[SI-LIST] Re: Copper pours on a 2-layer PCB
- From: "Jack Olson" <pcbjack@xxxxxxxxx>
- To: torocar@xxxxxxxxx
- Date: Mon, 13 Nov 2006 08:53:18 -0600
Are there any bare-board vendors in Columbia
that can manufacture 4-layer boards?
Otherwise,
1) It doesn't matter if the +5v pour "bonds with"
the +5v traces
2) no
3) no. Let the GND pour fill wherever it can.
Jack
-=-=-=-
On 11/11/06, Carlos Toro <torocar@xxxxxxxxx> wrote:
>
> Hello you all. Unfortunelly, the local company which we pretend to hire
> for
> manufacturing our board just makes 2 layer boards (max). Probably our
> design
> wouldn't require more than that but since it is our the first time we
> pretend to hire the services of such a company some doubts have come up.
> The PCB engineers have assigned both the TOP and BOTTOM layers as routing
> layers (not plane layers, since there are only two layers to work on). The
> TOP layer is being used for routing as many signals and +5V power traces
> as
> possible while in the BOTTOM layer a copper pour attached to GND is to be
> placed (there are some spots where signal traces partially go in the
> BOTTOM
> layer since sometimes they cross, however, one of the goals is to chop the
> BOTTOM layer as less as possible). The PCB is basically a development
> board
> prototype for a microcontroller. There are not high power components
> involved.
> *Now, these are the doubts that have come up through the layout process
> and
> I would like you to kindly give me your advice on:*
> **
> *1. Should a copper pour attached to +5V be placed in the TOP layer?. An
> effort has been put on for distributing both power and GND in a star shape
> fashion (in order to avoid impedance coupling between ICs). But I'm afraid
> that If a +5V copper pour is placed in the TOP layer the star
> POWER/GND distribution topology will be lost (since the pour will bond to
> the +5V traces because it is electrically the same net). Should the copper
> pour respect the star topology +5V traces ?*
> **
> *2. Should the copper pour of the TOP layer be attached to the GND net
> instead?*
> **
> *3. A star topology has been used for placing the GND supply traces
> (trying
> to locate them underneath +5V traces). If a copper pour is placed in the
> BOTTOM layer attached to GND, the star topology will be lost (for the same
> reason as topic # 1). Acording to the theory, the returning current of all
> the signal traces and power traces will try to go come back right under
> the
> respective trace providing there is a GND return trace or plane underneath
> (that is, the returning current always seeks for the **least impedance
> path). If +5V (TOP layer) is distributed in a star fashioned way, the
> physics would take care of the rest, right? (I mean even if the bottom
> layer
> has a GND copper pour eating up the star topology GND traces, the "mirror
> effect" would "copy" the star topology from the TOP layer to BOTTOM?).
> Should the copper pour respect the star topology GND traces ?*
> **
> I would REALLY appreaciate if you kindly could provide some advices about
> these matters.
>
> THANK YOU SO MUCH BEFOREHAND.
>
> --
> Carlos Toro B
> Design Engineer
> JAVERIANA STEREO
> Calle 18 No. 118-250
> Cali, Colombia
> South America
>
> Office Phone: +57 2 2725032
> Mobile Phone: +57 315 474 5872
>
>
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