The dimensions of printed circuit boards, the position of the hole centers, and the hole diameters are standardized. The boards are 10–360 mm long, 10–240 mm wide, and 0.05–3.0 mm thick (depending on the rigidity required). The spacing of the coordinate grid for marking the holes is 2.5 mm or, less frequently, 1.25 mm, and the hole diameters range from 0.2 to 3 mm. A distinction is made among one-sided, two-sided, and multilayer boards (up to 15 layers). Multilayer boards are made by using extended leads, by metallizing the walls of through holes, by molding two-sided boards in pairs, or by layer-by-layer buildup. The material most often used for printed circuit boards are metal-clad and plain Micarta and fiberglass laminates, reinforced fluorine plastic, polystyrene, polyethylene terephthalate, polyamide, polycarbonate, and radioceramics.
Block diagrams that define each principal working component of an article or installation and the component’s purpose and interconnections are developed concurrently with the design of the article, before any other type of diagram; they are used in studying the article’s structure and functioning and are referred to when the article is in actual use.
Electric circuit theory is often divided into special topics, either on the basis of how the voltages and currents in the circuit vary with time (direct-current, alternating-current, nonsinu-soidal, digital, and transient circuit theory) or by the arrangement or configuration of the electric current paths (series circuits, parallel circuits, series-parallel circuits, networks, coupled circuits, open circuits, and short circuits). Circuit theory can also be divided into special topics according to the physical devices forming the circuit, or the application and use of the circuit (power, communication, electronic, solid-state, integrated, computer, and control circuits).
Schematic diagrams define the components of the article that constitute a complete set and the interconnections between components; they usually give a detailed representation of the working principle of the article and may serve as a basis for developing other design documents, such as electrical installation blueprints and specification sheets.