Ground water is often used as a primary drinking water because of good
quality, it's quite pure and doesn't need so much chemical treatment. But
there is not enough of it in every area. To serve these areas, several water
supply systems using artificial groundwater have been constructed.
Artificial ground water is made by pumping lake water through sandy ridge.
The ridge works as a filter. If you are interested to know more about
Finnish environment and water check http://www.vyh.fi/eng/environ/
It is good that you emphasized the meaning of drying. Efficient removing of
remaining water mechanically is required.
B.R
Jarmo Kiiski
> -----Original Message-----
> From: Brian Ellis [SMTP:[log in to unmask]]
> Sent: 19. kesäkuuta 2000 10:56
> To: [log in to unmask]
> Subject: Re: [TN] Chloride - Chlorine
>
> 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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