Before we can go any further, you'll need to pull out the GA1A1S202WP datasheet (or whatever other datasheet), and find the package outline. It's usually on the last couple pages of any datasheet, but in the case of this part it's on page 6 of the PDF.
For convenience sake, we've included a screenshot of the package outline below:
There are two important elements that we need to take into account create a package:
- The package 'dimensions', which is the physical outline of the package. We'll come back to this one later.
- The pad locations and sizes, which are the metal pads we will creates where to 'leads' or 'contacts' on your part will get soldered to your PCB.
The first step we'll do to actually start creating a package for our sensor, is to start laying down the pads in the right size and location.
There are four pads on this part, represented by the four dark, hatched squares in the diagram.
To create a 0.6 x 0.6mm pad, we need to click the 'pad placement' tool we discovered in the previous page (the 'Smd' tool in the left-hand toolbar), and then adjust the size of the pad.
Once you've select the Smd tool, a new toolbar will appear at the top of your display with the settings for the new pad(s):
The toolbar contains four items, but we only need to worry about two of them here:
- Layer Selection: The first drop-down box (shown with '1 Top' here) indicates on which 'layer' our pad should be placed. We'll explain layers later, but for now leave this at '1', which is the top copper layer, and where we want to place our pads 99% of the time.
- Smd Size: The second box (labelled 'Smd:') is the most important one here. This is where we indicate the size of our new pad. It's currently 1.27 x 0.635.
Do you remember your Eagle BFF from a previous page, the Grid Dialogue? You'll see one reason why this little icon is so important here.
Our pad size in the screenshot above is set to 1.27 wide by 0.635 high, but there are no units specified!
This is because the 'units' in Eagle are controlled via the grid settings, and we are free to switch back and forth between mm, mil, or any other supported unit, and the numbers will be adjusted accordingly.
For now, keep these in mm, though, since 99% of parts today are specified in mm.