Re: [SI-LIST] : ?Dumb Question Regarding Multilayer Boards

Jeff Seeger ([email protected])
Fri, 27 Mar 1998 06:01:05 -0500

Mark Randol wrote:
> Here's the setup. I'm thinking that it's time to go to more than
> 2 layers for some of our internal boards, and some that we demo
> to customers. The objection I hear from management and co-workers
> is regarding the expense.
> I've done a little digging on my own, and it seems that going
> from a 2 to 4 layer board, in "production" quantities, raises
> the cost by about 2X - assuming the same size board. I SWAG
> snip of SWAG <
> Am I about right here, or am I dreaming? Performance, as long
> as it's "reasonable", isn't an issue. We can get that on
> a 2 layer board (mostly). EMI/EMC isn't an issue either (since
> we don't do compliance testing - yet?)

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.

Best regards,

      Jeff Seeger                             Applied CAD Knowledge Inc
      Chief Technical Officer                      Tyngsboro, MA  01879
      jseeger "at" appliedcad "dot" com                    978 649 9800