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Chapter 7
Autorouting and Autoplacement
Autorouting
Understanding How the Autorouter Works
NI Ultiboard User Manual
•
Use smaller Keep-out or Keep-in areas. Often, a PCB with Keep-in
areas can be designed with an equivalent set of Keep-out areas, or
vice-versa. Whenever possible, choose a design strategy that
minimizes the total area of the board covered by these Keep-in or
Keep-out areas since each area radically decreases the autoplacement
algorithms' effectiveness.
•
With very dense boards, the last few parts may need to be
hand-placed. The autoplacement algorithms have been carefully
tuned to optimize the routability of the final layout, rather than trying
to pack all the parts into the smallest possible area. If the autoplacer
places all but one or two parts, it may be faster to simply place them on
the board by hand—using Ultiboard's part shoving facility (not
available in all versions) to ensure that parts do not overlap—than to
spend time trying to tune the autoplacement parameters to achieve
complete placement.
The following sections describe the autorouting functions in Ultiboard.
Ultiboard contains four fundamental trace-routing functions:
•
router preprocessing
•
initial routing
•
rip-up and retry passes
•
optimization.
Ultiboard uses combinations of these functions to route a board. They are
described in the
Understanding the Four Fundamental Routing Functions
section. Information on how to use these functions can be found in the
Running the Autorouter
section.
7-6
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