I'll make a WAG of my own that from your affiliation (Semi-
conductor Products) that you're talking about test and/or
eval type boards.
My knee-jerk reaction is that if your performance and EMC
envelopes are currently adequate w/2 layer boards, it may
be testamonial to the product you're showcasing. "Look, its
even works on TWO layers!" These two elements, combined
with density, are the usual motivators for multilayer boards.
You mention possible space savings only in passing. What
do you seek to buy with your 1.5-to-2x cost increase if
you're not driven there by density, performance, or EMC?
(just food for thought).
OTOH, it does sound like you are having occaisional per-
formance issues with the two layer solution. I suspect
that when those grow to have costs associated with them
(extra spins, too much time in layout, or too much spent
on hardware-based shielding) you'll have the justification
for the jump to multilayer.
-- Jeff Seeger Applied CAD Knowledge Inc Chief Technical Officer Tyngsboro, MA 01879 jseeger "at" appliedcad "dot" com 978 649 9800