All I can tell you is that I've used via in pad on a very tight board once.  We didn't have any problems with it, but I do hear that there can be an issue with flatness.  If you have a reliable board house that can deal with this process, it shouldn't be a problem.  I wouldn't try to put it thru the solder wave, and I'd make the vias part of the cap pads to avoid drc errors.
Good Luck with it!

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of Gary
Boccoleri
Sent: Wednesday, December 08, 2004 7:04 PM
To: [log in to unmask]
Subject: [DC] FW: Bypass caps under BGAs using via in pad


pad

Hi All,

I'm looking at a spec for a new processor we may be using. They
recommend using via in pad and show a diagram of how to place 0402
bypass caps right on the vias under the chip. Has anybody done this?
This brings up a few questions. Since 2 adjacent vias will form the
footprint for the caps, should I make the bottom pad of the via a square
that approximates the pads I normally use on these caps? How do I place
the caps without creating DRCs? Will our assembly house be completely
dumbfounded when they see this? Is this whole idea just a figment of
some engineers imagination with no basis in reality?

Thanks for all help 

Gary Boccoleri
Bivio Networks
925-924-8621
www.bivio.net
 


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