Class 100 cleanrooms (equivalent to ISO 14644-1 Class 5) enforce ultra-stringent contamination control—allowing no more than 100 particles (≥0.5μm) per cubic foot of air. In environments like semiconductor wafer fabrication, medical device manufacturing, or microelectronics assembly, even a single fiber or trace residue can ruin high-value products. Cleanroom wipes (dry, lint-free variants) and cleaning wipes (pre-moistened with high-purity solutions) are critical tools here, but their effectiveness depends on strict adherence to standard operations (SOPs) that minimize particle generation, prevent cross-contamination, and ensure compliance. Below is a comprehensive breakdown of these SOPs, tailored to Class 100 cleanroom requirements.
1. Pre-Operation Preparation: Ensure Wipe and Operator Readiness
Before entering the Class 100 cleanroom, thorough preparation eliminates external contamination risks:
- Wipe Selection & Inspection:
- Choose wipes certified to ISO 14644-1 Class 5 (or better) with ultra-low linting (≤1 particle ≥0.1μm per wipe) and, if using pre-moistened cleaning wipes, a residue-free solution (e.g., 99.9% IPA, deionized water).
- Inspect wipes under a Class 100-compatible light (e.g., LED task light) for tears, loose fibers, or visible contaminants. Discard any defective wipes—even minor flaws can shed particles.
- Operator Gowning & Grounding:
- Don cleanroom-appropriate attire (e.g., full-body bunny suit, gloves, face mask, shoe covers) following ISO 14644-3 gowning protocols to prevent operator-borne particles.
- For anti-static needs (e.g., semiconductor cleanrooms), wear an ESD wrist strap connected to a grounded surface and anti-static gloves—this prevents static from attracting particles to wipes or surfaces.
- Wipe Storage & Handling:
- Store unopened wipes in sealed, cleanroom-grade packaging (e.g., foil-lined bags with zip closures) in a Class 100 storage cabinet. Never bring non-Class 100 wipe packaging into the cleanroom.
- Open wipe dispensers only inside the cleanroom, and reseal them immediately after each use to avoid exposure to ambient air (which carries particles).
2. Standard Wiping Procedures for Class 100 Cleanrooms
The wiping technique directly impacts particle control—follow these steps for both dry cleanroom wipes and pre-moistened cleaning wipes:
A. Dry Cleanroom Wipes (for Particle Removal)
Use dry wipes first to eliminate loose dust before wet cleaning—this prevents particles from being pushed into surfaces or dissolved in cleaning solutions:
- Wipe Folding: Fold the dry wipe into a 4-layer pad (e.g., 4”x4” from a 8”x8” wipe). This creates a dense, low-linting surface and reduces the risk of the wipe edge fraying (a common particle source).
- Wiping Pattern: Wipe in a single, continuous direction (e.g., horizontal for flat surfaces like workbenches, vertical for walls) with overlapping strokes (50% overlap). Never use circular motions—these redistribute particles instead of trapping them.
- Pressure Control: Apply light, even pressure (≤1 psi). Excessive force compresses the wipe’s fibers, reducing particle-trapping capacity and increasing friction (which can generate static).
- Wipe Rotation: Rotate the wipe to a clean layer after every 2–3 strokes. Once all layers are used, discard the wipe immediately in a Class 100-compatible waste bin (sealed, anti-static, if needed).
B. Pre-Moistened Cleaning Wipes (for Residue/Oil Removal)
Use cleaning wipes only after dry particle removal, and prioritize residue-free solutions to avoid leaving contaminants:
- Moisture Check: Ensure the wipe is damp (not dripping). Excess liquid can pool in crevices (e.g., equipment seams) and evaporate, leaving mineral deposits or solvent residues. Blot excess moisture on a clean dry wipe if needed.
- Targeted Cleaning: For small surfaces (e.g., wafer chucks, optical lenses), use the edge of the folded wipe to reach tight spaces. For large areas, divide the surface into 1ft x 1ft sections and clean one section at a time to avoid missing spots.
- Evaporation Wait: After wiping, allow the surface to air-dry completely (10–30 seconds, depending on the solution) in the cleanroom’s filtered air. Do not use compressed air to speed drying—this can stir up particles.
- Post-Clean Dry Wipe: For critical surfaces (e.g., semiconductor wafers), follow the cleaning wipe with a fresh dry wipe to ensure no residue remains.
3. Post-Operation Protocols
- Waste Disposal: Place used wipes in a sealed, labeled waste container (marked “Class 100 Cleanroom Waste”) and remove it from the cleanroom at the end of each shift. Do not leave used wipes inside—they can release trapped particles.
- Dispenser Maintenance: Clean wipe dispensers weekly with a dry Class 100 wipe to remove dust from the opening. Replace dispensers if they show signs of wear (e.g., cracked lids) that could allow contamination.
- Documentation: Log wipe usage (lot number, quantity, cleaning area) and any anomalies (e.g., defective wipes, particle spikes) in the cleanroom’s SOP log. This supports traceability for compliance audits (e.g., FDA, SEMI).
4. Critical Compliance Checks
- Particle Monitoring: After cleaning, use a particle counter to verify surface particle levels (≤1 particle ≥0.5μm per cm²) and air particle counts (≤100 particles ≥0.5μm per cubic foot).
- Residue Testing: For pre-moistened wipes, conduct monthly residue tests (e.g., ion chromatography, FTIR spectroscopy) to confirm no solvent or additive residues remain on cleaned surfaces.
By following these standard operations, cleanroom wipes and cleaning wipes consistently meet Class 100 requirements—protecting products from contamination, ensuring regulatory compliance, and maintaining the cleanroom’s integrity for high-precision manufacturing.