Re: gEDA-user: six-layer stack

[sdb@xxxxxxxxxx (Stuart Brorson)]

> 
> My question to this group (thanks for your patience) is whether this
> Adv.Cir. six-layer stack is typical for the industry?  

The web page you linked to is not really a stackup.  Rather, it is
just a drawing showing  where they use prepreg vs. core material.  

> Or are there
> just as many companies out there for whom my original concept is
> standard?  I think I read that commodity motherboards have recently
> moved from four layers to six.  What's their typical stackup?

The usual  six layer stackup looks like this:

----  sig ----

====   gnd   ====

----  sig ----

----  sig ----

====  pwr/gnd  ====

----  sig ----

Notes:  The layers need to be symmetrical in the vertical direction to
prevent board warpage.  The above stackup also gives each sig layer a
reference plane next to it.  The laminate thickness between the two
inner sig layers should be large. 

If you Google around, you can find lots of discussion about good
stackups.  Here's one:

http://www.ce-mag.com/ARG/Grasso.html

(page waaay down the article.)  Also, the Howard Johnson book
("High speed digital design, a handbook of black magic") has a chapter
about good stackups.

Stuart