PCB pad treatment refers to the processes applied to the copper pads on printed circuit boards to prepare them for soldering, ensure strong mechanical and electrical bonds with components, and protect against oxidation. The pads are critical connection points where components (such as resistors, capacitors, and integrated circuits) are attached to the PCB, making their treatment essential for reliable performance. Common pad treatment methods include plating, coating, and surface finishing, each designed to optimize solderability, conductivity, and durability.

Plating is a widely used pad treatment technique, where a thin layer of metal (such as tin, gold, or nickel) is deposited onto the copper pad. Tin plating is cost-effective and provides good solderability, making it suitable for general-purpose applications. Gold plating, often applied over a nickel underlayer (known as gold over nickel), offers excellent corrosion resistance and conductivity, making it ideal for high-reliability applications like aerospace or medical devices. The nickel layer acts as a barrier, preventing diffusion between the copper and gold, which can degrade solderability.

Another common treatment is the application of solder mask, a polymer material that covers the PCB surface except for the pads, preventing solder from flowing onto unwanted areas during assembly. Solder mask also protects the pads from environmental damage and mechanical wear. For surface-mount technology (SMT) pads, additional treatments such as electroless nickel immersion gold (ENIG) or organic solderability preservatives (OSP) are used to ensure that the pads remain free from oxidation until soldering. ENIG provides a flat, solderable surface with long-term stability, while OSP forms a temporary organic layer that is removed during soldering, exposing the clean copper for bonding.

Pad treatment also involves ensuring proper pad geometry, such as correct size, shape, and spacing, to facilitate component placement and soldering. For example, pads for fine-pitch components must be precisely sized to prevent solder bridges, while through-hole pads require sufficient plating thickness to withstand the mechanical stress of component insertion. Proper pad treatment reduces the risk of soldering defects such as cold joints, dewetting, or tombstoning, ensuring that components remain securely attached and maintain reliable electrical contact throughout the device’s lifespan.