printed circuit boards (PCBs) touch the lives of people in ways we take for granted, from your basic computer to medical devices used to regulate blood flow or monitor heart rate. The resources that are required to build PCBs are numerous, and the hard work that goes in to the process of creating each PCB is often overlooked by the electronics consumer. The design stage and production process only hint at the complexity of a technology that seems so ordinary to most of us.
Definition
A printed circuit board (PCB) contains a printed pattern of copper metal or India ink over a nonconductive glass or plastic board. The electrically conductive pattern portion of the PCB directs electrical currents to various electronic components populating the circuit board. These electronic components control the rate of electrical flow and electrical behavior across the nonconductive medium by resisting (resistors), amplifying (amplifiers) or changing the direction of (transistors) electrical current.
Industry
PCB boards are used in a number of technical industries, including semiconductors (for computer microprocessors) and sensors in aerospace engineering (such as airplane and missile wing sensors). Other industries include the military, such as the implementation of PCB boards in rockets and missiles. Just about every electronic gadget today has a PCB board in it. The PCB board is really just the stepping stone in the industry's pursuit of the smallest circuit device. One example of such a small PCB product is the microchip implants available for dogs. As the technology advances, industry will expand PCB technology to human implants.
Etching
A printed circuit board is a substrate (an electrically nonconductive material, such as plastic) that has a printed pattern on it. This printed pattern dictates where, and in which direction, electrons will travel across the surface of the PCB. For the electrons to move across the PCB, the pattern is etched onto the substrate in copper. To etch the board, copper sheet metal is cut to the size of the substrate perimeter. Epoxy (a type of resin used to bind materials) is pasted over the surface area of the substrate. The copper sheet and adhesive substrate are pressed together. An etching machine cuts out a pattern in the copper sheet so that the remaining copper forms a circuit pattern on the substrate. Because the lines are made of conductive copper and the substrate is made of nonconductive plastic, any electricity applied to the circuit will follow only the copper pattern.
Silkscreen printing
Another method used for the printing of PCB boards is silkscreen printing. The circuit board pattern is printed on to a nonconductive plastic board (substrate) by a silkscreen printer. The ink is electrically conductive ink (such as India ink), and thus any printed pattern on the substrate will allow electrons to travel through it.
Components
PCB board assemblies (PCBA) are printed circuit boards with electronic components embedded. Such components as diodes or resistors populate PCB boards in devices as simple as radios and in devices as complex as airplane (or missile) wing sensors. Some PCB boards contain magnets or other heat-sensitive materials. To reduce heat, the PCB and heat-resistant material (heat sync) are laminated between two layers of plastic. Leads are a vital component in a printed circuit board assembly, because these special wires act as conduits from the PCB to another electronic device. For example, a radio's PCB assembly has leads that transfer the electric signal from the circuit to an amplifier---which then produces sound inside of a radio speaker. High-quality PCBs (as used in aerospace sensors) are constructed from gold, because gold is highly conductive and flexible. Unlike other electronic components that are soldered on to the surface of the board, wire leads are soldered to pads (foil squares), or the leads are pushed through holes drilled in the circuit board. The housing, or chassis, is the case of plastic or metal that encloses the completed PCB assembly (all components and leads intact).
