Key Takeaways
- Semiconductor exhaust ducting is selected by stream class, not by material brand. Semiconductor exhaust ducting is the hook-up ductwork that carries process exhaust from a tool or wet bench toward the house header, and the stream decides which material fits which section.
- Polypropylene has a defined band, and the band has edges. Acid, alkali and dilute-solvent streams sit inside it; furnace heat, high-purity wetted surfaces and system-level fire ratings sit outside.
- The joints carry the air-tightness duty, not the pipe wall. A run under suction leaks at its connections first, so the joint, the gasket and the reinforcement set the result.
- A material grade and a system listing are different layers of compliance. A grade answers for the compound; a listing or the authority having jurisdiction answers for the installation.
- A quote closes faster when the stream data travels with the schedule. Composition, temperature, moisture and available static pressure turn a drawing enquiry into a confirmable offer.
A fab exhaust run is priced long before anyone has classified the stream it has to carry. A duct schedule reaches the manufacturer with diameters, lengths and a material note, while the chemistry, the continuous temperature and the review items that decide the material never leave the process group. That gap produces the familiar misconception: that semiconductor exhaust ducting forces a single correct material, and that polypropylene duct sits outside it. The candidates follow the stream class rather than the brand on a datasheet. This guide moves through the stream classification, the polypropylene band and its solvent and heat edges, section ownership, joints and air-tightness, the compliance layers, and the enquiry that closes them. The reference series runs from φ20 mm to φ500 mm, made to drawing.
Semiconductor Exhaust Ducting Starts With the Stream, Not the Duct
Six Streams, Six Material Answers
Classify process exhaust by stream, not by department: general exhaust (GEX), acid exhaust (AEX), alkaline exhaust (ALEX), solvent and VOC exhaust (SEX), toxic or pyrophoric specialty gas exhaust (TEX), and high-temperature exhaust (HEX). The chemistry behind those names is wide. Per OSHA’s overview of semiconductor device fabrication, wet processing uses HF, sulfuric acid with hydrogen peroxide, hydrochloric, nitric and ammonium hydroxide among the acids and bases, alongside solvents such as IPA and acetone. Fab HVAC engineering practice describes the same set as separately named systems, because the duct material, the fan and the treatment step all change with the stream. The fab’s own specification defines the stream naming for a project, and that project-adopted specification governs. The stream class is the first screening tool for duct material, because the chemistry, the temperature and the required review items move together with the class.
| Stream | Typical media in fab exhaust | Temperature context | Candidate duct materials | What to confirm |
|---|---|---|---|---|
| General (GEX) | Cleanroom airlock, utility and non-process areas carrying no corrosive media | Ambient, close to room temperature | Metal duct where nothing corrosive is present | Whether any corrosive trace enters the run |
| Acid (AEX) | HF, sulfuric acid with hydrogen peroxide, hydrochloric and nitric acid vapours, wet etch and clean benches | Ambient at the bench, elevated at the tools; soft-bake steps run at 70–90 °C | A corrosion-resistant thermoplastic route, with polypropylene among the candidates, per industry practice | The worst-case concentration and the highest continuous temperature |
| Alkaline (ALEX) | Ammonium hydroxide and alkaline cleaning baths | Ambient, close to room temperature | A corrosion-resistant thermoplastic route, with polypropylene among the candidates, per industry practice | Whether alkaline and acid streams are split or combined |
| Solvent and VOC (SEX) | IPA, acetone and other organic solvents from coating, cleaning and lithography steps | Ambient to elevated, depending on the step | Metal duct for concentrated solvent loads; polypropylene only for dilute loads, per industry practice | Solvent identity, expected concentration and stream segregation |
| Toxic and pyrophoric specialty gas (TEX) | Specialty gases that require dedicated treatment and equipment-level provisions | Ambient at the tool exhaust connection | Equipment-level treatment comes first; duct material is the secondary question | The tool supplier’s exhaust interface and the required treatment route |
| High temperature (HEX) | Oxidation furnace, diffusion and CVD sections | Oxidation furnaces run at approximately 1,200 °C | A high-temperature route outside any thermoplastic window | Where the high-temperature section ends and the thermoplastic section begins |
Two numbers in that table set the outer edges. Soft-bake steps run at 70–90 °C, well inside common thermoplastic practice, while oxidation furnaces run at approximately 1,200 °C, far outside any thermoplastic window. The class also sets the review items: the worst-case concentration, the highest continuous temperature, whether streams are split or combined, and whether the project requires a specific material protocol. Velocity follows the stream as well. Fab exhaust practice commonly specifies 8–12 m/s in acid and alkali exhaust, and 12–15 m/s where toxic gases are handled, to keep the duct clear of settling aerosol and to limit leakage. That range is a practice figure reported by a fab HVAC engineering firm, not a code requirement and not a manufacturer recommendation. Decide the stream class before anyone prices a metre of duct — the classification names the material candidates and the review items that follow.
Hook-Up Duct vs House Exhaust: Where the Duct Scope Ends
Hook-up ducting is the connection ductwork between a process tool or wet bench and the sub-main or branch that leads into the house exhaust system; house exhaust is the fab-wide header network those branches tie into. Per fab engineering practice, the term covers the tool-side connection run. The fab’s engineering group owns the header topology, the professional designer owns the sub-fab layout and the fan-system balancing, and the treatment vendor owns the abatement equipment selection. A duct material decision ends at that handover. Change the stream class, and the material answer and the review items change with it.
The tool-side exhaust interface parameters come from the equipment supplier and the fab specification, so the duct side receives and verifies them rather than setting them. Flow, maximum static pressure, stream class and temperature arrive with the tool package, and the schedule has to agree with them before fabrication. SEMI S6 is the EHS guideline for exhaust ventilation of semiconductor manufacturing equipment. OSHA’s semiconductor standards page lists it among the consensus standards and guidance documents relevant to the industry, and notes that they are not OSHA regulations. No clause text is quoted here, and the project-adopted edition governs. A duct supplier answers for material grade, joint type, section lengths and the air-tightness basis — the inputs that let a contractor place a workable order. That same set is what a supplier needs before quoting, and the PP duct applications overview shows where this run sits among the other plant exhaust scenarios.
Decide the stream class alongside the equipment supplier’s interface data, then keep the house header, the fan system and the treatment equipment with their owners.
Where Polypropylene Fits in Semiconductor Exhaust Ducting — and Where It Does Not
The PP Band: Temperature, Chemistry, and Purity
Polypropylene duct can be used for semiconductor exhaust, but only inside a bounded window — and the answer changes per stream, not per site. Yes for acid, alkali and dilute-solvent loads that run from ambient to moderate temperature; not where continuous heat, a high-purity wetted surface or a system-level fire rating takes over. The window is the whole answer, so state it precisely. An enquiry about a PP duct for semiconductor service therefore starts with two questions: what is the worst-case concentration, and what is the highest continuous temperature?
The PP duct working window is −15 °C to 80 °C on the product datasheet; the material grade sets the actual limit, so confirm it against the duty rather than assuming the ceiling applies to every compound. PP carries an acid-and-alkali envelope of pH 1–14; oxidizer strength and concentration are confirmed case by case against the datasheet, and no concentration threshold can be quoted from a material page. The duct range covers a reference series from φ20 mm to φ500 mm, made to drawing — the PP air duct range.
Solvents read differently from acids on the same pipe. Dilute solvent loads sit inside the band, while some organic solvents attack polypropylene over time. A solvent-bearing stream is therefore checked on its own rather than inherited from an acid line: industry practice treats PP as a general acid and alkali material and tests solvent compatibility per stream, and chemical resistance limits of PP carries the detailed resistance reading. Three conditions move the answer off PP: a continuous temperature above the window, a wetted surface that must stay high-purity, and a requirement for a system-level fire rating.
Material Positions Around It: CPVC, Fluoropolymer, Vinyl Ester FRP, Lined Steel
PP covers the ambient-to-moderate corrosive position in fab exhaust; the materials around it answer for higher temperature, higher purity or system-level fire, and each keeps its own attribution. The table below gives positions, not ratings.
| Material | Common temperature basis | Where it sits in fab exhaust | Compliance layer it answers | Supplied by XICHENG |
|---|---|---|---|---|
| Polypropylene (PP) | −15 °C to 80 °C, grade-dependent | Acid and alkali streams at ambient to moderate temperature; dilute solvents | Material grade | Yes |
| Flame-retardant PP | Same window | Same positions where the project calls for a flame-retardant compound | Material grade, UL 94 V-0 only, on request | Yes, on request |
| CPVC | 200 °F (≈93 °C), one maker’s published figure | Corrosive service above the PP ceiling | Material grade | No |
| Fluoropolymer (PFA / PTFE) | Not quoted here | High-purity wetted surfaces | Material and purity protocols | No |
| Vinyl ester FRP | Not quoted here | Mixed acid, alkali and solvent streams | Material grade | No |
| Lined steel | Not quoted here | Metal route with a corrosion-resistant liner, where metal is required | Material grade plus the metal construction | No |
Wet bench exhaust is the clearest test of this reading: PP is common for general acid and alkali service and PVDF where HF is present, per industry practice. For an HF-bearing stream, run the compatibility check — PVDF and PP are both common candidates, and the project decides. Read the table as a screening start, not a promise: ratings and compliance come from the datasheet and the project specification, and the full duct material comparison covers the remaining materials.
Where PP Is the Wrong Answer
PP is the wrong answer in three semiconductor cases, and a specifier who recognizes them early avoids a redesign. The first is the furnace, diffusion and CVD sections, where the approximately 1,200 °C quoted for oxidation furnaces is far outside any thermoplastic window, so the boundary where the hot section ends is fixed on the drawing. The second is a high-purity wetted surface, where the industry answer is a fluoropolymer such as PFA or PTFE; PP is a service-material answer, not a high-purity answer. The third is an installation where the project requires a system-level fire or smoke rating: a UL 94 V-0 compound is a material grade, and it does not make that system.
Weigh both sides of the choice before the schedule is fixed. Choosing PP buys weldable fabrication, light sections, a wide acid and alkali band inside its window, and made-to-drawing sizes. It costs a temperature ceiling that forces a section split before any hot section, a compliance layer that stops at the material grade, and a solvent question that has to be checked stream by stream. Every one of those is a scope boundary rather than a defect.
Choose PP for the acid, alkali and dilute-solvent band, and recognize the three conditions that move the answer elsewhere — a continuous temperature above the window, a high-purity wetted surface, or a system-level fire rating.
Segment the Run: Acid and Solvent Sections, High-Temperature Sections, High-Purity Sections
A Segmentation Table You Can Take to the Fab
Segment the run by stream and by material, then name who answers for each section. A single physical run can cross two stream classes, so the section boundary is fixed on the drawing by the fab specification rather than assumed by the duct supplier. Table T3 below is that list in the form a duct supplier can price.
| Section of the run | Typical media and temperature | Recommended material route | Who decides |
|---|---|---|---|
| Acid and alkaline wet-bench sections | HF, sulfuric acid with hydrogen peroxide, hydrochloric and nitric acid, ammonium hydroxide; ambient at the bench, within the polypropylene window at most benches, elevated at soft-bake tools that run at 70–90 °C | Polypropylene inside the −15 °C to 80 °C window | The fab specification confirms the stream and the equipment supplier sets the tool interface |
| Solvent and VOC sections | IPA, acetone and other organic solvents; ambient, close to room temperature | Polypropylene only for dilute loads; the route is confirmed per stream before it is committed | The fab specification, with the equipment supplier confirming the stream at the tool |
| High-temperature sections (furnace, diffusion, CVD) | Furnace, diffusion and CVD tool exhaust; oxidation furnaces run at approximately 1,200 °C | A high-temperature route outside any thermoplastic window; the duct supplier does not choose it | The equipment supplier for the hot boundary, with the professional designer fixing where that section ends |
| High-purity wetted sections | High-purity wetted tool exhaust at ambient | Fluoropolymer such as PFA or PTFE | The fab specification, with the treatment vendor where the section serves a treatment step |
The deciding party differs from row to row. Acid and alkaline sections inside the polypropylene window are a material and joint question, and the boundary itself is fixed on the drawing by the fab specification rather than assumed by the duct supplier. High-temperature and high-purity sections are handoffs instead: the duct supplier receives the section boundary and fabricates to it.
Read the fourth column before the third. The three numbers that settle most arguments are the bottom of the window at −15 °C, the soft-bake range at 70–90 °C, which sits inside the polypropylene window, and the approximately 1,200 °C at oxidation furnaces, which sits far outside it. A specification that names the section owner removes the rework conversation later.
The duct reference series is supplied in 3 m sections for the larger diameters and 4 m for the small end, so section boundaries and support points are worth fixing before fabrication. A boundary drawn at an awkward position costs a cut and an unsupported joint, and both are cheaper to move on paper than on site.
Air volume and pressure-drop checks then run per section rather than on the run as a whole, and the duct schedule carries the result; duct sizing and pressure-loss design covers that calculation. In wafer fab ventilation, the sections that are defined late are the ones that return to the fabricator for a second pass.
Who Owns Which Decision
Ownership is what makes the segmentation hold.
| Decision | Owner |
|---|---|
| Stream class and cleanliness requirement | The fab specification |
| Tool-side exhaust interface: flow, maximum static pressure, stream class, temperature | The equipment supplier |
| Sub-fab layout and header topology | The professional designer |
| Abatement equipment | The treatment vendor |
| Material, joints, section lengths and the air-tightness basis | The duct supplier |
| Weld quality and dimensional checks | The fabricator |
The duct supplier commits to that last row and to nothing beyond it, because the stream class is an interface parameter handed over by the equipment supplier rather than a value a duct supplier sets.
Write those boundaries into the enquiry rather than discovering them after fabrication, because a section that a supplier was never told about is a section nobody priced. Two adjacent disciplines handle the grading and the safety questions that sit beside this one: corrosive media classification in chemical plants covers how a chemical plant grades media, and lithium-battery exhaust ventilation carries the solvent and safety side. Neither belongs in the duct schedule, and neither is expanded here.
The practical test is one question per section: who is named on the drawing? The stream class already belongs to the fab specification, and the duct supplier cannot settle it by fabricating. Determine section ownership before fabrication: the fab specification sets the stream, the equipment supplier defines the tool connection, and the duct supplier answers only for material, joints and schedule.
Joints, Air-Tightness and Negative-Pressure Service in Semiconductor Exhaust Ducting
Why Fab Exhaust Runs Under Negative Pressure
Negative pressure is a design choice, not an accident of layout. In semiconductor exhaust ducting the fan sits at the far end and pulls air toward itself rather than pushing it from the tool, so the pressure inside the duct stays below the pressure of the clean space around it. That direction is the whole point: any leak at a connection draws room air inward instead of discharging process exhaust outward, which is why fab exhaust duct is designed to run under suction. In industrial exhaust systems a centrifugal fan is normally installed at the end of the run and holds the duct under negative pressure, and that arrangement is standard engineering practice rather than a site preference.
That choice has a cost, and the cost lands on the joint. A run held below ambient pressure puts a pressure difference across the wall, so the wall carries a load a positive-pressure run never sees, and the first place a leak appears is the connection rather than the wall. How much vacuum a run can hold depends on wall thickness, reinforcement and support arrangement together, which is why the duct is specified for the pressure it will actually see. Design velocity is part of the same review. Fab exhaust practice commonly specifies 8–12 m/s in acid and alkali exhaust and 12–15 m/s where toxic gases are handled, so the stream keeps moving and leakage stays limited. That range is a practice figure reported by a fab HVAC engineering firm, and neither a code requirement nor a manufacturer recommendation. State the pressure the run actually sees as the first number to write down.
Three Joints, One Sealed Circuit
Three joint types cover the run, and the choice between them is decided by whether that part of the circuit will ever need to come apart. Flanged connections are bolted for repeat access, socket-welded connections are built for fast field assembly along a long straight run, and hot-air welded seams turn the run into one continuous sealed line.
| Joint type | How it seals | Removable? | Where it suits | What to verify |
|---|---|---|---|---|
| Flanged | PP flanges welded to each section end and bolted together with a gasket between the faces | Yes | Connections to tools, dampers and equipment where a break is needed | Gasket material, flange face condition and bolt tightness |
| Socket | A PP sleeve welded at the section end, with the next section inserted into it | Limited | Long straight runs assembled on site | The sleeve weld and the insertion depth |
| Hot-air welded | A continuous welded seam that makes the run monolithic | No | Runs where a continuous sealed line matters more than future disassembly | Weld continuity and the trial weld |
Hot-air hand welding runs at 305–315 °C, measured 5 mm from the nozzle centre. The set is 40–50 l/min of hot air, 60–85 mm/min of travel and a 3 mm rod fed at 8–10 N, on same-material rod and a trial weld before production. Section welding procedure and inspection belong to the PP duct installation guide, so the parameters are quoted here for the joint decision only.
Because the run is under suction, the joint is the first place a leak shows, so gasket choice, flange face condition and weld continuity decide whether the circuit stays sealed. Thermal movement on long or warm runs needs a compensation point, which puts expansion into the support and joint layout rather than into the material choice; duct wall thickness selection carries the thickness side of the same relationship. Set the joint type by how that part of the run will be maintained, then hold every connection to the same air-tightness duty.
Pressure Class, Seal Class, and What to Ask For
Pressure class and seal class are the vocabulary a contractor uses for air-tightness. SMACNA’s air duct leakage test manual, in the edition referenced by the U.S. Code of Federal Regulations, defines seal class A for transverse joints, longitudinal seams and wall penetrations, seal class B for joints and seams, and seal class C for transverse joints alone. Those classes are commonly paired with pressure classes of 1,000 Pa, 750 Pa and 500 Pa, and 250 Pa where the designer assigns no class. That manual addresses metal and flexible duct construction, so a thermoplastic rating does not come from it — the rating for a PP run comes from the product datasheet and the project specification.
Leakage is a function of the class, the length of duct and the pressure raised to an exponent, which is why the class, not the material brand, sets the leakage target. That distinction matters most when a supplier publishes a vacuum figure without saying what stands behind it, so the request list below is the part of this module worth sending.
| What to ask the supplier | Why it decides the order |
|---|---|
| Is the rating a negative-pressure or positive-pressure basis, and at what value? | The run is designed to hold suction, so a positive-pressure figure does not answer the question the fab asked. |
| At what temperature does the rating apply? | A rating published at ambient temperature is not the rating at the highest continuous temperature of the stream. |
| What safety factor stands behind the published rating? | One CPVC duct maker publishes its rating table on a 1.5:1 factor — one maker’s basis, not an industry standard. |
| Does the figure allow for joint or system derating, or does it apply to the pipe body only? | Under suction the joint is the first leak path, so a pipe-body figure is not a system figure. |
| What support spacing and fixing conditions does the rating assume? | Support spacing varies with the diameter, the wall thickness and the vacuum the run is rated for. |
| Which failure mode should the design work against, and what reinforcement is offered? | The PP reference series is reinforced externally, for example a 3 m section with two external flanges — a construction feature rather than a pressure rating. |
State the rating basis you will accept — negative or positive, at which temperature, with or without joint derating — and list the joint type and reinforcement for every section of the run.
Cleanroom Installation and the Three Compliance Layers
Cleanliness Is Managed at the Joint, Not in the Catalog
Cleanroom installation quality is settled at the connections, not at the material order. Cutting and welding create the particle risk in this service, so installation practice in clean systems caps open duct ends and cleans the interior of cuttings and swarf after every cut, weld or opening, rather than leaving debris to travel downstream.
That discipline is written into the method statement: the gasket between flange faces is chosen for the stream and for temperature rather than taken from a default, and flexible connectors must not shed particles and must have a smooth bore. The same document carries the last two control points. Pre-installation cleanliness requires every section to be wiped and inspected, inside and out, with sign-off by the client or supervisor before the section is hoisted. The connections in a concealed run are verified and recorded before the enclosure closes.
| Control point | What it protects | How it is checked |
|---|---|---|
| Cutting and opening work | The bore of the run | Clean cuttings and swarf out of the section interior, then cap every open end |
| Gasket between flange faces | The connection | Select the gasket for the stream and the temperature rather than by default |
| Flexible connectors | Particle generation and airflow | Confirm the connector does not shed particles and that the bore stays smooth |
| Pre-installation cleanliness | The interior before hoisting | Wipe and inspect each section inside and out, then obtain sign-off from the client or supervisor |
| Pre-concealment records | The connection once it is closed in | Verify the connections and document them before the run is concealed |
The boundary is plain: ISO 14644-1:2015 classifies cleanrooms and clean zones by airborne particle concentration, so it grades the air of the space, not the duct material — a duct does not carry a cleanliness class. Class follows the process area rather than the ductwork, per industry practice: lithography and etch typically run ISO Class 1–3, CMP and implant ISO Class 4–5, and downstream areas ISO Class 6–7. Make-up air and the pressure cascade are air-side decisions, and no class number belongs on a duct schedule; a fume-exhaust layout follows the same joint discipline through laboratory fume exhaust ducting.
Material Grade, System Rating, Project Authority
The compliance layer is where projects most often buy the wrong document. Three layers exist — material grade, system rating and project authority — and each answers a different question, with its own evidence and its own owner. The table below is the separation.
| Layer | What it answers for | Typical evidence | Who owns it |
|---|---|---|---|
| Material grade | How the compound behaves under test | A UL 94 V-0 flame-retardant grade, available on request for the PP duct | The project specification |
| System rating | How a duct system performs as an assembly | A system-level listing, such as FM Approvals 4922 | The project specification, with the listing body |
| Project authority | What the installation must satisfy | The specification and NFPA 318, which OSHA lists without treating it as an OSHA regulation | The authority having jurisdiction |
A UL 94 V-0 flame-retardant grade is a material-level result, and FM Approvals 4910 is a material-level flammability protocol for cleanroom materials, not a fire rating for a duct system. XICHENG PP duct is not a listed product under the UL, FM, AMCA or SEMI programmes; acceptance runs on the product datasheet, and fire or cleanroom compliance is decided by the project specification and the authority having jurisdiction. The flame-retardant grade is a material-level V-0 grade, and the duct is not a certified fire-rated or smoke-control duct and carries no fire-resistance rating. The manufacturer holds ISO 9001 and ISO 14001 system certificates and RoHS material compliance, which are system and material credentials rather than product listings.
The industry route for smoke and exhaust duct systems is a system-level listing such as FM Approvals 4922. Cleanroom installations are commonly specified with Class I flame and smoke limits, expressed as ASTM E84 flame spread of 25 or less and smoke developed of 50 or less. That expression is quoted by FRP duct suppliers; the project specification governs. Flame-retardant grade definitions covers where the material grades sit, and the flame-retardant PP duct grade is the material-level answer a V-0 request returns, not a system rating.
Before award, ask three questions and write the answers into the enquiry: whether the project requires a system-level listing, whether it requires a specific material protocol, and whether the cleanroom imposes material restrictions. A compliance answer obtained after installation is an argument; the same answer obtained before award is a line in the offer. Flag the compliance layer the project actually requires — material grade, system listing or the authority having jurisdiction — and never let a material certificate stand in for a system rating.
Worked Example: An Acid Exhaust Hook-Up from a Wet Bench
Walking the Chain: Stream → Material → Segment → Joint → RFQ
Step 1 — Stream. For a worked example, take the acid exhaust branch of a four-station wet bench: sulfuric acid with hydrogen peroxide and hydrochloric acid from the etch and clean baths, plus a deionised rinse. The bench itself sits at ambient, while the soft-bake tools run at 70–90 °C. The branch is φ250 mm, supplied in standard 3 m sections, running to the sub-main, and held under suction by a fan at the far end. The duty classifies as acid exhaust, and that classification travels with the enquiry from the first line.
Step 2 — Material. Apply the polypropylene window to this stream: −15 °C to 80 °C, grade-dependent, with an acid-and-alkali envelope of pH 1–14 and oxidizer strength checked case by case. The reference series spans φ20 mm to φ500 mm, made to drawing. The higher-temperature route was declined because CPVC is published on a 200 °F (≈93 °C) basis while this stream sits inside the polypropylene window. No high-purity wetted surface is present, so a fluoropolymer is not required. The answer is polypropylene, with the grade confirmed on the enquiry.
Step 3 — Segment. This hook-up is one section class — ambient to moderate acid — so it is one polypropylene section, and any hot boundary is fixed on the drawing by the fab specification rather than by the duct supplier. Segmenting a hook-up this small is a matter of marking where the class changes, if it changes at all: a hot tool drawing on the same header splits the run at the boundary, and everything downstream of it stays polypropylene. For reference, the same series ships in 3 m sections at this diameter and in 4 m sections at the small end.
Step 4 — Joint. Flanged joints go where the run is broken for service at the bench; hot-air welds close the continuous run. The parameters for this run come from the joint table above. Hot-air hand welding runs at 305–315 °C, measured 5 mm from the nozzle centre, with 60–85 mm/min of travel, a 3 mm rod fed at 8–10 N and 40–50 l/min of hot air, on same-material rod with a trial weld before production. Request a negative-pressure rating basis at the stream’s highest continuous temperature, and use the seal-class vocabulary with pressure classes of 1,000 Pa, 750 Pa and 500 Pa, plus 250 Pa where the designer assigns no class. A 3 m section carries two external flanges; that is a construction feature, not a pressure rating.
Step 5 — RFQ. Assemble the enquiry from the fields the chain has already established: diameter and wall thickness, section length, quantity, material grade, connection type, application, destination port, plus composition, concentration, temperature, moisture and available static pressure. The schedule alone will not close a quote; the stream data is what turns it into a confirmable offer. Polypropylene fits this acid hook-up inside the −15 °C to 80 °C window and the pH 1–14 envelope, the joints are chosen by maintenance access, and the negative-pressure rating basis is confirmed against the datasheet and the project specification.
Condition swap A — solvent vapour. Change the stream to solvent vapour and the class moves to solvent/VOC; solvent runs are held under higher design velocities, commonly 12–15 m/s where the stream is hazardous. The material answer becomes a case-by-case compatibility check against the datasheet, and concentration monitoring together with hazard-classified design return to the fab specification and the professional designer. The conclusion changes from “polypropylene fits” to “confirm per stream”.
Condition swap B — over-temperature. If the continuous temperature exceeds the window — furnace, diffusion or CVD exhaust, where the approximately 1,200 °C quoted for oxidation furnaces sits far outside any thermoplastic band — that hot section leaves the polypropylene band. The section boundary is fixed on the drawing, and the hot route is chosen by the equipment supplier together with the professional designer. The PP recommendation then applies only to the sections below the boundary.
| Decision outside the duct schedule | Who owns it |
|---|---|
| Cleanliness class | The fab specification |
| System-level fire or smoke compliance | The project-adopted code edition and the authority having jurisdiction |
| Abatement equipment selection | The treatment equipment vendor |
| The tool-side exhaust interface | The equipment supplier, per the fab specification |
Run the chain once on paper — stream, material, section, joint, enquiry — and assemble the fields the offer will close on before the project asks for them.
RFQ Checklist for Semiconductor Exhaust Ducting
What to Send, and What to Confirm Before Award
A quote closes on the fields the enquiry carries, not on the drawing it arrives with. The two failures that cost the most time are a missing stream datum and a missing rating basis: both leave the supplier guessing, and a guess comes back as an assumption written into the offer. A duct schedule alone answers the dimensional questions — diameter, length, quantity — but it says nothing about the material grade or the air-tightness basis. The fields below cover what to send, and what to confirm once an offer is on the table.
| Field to send | Why it changes the quote | Example entry for this run |
|---|---|---|
| Diameter and wall thickness | Sets the size the section is built to, the joint geometry it takes, and how it packs for freight | φ250 mm branch diameter, wall thickness to the project drawing |
| Section length | Decides how many joints a run carries and how the sections are handled in transit | 3 m standard sections at this diameter, 4 m sections at the small end of the range |
| Quantity | Fixes the production run and the number of spare sections kept for the hook-up | Section count and spares for the single φ250 mm branch, taken from the run drawing |
| Material grade (standard or flame-retardant) | Fixes the compound, and the temperature limit moves with the grade rather than staying fixed | Standard polypropylene grade for this acid duty, inside the −15 °C to 80 °C window |
| Connection type per joint | Fixes the joint, the gasket and how the run is broken for service access | Flanged at each service break, hot-air welded along the continuous run |
| Application and destination port | Sets the delivery basis and the packing that the shipment is prepared to | Acid exhaust hook-up from a wet bench, delivered to the named destination port |
| Gas composition and worst-case concentration | Decides whether the material choice stands at all | Sulfuric acid with hydrogen peroxide and hydrochloric acid, plus a deionised rinse; worst-case concentration stated against the pH 1–14 envelope |
| Temperature and moisture at the operating point, plus available static pressure | Confirms the compound and the air-tightness basis at the real duty rather than at a nominal one | Operating point named inside −15 °C to 80 °C, with the 80 °C ceiling stated; moisture declared and the available static pressure quoted with its basis |
Read the checklist in blocks. Dimensions — diameter, wall thickness, section length, quantity — fix fabrication and freight, because they set the section count, the joint count and how the sections travel. Material grade fixes the compound. Connection type fixes the joint and the gasket. Stream data is the block that decides whether the material choice stands at all: composition and worst-case concentration, temperature and moisture, and the available static pressure the run has to live with. Sizes are made to drawing across the φ20 mm to φ500 mm reference series, so a size outside it is a normal request rather than a special one.
| Confirm before award | Why it matters |
|---|---|
| Whether the rating basis is negative-pressure or positive-pressure, and at what value — with pressure classes of 1,000 Pa, 750 Pa and 500 Pa, and 250 Pa where the designer assigns no class | The same section performs differently under suction and under pressure, and the value the offer is written against becomes the value the installation is judged on |
| The temperature at which that rating applies, read against the −15 °C to 80 °C working window | A rating quoted at one temperature and installed at another is not the rating that was bought, and the duty point is what the datasheet and the project specification are read against |
| The joint type and gasket for every break in the run, whether flanged or welded | The joints, not the wall, are the first leak path under suction, so the seal is a per-break decision rather than a system default |
| Reinforcement, such as the two external flanges carried on a 3 m section | Reinforcement is a construction feature and not a pressure rating, so it is confirmed as built rather than assumed from the section length |
| The inspection and the documents supplied with the shipment | Acceptance runs on the product datasheet and the project specification, so the record that travels with the duct decides how quickly the installation is signed off |
| Lead time, packing and the section lengths as they arrive at the destination port | Freight handling and site access follow the packed section size, so the receiving plan is set before the material lands |
Send the run schedule and the stream data together, then work through the confirmation items before award. When a field is missing, the offer returns conditional: the supplier prices an assumption or writes an exclusion, and the project pays for that gap during installation. Confirm the rating basis, the temperature it applies at, the joint and gasket at each break, and reinforcement. Send the stream data and the run schedule, and check the PP air duct range against the duty. List every field with its boundary condition, then confirm the rating basis before award — an offer cannot close on a missing temperature or a missing available static pressure.
FAQ: Semiconductor Exhaust Ducting
Can polypropylene duct be used for semiconductor exhaust?
Yes, across the acid, alkali and dilute-solvent streams that stay inside the polypropylene duct working window of −15 °C to 80 °C and inside the acid-and-alkali envelope of pH 1–14. That window is grade-dependent, so the compound is confirmed against the duty rather than assumed to hold at every stream condition, and oxidizer strength is checked case by case against the datasheet. The answer turns to no in three places: where the continuous temperature sits above the window, where the wetted surface has to stay high-purity, and where the project requires a system-level fire or smoke rating. Around that band the reference series runs from φ20 mm to φ500 mm, made to drawing, so a diameter outside it is a normal request rather than a special one. Where the stream leaves the band, the material route moves to the material that answers for it.
Do semiconductor exhaust ducts have to be fire-rated?
Compliance splits into three layers, and only the last one answers that question. A material grade describes how the compound behaves under test; a system listing describes how an assembly performs; the project authority states what the installation has to satisfy. A flame-retardant polypropylene grade is available at UL 94 V-0, a material-level result on its own. FM Approvals 4910 is a flammability test protocol for cleanroom materials, material-level again, while FM Approvals 4922 is the system-level listing route for fume and smoke exhaust ducts. The flame-retardant PP duct is not a certified fire-rated or smoke-control duct, carries no fire-resistance rating, and is not a listed product under the UL, FM, AMCA or SEMI programmes. Acceptance runs on the product datasheet, and the project specification with the authority having jurisdiction decides whether a system rating is required at all.
What static pressure should a fab exhaust duct be rated for?
The number comes from the project specification and the product datasheet, not from the material brand. Six items make the request answerable. Three are about the figure itself: whether the basis is negative-pressure or positive-pressure and at what value, the temperature at which it applies, and the safety factor behind it. Three are about its scope: whether joint or system derating is included, the support spacing and fixing conditions it assumes, and the failure mode the design works against with the reinforcement offered. Contractors express the same requirement through seal class A, B or C, matched to pressure classes of 1,000 Pa, 750 Pa and 500 Pa, with 250 Pa as the basis where the designer assigns no class. Those classes come from a manual written for metal and flexible duct construction, so a thermoplastic rating is read from the datasheet and the project specification. State the basis you will accept before award.
Conclusion: Next Step — Turn the Stream Classification Into a Quote
The material question is settled before the quote is written, not after the installation. Classify the stream first — acid, alkaline, solvent, specialty gas or high-temperature — because the class names the material candidates and the review items that follow. Fix the section and the joint for each part of the run next, so the length inside the polypropylene window, the hot boundary and the service breaks are priced as drawn. Then send the enquiry with the stream data attached: composition, concentration, temperature, moisture and available static pressure alongside the duct schedule. That turns semiconductor exhaust ducting into a confirmable offer, and the PP air duct guide covers the material side while you prepare to send the stream data and the run schedule. Decide the stream class first, state the section and joint for every part of the run, and the enquiry will come back answerable.
