In industries with extremely high cleanliness requirements such as semiconductor manufacturing, precision electronics, and medical equipment, the Air Particle Count (APC) of cleanroom wipes is a key indicator to evaluate their cleanliness and suitability. Even microscopic particles at very low concentrations can cause circuit shorts, device failures, or contamination of medical instruments, affecting product yield and safety. This article provides a detailed overview of the purpose, principles, procedures, and quality control aspects of APC testing for cleanroom wipes, helping enterprises scientifically select high-quality wipes.
1. Purpose and Significance of APC Testing
APC testing aims to simulate particle release during the dry, dynamic use of cleanroom wipes and quantitatively assess their potential contamination risk to the cleanroom environment. In ultra-clean processes like semiconductor wafer fabrication, particle presence can directly cause manufacturing defects. APC testing helps screen low-particle-release wipes to ensure they meet strict cleanroom requirements.
2. Principles and Key Parameters of APC Testing
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Testing Principle
APC testing is based on light scattering technology. Particles suspended in air scatter a laser beam; the intensity of scattered light correlates with particle size and number. Particle counters capture the scattered signals, enabling precise counting of particles in the 0.3–2.0 μm size range, focusing especially on critical particles ≥0.5 μm. -
Key Parameters
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Testing Equipment: Helmke Drum simulates real wiping action by rotating at 10 rpm, generating mechanical friction similar to actual use.
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Units: Results are reported as counts/ft³/min/pc (particles per cubic foot per minute per piece) or counts/m² (particles per square meter), indicating particle release intensity per unit area or per wipe piece.
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Sample Requirements: Five sealed samples with neat-cut edges to avoid fiber shedding from edges that might interfere with results.
3. Standardized Testing Procedure
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Sample Preparation
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Samples are unpacked in an ISO Class 5 or better clean environment to avoid external contamination.
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Cleanroom tweezers are used to fix wipes flat onto the Helmke Drum’s inner wall, avoiding folds or pressure.
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Equipment Operation
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The drum rotates steadily at 10 rpm, simulating wiping-induced mechanical stress.
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The air sampling tube is positioned 5 ± 2 cm from the drum’s edge, connected via flexible conductive tubing to the particle counter, sampling at 28.3 L/min.
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Data Collection
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The particle counter measures particle counts mainly ≥0.5 μm over about 40 minutes per sample, recording the dynamic release curve and calculating average particle release.
4. Quality Control and Considerations
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Environmental Control
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Laboratory conditions are maintained at 20–25°C, 40–60% humidity, and ISO Class 5 cleanliness.
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The same operator performs all tests to minimize human error.
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Equipment Calibration
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Regular calibration of particle counter sensitivity and Helmke Drum speed is mandatory.
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Blank control tests (empty drum runs) are conducted to exclude background particle interference.
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Sample Uniformity
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Wipes from different batches and edge finishing methods (laser cutting, ultrasonic sealing) are tested separately since edge quality directly impacts fiber shedding.
5. Application Scenarios and Standards Reference
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Semiconductor Manufacturing: Compliance with Class 1 cleanroom standards (≤10 particles ≥0.1 μm per cubic meter) to prevent manufacturing defects.
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Medical Sterile Packaging: Minimizing microparticle contamination to ensure surgical instrument and pharmaceutical safety.
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Optical Device Cleaning: Avoiding scratches or fogging on lenses and sensors caused by particulate matter.
Relevant Standards:
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SJ/T 11480-2014: Specifies instrument parameters and operational procedures for APC testing.
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ASTM E1560: Relates non-volatile residue (NVR) analysis to particle release characteristics.
6. Conclusion
APC testing of cleanroom wipes scientifically simulates actual usage environments to quantify particle release risk, providing essential guidance for selecting materials suitable for high-cleanliness industries. As cleanroom technologies advance, future APC testing will integrate micro/nano particle characterization and AI data analytics to drive upgrades in wipe performance standards.