Re: gEDA-user: Design with a 144 pin QFP

[Ben Jackson <ben@xxxxxxx>]

On Sat, Feb 02, 2008 at 12:09:37PM +0000, ST de Feber wrote:
> 
> Has any one of you designed a PCB with a 144 pin
> QFP/TQFP package ? (with or without exposed die pad)

I just made a board with a QFP208 (0.5mm), 100 (0.65mm rectangular) and
80 (0.65mm square).

> How many layers will such a board have ?

It depends entirely on the function of the chips.  If it's a digital chip
and only uses a single power supply you might be able to use just two
layers.  If it's fast digital and/or analog and has multiple supplies
you will probably need at least 4 layers.  If it's an FPGA you can simplify
your routing because most of the pins are interchangable.  If it's a
CPU you might need more layers to get the connections to the right places.
I probably could not have routed my two SRAM chips on less than 4 layers
(just too many power and ground pins plus the need to bus together the
A and D lines) but if I'd only used one, larger SRAM I might have gotten
away with 2.

-- 
Ben Jackson AD7GD
<ben@xxxxxxx>
http://www.ben.com/


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