Brian,
Yes, yes, yes, you are correct. Thanks for the detailed support. But my
personal experience came from having build precision, CLEAN ceramic gas
bearing wheels with 50 micro-inch running clearances for inertial navigation
systems. We went through extensive cleaning processes to make these things
"contamination free" and run for 10 years without failure. The water break
free test was one of the gates we had to pass before final assembly...and it
worked. We also used the WBF test on glass slides to qualify operation of
high vacuum chambers as "non-contaminating" to the things we put inside
them. I understand and agree with you totally that there are contradictions
and that failing the test is not proof of contamination, but it worked well
as an indicator of "not clean enough" in our application.
---------Rainer
-----Original Message-----
From: Brian Ellis [mailto:[log in to unmask]]
Sent: Wednesday, March 01, 2000 11:08 AM
To: [log in to unmask]
Subject: Re: [TN] How to detect contamination on metal surface
Rainer
I'm sorry, but the so-called water-break test is as useless as the name is
long. It is
one of the biggest myths and fallacies that occurs in our industry and
should be
drowned in the water required for it and then laid to permanent rest.
Proofs:
1) Take some new blown glass, as soon as it cools: it dewets in pure water:
therefore
it is contaminated, according to your theory. Wash and rinse it in a
household
dishwashing fluid: it wets: therefore it is clean according to your theory.
The
difference: some surfactant is contaminating the surface in the second case.
2) Take a freshly vacuum deposited copper mirror: it dewets in pure water:
therefore
it is contaminated, according to your theory. Leave it lying around for a
few days to
nicely oxidise: it wets: therefore it is clean according to your theory. The
difference: the oxidateion is more hydrophilic than the bare metal.
3) Vacuum deposit copper on a smooth glass slide and on a piece of heavily
frosted
glass (not too thick a deposit though). The smooth glass mirror dewets:
therefore it is
contaminated, according to your theory. The rough copper wets: therefore it
is clean
according to your theory. In fact, they have identical levels of
cleanliness. The
difference: the surface tension of the water holds it in place much better
on the rough
surface.
All these comparisons should be done with the purest water because tap water
will
contain an unknown soup of things which will alter the surface tension and
therefore
might change the results significantly. In fact, if you study the action of
soaps and
detergents, as well as any micellar or non-micellar tensio-active surface
agent (which
are found in most water including DI), you will understand that a wetting
surface
probably means that the surface has, at some time in its history, been
subjected to
such a substance.
Refs: Surface Phenomena by S.R. Rao, Hutchinson Educational Ltd, ISBN 0 09
112300 3
Any work by K.L. Mittal including his collected Treatise on Clean Surface
Technology
Volumes 1 and 2, Plenum Publishing, ISBN 0-306-42420-7
And dare I mention it without getting flamed for publicity?, my own book
specifically
for the electronics industry.
Can we please lay this old red herring to its well deserved and everlasting
rest?
Brian
"Blomberg, Rainer (FL51)" wrote:
> Marvin,
>
> A simple test for cleanliness is what we call the "water break free" test.
> Apply D.I. water to the surface to be tested and observe how well the
water
> wets the surface. It should flow out, onto the surface and not bead up
> (like on a waxed surface). As the water flows off the surface, when the
> sample is held vertical, it should sheet off in a thin film and not bead
on
> the surface for 5-10 seconds. Another method is to apply a few drops to
the
> horizontally held surface and judge the angle the meniscus makes. The
> cleaner the surface, the shallower the angle. As for identifying the
> contamination, we typically use SEM and IR Spectroscopy.
> Hope this helps.
>
> -----Rainer Blomberg
>
> -----Original Message-----
> From: marvin v. picardal [mailto:[log in to unmask]]
> Sent: Wednesday, March 01, 2000 6:34 AM
> To: [log in to unmask]
> Subject: [TN] How to detect contamination on metal surface
>
> Dear Techneters,
>
> I would like to ask some information as to
> how to detect contamination on metal surface and
> how do I determine what type of contamination that is.
> The said contamination results to poor adhesion
> between the glue and the metal surface.
>
> I do hope you would take time in helping me out with this.
> Thank you in advance.
>
> Marvin
>
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