By [email protected] — Charting the depths of expertise
Definitions of LPC, APC, IC, and NVR
LPC: Liquid Particle Count
This refers to the quantity and size distribution of particles released from a cleanroom wipe when subjected to mechanical stress (like rubbing or sonication) in a liquid medium (usually ultrapure water).
APC: Airborne Particle Count
This refers to the capacity of a cleanroom wipe to release solid particles (including fibers) into the air when subjected to mechanical friction or flexing in a dry state.
Unlike LPC, which is a wet test, APC is a dry test, typically performed using methods like the Helmke Drum test.
This parameter is crucial for evaluating the wipe's particle-shedding performance in an air environment.
IC (Ion Chromatography): Ion content analysis via ion chromatography
This refers to the types and quantities of extractable anions and cations (e.g., Cl⁻, SO₄²⁻, Na⁺, K⁺) in a cleanroom wipe.
NVR: Non-Volatile Residue
This refers to the mass of non-volatile substances remaining after a wipe is extracted with a specific solvent (like IPA or ultrapure water) and the solvent is evaporated.
Cleanroom Wipe Class Parameter Reference Table
Note: The parameters in the table below may not be entirely accurate. Different industries often have different requirements, and there is no universally accepted standard for class divisions. Most factories define wipe classes primarily based on APC.
| Class | Wet Particle Release (LPC) ≥ 0.5 µm | Dry Particle Release (APC) ≥ 0.5 µm | Ion Content (IC) | NVR (IPA Extraction) |
|---|---|---|---|---|
| Class 10 | ≤1200 particles/cm² | ≤ 10 particles/ft³ | ≤1.0 µg/g | ≤0.5 mg/g |
| Class 100 | ≤3000 particles/cm² | ≤ 100 particles/ft³ | ≤2.0 µg/g | ≤0.8 mg/g |
| Class 1000 | ≤6000 particles/cm² | ≤ 1000 particles/ft³ | ≤3.0 µg/g | ≤1.0 mg/g |
Main Sources of LPC (Wet Particle Release) / APC (Dry Particle Release)
Shedding from the wipe material itself:
Shed Fibers: Elongated particles typically larger than 100 micrometers are classified as fibers. Non-fibrous particles: Very small non-fibrous debris, powders, or particles generated by the mechanical action of weaving, washing, and cutting. Residues from the production process:
Process residues: Dried remnants of chemicals, additives, surfactants, and cleaning agents. These residues can exist as solid particles and be released during LPC testing. Environmental particles: Even when produced in a controlled cleanroom environment, microscopic dust cannot be completely avoided. A small amount of airborne dust, or micro-particles from equipment wear, can adhere to the wipe's surface or within its structure and be released during testing. Contaminants from packaging and handling:
If not properly controlled, the packaging and shipping processes can also introduce tiny particulate matter.
LPC primarily reflects internal and residual contaminants within the wipe, while APC mainly reflects particles and fibers released from the surface and edges under dry mechanical stress. High APC values are often associated with "loose surface fibers," "unsealed edges," and the material's inherent resistance to friction/flexing. In contrast, high LPC values are often linked to "incomplete washing" and "residual processing agents."
Main Sources of IC (Ion Content)
Raw Materials:
The fiber materials used to make cleanroom wipes (e.g., polyester, nylon, cellulose) may contain or have residual inorganic salts or other ionic chemicals from the polymerization and production processes. These are inherent impurities in the material.
Manufacturing and Processing:
Washing Water: Although high-end cleanroom wipes are washed with high-purity or even ultrapure water (DI/UPW), the water may still contain trace amounts of residual ions. If the water purity is insufficient, it can significantly introduce ions like sodium, calcium, and chloride. Chemical Additives: During the manufacturing, washing, or finishing stages, various chemical additives like detergents, softeners, antistatic agents, or other functional treatments may be used. If these additives are not thoroughly removed, or if their components contain ions, they will remain in the fabric. Manufacturing Equipment: Equipment used in production, especially metal parts, can generate metal ions through wear or corrosion, which can then be transferred to the wipe. Environmental Factors:
Even in a cleanroom production environment, the air may contain trace ionic contaminants (such as acidic gases, alkaline gases, or ion-containing particles). These contaminants can be adsorbed onto the wipe's surface.
Packaging Materials:
If packaging materials are not sufficiently clean or release volatile substances, they could also cause ionic contamination, although this is less common for high-standard cleanroom wipes.
Unlike the physical particles measured in LPC tests, ions are chemical species dissolved in a medium, not physically visible solid particles. The IC test involves soaking the wipe in a specific solution to "extract" the soluble ions into the solution. An ion chromatograph is then used to analyze the types and concentrations of various ions in the solution (usually in ppm or ppb).
High-standard cleanroom wipe manufacturers implement strict controls, including using high-purity raw materials, multiple washes with ultrapure water, optimizing the use and removal of chemical additives, and manufacturing and packaging in highly controlled cleanroom environments. This minimizes ionic residue to meet the stringent cleanliness requirements of high-tech industries like semiconductors, pharmaceuticals, and electronics. Therefore, the residual ions in cleanroom wipes primarily originate from the raw materials, water, and chemicals used during production, which are targeted for removal through a rigorous washing process.
Main Sources of NVR (Non-Volatile Residue)
Residual chemicals and additives from production and processing:
This is one of the primary sources of NVR. Various chemical additives (such as lubricants, emulsifiers, surfactants, softeners, antistatic agents, finishing agents) are used in the manufacturing, weaving, washing, and treatment of cleanroom wipes. Although washing is performed, these chemicals or their byproducts may not be completely removed and can remain in the wipe as non-volatile matter.
The cleaning agents used in the washing process can also contribute to NVR if they are not fully rinsed out.
Impurities in the raw materials:
The raw fiber materials (e.g., polymers like polyester, nylon) may contain low-molecular-weight polymers, residual monomers, or production aids from the synthesis process, all of which can be sources of NVR.
Contaminants from equipment and the environment:
Lubricating oils from production equipment (like looms and slitters), micro-particles from wear, and uncontrolled volatile organic compounds (VOCs) or dust in the manufacturing environment can all be transferred to the wipe, forming NVR.
Migration from packaging materials:
If the packaging material itself contains migratable non-volatile substances (like plasticizers), these can transfer to the cleanroom wipe's surface over time, increasing NVR.
Degradation products of the material itself:
During heat treatment in production or long-term storage, the wipe material itself may undergo slight degradation, generating small-molecule, non-volatile compounds that also contribute to NVR.
Unlike the solid particles (like fibers and micro-particles) measured in LPC tests, NVR consists more of chemical residues that can be dissolved by specific solvents. In a cleanroom environment, high NVR can lead to the formation of a thin film on surfaces, interfere with subsequent processes (like coating or bonding), cause corrosion, or affect product performance. Therefore, its strict control is essential. Managing NVR to low levels is a key indicator of a cleanroom wipe's cleanliness class.
