From ISO Class 1 to ISO Class 9, allowed particle count spans 10⁸ — 100 million times. One end is quantum-lab territory, the other is basically a tidy warehouse. Where does your process sit?

Why FED-STD-209E Retired and ISO 14644 Took Over

First published in 1999, with the US FED-STD-209E formally retired in 2001, the current ISO 14644-1:2015 is the most widely adopted cleanroom classification standard globally.

It did two things:

  1. 1Unified classification — replacing the patchwork of US / European / Japanese schemes
  2. 2Defined a formula, Cn = 10^N × (0.1/D)^2.08, giving a concentration limit for every particle size — so a class is a whole size-vs-concentration curve, not just a single number

What Do the Nine Classes Actually Look Like?

At the most common 0.5 μm particle size:

Biểu đồ 1: Chín cấp ISO 14644-1 (ở 0.5 μm)

Từ Class 1 nghiêm ngặt nhất đến Class 9 nới lỏng nhất, mỗi cấp cao hơn cho phép 10× hạt

CấpMax ở 0.5 μm (hạt/m³)US cũỨng dụng
Class 335Class 1Nghiên cứu cơ bản
Class 4352Class 10Bán dẫn tiên tiến
Class 53,520Class 100Quang khắc, OLED, dược vô trùng
Class 635,200Class 1,000Lắp ráp điện tử
Class 7352,000Class 10,000Dược C, quy trình chung
Class 83,520,000Class 100,000Đóng gói thực phẩm
Class 935,200,000—Không gian hỗ trợ

Nồng độ hạt theo Cn = 10^N × (0.1/D)^2.08.

Key mappings:

  • ▸ISO Class 5 = old US Class 100 — the workhorse for lithography, OLED deposition, aseptic fill
  • ▸ISO Class 7 = old US Class 10,000 — electronic assembly, pharma grade C
  • ▸ISO Class 8 = old US Class 100,000 — food packaging, general clean workspace

Each step up multiplies the allowed particle count by 10. That's why stepping from ISO Class 5 to Class 4 can double the build cost, not add 20 %.

What Is the Formula Computing?

Cn = 10^N × (0.1/D)^2.08

Unpacked:

  • ▸10^N: every class number multiplies the limit by 10
  • ▸(0.1/D)^2.08: larger particle size → exponentially stricter limit. 0.5 μm is ~28× lower than 0.1 μm

Sanity check on ISO Class 5 @ 0.5 μm: 10⁵ × (0.1/0.5)^2.08 = 100,000 × 0.0352 = 3,520 particles/m³ ✓

This also explains why ISO Class 1–2 drops below 1 particle/m³ at 0.5 μm — essentially unmeasurable. Those classes get verified using smaller particles (0.1–0.2 μm) instead.

Why Qualification State Matters More Than the Class Number

ISO 14644-3 defines three qualification states:

Biểu đồ 2: Ba trạng thái nghiệm thu ISO 14644-3

Cùng một phòng có thể chênh >10× số hạt giữa các trạng thái

As-built

★☆☆

Chưa lắp máy, chưa có người

Nguồn tối thiểu

At-rest

★★☆

Đã lắp máy, không hoạt động

Chỉ tồn dư máy

Operational

★★★

Máy chạy, có người, dòng vật liệu

Người + máy + quy trình

Ngành bán dẫn và chiết rót vô trùng yêu cầu đạt ở Operational.

The three can differ by more than 10×:

  • ▸As-built — cleanest: no tools, no people. Easy to pass at handover
  • ▸At-rest — tools installed but not running, no staff
  • ▸Operational — tools running, people working, material flowing. Live production
Semiconductor and aseptic-fill industries typically mandate ISO Class 5 under Operational — only this reflects real-world contamination load. Passing At-rest does not guarantee passing Operational.

Some specs just say "ISO Class 5" without naming the state — that's nearly meaningless. Before signing, pin down whether it's As-built / At-rest / Operational, or you may pay for operational and get as-built.

How Much Ceiling Area Should Be Filter?

Ceiling coverage drives most of the build cost. Stricter class = denser ceiling:

Biểu đồ 3: Tỷ lệ phủ lọc trần vs cấp sạch

Cấp càng nghiêm, trần phải phủ càng kín

ISO 1–3
80–100 %
ULPALớp· Trần lớp toàn phần
ISO 4–5
40–80 %
H14Lớp· Lớp trên máy
ISO 6–7
15–40 %
H13Rối được· FFU phân tán
ISO 8–9
< 15 %
Trung / caoRối· Ống gió thường

Tỷ lệ phủ = diện tích trần có FFU.

  • ▸ISO Class 1–3 — whole ceiling is FFU (ULPA + laminar), 80–100 % coverage
  • ▸ISO Class 4–5 — 40–80 % (H14 HEPA + laminar), dense over tools, sparse in support zones
  • ▸ISO Class 6–7 — 15–40 % (H13 HEPA), grid-distributed, turbulent flow OK
  • ▸ISO Class 8–9 — under 15 %, ordinary ventilation filters suffice

Jumping from ISO Class 7 to Class 5 can require 3–5× more filters — add the laminar ceiling structure, fan power, pressure-differential control, return air, and waterfall flooring, and the total build can shift by a whole budget tier.

What Does Qualification Actually Measure?

ISO 14644-3 core tests:

  • ▸Particle concentration — via optical particle counter (OPC)
  • ▸Airflow velocity and air change rate — the dilution capacity
  • ▸Pressure differential — zone-to-zone isolation
  • ▸Airflow visualization — smoke test, confirming laminar really is laminar
  • ▸Recovery test — how fast the room clears after a spike
Particle count is just the start. Airflow, pressure cascade, and recovery are what sustain a class over time.

A Class You Can Sustain Beats a Class You Barely Passed

Cleanroom classification is a continuous engineering problem, not a single test day:

  1. 1Design — pick the right ISO Class, no over- or under-spec
  2. 2Build — filter coverage, fans, pressure cascade, floor drainage
  3. 3Qualification — specify Operational state, that's the real capability
  4. 4Operation — periodic requalification (ISO 14644 recommends every 6–12 months), filter replacement, personnel training

There is always a sweet spot between cost and compliance — the discipline is defining the problem clearly before picking a configuration.