I’d like to share this trick. If you’re new to Eagle, placing SMD parts on your bottom copper layer seems to be a mystery.But it’s real easy and I’ll show you.
In this example, we want to put C6 and C6 (both 0.1uf capacitor) to the bottom of the PCB. As you can see, the solder pads on C5 and C6 are colored “red”, which means they’re still on the top (default) layer.