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Re: 4 layers versus two layers for PCI cards



How are currently figuring the trace velocities and impedance? This
would change depending on the 4 layer stack up you'd use...

The PCI spec dictates the acceptable board and trace geometries for
compliance.

Daniel DeConinck wrote:

> Hello, I am shipping a 2 layer PCI card (33mhz-32bit). It uses a
> Xilinx with a 2.5V core and 5Volt tolerant IOs.  ( XC2S50-5PQ208C) I
> laid out the board with as much ground plane on the bottom as
> possible. Its 90+% ground plane. I believe that this works OK on many
> PCs but I think I need to move to 4 layers for proper operation across
> all PCs. I currently use through hole by pass caps all around the
> perimeter of the Xilinx chip. I am sure things will get better by
> switching to both surface mount caps and a four layer PCB. My question
> is how important is each of these two improvements when compared to
> one another ? For example X% of the improvement will come by switching
> from  through hole caps to surface mount and (100-X) % of the
> improvment will come from switching from two layers to four layers. I
> am wondering if simply switching to surace mount caps will give enough
> of a boost in performance. Sincerely
> Daniel DeConinck
> www.PixelSmart.com
> TEL: 416-248-4473

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