What is a Pad in PCB Design and Development

Pads serve as the landing spots for the legs or leads of electronic components, allowing these components to be soldered onto the PCB securely. They are small, copper exposed conductive areas that enable both electrical and mechanical connections between components and the board. Traces can be routed from pads to all over the PCB, they also help to hold the component pins in place with the application of soldering. Pads are critical because they:

• Ensure strong electrical connections between components and traces on the PCB.

• Provide mechanical support to hold components in place.

• Enable easier assembly and soldering processes during manufacturing.

In this blog, we will explore the different types of pads used in PCB Design, their importance in the overall functionality of the board, and best practices for designing and placing pads in your PCB.

Types of Pads in PCB Design

PCB pads represent copper areas in several shapes, like rectangular, round, square, and more. There are two main types of pads commonly used in PCB design:

Through-Hole Pads (THT):

These are used in traditional through-hole technology, where component leads pass through drilled holes in the PCB and are soldered on the opposite side. These pads have copper around the hole on both sides of the board. There are two types of through-hole pads. Below are the types of these pads:

Plated through-hole pads: PTH pads are pads with holes that are lined or coated with conductive material, usually copper, during the PCB manufacturing process. The copper plating in the hole creates a conductive path through the board, connecting the top and bottom layers or internal layers. These pads can be used for mounting components with leads, as well as for vias that connect different layers of a PCB. The inner wall of the hole is covered with a copper layer, often visible when inspecting the hole.

Non-plated through-hole: NPTH pads have holes without any conductive plating. The holes are simply drilled through the board, and no conductive material lines the inside of the hole. They provide a place for screws, fasteners, or alignment pins but do not conduct electricity.

Surface-Mount Pads (SMD):

Surface-mount technology (SMT) pads are designed for components that are mounted directly onto the surface of the PCB without the need for holes. SMT pads are typically smaller and enable more compact designs, which is essential for modern electronics. Here are two main types of SMD pads:

SMD BGA pads: The solder mask aperture applied to the BGA pads defines the SMD pads. These BGA pads have solder mask apertures that are smaller than the pad diameters they are covering. This is performed to shrink the PCB pad sizes of the copper.

NSMD pads: The mask is created in such a way that a gap is created between the solder mask and the edge of the pad.

Manual and Automatic PCB Pad Design:

Pad manual PCB Design includes designing the required pad shape with the help of PCB design software tools. This can be represented with the help of formulas and datasheets for general pad size and shape.

Hand-operated procedures are prone to errors because fabricator specifications do designers adhere to formulas as they do in automated systems. It leads to designing pcb pad sizes and shapes, which leads to undesirable results like:

• Through-hole breakout
• Insufficient solder joint
• Floating parts
• Tombstoning parts

Therefore most of the design softwares use an automatic design wizard for creating pads and component footprints.

PCB Pad Design and Development Methods?

PCB design and development involve creating the board’s layout, selecting the appropriate components, and designing the interconnections between them. Different components come with different pin configurations, numbers and package types. The uncovered metal area on an electrical circuit board where the factor lead has been soldered is known as the PCB pad. Aligning these pads together creates the component footmark PCB design model. The pad design involves two main factors:

1. Symbol design
2. Footprint design

We are using EasyEDA for the design because of its open source library and online environment.

Symbol Design:

Launch EasyEDA and go to the Schematic Editor. Open the Symbol Editor on the top menu, click on Libraries > Create Symbol.

• Use the drawing tools like Rectangle, Line, and Pin from the left toolbar to create the visual representation of your component.
• Add pins by selecting the "Pin" tool and placing them on your symbol. Make sure to number them according to your component’s datasheet.
• Label the pins with pin numbers and names to match the component’s specifications.
• Right-click the symbol and choose Properties. Here, you can enter the name, description, and other properties like reference designators (e.g., R for resistors, C for capacitors).
• Once your symbol is complete, click on Save and name your symbol appropriately. It will be saved to your personal library.

Footprint Design:

Click on Libraries > Create Footprint to open the footprint editor.

• Set your grid to an appropriate size depending on the component you're designing. Ensure you’re working on the Top Layer for SMD components or the Top/Bottom Layers for through-hole components.
• Use the Pad Tool for through-hole pads or the Surface Mount Pad Tool for SMD pads. This is a wizard which draws and creates the symbol instantly automatically.
• Place pads according to the component's pin configuration from the datasheet. Ensure the size, shape, and hole diameter (for THT) match the manufacturer’s specifications.
• Use the Line Tool and Text Tool to add silkscreen markings like component outlines and reference designators.
• Ensure the outline corresponds to the actual dimensions of your component. After completing the footprint, click on Save to store it in your personal library.

After creating the symbol and footprint, you can link them by opening the symbol, going to Properties, and choosing the corresponding footprint from your library. To know more about different packages see our detailed article.

Via in Pad Design?

Wherever space is limited in HDI patterns, it is necessary to place vias on pads. Conventional vias come with signals and traces routed away from the pad and via. Via-in-pad reduces the space used by trace rooting to reduce the form component of a PCB pad. These pads are used for BGA elements with pitches of less than 0.5 mm. JLCPCB has introduced this new design approach recently which can be tried by manufacturing the PCBs, Quote can be made directly.

What is Via Plugging in the PCB?

Via plugging is a method for filling vias with resin or closing them with solder masks. This method differs from via tenting because resin or solder masks do not fill the via hole. It only provides cover. This technique is employed to protect the vias from the undesirable flow of the solder throughout the soldering process. The solder can flow into the via from the pads when the via is not plugged. It leads to the creation of unwanted solder joints.

What Factors Dictate the Size of Pads in PCB?

The size of PCB pads is determined by factors such as component shape and size, board type and quality, assembly equipment capabilities, the type and capabilities of the process used, and the required quality level and standard. Some size spacing and tolerances play an important role here, which can be found usually at the end of the component datasheet.

When designing the size of the pads, consideration must be given to component size spacing and tolerances, solder joint size requirements, board accuracy, stability and processability (e.g., placement and positioning accuracy), and the size of the board substrate.

PCB Pad Design Considerations:

When designing pads, several factors need to be considered:

• Size and Shape: The pad must be large enough to support the component lead and allow for effective soldering but not so large that it wastes valuable board space.

• Spacing: Proper spacing between pads ensures no short circuits occur due to solder bridges.

• Material: Pads are usually made of copper and are plated with materials like gold or silver for better solderability and corrosion resistance.

Conclusion:

Pads are integral to the PCB Design and development process. These small conductive areas are critical in connecting components to the rest of the circuit and routing signals and power between them.  Pads are vital to the board's functionality and reliability. Whether you are using through-hole components or surface-mounted devices, careful attention to pad design is essential for a successful PCB layout. Without well-designed pads, soldering issues and connection failures can occur, leading to malfunctioning electronics. Therefore, mastering pad design is a key step in creating efficient and durable printed circuit boards.