One-sided PCB board: The solder joints are concentrated on one particular facet, and components are generally inserted on the other side. Some products continue to have SMD components over the copper-clad aspect. Double-sided board: Either side could be structure, and both can have plug-in components or SMD components. According to https://beaugkmny.blogaritma.com/29782348/the-fact-about-four-layer-inner-and-outer-layers-2oz-copper-thick-pcb-circuit-board-that-no-one-is-suggesting