Lined Pipe for Semiconductor and High-Purity Plants
A wafer fab measures contamination in parts per trillion, and the pipe is part of the contamination budget. Every ion of iron, chromium, nickel or copper that a steel wall gives up to ultrapure water or a process acid is a defect on a wafer, and every pinhole in a liner is a leak waiting to happen. Marspec Technical Products fabricates PVDF-, PTFE- and polypropylene-lined pipe spools and supplies PFA-lined valves and accessories for the chemical pad, the sub-fab and the waste plant, where flanged steel pressure ratings and metal-free wetted surfaces have to coexist. Call 251-625-4949.
The same rules govern polysilicon plants, electronic-grade chemical producers, circuit board shops and other high-purity operations. Contact us online with the chemistry and the metals specification and we will match a liner to it.
What a fab moves, and where lined steel begins
Ultrapure water
A large fab draws millions of gallons of water a day and polishes it to 18 megohm-cm resistivity through reverse osmosis, ion exchange, electrodeionization, ultraviolet and degasification, then reclaims most of it. Water that pure leaches ions from any metal it touches and corrodes carbon steel outright. Inside the polishing loop the industry uses all-plastic PVDF piping; the lined-steel case is upstream and alongside it: makeup and reject headers, ion exchange regeneration with hydrochloric or sulfuric acid and caustic, degasifier vacuum lines and the reclaim plant, where PVDF-lined carbon steel gives a flanged pressure rating with a liner that adds nothing to the water.
Bulk chemical delivery and the wet benches
Chemical delivery starts at the pad, where tank trucks unload 49 percent hydrofluoric acid, 96 percent sulfuric acid, 30 percent hydrogen peroxide, 70 percent nitric acid, 85 percent phosphoric acid, 29 percent ammonium hydroxide, 37 percent hydrochloric acid, isopropyl alcohol and TMAH developer into day tanks, and from there to the sub-fab. The wet benches blend them: sulfuric acid and peroxide at 250 F and above for resist strip, ammonium hydroxide and peroxide for particles, hydrochloric acid and peroxide for metals, dilute and buffered HF for oxide etch, and hot phosphoric acid near 320 F for nitride strip. Tool hookups are PFA tubing; from the unloading rack through the day tanks and distribution headers, lined steel carries the bulk chemicals at pressure. PVDF handles the acids and peroxide, PTFE takes the hot sulfuric and peroxide blend and the hot phosphoric acid that exceed PVDF's 275 F limit, and PTFE carries ammonium hydroxide and TMAH, since PVDF is not for strong bases; polypropylene is available there where a specification calls for it.
Waste: neutralization, fluoride and solvent
What leaves the tools is mixed: acid waste neutralized with caustic or lime, fluoride waste precipitated with calcium chloride or lime to calcium fluoride, ammonia, peroxide and solvent waste, CMP slurry with silica or ceria abrasive, copper plating waste and the caustic scrubber loops on the acid exhaust. Composition changes shift to shift, which is why PTFE-lined spools and PTFE-lined plug valves are the default on mixed acid headers and neutralized effluent, PVDF on slurry and fluoride lines, and lined diaphragm valves wherever solids are present.
Beyond the fab
Polysilicon and silicon wafer plants run trichlorosilane, hydrogen chloride and chlorosilane chemistry, and the HCl absorbers and wet scrubbers behind them are PTFE service. Electronic-grade chemical producers purify sulfuric acid, peroxide, HF and TMAH to parts-per-trillion metals and can tolerate no steel in the product line. Printed circuit board shops etch with cupric chloride and ammoniacal etchant and strip tin in nitric acid; solar cell lines texture wafers in HF and nitric acid. The battery and lithium plants that share these corridors hold electrolyte solvents and process water to the same standard.
Liner selection for high-purity service
- Ultrapure water makeup, reject and regenerant headers: PVDF
- HF, HCl and dilute mixed acids: PVDF or PTFE in vented housings
- Hot sulfuric and peroxide, hot phosphoric acid: PTFE
- Ammonium hydroxide and TMAH: PTFE, never PVDF; polypropylene available where specified
- Hydrogen peroxide: PVDF or PTFE, vented, no dead legs
- CMP slurry and fluoride precipitation: PVDF with lined diaphragm valves
PFA-lined diaphragm valves are the high-purity standard because the wetted path is smooth, drainable and cavity-free. PFA-lined ball valves give quarter-turn shutoff at the unloading rack, PTFE-lined plug valves isolate waste headers, lined check valves guard dosing pumps and lined sampling valves pull a metals sample without opening the line. Every pattern and lining is on our lined valves page; automated packages ship with actuators and positioners mounted and tested.
The package, venting, vacuum and the spark test
A fab package from us is typically 1" through 6" PVDF- or PTFE-lined spools in carbon steel or 316 stainless housings, built to isometrics in lengths up to 20 ft with class 150 ANSI B16.5 rotating flanges, matching lined fittings, PTFE spacers and spectacle blinds for isolation, lined strainers ahead of the acid waste pumps, sight glasses on the dosing lines and PTFE-bellows expansion joints on outdoor chemical pads. Sizes and liners are on our lined pipe and fittings page and the accessories under piping accessories.
HF and HCl permeate every fluoropolymer, PVDF less than PTFE, so those housings are vented and the flanges inspected. Hydrogen peroxide decomposes on metal and releases oxygen, so peroxide lines are vented and run without dead legs. Degasifiers and vacuum waste collection operate below atmospheric pressure, and the vacuum rating of each liner by size is on our technical details page. The spark test matters more here than anywhere: every lined part is tested at a minimum of 10,000 volts, because a pinhole harmless on a caustic line is a metals excursion in a fab. Northern fabs see winters that crystallize the 50 percent caustic at the neutralization plant; electric tracing with heat-transfer compound from our temperature maintenance line keeps it moving inside the liner's rating.
Where the fabs are, standards and ordering
The newest 300 mm fabs are rising in north Phoenix and Chandler, Arizona, at Taylor and Sherman in Texas, in Saratoga County and the Mohawk Valley of New York and in Licking County, Ohio. The established clusters are the Silicon Forest around Hillsboro, Oregon, the memory fabs of Boise, Idaho, Austin and Richardson in Texas, and the analog and compound semiconductor fabs of Massachusetts and southern Maine. Electronic-grade chemical plants follow the fabs, and polysilicon follows cheap Columbia Basin hydropower.
Our lined products comply with ASTM F1545, fittings conform dimensionally to ANSI B16.5 and are welded to ASME B31.3 by welders certified to ASME Section IX. Send isometrics and a line list, call 251-625-4949 or contact us online. Fab packages ship nationwide from Fairhope, Alabama.
FAQ: Lined Pipe for Semiconductor and High-Purity Plants
Why specify lined steel instead of all-plastic PVDF pipe in a fab?
Both have their place. Inside the polishing loop and at the tools, all-plastic PVDF and PFA are standard. On the chemical pad, the distribution headers, the waste plant and anywhere the rigidity, support spans and flanged pressure rating of a steel housing matter, lined steel gives the same wetted surface with the mechanical properties of pipe.
Which liner do you recommend for 49 percent hydrofluoric acid?
PVDF or PTFE in a vented housing. HF attacks glass and silica, so glass-lined equipment and silica-filled materials are excluded entirely. We vent the housing because HF permeates slowly through any fluoropolymer, and we recommend flange inspection on a schedule.
Can you line pipe for the hot sulfuric acid and peroxide resist strip supply?
Yes, in PTFE. The blend runs well above PVDF's 275 F limit, and PVDF is not used in hot concentrated sulfuric acid in any case. PTFE is rated to 450 F and is unaffected by either component.
How do you keep metal ions out of a lined spool?
The liner is the only wetted surface, and the spark test at a minimum of 10,000 volts proves there is no pinhole through to the steel. PVDF and PFA are the usual choices for high-purity loops because they add nothing to the stream; send us your metals specification and we will match the liner and the valve lining to it.