Re: gEDA-user: 3 questions on a 4 layer board

[Rick Collins <gnuarm.2007@xxxxxxxxx>]

At 10:53 AM 4/29/2008, you wrote:

> > Question 1: Each "Group" will be a physical layer of copper, correct?
>
>Yes.
>
> > Question 2: In this a reasonable assignment, or am I missing something?
>
>That's the stackup I use.  In general, you want the ground plan near
>the signal plane with the most signals.  For surface mount, that's the
>top.  For through-hole it might be the bottom.

I took an excellent class in high speed digital design by Lee 
Ritchey.  One of the things he covered was using ground planes and 
controlling impedance.  Turns out that for the purpose of impedance 
(which is why you want your traces close to the plane) a power plane 
is exactly the same as a ground plane.  So it does not matter if your 
signals are next to the power or the ground plane, they are both at AC ground.

Just thought I would chime in with my two cents worth.


> > Question 3: I'm assuming the best way to make the power and ground
> > layers are to simply flood-fill them with copper, and then the
> > components will attach by the pin connections.  Is it really just
> > that easy?
>
>Yes.  Draw a rectangle keeping 25 mil away from your board outlines,
>then use the thermal tool to connect pins to it as needed.


Rick

Arius - A Signal Processing Solutions Company
Specializing in DSP and FPGA design      URL http://www.arius.com
4 King Ave                               301-682-7772 Voice
Frederick, MD 21701-3110                 301-682-7666 FAX



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