At .8 mm pitch, you are entering the world of HDI and microvias. If the
device pin count is small enough, and it's not a perimeter matrix, try to
fan out the vias as usual. If it is high pin count, and/or full matrix and
you need to do a 'dog bone' fanout or via in pad, then microvia's is the way
you need to go. Get a copy of IPC-2315 and IPC-2226 (working draft) through
the IPC. There are numerous web sites available with info on microvia
design, such as Motorola, Merix, Hadco, and DDI, to name a few. Remember to
work with your board supplier in advance. Also see the informative article
in the Feb 2000 issue of Printed Circuit Design magazine.

Good luck!

Cliff Lamson, C.I.D.
Manager, PCB Design
Plexus Technology Group
940 Main Campus Drive, Suite 200
Raleigh, N.C. 27606
919-807-8047
The Product Realization Company
www.plexus.com <http://www.plexus.com>

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