FreeLists / si-list / [SI-LIST] Re: BGA routing

["Ken Cantrell" <Ken.Cantrell@xxxxxxxxxxxxxxxx>]

Darshan,
My understanding from the CAD guys is that you get a lot of cold solder
joints from outgassing at the via site, even with micro-vias.  The fill on a
via is never flat, there is a small void.  When you flow the BGA on top of
that, the trapped gas expands and forms an even larger void in the ball-pad
interface.
Ken

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Darshan Mehta
Sent: Thursday, November 11, 2004 4:41 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] BGA routing


Hi All,



I have one general question regarding BGA routing. I have seen many BGA
boards and nobody puts via exactly below the BGA pad. Most of the times, we
generate Fanout outside the BGA pad. Is there is a specific reason for that?
I think we can save lot of space if we put via exactly below BGA pad. Is
there will be any problem if we put via exactly below the pad of BGA?
Thanks.



Best Regards,

Darshan Mehta




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