Ed

I'll break silence over this one. Firstly, IMHO, this is a great danger
from closed-loop systems. Microorganisms are not killed without specific
measures. UV irradiation, followed by ultrafiltration, is one method.
Without ultrafiltration, the microorganisms "corpses" will still be
present but there will also be a small proportion of live ones which
will thrive on the cannibalistic food source of the dead uns. The
ultrafilter membranes will need backwashing daily to eliminate this
organic soup.

Better still, clean with a sterile open loop system, at least for the
final rinse. If you add 10% IPA to the final rinse, this will help kill
any residual live organisms or inhibit their reproduction, it will
facilitate drying and the reduction of surface tension will allow better
penetration into the traps where the beasties can proliferate.

Brian

> Ed Popielarski wrote:
>
> Hi 'netters,
>
> I have a client that is building extremely high impedance low voltage
> assemblies (counting electrons from a photomultiplier type
> circuit) that recently are failing test due to "leakage" They are
> running water soluble flux with an SMT type aqueous cleaner fed by
> closed loop D.I. water 1Meg/cm3 or better. Dynamic Ion testing shows
> very good results. They ran a culture and found very high bacteria
> counts, well beyond fed drinking water standards.Subsequent cleaning
> at the end user site (conditions unknown at this time) seems to
> resolve the failures. I suggested UV sterilization (not too
> expensive/risky) and also to verify "under soldermask" cleanliness as
> well as "localized" contamination sites which "average" into the
> overall assembly.
>
> My question is if anyone has had any electrical failures due to
> bacteria in the rinse water and what solution(s) were successful. Any
> other suggestions or suspicions would be appreciated.
>
>
> Regards,
>
> Ed Popielarski
> QTA Machine
> 10 Mc Laren, Ste D
> Irvine, Ca. 92618
>
> Phone:949-581-6601
> Fax: 949-581-2448
> Cel: 949-337-2578
>
> WWW.QTA.NET
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