What Is a Printed Circuit Board?

Printed circuit boards (PCB) are electronic hardware pieces that facilitate the electrical connection of electronic components, and its construction allows for components to be soldered or mechanically fastened for the support of assemblies. With their flexibility in construction and design, PCBs may be found in all but the most basic electronic products. PCBs also serve as translation of circuit schematics, often specifically created with an intended system in mind so that all components may be facilitated and connected.

In their most simplistic form, printed circuit boards are constructed from a flat, rigid sheet of insulating material that has copper conductive structures adhered onto a single side. With geometric patterns created with the conductive structures, the copper serves as wires and connection points for electronics to be attached and for current to be transferred. As single layer printed circuit boards are limited in their available area, many designers will implement multiple conductive layers to facilitate all interconnections and ensure a more compact and efficient design. For many applications, four or more layers within the board are quite common, and a standard four-layer board will have a top and bottom layer with two internal layers between.

To connect the layers of copper to maintain a connected circuit, vias are used. Vias are copper-plated holes, and they may be used as electrical tunnels that pass through the substrate. Through-hole components may also serve as vias as well, and they may be mounted by having wire leads pass through the board before being soldered onto traces on the opposite side of the assembly. Surface mount electronic components are the other common type, and they may be connected to the board by having their leads attached to copper traces on the same side. Generally, common surface mounting components include transistors, diodes, integrated circuit chips, capacitors, and resistors. For through-hole components on the other hand, such parts are typically larger such as electrolytic capacitors and connectors.

While early printed circuit boards were designed through manual means such as creating a photomask on a mylar sheet, modern design processes utilize dedicated layout software. With such applications, a schematic capture is created with an electronic design automation tool, and then determinations are made for card dimensions, templates, and the positioning of components and heat sinks. After, the amount of layers for the printed circuit board is decided, and ground and power planes follow suit. On the signal plane, signal interconnections are traced, and such planes may either be outer or inner layers. Using dielectric layer thickness, line impedance is determined. Once all signals have been routed, the components are placed on the board while taking into consideration thermal and geometrical properties. After marking the vias and lands, the signal traces are routed and automation tools create the necessary clearances and connections to ensure proper functionality. Once all steps have been completed, Gerber files are generated for the means of manufacturing.

The manufacturing stage of PCBs is much more complex, consisting of numerous steps to ensure a robust product is made. From the importing of fabrication data to the eventual assembly of the board, each step is carefully undertaken with machinery to achieve the extreme precision necessary to assemble such complex and small electronics. As PCBs are most often sensitive to static electricity, they are placed within special antistatic bags for their transportation and handling before use.


February 12, 2021

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