Alexis,
  We used via in pad for some through-vias and blind vias.  They were
all small (~.014in) BGA pads.  All the holes were filled with
non-conductive material, planerized and plated.  Manufacturing had
issues with the solderability of the VIPs.  
   We discontinued the practice due to cost and manufacturing issues.
We were also able to use other routing methods and footprint types to
avoid them.  I am confident we would have overcome the issues had we
worked more on the problem.
  I don't believe the same manufacturing problems will exist on the
larger 0603 pad if you are using a small hole size.  You should to talk
to your fab house to see if it's cheaper/easier to fill all of the holes
vs. selectivly filling.  In addition, I would suggest specifying the
planarity requirement on the fab drawing.

Best Regards,
Brandon G. Luther  C.I.D.
Design Services Manager
Dataram Corp
609.799.0071 x3481
[log in to unmask] 

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Alexis Meehan
Sent: Wednesday, January 28, 2009 10:00 PM
To: [log in to unmask]
Subject: [DC] Via-In-Pad

One of our engineers has asked if we can implement via-in-pad on a
handful of 0603 pads to facilitate routing of critical lines. We've
never done it here before, and I know that it increases both fab and
assembly costs. I'm also concerned about the risks involved (trapped
solvents, rising via plugs, etc). Has anyone out there used this
technology on only a few components with success (and minimal problems)?
I'm not sure if we should be doing this on a layout spin that needs to
be our production version. Thanks in advance for any feedback.

Alexis Meehan
Opnext Subsystems, Inc.
Desk: 408-385-3040

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