Judy,  One word of caution.  If you ever have to remove the BGA for any
reason, and have to clean up the PWB, chances are that you might damage (or
completely remove) the solder mask on the dog bone pattern.  I would suggest
moving the ground layer to layer 2 and have "pads only" on layer 1.

Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]>
631-595-5879


        -----Original Message-----
        From:   Kile, Judy K (MED) [SMTP:[log in to unmask]]
        Sent:   Tuesday, September 30, 2003 5:11 PM
        To:     [log in to unmask]
        Subject:        [TN] BGA780 tied directly to gnd plane

        Hello,
        I am looking for potential issues with a proposed design "solution"
on a
        780pin BGA.

        Reason for this approach
        1.) reduce ground bound to this BGA by tying unused pins to gnd
        2.) minimize routing layers

        Proposed solution for the 1mm 780 BGA is to tie the BGA pads
directly to

        a gnd plane (top side assembly & plane) very similar to the dog bone
        pattern.
        The thermal tie will be 1 "spoke" and covered with soldermask.

        There is ~25-30 unused pins that would be tied in this manner.

        ???
        1.) What are the potential assembly issues with solution?
        2.) Are there any reliability issues long term?
        3.) Are there other issues with this design proposal?

        Thanks for your advice,

        Judy Kile
        Global Electrical Technology Center
        Phone: 262-548-2241
        Fax: 414-908-9584

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