What Is a Printed Circuit Board (PCB)?
A printed circuit board (PCB) is a self-contained module that mechanically supports and electrically connects components using conductive copper pathways, “printed” onto an insulating substrate. Instead of loose wires running between components, a PCB embeds those connections directly into the board itself, which is what makes compact, mass-producible electronics possible.
PCB, PWB, and CCA: What’s the Difference?
The terms PCB, PWB, and CCA are often used interchangeably in the industry, but they refer to slightly different things. A PWB (printed wiring board) is the bare board itself, conductive traces etched onto an insulating substrate, with no components attached. A PCB (printed circuit board), by contrast, is typically used to describe the board once components are mounted and connected, though usage varies. A CCA (circuit card assembly) refers to the same populated, functional board as a PCB, the term is more common in defense and aerospace contexts. In practice, most people use these terms loosely, but if precision matters for your documentation, PWB specifically means the unpopulated board.
How Are PCBs Constructed?
PCBs are most commonly classified by copper layer count: single-sided (one copper layer, components mounted on the opposite face), double-sided (copper on both faces of a single substrate, connected through plated holes), and multi-layer (three or more copper layers laminated together with insulation between them). PCBs are also classified by substrate flexibility, rigid, flexible, or rigid-flex, which describes whether the board can bend, not how many copper layers it has; a multi-layer board can also be rigid-flex.
PCBs are most commonly classified by copper layer count: single-sided (one copper layer, components mounted on the opposite face), double-sided (copper on both faces of a single substrate, connected through plated holes), and multi-layer (three or more copper layers laminated together with insulation between them, common in computers, servers, and satellite systems). PCBs are also classified by substrate flexibility, rigid, flexible, or rigid-flex, which describes whether the board can bend, not how many copper layers it has; a multi-layer board can also be rigid-flex. Rigid boards (built on materials like fiberglass) are the default for most electronics, including computer motherboards. Flexible boards conform to a shape and tolerate repeated bending in use. Rigid-flex boards combine both and have been standard in military and aerospace applications for decades, where reducing connectors and cabling improves reliability.
How Are PCBs Made?
PCB assemblers connect components to the board using one of two primary methods:
Through-hole technology (THT): Component leads pass through plated holes drilled in the board, held in place by friction and gravity until soldered. This method produces strong mechanical connections and remains common for larger components and connectors.
Surface-mount technology (SMT): Solder paste, a mixture of solder, flux, and glue, is applied to pads on the board’s surface. Components are placed directly onto the paste, which is then melted in a reflow oven to form the connection. SMT eliminates the need for drilled holes and supports smaller, more densely packed components, though it demands more precise placement than through-hole assembly.
Most modern boards use a mix of both methods, SMT for the bulk of components, through-hole for parts that need the added mechanical strength.
Why Are Most PCBs Green?
The green color comes from the solder mask, the protective coating applied over the copper traces, not from the board material itself. No single explanation is confirmed, but a few theories persist: the U.S. military’s early adoption of PCBs may have set green as a de facto standard that stuck; green offers strong visual contrast, making it easier for inspectors to spot trace defects and solder issues; and residue from early solder mask formulations may simply have been green by chance, with the convention outliving the original material. Modern solder mask is available in virtually any color, but green remains the industry default.
Who Invented the PCB?
Austrian engineer Paul Eisler is credited with inventing the printed circuit board in 1936, developing the technique while working on a radio. The concept built on component and materials research dating back to the 1890s, but Eisler’s approach didn’t see widespread manufacturing use until the 1950s, when the U.S. military adopted it at scale. From there, PCB technology spread into commercial electronics and has been the standard method of connecting circuit components ever since.
Frequently Asked Questions
How has PCB manufacturing evolved over time?
Early boards were assembled by hand onto point-to-point wiring, before automated assembly and surface-mount technology took over through the latter half of the 20th century. Today’s boards are increasingly dense, with high-density interconnect (HDI) and multilayer designs packing more functionality into smaller footprints to meet demand from IoT and 5G applications. The next shift is already underway: AI-assisted inspection and quality control, and growing attention to sustainable manufacturing and e-waste reduction.
What's the difference between through-hole and surface-mount assembly?
Through-hole technology (THT) passes component leads through plated holes in the board for a strong mechanical connection, while surface-mount technology (SMT) places components directly onto solder paste on the board’s surface, then reflows it to form the connection. SMT supports smaller, more densely packed components; THT is generally used for parts that need extra mechanical strength. Most modern boards use both methods together. For a full comparison, including when mixed assembly makes sense, see Understanding Different PCB Assembly Techniques: SMT vs. Through-Hole vs. Mixed.
Why is solder mask usually green instead of another color?
No single confirmed reason exists, but the leading theories point to early military adoption setting the convention, green’s strong visual contrast making defects easier to spot during inspection, and the color of early solder mask residue. Modern solder mask is available in nearly any color; green simply remains the default by convention.
What's the difference between a PCB, a PWB, and a CCA?
A PWB (printed wiring board) refers to the bare, unpopulated board with conductive traces but no components attached. PCB and CCA generally refer to the same board once components are mounted and soldered; PCB is the more common general term, while CCA is used more often in defense and aerospace contexts. In everyday industry conversation, people often use the terms interchangeably.
Work with BESTProto for Your PCB Assembly Needs
Understanding how a PCB is built is the first step; getting it assembled to spec is where BESTProto comes in. Contact us today for a quote on your project.