Greetings,

Well,
(deep breath...)
(or was that a sigh?)
While I agree with you in THEORY (and I have respected your
opinion on just about everything I've ever read from you)
I just can't seem to make 1 and 6 work as decent routing layers.

I usually place pretty tight clumps of circuitry, route clumps with
really short traces on 1-6, and then route BETWEEN clumps on
inner layers. I would have to rewire my whole brain to do it any
other way.... (grin)
hmmm... intra-clump vs inter-clump routing. I should write a book!

And speaking of theory vs. reality, the statement that
"Changes from one reference to another should only be done at
points where decoupling or other filtering will allow the signal return
energy to be transferred between planes quickly and with minimum
loop area" kinda makes me smile, but I AGREE with ya!.

and learnin' HDI is one o' those things I been puttin' off, ya know?

thanks (I couldn't resist teasing you but I appreciate the response)

Sincerely,
Jbro
.


On 1/4/07, McGlaughlin, Jeffrey A <[log in to unmask]> wrote:
>
> Jack -
>
> PWR and "Ground" are DC values. Signals are switching therefore they are
> AC (even digital bus signals.) Any DC Plane can serve as an AC return
> path (a much better term than ground.) The real issue to watch for when
> routing is switching between reference planes, i.e. when changing from
> vertical to horizontal routing directions. Changes from one reference to
> another should only be done at points where decoupling or other
> filtering will allow the signal return energy to be transferred between
> planes quickly and with minimum loop area.
>
> If you are working with a 6-layer PWB keeping 1-3 and 4-6 as routing
> pairs would be the most efficient, even though one pair uses PWR as a
> signal reference. Watch out for layer stack-up's that create copper
> imbalances or you will end up with potato-chip shaped boards, warp bow
> and twist all working against you.
>
> If placement density keeps you from using external layers for routing it
> may be better to treat the board as an HDI 4-layer +2 cap layers and
> place your planes as layers 3 and 4.
>
> Onward thru the ...um... fog, yeah that's it its fog ;-D....
>
> Jeffrey McGlaughlin, CID
> Engineering Designer
> Battelle
> 505 King Avenue
> Columbus Ohio 43201-2693
> (614)424-7582 Phone
> (614)458-7582 Fax
>
>

---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
---------------------------------------------------------------------------------