured at work surface height.
|FED STD 209E equivalent|
|ISO 5||100,000||23,7000||102,000||3,520||8,320||293||Class 100|
|ISO 7||352,000||83,200||2,930||Class 10,000|
|ISO 8||3,520,000||832,000||29,300||Class 100,000|
|ISO 9||35,200,000||8,320,000||293,000||Room Air|
Air Change Rates & Classification
Cleaning the air itself is usually not the most difficult part of maintaining a cleanroom environment. Keeping the air clean is the biggest challenge. And to keep the air clean, you need to keep it fresh.
The air change rate (or ACR) of a cleanroom is a key factor in determining its classification. “Air change rate” refers to how quickly the air inside a cleanroom is pumped through and replaced with newly filtered air coming in from outside the cleanroom. How long does it take for fresh air that is pumped into a cleanroom to be exhausted out and replaced?
For ISO Class 9 through Class 6 cleanrooms, ACR is calculated by changes-per-hour; for Class 5 through Class 1 cleanrooms, ACR requirements are measured in meters per second of airflow. For example, an ISO Class 8 cleanroom requires a minimum of 10 air changes per hour—the air inside the cleanroom will be entirely “new” every six minutes or less. In a Class 5 cleanroom, air must travel through the room (from the filter input to the exhaust ports) at no less than 40 feet per minute.
Modular Cleanroom Requirements
|Air changes per HR/Min||300 to 480 / 5 to 8||180 / 3||60 /1||20 /0.33|
|Filter coverage %||60 – 70||20 – 30||7 – 15||4 – 5|
|CFM per square foot||36 – 65||18 – 32||9 – 16||4 – 8|
|Filter Efficiency||99.997% HEPAs||99.997% HEPAs||99.997% HEPAs||99.97% HEPAs|
|Ceiling Type||Aluminum T-bar grid||Aluminum T-bar grid||Conventional T-bar grid||Conventional T-bar grid|
|Light Fixture type||Tear drop or 2’x4’ cleanroom fixture||2’x4’ cleanroom fixture||2’x4’ cleanroom fixture||2’x4’ standard fixture|
|Ceiling Panel||FRP, Vinyl rock or Mylar||Vinyl rock or Mylar||Vinyl rock or Mylar||Vinyl rock or Mylar|
|Flooring cover||Welded sheet vinyl or Epoxy||Welded Sheet vinyl or Epoxy||Sheet vinyl or VCT||Sheet vinyl or VCT|
|Flooring base||Cove or Aluminum base channel||Cove or Aluminum base channel||Cove or Aluminum base channel||Cove or Aluminum base channel|
|Air Returns||Low wall on long axis||Low wall at perimeter||Low wall||Low wall or ceiling|
HEPA Air Filtration in Modular Cleanrooms
Because the contained space of a modular clean room is intended to reduce particulate contamination, HEPA air filters are key to their performance. All of the air delivered into a modular clean room passes through one or more High Efficiency Particulate Air filters, which trap any particles larger than 0.3 microns in size. For applications that require even greater cleanliness, ULPA (Ultra Low Particulate Air) filters that trap particles as small as 0.12 microns can be used.
Filtered air is supplied from overhead and, in most cases, passes out of the cleanroom via low wall vents. Single pass modular cleanrooms simply pull air in through the ceiling and exhaust it out; recirculating modular cleanrooms recycle the exhaust air back into the filter in a process of continuous circulation. Each design provides different benefits, and can impact other environmental parameters, such as temperature, humidity, and pressure.
Sources of Contamination in Cleanrooms
Contamination is any 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 lead to defects in miniature circuits, and ultimately destroy them. Film contaminants of only 10 nm (nanometers) can drastically reduce coating adhesion on a wafer or chip. With that in mind, cleanrooms are designed to eliminate as many contaminants from the air as possible.
The most common contaminants that can cause problems in cleanroom environments are generated from five basic sources: the facilities, people, tools, fluids, and the product(s) being manufactured can all contribute to contamination.
Key Elements of Contamination Control
- Cleanroom Design: Prefabricated cleanrooms are designed to achieve and maintain an airflow in which essentially the entire body of air within a confined area moves with uniform velocity along parallel flow lines. This air flow is called laminar flow. The more restriction of air flow, the more turbulence; turbulence can cause particle movement.
- High Efficiency Particulate Air (HEPA) Filters: These filters are the key component in maintaining contamination control in a modular clean room. HEPA filters remove particles as small as 0.3 microns, with a 99.97% minimum particle-collective efficiency.
- Filtration: In addition to HEPA filters, modular cleanrooms may use a number of other filtration mechanisms 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).
- 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 static charge. Special care is taken to use ESD protective materials in modular cleanrooms to prevent damage to products caused by ESD.
Cleanroom Gowning Requirements
People and clothing are two of the main sources of particulate contamination in a cleanroom environment. Therefore, a well maintained gowning rooms and proper gowning procedures are critical to maintaining cleanroom cleanliness.
The requirements for cleanroom garments vary based on the classification level and industry you work in. Lower classified cleanrooms (ISO 7 and 8) typically require smocks, shoe covers, gloves, and hairnets, while more stringent cleanrooms (ISO 6 and up) require full coveralls made of Goretex or similar nonwoven (and therefore non-shedding) materials, along with hoods, gloves, and shoe covers.
Important information for personnel to remember when gowning prior to entering the cleanroom include:
- Always clean your street shoes before entering the gowning room. Automatic shoe cleaners and adhesive floor mats are an effective way to remove dirt and contaminants from shoes. Be sure to put on shoe covers before entering the gowning area.
- Never let clean surfaces contact dirty ones. Always wash your hands before handling cleanroom garments, and never let clean garments touch a dirty floor or other surfaces.
- When gowning, start with your gloves, then work from the top down. As needed, put on your hairnet, hood, mask, and coveralls, with the hood tucked inside. Finally, put on boot covers. Boot covers and gloves should overlap coveralls.