5 Things to Know About PCB Footprints

The process of putting together a printed circuit board is not an easy task. From PCB designing to assembly, different details are involved. Along with this amalgamation of different components, the process of PCB footprint is also a crucial task. In this process, electrical points and physical layouts are allocated to the various elements mounted on a PCB board.

To put it in simple terms, PCB footprints refer to the area that the different components occupy on a printed circuit board. From the pad size and shape to the component outline, all the things come under PCB footprints. This blog will provide various insights into PCB footprints.

1. Information on the Components of PCB Footprints

A circuit board design components come with general information, which are:

• Pads: This indicates copper areas where the component leads or pins will be soldered during the assembly process.

• Component outline: The area that the components occupy on the PCB is the outline or courtyard. This boundary defines the component shape.

• Reference designator: In the PCB layout, you can witness alphanumeric codes. These codes identify the components on the PCB.

2. Libraries for PCB Footprints

An enthusiastic PCB designer would know how important it is to create a PCB footprint library just like its component library. Generally, PCB footprint libraries are available to organizations that are Component manufacturers, third parties, or those who create design software for printed circuit boards. There are various PCB footprints available online. The most popular of them are SnapEDA and Ultra Librarian. The Ultra Librarian is considered to be the world’s largest PCB CAD library. The data of this library can be imported into well-known PCB CAD apps.

3. PCB Footprint Creation

If a PCB footprint library is not available, PCB designers will not have any other choice but to create a PCB footprint on their own. Later, they will upload it to the PCB library database. To create a PCB footprint from scratch, it is essential to have the correct specifications of the concerned components. Start with the general information like pad sizes, hole diameter, pitch and spacing, the component layouts, etc. Ensure the PCB footprint creation is complete otherwise, it can cause problems when you have to define the PCB layout.

4. Specific Standards

To define the PCB layout, its schematic symbol, or 3D model, the PCB footprint should apply to specific international standards:

• For PCB footprint, the standard is IPC 7351. The IPC-SM-7351-B version of this standard considers a range of formulas to define the footprint. Many PCB CAD models have been designed, aligning with this standard.

• For schematic symbols, the standard is ANSI Y32.2-1975. In electronic and electrical diagrams, certain graphic symbols and designated letters are used. This standard is used to define such elements.

• For 3D models, ISO 10303-21 is used. This standard classifies the STEP model file format.

5. Guidelines for PCB Footprints

If a PCB designer wants to create the footprint from the beginning, individuals should follow the guidelines mentioned below:

• The component layout on the PCB should be aligned perfectly. The pads of the components on opposite sides should be of similar shapes and sizes to ensure symmetry.

• The component outline and the pads should have enough space in between. This would make sure that the desired pins are connected to the right component pads.

• To indicate polarized components, integrate polarity indicators.

• Don’t use components that are too small, as the automated production process may fail to recognize those parts.

Conclusion

During the PCB manufacturing process, PCB footprints play a crucial role. They contain information about all the components mounted on the PCB layout. By going through the essential set of information, the soldering process can be done accurately. Usually, PCB footprints are available online, but if a designer wants to create it from scratch, they can do so by following the guidelines.

Frequently Asked Questions:

What is a PCB footprint in PCB design?

• A PCB footprint is the physical layout of a component on a circuit board, including pad positions, outlines, and reference markings for accurate placement and soldering.

Why are PCB footprints important?

• PCB footprints ensure correct component placement, prevent assembly errors, and improve PCB reliability by following industry standards like IPC 7351.

How do I create a PCB footprint?

• PCB footprints can be created using PCB design software by defining pad sizes, hole spacing, and component outlines, or downloaded from libraries like SnapEDA or Ultra Librarian.

What are the best practices for PCB footprint design?

• Ensure correct pad alignment, spacing, and polarity marking, and follow IPC standards to avoid soldering defects and improve manufacturability.