... Now Meet Your Eagle BFF

You see that little dot-dottly-doo icon in the rop-right hand corner there? Ya ... that unassuming little 32x32 pixel icon just below the folder: It's the secret to reliable, manufacturable designs in Eagle! Get to know it and love it, since you'll be spending a lot of time together with it:

Click that little icon and you'll see a dialogue box similar to the following:

This dialogue box controls the 'grid' in Eagle, and determines where you lines and shapes snap to when you're drawing stuff. This is extremely useful when designing parts, because you can adjust the grid to the exact dimensions you need, draw a precise line along one axis at that position, or continually copy and paste parts at a specific pitch (like a pad on a QFP package every 0.5mm, of every 0.65mm on a QFN IC, etc.).

Learning to use the grid to your advantage is the key to quick but accurate footprint design.

There are several values here, but the only one that really matters is 'Size' and the unit dropdown box just beside it.

• Size sets the distance between each line or 'snap point' on the grid. Every new line you draw or pad you place or copy/paste will be centered on a multiple of this size. If you have a 0.65mm pitch QFN package, you place one pad at the right position, set the grid to 0.65mm, and then copy and paste the rest of the row
• Units Drop-Down: Use this to select between common engineering units (mm, inch, mil, etc.). In generall, I always use mm since every modern datasheet is based on the metric system (and yes, that's a good thing).

For the GA1A1S202WP lets go ahead and set the grid to something small like 0.1mm:

1. Set 'Size' to 0.1
2. Select 'mm' in the drop-down box right beside it
3. Make sure the 'Display' radio button is set to 'On' as well so that you can see your grid
4. Click 'OK'

After clicking OK, you should see a much tighter grid, with a small white '+' marking the 0,0 position in the middle of the screen:

Zoom in a bit using the scroll wheel on your mouse of the zoom icons (highlighted in the image below) until you get something resembling the zoom level below (click the image to see the grid):