User Guide

Inner layers are converted to supply layers if they are renamed to
$name,where name isavalidsignalname.Theselayersarenotrouted.
Supply layers with more than one signal can be implemented with poly
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gons.Theselayersaretreatedasnormalsignallayers.
In the case of boards that are so complex that it is not certain whether
they can be wired on two sides, it is helpful to define them as multilayer
boards, and to set very high costs for the inner layers. This will cause the
Autorouter to avoid the inner layers and to place as many connections
as possible in the outer layers. It can, however, make use of an inner
layerwhennecessary.
ThesesettingsaremadeintheAutoroutermenu(seepage 128).
PreferredDirections
On the two outside layers the preferred directions are normally set to 90
degrees from each other. For the inner layers it may be useful to choose
45 and 135 degrees to cover diagonal connections. Before setting the
preferred direction it is well worth examining the board (based on the
airwires) to see if one direction offers advantages for a certain side of
theboard.ThisisparticularlylikelytobethecaseforSMDboards.
Please also follow the preferred direction when pre-placing tracks. The de
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faultsareverticalfortheTop(red)andhorizontalfortheBottom(blue).
Experience has shown that small boards containing mainly SMD com
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ponents are best routed without any preferred direction at all (set * in
the Autorouter setup). The router then reaches a usable result much
faster.
Singlesidedboardsshouldberoutedwithoutapreferreddirection.
RestrictedAreasfortheAutorouter
If the Autorouter is not supposed to route tracks or place vias within
certain areas, you can define restricted areas by using the commands
RECT, CIRCLE, and POLYGON in the layers 41, tRestrict, 42, bRe
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strict, and43, vRestrict.
tRestrict: RestrictedareasfortheToplayer.
bRestrict: RestrictedareasfortheBottomlayer.
vRestrict: Restrictedareasforvias.
Such restricted areas can already be defined in a device package (around,
for instance, the fixing holes for a connector, or for a flat-mounted tran
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sistorunderwhichthereshouldnotbeanytracks).
Wires drawn in layer 20, Dimension, are boundary lines for the Auto
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router.Trackscannotbelaidbeyondthisboundary.
Typicalapplication:boardboundaries.
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TheAutorouter