Thanks a lot for your help, both answers helped a lot. Now I have another question. When I was working with a ground plane (layer stack with two signal layers and a GND plane), the autorouter, whenever there was a pad connected to ground, it used a via to connect it to it. Now, I just removed the ground plane from the board, having two signal layers, top and bottom, and I want to use the bottom layer as a GND plane, having the router to put vias whenever a pad is connected to GND. But istead the autorouter tries to connect all the pads through lines on the top layer...
What I did before was to add a Ground plane to the stack and ignore the bottom signal layer. Is that a fine solution or is there a way to have the board with two layers, and have one act as if it was a ground plane??
Thanks in advance,
Marcos