What cleanroom class does an electronics or PCB plant actually need?

The first question an engineering team asks when a clean area appears on the plant layout: which class does the law require? The answer is shorter than expected: none. No Thai regulation prescribes a cleanroom class for electronics or PCB manufacture. Pharmaceutical and medical-device GMP grades its rooms explicitly; electronics has no such rule. Your class comes from exactly two places: your own process specification, and whatever your customer's audit checklist says.

What ISO 14644-1 counts

The reference the whole industry uses is ISO 14644-1:2015. The principle is plain: count particles per cubic metre of air and assign a class from ISO 1 to ISO 9, lower being cleaner. The familiar names Class 10,000 and Class 100,000 come from the old US standard FED-STD-209E, which counted per cubic foot and was cancelled in 2001. The names outlived the document. Most Thai contractor quotations still print them.

• ISO Class 7: no more than 352,000 particles of 0.5 micron and larger per cubic metre. The old name is Class 10,000
• ISO Class 8: no more than 3,520,000 particles per cubic metre. The old name is Class 100,000

Those numbers mean nothing without the occupancy state next to them. The standard declares a class together with the room's state: as-built (empty shell), at-rest (equipment installed, nobody inside), or in-operation (production running). The same room can pass ISO 7 at rest and fail it in operation without anything being wrong with the construction, because the largest particle source in any cleanroom is people. A quotation that says Class 10,000 with no state is not yet a comparable offer.

What PCB and SMT plants actually run

This part is industry convention, not law: general SMT and assembly floors usually run ISO 8, while the genuinely particle-sensitive steps, imaging, film rooms and solder mask, step up to ISO 7. Wafer front-end work at ISO 5 and cleaner is another world entirely, and not one a Thai assembly or PCB plant has to carry. If your customer has sent an audit checklist, use its numbers. If not, start at ISO 8 and tighten only the rooms whose process demands it.

Our position: a class cleaner than the process needs is the most expensive sentence in the TOR. Every step up the scale grows the air-change rate and the filter area, and the electricity bill repeats monthly for the life of the room. The standard is a ruler, not a design. Do not write ISO 5 into a TOR because it sounds safe when no auditor has ever asked you for it.

Split the scope in three, and the prices become comparable

One cleanroom is three scopes, and a TOR should keep them on separate lines. First, the envelope: walls, ceiling and doors in prefabricated insulated panel. Second, the air system: HVAC, fan filter units and filters, which is the part that actually produces the class. Third, certification: particle counting to the method in ISO 14644-1, with the measured state named. Split them and competing quotations line up; you also see immediately what each bidder has quietly bundled.

One recurring mistake is asking the panel contractor to guarantee the class. The class comes from the air system, not the wall. What the envelope owes you is flush joints, cleanable surfaces, and compliance with what the air-system designer specified. We quote envelope work of exactly this kind with our partner CK Design & Service, issuing the quotation and the invoice ourselves so the room and the lab instruments inside it share one purchase order; details are on the cleanroom and cold room service page. Certification should belong to a third party with a calibrated particle counter, not to whoever built the room.

Why this question is landing in Thailand now

Over the past three years the Board of Investment reports 26.8 billion US dollars in semiconductor and advanced-electronics investment applications. PCB alone accounts for 224 projects worth 9.85 billion dollars, with close to 60 Chinese and Taiwanese makers concentrating around Prachinburi and Ayutthaya. Every one of those plants needs controlled areas and its own QC laboratory. The lab side has its own article: what a PCB factory's QC lab actually needs

Class figures checked against the text of ISO 14644-1:2015 on 30 August 2026. The investment figures are what the BOI told the press; we verified them against news reports, not a formal notification, so use them to size the wave and not as citations in official documents.