> Thanks for the hint, Mike. I will try like you suggest. I would like to
> avoid to have to do manual preroutes on almost all SMD fanouts. As these
> will be blind vias, I need different vias for connecting the inner layers.
>

Gisbert,

I found the easiest method of defining blind and buried vias for autorouting
is to place a dozen vias down, then edit them by desired layer pair.

I worked with designing MCM substrates and we had to define each layer
combination used.

i.e.  a 10 layer design Layers 1-2 , 1-3, 1-4, and so forth until 1-10, then
2-3, 2-4...and so forth until 2-10,  then all over for layers 3 -9  so you
could end up with a via count of about 96 possibilities.  The drill chart
becomes a night mare, but the process we used we didn't use a drill chart,
we derived the drill info from the gerber file......very unconventional.

For your purposes, I would use sequential pairs, make sure the limit way
command is used in spectra, place an array of vias, modify them by pair.

Then go to the Layer stack manager, drill pairs, rt click mouse and create
drill pairs from used vias.   When you export to spectra, open the dsn file
in note pad and  identify the blind vias,  unselect all vias, then select
your vias for routing.  Spectra will automatically pull the best via for the
route.   One thing I would do is fan out all power in Protel first

As far as I know, Spectra will not place blind vias directly over each other
on the same net  ( someone may correct me on this)  it will drop down, add a
track then use another via.   I haven't tried it on the latest version of
Spectra. it may be supported.


Anyway just a few tips

Mike Reagan
EDSI
Frederick Md






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