Jason

The problems may be more complex. I don't know the machine in question,
but I gather it is a closed circuit type with an in-line DI Column and
possibly carbon filter. This is a very dangerous combination a) because
most machines of this type regenerate the water slower than the water is
recontaminated b) the carbon filter (if fitted) saturates with the
non-ionics from the solvent very rapidly, so these are recirculated
straight through the system and back onto your board. These will mostly
be terpenes but there are also surfactants which are hygroscopic. c) the
drying system may evaporate the water off, leaving the non-volatile
contaminants neatly in place.

My advice with HCS products, such as EC-7R, is to a) ensure minimum
drag-out from the solvent to the first water wash, by a long hold period
and preferably an air-knife (preferably with collected and filtered
exhaust to prevent operator exposure to d-limonene). The first wash
should be lengthy (say 10 min) with a very powerful pump at a
temperature a few degrees under the flash point of the solvent, for
safety. The first rinse should be open-circuit with water taken from the
final rinse sump. The final rinse should be with freshly deionised water
at 1 uS-cm or better, without recirculation. Drying should start with
mechanical removal, such as powerful air knives, to blow out
contaminated water from under the components. Only then should you allow
evaporation.

Brian

Jason Wilson wrote:
> Hi Everyone,
>
> I am a new member to the list and I have a question on cleaning.  Thanks in
> advance for any help you can provide.  It is much appreciated.
>
> What should the value be for rinse water resistivity? The cleaner we have
> is a AAT Corp Emulsonator 9700.
>
> We use an RMA flux (both in wave solder, and in solder paste). The solvent
> we use is EC7R.
>
> Also, we currently rinse for 10 min (+ time to reach resistivity).  Does
> this seem low?  We are having trouble with board cleanliness.
>
> Once again, thanks for any help provided.
>
> Jason
>
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