RE: [SI-LIST] : GND on the outer layers

Dawson Yee (dawsony@microsoft.com)
Fri, 16 Jul 1999 10:03:07 -0700

I've done both 4l and multi-layer PCB's with solid reference planes on the
outside (in my former life at another company).
The system operating frequencies were <500 MHz (with corresponding edge
rates) and quantities in the millions (should be by now I think). This was
done with standard technology PCB: FR4, through the board drilled VIA's,
SMT(Soic,PQFP,BGA) + THM, dry soldermask. No pad in VIA, blind, buried,
laser, fine lines or other expensive stuff.

Just be sure to make the stack up symmetric to avoid warpage. Package pads,
escapes and break outs have to be done carefully (short, well thought out,
and referenced).

Results in all cases were lowest observed EMI, and the first PCB being
production worthy (i.e. No EMI, Mfg, Power Delivery or Signal integrity
issues). You have to do your homework up front and sit with the layout
person and walk them through the design, check, check and keep re-checking.

If you don't do your homework up front, board spins won't help you
(especially when all of the interconnect traces are buried)...you can't blue
wire! Of course, you HAVE to do the Signal Integrity analysis at these
frequencies and edge rates.

Regards, Dawson Yee

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