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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