Non-Volatile Residue (NVR) is a critical indicator for assessing surface cleanliness of materials in industrial production, directly affecting product reliability in electronics, pharmaceuticals, and precision manufacturing. This article focuses on wipers and swabs, establishing a high-sensitivity NVR testing method based on solvent extraction and gravimetric analysis. By standardizing the process, the method enables quantitative analysis of residues on textiles and swabs, providing scientific support for quality control in cleaning processes.
2. Introduction
NVR refers to non-volatile substances remaining on material surfaces after solvent extraction. Its content directly impacts product performance in fields such as semiconductor manufacturing, where wafer surface NVR can cause circuit shorts or device failures. This paper develops a quantifiable NVR detection system for wipers and swabs by optimizing solvent selection, extraction procedures, and data calculation models.
3. Materials and Methods
1. Experimental Materials
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Samples: Wipers (6 pieces), Swabs (120 swab tips)
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Solvents: Isopropanol (IPA, ≥99.7%), Ultrapure Water (DIW, 18.2 MΩ·cm), Anhydrous Ethanol (≥99.8%), Petroleum Ether (boiling range 60–90°C)
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Equipment: Temperature-controlled evaporation apparatus (±0.1°C), electronic balance (accuracy 0.1 mg), vacuum filtration unit (0.45 μm pore size)
2. Testing Procedure
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Solvent Soaking:
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Wipers: Cut to a standard size (e.g., 10×10 cm²) and soaked in 200 mL of selected solvent with ultrasonic agitation for 30 minutes.
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Swabs: 120 swab tips soaked in 500 mL solvent with mechanical shaking for 1 hour.
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Solution Processing: Filter to remove particles (>0.45 μm), collect filtrate.
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Evaporation to Constant Weight: Transfer filtrate to pre-weighed evaporation dishes; evaporate in 80°C water bath until constant weight (mass difference ≤0.2 mg between two weighings).
3. Residue Calculation Formulas
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Wipers NVR (mg/cm²) = (Residue mass in mg) / (Wiper area in cm²)
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Swabs NVR (mg/tip) = (Residue mass in mg) / (Number of swab tips)
4. Key Parameters
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Total test duration: Approximately 9 hours (including 6–7 hours evaporation)
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Temperature control during evaporation: 80±2°C to avoid residue decomposition and measurement bias
4. Results and Discussion
1. Effect of Solvent Choice on Extraction Efficiency
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Isopropanol (IPA) achieves extraction efficiency up to 92% for oil-based residues, suitable for electronics industry wiper testing.
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Ultrapure water is more sensitive to water-soluble ionic residues such as Na⁺ and Cl⁻, making it ideal for pharmaceutical-grade swab testing.
2. Method Validation
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Wipers spiked with silicone oil (1.0 mg/g) showed recovery rate of 98.5% with relative standard deviation (RSD) of 2.1%.
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Swabs spiked with polyethylene glycol (0.05 mg/tip) showed recovery rate of 95.3%, RSD 3.8%, confirming accuracy and repeatability.
3. Comparison with Industry Standards
The method’s results for textile NVR closely match ISO 9022-12:2015 optical component cleanliness tests, with deviations less than 5%. Increased swab sample size (120 tips) improved statistical significance (p<0.01).
4. Application Cases
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A semiconductor company applying this method found that reducing wiper NVR from 0.8 mg/g to 0.2 mg/g increased wafer yield by 12%.
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In a medical device production line, NVR testing traced a microbial contamination incident to swab residue exceeding limits (0.15 mg/tip, 50% over limit).
5. Conclusion
The presented NVR testing method, combining multi-solvent extraction and high-precision gravimetric analysis, enables accurate quantification of residues on wipers and swabs. Coupled with standardized procedures, it provides robust technical support for quality control in cleaning consumables, especially for industries demanding high cleanliness.