Printed Circuit Boards (PCBs)
PCBs are complex assemblies of functional components. The recovery of valuable materials can be optimised if specific components can be removed for recycling.
A printed circuit board, or PCB, is an assembly of components mounted on a base formed of layers of non-conductive material with conductive lines printed or etched onto them. Electronic components are mounted on the board and are connected via the conductive lines to form working circuits. PCBs are present in the electronic systems that control many modern information and communications technology devices, drives, and control systems.
PCB generally consists of four layers, which are heat laminated together into a single layer. The different types of PCB materials used in PCB from bottom to top includes substrate, solder mask, silkscreen, and copper.
Each of the four layers play a specific role in the complex construction of the PCB. The non-conductive substrate is typically made up of fibre glass bonded with epoxy resin and may contain a flame retardant. A thin layer of metallic copper is mounted on the base (on one or both sides) with the application of adhesive and heat. Copper is an integral part of PCB design because it has the electrical and thermal characteristics necessary for signal transmission and heat dissipation.
During PCB fabrication, a non-conductive layer of green solder mask ink is printed or sprayed on the surface of the board and then baked or exposed under UV light according to the wiring design. In this way, the ink dries and forms a protective coating – it typically consists of some form of polymer such as an epoxy resin.
Above the green solder mask is a silkscreen layer, which adds letters and numerical indicators that make a PCB readable to tech programmers. This, in turn, makes it easier for electronics assemblers to place each PCB in the proper place and in the right direction on each component. The silkscreen layer is usually white, though red, yellow, gray and black are sometimes used.
Finally, a wide range of components can be utilised on PCBs, such as, resistors, capacitors, inductors, potentiometers, transformers, diodes, transistors, silicon-controlled rectifiers (SCRs), integrated circuits, crystal oscillators, switches, relays, sensors. The components mounted onto the base are connected with tin solders, which may also contain variously silver, gold or palladium. The components themselves are made of the functional materials that give them the required properties. These include high-quality electronic grade silicon chips and capacitors that contain vanadium, manganese, and silver.
Due to the increasing use of integrated circuit assemblies, interconnection lines are so dense that multi-substrate boards have become necessary. During the manufacturing procedure, after routing for each layer has been finished with positioning and lamination completed, multiple layers of signals can be pressed into a single board to form a multilayer PCB.