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2.3 Compressed Air Standards (ISO 8573)

Compressed air is the "Fourth Utility," but unlike electricity or water, you manufacture it on-site. If your air quality fails, you are injecting pollution directly into your precision equipment.

Pneumatic actuators in pick-and-place heads operate at millisecond speeds. Contaminants (water, oil, dust) cause Stiction—the friction that kills repeatability. A 0.1-second valve delay turns a perfect placement into a skewed defect.

The ISO 8573-1 Standard (Class 1.2.1)

Do not ask for "Clean Dry Air." That is a subjective wish.

Demand ISO 8573-1 Class 1.2.1. This is the engineering definition of "clean" for electronics.

1. Solids (Class 1):

  • Limit: < 100 particles (0.1 – 0.5 µm) per m³.
  • The Risk: SMT vacuum nozzles have internal filters with 10 µm mesh. Class 1 particulates pass right through and grind against the solenoid spool, causing premature wear.

2. Water (Class 2):

  • Limit: Pressure Dew Point (PDP) ≤ -40°C.
  • The Physics: As compressed air expands at the point of use, it cools rapidly (Joule-Thomson effect). If the dew point is not low enough, invisible vapor turns into liquid water.
  • Consequence: Water washes away the "lifetime grease" inside pneumatic cylinders, leading to rust and seizure.

3. Oil (Class 1):

  • Limit: Total Oil Content ≤ 0.01 mg/m³.
  • The "Silent Killer": Oil mist atomizes at the exhaust port of the machine. It settles on optical sensors and camera lenses, slowly blinding the machine's vision system.
  • Control: Use Oil-Free compressors. If using oil-injected screw compressors, active carbon towers are mandatory.

Nitrogen (N2) Generation

Nitrogen is an expensive necessity for Reflow, Wave, and Selective Soldering. It displaces Oxygen to prevent oxidation, widening the process window for wetting, especially with OSP (Organic Solderability Preservative) finishes.


Purity Standard (EMS Requirement):

  • Target: 99.99% (4N).
  • Context: This purity is sufficient to prevent oxidation on copper pads and component terminations during the thermal spike. Higher purity (5N) is unnecessary cost for standard SMT/Through-hole assembly.

Process Control Logic:

  • If Reflow O2 ppm > 1000 -> Then Stop the conveyor. Solder joints will exhibit "Grapeing" or Head-in-Pillow defects.
  • If N2 tank pressure < 4 bar -> Then Alarm immediately. Low pressure allows air ingress into the oven tunnel.

Pro-Tip: Leaks are money evaporating. Install flow meters on the main N2 line. If flow exists when production is idle (weekend), you have a leak. Find it.

Filtration Architecture

You cannot filter a problem away at the end of the pipe. You must treat it in stages.

  1. Compressor Room: Water Separator -> Refrigerant Dryer -> Coalescing Filter.
  2. Point of Use (Machine): Desiccant Dryer (to hit -40°C) -> Active Carbon (Oil) -> Dust Filter.

Final Checklist

Parameter

Specification (ISO 8573)

Critical Failure Mode

Particulates

Class 1 (0.1 – 0.5 µm)

Valve / Cylinder abrasion

Water (Dew Point)

Class 2 (≤ -40°C)

Rust / Lubricant Washout

Oil Content

Class 1 (≤ 0.01 mg/m³)

Lens/Sensor Fogging

N2 Purity

99.99% (4N)

Oxidation / Poor Wetting

Filter Service

Based on ∆P (Pressure Drop)

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