Charlie
I hate the term "semi-aqueous", not only because monohydrogendemioxide
doesn't exist but because, psychologically, it is very misleading,
implying, as you say, that a simple rinse is sufficient when, in fact,
the wash/rinse cycle must be at least as good as if you were cleaning
off water-soluble flux residues. The process is to solubilise the
residues in a solvent and then to clean off the solubilised residues.
This is why the United Nations have opted for the alternative title HCS
or hydrocarbon/surfactant, which is more descriptive and scientifically
more correct (originally, when it was a terpene/surfactant mix).
Actually, historically, the term goes back to London Chemicals'
Loncoterge 444 series saponifiers in the 1960s, then DuPont pinched it
for their Axarel and that's how it got stuck to where it is today.
How many people have come to grief because they did not wash off the
solvent+residue mix well enough? Legions.
Brian
Charlie Pitarys wrote:
> Just saw this on the net in regards to cleaning BGA's
> http://www.circuitnet.com/articles/article_2811.htm
>
>
>
>
> In regards to bench top/ rework cleaning....
> I think the assembly world in general has a mind set that hydrocarbons,
> terpenes and ester solvents are all that is available in bench top
> cleaning.
>
> Brian is correct and his statement closely relates to rinsing of
> solvents that are not water miscible. This was why the rinse sections in
> some of the semi aqueous inlines built years ago were 2x to 3x longer
> than the wash sections. Kind of hard to dissolve an oil so pressure and
> time was required to remove the cleaning solutions. Great effective
> cleaners, just hard as hell sometimes to rinse out under components,
> inside connectors, etc. No transfer this chemical process to the
> bench.......?
>
> An easy check to see on how your cleaning solvent/agent dissolves
> (miscible) in water is in most cases listed on the msds in Section 9
> "Physical and Chemical Properties" or some labeled section closely
> described as "Physical Data". If there are words like "insoluble",
> "negligible" or "emuslifiable" next to the title "Solubility in Water".
> Then your rinsing process should get just as much or more attention as
> the wash process.
>
>
> Today there is the option to use semi-aqueous solutions on the bench
> that that are 100% water miscible. When these semi aqueous solutions mix
> with water they consequently lower the surface tension of water (now the
> water is able to get under these low stand off components) and allow for
> complete and effective rinsing.
>
> Regards,
>
> Charlie
>
>
> -----Original Message-----
> From: Brian Ellis [mailto:[log in to unmask]]
> Sent: Sunday, April 27, 2003 3:09 AM
> To: [log in to unmask]
> Subject: Re: [TN] cleaning under BGAs
>
>
> Big problem! IPA is not a good solvent for flux residues and is
> flammable and must be used, especially if spraying, in a
> flameproof/explosion-proof zone. Whatever mechanical method is used with
> whatever liquid, you need to establish a cleaning protocol (method, time
> and temperature + safety margin).
>
> Remember that, if you apply, e.g., a saponifier or an alcohol, the
> residual liquid is a dangerous, ionic, chemical and has to be thoroughly
> removed by several successive rinses. This is more difficult than the
> initial cleaning, as each rinse must displace the liquid which is firmly
> lodged there by capillary forces. It is absolutely no use just passing
> it through a cleaning machine unless you can be sure that every
> microgram of liquid is eliminated and replaced by clean water. For
> example, if you use a "water-pik" or similar, you should have another,
> more powerful one, with pure DI water, just to displace the contaminated
> liquid. If the cleaning takes 5 minutes, for example, the rinsing may
> take as much as 15 minutes before you have a satisfactory level of
> cleanliness in the middle of a large BGA.
>
> Much better and cheaper would be to use a "no-clean" flux and not to
> attempt to clean, at all. Remember the old adage, dating back 40-odd
> years, "Poor cleaning is far worse than not cleaning".
>
> Brian
>
> Macko, Joe @ IEC wrote:
> > Fellow Technets,
> >
> > Periodically, BGAs are reflowed using our AIR-VAC hot air rework
> station.
> > RMA liquid flux is 1st flowed under the BGA prior to reflow and then
> clean
> > afterwards starting with IPA spray followed by an in-line cleaner wash.
> > Occasionally, flux residue remains which requires additional cleaning.
> >
> > I am in need of a creative and operator safe way to either spray/flow
> warm
> > IPA or a mixture of hot saponifier/DI water (from our in-line
> cleaner) under
> > BGAs to expedite cleaning. I do not know of any equipment on the market
> > that can be used for this application.
> >
> > Welcome ALL suggestions and proven methods. thanks
> >
> > joe
> >
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