As Rudy said and another member often quotes, "it depends"! Mainly on
the water quality, your cleaning process and your application, as well
as the desired reliability of your products.
The first thing I would add is NEVER use softened water, as this
exchanges relatively benign calcium/magnesium cations for electrically
dangerous sodium cations.
If your tap water has a conductivity of, say, <200 µS-cm and has a low
sodium and potassium content (say, <10 ppm), you will have a better
chance than >400 µS-cm or >50 ppm Na or K. Note that this is only a
rough guideline with no responsibility incurred or offered.
Your cleaning and, especially, drying process is also critical. Above
all, if >90% of the residual water on the assemblies is removed by
mechanical means (very violent air knives from different angles, rapid
centrifugation etc.), then you will have a better chance of getting away
with it. If you dry by evaporation, even with an air flow, then you may
be better to forget the idea, especially with iffy water quality,
because the dissolved solids will dry out exactly where you least want
them, under the components and round the solder joints.
I used to make high tech batch washers and dryers of a type no longer
available on the market (they cost more than small in-line machines).
The dryers used rotary air knives with a velocity of ~200 km/h which
really blasted 90% of the water away in a few seconds, even from under
large components with a 0.1 mm spacing, the rotation ensuring varying
angles. Although most of my clients used DI water, a few used tap water.
One, in particular springs, to mind, as he was situated in the Jura
mountains with his water coming from wells in limestone. The water was
so hard you would not believe it (but excellent drinking water), but he
got away with it. His product was not particularly hi-tech nor used in
harsh environments. Prior to buying my machines, he used a "dishwasher"
type and he had real problems with failures from lime deposits. He did
not want to go DI as he was afraid that the resin life would be too
short, with his hard water, to be economically viable.
Another factor you may wish to consider was with a client in Germany who
also used tap water. The problem he had was that the water, when heated
in the machine, deposited solids onto the stainless-steel walls and
heaters. He found that machine maintenance was prohibitively expensive.
He therefore, on my advice, installed a deioniser and found that what he
saved on maintenance costs more than paid for the cost of deionising the
water. In addition, he increased his throughput as the machine down time
was cut by 80%.
Brian
Chafin, Ken G. wrote:
> This question may not provide adequate information for an unequivocal
> answer but I need to get something going.
>
> Is it practical or common for a PCB Assembly House to achieve desirable
> cleanliness levels (e.g. x micrograms equivalent NaCl per square inch
> per IPC-A-610 default) without using deionized water in their aqueous
> cleaning process.
>
> If practical is it common?
>
> Are there significant risks of leaving inorganic residue entrapped in
> areas?
>
> Thanks
>
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