When I route a PCB for "home" construction, I try to put as much of the
routed traces on the bottom as I can, leaving a minimum of traces on
the top.  The idea is to minimize the number of top-to-bottom connections,
since there are no plated through holes (ideally, everything routes on the
bottom.)

If I'm designing a board for professional fabrication, that WILL have
plated-though holes, are there any advantages or disadvantages to maintaining
this sort of "bottom heavy" routing?  (by default, Eagle will autoroute
pretty evenly; but I don't know WHY.)  The only thing I can think of is that
by doing half-and-half, you can use more conservative design rules on each
side and reduce the chances for errors (solder bridges, etc.)  But since I'm
basically aiming at "homebrew" design rules for the bottom anyway, my design
rules are already pretty (very) conservative.

(I guess for complex designs, you actually start seeing boards where that
horizontal/vertical dichotomy starts to pay off.  So far, most of the boards
I've done have a microcontroller, one or two other chips, and a bunch of
non-chip components, and I haven't see the autorouter even get close to
having either side REALLY run in one direction...)

Thanks
Bill W

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