User Guide

LAYER2$GND
This specifies that layer number 2 (previously known as Route2)is
henceforth known as $GND, and that it will be treated as a power sup
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plylayer
The preferred direction for the Autorouter is to be set to N/A for power
supplylayers.ThiswillcausetheAutorouternottousethislayer.
Pads are connected to power supply layers with what are known as ther
-
mal symbols, or are isolated with annulus symbols. Thermal symbols
usually just have four thin bridges as a conductive connection to the
through-plated hole. They are used because the high thermal conduc
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tion of a continuous copper plane would result in the pad being no
longer solderable. The shape and size of the annulus and thermal sym
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bolsarespecifiedintheDesignRules(DRCcommand, Supply tab).
Supply layers are inverse plotted. You should draw a wire in such layers
around the edge of the board to keep it free from copper. This will pre
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vent the possibility of shorts between neighboring (power supply) lay
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ers. If you use the Autorouter however, this wire must not be drawn
until after the routing. As described above, power supply layers are not
available to the Autorouter, but this in fact only applies to layers which
donotcontainanysignals(wires).
The Autorouter includes the inner layers, and so delivers the full set of
patterns for multilayer boards. It connects SMD pads to inner layers
withvias.
No additional signals or signal polygons may be drawn in these layers. That
wouldleadinevitablytoanunusablecircuitboard!
GroundAreasandSupplyLayerswithMorethan
OneSignal
Areas of the board can be filled with a particular signal (e.g. ground) us
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ing the POLYGON command. The associated pads are then automati
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cally connected using thermal symbols. The isolate value for the thermal
symbols is specified in the Design Rules (DRC command, Supply tab).
The width of the connecting bridge depends on the line thickness with
which the polygon is drawn (see page 106). You can also specify whether
or not vias are to be connected through thermals. The minimum clear
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ances from elements carrying other signals specified in the Design Rules
are maintained (Clearance and Distance tabs). Changes are shown in the
layoutwhenthepolygonisnextcomputed(RATSNESTcommand).
In this way you can also create layers in which several areas are filled
with different signals. In that case you can assign different ranks (priori
-
ties) for the polygons. The rank property determines which polygon is
subtracted from others if they overlap. Rank = 1 signifies the highest
priority in the layout; nothing will be subtracted from such a polygon
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FromSchematictoFinishedBoard