Now that we've specified the size of our new pad (0.6 x 0.6 mm in this case), it's time to place it in our package.
This is where you really need to have a bit of attention to detail, since pad size and placement is critical to creating a functional and manufacturable footprint!
Selecting the 'Smd' tool (the red box in bottom of the the left-hand toolbar), and adjusting the 'Smd Size' to 0.6 x 0.6 on a mm grid, we should see something similar to the following if you zoom in or out a bit:
If you zoom in, you can see that this pad is indeed 0.6mm x 0.6mm thanks to the 0.1mm grid lines we've set. The pad should align perfectly with six 'squares' in each direction on the grid.
You can also see that the pad moves relative to it's 'center' position, so if we place the pad at 0 x 0, it would actually extend 0.3mm out in every direction.
This is very important to understand when placing pads. A 0.6x0.6mm pad placed at 0 x 0 would actually start at X -0.3mm and Y -0.3mm and end at X 0.3mm and Y 0.3mm!
You need to fully understand this, since the only way to create good footprints is to manually calculate the exact position for your pads, and you need to enter the position data relative to the center of the pad.
Place Your First Pad
Generally the easiest way to start placing your pads, it to place a single pad at the 0 x 0 position, which we'll refer to as the 'home' or 'zero' position.
Place a 0.6 x 0.6 mm pad at the home position by selecting the Smd tool, setting the size, and then simply clicking the mouse at 0 x 0, which is indicated by a small white '+' on your grid:
You can also see the current position on the grid via the little text box in the upper left-hand corner of Eagle, which will update as you move your move around.
We can see in the image below that we are on a 0.1 (mm) grid, and the mouse is currently at -0.4 x 0.0:
For now, go back to the 0.0 x 0.0 position, though, and click the mouse button once, which should create a new 0.6 x 0.6mm pad centered at 0 x 0:
It's extremely important that all of your parts are designed around a sensible home or center position, preferably the mechanical center of the part!
There are a number of reasons for this, but one of the key reasons is that parts are 'rotated' around their home position. By laying out your package around the mechanical center of the device, you can rotate your parts on your PCB without making a huge mess of the rest of the layout.