Electronics Manufacturing

The electronics industry includes: the manufacture of: passive components (resistors, capacitors, inductors); semiconductor components (discretes, integrated circuits); printed circuit boards (single and multilayer boards); and printed wiring assemblies. This document addresses the environmental issues associated with the latter three manufacturing processes. The manufacturing of passive components is not included since it is similar to the manufacturing of semiconductors, (although passive component manufacturing uses less of the toxic chemicals used in doping semiconductor components and more of organic solvents, epoxies, plating metals, coatings, and lead). Semiconductors: Semiconductors are produced by treating semiconductor substances with dopants such as boron or phosphorous atoms to give them electrical properties. Important semiconductor substances are silicon and gallium arsenide. Manufacturing stages include: crystal growth; acid etch and epitaxy formation; doping and oxidation; diffusion and ion implantation; metallization; chemical vapor deposition; die separation; die attachment; post-solder cleaning; wire bonding, encapsulation packaging; and final testing, marking and packaging. Several of these process steps are repeated several times so that the actual length of the production chain may well exceed one hundred single processing steps. Between the repetitions a cleaning step which contributes to the amount of effluent produced by the process is often necessary. Production involves carcinogenic and mutagenic substances and therefore production should be carried out in closed systems. Printed circuit board (PCB) manufacturing: There are three types of boards: single sided boards (circuits on one side only); double sided boards (circuits on both sides); and multilayer boards (three or more circuit layers). Board manufacturing is accomplished by producing patterns of conductive material on a nonconductive substrate by subtractive or additive processes (the conductor is usually copper; the base can be pressed epoxy, teflon, or glass). The subtractive process is the preferred route and the steps include: cleaning and surface preparation of the base; electroless copper plating; pattern printing and masking; electroplating; and etching. Printed wiring assemblies: Printed wiring assemblies consist of components attached to one or both sides of the printed circuit board. Attachment may be by ‘through hole’ technology where the ‘legs’ of the components are inserted through holes in the board and are soldered (solder is usually a tin-lead alloy) in place from underneath, or by ‘surface mount’ technology (SMT) where components are attached to the surface by solder or conductive adhesive. PCBs of all types may require that drilled holes be copper-plated to ensure interconnections between the different copper layers. SMT allows much denser packing of components, especially when components are mounted on both sides. It also offers higher speed performance and is gaining importance over ‘through-hole’ technology.