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Although we tend to think of printed circuit boards, commonly abbreviated to PCBs, as modern technology, it is surprising to find that they developed from as early as the 1930s, being first applied to radio technology. When the idea of printing or etching a conductive pattern onto a suitable surface, called a substrate, was discovered, it was not until the introduction of the transistor in the 1950's that the technique was really useful. Until then the large size of vacuum tubes and other components impeded miniaturization.
Glass fiber, reinforced epoxy resin, is the usual substrate for modern PCBs. Copper foil is bonded to one or both sides of the substrate and the circuits are printed or etched onto this surface. Contamination is a problem in creating PCBs, so they are manufactured in a clean environment to eliminate this risk. The three main types of PCBs are single sided, double sided and multi-layered and they may contain circuits that handle a single function or multiple functions. The substrate is made by combining woven glass fiber with resin and passing it through rollers to achieve the correct thickness. It is then semi-cured in an oven, and then cut into sheets. These sheets are stacked in alternating layers with adhesive backed copper foil. These stacks are baked and pressurized which totally cures the resin and securely attaches the copper foil.
Either an additive or subtractive process can be used to create circuits on the board, preparing the board to accept external components. Components can be connected to the circuit in one of two ways. Tiny holes can be drilled through the board and the connection wires pushed through and soldered to a circuit connection on the rear of the board. In surface mount technology, the components are soldered directly to the surface of the board. Components are added to the board by machines. Chip shooters rapidly add items to boards, and some items may be placed by automated machines. A large or awkwardly shaped component may be placed by hand.
Each printed circuit board design is uniquely created to perform a particular function or functions, and special software and CAD programs are used in the design. Current PCBs incorporate micro-chips which in themselves are like a miniature PCB. Microchips contain components and circuitry that is grown electrochemically on a chip of silicone. These microchips contain many thousands of components, allowing for extremely complex circuits.
The development of PCBs is currently trending towards further miniaturization, incorporating more microchips and denser packing on the board. This will allow for increasingly complex operations being performed by a single board. One of the most important developments is the use of heavy copper circuits on the boards. This offers significant advantages in terms of more resistance to thermal strains, increased current carrying capabilities and better constructional strength. Another advance is that of three dimensional plastic molded boards built up of three-dimensional substrates and having integral, metalized connectors.
PCBs can be custom-developed for practically any applicable operation. A large number of manufacturers are available for designing and producing PCBs and so careful research is needed to ensure finding a manufacturer offering the price, quality and service required.
