Ultrasonic Cavitations and Precision Cleaning Article0 pages

Ultrasonic
Cavitations
and Precision
Cleaning
BY SAMI AWAD, PH.D.,
VICE PRESIDENT
CREST ULTRASONICS CORP.

As the quest for
higher cleanliness
levels becomes
more intense, the
combination of
chemistry and
process chosen is
more crucial to the
success of the
cleaning.

CREST
ULTRASONICS

P

recision or critical cleaning is currently in great demand and is
expected to increase in the future.
The rapid advancements in various current technologies and the constant trend
in miniaturizing of components have created a need for higher cleanliness levels.
Contamination in the level of monolayers can drastically alter surface properties
such as wettability, adhesion, optical or
electrical characteristics. Particles in the
range of few microns down to submicron
levels, trace contaminants such as nonvolatile residues (NVR) in the range of
micrograms/cm2 and pictogram/cm2, ionics in the same range or traces of corrosion
have become part of the daily concerns of
the manufacturing engineers in major
industries such as semiconductors, automotive, disk drive, optics, ophthalmic,
glass, medical, aerospace, pharmaceuticals
and tool coatings, among others.
The specifications on trace contaminants and particle sizes are being tightened periodically to reflect the new technology trends. Every industry has its own
set of cleanliness specifications and the
focus differs.
For example, while NVR has not been
an automotive industry issue until now,
it has been crucial for the semiconductor
and the disk drive industries for years.
Trace contaminants are not acceptable in
the carbide, optics and ophthalmic
industries, as they may cause adhesion

failures in a multi-coating process that
follows cleaning.
For obvious reasons, absolutely clean surfaces are an extremely critical requirement
in cleaning medical devices. Concern
about particles has become a common
denominator among all industries.

Precision Cleaning
Precision or critical cleaning of components or substrates is the complete
removal of undesirable contaminants to a
desired preset level. The preset level is
normally the minimum level at which no
adverse effects take place in a subsequent
operation. To achieve this level, it is critical not to introduce new contaminant(s)
into the cleaning process.
For example, if the cleaning of organic
and ionic contaminants is achieved by an
aqueous process, it is important to have
high quality water and the proper parameters in the rinsing stages. Otherwise,
residual detergent and/or ionics from the
rinsing water will be the new contaminants. If drying is slow, deionized rinse
water may react with some metallic surfaces at high temperatures and create
undesirable stains or marks. Re-contamination of cleaned parts with outgassed
residues produced from packaging or storing materials is another big concern.
To select an effective cleaning method,
the three essential factors directly influencing cleaning results are the cleaning