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Oct. 22, 2026
Semiconductor-grade ultrapure water (UPW) must reach 18.2 MΩ·cm resistivity and hold particle counts in the parts-per-trillion range. Every unit of water that reaches a wafer must be cleaner than the last process step. Ultrafiltration (UF) sits in two critical positions of a UPW train: as pretreatment before reverse osmosis (RO), and as the final point-of-use (POU) polishing step. This article goes deeper on UF pore size and the quality specs that matter.
A typical UPW system runs: raw water → multimedia filtration → UF → RO → EDI or mixed-bed polisher → UV oxidation → final UF → point of use. The UF before RO protects the membranes from colloids and particles. The final UF catches resin fines and particles shed by polishing steps.
UF pore sizes: roughly 0.001 to 0.1 µm.
A typical nominal rating is about 0.03 µm.
In semiconductor UPW service, a common cutoff is 0.05 µm (50 nm) — the UF must hold back all particles larger than 50 nm to under 1 particle per milliliter.
Molecular weight cutoff (MWCO) is the other common spec. Manufacturers report in daltons. UPW-grade hollow fiber modules commonly use 4,000 to 6,000 daltons MWCO for polishing stages.
Transmembrane pressure (TMP): typically 1–3 bar for stable, gentle operation.
Flux: 100–300 L per m² per hour (LMH) is a common design window.
Water permeability: stable over long runs, not just at start-up.
SDI (Silt Density Index): UF pretreatment should feed RO at SDI well below 5.
Particle removal: >99% of particles above rated pore size.
PVDF and PES are the common choices. PVDF resists chlorine and chemical cleaning well. PES offers tighter pore control for polishing. Hollow fiber modules dominate UPW because of high surface area per module. Tubular UF is reserved for highly fouling feed water, not typical UPW service.
Final rinse water from a new module must not leach organics.
Integrity test (pressure hold) after installation.
Clean-in-place (CIP) chemicals must be UPW-compatible.
Drain and vent design must avoid dead legs that breed biofilm.
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