placing componets below an atmega328 good idea?

Im trying to make a small pcb for a circuit of mine, the first one I made was 4.5sq in and I know would work however I tried to really packin the components in a second version for 2.9 sq in, but to save space I put 2 resistors, the crystal, and two caps under(backside) the atmega 328 and 2 caps and a resistor flipside an 8 pin ic is this a good space saving idea? Or just a problem waiting to happen?t'll save me like 5$ on the pcb, but if it doesn't work then obviously its a waste are there any other standards on component spacing? All I usually do is keep decoupling caps and the crystal short, anything else to worry about?

The issue would be of servicability more than anything else. You may be building the board in such a fashion that devices cannot be desoldered and replaced in the event of a component failure.

If you want to save space and cost, then replacing the 22pF caps and crystal by a 3-terminal ceramic resonator will achieve both, at the cost of a slightly less accurate clock frequency.

Also a .032 trace would be fine for 1 amp continuous right?

This page

http://www.armisteadtechnologies.com/trace.shtml

says yes.

I'd have no problems placing components under the uC, I think that's quite common now with SMDs.


Rob

Passive components shouldn't be a concern. Make sure you put as much ground plane as you can (even between the pads of the components) and a couple of vias connecting both the top and bottom ground plane. I wouldn't run anything high frequency (or high power) under the micro.