Cleanrooms are contamination-free environments where high-tech manufacturing and assembly takes place. They range from very small chambers, called microenvironments, to large-scale rooms, called ballrooms. Cleanroom technology is used in a wide range of industries including semiconductor assembly, biotechnology, pharmaceutical, aerospace, food, medical devices and hospitals.
There are a number of important aspects to consider when determining which cleanroom type will fit the needed application. This includes the cleanliness class, fabrication type, and special features such as ESD control, pass throughs, and a gowning area.
Cleanliness class is a standard determined by the contamination control industry. This classification is based on particle concentration. Each designated class represents a maximum amount of particulates of known sized to be present per unit volume within the cleanroom. There are two governing agencies that have developed classification schemes used to decipher the cleanroom class: the International Organization for Standardization (ISO) and the US Federal Standards.
International Organization for Standardization (ISO)
ISO 14644-1 is a standard developed by ISO that describes the methodology of classifying a cleanroom to one of several classes. This standard is periodically reviewed and revamped to address the needs of the industry. ISO cleanroom classes are defined by the following formula:
Cn = Maximum number of particulates per cubic meter that are equal to or greater than size D
N = ISO class number, a multiple of 0.1 that is less than 9
D = Size of particulate in micrometers (μm)
US Federal Standards
FED-STD-209 is a US federal government standard that is used to classify the cleanliness of a cleanroom. The class number used refers to the maximum number of particles bigger than one-half of a micron that would be allowed in one cubic foot of cleanroom air. A Class 100 cleanroom, for example, would not contain more than 100 particles bigger than half a micron in a cubic foot of air. The six classes and ISO equivalents are Class 1 (ISO 3), Class 10 (ISO 4), Class 100 (ISO 5), Class 1,000 (ISO 6), Class 10,000 (ISO 7), and Class 100,000 (ISO 8).
Image Credit: American Cleanroom Systems
There are five main fabrication styles for cleanrooms (although custom styles are available). They are conventional, modular hardwall, modular softwall, mini environment, and micro environment.
Conventional construction is the most common type, and these are generally permanent structures.
Modular cleanrooms are constructed on site from pre-cut and assembled components, such as walls, ceiling grid struts and other components.
Modular hardwall cleanrooms provide the rigidity and durability of a freestanding room. The walls of the cleanroom are of a solid material, rather than fabric.
Modular softwall cleanrooms are constructed from fabric, either of free-hanging strips or stretched tightly over a frame.
Mini environments are localized clean environments used in semiconductor manufacturing applications. They are created around a specific tool, or only within a tool, to protect the semiconductor wafer from atmospheric exposure. Wafers are moved from one mini environment equipped tool to another in sealed containers and only exposed to the atmosphere inside of the clean mini environment.
Micro environments are similar to mini environments, but they are smaller. They are used to protect the wafer itself, or a part thereof, instead of encapsulating the manufacturing tool.
Electrostatic Discharge (ESD) Control — Some cleanrooms are available with Electrostatic Discharge (ESD) control. A cleanroom with ESD control is able to measure and contain electrical discharge thereby avoiding rapid, spontaneous and usually uncontrolled transfer of an electrical charge between two conductors induced by a strong electrostatic field.
Cleanroom Pass Throughs — Cleanroom pass throughs consist of a small airlock chamber with two doors and allow equipment and personnel to enter a cleanroom while preventing particle contamination of the cleanroom environment. They can consist of a chamber, air shower, or tunnel. Cleanroom pass throughs are very important in laboratories or manufacturing facilities that require clean and/or sterile rooms for research, manufacturing, assembly of a product. The cleanrooms allow the room to stay clean as the product or item is moved into or out of the room.
Image Credit: Terra Universal, Inc.
Gowning Area — Cleanrooms equipped with gowning areas allow additional protection from contamination. The gowning area serves as an intermediate cleanroom where personnel can suit up in the appropriate personal protective equipment (PPE) that will safeguard the user as well as the exposed surfaces and materials within the cleanroom. Gowning areas are typically adjoined to the cleanroom via a pass through with an air shower that washes any residual contamination from fully suited personnel before entering the cleanroom.
Image Credit: Terra Universal, Inc.