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November 2009

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Subject:
From:
Chris Mahanna <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Chris Mahanna <[log in to unmask]>
Date:
Mon, 30 Nov 2009 22:04:15 -0500
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Hey Doug and Dave,
out of curiosity-
So why not use an underfill material as the coating?  Do you not trust the electrical properties of the underfill, or is it a processing issue (e.g. wetting,voids...)?

Chris

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Monday, November 30, 2009 11:52 AM
To: [log in to unmask]
Subject: Re: [TN] BGAs & Conformal Coating

Thank you Steve for posting the pictures.  Here are the links.
 
http://stevezeva.homestead.com/files/deformed_Balls.jpg
 
http://stevezeva.homestead.com/files/Squished_Ball_1.jpg
 
http://stevezeva.homestead.com/files/Squished_Ball_2.jpg

To give a little background, we have certain design engineers who 
absolutely, positively believe that every ball on a BGA must be coated 
with conformal coating or it will fail in humidity.  They put silly notes 
on the engineering drawing to this effect, resulting in conformal coating 
being used like an underfill or a potting material.  Dave Hillman and I 
did an internal study this last year to demonstrate the effects.  We 
forceably filled the area under the BGAs with conformal coating, one a 
popular solvent based acrylic, the other a water based acrylic urethane. 
We left the material come to a tack free condition, fully cured the 
material, and then put it through thermal cycling, monitoring resistance. 
The cycle was -55C to +125C, 15 min dwells at either extreme, 8-10C/min 
ramp rates.  The test ran for a little over 2100 cycles.  The solvent 
based acrylic had a 73% failure rate by the end of the test.  The water 
based acrylic urethane had none.  The pictures are all of the solvent 
based acrylic, which has a higher CTE than the acrylic-urethane.  We 
tested BGAs, QFPs, a couple of QFNs, and some SOICs.  The only significant 
failures were for the BGAs.  Can't really say much more than this.

Doug Pauls
Rockwell Collins



"Steve Gregory" <[log in to unmask]> 
11/30/2009 07:33 AM

To
"'TechNet E-Mail Forum'" <[log in to unmask]>, <[log in to unmask]>
cc

Subject
RE: [TN] BGAs & Conformal Coating






Hi Doug!

Send them here: [log in to unmask]

Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Monday, November 30, 2009 8:29 AM
To: [log in to unmask]
Subject: Re: [TN] BGAs & Conformal Coating

Good morning Juan,
I suspect that Xilinx wants you do do a thermal cycle study on solder 
joint reliability when conformal coating gets under the BGA.  The stresses 

brought about by a mismatches in the coefficient of thermal expansion 
(CTE) can rip a BGA off the board and can severely deform the balls. 
Hillman and I did such a study here a few years ago.  I can share a few 
pictures of what happens, if Steve Gregory would be kind enough to forward 

his present e-mail address for the photos.  Not sure I have the right one.

Doug Pauls



"Juan T. Marugán" <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
11/26/2009 11:53 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Juan T. Marugán" <[log in to unmask]>


To
[log in to unmask]
cc

Subject
[TN] BGAs & Conformal Coating






Hi,

I've read in a Xilinx guide that: "Xilinx has no experience or reliability 

data on 
flip-chip BGA packages on board after exposure to conformal coating. It is 


recommended that the end-user should characterize the board level 
reliability 
performance of Xilinx packages before production use."

Does anybody know any infomation or study related with this topic?

Thank you.

Juan T. Marugán
Indra Sistemas SA
Espańa

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