A two-layer PCB is also called a double-layer or double-sided PCB. It is basically made of an FR-4 glass epoxy substrate laminated with thin copper film or layers on both side. two-layer PCB is the simplest and the most economical PCB to design. A two-layer PCB can easily be manufactured by a professional PCB Prototyping factory (e.g. wellpcb.com), and can also be made at home. Two-layer PCB has only the top and the bottom copper layers.
Compared to a single sided PCB, it is much easier to route traces on a two-layer PCB by making use of through vias. These through vias electrically connect the top trace of the two-layer PCB with the bottom trace of the same board. The result is that, with two-layer PCB, you are able to conveniently and effectively place more PCB components on a single board using a smaller sized board as compared to a single layer PCB. With two-layer PCB, you can comfortably use the standard through-hole components to make your PCB or you can opt to use surface mount (SMD) Components. When designing your two-layer PCB, maximize the use of SMD Components as opposed to through-hole components. This makes it easy to manufacture your PCB and greatly cuts down on cost.