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May 2009

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Subject:
From:
Vladimir Igoshev <[log in to unmask]>
Reply To:
Date:
Wed, 27 May 2009 15:39:24 +0000
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Great point George! That is exactly what I suggested a few e-mails earlier: data are much better than guessing :-)



Vladimir

SENTEC

SENTEC

11 Canadian Road, Unit 7.

Scarborough, ON M1R 5G1

Tel: (416) 899-1882

Fax: (905) 882-8812

www.sentec.ca





-----Original Message-----

From: "Wenger, George M." <[log in to unmask]>



Date:         Wed, 27 May 2009 11:02:18 

To: <[log in to unmask]>

Subject: Re: [TN] humidity test failure





Without some analytical data it is difficult to determine

Wayne,



Without some analytical data it is difficult to determine exactly what

the problem is.  The photo you sent Steve appears to show flux residue

coming from under the capacitor rather than a dendritic growth but an

analysis should be able to tell what it is.  I don't have lots of

experience with Axarel 2200 but I do know that IPA isn't an effective

cleaning solvent for RMA and soak tanks are certainly not an effective

process for cleaning flux residue from under chip capacitors.



My experience in the Bell System has convinced my that using Bellcore

(Telcoria) compliant fluxes, which I call 'leave-behind' because if you

don't clean them off they aren't a reliability issue, you wouldn't see

dendritic growth if the flux residue wasn't cleaned off.  However, the

worst thing you can do when using a Belcore compliant RMA flux is to use

try and clean if off with marginal cleaning solvent/process because all

you wind up doing is removing most, but not all, of the rosion/resin

which was trapping the ionic activators thus allowing the ionics to

cause problems when heat and humidity are applied. 



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: Thayer, Wayne [mailto:[log in to unmask]] 

Sent: Wednesday, May 27, 2009 9:50 AM

To: 'TechNet E-Mail Forum'; Wenger, George M.

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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