Bryan K. Douglas wrote:
>
> With quick survey of large (10" x 20") printed board assembly (PBA), we
> found that major issues include equipment capabilities, scrap and rework
> costs, design complexity, and warp.
>
> Assuming SMT, DSR, and press in connectors would be used on this type of
> assembly, are there other major gotcha's related to large PBA? Are there
> examples of boards this size in telecommunications transmission or
> switching equipment?
We see lots of large PBA's in comms and other markets. They cer-
tainly pose the challenges you list, and I echo the other replies
but I'd like to add to the list.
Stencil vs PWB registration becomes increasingly difficult, so
expect problems as your attach pitch decreases; compensation of
both overall and feature size become exponentially more critical.
As board size increases and rise times decrease, a larger
percentage of connections become topology critical.
As connections lengthen, propogation delays and DC series resis-
tance become genuine components to be dealt with.
Use high Tg laminate, to limit damage due to reworks and accomodate
higher-energy oven profiling.
Increasing escapes in bare-board and ICT as the sheer quantity of
probes needed burden each system. Not funny is the tug-of-war
between increasing need for fault coverage and difficulty achieving
it.
Power up is a real burden on almost *any* power system, either in
situ or at ICT. On board, your power system is also tough; to
keep supply from fading 1 1/2 feet and 5-800 loads away from the
power entry. Not to mention getting that much power onto the PWB.
Someone once said that continued integration would eliminate the
BUT (big, ugly, thick) board. I believe we have simply increased
the functional block size to match capabilities. I still enjoy
the large board genre, nothing quite takes my design breath away
like starting a 10000 net board. There are also few "breaths of
fresh air" that compare to the sigh that accompanies finishing
one.
No wonder I'm balding.
Good luck, and best regards,
--
Jeff Seeger Applied CAD Knowledge Inc
Chief Technical Officer Tyngsboro, MA 01879
[log in to unmask] 508 649 9800
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