The Complete Handbook of Circuit Boards & Components

Chapter 1: Understanding Circuit Boards & Components

A circuit board is a substrate—typically a sheet of fiberglass, resin, or flexible polymer—that holds electronic components in place and connects them electrically. It is the physical and electrical foundation of every electronic device: smartphones, industrial controllers, medical equipment, automotive systems, power supplies, consumer appliances, and hobbyist projects all depend on circuit boards to organize their components and route signals between them. To understand circuit boards and components, you need to understand what they physically are, how they work together electrically, why they matter, and what causes them to fail in real use.

What Circuit Boards Are

At its core, a circuit board is a piece of manufactured material with conductive pathways printed or etched onto it and holes or pads designed to accept electronic components. The most common type is a printed circuit board (PCB), which consists of layers of copper bonded to an insulating substrate. A two-layer board has conductive copper on the top and bottom surfaces, with insulation in the middle. More complex boards may have four, six, eight, or even more layers, each carrying traces (the thin copper pathways) and each insulated from the next.

Components are soldered or otherwise mechanically and electrically connected to the board at specific points called pads or lands. Holes drilled through the board allow leads from through-hole components to pass through, and those holes themselves may be plated with copper to create electrical connections between layers. Surface-mount components (which sit on top of