[SI-LIST] help with a stack ??

hello,

for the first time, i've got ecl and ttl on the same
board.  so i've got two power planes and i figure on
matching them with a ground plane each, with a narrow
core between to give me a good switching capacitance.
here's what i have in mind for an 8-layer stack:

critical traces
gnd
-5.2V
noncritical traces
noncritical traces
+5V
gnd
critical traces

does this seem reasonable?  if no, then could you 
suggest an alternative?  if yes, then how should i
tie the two grounds together.  that makes me very
nervous.  would a bunch of vias do the trick?  should
i only have one ground?  should i put one of the non-
critical trace layers between a power and ground?

and another thing.  the board shop roughly doubles the
price of the board if i want to do controlled impedance
and designate the core thickness.  this is just a proto
board, so what i'm thinking is that if a        NORMAL core 
minimum is around 6 to 7 mils, then with an 8-layer
board at a standard 62mil, they can't help but give me
about a 6 to 7mil core, without me paying extra to spec
it.  is that reasonable, or faulty thinking?

thank you, miker


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