My experience with bacteria was similar to Doug's. I don't think we
detected the issue with ROSE test methods at the assembly level but
noticed reduced performance from the mixed beds. And like Doug's we
cleaned the heck out of everything and installed UV in-line to kill life
in the water. Here, at the EMPF today we use a similar system to prevent
growth in the lab water. But, I'm not sure how much good it would do to
kill the bacteria once deposited on the boards, which it sounds like you
are proposing. I don't recall even considering that approach.
Bev suggested that live contamination brings with it electrolytes. Would
merely killing them remove the contaminate?

I suspect that you will have to get them off the board, dead or alive.
Let us know what happens.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ed Popielarski
Sent: Wednesday, July 17, 2002 2:54 PM
To: [log in to unmask]
Subject: [TN] Bacteria


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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