The printed circuit board, or PCB, is considered a key concept and component in electronics design. Ever since they were first made available, printed circuit boards have been indispensible in the manufacture of electronic devices.
PCBs are also referred to as printed wiring boards or printed wiring cards. Before the birth of the PCB, electronic and electrical circuits were composed wires laboriously connected point-to-point with other components. They were messy and confusing, making troubleshooting very difficult. They were also more prone to malfunction and short circuit, since the wires are exposed to the elements subjecting them to wear and tear.
The first printed circuit board came out in 1936 and was invented and patented by Austrian engineer Paul Eisler. His method involved the etching of copper foil onto a non-conductive material surface, which during those times, is reinforced glass. It was only after the war in 1948 that the invention was released for use commercially, but printed circuit boards only picked up in popularity and use during the mid 1950s. The dawn of solid state electronics further established the PCB’s position in the electronics industry.
Basically, a PCB is a board made of non-conductive material etched with pads and lines made of copper foil. These pads and lines connect together various points wherein the electronic components are soldered or stamped. The copper foil allows the power and signals to be directed to the components. When components are soldered, lead is melted using a soldering device to make the electrical connection between the board and the component. The cooled solder also acts as adhesive.
Three types of printed circuit boards exist – single-sided, double-sided and multi-layered. In single-sided boards, the components are located on one side of the board. This type is often used in non-complex circuits. In case of more complex electronic design where more components are needed, double-sided boards can be used. Components can now be placed on both sides of the board and they are connected by drilling holes at certain points on the board. Although much more difficult to design, multi-layered boards simplify the circuit pattern since all the layers have circuit patterns; in other words, these boards reduce the surface area needed for the connection of components.
Think of the PCB as something like lasagna or a layer cake. Different materials are layered one over the other and then joined using heat and adhesive, resulting in a single component.
The material most commonly used as the substrate or base is fiberglass. The base is responsible for the board’s thickness and rigidity. Thickness differs according to usage of the circuit. There are flexible printed circuit boards built using Kapton – a high temperature plastic. Cheaper materials like phenolics and epoxies are also used for manufacturing cheap electronic devices. These substrates are characterized by a bad smell during soldering.
The thin copper foil is the next layer. It is attached to the base using adhesive and heat. On double sided boards, both sides will have thin copper foil etched on them. Copper thickness also varies depending on the purpose.
The soldermask layer protects the copper areas from unnecessary contact with solder, metals, or conductive bits. It also prevents solder jumps by only exposing the soldering rings and coating the rest of the areas. The soldermask layer is what gives printed circuit boards the green or red color.
The silkscreen adds the numbers, letters, symbols to the printed circuit board. This allows for easier component assembly. Some silkscreen labels also indicate the function of each LED or pin of the component. Silkscreen is usually white in color.
All in all, PCBs are far from simple, but they have truly simplified the process of manufacturing electronics.