These are referred to as “through-hole” components. Traditionally, components were mounted on the top layer in holes which extended through all layers. Most modern systems consist of multilayer boards of anywhere up to eight layers (or sometimes even more).
They comprise a sandwich of one or more insulating layers and one or more copper layers which contain the signal traces and the powers and grounds the design of the layout of PCBs can be as demanding as the design of the electrical circuit. Printed circuit boards (PCBs) are by far the most common method of assembling modern electronic circuits. Hank Zumbahlen, with the engineering staff of Analog Devices, in Linear Circuit Design Handbook, 2008 Chapter Introduction
When all steps to layout have been completed, the design is ready for submission for manufacture. If not, the design layout, schematic, or specification will require modification. On successful completion of the layout, it undergoes analysis by (i) resimulating the schematic design to account for the track parasitic components (usually the parasitic capacitance is used), and (ii) using specially designed signal integrity tools to confirm that the circuit design on the PCB will function correctly. When the design schematic is complete, the PCB layout is created, taking into account layout directives (set by the particular design project) and the manufacturing process design rules. If the design does not meet the required specification, then either the design must be modified, or in extreme cases, the design specification must be changed. The design schematic is analyzed through simulation using a suitably defined test stimulus, and the operation of the design is verified. From this, the designer creates the circuit design, which is entered into the PCB design tools. Initially, a design specification (document) is written that identifies the required functionality of the PCB. This pattern or track is the key to making connections between components. Photo 12.2 shows how the copper on a printed circuit board comprises a pattern of copper – sometimes called the copper track – rather than a solid layer. The printed circuit board shown is quite a complex one, with hundreds of components – from a computer actually – but the printed circuit board in a washing machine, say, may only hold a handful of components. Photo 12.1 shows a fairly modern printed circuit board to show you what they look like.
(If copper is only on one surface it’s then known as single-sided printed circuit board if copper is on both surfaces it’s known as double-sided printed circuit board.) The copper on the surface of a printed circuit board has been printed as a circuit (yes, OK, that’s why it’s called printed circuit board – geddit?), so that components on the printed circuit board can be soldered to the copper, and thus be connected to other components similarly soldered. A printed circuit board is a thin baseboard (about 1.5 mm) of insulating material such as resin-bonded paper or fiberglass, with an even thinner layer of copper (about 0.2 mm) on one or both surfaces.