Conventional Printed Circuit Boards (PCBs) is a term most commonly used to refer to single-sided (S/S) and, less commonly these days, double-sided (D/S) non plated through hole (non PTH). The former can still be found as new designs in their original layout of solder side, comprising tracks and pads, and component side, carrying the details of the component location. The former may or may not be complemeted with a solder mask to cover the tracks and expose the pads. The latter is usually screen printed and may be referred to as the component location, ident, silk screen, or legend. This means, of course, that a S/S board may actually require three layers to be designed and plotted as a prerequisite to manufacture, namely: component location, tracking, and soldermask. At this stage it would seem relevant to complete the picture for the uninitiated by mentioning that assemblers position the components on the component side with the legs through the component holes to be soldered to the pads on the solder side.
These days S/S circuits can be much more sophisiticated due to the arrival of surface mount. This means that some or all of the components will actually sit on the solder side. Another innovation is aluminum or copper backed dielectric with the tracking for the circuitry etched out of a copper layer on top of the dielectric. This has especial relevance for LEDs (Light Emitting Diodes) when they are sufficiently numerous on a circuit to make the conducting away of heat by the aluminium or copper backing to be advantageous.