Printed Circuit Boards Explained

What is a PCB?

A printed circuit board, or PCB, is the structural and electrical foundation of almost every electronic device. It mechanically supports electronic components and provides the conductive pathways that allow those components to communicate with each other and with a power source.

Without a PCB, the components inside a device would have no reliable way to connect. The board replaces what would otherwise be a complex tangle of individual wires, consolidating all of those connections into a compact, repeatable, and manufacturable structure.

How is a PCB constructed?

A PCB is built up from multiple layers of material bonded together under heat and pressure.

The core of the board is a non-conductive substrate, most commonly FR4, a glass-reinforced epoxy laminate. Copper foil is laminated onto the substrate to form the conductive layers. These copper layers are then etched to create the tracks, pads, and other features that carry electrical signals between components.

On top of the outer copper layers sits the solder mask, a thin protective coating that insulates the copper and prevents accidental bridging during soldering. The solder mask is what gives most PCBs their familiar green colour, though other colours are available depending on specification.

The final layer is the silkscreen, a printed layer of text and symbols that identifies component locations, reference designators, and other information used during assembly and inspection.

Single-sided, double-sided, and multilayer PCBs

PCBs are available in several configurations depending on the complexity of the circuit and the space available.

A single-sided PCB has one copper layer on one side of the substrate. It is the simplest construction and suits straightforward, low-density circuits.

A double-sided PCB has copper on both sides of the substrate. Holes drilled through the board, known as vias, allow circuits on one side to connect to the other. This increases routing density and design flexibility without significantly increasing board size.

A multilayer PCB adds further copper layers within the board stack, separated by insulating substrate layers. This allows far greater circuit density and is used in more complex applications where signal integrity, power distribution, and space are all critical considerations. Exception PCB manufactures multilayer boards from two layers up to 32 layers as standard, with advanced builds available beyond that.

What materials are used?

The material choice for a PCB depends on the application. FR4 is the most widely used substrate for standard digital and analogue circuits. For applications requiring high-frequency signal transmission, such as RF and microwave designs, specialist materials including Rogers, PTFE-based laminates, and other low-loss substrates are used instead. These materials have tightly controlled dielectric properties that maintain signal integrity at high frequencies.

Copper weight, surface finish, and solder mask specification are also chosen based on the electrical, mechanical, and environmental requirements of the application.

Where are PCBs used?

PCBs are found in virtually every electronic device, from consumer products such as mobile phones, laptops, and televisions, through to highly engineered systems in aerospace, defence, medical, automotive, and industrial applications.

In safety-critical and high-reliability sectors, the manufacturing standards applied to a PCB are as important as the design itself. Boards used in aerospace platforms, implantable medical devices, or defence systems are manufactured and tested to significantly tighter tolerances and higher quality standards than those used in consumer electronics.

Exception PCB manufactures high-reliability PCBs from its facility in Tewkesbury, supporting customers in aerospace, defence, medical, industrial and other sectors. To discuss your requirements, get in touch with our team.