In order to give you an meaningful answer I think we need
Wayne,
In order to give you an meaningful answer I think we need more
information from your side.
1. Where the capacitors wave soldered or reflow soldered?
2. What type of flux was used?
3. What solvent was used?
4. What type of cleaning process was used?
Regards,
George
George M. Wenger
Andrew Solutions
Senior Principal FMA/Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 (Office) (732) 309-8964 (cell)
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden
Sent: Wednesday, May 27, 2009 8:24 AM
To: [log in to unmask]
Subject: Re: [TN] humidity test failure
Looks like whatever it is it may have started from residues leaching
from
UNDER the component. The voltage bias and environment would have only
accelerated this. The solder joints exposed to the cleaning process
look
fine. You should review your cleaning procedures and perform testing
(IC/SIR) to determine if you are adequately cleaning, rinsing, and
drying to
remove contaminants from under low-standoff components. My suspicion is
that if that is in fact the case, and you decided to try to conformal
coat,
the problem would have only manifested itself sooner with conformal coat
adhesion problems.
-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Wednesday, May 27, 2009 8:00 AM
To: [log in to unmask]
Subject: Re: [TN] humidity test failure
Good Morning!
Half the week down already. That's another nice thing about 3-day
weekends;
you also get a 4-day work week either prior to, or after the weekend.
I have Wayne's picture posted now. It's at:
http://stevezeva.homestead.com/files/C23_Humidity_failure.JPG
Definitely some kinda' junk there!
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne
Sent: Tuesday, May 26, 2009 9:01 PM
To: [log in to unmask]
Subject: [TN] humidity test failure
Hi Technet Gurus!
I have attached a picture of a part responsible for excess current draw
during an extended humidity/temperature cycling test. (I copied Steve so
he
can hopefully post!)
The board was carefully solvent cleaned, but no SIR test validating the
process strips all ionic contamination. The board is in an enclosure
where
plenty of ionic contaminants are available.
Humidity was supposed to not exceed 90% and was to be non-condensing
during
cycling. There were a handful of components which displayed similar
deposits on the same circuit board. These were the only parts biased
during
the humidity test. I believe the evidence suggests at least some
condensation occurred. To me the deposits look like salts.
But what do "the experts" think?
Is there any rule of thumb as to humidity levels where we are nuts to
try to
survive without conformal coating? Part of the adjacent circuitry
contains
RF devices and those guys get panic-stricken when told we probably need
to
conformal coat!
Wayne Thayer
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