Jarmo

What is artificial ground water? 100 uS-cm is quite low for tap water.

In fact, the key factor in using a reasonable quality tap water is not the washing but
the drying. If you remove the water mechanically (centrifugation or air-knifing), then
most of the residual impurities from either the water itself or from the successive
dilutions of the flux residues will be removed with it, using little energy. If you dry
by evaporation, not only will you require typically 10 times as much energy, but all
the impurities will be left on the circuit, usually close to the solder joints where
they can cause the most harm. We have found that, on a medium density single-sided
typical SMD circuit, the retained water before drying is about 4 - 6 g/dm2 (obviously
~ pro rata to the density). This may not sound much until you multiply the figure by
the number of dm2 of a day's production. In most cases, we no longer speak of g but of
kg and g of residual contamination in the water to be eliminated. With rotary air knife
drying over minutes, I know of companies using tap water with conductivities in the 300
- 500 uS-cm range, quite successfully, with no drying marks and no reliability
problems, even for critical apps. Notwithstanding, I feel DI water is generally a safer
approach, in most cases.

If you care to contact me privately, I can expand on this.

Brian

Kiiski Jarmo wrote:

> We in middle of Finland have used artificial ground water for washing PCA's
> after wave soldering with water-soluble flux for over ten years with
> excellent results. The quality of water is:
> pH: 8,5
> Hardness: 2 dH (soft)
> Conductivity: 100 microS.
>
> Don't understand that so that if you have similar water, you will get
> similar excellent results. It only shows that it is possible.
>
> The quality of water is one of the most important factors when washing PCA's
> among the time and temperature. I believe that this conversation has been
> very useful for many of us. Sometimes very simple thing (like just water)
> can turn very complex matter and things are not any more like they were
> before. I appreciate courage and enthusiasm of you all TechNetters to share
> you knowledge with this community.
>
> B.R.
> Jarmo Kiiski
>
> > -----Original Message-----
> > From: Brian Ellis [SMTP:[log in to unmask]]
> > Sent: 17. kesäkuuta 2000 11:12
> > To:   [log in to unmask]
> > Subject:      Re: [TN] Chloride - Chlorine
> >
> > Sorry, Franklin, it is not semantics. You are putting forward a scientific
> > statement
> > and the essence of science is precision. Hopefully, your "crystalline
> > growths" were
> > mostly calcium/magnesium hydroxides, carbonates and hydrocarbonates, which
> > are common
> > in many tap waters, rather than chlorides. Calcium chloride is
> > physiologically not very
> > good, especially for children, and excess sodium chloride (>~400 mg/l) is
> > worse for
> > hypertensive patients.
> >
> > Interestingly, chlorination can produce minute amounts of hydrochloric
> > acid if the
> > water has a heavy microorganic content and this may react with dissolved
> > calcium
> > hydroxide (lime) to produce calcium chloride, but the quantities involved
> > are
> > negligible. Care should always be taken to introduce sufficient chlorine
> > to kill off
> > the microorganisms but not sufficient excess chlorine that the water
> > becomes
> > objectionably odoriferous. It is for this reason that UV irradiation is
> > sometimes
> > preferred, by itself or as a pretreatment before a milder chlorination, as
> > a biocide,
> > e.g. in desalination plants for potable water. Incidentally, the NaCl
> > limit for many
> > desalination plants is ~400 - 800 mg/l, but this is often mixed with
> > ground water or
> > other sources in the reservoirs, to dilute it down to under 200 - 300 mg/l
> > NaCl. About
> > 800 mg/l is the threshold of taste.
> >
> > Anyway, not all municipal water is bad. In Scotland, for instance, many
> > highland lochs
> > have negligible TDS. In fact, Loch Katrine is a major reservoir for
> > Glasgow and they
> > actually add some lime to it because the water is so soft, with a pH of
> > about 5,5, that
> > it corrodes the cast iron conduits (not to mention kid's teeth and bones).
> > In Glasgow,
> > before the 39-45 war, over 1/3 of the kids had rickets in some degree or
> > other because
> > the water was so poor in calcium and they drank little milk (heavily
> > depressed area and
> > milk was beyond the purses of many households). I know some plants in some
> > parts of
> > Scotland that use unpurified water for  cleaning PCBs, quite successfully,
> > but this is
> > the exception that proves your generalisation.
> >
> > Brian
> >
> > Franklin D Asbell wrote:
> >
> > > Semantics, or the wrong choice of word, contaminates in the city water
> > > rinse used at that company caused crystalline growth as evident by SEM
> > > and Auger analysis.
> > >
> > > The point being city water....bad!!!
> > >
> > > ~grin~
> > >
> > > Sorry to stir the pot...
> > >
> > > Franklin
> > >
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