Leo
As you say, the physics of wetting is very complex and it would require
much more space than would be politically correct here, to give a full
explanation. Suffice it to say, and this you can prove empirically any
day, that if you take a perfectly clean metal (unoxidised) or glass
surface (no fillers or any other additives), the rougher the surface,
the easier it is to wet with pure DI water (no surfactants), where a
glossy one will be difficult. Reason: the high surface tension of the
water holds the water between the asperities. This is one of the reasons
why the so-called water-break test is valueless as a means of
determining cleanliness. As often as not, a surface that passes this
test is one which is contaminated with a monolayer of surfactant packed
tight by Van der Waals' forces.
Brian
Leo Roos wrote:
>
> Hate to throw water on your "classic explanation" but you should look at
> surface energies for spreading or beading up of water on either matte our
> gloss surfaces. When water beads up there is high surface tension
> (dynes/cm2) and visa versa. Matte surfaces tend to have additives to
> disperse the fillers etc. that seem to have an effect on the surface
> tension. However, there are many theories floating around regarding the
> differences. A paper, presented many years ago by Allan-Bradley might help
> to give a better explanation that is to detailed for here.
>
> Leo Roos
> ----- Original Message -----
> From: "b_ellis" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Wednesday, June 19, 2002 1:04 AM
> Subject: Re: [TN] Washing Semi gloss boards.
>
> > Sorry to be negative, but, in all probability, you could be suffering
> > from the problems often engendered by a closed loop system which doesn't
> > remove all the chemicals effectively. I ALWAYS recommend the final rinse
> > to be an open circuit one with freshly deionised incoming water, unless
> > you have a VERY sophisticated recycling system that will remove all the
> > organics (carbon filters are effective only for a given range of
> > molecule sizes and, even then, only if they are changed/regenerated
> > regularly: they are quickly overloaded by flux components). The
> > difference between glossy and matt is classic: water will spread more
> > readily on a structured surface and form globules on an unstructured
> > surface of a similar composition. It isn't because there is more
> > residual contamination on the glossy surface: you just see it more
> > easily.
> >
> > Brian
> >
> > [log in to unmask] wrote:
> > >
> > > Hello fellow Technetters
> > >
> > > I have been reading the postings for a long time, thought this would be
> > > a good place to get my questions answered.
> > > I have an Aqueous technology batch cleaner.
> > > The cleaner washes the board then go into a drying cycle.
> > > It is a closed loop system with a 5 micron filter.
> > > Everything I use in my process is water soluble.
> > > Everytime I wash semi-gloss finish boards there are water spots all
> > > over the boards.
> > > Mat finish boards come out spot less.
> > > Has any one experience this before ?
> > > Why is this happening ?
> > > Do I need to add any chemical or solvent to the water?
> > >
> > > Any comments would be greatly appreciated.
> > >
> > > Thanks in advance
> > > Carl.
> > >
> >
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