David wrote:
> Do people use the auto-router?

I certainly do.  It's a great tool as long as you undertand it can't take
care of everyting for you, and that you really have to read the manual
several times to understand what all the tweaks do and then how to use them
to achieve what you want.

I usually route a few critical sections manually, then iterate with the aut=
o
router to do the rest.  In the beginning I use just a single route pass to
see what kind of solution it comes up with.  Then I may move some things
around, tweak the net classes, and manually route a few things.  Repeat
until you get a reasonable enough first pass route.  Then crank up the
optimization passes.  I usually use 8 for the final route.  The first pass
is optimized to find a solution.  The remaining passes try to tweak the
solution to minimize via, use of the bottom layer, or whatever is important
in that design.

> Would it be more sensible to layout on 2 sides somehow
> (e.g. Vcc/GND on one, signal on the other).  Do I just need lots more
> practise at component layout and routing?

Good layout is the first step to good routing.  If the layout is a mess, th=
e
route will be too.  Place anything that needs to be in a fixed place first
(external connectors, mounting holes, etc), then try to have the layout
follow the logical structure of the circuit.  That minimizes the impact of
interconnects between subsystems and keeps the connections inside subsystem=
s
small and local.

For two layer boards, I often make the bottom layer a pseudo ground plane.
That means its mostly a ground plane except for short "jumpers" to make the
toplogy work.  Setting the cost of routing inside polygons high helps the
autorouter do this, but it then unfortunately tends to lump the jumpers
together.  In this case the success metric is not the number of islands in
the ground plane but how small their largest dimensions are.  In other
words, a bunch of small islands is better than a big one, as long as the
ground signal can reasonably flow around the small islands.


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