Chris,

In general:
- route manually all "important" nets
- fanout manually all power pins
- run the autoroute from there.

Many people complain about the poor results. You can
never get as good layour as you'd do it manually but
it also depends on how you'll set the autorouter.
You'll have to repeat it several times.

Mira

--- Chris Fisher <[EMAIL PROTECTED]> wrote:

> 
> 
> 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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