Hmm kind of long established process.
IMHO
Assuming this is a new problem on established process the most likely answer
is insufficient cleaning and most likely cause is process control.
RMA flux looks quite bad after high humidity, it effloresces to large off
white deposits, look like dry rot fungi similar to your pic. Part removed
flux behaves the same.
Try touching with a hot iron or blow with hot air and see what happens.
Break some components off cold and see what you have underneath and then do
same.
If deposits stay same appearance then likely you are growing Ag migration
from component terminations in conductive path left by ionics from redcued
cleaning efficiency under device.
Either way solution is same just a matter of degree.
What is your process control measure for cleaning process?
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne
Sent: Wednesday, May 27, 2009 2:50 PM
To: [log in to unmask]
Subject: Re: [TN] humidity test failure
1. Air convection reflow.
2. RMA
3&4. Axarel 2200 then IPA in soak tanks with circulating pumps.
Thanks!
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Wednesday, May 27, 2009 8:31 AM
To: [log in to unmask]
Subject: Re: [TN] humidity test failure
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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