Judy,

To paraphrase, you are going to take unsused pins and route traces to them,
from ground net without providing access via hole to them.

I don't see why this wouldn't work, but getting to them may be an issue.
You may want to evaluate option like via in pad, or step drilling if the
layer count and penetration through your planes are not allowing enough
current capacity.  You have probably already considered increased plating as
well, but that is a thought.  Since we don't know what he art looks like, we
are being general in response... I don't think clean up should be a problem,
especially if youre solder finish is electroplated variety and the mask is
properly applied over tented vias.


Rodney L. Miller, CID
VP / Director of Manufacturing
Tri-onics Inc.
ph (618) 654-9831
fx  (618) 654-6122
e   [log in to unmask] <mailto:[log in to unmask]>


-----Original Message-----
From: Kile, Judy K (MED) [mailto:[log in to unmask]]
Sent: Tuesday, September 30, 2003 4:11 PM
Subject: 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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