printed circuit board (PCB) provides a method to connect circuits and devices together. In addition to electrical connections, PCB provides a mechanical structure to hold the circuits and components together. Due to the inherent insulation properties of organic material, many PCB substrates are composed of fiber glass with organic resin. PCBs made from inorganic substrate like ceramic or metal can be counted as member of heat dissipation system to conduct heat away from the circuit. For consumer electronics and industrial application, it is common to require a circuit board to withstand 105 deg C to 130 deg C. Some application such as uninhabited airborne application may demand for higher temperature circuit. It is common to use inorganic substrate to combat such environment. For example, ceramic substrate can operate up to 200 deg. C without insulation breakdown and metallic substrate with aluminium and copper are being used in power module packaging so as to achieve high power density or output power per unit volume. As there are many kinds of PCB available, for training needs, we shall focus on PCBs that can be easily fabricated for prototype testing; the fabrication of single-sided and double-sided PCB. Traditional plated-through-hole fabrication techniques are discussed.
In the electronic industry, single-sided PCB and double-sided PCB are the most popular interconnection device because of their low cost and easy to fabricate. In general, printed circuit board fabrication mainly consists of photolithography and photochemical techniques with chemical etching and surface finishing technologies. Some of the chemical processes in making single-sided PCB and double-sided plated-through-holes (PTH) PCB are similar. Minor adjustment is needed so as to adapt to different material or tolerance requirement. In a workshop environment when making PCB is mainly for the purpose of small scale prototype tests. Double-sided and single-sided processes are sufficient for most purposes. Making PTH requires a good drilling process and more complicate chemical processes and much longer time in fabrication. PCB fabrication processes are designed with the production rate in mind. Process for mass production is very different from small batch production. In this section we shall discuss process available for training or sampling purposes for an electronics workshop.
The PCB is said to be "printed" because its conductive area is usually generated be means of a printing like process; artwork preparation, film development, photo-chemical etching, silk screen printing and surface finishing. Common thickness of rigid PCB is 1.6 mm, in some cases where space is critical, 0.8 mm thick laminate is a popular choice.
Depending on the number of layers of copper clad and process, 3 basic types of PCB are listed below in ascending order of interconnection wiring and component density.
Single sided PCB: conductors on only one surface of a dielectric base.
Double sided PCB: conductors on both sides of a dielectric base; usually interconnected the two layers with plated-through-holes (PTHs).
Multi-layer: conductors on 3 or more layers separated by dielectric material and interconnected by PTH or pads.
