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TechNet E-Mail Forum <[log in to unmask]>, Inge <[log in to unmask]>
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Mon, 30 Nov 2009 22:26:21 +0100
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I forgot to mention, that I have seen how the solder balls elongate during 
pull or prey test. They change from a flatted ball to a barrel. That means 
that the volume between the BGA and the board nearly doubles! I was very 
surprised. Didn't think solder was like chewing gum. Does the coating or 
underfiller really expand that much?
I'm very interested in this, as we produce boards with a lot of largest 
available BGAs.

Inge

PS. Will see if I still have the amazing photos from the test.

----- Original Message ----- 
From: "Inge" <[log in to unmask]>
To: "TechNet E-Mail Forum" <[log in to unmask]>; <[log in to unmask]>
Sent: Monday, November 30, 2009 10:15 PM
Subject: Re: [TN] BGAs & Conformal Coating


> Doug,
>
> how can that be possible? When temperature rises, the coating ought to 
> soften and should expand even horisontally, and when at lower 
> temperatures, the coating should crimp. The only way I can see is if you 
> have the situation of a closed in liquid, which one cannot be compressed.
> BGAs use to be very hard to rip from the board. I measured some 350 kg 
> force necessary to pull off a very large BGA.
>
> Inge
>
>
>
> ----- Original Message ----- 
> From: "Douglas Pauls" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Monday, November 30, 2009 2:29 PM
> 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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