Bagotronix Tech Support wrote:

I thought that the following stackup was prefered because then every
signal is one layer from a ground plane.

1 signal
2 gnd
3 signal
4 pwr
5 pwr
6 signal
7 gnd
8 signal



But then you don't have as good decoupling between your pwr and gnd planes, since they are farther apart.

My stackup (as mentioned in an earlier post, and repeated below) gives you
copper balance, better decoupling, and your signals are still only 1 layer
away from a pwr or gnd plane.  And since the pwr and gnd planes are
effectively the same thing to high frequencies, a signal being next to a pwr
plane is the same as that signal being next to a gnd plane.

sig
gnd1
pwr1
sig
sig
gnd2
pwr2
sig

While we are on this subject, I like to use 0.01 uF caps for decoupling, not
the 0.1 uF caps you frequently see on digital circuits.  The reason is that
0.01 uF caps have a higher self-resonance frequency than 0.1 uF caps, which
makes them better able to decouple the high-speed transients that are so
common in today's circuits.  Also, 0.01 uF caps are less expensive and take
up less space (0805 vs. 1206).

One last comment: DO NOT put vias within your pads. Some folks advocate
this in order to reduce the track inductance from the part pin to the via.
The problem is that this causes hell for manufacturing. During the reflow
process, solder flows down into the via barrel, away from the part pin/pad
junction, resulting in insufficient solder at the junction.


Have to agree with the above paragraph. We did our first bga board a few months ago and all the solder flowed through the vias creating a few no conductive connections even thou they appeared connected after x-raying. Lucky for us they were only prototypye boards.

Sorry if the previous 2 paragraphs are obvious, but there might be some
folks lurking on this list who are new to PCB design and need a rehash of
"da rules". Or should I say "(e)da rules".


I have to say I am a newbie to multi-layer boards and high speed / RF so even thou it may seem obvious to everyone else alot of this is all new to me and probale others out there as well.

Whaddaya know, I was on topic this time...

Best regards,
Ivan Baggett
Bagotronix Inc.
website:  www.bagotronix.com


----- Original Message ----- From: <[EMAIL PROTECTED]> To: "Protel EDA Forum" <[EMAIL PROTECTED]> Sent: Tuesday, June 03, 2003 11:02 AM Subject: Re: [PEDA] six or eight-layer (or more?) stackups




The "text book" standard that is

1    signal
2    gnd
3    signal
4    gnd
5    pwr
6    signal
7    pwr
8    signal



I thought that the following stackup was prefered because then every
signal is one layer from a ground plane.

1    signal
2    gnd
3    signal
4    pwr
5    pwr
6    signal
7    gnd
8    signal

Any comments?

Also anyone else losing messages, or is it just my IT department and Lotus
Notes?

Robert D. LaMoreaux
MTS Systems Corp.
Powertrain Technology Division
4622 Runway Blvd.
Ann Arbor, MI 48108
734-822-9696
Fax 734-973-1103
Main Desk 734-973-1111









--
Nathan Horsfield Inspiration Technology P/L Ph: +61 8 8211 9668
Fax: +61 8 8211 9658 www.instech.com.au





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