1. What is a cleanroom?
A cleanroom is a space with tightly controlled airborne particle concentration, along with temperature, humidity and pressure. Air is continuously filtered through HEPA/ULPA filters to keep particle counts extremely low — a mandatory condition for fabricating silicon wafers and integrated circuits.
2. ISO 14644 cleanliness classes
The ISO 14644-1 standard classifies cleanrooms by the maximum particles per cubic meter of air. The lower the ISO number, the cleaner the room:
| ISO Class | US FED equivalent | Typical use |
|---|---|---|
| ISO 3 | Class 1 | Advanced lithography |
| ISO 4 | Class 10 | Leading-edge chip fab |
| ISO 5 | Class 100 | Semiconductors, MEMS |
| ISO 6 | Class 1,000 | Electronics assembly |
| ISO 7 | Class 10,000 | R&D labs, packaging |
| ISO 8 | Class 100,000 | Support areas |
3. Contamination control
People are the largest source of particles in a cleanroom. Control measures therefore include:
- Protective gear: bunny suits, nitrile gloves, face masks, anti-static shoe covers.
- Airflow: unidirectional (laminar) flow from ceiling to floor, positive pressure.
- Entry procedures: air showers, static discharge, low-lint wipes.
4. Choosing the right cleanliness class for your work
The governing principle: construction and operating costs rise steeply as the class tightens, while the benefit only materialises once feature sizes are small enough that particles genuinely cause failures. Over-specifying wastes operating budget every year.
| ISO class | Suitable for |
|---|---|
| ISO 3–4 | Advanced-node lithography, commercial chip production |
| ISO 5 | Research lithography, MEMS fabrication, sensitive device packaging |
| ISO 6 | Thin-film deposition, etching, buffer zones around ISO 5 areas |
| ISO 7 | Materials research labs, sample preparation, gowning areas |
| ISO 8 | Support areas, clean supply storage, service corridors |
5. People are the largest contamination source
Air filtration gets the most attention, but in most operating cleanrooms the majority of particles come from the people inside. The human body continuously sheds skin cells, and every movement releases particles into the air.
- Move slowly. Fast walking or abrupt gestures spike particle counts. This is the most frequently broken rule and the easiest to fix.
- Correct garments, correct order. Coverall, hood, face mask, nitrile gloves, overshoes. Gown top-down so falling particles do not land on already-clean layers.
- No ordinary paper, pencils or cardboard. Standard paper sheds heavily; use cleanroom paper and ballpoint pens.
- Limit occupancy. Particle counts scale almost linearly with the number of people present.
- No cosmetics or fragrance, and avoid cotton-fibre clothing under the cleanroom suit.
6. Measuring and maintaining the class
A cleanroom does not hold its class without monitoring. ISO 14644 distinguishes three occupancy states, and a number only means something when the state is stated:
- As-built — the room is complete, equipment not installed, no personnel.
- At-rest — equipment installed and running, but no personnel working.
- Operational — equipment running with people working normally. This is the number that reflects real production, and it is always the worst of the three.
When a supplier or a report claims "the room is ISO 5", the first question must be: measured in which state? Many rooms meet ISO 5 at rest but fall to ISO 6–7 once people are working. Beyond particle counting, periodic checks should cover HEPA/ULPA filter integrity, differential pressure between rooms, air changes per hour, and temperature and humidity.
Frequently asked questions
Which ISO class does a research lab need?
Most materials and semiconductor research labs work well at ISO 7, combined with ISO 5 laminar flow hoods at sensitive steps such as lithography. Building an entire room to ISO 5 is only warranted when routinely working below one micrometre.
What is differential pressure for?
The cleaner room is always held at higher pressure than the less clean room next to it, so that when a door opens air flows outward rather than drawing dust inward. The differential is typically kept in the range of a few tens of pascals between adjacent classes.
How often must a cleanroom be recertified?
Recertification intervals depend on the class and on industry requirements, with higher classes generally tested more frequently. Beyond scheduled certification, continuous or more frequent particle counting at critical locations gives early warning when filters degrade or gowning discipline slips.
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