Cleanrooms for Electronics & Semiconductor Manufacturing: Class 1-100 and the ULPA Requirement

When Samsung expanded in Thái Nguyên, Foxconn built its complex in Bắc Giang, and Intel grew its chip-packaging facility in TP.HCM, one technical term came up again and again: Class 1 cleanroom. This is the most stringent cleanroom grade, demanding ULPA filtration and a special architecture. This article explains why semiconductors need such demanding cleanrooms and lays out the core technical elements.

1. Why do semiconductors need Class 1 cleanrooms?

Modern chips have transistor features smaller than 14 nanometres (nm) — smaller than a virus. A 300 mm silicon wafer can carry billions of transistors, every one of which must be perfect.

A single 0.3 µm dust particle landing on a wafer during photolithography ruins thousands of transistors — turning a 5,000-20,000 USD wafer into scrap. That is why the production environment must control particles so tightly that the cleanroom is cleaner than Antarctic air.

A Class 1 cleanroom (ISO 3) requires no more than 10 particles ≥ 0.1 µm per m³ of air — a hard figure to imagine. For comparison: the air on a Hà Nội street during the inversion season can contain billions of PM2.5 particles per m³.

2. Process steps requiring cleanrooms in semiconductor manufacturing

A semiconductor process (front-end fabrication) has over 1,000 steps. The steps that demand the highest classes:

• Photolithography — the step that "prints circuits" onto the wafer. Class 1.
• Etching and Deposition — Class 10.
• Implantation and Diffusion — Class 100.
• CVD, PVD — Class 100.
• Wafer cleaning — Class 10.
• Probe test and packaging — Class 1,000 (back-end).

Each step sits in a bay (a sealed area with dedicated airflow), separated from common corridors — this is the ballroom + bay/chase architecture.

3. Electronics cleanroom architecture — Vertical Laminar

Unlike pharmaceutical cleanrooms (which often use horizontal flow or zonal flow), semiconductor cleanrooms use vertical laminar flow with three characteristics:

a. 100% FFU ceiling coverage

The cleanroom ceiling is packed with 1175×1175 or 575×1175 FFUs fitted with HEPA/ULPA, at near-100% filter coverage — creating "clean-air rain" falling evenly to the floor.

b. A raised access floor with ventilated tiles

The floor uses perforated tiles that let air pass into the sub-floor — where drainage piping, supply ducts, and power cables run. Air returns via the sub-floor back to the MAU + FFUs.

c. Laminar velocity of 0.4-0.5 m/s

This velocity is calculated to sweep particles down to the floor before they can settle on a wafer. Verified by periodic smoke tests.

4. Filter grades by zone

For electronics cleanrooms, ULPA is the mandatory standard:

Zone	ISO Class	Final filter grade
Common corridor	ISO 7-8	HEPA H13
Test bay, packaging	ISO 7	HEPA H14
Etching, deposition bay	ISO 4-5	ULPA U16
Photolithography bay	ISO 3	ULPA U17
Mini-environment in tool	ISO 1-2	ULPA U17 + gas-phase HEPA

Mini-environments inside production tools (steppers, scanners, CVD chambers) also include a chemical filter (gas-phase filter) to remove ammonia and organic sulphurs — substances that can react with resists and ruin patterns.

5. The MAU (Make-up Air Unit) — semiconductor-specific

Unlike pharma's recirculating AHU, semiconductor cleanrooms use:

• 100% fresh-air MAU — always drawing outside air through the full Pre + Medium + HEPA + carbon-filter chain.
• RCU (Recirculation Unit) — a large recirculation fan pushing air through the ceiling FFU array.
• MAU/RCU ratio typically 5-10% — i.e. 90-95% recirculated air, saving energy.

The system is a heavy electricity consumer — a 300 mm fab can consume 30-50 MW for HVAC alone, equivalent to the power use of a small city.

6. Multi-stage differential pressure

Semiconductor cleanrooms have multiple pressure stages:

Outside (0 Pa) → Lobby (+5 Pa) → Locker (+10 Pa) → Air shower (+15 Pa) → Chase (+20 Pa) → Ballroom (+25 Pa) → Bay (+35 Pa) → Photo bay (+45 Pa).

Each level rises by at least 10-15 Pa. Airlocks and air showers have door sensors — if two doors open simultaneously, the system raises an alarm.

7. Air showers and entry procedure

Entering a semiconductor cleanroom is a strict choreography:

1. Remove street clothes in the lobby.
2. Don a bunny suit (one-piece) — cap, goggles, gloves, boots — in the locker room.
3. Go through the air shower — 25 m/s air jets blow dust off the suit for 30 seconds.
4. Enter the cleanroom — no phones, no jewellery, no particulate cosmetics allowed.

Each person sheds 5 million particles/minute standing still and 10-20 million particles/minute moving. That is why semiconductor cleanrooms aim for as few people as possible — and why many modern fabs use AGVs (Automated Guided Vehicles) to move wafers instead of humans.

8. Special construction materials

• ESD vinyl flooring — anti-static, low-shedding.
• Raised floor with grating tiles — even airflow.
• Rockwool / PU-foam panel walls with metal facing — exceptionally flat, with no grain or gaps.
• 316L stainless steel for piping and conduits — does not shed rust particles.
• Flush LED lighting — no dust-catching gaps.

9. Vietnamese case studies

Samsung — Thái Nguyên, Bắc Ninh

Samsung Electronics' two largest sites in Vietnam, producing smartphones and electronic components. Total cleanroom area in the tens of thousands of m² with tens of thousands of FFUs.

Intel — Saigon Hi-Tech Park

Intel's largest chip-packaging and -test (back-end) facility in the world. Class 100-1,000 cleanrooms for assembly and test.

Foxconn — Bắc Giang

Apple-device assembly. Class 1,000-10,000 cleanrooms for precision component assembly.

Domestic suppliers

Hundreds of Vietnamese businesses produce components for the chain — camera modules, cover glass, connectors, cables — all requiring ISO 7-8 cleanrooms.

10. Opportunities and challenges for Vietnamese businesses

• Opportunity: rising electronics-FDI inflows, especially as US, Korean, and Japanese groups diversify supply chains away from China.
• Challenge: semiconductor cleanroom capex is very high (500-2,000 USD/m² civil works, equipment on top); shortage of experienced operators; very high electricity costs.
• Solution: start with Class 10,000 (ISO 7) cleanrooms for assembly/modules, invest in EC-motor FFUs to save electricity, hire a domestic consultant with experience.

Conclusion

Semiconductor cleanrooms are the pinnacle of cleanroom technology — where every dust particle can cost thousands of dollars. Understanding the role of ULPA U17, the vertical-laminar architecture, and the strict operating procedures is the entry condition for Vietnamese businesses to join the global electronics supply chain.

---

About Green Filter

Green Filter supplies ULPA U15/U16/U17, HEPA H13/H14, and FFUs certified to EN 1822-1:2009 for electronics and semiconductor cleanrooms. Products come with PAO/PSL scan-test certificates and are available in the popular 575×1175 and 1175×1175 module sizes for large-scale projects.

📞 Contact Green Filter for ULPA selection for your electronics cleanroom project: [insert hotline / email / website]

See also: ULPA Filters U15/U16/U17 · Bắc Ninh - Bắc Giang industrial parks: the electronics FDI boom · Samsung, Foxconn, Intel case studies.