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Measuring Parts Cleanliness Using a Quartz Crystal Microbalance

IP.com Disclosure Number: IPCOM000107192D
Original Publication Date: 1992-Jan-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 3 page(s) / 130K

Publishing Venue

IBM

Related People

Brand, JL: AUTHOR

Abstract

Contamination on parts and in process fluids can be measured using non-volatile residue (NVR) techniques. NVR requires that a large amount of solvent be used and evaporated off. The residue is quantified gravimetrically. A Quartz Crystal Microbalance (QCM) can be used to quantify the amount of residue. The advantage of the QCM is that the amount of wasted solvent is reduced from tens of milliliters to a few microliters. The QCM technique has also proven to be very successful at measuring the amount of contamination on small components.

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Measuring Parts Cleanliness Using a Quartz Crystal Microbalance

       Contamination on parts and in process fluids can be
measured using non-volatile residue (NVR) techniques.  NVR requires
that a large amount of solvent be used and evaporated off. The
residue is quantified gravimetrically.  A Quartz Crystal Microbalance
(QCM) can be used to quantify the amount of residue.  The advantage
of the QCM is that the amount of wasted solvent is reduced from tens
of milliliters to a few microliters.  The QCM technique has also
proven to be very successful at measuring the amount of contamination
on small components.

      The amount of contamination on a part can be measured using NVR
techniques.  Contamination analysis with NVR involves washing the
part with a solvent, evaporating the solvent in a pre-weighed pan,
and weighing the pan after the solvent has completely evaporated.
The difference in mass is the amount of contamination.  NVR is
limited by the sensitivity of the balance which is used to weigh the
pans. The best analytical balances have a sensitivity of 3
micrograms.  In order to measure small and/or very clean parts, many
parts must be included in an extraction so that the total amount of
contamination is greater than 100 micrograms.

      The prime example for where the NVR technique fails is
measuring contamination on small components.  The amount of
contamination on a small part is typically less than 0.1 micrograms.
In order to get a reliable NVR result, 1000 parts need to be combined
in each analysis.  Using that many parts in a single experiment is
prohibitive.  Further more, the NVR technique suffers from the fact
that 5-10 mL of solvent is used in each extraction.  NVR is an
environmentally objectionable technique.  The NVR technique also
requires 1 to 4 hours for a complete analysis.  In summary, the NVR
technique cannot be cost effectively applied to small, clean parts
because the absolute amount of contamination is small; many parts
need to be included in each determination; and there is a large
solvent loss which has severe environmental implications.

      A Quartz Crystal Microbalance can be used to measure small
quantities of contamination on parts.  QCMs are widely used to
measure thin films in vacuum chambers.  In vacuum, QCMs can measure
films less than 0.01 monolayers or tens of picograms in mass.  QCMs,
however, have never been applied to the measurement of parts
cleanliness.  In order to measure the amount of contamination on a
part, the part is placed in a microvial.  Five to eight microliters
of an appropriate solvent is used to wash the part in the microvial
and then the solvent is sucked back up into a syringe.  The solvent
is slowly dropped on the center of a QCM.  The solvent is dispensed
on the QCM in small microdrops of 0.1 microliters at a time, allowing
enough time between ea...