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November 2009

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Subject:
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Werner Engelmaier <[log in to unmask]>
Date:
Mon, 30 Nov 2009 10:26:00 -0500
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 Hi Rex,
Right you are.
It actually gets worse.As was found out, the modulus of elasticity is very important to the working of an underfill material because in most cases—and when CC gets under a component, it is an 'underfill,' unintentional as it may be. The modulus in most cases is measured in tension, while the loading is in compression—not the same thing. Now the question of course, becomes, how compressible is this material?
Werner

 

 

-----Original Message-----
From: Rex Waygood <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, Nov 30, 2009 9:56 am
Subject: Re: [TN] BGAs & Conformal Coating


I am not a materials expert but I've always wondered if a quick glance at the 
linear coefficients of expansion was inadequate to evaluate the stresses applied 
by a thin layer of organic material under a large device.
At the centre of the device the edge may appear to be at 'infinity' therefore an 
elemental cube of the material at the centre will experience a linear expansion 
3 times the unconstrained linear expansion. This makes the assumption that the 
bulk modulus (k) of the material will be very high.
Can anyone tell me if my wonder is right or wrong?
Rex 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: 30 November 2009 13:29
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]
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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
España

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