Cleanroom Wiper Testing Guide: Methods, Parameters, and How to Interpret Results

Cleanroom wipers may look simple, but their performance depends on measurable technical indicators that directly affect production outcomes. Fibers, particles, non-volatile residues (NVR), metallic ions, and sorbency characteristics determine whether a wiper is suitable for sensitive environments. This guide provides a practical overview of the main test methods, how to interpret results, and what buyers should focus on when selecting cleanroom wipers.

Why Testing Matters

The performance of a cleanroom wiper cannot be judged by appearance alone. Even materials that look smooth can shed fibers or leave residues that impact production. Industries such as semiconductors, flat-panel displays, medical devices, optics, and biopharmaceuticals require specific performance levels for their processes.

Understanding test parameters helps engineers and procurement teams:

• Choose materials suitable for their application

• Reduce contamination risk

• Ensure stable and consistent cleaning performance

The most common categories of evaluation are:

1. Cleanliness: fibers, liquid-borne particles, airborne particles

2. Sorbency: capacity, efficiency, absorption rate

3. Purity: non-volatile residue, metallic ions

Cleanliness Testing

Cleanliness is an indicator of how many particles or fibers a wiper will release during actual use. It is typically divided into fiber release, liquid-borne particles, and airborne particles.

1 Fiber Release

Fiber release measures how many fibers detach from a wiper under controlled conditions. Fibers ≥100 µm are counted after the wiper is agitated in water.

• Test method: A wiper is washed for five minutes in water using a biaxial or orbital shaker. Released fibers are captured on a membrane and counted under a microscope. Results are expressed as fibers per square centimeter.

• Importance: High fiber release can cause contamination on wafers, lenses, or coatings.

Impact by application:

For high-precision processes, choose polyester knit or microfiber wipers with low fiber counts. Avoid high-cellulose blends.

2 Particles

Particles are released when a wiper is submerged and agitated in water.

• Test method: A liquid-borne particle counter tallies particles ≥0.5 µm. Results are normalized per square centimeter.

• Importance: Particles can settle on sensitive surfaces, causing defects or reducing product reliability.

Industry relevance:

Check test results per cm² rather than relying solely on “Class 1000” labels.

3 Airborne Particles (Helmke Drum Test)

The Helmke Drum simulates particle release when wipers are handled or moved.

• Test method: Ten wipers are tumbled in a rotating drum. Airborne particles are counted per cubic foot of air.

• Importance: Wipers may pass liquid particle tests but still release airborne particles during folding or wiping.

If your process involves dry wiping, prioritize wipers with low airborne particle release.

Sorbency Testing

Sorbency determines how effectively a wiper absorbs liquids. There are three key measurements: capacity, efficiency, and rate.

1 Capacity

Capacity measures the total volume of liquid a wiper can hold.

• Test method: Saturate a sample with liquid, wait one minute, then weigh. Expressed in milliliters per square meter.

• Importance: High capacity helps with large spills and solvent-heavy cleaning.

2 Efficiency

Efficiency measures absorption relative to material weight, expressed as milliliters per gram.

• Importance: Allows comparison of raw materials. Microfiber typically shows higher efficiency, while cellulose blends may have high capacity but lower efficiency.

3 Absorption Rate

Absorption rate measures how quickly the wiper absorbs liquid, expressed in seconds.

• Importance: Fast absorption is needed for IPA wiping or solvent cleaning. Controlled absorption is preferred for optics to avoid streaks.

Sorbency comparison table:

Match absorption characteristics to your process, not just pick the highest capacity.

Purity Testing

Purity determines chemical cleanliness. Two main tests are Non-Volatile Residue (NVR) and metallic ions.

1 Non-Volatile Residue (NVR)

• Test method: Extract wiper in DI water and IPA, evaporate, and weigh residue. Expressed in g/m².

• Importance: Residue can affect surface energy, coating adhesion, and device reliability.

2 Metallic Ions

• Test method: Extract wiper in DI water, analyze with ion chromatography.

• Monitored ions: Na⁺, K⁺, Cl⁻, Ca²⁺, Mg²⁺

• Importance: Excess ions can cause corrosion, short circuits, or film defects.

Application relevance:

Always request full NVR and ion data to assess chemical compatibility.

Material and Construction

Material and edge treatment affect fiber release, particles, and sorbency.

• Materials: Polyester knit, microfiber, cellulose/polyester blends, meltblown

• Edge Sealing: Laser-cut, ultrasonic, or cold knife

• Packaging: Double-layer vacuum preserves cleanliness

For critical processes, prioritize laundered, laser-cut, or ultrasonic-cut microfiber wipers with proper packaging.

Matching Test Results to Applications

How to Evaluate Supplier Test Reports

• Compare results per cm² or per m², not by generic class

• Ensure test conditions match IEST-RP standards

• Review NVR, ion profile, sorbency data

• Confirm packaging and handling conditions

• Request multiple batches to verify consistency

Buyer checklist:

• Fiber release (fibers/cm²)

• Liquid-borne particles (particles/cm²)

• Airborne particles (per cubic foot)

• Sorbency (capacity, efficiency, rate)

• NVR (g/m²)

• Metallic ions (ppm)

• Edge-cut method and packaging