hi,
i'm sorry too, because the water-break-free test is not as useless as the name is long. for example, it is a very quick and inexpensive test to determine whether or not aluminum substrates have been adequately prepared (for example with the forest products laboratory fpl etchant) for structural bonding with epoxy adhesives. it's been used forever. of course it has limitations, but who wants to perform sem analyses on every surface prior to bonding in a production environment. i mean, cut a little slack.
phil
-----Original Message-----
From: Brian Ellis [mailto:[log in to unmask]]
Sent: Wednesday, March 01, 2000 8:08 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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