PCB Footprint Creation Guidelines: Avoid Redundant Library Demands

Your components are like the backbone for your new system and your new product won’t function without the right components. If you’re designing a new electronic product, it all starts with component selection. Before you create your schematic, you need to know which components will power your system and provide the desired functionality. Everything from form factor to sourceability needs to be considered during the initial design phase, especially if you want to avoid redesigns and long manufacturing delays.

When you need fast access to a large number of components, and you don’t have them in your library, where can you get them quickly? Of course, finding these components is only half the battle: verifying their accuracy across footprints, ensuring availability and cost, as well as delineating clear mechanical constraints are necessary too. 

There are a few options available to quickly create or purchase components for your system. To create symbols and footprints for your new design, follow these PCB footprint creation guidelines and processes.

PCB Footprint Creation Guidelines and Process

Once you’ve decided on the critical components you need for your new system, you’ll need to rummage through your libraries and determine which footprints you need to create. In the past, you would have to open up a CAD application and create schematic symbols and footprints yourself. You would then have to import them into your CAD software and create library files for your components. If your current job description is “PCB Librarian” or you have a backlog of component models, you can usually open an old model and create a new PCB footprint for your desired component.

Below you can find two common options for creating PCB footprints. 

Manual Creation from Datasheets

If you’ve been involved in the systems design process, then you probably have datasheets available for your desired components. Many datasheets will include physical dimensions for PCB footprints and pin diagrams that can be used to create schematic symbols. The typical process for designing PCB footprints and schematic symbols from your datasheets is shown below.

Using Existing Library Parts

Another way to start creating your PCB footprint library is to use existing library parts. Many component footprints are standardized, so you might be able to import existing footprints to a new component as long as the footprints match exactly. The required modifications might involve changing the component thickness in a 3D model or adding a ground pad (die attached paddle) to the bottom of the component.

Note that you would still have to create a new corresponding schematic symbol for the imported component. You’ll also need to access the datasheet and read through the pin diagram. Then, create the schematic symbol in your CAD software and export the part data to a component library. However, if you are using Ultra Librarian data, the symbol will match the footprint so long as the user hasn’t edited the footprint post-download. 

Either of these options can be useful for you and your design teams; however, there are hazards and constraints to each that may impede your design and production process. 

Pitfalls of Manual PCB Footprint Creation

PCB footprint creation is a task that gets shoved onto junior engineers who are not yet CAD experts. They often need to create components from scratch, especially when working with custom-designed mechanical components, fans or heatsinks, and proprietary SoCs. If your footprints are created improperly, though, it can spell disaster in future designs and destabilize workflows. 

Rather than focus the sole blame on these still-learning engineers, it’s best to offer proper guidance from the get-go. Here are some common mistakes that can occur during component footprint creation:

• Incorrect pad sizes. CAD tools will allow you to design any pad size you like and the pad size may not be manufacturable. Small pads create breakout problems for through-hole components and bad solder joints for SMT components. If a pad is too large, the temperature during reflow soldering may be too low and the part can float out of position.
• Low pad spacing. If pads are too close together, there is always the possibility of bridging during soldering. This creates a short that will cause a device to fail and the failure won’t be noticed until in-circuit testing or a boundary scan. This then incurs rework during assembly.
• Incorrect component outlines. Your component outline needs to match the lateral size of the component, especially if you plan for automated assembly. Manufacturers may send a board back for redesign if they cannot fix the error easily.

Saving Time During PCB Footprint Creation

Because of the time involved in manual footprint creation, and the potential for mistakes, there are some 3rd party “component wizard” applications you might consider. Also, high-quality CAD tools often include component creation wizards (including IPC-compliant footprint wizards). These tools are great for integrated circuit design, but unique electronic components and mechanical parts will still need to be created or edited manually, taking time and effort away from more intensive processes like layout, routing, or verification.

PCB designers should focus on creating great new technology, rather than focusing on following PCB footprint creation guidelines. The time-consuming process for component creation is one reason “PCB Librarian” is still a common job title at many companies. Instead of manually creating and managing your component footprints, you can take advantage of a 3rd party tool or service to acquire component footprints.

Ultra Librarian works with major component manufacturers and worldwide distributors to obtain verified PCB footprints and models. Rather than paying for a subscription to a component data supplier, or scouring manufacturer websites for component data, you can access millions of verified components for free. You shouldn’t have to completely change your design simply because you can’t find a component model. Instead, you can instantly download part data and immediately import it into popular ECAD tools.
While footprint creation and manually creating design libraries can be optimized and done properly, in most settings it is easier to work from what’s already out there. Whether it’s finding the component models and footprints you need now, or setting up your team for long term success, Ultra Librarian is an easy and efficient way of procuring the information you need. Register today for free!