What is clean dry air (CDA) and why does electronics need it?
CDA is compressed air treated to remove water, oil and particles to levels set by the tool makers and the facility specification. The term itself does not fix a number: one plant’s CDA can be another’s general plant air. That is why every project starts with the tool installation requirements, not with a compressor brochure.
Electronics needs clean, dry air because the product is small, sensitive and expensive. A droplet of water or oil, or a few particles, can cause solder defects, contaminate a bond pad, mark an optical surface or upset a precision actuator. Moisture also feeds corrosion and electrostatic issues in handling equipment. Air that is acceptable for a workshop tool can be a defect source on an SMT line.
Where is compressed air used in electronics and semiconductor plants?
| User | Typical pressure at use | Flow pattern | Typical quality (ISO 8573-1, indicative) |
|---|---|---|---|
| SMT pick-and-place, feeders, vacuum generators | Around 5–6 bar (72.5–87 psig) | Continuous with fast pulses | Class 1–2 particles, class 2 water (−40 °C), class 1 oil |
| Reflow, wave and selective soldering (actuation, nozzle cleaning) | 5–6 bar | Continuous | Class 1–2 particles and oil, dry |
| Automatic optical inspection, test handlers | 5–6 bar | Intermittent | Clean and dry to the tool maker’s requirement |
| Wafer handling, load ports, valve actuation in fab tools | Set by tool | Continuous, steady | Oil-free, class 1 particles, very low dew point; point-of-use purification common |
| Cleanroom blow-off, part drying | Low, regulated | Intermittent | Class 1 particles and oil, often ionised |
| Packaging, die bonding, wire bonding | 5–6 bar | Continuous | Class 1–2 |
| Pneumatic conveyors, tray handling, general automation | 6–7 bar | Intermittent | Class 2–3 depending on area |
| Workshop, maintenance, utilities | 6–7 bar | Intermittent | General purpose, refrigerated dew point |
These are typical starting points only. Tool installation manuals, the process engineer and the facility specification set the final values, and some fab tools specify their own test method.
Particle, dew-point and oil limits explained
ISO 8573-1 grades air by three numbers: solid particles, water and total oil. A class written as 1.2.1 means particle class 1, water class 2 and oil class 1. Lower numbers are cleaner.
| Class | Water: pressure dew point | Total oil (aerosol, liquid, vapour) | Particles |
|---|---|---|---|
| 1 | −70 °C or lower | 0.01 mg/m³ or less | Tightest count limit by particle size |
| 2 | −40 °C or lower | 0.1 mg/m³ or less | Tight |
| 3 | −20 °C or lower | 1 mg/m³ or less | Moderate |
| 4 | +3 °C or lower | 5 mg/m³ or less | General purpose |
Class 0 exists for each contaminant, but it is not a fixed number: it means a limit stricter than class 1 agreed between the user and the supplier, with the measuring method stated.
Three practical points follow:
- Dew point is about pressure. A −40 °C pressure dew point at 7 bar is a different quantity from an atmospheric dew point. Specify and measure it at line pressure.
- Oil includes vapour. Coalescing filters remove aerosol; only activated carbon or oil-free compression deals with vapour.
- Particles come from the pipe too. Rust, scale, desiccant dust and filter media fragments can enter downstream of the dryer, so final filtration belongs close to the tool.
Oil-free or oil-injected compressors for electronics?
Most semiconductor fabs and many electronics plants specify oil-free compressors, such as dry oil-free screws, water-injected screws, scroll or oil-free piston machines. The reason is risk: an oil-injected compressor depends on filters to remove oil, and a failed separator, a saturated carbon filter or a missed element change sends oil into the network. Cleaning an oil-contaminated CDA network is slow and expensive.
Oil-injected compressors with a full treatment train can still meet class 1 oil at the outlet when the filters are well maintained, and they are common in assembly plants and in general utility air. The choice should weigh:
- The consequence of one oil event on product and tools.
- The cost and discipline of filter and carbon changes.
- Energy and life-cycle cost of each option.
- Intake air: in polluted urban air, even an oil-free compressor ingests hydrocarbons, so carbon filtration may still be needed.
See our pages on oil-free air compressors and what oil-free really means.
Typical CDA system architecture
- Intake from a clean, cool location, away from generator exhausts, solvent stores and kitchen vents.
- Compressors in an N+1 arrangement, often with a variable-speed machine to trim demand and hold steady pressure.
- Aftercooler and wet receiver to remove bulk water.
- Pre-filter to protect the dryer.
- Desiccant dryer for −40 °C or lower; heated or blower-purge types reduce purge losses on larger plants.
- After-filters: particle filter for desiccant dust, then fine coalescing and, where needed, activated carbon.
- Dry receiver sized to absorb rapid tool demand pulses.
- Distribution in clean, non-corroding pipe (aluminium or stainless steel), installed and flushed with clean practice.
- Point-of-use filtration and purifiers at sensitive tools.
- Monitoring: continuous dew point, pressure and flow, with alarms; periodic particle and oil sampling.
A separate, less treated plant-air header for workshops and general automation avoids paying CDA cost for air that does not need it.
Reliability and continuous supply
Electronics lines run in shifts or around the clock, and many tools stop or alarm on low air pressure. Fabs are less tolerant still: an interruption can scrap work in progress. Plan for:
- Standby compressor and dryer capacity so that one machine can be serviced or fail without affecting supply.
- Dryer bypass arrangements that keep dew point within limits; a bypass that sends wet air to the tools is not a standby.
- Stable pressure: a pressure band tight enough for the tools, set by controls and receivers rather than by running the whole plant at high pressure.
- Power-quality protection: voltage dips trip compressors and dryers, so check restart behaviour and consider standby power for critical machines.
- A planned tie-in for a rental oil-free compressor and dryer, so emergency air still meets the CDA specification. See temporary air engineering.
Energy and running cost
CDA is costly air: it carries the cost of compression, drying, filtration pressure drop and dryer purge. The biggest savings usually come from:
- Not over-treating. Serve workshop and general users from plant air, not CDA.
- Right pressure. About 7% more power for every extra bar. Find the tool that forces the header pressure up and treat it locally.
- Dryer purge. Heatless desiccant dryers use a significant share of their dried air as purge; dew-point-dependent switching or a heated design reduces this.
- Filter pressure drop. Change elements on differential pressure, not only by calendar.
- Leaks at tool connections, quick couplings and blow guns.
Indian context: electronics growth in Telangana and Andhra Pradesh
Electronics manufacturing in India is growing fast, supported by national and state incentive schemes. Telangana has electronics manufacturing clusters around Hyderabad, and Andhra Pradesh has electronics and component units in industrial zones in the south of the state. Plants range from mobile and consumer-electronics assembly and EMS lines to component, display, solar-cell and semiconductor packaging projects.
Local conditions shape the air system. Summer ambient of 40–45 °C increases the moisture and heat load on dryers and cuts compressor capacity. Monsoon humidity can be very high, so dryers sized on dry-season data may fall short. Dust in dry months loads intake filters quickly. Power interruptions and voltage dips are common in some industrial areas, which makes restart logic, standby power and stored air important.
Common problems and fixes
| Symptom | Likely causes | What we check and fix |
|---|---|---|
| Dew-point alarms in summer or monsoon | Dryer undersized for high inlet temperature, failed valves, saturated desiccant | Measure inlet conditions, check dryer cycle and desiccant, add cooling or capacity |
| Particles or white dust at tools | Desiccant fines, missing after-filter, corroded pipe | Install particle after-filter, inspect pipe, add point-of-use filters |
| Oil traces or odour | Separator or filter failure, saturated carbon, polluted intake | Test oil content, change elements, review intake and compressor type |
| Tool alarms on pressure dips | Small receiver, long or undersized pipe, slow control | Pressure profile, add local receiver, improve control and pipe sizing |
| High energy use | Over-pressure, purge losses, leaks, part-loaded machines | Power and flow logging, leak survey, control review |
Sizing CDA for an SMT plant: a worked demand build-up
Most undersized CDA systems in electronics plants are not wrong in the compressor choice. They are wrong in the demand estimate: the nameplate flows of the line were added up once, at the time of purchase, and leakage, dryer purge, hot-day inlet conditions and the next line were never counted. The build-up below shows the method. The machine flows are typical of small and mid-size equipment and are for illustration only; always take real figures from each machine’s data sheet, which usually states consumption in litres per minute ANR (free air at 20 °C and 1.013 bar(a)).
| Consumer (per line) | Quantity | Flow each, L/min ANR | Line total, L/min ANR |
|---|---|---|---|
| Solder paste printer | 1 | 60 | 60 |
| Solder paste inspection (SPI) | 1 | 25 | 25 |
| Pick-and-place machines | 3 | 120 | 360 |
| AOI | 1 | 25 | 25 |
| Conveyors, buffers, loaders and unloaders | 6 | 10 | 60 |
| Ionising air bars | 4 | 40 | 160 |
| Blow guns (150 L/min each, about 25% of the time) | 2 | 37.5 | 75 |
| Total per line | 765 |
Worked example (illustrative): a plant with two such lines.
- Connected demand: 2 × 765 = 1,530 L/min ANR.
- Leakage allowance of 10% for a new, well-built system: 1,530 × 1.10 = 1,683 L/min.
- Growth allowance of 20% for a third line or extra machines: 1,683 × 1.20 = 2,019.6 L/min.
- Inlet correction. Compressor free air delivery (FAD) is stated at inlet conditions. At 40 °C inlet, the same mass of air takes up 313.15 ÷ 293.15 = 1.068 times the volume it does at 20 °C. At an inlet pressure of about 0.955 bar(a), typical of a site around 500 m above sea level such as Hyderabad, it takes up a further 1.01325 ÷ 0.955 = 1.061 times. So the compressor must deliver 2,019.6 × 1.068 × 1.061 = 2,289 L/min of FAD.
- Heatless desiccant dryer purge of about 15% of the dryer inlet flow at −40 °C pressure dew point: 2,289 ÷ (1 − 0.15) = 2,693 L/min.
- Required compressor FAD: 2,693 L/min = 2.69 m³/min, and 2.69 × 35.315 = about 95 cfm, at a discharge pressure set to give about 6 bar(g) at the farthest machine. On a humid monsoon day the water vapour drawn in with the air, which the dryer later removes, adds a few percent more, so round up to the next standard compressor size rather than down.
Two points matter in practice. First, choose the dryer type before fixing the compressor size: a heated or blower-purge desiccant dryer uses far less purge air than a heatless one, which can drop a size of compressor. Second, a −70 °C dew point needs more purge than −40 °C on a heatless dryer, so do not specify class 1 water for the whole plant if only a few tools need it; a small point-of-use dryer is often cheaper.
Nitrogen for reflow and selective soldering
Nitrogen reflow lowers the oxygen level in the oven so that solder wets better and joints oxidise less, which helps with fine-pitch parts, lead-free alloys and no-clean pastes. The oven maker states two numbers that matter: the residual oxygen target in the process zone (often in the range of a few hundred to about 1,000 ppm) and the nitrogen flow needed to hold it. Supply purity is commonly set at 99.99% (100 ppm oxygen) or better so that the oven can reach its target; confirm with the oven maker before choosing a generator.
A PSA nitrogen generator needs several volumes of compressed air for each volume of nitrogen, and that ratio (the air factor) rises steeply with purity. The table gives typical ranges; the generator data sheet gives the real figure for its own design and pressure.
| Nitrogen purity | Oxygen remaining | Typical PSA air factor (air in ÷ nitrogen out) |
|---|---|---|
| 99.5% | 5,000 ppm | about 3 |
| 99.9% | 1,000 ppm | about 4 to 4.5 |
| 99.99% | 100 ppm | about 6 to 7 |
| 99.999% | 10 ppm | about 9 to 11 |
Worked example (illustrative). Two reflow ovens at 20 Nm³/h each and one selective soldering machine at 8 Nm³/h give 2 × 20 + 8 = 48 Nm³/h. Adding 20% for start-up purging and oven door openings gives 48 × 1.20 = 57.6 Nm³/h at 99.99% purity. With an assumed air factor of 6.5, the generator needs 57.6 × 6.5 = 374.4 Nm³/h of air, which is 374.4 ÷ 60 = 6.24 Nm³/min. Nm³ is referred to 0 °C and 1.01325 bar(a), so at a 40 °C, 0.955 bar(a) compressor inlet the FAD needed is 6.24 × (313.15 ÷ 273.15) × (1.01325 ÷ 0.955) = 7.59 m³/min, or about 268 cfm. That is nearly three times the CDA demand of the two SMT lines worked out above, which is why the nitrogen decision usually decides the size of the compressor plant.
The feed air to a PSA generator must be dry and oil-free enough to protect its carbon molecular sieve; a refrigerated dryer with coalescing and activated carbon filters is the usual minimum, as the generator maker specifies. It does not need desiccant-dried CDA, so take its feed upstream of the CDA desiccant dryer, through its own refrigerated dryer and filters, rather than adding its flow to the desiccant dryer and its purge. Compare the running cost of generated nitrogen against bulk liquid supply on a cost-per-Nm³ basis, including the compressor energy.
Ionising air and ESD-safe blow-off
Blowing dust off a board with plain compressed air charges the board and its parts by friction, and an electrostatic discharge can damage sensitive devices without any visible mark. Ionising air guns, nozzles and bars add positive and negative ions to the air stream so that the charge on the surface is neutralised while it is being cleaned.
- Air quality. Oil mist and fine particles collect on the emitter pins and upset the ion balance, so ionisers need the same oil-free, filtered CDA as the placement machines. Water in the air also shortens emitter life; the plant CDA dew point is normally more than enough.
- Pressure. Most ionising tools work at a low, regulated pressure, often 2–5 bar(g); fit a regulator at each station rather than lowering the plant header.
- Flow. Continuous bars run all shift and belong in the base-load demand, as in the table above. Hand guns are intermittent but large when open; count them with a duty factor.
- Verification. Check ion balance and decay time with a charged plate monitor at the interval the ESD control programme sets, and after any change in air supply or filter replacement.
Tool CDA and ultra-high-purity CDA in semiconductor fabs
A wafer fab usually runs two or more grades of dry air. Tool or house CDA drives valves, actuators and vacuum generators and is typically specified at a pressure dew point of −40 °C to −70 °C with oil class 1 or better under ISO 8573-1. Ultra-high-purity (UHP) CDA, sometimes called extra-clean dry air, is used where air touches the wafer or its surroundings: purging wafer carriers and stockers, some lithography and metrology purges, and tool mini-environments. UHP specifications are written in parts per billion for water, hydrocarbons and other airborne molecular contaminants, and in particle counts at very small sizes. These limits are far tighter than ISO 8573-1 class 1, so they are normally stated as ISO 8573-1 class 0 (a limit agreed between user and supplier that is stricter than class 1; class 0 does not mean zero) or written as a separate fab specification.
The compressor plant’s role is to supply a stable, oil-free feed. UHP grade is reached downstream by purifiers (often heated catalytic and adsorbent units), ultra-fine filters, and electropolished stainless steel distribution. Specifying the compressor plant itself to UHP limits is not practical, and the fab specification does not normally ask for it. What the compressor plant must guarantee is:
- no oil carry-over under any fault condition, which is why oil-free compression is the normal choice;
- a dew point well below the purifier’s inlet limit, so the purifier is not overloaded;
- pressure held within the narrow band the purifiers and tools expect, with N+1 capacity for maintenance;
- an intake away from exhausts, cooling towers and chemical vents, because airborne hydrocarbons pass straight through an oil-free compressor.
Keeping CDA clean between the dryer and the tool
A dryer that meets −40 °C at its outlet does not guarantee −40 °C at the tool. Most dew-point and particle problems in electronics plants start in the distribution system.
| Detail | Good practice | Why it matters |
|---|---|---|
| Installation cleanliness | Degreased, capped pipe and fittings; no thread oil or jointing compounds that contain oil; blow down and purge before connecting tools | Oil and swarf left from installation show up as contamination for weeks |
| Branch connections | Take every drop from the top of the header | Any liquid or particles that do reach the header stay in the main and do not fall into tool supplies |
| Dead legs | Remove unused branches or fit a small bleed | Stagnant sections pick up moisture through fittings and release it in a slug when opened |
| Hoses and tubing | Short runs of low-permeation tubing (such as polyamide or PTFE) at the tool | Some rubber hoses let moisture in and shed particles |
| Point-of-use filters | Size for flow at less than about 0.1 bar clean pressure drop; change on differential pressure | Undersized filters cause the pressure dips that trigger tool alarms |
| Verification | Measure dew point at the farthest tool as well as at the dryer outlet | A rise along the system points to leaks or permeation, not to the dryer |
How Reddy Compressors helps
Reddy Compressors, based at Tarnaka, Secunderabad, has served industry since 2002 as an independent multi-brand specialist. We are not an authorised distributor of any brand; we sell, rent and service oil-free and oil-injected compressors and dryers from ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and others. We have tie-ups with all major and reputed brands.
- Sales: new oil-free compressors, desiccant dryers, filters and receivers, and used or refurbished machines where suitable.
- Rental: compressors from 50 to 2,000 cfm and 2 to 30 bar from our own fleet, with dryers and filtration for temporary CDA during breakdowns, commissioning or expansion.
- Service and AMC: over 20 service engineers and technicians covering all of Telangana and Andhra Pradesh, including dryer and filter service. See compressor AMC.
- Spares: filter elements, desiccant, dryer valves and compressor parts identified from the nameplate, with fit confirmed before quoting.
- Audits: dew point, pressure, leak and energy surveys.
We supply equipment, rentals and spares across India, with project-based site support where feasible.
Our track record. We have supplied compressors to leading companies in electronics and semiconductor manufacturing across Telangana, Andhra Pradesh and beyond – new and used machines, long-term rental, and breakdown cover when a plant’s own compressor fails – backed by our own service team.
What to send us
- Type of plant: assembly, EMS, component, packaging or fab.
- Required air quality (ISO 8573-1 class), dew point and pressure at the tools.
- Total flow and the largest tool demands; shift pattern.
- Existing compressors, dryers and filters: make, model, nameplate photos.
- Pipe material and layout, and any current quality problems.
- Site location and power supply details.
Frequently asked questions
What is clean dry air in electronics manufacturing?
Clean dry air, or CDA, is compressed air treated to remove water, oil and particles to the levels the production tools need. For electronics assembly this is typically around ISO 8573-1 class 1 or 2 for particles and oil, with a pressure dew point of −40 °C. Semiconductor fabs often specify stricter limits and add point-of-use purifiers. The exact numbers come from your tool and facility specification.
What ISO 8573-1 class is needed for SMT lines?
Many SMT and electronics assembly lines work to around class 1.2.1 or 2.2.1, meaning tight particle filtration, a −40 °C pressure dew point and very low oil. Some equipment makers state their own limits in installation manuals, and these take priority. General automation and workshop air in the same plant can usually be served at a lower class from a separate header.
Do semiconductor plants need oil-free compressors?
Most semiconductor fabs specify oil-free compressors because the cost of a single oil contamination event is very high. An oil-injected machine relies entirely on filters and separators to keep oil out. Even with oil-free compression, carbon filtration may be needed to remove hydrocarbons drawn in from polluted intake air, and point-of-use purification is common for the most sensitive tools.
Why does my CDA dew point rise in summer?
Hot ambient air raises the compressor discharge temperature and the moisture load reaching the dryer. A desiccant dryer sized on cooler conditions can be overloaded, and an aftercooler struggling in 45 °C weather passes more water forward. Worn changeover valves or tired desiccant make it worse. Measuring inlet temperature, flow and dryer cycle shows whether you need service, extra cooling or more drying capacity.
What pipe material is best for clean dry air?
Aluminium and stainless steel are the usual choices because they do not rust and shed far fewer particles than galvanised or black steel. Installation matters as much as material: cut ends should be deburred, pipes flushed before commissioning, and drops taken from the top of the header. Final particle filters close to sensitive tools protect against anything the network still releases.
Can you provide temporary clean dry air during a compressor breakdown?
Yes. We rent compressors from 50 to 2,000 cfm and 2 to 30 bar, and can include desiccant dryers and filters so that temporary air meets your dew point and filtration needs. Tell us the flow, pressure and quality class, and where the tie-in point is. Preparing a connection in advance makes changeover quicker and keeps contamination risk down.
Can I use a refrigerated dryer for an SMT line?
A refrigerated dryer gives a pressure dew point of about +3 °C (ISO 8573-1 water class 4). Many placement machine makers ask for a lower dew point, and in a cooled cleanroom any section of pipe or tubing near or below +3 °C can collect condensate. For SMT, a desiccant dryer at −40 °C is the common choice for the line supply. A refrigerated dryer can still serve general utilities, a nitrogen generator feed, or act as a pre-dryer ahead of a desiccant dryer to reduce its load. Check each machine’s data sheet for the required air class before deciding.
How much nitrogen does a reflow oven use?
It depends on the oven length, the number of zones, conveyor openings and the residual oxygen target. Many convection reflow ovens are in the range of about 15–30 Nm³/h when running in nitrogen, and selective soldering machines use less. The oven maker’s data sheet gives the figure for its model and oxygen setting. To size a PSA generator, add the flows of all machines, allow about 20% for start-up and door openings, then multiply by the generator’s air factor at the purity you need to get the compressed air demand.
What is the difference between CDA and UHP CDA?
CDA (clean dry air) is compressed air treated to a stated ISO 8573-1 class, typically −40 °C to −70 °C pressure dew point with very low oil and particles, and is used for tool pneumatics and general process air. UHP CDA (ultra-high-purity clean dry air) is CDA purified further, with water, hydrocarbons and other molecular contaminants limited to parts per billion, and is used where air contacts wafers or their surroundings. UHP is reached with purifiers and fine filters after the main dryer. The compressor plant supplies the oil-free, dry feed.
Do ionisers need clean dry air?
Yes. Ionising air bars, guns and nozzles need oil-free, filtered and dry air. Oil mist and fine dust collect on the emitter pins, upset the balance between positive and negative ions and reduce the neutralising effect, so boards can still be charged. Wet air shortens emitter life. Feed ionisers from the same CDA as the placement machines, fit a regulator at each station for the low pressure they need, often 2–5 bar(g), and check ion balance and decay time with a charged plate monitor at regular intervals.
Related pages
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 7 November 2026. How our engineering content is reviewed.