Chemtronics all products Technical Guide

Technical

Using Black Inspection Wipes: Is It Really Clean?

White polyester wipe hides contamination because of

Contamination more apparent on black polyester wipe

Close-up of contamination on the black

By Paul Blair, Marketing Director
Coventry™ Cleanroom Products

The whole point of wiping a surface with a cleanroom wipe is to remove
contaminants including dust, dirt, oil, greases, soot, fluxes and so on. But,
after wiping, how clean is the surface? How can it be guaranteed? How can
an operator or quality inspector be sure?

Visually inspecting the wipe is the quickest and easiest way to check
cleanliness. If the wipe looks dirty and the substrate looks clean, the wiping
process was successful. That works well if the wipe and the contaminants
are contrasting colors. Since most wipes are white (a sign of cleanliness
perhaps) black or darkly color soils are easily seen. However, many
contaminants are not dark colored. Instead they are white or light colored.
Since they are the same color as the wipe, visually inspecting the used
wipe is not completely useful. This is especially true if the contaminant is
particulate; especially small particulates.

lack of contrast.

Guide

Color is actually specific energies of light waves which fall into the range of
wavelengths humans are able to see, the visible spectrum between red and
violet. Objects appear to have color since they selectively absorb and reflect
certain wavelengths of visible. For example when a blue object is hit with
white light rays the object reflects only wavelengths that we see as blue light
and absorbs all other light, that is, all the other wavelengths of light.

As particles become smaller and more dispersed, their actual color or lack of
color (transparency) becomes less visible and the light scattering effect
becomes more visible. For example, Mie Scattering is responsible for the
white appearance of clouds. Cloud droplets are transparent water but with
a diameter of 20 micrometers or so, they are large enough to scatter all visible
wavelengths more or less equally. This means that almost all of the light which enters
clouds will be scattered. Because all wavelengths are scattered, clouds appear to be
white. Liquid particle counters rely on Tyndall Scattering to report determine particle
numbers and measure turbidity in a sample.

Consequently, dust and particulate contamination is not reliably detected by white
wipes. Instead, ‘cleanroom clean’ black wipes have been developed to clearly and
visibly show small particulate contamination. Black inspection wipes like Coventry™
Poly-Onyx™ were originally developed to be the final check of the cleanliness of
hands and faces (make-up and cigarette smoke particles) of workers entering class
10 cleanrooms in semi-conductor and other micro-electronic manufacturing.

because of visual contrast.

wipe material.

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Technical

Guide

Availability

However, their properties make them useful for both the final wipe down and for the final inspection of any surface in a critical
environment or anywhere particles compromise quality or performance.

Inspection wipes must have the following properties since they either clean the surface to its ultimate cleanliness or make final
contact with the surface after the final cleaning.

• Cleanliness - The inspection wipe must be at least as clean as the most critical wipe used in the cleaning process. In
fact it should be the cleanest wipe. Therefore it must be cleanroom laundered to remove all particulate, non-volatile
(NVR) and ionic contamination. Preferably, it should have sealed edges or sealed borders since this is where much
contamination is shed from wipes.

• Absorbency - The absorbency of the inspection wipe must equal or surpass all the other wipes used in the cleaning
process so it can be the final cleaning and catch any contamination left by the previous wiping.

• Durability - The wipes must be colorfast and resistant to any chemical or mechanical (abrasive) attack. Pure 100%
monofilament polyester is ideal for this task and the reason why it is used in the cleanest cleanroom wipe.

• Visibility - The particles and contaminants must be clearly visible on the wiper. Dark contaminants are clearly visible
on the typical white wipe. However, the most jet black wipe is necessary to see all other remnant contaminants. Blue
wipes are not adequate.

• Properly sized - the wipe must be large enough (6”x6” minimum; 9”x9” preferred) to be properly manipulated

Coventry™ Poly-Onyx™ cleanroom polyester wipes meet these criterion. And, because they do, function equally well as a
high performance cleaning wipe as well as an inspection wipe.

The best way to use an inspection wipe is to quarter fold it. The wipe is then held in the hand with the laser or heat cut edges
in the palm. The thumb should hold the four cut corners in the palm of the hand while the fingers apply gentle wiping pressure
on the wipe, just behind the folded edges. The wipe can then be refolded to expose four fresh cleaning surfaces that are
neither touched by the hands (or gloved hands) of the wiped surface. This is the same method recommended for high
performance cleaning wipes.

Is it clean? Black inspection wipes, like Coventry™ Poly-Onyx™ 6259BESD answer that question – and make it so.

Coventry™ Poly-OnyxTM ESD Wipes
6259BESD 9" x 9" (22.9 cm x 22.9 cm), 150 wipes/bag
6254BESD 4"x4" (10.2 cm x 10.2 cm), 600 wipes/bag

Note:

This information is believed to be accurate. It is intended for
professional end users having the skills to evaluate and use
the data properly. CHEMTRONICS does not guarantee the
accuracy of the data and assumes no liability in connection
with damages incurred while using it.

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