High-Purity Lined Pipe for Semiconductor 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 PTFE- and PVDF-lined pipe spools and supplies PFA-lined valves and accessories for bulk chemical supply, acid waste and neutralization, where chemical resistance and the strength of a flanged steel housing 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. Ultrapure water itself runs in solid natural PVDF, and our PVDF liner is black-pigmented, so lined pipe is not a UPW pipe. The lined-steel case in the water plant is the bulk chemical supply, acid waste and neutralization around it: ion exchange regeneration with hydrochloric or sulfuric acid and caustic, the spent regenerant, and the neutralization of reject and reclaim streams.
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 (121 °C) 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 (160 °C) for nitride strip. Electronic-grade chemicals run in solid PFA or natural PVDF from the day tanks to the tools, with PFA tubing at the hookups. Lined steel is for bulk chemical supply, acid waste and neutralization: the unloading rack, bulk storage transfer and the waste side. There, PTFE carries the concentrated acids, the peroxide, the hot sulfuric and phosphoric acid, and the ammonium hydroxide and TMAH, since amines and caustic attack PVDF; PVDF is an option on the cooler, dilute acids. Sulfuric acid and peroxide travel in separate lines and are blended at the tool, because the premixed blend gives off oxygen and cannot be held in closed piping. Polypropylene is not used in fab chemical distribution: it leaches stabilizers that a parts-per-trillion specification cannot accept.
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 PFA-lined cylindrical 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 mono wafers in hot KOH and strip oxide in dilute HF. 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
- Water plant regenerant and RO reject headers: PTFE, with PVDF an option on the cooler, dilute acid regenerant; ultrapure water itself runs in solid natural PVDF, not lined pipe
- HF, HCl and mixed acids: PTFE, with PVDF an option on dilute acid near ambient temperature
- Hot sulfuric acid and hot phosphoric acid: PTFE, with peroxide in its own line and blended at the tool
- Ammonium hydroxide and TMAH: PTFE, since amines and caustic attack PVDF
- Hydrogen peroxide: PTFE, or PVDF when cool, vented, no dead legs
- CMP slurry and fluoride precipitation: PVDF with lined diaphragm valves
On bulk chemical supply, acid waste and neutralization lines, lined diaphragm valves, with a PFA-lined body and a PTFE-faced diaphragm, are the usual choice because the wetted path is smooth, drainable and cavity-free. PFA-lined ball valves give quarter-turn shutoff at the unloading rack, PFA-lined cylindrical plug valves, 1/2" through 2" full port and 3" through 6" reduced port, cavity-free, with no in-line adjustment, 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" PTFE- or PVDF-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 the flanges are inspected, and the vent holes drilled as standard in every housing relieve the permeant pressure to prevent liner collapse. Hydrogen peroxide decomposes on metal and releases oxygen, so peroxide lines are vented and run without dead legs. Vacuum waste collection operates below atmospheric pressure, so tell us the vacuum level and we will confirm the liner by size; liner temperature limits, liner thicknesses, flange dimensions and torque tables are on our technical details page. The spark test matters more here than anywhere: every lined spool and fitting 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. For jacketed or traced service, we recommend specifying PTFE.
Where the fabs are, standards and ordering
Large 300 mm fabs run in north Phoenix and Chandler, Arizona, at Sherman in Texas and in Saratoga County, with a silicon carbide fab in the Mohawk Valley of New York. Other clusters are the Silicon Forest around Hillsboro, Oregon, Micron's R&D fab in Boise, Idaho, the logic fabs of Austin and the analog fabs of Richardson, Texas, and the analog and compound semiconductor fabs of Massachusetts. Electronic-grade chemical plants follow the fabs.
Our lined pipe and fittings 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. Ultrapure water and electronic-grade chemicals run in solid natural PVDF or PFA from the water plant and the day tanks to the tools, and our PVDF liner is black-pigmented, so lined pipe is not for those lines. Lined steel is for bulk chemical supply, acid waste and neutralization, where chemical resistance, temperature and the mechanical protection of a steel housing matter.
Which liner do you recommend for 49 percent hydrofluoric acid?
PTFE. HF attacks glass and silica, so glass-lined equipment and silica-filled materials are excluded entirely. HF permeates slowly through any fluoropolymer, and the vent holes drilled as standard in every housing relieve that permeant pressure to prevent liner collapse; we recommend flange inspection on a schedule.
Can you line pipe for the sulfuric acid and peroxide resist strip supply?
For the bulk supply, yes, in separate lines: sulfuric acid in PTFE and peroxide in its own vented line, blended at the tool, because the premixed blend gives off oxygen and cannot be held in closed piping. The strip runs at 250 °F (121 °C) and above in concentrated sulfuric acid, which takes PTFE, rated to 450 °F (232 °C); PVDF is not used in concentrated sulfuric acid. Electronic-grade chemical lines to the tools run in solid PFA or natural PVDF.
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 detects any pinhole through to the steel. On bulk chemical supply, acid waste and neutralization lines that keeps steel out of the stream; ultrapure water and electronic-grade chemicals at the tools run in solid natural PVDF or PFA. Send us your metals specification and we will match the liner and the valve lining to it.