Ordering Circuit Boards

Understanding Printed Circuit Boards (PCBs)

barebones-pcbVersion 2
Left: A “bare-bones” PCB, consisting of copper laminated onto a substrate. Right: a PCB complete with solder-mask and silk-screen.

A printed circuit board (PCB) consists of a number of different layers of different materials. The electrical connections themselves are made of a thin layer of copper, etched to form the pattern specified by your design. The copper is laminated onto a substrate, usually FR4, a composite of fiberglass and epoxy. Simple circuit boards have two layers of copper, one on either side of the FR4 or other substrate. More complex boards will have multiple layers of copper on either side giving, for example, four or more total copper layers. (Very simple boards, particularly those designed for home etching or milling, may only have a layer of copper on one side.) For so-called “bare-bones” PCBs, the substrate and copper are the only layers.

Typical PCBs add a couple of additional layers, solder-mask and silk-screen. Solder-mask is a thin lacquer-like material (often green) that covers the copper. Typically, there are only holes in the solder mask at places where solder needs to be applied to the copper. (The solder-mask masks the solder, hence the name.) This prevents accidentally soldering to other parts of the circuit and reduces the risk of short circuits. Finally, a silk-screen (or “legend”) layer – typically white – allows for text, diagrams, or other helpful information for someone assembling or debugging the board.

For more information, see SparkFun’s PCB basics tutorial.

Leave a Reply