Re: gEDA-user: PCB Ground Plane - Autowiring?

[Gabriel Paubert <paubert@xxxxxxx>]

On Tue, Feb 03, 2009 at 06:45:53AM +0100, Marcel.Schmedes.EXTERN@xxxxxxxxxxxxxxxxxx wrote:
> Hello @all,
> during the last Week is started a Project with gEDA, right now the 
> Schematics are complete, but now I want to layout the whole thing using 
> PCB. I want to use a 4-layer pcb (signal, vcc, gnd, signal).
> 
> 1. Is there an comfortable way of telling pcb to connect all vcc and gnd 
> nets to the correct plane? To put and connect every pad by hand-putting a 
> via and connecting it with a thermal to the plane doesn't seem very 
> comfortable to me... BTW the design is using SMD-only components.
> 
> 2. I'm using a PowerPAD (TM) Device, which has a pad to connect thermal 
> and electrical to the ground plane. How to connect best to the plane? 
> (Also thermal - so not using "thermal".)
> 
> 3. I need to connect the output from my onboard switching power supply to 
> the corresponding planes (5.1V/2.2A). Do you have any recommendations how 
> to connect a high current trace to a plane?


I have recently built a board with an LT3510 which provides +6.8V at about
3A for a project (using the two outputs of the LT3510). Efficiency is 88%.

All high current tracks are quite wide and with several vias in parallel
(except close to the chip since 0.65mm pin spacing really limits track width)
where they switch plane. The underside of the LT3510 is also the only
ground contact and I have small heat sinks on both sides of the board
(otherwise the LT3510 enters thermal shutdown).

I can send you the PCB file if you want, I still measure about 1 milli ohm
between the output of the LT3510 and the final voltage (3mV loss).

	Gabriel


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