Edge plating on PCBs: a short guide

A plated through-hole (PTH) is a common feature in multilayered printed circuit boards. Fabricators drill holes through the stack and electroplate the walls with a layer of copper connecting two pads, one on the top-most layer and the other on the bottom-most layer of the board.

The two pads may further connect to other copper traces or planes on the two layers and, if necessary, to traces or planes on some inner layers as well. PCB manufacturers can extend this technique to edge plating, connecting the top and bottom planes of a PCB by electroplating around its external edges.

The process

Edge plating requires precision handling of the boards, while fabricators face several challenges — chiefly around preparing the edges for plating and creating a lifetime adhesion for the plated material. This requires a controlled process during circuit board fabrication to limit any potential hazard for PTH and edge plating. The most significant concern is the creation of burrs, which leads to discontinuities in PTH walls and limits the life of adhesion of the edge plating.

Applications

Several industries require edge-plated boards, especially in applications that require better support for connections such as for boards that slide into metal casings. Edge plating has other uses as well as it improves the current-carrying capabilities of the board, provides edge connection and protection, and offers the possibility of edge soldering to improve fabrication.

Although edge plating on printed circuit boards is a simple addition in most cases, fabricators need specialised equipment and trained personnel for the process. Designers must take care that internal power planes do not come up to the edge, and fabricators must make sure there is a gap before they take up edge plating. Designers must make sure there is a band of copper on both edges of the top and bottom side, as the plating will connect to these copper bands.

Limitations

As fabricators need to hold the board within the production panel during processing, they will not be able to plate round the complete length of the edge; therefore, some gaps are necessary for placing rout tabs. Manufacturing a board with edge plating requires routing the board profile at the place the edge plating is required before starting the process of through-hole plating. That precludes V-cut scoring on boards that need to undergo edge plating.

Working towards success

Designers must confirm with their fabricators the possibility of manufacturing PCBs with edge plating and the extent to which the fabricator can edge plate the PCB. Designers should indicate clearly in a mechanical layer where they need the edge plating and the type of surface finish they need on it. Most fabricators prefer a selective chemical nickel-gold as the only surface finish suitable for round edge plating.

Additional function

Edge plating is the copper plating connecting the top to the bottom surface of a PCB, running along at least one of its perimeter edges. This has an additional function, that of preventing electromagnetic emissions from radiating or leaking out the edges of a backplane — it is a practical solution and a cost-effective one.

PCB Global

PCB Global has experienced many PCB designs that have required edge plating. For technical details on the edge plating process and specifications, feel free to contact our sales team and we will be able to assist accordingly.

Originally published here.