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Subject:	uBGA routing
From:	Alan Groves <[log in to unmask]>
Reply To:	[log in to unmask]
Date:	Mon, 22 Apr 2002 12:19:38 +0100
Content-Type:	text/plain
Parts/Attachments:	text/plain (40 lines)

Hi Technetters, any help that could be given on following problem would be
greatly appreciated...

I am currently routing a PCB which has 532 pin uBGAs on it, these have a
pitch of 0,8mm (31,5 thou). I have followed manufacturer's design guidelines
in the past but am still receiving complaints from fabricators. I have
resolved vertically by having a 6 thou microvia drilled thru pad centres to
layer 2, then routed on layer 2 to a buried via (layers 2-7) of 10 thou
drill, 19 thou land. The track and gap allowance is 4 thou minimum. I am
using thermal connection pads of 17 (internal) and 26 (external) thou, and
isolating pads of 24 thou - all only on buried vias, I cannot increase these
pad sizes (much) or I could block GND and PWR from getting to destinations.
Fabricators complain of copper features too close to drill hole, are they
talking skew, or 'tear out' by that much (8 thou 'ish)?
The board is 1,6mm thick FR4, 8 conducting layers, no controlled impedance.

Can anyone suggest any tricks or tweaks to sizes that would assist?

Thanks in advance,

Alan Groves,
Senior PCB Designer CID
Spectel Head Office, 21 Stillorgan Ind. Park, Stillorgan,
Co. Dublin. Ireland.
Phone: 353 907 62803
Fax: 353 1 2953740
Email: [log in to unmask]
Internet: www.spectel.com

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