printed circuit board

A printed circuit board is a laminated substrate, typically fiberglass reinforced epoxy resin (FR-4 grade), onto which copper conductors are etched or plated to form electrical circuits. Components such as resistors, capacitors, integrated circuits, and connectors are soldered to the board's surface or inserted through drilled holes. The copper traces replace the manual wiring harnesses that once connected discrete components; the board itself becomes the wiring diagram made physical.

PCBs exist in single-layer, double-layer, and multilayer configurations. A single-sided board has copper only on one face; double-sided boards use both surfaces. Multilayer boards stack four, six, eight, or more copper layers separated by insulating dielectric, allowing dense routing of signals and power distribution. Trace width, spacing, and thickness are specified in thousandths of an inch or micrometers; thinner traces carry less current and occupy less space, but finer geometries demand more precise manufacturing. Via holes, drilled and plated through the board, connect traces on different layers.

Manufacturing and defects

PCBs are manufactured by photolithography: a photoresist coating is exposed through a film mask, developed to remove unwanted resist, and the exposed copper is etched away chemically or electrochemically. The remaining copper forms the circuit. Component placement is performed by pick-and-place machines that position leads or surface-mount pads with micron-level accuracy. Soldering occurs in a reflow oven (for surface-mount components) or wave solder machine (for through-hole components), where solder melts and cools to form permanent joints.

Common defects include cold solder joints, where insufficient heat creates a weak electrical connection; lifted pads, where plated copper separates from the substrate; trace breaks from mechanical stress or manufacturing error; and solder bridges, where excess solder shorts adjacent traces. Warping occurs when laminate absorbs moisture and swells unevenly; vias can fracture if traces sustain repeated thermal cycling. Inspection is performed optically, electrically (flying-probe testers), or by X-ray to detect internal voids and hidden defects.

The term 'printed' reflects the original silk-screen printing process used to apply solder mask and component labels, though modern photolithography is not truly printing. PCBs are foundational to nearly every electronic device: industrial controls, medical instruments, automotive systems, telecommunications equipment, and consumer electronics all depend on reliable board design and manufacturing. Tolerances, material selection, and layer count are chosen to match the electrical requirements and environmental conditions of each application.