All of our present BGA designs incorporate via-in-pad technology.
(Something like a .035" pad with .020" via., 8 layers, .062 thick)  The via
is epoxy filled and plated over with Cu then HASL.  We've been using this
design for many years, even before BGAs, where real estate was a problem.
We had many designs with vias in SMT pads.  It has been tough over the years
to find a supplier who can provide a quality produce consistently.

Jim Marsico
Senior Engineer
Production Engineering
AIL/Electronics Systems Group
An EDO Company
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        -----Original Message-----
        From:   Michael Forrester [SMTP:[log in to unmask]]
        Sent:   Thursday, March 08, 2001 4:25 PM
        To:     [log in to unmask]
        Subject:        [TN] MicroVia In Pad Vs Silver VIA fill

        We currently have a design with  15 X 15 array BGA patterns a 12
layer 0.62 bd.
        There are 10 mil vias in every BGA pad (22 mil pad) .
        The reason for the Via in pad is keep the runs as short as possible.
Currently
        we fill the vias with conductive silver epoxy and plate E Ni/I Au
        over the entire pad surface.  I would like to try a microvia in pad,
no via
        fill, and OSP.  My questions are:

                  1) Can I get away with not filling the microvia to prevent
solder
        thieving?
                  2) Are there any problems with this approach?  If NG,
other ideas to
        get rid of silver fill?
                  3) Is there any disadvantage/reliability risk, to using
silver via
        fill other than cost and longer lead time?

             Thank you in advance.

        Best Regards,

        Michael Forrester


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