316L Sanitary & Hygienic
Valves for Semiconductor UPW and High-Purity Chemical Delivery Systems
Semiconductor wet processing is the most demanding fluid-handling environment there is. The fluid is ultrapure, the contaminants of interest are measured in parts per trillion, and a single particle can destroy a die. Valve selection is dominated by extractables, particle generation and surface chemistry rather than by pressure and flow.
What purity actually means
| Parameter | Typical UPW specification (at point of use) | Why the valve matters |
|---|---|---|
| Resistivity | 18.2 MΩ·cm (theoretical maximum) | Any ionic extractable from the valve shows immediately |
| TOC | < 1–5 ppb | Elastomers and lubricants are the usual organic source |
| Particles ≥ 0.05 µm | < 1–10 per mL (node dependent) | Particle shedding from seats and sliding surfaces |
| Dissolved oxygen | < 1–10 ppb | Permeation through polymer components |
| Metals | < 1 ppt–1 ppb per element | Leaching from stainless and from weld heat tint |
| Bacteria | < 1 CFU / 100 mL | Surface finish and dead legs determine colonisation |
Material routes
| Option | Used for | Advantages | Limitations |
|---|---|---|---|
| 316L electropolished (Ra ≤ 0.25 µm, passivated) | UPW bulk distribution, hot UPW loops | Mechanically strong, weldable, low extractables after passivation | Metallic ion release during start-up; rouging if passivation is poor |
| 316L VAR / VIM-VAR (vacuum arc remelt) | High-purity bulk gas and specialty chemical systems | Very low inclusion content, consistent weld penetration, superior surface after electropolish | Cost and lead time |
| PVDF (polyvinylidene fluoride) | UPW, dilute chemicals, drain lines | Very low extractables, no metallic ions, excellent chemical resistance | Temperature limit ≈ 120–140 °C; permeation; requires support |
| PFA / PTFE | Aggressive chemicals (HF, H₂SO₄/H₂O₂, SC-1, SC-2), hot chemistry | Broadest chemical resistance; high purity grades available | Permeation, cold flow, lower pressure rating |
| PTFE / PFA-lined 316L | Where pressure and chemical resistance are both needed | Strong shell with an inert wetted surface | Liner permeation and thermal cycling limits |
Valve types used in fab systems
- Diaphragm valves (PFA/PTFE diaphragm, PFA or PVDF body) — the workhorse of wet benches and chemical delivery. No stem seal in the fluid path, low particle generation, and excellent drainability in a weir body.
- Bellows-sealed valves — where a metal valve is required with zero stem emission and no elastomer in the fluid path.
- High-purity ball and butterfly valves (316L EP or PVDF) — bulk UPW distribution and isolation; cavity-filled designs for cleanability.
- Air-operated valves with position feedback — every automated valve reports its position to the tool; a valve that fails to confirm is a tool fault.
Surface and cleanliness requirements
• Electropolish plus passivation: electropolish to remove inclusions and free iron, then passivate (typically citric or nitric acid per ASTM A967) to build a chromium-oxide layer.
• Cleaning: precision cleaning to SEMI or customer specification, followed by double bagging in a controlled environment with particle and extractables certification.
• Welds: automatic orbital welding with an inert purge on both sides to prevent heat tint (chromium oxide discolouration), which is a major source of metallic extractables and rouging.
Standards that appear in fab specifications
| Standard | Scope |
|---|---|
| SEMI F57 | Materials and components for ultrapure water and liquid chemical distribution — extractables and leachables |
| SEMI F20 | Surface condition and finish of stainless steel components for UPW |
| SEMI F19 | PVDF components for UPW and chemical distribution |
| SEMI F40 / F48 | PFA and other fluoropolymer components, including jointing methods |
| SEMI F1 / F61 | Pipe and tubing for UPW; welded pipe specifications |
| ASTM A967 / A380 | Passivation and cleaning of stainless steel parts |
Design practices that reduce risk
- Minimise wetted surface area and eliminate dead legs — in UPW the loop is continuously circulating precisely so nothing stagnates.
- Keep velocity in the turbulent range (typically 1–3 m/s in UPW loops) to prevent biofilm, but avoid excessive velocity which generates particles by erosion.
- Design for drainability: a fab tool drain that cannot drain fully will contaminate the next batch.
- Specify double containment for hazardous chemicals, with leak detection at the annulus.
- Qualify by extractables testing on the actual assembly, not by material datasheet — the diaphragm and the body together determine what leaches.
KOSA supplies 316L electropolished and PVDF/PFA hygienic valves and fittings for UPW and high-purity chemical duty with full documentation. Send your specification for review.
Frequently Asked Questions
Why is 316L electropolished for UPW rather than standard 316L?
Electropolishing removes embedded free iron and non-metallic inclusions, rounds the surface profile and enriches chromium at the surface, all of which reduce metallic extractables and rouging. It brings the roughness to Ra 0.25 micrometres or better, which lowers the surface area available for contamination and bacterial colonisation.
What is SEMI F57?
SEMI F57 is the semiconductor industry standard covering materials and components used in ultrapure water and liquid chemical distribution systems. It sets requirements and test methods for extractables and leachables so that components do not contaminate the process fluid at parts-per-trillion levels.
When is PVDF used instead of stainless steel?
PVDF is used for ultrapure water distribution, dilute chemical lines and drains where freedom from metallic ion release matters more than mechanical strength. It has very low extractables and broad chemical resistance, but is limited to roughly 120 to 140 degrees Celsius and is more permeable than metal.
Why must hygienic welds be purged with inert gas?
If oxygen is present during welding, a coloured chromium oxide layer called heat tint forms on the inside of the weld. Heat tint is chromium-depleted beneath the oxide and is a major source of metallic extractables and subsequent rouging in ultrapure water, so the inside of the tube is purged with argon on both sides of the weld.
Send us the process data — fluid, inlet pressure, differential pressure, temperature, required flow and pipe size — and our engineers will return a sized selection with Cv calculation, leakage class and material recommendation, plus documentation packs for FAT / IQ-OQ.
Request a valve sizing quoteUPW valvesemiconductor valvehigh purity chemicalSEMI F57316L electropolishedPFA PVDF