I've run into this (non-PTH problem) as I often make
my own PCBs.  Its fairly easy to look at a part/pin
and decide if you can solder it on both sides -
resistors, axial caps and diodes, for example. 
Sockets, for example, aren't.   I avoid doing it with
ICs because of heating issues.  You do need to take
into account placement/installation order.  So you
form a set of mental design rules for non-PTH boards. 
Vias can be made with a simple piece of wire soldered
on both sides.  Its kind of ugly but does work.  I can
turn a board around in hours rather than days and a
board designed with the non-PTH rules still works when
made by a board house.

For the autorouter, you weight the top really costly
and it will route mostly on the bottom.  But you still
need to fix up the board to handle the non-PTH design
rules.  A via will do the trick but I've found its not
that hard to do it "right" and avoid a via.  I don't
bother with the autorouter for a number of reasons
though non-PTH isn't one of them.

Phil


--- Olin Lathrop <olin_piclist@embedinc.com> wrote:
> Bob Blick wrote:
> > I don't use Eagle, but in general the advice is to
> raise the cost of
> > top layer, and raise the cost of vias. Sometimes
> it ends up being a
> > tossup between running the autorouter over and
> over while adjusting
> > it, and routing by hand.
> 
> I've never tried doing a single sided board with
> Eagle.  I guess your method
> uses the second layer to have Eagle tell you where
> the jumpers need to be.
> However, I see a problem when using thru hole parts.
>  Eagle will assume the
> holes are plated and connect to both layers.  That
> will not be valid in
> cases when the pins under a component on the top
> side are inaccessible.
> Somehow you need Eagle to think that thru hole pads
> only connect to the
> bottom layer, but I don't know how to do that short
> of defining new packages
> in the libraries.
> 
> 
>
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