PCB footprints show where your components need to sit in your PCB layout, and they become part of the production files you'll send off to your manufacturer once you start production. Because portions of your footprints become part of the stencil used for resist exposure and etching, they need to be extremely accurate, right down to the solder mask exposure and pad pitch.
There's more that goes into your PCB footprint checklist than the locations of pads on your components. Courtyard areas, component designators, and more are encoded in your component model and will appear directly on the PCB layout once you place a footprint. If a footprint is incorrect, you might get partially through a fabrication run before anyone notices there are problems with your board. Don't get caught off-guard by incorrect footprints, use our PCB footprint checklist to help you avoid problems and create a smooth design workflow.
Every component that will appear on a circuit board layout will have a PCB footprint. Whenever you start a new project and jump into a layout, schematic symbols and PCB footprints need to be correct before a single design document is created. In my experience, it's much more common for PCB footprints to have some kind of problem rather than schematic symbols. This is why you should develop a PCB footprint checklist and a process for validating PCB footprints for your components.
Every PCB footprint will contain the following elements:
A basic footprint for an SMD component.
Many designers have a set of verified PCB libraries they use for creating layouts, or they use a service that handles footprint creation. There are many times where a customer will send a library with some pre-made PCB footprints for proprietary components or COTS parts. Sometimes you might be using a library from a reference design; it's common for these designs to have incorrect footprints, even if they came from a major manufacturer. In any case, it's important to run through a basic PCB footprint checklist to ensure your footprints match the real components that will be put on the board during PCB assembly.
When we receive new libraries from customers, we run through the components to make sure the footprints are correct. The PCB footprint checklist I've shown below is a good place to start validating footprints. After bringing up some datasheets, here are some things I always want to check in component data before starting a PCB layout.
You can spot components with missing data and NRND/obsolete/EOL components with the right sourcing tools in your PCB design software.
Once you've worked through your PCB layout and you're getting ready for signoff, you should run through a DFM checklist to address any outstanding manufacturability problems. Going through these checklists takes extra time on the front end, but this small investment can help you prevent a failed fabrication run (and unhappy customers) on the back end.
The experienced PCB design and layout team at NWES knows how to spot and correct design data when starting a new project. We help our clients stay at the cutting edge with advanced PCB design and layout services. We've also partnered directly with EDA companies and advanced PCB manufacturers, and we'll make sure your next design is fully manufacturable at scale. Be sure to follow our PCB footprint checklist before you send your project files to a service bureau. Contact NWES for a consultation.