Methods for Measuring Cleanliness

Question:
What methods can be used to detect cleanliness at 0.01, 0.01 to 0.001, and below 0.001 grams of soil per square centimeter?

Answer:
Depending upon method selected, cleanliness can be detected to varying degrees or levels.

Cleanliness can be detected to 0.01 grams per square centimeter levels by using visual inspection, low power microscope inspection, wiping and visual inspecting, water break tests, atomizer tests, nonvolatile residue inspection, surface UV Fluorescence detection, tape test.

The level of cleanliness typically suitable for automotive, aerospace, electrical and many surface preparations is between 0.01 to 0.001 grams per square centimeter. This level of detection can be achieved through Millipore filter measurement techniques such as optical microscopy, extraction, oil evaporation, oil soluble Fluorescence, gravimetric analysis, surface energy tests, contact angle measurement, particle counting.

The highest level of cleanliness measurement, below 1 microgram per square centimeter, is suitable for use in semiconductor, disk drive, and medical device applications. Techniques that are used for this level of precise cleanliness measurement include carbon coulometry, electron spectroscopy for chemical analysis (ESCA), Fourier transform infrared (FTIR), Gas chromatography/mass spectrophotometry (GC/MS), Ion chromatography (IC), Optically stimulated electronic emissions (OSEE), Particle counting, scanning electron microscopy (SEM) and Secondary ion mass spectroscopy (SIMS).

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