PCB Pad Fundamentals

We know that the prerequisite for PCB to function in electronic devices is the perfect connection between components and the PCB board. During the manufacturing process, components are connected to the PCB through pinholes and are fixed on pads through soldering. However, improper soldering temperature and time can lead to pad damage, affecting the reliability of electrical connections. This article will delve into the concept of pads, their importance, and the correct design methods to ensure that readers have a clearer understanding of this critical step in electronic manufacturing.

pcb pad

What are PCB Pads and Their Functions

PCB pads, also known as solder pads, are areas on a printed circuit board specifically designed for connecting components. They are typically made of copper or other conductive materials and are located at the endpoints of traces. Based on the installed components, pads can be divided into through-hole pads and surface mount pads. Regardless of their shape, the core function is to connect components and keep them stable on the circuit board.

In addition to serving as electrical connection points, pads also play a minor role in heat dissipation. It’s essential to note that they cannot solely determine the thermal management of the entire PCB board. When electronic devices are powered, current flows through traces to components, generating heat during operation. Large and wide pads provide a larger surface area, helping to improve heat conduction efficiency and acting as a heat dissipation aid.

Types of PCB Pads

Based on Components:

Through-Hole Pads

Used to connect through-hole components, typically circular or oval to accommodate the shape of the hole. During soldering, component pins are inserted into the hole and soldered on the other side.

Surface Mount Pads

Used for SMD components, which are connected to the PCB in a patch form without the need for pin insertion. Their smaller size is advantageous for dense designs.

BGA Pads

Essentially a type of surface mount pad, notable for the array of solder balls arranged at the bottom of BGA packaging instead of traditional pins.

Pads by component

Based on Shape:

Square Pads

Commonly used when components on the circuit board are relatively large, and the design is simple.

Round Pads

Versatile and applicable in various designs, allowing for larger sizes to enhance reliability.

Island Pads

The design integrates connections between pads, often seen in vertical, irregular, or high-density layouts.

Flower Shaped Pads

Designed to prevent clogging and adapt to stress changes, especially beneficial for larger hole diameters or pad diameters exceeding 3.0mm.

Oval Pads

Suitable for DIP components and directional elements, providing a larger pad area.

Pads by shape

PCB Pad Design Guidelines

Ensure that the size of each pad on the PCB is not less than 0.25mm on one side, and the pad diameter should not exceed three times the component hole diameter.

For through-hole components, circular pads are the best choice, with a pad diameter not less than 1.8 times the hole diameter.

For double-sided PCB, the pad size should ideally be 2.5 times the hole diameter, with a slight increase for automated processes.

The edge-to-edge distance between pads should not be less than 0.4mm, and for a row of pads perpendicular to the wave soldering direction, it should not be less than 0.5mm to prevent bridging.

Keep pad sizes as uniform as possible, and the outward extension length should neither be too short nor too long to avoid tombstoning issues when entering the soldering oven.

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