PCB, or printed circuit board, is the mother of electronic products. The number of layers of the printed circuit board can be divided into single-sided PCB, double-sided PCB, and multilayer PCB.
Single-Sided PCB Boards
On the most straightforward PCB circuit board, the electronic components are concentrated on one side, and the circuits are on the other. Because the courses only appear on one side, this circuit board is called Single-sided PCB. Because single-layer PCB has many strict circuit designs (because there is only one side, the circuit cannot cross), only the first circuits use this type of board.
Double-Sided PCB Boards
There are circuits on both sides of a double-sided PCB, but for the circuits to work, there must be a proper circuit connection between the two sides of the circuit board. The “bridge” between such circuits is called a via. A via is a small hole filled or coated with metal on the PCB circuit board, connected to the course on both sides. Because the double board area is twice as large as the single-sided board, and because the circuit can be interleaved (it can be wound to the other side), it is more suitable for use in more complicated circuits than the single-sided PCB board.
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Multi-Layer PCB Boards
As the name suggests, a multilayer circuit board can be called a multilayer circuit board with more than two layers, such as four, six, eight, and so on. Multilayer PCB circuit boards use more single-sided or double-sided circuit boards to increase circuit wiring. Use a double-sided board as the inner layer, two single-sided boards as the outer layer, two double-sided printed circuit boards as the inner layer, and two single-sided printed circuit boards as the outer layer. The positioning system and the insulating adhesive material alternately form a conductive pattern. According to design requirements, printed circuit boards become four-layer or six-layer printed circuit boards, also known as multilayer printed circuit boards. The number of layers of the circuit board means several independent wiring layers; usually, the number of layers is even and contains the two outermost layers. Most motherboards have a 4 to 8-layer structure, but it can be a PCB circuit board with nearly 100 layers in theory. Most large supercomputers use fairly multi-layered motherboards, but because clusters of many ordinary computers can already replace these types of computers, super-multilayered boards have gradually ceased to be used.
The advantage of the multilayer PCB circuit board is that the lines can be distributed in multiple layers to be designed more precisely. Or smaller products can be realized by multilayer boards, such as mobile phone circuit boards, micro projectors, voice recorders, and other products with relatively large volumes. Besides, multilayer can increase the flexibility of design, better control the differential impedance and single-ended impedance, and give some signal frequency better output.
Multilayer printed circuit boards are widely used to manufacture electronic products due to their flexible design, stable and reliable electrical performance, and excellent economic performance. Especially with the extensive and in-depth application of large-scale integrated circuits, multilayer PCBs are developing in the direction of high density, high precision, and high-level digitization. Fine lines, slight aperture penetration, and blind hole technologies (such as buried via and high plate thickness to aperture ratio) can meet market needs.
Structure of Multilayer PCB Boards
Dielectric: Used to maintain the insulation between the circuit and each layer, commonly known as the substrate.
Through-hole / via Vias can connect the lines of more than two layers, larger vias are used to insert components, and non-plating through-hole (NPTH) is used for surface mount positioning and fixing screws during assembly.
Solder resistant /Solder Mask: According to different processes, it is divided into green oil, red oil, and blue oil.
Legend /Marking/Silkscreen: This is a non-essential structure. The primary function is to mark each part’s name and position frame on the circuit board to facilitate maintenance and identification after assembly.
Surface Finish: Since the copper surface is easily oxidized in the general environment, resulting in poor solderability, it is necessary to protect the copper surface. The protection methods are HASL, ENIG, Immersion Gold, Immersion Silver, Immersion Tin, and OSP. Each has its advantages and disadvantages, collectively referred to as surface treatment.