Chris,

Go to http://www.connecteda.com/   I wrote an article for ELECTRA that may help you 
route your design.  This is not an advertisement for Electra,  I am just sharing my 
knowledge.

Mike Reagan
EDSI
Frederick MD


---------- Original Message ----------------------------------
From: Chris Fisher <[EMAIL PROTECTED]>
Reply-To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Date:  Fri, 13 Aug 2004 08:57:40 -0700 (PDT)

>
>
>I have a large? project I am trying to route with DXP 2004.  This is my 
>first project using DXP, although I have spent time with test designs and 
>tutorials.
>
>The big SMT parts of my design are four 34x34 BGAs @ 1mm spacing and 24 
>160-pin 0.8mm spacing connectors.  I am planning to escape two nets 
>between vias under the BGA.
>
>The first thing I found is that the auto fanout of the connectors was
>rather poor.  Also the autorouter did very poorly with escaping the
>via-grid under the BGA.  I then tried prerouting the fanouts and escapes
>in the footprints.  With careful layer assignment and fanout, each net
>going between BGAs and connectors can be routed on one layer (between
>fanout vias).
>
>At this point when I run the autorouter, it does a fairly poor jobs (lots 
>of vias and bad decisions that lead to contention & failures).
>
>Most FPGA boards I have seen use a layer topology that is radial, where
>the FPGA is the center (at least in the area around the FPGA).  The
>closest match in DXP is the "Any" setting.  This setting appears to assign
>one of the fixed directions for the layer, instead of letting each net go
>any direction on that layer.
>
>What I am hoping is that I can get the autoroute to connect (without 
>changing layers) all the nets between my BGAs and connectors.  Can this be 
>done?
>
>This board also has a small number of 100 ohm differential pairs.  At this
>time the autorouter does not support differential pair routing, so I was
>planning on hand-routing these signals.  Is this what everyone else does?
>
>Questions:
>
>Has anyone else tried using the autorouter this way (partial prerouting
>of nets)?
>The autorouter seems to ignore the copper on partially pre-routed nets?
>Is there a workaround to get it to start from a section of copper instead 
>of a pad?
>
>Is there a way to individually restrict the signal layers used for each
>net?
>Is there a way to restrict the autorouter to only use only one layer?
>
>
>Is a radial layer direction possible to support with the autorouter?
>
>
>
>
>Does anyone have any further ideas?
>
>Thanks,
>Chris Fisher
>
>
>
>
>
>
>
>
>



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