PCB Design Guide – PCB Footprints
Step 4 in the pcb design guide is PCB footprints.
As you’re creating your circuit design / schematic be sure to keep a directory of all your component datasheets. These datasheets will minimize your time searching for manufacturer recommended land patterns. Many pcb design software packages come with a library of pcb footprints a designer can use, however they are limited in the number of packages as components are constantly changing and shrinking in size. It’s likely you’ll end up having to create several new footprints during your design.
Footprint Naming Convention
If you can’t find the component footprint in your software’s library you’ll need to create your own. If its a small project footprint naming may not seem like a big deal, but if you’ve got hundreds of components or you plan on reusing any of your footprints at a later date, being able to find those newly created footprints is critical. An excellent resource for pcb footprint naming convention is IPC-7351. The latest version of the standard naming convention is found below for your reference.
Anatomy of a Footprint
Before we go to much further you need to have a good understanding what is included in a footprint. Most pcb software bundles the same information in the footprint file, so we’ll discuss this information generally in hopes you can correlate it back to your specific software.
PCB Footprint Resources
In order to accurately design your footprints you really need access to the IPC-7351 standard. However, IPC has teamed with PCB Matrix and is distributing a free Land Pattern Viewer. This tool is essential for design land patterns and will save you hundreds of hours. This tool will provide the dimensions for pad dimensions, pin spacings, solder masks, etc. Therefore its still a manual process, but the outcome is a land pattern guaranteed to meet manufacturing standards.
You can spend hundreds of hours working on pcb footprints. Hopefully a couple of these tools, resources, and articles will help you get started in the right direction and drastically reduce that time.
Since Step 5 is heavily realted to the footprints we’ll go ahead and cover that here.
PCB Board Outline
The board outline is basically just another footprint, just bigger. It has a outline like a component, mounting holes, keepin and keepout zones, serial numbers, etc. The board outline should be roughed out early in the design phase as an estimate will need to be made for board density.
A standard practice is to place the origin of the board in the bottom left hand corner.