First, for the single-sided pcb, parts focused on one side of the wire is concentrated on the other side. Because the wire only in one side, so we call this PCB as single-sided circuit boards. Usually when produce single-sided pcb board, its advantage is low cost and easy job while it’s disadvantage is not suitable for too complex products.

    Second, for the double-sided pcb, it’s an extension of a single-sided pcb. When the single-layer wiring can’t meet the needs of electronic products, it is necessary to use a double-sided. There have sided copper traces, and can pass through the hole to guide the line between the two layers, so as to form the desired network connection.

   Third, for multilayer pcb, it refers insulating material having three or more conductive pattern layer there between in spaced laminated and conductive patterns as required during the interconnect PCB.

   Multilayer circuit boards is the result of the development of electronic information technology on the road to high-speed, multi-function, high-capacity, small size, thin, lightweight level.
The current boards are mainly consisted as bellow:

   Line and drawing (Pattern): line is used as tool conducting between the original, the design will also devise a large copper surface as the ground and power planes. Line and drawing are made simultaneously.The dielectric layer (Dielectric): used to hold the line and insulation between the layers, commonly known as substrate.Hole (Through hole / via): vias allow two levels above each line is turned on, the larger the vias used as a plug-in parts. Then another non-conductive hole (nPTH) is usually used as a surface mount loaded position when assembled fixing screws.

    Solder Mask (Solder resistant / Solder Mask): It’s no need to eat tin copper surface on all parts, so on the non-food area of tin, copper will be printed on one side eaten tin isolated substance(usually an epoxy resin),avoid non-food tin between short-circuit. Depending on different process, it divided into green oil, oil, oil blue.
   Screen printing (Legend / Marking / Silk screen): This is not a necessary structure, its main function is to mark the label name, the location of the box on the board, which is helpful to repair and identify in the later need.

   Surface treatment (Surface Finish): since the copper exposed in the general environment, it is easily oxidized, which will cause solder bad, so it’s need to protect the eat tin of copper surface. There are many protect methods, such as HAL (HASL),gold (ENIG),silver(Immersion Silver), tin (Immersion Tin), organic solder ability preservative (OSP)and so on. Different methods have their advantages and disadvantages, all these protect methods are called surface treatment.